Rolling Contact Fatigue Performances of Carburized and High-C Nanostructured Bainitic Steels.

Science.gov (United States)

Wang, Yanhui; Zhang, Fucheng; Yang, Zhinan; Lv, Bo; Zheng, Chunlei

2016-11-25

In the present work, the nanostructured bainitic microstructures were obtained at the surfaces of a carburized steel and a high-C steel. The rolling contact fatigue (RCF) performances of the two alloy steels with the same volume fraction of undissolved carbide were studied under lubrication. Results show that the RCF life of the carburized nanostructured bainitic steel is superior to that of the high-C nanostructured bainitic steel in spite of the chemical composition, phase constituent, plate thickness of bainitic ferrite, hardness, and residual compressive stress value of the contact surfaces of the two steels under roughly similar conditions. The excellent RCF performance of the carburized nanostructured bainitic steel is mainly attributed to the following reasons: finer carbide dispersion distribution in the top surface, the higher residual compressive stress values in the carburized layer, the deeper residual compressive stress layer, the higher work hardening ability, the larger amount of retained austenite transforming into martensite at the surface and the more stable untransformed retained austenite left in the top surface of the steel.

Cluster carburizing. Final report, June 1, 1973-May 31, 1979

International Nuclear Information System (INIS)

Morral, J.E.

1979-05-01

Three major accomplishments of the cluster carburizing program were showing that the hardness of aged and carburized materials could be controlled via the aged structure; developing a new and analytical theory of subscale formation; and characterizing the properties of Ta-Hf alloys with respect to precipitation kinetics and morphology, diffusion kinetics, age hardening, and subscale formation. The first of these verified the cluster carburizing concept, which has potential use in the development of high strength materials. The second has applications in the fields of hot corrosion, oxidation, and high temperature coatings. The third provided necessary background for this study and provided a further understanding of the behavior of refractory metals. Details about the above are contained in this final report as well as comments on the Ta-Hf, TaC-HfC and NbC-HfC phase diagrams, a comparison of hardening in the Nb-Hf and Ta-Hf system, and a discussion of possible future work

Carburization of austenitic alloys by gaseous impurities in helium

International Nuclear Information System (INIS)

Lai, G.Y.; Johnson, W.R.

1980-03-01

The carburization behavior of Alloy 800H, Inconel Alloy 617 and Hastelloy Alloy X in helium containing various amounts of H 2 , CO, CH 4 , H 2 O and CO 2 was studied. Corrosion tests were conducted in a temperature range from 649 to 1000 0 C (1200 to 1832 0 F) for exposure time up to 10,000 h. Four different helium environments, identified as A, B, C, and D, were investigated. Concentrations of gaseous impurities were 1500 μatm H 2 , 450 μatm CO, 50 μatm CH 4 and 50 μatm H 2 O for Environment A; 200 μatm H 2 , 100 μatm CO, 20 μatm CH 4 , 50 μatm H 2 O and 5 μatm CO 2 for Environment B; 500 μatm H 2 , 50 μatm CO, 50 μatm CH 4 and 2 O for Environment C; and 500 μatm H 2 , 50 μatm CO, 50 μatm CH 4 and 1.5 μatm H 2 O for Environment D. Environments A and B were characteristic of high-oxygen potential, while C and D were characteristic of low-oxygen potential. The results showed that the carburization kinetics in low-oxygen potential environments (C and D) were significantly higher, approximately an order of magnitude higher at high temperatures, than those in high-oxygen potential environments (A and B) for all three alloys. Thermodynamic analyses indicated no significant differences in the thermodynamic carburization potential between low- and high-oxygen potential environments. It is thus believed that the enhanced carburization kinetics observed in the low-oxygen potential environments were related to kinetic effects. A qualitatively mechanistic model was proposed to explain the enhanced kinetics. The present results further suggest that controlling the oxygen potential of the service environment can be an effective means of reducing carburization of alloys

Rolling Contact Fatigue Performances of Carburized and High-C Nanostructured Bainitic Steels

OpenAIRE

Wang, Yanhui; Zhang, Fucheng; Yang, Zhinan; Lv, Bo; Zheng, Chunlei

2016-01-01

In the present work, the nanostructured bainitic microstructures were obtained at the surfaces of a carburized steel and a high-C steel. The rolling contact fatigue (RCF) performances of the two alloy steels with the same volume fraction of undissolved carbide were studied under lubrication. Results show that the RCF life of the carburized nanostructured bainitic steel is superior to that of the high-C nanostructured bainitic steel in spite of the chemical composition, phase constituent, plat...

The sort of carburization and the quality of obtained cast iron

Directory of Open Access Journals (Sweden)

K. Janerka

2008-12-01

Full Text Available In the production of cast iron, the pig iron’s amount in charge material is more and more often limited, and replaced by steel scrap. That extorts the necessity of know-how the carburization and one is looking for carburizers, which ensure obtaining big carbon increment as quickly as possible with the high repeatability and the ones which ensure getting the adequate quality of cast iron. The object of presented research was definition of the influence of charge materials’ sort on the structure, course of solidification, and the effectiveness of process. The cast iron melts, which are presented below, are made only on the basis of steel scrap with portion of graphitoidal, coke and anthracite carburizers, which were added to the charge in solid. In the article one compared the carburizers in respect of their structure, chemical constitution and the effectiveness obtained during the carburization of liquid metal. The melting of cast iron, based on the special pig iron, was carried out as well. The course of melts, chemical constitution of obtained cast iron and its structure were presented. The comparison between quality distribution and the volume fraction of graphite in classes of size for the individual melts were achieved and the TDA curves were inserted.

Plasma carburizing with surface micro-melting

Science.gov (United States)

Balanovsky, A. E.; Grechneva, M. V.; Van Huy, Vu; Ponomarev, B. B.

2018-03-01

This paper presents carburizing the surface of 20 low carbon steel using electric arc and graphite prior. A carbon black solution was prepared with graphite powder and sodium silicate in water. A detailed analysis of the phase structure and the distribution profile of the sample hardness after plasma treatment were given. The hardened layer consists of three different zones: 1 – the cemented layer (thin white zone) on the surface, 2 – heat-affected zone (darkly etching structure), 3 – the base metal. The experimental result shows that the various microstructures and micro-hardness profiles were produced depending on the type of graphite coating (percentage of liquid glass) and processing parameters. The experiment proved that the optimum content of liquid glass in graphite coating is 50–87.5%. If the amount of liquid glass is less than 50%, adhesion to metal is insufficient. If liquid glass content is more than 87.5%, carburization of a metal surface does not occur. A mixture of the eutectic lamellar structure, martensite and austenite was obtained by using graphite prior with 67% sodium silicate and the levels of the hardness layer increased to around 1000 HV. The thickness of the cemented layer formed on the surface was around 200 μm. It is hoped that this plasma surface carburizing treatment could improve the tribological resistance properties.

Surface modification of superaustenitic and maraging stainless steels by low-temperature gas-phase carburization

Science.gov (United States)

Gentil, Johannes

Low-temperature gas-phase carburization of 316L austenitic stainless steel was developed in recent years by the Swagelok company. This process generates great mechanical and electrochemical surface properties. Hardness, wear resistance, fatigue behavior, and corrosion resistance are dramatically improved, while the formation of carbides is effectively suppressed. This new technique is of technical, economical, but especially of scientific interest because the surface properties of common stainless steel can be enhanced to a level of more sophisticated and more expensive superalloys. The consequential continuation of previous research is the application of the carburization process to other steel grades. Differences in chemical composition, microstructure, and passivity between the various alloys may cause technical problems and it is expected that the initial process needs to be optimized for every specific material. This study presents results of low-temperature carburization of AL-6XN (superaustenitic stainless steel) and PH13-8Mo (precipitation-hardened martensitic stainless steel). Both alloys have been treated successfully in terms of creating a hardened surface by introducing high amounts of interstitially dissolved carbon. The surface hardness of AL-6XN was increased to 12GPa and is correlated with a colossal carbon supersaturation at the surface of up to 20 at.%. The hardened case develops a carburization time-dependent thickness between 10mum after one carburization cycle and up to 35mum after four treatments and remains highly ductile. Substantial broadening of X-ray diffraction peaks in low-temperature carburized superaustenitic stainless steels are attributed to the generation of very large compressive biaxial residual stresses. Those large stresses presumably cause relaxations of the surface, so-called undulations. Heavily expanded regions of carburized AL-6XN turn ferromagnetic. Non-carburized AL-6XN is known for its outstanding corrosion resistance

Internal residual strain mapping in carburized chrome molybdenum steel after quenching by neutron strain scanning

International Nuclear Information System (INIS)

Sakaida, Yoshihisa; Serizawa, Takanobu; Manzanka, Michiya

2011-01-01

A hollow circular cylinder specimen with an annular U-notch of chrome molybdenum steel with 0.20 mass% C (SCM420) was carburized in carrier gas and quenched in oil bath. In order to determine the case depth, the specimen was cut off and carbon content and Vickers hardness gradients were measured experimentally near the carburized surface. The residual strain mapping in the interior of carburized cylinder was conducted nondestructively by neutron strain scanning. In this study, the neutron diffraction from Fe-211 plane was used for strain scanning. The neutron wavelength was tuned to 0.1654nm so that diffraction angle became about 90deg. Radial, hoop and axial residual strains were measured by scanning diffracting volume along the axial direction of cylinder specimen. Each residual strain was calculated from lattice spacing change. Unstressed lattice spacing was determined experimentally using reference coupon specimens that were cut from the interior of same carburized cylinder. As a result, the diffraction peak width at half height, FWHM, near the carburized surface was about 3.7 times wider than that of coupon specimens. On the other hand, the most peak widths in the interior equaled to that of coupon specimens. Peak width broadened slightly as the diffracting volume approached the carburized case layer. From the center to the quarter of cylinder specimen, the hoop and axial strains were tensile, and the radial one was compressive in the interior. From the quarter to the edge of the cylinder specimen, the hoop tensile strain increased, radial and axial strains changed to tensile and compressive, respectively. Therefore, the interior of the cylinder specimen was found to be deformed elastically to balance the existence of compressive residual stresses in the carburized case layer. (author)

Acetylene Flow Rate as a Crucial Parameter of Vacuum Carburizing Process of Modern Tool Steels

Directory of Open Access Journals (Sweden)

Rokicki P.

2016-12-01

Full Text Available Carburizing is one of the most popular and wide used thermo-chemical treatment methods of surface modification of tool steels. It is a process based on carbon diffusive enrichment of the surface material and is applied for elements that are supposed to present higher hardness and wear resistance sustaining core ductility. Typical elements submitted to carburizing process are gears, shafts, pins and bearing elements. In the last years, more and more popular, especially in highly advanced treatment procedures used in the aerospace industry is vacuum carburizing. It is a process based on chemical treatment of the surface in lower pressure, providing much higher uniformity of carburized layer, lower process cost and much lesser negative impact on environment to compare with conventional carburizing methods, as for example gas carburizing in Endo atmosphere. Unfortunately, aerospace industry requires much more detailed description of the phenomena linked to this process method and the literature background shows lack of tests that could confirm fulfilment of all needed requirements and to understand the process itself in much deeper meaning. In the presented paper, authors focused their research on acetylene flow impact on carburized layer characteristic. This is one of the most crucial parameters concerning homogeneity and uniformity of carburized layer properties. That is why, specific process methodology have been planned based on different acetylene flow values, and the surface layer of the steel gears have been investigated in meaning to impact on any possible change in potential properties of the final product.

Study of the carburization of an austenitic steel through optical and scanning electron microscopy, microhardness and X ray microanalysis of C

International Nuclear Information System (INIS)

Champigny, Michel; Gauvain, Danielle; Meny, Lucienne

1977-01-01

Carburization tests of 316 L stainless steel have been performed in liquid sodium at 550, 600 and 650 0 C; the depth of penetration of carbon is of the order of 300 μm. The structure of the carburized layer has been studied through optical and scanning electron microscopy: the carbides precipitate first within the grain boundaries, making a nearly continuous superficial carbide layer. The Vickers and Knoop (under 50 g load) microhardness measurements determine the depth of carburization with an error of +-50μm. Though the tensile strength does not vary much with the carburization, the striction, and then the deformation capability, is highly decreased. The variation of the concentration in carbon versus distance has been measured by quantitative X ray microanalysis, using diamond as a standard; the best experimental conditions, regarding the overlapping of the Cr 2 Lα and Ni 3 Lα lines with CK line have been chosen, and the minimum contamination during the measurements has been performed. The results have been confirmed by the analysis of carbon in Fe Ni standards containing less than 1 w/o carbon. The results are discussed with the published data. This work shows that: the increase of microhardness is not related in a simple way with the carbon content of the stainless steel; the carbon concentration can be measured quickly with an error of +-5% when 0,2 [fr

The effect of chromium diffusion redistribution on wear resistance of carburized 3Kh13 steel

International Nuclear Information System (INIS)

Shcherbedinskij, G.V.; Shumakov, A.I.; Zemskij, S.V.; Pereverzev, V.M.

1977-01-01

The redistribution of chromium in steel 3Kh13 on carburization in a high-activity carburizer and the wear-resistance of the steel have been investigated. Surface layers with an increased chromium concentration show the highest wear-resistance. The chromium content in the surface layer increases due to its diffusion from the interior. The distribution of carbon and chromium in the carburized layers has been studied with the aid of the radioactive isotope 14 C by the method of layer-by-layer spectral analysis on a vacuum quantometer, layer-by-layer chemical and X-ray structure analysis. The composition of the carbides has been determined by physicochemical analysis. It has been established that the carburized layer can be divided into four zones with respect to its phase composition: first zone - hematite and spinal with 0.5-2.0% C; second zone - solid carbides (Fe,Cr) 7 C 3 ; up to 5% C; third zone - globular carbides in a troostite matrix (Cr,Fe) 7 C 3 and Cr 23 C 6 ; up to 3.5% C; fourth, transitional, zone - troostite carbide mixture Cr 23 C 6 ; up to 1% C. The chromium diffusion in the carburized layer is faster than in the initial austenite. The chromium counterdiffusion is due to the development of a zone of solid carbides M 7 C 3

Creep properties of Hastelloy X in a carburizing helium environment

International Nuclear Information System (INIS)

Nakanishi, T.; Kawakami, H.

1982-01-01

In this work, we investigate the environmental effect on the creep behavior of Hastelloy X at 900 0 C in helium and air. Since helium coolant in HTGR is expected to be carburizing and very weakly oxidizing for most metals, testings were focused on the effect of carburizing and slight oxidation. Carburization decreases secondary creep strain rate and delays tertiary creep initiation. On the other hand, the crack growth rate on the specimen surface is enhanced due to very weak oxidation in helium, therefore the tertiary creep strain rate becomes larger than that in air. The rupture time of Hastelloy X was shorter in helium when compared with in air. Stress versus rupture time curves for both environments do not deviate with each other during up to 5000 hours test, and a ratio of rupture stress in helium to that in air was about 0.9

Contribution to the study of xenotime and zircon flotation

International Nuclear Information System (INIS)

Scorzeli, Isabella Bernstein; Torem, Mauricio Leonardo

1995-01-01

Flotation and electrokinetics behaviour have studied with xenotime (YPO 4 ) and zircon (Zr Si O 4 ) from a mixture of grains with 90% xenotime and 10% zircon, produced in cassiterite concentration process. Micro flotation and zeta potential have been also studied, by using oleic acid P.A. and DP1-6256 as collectors, and sodium metasillicate and Procol DA911 as modifier agents

EFFECTS OF CARBURIZING AND NITRIDING PROCESSES ON THE COST AND QUALITY OF GEARS PRODUCED WITH AISI 4140 AND 8620 STEELS

Directory of Open Access Journals (Sweden)

Claudio José Leitão

2012-09-01

Full Text Available This study compares the effects of nitriding and carburizing processes applied to gears subjected to contact stresses below 1300 MPa. The manufacturing cost, as well the depth of hardened layer and the distortion produced by two processes are analyzed. AISI 4140 gears quenched, tempered, liquid and gas nitriding and AISI 8620 gears after liquid carburizing, quenching and tempering are analyzed. The dimensional control of the gears was carried out before and after heat and thermochemical treatments. It is concluded that liquid or gas nitriding processes are about 30% more economical than liquid carburizing an also they reduce the dimensional changes. By the other hand liquid carburizing achieves greater case depth. Liquid nitriding process presents the lowest cost, dimensional changes and case depth.

Carburizing treatment of low alloy steels: Effect of technological parameters

Science.gov (United States)

Benarioua, Younes

2018-05-01

The surface areas of the parts subjected to mechanical loads influence to a great extent the resistance to wear and fatigue. In majority of cases, producing of a hard superficial layer on a tough substrate is conducive to an increased resistance to mechanical wear and fatigue. Cementation treatment of low alloy steels which bonds superficial martensitic layer of high hardness and lateral compressive to a core of lower hardness and greater toughness is an example of a good solution of the problem. The high hardness of the martensitic layer is due to an increased concentration of interstitial carbon atoms in the austenite before quenching. The lower hardness of the core after quenching is due to the presence of ferrite and pearlite components which appear if the cooling rate after austenitization becomes lower than the critical on. The objective of the present study was to obtain a cemented surface layer on low alloy steel by means of pack carburizing treatment. Different steel grades, austenitization temperatures as well as different soaking times were used as parameters of the pack carburizing treatment. During this treatment, carbon atoms from the pack powder diffuse toward the steels surface and form compounds of iron carbides. The effect of carburizing parameters on the transformation rate of low carbon surface layer of the low alloy steel to the cemented one was investigated by several analytical techniques.

Raman study of radiation-damaged zircon under hydrostatic compression

Science.gov (United States)

Nasdala, Lutz; Miletich, Ronald; Ruschel, Katja; Váczi, Tamás

2008-12-01

Pressure-induced changes of Raman band parameters of four natural, gem-quality zircon samples with different degrees of self-irradiation damage, and synthetic ZrSiO4 without radiation damage, have been studied under hydrostatic compression in a diamond anvil cell up to ~10 GPa. Radiation-damaged zircon shows similar up-shifts of internal SiO4 stretching modes at elevated pressures as non-damaged ZrSiO4. Only minor changes of band-widths were observed in all cases. This makes it possible to estimate the degree of radiation damage from the width of the ν3(SiO4) band of zircon inclusions in situ, almost independent from potential “fossilized pressures” or compressive strain acting on the inclusions. An application is the non-destructive analysis of gemstones such as corundum or spinel: broadened Raman bands are a reliable indicator of self-irradiation damage in zircon inclusions, whose presence allows one to exclude artificial color enhancement by high-temperature treatment of the specimen.

The formation of structures and properties of carburized elements and hardened in different quenching medium

International Nuclear Information System (INIS)

Przylecka, M.; Gestwa, W.

2003-01-01

In work structure and selected properties of hardened carburized layers were introduced produced on chromium-manganese steel (16HG - 16CrMn5), after processes of gas carburizing (850 o C/1-10 h) and vacuum carburizing (950 o C/2 h) as well as direct hardening (center cooling: distillated water, Water polymer solution - polyglycol oxyalkylen, oil and gas-nitrogen) and tempering. Results of investigations permitted to affirm, that layer with structure martensite - retained austenite, as carbides - martensite - retained austenite produced in process of hardening applying cooling centre water polymer solution, the impact strength of element (at define thickness of carburized layer) give profitable, suitable hardness and microhardness as well as changes of microhardness on section in comparison to produced layers during cooling in water or oil and gas. (author)

The effect of variations in carbon activity on the carburization of austenitic steels in sodium

International Nuclear Information System (INIS)

Gwyther, J.R.; Hobdell, M.R.; Hooper, A.J.

1978-07-01

Experience has shown that the liquid sodium coolant of fast breeder reactors is an effective carbon-transport medium; the resulting carburization of thin austenitic stainless steel components (eg IHX and fuel cladding) could adversely affect their mechanical integrity. The degree and nature of steel carburization depend, inter alia, on the carbon activity of the sodium environment. Exploratory tests are described in which specimens of austenitic stainless steel were carburized in sodium, the carbon activity of which was continuously monitored by a BNL electrochemical carbon meter. The sodium carbon activity was initially high, but decreased with time, simulating conditions equivalent to plant start-up or coolant clean-up following accidental oil ingress. The extent and nature of steel carburization was identified by metallography, electron microscopy, X-ray crystallography and chemical analysis. (author)

Response of cast austenitic stainless steel to low temperature plasma carburizing.

OpenAIRE

Sun, Yong

2008-01-01

The response of a cast 316 type austenitic stainless steel to the novel low temperature plasma carburizing process has been investigated in this work. The cast steel has a dendritic structure with a mix of austenite, ferrite and carbide phases. The results show that such a complex structure responds well to the carburizing process, and the inter-dendrite regions containing ferrite and carbides can be transformed to expanded austenite to form a continuous and uniform layer supersat...

Paraequilibrium Carburization of Duplex and Ferritic Stainless Steels

Science.gov (United States)

Michal, G. M.; Gu, X.; Jennings, W. D.; Kahn, H.; Ernst, F.; Heuer, A. H.

2009-08-01

AISI 301 and E-BRITE stainless steels were subjected to low-temperature (743 K) carburization experiments using a commercial technology developed for carburization of 316 austenitic stainless steels. The AISI 301 steel contained ~40 vol pct ferrite before carburization but had a fully austenitic hardened case, ~20- μm thick, and a surface carbon concentration of ~8 at. pct after treatment; this “colossal” paraequilibrium carbon supersaturation caused an increase in lattice parameter of ~3 pct. The E-BRITE also developed a hardened case, 12- to 18- μm thick, but underwent a more modest (~0.3 pct) increase in lattice parameter; the surface carbon concentration was ~10 at. pct. While the hardened case on the AISI 301 stainless steel appeared to be single-phase austenite, evidence for carbide formation was apparent in X-ray diffractometer (XRD) scans of the E-BRITE. Paraequilibrium phase diagrams were calculated for both AISI 301 and E-BRITE stainless steels using a CALPHAD compound energy-based interstitial solid solution model. In the low-temperature regime of interest, and based upon measured paraequilibrium carbon solubilities, more negative Cr-carbon interaction parameters for austenite than those in the current CALPHAD data base may be appropriate. A sensitivity analysis involving Cr-carbon interaction parameters for ferrite found a strong dependence of carbon solubility on relatively small changes in the magnitude of these parameters.

Surface composition of carburized tungsten trioxide and its catalytic activity

International Nuclear Information System (INIS)

Nakazawa, M.; Okamoto, H.

1985-01-01

The surface composition and electronic structure of carburized tungsten trioxide are investigated using x-ray photoelectron spectroscopy (XPS). The relationship between the surface composition and the catalytic activity for methanol electro-oxidation is clarified. The tungsten carbide concentration in the surface layer increases with the carburization time. The formation of tungsten carbide enhances the catalytic activity. On the other hand, the presence of free carbon or tungsten trioxide in the surface layer reduces the activity remarkably. It is also shown that, the higher the electronic density of states near the Fermi level, the higher the catalytic activity

Silica-calcium zirconate nanocomposite, studying its thermal

Indian Academy of Sciences (India)

Silica–calcium zirconate nanocomposite was prepared in a two-step procedure. First, nanocalcium zirconate was synthesized by the modified sol–gel method; then, silica was added to the prepared sol and the resulting product was calcined at 700–1000° C. Dilatometric measurements were performed to determine the ...

Effect on stress-strain relations brought by surface carburization of 316 stainless steel

International Nuclear Information System (INIS)

Matsumoto, K.

1977-01-01

The effect of sodium. environment on austenitic stainless steels used as structural materials in Liquid Metal Cooled Fast Breeder Reactors (LMFBRs) has long been the subject of extensive studies in many countries. Recent developments tending toward stricter control of the oxygen content permitted to be present in the circulating sodium have come to allay the apprehensions formerly held on the possibility of general corrosion affecting the mechanical properties of structural materials expected to be used In LMFBR plants. Grain boundary corrosion and depletion of elements from the structure surface also have come to be considered to provide little cause of fear in this regard, though some uncertainty is still left concerning the influence that these phenomena might exert toward the end of plant life. What still remains essentially to be clarified relates to carbon mass transfer. Decarburization and/or carburization are phenomena that cannot be disregarded even in the primary heat transfer system of LMFBRs, on account of the temperature dependence of carbon activity in steels, which could cause the carbon to leak out from structural material into the circulating sodium in the higher temperature zones of a circuit, to deposit itself on the channel walls in the lower temperature parts. Recent reports on loop experiments point toward the possibility of carboneous matter leaching into flowing sodium and into the cover gas to produce significant carburization phenomena. Carburization, in particular, can bring about loss of ductility and deterioration of fatigue properties, and hence serious consideration of this aspect is called for in the design of components incorporating thin stainless steel plates. To represent the stress-strain behavior at 550 deg. C of 316 stainless steel affected by surface carburization, an empirical formula was adopted. It was proposed by Voce for relating true stress to true plastic strain: σ = Aexp(C ε p ) + B, where σ is the true stress, and

Evaluation of Bending Strength of Carburized Gears Based on Inferential Identification of Principal Surface Layer Defects

Science.gov (United States)

Masuyama, Tomoya; Inoue, Katsumi; Yamanaka, Masashi; Kitamura, Kenichi; Saito, Tomoyuki

High load capacity of carburized gears originates mainly from the hardened layer and induced residual stress. On the other hand, surface decarburization, which causes a nonmartensitic layer, and inclusions such as oxides and segregation act as latent defects which considerably reduce fatigue strength. In this connection, the authors have proposed a formula of strength evaluation by separately quantifying defect influence. However, the principal defect which limits strength of gears with several different defects remains unclarified. This study presents a method of inferential identification of principal defects based on test results of carburized gears made of SCM420 clean steel, gears with both an artificial notch and nonmartensitic layer at the tooth fillet, and so forth. It clarifies practical uses of presented methods, and strength of carburized gears can be evaluated by focusing on principal defect size.

The effects of retained austenite on dry sliding wear behavior of carburized steels

Energy Technology Data Exchange (ETDEWEB)

Kim, Hyung-Jun [Research Inst. of Industrial Science and Technology, Steel Products Dept., Pohang (Korea, Republic of); Kweon, Young-Gak [Research Inst. of Industrial Science and Technology, Steel Products Dept., Pohang (Korea, Republic of)

1996-04-01

Ring-on-square tests on two kinds of low-alloy carburized steel which were AISI 8620 and 4140 were carried out to study the dry sliding wear behavior. The influence of different retained austenite level of 6% to 40% was evaluated while trying to eliminate other factors. Test results show that the effects of grain size and carburized steel species are negligible in dry sliding wear behavior. While the influence of retained austenite is negligible at 20 kg load condition, wear resistance is decreased at 40 kg load condition as the retained austenite level is increased from 6% to 30%. However, wear resistance is again increased above about 30% of retained austenite level at 40 kg load condition. (orig.)

LOW PRESSURE CARBURIZING IN A LARGE-CHAMBER DEVICE FOR HIGH-PERFORMANCE AND PRECISION THERMAL TREATMENT OF PARTS OF MECHANICAL GEAR

Directory of Open Access Journals (Sweden)

Emilia Wołowiec-Korecka

2017-03-01

Full Text Available This paper presents the findings of research of a short-pulse low pressure carburizing technology developed for a new large-chamber furnace for high-performance and precision thermal treatment of parts of mechanical gear. Sections of the article discuss the novel constructions of the device in which parts being carburized flow in a stream, as well as the low-pressure carburizing experiment. The method has been found to yield uniform, even and repeatable carburized layers on typical gear used in automotive industry.

Contribution to the study of gaseous Carburization of Uranium; Contribucion al estudio de la Carburacion gaesosa del uranio

Energy Technology Data Exchange (ETDEWEB)

Esteban Hernandez, J A; Jimenez Moreno, J M; Villota Ruiz, P de

1966-07-01

Thermal decomposition of uranium hydride powder obtained by hydrogenation of uranium turnings is studied on the first part of this paper. Carburization of the uranium hydride or metallic uranium powder with methane is studied in the second part. A method of uranium monocarbide fabrication under static atmosphere is described. On this method hydrogen is removed by means of an uranium getter. (Author) 6 refs.

Point defects in crystalline zircon (zirconium silicate), ZrSiO4: electron paramagnetic resonance studies

Science.gov (United States)

Tennant, W. C.; Claridge, R. F. C.; Walsby, C. J.; Lees, N. S.

This article outlines the present state of knowledge of paramagnetic defects in crystalline zircon as obtained mainly, but not exclusively, from electron paramagnetic resonance (EPR) studies in crystalline zircon (zirconium silicate, ZrSiO4). The emphasis is on single-crystal studies where, in principle, unambiguous analysis is possible. Firstly, the crystallography of zircon is presented. Secondly, the relationships between available crystal-site symmetries and the symmetries of observed paramagnetic species in zircon, and how these observations lead to unambiguous assignments of point-group symmetries for particular paramagnetic species are detailed. Next, spin-Hamiltonian (SH) analysis is discussed with emphasis on the symmetry relationships that necessarily exist amongst the Laue classes of the crystal sites in zircon, the paramagnetic species occupying those sites and the SH itself. The final sections of the article then survey the results of EPR studies on zircon over the period 1960-2002.

Effect on stress-strain relations brought by surface carburization of 316 stainless steel

Energy Technology Data Exchange (ETDEWEB)

Matsumoto, K [Ishikawajima-Harima Heavy Industries, Tokyo (Japan)

1977-07-01

The effect of sodium. environment on austenitic stainless steels used as structural materials in Liquid Metal Cooled Fast Breeder Reactors (LMFBRs) has long been the subject of extensive studies in many countries. Recent developments tending toward stricter control of the oxygen content permitted to be present in the circulating sodium have come to allay the apprehensions formerly held on the possibility of general corrosion affecting the mechanical properties of structural materials expected to be used In LMFBR plants. Grain boundary corrosion and depletion of elements from the structure surface also have come to be considered to provide little cause of fear in this regard, though some uncertainty is still left concerning the influence that these phenomena might exert toward the end of plant life. What still remains essentially to be clarified relates to carbon mass transfer. Decarburization and/or carburization are phenomena that cannot be disregarded even in the primary heat transfer system of LMFBRs, on account of the temperature dependence of carbon activity in steels, which could cause the carbon to leak out from structural material into the circulating sodium in the higher temperature zones of a circuit, to deposit itself on the channel walls in the lower temperature parts. Recent reports on loop experiments point toward the possibility of carboneous matter leaching into flowing sodium and into the cover gas to produce significant carburization phenomena. Carburization, in particular, can bring about loss of ductility and deterioration of fatigue properties, and hence serious consideration of this aspect is called for in the design of components incorporating thin stainless steel plates. To represent the stress-strain behavior at 550 deg. C of 316 stainless steel affected by surface carburization, an empirical formula was adopted. It was proposed by Voce for relating true stress to true plastic strain: {sigma} = Aexp(C {epsilon}{sub p} ) + B, where {sigma

Study of the 1.25Cr-1Mo-0.25V steel microstructure after a carburization phenomenon

Energy Technology Data Exchange (ETDEWEB)

Simonetti, S., E-mail: ssimonet@uns.edu.ar [Departamento de Fisica, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca (Argentina); Departamentos de Ciencias Basicas e Ingenieria Mecanica, Universidad Tecnologica Nacional, 11 de Abril 461, 8000 Bahia Blanca (Argentina); Lanz, C. [Departamento de Ingenieria, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca (Argentina); Brizuela, G.; Juan, A. [Departamento de Fisica, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca (Argentina)

2010-08-20

We studied the changes in the structure and carbide particle size in 1.25Cr-1Mo-0.25V steel under 600 deg. C and 168 MPa, after 4000 h service. We used microscopy and microanalysis techniques to analyze the carbide particles. We performed a complementary theoretical study on the chemical bonding and electronic structure of the carbide-Fe matrix interaction. The results contribute to the understanding of the changes in the alloy microstructure caused by the carburization phenomenon.

Low temperature plasma carburizing of AISI 316L austenitic stainless steel and AISI F51 duplex stainless steel

OpenAIRE

Pinedo,Carlos Eduardo; Tschiptschin,André Paulo

2013-01-01

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480ºC, using CH4 as carbon carrier gas. For the austenitic AISI 316L stainless steel, low temperature plasma carburizing induced a strong carbon supersaturation in the austenitic lattice and the formation of carbon expanded austenite (γC) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to ∼13 at% c...

Low temperature plasma carburizing of AISI 316L austenitic stainless steel and AISI F51 duplex stainless steel

OpenAIRE

Pinedo, Carlos Eduardo; Tschiptschin, André Paulo

2013-01-01

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480ºC, using CH4 as carbon carrier gas. For the austenitic AISI 316L stainless steel, low temperature plasma carburizing induced a strong carbon supersaturation in the austenitic lattice and the formation of carbon expanded austenite (γC) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to ∼13 at% carbon super...

Estimation of fatigue strength enhancement for carburized and shot-peened gears

Science.gov (United States)

Inoue, Katsumi; Kato, Masana

1994-05-01

An experimental formula has been proposed to estimate the bending fatigue strength of carburized gears from the hardness and the residual stress. The derivation of the formula is briefly reviewed, and the effectiveness of the formula is demonstrated in this article. The comparison with many test results for carburized and shot-peened gears verifies that the formula is effective for the approximate estimation of the fatigue strength. The formula quantitatively shows a way of enhancing fatigue strength, i.e., the increase of hardness and residual stress at the fillet. The strength is enhanced about 300 MPa by an appropriate shot peening, and it can be improved still more by the surface removal by electropolishing.

Creep behavior of plasma carburized Ti-6Al-4V alloy

International Nuclear Information System (INIS)

Oliveira, Veronica Mara Cortez Alves de; Barboza, Miguel Justino Ribeiro; Silva, Mariane Capellari Leite da; Pinto, Catia Gisele; Suzuki, Paulo Atsushi; Machado, Joao Paulo B.

2010-01-01

This paper aims to evaluate the effect of plasma carburizing on the Ti-6Al-4V alloy submitted to creep tests. The results showed that the alloy Ti-6Al-4V had a hardness of 334 ± 18 HV. After treatment thermochemical by plasma, was observed the formation of a layer of average thickness of 1,5 μm and hardness of 809 ± 79 HV due to the presence of TiC phase identified by X-ray diffraction. The treatment increased the values of average roughness of 1,28 to 2,02 μm. The creep properties of carburized specimens were improved in comparison with those of the uncarburized Ti-6Al-4V alloy. (author)

PENGARUH KOMPOSISI ARANG AKTIF DAN KALSIUM KARBONAT PADA PACK CARBURIZING TERHADAP MICROSTRUCTURE

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Hafni, Syafrul Hadi

2016-05-01

Full Text Available Penelitian ini bertujuan untuk mendapatkan metode pengerasan  permukaan pada baja lunak, dengan proses pack carburizing. Baja lunak banyak digunakan sebagai bahan dalam pembuatan suatu produk.  Untuk mendapatkan sifat yang keras pada permukaan dan tetap lunak pada intinya maka  dilakukan proses pengerasan permukaan, sehingga produk tersebut dapat difungsikan sesuai dengan  tujuan desainnya. Proses carburizing ini, diperlukan sebuah tungku pembakar yang dirancang tahan panas serta mudah dioperasikan. aman dengan bahan bakar batu bara . untuk penguji tungku yang telah dirancang dilakukan pengujian pada baja rabon rendah dengan mengunakan media karburisasi 1000 gr arang aktif dengan variasi :  200 gram, 100 grm, 66.7 gram Kalsium  karbonat ( CaCo3 pada temperatur   pemanasan 950 0C dan  waktu tahan 4 jam   Kemudian dilanjukan dengan proses quenching. Dari hasil pengujian menunjukan bahan uji dengan komposisi 1000 gr arang aktif dengan 200 gram calcium carbonat lebih baik penambahan unsur karbon sehingga waktu dilakukan quenching terbentuk struktur mikro martensite Kata kunci : Komposisi Arang aktif dan CaCo3, Temperatur, Waktu tahan The goal of the research to obtain surface hardening method on mild steel, with a pack carburizing process. Mild steel is widely used as an ingredient in the manufacture of a product. To get hard on the nature of the surface and remains soft at the core surface hardening process is carried out, so that the product can be used in accordance with the purpose of design.To do this carburizing process, required a stove burner designed heat resistant and easy to operate. safe with fuel coal. for testers furnace that has been designed to do testing on steel Rabon low by using media carburizing 1000 grams of activated charcoal with variations: 200 grams, 100 grm, 66.7 grams of calcium carbonate (CaCO3 at the heating temperature of 950 0C and holding time 4 hours Then dilanjukan with process quenching. Test results

Work function of carburized rhenium

International Nuclear Information System (INIS)

Pallmer, P.G. Jr.; Gordon, R.L.; Dresser, M.J.

1980-01-01

Variations of the electronic work function of carburized rhenium foils containing approximately 5 at.% carbon have been observed using the contact potential difference technique. Surface work function was observed to vary between 5.25 and 4.1 eV, with the work function of pure rhenium taken as 5.0 eV. Decrease in work function has been ascribed to the formation of graphitic layers on the surface at temperatures below the temperature of saturated solubility. The high work function surface was observed with all carbon in solution and has been ascribed to the presence of amorphous carbon near the surface

A model for fracture toughness evaluation of the carburized layer for SAE 5115 steel

OpenAIRE

Sandor, Leonardo Taborda; Ferreira, Itamar

2006-01-01

The purpose of this work is to propose a model for evaluating the fracture toughness along the SAE 5115 steel carburized layer. Due to the small thickness of those layers, it is impossible to machine specimens from those layer in accordance with standards. For simulating the microstructures of the carburized layer in order to get samples for tensile and the fracture toughness testing, specimens of SAE 5115, 5140, 5160, and 52100 steels have been machined, assuming the local influence just the...

The efficiency of different types of wood charcoal on increasing carbon content on surfaces of low carbon steel in the pack carburizing process

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Narongsak Thammachot

2014-09-01

Full Text Available The purpose of this research is to compare the efficiency of five types of wood charcoal, eucalyptus, coconut shell, tamarind, bamboo and cassava root in increasing carbon content on surfaces of low carbon steel by the pack carburizing process. The experiment for pack carburized low carbon steel (grade AISI 1020 was conducted by using the different wood charcoals as carburizers, mixed with 10% limestone (by weight as the energizer. The carburizing temperature of 950°C, and carburizing times of 2, 4 and 6 hours were used in the experiment. After grinding, the specimens in each case were checked for carbon content by optical emission spectroscopy. Micro-Vickers hardness testing and microstructure inspections were carried out. The results of the experiment showed that the efficiency of eucalyptus charcoal as the carburizer (for increasing carbon content on surfaces of low carbon steel was higher than that of tamarind, cassava root, coconut shell and bamboo charcoals. The averages for carbon content were: 1.16, 1.06, 0.97, 0.83 and 0.77% respectively.

Morphology versus U-Pb systematics in zircon: A high-resolution isotopic study of a zircon population from a Variscan dike in the Central Alps

International Nuclear Information System (INIS)

Bossart, P.J.; Meier, M.; Oberli, F.; Steiger, R.H.

1986-01-01

U/Pb isotopic measurements on individual zircon crystals combined with morphological analyses permit the identification of three distinct components within the zircon population of the Saedelhorn diorite, a Variscan dike from the western Gotthard (Central Alps, Switzerland): (i) 94% of the grains in the zircon population are elongate crystals with pronounced skeletal morphology indicative of rapid growth from a supercooled melt. (ii) 5% of the population consist of turbid, mostly subhedral zircons frequently showing D-type morphology and elevated uranium contents compared to the skeletal variety. Single-crystal and multi-grain U-Pb isotopic data of group (i) and (ii) zircons define an intrusion age of 293 + 5/ -4 m.y. for the dike. (iii) Rare, transparent zircon crystals (< 1% of the zircons population) yield apparent U-Pb ages in the range of 370-490 m.y. and display morphological and isotopic characteristics closely resembling those of a Caledonian orthogneiss intruded by the dike. This implies presence of assimilated wall-rock components in the macroscopically homogeneous dike sample. (orig./WB)

Inflight dissociation of zircon in air plasma

Energy Technology Data Exchange (ETDEWEB)

Yugeswaran, S; Selvarajan, V [Bharathiar University, Coimbatore 641046 (India); Ananthapadmanabhan, P V; Thiyagarajan, T K [Laser and Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai - 400 085 (India); Nair, Janardhanan [Ion Arc Technologies Pvt Ltd, Coimbatore (India)

2010-02-01

Thermal dissociation of zircon can be conveniently carried out in a plasma reactor, which is characterized by high temperature, high energy density and high quench rate. Zirconia is recovered from this partially dissociated zircon by alkali leaching. Dissociation of zircon has been conventionally carried out in argon gas, which is expensive. The present paper reports experimental results on thermal dissociation of zircon in air plasma medium. Process simulation for 'inflight' dissociation of zircon in air plasma medium is also presented. The experimental system consists of a central hollow graphite electrode, which acts as the cathode and a graphite anode. The material to be processed is fed centrally through the cathode. The unique feature of the system is that it uses air as the working gas to generate the thermal plasma. The system has been used to study in-flight dissociation of zircon in the thermal plasma jet. Dissociation was carried out over 10-25 kW power range. Results of the study indicate that complete dissociation of zircon to ZrO{sub 2} and silica could be accomplished at 25 kW in air plasma.

Inflight dissociation of zircon in air plasma

International Nuclear Information System (INIS)

Yugeswaran, S; Selvarajan, V; Ananthapadmanabhan, P V; Thiyagarajan, T K; Nair, Janardhanan

2010-01-01

Thermal dissociation of zircon can be conveniently carried out in a plasma reactor, which is characterized by high temperature, high energy density and high quench rate. Zirconia is recovered from this partially dissociated zircon by alkali leaching. Dissociation of zircon has been conventionally carried out in argon gas, which is expensive. The present paper reports experimental results on thermal dissociation of zircon in air plasma medium. Process simulation for 'inflight' dissociation of zircon in air plasma medium is also presented. The experimental system consists of a central hollow graphite electrode, which acts as the cathode and a graphite anode. The material to be processed is fed centrally through the cathode. The unique feature of the system is that it uses air as the working gas to generate the thermal plasma. The system has been used to study in-flight dissociation of zircon in the thermal plasma jet. Dissociation was carried out over 10-25 kW power range. Results of the study indicate that complete dissociation of zircon to ZrO 2 and silica could be accomplished at 25 kW in air plasma.

Wear resistance of AISI 304 stainless steel submitted to low temperature plasma carburizing

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Marcos Antônio Barcelos

Full Text Available Abstract Despite the AISI 304 stainless steel has high corrosion/oxidation resistance, its tribological properties are poor, being one of the barriers for use in severe wear applications. Thus, there is a wide field for studying technologies that aim to increase the surface hardness and wear resistance of this material. In this work, hardness and wear resistance for AISI 304 stainless steel submitted to the thermochemical treatment by low temperature plasma carburizing (LTPC in a fixed gas mixture composition of 93% H2 and 7% CH4 are presented. Through the evaluation of the carburizing layers, it was possible to observe a substantial improvement in tribological properties after all temperature and time of treatment. This improvement is directly related to the increase of the process variables; among them temperature has a stronger influence on the wear resistance obtained using LTPC process.

Evaluation of carburization depth in service exposed ferritic steel using magnetic Barkhausen noise analysis

International Nuclear Information System (INIS)

Vaidyanathan, S.; Moorthy, V.; Jayakumar, T.; Baldev Raj

1996-01-01

The feasibility of using magnetic Barkhausen (MBN) measurement for the evaluation of carburization depth in ferritic steels has been reported in this paper. MBN measurements were carried out on samples from service exposed 0.5Cr-0.5Mo ferritic steel tube at different depths (cross section) from carburised ID surface to simulate the variation in carbon concentration gradient within the skin depth of MBN with increasing time of exposure to carburization. It has been observed that the MBN level increases with increasing depth of measurement. An inverse relation between MBN level and carbon content/hardness value has been observed. This study suggests that, the MBN measurements on the carburised surface can be correlated with the concentration gradient within the skin depth of the MBN which would help in predicting the approximate depth of the carburised layer with proper prior calibration. (author)

Effect of pressure on Zircon's (ZrSiO4) Raman active modes: a first-principles study

Science.gov (United States)

Sheremetyeva, Natalya; Cherniak, Daniele; Watson, Bruce; Meunier, Vincent

Zircon is a mineral commonly found in the Earth crust. Its remarkable properties have given rise to considerable attention. This includes possible inclusion of radioactive elements in natural samples, which allows for geochronological investigations. Subsequently, Zircon was proposed as possible host material for radioactive waste management. Internal radiation damage in zircon leads to the destruction of its crystal structure (an effect known as metamictization) which is subject to ongoing research. Recently, the effect of pressure and temperature on synthetic zircon has been analyzed experimentally using Raman spectroscopy which led to the calibration of zircon as a pressure sensor in diamond-anvil cell experiments. While there have been a number of theoretical studies, the effect of pressure on the Raman active modes of zircon has not been investigated theoretically. Here we present a first-principles pressure calibration of the Raman active modes in Zircon employing density-functional theory (DFT). We find excellent quantitative agreement of the slopes ∂ω / ∂P with the experimental ones and are able to rationalize the ω vs. P behavior based on the details of the vibrational modes.

Fatigue studies in compensated bulk lead zirconate titanate

International Nuclear Information System (INIS)

Verdier, Cyril; Morrison, Finlay D.; Lupascu, Doru C.; Scott, James F.

2005-01-01

Impedance analysis studies were carried out on compensated bulk lead zirconate titanate samples. Fatigue is concomitant with the onset of dielectric loss. This is shown to be dominantly due to an irreversibly modified near-surface layer that can be polished off. The highly compensated nature of these samples minimizes the role of oxygen vacancies

Testing the reliability of information extracted from ancient zircon

Science.gov (United States)

Kielman, Ross; Whitehouse, Martin; Nemchin, Alexander

2015-04-01

Studies combining zircon U-Pb chronology, trace element distribution as well as O and Hf isotope systematics are a powerful way to gain understanding of the processes shaping Earth's evolution, especially in detrital populations where constraints from the original host are missing. Such studies of the Hadean detrital zircon population abundant in sedimentary rocks in Western Australia have involved analysis of an unusually large number of individual grains, but also highlighted potential problems with the approach, only apparent when multiple analyses are obtained from individual grains. A common feature of the Hadean as well as many early Archaean zircon populations is their apparent inhomogeneity, which reduces confidence in conclusions based on studies combining chemistry and isotopic characteristics of zircon. In order to test the reliability of information extracted from early Earth zircon, we report results from one of the first in-depth multi-method study of zircon from a relatively simple early Archean magmatic rock, used as an analogue to ancient detrital zircon. The approach involves making multiple SIMS analyses in individual grains in order to be comparable to the most advanced studies of detrital zircon populations. The investigated sample is a relatively undeformed, non-migmatitic ca. 3.8 Ga tonalite collected a few kms south of the Isua Greenstone Belt, southwest Greenland. Extracted zircon grains can be combined into three different groups based on the behavior of their U-Pb systems: (i) grains that show internally consistent and concordant ages and define an average age of 3805±15 Ma, taken to be the age of the rock, (ii) grains that are distributed close to the concordia line, but with significant variability between multiple analyses, suggesting an ancient Pb loss and (iii) grains that have multiple analyses distributed along a discordia pointing towards a zero intercept, indicating geologically recent Pb-loss. This overall behavior has

Protoliths of enigmatic Archaean gneisses established from zircon inclusion studies: Case study of the Caozhuang quartzite, E. Hebei, China

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Allen P. Nutman

2014-07-01

Full Text Available A diverse suite of Archaean gneisses at Huangbaiyu village in the North China Craton, includes rare fuchsite-bearing (Cr-muscovite siliceous rocks – known as the Caozhuang quartzite. The Caozhuang quartzite is strongly deformed and locally mylonitic, with silica penetration and pegmatite veining common. It contains abundant 3880–3600 Ma and some Palaeoarchaean zircons. Because of its siliceous nature, the presence of fuchsite and its complex zircon age distribution, it has until now been accepted as a (mature quartzite. However, the Caozhuang quartzite sample studied here is feldspathic. The shape and cathodoluminescence petrography of the Caozhuang quartzite zircons show they resemble those found in immature detrital sedimentary rocks of local provenance or in Eoarchaean polyphase orthogneisses, and not those in mature quartzites. The Caozhuang quartzite intra-zircon mineral inclusions are dominated by quartz, with lesser biotite, apatite (7% and alkali-feldspar, and most inclusions are morphologically simple. A Neoarchaean orthogneiss from near Huangbaiyu displays morphologically simple inclusions with much more apatite (73%, as is typical for fresh calc-alkaline granitoids elsewhere. Zircons were also examined from a mature conglomerate quartzite clast and an immature feldspathic sandstone of the overlying weakly metamorphosed Mesoproterozoic Changcheng System. These zircons have oscillatory zoning, showing they were sourced from igneous rocks. The quartzite clast zircons contain only rare apatite inclusions (<1%, with domains with apatite habit now occupied by intergrowths of muscovite + quartz ± Fe-oxides ± baddeleyite. We interpret that these were once voids after apatite inclusions that had dissolved during Mesoproterozoic weathering, which were then filled with clays ± silica and then weakly metamorphosed. Zircons in the immature feldspathic sandstone show a greater amount of preserved apatite (11%, but with petrographic

A short and long range study of mullite-zirconia-zircon composites

Energy Technology Data Exchange (ETDEWEB)

Rendtorff, Nicolas M.; Conconi, Maria S.; Aglietti, Esteban F. [Centro de Tecnologia de Recursos Minerales y Ceramica (CETMIC: CONICET-CIC) (Argentina); Chain, Cecilia Y.; Pasquevich, Alberto F. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina); Rivas, Patricia C. [CONICET (Argentina); Martinez, Jorge A., E-mail: toto@fisica.unlp.edu.ar; Caracoche, Maria C. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina)

2010-06-15

In the field of refractory materials, ceramics containing mullite-zirconia are the basis of those most used in the industry of glass and steel. It is known that the addition of zircon improves the behavior of the refractory used in service. Knowing that some mullite-zirconia composites properties as fracture strength and the elastic modulus E are associated with the material microstructure integrity, the eventual thermal decomposition of zircon into zirconia and silica could seriously alter the material elastic properties. In this paper the phase content of a series of mullite-zirconia-zircon (3Al{sub 2}O{sub 3}.2SiO{sub 2}-ZrO{sub 2}-ZrSiO{sub 4}) composites is determined at atomic level via perturbed angular correlations (PAC) and compared with that derived from the long range X-ray diffraction technique. PAC results on the as-prepared materials indicate that all nominal zircon is present and that it involves two types of nanoconfigurations, one of them describing aperiodic regions. The thermomechanical properties already reported for these materials could be related to the crystalline to aperiodic zircon concentrations ratio they exhibit.

At what conditions does zircon grow/dissolve during high-T metamorphism? Relating zircon textures to PT-conditions

Science.gov (United States)

Kunz, Barbara E.; Regis, Daniele; Manzotti, Paola; Engi, Martin

2015-04-01

A key question in ziconology is when and how zircon grows during metamorphism. To shed light on zircon forming processes and the corresponding PT-conditions during high-T metamorphism a case study was undertaken. The Ivrea Zone (N-Italy) exposes a lower continental crustal section in which a continuous metamorphic field gradient from amphibolite to granulite facies is documented. This field gradient is thought to reflect protracted heating during late Paleozoic times, with a probable high-T peak in the Permian. We present first results from a primarily textural study supported by U-Pb ages, Th/U ratios and Ti-in-Zrn thermometry. Four types of zircon were identified based on their overgrowth proportions and the preservation of detrital cores. Zircon grains were thus classified as Type1 - detrital grains with no overgrowth or very narrow rims (300 Ma) and appears to reflect an early dehydration phase. Rim2b has Permian ages (median 275 Ma), is by far the most common overgrowth type, found in a wide PT-range. Its development appears related to biotite breakdown. Rim3 is texturally indicative of magmatic zircon, occurs only in diatexites. Rim4 is the latest overgrowth and is locally found at all metamorphic grades. Textural features suggest late fluid-related recrystallization of existing zircon. At lowest grade (675±35°C, 6±2 kbar) zircons show type1 only, overgrowths are too thin to clearly identify the rim type. Further upgrade (~700°C, 7 kbar) type1 and type2 dominate. Type2 zircons show rim1, rim2a and occasionally rim4. At the Mu-out isograd (750±50°C, 8.2±1.4 kbar) most zircons are of type2, now with rim2b instead of 2a, in addition to rim1 and rim4. Near and in granulite facies (to 800°C, 8±2 kbar) mostly zircon type2 and type4 are present. While rim1 gets more narrow with increasing metamorphic grade, rim2b grows significantly thicker. Occasionally rim2a and rim4 occur. Close to the Bt-out isograd (~860°C, 9.2±1.7 kbar), mostly type3 and type4 are

Fission track dating of zircon: a multichronometer

International Nuclear Information System (INIS)

Carpena, J.

1992-01-01

Scattering in Fission Track ages of zircons of a single rock is possible when they present morphological and geochemical variations, if the greatest care is not taken in the choice of the etching conditions and the counting of tracks. The Fission Track study of two heterogeneous populations of zircons from the Mont Blanc granite and from the Gran Paradiso gneisses allows to show that zircon may work as a multichronometer

Study of Effect of Quenching Deformation Influenced by 17CrNiMo6 Gear Shaft of Carburization

Science.gov (United States)

Pang, Zirui; Yu, Shenjun; Xu, Jinwu

The 17CrNiMo6 steel is mainly used for the gear shaft of large modulus in many fields of heavy industry such as mining, transit, hoist, forging and so on[1]. The size of addendum circle and common normal line is changed a lot beyond the tolerance because of the long time of carburizing process and the out-of-step structural stress and thermal stress during the quenching process. And thus the posterior grinding efficiency and quality are influenced. In the paper comparison and analysis of the deformation affected by solid and hollow gear shafts were done and the methods of simulation and practice were both used. The results are as follows: the deformation of gear shaft was small before and after carburizing while that of gear shaft was large before and after quenching because of different cooling velocity, structure and hardness of each position. And the deformation of hollow was much smaller than that of solid. Therefore, if the hollow gear shaft is used, the waste of material will be decreased, and finishing cost will be reduced, and thus the technology of heat treatment will be optimized.

Separation of zircon from the beach sand deposit of Srikurmam area, Srikakulam district, Andhra Pradesh - a case study

International Nuclear Information System (INIS)

Rao, G.V.S.U.; Sharma, A.K.; Seshadrinath, S.T.; Fahmi, Sohail; William Prasad, Ch.; Nagabhushanam, B.

2011-01-01

Beach sand placer deposits occur along the eastern and western coasts of India, which contain heavy minerals, such as ilmenite, rutile, garnet, monazite, zircon and sillimanite. Among these, zircon is used in zircaloys (nuclear industry), ceramics, refractories, abrasives, etc. Separation and chemical characterization of pure zircon is a prelude for understanding the different elements and impurities present and its industrial application. In recent times, several methods are developed for beneficiation and separation of individual heavy minerals from beach sands. In this paper, separation of zircon from beach sand of Srikurmam area, Andhra Pradesh was taken up as a case study. The process flow sheet adopted for separation and isolation of pure zircon from beach sand sample consists of desliming of beach sand, wet tabling of sand fraction, removal of magnetite by low intensity magnetic separation from table concentrate, perm roll magnetic separation and induced roll magnetic separation of table concentrate. The concentrates were further subjected to iso-dynamic magnetic separator after observing impurity present in the sample under binocular stereomicroscope. In the present process, about 95% pure zircon was obtained. Further concentration of zircon was carried out under the binocular stereomicroscope by hand picking of impurity to obtain 99.5% pure zircon concentrate. The pure zircon concentrate was analyzed for major, minor and trace elements by chemical method for characterization of zircon and cross validation of physical processes through which the zircon concentrate was obtained. Chemical analysis of the pure zircon concentrate indicated 63.15 to 64.79% ZrO 2 and 32.2 to 32.8% SiO 2 . These values are nearer to that of pure zircon, which stoichiometrically contains 67.2% ZrO 2 and 32.8 % SiO 2 with little iron. In the present study, ZrO 2 +HfO 2 content varies from 65.27 to 66.17% and hafnium from 1.25 to 1.46% HfO 2 in the zircon concentrate. The variation

Gold in Accessory Zircon (the Kozhim Massif, Subpolar Urals)

Science.gov (United States)

Denisova, Yuliya; Pystin, Aleksandr

2017-12-01

The crystals of zircon due to their resistance to external impact of various processes can reveal information about the environment of their formation and the inclusions observed of them. Zircon contains different mineral inclusions: biotite, plagioclase, quartz, apatite, etc. However, there is no information about gold inclusions in the zircons from granites of the Sudpolar Urals. The study results of the inclusions of gold in accessory zircon of the Kozhim granitic massif are presented in this paper. The studied mineral is a dark-brown translucent short-prismatic crystal containing the inclusion of gold and the allocations of quartz. According to studies, the inclusion of gold formed during the growth of zircon and it is the gold covered with a thin film of oxide gold. It was confirmed that the crystallization of the studied zircon occurred at a temperature of 800°C and above on the stage of formation of granites of Kozhim massif. The assumption is made about the additional temperature in the course of which was caused by decreasing of temperature up to 700° C and below during postmagmatic stage.

Ti-in-zircon thermometry: applications and limitations

Science.gov (United States)

Fu, Bin; Page, F. Zeb; Cavosie, Aaron J.; Fournelle, John; Kita, Noriko T.; Lackey, Jade Star; Wilde, Simon A.; Valley, John W.

2008-08-01

The titanium concentrations of 484 zircons with U-Pb ages of ˜1 Ma to 4.4 Ga were measured by ion microprobe. Samples come from 45 different igneous rocks (365 zircons), as well as zircon megacrysts (84) from kimberlite, Early Archean detrital zircons (32), and zircon reference materials (3). Samples were chosen to represent a large range of igneous rock compositions. Most of the zircons contain less than 20 ppm Ti. Apparent temperatures for zircon crystallization were calculated using the Ti-in-zircon thermometer (Watson et al. 2006, Contrib Mineral Petrol 151:413-433) without making corrections for reduced oxide activities (e.g., TiO2 or SiO2), or variable pressure. Average apparent Ti-in-zircon temperatures range from 500° to 850°C, and are lower than either zircon saturation temperatures (for granitic rocks) or predicted crystallization temperatures of evolved melts (˜15% melt residue for mafic rocks). Temperatures average: 653 ± 124°C (2 standard deviations, 60 zircons) for felsic to intermediate igneous rocks, 758 ± 111°C (261 zircons) for mafic rocks, and 758 ± 98°C (84 zircons) for mantle megacrysts from kimberlite. Individually, the effects of reduced a_{TiO2} or a_{SiO2}, variable pressure, deviations from Henry’s Law, and subsolidus Ti exchange are insufficient to explain the seemingly low temperatures for zircon crystallization in igneous rocks. MELTs calculations show that mafic magmas can evolve to hydrous melts with significantly lower crystallization temperature for the last 10-15% melt residue than that of the main rock. While some magmatic zircons surely form in such late hydrous melts, low apparent temperatures are found in zircons that are included within phenocrysts or glass showing that those zircons are not from evolved residue melts. Intracrystalline variability in Ti concentration, in excess of analytical precision, is observed for nearly all zircons that were analyzed more than once. However, there is no systematic change in Ti

Positron annihilation lifetime study of radiation-damaged natural zircons

Energy Technology Data Exchange (ETDEWEB)

Roberts, J. [Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, The Australian National University, Canberra (Australia); Gaugliardo, P. [Centre for Antimatter-Matter Studies, School of Physics, University of Western Australia (Australia); Farnan, I.; Zhang, M. [Department of Earth Sciences, University of Cambridge (United Kingdom); Vance, E.R.; Davis, J.; Karatchevtseva, I.; Knott, R.B. [Australian Nuclear Science and Technology Organisation (Australia); Mudie, S. [The Australian Synchrotron, Victoria (Australia); Buckman, S.J. [Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, The Australian National University, Canberra (Australia); Institute for Mathematical Sciences, University of Malaya, Kuala Lumpur (Malaysia); Sullivan, J.P., E-mail: james.sullivan@anu.edu.au [Centre for Antimatter-Matter Studies, Research School of Physics and Engineering, The Australian National University, Canberra (Australia)

2016-04-01

Zircons are a well-known candidate waste form for actinides and their radiation damage behaviour has been widely studied by a range of techniques. In this study, well-characterised natural single crystal zircons have been studied using Positron Annihilation Lifetime Spectroscopy (PALS). In some, but not all, of the crystals that had incurred at least half of the alpha-event damage of ∼10{sup 19} α/g required to render them structurally amorphous, PALS spectra displayed long lifetimes corresponding to voids of ∼0.5 nm in diameter. The long lifetimes corresponded to expectations from published Small-Angle X-ray Scattering data on similar samples. However, the non-observation by PALS of such voids in some of the heavily damaged samples may reflect large size variations among the voids such that no singular size can be distinguished or. Characterisation of a range of samples was also performed using scanning electron microscopy, optical absorption spectroscopy, Raman scattering and X-ray scattering/diffraction, with the degree of alpha damage being inferred mainly from the Raman technique and X-ray diffraction. The observed void diameters and intensities of the long lifetime components were changed somewhat by annealing at 700 °C; annealing at 1200 °C removed the voids entirely. The voids themselves may derive from He gas bubbles or voids created by the inclusion of small quantities of organic and hydrous matter, notwithstanding the observation that no voidage was evidenced by PALS in two samples containing hydrous and organic matter. - Highlights: • Study of a range of naturally occurring zircons damaged by alpha radiation. • Characterised using a range of techniques, including PALS spectroscopy. • Effects on hydrous material appear important, rather than direct radiation damage. • Annealing is shown to remove the observed voids.

Fission track dating of kimberlitic zircons

International Nuclear Information System (INIS)

Haggerty, S.E.

1983-01-01

The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206 Pb and 238 U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.0 +- 6.5 m.y.), Orapa (87.4 +- 5.7 and 92.4 +- 6.1 m.y.), Nzega (51.1 +- 3.8 m.y.), Koffiefontein (90.9 +- 8.2 m.y.), and Val do Queve (133.4 +- 11.5 m.y.). In addition we report the first radiometric ages (707.9 +- 59.6 and 705.5 +- 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption. (orig.)

Isotope ratio measurements of pg-size plutonium samples using TIMS in combination with the 'Multiple Ion Counting' and filament carburization

Energy Technology Data Exchange (ETDEWEB)

Jakopic, Rozle; Richter, Stephan; Kuehn, Heinz; Aregbe, Yetunde [European Commission, Directorate General Joint Research Centre Institute for Reference Materials and Measurements, IRMM Retieseweg 111, B-2440 Geel (Belgium)

2008-07-01

A new sample preparation procedure for isotopic measurements using the Triton TIMS (Thermal Ionization Mass Spectrometer) was developed which employed the technique of carburization of rhenium filaments. Carburized filaments were prepared in a special vacuum chamber in which the filaments were heated and exposed to benzene vapor. Ionization efficiency was improved by an order of magnitude. Additionally, a new 'multi-dynamic' measurement technique was developed for Pu isotope ratio measurements using the 'multiple ion counting' (MIC) system. This technique was further combined with the filament carburization technique and applied to the NBL-137 isotopic standard and samples of the NUSIMEP 5 inter-laboratory comparison campaign. The results clearly show an improved precision and accuracy for the 'multi-dynamic' measurement procedure, compared to measurements carried out either in peak-jumping or in static mode using the MIC system with non-carburized filaments. (authors)

Corrosion and carburization behavior of Al-rich surface layer on Ni-base alloy in supercritical-carbon dioxide environment

Energy Technology Data Exchange (ETDEWEB)

Lee, Ho Jung, E-mail: leehojung@kaist.ac.kr; Kim, Sung Hwan, E-mail: sciencetom@kaist.ac.kr; Kim, Hyunmyung, E-mail: h46kim@kaist.ac.kr; Jang, Changheui, E-mail: chjang@kaist.ac.kr

2016-12-01

Highlights: • Al-rich layer was developed on Alloy 600 by Al deposition and EB remelting. • When exposed to S-CO{sub 2} at 600 °C, mostly Cr{sub 2}O{sub 3} with transition Al{sub 2}O{sub 3} was formed. • Carburized region of amorphous C layer was observed at the oxide/matrix interface. • α-Al{sub 2}O{sub 3} was formed after pre-oxidation which resulted in superior resistance. - Abstract: In order to improve the corrosion and carburization resistance in a high-temperature supercritical-carbon dioxide (S-CO{sub 2}) environment, an Al-rich surface layer was developed on Alloy 600 by Al deposition and a subsequent high energy electron beam (EB) remelting. As a result of the EB surface treatment, an Al enriched (5–7 wt.%) micro-alloying zone (40 μm) was produced. When the EB surface-treated Alloy 600 was corroded in S-CO{sub 2} at 600 °C (20 MPa) for 500 h, the surface oxide layer mostly consisted of chromia (Cr{sub 2}O{sub 3}) with small amount of transition alumina (Al{sub 2}O{sub 3}). In addition, a carburized region of an amorphous C layer inter-mixed with the alumina was observed at the oxide/matrix interface. Meanwhile, when the EB surface-treated specimen was pre-oxidized in helium at 900 °C, α-alumina layer was formed on the surface, which showed superior corrosion and carburization resistance in S-CO{sub 2} environment. Therefore, it could be said that the presence of Al-rich surface layer alone is not enough to provide sufficient corrosion and carburization resistance in S-CO{sub 2} environment at 600 °C, unless pre-oxidation at higher temperature is applied to form a more protective α-alumina on the surface.

Application of energy-dispersive XRF technique in the hydrometallurgy study of local zircon

International Nuclear Information System (INIS)

Meor Yusoff Sulaiman; Kamaruddin Hussin; Azizan Aziz

1996-01-01

In this study, energy-dispersive X-ray Fluorescence (EDXR-F) was used to analyse the elemental composition of the starting zircon mineral associated elements in the leaching solution. Besides analysing the major elements i.e. of zirconium, silicon and hafnium, trace elemental analysis for iron, titanium and the naturally occurring radioactive element thorium and uranium are important in establishing the grades of Malaysian zircon. The technique was also used in determine the optimum conditions for zirconium and hafnium recovery during the leaching process

High temperature studies on scheelite and zircon type ThGeO4

International Nuclear Information System (INIS)

Patwe, S.J.; Achary, S.N.; Tyagi, A.K.

2008-01-01

The detailed structural analyses of two polymorphs of ThGeO 4 , namely, zircon (stable) and scheelite (metastable) types have been carried out from the in situ high temperature X-ray diffraction studies. Though both the polymorphs show positive thermal expansion, the coefficient of volume thermal expansion of scheelite modification is almost double of that for zircon modification. The anisotropies in thermal expansion behaviors are also different for the two modifications. The differences in thermal expansion behaviors have been explained from the differences in structural arrangements and anisotropy of the ThO 8 polyhedra in these two modifications. (author)

The carbide M7C3 in low-temperature-carburized austenitic stainless steel

International Nuclear Information System (INIS)

Ernst, Frank; Li, Dingqiang; Kahn, Harold; Michal, Gary M.; Heuer, Arthur H.

2011-01-01

Prolonged low-temperature gas-phase carburization of AISI 316L-type austenitic stainless steel can cause intragranular precipitation of the carbide M 7 C 3 (M: randomly dispersed Fe, Cr, Ni). Transmission electron microscopy revealed that the carbide particles have the shape of needles. They grow by a ledge-migration mechanism and in a crystallographic orientation relationship to the austenite matrix that enables highly coherent interphase interfaces. A small solubility limit of Ni in the carbide and restricted Ni diffusivity at the processing temperature leads to Ni pileup around the particles and may explain the extreme aspect ratio of the particle shape. These characteristics closely resemble what has been observed earlier for precipitates of M 5 C 2 under slightly different processing conditions and can be rationalized by considering the particular constraints imposed by carburization at low temperature.

Single-zircon dating by stepwise Pb-evaporation constrains the Archean history of detrital zircons from the Jack Hills, Western Australia

International Nuclear Information System (INIS)

Kober, B.; Lippolt, H.J.; Pidgeon, R.T.

1989-01-01

Pb isotope analyses have been carried out on 42 zircon grains from a Western Australian metaconglomerate using stepwise Pb-evaporation directly in the ion source of a thermal ionization mass spectrometer. The metaconglomerate is from the Archean Jack Hills Metasedimentary Belt, and is known from ion microprobe (''SHRIMP'') analyses to contain a complex zircon population with ages between 4.2 Ga and 3.1 Ga. The same complex pattern of ages is found by the Pb evaporation studies. Five grains yielded minimum crystallization ages from 4.17 Ga to 4.07 Ga. The main population appears significantly younger, having been generated at about 3.55-3.3 Ga. The agreement between the two analytical approaches confirms the SHRIMP results and demonstrates the value of the stepwise-evaporation technique in determining the age patterns of mixing zircon populations. In many of the evaporative Pb isotope records the 207/206 ratios remained constant for all evaporation steps, which we interpret as evaporation from concordant zircon phases. However, for the majority of zircons 207/206 ratios increased with increasing evaporation temperature, and usually approached constant values during evaporation at the highest temperatures. This can be attributed to mixing of different radiogenic Pb components from either crystalline zircon phases of different ages or from domains of isotopically disturbed metamict zircon. Present results confirm > 4 Ga zircon ages in the metaconglomerate from the Hack Hills and substantiate formation of crust at a very early stage in the evolution of the earth. Results also confirm a major crust-forming event 3.55-3.3 Ga ago. (orig.)

THE INFLUENCE OF GRINDING CONDITIONS ON THE DISTRIBUTION OF RESIDUAL STRESS IN THE SURFACE LAYER OF 17crni6-6 STEEL AFTER CARBURIZING

Directory of Open Access Journals (Sweden)

Jacek Sawicki

2017-06-01

Full Text Available This paper presents the results of a study aimed at determining the residual stress which results from developing the surface layer by low-pressure and conventional carburizing and grinding of 17CrNi6-6 steel. A synergistic effect of thermochemical and abrasive treatment was examined on ring samples used to study residual stress by Davidenkov’s method. Samples were subjected to vacuum carburizing and conventional carburizing, which was followed by grinding with a 38A60K8V aloxite grinding wheel and a CBN grinding wheel - RNB80/63B75V. The following cutting fluids were used during the grinding process: oil emulsion 5%, supply rate ca. 20 l/min, Micro5000 oil supplied at the minimum quantity lubrication (MQL of ca. 25 ml/h, dry machining. The study determined the effect of the type of grinding wheel and the cooling and lubricating agent on the distribution of residual stress in the sur-face layer. The best effects of grinding with respect to the residual stress were achieved with flood cooling with oil emulsion and grinding with a CBN grinding wheel.

Zircon-rutile-ilmenite froth flotation process

International Nuclear Information System (INIS)

Schmidt, R.; Denham, D.L. Jr.

1992-01-01

This patent describes a method for separating a mixture of minerals comprising at least zircon, ilmenite and rutile. It comprises adding an acid solution to the mixture to acidify to a pH of between about 2.0 and 6.0; adding starch to the mixture to depress the ilmenite and the rutile; adding a source of fluoride ions to the mixture to provide a negative surface charge on the zircon surface to activate the zircon; adding an amine cationic collector to the mixture to float the activated zircon; subjecting the mixture containing the added acid solution, the fluoride ions, the starch and the cationic collector, to froth flotation; and withdrawing a float product comprising the zircon and a sink product comprising the ilmenite and rutile

Effect of carburizing helium environment on creep behavior of Ni-base heat-resistant alloys for high-temperature gas-cooled reactors

International Nuclear Information System (INIS)

Kurata, Yuji; Ogawa, Yutaka; Nakajima, Hajime

1988-01-01

Creep tests were conducted on Ni-base heat-resistant alloys Hastelloy XR and XR-II, i.e. versions of Hastelloy X modified for nuclear applications, at 950degC using four types of helium environment with different impurity compositions, and mainly the effect of carburization was examined. For all the materials tested, the values of creep rupture time obtained under the carburizing conditions were similar to or longer than those in the commonly used, standard test environment (JAERI Type B helium). The difference among the results was interpreted by the counterbalancing effects of the strengthening due to carburization and possible weakening caused under very low oxidizing potential. In the corrosion monitoring specimens pronounced carbon pick-up was observed in the environment with high carbon activity and very low oxidizing potential. Based on the results obtained in the present and the previous works, it is suggested that a moderate control of the impurity chemistry is important rather than simple purification of the coolant in protecting the material from the environment-enhanced degradation. Either condition with high or low extremes in the oxidizing and carburizing potentials may cause enhanced degradation and thus are desirable to be avoided at the elevated temperatures. (author)

Laser-Assisted Atom Probe Tomography of Deformed Minerals: A Zircon Case Study.

Science.gov (United States)

La Fontaine, Alexandre; Piazolo, Sandra; Trimby, Patrick; Yang, Limei; Cairney, Julie M

2017-04-01

The application of atom probe tomography to the study of minerals is a rapidly growing area. Picosecond-pulsed, ultraviolet laser (UV-355 nm) assisted atom probe tomography has been used to analyze trace element mobility within dislocations and low-angle boundaries in plastically deformed specimens of the nonconductive mineral zircon (ZrSiO4), a key material to date the earth's geological events. Here we discuss important experimental aspects inherent in the atom probe tomography investigation of this important mineral, providing insights into the challenges in atom probe tomography characterization of minerals as a whole. We studied the influence of atom probe tomography analysis parameters on features of the mass spectra, such as the thermal tail, as well as the overall data quality. Three zircon samples with different uranium and lead content were analyzed, and particular attention was paid to ion identification in the mass spectra and detection limits of the key trace elements, lead and uranium. We also discuss the correlative use of electron backscattered diffraction in a scanning electron microscope to map the deformation in the zircon grains, and the combined use of transmission Kikuchi diffraction and focused ion beam sample preparation to assist preparation of the final atom probe tip.

Effects of niobium additions on the structure, depth, and austenite grain size of the case of carburized 0.07% C steels

Science.gov (United States)

Islam, M. A.; Bepari, M. M. A.

1996-10-01

Carbon (0.07%) steel samples containing about 0.04% Nb singly and in combination with nitrogen were carburized in a natural Titas gas atmosphere at a temperature of 1223 K (950 °C) and a pressure of about 0.10 MPa for 1/2 to 4 h, followed by slow cooling in the furnace. Their microstructures were studied by optical microscopy. The austenite grain size of the case and the case depths were determined on baseline samples of low-carbon steels and also on niobium and (Nb + N) microalloyed steel samples. It was found that, when compared to the baseline steel, niobium alone or in combination with nitrogen decreased the thickness of cementite network near the surface of the carburized case of the steels. However, niobium in combination with nitrogen was more effective than niobium in reducing the thickness of cementite network. Niobium with or without nitrogen inhibited the formation of Widmanstätten cementite plates at grain boundaries and within the grains near the surface in the hypereutectoid zone of the case. It was also revealed that, when compared to the baseline steel, niobium decreased the case depth of the carburized steels, but that niobium with nitrogen is more effective than niobium alone in reducing the case depth. Niobium as niobium carbide (NbC) and niobium in the presence of nitrogen as niobium carbonitride, [Nb(C,N)] particles refined the austenite grain size of the carburized case, but Nb(C,N) was more effective than NbC in inhibiting austenite grain growth.

ALKALI FUSION OF ROSETTA ZIRCON

International Nuclear Information System (INIS)

DAHER, A.

2008-01-01

The decomposition of Rosetta zircon by fusion with different types of alkalis has been investigated. These alkalis include sodium hydroxide, potassium hydroxide and eutectic mixture of both. The influences of the reaction temperature, zircon to alkalis ratio, fusion time and the stirring of the reactant on the fusion reaction have been evaluated. The obtained results favour the decomposition of zircon with the eutectic alkalis mixture by a decomposition efficiency of 96% obtained at 500 0 C after one hour

A study of a production process for hafnium-free zirconium from zircon

International Nuclear Information System (INIS)

Ratanalert, N.

1985-01-01

The purpose of this experiment was to extract and purify the zirconium from zircon. The effects of time of extraction and stripping of zirconium, concentration of feed solution, concentration of hydrochloric acid in stripping process, equilibrium curve of extraction of zirconium and hafnium and equilibrium curve of stripping zirconium or scrubbing hafnium were studied from standard zirconium and hafnium. The results, subsequently were applied to the extraction procedures for zirconium from zircon. Minus 100 mesh zircon was fused with sodium hydroxide in the ratio of 1 : 6 at 700 degree C for l hour. After fusion the zirconate was leached with water and dissolved in hot concentrated hydrochloric acid. Zirconyl chloride octahydrate crystallized out when the solution was cooled. An agueons solution of zirconyl chloride was used as the feed to the hexone - thiocyanate solvent extraction process. This was prepared by dissolving zirconyl chloride octahydrate crystal in waster. This zirconium feed solution in 1 M HCl and 1 M N H 4 CNS was extracted with 2.7 m N H 4 CNS in hexone and then stripped with 3.6 M HCl the aqueous phase was got rid of thiocyanate ion by extracting with pure hexone, then the zirconium in aqueous phase was precipitated with sulfuric acid and ammonium hydroxide at pH 1.8 - 2.0 and zirconium oxide was obtained by ignition at 700 degree C. The process could be modified to improve the purity of zirconium by using cation exchange resin to get rid of thiocyanate ion after solvent extraction process

Influence of some additions on zircon synthesis and its properties

International Nuclear Information System (INIS)

Goryacheva, Z.E.; Poplevina, O.G.; Suvorov, S.A.; Toropov, A.N.

1978-01-01

Kinetics of zircon synthesis from pure ZrO 2 and SiO 2 is studied in the presence of additions of magnesium, calcium and rare earth oxides. The addition introduction accelerates zircon formation, its yield reaching 97% at 1600 deg C. Constants of zircon formation reaction rate are determined in the presence of additions of various oxides. It is shown that synthetic zircon surpasses the natural one in tensile and density properties at similar thermostability. It is stable to the effect of molten alkaline borosilicate glass and does not polute it

Boronization and Carburization of Superplastic Stainless Steel and Titanium-Based Alloys

Directory of Open Access Journals (Sweden)

Masafumi Matsushita

2011-07-01

Full Text Available Bronization and carburization of fine-grain superplastic stainless steel is reviewed, and new experimental results for fine grain Ti88.5Al4.5V3Fe2Mo2 are reported. In superplastic duplex stainless steel, the diffusion of carbon and boron is faster than in non-superplastic duplex stainless steel. Further, diffusion is activated by uniaxial compressive stress. Moreover, non-superplastic duplex stainless steel shows typical grain boundary diffusion; however, inner grain diffusion is confirmed in superplastic stainless steel. The presence of Fe and Cr carbides or borides is confirmed by X-ray diffraction, which indicates that the diffused carbon and boron react with the Fe and Cr in superplastic stainless steel. The Vickers hardness of the carburized and boronized layers is similar to that achieved with other surface treatments such as electro-deposition. Diffusion of boron into the superplastic Ti88.5Al4.5V3Fe2Mo2 alloy was investigated. The hardness of the surface exposed to boron powder can be increased by annealing above the superplastic temperature. However, the Vickers hardness is lower than that of Ti boride.

Study of nanoconfigurations in Zircon-Mullite composites using perturbed angular correlations

Energy Technology Data Exchange (ETDEWEB)

Chain, Cecilia Y., E-mail: yamil@fisica.unlp.edu.ar; Pasquevich, Alberto F. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina); Rivas, Patricia C. [CONICET (Argentina); Martinez, Jorge A.; Caracoche, Maria C. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina); Rendtorff, Nicolas M. [CONICET (Argentina); Conconi, Maria S. [Centro de Tecnologia de Recursos Minerales y Ceramica (CETMIC: CONICET-CIC) (Argentina); Aglietti, Esteban F. [CONICET (Argentina)

2010-06-15

It has been already published that, at nanoscopic level, zircon exhibits wide regions of aperiodic material not detected by the ordinary techniques used to analyse the obtained product in the production of ceramic materials. In this paper it is reported how the Perturbed Angular Correlations (PAC) technique has assisted the interpretation of a mismatch between experiment and theoretical estimation of a mechanical property in some zircon-mullite composites. In fact, it has been proved that the difference observed between the calculated and the experimental value of the elastic modulus in composites of the form (1-x) ZrSiO{sub 4} - x 3Al{sub 2}O{sub 3}.2SiO{sub 2} (with x = 15, 25, 35 and 45 wt.%) behaves very similarly as the relative amount of aperiodic zircon determined by PAC. This result allows to re-interpret the mullite role during the materials preparation.

Sulfur in zircons: A new window into melt chemistry

Science.gov (United States)

Tang, H.; Bell, E. A.; Boehnke, P.; Barboni, M.; Harrison, T. M.

2017-12-01

The abundance and isotopic composition of sulfur are important tools for exploring the photochemistry of the atmosphere, the thermal history of mantle and igneous rocks, and ancient metabolic processes on the early Earth. Because the oldest terrestrial samples are zircons, we developed a new in-situ procedure to analyze the sulfur content of zircons using the CAMECA ims 1290 at UCLA. We analyzed zircons from three metaluminous/I-type granites (reduced and oxidized Peninsular range and Elba), which exhibit low sulfur abundance with the average of 0.5ppm, and one peraluminous/S-type zircon (Strathbogie Range), which shows an elevated sulfur level with the average of 1.5ppm. Additionally, we found that sulfur content ranges between 0.4 and 2.3 ppm in young volcanic zircons (St. Lucia). Our analyses of zircons from the Jack Hills, Western Australia, whose ages range between 3.4 and 4.1 Ga, show a variety of sulfur contents. Three out of the ten zircons are consistent with the sulfur contents of S-type zircons; the rest have low sulfur contents, which are similar to those of I-type zircons. The high sulfur content in some of these Jack Hills zircons can be interpreted as indicating their origin in either a S-type granite or a volcanic reservoir. We favor the former interpretation since the Ti-in-zircon temperatures of our Jack Hills zircons is lower than those of volcanic zircons. Future work will be undertaken to develop a systematic understanding of the relationship between melt volatile content, melt chemistry, and zircon sulfur content.

Applied and theoretical study of textural and structural evolution of pure and doped zircon powders

International Nuclear Information System (INIS)

Methivier, A.

1992-02-01

Using different preparation methods, undoped zircon constituted of quadratic and monoclinic phases, and quadratic phase zircon doped with lanthanum, magnesium or silicon were obtained and characterized. An applied kinetic study of the influence of the gaseous phase, and of the doping on pre-sintering shows an accelerating effect of water vapour, an important stabilization effect of lanthanum or silicon additions and a little effect of magnesium additions. This kinetic study leads to a model giving two parallel types of matter transport: one using water vapour catalytic effect, and the other oxygen diffusion

Carbon Dioxide Adsorption by Calcium Zirconate at Higher Temperature

Directory of Open Access Journals (Sweden)

K. B. Kale

2012-12-01

Full Text Available The CO2 adsorption by calcium zirconate was explored at pre- and post- combustion temperature condition. The several samples of the calcium zirconate were prepared by different methods such as sol-gel, solid-solid fusion, template and micro-emulsion. The samples of the calcium zirconate were characterized by measurement of surface area, alkalinity/acidity, and recording the XRD patterns and SEM images. The CO2 adsorptions by samples of the calcium zirconate were studied in the temperature range 100 to 850 oC and the CO2 adsorptions were observed in the ranges of 6.88 to 40.6 wt % at 600 0C and 8 to 16.82 wt% at in between the temperatures 200 to 300 oC. The effect of Ca/Zr mol ratio in the samples of the calcium zirconate on the CO2 adsorption and alkalinity were discussed. The adsorbed moisture by the samples of the calcium zirconate was found to be useful for the CO2 adsorption. The promoted the samples of the calcium zirconate by K+, Na+, Rb+, Cs+, Ag+ and La3+ showed the increased CO2 adsorption. The exposure time of CO2 on the samples of the calcium zirconate showed the increased CO2 adsorption. The samples of the calcium zirconate were found to be regenerable and reusable several times for the adsorption of CO2 for at the post- and pre-combustion temperature condition. Copyright © 2012 by BCREC Undip. All rights reservedReceived: 23rd June 2012, Revised: 28th August 2012, Accepted: 30th August 2012[How to Cite: K. B. Kale, R. Y. Raskar, V. H. Rane and A. G.  Gaikwad (2012. Carbon Dioxide Adsorption by Calcium Zirconate at Higher Temperature. Bulletin of Chemical Reaction Engineering & Catalysis, 7 (2: 124-136. doi:10.9767/bcrec.7.2.3686.124-136] [How to Link / DOI: http://dx.doi.org/10.9767/bcrec.7.2.3686.124-136 ] | View in 

Auto-regenerative thermoluminescence dating using zircon inclusions

International Nuclear Information System (INIS)

Templer, R.H.

1993-01-01

Fired ceramics containing zircon inclusions have been dated by allowing the zircons to regenerate their own thermoluminescence (TL) signal, hence auto-regenerative TL dating. The technique is conceptually straightforward. One first measures the TL accrued since the last heating of the material. The zircon grains are then stored for six months and the TL signal regenerated through self-irradiation is measured. Since the internal dose-rate for zircon is dominated by the internal component the age of the sample is simply given by the ratio of the natural to auto-regenerated signal times the laboratory storage period. The technique, however, requires the measurement of a very small auto-regenerated signal, which introduces a number of experimental and physical complications. The methods for overcoming these problems and successfully dating zircons by auto-regeneration are described. (Author)

The carbide M{sub 7}C{sub 3} in low-temperature-carburized austenitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Ernst, Frank, E-mail: frank.ernst@cwru.edu [Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106-7204 (United States); Li, Dingqiang; Kahn, Harold; Michal, Gary M.; Heuer, Arthur H. [Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106-7204 (United States)

2011-04-15

Prolonged low-temperature gas-phase carburization of AISI 316L-type austenitic stainless steel can cause intragranular precipitation of the carbide M{sub 7}C{sub 3} (M: randomly dispersed Fe, Cr, Ni). Transmission electron microscopy revealed that the carbide particles have the shape of needles. They grow by a ledge-migration mechanism and in a crystallographic orientation relationship to the austenite matrix that enables highly coherent interphase interfaces. A small solubility limit of Ni in the carbide and restricted Ni diffusivity at the processing temperature leads to Ni pileup around the particles and may explain the extreme aspect ratio of the particle shape. These characteristics closely resemble what has been observed earlier for precipitates of M{sub 5}C{sub 2} under slightly different processing conditions and can be rationalized by considering the particular constraints imposed by carburization at low temperature.

The Effects of CO{sub 2} Pressure on Corrosion and Carburization Behaviors of Chromia-forming Austenitic Alloys

Energy Technology Data Exchange (ETDEWEB)

Lee, Ho Jung; Kim, Sung Hwan; Jang, Changheui [KAIST, Daejeon (Korea, Republic of)

2015-05-15

By applying S-CO{sub 2} cycle to SFR, the inherent safety could be improved by alleviating the concern of explosive reaction between high temperature steam and liquid sodium as well as increased thermal efficiency at 500-550 .deg. C compared to helium Brayton cycle. Meanwhile, from the material point of view, a compatibility such as corrosion and carburization of candidate materials in S-CO{sub 2} environment should be evaluated to assure the long-term integrity of IHX. It has been previously reported that Ni-base alloys and high-Cr Fe-base austenitic alloys showed a good corrosion resistance by the formation of thin chromia layer while carburization behaviors of those materials were not properly investigated. Corrosion and carburization behaviors of three chromia-forming austenitic alloys (Ni-base alloys and Alloy 800HT) were evaluated in S-CO{sub 2} (200 bar) and CO{sub 2} (1 bar) environment at 550.650 .deg. C for 1000 h. For all test materials, a good corrosion resistance was exhibited by the formation of thin chromia (Cr{sub 2}O{sub 3}) with small amount of minor oxides such as Mn1.5Cr1.5O{sub 4}, Al{sub 2}O{sub 3}, and TiO{sub 2}.

Studies on upgrading quality of zircon concentrate by flotation method

International Nuclear Information System (INIS)

Nguyen Duy Phap; Nguyen Duc Hung; Nguyen Duc Thai and others

2004-01-01

Results of this study show that it is possible to apply flotation to upgrading quality of zircon concentrate based on a simple technological flow-sheet and simple flotation agents. It is possible to use flotation equipment of Mexanov. Product criteria include ZrO 2 >64%; TiO 2 2 O 3 <0.1%. Flotation agents are simple, little noxious and easy for preparation. (PQM)

Zircon-scale insights into the history of a Supervolcano, Bishop Tuff, Long Valley, California, with implications for the Ti-in-zircon geothermometer

Science.gov (United States)

Reid, M.R.; Vazquez, J.A.; Schmitt, A.K.

2011-01-01

Zircon has the outstanding capacity to record chronological, thermal, and chemical information, including the storage history of zoned silicic magma reservoirs like the one responsible for the Bishop Tuff of eastern California, USA. Our novel ion microprobe approach reveals that Bishop zircon rims with diverse chemical characteristics surround intermediate domains with broadly similar compositions. The highest Y, REE, U, and Th concentrations tend to accompany the largest excesses in Y + REE3+:P beyond what can be explained by xenotime substitution in zircon. Apparent Ti-in-zircon temperatures of Ti-in-zircon temperatures are probably better explained by sources of inaccuracy in the temperature estimates. After apparently nucleating from different melts, zircons from across the Bishop Tuff compositional spectrum may have evolved to broadly similar chemical and thermal conditions and therefore it is possible that there was no significant thermal gradient in the magma reservoir at some stage in its evolution. There is also no compelling evidence for punctuated heat ?? chemical influxes during the intermediate stages of zircon growth. Judging by the zircon record, the main volume of the erupted magma evolved normally by secular cooling but the latest erupted portion is characterized by a reversal in chemistry that appears to indicate perfusion of the magma reservoir by-or zircon entrainment in-a less evolved melt from the one in which the zircons had previously resided. ?? 2010 Springer-Verlag.

Isotope, scanning electron microscope, and energy dispersive spectrometer studies of heterogeneous zircons from radioactive granites in the Grenville structural province, Quebec and Ontario

International Nuclear Information System (INIS)

Rimsaite, J.

1981-01-01

Heterogeneous zircons yielded discordant Pb-U, Pb-Th, and 207 Pb- 206 Pb isotopic ages. Most data points fall below the concordia curve, implying losses of daughter elements, bqt they define a discordia line that intersects the concordia at approximately 90 Ma and 1020 Ma. To obtain evidence for mobilization of U and radiogenic Pb, zircon grains were studied using a scanning electron microscope coupled with an energy dispersive spectrometer. High magnification backscattered and secondary electron images of the zircon revealed narrow fractures, zoning and diverse mineral inclusions. Three groups of mineral inclusions observed were: 1) those predating zoned zircon and apparently serving as a nucleus; 2) uraninite, feldspar, and apatite associated with the growth and zoning of the host zircon; and 3) fracture-fillings that postdate crystallization of the host zircon. The U- and Pb-rich inclusions incorporated into the zircon grains during and after its crystallization markedly affect isotopic ages of the host zircon. Migration of Pb and U have occurred along fractures in zircon. Zircon, uraninite, and other associated minerals have decomposed and complex reactions have taken place between the liberated Zr, U, Th and other elements to produce overgrowths on mineral grains and unidentified Zr-bearing material in fractures

Spectroscopic determination of optimal hydration time of zircon surface

Energy Technology Data Exchange (ETDEWEB)

Ordonez R, E. [ININ, Departamento de Quimica, Carretera Mexico-Toluca s/n, 52750 Ocoyoacac, Estado de Mexico (Mexico); Garcia R, G. [Instituto Tecnologico de Toluca, Division de Estudios del Posgrado, Av. Tecnologico s/n, Ex-Rancho La Virgen, 52140 Metepec, Estado de Mexico (Mexico); Garcia G, N., E-mail: eduardo.ordonez@inin.gob.m [Universidad Autonoma del Estado de Mexico, Facultad de Quimica, Av. Colon y Av. Tollocan, 50180 Toluca, Estado de Mexico (Mexico)

2010-07-01

When a mineral surface is immersed in an aqueous solution, it develops and electric charge produced by the amphoteric dissociation of hydroxyl groups created by the hydration of the solid surface. This is one influential surface property. The complete hydration process takes a time which is specific for each mineral species. The knowledge of the aqueous solution contact time for complete surface hydration is mandatory for further surface phenomena studies. This study deals with the optimal hydration time of the raw zircon (ZrSiO{sub 4}) surface comparing the classical potentiometric titrations with a fluorescence spectroscopy technique. The latter is easy and rea liable as it demands only one sample batch to determine the optimal time to ensure a total hydration of the zircon surface. The analytical results of neutron activation analysis showed the presence of trace quantities of Dy{sup 3+}, Eu{sup 3+} and Er{sup 3} in the bulk of zircon. The Dy{sup 3+} is structured in the zircon crystalline lattice and undergoes the same chemical reactions as zircon. Furthermore, the Dy{sup 3+} has a good fluorescent response whose intensity is enhanced by hydration molecules. The results show that, according to the potentiometric analysis, the hydration process for each batch (at least 8 sample batches) takes around 2 h, while the spectrometric method indicates only 5 minutes from only one batch. Both methods showed that the zircon surface have a 16 h optimal hydration time. (Author)

Spectroscopic determination of optimal hydration time of zircon surface

International Nuclear Information System (INIS)

Ordonez R, E.; Garcia R, G.; Garcia G, N.

2010-01-01

When a mineral surface is immersed in an aqueous solution, it develops and electric charge produced by the amphoteric dissociation of hydroxyl groups created by the hydration of the solid surface. This is one influential surface property. The complete hydration process takes a time which is specific for each mineral species. The knowledge of the aqueous solution contact time for complete surface hydration is mandatory for further surface phenomena studies. This study deals with the optimal hydration time of the raw zircon (ZrSiO 4 ) surface comparing the classical potentiometric titrations with a fluorescence spectroscopy technique. The latter is easy and rea liable as it demands only one sample batch to determine the optimal time to ensure a total hydration of the zircon surface. The analytical results of neutron activation analysis showed the presence of trace quantities of Dy 3+ , Eu 3+ and Er 3 in the bulk of zircon. The Dy 3+ is structured in the zircon crystalline lattice and undergoes the same chemical reactions as zircon. Furthermore, the Dy 3+ has a good fluorescent response whose intensity is enhanced by hydration molecules. The results show that, according to the potentiometric analysis, the hydration process for each batch (at least 8 sample batches) takes around 2 h, while the spectrometric method indicates only 5 minutes from only one batch. Both methods showed that the zircon surface have a 16 h optimal hydration time. (Author)

A preliminary geochemical study of zircons and monazites from ...

Indian Academy of Sciences (India)

R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

equation of Watson and Harrison (1983) predicts that zircon with Zr-contents ... tion equation of Montel (1993) predicts that the .... and geochemistry of the basalts of Gujarat state (western ... solution kinetics: implications for the thorium and light.

The Effect of Element Substitution on Ti-in-Zircon Geothermometry in Volcanic Zircons from Mount Pinatubo, Philippines

Science.gov (United States)

Lee, S. L.; Hattori, K.

2017-12-01

Despite the extensive application of the Ti-in-zircon geothermometer, its accuracy in natural systems remains uncertain. In order to investigate the parameters contributing to Ti in zircon, we examined zircons from dacitic eruption products of Mount Pinatubo, Philippines, from the Pliocene (>2.5-2.7 Ma), 35000BP and 1991AD. All samples are unaltered and quenched from magmas at 790-825°C (Fe-Ti-oxide thermometry). Furthermore, the magma conditions of 1991 samples are well characterized: 780°C (cummingtonite rims on hornblende, Fe-Ti-oxide thermometry), 2 kbar pressure, 5.5-6.5 wt.% H2O and fO2 of NNO+1.6. Calculated zircon saturation temperatures are 760, 744 and 738°C (oldest to youngest). Zircon Ti concentrations are low (2.0-8.8 ppm), show positive covariation with U (35.6-639 ppm), Th (18.7-696 ppm), ∑REE (237-1310 ppm) and Y (247-1770 ppm), and negative covariation with Hf (7610-12000 ppm). The Ti-in-zircon geothermometer by Ferry and Watson (2007) yields mean temperatures of 690, 666 and 663°C (oldest to youngest), using TiO2 activity=0.6, SiO2 activity=1 and -40°C pressure correction. Therefore, temperatures calculated using this method are underestimated by >100°C. We suggest that elements in the Zr site impact the substitution of Ti in the Si site of zircon. Ti shows a positive covariation with Zr/Hf (37.0-57.3, r2=0.551). The ionic radius of Hf4+ is smaller than Zr4+, whereas cations like U4+, Th4+, REE3+ and Y3+ are larger. The departure from the ideal crystal configuration is evaluated using the parameter Zr/(Hf-x), whereby x=U4+, Th4+, ∑REE and Y3+. Ti contents are more strongly correlated with the parameter than Zr/Hf (r2=0.559, 0.565, 0.608, 0.616; respectively). This suggests that large cations replacing Zr strain the lattice, reducing the amount of Ti incorporated into zircon. This further suggests that ZrSiO4 activity is less than 1 in natural rocks, resulting in the systematic underestimation of Ti-in-zircon temperatures.

Transformations to granular zircon revealed: Twinning, reidite, and ZrO2 in shocked zircon from Meteor Crater (Arizona, USA)

Science.gov (United States)

Cavosie, Aaron; Timms, Nicholas E.; Erickson, Timmons M.; Hagerty, Justin J.; Hörz, Friedrich

2016-01-01

Granular zircon in impact environments has long been recognized but remains poorly understood due to lack of experimental data to identify mechanisms involved in its genesis. Meteor Crater in Arizona (United States) contains abundant evidence of shock metamorphism, including shocked quartz, the high pressure polymorphs coesite and stishovite, diaplectic SiO2 glass, and lechatelierite (fused SiO2). Here we report the presence of granular zircon, a new shocked mineral discovery at Meteor Crater, that preserve critical orientation evidence of specific transformations that occurred during its formation at extreme impact conditions. The zircon grains occur as aggregates of sub-µm neoblasts in highly shocked Coconino Formation Sandstone (CFS) comprised of lechatelierite. Electron backscatter diffraction shows that each grain consists of multiple domains, some with boundaries disoriented by 65°, a known {112} shock-twin orientation. Other domains have crystallographic c-axes in alignment with {110} of neighboring domains, consistent with the former presence of the high pressure ZrSiO4 polymorph reidite. Additionally, nearly all zircon preserve ZrO2 + SiO2, providing evidence of partial dissociation. The genesis of CFS granular zircon started with detrital zircon that experienced shock-twinning and reidite formation from 20 to 30 GPa, ultimately yielding a phase that retained crystallographic memory; this phase subsequently recrystallized to systematically oriented zircon neoblasts, and in some areas partially dissociated to ZrO2. The lechatelierite matrix, experimentally constrained to form at >2000 °C, provided an ultra high-temperature environment for zircon dissociation (~1670 °C) and neoblast formation. The capacity of granular zircon to preserve a cumulative P-T record has not been recognized previously, and provides a new method for retrieving histories of impact-related mineral transformations in the crust at conditions far beyond which most rocks melt.

Zircon U-Pb ages of Guyana greenstone-gneiss terrane

Energy Technology Data Exchange (ETDEWEB)

Gibbs, A.K. (Cornell Univ., Ithaca, NY (USA)); Olszewski, W.J. Jr. (New Hampshire Univ., Durham (USA))

1982-04-01

Isotopic U-Pb studies of zircons collected from weathered metagreywackes of the Barama-Mazaruni Supergroup of northern Guyana, South America, demonstrate an age of origin of ca. 2250 Ma. This is the best estimate for the age of the associated metavolcanic rocks. Zircons from weathered gneiss of the Bartica complex, adjacent to the volcanic-sedimentary belts, yield a similar age. The contiguous greenstone-gneiss terrane of eastern Venezuela is also of similar age and comparable greenstone-gneiss terranes of eastern Suriname and French Guiana are probably also of this age. Continental crust formation of a style closely comparable to that of the Canadian Archean occurred on a very widespread scale in the Lower Proterozoic of the Guiana shield. The lead losses from the weathered zircons are comparable to those from zircons from fresh rock from the adjacent terrane of Venezuela, and the advantages of field concentration from numerous saprolite exposures warrant use of such material in future geochronological studies of the region.

Natural radioactivity and radon specific exhalation rate of zircon sands

International Nuclear Information System (INIS)

Righi, S.; Verita, S.; Bruzzi, L.; Albertazzi, A.

2006-01-01

The study focuses on the radon emanation from zircon sands and their derivatives, which are widely used in many sectors of industry. In particular, the results obtained by experimental measurements on samples of zircon sands and zircon flours commonly used in Italian ceramic industries are reported. Zircon sands contain a significant concentration of natural radioactivity because Th and U may substitute zirconium in the zircon crystal lattice. The relevant routes of exposure of workers to T.E.N.O.R.M. from zircon materials are external radiation and internal exposure, either by inhalation of aerosols in dusty working conditions or by inhalation of radon in workplaces. The main objective of this investigation is to provide experimental data able to better calculate the internal exposure of workers due to radon inhalation. Zircon samples were surveyed for natural radioactivity, radon specific exhalation rate and emanation fraction. Measurements of radioactivity concentration were carried out using γ-spectrometry. Methods used for determining radon consisted in determining the 222 Rn activity accumulated in a vessel after a given accumulation build-up time. The average activity concentrations of 238 U and 232 Th in samples result about 2600 and 550 Bq kg-1, respectively; these concentrations are significantly higher than the world average noticed in soils, rocks and Earth crust. The 222 Rn specific exhalation rates result very low probably due to the low porosity of the material and the consequent difficulty for radon to be released from the zircon crystal lattice. (author)

(De)coupled zircon metamictization, radiation damage, and He diffusivity

Science.gov (United States)

Ault, A. K.; Guenthner, W.; Reiners, P. W.; Moser, A. C.; Miller, G. H.; Refsnider, K. A.

2017-12-01

We develop and apply a new protocol for targeting crystals for the zircon (U-Th)/He (He) thermochronometry to maximize effective U (eU) and corresponding closure temperature variability to develop zircon He date-eU correlations observed in some datasets. Our approach exploits visual proxies for radiation damage accumulation (metamictization) during zircon selection. We show that by purposefully targeting a spectrum of zircon textures from pristine to metamict grains, it is possible to generate broad eU variation in suites of zircon from a single sample and zircon He date-eU-metamictization trends that can be exploited to resolve increasingly complex thermal histories. We present plane light photographs, eU concentration, and zircon He results from 59 individual zircons from nine crystalline rock samples. Six of the nine samples come from exposed Proterozoic granitoids on SE Baffin Island, Canada; Boulder Creek, CO; Sandia Mountains, NM; and Mecca Hills, CA. We report data from three Archean Baffin samples to compare with the Proterozoic Baffin sample date-eU-metamictization trend. In each Proterozoic sample, target zircons display a spectrum of metamictization from pristine, transparent crystals to purple-brown, translucent grains. Progressive loss of transparency and increase in discoloration consistently corresponds to an increase in eU in all samples. Individual zircon eU varies from 89-1885 ppm and, within each sample, the total eU spread is 538 ppm to 1374 ppm. For any given eU value, the Archean zircon appear comparatively more metamict than the Proterozoic Baffin grains and samples collectively define a 1681 ppm range in eU, with more restrictive intrasample eU spreads (199-1120 ppm). Proterozoic samples from Baffin, Sandia, and Front Range yield negative zircon He date-eU correlations with intrasample date ranges of 90-783 Ma. Increasing eU and younger dates correspond with increasing metamictization. In contrast, all three Proterozoic Mecca Hills samples

Role of zircon in tracing crustal growth and recycling

Science.gov (United States)

Compston, W.; Williams, I. S.; Armstrong, R. A.; Claoue-Long, J. C.; Kinny, P. D.; Foster, J. J.; Kroener, A.; Pidgeon, R. T.; Myers, J. S.

Single crystal ion probe ages of zircons is discussed, which allow much better time resolution compared to other geochronological methods, although the technique is not without problems. Rocks from two areas that contain composite zircon populations, including true magmatic zircons as well as a variety of xenocrystic types are described. It is often difficult to distinguish these; xenocrystic zircons, for example, cannot always be identified on the basis of morphology alone. Additional evidence is needed before making age interpretations. Evidence is also presented of zircon growth long after the original time of crystallization, in some cases apparently at temperatures less than 300 C. The spectacular discovery of 4.1 to 4.2 Ga detrital zircons in metaquartzites from the Mount Narryer area of Western Australia is described. Similar zircons with ages as old as 4276 Ma have been found in the nearby Jack Hills area. The source areas or parent lithologies of these zircons have not yet been determined, but the author expects that they may be unrecognized or buried antecedents of the K rich Narryer gneisses. U or Th concentrations of zircon cannot be used to discriminate between felsic and mafic source rocks.

Thermoluminescence of zircon: a kinetic model

CERN Document Server

Turkin, A A; Vainshtein, D I; Hartog, H W D

2003-01-01

The mineral zircon, ZrSiO sub 4 , belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such a model. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time anneali...

Beneficiation of low grade zircon concentrate

International Nuclear Information System (INIS)

Rehim, A.A.

1976-01-01

The zircon concentrate obtained from black sands, contains considerable amount of rutile and some ilmenite. It is necessary to separate these minerals before the metallurgical processing of zircon, as otherwise the zirconium products obtained will be contaminated with large amount of titanium. The present work explores the possibility of purification of zircon from rutile and other minerals by flotation. Effective separation can be obtained by selective flotation using oleic acid and liquid glass in alkaline medium or sodium silicon fluoride in weak acidic medium. (author)

Characterization of inclusions in terrestrial impact formed zircon: Constraining the formation conditions of Hadean zircon from Jack Hills, Western Australia

Science.gov (United States)

Faltys, J. P.; Wielicki, M. M.; Sizemore, T. M.

2017-12-01

Due to the discovery and subsequent geochemical analysis of Hadean terrestrial material (e.g. detrital zircon from Jack Hills, Western Australia), a dramatic paradigm shift has occurred in the hypothesized near surface conditions of the first 500 million years of Earth's evolution. From a hellish setting riddled with impactors and not fit for life to a much milder environment that may have been uniquely suitable for the origin of life. Geochemical analyses of these ancient materials have been used to suggest the presence of water at or near the surface as well as the existence of continental crust during the Hadean, both of which have been suggested as necessary for the origin of life. However, the intensity of extraterrestrial bombardment during the Hadean and the effects of such events on the origin of life remains poorly understood. Clearly, as evidenced by Phanerozoic impact events, extraterrestrial impactors have the potential to dramatically effect the environment, particularly the biosphere. Early Earth likely experienced multiple large impact events, as evidenced by the lunar record, however whether those impacts were sufficient to frustrate the origin of life remains an open question. Although multiple lines of evidence, including the inclusion population, suggest the formation of Hadean zircon from Jack Hills as crystallizing in an under-thrust environment from S-type magmas, a recent study has suggested their formation in an impact melt environment analogous to a portion of the Sudbury Igneous Complex at the Sudbury impact structure. To determine between these two formation scenarios we have under-taken an inclusion study of terrestrial impact formed zircon from four of the largest terrestrial impact structures (Sudbury, Canada; Manicouagan, Canada; Vredefort, South Africa; Morokweng, South Africa), to compare to the vast inclusion dataset that exists for Jack Hills zircon. Preliminary data suggests a different inclusion population, from Hadean zircon

Lithofacies control in detrital zircon provenance studies: Insights from the Cretaceous Methow basin, southern Canadian Cordillera

Science.gov (United States)

DeGraaff-Surpless, K.; Mahoney, J.B.; Wooden, J.L.; McWilliams, M.O.

2003-01-01

High-frequency sampling for detrital zircon analysis can provide a detailed record of fine-scale basin evolution by revealing the temporal and spatial variability of detrital zircon ages within clastic sedimentary successions. This investigation employed detailed sampling of two sedimentary successions in the Methow/Methow-Tyaughton basin of the southern Canadian Cordillera to characterize the heterogeneity of detrital zircon signatures within single lithofacies and assess the applicability of detrital zircon analysis in distinguishing fine-scale provenance changes not apparent in lithologic analysis of the strata. The Methow/Methow-Tyaughton basin contains two distinct stratigraphic sequences of middle Albian to Santonian clastic sedimentary rocks: submarine-fan deposits of the Harts Pass Formation/Jackass Mountain Group and fluvial deposits of the Winthrop Formation. Although both stratigraphic sequences displayed consistent ranges in detrital zircon ages on a broad scale, detailed sampling within each succession revealed heterogeneity in the detrital zircon age distributions that was systematic and predictable in the turbidite succession but unpredictable in the fluvial succession. These results suggest that a high-density sampling approach permits interpretation of finescale changes within a lithologically uniform turbiditic sedimentary succession, but heterogeneity within fluvial systems may be too large and unpredictable to permit accurate fine-scale characterization of the evolution of source regions. The robust composite detrital zircon age signature developed for these two successions permits comparison of the Methow/Methow-Tyaughton basin age signature with known plutonic source-rock ages from major plutonic belts throughout the Cretaceous North American margin. The Methow/Methow-Tyaughton basin detrital zircon age signature matches best with source regions in the southern Canadian Cordillera, requiring that the basin developed in close proximity to the

Carburization of austenitic and ferritic alloys in hydrocarbon environments at high temperature

Directory of Open Access Journals (Sweden)

Serna, A.

2003-12-01

Full Text Available The technical and industrial aspects of high temperature corrosion of materials exposed to a variety of aggressive environments have significant importance. These environments include combustion product gases and hydrocarbon gases with low oxygen potentials and high carbon potentials. In the refinery and petrochemical industries, austenitic and ferritic alloys are usually used for tubes in fired furnaces. The temperature range for exposure of austenitic alloys is 800-1100 °C, and for ferritic alloys 500-700 °C, with carbon activities a_c > 1 in many cases. In both applications, the carburization process involves carbon (coke deposition on the inner diameter, carbon absorption at the metal surface, diffusion of carbon inside the alloy, and precipitation and transformation of carbides to a depth increasing with service. The overall kinetics of the internal carburization are approximately parabolic, controlled by carbon diffusion and carbide precipitation. Ferritic alloys exhibit gross but uniform carburization while non-uniform intragranular and grain-boundary carburization is observed in austenitic alloys.

La corrosión a alta temperatura, tal como la carburación de materiales expuestos a una amplia variedad de ambientes agresivos, tiene especial importancia desde el punto de vista técnico e industrial. Estos ambientes incluyen productos de combustión, gases e hidrocarburos con bajo potencial de oxígeno y alto potencial de carbono. En las industrias de refinación y petroquímica, las aleaciones austeníticas y ferríticas se utilizan en tuberías de hornos. El rango de temperatura de exposición para aleaciones austeníticas está entre 800-1.100°C y para aleaciones ferríticas está entre 500-700°C, con actividades de carbono a_c>1 en algunos casos. En tuberías con ambas aleaciones, el proceso de carburación incluye deposición de carbón (coque en el diámetro interno, absorción de carbono en la superficie

Zircon/fluid trace element partition coefficients measured by recrystallization of Mud Tank zircon at 1.5 GPa and 800-1000 °C

Science.gov (United States)

Ayers, John C.; Peters, Timothy J.

2018-02-01

Hydrothermal zircon grains have trace element characteristics such as low Th/U, high U, and high rare earth element (REE) concentrations that distinguish them from magmatic, metamorphic, and altered zircon grains, but it is unclear whether these characteristics result from distinctive fluid compositions or zircon/fluid fractionation effects. New experiments aimed at measuring zircon/fluid trace element partition coefficients Dz/f involved recrystallizing natural Mud Tank zircon with low trace element concentrations in the presence of H2O, 1 m NaOH, or 1 m HCl doped with ∼1000 ppm of rare earth elements (REE), Y, U and Th and ∼500 ppm of Li, B, P, Nb, Ba, Hf, and Ta. Experiments were run for 168 h at 1.5 GPa, 800-1000 °C, and fO2 = NNO in a piston cylinder apparatus using the double capsule method. LA-ICP-MS analysis shows that run product zircon crystals have much higher trace element concentrations than in Mud Tank zircon starting material. Dz/f values were estimated from run product zircon analyses and bulk composition using mass balance. Most elements behave incompatibly, with median Dz/f being highest for Hf = 8 and lowest for B = 0.02. Addition of NaOH or HCl had little influence on Dz/f values. Dz/f for LREE are anomalously high, likely due to contamination of run product zircon with quenched solutes enriched in incompatible elements, so DLREE were estimated using lattice strain theory. Brice curves for +3 ions yield zircon/fluid DLu/DLa of ∼800-5000. A Brice curve fit to +4 ions yielded DCe4+ values. Estimated concentrations of Ce3+ and Ce4+ show that the average Ce4+/Ce3+ in zircon of 27 is much higher than in fluid of 0.02. Th and U show little fractionation, with median DTh/DU = 0.7, indicating that the low Th/U in natural hydrothermal zircon is inherited from the fluid. Natural fluid compositions estimated from measured Dz/f and published compositions of hydrothermal zircon grains from aplite and eclogite reflect the mineralogy of the host rock, e

Structural analysis of radiation damage in zircon and thorite: An X-ray absorption spectroscopic study

International Nuclear Information System (INIS)

Farges, F.; Calas, G.

1991-01-01

Metamictization effects have been investigated in zircon, thorite, uranothorite, and thorogummite using X-ray absorption spectroscopy at Zr-K, Th-L III edges. Extended X-ray absorption fine structure (EXAFS) spectra of metamict samples are characterized by a major contribution due to the O nearest neighbors with some contributions from next-nearest neighbors (Si and Zr in zircon, Si in thorite). In zircon, Zr-O distances decrease by ∼0.1 angstrom while the coordination number of Zr decreases from 8 to 7. In contrast, the eightfold coordination of Th in crystalline thorite is preserved in metamict thorite, Si second neighbors around Zr or Th are generally observed in metamict samples with distances close to those measured in crystalline phases. No other contribution to EXAFS is observed in thorite, but Zr-Zr distances are observed in zircon. They decrease by ca. 0.3 Angstrom as a function of zircon metamictization. Metamictization processes are characterized by a loss of medium range order. There is no evidence for decomposition into crystalline oxides. The structural interpretation of EXAFS data must take into account the creation of O vacancies arising from a displacement or tilting of the SiO 4 tetrahedra during metamictization of zircon-like structures. If the cation can take a lower coordination number (as in the case of Zr), a coordination change allows the local structure to be partly maintained during metamictization. If not, as for Th, the local structure is rapidly destroyed

Thermal diffusivity of samarium-gadolinium zirconate solid solutions

International Nuclear Information System (INIS)

Pan, W.; Wan, C.L.; Xu, Q.; Wang, J.D.; Qu, Z.X.

2007-01-01

We synthesized samarium-gadolinium zirconate solid solutions and determined their thermal diffusivities, Young's moduli and thermal expansion coefficients, which are very important for their application in thermal barrier coatings. Samarium-gadolinium zirconate solid solutions have extremely low thermal diffusivity between 20 and 600 deg. C. The solid solutions have lower Young's moduli and higher thermal expansion coefficients than those of pure samarium and gadolinium zirconates. This combination of characteristics is promising for the application of samarium and gadolinium zirconates in gas turbines. The mechanism of phonon scattering by point defects is discussed

Empirical constraints on the effects of radiation damage on helium diffusion in zircon

Science.gov (United States)

Anderson, Alyssa J.; Hodges, Kip V.; van Soest, Matthijs C.

2017-12-01

In this study, we empirically evaluate the impact of radiation damage on zircon (U-Th)/He closure temperatures for a suite of zircon crystals from the slowly cooled McClure Mountain syenite of south-central Colorado, USA. We present new zircon, titanite, and apatite conventional (U-Th)/He dates, zircon laser ablation (U-Th)/He and U-Pb dates, and zircon Raman spectra for crystals from the syenite. Titanite and apatite (U-Th)/He dates range from 447 to 523 Ma and 88.0 to 138.9 Ma, respectively, and display no clear correlation between (U-Th)/He date and effective uranium concentration. Conventional zircon (U-Th)/He dates range from 230.3 to 474 Ma, while laser ablation zircon (U-Th)/He dates show even greater dispersion, ranging from 5.31 to 520 Ma. Dates from both zircon (U-Th)/He datasets decrease with increasing alpha dose, indicating that most of the dispersion can be attributed to radiation damage. Alpha dose values for the dated zircon crystals range from effectively zero to 2.15 × 1019 α /g, spanning the complete damage spectrum. We use an independently constrained thermal model to empirically assign a closure temperature to each dated zircon grain. If we assume that this thermal model is robust, the zircon radiation damage accumulation and annealing model of Guenthner et al. (2013) does not accurately predict closure temperatures for many of the analyzed zircon crystals. Raman maps of the zircons dated by laser ablation document complex radiation damage zoning, sometimes revealing crystalline zones in grains with alpha dose values suggestive of amorphous material. Such zoning likely resulted in heterogeneous intra-crystalline helium diffusion and may help explain some of the discrepancies between our empirical findings and the Guenthner et al. (2013) model predictions. Because U-Th zoning is a common feature in zircon, radiation damage zoning is likely to be a concern for most ancient, slowly cooled zircon (U-Th)/He datasets. Whenever possible, multiple

Identification of a process window for tailored carburization of sheet metals in hot stamping

Science.gov (United States)

Horn, Alexander; Merklein, Marion

2018-05-01

Due to governmental regulations concerning the reduction of CO2 emissions and increasing safety standards, hot stamping of high strength boron manganese steel sheets has evolved into a state of the art process for manufacturing structural car body parts. The combined forming and in-die quenching process enables the formation of a fully martensitic microstructure. Therefore, press hardened steels offer high strength, but low ductility. In order to further improve passenger safety, a tailored configuration of mechanical properties is desired. Besides state of the art methods, like the application of locally different heat treatment temperatures or varying quenching rates, the adjustment of mechanical properties of sheet metals by a tailored carburization is a novel approach. For the carburization process, the specimens are first coated with graphite and subsequently heat treated. Within this contribution, different coating strategies as well as heat treatment temperatures and dwell times are investigated. For the determination of a process window, mechanical properties such as tensile strength and microhardness will be analyzed and correlated with the resulting microstructure.

Study of the pelletizing process zirconium oxide and zircon sand

International Nuclear Information System (INIS)

Seo, E.S.M.; Paschoal, J.O.A.; Acevedo, M.T.P.

1990-12-01

The study of the process to obtain zirconium tetrachloride under development at IPEN, can be divide into two steps: pelletizing and chlorination. Pelletizing is an important step in the overall process as it facilitates greater contact between the particles and permits the production of pellets with dimensional uniformity and mechanical strength. In this paper, the results of the study of pelletizing zirconium oxide and zircon sand are presented. The influence of some variables related to the process and the equipment on the physical characteristics of the pellets are discussed. (author)

Do Hf isotopes in magmatic zircons represent those of their host rocks?

Science.gov (United States)

Wang, Di; Wang, Xiao-Lei; Cai, Yue; Goldstein, Steven L.; Yang, Tao

2018-04-01

Lu-Hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution, assuming that zircon Hf isotopes can represent initial Hf isotopes of their parental whole rock. However, this assumption may not always be valid. Disequilibrium partial melting of continental crust would preferentially melt out non-zircon minerals with high time-integrated Lu/Hf ratios and generate partial melts with Hf isotope compositions that are more radiogenic than those of its magma source. Dissolution experiments (with hotplate, bomb and sintering procedures) of zircon-bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic Hf isotope compositions than fully dissolved samples. A case study from the Neoproterozoic Jiuling batholith in southern China shows that about half of the investigated samples show decoupled Hf isotopes between zircons and the bulk rocks. This decoupling could reflect complex and prolonged magmatic processes, such as crustal assimilation, magma mixing, and disequilibrium melting, which are consistent with the wide temperature spectrum from ∼630 °C to ∼900 °C by Ti-in-zircon thermometer. We suggest that magmatic zircons may only record the Hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their Hf isotopic compositions can represent the primary Hf isotopic compositions of the bulk magmas. In this regard, using zircon Hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts.

Developing Zircon as a Probe of Planetary Impact History

Science.gov (United States)

Wielicki, Matthew

2014-12-01

the Hadean population remains difficult and this study hopes to develop criteria to recognize impact zircon and possibly provide constraints on the early impactor flux. Five large terrestrial craters, Vredefort and Morokweng, South Africa, Sudbury and Manicouagan, Canada, and Popigai, Russia, are the focus of this study as smaller craters do not have the energy to produce thick melt sheets, which persist over time-scales sufficient for crystallization of zircon, permitting geochemical and geochronological analysis. Geochemical analysis of these impact-produced zircons yields similar chemical signatures to endogenic igneous zircon from crustal melts and highlights the need for well-developed criteria for discriminating impact and endogenic grains for impact geochronology. One such criterion is modeling of impact zircon crystallization temperature spectra for simulated impact events on targets of varying composition. Provided some assumptions the zircon crystallization spectra can be estimated from well established Zr systematics in crustal melts. Results for impacts into an Archean terrestrial surface (used as a proxy for the Hadean as little to no rock record exists >4.0 Ga) yields a crystallization spectra significantly higher than that reported for the Hadean zircon population and appears to rule out impacts as a dominant source for these ancient grains. When no dateable impact melt sheet exists, either due to the lack of energy of the impact itself or from subsequent erosion at Earth's surface, loss of radiogenic lead, Pb*, has been suggested as an alternative method to date the event. Pb*-loss was investigated from target rocks from Vredefort and Morokweng and suggests that Pb* diffusion, even in zircon isolated from shocked and brecciated target rocks, is remarkably slow. This may explain the seeming lack of 'reset' zircon in terrestrial impactites. Little is known about Pb* diffusion pathways associated with shock microstructures introduced during impact

Oxygen diffusion in zircon

Science.gov (United States)

Watson, E. B.; Cherniak, D. J.

1997-05-01

Oxygen diffusion in natural, non-metamict zircon was characterized under both dry and water-present conditions at temperatures ranging from 765°C to 1500°C. Dry experiments were performed at atmospheric pressure by encapsulating polished zircon samples with a fine powder of 18O-enriched quartz and annealing the sealed capsules in air. Hydrothermal runs were conducted in cold-seal pressure vessels (7-70 MPa) or a piston cylinder apparatus (400-1000 MPa) on zircon samples encapsulated with both 18O-enriched quartz and 18O water. Diffusive-uptake profiles of 18O were measured in all samples with a particle accelerator, using the 18O(p, α) 15N reaction. For dry experimental conditions at 1100-1500°C, the resulting oxygen diffusivities (24 in all) are well described by: D dry (m 2/s) = 1.33 × 10 -4exp(-53920/T) There is no suggestion of diffusive anisotropy. Under wet conditions at 925°C, oxygen diffusion shows little or no dependence upon P H 2O in the range 7-1000 MPa, and is insensitive to total pressure as well. The results of 27 wet experiments at 767-1160°C and 7-1000 MPa can be described a single Arrhenius relationship: D wet (m 2/s) = 5.5 × 10 -12exp(-25280/T) The insensitivity of oxygen diffusion to P H 2O means that applications to geologic problems can be pursued knowing only whether the system of interest was 'wet' (i.e., P H 2O > 7MPa ) or 'dry'. Under dry conditions (presumably rare in the crust), zircons are extremely retentive of their oxygen isotopic signatures, to the extent that δ 18O would be perturbed at the center of a 200 μm zircon only during an extraordinarily hot and protracted event (e.g., 65 Ma at 900°C). Under wet conditions, δ 18O may or may not be retained in the central regions of individual crystals, cores or overgrowth rims, depending upon the specific thermal history of the system.

Annealing effects on cathodoluminescence of zircon

Science.gov (United States)

Tsuchiya, Y.; Nishido, H.; Noumi, Y.

2011-12-01

U-Pb zircon dating (e. g., SHRIMP) is an important tool to interpret a history of the minerals at a micrometer-scale, where cathodoluminescence (CL) imaging allows us to recognize internal zones and domains with different chemical compositions and structural disorder at high spatial resolution. The CL of zircon is attributed by various types of emission centers, which are extrinsic ones such as REE impurities and intrinsic ones such as structural defects. Metamictization resulted from radiation damage to the lattice by alpha particles from the decay of U and Th mostly causes an effect on the CL features of zircon as a defect center. However, slightly radiation-damaged zircon, which is almost nondetectable by XRD, has not been characterized using CL method. In this study, annealing effects on CL of zircon has been investigated to clarify a recovery process of the damaged lattice at low radiation dose. A single crystal of zircon from Malawi was selected for CL measurements. It contains HfO2: 2.30 w.t %, U: 241 ppm and Th: 177 ppm. Two plate samples perpendicular to c and a axes were prepared for annealing experiments during 12 hours from room temperature to 1400 degree C. Color CL images were captured using a cold-cathode microscope (Luminoscope: Nuclide ELM-3R). CL spectral measurements were conducted using an SEM (JEOL: JSM-5410) combined with a grating monochromator (Oxford: Mono CL2) to measure CL spectra ranging from 300 to 800 nm in 1 nm steps with a temperature controlled stage. The dispersed CL was collected by a photoncounting method using a photomultiplier tube (Hamamatsu: R2228) and converted to digital data. All CL spectra were corrected for the total instrumental response. Spectral analysis reveals an anisotropy of the CL emission bands related to intrinsic defect center in blue region, radiation-induced defect center from 500 to 700 nm, and trivalent Dy impurity center at 480 and 580 nm, but their relative intensities are almost constant. CL on the

Are there impact-formed zircons in the Hadean record?

Science.gov (United States)

Wielicki, M. M.; Lu, X.; Bell, E. A.; Schmitt, A. K.; Harrison, T. M.

2008-12-01

Detrital Hadean zircons from the Jack Hills, Western Australia, show a remarkable cluster of crystallization temperatures at 680±25°C. This is particularly surprising as a simple model relating rock composition and Zr concentration predicts that a very broad spectrum of crystallization temperatures (ca. 650°C to 1000°C) with a median value of 780°C, would result from impact melting of the Earth's surface. Magmatic fractionation would tend to increase the aforementioned values. Given the predicted high rate of impacts during the Hadean, the absence of such a population in the Jack Hills zircons could signal a profound sampling problem, a hint of a history much different than previously supposed, or our lack of understanding of zircon formation due to impact related processes. We have begun to examine the latter issue by investigating the crystallization temperatures of zircons formed in melt sheets preserved in the geologic record. The Sudbury Igneous Complex, formed at 1850±3 Ma within the second largest impact crater on Earth, includes two igneous units termed the Black and Felsic Norites. Examination of zircons from each by SIMS confirms their crystallization age at 1847.3±2.2 Ma and yields Ti-in-zircon temperatures of 720°C and 750°C, respectively. This is consistent with that predicted from zircon saturation systematics. A statistical test indicates that the combined norite population is distinct from the Hadean temperature distribution. Thus the question arises: where are the Hadean zircons expected to have formed at >780°C via impact processes? Similar analysis is being pursued for zircons from the Vredefort Impact Structure, South Africa, which should provide further information on impact-formed zircon temperature spectra.

Mass-spectrometric mining of Hadean zircons by automated SHRIMP multi-collector and single-collector U/Pb zircon age dating: The first 100,000 grains

Science.gov (United States)

Holden, Peter; Lanc, Peter; Ireland, Trevor R.; Harrison, T. Mark; Foster, John J.; Bruce, Zane

2009-09-01

significant numbers of zircons for statistically limited studies including correlations between age and morphology, mineral-inclusion paragenesis, as well as isotopic studies including Hf and O isotopic compositions, Pu-Xe, and Sm-Nd isotopes.

Preparation and properties of calcium zirconate

International Nuclear Information System (INIS)

Dudek, M.; Bucko, M.; Rog, G.

2001-01-01

Dense samples of calcium zirconate were prepared. Electrical conductivity of the samples were measured in the temperature range 873 - 1273 K by both the d.c. four probe and the impedance spectroscopy methods. Calcium zirconate with small excess of calcium oxide appeared to be oxygen ion conductor. It was applied as an electrolyte in solid-state galvanic cells. (author)

Chemical characterisation of zircon-cadmium sulfoselenide ceramic pigments

International Nuclear Information System (INIS)

Gazulla Barreda, M. F.; Rodrigo Edo, M.; Blasco Roca, E.; Orduna Cordero, M.

2013-01-01

The present paper addresses the development of a methodology that allows the complete chemical characterisation of zircon cadmium sulfoselenide ceramic pigments including minor and major elements. To develop the methodology, five zircon-cadmium sulfoselenide pigments with different hues were selected, studying the different measurement process steps, from sample preparation to the optimisation of the measurement of the different components of the pigments by spectroscopic techniques (WD-XRF and elemental analysis by combustion and IR detection). The chemical characterisation method developed was validated with synthetic standards prepared from the mixture of certified reference materials and pure oxides because no certified referenced materials of this type of pigments were commercially available. The developed method can be used for a complete chemical characterization of zircon-cadmium sulfoselenide ceramic pigments with a very low uncertainty for all the elements analysed. (Author)

Relationship between carburization and zero-applied-stress creep dilation in Alloy 800H and Hastelloy X

International Nuclear Information System (INIS)

Inouye, H.; Rittenhouse, P.L.

1981-01-01

Typical HTGR candidate alloys can carburize when exposed to simulated service environments. The carbon concentration gradients so formed give rise to internal stresses which could cause dilation. Studies performed with Hastelloy X and Alloy 800H showed that dilations of up to almost 1% can occur at 1000 0 C when carbon pickup is high. Dilation was normally observed only when the carbon increase was >1000 μg/cm 2 and ceased when diffusing carbon reached the center of the specimen. (Auth.)

Provenance of zircon of the lowermost sedimentary cover, Estonia, East-European Craton

Directory of Open Access Journals (Sweden)

Konsa, M.

1999-12-01

Full Text Available Bulk and accessory mineral composition of fresh and weathered crystalline rocks, and sedimentary deposits overlying the crystalline-sedimentary unconformity have been examined in core samples from 28 drill holes in Estonia. Before the Late Vendian to Early Cambrian regional subsidence and sedimentation, the region represented a flat plateau within the Svecofennian Domain. Palaeo-and Mesoproterozoic crystalline rocks, regardless their different initial mineral composition, subcrop under the Upper Vendian/Lower Cambrian sedimentary cover as usually intensely weathered rocks (saprolites composed of residual quartz, altered micas and prevailing clay minerals mainly of the kaolinite group. Thus, the bulk mineral composition of any basement crystalline rocks imparts no specific inherited rock-forming minerals into the covering sedimentary rocks. From the variety of accessory and opaque minerals of crystalline rocks, only zircon populations survived in saprolites. Crystalline rocks of different origin yield different zircons. Relationships between the zircon typology of the basement rocks having specific areas of distribution and the sedimentary rocks immediately overlying those crystalline rocks were the main subject of this study. The result is that siliciclastic sedimentary rocks covering weathered crystalline rocks only in places inherited zircons with typological features characteristic of specific basement areas. In northeastern Estonia, local lenses of the Oru Member (the earliest Upper Vendian sedimentary rocks in Estonia resembling the debris of weathered crystalline rocks yield accessory zircon which in a 1-2 m thick layer above the basement surface is similar to the zircons of the underlying weathering mantle of certain crystalline rocks. In the next unit, the Moldova Member, up to 43 m above the basement surface, a mixture of zircons resembling those of various local basement rocks has been found. Further upwards, in the Vendian and Lower

Effect of nanograin-boundary networks generation on corrosion of carburized martensitic stainless steel.

Science.gov (United States)

Boonruang, Chatdanai; Thong-On, Atcharawadi; Kidkhunthod, Pinit

2018-02-02

Martensitic stainless steel parts used in carbonaceous atmosphere at high temperature are subject to corrosion which results in a large amount of lost energy and high repair and maintenance costs. This work therefore proposes a model for surface development and corrosion mechanism as a solution to reduce corrosion costs. The morphology, phase, and corrosion behavior of steel are investigated using GIXRD, XANES, and EIS. The results show formation of nanograin-boundary networks in the protective layer of martensitic stainless steel. This Cr 2 O 3 -Cr 7 C 3 nanograin mixture on the FeCr 2 O 4 layer causes ion transport which is the main reason for the corrosion reaction during carburizing of the steel. The results reveal the rate determining steps in the corrosion mechanism during carburizing of steel. These steps are the diffusion of uncharged active gases in the stagnant-gas layer over the steel surface followed by the conversion of C into C 4- and O into O 2- at the gas-oxide interface simultaneously with the migration of Cr 3+ from the metal-oxide interface to the gas-oxide interface. It is proposed that previous research on Al 2 O 3 coatings may be the solution to producing effective coatings that overcome the corrosion challenges discussed in this work.

Sliding wear characteristics of carburized steels and thermally refined steels implanted with nitrogen ions

International Nuclear Information System (INIS)

Terashima, Keiichi; Koda, Hiroyuki; Takeuchi, Eiichi.

1995-01-01

In order to concretely examine the application of surface reforming by ion implantation, nitrogen ion implantation was applied to the thermally refined steels S45C and SCM440 and the carburized steel SCM415, which are high versatile steels for mechanical structures, and their friction and wear characteristics were examined. The results are summarized as follows. In the surface-reformed material, in which nitrogen was implanted for the purpose of improving the seizure durability of the carburized steel, the load-frictional coefficient curve in lubricated sliding friction was similar to that of the material without implantation, but it was recognized that the load at which seizure occurred reached 2000 kgf or more, and as the amount of implantation was more, the material withstood higher load. In the lubricated sliding friction using a pin-ring type wear testing machine of the thermally refined steels and those to which implantation was applied, it was recognized that the specific wear amount was less in the implanted steels than in those without implantation. The results of the analysis of the implanted surface layers and the friction surfaces are reported. (K.I.)

Peculiar Feldspar And Quartz Inclusions Within Zircons From Anorthosites, North Eastern Desert, Egypt

Science.gov (United States)

Eliwa, H. A.; Dawoud, M. I.; Khalaf, I. M.; Negendank, J. F.; Itaya, T.

2004-12-01

Zircons from three anorthosite outcrops along Wadi Dib area, north Eastern Desert of Egypt contain abundant and conspicuous inclusions of quartz, feldspar, amphibole and apatite. These anorthosites, as (50-100m thick) layers, represent the top of mafic-ultramafic intrusions exhibiting rhythmic layering visible by reputation of melanocratic and leucocratic layers. Field and microscopic studies exhibit that these anorthosites were affected by the action of residual magmatic solutions associated with the late stage crystallization of the younger granites, which modified their mineralogical composition. They are composed totally of plagioclase with subordinate amount of clinoenstatite, augite, amphibole, biotite, K-feldspar, and quartz. Accessories are magnetite, ilmenite, apatite and zircon. The abundance and the mode of occurrence of K-feldspar, quartz, and biotite with apatite and zircon among the megacrysts suggest their formation is ascribed to the interaction with the residual solutions. The microprobe data exhibit difference between feldspar and amphiboles contained herein zircons and those as anorthosite mineral constituents. The genetic relationship between zircons and their inclusions suggests later growth of zircons than inclusions and most probably at the final stage of rock modification. Zircons are magmatic and found in the interstitial feldspar and quartz among plagioclase megacrysts in aggregates or as individual grains. The microscopic and SEM images investigation exhibit that most zircons are subhedral to euhedral equant and prismatic crystals. Most zircons have same range of crystal morphologies and internal growth structures with predominance of prism /{100/} and pyramid /{101/} and occasionally prism /{110/} and pyramid /{111/}. No evidences for poly-faceted grains, inherited cores or later overgrowths were detected. CL images distinguished zircons with visible core-rim structures and others with regular and continuous growth zones contained herein

Les nouveaux carburants pour l'automobile. Carburants oxygénés : emploi et émissions New Automotive Fuels. Oxygenated Fuels: Their Use and Emissions

Directory of Open Access Journals (Sweden)

Guibet J. C.

2006-11-01

Full Text Available A la lumière de résultats nouveaux obtenus à l'IFP et de publications récentes sur le sujet, on étudie les principales répercussions de l'emploi de carburants oxygénés sur les émissions de polluants à l'échapement et sur les risques possibles associés à la manipulation des produits. Les polluants examinés sont les alkyles de plomb, l'oxyde de carbone, les oxydes d'azote, les produits imbrûlés, les aldéhydes et les hydrocarbures aromatiques polynucléaires. Les émissions de fumées et de particules solides par les moteurs diesel font aussi l'objet de quelques commentaires. On aborde également les problèmes de pertes par évaporation et on fournit quelques informations sur la toxicité des alcools et des aldéhydes. L'étude fait apparaître un besoin réel de nouvelles recherches dans le domaine, mais elle indique déjà que l'emploi de produits organiques oxygénés comme carburants ne devrait pas changer l'ordre de grandeur des niveaux de polluants. In the light of new results from IFP and recent publications on the subject, this article examines the main repercussions of the use of oxygenated fuelss on pollutant exhauts emissions and on possible risks associated with the handling of products. The pollutants examined are lead alkyls, carbon monoxide, nitrogen oxides, unburned products, aldehydes and polynuclear aromatic hydrocarbons. Emissions of smoke and solid particles by diesel engines are also the subject of various comments. Likewise, the article takes up the problem of losses by evaporation, and some information is provided on the toxicity of alcohols and aldehydes. This study reveals the real need for further research in the field, but it already shows that the use of oxygenated organic products as fuels should not bring about much change in the order of magnitude of pollutant levels.

Twinning in Zircon: Not a High-Pressure Phenomenon

Science.gov (United States)

Jones, G. A.; Moser, D.; Shieh, S. R.; Barker, I.

2017-12-01

Microtwins in zircon are commonly found in shocked terrestrial and extraterrestrial samples and are potentially important for shock history and crater reconstruction. Twinning is easily observed with both the optical microscope and variety of electron beam techniques. Twinning as a deformation mechanism is consistent with the high strain rates generated during impact. No constitutive relationships, or even general limits on the physical conditions required for twinning in zircon are known, however. Present speculation on the critical quantity for twin formation, i.e. 10s of GPa of shock pressure (Moser et al. 2011, Timms et al., 2012), has no basis in the underlying mechanisms of twin nucleation, which are related to the motion of dislocations. This erroneous value is due to conflation of twinning sensu stricto with a phase transformation to reidite. Reidite occurs as twin-like lamellae occupying the {112} planes which are thought to be a mirror plane for twinning. We review the crystallographic theory of twinning in zircon. We then evaulate several theories on the nucleation of twins along with their necessary stresses involved. Our aim is to show that shock microtwins in zircon can be a `low pressure' shock phenomenon. This 'low pressure' hypothesis is supported by natural samples. These zircons are from the lower crust nearly 80 km from the centre of the Vredefort impact structure—the most distal zircon shock microstructures yet found in the lithosphere. Twins are present in 10% of the zircon grains greater than 50 µm in diameter. As an extensive, 'low pressure' phenomenon, twins are an easily recognized and potentially widespread record of Earth's impact history.Moser, D.E., Cupelli, C. L., Barker, I., Flowers, R. M., Mowman, J. R., Wooden, J. and Hart, R. (2011) New zircon shock phenomena and their use for dating and […] analysis of the Vredefort dome, Canadian Journal of Earth Sciences 48(2), 117-139.Timms, N.E., Reddy, S. M., Healy, D., Nemchin, A. A

Laws of alloyed cementite particles nucleation during heat-resistant steels carburizing

Directory of Open Access Journals (Sweden)

M. Yu. Semenov

2014-01-01

Full Text Available The article considers a problem analyzing a nucleation of cementite type carbides in carburized heat-resistant steels for the turbofan engines gear wheels.The verification of previously hypothesized mechanism of dislocation nucleation particles chromium-alloyed cementite during process of carburizing was accepted as an objective of the work.As a methodological basis of this paper were accepted the numerical experiments based on the kinetic theory of nucleation, as well as on the known results of experimental studies.According to the kinetic theory of nucleation, a new phase in the solid solutions take place in the defects of the crystal structure of the metal such as inter-grain boundaries and dislocations clusters. A principle feature of the inter-grain boundary mechanism of nucleation is formation of carbide lattice. It is of great practical interest because the cementite lattice drops mechanical properties of hardened parts.According to the experimental studies, the average chromium concentration in the alloyed cementite twice exceeds its Cr content in the heat-resistant steels. Furthermore, the areas of abnormally high (more than ten times in comparison with the average content chromium concentration in cementite have been experimentally revealed.Numerical experiments have revealed that the nucleation of cementite particles alloyed with chromium (chromium concentration of 3% or more occurs, mainly, by the dislocation mechanism on the concentration fluctuations of the alloying element. According to calculations, an obligatory prerequisite to start an active nucleation process of new phase in the solid solution is a local increase of the chromium concentration up to 40%.Despite the lack of physical prerequisites for the formation of chromium precipitates, this phenomenon is explained by a strong chemical affinity of chromium and carbon, causing diffusion of chromium atoms in the region of the carbon atoms clusters. The formation of carbon

EBSD analysis of tungsten-filament carburization during the hot-wire CVD of multi-walled carbon nanotubes

CSIR Research Space (South Africa)

Oliphant, CJ

2014-02-01

Full Text Available the carburization of tungsten filaments. During the synthesis, the W-filaments transform to W(sub2)C and WC.W-carbide growth followed a parabolic behavior corresponding to the diffusion of C as the rate-determining step. The grain size of W, W(sub2)C, and WC...

Crystallization process of zircon and fergusonite during hydrothermal alteration in Nechalacho REE deposit, Thor Lake, Canada

Science.gov (United States)

Hoshino, M.; Watanabe, Y.; Murakami, H.; Kon, Y.; Tsunematsu, M.

2012-04-01

The core samples of two drill holes, which penetrate sub-horizontal mineralized horizons at Nechalacho REE deposit in the Proterozoic Thor Lake syenite, Canada, were studied in order to clarify magmatic and hydrothermal processes that enriched HFSE (e.g. Zr, Nb, Y and REE). Zircon is the most common REE minerals in Nechalacho REE deposit. The zircon is divided into five types as follows: Type-1 zircon occurs as single grain in phlogopite and the chondrite-normalized REE pattern is characterized by a steeply-rising slope from the LREE to the HREE with a positive Ce-anomaly and negative Eu-anomaly. This chemical characteristic is similar to that of igneous zircon. Type-2 zircon consists of HREE-rich magmatic porous core and LREE-Nb-F-rich hydrothermal rim. This type zircon is mostly included in phlogopite and fluorite, and occasionally in microcline. Type-3 zircon is characterized by euhedral to anhedral crystal, occurring in a complex intergrowth with REE fluorocarbonates. Type-3 zircons have high contents of REE, Nb and fluorine. Type-4 zircon consists of porous-core and -rim zones, but their chemical compositions are similar to each other. This type zircon is a subhedral crystal rimmed by fergusonite. Type-5 zircon is characterized by smaller, porous and subhedral to anhedral crystals. The interstices between small zircons are filled by fergusonite. Type-4 and -5 zircons show low REE and Nb contents. Occurrences of these five types of zircon are different according to the depth and degree of the alteration by hydrothermal solutions rich in F- and CO3 of the two drill holes, which permit a model for evolution of the zircon crystallization in Nechalacho REE deposit as follows: (1) type-1 (single magmatic zircon) is formed in miaskitic syenite. (2) LREE-Nb-F-rich hydrothermal zircon formed around HREE-rich magmatic zircon (type-2 zircon); (3) type-3 zircon crystallized thorough F and CO3-rich hydrothermal alteration of type-2 zircon which formed the complex

Fabrication of zircon for disposition of weapons plutonium

International Nuclear Information System (INIS)

Kim, K.C.; Huang, J.Y.; Serrano, P.L.

1997-01-01

This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). In an effort to address the problems of long term storage and nuclear waste minimization, zircon has been proposed as a host medium for plutonium and other actinides recovered from dismantled nuclear weapons. The objective of this work is to investigate the feasibility of large scale fabrication of Pu-bearing zircon. Since PuO 2 is thermodynamically less stable than ZrO 2 , it is expected that the process parameters determined for synthesizing ZrSiO 4 (zircon) would be applicable to those for PuSiO 4 (Pu-zircon). Furthermore, since the foremost concern in plutonium processing is the potential for contamination release, this work emphasizes the development of process parameters, using zircon first, to anticipate potential material problems in the containment system for reaction mixtures during processing. Stoichiometric mixtures of ZrO 2 and SiO 2 , in hundred-gram batches, have been subjected to hot isostatic pressing (HIP) at temperatures near 1,500 C and pressures approximately 10,000 psi. The product materials have been analyzed by x-ray powder diffraction, and are found to consist of zircon after approximately two hours of reaction time. From this work, it is clear that the fabrication of large quantities of Pu-zircon is feasible. The most notable result of this work is evidence for the existence of container problems. This result, in turn, suggests potential solutions to these problems. Experiments with the quartz inner container, the glass sealant, a sacrificial metal barrier, and a metal outer container are being investigated to mitigate these potential hazards

Gas carburizing end-discharge pusher furnaces for the automatic hardening of single gear components. Gasaufkohlungs-Durchstossanlagen mit automatischer Einzelhaertung von Getriebeteilen

Energy Technology Data Exchange (ETDEWEB)

Grassl, D; Washausen, R

1989-09-01

Apart from rotary hearth furnaces, end-discharge pusher furnaces are increasingly used for carburizing and hardening single components. These furnaces offer the following advantages: There is no limitation to the depth of case. The furnace zones can be controlled separately permitting carburizing to be optimized. The furnace can be designed to permit hardening of single components or quenching in batches. Process data relating to the components can be stored and called automatically (reproducibility of product quality). Heat treatment can be integrated in production control by process computer even if the furnace is installed separately. Regardless of what type of furnace is used, specific requirements have to be met to ensure reliable automatic discharge of single components. (orig./BWI).

Synthetic Or Reformulated Fuels: a Challenge for Catalysis Carburants de synthèse ou reformulés : un défi pour la catalyse

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Courty P.

2006-12-01

Full Text Available Despite comparative figures for wordwide crude oil and natural gas proven reserves, present time contribution of syngas chemistry to motorfuels remains marginal when the refining industry is faced to main constraints: market demand evolution, stringent specifications and environmental issues. Actually natural gas upgrading via syngas chemistry yields key products (e. g. methanol among which clean motorfuels (ethers, FT products should develop despite the huge investments required, mostly for syngas production. Main challenges and corresponding issues for catalysts and related technologies are identified for Fischer-Tropsch synthesis and motorfuels long-term reformulation. Among other, mastering the chain-growth (FT synthesis improving the FCC products: gasoline, and LCO for Diesel pool. All these issues need significant progresses in catalyst and technology to be solved. Lastly, our economical study, focused on Diesel-fuel production, shows up that clean diesel (from SR-LCO mixtures and FT Diesel reach similar production costs when cheap NG is available. In the future, FT middle distillates should amount to a few percent (5-150 Mt of the 1700-2000 Mt of transport middle distillates expected from oil refining. However they should more and more be a compulsory part of diesel pool if the level of investment for an FT process continues to decrease significantly. Malgré des réserves prouvées en pétrole et en gaz du même ordre de grandeur, la contribution de la chimie du gaz de synthèse à la production de carburants reste marginale, alors que l'industrie du raffinage est confrontée à des contraintes majeures : évolution de la demande, durcissement des spécifications des produits et contraintes environnementales. Cependant, la conversion chimique du gaz, via la chimie du gaz de synthèse, fournit des produits stratégiques (e. g. méthanol parmi lesquels les carburants propres (éthers, produits Fischer-Tropsch devraient se développer, bien

Mid-1970's imbalance in zircon supply and demand

International Nuclear Information System (INIS)

Van Gordon, D.V.; Collins, R.E.

1975-01-01

Mining and the historical development of the zircon market are briefly reviewed. Causes of the fluctuations in the zircon demand and supply and in the price are discussed. Possible adjustments (such as substitution of other materials in the steel foundry) are listed. Future uses of zircon will probably be limited to those which can justify high prices and those for which there are no substitutes. (DLC)

Rational Formulation of Alternative Fuels using QSPR Methods: Application to Jet Fuels Développement d’un outil d’aide à la formulation des carburants alternatifs utilisant des méthodes QSPR (Quantitative Structure Property Relationship: application aux carburéacteurs

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Saldana D.A.

2013-06-01

Full Text Available Alternative fuels are a promising solution for road transport but also for aircraft. In the aviation field, a huge amount of work has been done in the past years with the approval to use up to 50 % by volume of SPK (Synthetic Paraffinic Kerosene in blends with conventional fossil Jet A-1. SPK are Fischer-Tropsch (FT fuels but also Hydroprocessed Esters and Fatty Acids (HEFA. However, these alternative fuels can have different chemical properties depending on the process used for their production. These properties include normal to iso paraffin ratio, carbon chain length and level of branching. R&D studies of alternative fuels are based on the evaluation of products coming from identified production processes. However, it appears that a better way of studying them could be firstly to determine the best chemical composition regarding aviation problems and secondly to find the best process and finishing process in order to obtain such a product. The objective of this work is to design a tool that aims to guide the future formulation of alternative fuels for aviation through the prediction of targeted physical properties. Thus, it is proposed to apply a methodology that identifies relationships between the structure and properties of a molecule (QSPR for Quantitative Structure Property Relationship, with the aim of establishing predictive models. These models will be built for hydrocarbons (normal and iso paraffins, naphthenes, aromatics, etc. and oxygenated compounds (esters and alcohols. For aviation, oxygenated compounds are not considered as a drop-in fuel. It could be seen as a disruptive solution in a long term view. There are concerns with oxygenates in aviation that are covered in this paper such as the flash point but others such as the energetic content, the water affinity that are not taken into account in this paper. The properties currently studied are flash point, cetane number, density and viscosity. The data sets will contain data

Cryptic crustal events during the Taconic Orogeny elucidated through LA-ICPMS studies of volcanic zircons, southern Appalachians, Alabama

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Herrmann, A. D.; Leslie, S.; Haynes, J.

2017-12-01

Despite a long history of stratigraphic work, many questions remain about the tectonic setting of the Taconic orogeny during the early late Ordovician. Several different global paleogeographic hypotheses exist about the driving force that led to this orogeny. While some studies suggest that the closing of the Iapetus ocean was caused by the collision of the North American and South American plates, most studies suggest that island arc systems collided with the passive continental margin of North America. Nevertheless, disagreement exists on how to explain the stratigraphic architecture of the siliciclastic sequences representing the erosion of the Taconic Highlands in an island arc setting. Some studies suggest the collision was analogous to the modern Banda Arc system with the development of a foreland basin and a sedimentary wedge, while other studies call for the presence of a back arc basin. Here we present U-Pb results of volcanic zircons that are associated with the magmatic activity during this time. Previous studies focused on slender zircons for age dating. However, in this study we analyzed several large zircons from close to the volcanic center in Alabama that have inherited cores in order to test for the presence of geochemical evidence for multiple crustal events. While the rims have ages consistent with the Taconic Orogeny ( 450 my), the cores have much older ages ( 1000 my). Our results support the hypothesis that during the closing of the Iapetus ocean, Precambrian and Cambrian sediments from the passive continental margin were subducted and incorporated into the volcanic system. This led to the inclusion of Precambrian zircons into melts associated with the Taconic Orogeny. Overall, our study supports the presence of subduction of preexisting sedimentary rocks and potentially the presence of a sedimentary wedge.

Response of zircon to melting and metamorphism in deep arc crust, Fiordland (New Zealand): implications for zircon inheritance in cordilleran granites

Science.gov (United States)

Bhattacharya, Shrema; Kemp, A. I. S.; Collins, W. J.

2018-04-01

The Cretaceous Mount Daniel Complex (MDC) in northern Fiordland, New Zealand was emplaced as a 50 m-thick dyke and sheet complex into an active shear zone at the base of a Cordilleran magmatic arc. It was emplaced below the 20-25 km-thick, 125.3 ± 1.3 Ma old Western Fiordland Orthogneiss (WFO) and is characterized by metre-scale sheets of sodic, low and high Sr/Y diorites and granites. 119.3 ± 1.2 Ma old, pre-MDC lattice dykes and 117.4 ± 3.1 Ma late-MDC lattice dykes constrain the age of the MDC itself. Most dykes were isoclinally folded as they intruded, but crystallised within this deep-crustal, magma-transfer zone as the terrain cooled and was buried from 25 to 50 km (9-14 kbar), based on published P-T estimated from the surrounding country rocks. Zircon grains formed under these magmatic/granulite facies metamorphic conditions were initially characterized by conservatively assigning zircons with oscillatory zoning as igneous and featureless rims as metamorphic, representing 54% of the analysed grains. Further petrological assignment involved additional parameters such as age, morphology, Th/U ratios, REE patterns and Ti-in-zircon temperature estimates. Using this integrative approach, assignment of analysed grains to metamorphic or igneous groupings improved to 98%. A striking feature of the MDC is that only 2% of all igneous zircon grains reflect emplacement, so that the zircon cargo was almost entirely inherited, even in dioritic magmas. Metamorphic zircons of MDC show a cooler temperature range of 740-640 °C, reflects the moderate ambient temperature of the lower crust during MDC emplacement. The MDC also provides a cautionary tale: in the absence of robust field and microstructural relations, the igneous-zoned zircon population at 122.1 ± 1.3 Ma, derived mostly from inherited zircons of the WFO, would be meaningless in terms of actual magmatic emplacement age of MDC, where the latter is further obscured by younger (ca. 114 Ma) metamorphic overgrowths

Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism

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Kovaleva, Elizaveta; Klötzli, Urs; Wheeler, John; Habler, Gerlinde

2018-02-01

This study documents the strain accommodation mechanisms in zircon under amphibolite-facies metamorphic conditions in simple shear. Microstructural data from undeformed, fractured and crystal-plastically deformed zircon crystals are described in the context of the host shear zone, and evaluated in the light of zircon elastic anisotropy. Our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral. Crystal-plastically deformed zircon grains have axis oriented parallel to the foliation plane, with the majority of deformed grains having axis parallel to the lineation. Zircon accommodates strain by a network of stepped low-angle boundaries, formed by switching between tilt dislocations with the slip systems {010} and {110} and rotation axis [001], twist dislocations with the rotation axis [001], and tilt dislocations with the slip system {001} and rotation axis [010]. The slip system {110} is newly described for zircon. Most misorientation axes in plastically-deformed zircon grains are parallel to the XY plane of the sample and have [001] crystallographic direction. Such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology, deformation mechanisms and dominant slip systems in zircon. Young's modulus and P wave velocity have highest values parallel to zircon [001] axis, indicating that zircon is elastically strong along this direction. Poisson ratio and Shear modulus demonstrate that zircon is also most resistant to shearing along [001]. Thus, [001] axis is the most common rotation axis in zircon. The described zircon behaviour is important to take into account during structural and geochronological investigations of (poly)metamorphic terrains. Geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone(s), large-scale stresses in the crust, and, possibly, the timing of

Analysis of carburizing steel with lath bainite in matrix by magnetic method

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Weiwu ZOU

2017-12-01

Full Text Available The cryogenic treatment is used to reduce the large amount of retained austenite in the steel infiltration layer which affects the hardness. The vibrating sample magnetometer (VSM and direct reading spectroscopy are combined to compare and analyze the organization structure status of the test carburizing steel after air-cooling and low temperature tempering (T at 453 K × 1 h, or after cryogenic treatment at 113 K × 30 min and low temperature tempering (T at 453 K × 1 h. The cryopreservation effect of the 1 203 K × 9 h carburizing air-cooled bainitic steel is carried out. The results show that both the effective hardening layer depths are about 1.35 mm. The retained austenite mass fractions of T and CT in the effective hardened layer are approximately 29.8% and 12.6%, respectively, and the highest hardnesses of the effective hardened layer of T and CT are 679 HV and 821 HV, respectively. The matrix structure is lath bainite, and the retained austenite mass fractions in the matrix are approximately 7.4% for T and 6.9% for CT, respectively, and both the hardnesses of the matrixes are approximately 430 HV. After the cryogenic treatment, the austenite content in the infiltration layer is effectively reduced, so that the maximum hardness of the hardened layer increases by 20% or more. It can be widely used because of the decreased material cost and remarkable economical benefit.

The significance of zircon characteristic and its uranium concentration in evaluation of uranium metallogenetic prospect

International Nuclear Information System (INIS)

Li Yaosong; Zhu Jiechen; Xia Yuliang

1992-02-01

Zircon characteristic and its relation to uranium metallogenetic process have been studied on the basis of physics properties and chemical compositions. It is indicated that the colour of zircon crystal is related to uranium concentration; on the basis of method of zircon population type of Pupin J.P., the sectional plan of zircon population type has been designed, from which result that zircon population type of uranium-producing rock body is distributed mainly in second section, secondly in fourth section; U in zircon presents synchronous increase trend with Th, Hf and Ta; the uranium concentration in zircon from uranium-producing geologic body increases obviously and its rate of increase is more than that of the uranium concentration in rock; the period, in which uranium concentration in zircon is increased, is often related to better uranium-producing condition in that period of this area. 1785 data of the average uranium concentration in zircon have been counted and clear regularity has been obtained, namely the average uranium concentrations in zircon in rich uranium-producing area, rock, geologic body and metallogenetic zone are all higher than that in poor or no uranium-producing area, rock, geologic body and metallogenetic zone. This shows that the average uranium concentration in zircon within the region in fact reflects the primary uranium-bearing background in region and restricts directly follow-up possibility of uranium mineralization. On the basis of this, the uranium source conditions of known uranium metallogenetic zones and prospective provinces have been discussed, and the average uranium concentrations in zircon from magmatic rocks for 81 districts have been contrasted and graded, and some districts in which exploration will be worth doing further are put forward

Investigating the Early Carbon Cycle Using Carbonaceous Inclusions and Dissolved Carbon in Detrital Zircon

Science.gov (United States)

Bell, E. A.; Boehnke, P.; Harrison, M.; Mao, W. L.

2015-12-01

Because the terrestrial rock record extends only to ~4 Ga and older materials thus far identified are limited to detrital zircons, information about volatile abundances and cycles on early Earth is limited. Carbon, for instance, plays an important role not only in the modern biosphere but also in deep recycling of materials between the crust and mantle. We are investigating the record of carbon abundance and origin in Hadean zircons from Jack Hills (W. Australia) using two main approaches. First, carbon may partition into the zircon structure at trace levels during crystallization from a magma, and better understanding of this partitioning behavior will allow for zircon's use as a monitor of magmatic carbon contents. We have measured carbon abundances in zircon from a variety of igneous rocks (gabbro; I-, A-, and S-type granitoids) via SIMS and found that although abundances are typically low (average raw 12C/30Si ~ 1x10-6), S-type granite zircons can reach a factor of 1000 over this background. Around 10% of Hadean zircons investigated show similar enrichments, consistent with other evidence for the derivation of many Jack Hills zircons from S-type granitoids and with the establishment of modern-level carbon abundances in the crust by ca. 4.2 Ga. Diamond and graphite inclusions reported in the Jack Hills zircons by previous studies proved to be contamination by polishing debris, leaving the true abundance of these materials in the population uncertain. On a second front, we have identified and investigated primary carbonaceous inclusions in these zircons. From a population of over 10,000 Jack Hills zircons, we identified one concordant 4.10±0.01 Ga zircon that contains primary graphite inclusions (so interpreted due to their enclosure in a crack-free zircon host as shown by transmission X-ray microscopy and their crystal habit). Their δ13CPDB of -24±5‰ is consistent with a biogenic origin and, in the absence of a likely inorganic mechanism to produce such a

Dating of zircons by the fission track method

International Nuclear Information System (INIS)

Tenorio Hernandez, L.M.

1992-01-01

This work describes the methodology to date zircons by the Fission Track Method. A brief discussion is made of the physical principles of the method, physical properties of zircons and the geochemical properties of uranium. When starting with a hand sample, a mineral separation is required; to do this the following steps are needed: crushing and sieving of the sample, washing and drying, magnetic separation, heavy liquid separation (Bromoform 2.89 g/cm 3 , Diyodomethane = 3.31 g/cm 3 ), and manual separation on a stereoscopic microscope. Once the zircon concentrate is obtained, these are mounted on a FEP teflon mount, then polished and etched on an eutectic mix of 10 g. of KOH + 7.2 g. of NaOH, heated to 210 Centigrade degrees. Afterwards the mounts are prepared for irradiation, sterilizing and putting on top of them an external detector (a thin sheet of muscovite poor in uranium content). The package is then wrapped in plastic and sent to the reactor together with standard zircons of known age (Fish Canyon Tuff: Naeser et.al., 1981), mounted in the same way, plus standard glasses of known uranium content. The package was irradiated in a site known as SIRCA (Rotatory Capsules Irradiation System). Then the package is left to decay for several days, and then the external detectors are etched in a 48% concentrated hydrofluoric acid for 5 minutes. Once the samples are processed through the mentioned steps, spontaneous tracks appear in the zircons and induced tracks appear in the external detectors. On counting the tracks one obtains ρ s (spontaneous track density) and ρ 1 (induced track density). These two parameters together with another one called '#zeta #' (obtained from the standard zircons and glasses), are used to obtain the age of the sample. Zircons from Cerro de Mercado, Durango were dated and the age obtained was 30 ±5 Ma. This date is in agreement with similar results obtained by Fleisher and Naeser (1975) for zircons of the same locality and dated by the

Detrital Zircons Split Sibumasu in East Gondwana

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Zhang, X.; Chung, S. L.

2017-12-01

It is widely accepted that Sibumasu developed as a united terrane and originated from NW Australian margin in East Gondwana. Here we report new detrital zircon U-Pb-Hf isotopic data from Sumatra that, in combination with literature data, challenge and refute the above long-held view. In particular, the East and West Sumatra terranes share nearly identical Precambrian to Paleozoic detrital zircon age distributions and Hf isotopes, indicating a common provenance/origin for them. The Sumatra detrital zircons exhibit a prominent population of ca. 1170-1070 Ma, indistinguishable from those of the Lhasa and West Burma terranes, with detritus most probably sourcing from western Australia. By contrast, Sibuma (Sibumasu excluding Sumatra) detrital zircons display a prevailing population of ca. 980-935 Ma, strongly resembling those of the western Qiangtang terrane, with detrital materials most likely derived from Greater India and Himalayas. Such markedly distinct detrital zircon age profiles between Sumatra and Sibuma require disparate sources/origin for them, provoking disintegration of the widely-adopted, but outdated, term Sibumasu and thus inviting a new configuration of East Gondwana in the early Paleozoic, with Sumatra and West Burma lying outboard the Lhasa terrane in the NW Australian margin and Sibuma situated in the northern Greater Indian margin. More future investigations are needed to establish the precise rifting and drifting histories of Sumatra and Sibuma, as two separated terranes, during the breakup of Gondwana.

Direct Chlorination of Zircon Sand

International Nuclear Information System (INIS)

Dwiretnani Sudjoko; Budi Sulistyo; Pristi Hartati; Sunardjo

2002-01-01

It was investigated the direct chlorination of zircon sand in a unit chlorination equipment. The process was in semi batch. The product gas was scrubbed in aqueous NaOH. It was search the influence of time, ratio of reactant and size of particle sand to the concentration of Zr and Si in the product. From these research it was found that as the times, ratio of reactant increased, the concentration of Zr increased, but the concentration of Si decreased, while as grain size of zircon sand decreased the concentration of Zr decreased, but the concentration of Si increased. (author)

What can zircon ages from the Jack Hills detrital zircon suite really tell us about Hadean geodynamics?

Science.gov (United States)

Whitehouse, Martin; Nemchin, Alexander

2015-04-01

As the only direct sample of the Hadean Earth, detrital zircon grains from the Jack Hills, Western Australia, have been the subject of intense investigation over the almost three decades since their discovery. A wide variety of geochemical and isotopic analyses of these grains, as well as their mineral inclusions, have been used variously to support two fundamentally different models for Hadean geodynamics: (i) Some form of (not necessarily modern-style) plate recycling generating felsic (continental-type?) crust at the boundaries [1, 2], or conversely (ii) the persistence of a long-lived, stagnant basaltic lid within which magmatism occurred as a result of internal temperature perturbations and/or impacts [3, 4], a model also generally consistent with a wide range of observations from post-Hadean geochemical reservoirs. Despite the considerable time and resources expended, the majority of these studies uncritically accept the individual U-Pb zircon ages, even though their veracity is key to many of the interpretations [5, 6]. We report here the results of an in-depth evaluation of all published (and new) U-Pb ages from the Jack Hills zircon suite in order to define age populations that can be used with a high degree of confidence in geodynamic interpretations. A notable problem in the interpretation of U-Pb data from ancient zircon grains (including those as young as the Neoarchean) is that disturbance of the systematics even several 100 Ma after crystallization causes data to spread along the concordia curve without becoming discernably discordant within the relatively large error bounds associated with U/Pb ages from in situ dating methods (e.g. SIMS). While 207Pb/206Pb ages are typically more precise, individually they provide no means to detect Pb-loss-induced younging. However, if two or preferably more analyses have been made in the same zircon growth zone, a reasonable evaluation of the possibility of Pb-loss can be made. In the available Jack Hills zircon

Silicic melt evolution in the early Izu-Bonin arc recorded in detrital zircons: Zircon U-Pb geochronology and trace element geochemistry for Site U1438, Amami Sankaku Basin

Science.gov (United States)

Barth, A. P.; Tani, K.; Meffre, S.; Wooden, J. L.; Coble, M. A.

2016-12-01

Understanding the petrologic evolution of oceanic arc magmas through time is important because these arcs reveal the processes of formation and the early evolution of juvenile continental crust. The Izu-Bonin (IB) arc system has been targeted because it is one of several western Pacific intraoceanic arcs initiated at 50 Ma and because of its prominent spatial asymmetry, with widespread development of relatively enriched rear arc lavas. We examined Pb/U and trace element compositions in zircons recovered at IODP Site 351-U1438 and compared them to regional and global zircon suites. These new arc zircon data indicate that detrital zircons will yield new insights into the generation of IB silicic melts and form a set of useful geochemical proxies for interpreting ancient arc detrital zircon provenance. Project IBM drilling target IBM1 was explored by Expedition 351 at Site U1438, located in the proximal back-arc of the northern Kyushu-Palau Ridge (KPR) at 27.3°N. A 1.2 km thick section of Paleogene volcaniclastic rocks, increasingly lithified and hydrothermally altered with depth, constitutes a proximal rear arc sedimentary record of IB arc initiation and early arc evolution. The ages and compositions of U1438 zircons are compatible with provenance in one or more edifices of the northern KPR and are incompatible with drilling contamination. Melt zircon saturation temperatures and Ti-in-zircon thermometry suggest a provenance in relatively cool and silicic KPR melts. The abundances of selected trace elements with high native concentrations provide insight into the petrogenesis of U1438 detrital zircon host melts, and may be useful indicators of both short and long-term variations in melt compositions in arc settings. The U1438 zircons are slightly enriched in U and LREE and are depleted in Nb compared to zircons from mid-ocean ridges and the Parece-Vela Basin, as predicted for melts in a primitive oceanic arc setting with magmas derived from a highly depleted mantle

U-Pb dating by zircon dissolution method using chemical abrasion

Energy Technology Data Exchange (ETDEWEB)

Takehara, Lucy, E-mail: lucytakehara@gmail.com.br [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil); Chemale Junior, Farid [Universidade de Brasilia (UnB), Brasilia, DF (Brazil). Inst. de Geociencias. Lab. de Geocronologia; Hartmann, Leo A. [Universidade Federal do Rio Grande do Sul (UFRS), Porto Alegre, RS (Brazil). Inst. de Geociencias; Dussin, Ivo A.; Kawashita, Koji [Universidade de Sao Paulo (USP), SP, (Brazil). Centro de Pesquisa Geocronologicas

2012-06-15

Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating prior to analyses using in situ Laser Ablation-Multi Collector Ion Coupled Plasma Mass Spectrometer (LA-ICPMS) followed by the Isotope Dissolution Thermal Ionization Mass Spectrometer (ID-TIMS) method. The proposed methodology was herein applied in order to reduce primarily the effects of secondary Pb loss, the presence of common lead and/or silicate impurities. Nine Temora II zircon grains were analyzed by the laser ablation method yielding an age of 418.3 +- 4.3 Ma. Zircon grains of a same population were separated for chemical abrasion before dissolution and mass spectrometry analyses. Six fractions of them were separated for isotope dissolution using {sup 235}U-{sup 205}Pb mixed spike after we have checked and assured the laboratory conditions of low blank values for total Pb of less than 2 pg/g. The obtained U-Pb zircon age by the ID-TIMS method was 415.7 +- 1.8 Ma (error 0.43 %) based on four successful determinations. The results are consistent with the published ages for the Temora diorite (Temora I - 416.75 +- 1.3 Ma; Temora II - 416.78 +- 0.33 Ma) and established as 416 +- 0.33 Ma. The technique is thus recommended for high precision U-Pb zircon analyses (error < 1 %), mainly for high resolution stratigraphic studies of Phanerozoic sequences. (author)

Carburizing plasma in a low temperature austenitic stainless steel AISI 304

International Nuclear Information System (INIS)

Mota, W.T.; Ramos, F.D.; Rocha, R.C.; Barcelos, M.V.; Barcelos, M.A.

2014-01-01

The industrial use of thermochemical treatment assisted by the cold plasma has been widely employed in recent years, mainly oriented to the excellent results obtained in the surface modification of engineering materials, when compared to more traditional methods. In this work, we studied the plasma carburizing low temperature steel AISI 304 mechanical parts used in construction. The thermochemical treatment was performed at a fixed gas atmosphere 7% CH 4 (g) and 93 % H 2 (g), 350 ° C and times of 1, 3 and 5 hours. Samples being tested for Vickers hardness, abrasive microwear, microstructure evaluation by optical microscopy and SEM and X-ray diffraction. The results show significant improvement in surface hardness, wear resistance and good formation of expanded austenite layer and no identifiers peaks of carbides. The results achieved are due to diffusion/adsorption of carbon present in the gaseous atmosphere to the evaluated samples. (author)

Possibility of surface carburization of refractory metals of electric spark alloying

International Nuclear Information System (INIS)

Verkhoturov, A.D.; Isaeva, L.P.; Timofeeva, I.I.; Tsyban', V.A.

1981-01-01

The paper is concerned with a study in the alloying layer formation under electric spark alloying of refractory (Ti, Zr, Nb, Mo, W, Co, Fe) metals with graphite in argon and in air using the EhFI-46A installation. It is shown that in electric spark alloying with graphite there appear certain specific conditions for the alloying layer formation manifested in the cathode mass decrease during treatment. In this case an alloying layer consisting of carbides, oxides of the corresponding metals and material of the base is formed on the metal surface. The best carburization conditions in the process of electric spark alloying are realized for group 4 metals when treating them in ''soft'' regime, specific time of alloying being 1-3 min/sm 2 and for group 5 and 6 metals - in ''rigid'' regime of treatment and specific time of alloying 3-5 min/cm 2 [ru

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Science.gov (United States)

Kunz, Barbara E.; Regis, Daniele; Engi, Martin

2018-03-01

Granulite facies rocks frequently show a large spread in their zircon ages, the interpretation of which raises questions: Has the isotopic system been disturbed? By what process(es) and conditions did the alteration occur? Can the dates be regarded as real ages, reflecting several growth episodes? Furthermore, under some circumstances of (ultra-)high-temperature metamorphism, decoupling of zircon U-Pb dates from their trace element geochemistry has been reported. Understanding these processes is crucial to help interpret such dates in the context of the P-T history. Our study presents evidence for decoupling in zircon from the highest grade metapelites (> 850 °C) taken along a continuous high-temperature metamorphic field gradient in the Ivrea Zone (NW Italy). These rocks represent a well-characterised segment of Permian lower continental crust with a protracted high-temperature history. Cathodoluminescence images reveal that zircons in the mid-amphibolite facies preserve mainly detrital cores with narrow overgrowths. In the upper amphibolite and granulite facies, preserved detrital cores decrease and metamorphic zircon increases in quantity. Across all samples we document a sequence of four rim generations based on textures. U-Pb dates, Th/U ratios and Ti-in-zircon concentrations show an essentially continuous evolution with increasing metamorphic grade, except in the samples from the granulite facies, which display significant scatter in age and chemistry. We associate the observed decoupling of zircon systematics in high-grade non-metamict zircon with disturbance processes related to differences in behaviour of non-formula elements (i.e. Pb, Th, U, Ti) at high-temperature conditions, notably differences in compatibility within the crystal structure.

Pengaruh Temperatur, Waktu, dan Aditif Dalam Pembuatan Zircon Micronized

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Sajima

2017-05-01

Full Text Available Research on temperature, time and additives effects on milling process in micronized-zircon production has been conducted. The production of zircon micronized started from sorting process on mining products then followed by beneficiation, roasting, leaching, dryng and milling processes. The results showed that the optimum conditions of the roasting process was at the temperature of 425 °C, in 25 minutes and using 4% additives. In these conditions, micronized zircon (2 µm obtained as much as 92.10% in10 minutes milling time.

PALEOTECTONIC AND PALEOGEOGRAPHIC CONDITIONS FOR THE ACCUMULATION OF THE LOWER RIPHEAN AI FORMATION IN THE BASHKIR UPLIFT (SOUTHERN URALS: THE TERRANECHRONE® DETRITAL ZIRCON STUDY

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T. V. Romanyuk

2018-01-01

Full Text Available The TerraneChrone® (LA-ICP-MS technique has been applied to carry out an integrated study of detrital zircons in sandstones sampled from the basal horizons of the stratotypical Riphean sequence in the Southern Urals, specifically the Navysh and Chudin suites of the Ai Formation of the Burzyan Group in the Bashkir Uplift. The concentrations of trace elements in the detrital zircons suggest that the role of oceanic or marginal-marine complexes among the primary sources of zircons was insignificant, and show a better agreement with the intra-continental rather than passive-margin origin of the Riphean basin, whose basal levels are composed by the Ai Formation. The U/Pb ages of zircons from samples K13-206 and M08-16-1 are generally similar: the Paleoproterozoic zircons predominate (the dominant peaks are actually coincident, 2063 and 2055 Ma, and only a few grains of the Archean age are present. Despite the similar U/Pb ages of the detrital zircons, these two samples considerably differ in their Hf isotopic features and the concentrations of trace elements, which means that the zircons in the studied sandstones are of different geodynamic origin. The characteristics of these zircons can be explained by a model showing the Ai Formation in the Navysh graben that is a rift structure and a predecessor of the Kama-Belaya aulacogene in the inner Volga-Ural region of the Paleoproterozoic supercontinent Columbia. At the initial stage of rifting, the granitoid complexes with a lower total silicic acidity, which composed the graben walls, had been eroded; as a result of erosion, coarse clastic rocks accumulated within the Navysh graben and formed the Navysh suite. A specific “carbonatitic” complex containing zircons (about 2.0, 2.5, 2.85 and 3.6 Ga and the Palaeoarchean crustal material in the substrate of their parent rocks was also eroded. In the final stage of rifting, already at the initial stages of the development of the Kama-Belaya aulacogen

The Influence of Calcium Carbonate Composition and Activated Carbon in Pack Carburizing Low Carbon Steel Process in The Review of Hardness and Micro Structure

Science.gov (United States)

Hafni; Hadi, Syafrul; Edison

2017-12-01

Carburizing is a way of hardening the surface by heating the metal (steel) above the critical temperature in an environment containing carbon. Steel at a temperature of the critical temperature of affinity to carbon. Carbon is absorbed into the metal form a solid solution of carbon-iron and the outer layer has high carbon content. When the composition of the activator and the activated charcoal is right, it will perfect the carbon atoms to diffuse into the test material to low carbon steels. Thick layer of carbon Depending on the time and temperature are used. Pack carburizing process in this study, using 1 kg of solid carbon derived from coconut shell charcoal with a variation of 20%, 10% and 5% calcium carbonate activator, burner temperature of 950 0C, holding time 4 hours. The test material is low carbon steel has 9 pieces. Each composition has three specimens. Furnace used in this study is a pack carburizing furnace which has a designed burner box with a volume of 1000 x 600 x 400 (mm3) of coal-fired. Equipped with a circulation of oxygen from the blower 2 inches and has a wall of refractory bricks. From the variation of composition CaCO3, microstructure formed on the specimen with 20% CaCO3, better diffusion of carbon into the carbon steel, it is seen by the form marten site structure after quenching, and this indicates that there has been an increase of or adding carbon to in the specimen. This led to the formation of marten site specimen into hard surfaces, where the average value of hardness at one point side (side edge) 31.7 HRC

U-Th-Pb systematics in zircon and titanite

International Nuclear Information System (INIS)

Zartman, R.E.; Kwak, L.M.

1990-01-01

U-Th-Pb isotopic analyses of zircon and titanite were made for two core samples of granite from borehole ATK-1 drilled into the Eye-Dashwa Lakes pluton. One of the samples from near the bottom of the hole (990.97 to 996.78 m) yielded zircon and titanite that were slightly to severely disturbed isotopically. Eight fractions of zircon give an upper concordia intercept age of 2625 ± 16 Ma (MSWD = 34), which, based on an evaluation of the more concordant data points and on other geochronological results, is interpreted as being slightly too young. The time of crystallization is probably better approximated by the 207 Pb/ 206 Pb age of 2665 Ma determined on a slightly (∼8 percent) discordant titanite. The other sample from near the surface (3.85 to 9.61 m) generally revealed even more severely disturbed isotopic systematics for both zircon and titanite. The complex nature of the disturbances probably resulted from the penetration of meteoritic water into rock already modified by post-crystallization hydrothermal alteration. Nuclide migration occurred in both minerals -- during the Middle or Late Proterozoic for the zircon and during the modern weathering cycle for the titanite. Material balance calculations are used to demonstrate a recent relative gain of radiogenic Pb and/or loss of Th and U from the freshest-looking, least-altered titanite by exchange with altered, leucoxenite-bearing titanite

Green fuels, growth engines after petroleum; Les carburants verts, moteurs de la croissance apres le petrole

Energy Technology Data Exchange (ETDEWEB)

Mili, Dino

2010-09-15

The contribution of the new fuels to a greener environment is important and immediate. Thanks to clean novel technologies and to commercial plant projects in development, companies like Enerkem contribute to satisfy increasing global demand for clean energy. They stimulate local economies by creating jobs in an industry that offers real growth potential. Green fuels will gradually allow us to let go of non sustainable energy sources like oil to adopt a way of life based on sustainable development. They will also allow a shift towards a green economy. [French] La contribution des nouveaux carburants a un environnement plus vert est importante et immediate. Grace a des technologies propres novatrices et a des projets d'sines commerciales en developpement, des entreprises comme Enerkem contribuent a satisfaire a la demande mondiale croissante en energie propre. Elles stimulent les economies locales par la creation d'emplois dans une industrie qui offre un veritable potentiel de croissance. Les carburants verts permettront graduellement de nous affranchir des sources d'energie non renouvelables comme le petrole pour adopter un mode de vie base sur le developpement durable. Ils permettront aussi un virage vers une economie verte.

Zircon (Hf, O isotopes) as melt indicator: Melt infiltration and abundant new zircon growth within melt rich layers of granulite-facies lenses versus solid-state recrystallization in hosting amphibolite-facies gneisses (central Erzgebirge, Bohemian Massif)

Science.gov (United States)

Tichomirowa, Marion; Whitehouse, Martin; Gerdes, Axel; Schulz, Bernhard

2018-03-01

In the central Erzgebirge within the Bohemian Massif, lenses of high pressure and ultrahigh pressure felsic granulites occur within meta-sedimentary and meta-igneous amphibolite-facies felsic rocks. In the felsic granulite, melt rich parts and restite form alternating layers, and were identified by petrology and bulk rock geochemistry. Mineral assemblages representing the peak P-T conditions were best preserved in melanocratic restite layers. In contrast, in the melt rich leucocratic layers, garnet and related HP minerals as kyanite are almost completely resorbed. Both layers display differences in accessory minerals: melanosomes have frequent and large monazite and Fe-Ti-minerals but lack xenotime and apatite; leucosomes have abundant apatite and xenotime while monazite is rare. Here we present a detailed petrographic study of zircon grains (abundance, size, morphology, inclusions) in granulite-facies and amphibolite-facies felsic gneisses, along with their oxygen and hafnium isotope compositions. Our data complement earlier Usbnd Pb ages and trace element data (REE, Y, Hf, U) on zircons from the same rocks (Tichomirowa et al., 2005). Our results show that the degree of melting determines the behaviour of zircon in different layers of the granulites and associated amphibolite-facies rocks. In restite layers of the granulite lenses, small, inherited, and resorbed zircon grains are preserved and new zircon formation is very limited. In contrast, new zircons abundantly grew in the melt rich leucocratic layers. In these layers, the new zircons (Usbnd Pb age, trace elements, Hf, O isotopes) best preserve the information on peak metamorphic conditions due to intense corrosion of other metamorphic minerals. The new zircons often contain inherited cores. Compared to cores, the new zircons and rims show similar or slightly lower Hf isotope values, slightly higher Hf model ages, and decreased oxygen isotope ratios. The isotope compositions (Hf, O) of new zircons indicate

Analyses of quenching process during turn-off of plasma electrolytic carburizing on carbon steel

International Nuclear Information System (INIS)

Wu, Jie; Liu, Run; Xue, Wenbin; Wang, Bin; Jin, Xiaoyue; Du, Jiancheng

2014-01-01

Highlights: • Cooling rate of carburized steel at the end of PEC treatment is measured. • The quench hardening in the fast or slow turn-off mode hardly takes place. • Decrease of the surface roughness during slow turn-off process is found. • A slow turn-off mode is recommended to replace the conventional turn-off mode. - Abstract: Plasma electrolytic carburizing (PEC) under different turn-off modes was employed to fabricate a hardening layer on carbon steel in glycerol solution without stirring at 380 V for 3 min. The quenching process in fast turn-off mode or slow turn-off mode of power supply was discussed. The temperature in the interior of steel and electron temperature in plasma discharge envelope during the quenching process were evaluated. It was found that the cooling rates of PEC samples in both turn-off modes were below 20 °C/s, because the vapor film boiling around the steel sample reduced the cooling rate greatly in terms of Leidenfrost effect. Thus the quench hardening hardly took place, though the slow turn-off mode slightly decreased the surface roughness of PEC steel. At the end of PEC treatment, the fast turn-off mode used widely at present cannot enhance the surface hardness by quench hardening, and the slow turn-off mode was recommended in order to protect the electronic devices against a large current surge

The composition of zircon in Variscan granites from Northern Portugal

Directory of Open Access Journals (Sweden)

Martins, H. C.B.

2014-12-01

Full Text Available A group of slightly peraluminous Variscan plutons in Northern Portugal were selected from the study of zircon composition. The selected plutons are: the Vila Pouca de Aguiar and the Lavadores-Madalena plutons with I-type affinities and the Vieira do Minho pluton, an l-S transitional type. Zircon occurs as euhedral to subhedral crystals and exhibit finely concentric oscillatory magmatic zoning mainly related to variations of Hf, Y, U and Th concentrations. Most zircon crystals show the dominant “xenotime” substitution. The zircon crystals have Zr/Hf ratio in the range of 21 to 52, with no significant differences between the different granites. These values are in the same range of other peraluminous granites and are in accordance with a crustal signature of zircon. Moreover, the range of Zr/Hf values in zircon crystals overlaps with that of crustal sources and consequently to the potential protoliths proposed in the genesis of the Vieira do Minho and the Vila Pouca de Aguiar plutons, namely meta-igneous crustal sources at different levels. Although zircon from the Lavadores-Madalena pluton has a compositional range similar to the other plutons, an origin by hibridisation has been proposed. However, similar zircon chemistry between this pluton and Vila Pouca de Aguiar and Vieira do Minho plutons could also suggest a similar crustal source.Se han seleccionado tres plutones graniticos variscos en el norte de Portugal para el estudio de la composición del circón. Los plutones son: Vila Pouca de Aguiar y Lavadores-Madalena con afinidad de tipo-I y el plutón de Vieira do Minho de tipo transicional I-S. Los circones se presentan en cristales euhédricos a subhédricos y tienen zonados magmáticos, concéntricos oscilatorios finos ligados principalmente a variaciones de las concentraciones del Hf, Y, U y Th. La mayoría de los cristales de circón muestran la sustitución dominante “xenotima”. Los zircones tienen relaciones Zr/Hf que var

Two-stage model of development of heterogeneous uranium-lead systems in zircon

International Nuclear Information System (INIS)

Mel'nikov, N.N.; Zevchenkov, O.A.

1985-01-01

Behaviour of isotope systems of multiphase zircons at their two-stage distortion is considered. The results of calculations testify to the fact that linear correlations on the diagram with concordance can be explained including two-stage discovery of U-Pb systems of cogenetic zircons if zircon is considered physically heterogeneous and losing in its different part different ratios of accumulated radiogenic lead. ''Metamorphism ages'' obtained by these two-stage opening zircons are intermediate, and they not have geochronological significance while ''crystallization ages'' remain rather close to real ones. Two-stage opening zircons in some cases can be diagnosed by discordance of their crystal component

Uranium and Thorium in zircon sands processed in Northeastern Brazil

International Nuclear Information System (INIS)

Hazin, Clovis A.; Farias, Emerson E. G. de

2008-01-01

Zircon the main mineral of zirconium is a silicate mineral product (ZrSiO 4 ) obtained from beach sand deposits, along with other minerals such as kyanite, ilmenite, and rutile. All zircons contain some radioactive impurities due to the presence of uranium, thorium and their respective decay products in the crystalline structure of zircon, as well as potassium-40. Uranium and thorium substitute Zr 4+ in the mineral through an internal process called isomorphous replacement of zirconium. For this study, samples were collected both from a mineral sand processing plant located in the coastal region of Northeastern brazil and from the beach sands used in the process. The aim of this study was to assess the 238 U, 232 Th and 40 K contents in the beach sands and in the mineral products extracted from the sands in that facility, with special emphasis on zircon. Measurements were performed through gamma spectrometry, by using a high-purity germanium detector (HPGe) coupled to a multichannel analyzer. Activity concentration for 238 U and 232 Th in zircon sands ranged from 5462±143 to 19286±46 Bq kg -1 and from 1016±7 to 7162±38 Bq kg -1 , respectively. For 40 K, on the other hand, activity concentration values ranged from 81±14 to 681±26 Bq Kg -1 . The results of the measurements carried out for raw sand samples showed activity concentrations between 2.7±0.6 and 7.9±0.9 Bq kg -1 and 6.5±0.4 and 9.4±0.6 Bq kg -1 for 238 U and 23T h respectively, and from 48.8±3.1 to 76.1±2.4 Bq kg -1 for 40 K. Activity concentrations of 238 U and 232 Th in kyanite, ilmenite and rutile samples were also determined. (author)

Detrital zircon study along the Tsangpo River, SE Tibet

Science.gov (United States)

Liang, Y.; Chung, S.; Liu, D.; O'Reilly, S. Y.; Chu, M.; Ji, J.; Song, B.; Pearson, N. J.

2004-12-01

The interactions among tectonic uplift, river erosion and alluvial deposition are fundamental processes that shape the landscape of the Himalayan-Tibetan orogen since its creation from early Cenozoic time. To better understand these processes around the eastern Himalayan Syntaxis, we conducted a study by systematic sampling riverbank sediments along the Tsangpo River, SE Tibet. Detrital zircons separated from the sediments were subjected to U-Pb dating by the SHRIMP II at the Beijing SHRIMP Center and then in-situ measurements of Hf isotope ratios using LA-MC-ICPMS at GEMOC. These results, together with U-Pb ages and Hf isotope data that we recently obtained for the Transhimalayan plutonic and surrounding basement rocks, allow a more quantitative examination of the provenance or protosource areas for the river sediments. Consequently, the percentage inputs from these source areas can be estimated. Our study indicates that, before the Tsangpo River flows into the Namche Barwa Syntaxis of the eastern Himalayas where the River forms a 180° Big Bend gorge and crosscuts the Himalayan sequences, the Gangdese batholith that crops out just north of the River appear to be an overwhelming source accounting for ˜50 % of the bank sediments. The Tethyan Himalayan sequences south of the River are the second important source, with an input of ˜25 %. The proportion of sediment supply changes after the River enters the Big Bend gorge and turns to south: ˜25 % of detrital zircons are derived from the Greater Himalayas so that the input from the Tethyan Himalayas decreases (< 10 %) despite those from the Gangdese batholith remains high ( ˜40 %). Comparing with the sediment budget of the Brahmaputra River in the downstream based on literature Sr, Nd and Os isotope information, which suggests dominant ( ˜90-60 %) but subordinate ( ˜10-40 %) contributions by the (Greater and Lesser) Himalayan and Tibetan (including Tethyan Himalayan) rocks, respectively, the change is interpreted

Electronic specific heat of transition metal carbides; Chaleur specifique electronique de carbures de metaux de transition

Energy Technology Data Exchange (ETDEWEB)

Conte, R [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

1964-07-15

The experimental results that make it possible to define the band structure of transition metal carbides having an NaCI structure are still very few. We have measured the electronic specific heat of some of these carbides of varying electronic concentration (TiC, either stoichiometric or non-stoichiometric, TaC and mixed (Ti, Ta) - C). We give the main characteristics (metallography, resistivity, X-rays) of our samples and we describe the low temperature specific heat apparatus which has been built. In one of these we use helium as the exchange gas. The other is set up with a mechanical contact. The two use a germanium probe for thermometer. The measurement of the temperature using this probe is described, as well as the various measurement devices. The results are presented in the form of a rigid band model and show that the density of the states at the Fermi level has a minimum in the neighbourhood of the group IV carbides. (author) [French] Les donnees experimentales permettant de preciser la structure de bandes des carbures de metaux de transition de structure NaCI sont encore peu.nombreuses. Nous avons mesure la chaleur specifique electronique de certains de ces carbures, de differentes concentrations electroniques (TiC stoechiometrique ou non, TaC et mixtes (Ti, Ta) - C). Nous donnons les principales caracteristiques (metallographie, resistivite, rayon X), de nos echantillons, et nous decrivons l'appareillage de chaleur specifique a basse temperature realise. Dans l'un nous utilisons l'helium comme gaz d'echange. L'autre est monte avec un contact mecanique. Les deux utilisent une sonde au germanium comme thermometre. La mesure de la resistance de cette sonde est decrite, ainsi que les differents montages de mesure. Les resultats, presentes dans un modele de bande rigide, font apparaitre que la densite des etats au niveau de Fermi presente un minimum au voisinage des carbures du groupe IV. (auteur)

Theoretical modeling of zircon's crystal morphology according to data of atomistic calculations

Science.gov (United States)

Gromalova, Natalia; Nikishaeva, Nadezhda; Eremin, Nikolay

2017-04-01

Zircon is an essential mineral that is used in the U-Pb dating. Moreover, zircon is highly resistant to radioactive exposure. It is of great interest in solving both fundamental and applied problems associated with the isolation of high-level radioactive waste. There is significant progress in forecasting of the most energetically favorable crystal structures at the present time. Unfortunately, the theoretical forecast of crystal morphology at high technological level is under-explored nowadays, though the estimation of crystal equilibrium habit is extremely important in studying the physical and chemical properties of new materials. For the first time, the thesis about relation of the equilibrium shape of a crystal with its crystal structure was put forward in the works by O.Brave. According to it, the idealized habit is determined in the simplest case by a correspondence with the reticular densities Rhkl of individual faces. This approach, along with all subsequent corrections, does not take into account the nature of atoms and the specific features of the chemical bond in crystals. The atomistic calculations of crystal surfaces are commonly performed using the energetic characteristics of faces, namely, the surface energy (Esurf), which is a measure of the thermodynamic stability of the crystal face. The stable crystal faces are characterized by small positive values of Esurf. As we know from our previous research (Gromalova et al.,2015) one of the constitutive factors affecting the value of the surface energy in calculations is a choice of potentials model. In this regard, we studied several sets of parameters of atomistic interatomic potentials optimized previously. As the first test model («Zircon 1») were used sets of interatomic potentials of interaction Zr-O, Si-O and O-O in the form of Buckingham potentials. To improve playback properties of zircon additionally used Morse potential for a couple of Zr-Si, as well as the three-particle angular harmonic

Ancient xenocrystic zircon in young volcanic rocks of the southern Lesser Antilles island arc

Science.gov (United States)

Rojas-Agramonte, Yamirka; Williams, Ian S.; Arculus, Richard; Kröner, Alfred; García-Casco, Antonio; Lázaro, Concepción; Buhre, Stephan; Wong, Jean; Geng, Helen; Echeverría, Carlos Morales; Jeffries, Teresa; Xie, Hangqian; Mertz-Kraus, Regina

2017-10-01

The Lesser Antilles arc is one of the best global examples in which to examine the effects of the involvement of subducted sediment and crustal assimilation in the generation of arc crust. Most of the zircon recovered in our study of igneous and volcaniclastic rocks from Grenada and Carriacou (part of the Grenadines chain) is younger than 2 Ma. Within some late Paleogene to Neogene ( 34-0.2 Ma) lavas and volcaniclastic sediments however, there are Paleozoic to Paleoarchean ( 250-3469 Ma) xenocrysts, and Late Jurassic to Precambrian zircon ( 158-2667 Ma) are found in beach and river sands. The trace element characteristics of zircon clearly differentiate between different types of magmas generated in the southern Lesser Antilles through time. The zircon population from the younger arc (Miocene, 22-19 Ma, to Present) has minor negative Eu anomalies, well-defined positive Ce anomalies, and a marked enrichment in heavy rare earth elements (HREE), consistent with crystallization from very oxidized magmas in which Eu2 + was in low abundance. In contrast, zircon from the older arc (Eocene to mid-Oligocene, 30-28 Ma) has two different REE patterns: 1) slight enrichment in the light (L)REE, small to absent Ce anomalies, and negative Eu anomalies and 2) enriched High (H)REE, positive Ce anomalies and negative Eu anomalies (a similar pattern is observed in the xenocrystic zircon population). The combination of positive Ce and negative Eu anomalies in the zircon population of the older arc indicates crystallization from magmas that were variably, but considerably less oxidized than those of the younger arc. All the igneous zircon has positive εHf(t), reflecting derivation from a predominantly juvenile mantle source. However, the εHf(t) values vary significantly within samples, reflecting considerable Hf isotopic heterogeneity in the source. The presence of xenocrystic zircon in the southern Lesser Antilles is evidence for the assimilation of intra-arc crustal sediments and

Improvement of conditions for ceramics sintering on the base of lead zirconate-titanate

International Nuclear Information System (INIS)

Glinchuk, M.D.; Kim, P.V.; Bykov, I.P.; Lyashchenko, A.B.

1989-01-01

Lead zirconate-titanate powders of different graininess are studied for their phase composition. The finest grains of the powder consist of lead zirconate-titanate with the rhombohedral structure. Grains of 3-5 μm size are a mixture of lead zirconate-titanate and lead titanate, the latter exceeding 50% (by weight) causes the effect of anomalous expansion in the process of sintering. Control of the technological parameters of the synthesis permits producing powder with favourable correlation of the above phases and grain sizes. Sintering of such a powder induces no effect of the anomalous expansion with an increased density of the product attained

On the connection of the ESR characteristics of zircons with the degree of their defectiveness

International Nuclear Information System (INIS)

Matyash, I.V.; Brik, A.E.; Derski, L.S.; Larikov, A.L.; Ponomarenko, A.N.

1989-01-01

The dynamic characteristics of the electron-hole centres (EHC) in zircons with various degree of defectiveness have been studied. Crystalline and amorphous regions are typical of different sets of EHC, having essentially different relaxation characteristics. Lack of cross-relaxation between these centres shows that they are localized in different parts of the crystal. The influence of autoirradiation and of corresponding defectiveness of the matrix upon the intensity of the EHC signals (V i ) has been studied. In the specimens of high crystallinity V i increases as the content of radioactive elements and defectiveness increases. In the essentially metamict specimens the situation reverses. Interpretation of this effect is given considering the dose dependence of the ESR signals and the ratio of the crystal and metamict volumes in the studied object. The transformations of the EHC set is traced along the amorphization of the zircon matrix due to the autoirradiation. ESR signals corresponding to different phases in zircon have been recorded. The correlation of the zircon grain size and the static magnetic susceptibility with V i have been studied. In the specimens of high crystallinity such correlation is absent and in metamict specimens the intensities V i decrease as the grain sizes decrease. The interpretation of this fact is proposed. It has been shown that the ESR studies reflect the processes of income and migration of the impurity elements in zircons and the ways of the zircon crystal matrix decay in a geological time scale. The factors controlling such a decay have been found. (author)

Study in determining optimum conditions for reducing NORM in Malaysian zircon mineral

International Nuclear Information System (INIS)

Meor Yusoff Meor Sulaiman

2002-01-01

Malaysian zircon contains higher level of NORM especially uranium and thorium than the permissible level set by many importing countries. These elements are present mainly on the mineral surface as well as in its crystal lattice. A study was conducted using selective leaching to reduce NORM content in the mineral. Various parameters such as temperature, time, concentration of leachants, particle size and heat treatment affect the rate of leaching. Optimum conditions for these parameters were determined in order for maximum reduction will be obtained. (Author)

Zircon evidence for incorporation of terrigenous sediments into the magma source of continental basalts.

Science.gov (United States)

Xu, Zheng; Zheng, Yong-Fei; Zhao, Zi-Fu

2018-01-09

Crustal components may be incorporated into continental basalts by either shallow contamination or deep mixing. While the former proceeds at crustal depths with common preservation of refractory minerals, the latter occurs at mantle depths with rare survival of relict minerals. Discrimination between the two mechanisms has great bearing to subcontinental mantle geochemistry. Here we report the occurrence of relict zircons in Cenozoic continental basalts from eastern China. A combined study of zircon U-Pb ages and geochemistry indicates that detrital zircons were carried by terrigenous sediments into a subcontinental subduction zone, where the zircon were transferred by fluids into the magma sources of continental basalts. The basalts were sampled from three petrotectonic units with distinct differences in their magmatic and metamorphic ages, making the crustal contamination discernible. The terrigenous sediments were carried by the subducting oceanic crust into the asthenospheric mantle, producing both soluble and insoluble materials at the slab-mantle interface. These materials were served as metasomatic agents to react with the overlying mantle wedge peridotite, generating a kind of ultramafic metasomatites that contain the relict zircons. Therefore, the occurrence of relict zircons in continental basalts indicates that this refractory mineral can survive extreme temperature-pressure conditions in the asthenospheric mantle.

In situ detrital zircon (U-Th)/He thermochronology

Science.gov (United States)

Tripathy, A.; Monteleone, B. D.; van Soest, M. C.; Hodges, K.; Hourigan, J. K.

2010-12-01

Detrital studies of both sand and rock are relevant to many problems, ranging from the climate and tectonics feedback debate to the long-term record of orogenic evolution. When applying the conventional (U-Th)/He technique to such studies, two important issues arise. Often, only euhedral grains are permissible for analysis in order to make simple geometric corrections for α-recoil. In detrital samples, this is problematic because euhedral grains can be scarce due to mechanical abrasion during transport, and potentially introduce bias in favour of more proximally sourced grains. Second, inherent to detrital studies is the need to date many grains (>100) per sample to ensure a representative sampling of the sediment source region, thus making robust conventional detrital studies both expensive and time-consuming. UV laser microprobes can improve this by permitting careful targeting of the grain interior away from the α-ejection zone, rendering the α-recoil correction unnecessary, thus eliminating bias toward euhedral grains. In the Noble Gas, Geochemistry, and Geochronology Laboratory at ASU, apatite and zircon have been successfully dated using in situ methods. For this study, the conventional and in situ techniques are compared by dating zircons from a modern river sand that drains a small catchment in the Mesozoic-Cenozoic Ladakh Batholith in NW India. This sample has a simple provenance, which allows us to demonstrate the robustness of the in situ method. Moreover, different microbeam techniques will be explored to establish the most efficient approach to obtain accurate and precise U-Th concentrations using synrock, which is our powdered, homogenized, and reconstituted zircon-rock standard. Without this, such in situ U-Th data would be difficult to obtain. 117 zircons were dated using the conventional (U-Th)/He method, revealing dates ranging from 9.70±0.35 to 106.6±3.5 Ma (2σ) with the major mode at 26 Ma. For comparison, 44 grains were dated using the in

Radioactivity in the zircon industry

International Nuclear Information System (INIS)

Selby, J.H.

2002-01-01

In a presentation from the Zircon Industry, it was shown that zircon sand contains significant concentrations of uranium, 3,500 to 4,500 Bq/kg, and thorium, 400 to 600 Bq/kg. Deposits mainly occur in South Africa, Australia, India and the USA. The mining is done by dredging or by just shoveling the sand onto trucks. The separation could be done by dry or wet concentration. Also the milling could be by dry or wet processes. The dry process has the highest risk of dust generation. The maximum potential annual dose for the milling process has been assessed to be about 5mSv. Measurements from South Africa and Australia indicate lower doses, 0.2 to 1 mSv/y

Zircon and ilmenite from the beach placers of southern coast of Tamil Nadu, east coast of India

International Nuclear Information System (INIS)

Angusamy, N.; Rajamanickam, G.V.; Loveson, V.J.

2004-01-01

Zircons were studied from the two different zones of enrichment of placer deposits namely, Kanyakumari-Kuttankuli (KK) and Kallar-Vaippar (VP) along the southern coast of Tamil Nadu. The average heavy mineral contents were 67 wt % for KK and 64 wt % in VP region. The heavy mineral assemblage of the two zones were akin to each other. However, monazite was present in the KK region. In KK, zircons were rounded (44.5 - 63.2 %), overgrown (4.1-16 %), and euhedral (9-4.9 %) while in VP, they are largely broken (47.8-59.6 %), rounded (22.2-38.9 %), and euhedral (7.3-8.1 %). Mean length and breadth of zircons of KK and VP ranged from 0.22-0.26 mm and 0.07-0.13 mm and, 0.06 - 0.16 mm and 0.07-0.11 mm, respectively. Zircons of VP are more fine-grained and well-rounded than KK. The northerly currents, in the Gulf of Mannar, must have transported and deposited the heavy minerals due to the inflection of coastline, and downwarped basinal structure. REE pattern of zircons exhibit Eu and Ce anomalies which could be explained only in terms of crystallochemical factors and the bulk compositional differences of the melt. In the study area, abundance of rounded zircons, length/breadth (L/B) ratios, reduced major axis (RMA) angles, indicated that the source rock for zircons must have been primarily of charnockites. The distribution, composition and REE content of zircons compare well with that of other countries where it is currently under exploitation. (author)

The Origin of the Chinese Central Tianshan Block in the Southern Central Asian Orogenic Belt: Evidence from Detrital Zircon Study

Science.gov (United States)

Huang, Z.; Long, X.; Yuan, C.

2016-12-01

The Chinese Central Tianshan Block (CTB) is one of the oldest continental fragments in the southern Central Asian Orogenic Belt (CAOB). Although it is vital for understanding the evolution of the CAOB, its origin has been poorly studied. The CTB was previously suggested to have been originated from the North China, the South China, the Tarim cratons or the East European Craton (Baltica). A total of 165 concordant U-Pb and Hf isotopic analyses of detrital zircon are obtained from three meta-sediments in the CTB, including one meta-sandstone from Xingxingxia formation and one meta-sandstone as well as one quartzite from Kawabulake formation. Detrital zircon grains from the Xingxingxia and Kawabulake formations are dominated by respective youngest age populations at 1002 Ma and 930-960 Ma, providing constraints on the maximum depositional ages for these two formations. Zircon grains from the meta-sediments have very similar age distributions, with two dominant peaks at 0.93-1.0 Ga and 1.0-1.6 Ga and a minor peak at 2.3-2.7 Ga. They have similar Hf isotopic signatures, suggesting that the meta-sediments in the CTB share similar sedimentary provenance. The early Neoproterozoic detrital zircon grains are mainly local-derived, whereas the Paleo-Mesoproterozoic grains are both autochthonous and allochthonous. The occurrence of these Mesoproterozoic and Neoproterozoic zircon grains are coincident with the Nuna breakup and the Rodinia assembly. This suggests that the CTB might experience the tectonic switching of the Nuna to the Rodinia. The distinct Meso-Neoproterozoic age patterns and Hf isotopic compositions of these detrital grains from the CTB and the surrounding blocks indicate that the CTB was not located close to the North China, the South China or the Tarim cratons in Precambrian. Our new data suggest that the CTB was most likely once a part of the East European Craton before the Neoproterozoic. This study was supported by National Basic Research Program of China

Reaction of strontium zirconate with refractory borides and carbides

International Nuclear Information System (INIS)

Bowker, J.C.; Lane, J.E.

1990-01-01

The chemical compatibility of the potential oxide ceramic matrix material, strontium zirconate, and several different potential nonoxide ceramic reinforcement materials was studied by elevated temperature reaction. Results are presented in this paper

Interpretation of zircon coronae textures from metapelitic granulites of the Ivrea–Verbano Zone, northern Italy: two-stage decomposition of Fe–Ti oxides

Directory of Open Access Journals (Sweden)

E. Kovaleva

2017-07-01

Full Text Available In this study, we report the occurrence of zircon coronae textures in metapelitic granulites of the Ivrea–Verbano Zone. Unusual zircon textures are spatially associated with Fe–Ti oxides and occur as (1 vermicular-shaped aggregates 50–200 µm long and 5–20 µm thick and as (2 zircon coronae and fine-grained chains, hundreds of micrometers long and ≤ 1 µm thick, spatially associated with the larger zircon grains. Formation of such textures is a result of zircon precipitation during cooling after peak metamorphic conditions, which involved: (1 decomposition of Zr-rich ilmenite to Zr-bearing rutile, and formation of the vermicular-shaped zircon during retrograde metamorphism and hydration; and (2 recrystallization of Zr-bearing rutile to Zr-depleted rutile intergrown with quartz, and precipitation of the submicron-thick zircon coronae during further exhumation and cooling. We also observed hat-shaped grains that are composed of preexisting zircon overgrown by zircon coronae during stage (2. Formation of vermicular zircon (1 preceded ductile and brittle deformation of the host rock, as vermicular zircon is found both plastically and cataclastically deformed. Formation of thin zircon coronae (2 was coeval with, or immediately after, brittle deformation as coronae are found to fill fractures in the host rock. The latter is evidence of local, fluid-aided mobility of Zr. This study demonstrates that metamorphic zircon can nucleate and grow as a result of hydration reactions and mineral breakdown during cooling after granulite-facies metamorphism. Zircon coronae textures indicate metamorphic reactions in the host rock and establish the direction of the reaction front.

Analyze of viability of ZrSiO_4-Fe_2O_3 pigments synthesis, from decomposition of the zircon

International Nuclear Information System (INIS)

Prim, S.R.; Folgueiras, M.V.; Winter, D.M.

2011-01-01

Zircon pigments are commonly used in ceramic industry due to their high chemical and thermal stability. In the present work, the viability of synthesis of a zircon ceramic pigment from intermediate products obtained from decomposition zircon sand with NaOH and/or KOH at 750 and 850 °C was studied. The intermediate products were used as raw materials to produce pigments. Iron oxide from rolling process of sheet metal was used as chromophore. The crystalline phases formed were characterized by X-ray diffraction. The results have shown that it was possible to obtain the partial decomposition of zircon which enables the development of the synthesis of zircon pigment. (author)

Wear and microstructural characteristics of spray atomized zircon sand reinforced LM13 alloy

Energy Technology Data Exchange (ETDEWEB)

Kaur, K.; Pandey, O.P. [School of Physics and Materials Science, Thapar University Patiala, Punjab (India)

2010-07-15

The requirement of the high performance light weight materials demands the development of varieties of materials within the economical range to get it commercialized. Light weight aluminium alloys are used in several structural applications like automotive, aerospace, defense industry and other fields of engineering. The ceramic particle reinforced aluminium metal matrix composites (AMCs) have emerged as a suitable candidate for commercial applications. A variety of processing routes have been adopted to manufacture AMCs. In the present work LM13 alloy reinforced with zircon sand is formed via spray forming. During experimentation a self prepared convergent-divergent nozzle is used for inert gas atomization of the melt which is subsequently deposited on copper substrate placed vertically below the atomizer. The zircon sand particles are injected in the atomization zone by external injectors aligned perpendicular to the gas atomization axis. Zircon sand has been found to have new promising economical commercial candidate due to its easy availability and good mechanical properties like high hardness, high modulus of elasticity and good thermal stability. The microhardness of cast alloy and spray formed composite shows that the spray formed zircon sand reinforced composite has higher hardness. Also the lower wear rate has been observed in case of the zircon sand reinforced AMC as compared to LM13 alloy. This behaviour is further analyzed in light of microstructural features of the spray deposited composite using optical and scanning electron microscope (SEM). A comparative study of this material (LM13/Zircon sand) with the parent alloy (LM13) is presented in this work. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Extrapolation of zircon fission-track annealing models

International Nuclear Information System (INIS)

Palissari, R.; Guedes, S.; Curvo, E.A.C.; Moreira, P.A.F.P.; Tello, C.A.; Hadler, J.C.

2013-01-01

One of the purposes of this study is to give further constraints on the temperature range of the zircon partial annealing zone over a geological time scale using data from borehole zircon samples, which have experienced stable temperatures for ∼1 Ma. In this way, the extrapolation problem is explicitly addressed by fitting the zircon annealing models with geological timescale data. Several empirical model formulations have been proposed to perform these calibrations and have been compared in this work. The basic form proposed for annealing models is the Arrhenius-type model. There are other annealing models, that are based on the same general formulation. These empirical model equations have been preferred due to the great number of phenomena from track formation to chemical etching that are not well understood. However, there are two other models, which try to establish a direct correlation between their parameters and the related phenomena. To compare the response of the different annealing models, thermal indexes, such as closure temperature, total annealing temperature and the partial annealing zone, have been calculated and compared with field evidence. After comparing the different models, it was concluded that the fanning curvilinear models yield the best agreement between predicted index temperatures and field evidence. - Highlights: ► Geological data were used along with lab data for improving model extrapolation. ► Index temperatures were simulated for testing model extrapolation. ► Curvilinear Arrhenius models produced better geological temperature predictions

Chemical abrasion-SIMS (CA-SIMS) U-Pb dating of zircon from the late Eocene Caetano caldera, Nevada

Science.gov (United States)

Watts, Kathryn E.; Coble, Matthew A.; Vazquez, Jorge A.; Henry, Christopher D.; Colgan, Joseph P.; John, David A.

2016-01-01

Zircon geochronology is a critical tool for establishing geologic ages and time scales of processes in the Earth's crust. However, for zircons compromised by open system behavior, achieving robust dates can be difficult. Chemical abrasion (CA) is a routine step prior to thermal ionization mass spectrometry (TIMS) dating of zircon to remove radiation-damaged parts of grains that may have experienced open system behavior and loss of radiogenic Pb. While this technique has been shown to improve the accuracy and precision of TIMS dating, its application to high-spatial resolution dating methods, such as secondary ion mass spectrometry (SIMS), is relatively uncommon. In our efforts to U-Pb date zircons from the late Eocene Caetano caldera by SIMS (SHRIMP-RG: sensitive high resolution ion microprobe, reverse geometry), some grains yielded anomalously young U-Pb ages that implicated Pb-loss and motivated us to investigate with a comparative CA and non-CA dating study. We present CA and non-CA 206Pb/238U ages and trace elements determined by SHRIMP-RG for zircons from three Caetano samples (Caetano Tuff, Redrock Canyon porphyry, and a silicic ring-fracture intrusion) and for R33 and TEMORA-2 reference zircons. We find that non-CA Caetano zircons have weighted mean or bimodal U-Pb ages that are 2–4% younger than CA zircons for the same samples. CA Caetano zircons have mean U-Pb ages that are 0.4–0.6 Myr older than the 40Ar/39Ar sanidine eruption age (34.00 ± 0.03 Ma; error-weighted mean, 2σ), whereas non-CA zircons have ages that are 0.7–1.3 Myr younger. U-Pb ages do not correlate with U (~ 100–800 ppm), Th (~ 50–300 ppm) or any other measured zircon trace elements (Y, Hf, REE), and CA and non-CA Caetano zircons define identical trace element ranges. No statistically significant difference in U-Pb age is observed for CA versus non-CA R33 or TEMORA-2 zircons. Optical profiler measurements of ion microprobe pits demonstrate consistent depths of ~ 1.6�

Reaction of uranium and plutonium carbides with austenitic steels; Reaction des carbures d'uranium et de plutonium avec des aciers austenitiques

Energy Technology Data Exchange (ETDEWEB)

Mouchnino, M [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

1967-07-01

The reaction of uranium and plutonium carbides with austenitic steels has been studied between 650 and 1050 deg. C using UC, steel and (UPu)C, steel diffusion couples. The steels are of the type CN 18.10 with or without addition of molybdenum. The carbides used are hyper-stoichiometric. Tests were also carried out with UCTi, UCMo, UPuCTi and UPuCMo. Up to 800 deg. C no marked diffusion of carbon into stainless steel is observed. Between 800 and 900 deg. C the carbon produced by the decomposition of the higher carbides diffuses into the steel. Above 900 deg. C, decomposition of the monocarbide occurs according to a reaction which can be written schematically as: (U,PuC) + (Fe,Ni,Cr) {yields} (U,Pu) Fe{sub 2} + Cr{sub 23}C{sub 6}. Above 950 deg. C the behaviour of UPuCMo and that of the titanium (CN 18.12) and nickel (NC 38. 18) steels is observed to be very satisfactory. (author) [French] La reaction des carbures d'uranium et de plutonium avec des aciers austenitiques a ete etudiee entre 650 deg. C et 1050 deg. C a partir de couples de diffusion UC, acier et (UPu)C, acier. Les aciers sont du type CN 18.10 avec ou sans addition de molybdene. Les carbures utilises sont hyper-stoechiometriques. En outre on a fait des essais avec UCTi, UCMo, UPuCTi, UPuCMo. Jusqu'a 800 deg. C on ne detecte pas de diffusion sensible du carbone dans l'acier inoxydable. Entre 800 et 900 deg. C il y a diffusion dans l'acier du carbone provenant de la decomposition des carbures superieurs. A partir de 900 deg. C il y a decomposition du monocarbure selon une reaction que l'on ecrit schematiquement: (U,PuC) + (Fe, Ni, Cr) {yields} (U,Pu)Fe{sub 2} + Cr{sub 23}C{sub 6}. Nous notons a 950 deg. C le bon comportement de UPuCMo ainsi que celui des aciers au titane (CN 18. 12) et au nickel (NC 38.18). (auteur)

Late magmatic stage of the zoned Caleu pluton (Central Chile): insights from zircon crystallization conditions

Science.gov (United States)

Molina, P. G.; Parada, M.; Gutierrez, F. J.; Chang-Qiang, M.; Jianwei, L.; Yuanyuan, L.

2012-12-01

(IV)/Ce(III) decrease with temperature gives rise to separate trends for each zone, suggesting an independent unbuffered development at time of zircon formation. Taking into account variations in zircon ages, morphologies and crystallization ranges in the collected samples, it is suggested that zircon crystallization took place independent of the magma composition. Furthermore, old inherited zircon grains in the GDZ could be antecrysts, or products of a restricted and not major host rock assimilation, owing to the impossibility of basaltic magmas to saturate zircon crystals, and the isotopically depleted signature. This study is financed by CONICYT-FONDAP grant 15090013, Centro de Excelencia en Geotermia de los Andes (CEGA); and the CONICYT PBCT-PDA07, Programa Bicentenario de Ciencia y Tecnología.

Metallographical procedure for detecting carburized layer in the 12Kh18N10T steel tubes

International Nuclear Information System (INIS)

Najmark, S.I.; Shmalenyuk, R.P.

1977-01-01

The various causes of the tendency to intercrystalline corrosion of stainless steel tubing were studied. 12Kh18N10T steel tube specimens were metallographically investigated to reveal the presence and depth of the carburized layer. Unlubricated specimens and specimens with the graphite-saltpeter lubrication applied on them were austenized in the temperature range from 950 to 1250 deg C and then exposed to a provoking anneal at 650 deg C for 24 h. All the lubricated specimens showed a carbide network along grain boundaries and intercrystalline cracks. The specimens treated without lubrication had no cracks. The method offered can differentiate poor tube cleaning and the undesirable effect of other processing steps on the tubes

Development of CSS-42L{trademark}, a high performance carburizing stainless steel for high temperature aerospace applications

Energy Technology Data Exchange (ETDEWEB)

Burrier, H.I.; Milam, L. [Timken Co., Canton, OH (United States); Tomasello, C.M.; Balliett, S.A.; Maloney, J.L. [Latrobe Steel Co., Latrobe, PA (United States); Ogden, W.P. [MPB Corp., Lebanon, NH (United States)

1998-12-31

Today`s aerospace engineering challenges demand materials which can operate under conditions of temperature extremes, high loads and harsh, corrosive environments. This paper presents a technical overview of the on-going development of CSS-42L (US Patent No. 5,424,028). This alloy is a case-carburizable, stainless steel alloy suitable for use in applications up to 427 C, particularly suited to high performance rolling element bearings, gears, shafts and fasteners. The nominal chemistry of CSS-42L includes: (by weight) 0.12% carbon, 14.0% chromium, 0.60% vanadium, 2.0% nickel, 4.75% molybdenum and 12.5% cobalt. Careful balancing of these components combined with VIM-VAR melting produces an alloy that can be carburized and heat treated to achieve a high surface hardness (>58 HRC at 1mm (0.040 in) depth) with excellent corrosion resistance. The hot hardness of the carburized case is equal to or better than all competitive grades, exceeding 60 HRC at 427 C. The fracture toughness and impact resistance of the heat treated core material have likewise been evaluated in detail and found to be better than M50-NiL steel. The corrosion resistance has been shown to be equivalent to that of 440C steel in tests performed to date.

U-Pb Dating of Zircons and Phosphates in Lunar Meteorites, Acapulcoites and Angrites

Science.gov (United States)

Zhou, Q.; Zeigler, R. A.; Yin, Q. Z.; Korotev, R. L.; Joliff, B. L.; Amelin, Y.; Marti, K.; Wu, F. Y.; Li, X. H.; Li, Q. L.;

Detrital zircon ages from southern Norway - implications for the Proterozoic evolution of the southwestern Baltic Shield

Science.gov (United States)

Knudsen, T.-L.; Andersen, T.; Whitehouse, M. J.; Vestin, J.

An ion-microprobe (SIMS) U-Pb zircon dating study on four samples of Precambrian metasediments from the high-grade Bamble Sector, southern Norway, gives the first information on the timing of discrete crust-forming events in the SW part of the Baltic Shield. Recent Nd and Pb studies have indicated that the sources of the clastic metasediments in this area have crustal histories extending back to 1.7 to 2.1Ga, although there is no record of rocks older than 1.6Ga in southern Norway. The analysed metasediments are from a sequence of intercalated, centimetre to 10-metre wide units of quartzites, semi-metapelites, metapelites and mafic granulites. The zircons can be grouped in two morphological populations: (1) long prismatic; (2) rounded, often flattened. The BSE images reveal that both populations consist of oscillatory zoned, rounded and corroded cores (detrital grains of magmatic origin), surrounded by homogeneous rims (metamorphic overgrowths). The detrital zircons have 207Pb/206Pb ages between 1367 and 1939Ma, with frequency maxima in the range 1.85 to 1.70Ga and 1.60 to 1.50Ga. There is no correlation between crystal habit and age of the zircon. One resorbed, inner zircon core in a detrital grain is strongly discordant and gives a composite inner core-magmatic outer core 207Pb/206Pb age of 2383 Ma. Two discrete, unzoned zircons have 207Pb/206Pb ages of 1122 and 1133Ma, representing zircon growth during the Sveconorwegian high-grade metamorphism. Also the μm wide overgrowths, embayments in the detrital cores and apparent ``inner cores'' which represent secondary metamorphic zircon growth in deep embayments in detrital grains, are of Sveconorwegian age. The composite-detrital-metamorphic zircon analyses give generally discordant 206Pb/238U versus 207Pb/235U ratios and maximum 207Pb/206Pb ages of 1438Ma. These data demonstrate the existence of a protocrust of 1.7 to 2.0Ga in the southwestern part of the Baltic Shield, implying a break in the overall westward

Finding the "true" age: ways to read high-precision U-Pb zircon dates

Science.gov (United States)

Schaltegger, U.; Schoene, B.; Ovtcharova, M.; Sell, B. K.; Broderick, C. A.; Wotzlaw, J.

2011-12-01

Refined U-Pb dating techniques, applying an empirical chemical abrasion treatment prior to analysis [1], and using a precisely calibrated double isotope Pb, U EARTHTIME tracer solution, have led to an unprecedented two problems: (A) Post-crystallization Pb loss from decay damaged areas is considered to be mitigated by applying chemical abrasion techniques. The success of such treatment can, however, not be assumed a priori. The following examples demonstrate that youngest zircons are not biased by lead loss but represent close-to-youngest zircon growth: (i) coincidence of youngest zircon dates with co-magmatic titanite in tonalite; (ii) coincidence with statistically equivalent clusters of 206Pb/238U dates from zircon in residual melts of cogenetic mafic magmas; (iii) youngest zircons in ash beds of sedimentary sequences do not violate the stratigraphic superposition, whereas conventional statistical interpretation (mean or median values) does; (iv) results of published inter-laboratory cross-calibration tests using chemical abrasion on natural zircon crystals of the same sample arrive at the same 206Pb/238U result within case of single, significantly younger dates (>3 sigma), and are common in many pre-Triassic and hydrothermally altered rocks. (B) Pre-eruptive/pre-intrusive growth is found to be the main reason for scattered zircon ages in igneous rocks. Zircons crystallizing from the final magma batch are called autocrystic [3]. Autocrystic growth will happen in a moving or stagnant magma shortly before or after the rheological lockup by the crystals. Last crystallizing zircons in the interstitial melt may therefore postdate emplacement of the magma. The range of 206Pb/238U ages may yield a time frame for the cooling of a given magma batch, which could be added to quantitative thermal models of magma emplacement and cooling. Hf isotopes and trace elements of the dated zircon are used to trace the nature of the dated grains [4], specifically for identification of

Molybdenum acetate like precursor of molybdenum carburized supported on alumina: a catalyst for hydrogenation reactions

International Nuclear Information System (INIS)

Petkovic, Lucia M; Parra, Ruben D; Marquez Manuel; Larsen, Gustavo

1994-01-01

The stability of the Al203 supported dimers under relatively high temperatures and hydrocarbon/H2 (carburizing) atmospheres is reported also, it has been developed a new method for Mo2 loading of the support based on the wet impregnation of the latter. Since carbided Mo is active for hydrogenations, the isobutene/H2 has been chosen as the probe reaction. Al203 supported Mo2(Ac)4 results in a catalyst active for isobutene hydrogenation after treatment with a H2/C2H6 2:1 mixture at 753 k

Refractory Materials of Zirconate. Part 2: Synthesis and some properties of strontium, zirconate, calcium zirconate and barium zirconate

Science.gov (United States)

Okubo, Tsutomo; Yonemochi, Osamu; Nakamura, Kazuo; Maeda, Minoru

1988-01-01

Chemical compounds SrZrO3, CaZrO3, and BaZrO3 were synthesized by solid reaction and arc fusion, and their properties examined. Results were as follows: (1) in the synthesis of CaZrO3 by solid reaction, ZrO2 solid solution with cubic form was produced, which then changed into CaZrO3; (2) the BaZrO3 was a cubic form and did not show any transformation, while SrZrO3 and CaZrO3 with an orthorhombic form transformed to a cubic form at high temperature; and (3) the solubility of BaZrO3 in acid and its vaporization rate at a high temperature were greater than those of zirconates.

Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust

Science.gov (United States)

Ushikubo, Takayuki; Kita, Noriko T.; Cavosie, Aaron J.; Wilde, Simon A.; Rudnick, Roberta L.; Valley, John W.

2008-08-01

In situ Li analyses of 4348 to 3362 Ma detrital zircons from the Jack Hills, Western Australia by SIMS reveal that the Li abundances (typically 10 to 60 ppm) are commonly over 10,000 times higher than in zircons crystallized from mantle-derived magmas and in mantle-derived zircon megacrysts (typically Jack Hills zircons also have fractionated lithium isotope ratios ( δ7Li = - 19 to + 13‰) about five times more variable than those recorded in primitive ocean floor basalts (2 to 8‰), but similar to continental crust and its weathering products. Values of δ7Li below - 10‰ are found in zircons that formed as early as 4300 Ma. The high Li compositions indicate that primitive magmas were not the source of Jack Hills zircons and the fractionated values of δ7Li suggest that highly weathered regolith was sampled by these early Archean magmas. These new Li data provide evidence that the parent magmas of ancient zircons from Jack Hills incorporated materials from the surface of the Earth that interacted at low temperature with liquid water. These data support the hypothesis that continental-type crust and oceans existed by 4300 Ma, within 250 million years of the formation of Earth and the low values of δ7Li suggest that weathering was extensive in the early Archean.

U-Pb ages of detrital zircon from Pegasus Group, Stewart Island

International Nuclear Information System (INIS)

Walker, N.; Tulloch, A.J.; Allibone, A.

1998-01-01

Stewart Island (New Zealand) is relatively unaffected by Cenozoic deformation related to the present-day plate boundary and has thus been a locale of investigations that focus on the relationship between Mesozoic continental margin magmatic rocks and the Western Province (WP) of NZ. Pegasus Group metasedimentary rocks represent the only candidate for WP equivalents on Stewart Island. We measured U-Pb and 207 Pb / 206 Pb ages of detrital zircons from the Pegasus Group in an effort to validate the correlation with the WP. On SI, Pegasus Group is exposed over a small area in the southern Tin Range where it forms amphibolite facies roof pendants and screens among plutons of mid Paleozoic to mid Cretaceous age. Mica schists predominate, with lesser amounts of psammite and metaquartzite and rare calcareous schist and amphibolite. Zircons were extracted from metaquarzite and 24 grains were chosen on the basis of morphology for geochronologic investigation. Sixteen single crystals were dated by U-Pb TIMS; 8 additional grains were studied by the total evaporation method described by Kober. Despite vigorous air abrasion prior to processing, the 16 grains measured by conventional U-Pb TIMS yielded slightly normally discordant ages that we interpret to reflect minor Pb-loss. The 8 grains studied by the total evaporation method yielded more than four analytically identical /sup 207 Pb / 206 Pb ages within each grain at progressively higher temperatures (1515-1580 degrees C) of evaporation. The results permit the following general conclusions: 1) the age range of 420-2700 Ma is grossly similar to that reported from the Greenland Group/Victoria Paragneiss (Ireland 1992) of the Buller Terrane, WP; 2) the zircon population is dominantly 530-680 Ma but a subsidiary population is 900-1100 Ma; 3) no zircons with ages that match the timing of the Ross Orogen (530-480 Ma) were identified; 4) two grains of 420 Ma and a 453 Ma are probably too young for the paleontogically

Chemical evolution of Himalayan leucogranites based on an O, U-Pb and Hf study of zircon

Science.gov (United States)

Hopkinson, Thomas N.; Warren, Clare J.; Harris, Nigel B. W.; Hammond, Samantha J.; Parrish, Randall R.

2015-04-01

Crustal melting is a characteristic process at convergent plate margins, where crustal rocks are heated and deformed. Miocene leucogranite sheets and plutons are found intruded into the high-grade metasedimentary core (the Greater Himalayan Sequence, GHS) across the Himalayan orogen. Previously-published Himalayan whole-rock data suggest that these leucogranites formed from a purely meta-sedimentary source, isotopically similar to those into which they now intrude. Bulk rock analyses carry inherent uncertainties, however: they may hide contributions from different contributing sources, and post-crystallization processes such as fluid interaction may significantly alter the original chemistry. In contrast, zircon is more able to retain precise information of the contributing sources of the melt from which it crystallises whilst its resistant nature is impervious to post-magmatic processes. This multi-isotope study of Oligocene-Miocene leucogranite zircons from the Bhutan Himalaya, seeks to differentiate between various geochemical processes that contribute to granite formation. Hf and O isotopes are used to detect discrete changes in melt source while U-Pb isotopes provide the timing of zircon crystallisation. Our data show that zircon rims of Himalayan age yield Hf-O signatures that lie within the previously reported whole-rock GHS field, confirming the absence of a discernible mantle contribution to the leucogranite source. Importantly, we document a decrease in the minimum ɛHf values during Himalayan orogenesis through time, correlating to a change in Hf model age from 1.4 Ga to 2.4 Ga. Nd model ages for the older Lesser Himalayan metasediments (LHS) that underthrust the GHS are significantly older than those for the GHS (2.4-2.9 Ga compared with 1.4-2.2 Ga), and as such even minor contributions of LHS material incorporated into a melt would significantly increase the resulting Hf model age. Hence our leucogranite data suggest either a change of source within

SHRIMP U-Pb dating of detrital zircons in metamorphic rocks from northern Kyushu, western Japan

International Nuclear Information System (INIS)

Tsutsumi, Yukiyasu; Yokoyama, Kazumi; Terada, Kentaro; Sano, Yuji

2003-01-01

Radiometric ages of detrital zircons in psammitic schists from the Nagasaki, Kurume, Konoha and Kiyama areas, northern Kyushu, were obtained from 238 U/ 206 Pb ratio and isotopic compositions of Pb using a Sensitive High Resolution Ion Microprobe (SHRIMP II). Zircons from the Nagasaki, Kurume and Konoha areas show bimodal age distribution with peaks at ca. 1900 Ma and 250 Ma. It is suggested from this study that the older zircons were derived from Proterozoic landmass and the Korean Peninsula. Zircons from the Kiyama metamorphic rock show a different pattern with ages concentrated at 380-590 Ma. Such zircons are rare in rock samples from the Nagasaki, Kurume and Konoha areas, indicating that Kiyama rocks and a different origin than those from the other three areas. The youngest zircons from the Kiyama, Nagasaki, Kurume and Konoha areas show ages of 382±23 Ma, 238±13 Ma, 249±13 Ma, and 175±4 Ma, respectively, These data mark the upper age limit of their deposition. Since a continuous igneous activity occurred during the period from 300 to 170 Ma in Far East Asia, and the metamorphic age has been close to the zircon age of each area, these youngest ages for the Nagasaki, Kurume and Konoha areas are considered nearly contemporary to the depositional ages. An evaluation of the nature of metamorphism and available ages suggest the possibility that the Nagasaki metamorphic rocks as well as the schist from the Kurume area belong to the Suo zone of the Sangun belt, whereas the metamorphic rocks in the Konoha area may belong to the Ryoke belt or Suo zone of the Sangun belt. (author)

Application of experiment planning during investigation of cementation process in solid carburizers

International Nuclear Information System (INIS)

Lisenkov, A.N.; Denisov, V.M.; Prigozhina, E.L.

1981-01-01

A mathematical model of cementation process in solid carburizirs is obtained, the most effective contents of carburizers are chosen. Specimens are produced out of St20, 12KhN3A, 40Kh13, KhVG steels. It is shown that specimens of St20 and 12KhN3A steels have the higher depth of cementated layer, specimens made of 40Kh13 and KhVG steels-the lower depth. It is shown that the quality of cementated layer structure at recommended regimes improved, cementated layer depth for low-carbon steels changed a little and for tool steels increased infficiently: for KhVG steel in 2-3 times for 40Kh13 steel in 1.5-2.5 times

Gamma-rays attenuation of zircons from Cambodia and South Africa at different energies: A new technique for identifying the origin of gemstone

International Nuclear Information System (INIS)

Limkitjaroenporn, P.; Kaewkhao, J.

2014-01-01

In this work, the gamma-rays interaction properties of zircons from Cambodia and South Africa have been studied. The densities of Cambodian and South African’s zircons are 4.6716±0.0040 g/cm 3 and 4.5505±0.0018 g/cm 3 , respectively. The mass attenuation coefficient and the effective atomic number of gemstones were measured with the gamma-ray in energies range 223–662 keV using the Compton scattering technique. The mass attenuation coefficients of both zircons decreased with the increasing of gamma-rays energies. The different mass attenuation coefficients between the two zircons observed at gamma-ray energies below 400 keV are attributed to the differences in the photoelectric interaction. The effective atomic number of zircons was decreased with the increasing of gamma-ray energies and showed totally different values between the Cambodia and South Africa sources. The origins of the two zircons could be successfully identified by the method based on gamma-rays interaction with matter with advantage of being a non-destructive testing. - Highlights: • Gamma-rays interaction of zircons from Cambodia and South Africa studied. • Measured energy is during 223–662 keV. • Different μ m between the two zircons observed at gamma-ray energies below 400 keV. • The origins the two zircons could be successfully identified

New Insights on the Recrystallization and New Growth of Extensively Radiation-damaged Zircon

Science.gov (United States)

Hanchar, J. M.; Schmitz, M. D.; Wirth, R.

2012-12-01

Approximately 10 grams of cm-sized nearly metamict zircon crystals from the Saranac Prospect in the Bancroft District of Ontario were combined by breaking into small pieces and then ground under ethanol to a fine powder with an agate mortar and pestle in order to make enough homogeneously mixed material for multiple powder X-Ray and diffraction scans, high-resolution transmission electron microscopy (HR-TEM) measurements, and chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-TIMS). While these large zircon crystals ground to a powder have a larger surface area and not in the same physical state (i.e., brown and metamict) as what is typically analyzed in single zircon CA-ID-TIMS U-Pb analysis (clear euhedral grains), the physical and chemical changes that occur during the heat treatment used in CA-TIMS are thought to be similar processes. Aliquots of the ground zircon powder were annealed in situ using a Pt furnace in a powder diffractometer during which time simultaneous powder diffraction patterns were acquired starting at 25°C, at elevated temperature (from 500°C to 1400°C) at selected time intervals, and then again at 25°C. The powder X-ray diffraction results indicate that below ~900°C the recrystallization of the zircon powder commences but is incomplete, even after 36 hours, with diffuse low intensity diffraction peaks. At 1150°C the zircon powder shows significant recrystallization. At 1150°C, the recrystallization is essentially complete in less than one hour. Before heating the zircon powder samples consisted of clear, transparent to brown, translucent, complexly zoned fragments. After heating at 900°C the zircon powder retained a smaller percentage of clear or brown complexly zoned fragments, while the majority of material had transformed to oscillatory or irregularly zoned, dominantly white opaque microcrystalline fragments. The clear fragments were hypothesized to be preexisting original crystalline zircon, the brown

Strontium zirconate as silicon and aluminum scavenger in yttria stabilized zirconia

DEFF Research Database (Denmark)

Andersen, Thomas; Hansen, Karin Vels; Chorkendorff, Ib

2011-01-01

Here we report on strontium zirconate as a getter for silicon dioxide and aluminum oxide in yttria stabilized zirconia (YSZ) single crystals for cleaning purposes. YSZ single crystals were covered with strontium zirconate powder and heat treated at 1450°C in water vapor. After treatment the YSZ...... by transmission electron microscopy (TEM) the interface region between bump and YSZ single crystal bulk was examined. EDS showed a homogeneous distribution of silicon and aluminum through the cross section of a bump. The results suggest strontium zirconate as a good getter for silicon and aluminum from bulk...

Multi-mode Li diffusion in natural zircons: Evidence for diffusion in the presence of step-function concentration boundaries

Science.gov (United States)

Tang, Ming; Rudnick, Roberta L.; McDonough, William F.; Bose, Maitrayee; Goreva, Yulia

2017-09-01

Micron- to submicron-scale observations of Li distribution and Li isotope composition profiles can be used to infer the mechanisms of Li diffusion in natural zircon. Extreme fractionation (20-30‰) within each single crystal studied here confirms that Li diffusion commonly occurs in zircon. Sharp Li concentration gradients frequently seen in zircons suggest that the effective diffusivity of Li is significantly slower than experimentally determined (Cherniak and Watson, 2010; Trail et al., 2016), otherwise the crystallization/metamorphic heating of these zircons would have to be unrealistically fast (years to tens of years). Charge coupling with REE and Y has been suggested as a mechanism that may considerably reduce Li diffusivity in zircon (Ushikubo et al., 2008; Bouvier et al., 2012). We show that Li diffused in the direction of decreasing Li/Y ratio and increasing Li concentration (uphill diffusion) in one of the zircons, demonstrating charge coupling with REE and Y. Quantitative modeling reveals that Li may diffuse in at least two modes in natural zircons: one being slow and possibly coupled with REE+Y, and the other one being fast and not coupled with REE+Y. The partitioning of Li between these two modes during its diffusion may depend on the pre-diffusion substitution mechanism of REE and Y in the zircon lattice. Based on our results, sharp Li concentration gradients are not indicative of limited diffusion, and can be preserved at temperatures >700 °C on geologic timescales. Finally, large δ7 Li variations observed in the Hadean Jack Hills zircons may record kinetic fractionation, rather than a record of ancient intense weathering in the granite source materials.

Paleozoic and Paleoproterozoic Zircon in Igneous Xenoliths Assimilated at Redoubt Volcano, Alaska

Science.gov (United States)

Bacon, C. R.; Vazquez, J. A.; Wooden, J. L.

2010-12-01

Historically active Redoubt Volcano is a basalt-to-dacite cone constructed upon the Jurassic-early Tertiary Alaska-Aleutian Range batholith. New SHRIMP-RG U-Pb age and trace-element concentration results for zircons from gabbroic xenoliths and crystal-rich andesitic mush from a late Pleistocene pyroclastic deposit indicate that ~310 Ma and ~1865 Ma igneous rocks underlie Redoubt at depth. Two gabbros have sharply terminated prismatic zircons that yield ages of ~310 Ma. Zircons from a crystal mush sample are overwhelmingly ~1865 Ma and appear rounded due to incomplete dissolution. Binary plots of element concentrations or ratios show clustering of data for ~310-Ma grains and markedly coherent trends for ~1865-Ma grains; e.g., ~310-Ma grains have higher Eu/Eu* than most of the ~1865-Ma grains, the majority of which form a narrow band of decreasing Eu/Eu* with increasing Hf content which suggests that ~1865-Ma zircons come from igneous source rocks. It is very unlikely that detrital zircons from a metasedimentary rock would have this level of homogeneity in age and composition. One gabbro contains abundant ~1865 Ma igneous zircons, ~300-310 Ma fluid-precipitated zircons characterized by very low U and Th concentrations and Th/U ratios, and uncommon ~100 Ma zircons. We propose that (1) ~310 Ma gabbro xenoliths from Redoubt Volcano belong to the same family of plutons dated by Aleinikoff et al. (USGS Circular 1016, 1988) and Gardner et al. (Geology, 1988) located ≥500 km to the northeast in basement rocks of the Wrangellia and Alexander terranes and (2) ~1865 Ma zircons are inherited from igneous rock, potentially from a continental fragment that possibly correlates with the Fort Simpson terrane or Great Bear magmatic zone of the Wopmay Orogen of northwestern Laurentia. Possibly, elements of these Paleoproterozoic terranes intersected the Paleozoic North American continental margin where they may have formed a component of the basement to the Wrangellia

Pan-African U-Pb zircon age from apatite-magnetite veins of eastern ghats granulite belt, India

International Nuclear Information System (INIS)

Kovach, V.P.; Salnikova, E.B.; Kotov, A.B.; Yakovleva, S.Z.; Rao, A.T.

1997-01-01

206 Pb/ 238 U ages of zircon correspond to 502±3 Ma and 207 Pb/ 206 Pb ages are equal to 508±14 Ma. U-Pb isotopic study of the Kasipatnam zircon has led to the recognition of pan-African thermal event in the eastern ghats granulite belt, India. (author)

Constraints on the timing of multiple thermal events and re-equilibration recorded by high-U zircon and xenotime: Case study of pegmatite from Piława Górna (Góry Sowie Block, SW Poland)

Science.gov (United States)

Budzyń, Bartosz; Sláma, Jiří; Kozub-Budzyń, Gabriela A.; Konečný, Patrik; Holický, Ivan; Rzepa, Grzegorz; Jastrzębski, Mirosław

2018-06-01

The application of zircon and xenotime geochronometers requires knowledge of their potential and limitations related to possible disturbance of the age record. The alteration of the intergrown zircon and xenotime in pegmatite from the Góry Sowie Block (SW Poland) was studied using the electron microprobe analysis, X-ray WDS compositional mapping, micro-Raman analysis, and LA-ICP-MS U-Pb dating of zircon and xenotime, as well as the U-Th-total Pb dating of uraninite. These microanalytical techniques were applied to understand the formation mechanisms of the secondary textures related to post-magmatic processes in the zircon and xenotime intergrowth, and to constrain their timing. Textural and compositional features combined with U-Pb data indicate that the pegmatite-related crystallization of the zircon and xenotime intergrowth occurred ca. 2.09 Ga (2086 ± 35 Ma for zircon and 2093 ± 52 Ma for xenotime), followed by the re-equilibration of zircon and xenotime ca. 370 Ma (373 ± 18 Ma and 368 ± 6 Ma, respectively) during the formation of the younger pegmatite. The zircon and xenotime were most likely derived from Precambrian basement rocks and emplaced in the pegmatite as a restite. The zircon preserved textures related to diffusion-reaction processes that affected its high-U core (up to ca. 9.6 wt% UO2), which underwent further metamictization and amorphization due to self-radiation damage. The zircon rim and xenotime were affected by coupled dissolution-reprecipitation processes that resulted in patchy zoning, age disturbance and sponge-like textures. Xenotime was also partially replaced by fluorapatite or hingganite-(Y) and Y-enriched allanite-(Ce). The termination of the low-temperature alteration was constrained by the U-Th-total Pb age of the uraninite inclusions that crystallized in zircon at 281 ± 2 Ma, which is consistent with the age of 278 ± 15 Ma obtained from the youngest cluster of U-Pb ages in the re-equilibrated high-U zircon domains. This study

Major zircon megacryst suites of the Indo-Pacific lithospheric margin (ZIP) and their petrogenetic and regional implications

Science.gov (United States)

Sutherland, Lin; Graham, Ian; Yaxley, Gregory; Armstrong, Richard; Giuliani, Gaston; Hoskin, Paul; Nechaev, Victor; Woodhead, Jon

2016-04-01

Zircon megacrysts (± gem corundum) appear in basalt fields of Indo-Pacific origin over a 12,000 km zone (ZIP) along West Pacific continental margins. Age-dating, trace element, oxygen and hafnium isotope studies on representative zircons (East Australia-Asia) indicate diverse magmatic sources. The U-Pb (249 to 1 Ma) and zircon fission track (ZFT) ages (65 to 1 Ma) suggest thermal annealing during later basalt transport, with < 1 to 203 Ma gaps between the U-Pb and ZFT ages. Magmatic growth zonation and Zr/Hf ratios (0.01-0.02) suggest alkaline magmatic sources, while Ti—in—zircon thermometry suggests that most zircons crystallized within ranges between 550 and 830 °C. Chondrite-normalised multi-element plots show variable enrichment patterns, mostly without marked Eu depletion, indicating little plagioclase fractionation in source melts. Key elements and ratios matched against zircons from magmatic rocks suggest a range of ultramafic to felsic source melts. Zircon O-isotope ratios (δ18O in the range 4 to 11‰) and initial Hf isotope ratios (ɛHf in the range +2 to +14) encompass ranges for both mantle and crustal melts. Calculated Depleted Mantle (TDM 0.03-0.56 Ga) and Crustal Residence (0.20-1.02 Ga) model ages suggest several mantle events, continental break-ups (Rodinia and Gondwana) and convergent margin collisions left imprints in the zircon source melts. East Australian ZIP sites reflect prolonged intraplate magmatism (~85 Ma), often during times of fast-migrating lithosphere. In contrast, East Asian-Russian ZIP sites reflect later basaltic magmatism (<40 Ma), often linked to episodes of back-arc rifting and spreading, slow-migrating lithosphere and slab subduction.

Zirconium oxide obtainment from brazilian zircon concentrate

International Nuclear Information System (INIS)

Ribeiro, S.; Martins, A.H.

1991-01-01

This work presents the experimental results of studies about alkaline melting, acid leaching and sulfation steps for obtention of zirconium oxide and partially stabilized zirconia by yttrium and rare-earth coprecipitation in chlorine medium, starting from the brazilian zircon concentrate. Using statistical methods of factorial design and the Packett-Burman approach, the results are discussed and the optimal conditions of the production steps were determined. (author)

Contrasting Cu-Au and Sn-W Granite Metallogeny through the Zircon Geochemical and Isotopic Record

Science.gov (United States)

Gardiner, Nicholas; Hawkesworth, Chris; Robb, Laurence; Whitehouse, Martin; Roberts, Nick; Kirkland, Chris

2017-04-01

Magmatic genesis and evolution - mediated by geodynamic setting - exert a primary control on the propensity of granites to be metal fertile. A revolution in our understanding of these petrogenetic processes has been made through a range of mineral-based tools, most notably the common accessory mineral zircon. There is consequently considerable interest in whether the geochemical and isotopic compositions of zircon can be applied to metallogenic problems. The paired magmatic belts of Myanmar have broadly contrasting metallogenic affinities (Sn-W versus Cu-Au), and are interpreted to have formed on the accretionary margin of the subducting Neo-Tethys Ocean. They therefore present the opportunity to geochemically compare and contrast the zircon compositions in two end-member types of granite-hosted mineral deposits generated in collisional settings. We present an integrated zircon isotope (U-Pb, Lu-Hf, O) and trace element dataset that fingerprint: (a) source; (b) redox conditions; and (c) degree of fractionation. These variables all impact on magma fertility, and our key question to address is whether they can be reliably traced and calibrated within the Myanmar zircon record. Granitoid-hosted zircons from the I-type copper arc have juvenile ɛHf (+7 to +12) and mantle-like δ18O (5.3 ‰), whereas zircons from the S-type tin belt have low ɛHf (-7 to -13) and heavier δ18O (6.2-7.7 ‰). Plotting Hf versus U/Yb reaffirms that the tin belt magmas contain greater crustal contributions than the copper arc rocks. Links between whole rock Rb/Sr and zircon Eu/Eu* highlights that the latter can be used to monitor magma fractionation in systems that crystallize plagioclase (low Sr/Y). Ce/Ce* and Eu/Eu* in zircon are thus sensitive to redox and fractionation respectively, and can be used to evaluate the sensitivity of zircons to the metallogenic affinity of their host rocks. Tin contents that exceed the solubility limit are required in order to make a magmatic

NORM exposure to workers at a zircon sand processing factory

International Nuclear Information System (INIS)

Andersen, T.; Israelson, C.

2003-01-01

The National Institute of Radiation Hygiene (NIRH) has estimated doses to workers at a Danish zircon-processing industry. Calculations of internal doses were made after measuring dust concentrations in the working area and content of radium-226 and thorium-232 in the zircon sand. The total effective dose from internal and external irradiation was calculated to approximately 0,75 mSv/y. (orig.)

On the valency state of radiogenic lead in zircon and its consequences

DEFF Research Database (Denmark)

Kramers, J.; Frei, Robert; Newville, M.

2009-01-01

nucleus comes to rest. Further, a zircon grain, being small, should remain highly oxidizing in its interior by the constant loss of ß-particles, maintaining the 4+ state of radiogenic Pb. From its effective ion radius, similar to that of Zr4+, and its charge, Pb4+ has to be compatible in the zircon...... not resemble that of PbO2. The arguments why radiogenic Pb should be tetravalent are based on analogies with studies relating to the tetravalent state of 234Th and the hexavalent state of 234U, which show that a-recoil in silicates generates a strongly oxidizing environment at the site where the recoiling......-recoil damaged sites could be leached out by any electrolyte solution that reduces it to the divalent state, making it both incompatible and soluble. Thus, discordia can be generated in weathering. The curious observation that discordant Archaean zircon suites generally define trends to lower intercepts at up...

Chemical characteristics of zircon from A-type granites and comparison to zircon of S-type granites

Czech Academy of Sciences Publication Activity Database

Breiter, Karel; Lamarão, C. N.; Krás Borges, R. M.; Dall'Agnol, R.

1192/195, April (2014), s. 208-225 ISSN 0024-4937 Institutional support: RVO:67985831 Keywords : zircon * A-type granites * S-type granites * Wiborg batholith * Brazil * Krušné hory/Erzgebirge Subject RIV: DD - Geochemistry Impact factor: 4.482, year: 2014

Pulverization of boron element and proportions of boron carbide in boron; Broyage de bore element et dosage de carbure de bore dans le bore

Energy Technology Data Exchange (ETDEWEB)

Lang, F M; Finck, C [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1956-07-01

It is possible to reduce boron element into fine powder by means of a mortar and pestle made of sintered boron carbide, the ratio of boron carbide introduced being less than one per cent. Boron element at our disposal is made of sharp edged, dark brown, little grains of average size greater than 5 {mu}. Grain sizes smaller than 1{mu} are required for applying thin layers of such boron. (author) [French] Il est possible de pulveriser finement du bore element au moyen de mortier et pilon en carbure de bore fritte, le taux de carbure de bore introduit etant inferieur a 1 pour cent. Le bore element dont nous disposons est constitue de petits grains brun fonce, a aretes vives, de dimension moyenne superieure a 5 {mu}. L'application de ce bore en couches minces demande des grains de dimensions inferieures a 1 {mu}. (aute0008.

Phase quantification of mullite-zirconia and zircon commercial powders using PAC and XRD techniques

Energy Technology Data Exchange (ETDEWEB)

Rendtorff, Nicolas M.; Conconi, Maria S.; Aglietti, Esteban F. [Centro de Tecnologia de Recursos Minerales y Ceramica (CETMIC: CONICET-CIC) (Argentina); Chain, Cecilia Y.; Pasquevich, Alberto F. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina); Rivas, Patricia C. [CONICET (Argentina); Martinez, Jorge A., E-mail: toto@fisica.unlp.edu.ar; Caracoche, Maria C. [Universidad Nacional de La Plata, Departamento de Fisica, IFLP, Facultad de Ciencias Exactas (Argentina)

2010-06-15

The short range technique of the Perturbed Angular Correlation (PAC) and x-ray diffraction (Rietveld) methods have been employed to determine the phase content in commercial mullite-zirconia and zircon raw materials that are ordinarily used to produce ceramic materials. The PAC technique, which probes zirconium-containing compounds at nanoscopic level, showed that zircon contains crystalline ZrSiO{sub 4} and an important amount of a structurally distorted zircon, which is also observed accompanying monoclinic zirconia in mullite-zirconia. This particular zircon phase was not detected by the long range x-ray diffraction-Rietveld technique. After an annealing treatment, important changes in crystalline contents of the powders allow confirming, by the x-ray diffraction-Rietveld method, the preexistence of this particular zircon phase. This fact must be taken into account when preparing multicomposites based on the present raw materials.

Ion Irradiation Damage in Zirconate and Titanate Ceramics for Pu Disposition

International Nuclear Information System (INIS)

Stewart, Martin W.; Begg, Bruce D.; Finnie, K.; Colella, Michael; Li, H.; McLeod, Terry; Smith, Katherine L.; Zhang, Zhaoming; Weber, William J.; Thevuthasan, Suntharampillai

2004-01-01

In this paper, we discuss the effect of ion irradiation on pyrochlore-rich titanate and defect-fluorite zirconate ceramics designed for plutonium immobilization. Samples, with Ce as an analogue for Pu, were made via oxide routes and consolidated by cold-pressing and sintering. Ion irradiation damage was carried out with 2 MeV Au2+ ions to a fluence of 5 ions nm-2 in the accelerator facilities within the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory. Irradiated and non-irradiated samples were examined by x-ray diffraction, scanning and transmission electron microscopy, x-ray photoelectron and infrared spectroscopy, and spectroscopic ellipsometry. Samples underwent accelerated leach testing at pH 1.75 (nitric acid) at 90 C for 28 days. The zirconate samples were more ion-irradiation damage resistant than the titanate samples, showing little change after ion-irradiation whereas the titanate samples formed an amorphous surface layer ∼ 500 nm thick. While all samples had high aqueous durability, the titanate leach rate was ∼ 5 times that of the zirconate. The ion-irradiation increased the leach rate of the titanate without impurities by ∼ 5 times. The difference in the leach rates between irradiated and unirradiated zirconate samples is small. However, the zirconates were less able to incorporate impurities than the titanate ceramics and required higher sintering temperatures, ∼ 1500 C compared to 1350 C for the titanates.

Evolution of the Gondwanaland Archaean Shield: ion microprobe zircon dating and southwestern Australia/Wilkes Land, Antartica

International Nuclear Information System (INIS)

Lovering, J.F.; Comaford, D.J.

1979-01-01

The ion microprobe has been used to study 207 Pb/ 206 Pb ages on 20μm-sized sites on single zircon grains from coastal rocks on either side of the rift in the Gondwanaland Archaean Shield between southwestern Australia and Wilkes Land, Antarctica. The ages on individual sites on zircon grains from a variety of rock types from southwestern Australia show a range from 1600 m.y. to about 3400 m.y., with an inverse dependence on the uranium abundance at each site. Ages of zircons from rocks from the Antartic region show a range from 1600 m.y. to 3100 m.y

Extrusion and properties of lead zirconate titanate piezoelectric ceramics

DEFF Research Database (Denmark)

Cai, S.; Millar, C.E.; Pedersen, L.

1997-01-01

The purpose of this work was to develop a procedure for fabricating electroceramic actuators with good piezoelectric properties. The preparation of lead zirconate titanate (PZT) piezoelectric ceramic rods and tubes by extrusion processing is described. The microstructure of extrudates was investi......The purpose of this work was to develop a procedure for fabricating electroceramic actuators with good piezoelectric properties. The preparation of lead zirconate titanate (PZT) piezoelectric ceramic rods and tubes by extrusion processing is described. The microstructure of extrudates...

3-D Characterization of Detrital Zircon Grains and its Implications for Fluvial Transport, Mixing, and Preservation Bias

Science.gov (United States)

Markwitz, V.; Kirkland, C. L.; Mehnert, A.; Gessner, K.; Shaw, J.

2017-12-01

Detrital zircon studies can suffer from selective loss of provenance information due to U-Pb age discordance, metamictization, metamorphic overprinting and fluviatile transport processes. The relationship between isotopic composition and zircon grain shape, and how grain shape is modified during transport, is largely unknown. We combine X-ray tomography with U-Pb geochronology to quantify how fluvial transport affects 3-D zircon shape, detrital age signature, and grain density along the Murchison River, whose catchment comprises Eoarchean to Early Paleozoic source rocks in Western Australia. We acquired tomographic volumes and isotopic data from 373 detrital zircons to document changes in size, shape and density in transport direction, and explore how grain shape, age spectra and the proportion of discordant material vary along the channel. Results show that shape characteristics are sensitive to transport distance, stream gradient, proximity to source material, and whether the source consists of primary or recycled zircons. With increasing transport distance, grain lengths decrease more than their widths. Furthermore, the loss of metamict grains occurs at a near constant rate, resulting in a linear increase of mean calculated zircon density by ca. 0.03 g/cm3 per 100 km transport distance. 3-D grain shape is therefore strongly linked to detrital age signature, and mean grain density is a function of the absolute transport distance. 3-D shape characteristics provide valuable information on detrital zircon populations, including the interaction between source materials with fluvial transport processes, which significantly affects preservation bias and, by inference, the representativeness of the sampled data.

Influence of gadolinium concentration on the EMR spectrum of Gd{sup 3+} in zircon

Energy Technology Data Exchange (ETDEWEB)

Biasi, R.S. de, E-mail: rsbiasi@ime.eb.b [Secao de Engenharia Mecanica e de Materiais, Instituto Militar de Engenharia, 22290-270 Rio de Janeiro, RJ (Brazil); Grillo, M.L.N., E-mail: mluciag@uerj.b [Instituto de Fisica, Universidade do Estado do Rio de Janeiro, 20550-013 Rio de Janeiro, RJ (Brazil)

2009-11-01

Electron magnetic resonance (EMR) spectra of gadolinium-doped zircon (ZrSiO{sub 4}) powders have been studied at room temperature for gadolinium concentrations between 0.20 and 1.0 mol%. The results suggest that Gd{sup 3+} ions occupy substitutional sites in the zircon lattice, that the electron magnetic resonance linewidth increases with increasing gadolinium concentration and that the range of the exchange interaction between Gd{sup 3+} ions is about 1.17 nm, larger than that of the same ion in other host lattices, such as ceria (CeO{sub 2}), strontium oxide (SrO) and calcium oxide (CaO). The fact that the electron magnetic resonance linewidth of the Gd{sup 3+} ion in polycrystalline zircon increases, regularly and predictably, with Gd concentration, shows that the Gd{sup 3+} ion can be used as a probe to study, rapidly and non-destructively, the crystallinity and degradation of ZrSiO{sub 4}.

High-temperature mechanical properties of a uniaxially reinforced zircon-silicon carbide composite

International Nuclear Information System (INIS)

Singh, R.N.

1990-01-01

This paper reports that mechanical properties of a monolithic zircon ceramic and zircon-matrix composites uniaxially reinforced with either uncoated or BN-coated silicon carbide monofilaments were measured in flexure between 25 degrees and 1477 degrees C. Monolithic zircon ceramics were weak and exhibited a brittle failure up to abut 1300 degrees C. An increasing amount of the plastic deformation was observed before failure above about 1300 degrees C. In contrast, composites reinforced with either uncoated or BN-coated Sic filaments were stronger and tougher than the monolithic zircon at all test temperatures between 25 degrees and 1477 degrees. The ultimate strength and work-of-fracture of composite samples decreased with increasing temperature. A transgranular matrix fracture was shown by the monolithic and composite samples tested up to about 1200 degrees C, whereas an increasing amount of the intergranular matrix fracture was displayed above 1200 degrees C

Sample-scale zircon geochemical and geochronological heterogeneities as indicators of residual liquid infiltration events in the incrementally assembled Caleu Pluton, Central Chile

Science.gov (United States)

Molina, P. G.; Parada, M. A.; Gutiérrez, F. J.; Ma, C.; Li, J.; Liu, Y.

2013-12-01

. Inconsistencies in whole-rock major and some trace elements concentrations are observed in the studied samples, these differences are attributable to open-system compositional perturbations. The sample-scale heterogeneities in zircon age and composition, points out to remobilization of a zircon-bearing interstitial melt, possibly by segregation from a locked-crystal mush, or infiltration of a zirconium-rich melt (and other incompatible elements) capable of crystallize zircons, even across a nearly solidified system during rapid exhumation. This study is financed by the CONICYT-FONDAP project 15090013, Centro de Excelencia en Geotermia de los Andes (CEGA).

Pyroelectricity versus conductivity in soft lead zirconate titanate (PZT) ceramics

NARCIS (Netherlands)

Kamel, T.M.; With, de G.

2007-01-01

The electrical behavior of modified soft lead zirconate titanate (PZT) ceramics has been studied as a function of temperature at different direct current (dc) electric fields and grain sizes. As ferroelectrics, such as PZT, are highly polarizable materials, poling, depolarization, and electric

Enthalpy of formation of zircon

International Nuclear Information System (INIS)

Ellison, A.J.G.; Navrotsky, A.

1992-01-01

Using high-temperature solution calorimetry in molt 2PbO · B 2 O 3 , the enthalpy of reaction of the formation of zircon, ZrSiO 4 , from its constituent oxides has been determined: Δ 4 H 977 (ZrSiO 4 ) = -27.9 (±1.9) kJ/mol. With previously reported data for the heat contents of ZrO 2 SiO 2 and ZrSiO 4 and standard-state enthalpies of formation of ZrO 2 and SiO 2 , we obtain Δ f H 298 degrees. (ZrSiO 4 ) = -2034.2 (±3.1) kJ/mol and Δ t G 298 degrees (ZrSiO 4 ) = -1919.8 kJ/mol. The free energy value is in excellent agreement with a range previously estimated from solid-state reaction equilibria. At higher temperature also the data are in close agreement with existing data, though the data sets diverge somewhat with increasing T. In this paper the limitations of the data for predicting the breakdown temperature of zircon into its constituent oxides are discussed

Current—voltage characteristics of lead zirconate titanate/nickel bilayered hollow cylindrical magnetoelectric composites

International Nuclear Information System (INIS)

De-An, Pan; Shen-Gen, Zhang; Jian-Jun, Tian; Li-Jie, Qiao; Jun-Sai, Sun; Volinsky, Alex A.

2010-01-01

Current–voltage measurements obtained from lead zirconate titanate/nickel bilayered hollow cylindrical magnetoelectric composite showed that a sinusoidal current applied to the copper coil wrapped around the hollow cylinder circumference induces voltage across the lead zirconate titanate layer thickness. The current–voltage coefficient and the maximum induced voltage in lead zirconate titanate at 1 kHz and resonance (60.1 kHz) frequencies increased linearly with the number of the coil turns and the applied current. The resonance frequency corresponds to the electromechanical resonance frequency. The current–voltage coefficient can be significantly improved by optimizing the magnetoelectric structure geometry and/or increasing the number of coil turns. Hollow cylindrical lead zirconate titanate/nickel structures can be potentially used as current sensors. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Detrital zircon ages in Buller and Takaka terranes, New Zealand : constraints on early Zealandia history

International Nuclear Information System (INIS)

Adams, C.J.; Mortimer, N.; Campbell, H.J.; Griffin, W.L.

2015-01-01

Detrital zircon ages are presented for 34 early Palaeozoic sandstones from Buller and Takaka terranes, New Zealand, and formerly adjacent parts of Australia-Antarctica. The Buller-Takaka datasets always have two major groups: Ordovician-late Neoproterozoic, 444-700 Ma (but mainly 540-700 Ma), termed 'Gondwana Assembly' (GA), and early Neoproterozoic-Mesoproterozoic, 700-1600 Ma (but mainly 900-1200 Ma), termed 'Rodinia Assembly' (RA). In both terranes, significant age components within these groups are strikingly similar and also have RA/GA ratios, 0.6-1.8. The Cambrian volcanic arc of the Takaka Terrane has contributed little to the zircon patterns. Proportions of Late Cambrian-Early Ordovician zircons, characteristic of granitoid sources in the Ross-Delamerian Orogen are low. The zircons are predominantly reworked with contemporary zircons only evident in a few Buller datasets. The zircon patterns suggest that two major sources (late Mesoproterozoic and late Neoproterozoic), enduring over 120 Ma, were widely distributed and it is postulated they form Precambrian basement beneath southern Zealandia. (author).

Using the magmatic record to constrain the growth of continental crust-The Eoarchean zircon Hf record of Greenland

Science.gov (United States)

Fisher, Christopher M.; Vervoort, Jeffrey D.

2018-04-01

Southern West Greenland contains some of the best-studied and best-preserved magmatic Eoarchean rocks on Earth, and these provide an excellent vantage point from which to view long-standing questions regarding the growth of the earliest continental crust. In order to address the questions surrounding early crustal growth and complementary mantle depletion, we present Laser Ablation Split Stream (LASS) analyses of the U-Pb and Hf isotope compositions of zircon from eleven samples of the least-altered meta-igneous rocks from the Itsaq (Amîtsoq) Gneisses of the Isukasia and Nuuk regions of southern West Greenland. This analytical technique allows a less ambiguous approach to determining the age and Hf isotope composition of complicated zircon. Results corroborate previous findings that Eoarchean zircon from the Itsaq Gneiss (∼3.85 Ga to ∼3.63 Ga) were derived from a broadly chondritic source. In contrast to the Sm-Nd whole rock isotope record for southern West Greenland, the zircon Lu-Hf isotope record provides no evidence for early mantle depletion, nor does it suggest the presence of crust older than ∼3.85 Ga in Greenland. Utilizing LASS U-Pb and Hf data from the Greenland zircons studied here, we demonstrate the importance of focusing on the magmatic (rather than detrital) zircon record to more confidently understand early crustal growth and mantle depletion. We compare the Greenland Hf isotope data with other Eoarchean magmatic complexes such as the Acasta Gneiss Complex, Nuvvuagittuq greenstone belt, and the gneissic complexes of southern Africa, and all lack zircons with suprachondritic Hf isotope compositions. In total, these data suggest only a very modest volume of crust was produced during (or survived from) the Hadean and earliest Eoarchean. There remains no record of planet-scale early Earth mantle depletion in the Hf isotope record prior to 3.8 Ga.

Perfect zircon for rock dating no fairy tale

International Nuclear Information System (INIS)

Anon

2000-01-01

The scheme used to date rocks is based on the radioactive decay of uranium. Minute traces of uranium locked inside the zircon crystals have been decaying over aeons, producing lead. Scientists know that the decay occurs at a fixed rate and how quickly it happens. By measuring the relative amounts of uranium and lead encased in the crystals, scientists can determine how old the rock is. But sometimes lead is lost from zircon crystals via processes such as weathering (if the rocks were exposed on the surface) or deformation and metamorphism (if the rocks had crystallised deep in the earth and been subjected to high temperatures and pressure). Hence the special nature of the Temora rocks- a 417 million years old zirconium-containing rock which have been partially exposed in recent times in a remote paddock in NSW, Australia. SHRIMP dating was used for initial tests on the Temora rocks. Then, in December last year, the sample was sent to the world-recognised authority, Canada's Royal Ontario Museum, for independent analysis and dating via chemical decomposition. The museum confirmed the near perfect quality of the zircon and its age

Detrital zircon geochronology and provenance of the Chubut Group in the northeast of Patagonia, Argentina

Science.gov (United States)

Navarro, Edgardo L.; Astini, Ricardo A.; Belousova, Elena; Guler, M. Verónica; Gehrels, George

2015-11-01

The Chubut Group constitutes the most widespread sedimentary unit in NE Patagonia, characterized by variable-energy fluvial deposits. U-Pb analysis of detrital zircons from two sections of the Chubut Group constraint the age of the oldest sedimentary rocks in the northeast of the Somuncurá - Cañadón Asfalto Basin. In the Cañadón Williams area, at San Jorge section, 20 km NW of Telsen locality, dating of 56 detrital zircons from a medium to coarse sandstone indicated a maximum depositional age of 109 ± 1 Ma (n = 4). These sandstones were interpreted to represent shallow channels, associated with a lacustrine system. In the Telsen locality, a laser ablation analysis of 115 detrital zircons from a medium to coarse-grained sandstone, from fluvial channel facies, yielded a maximum depositional age of ca. 106 ± 1 Ma (n = 8). Both ages are consistent with volcanic events of the Barremian to Albian age in the central Patagonian Andes Region. Cathodoluminescence images of zircons from the San Jorge sample suggest an igneous origin, which is further supported by Th/U values above 0.5 in most of the grains. The distribution of the statistical modes of the main age populations of detrital zircons for the two samples [182, 185 and 189 Ma for Telsen sample (T2S) and 181 ± 1 Ma for San Jorge sample (SJS)] matches the age of the volcanic Marifil Formation. The rocks of the Marifil Formation of these ages are exposed NE to SE of the study area. The abundance of zircons of similar Jurassic ages (n = 52 for SJS and n = 105 for T2S) and the external morphology of the zircons in the sample SJS, implies a close proximity of the source area. Suggestion that the Marifil Formation was the main provenance source is also supported by northeast-southeasterly paleocurrents measured at the San Jorge and Telsen sections.

Simultaneous determinations of U-Pb age and REE abundances for zircons using AfF excimer laser ablation-ICPMS

International Nuclear Information System (INIS)

Iizuka, Tsuyoshi; Hirata, Takafumi

2004-01-01

Using a laser-ablation-inductively coupled plasma mass spectrometer (LA-ICPMS), U-Pb age and rare earth element (REE) abundances have been determined simultaneously from a single 20 μm ablation pit of zircon. The laser ablation system utilizing 193 nm wave-length ArF excimer laser produces stable and reproducible signal intensities resulted in good precisions on measurements of element concentrations and isotopic ratios. Because of the higher energy density of the deep ultra-violet laser beam, ablation fractionation between Pb and U were reduced even with the prolonged ablation, and thus accuracy of Pb-U age was improved significantly. A chicane-type ion lens system was applied to a quadrupole-based ICPMS instrument. With the chicane ion lens, higher elemental sensitivity (4 times or light mass range and 3 times for mid to heavy mass range) and lower white background ( 238 U- 206 Pb ages for Nancy standard zircon (Nancy 91500), SHRIMP calibration standard zircon (SL13) and Antarctic zircon (PMA7) obtained in this study were 1064 ± 24 Ma, 569 ± 78 Ma and 2438 ± 101 Ma (2-sigma), respectively. Relative age differences from previous reports were 0.2%, 0.4% and 3.2% respectively, demonstrative of high reliability of the method. The REE abundances in zircon samples were calibrated using a NIST 610 glass standard reference material. The resulting REE abundance data for zircons (Nancy 91500 and SL13) show good agreement with those for literature values within the analytical precision of ∼20%. The matrix effect that may occur between the synthetic glass standard and zircon crystals is obviously smaller than the precision and thus negligible for this precision levels. The data presented here demonstrate clearly that the combination of ArF excimer laser an ICPMS equipped with the chicane ion lens has a potential to become a significant tool for zircon geochemistry. (author)

Age of meta-rhyolite of Marata sequence, Araxa Group, Goias: geochronology study by U-Pb in zircon, Rb-Sr and Sm-Nd methods

International Nuclear Information System (INIS)

Pimentel, M.M.; Heaman, L.; Fuck, R.A.

1992-01-01

U-Pb isotopic analyses in eight zircon fractions separated from a meta-rhyolite sample of the Marata sequence (Araxa Group, Goias) are presented. Two morphologically distinct zircon populations were identified: stubby prismatic crystals (width:length of 1:2 to 1:3) in which core-overgrowth relationships are observed; long prismatic crystals (needles) with width:length ratios of ca. 1:10. Analyses performed on group zircons indicated the presence of a ca. 2.0 Ga. old inherited component. Analyses of group zircons plot very close to the concordia and yield an upper intercepts age of 794 ± 10 Ma for the crystallization of the volcanic protolith. The study was complemented with whole-rock isotopic analyses by the Rb-Sr and Sm-Nd methods. Rb-Sr isochron obtained with samples from two different outcrops gave data of 829 ± 82 Ma (initial 87 Sr/ 86 Sr of 0.7057 ± 0.0157) and 691 ± 30 Ma (initial 87 Sr/ 86 Sr of 0.7337 ± 0.0034). The latter reflects a later Sr-isotopic re-homogenization episode, possibly associated with the intense deformation and metamorphism suffered by these rocks. Sm-Nd isotopic analyses on three samples reveal EN d (T) (T =794 Ma) values in the range of -6.1 to -9.5 which indicate the presence of older (early Proterozoic) crustal Nd. This is consistent with the inheritance pattern shown in the U-Pb isotopic results. (author)

Low temperature plasma carburizing of AISI 316L austenitic stainless steel and AISI F51 duplex stainless steel Cementação sob plasma à baixa temperatura do aço inoxidável austenítico AISI 316L e do aço inoxidável duplex AISI F51

OpenAIRE

Carlos Eduardo Pinedo; André Paulo Tschiptschin

2013-01-01

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480ºC, using CH4 as carbon carrier gas. For the austenitic AISI 316L stainless steel, low temperature plasma carburizing induced a strong carbon supersaturation in the austenitic lattice and the formation of carbon expanded austenite (γC) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to ∼13 at% c...

Magmatic Longevity Constrained by ID-TIMS U-Pb Dating of Zircon and Titanite

Science.gov (United States)

Szymanowski, D.; Wotzlaw, J. F.; Ellis, B. S.; Bachmann, O.; Von Quadt, A.

2016-12-01

Clues about the timescales and thermal conditions associated with the growth and evacuation of large silicic magma reservoirs are frequently drawn from radiometric dating, diffusion modelling, or thermomechanical modelling. A growing amount of petrological and geochronological evidence, supported by thermal modelling, suggests that many silicic magma reservoirs may exist for some 104-106 years in the form of high-crystallinity mushes at relatively low temperatures ( 700-750°C; [1-3]). Geochronological studies addressing this issue typically utilise the U-Pb system in zircon capable of recording extended periods of crystallisation, particularly in evolved calc-alkaline systems that spend most of their lifetime zircon-saturated. In this study, we integrate U-Pb dating of zircon and titanite to investigate the longevity of the magma reservoir that produced the Kneeling Nun Tuff, a 35 Ma, >900 km3 crystal-rich rhyolitic super-eruption from the Mogollon-Datil volcanic field in New Mexico (USA). High-precision ID-TIMS U-Pb dates of single crystals of both zircon and titanite independently record a continuous crystallisation history over >400,000 years. We combine the dating of both accessory phases with textural, major, trace element and isotopic studies of single crystals, placing tight constraints on the thermal conditions of magma accumulation and storage while recording differentiation and rejuvenation processes within the magma reservoir. The results suggest a protracted `cool' upper-crustal storage of magma prior to the Kneeling Nun Tuff eruption followed by a melting event which reduced the magma crystallinity and conditioned it for eruption. [1] Bachmann & Bergantz (2004), J. Petrol. 45, 1565-1582. [2] Gelman et al. (2013), Geology 41, 759-762. [3] Cooper & Kent (2014), Nature 506, 480-483.

Geochemical fingerprints and pebbles zircon geochronology

Indian Academy of Sciences (India)

Home; Journals; Journal of Earth System Science; Volume 125; Issue 7. Geochemical fingerprints and pebbles zircon geochronology: Implications for the provenance and tectonic setting of Lower Cretaceous sediments in the Zhucheng Basin (Jiaodong peninsula, North China). Jin-Long Ni Jun-Lai Liu Xiao-Ling Tang ...

Archean and proterozoic in the West-European Hercynian chain: isotopic geochemistry (Sr-Nd-Pb) and U-Pb geochronology on zircons

International Nuclear Information System (INIS)

Guerrot, C.

1989-01-01

The first part of this research thesis reports the study of isotopic (Sr-Nd-Pb) geochemistry and U-Pb geochronology on zircons in the immersed granulites of the Bay of Biscay: U-Pb geochronology on zircons, Nd isotopic geochemistry, Sr isotopic geochemistry, common Pb, Rb-Sr, Sm-Nd and rare earth data on minerals, comparison with other European granulites, comparison with West-Africa, study of Archean and proterozoic in the Hercynian chain. The second part reports the study of the U-Pb geochronology on zircon in the Cadomian, and the third part addresses the Sr-Nd isotopic geochemistry of some Cadomian granitoid, and the crust contamination in different regions [fr

Effect of naturally-occurring uranium and thorium on the level of crystal lattice damage of Malaysian Zircon

International Nuclear Information System (INIS)

Meor Yusoff Sulaiman; Khangoankar, P.R.; Kamarudin Husin

1999-01-01

Malaysian zircon is classified as a radioactive mineral due to its high uranium and thorium content. Recoil α, which is produce from the decay process of these radioactive elements, could results to the damage of the crystal. Metamictization or crystal lattice damage level of this mineral can be determined from their crystallise size and lattice strain values. Results for two local zircon samples with different uranium and thorium content seem to suggest that there is some relationship between the concentration of these elements and its metamictization level. Comparison of the lattice strain value with previous results conducted on zircon from different country shows that the value is still within the range obtained. Microstructure analysis was also done on the samples. Fractures and pores formed on the mineral surface support the lattice expansion phenomena obtained from the crystallographic analysis. Production of a clean, white non-radioactive zircon pigment is among the commercial potential that could be derived from this study. (Author)

Effect of pressure on the Raman-active modes of zircon (ZrSiO4): a first-principles study

Science.gov (United States)

Sheremetyeva, Natalya; Cherniak, Daniele J.; Watson, E. Bruce; Meunier, Vincent

2018-02-01

Density-functional theory (DFT) was employed in a first-principles study of the effects of pressure on the Raman-active modes of zircon (ZrSiO4), using both the generalized gradient and local density approximations (GGA and LDA, respectively). Beginning with the equilibrium structure at zero pressure, we conducted a calibration of the effect of pressure in a manner procedurally similar to an experimental calibration. For pressures between 0 and 7 GPa, we find excellent qualitative agreement of frequency-pressure slopes partial ω /partial P calculated from GGA DFT with results of previous experimental studies. In addition, we were able to rationalize the ω vs. P behavior based on details of the vibrational modes and their atomic displacements. Most of the partial ω /partial P slopes are positive as expected, but the symmetry of the zircon lattice also results in two negative slopes for modes that involve slight shearing and rigid rotation of SiO4 tetrahedra. Overall, LDA yields absolute values of the frequencies of the Raman-active modes in good agreement with experimental values, while GGA reproduces the shift in frequency with pressure especially well.

Assessment of source material (U and Th) in exploration, mining, processing of zircon sand in Central Kalimantan

International Nuclear Information System (INIS)

Dedi Hermawan; Pandu Dewanto; Sudarto

2011-01-01

From 2004 to 2008, according to data released by the Commerce Department, the volume of zircon sand and concentrates exports has increased highly. One of many locations in Indonesia that widely available zircon sand is Kalimantan island. For example, Central Kalimantan Province in 2007 to 2008 exports about 51,000 tones up to 79,000 tones of zircon sand annually. The concentration of source material in the zircon sand is important to be known because the presence of natural radioactive U and Th in zircon sand has the potential radiation hazard. Therefore it is necessary to conduct an assessment the potential reserves related to the source material contained in the zircon sand and radiation safety that are applied in the process of mining or processing of zircon sand. In this paper the location of mining and processing of zircon sand is restricted to the province of Central Kalimantan. From the assessment obtained that source material which is carried by zircon sand export form the province of Central Kalimantan have the potential to exceed the limits set by the BAPETEN Chairman Decree No.9 of 2006 About the Implementation of the Additional Protocol to the Accountability System and Control of Nuclear Materials. In terms of compliance with radiation safety, required increased surveillance of K3 during mining, process / processing by the worker, supervisor / supervisors and regional management company to be able the achievement of compliance with the provisions of the management of materials and the safety of radiation sources based on national regulations (BAPETEN) and international. (author)

Zircon and monazite petrochronologic record of prolonged amphibolite to granulite facies metamorphism in the Ivrea-Verbano and Strona-Ceneri Zones, NW Italy

Science.gov (United States)

Guergouz, Celia; Martin, Laure; Vanderhaeghe, Olivier; Thébaud, Nicolas; Fiorentini, Marco

2018-05-01

In order to improve the understanding of thermal-tectonic evolution of high-grade terranes, we conducted a systematic study of textures, REE content and U-Pb ages of zircon and monazite grains extracted from migmatitic metapelites across the amphibolite to granulite facies metamorphic gradient exposed in the Ivrea-Verbano and Strona-Ceneri Zones (Italy). This study documents the behaviour of these accessory minerals in the presence of melt. The absence of relict monazite grains in the metasediments and the gradual decrease in the size of inherited zircon grains from amphibolite to granulite facies cores indicate partial to total dissolution of accessory minerals during the prograde path and partial melting. The retrograde path is marked by (i) growth of new zircon rims (R1 and R2) around inherited cores in the mesosome, (ii) crystallisation of stubby zircon grains in the leucosome, especially at granulite facies, and (iii) crystallisation of new monazite in the mesosome. Stubby zircon grains have a distinctive fir-tree zoning and a constant Th/U ratio of 0.20. Together, these features reflect growth in the melt; conversely, the new zircon grains with R1 rims have dark prismatic habits and Th/U ratios ages obtained on both types are similar, indicating contemporaneous growth of stubby zircon and rims around unresorbed zircon grains, reflecting the heterogeneous distribution of the melt at the grain scale. In the Ivrea-Verbano Zone the interquartile range (IQR) of U-Pb ages on zircon and monazite are interpreted to represent the length of zircon and monazite crystallisation in the presence of melt. Accordingly, they provide an indication on the minimum duration for high-temperature metamorphism and partial melting of the lower crust: 20 Ma and 30 Ma in amphibolite and granulite facies, respectively. In amphibolite facies, zircon crystallisation between 310 and 294 Ma (IQR) is interpreted to reflect metamorphic peak condition and earlier retrograde history; conversely

Tracing the depositional history of Kalimantan diamonds by zircon provenance and diamond morphology studies

Science.gov (United States)

Kueter, Nico; Soesilo, Joko; Fedortchouk, Yana; Nestola, Fabrizio; Belluco, Lorenzo; Troch, Juliana; Wälle, Markus; Guillong, Marcel; Von Quadt, Albrecht; Driesner, Thomas

2016-11-01

Diamonds in alluvial deposits in Southeast Asia are not accompanied by indicator minerals suggesting primary kimberlite or lamproite sources. The Meratus Mountains in Southeast Borneo (Province Kalimantan Selatan, Indonesia) provide the largest known deposit of these so-called "headless" diamond deposits. Proposals for the origin of Kalimantan diamonds include the adjacent Meratus ophiolite complex, ultra-high pressure (UHP) metamorphic terranes, obducted subcontinental lithospheric mantle and undiscovered kimberlite-type sources. Here we report results from detailed sediment provenance analysis of diamond-bearing Quaternary river channel material and from representative outcrops of the oldest known formations within the Alino Group, including the diamond-bearing Campanian-Maastrichtian Manunggul Formation. Optical examination of surfaces of diamonds collected from artisanal miners in the Meratus area (247 stones) and in West Borneo (Sanggau Area, Province Kalimantan Barat; 85 stones) points toward a classical kimberlite-type source for the majority of these diamonds. Some of the diamonds host mineral inclusions suitable for deep single-crystal X-ray diffraction investigation. We determined the depth of formation of two olivines, one coesite and one peridotitic garnet inclusion. Pressure of formation estimates for the peridotitic garnet at independently derived temperatures of 930-1250 °C are between 4.8 and 6.0 GPa. Sediment provenance analysis includes petrography coupled to analyses of detrital garnet and glaucophane. The compositions of these key minerals do not indicate kimberlite-derived material. By analyzing almost 1400 zircons for trace element concentrations with laser ablation ICP-MS (LA-ICP-MS) we tested the mineral's potential as an alternative kimberlite indicator. The screening ultimately resulted in a small subset of ten zircons with a kimberlitic affinity. Subsequent U-Pb dating resulting in Cretaceous ages plus a detailed chemical reflection make

Proterozoic to Mesozoic evolution of North-West Africa and Peri-Gondwana microplates: Detrital zircon ages from Morocco and Canada

Science.gov (United States)

Marzoli, Andrea; Davies, Joshua H. F. L.; Youbi, Nasrrddine; Merle, Renaud; Dal Corso, Jacopo; Dunkley, Daniel J.; Fioretti, Anna Maria; Bellieni, Giuliano; Medina, Fida; Wotzlaw, Jörn-Frederik; McHone, Greg; Font, Eric; Bensalah, Mohamed Khalil

2017-05-01

The complex history of assemblage and disruption of continental plates surrounding the Atlantic Ocean is in part recorded by the distribution of detrital zircon ages entrained in continental sedimentary strata from Morocco (Central High Atlas and Argana basins) and Canada (Grand Manan Island, New Brunswick). Here we investigate detrital zircon from the latest Triassic (ca. 202 Ma) sedimentary strata directly underlying lava flows of the Central Atlantic magmatic province or interlayered within them. SHRIMP (Sensitive High-Resolution Ion MicroProbe) and LA-ICP-MS (Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry) U-Pb ages for zircon range from Paleozoic to Archean with a dominant Neoproterozoic peak, and significant amounts of ca. 2 Ga zircon. These ages suggest a prevailing West African (Gondwanan) provenance at all sampling sites. Notably, the Paleoproterozoic zircon population is particularly abundant in central Morocco, north of the High Atlas chain, suggesting the presence of Eburnean-aged rocks in this part of the country, which is consistent with recent geochronologic data from outcropping rocks. Minor amounts of late Mesoproterozoic and early Neoproterozoic zircon ages (ca. 1.1-0.9 Ga) in Moroccan samples are more difficult to interpret. A provenance from Avalonia or Amazonia, as proposed by previous studies is not supported by the age distributions observed here. An involvement of more distal source regions, possibly located in north-eastern Africa (Arabian Nubian Shield) would instead be possible. Paleozoic zircon ages are abundant in the Canadian sample, pointing to a significant contribution from Hercynian aged source rocks. Such a signal is nearly absent in the Moroccan samples, suggesting that zircon-bearing Hercynian granitic rocks of the Moroccan Meseta block were not yet outcropping at ca. 200 Ma. The only Moroccan samples that yield Paleozoic zircon ages are those interlayered within the CAMP lavas, suggesting an increased dismantling

U-Pb systematics of zircon and titanite from the Gardnos impact structure, Norway: Evidence for impact at 546 Ma?

Science.gov (United States)

Kalleson, E.; Corfu, F.; Dypvik, H.

2009-05-01

Zircon and titanite were investigated in impactites of the Gardnos structure, a crater formed in Sveconorwegian (ca. 1 Ga) crust, which was then overridden in the Devonian by Caledonian nappes. Observed deformation features in zircons are granular texture, planar microstructures, and likely the incorporation of organic carbon during impact causing black staining of the zircon grains. The grains were studied by scanning electron microscopy (SEM) and cathode luminescence (CL) and dated by U-Pb isotope dilution - thermo-ionization mass spectrometry (ID-TIMS). Zircon grains without impact related features have U-Pb data showing moderate discordance (5-13%) and indicating formation ages mostly in the range of 1600-1000 Ma, except detrital zircon ages as old as >2481 Ma, reflecting the diversity of target rocks in the area. Titanite with concordant ages of 995-999 Ma dates metamorphism during final juxtaposition of the Telemarkia on the Idefjorden terrane to the east. Zircon grains with demonstrated or presumed shock features yield highly discordant (14-40%) U-Pb data, with a majority of them plotting along an array with a lower intercept of about 340 Ma reflecting the influence of the Caledonian orogeny and recent Pb-loss. One zircon grain was totally reset at 379 Ma during late Caledonian metamorphism, which also caused local growth of new titanite. A specific group of zircon grains yields data with relatively high discordance for moderate U contents, and five of these analyses, including that of a grain with proven granular or aggregate texture, fit a discordia line with an upper intercept of 546 ± 5 Ma. These features are interpreted as indicating zircon break-down to an amorphous state during impact, with subsequent recrystallization into microcrystalline aggregates causing extensive to complete Pb loss. We further suggest that their crystallinity prevented Pb loss during the Caledonian orogeny, while the small subgrain size and increasing metamictisation allowed

Provenance of sediments from Sumatra, Indonesia - Insights from detrital U-Pb zircon geochronology, heavy mineral analyses and Raman spectroscopy

Science.gov (United States)

Liebermann, C.; Hall, R.; Gough, A.

2017-12-01

The island of Sumatra is situated at the southwestern margin of the Indonesian archipelago. Although it is the sixth largest island in the world, the geology of the Sumatra sedimentary basins and their underlying basement is relatively poorly understood in terms of their provenance. This work is a multi-proxy provenance study utilizing U-Pb detrital zircon dating by LA-ICP-MS combined with optical and Raman spectroscopy-based heavy mineral analysis. It will help to unravel the stratigraphy of Sumatra, contribute to paleogeographic reconstruction of western SE Asia, and aid a wider understanding of Sumatran petroleum plays. Thin section analyses, heavy mineral assemblages, and >3500 concordant U-Pb zircon ages, from samples acquired during two fieldwork seasons indicate a mixed provenance for Cenozoic sedimentary formations, including both local igneous sources and mature basement rocks. Characteristic Precambrian zircon age spectra are found in all analysed Cenozoic sedimentary strata. These can be correlated with zircon age populations found in Sumatran basement rocks; Neoproterozoic and Mesoproterozoic age groups are dominant (c. 500-600 Ma, c. 850-1000 Ma, c. 1050-1200 Ma). Paleoproterozoic to Archaean zircons occur as minor populations. The Phanerozoic age spectra of the Cenozoic formations are characterised by distinct Carboniferous, Permo-Triassic, and Jurassic-Cretaceous zircon populations. Permo-Triassic zircons are interpreted to come from granitoids in the Malay peninsula or Sumatra itself. Eocene to Lower Miocene strata are characterised by ultrastable heavy minerals such as zircon, tourmaline, and rutile, which together with garnet, suggest the principal sources were igneous and metamorphic basement rocks. Cenozoic zircons appear only from the Middle Miocene onwards. This change is interpreted to indicate a new contribution from a local volcanic arc, and is supported by the occurrence of unstable heavy minerals such as apatite and clinopyroxene, and the

Apollo 12 breccia 12013: Impact-induced partial Pb loss in zircon and its implications for lunar geochronology

Science.gov (United States)

Thiessen, F.; Nemchin, A. A.; Snape, J. F.; Bellucci, J. J.; Whitehouse, M. J.

2018-06-01

Apollo 12 breccia 12013 is composed of two portions, one grey in colour, the other black. The grey portion of the breccia consists mainly of felsite thought to have formed during a single crystallisation event, while the black part is characterized by presence of lithic fragments of noritic rocks and individual plagioclase crystals. In this study, U-Pb analyses of Ca-phosphate and zircon grains were conducted in both portions of the breccia. The zircon grains within the grey portion yielded a large range of ages (4154 ± 7 to 4308 ± 6 Ma, 2σ) and show decreasing U and Th concentrations within the younger grains. Moreover, some grains exhibit recrystallisation features and potentially formation of neoblasts. The latter process requires high temperatures above 1600-1700 °C leading to the decomposition of the primary zircon grain and subsequent formation of new zircon occurring as neoblasts. As a result of the high temperatures, the U-Pb system of the remaining original zircon grains was most likely open for Pb diffusion causing partial resetting and the observed range of 207Pb/206Pb ages. The event that led to the Pb loss in zircon could potentially be dated by the U-Pb system in Ca-phosphates, which have a weighted average 207Pb/206Pb age across both lithologies of 3924 ± 3 Ma (95% conf.). This age is identical within error to the combined average 207Pb/206Pb age of 3926 ± 2 Ma that was previously obtained from Ca-phosphates within Apollo 14 breccias, zircon grains in Apollo 12 impact melt breccias, and the lunar meteorite SaU 169. This age was interpreted to date the Imbrium impact. The zircon grains located within the black portion of the breccia yielded a similar range of ages (4123 ± 13 to 4328 ± 14 Ma, 2σ) to those in the grey portion. Given the brecciated nature of this part of the sample, the interpretation of these ages as representing igneous crystallisation or resetting by impact events remains ambiguous since there is no direct link to their

Timing of the Permian-Triassic biotic crisis: implications from new zircon U/Pb age data (and their limitations)

Science.gov (United States)

Mundil, Roland; Metcalfe, Ian; Ludwig, Kenneth R.; Renne, Paul R.; Oberli, Felix; Nicoll, Robert S.

2001-04-01

The most profound biotic crisis in the Earth's history, causing the near extinction of both terrestrial and marine life, occurred at the end of the Permian period about 253 Myr ago and marks the Paleozoic-Mesozoic era boundary. The cause of this event is still a matter of vigorous debate, with both brief and catastrophic as well as gradual mechanisms having been proposed. Similar to a recent landmark study, this study uses the U-Pb method on zircons from the uppermost Permian/lowermost Triassic ash fall deposits at Meishan (Zhejiang Province, SE China) in order to examine time and rate constraints for these events. The results of both this study and previous work show that for these ash layers, the effects of Pb loss are combined with varying amounts and sources of inheritance, resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases. Though the effects of Pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid (as opposed to commonly applied air abrasion) prior to analysis, the presence within a single ash layer of multiple generations of older xenocrysts (in many cases only slightly older than the depositional age) has made quantitative interpretation even more difficult. When these combined phenomena bias individual zircon ages by less than a percent, they are extremely difficult to deconvolute, and, if multi-grain analyses are used, can become impossible to recognize (because of the resulting age averaging). Monte Carlo simulations using actual measurements of individual zircon crystals show that age excursions due to Pb loss and xenocrystic contamination for the Meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi-grain zircon samples are compared. Thus this study uses only high-precision analyses of single crystals, whether from our work or that of previous studies. Three main conclusions have emerged. First, our

U-Pb (SHRIMP II) Age of zircons from ash tuffs of the upper vendian Chernyi Kamen formation (Sylvitsa group, Middle Urals)

International Nuclear Information System (INIS)

Ronkin, Yu.L.; Grazhdankin, D.V.; Maslov, A.V.; Mizens, G.A.; Matukov, D.I.; Krupenin, M.T.; Petrov, G.A.; Lepikhina, O.P.; Kornilova, A.Yu.

2006-01-01

To make more precise the model of correlation of the Middle Urals western slope upper vendian layers with the White Sea remote layers one carried out the SHRIMP-II procedure base U-Pb-dating of the volcanogenic zircons from the ash tuffs and of the volcanogenic zircon enclosing argillites of the Middle Urals Chernyi Kamen formation. The obtained age value of the studied zircons equal to 557+-13 million years is in line with the geological data [ru

Going back in time with zircon

International Nuclear Information System (INIS)

Burger, A.; Faurie, J.

1978-01-01

Uranium-lead age dating, with zircon as the agent is the most recent advance in exploring rocks and minerals to define their stratigraphic sequence. The authors believe it will have a tremendous effect on the accurate mapping of the earth's mineral resources, including those of Antartica; indeed, even of the moon

Paleoproterozoic mojaveprovince in northwestern Mexico? Isotopic and U-Pb zircon geochronologic studies of precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora

Science.gov (United States)

Lang, Farmer G.; Bowring, S.A.; Matzel, J.; Maldonado, G.E.; Fedo, C.; Wooden, J.

2005-01-01

Whole-rock Nd isotopic data and U-Pb zircon geochronology from Precambrian crystalline rocks in the Caborca area, northern Sonora, reveal that these rocks are most likely a segment of the Paleoproterozoic Mojave province. Supporting this conclusion are the observations that paragneiss from the ??? 1.75 Ga Bamori Complex has a 2.4 Ga Nd model age and contains detrital zircons ranging in age from Paleo- proterozoic (1.75 Ga) to Archean (3.2 Ga). Paragneisses with similar age and isotopic characteristics occur in the Mojave province in southern California. In addition, "A-type" granite exposed at the southern end of Cerro Rajon has ca 2.0 Ga Nd model age and a U-Pb zircon age of 1.71 Ga, which are similar to those of Paleoproterozoic granites in the Mojave province. Unlike the U.S. Mojave province, the Caborcan crust contains ca. 1.1 Ga granite (Aibo Granite), which our new Nd isotopic data suggest is largely the product of anatexis of the local Precambrian basement. Detrital zircons from Neoproterozoic to early Cambrian miogeoclinal arenites at Caborca show dominant populations ca. 1.7 Ga, ca. 1.4 Ga, and ca. 1.1 Ga, with subordinate Early Cambrian and Archean zircons. These zircons were likely derived predominately from North American crust to the east and northeast, and not from the underlying Caborcan basement. The general age and isotopic similarities between Mojave province basement and overlying miogeoclinal sedimentary rocks in Sonora and southern California is necessary, but not sufficient, proof of the hypothesis that Sonoran crust is allochthonous and was transported to its current position during the Mesozoic along the proposed Mojave-Sonora megashear. One viable alternative model is that the Caborcan Precambrian crust is an isolated, autochthonous segment of Mojave province crust that shares a similar, but not identical, Proterozoic geological history with Mojave province crust found in the southwest United States ?? 2005 Geological Society of America.

Excellent durability of DLC film on carburized steel (JIS-SCr420) under a stress of 3.0 GPa

International Nuclear Information System (INIS)

Yakabe, F; Kumagai, M; Kuwahara, H; Ochiai, S; Jinbo, Y; Horiuchi, T

2008-01-01

To improve durability of transmission gears, Diamond Like Carbon (DLC) film coated on roller was estimated as well as TiN film. These films were coated on JIS-SCr420 steel, which was carburized, quenched, and tempered. DLC and TiN films were deposited by PCVD and PVD process, respectively. These surface modified rollers were estimated by usual metallurgical methods (observation of microstructure by optical microscope, SEM, and TEM, measurement of hardness by Vickers hardness tester and nano-indentator), measurement of friction coefficient by ball-on-disk in dry atmosphere, analysis of carbon by Raman spectroscopy and hydrogen by EDRA, and lifetime of pitting by the roller-pitting test. The hardness values were 21 GPa and 26 GPa, the elasticity coefficients were 192 GPa and 336 GPa, the friction coefficients were 0.1∼0.15 and 0.5∼0.6 for DLC and TiN films, respectively. The present DLC was a typical DLC called as hydrogenated amorphous carbon (a-C: H). The hydrogen content was about 20%. The surface fatigue resistance of DLC-coated specimen had 100 times longer life than that the carburized and quenched one even under Hertzian contact stress of 3.0 GPa. TiN coated specimen was failed at 3.0 GPa by 5.17·10 5 cycles despite that the strength of the surface of the substrate was reduced due to the exposure at higher temperature in the coating process than the temperature for tempering

Late cenozoic magmatism in the South Patagonian batholith: SHRIMP U-Pb zircon age evidence

International Nuclear Information System (INIS)

Fanning, C.M; Herve, F; Pankhurst, R.J; Thomson, S; Faundez, V

2001-01-01

The North Patagonian Batholith (NPB) has a zonal age pattern which includes a well defined belt of Miocene and Mio-Pliocene plutons in its central portion (Pankhurst et al., 1999) which are spatially, and probably genetically related to the Liquine-Ofqui Fault Zone. Previous geochronological studies in the Southern Patagonian Batholith (SPB), as summarized by Bruce et al. (1991), have yielded 9 late Cenozoic K-Ar or Ar-Ar ages out of a total of 116 age determinations. None of these young ages correspond to U-Pb determinations on zircons, and some of the young ages correspond to satellite plutons east of the SPB proper, such as the Torres del Paine intrusion. In this paper we present the first late Cenozoic SHRIMP U-Pb zircon ages in the area of the SPB. The morphology of the analysed zircon crystals is described and leads to some inferences on the methodology and on the geological interpretation of the obtained ages (au)

Synthesis, Characterization and Thermal Diffusivity of Holmium and Praseodymium Zirconates

OpenAIRE

Stopyra M.; Niemiec D.; Moskal G.

2016-01-01

A2B2O7 oxides with pyrochlore or defected fluorite structure are among the most promising candidates for insulation layer material in thermal barrier coatings. The present paper presents the procedure of synthesis of holmium zirconate Ho2Zr2O7 and praseodymium zirconate Pr2Zr2O7 via Polymerized-Complex Method (PCM). Thermal analysis of precursor revealed that after calcination at relatively low temperature (700°C) fine-crystalline, single-phase material is obtained. Thermal diffusivity was me...

Zircon reveals protracted magma storage and recycling beneath Mount St. Helens

Science.gov (United States)

Claiborne, L.L.; Miller, C.F.; Flanagan, D.M.; Clynne, M.A.; Wooden, J.L.

2010-01-01

Current data and models for Mount St. Helens volcano (Washington, United States) suggest relatively rapid transport from magma genesis to eruption, with no evidence for protracted storage or recycling of magmas. However, we show here that complex zircon age populations extending back hundreds of thousands of years from eruption age indicate that magmas regularly stall in the crust, cool and crystallize beneath the volcano, and are then rejuvenated and incorporated by hotter, young magmas on their way to the surface. Estimated dissolution times suggest that entrained zircon generally resided in rejuvenating magmas for no more than about a century. Zircon elemental compositions reflect the increasing influence of mafic input into the system through time, recording growth from hotter, less evolved magmas tens of thousands of years prior to the appearance of mafic magmas at the surface, or changes in whole-rock geochemistry and petrology, and providing a new, time-correlated record of this evolution independent of the eruption history. Zircon data thus reveal the history of the hidden, long-lived intrusive portion of the Mount St. Helens system, where melt and crystals are stored for as long as hundreds of thousands of years and interact with fresh influxes of magmas that traverse the intrusive reservoir before erupting. ?? 2010 Geological Society of America.

Wear of tin coating and Al-Si alloy substrate against carburized steel under mixed lubrication

Science.gov (United States)

Wang, Q.; Cheng, H. S.; Fine, M. E.

1994-04-01

Tin coatings on Al-Si alloys are widely used in the automotive industries. The soft tin coating and the harder substrate alloy form a tribological system with the advantages of low friction and reasonably high load-bearing capacity. Wear tests of tin coated Al-Si Z332 alloy in conformal contact against carburized 1016 steel have been carried out under mixed lubrications with SAE 10W30 oil to study the wear mechanisms. Two major wear mechanisms, uniform wear of the tin coating due to micro-plowing and spall pitting related to the substrate are found to contribute to the bearing material loss when the fluid lubrication film is relatively thick (Lambda about 1.6). Under conditions of thinner films (Lambda approximately = 0.8), some local coating debonding occurs. The pitting and local coating debounding are closely related to fracture in the substrate. The bonding between silicon and tin seems to be weaker than between aluminum and tin. During wear, oxidation occurs.

Gamma-rays attenuation of zircons from Cambodia and South Africa at different energies: A new technique for identifying the origin of gemstone

Science.gov (United States)

Limkitjaroenporn, P.; Kaewkhao, J.

2014-10-01

In this work, the gamma-rays interaction properties of zircons from Cambodia and South Africa have been studied. The densities of Cambodian and South African's zircons are 4.6716±0.0040 g/cm3 and 4.5505±0.0018 g/cm3, respectively. The mass attenuation coefficient and the effective atomic number of gemstones were measured with the gamma-ray in energies range 223-662 keV using the Compton scattering technique. The mass attenuation coefficients of both zircons decreased with the increasing of gamma-rays energies. The different mass attenuation coefficients between the two zircons observed at gamma-ray energies below 400 keV are attributed to the differences in the photoelectric interaction. The effective atomic number of zircons was decreased with the increasing of gamma-ray energies and showed totally different values between the Cambodia and South Africa sources. The origins of the two zircons could be successfully identified by the method based on gamma-rays interaction with matter with advantage of being a non-destructive testing.

Zircon U-Pb and Hf isotopic constraints on the magmatic evolution of the Northern Luzon Arc

Directory of Open Access Journals (Sweden)

Yu-Ming Lai

2018-01-01

Full Text Available The complete volcanic sequences restored in the Coastal Range of Taiwan are key archives for better understanding the magmatic and tectonic evolution of the Northern Luzon Arc. This paper reports (1 new zircon U-Pb ages and Hf isotopic data of fourteen volcanic samples from different sequences of four major volcanoes in the Coastal Range, (2 Hf isotopic data of dated magmatic and detrital zircons from two offshore volcanic islands, Lutao and Lanyu. These data indicate that the arc magmatism in the Coastal Range started at ~15 Ma, most active at ~9 Ma, and ceased at ~4.2 Ma. Magmatic zircons from the arc rocks show a significant variation in Hf isotopic composition, with εHf(T values varying from +24.9 to +4.8. As pointed out by our previous studies, old continental zircons that show Cathaysian-type ages and Hf isotope features are common in samples from the Yuemei, Chimei, and Lanyu volcanoes, supporting the notion for the influence of the existence of an accreted micro-continent or continental fragment plays a role in the petrogenesis. Such inherited zircons are not observed in the Chengkuang’ao and Tuluanshan volcanoes and uncommon in Lutao, implying the discontinuity or a limited extent of the accreted continental fragment. The εHf(T values are high and positive from ~15 - 8 Ma (+25 to +15; ±5ε-unit variation, and became lower from ~6 to 4.2 Ma (+20 to +8; ±6ε units and the lowest from ~1.3 Ma (+19 to +5; ±7ε units. Such a temporal variation in zircon Hf isotopic ratios can be also identified in whole-rock Hf and Nd isotopic compositions, which decrease from ~6 Ma when the Northern Luzon Arc may have started colliding with the Eurasian continental margin.

Elemental and Isotopic Tomography at Single-Atom-Scale in 4.0 and 2.4 Ga Zircons

Science.gov (United States)

Valley, J. W.; Reinhard, D. A.; Snoeyenbos, D.; Lawrence, D.; Martin, I.; Kelly, T. F.; Ushikubo, T.; Strickland, A.; Cavosie, A. J.

2012-12-01

Atom probe tomography can determine identity (mass/charge ratio) and 3-D position of individual atoms in minerals such as zircon. These data provide unique information for understanding the thermal history and mechanisms of mineral reaction and exchange, including radiation damage. Nine needle-shaped specimens ~100 nm in diameter (at the apex) were sampled from 2 zircons by FIB and analyzed with a local-electrode atom probe (LEAP), CAMECA LEAP 4000X HR. The LEAP uses pulsed-laser heating to field evaporate the tip of a zircon needle and accelerates the ions into a position-sensitive TOF-MS. With due care for complex isobaric interferences (molecules, multiple ionizations) and background correction, it is possible to individually identify up to 10E8 atoms/needle (36% detection efficiency) by mass/charge (MRP ~ 1000@ m/n=16Da) and position (X-Y-Z coordinates on 0.2 nm scale) (Kelly & Larson 2012). The 3-D distribution of Pb and Y differ at atom-scale in the 2 zircons. Zircon #1 (4007 Ma, Jack Hills, W. Australia, Cavosie 2005, Ushikubo et al. 2008, Bouvier et al. 2011) is homogeneous in Pb and Y. In contrast, incompatible elements, including Pb and Y, are concentrated in equant 5-10 nm dia. domains, spaced ~50 nm apart in zircon #2 (2438 Ma, Albion-Raft R-Grouse Ck core complex, Utah, Strickland et al. 2011). U is homogeneously distributed in both zircons. The analyzed domains suffered 4-8 x 10E15 α-decay events/mg due to U and Th decay and yet both zircons yield >97% concordant U-Pb ages by SIMS, suggesting annealing of radiation damage during the life of the zircons. The 207-Pb/206-Pb ratios for these nm-scale domains, as measured by LEAP, average 0.17 for the 2.4 Ga Zrc2 (3 needles) and 0.43 for the 4.0 Ga Zrc1 (5 needles). These ratios are less precise (±40% 2σ) due to ultra-small sample size, but are in excellent agreement with values measured by SIMS, 0.1684 and 0.4269, respectively. Thus Pb in both zircons is radiogenic. The Pb-Y-rich domains and lack of

REE, Sm-Nd and U-Pb zircon study of eclogites from the Alpine External Massifs (Western Alps): Evidence for crustal contamination

International Nuclear Information System (INIS)

Paquette, J.L.; Eidgenoessische Technische Hochschule, Zurich; Menot, R.P.; Peucat, J.J.

1989-01-01

A geochemical and geochronological study of the Alpine External Crystalline Massifs (AECM) of Aiguilles Rouges, Belledonne and Argentera was undertaken in order to constrain the geodynamic evolution of this segment of the Variscan foldbelt. Another aim of the study is to characterize the behaviour of isotopic markers, in particular the U-Pb zircon system, under high-grade metamorphic conditions. The whole-rock geochemistry of eclogites and amphibolites was investigated using major and trace element (including the REE) analytical techniques; isotopic studies were performed by application of the Sm-Nd whole-rock and U-Pb zircon methods. In terms of regional geological history, the early development of metamorphic and magmatic activity in the AECM is typical of the extensional tectonic regime observed throughout the Variscan foldbelt during the Cambro-Ordovician (i.e. basic magmatism dated at 475-450 Ma). The composition of the metabasic rocks is closely similar to tholeiites emplaced into thinned continental crust which are generally associated with the initial stages of oceanic rifting. The source regions for these metabasics are characterized by initial ε Nd values between +6 and +8, suggesting depleted mantle sources influenced by a weak crustal component and/or the existence of a metasomatised lithosphere. The multi-stage eclogite-facies metamorphism is dated at 425-395 Ma (i.e. Silurian). An application of the U-Pb method, associated with the artificial abrasion of zircon grains, has led to the recognition of a weak crustal contamination in the metabasic protoliths. This is implied by the Archaean and Lower Proterozoic upper intercepts on Concordia - devoid of geological significance - which reflect the presence of a pre-existing basement to the AECM. (orig./WL)

Proterozoic events recorded in quartzite cobbles at Jack Hills, Western Australia: New constraints on sedimentation and source of > 4 Ga zircons

Science.gov (United States)

Grange, Marion L.; Wilde, Simon A.; Nemchin, Alexander A.; Pidgeon, Robert T.

2010-03-01

Rare heavy mineral bands within quartzite cobbles were identified in two conglomerate units within the Jack Hills belt, Western Australia. Seven zircon-bearing cobbles were analysed from one location (site 152) and three from another (site 154), both approximately 1 km west of the site where zircons in excess of 4 Ga are abundant (W74 'discovery' site). Individual pebbles from the 152 site reveal three distinctive features, containing either zircons > 3.0 Ga in age, 4 Ga was discovered from the entire suite of pebbles, in contrast to the well-studied W74 site. A single detrital zircon with an age of 1220 ± 42 Ma from location 152 is the youngest grain so far reported from sedimentary rocks at Jack Hills. It shows magmatic oscillatory zoning and thus implies at least two sedimentary cycles within the Proterozoic; requiring erosion of an igneous precursor, incorporation into a clastic sediment, induration and subsequent erosion and transport to be hosted in the conglomerate. The nearest source for rocks of this age is the Bangemall Supergroup in the Collier Basin, ˜ 100 km northeast in the Capricorn Orogen. This would imply tectonic interleaving of originally more extensive Bangemall rocks, possibly related to activity along the Cargarah Shear Zone that traverses the Jack Hills belt. The lack of > 4.1 Ga zircons in the pebbles is highly significant, suggesting the immediate source of ancient zircons was no longer present at the Earth's surface. This equates with a general lack of ancient crystals noted in rocks that contain Proterozoic zircons from previous studies and implies that such grains diminish in number as earlier sedimentary rocks were successively recycled.

The first discovery of Hadean zircon in garnet granulites from the Sutam River (Aldan Shield)

Science.gov (United States)

Glukhovskii, M. Z.; Kuz'min, M. I.; Bayanova, T. B.; Lyalina, L. M.; Makrygina, V. A.; Shcherbakova, T. F.

2017-09-01

For the first time in Russia, a Hadean zircon grain with an age of 3.94 Ga (ID-TIMS) has been discovered in high-aluminous garnet granulites of the Aldan Shield among the U-Pb zircons with an age from 1.92 Ga. In this connection, the problems of its parental source, the petrogenesis of granulites that captured this zircon, and the mechanism of occurrence of these deep rocks in the upper horizons of the crust have been solved. The comparison of the geochemistry of garnet granulites and the middle crust has shown that the granulites are enriched in the entire range of rare-earth elements (except for the Eu minimum), as well as in Al2O3, U, and Th and are depleted in the most mobile elements (Na, Ca, Sr). In the upper part of the allitic weathering zone of the middle crust, which formed under conditions of arid climate, this zircon grain was originated from the weathered granites from the middle crust. In the latter case, they were empleced discretely in the upper granite-gneiss crust under high pressure conditions (the rutile age is 1.83-1.82 Ga). The zircon with an age of 3.94 Ga is comparable to the Hadean zircons from orthogneisses of the Acasta region (Canadian Shield, 4.03-3.94 Ga).

A Comprehensive Numerical Study on Effects of Natural Gas Composition on the Operation of an HCCI Engine Une étude numérique complète sur les effets de la composition du gaz naturel carburant sur le réglage d’un moteur HCCI

Directory of Open Access Journals (Sweden)

Jahanian O.

2011-11-01

Full Text Available Homogeneous Charge Compression Ignition (HCCI engine is a promising idea to reduce fuel consumption and engine emissions. Natural Gas (NG, usually referred as clean fuel, is an appropriate choice for HCCI engines due to its suitable capability of making homogenous mixture with air. However, varying composition of Natural Gas strongly affects the auto-ignition characteristics of in-cylinder mixture and the performance of the HCCI engine. This paper has focused on the influence of Natural Gas composition on engine operation in HCCI mode. Six different compositions of Natural Gas (including pure methane have been considered to study the engine performance via a thermo-kinetic zero-dimensional model. The simulation code covers the detailed chemical kinetics of Natural Gas combustion, which includes Zeldovich extended mechanism to evaluate NOx emission. Validations have been made using experimental data from other works to ensure the accuracy needed for comparison study. The equivalence ratio and the compression ratio are held constant but the engine speed and mixture initial temperature are changed for comparison study. Results show that the peak value of pressure/temperature of in-cylinder mixture is dependent of fuel Wobbe number. Furthermore, engine gross indicated power is linearly related to fuel Wobbe number. Gross indicated work, gross mean effective pressure, and NOx are the other parameters utilized to compare the performance of engine using different fuel compositions. Le moteur HCCI (Homogeneous Charge Compression Ignition, ou à allumage par compression d’une charge homogène est une idée prometteuse pour réduire la consommation de carburant et les émissions polluantes. Le gaz naturel, considéré généralement comme un carburant propre, est un choix approprié pour les moteurs HCCI en raison de sa capacité à former avec l’air un mélange homogène. Cependant, la composition du gaz naturel influe fortement sur les caract

EFFECT OF FLUORINE AND CHLORINE IONS ON THE REACTION SINTERING OF MECHANICALLY ACTIVATED ZIRCON-ALUMINA MIXTURE

Directory of Open Access Journals (Sweden)

R. Zamani Foroshani

2015-09-01

Full Text Available The aim of this work was to study the effect of fluorine and chlorine ions on the formation of mullite during the reaction sintering of mechanically activated zircon-alumina powder mixture. The results showed that mechanical activation of zirconalumina powder mixture for 20 h led to grain refinement and partial amorphization. In the presence of fluorine and chlorine ions, complete formation of mullite in the mechanically activated sample occurred after 2 h of reaction sintering at 1300oC and 1400oC, respectively. In the sample lacking fluorine and chlorine ions, mullitization was not completed even after 2 h of reaction sintering at 1400oC. It was concluded that presence of fluorine and chlorine ions enhance the dissociation of zircon and formation of mullite during the reaction sintering of mechanically activated zircon-alumina mixture.

Pervasive remagnetization of detrital zircon host rocks in the Jack Hills, Western Australia and implications for records of the early geodynamo

Science.gov (United States)

Weiss, Benjamin P.; Maloof, Adam C.; Tailby, Nicholas; Ramezani, Jahandar; Fu, Roger R.; Hanus, Veronica; Trail, Dustin; Bruce Watson, E.; Harrison, T. Mark; Bowring, Samuel A.; Kirschvink, Joseph L.; Swanson-Hysell, Nicholas L.; Coe, Robert S.

2015-11-01

It currently is unknown when Earth's dynamo magnetic field originated. Paleomagnetic studies indicate that a field with an intensity similar to that of the present day existed 3.5 billion years ago (Ga). Detrital zircon crystals found in the Jack Hills of Western Australia are some of the very few samples known to substantially predate this time. With crystallization ages ranging from 3.0-4.38 Ga, these zircons might preserve a record of the missing first billion years of Earth's magnetic field history. However, a key unknown is the age and origin of magnetization in the Jack Hills zircons. The identification of >3.9 Ga (i.e., Hadean) field records requires first establishing that the zircons have avoided remagnetization since being deposited in quartz-rich conglomerates at 2.65-3.05 Ga. To address this issue, we have conducted paleomagnetic conglomerate, baked contact, and fold tests in combination with U-Pb geochronology to establish the timing of the metamorphic and alteration events and the peak temperatures experienced by the zircon host rocks. These tests include the first conglomerate test directly on the Hadean-zircon bearing conglomerate at Erawandoo Hill. Although we observed little evidence for remagnetization by recent lightning strikes, we found that the Hadean zircon-bearing rocks and surrounding region have been pervasively remagnetized, with the final major overprinting likely due to thermal and/or aqueous effects from the emplacement of the Warakurna large igneous province at ∼1070 million years ago (Ma). Although localized regions of the Jack Hills might have escaped complete remagnetization, there currently is no robust evidence for pre-depositional (>3.0 Ga) magnetization in the Jack Hills detrital zircons.

Studies on upgrading quality of zircon concentrate to meet the standard for frit by a combination of using a screen plate electrostatic separator and other beneficiation methods

International Nuclear Information System (INIS)

Nguyen Duc Hung

2003-01-01

In the present work, researches on qualitative upgrade of zircon concentrate in order to meet the standard for frit were carried out by combinations of a screen plate type electrostatic separator with other physical beneficiation methods such as magnetic separation, flotation, gravity by air-table along with chemical treatment on laboratory scale was itself manufactured for studied scopes, after that zircon concentrate about 63.9-64.8% of ZrO 2 , less than 0.13% of TiO 2 and 0.128% of Fe 2 O 3 values were recovered. (NDH)

Determination of Uranium, Thorium and Radium 226 in Zircon containig sands by alpha spectrometry

International Nuclear Information System (INIS)

Spezzano, P.

1985-01-01

The industrial utilization of Zircon sands for the production of refractories presents radiological problems owing to the risk of inhalation of Uranium, Thorium and their decay products, present in high concentrations in such materials. A method of analysis was realized for the determination of Uranium, Thorium and Radium-226 in Zircon sands, including the total dissolution of the sample, radiochemical separation and final measurement by alpha spectrometry with surface barrier detector. The concentrations of the main alpha-emitting radionuclides presents in two samples of Zircon sands have been determined and the possibility of disequilibrium along the decay series has been pointed out

New SHRIMP U-Pb zircon ages of the metapelitic granulites from NW of Madurai, Southern India

International Nuclear Information System (INIS)

Prakash, D.

2010-01-01

Zircon cathodoluminescent imaging and SHRIMP U-Pb dating were carried out for metapelitic rocks (sapphirine-hearing granulites and garnet-cordierite gneisses) from the NW of Madurai, Southern India. The cathodoluminescence images reveal the complex, inhomogeneous internal structure having irregular-shaped core and overgrowths. Zircon grains have obliterated oscillatory zoning. SHRIMP U-Pb chronological results yield ages of 550 ± 15 Ma and 530 ± 50 Ma as a time of metamorphic overprint, and the age of 2509 ± 12 Ma and 2509 ± 30 Ma corresponding to a timing of protolith formation for sapphirine-bearing granulites and garnet-cordierite gneisses respectively. Zircon ages reflect that continental crust in the NW of Madurai region resulted from the recycling of Archaean protolith of an igneous origin similar to the preserved crust in the southern part of Dharwar craton. The present SHRIMP U-Pb zircon ages are in close agreement with earlier published Nd isotopic data which suggest an extended precrustal history of their protoliths. The abraded zircon grains indicate multiple recycling and repeated metamorphism that has ultimately resulted in present day continental crust exposed in Madurai region. These SHRIMP U-Pb zircon ages from metapelitic UHT granulites are also significant to understanding the architecture of the SGT during the amalgamation of Gondwana in Neoproterozoic time. (author)

Pb, U, Ti, Hf and Zr distributions in zircons determined by proton microprobe and fission track techniques

International Nuclear Information System (INIS)

Clark, G.J.; Gulson, B.L.; Cookson, J.A.

1979-01-01

A proton microprobe has been used to determine Pb, Tl, Hf and Zr distributions across four single zircon crystals separated from a 'rapakivi' granite. The Pb and Zr data are quantitative: Pb and Tl concentrations were below the measurable limits for determinations in situ by most other techniques. The distribution of U in the same crystals was determined by the fission track technique. Limits on precision of U allow only a qualitative correlation of U and Pb, whereas the Tl and Pb correlation is more exactly determined. Zircons with distinct cores and overgrowths exhibited uniform Zr and Hf concentrations across the crystals, whereas the high U rims and 'inclusions' (domains) also had high Tl and Pb contents. Since almost all the Pb in these zircons is derived by radioactive decay of U, the Tl substitution has paralleled that of U. The results indicate that the high U domains are 'hot spots' rather than a separate mineral phase. The strong positive correlation of U and Pb indicates that there is little U daughter product migration relative to U, within the crystal. However, for the zircon population investigated here, the data are equivocal on the question of whether U addition to zircon crystals is associated with new zircon growth or not. In either case, the heterogeneous U and Pb distributions complicate any interpretations of U-Pb isotopic analysis for such zircon populations. (author)

Feasibility of infrared analysis of iron in zircon

International Nuclear Information System (INIS)

Heard, I. Jr.

1980-05-01

A feasibility study has concluded that quantitative infrared analysis can be employed to determine the concentration of iron in zircon. The spectral transmission curves have shown that the iron absorption band is located at 1.15 microns. These curves also revealed a second absorption band at 1.49 microns. The source of this second peak is not known; but it exhibits some features which suggest its dependance on natural α-recoil damage. 23 references, 14 figures, 2 tables

Reaction of uranium and plutonium carbides with nitrogen; Reaction avec l'azote des carbures d'uranium et de plutonium

Energy Technology Data Exchange (ETDEWEB)

Lorenzelli, R; Martin, A; Schickel, R [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

1966-03-01

Uranium and plutonium carbides react with nitrogen during the grinding process preceding the final sintering. The reaction occurs even in argon atmospheres containing a few percent of residual nitrogen. The resulting contamination is responsible for the appearance of an equivalent quantity of higher carbide in the sintered products; nitrogen remains quantitatively in the monocarbide phase. UC can be transformed completely into nitride under a nitrogen pressure, at a temperature as low as 400 C. The reaction is more sluggish with PuC. The following reactions take places: UC + 0,8 N{sub 2} {yields}> UN{sub 1.60} + C and PuC + 0,5 N{sub 2} {yields} PuN + C. (authors) [French] Les carbures d'uranium et de plutonium reagissent avec l'azote au cours du broyage qui precede le frittage final. Cette reaction est sensible meme sous des atmospheres d'argon ne contenant que quelques pour cent d'azote. Cette contamination se traduit sur les produits frittes par l'apparition d'une quantite equivalente de carbure superieur, l'azote restant fixe quantitativement dans la phase monocarbure. On peut transformer entierement UC en nitrure par action de l'azote sous pression des 400 C. La reaction est plus difficile avec PuC. Les reactions sont les suivantes: UC + 0,8 N{sub 2} {yields} UN{sub 1.60} + C et PuC + 0,5 N{sub 2} {yields} PuN + C.

Electrophoretic growth of lead zirconate titanate nanorods

Energy Technology Data Exchange (ETDEWEB)

Limmer, S.J.; Seraji, S.; Forbess, M.J.; Wu Yun; Chou, T.P.; Nguyen, C.; Cao Guozhong [Washington Univ., Seattle, WA (United States). Dept. of Materials Science and Engineering

2001-08-16

Nanorods of lead zirconate titanate (PZT)-a ferro- and piezoelectric material-up to 10 {mu}m in length and 70 to 150 nm in diameter are produced by sol-gel electrophoresis of PZT in a track-etched polycarbonate membrane, which is used as a template. (orig.)

Rapid cooling rates at an active mid-ocean ridge from zircon thermochronology

Science.gov (United States)

Schmitt, Axel K.; Perfit, Michael R.; Rubin, Kenneth H.; Stockli, Daniel F.; Smith, Matthew C.; Cotsonika, Laurie A.; Zellmer, Georg F.; Ridley, W. Ian

2011-01-01

Oceanic spreading ridges are Earth's most productive crust generating environment, but mechanisms and rates of crustal accretion and heat loss are debated. Existing observations on cooling rates are ambiguous regarding the prevalence of conductive vs. convective cooling of lower oceanic crust. Here, we report the discovery and dating of zircon in mid-ocean ridge dacite lavas that constrain magmatic differentiation and cooling rates at an active spreading center. Dacitic lavas erupted on the southern Cleft segment of the Juan de Fuca ridge, an intermediate-rate spreading center, near the intersection with the Blanco transform fault. Their U–Th zircon crystallization ages (29.3-4.6+4.8 ka; 1δ standard error s.e.) overlap with the (U–Th)/He zircon eruption age (32.7 ± 1.6 ka) within uncertainty. Based on similar 238U-230Th disequilibria between southern Cleft dacite glass separates and young mid-ocean ridge basalt (MORB) erupted nearby, differentiation must have occurred rapidly, within ~ 10–20 ka at most. Ti-in-zircon thermometry indicates crystallization at 850–900 °C and pressures > 70–150 MPa are calculated from H2O solubility models. These time-temperature constraints translate into a magma cooling rate of ~ 2 × 10-2 °C/a. This rate is at least one order-of-magnitude faster than those calculated for zircon-bearing plutonic rocks from slow spreading ridges. Such short intervals for differentiation and cooling can only be resolved through uranium-series (238U–230Th) decay in young lavas, and are best explained by dissipating heat convectively at high crustal permeability.

Structural evolvement and the capability of resistance to γ-ray irradiation on zircon originating from nyainqentanglha granite

International Nuclear Information System (INIS)

Cui Chunlong; Zhang Dong; Kang Houjun; Wang Xiaoli; Zhou Yulin; Yi Facheng; Lu Xirui; Tang Jingyou

2010-01-01

In order to investigate the structural evolvement and the capability of resistance to γ-ray irradiation on zircon as mothball waste forms of radionuclide, the zircon crystals (11.01±0.24 M) were studied as investigative object, which were collected from nyainqentanglha granite. All the samples were irradiated using a 60 Co y-ray source with 576 kGy doses. Phases, structures and microstructures of the as-gained samples before and after y-ray irradiation were characterized by means of a multi-functional microscope, cathodoluminescence (CL), backscattered electron microprobe (BEM), X-ray diffraction (XRD), Raman spectroscopy (Raman), infrared spectroscopy (IR) and scanning electron microscopy (SEM), and so on. Moreover, the geological backgrounds and chemical compositions of zircons originating from natural rocks were analyzed as well. The results indicated that the as-gained crystals came from magmatic rock which undergone near 11 million years geological evolvement and still contain UO 2 and ThO 2 with the contents of 0.5729 wt%. The alteration of 10 -3 nm magnitude in the crystal cell parameters was measured (of the standard XRD card of zircon). The irradiation on the crystalline samples using γ-ray induced to the alteration of 10 -4 nm magnitude for their crystal cell parameters. The conclusion shows that zircon crystals with a certain amount of UO 2 and ThO 2 have better structural stability for the y-ray irradiation. (authors)

Evaluation of crack growth behavior and probabilistic S–N characteristics of carburized Cr–Mn–Si steel with multiple failure modes

International Nuclear Information System (INIS)

Li, Wei; Sun, Zhenduo; Zhang, Zhenyu; Deng, Hailong; Sakai, Tatsuo

2014-01-01

Highlights: • The stepwise S–N characteristics only for interior induced failure was observed. • The interior crack growth behavior with threshold conditions in different stages was clarified. • The distribution characteristics of test data in transition failure region was evaluated. • A model for evaluating the probabilistic S–N curve with multiple failure modes was developed. - Abstract: The unexpected failures of case-hardened steels in long life regime have been a critical issue in modern engineering design. In this study, the failure behavior of a carburized Cr–Mn–Si steel under very high cycle fatigue (VHCF) was investigated, and a model for evaluating the probabilistic S–N curve associated with multiple failure modes was developed. Results show that the carburized Cr–Mn–Si steel exhibits three failure modes including the surface flaw-induced failure, the interior inclusion-induced failure without the fine granular area (FGA) and the interior inclusion-induced failure with the FGA. As the predominant failure mode in the VHCF regime, the interior failure process can be divided into four stages: (i) the small crack growth around the inclusion, (ii) the stable macroscopic crack growth outside the FGA, (iii) the unstable crack growth outside the fish-eye and (iv) the momentary fracture outside the final crack growth zone. The threshold values are successively evaluated to be 2.33 MPa m 1/2 , 4.13 MPa m 1/2 , 18.51 MPa m 1/2 and 29.26 MPa m 1/2 . The distribution characteristics of the test data in transition failure region can be well characterized by the mixed two-parameter Weibull distribution function. The developed probabilistic S–N curve model is in good agreement with the test data with multiple failure modes. Although the result is somewhat conservative in the VHCF regime, it is acceptable for safety considerations

Nanogeochronology of discordant zircon measured by atom probe microscopy of Pb-enriched dislocation loops

Science.gov (United States)

Peterman, Emily M.; Reddy, Steven M.; Saxey, David W.; Snoeyenbos, David R.; Rickard, William D. A.; Fougerouse, Denis; Kylander-Clark, Andrew R. C.

2016-01-01

Isotopic discordance is a common feature in zircon that can lead to an erroneous age determination, and it is attributed to the mobilization and escape of radiogenic Pb during its post-crystallization geological evolution. The degree of isotopic discordance measured at analytical scales of ~10 μm often differs among adjacent analysis locations, indicating heterogeneous distributions of Pb at shorter length scales. We use atom probe microscopy to establish the nature of these sites and the mechanisms by which they form. We show that the nanoscale distribution of Pb in a ~2.1 billion year old discordant zircon that was metamorphosed c. 150 million years ago is defined by two distinct Pb reservoirs. Despite overall Pb loss during peak metamorphic conditions, the atom probe data indicate that a component of radiogenic Pb was trapped in 10-nm dislocation loops that formed during the annealing of radiation damage associated with the metamorphic event. A second Pb component, found outside the dislocation loops, represents homogeneous accumulation of radiogenic Pb in the zircon matrix after metamorphism. The 207Pb/206Pb ratios measured from eight dislocation loops are equivalent within uncertainty and yield an age consistent with the original crystallization age of the zircon, as determined by laser ablation spot analysis. Our results provide a specific mechanism for the trapping and retention of radiogenic Pb during metamorphism and confirm that isotopic discordance in this zircon is characterized by discrete nanoscale reservoirs of Pb that record different isotopic compositions and yield age data consistent with distinct geological events. These data may provide a framework for interpreting discordance in zircon as the heterogeneous distribution of discrete radiogenic Pb populations, each yielding geologically meaningful ages. PMID:27617295

Crystal-plastic deformation of zircon : effects on microstructures, textures, microchemistry and the retention of radiogenic isotopes

International Nuclear Information System (INIS)

Kovaleva, E.

2015-01-01

Dating of deep-crustal deformation events potentially can be achieved by using plastically-deformed accessory minerals found in high-temperature shear zones. Deformation microstructures, such as dislocations and low-angle boundaries, form due to plastic deformation in the crystal lattice and act as fluid migration pathways and trace element (e.g. Pb, Ti, U, Th, REE) diffusion pathways through so-called “pipe diffusion”. Deformation microstructures can alter the chemical and isotopic composition of certain grain parts and may lead to complete or partial isotopic resetting of certain geochronometers (e.g. U/Th/Pb, K/Ar, Rb/Sr) in the mineral domains. This work aims to better understand the processes of crystal-plastic deformation and associated trace element redistribution and the resetting of isotopic systems in zircon. This study finds that: a) there are three general finite deformation patterns in deformed zircons; b) suggests that it is possible to reconstruct the macroscopic kinematic framework of the shear zone based on the orientation of deformed zircon grains and the operating misorientation axes; c) and demonstrates the effect of deformation microstructures on trace elements and Pb isotopes in zircon. The final goal of this project is to develop a tool for isotopic dating of high-temperature deformation events in the deep crust. In addition to these results, zircon grains with planar deformation bands have been discovered in paleo-seismic zones; these deformation features have been described in detail and a possible mechanism of their origin and formation is suggested. The effect of planar deformation bands on trace element and isotopic behavior has also been investigated. (author) [de

Hydrogenation-disproportionation-desorption-recombination in Sm2Fe16M (M=Al, Ga and Si) and magnetic properties of their carburized powders

International Nuclear Information System (INIS)

Kubis, M.; Rave, W.; Cao, L.; Gebel, B.; Mueller, K.-H.; Schultz, L.

1998-01-01

The application of the hydrogenation-disproportionation-desorption-recombination (HDDR) process in Sm 2 Fe 16 M (M=Al,Ga and Si) was investigated. The hydrogen absorption behaviour was studied by temperature-pressure analysis (TPA). In the temperature range between 500 and 800 C, Sm 2 Fe 16 M samples with M=Ga and Si show a weaker hydrogen absorption than Sm 2 Fe 16 Al. This was confirmed by X-ray diffraction which showed a complete disproportionation of Sm 2 Fe 16 Al into SmH z (1.9 2 Fe 16 Ga and Sm 2 Fe 16 Si exhibit a fraction of undecomposed material with the Th 2 Zn 17 -type structure after the disproportionation procedure. These results point to a stabilization of Sm 2 Fe 16 M against disproportionation by hydrogen for M=Ga and Si. The magnetization processes of carburized HDDR powders were studied by VSM measurements and Kerr microscopy. The demagnetization curve of our HDDR processed Sm 2 Fe 16 AlC y is well shaped, whereas those of Sm 2 Fe 16 GaC y and Sm 2 Fe 16 SiC y show a large decrease of the polarization at low fields. The favourable behaviour of Sm 2 Fe 16 AlC y is due to a homogeneous submicron grain structure. In Sm 2 Fe 16 GaC y and Sm 2 Fe 16 SiC y samples, an additional, magnetically soft phase with larger domains was observed which causes the low coercivity. As a consequence, HDDR was only favourable for the preparation of Sm 2 Fe 16 MC y hard magnets with M=Al but not for M=Ga and Si. Optimization of the HDDR process in Sm 2 Fe 16 Al and subsequent nitrogenation or carburization led to coercivities of μ 0j H c =2.9 and 2.5 T, respectively. (orig.)

Influence of temperature in TL signal induced by gamma radiation in zircon prepared by sol gel via

International Nuclear Information System (INIS)

Salas, P.; Castano, V.M.; Mendoza A, D.; Gonzalez M, P.R.; Rosa C, E. de la

2000-01-01

In this work, it was realized a study of the temperature effects in thermoluminescent signal (Tl) induced by gamma radiation in zircon, which was prepared by the sol gel method. According to the obtained results, the zircon thermically treated at 500 C or over is sensitive to radiation. This sensitivity is increased when the temperature in study is augmented, moreover, the Tl spectra form also is modified with the temperature increment. The samples thermically treated at 750 C or over present a linear response in the dose interval 27 to 165 Gy; therefore, such materials result promissories for dosimetric purposes. (Author)

Pressure-induced phase transformation in zircon-type orthovanadate SmVO4 from experiment and theory

International Nuclear Information System (INIS)

Popescu, C; Garg, Alka B; Errandonea, D; Sans, J A; Rodriguez-Hernández, P; Radescu, S; Muñoz, A; Achary, S N; Tyagi, A K

2016-01-01

The compression behavior of zircon-type samarium orthovanadate, SmVO 4 , has been investigated using synchrotron-based powder x-ray diffraction and ab initio calculations of up to 21 GPa. The results indicate the instability of ambient zircon phase at around 6 GPa, which transforms to a high-density scheelite-type phase. The high-pressure phase remains stable up to 21 GPa, the highest pressure reached in the present investigations. On pressure release, the scheelite phase is recovered. The crystal structure of the high-pressure phase and the equations of state for the zircon- and scheelite-type phases have been determined. Various compressibilities, such as the bulk, axial and bond compressibilities, estimated from the experimental data are found to be in good agreement with the results obtained from theoretical calculations. The calculated elastic constants show that the zircon structure becomes mechanically unstable beyond the transition pressure. Overall there is good agreement between the experimental and theoretical findings. (paper)

Do Zircon age Spectra Record Magmatic Cyclicity at Soufrière (Saint Lucia, Lesser Antilles)?

Science.gov (United States)

Schmitt, A. K.; Stockli, D. F.; Lindsay, J. M.

2007-12-01

The Soufrière Volcanic Center (Saint Lucia, Lesser Antilles) is a long-lived arc-volcanic system that evolved over the past 5 - 6 Ma. Its most recent volcanic activity between 20 and 40 ka was concentrated within the prominent Qualibou topographic depression and produced two voluminous pyroclastic deposits: Choiseul and the overlying Belfond. In addition, several dacitic lava domes exist within the Qualibou depression. Because evidence of earlier volcanic activity in long-lived magma systems is frequently obliterated by subsequent eruptive or volcano-tectonic events, high spatial resolution U-Th dating of zircon combined with (U-Th)/He dating is a powerful tool to identify magma crystallization episodes at depth and to link these to the eruptive record. U-Th model ages and disequilibrium corrected U-Pb ages for 56 individual zircons from Soufrière lavas (Morne Bonin, Belfond, Terre Blanche) and pumice (Choiseul, Belfond) were determined by secondary ionization mass spectrometry. The majority of results is on unpolished zircons where analysis pits integrate over the outermost ~10 μm of individual grains with a lateral spatial resolution of ~40 μm. Selected grains were subsequently analyzed by (U-Th)/He methods. Belfond and Terre Blanche (U-Th)/He zircon ages (~20 ka) agree with previous 14C charcoal ages, whereas Morne Bonin ages are much older (~250 ka). Overall, the U-Th zircon crystallization age spectrum reveals a remarkable range between ~20 and ~600 ka and displays multiple peaks, among which the most prominent are tentatively identified at ~40 ka, ~80 ka, ~130 ka, ~200 ka and ~500 ka. The distribution of rim ages indicates that most zircons lack overgrowth dating from just prior to the eruption, but the youngest ages for each sample overlap with the eruption ages. Soufrière zircons thus reveal magma intrusion, cooling, and crystallization cycles within the underlying plutonic system for which the volcanic stratigraphic record is sketchy.

Mechanisms and timescales of generating eruptible rhyolitic magmas at Yellowstone caldera from zircon and sanidine geochronology and geochemistry

Science.gov (United States)

Stelten, Mark; Cooper, Kari M.; Vazquez, Jorge A.; Calvert, Andrew T.; Glessner, Justin G

2015-01-01

We constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at Yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the (ca. 170 – 70 ka) Central Plateau Member eruptive episode – the most recent post-caldera magmatism at Yellowstone. We present 238U-230Th crystallization ages and trace-element compositions of the interiors and surfaces (i.e., unpolished rims) of individual zircon crystals from each rhyolite. We compare these zircon data to 238U- 230Th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals. Zircon age and trace-element data demonstrate that the magma reservoir that sourced the Central Plateau Member rhyolites was long-lived (150 – 250 kyr) and genetically related to the preceding episode of magmatism, which occurred ca. 256 ka. The interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of Central Plateau Member magmatism or the preceding late Upper Basin Member magmatism (i.e., are antecrysts). Conversely, most zircon surfaces crystallized near the time of eruption from their host liquids (i.e., are autocrystic). The repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted Central Plateau Member rhyolites are genetically related. Sanidine separates from each rhyolite yield 238U-230Th crystallization ages at or near the eruption age of their host magmas, coeval with the coexisting zircon surfaces, but are younger than the coexisting zircon interiors. Chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts, which considered along with their near-eruption crystallization ages suggests that nearly all CPM sanidines are autocrystic. The paucity of antecrystic sanidine crystals relative to

Stabilization of mixed carbides of uranium-plutonium by zirconium. Part 1.: uranium carbide with small additions of zirconium; Etude de la stabilisation des carbures mixtes d'uranium et de plutonium par addition de zirconium. 1. partie: etude des carbures d'uranium avec de faibles additions de zirconium

Energy Technology Data Exchange (ETDEWEB)

Bocker, S [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

1969-07-01

Cast carbide samples, being of a high density and purity, are preferable for research purposes, to samples produced by powder metallurgy methods. Samples of uranium carbide with small additions of zirconium (1 to 5 per cent) were cast, as rods, in an arc furnace. A single phase carbide with interesting qualities was produced. As cast, a dendrite structure is observed, which does not disappear, after a treatment at 1900 deg. C during 110 hours. In comparison with uranium monocarbide the compatibility with stainless steel is much improved. The specific heat (between room temperature and 2500 deg. C) is similar to the specific heat of uranium monocarbide. A study of these mixed carbides, but having a part of the uranium replaced by plutonium is under way. (author) [French] Les echantillons de monocarbures obtenus par coulee sont tres interessants pour les recherches experimentales a cause de leur grande purete, de leur densite tres elevee et de la facilite d'obtention des lingots de forme et dimensions variees. On a prepare et coule dans un four a arc des echantillons de carbures d'uranium avec de faibles additions de zirconium (1 a 5 at. pour cent). On obtient ainsi des carbures monophases presentant de meilleures proprietes que le monocarbure d'uranium. A l'etat brut de coulee on observe une structure dendritique qui n'est pas detruite par un traitement thermique de 110 heures a 1900 deg. C. La compatibilite avec l'acier inoxydable 316 (a 925 deg. C pendant 500 heures) est nettement amelioree par rapport a UC. La chaleur specifique (entre la temperature ordinaire et 2500 deg. C) et la densite sont tres peu differentes de celles du monocarbure d'uranium. Une etude concernant les composes U-Pu-Zr-C est actuellement en cours. (auteur)

U-Pb ages and Hf isotope compositions of zircons in plutonic rocks from the central Famatinian arc, Argentina

Science.gov (United States)

Otamendi, Juan E.; Ducea, Mihai N.; Cristofolini, Eber A.; Tibaldi, Alina M.; Camilletti, Giuliano C.; Bergantz, George W.

2017-07-01

The Famatinian arc formed around the South Iapetus rim during the Ordovician, when oceanic lithosphere subducted beneath the West Gondwana margin. We present combined in situ U-Th-Pb and Lu-Hf isotope analyses for zircon to gain insights into the origin and evolution of Famatinian magmatism. Zircon crystals sampled from four intermediate and silicic plutonic rocks confirm previous observations showing that voluminous magmatism took place during a relatively short pulse between the Early and Middle Ordovician (472-465 Ma). The entire zircon population for the four plutonic rocks yields coherent εHf negative values and spreads over several ranges of initial εHf(t) units (-0.3 to -8.0). The range of εHf units in detrital zircons of Famatinian metasedimentary rocks reflects a prolonged history of the cratonic sources during the Proterozoic to the earliest Phanerozoic. Typical tonalites and granodiorites that contain zircons with evolved Hf isotopic compositions formed upon incorporating (meta)sedimentary materials into calc-alkaline metaluminous magmas. The evolved Hf isotope ratios of zircons in the subduction related plutonic rocks strongly reflect the Hf isotopic character of the metasedimentary contaminant, even though the linked differentiation and growth of the Famatinian arc crust was driven by ascending and evolving mantle magmas. Geochronology and Hf isotope systematics in plutonic zircons allow us understanding the petrogenesis of igneous series and the provenance of magma sources. However, these data could be inadequate for computing model ages and supporting models of crustal evolution.

Detrital zircon U-Pb geochronological and sedimentological study of the Simao Basin, Yunnan: Implications for the Early Cenozoic evolution of the Red River

Science.gov (United States)

Chen, Yi; Yan, Maodu; Fang, Xiaomin; Song, Chunhui; Zhang, Weilin; Zan, Jinbo; Zhang, Zhiguo; Li, Bingshuai; Yang, Yongpeng; Zhang, Dawen

2017-10-01

The paleo-Red River is suggested to have been a continental-scale drainage system connecting the Tibetan Plateau to the South China Sea. However, the evolution of the paleo-Red River is still under debate. This study presents new results from sedimentological analyses and detrital zircon U-Pb geochronologic data from fluvial sedimentary rocks of Paleocene to Oligocene age of the Simao Basin to constrain the nature of the paleo-drainage system of the Red River. The detrital zircon U-Pb results reveal multiple age groups at 190-240 Ma, 260-280 Ma, 450-540 Ma, 1700-1900 Ma and 2400-2600 Ma for the Paleocene to late Eocene Denghei Formation (Fm.), but only one conspicuous peak at 220-240 Ma for the late Eocene-Oligocene Mengla Fm. Provenance analyses illustrate that the former likely had source areas that included the Hoh-Xil, Songpan-Ganzi, northern Qiangtang, Yidun and western Yangtze Terranes, which are consistent with the catchments of the Upper and Lower Jinshajiang Segments, whereas the latter mainly transported material from a limited number of sources, such as the Lincang granitic intrusions west of the Simao Basin. Integrated with available detrital zircon U-Pb geochronologic and paleogeographic data, our study suggests the existence of a paleo-Red River during the Paleocene to late Eocene that was truncated and lost its northern sources after approximately 35 Ma, due to left-lateral strike-slip faulting of the Ailao Shan-Red River and clockwise rotation of the Lanping-Simao Terrane.

Dating of zircon from high-grade rocks: Which is the most reliable method?

Directory of Open Access Journals (Sweden)

Alfred Kröner

2014-07-01

Full Text Available Magmatic zircon in high-grade metamorphic rocks is often characterized by complex textures as revealed by cathodoluminenscence (CL that result from multiple episodes of recrystallization, overgrowth, Pb-loss and modifications through fluid-induced disturbances of the crystal structure and the original U-Th-Pb isotopic systematics. Many of these features can be recognized in 2-dimensional CL images, and isotopic analysis of such domains using a high resolution ion-microprobe with only shallow penetration of the zircon surface may be able to reconstruct much of the magmatic and complex post-magmatic history of such grains. In particular it is generally possible to find original magmatic domains yielding concordant ages. In contrast, destructive techniques such as LA-ICP-MS consume a large volume, leave a deep crater in the target grain, and often sample heterogeneous domains that are not visible and thus often yield discordant results which are difficult to interpret. We provide examples of complex magmatic zircon from a southern Indian granulite terrane where SHRIMP II and LA-ICP-MS analyses are compared. The SHRIMP data are shown to be more precise and reliable, and we caution against the use of LA-ICP-MS in deciphering the chronology of complex zircons from high-grade terranes.

Petrological and zircon evidence for the Early Cretaceous granulite-facies metamorphism in the Dabie orogen, China

Science.gov (United States)

Gao, Xiao-Ying; Zhang, Qiang-Qiang; Zheng, Yong-Fei; Chen, Yi-Xiang

2017-07-01

An integrated study of petrology, mineralogy, geochemistry, and geochronology was carried out for contemporaneous mafic granulite and diorite from the Dabie orogen. The results provide evidence for granulite-facies reworking of the ultrahigh-pressure (UHP) metamorphic rock in the collisional orogen. Most zircons from the granulite are new growth, and their U-Pb ages are clearly categorized into two groups at 122-127 Ma and 188 ± 2 Ma. Although these two groups of zircons show similarly steep HREE patterns and variably negative Eu anomalies, the younger group has much higher U, Th and REE contents and Th/U ratios, much lower εHf(t) values than the older group. This suggests their growth is associated with different types of dehydration reactions. The older zircon domains contain mineral inclusions of garnet + clinopyroxene ± quartz, indicating their growth through metamorphic reactions at high pressures. In contrast, the young zircon domains only contain a few quartz inclusions and the garnet-clinopyroxene-plagioclase-quartz barometry yields pressures of 4.9 to 12.5 kb. In addition, the clinopyroxene-garnet Fe-Mg exchange thermometry gives temperatures of 738-951 °C. Therefore, the young zircon domains would have grown through peritectic reaction at low to medium pressures. The younger granulite-facies metamorphic age is in agreement not only with the adjacent diorite at 125 ± 1 Ma in this study but also the voluminous emplacement of coeval mafic and felsic magmas in the Dabie orogen. Mineral separates from both mafic granulite and its adjacent diorite show uniformly lower δ18O values than normal mantle, similar to those for UHP eclogite-facies metaigneous rocks in the Dabie orogen. In combination with major-trace elements and zircon Lu-Hf isotope compositions, it is inferred that the protolith of mafic granulites shares with the source rock of diorites, both being a kind of mafic metasomatites at the slab-mantle interface in the continental subduction channel

Pb-Pb zircon ages of the Porto Nacional high-grade metamorphic terrain, northern portion of the Goias Massif, central Brazil

Energy Technology Data Exchange (ETDEWEB)

Gorayeb, Paulo Sergio de Sousa; Moura, Candido Augusto Veloso [Para Univ., Belem, PA (Brazil). Centro de Geociencias]. E-mail: gorayebp@ufpa.br; c_moura@ufpa.br; Barros, Gisele Ribeiro de [Para Univ., Belem, PA (Brazil). Programa Institucional de Bolsas de Iniciacao Cientifica (PIBIC)]. E-mail: agbarros@amazon.com.br

2000-03-01

Single zircon Pb-evaporation ages were determined for a mafic granulite, two enderbites and a kinzigite of the Porto Nacional High-Grade Metamorphic Terrain (PNHGT) in the Goias massif. Zircons from mafic granulites and one of the enderbites of yielded average {sup 207} Pb/{sup 206} Pb ages of 2125{+-}3 Ma and 2153{+-}1 Ma, respectively, being interpreted as minimum ages of the igneous protoliths. The other enderbite, whose zircons presented round terminations, yielded an average {sup 207} Pb/{sup 206} Pb age of 2097 {+-} 2 Ma. Zircons from the kinzigite, displaying cores and rims overgrowth, presented {sup 207} Pb/{sup 206} Pb ages ranging between 2027 and 2115 Ma. However, a very homogeneous zircon crystal without overgrowth yielded age of 2100 {+-} 2 Ma, with a distinctive low Th/U value (0.02). This zircon is interpreted as a metamorphic crystal and its age probably sets the age of the granulite facies metamorphism, indicating that the PNHGT is a result of the Transamazonian thermotectonic event. (author)

A Change in Igneous Activity of the Jack Hills Zircon Sources ca. 3.9 Ga

Science.gov (United States)

Bell, E. A.; Harrison, T. M.

2010-12-01

New Ti-in-zircon crystallization temperature (Txlln) data for Jack Hills zircons reveal that the tight clustering of Hadean grains around a Txlln of 680°C, possibly indicative of felsic-to-intermediate minimum melting conditions, continues to ~3.92 Ga. Between 3.92-3.82 Ga the 680°C clustering ceases and most concordant grains cluster around an apparent Txlln of 610°C. A small group of zircons with higher Txlln (~750°C), present during the Hadean, is also observed during this period. After 3.82 Ga a Hadean-like distribution resumes for ~100 Ma. This large, concordant, low-Ti group at ~3.9 Ga is statistically distinct from the Hadean distribution and appears to be unique in the Jack Hills zircon record. The existence of coeval high- and low-Ti groups suggests that two distinct zircon-forming processes are distinguishable ~3.9 Ga, unlike during the Hadean. The significant numbers of zircons with apparent Txlln below 600°C may be suggestive of subsolidus formation, since igneous units with solidii below 600°C are relatively rare. The higher-Ti group is more consistent with an intermediate to mafic igneous origin but metamorphic overprinting or subsolidus formation at granulite grade cannot be ruled out by Txlln alone. A substantial proportion of the high-Ti group display oscillatory and disrupted oscillatory zoning in cathodoluminescence images, usually indicative of igneous origins and later metamorphism, respectively; most low-Ti grains are homogeneous. Several of each group display patchy zonation indicative of metamorphic overprinting. Although several grains with apparent Txlln >600°C display oscillatory zonation, the majority of the low-Ti group do not show textural evidence for igneous origins. We interpret these results to indicate the transition from a mechanism(s) that produced dominantly 680°C apparent zircon temperatures at ca. 3.9 Ga to include a new zircon-forming process in the sediment source(s), likely a protracted period of metamorphism

Coeval Formation of Zircon Megacrysts and Host Magmas in the Eifel Volcanic Field (Germany) Based on High Spatial Resolution Petrochronology

Science.gov (United States)

Schmitt, Axel; Klitzke, Malte; Gerdes, Axel; Ludwig, Thomas; Schäfer, Christof

2017-04-01

Zircon megacrysts (approx. 0.5-6 mm in diameter) from the Quaternary West and East Eifel volcanic fields, Germany, occur as euhedral crystals in porous K-spar rich plutonic ejecta clasts, and as partially resorbed xenocrysts in tephrite lava. Their relation to the host volcanic rocks has remained contentious because the dominantly basanitic to phonolitic magma compositions in the Eifel are typically zircon undersaturated. We carried out a detailed microanalytical study of zircon megacrysts from seven locations (Emmelberg and Rockeskyll in the West Eifel; Bellerberg, Laacher See, Mendig, Rieden, and Wehr in the East Eifel). Crystals were embedded in epoxy, sectioned to expose interiors through grinding with abrasives, diamond-polished, and mapped by optical microscopy, backscattered electron, and cathodoluminescence imaging. Subsequently, isotope-specific analysis using secondary ionization mass spectrometry (SIMS) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was carried out placing 100 correlated spots on 20 selected crystals. Concordant U-Th disequilibrium and U-Pb ages determined by SIMS are between ca. 430 ka (Rieden) and 170 ka (Mendig) and indicate that the megacryst zircons crystallized almost always briefly before eruption. A significant gap between zircon megacryst crystallization (ca. 230 ka) and eruption (ca. 45 ka) ages was only detected for the Emmelberg location. SIMS trace element abundances (e.g., rare earth elements) vary by orders-of-magnitude and correlate with domain boundaries visible in cathodoluminescence; trace element patterns match those reported for zircon from syenitic origins. Isotopic compositions are homogeneous within individual crystals, but show some heterogeneity between different crystals from the same locality. Average isotopic values (δ18O SMOW = +5.3±0.6 ‰ by SIMS; present-day ɛHf = +1.7±2.5 ‰ by LA-ICP-MS; 1 standard deviation), however, are consistent with source magmas being dominantly mantle

The 230Th correction is the 1st priority for accurate dates of young zircons: U/Th partitioning experiments and measurements

Science.gov (United States)

Krawczynski, M.; McLean, N.

2017-12-01

One of the most accurate and useful ways of determining the age of rocks that formed more than about 500,000 years ago is uranium-lead (U-Pb) geochronology. Earth scientists use U-Pb geochronology to put together the geologic history of entire regions and of specific events, like the mass extinction of all non-avian dinosaurs about 66 million years ago or the catastrophic eruptions of supervolcanoes like the one currently centered at Yellowstone. The mineral zircon is often utilized because it is abundant, durable, and readily incorporates uranium into its crystal structure. But it excludes thorium, whose isotope 230Th is part of the naturally occurring isotopic decay chain from 238U to 206Pb. Calculating a date from the relative abundances of 206Pb and 238U therefore requires a correction for the missing 230Th. Existing experimental and observational constraints on the way U and Th behave when zircon crystallizes from a melt are not known precisely enough, and thus currently the uncertainty in dates introduced by they `Th correction' is one of the largest sources of systematic error in determining dates. Here we present preliminary results on our study of actinide partitioning between zircon and melt. Experiments have been conducted to grow zircon from melts doped with U and Th that mimic natural magmas at a range of temperatures, and compositions. Synthetic zircons are separated from their coexisting glass and using high precision and high-spatial-resolution techniques, the abundance and distribution of U and Th in each phase is determined. These preliminary experiments are the beginning of a study that will result in precise determination of the zircon/melt uranium and thorium partition coefficients under a wide variety of naturally occurring conditions. This data will be fit to a multidimensional surface using maximum likelihood regression techniques, so that the ratio of partition coefficients can be calculated for any set of known parameters. The results of

New zircon (U-Th)/He and U/Pb eruption age for the Rockland tephra, western USA

Science.gov (United States)

Coble, Matthew A.; Burgess, Seth D.; Klemetti, Erik W.

2017-09-01

Eruption ages of a number of prominent Quaternary volcanic deposits remain inaccurately and/or imprecisely constrained, despite their importance as regional stratigraphic markers in paleo-environment reconstruction and as evidence of climate-altering eruptions. Accurately dating volcanic deposits presents challenging analytical considerations, including poor radiogenic yield, scarcity of datable minerals, and contamination of crystal populations by magma, eruption, and transport processes. One prominent example is the Rockland tephra, which erupted from the Lassen Volcanic Center in the southern Cascade arc. Despite a range in published eruption ages from 0.40 to 0.63 Ma, the Rockland tephra is extensively used as a marker bed across the western United States. To more accurately and precisely constrain the age of the Rockland tephra-producing eruption, we report U/Pb crystallization dates from the outermost ∼2 μm of zircon crystal faces (surfaces) using secondary ion mass spectrometry (SIMS). Our new weighted mean 238U/206Pb age for Rockland tephra zircon surfaces is 0.598 ± 0.013 Ma (2σ) and MSWD = 1.11 (mean square weighted deviation). As an independent test of the accuracy of this age, we obtained new (U-Th)/He dates from individual zircon grains from the Rockland tephra, which yielded a weighted mean age of 0.599 ± 0.012 Ma (2σ, MSWD = 5.13). We also obtained a (U-Th)/He age of 0.628 ± 0.014 Ma (MSWD = 1.19) for the Lava Creek Tuff member B, which was analyzed as a secondary standard to test the accuracy of the (U-Th)/He technique for Quaternary tephras, and to evaluate assumptions made in the model-age calculation. Concordance of new U/Pb and (U-Th)/He zircon ages reinforces the accuracy of our preferred Rockland tephra eruption age, and confirms that zircon surface dates sample zircon growth up to the time of eruption. We demonstrate the broad applicability of coupled U/Pb zircon-surface and single-grain zircon (U-Th)/He geochronology to accurate

Old inherited zircons in two synkinematic variscan granitoids: the 'granite du Pinet' and the 'Orthogneiss de Marvejols' (Southern French Massif Central)

International Nuclear Information System (INIS)

Pin, C.

1981-01-01

Two granitic bodies outcropping in the metamorphic basement of the Southern French Massif Central have been studied with the zircon U-Pb method: the Pinet granite (Rouergue area) and the Marvejols orthogneisses (Serie du Lot). It is shown that neither of them are pre-Variscan intrusions but that they were emplaced synkinematically, during the early stages of the Hercynian tectonometamorphic event. As numerous other S-type granitoids, both formations are characterized by an important inherited zircon component, whose apparent age is 1800 +- 200 m.y. Lower intersections with the Concordia curve allow to settle an emplacement age around 350-360 m.y., although the Pinet zircons display a complex pattern, owing both to heterogeneity of the inherited component and to late isotopic disturbances. Regional consequences of the synkinematic character of these S-type granitoids are outlined. It is shown that inherited zircons occurences often hinder accurate dating and the possible petrogenetic significance of the old proterozoic component is discussed. (orig.)

Fractal cluster modeling of the fatigue behavior of lead zirconate titanate

OpenAIRE

Priya, Shashank; Kim, Hyeoung Woo; Ryu, Jungho; Uchino, Kenji; Viehland, Dwight D.

2002-01-01

The fatigue behavior of lead zirconate titanate ceramics (PZT) has been studied under electrical and mechanical drives. Piezoelectric fatigue was studied using a mechanical method. Under ac mechanical drive, hard and soft PZTs showed an increase in the longitudinal piezoelectric constant at short times, reaching a maximum at intermediate times. Systematic investigations were performed to characterize the electrical fatigue behavior. A decrease in the magnitude of the remanent polarization was...

Dielectric Strontium Zirconate Sprayed by a Plasma Torch.

Czech Academy of Sciences Publication Activity Database

Ctibor, Pavel; Sedláček, J.; Janata, Marek

2017-01-01

Roč. 10, č. 4 (2017), s. 225-230 ISSN 2008-2134 Institutional support: RVO:61389021 Keywords : Plasma spraying * Electrical properties * Strontium Zirconate * Insulators Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass OBOR OECD: Ceramics www.pccc.icrc.ac.ir/Articles/18/1/18/1010/

U-Pb geochronology of zircons form lunar Breccia 73217 using a sensitive high mass-resolution ion microprobe

International Nuclear Information System (INIS)

Compston, W.; Williams, I.S.

1984-01-01

U-Pb age determinations on four lunar zircons from existing thin-sections of one highland breccia, 73217, using the recently constructed ion microprobe SHRIMP, are reported. The analytical reproducibility of SHRIMP is demonstrated, and procedures for measuring Pb/U, Th/U, and corecting for initial Pb are explained. Electron microprobe analyses for the zircons are also reported. The results show that the four zircons survived the lunar cataclysm without any identifiable effects on their U-Pb systematics. All four indicate a single age of 4356 +23 or -14 m.y. The zircons have experienced small variable amounts of Pb loss since crystallization, from almost zero up to about 10 percent. If this occurred during one later event, then age of the latter is between 1100 and 2300 m.y. 18 references

Effect of zircon-based tricolor pigments on the color, microstructure, flexural strength and translucency of a novel dental lithium disilicate glass-ceramic.

Science.gov (United States)

Yuan, Kun; Wang, Fu; Gao, Jing; Sun, Xiang; Deng, Zai-Xi; Wang, Hui; Jin, Lei; Chen, Ji-Hua

2014-01-01

The purpose of this study was to investigate the effect of zircon-based tricolor pigments (praseodymium zircon yellow, ferrum zircon red, and vanadium zircon blue) on the color, thermal property, crystalline phase composition, microstructure, flexural strength, and translucency of a novel dental lithium disilicate glass-ceramic. The pigments were added to the glass frit, milled, pressed, and sintered. Ninety monochrome samples were prepared and the colors were analyzed. The effect of the pigments on thermal property, crystalline phase composition, and microstructure were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. Addition of the pigments resulted in the acquisition of subtractive primary colors as well as tooth-like colors, and did not demonstrate significant effects on the thermal property, crystalline phase composition, microstructure, and flexural strength of the experimental glass-ceramic. Although significant differences (p ceramics, the translucencies of the latter were sufficient to fabricate dental restorations. These results indicate that the zircon-based tricolor pigments can be used with dental lithium disilicate glass-ceramic to produce abundant and predictable tooth-like colors without significant adverse effects, if mixed in the right proportions. Copyright © 2013 Wiley Periodicals, Inc.

Cenozoic foreland basins of Central Andes: a preliminary provenance U-Pb zircon analysis of sedimentary sequences of Calchaqui Valley

International Nuclear Information System (INIS)

Oliveira, Alisson Lopes; Hauser, Natalia; Pimentel, Marcio Martins; Matteini, Massimo; Coira, Beatriz; Alonso, Ricardo; Barrientos, Andrea

2015-01-01

The Eocene of northwestern Argentina records complex basin and structural evolution, including continental sedimentation of the post-rift Salta Basin and the beginning of the Andean uplift and foreland system evolution. This illuminates a significant period of evolutionary history of this and surrounding basins in northwestern Argentina. U-Pb zircon analyses by LA-ICP-MS for three formations representing post-rift to foreland stages allowed interpretation about provenance terrains. The Lumbrera Formation, representing the post-rift stage, shows bimodal sources with a main zircon population around 462 Ma, and a second population around 1023 Ma. The Los Colorados and Angastaco Formations representing the sedimentation in a foreland basin, show a unimodal source around 490 Ma, and 517 Ma respectively. Zircons younger than 50 Ma were not identified during this study. (author)

Cenozoic foreland basins of Central Andes: a preliminary provenance U-Pb zircon analysis of sedimentary sequences of Calchaqui Valley

Energy Technology Data Exchange (ETDEWEB)

Oliveira, Alisson Lopes; Hauser, Natalia; Pimentel, Marcio Martins; Matteini, Massimo, E-mail: alisson_oliveira@hotmail.com [Universidade de Brasilia (UnB), DF (Brazil). Laboratorio de Geocronologia; Galli, Claudia Ines [Faculdad de Ingenieria, Universidad Nacional de Jujuy (Argentina); Coira, Beatriz [CIT Jujuy, CONICET. Instituto de Geologia y Mineria (Argentina); Alonso, Ricardo; Barrientos, Andrea [Instituto CEGA, CONICET. Universidad Nacional de Salta (Argentina)

2015-07-01

The Eocene of northwestern Argentina records complex basin and structural evolution, including continental sedimentation of the post-rift Salta Basin and the beginning of the Andean uplift and foreland system evolution. This illuminates a significant period of evolutionary history of this and surrounding basins in northwestern Argentina. U-Pb zircon analyses by LA-ICP-MS for three formations representing post-rift to foreland stages allowed interpretation about provenance terrains. The Lumbrera Formation, representing the post-rift stage, shows bimodal sources with a main zircon population around 462 Ma, and a second population around 1023 Ma. The Los Colorados and Angastaco Formations representing the sedimentation in a foreland basin, show a unimodal source around 490 Ma, and 517 Ma respectively. Zircons younger than 50 Ma were not identified during this study. (author)

U-Pb zircon geochronology of Late Devonian to Early Carboniferous extension-related silicic volcanism in the northern New England Fold Belt

International Nuclear Information System (INIS)

Bryan, S.E.; Holcombe, R.J.; Fielding, C.R.; Allen, C.M.

2004-01-01

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of zircons confirm a Late Devonian to Early Carboniferous age (ca 360-350 Ma) for silicic volcanic rocks of the Campwyn Volcanics and Yarrol terrane of the northern New England Fold Belt (Queensland). These rocks are coeval with silicic volcanism recorded elsewhere in the fold belt at this time (Connors Arch, Drummond Basin). The new U-Pb zircon ages, in combination with those from previous studies, show that silicic magmatism was both widespread across the northern New England Fold Belt (>250 000 km 2 and >500 km inboard of plate margin) and protracted, occurring over a period of -15 million years. Zircon inheritance is commonplace in the Late Devonian - Early Carboniferous volcanics, reflecting anatectic melting and considerable reworking of continental crust. Inherited zircon components range from ca 370 to ca 2050 Ma, with Middle Devonian (385-370 Ma) zircons being common to almost all dated units. Precambrian zircon components record either Precambrian crystalline crust or sedimentary accumulations that were present above or within the zone of magma formation This contrasts with a lack of significant zircon inheritance in younger Permo-Carboniferous igneous rocks intruded through,and emplaced on top of, the Devonian-Carboniferous successions. The inheritance data and location of these volcanic rocks at the eastern margins of the northern New England Fold Belt, coupled with Sr-Nd, Pb isotopic data and depleted mantle model ages for Late Palaeozoic and Mesozoic magmatism, imply that Precambrian mafic and felsic crustal materials (potentially as old as 2050 Ma), or at the very least Lower Palaeozoic rocks derived from the reworking of Precambrian rocks, comprise basement to the eastern parts of the fold belt. This crustal basement architecture may be a relict from the Late Proterozoic breakup of the Rodinian supercontinent. Copyright (2004) Geological Society of Australia

Geochronology and Geochemistry of Zircons from the IODP Site U1437 in the Rear of the Izu-Bonin Volcanic Arc

Science.gov (United States)

Andrews, G. D.; Schmitt, A. K.; Busby, C. J.; Brown, S. R.

2015-12-01

Zircons recovered from International Ocean Discovery Program Expedition 350 Site U1437 (31°47.390'N, 139°01.580'E) in the Izu-Bonin arc were analyzed by SIMS to constrain their age (U/Pb geochronology) and geochemistry (trace elements, δ18O); LA-ICP-MS ɛHf analyses are pending. Seven intervals were dated successfully: six tuffs and lapilli-tuffs between 680.99 and 1722.46 m below sea floor (mbsf) and a single peperitic rhyolitic intrusion at 1388.86 - 1390.07 mbsf. Thirty-two intervals which underwent mineral separation lacked zircon, or yielded zircon much older than age expectations for U1437. Geochronology results from separated zircons confirm and extend the shipboard age model to 1360.77 mbsf where Late Miocene (Tortonian) submarine volcanic rocks (11.3 ±0.7 Ma; n = 17) were sampled. In-situ measurement of zircons associated with magnetite crystals in the rhyolite intrusion yield an age of 13.6 ±1.7 Ma (n = 9). Zircon U contents are low (typically <300 ppm), with trace element ratios characteristic of oceanic lithosphere and near-mantle δ18O values (4-6 ‰). Individual Miocene zircon crystals are difficult to distinguish by age alone from those in the drilling mud (sepiolite) used during Expedition 350; the sepiolite is quarried by IMV Nevada in the Amargosa Valley. Our analysis of thirty-three zircons from the sepiolite finds that they have a broad and varied age distribution (2 - 2033 Ma) with a prominent peak at 12-14 Ma, bimodal δ18O values (peaks at 5-5.5 and 6.5-7.5 ‰), and dominantly continental trace element signatures. Three zircons from U1437 are tentatively identified as sepiolite-derived, but a single Eocene grain (51.7 ±2.4 Ma) recovered from 1722.46 mbsf has an age unlike those in the sepiolite, and potentially is genuinely xenocrystic. The majority of U1437 zircons thus crystallized from evolved melts lacking continental characteristics, although thermal and compositional conditions conducive for zircon crystallization appear to have

Zircon's Archean of the Ural

International Nuclear Information System (INIS)

Krasnobaev, A.A.; Cherednichenko, N.V.

2005-01-01

The age of zircons from metamorphic rocks of the Taratashsky complex located on the Western slope of the South Urals was determined by the methods of U-Pb isotope dating. The age values obtained suggest a two-stage model of the complex evolution at early stages of its existence. The age of 2913±133 mln. years identifies the age of granulite metamorphism, while the age 2127±65 mln. years indicates the period of the most intensive transformations of the rocks within the complex, which were accompanied by occurrence of high-temperature diaphthorites [ru

Soft mode of lead zirconate

International Nuclear Information System (INIS)

Pan'ko, G.F.; Prisedskij, V.V.; Klimov, V.V.

1983-01-01

Anisotropic diffusional scattering of electrons on PbZrO 3 crystal in the temperature range of phase transition has been recorded. As a result of its analysis it has been established that in lead zirconate the rotational vibrational mode G 25 plays the role of soft mode. The experiment is carried out using PbZrO 3 monocrystals in translucent electron microscope EhM-200, operating in the regime of microdiffraction at accelerating voltage of 150 kV and beam current 50 μA; sample preparation is realized using the method of shearing and fragmentation

Composition of zircons from the Cornubian Batholith of SW England and comparison with zircons from other European Variscan rare-metal granites

Czech Academy of Sciences Publication Activity Database

Breiter, Karel; Müller, A.; Shail, R.; Simons, B.

2016-01-01

Roč. 80, č. 7 (2016), s. 1-17 ISSN 0026-461X R&D Projects: GA ČR GA14-13600S Institutional support: RVO:67985831 Keywords : zircon * chemical composition * Cornwall * rare-metal granite Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.285, year: 2016

Mixture modeling of multi-component data sets with application to ion-probe zircon ages

Science.gov (United States)

Sambridge, M. S.; Compston, W.

1994-12-01

A method is presented for detecting multiple components in a population of analytical observations for zircon and other ages. The procedure uses an approach known as mixture modeling, in order to estimate the most likely ages, proportions and number of distinct components in a given data set. Particular attention is paid to estimating errors in the estimated ages and proportions. At each stage of the procedure several alternative numerical approaches are suggested, each having their own advantages in terms of efficency and accuracy. The methodology is tested on synthetic data sets simulating two or more mixed populations of zircon ages. In this case true ages and proportions of each population are known and compare well with the results of the new procedure. Two examples are presented of its use with sets of SHRIMP U-238 - Pb-206 zircon ages from Palaeozoic rocks. A published data set for altered zircons from bentonite at Meishucun, South China, previously treated as a single-component population after screening for gross alteration effects, can be resolved into two components by the new procedure and their ages, proportions and standard errors estimated. The older component, at 530 +/- 5 Ma (2 sigma), is our best current estimate for the age of the bentonite. Mixture modeling of a data set for unaltered zircons from a tonalite elsewhere defines the magmatic U-238 - Pb-206 age at high precision (2 sigma +/- 1.5 Ma), but one-quarter of the 41 analyses detect hidden and significantly older cores.

U-Pb ages in meta-rhyolite zircon from Arai Group and associated granites

International Nuclear Information System (INIS)

Pimentel, M.M.; Fuck, R.A.

1991-01-01

Geochronology results by V-Pb method in zircon of granite rocks from staniferous province of Goias and rhyolite Arai groups are revealed. Two distinct episode of acid magmatism in Paleo-and Meso proterozoic are presented. V-Pb data in zircon from Sucuri and Soledade granites of the province from Parana River with ages of higher intercepted are also defined. This ages are consider mistakes, similar the V-Pb age of a rhyolite from Arai group. (author)

U-Pb Detrital Zircon Ages from Sarawak: Changes in Provenance Reflecting the Tectonic Evolution of Southeast Asia

Science.gov (United States)

Breitfeld, H. T.; Galin, T.; Hall, R.

2014-12-01

Sarawak is located on the northern edge of Sundaland in NW Borneo. Five sedimentary basins are distinguished with ages from Triassic to Cenozoic. New light mineral, heavy mineral and U-Pb detrital zircon ages show differences in provenance reflecting the tectonic evolution of the region. The oldest clastic sediments are Triassic of the Sadong-Kuching Basin and were sourced by a Carnian to Norian volcanic arc and erosion of Cathaysian rocks containing zircons of Paleoproterozoic age. Sandstones of the Upper Jurassic to Cretaceous Bau-Pedawan Basin have distinctive zircon populations indicating a major change of tectonic setting, including initiation of subduction below present-day West Sarawak in the Late Jurassic. A wide range of inherited zircon ages indicates various Cathaysian fragments as major source areas and the arrival of the SW Borneo Block following subduction beneath the Schwaner Mountains in the early Late Cretaceous. After collision of the SW Borneo Block and the microcontinental fragments with Sundaland in the early Late Cretaceous, deep marine sedimentation (Pedawan Formation) ceased, and there was uplift forming the regional Pedawan-Kayan unconformity. Two episodes of extension were responsible for basin development on land from the latest Cretaceous onwards, probably in a strike-slip setting. The first episode formed the Kayan Basin in the Latest Cretaceous (Maastrichtian) to Early Paleocene, and the second formed the Ketungau Basin and the Penrissen Sandstone in the Middle to Late Eocene. Zircons indicate nearby volcanic activity throughout the Early Cenozoic in NW Borneo. Inherited zircon ages indicate an alternation between Borneo and Tin Belt source rocks. A large deep marine basin, the Rajang Basin, formed north of the Lupar Line fault. Zircons from sediments of the Rajang Basin indicate they are of similar age and provenance as the contemporaneous terrestrial sediments to the south suggesting a narrow steep continental Sundaland margin at the

Real-Time Salmonella Detection Using Lead Zirconate Titanate-Titanium Microcantilevers

National Research Council Canada - National Science Library

McGovern, John-Paul; Shih, Wan Y; Shih, Wei-Heng; Sergi, Mauro; Chaiken, Irwin

2005-01-01

.... We have developed and investigated the use of a lead zirconate titanate - titanium (PZT-Ti) microcantilever for in situ detection of the common food- and water-born pathogen, Salmonella typhimurium...

Annealing of natural metamict zircons. I low degree of radiation damage

CERN Document Server

Colombo, M

1998-01-01

In-situ time dependent high temperature X-ray powder diffraction was used to investigate the ordering process occurring during annealing of natural zircons with a low degree of radiation damage. It was possible to distinguish two stages of this process. Firstly, the diffusion of defects induced by alpha-particles, this stage contributes only to a certain degree of relaxation in the unit cell. In the second stage there is some degree of recrystallization. A hkl-dependence in the variation of the integrated intensity is observed and the increase in the volume of crystalline zircon is therefore related to a process of migration of dislocations.

Detrital zircon U-Pb geochronology of Cambrian to Triassic miogeoclinal and eugeoclinal strata of Sonora, Mexico

Science.gov (United States)

Gehrels, G.E.; Stewart, John H.

1998-01-01

One hundred and eighty two individual detrital zircon grains from Cambrian through Permian miogeoclinal strata, Ordovician eugeoclinal rocks, and Triassic post-orogenic sediments in northwestern Sonora have been analyzed. During Cambrian, Devonian, Permian, and Triassic time, most zircons accumulating along this part of the Cordilleran margin were shed from 1.40-1.45 and 1.62-1.78 Ga igneous rocks that are widespread in the southwestern United States and northwestern Mexico. Zircons with ages of approximately 1.11 Ga are common in Cambrian strata and were apparently shed from granite bodies near the sample site. The sources of 225-280 Ma zircons in our Triassic sample are more problematic, as few igneous rocks of these ages are recognized in northwestern Mexico. Such sources may be present but unrecognized, or the grains could have been derived from igneous rocks of the appropriate ages to the northwest in the Mojave Desert region, to the east in Chihuahua and Coahuila, or to the south in accreted(?) arc-type terranes. Because the zircon grains in our Cambrian and Devonian to Triassic samples could have accumulated in proximity to basement rocks near their present position or in the Death Valley region of southern California, our data do not support or refute the existence of the Mojave-Sonora megashear. Ordovician strata of both miogeoclinal and eugeoclinal affinity are dominated by >1.77 Ga detrital zircons, which are considerably older than most basement rocks in the region. Zircon grains in the miogeoclinal sample were apparently derived from the Peace River arch area of northwestern Canada and transported southward by longshore currents. The eugeoclinal grains may also have come from the Peace River arch region, with southward transport by either sedimentary or tectonic processes, or they may have been shed from off-shelf slivers of continents (perhaps Antarctica?) removed from the Cordilleran margin during Neoproterozoic rifting. It is also possible that the

Significance of zircon U-Pb ages from the Pescadero felsite, west-central California coast ranges

Science.gov (United States)

McLaughlin, Robert J.; Moore, Diane E.; ,; Martens, UWE C.; Clark, J.C.

2011-01-01

Weathered felsite is associated with the late Campanian–Maastrichtian Pigeon Point Formation near Pescadero, California. Poorly exposed, its age and correlation are uncertain. Is it part of the Pigeon Point section west of the San Gregorio–Hosgri fault? Does it rest on Nacimiento block basement? Is it dextrally offset from the Oligocene Cambria Felsite, ∼185 km to the southeast? Why is a calc-alkaline hypabyssal igneous rock intrusive into the outboard accretionary prism? To address these questions, we analyzed 43 oscillatory-zoned zircon crystals from three incipiently recrystallized pumpellyite ± prehnite ± laumontite-bearing Pescadero felsite samples by sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) techniques. Thirty-three zircons gave late Mesozoic U-Pb ages, with single-grain values ranging from 81 to 167 Ma; ten have pre-Mesozoic, chiefly Proterozoic ages. A group of the four youngest Pescadero zircons yielded an apparent maximum igneous age of ca. 86–90 Ma. Reflecting broad age scatter and presence of partly digested sandstone inclusions, we interpret the rest of the zircons (perhaps all) as xenocrysts. Twenty-three zircons were separated and analyzed from two samples of the similar Cambria Felsite, yielding a unimodal 27 Ma U-Pb age. Clearly, the origin of the Upper Oligocene Cambria Felsite is different from that of the Upper Cretaceous Pescadero felsite; these rocks are not correlated, and do not constrain displacement along the San Gregorio–Hosgri fault. Peak ages differ slightly, but relative probability curves for Mesozoic and pre-Mesozoic Pescadero zircons compare well, for example, with abundant U-Pb age data for detrital zircons from Franciscan metaclastic strata ∼100 km to the east in the Diablo Range–San Francisco Bay area, San Joaquin Great Valley Group turbidites, Upper Cretaceous Nacimiento block Franciscan strata, and Upper

Chemical characterisation of zircon-cadmium sulfoselenide ceramic pigments; Caracterizacion quimica de pigmentos ceramicos a base de sulfoseleniuro de cadmio

Energy Technology Data Exchange (ETDEWEB)

Gazulla Barreda, M. F.; Rodrigo Edo, M.; Blasco Roca, E.; Orduna Cordero, M.

2013-07-01

The present paper addresses the development of a methodology that allows the complete chemical characterisation of zircon cadmium sulfoselenide ceramic pigments including minor and major elements. To develop the methodology, five zircon-cadmium sulfoselenide pigments with different hues were selected, studying the different measurement process steps, from sample preparation to the optimisation of the measurement of the different components of the pigments by spectroscopic techniques (WD-XRF and elemental analysis by combustion and IR detection). The chemical characterisation method developed was validated with synthetic standards prepared from the mixture of certified reference materials and pure oxides because no certified referenced materials of this type of pigments were commercially available. The developed method can be used for a complete chemical characterization of zircon-cadmium sulfoselenide ceramic pigments with a very low uncertainty for all the elements analysed. (Author)

Effect of cryogenic treatment on distribution of residual stress in case carburized En 353 steel

International Nuclear Information System (INIS)

Bensely, A.; Venkatesh, S.; Mohan Lal, D.; Nagarajan, G.; Rajadurai, A.; Junik, Krzysztof

2008-01-01

The effect of cryogenic treatment on the distribution of residual stress in the case carburized steel (En 353) was studied using X-ray diffraction technique. Two types of cryogenic treatment: shallow cryogenic treatment (193 K) and deep cryogenic treatment (77 K) were adopted, as a supplement to conventional heat treatment. The amount of retained austenite in conventionally heat-treated, shallow cryogenically treated and deep cryogenically treated samples was found to be 28%, 22% and 14%, respectively. The conventionally heat-treated, shallow cryogenically treated and deep cryogenically treated samples in untempered condition had a surface residual stress of -125 MPa, -115 MPa and -235 MPa, respectively. After tempering the conventionally heat-treated, shallow cryogenically treated and deep cryogenically treated samples had a surface residual stress of -150 MPa, -80 MPa and -80 MPa, respectively. A comparative study of the three treatments revealed that there was an increase in the compressive residual stress in steel that was subjected to cryogenic treatment prior to tempering. The experimental investigation revealed that deep cryogenically treated steel when subjected to tempering has undergone a reduction in compressive residual stress. Such stress relieving behaviour was mainly due to the increased precipitation of fine carbides in specimens subjected to DCT with tempering

Fabrication and electrical characterization of 15% yttrium-doped barium zirconate-nitrate freeze drying method combined with vacuum heating

International Nuclear Information System (INIS)

Imashuku, Susumu; Uda, Tetsuya; Nose, Yoshitaro; Awakura, Yasuhiro

2011-01-01

Research highlights: → Very fine 15% yttrium-doped barium zirconate powder of particle size about 30 nm was obtained by synthesizing at 500 deg. C in vacuum from powder mixed by the nitrate freeze-drying method. → Large and homogeneous grains of 15% yttrium-doped barium zirconate were easily obtained using the synthesized powder. → Grain boundary resistance was not inversely proportional to the grain size as theoretically expected. → Specific grain boundary conductivity varies with samples because impurities and/or evaporation loss of barium oxide might affect the grain-boundary resistance in 15% yttrium-doped barium zirconate. - Abstract: We applied a nitrate freeze-drying method to obtain a fine synthesized powder of 15% yttrium-doped barium zirconate. Fine 15% yttrium-doped barium zirconate powder of particle size about 30 nm was obtained by synthesizing at 500 deg. C in vacuum from a powder mixed by the nitrate freeze-drying method. However, we could not obtain such fine powder by synthesizing in air. Using the powder synthesized in vacuum, large and homogeneous grains of 15% yttrium-doped barium zirconate were easily obtained after sintering. Then, the bulk and grain boundary resistance were evaluated by AC 2-terminal measurement of sample in the form of bar and pellet and DC 4-terminal measurement of bar-shape sample. The grain boundary resistance was not inversely proportional to the grain size as theoretically expected. We concluded that specific grain boundary conductivity varies with samples. Some impurities, evaporation loss of barium oxide and/or other unexpected reasons might affect the grain boundary resistance in 15% yttrium-doped barium zirconate.

Zircon U-Pb age and Hf-O isotopes of felsic rocks from the Atlantis Bank, Southwest Indian Ridge

Science.gov (United States)

Liu, C. Z.; Zhang, W. Q.

2017-12-01

Hole U1473A was drilled to 790 meters below seafloor on the Atlantis Bank, an oceanic core complex in the Southwest Indian Ridge, where the upper crust has been removed by detachment faulting. The recovered core consists dominantly of olivine gabbro, with subordinate gabbro, gabbro with varying Fe-Ti oxide concentrations. Felsic veins intermittently occur throughout the whole core section. Zircons separated from twenty-four felsic samples have been conducted for U-Pb dating and O isotope analyses on the Cameca 1280 and Lu-Hf isotopes by laser ablation coupled with a MC-ICPMS. The zircons have highly variable contents of U (12-2078 ppm) and Th (5-801 ppm), yielding Th/U ratios of 0.33-0.81. They are typical oceanic zircons as defined by the trace element discrimination plots of Grimes et al. (2015). The weighted mean 206Pb/238U ages of the analyzed zircons vary from 11.29 to 12.57 Ma. Age differences between felsic veins throughout the whole core are not resolved within analytical uncertainty of the SIMS measurements. All felsic samples have similar zircon Hf isotope compositions, with initial 176Hf/177Hf ratios of 0.283126-0.283197 and ɛHf values of 12.76-15.27. Zircons from all felsic samples but one have mantle-like δ18O values of 5.14-5.50‰. Zircons from one sample show partial resorption or total recrystallization; in comparison, they have lower δ18O values of 4.81±0.21‰. Such characteristics provide clear evidence for hydrothermal alteration after magmatic intrusion.

Detrital Zircons From the Jack Hills and Mount Narryer, Western Australia: Geochronological, Morphological, and Geochemical Evidence for Diverse >4000 Ma Source Rocks

Science.gov (United States)

Crowley, J. L.; Myers, J. S.; Sylvester, P. J.; Cox, R. A.

2004-05-01

Detrital zircons from all major clastic units in the Jack Hills and Mount Narryer metasedimentary belts, Western Australia, were analyzed for morphology, internal zoning, inclusion mineralogy, age, and trace element concentrations (latter two obtained by laser-ablation microprobe ICPMS). The results show that zircons were derived from a wide diversity of rocks, including previously described, >4000 Ma grains that are older than any known terrestrial rocks. In three metaconglomerate samples from the western Jack Hills, 4200-3800 Ma zircons ("old grains") comprise 14% of the population, 3800-3600 Ma grains form only 2%, and 3550-3250 Ma zircons ("young grains") are dominant with a significant peak at 3380 Ma. Old and young grains are interpreted as being from similar rock types because they are indistinguishable in trace element concentrations, size (several hundred microns), morphology (subequant, typically fragmented), internal zoning (typically both oscillatory and sector), and U concentration (50-200 ppm). Many of these properties suggest an intermediate plutonic source, whereas an evolved granitic source was previously interpreted from rare-earth element and oxygen isotope data. Detrital zircons in quartzites and metaconglomerates at Mount Narryer differ significantly from zircons from the western Jack Hills. Old grains comprise only 3% (most of which are 4200-4100 Ma), 3800-3600 Ma zircons form 31%, and there are peaks at 3650, 3600, and 3500 Ma. Old and young grains have similar properties that suggest granitic sources, such as elongate prismatic morphology, oscillatory zoning, high U concentrations (100-600 ppm), and xenotime and monazite inclusions. Trace element concentrations are broadly similar to those in Jack Hills zircons, with notable exceptions being generally higher U, smaller Ce and Eu anomalies, and lower Nb/Ta. It is considered unlikely that Jack Hills zircons were derived from granitic gneisses that surround the metasedimentary belts because

Some observations on the carburization of type 316 stainless steel foil in a low carbon activity sodium environment

International Nuclear Information System (INIS)

Thorley, A.W.; Jeffcoat, P.J.

1982-01-01

Work currently being undertaken to establish the equilibrium composition of carbides which form in stainless steel foils during their exposure to low carbon activity sodium environment is described. The time it takes the carbon to reach equilibrium during exposure to sodium of different carbon activity is discussed. The lowest carbon activity measureable in test loops where the sodium is just above carburizing to stainless steel is reported. Analytical techniques are used to determine the composition of the carbide and the austenite matrix and hence estimate the carbon activity of the equilibrium structure. This provides a comparison with carbon activity values determined by alternative methods such as the Harwell Carbon Meter and nickel tab techniques

Temperature dependent XAFS studies of local atomic structure of the perovskite-type zirconates

International Nuclear Information System (INIS)

Vedrinskii, R. V.; Lemeshko, M. P.; Novakovich, A. A.; Nazarenko, E. S.; Nassif, V.; Proux, O.; Joly, Y.

2006-01-01

Temperature dependent preedge and extended x-ray absorption fine structure measurements at the Zr K edge for the perovskite-type zirconates PbZr 0.515 Ti 0.485 O 3 (PZT), PbZrO 3 (PZ), and BaZrO 3 are performed. To carry out a more accurate study of the weak reconstruction of the local atomic structure we employed a combination of two techniques: (i) analysis of the preedge fine structure, and (ii) analysis of the Fourier transform of the difference between χ(k) functions obtained at different temperatures. A detailed investigation of local atomic structure in the cubic phase for all the crystals is also performed. It is shown that neither the displacive nor the order-disorder model can describe correctly the changes of local atomic structure during phase transitions in PZ and PZT. A spherical model describing the local atomic structure of perovskite-type crystals suffering structural phase transitions is proposed

Crustal growth history of the Korean Peninsula:Constraints from detrital zircon ages in modern river sediments

Institute of Scientific and Technical Information of China (English)

Taejin Choi; Yong Il Lee; Yuji Orihashi

2016-01-01

U-Pb analyses were carried out on detrital zircon grains from major river-mouth sediments draining South Korea to infer provenance characteristics and the crustal growth history of the southern Korean Peninsula, using a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). The Korean Peninsula is located in the East Asian continental margin and mainly comprises three Precambrian massifs and two metamorphic belts in between them. We obtained 515 concordant to slightly discordant zircon ages ranging from ca. 3566 to ca. 48 Ma. Regardless of river-mouth location, predominance of Mesozoic (249e79 Ma) and Paleoproterozoic (2491e1691 Ma) ages with subordinate Archean ages in-dicates that the zircon ages reflect present exposures of plutonic/metamorphic rocks in the drainage basins of the South Korean rivers and the crustal growth of the southern Korean Peninsula was focused in these two periods. Comparison of detrital zircon-age data between the North and South Korean river sediments reveals that the Paleoproterozoic zircon age distributions of both regions are nearly identical, while the NeoproterozoicePaleozoic ages exist and the Mesozoic ages are dominant in southern Korean Peninsula. This result suggests that Precambrian terrains in Korea record the similar pre-Mesozoic magmatic history and that the influence of Mesozoic magmatism was mainly focused in South Korea.

Enhanced provenance interpretation using combined U-Pb and (U-Th)/He double dating of detrital zircon grains from lower Miocene strata, proximal Gulf of Mexico Basin, North America

Science.gov (United States)

Xu, Jie; Stockli, Daniel F.; Snedden, John W.

2017-10-01

Detrital zircon U-Pb analysis is an effective approach for investigating sediment provenance by relating crystallization age to potential crystalline source terranes. Studies of large passive margin basins, such as the Gulf of Mexico Basin, that have received sediment from multiple terranes with non-unique crystallization ages or sedimentary strata, benefit from additional constraints to better elucidate provenance interpretation. In this study, U-Pb and (U-Th)/He double dating analyses on single zircons from the lower Miocene sandstones in the northern Gulf of Mexico Basin reveal a detailed history of sediment source evolution. U-Pb age data indicate that most zircon originated from five major crystalline provinces, including the Western Cordillera Arc (1800 Ma) terranes. Zircon (U-Th)/He ages record tectonic cooling and exhumation in the U.S. since the Mesoproterozoic related to the Grenville to Laramide Orogenies. The combined crystallization and cooling information from single zircon double dating can differentiate volcanic and plutonic zircons. Importantly, the U-Pb-He double dating approach allows for the differentiation between multiple possible crystallization-age sources on the basis of their subsequent tectonic evolution. In particular, for Grenville zircons that are present in all of lower Miocene samples, four distinct zircon U-Pb-He age combinations are recognizable that can be traced back to four different possible sources. The integrated U-Pb and (U-Th)/He data eliminate some ambiguities and improves the provenance interpretation for the lower Miocene strata in the northern Gulf of Mexico Basin and illustrate the applicability of this approach for other large-scale basins to reconstruct sediment provenance and dispersal patterns.

The 3.5 Ga granulites of the Bug polymetamorphic complex, Ukraine (U-Pb SHRIMP-II zircon data)

Science.gov (United States)

Lobach-Zhuchenko, Svetlana; Kaulina, Tatiana; Baltybaev, Shauket; Yurchenko, Anastasija; Balagansky, Victor; Skublov, Sergei; Sukach, Vitaliji

2014-05-01

The Bug polymetamorphic complex composes the south-west of the Ukrainian Shield. It experienced multistage deformation and metamorphism of 3.6 to 1.95 Ga. The age of protolith of the gneiss enderbite is up to 3.7-3.6 Ga (Claesson et al., 2006: Lobach-Zhuchenko et al., 2010, 2013; Bibikova et al, 2013). The 3.5 old granulitic zircon (sample UR132) was found in a light grey massive medium grained with weak foliation granulite from the Odessa quarry located at the right riverside of the Bug (N 48° 13' 55.2''; E 29° 59' 75''). The rock is mafic in composition (SiO2 = 51.50 wt%, #mg=0.43, (La/Yb)n =7.5), and shows enrichment in Sr (333 ppm), Zr (244 ppm), and Nb (12 ppm) compared to MORB. This contains antiperthitic plagioclase (An30-35), hypersthene (En0.46 Fs0.53 Wo0.01 ), diopside (En0.33 Fs0.20Wo0.47), quartz, ilmenite, magnetite, apatite, and zircon. Three types of zircon are recognized. (1) Large (~300 μm) isometric and oval grains displaying bright colour and sector zoning in CL. Some crystals have fir-tree texture. Isometric shape together with fir-tree zoning is typical for zircons growing under conditions of granulite- facies metamorphism (Hoskin and Schaltegger, 2003). These zircons are low in U and Th, have high Th/U ratios (0.61-1.1), and display decreasing of element contents from the centre to margin (ppm): U - 68 to 44, Th - 58 to 19, total REE - 723 to 406, Y - 1049 to 553, and Li - 1.23 to 0.91 at the constant (Lu/La)n ratios (4200-4600). Zircon's crystallization temperature calculated from the Ti content is 705 °C and is consistent with those calculated on the base of the mineral composition. (2) Small sized (60-100 μm) zircons. Most of these occur within plagioclase and truncate antiperthite lamellae. They show euhedral zoned cores and bright rims in CL. (3) Zircons principally distinguished from those of groups 1 and 2. These are dark in CL, some grains are severely structurally damaged and contain numerous inclusions (Qzt, Pl, Kfsp, rare Opx

Morphology and U-Pb ages of zircons from the high-grade metamorphic Precambrian in the Sirdal-Oersdal area, SW Norway

International Nuclear Information System (INIS)

Wielens, J.B.W.

1979-01-01

The U-Pb systematics of seven suites of zircons and two apatites were investigated in an attempt to obtain data about the pre-Sveconorwegian geochronology. Very little was known about this earlier history, as previous studies have shown that the high-grade metamorphism has obliterated most of the older Rb-Sr record. Three samples were investigated from the augengneisses, two from the pyroxene syenites, one garnetiferous migmatite and one magnetite-ilmenite-zircon veinlet cross-cutting the charnockitic migmatites. (Auth.)

Estimates of volume and magma input in crustal magmatic systems from zircon geochronology: the effect of modelling assumptions and system variables

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Luca eCaricchi

2016-04-01

Full Text Available Magma fluxes in the Earth’s crust play an important role in regulating the relationship between the frequency and magnitude of volcanic eruptions, the chemical evolution of magmatic systems and the distribution of geothermal energy and mineral resources on our planet. Therefore, quantifying magma productivity and the rate of magma transfer within the crust can provide valuable insights to characterise the long-term behaviour of volcanic systems and to unveil the link between the physical and chemical evolution of magmatic systems and their potential to generate resources. We performed thermal modelling to compute the temperature evolution of crustal magmatic intrusions with different final volumes assembled over a variety of timescales (i.e., at different magma fluxes. Using these results, we calculated synthetic populations of zircon ages assuming the number of zircons crystallising in a given time period is directly proportional to the volume of magma at temperature within the zircon crystallisation range. The statistical analysis of the calculated populations of zircon ages shows that the mode, median and standard deviation of the populations varies coherently as function of the rate of magma injection and final volume of the crustal intrusions. Therefore, the statistical properties of the population of zircon ages can add useful constraints to quantify the rate of magma injection and the final volume of magmatic intrusions.Here, we explore the effect of different ranges of zircon saturation temperature, intrusion geometry, and wall rock temperature on the calculated distributions of zircon ages. Additionally, we determine the effect of undersampling on the variability of mode, median and standards deviation of calculated populations of zircon ages to estimate the minimum number of zircon analyses necessary to obtain meaningful estimates of magma flux and final intrusion volume.

40Ar/39Ar dating and zircon chronochemistry for the Izu-Bonin rear arc, IODP site U1437

Science.gov (United States)

Schmitt, A. K.; Konrad, K.; Andrews, G. D.; Horie, K.; Brown, S. R.; Koppers, A. A. P.; Busby, C.; Tamura, Y.

2016-12-01

The scientific objective of IODP Expedition 350 drilling at Site U1437 (31°47.390'N, 139°01.580'E) was to reveal the "missing half of the subduction factory": the rear arc of a long-lived intraoceanic subduction zone. Site U1437 lies in a 50 km long and 20 km wide volcano-bounded basin, 90 km west of the Izu arc front, and is the only IODP site drilled in the rear arc. The Izu rear arc is dominated by Miocene basaltic to dacitic seamount chains, which strike at a high angle to the arc front. Radiometric dating targeted a single igneous unit (1390 mbsf), and fine to coarse volcaniclastic units for which we present zircon and 40Ar/39Ar (hornblende, plagioclase, and groundmass) age determinations. All zircons analyzed as grain separates were screened for contamination from drill-mud (Andrews et al., 2016) by analyzing trace elements and, where material was available, O and Hf isotope compositions. Igneous Unit 1 is a rhyolite sheet and yielded concordant in-situ and crystal separate U-Pb zircon ages (13.7±0.3 Ma; MSWD = 1.3; n = 40 spots), whereas the 40Ar/39Ar hornblende plateau age (12.9±0.3; MSWD = 1.1; n = 9 steps) is slightly younger, possibly reflecting pre-eruptive zircon crystallization, or alteration of hornblende. U-Pb zircon and 40Ar/39Ar plateau ages from samples above igneous Unit 1 are concordant with biostratigraphic and paleomagnetic ages (available to 1300 mbsf), but plagioclase and groundmass samples below 1300 m become younger with depth, hinting at post-depositional alteration. A single zircon from 1600 mbsf yielded a U-Pb age of 15.4±1.8 Ma; its trace element composition resembles other igneous zircons from U1437, and is tentatively interpreted as a Middle Miocene age for the lowermost lithostratigraphic unit VII. Oxygen and Hf isotopic values of igneous zircon indicate mantle origins, with some influence of assimilation of hydrothermally altered oceanic crust evident in sub-mantle oxygen isotopic compositions. Lessons from site U1437 are

High-precision ID-TIMS zircon U-Pb geochronology using new 1013 Ohm resistors

Science.gov (United States)

Von Quadt, A.; Buret, Y.; Large, S.; Peytcheva, I.; Trinquier, A.; Wotzlaw, J. F.

2015-12-01

Faraday cups equipped with high gain amplifiers provide a means to measure small ion beams in static mode without the limited linear range of ion counting systems. We tested the application of newly available 1013 Ohm resistors to ID-TIMS zircon U-Pb geochronology using a range of natural and synthetic reference materials. The TritonPlus-RPQ at the Institute of Geochemistry and Petrology, ETH Zurich, is equipped with five new 1013 Ohm resistors and one MasCom secondary electron multiplier, allowing to measure the 202-204-205-206-207-208Pb masses in static mode. U is measured subsequently as U-oxide (265-267-270UO2) during a second step, also in static Faraday mode. The gain calibration of the 1013 Ohm resistors was performed using the procedure of Trinquier (2014), with 144Nd-146Nd being measured using 1011 Ohm resistor and 142-143-145-148-150Nd being measured using 1013 Ohm resitors (Trinquier, 2014; Koornneef et al., 2014). Standard deviations of the noise in all five new 1013 Ohm resistors are lower than 5.0 x 10-6 over a 6 month period, with no shift occurring over this time interval. This new detector set-up was tested by analyzing natural zircon standard materials and synthetic U/Pb solutions (www.earthime.org), ranging in age from ~2 Ma to ~600 Ma. All natural zircon standards were chemically abraded (Mattinson, 2005) and all samples were spiked with the ET2535 tracer solution. U-Pb dates obtained using the static measurement routine are compared to measurements employing dynamic peak jumping routines on the MasCom multiplier. This study illustrates the benefits and current limitations of using high gain amplifiers to measure small ion beams for zircon U-Pb geochronology compared to conventional dynamic ion counting techniques. Mattinson, J.M. (2005) Chemical Geology 220:47-66; Trinquier, A. (2014) Application Note 30281; Koornneef, J. et al (2014) Analytica Chimica Acta 819:49-55.

Temporal Evolution of Volcanic and Plutonic Magmas Related to Porphyry Copper Ores Based on Zircon Geochemistry

Science.gov (United States)

Dilles, J. H.; Lee, R. G.; Wooden, J. L.; Koleszar, A. M.

2015-12-01

Porphyry Cu (Mo-Au) and epithermal Au-Ag ores are globally associated with shallow hydrous, strongly oxidized, and sulfur-rich arc intrusions. In many localities, long-lived magmatism includes evolution from early andesitic volcanic (v) and plutonic (p) rocks to later dacitic or rhyolitic compositions dominated by plutons. We compare zircon compositions from three igneous suites with different time spans: Yerington, USA (1 m.y., p>v), El Salvador, Chile (4 m.y., p>v), and Yanacocha, Peru (6 m.y., v>p). At Yerington granite dikes and ores formed in one event, at ES in 2 to 3 events spanning 3 m.y., and at Yanacocha in 6 events spanning 5 m.y. At both ES and Yanacocha, high-Al amphiboles likely crystallized at high temperature in the mid-crust and attest to deep magmas that periodically recharged the shallow chambers. At Yanacocha, these amphiboles contain anhydrite inclusions that require magmas were sulfur-rich and strongly oxidized (~NNO+2). The Ti-in-zircon geothermometer provides estimates of 920º to 620º C for zircon crystallization, and records both core to rim cooling and locally high temperature rim overgrowths. Ore-related silicic porphyries yield near-solidus crystallization temperatures of 750-650°C consistent with low zircon saturation temperatures. The latter zircons have large positive Ce/Ce* and small negative Eu/Eu*≥0.4 anomalies attesting to strongly oxidized conditions (Ballard et al., 2001), which we propose result from crystallization and SO2 loss to the magmatic-hydrothermal ore fluid (Dilles et al., 2015). The Hf, REE, Y, U, and Th contents of zircons are diverse in the magma suites, and Th/U vs Yb/Gd plots suggest a dominant role of crystal fractionation with lesser roles for both crustal contamination and mixing with high temperature deep-sourced mafic magma. Ce/Sm vs Yb/Gd plots suggest that magma REE contents at contamination are most evident in pre-ore magmas, whereas ore-forming intrusions at low temperatures are dominated by crystal

The earth's oldest known crust - A geochronological and geochemical study of 3900-4200 Ma old detrital zircons from Mt. Narryer and Jack Hills, Western Australia

Science.gov (United States)

Maas, Roland; Kinny, Peter D.; Williams, Ian S.; Froude, Derek O.; Compston, William

1992-03-01

Trace element characteristics were analyzed and inclusions were identified within a suite of pre-3.9 Ga detritral zircons from western Australia representing the earth's oldest-known minerals. A diversity of trace-element compositions was found, particularly in the REE compositions of the old Mt. Narryer zircons, implying a variety of source-rock compositions and hence, the presence of a differentiated crust in the earth 4.15-4.20 Ga ago. Comparisons drawn with data obtained from younger detrital zircons occurring within the same deposits indicate nothing unique about the chemical compositions of the old grains. A number of interelement covariations were observed among the analyzed grains which were independent of age and isotopic characteristics, most notably that occurring between Lu and Hf. A general positive correlation between total LREE and the U + Th contents is also apparent. The findings indicate an origin in felsic igneous rocks, which has implications for early-Archaean crustal evolution.

Alternative approaches used to assess structural changes of natural zircon caused by heat treatment

Science.gov (United States)

Huong, L. T. T.; Thuyet, N. T. M.; Phan, T. L.; Tran, N.; Toan, D. N.; Thang, P. D.; Huy, B. T.

2018-03-01

It is known that large changes in the crystal structure of zircon (ZrSiO4) can be assessed through the linewidth of the characteristic Raman mode (Δν3) at 1008 cm-1. However, the use of Δν3 to assess small changes caused by heat treatment at temperatures below its decomposition temperature of 1670 °C is difficult. The present work points out that the combination of X-ray diffraction (XRD) analyses, and photoluminescence (PL) and Raman (RS) measurements with different excitation wavelengths is an effective approach to solve the above problem. In this context, we have selected natural zircon containing some rare-earth (RE) impurities, and then studied the changes in its crystal structure caused by heat treatment at temperatures Tan=400-1600 °C. XRD analyses reveal that small modifications of the unit-cell parameters occur as Tan>600 °C. Taking the intensity ratios of the ν3 mode to RE-related emissions (Iν3/IRE) or the PL intensity ratios between RE-related emissions into consideration, the similar results in good agreement with the XRD analyses are also found. We believe that the small structural changes are related to the migration and redistribution of defects and impurities, and re-crystallization of zircon. This could be further confirmed though the relation between paramagnetic and ferromagnetic signals when Tan changes.

Zircon Supported Copper Catalysts for the Steam Reforming of Methanol

Science.gov (United States)

Widiastri, M.; Fendy, Marsih, I. N.

2008-03-01

Steam reforming of methanol (SRM) is known as one of the most favorable catalytic processes for producing hydrogen. Current research on zirconia, ZrO2 supported copper catalyst revealed that CuO/ZrO2 as an active catalyst for the SRM. Zircon, ZrSiO4 is available from the by-product of tin mining. In the work presented here, the catalytic properties of CuO/ZrSiO4 with various copper oxide compositions ranging from 2.70% (catalyst I), 4.12% (catalyst II), and 7.12%-mass (catalyst III), synthesized by an incipient wetness impregnation technique, were investigated to methanol conversion, selectivity towards CO formation, and effect of ZnO addition (7.83%CuO/8.01%ZnO/ZrSiO4 = catalyst V). The catalytic activity was obtained using a fixed bed reactor and the zircon supported catalyst activity was compared to those of CuO/ZnO/Al2O3 catalyst (catalyst IV) and commercial Kujang LTSC catalyst. An X-ray powder diffraction (XRD) analysis was done to identify the abundant phases of the catalysts. The catalysts topography and particle diameter were measured with scanning electron microscopy (SEM) and composition of the catalysts was measured by SEM-EDX, scanning electron microscope-energy dispersive using X-ray analysis. The results of this research provide information on the possibility of using zircon (ZrSiO4) as solid support for SRM catalysts.

Fuel Penalty Comparison for (Electrically Heated Catalyst Technology Comparaison de l’augmentation de consommation de carburant pour la technologie de catalyseurs chauffés à l’électricité

Directory of Open Access Journals (Sweden)

Kessels J. T.B.A.

2010-03-01

Full Text Available The conversion efficiency of three way catalytic converters is mainly defined by the temperature range wherein they are operating. Traditionally, ignition retard has been used to reduce the light-off time of the catalyst. This is however associated with a fuel penalty. With increasing vehicle electrification, electrically heating facilities present an alternative, especially for hybrid vehicles. Nevertheless, system complexity of hybrid vehicles prevents engineers to evaluate possible heating technologies and their corresponding fuel penalty with respect to traditional solutions. This paper evaluates the application of an electrically heated catalyst on a hybrid vehicle equipped with a Natural Gas (NG engine. The effect of heating power on light-off time and fuel penalty is determined, using analysis techniques emerging from integrated powertrain control. By means of a case study, the importance of an integral approach is explained by comparing the fuel penalty and conversion efficiency improvement of electric heating with that of ignition retard. In this process, a mix of simulation and test data were combined, forming the foundations for future control developments of a suitable light-off strategy. L’efficacité de conversion des catalyseurs est principalement définie par la gamme de température dans laquelle ils fonctionnent. Un retard du point d’allumage a traditionnellement été utilisé pour réduire le temps d’amorçage du catalyseur. Ceci est cependant associé à une augmentation de la consommation de carburant. Avec l’électrification des véhicules, la possibilité de chauffage électrique représente véritablement une alternative, tout particulièrement pour les véhicules hybrides. Cependant, la complexité des véhicules hybrides rend difficile l’évaluation des technologies de chauffage éventuelles ainsi que l’augmentation de la consommation de carburant associée ; il est aussi difficile de comparer ces r

Detrital zircon without detritus: a result of 496-Ma-old fluid-rock interaction during the gold-lode formation of Passagem, Minas Gerais, Brazil

Science.gov (United States)

Cabral, Alexandre Raphael; Zeh, Armin

2015-01-01

Zircon and xenotime occur in tourmaline-rich hydrothermal pockets in the auriferous lode of Passagem de Mariana, a world-class gold deposit. Zircon grains show pristine oscillatory zoning, but many of them are altered, exhibiting porous domains filled with graphite. Uranium-Pb dating of zircon, using in-situ laser ablation-inductively coupled plasma-mass spectrometry, yields ages between 3.2 and 2.65 Ga, which match those for detrital zircon of the footwall quartzite of the > 2.65-Ga-old Moeda Formation. Discordant analyses point to zircon-age resetting during the Brasiliano orogeny at ca. 500 Ma. This interpretation is supported by U-Pb dating of euhedral xenotime immediately adjacent to altered zircon within the same tourmaline pocket. The xenotime grains give a Concordia age of 496.3 ± 2.0 Ma, which is identical to that determined for monazite of a quartz-hematite vein-type deposit (i.e., jacutinga lode) in the region (Itabira), another important mineralisation style of gold. The occurrence of relatively abundant inherited detrital zircon, but absence of rock fragments in the tourmaline pocket investigated here, implies that detrital material was completely replaced by tourmaline. The graphite overprint on the altered detrital zircon attests to a reducing fluid, which was likely formed by fluid-rock interaction with carbonaceous phyllite of the Batatal Formation, the host rock of the Passagem lode.

Generation of Silicic Melts in the Early Izu-Bonin Arc Recorded by Detrital Zircons in Proximal Arc Volcaniclastic Rocks From the Philippine Sea

Science.gov (United States)

Barth, A. P.; Tani, K.; Meffre, S.; Wooden, J. L.; Coble, M. A.; Arculus, R. J.; Ishizuka, O.; Shukle, J. T.

2017-10-01

A 1.2 km thick Paleogene volcaniclastic section at International Ocean Discovery Program Site 351-U1438 preserves the deep-marine, proximal record of Izu-Bonin oceanic arc initiation, and volcano evolution along the Kyushu-Palau Ridge (KPR). Pb/U ages and trace element compositions of zircons recovered from volcaniclastic sandstones preserve a remarkable temporal record of juvenile island arc evolution. Pb/U ages ranging from 43 to 27 Ma are compatible with provenance in one or more active arc edifices of the northern KPR. The abundances of selected trace elements with high concentrations provide insight into the genesis of U1438 detrital zircon host melts, and represent useful indicators of both short and long-term variations in melt compositions in arc settings. The Site U1438 zircons span the compositional range between zircons from mid-ocean ridge gabbros and zircons from relatively enriched continental arcs, as predicted for melts in a primitive oceanic arc setting derived from a highly depleted mantle source. Melt zircon saturation temperatures and Ti-in-zircon thermometry suggest a provenance in relatively cool and silicic melts that evolved toward more Th and U-rich compositions with time. Th, U, and light rare earth element enrichments beginning about 35 Ma are consistent with detrital zircons recording development of regional arc asymmetry and selective trace element-enriched rear arc silicic melts as the juvenile Izu-Bonin arc evolved.

Comportement des matériaux organiques vis-à-vis des carburants oxygénés The Behavior of Organic Materials with Regard to Oxygenated Fuels

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Puisais M.

2006-11-01

Full Text Available Les incidences d'emploi des produits oxygénés dans les carburants ont été déterminées sur la tenue des principaux matériaux polymères utilisés dans les véhicules et les équipements de distribution. Des carburants renferment diverses teneurs en éthanol ou en méthanol, éventuellement en conjonction avec des co-solvants tels que le tertiobutanol ou un mélange acétonobutylique ont été examinés. Les méthodes d'essais appliquées ont permis de déterminer le comportement à long terme des matériaux au niveau de leur perméabilité, gonflement, vieillissement, fissuration sous contraintes, extraction et résistance à l'ozone. The effects of using oxygenated products in gasolines have been determined concerning the resistance of the leading polymer materials used in vehicles and distribution equipment. Fuels containing varying amounts of ethanol or methanol, possibly in conjunction with cosolvents such as tertiobutanol or a butanol-acetone mixture, have been examined. The test methods applied have determined the long-term behavior of materials with regard to their permeability, swelling, aging, stress cracking, extraction and ozone resistance.

Bimetallic NiFe2O4 synthesized via confined carburization in NiFe-MOFs for efficient oxygen evolution reaction

Science.gov (United States)

Fang, Zhiqiang; Hao, Zhaomin; Dong, Qingsong; Cui, Yong

2018-04-01

Transition metal oxides that derived from metal-organic framework (MOF) precursor have intensively received attention because of their numerous electrochemical applications. Bimetallic Ni-Fe oxides have been rarely reported on the basis of MOF-related strategy. Herein, a bimetallic NiFe2O4 was successfully synthesized via confined carburization in NiFe-MOF precursors and characterized by XRD, XPS, SEM, and TEM. After conducting an investigation of oxygen evolution reaction (OER), the as-synthesized NiFe2O4 material exhibited good catalytic efficiency and high stability and durability in alkaline media. The as-synthesized NiFe2O4 material would promote the development of MOFs in non-noble-metal OER catalyst.

Lead zirconate (PbZrO3 embedded in natural rubber as electroactive elastomer composites

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Anuvat Sirivat

2014-11-01

Full Text Available Perovskite lead zirconate (PbZrO3 was synthesized in an orthorhombic form at a temperature below the Curie temperature, TC. The orthorhombic form is a noncentrosymmetric structure which is capable of spontaneous polarization. Fourier transform infrared (FTIR spectra and X-ray diffraction (XRD patterns confirm the successful synthesis of the lead zirconate; and scanning electron microscopy (SEM micrographs indicate that PbZrO3 particles are moderately dispersed in the natural rubber (NR matrix. Without an electrical field, the particles merely act as a ferroelectric filler, which can absorb and store additional stress. Under an electrical field, particle-induced dipole moments are generated, leading to interparticle interaction and a substantial increase in the storage modulus. At a small amount of lead zirconate particulates present in the natural rubber matrix, at a volume fraction of 0.007306, the electrical conductivity increases dramatically by nearly two orders of magnitude at the electrical frequency of 500 kHz.

Precise U-Pb Zircon Dating of the Syenite Phase from the Ditrau Alkaline Igneous Complex

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Pană Dinu

2000-04-01

Full Text Available The Ditrău igneous complex represents the largest alkaline intrusion in the Carpathian-Pannonian region consisting of a plethora of rock types formed by complicated magmatic and metasomatic processes. A detailed U-Pb zircon age study is currently underway and the results for the syenite intrusion phase is reported herein. The U-Pb zircon emplacement age of the syenite of 229.6 +1.7/-1.2 Ma documents the quasi-contemporaneous production and emplacement of the gabbro and syenite magmas. We suggest that the syenite and associated granite formed by crustal melting during the emplacement of the mantle derived gabbroic magma around 230 Ma. The thermal contact aureole produced by the Ditrău alkaline igneous complex constrains the main tectonism recorded by surrounding metamorphic lithotectonic assemblages to be pre-Ladinian.

From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

Science.gov (United States)

Paquette, J.-L.; Ballèvre, M.; Peucat, J.-J.; Cornen, G.

2017-12-01

In the Variscan belt of Western Europe, the lifetime and evolution of the oceanic domain is poorly constrained by sparse, outdated and unreliable multigrain ID-TIMS U-Pb zircon dating. In this article, we present a complete in situ LA-ICP-MS dataset of about 300 U-Pb zircon analyses obtained on most of the ophiolitic and eclogitic outcrops of Southern Brittany, comprising new dating of previously published zircon populations and newly discovered rock samples. In situ dating and cathodo-luminescence imaging of each zircon grain yields new absolute time-constraints on the evolution of the Galicia-Moldanubian Ocean. The new results confirm that the opening of this oceanic domain is well defined at about 490 Ma. In contrast, the generally-quoted 400-410 Ma-age for the high-pressure event related to the subduction of the oceanic crust is definitely not recorded in the zircons of the eclogites. In light of these new data, we propose that the obduction of oceanic rocks occurred at about 370-380 Ma while the high-pressure event is recorded at 355 Ma in only a few zircon grains of some eclogite samples. Additionally, this large scale dating project demonstrates that the zircons from eclogites do not systematically recrystallise during the high pressure event and consequently their U-Pb systems do not record that metamorphism systematically. These zircons rather preserve the isotopic memory of the magmatic crystallization of their igneous protolith. Another example of an eclogite sample from the French Massif Central illustrates the frequent mistake in the interpretation of the ages of the early hydrothermal alteration of zircons in the oceanic crust versus partial or complete recrystallization during eclogite facies metamorphism.

U-Pb dating of zircons from the Modra Massif granodiorite of the Low Carpathians and from porphyroid of the Lower Paleozolic of the Spis-Gemer ore Mountains (Western Carpathians)

International Nuclear Information System (INIS)

Shcherbak, N.P.; Bartitskij, E.N.; Mitskevitch, N.Yu.; Stepanyuk, L.M.

1988-01-01

The method of radioisotope dating based on the ratio of uranium isotopes and lead isotopes was used to date certain rocks and zircon which they contain in the area of the Low Carpathians and the Spis-Gemer ore mountains. Zircon separated from tonalite is ca 320 million years old, zircon from porphyroid about 403 million years old. The obtained data serve to clarify the geological development of the studied area. (M.D.). 2 figs., 2 tabs., 17 refs

A neutron and synchrotron investigation of the electronic structure of lanthanide zirconates

International Nuclear Information System (INIS)

Clements, Richard; Kennedy, Brendan; Ling, Chris; Stampfl, Anton P.J.

2009-01-01

Full text: The lanthanide zirconates are of interest for use in inert matrix fuels and nuclear wasteforms. A variety of studies have been performed to determine the suitability of a material as an inert matrix or wasteform. For use in these applications, the material's structure must be resistant to radiation damage and its thermal, thermodynamic and mechanical properties must be known. The structure's ability to incorporate an actinide host into the lattice vacancy must also be known. These properties may be better understood by investigating the f-electronic structure, which has historically proved difficult to model. We have undertaken a synthesis of the full range of lanthanide zirconate series using solid state techniques. We have performed neutron powder diffraction on a selection of the series in conjunction with the following measurements using synchrotron radiation: powder x-ray diffraction, VUV photoluminescence spectra, x-ray photoemission spectroscopy (XPS) and x-ray absorption near edge spectroscopy (XANES) The results are to be analysed using OFT modeling techniques. These results will be presented, along with details of the analysis and synthetic techniques used.

Assessing the role of detrital zircon sorting on provenance interpretations in an ancient fluvial system using paleohydraulics - Permian Cutler Group, Paradox Basin, Utah and Colorado

Science.gov (United States)

Findlay, C. P., III; Ewing, R. C.; Perez, N. D.

2017-12-01

Detrital zircon age signatures used in provenance studies are assumed to be representative of entire catchments from which the sediment was derived, but the extent to which hydraulic sorting can bias provenance interpretations is poorly constrained. Sediment and mineral sorting occurs with changes in hydraulic conditions driven by both allogenic and autogenic processes. Zircon is sorted from less dense minerals due to the difference in density, and any age dependence on zircon size could potentially bias provenance interpretations. In this study, a coupled paleohydraulic and geochemical provenance approach is used to identify changes in paleohydraulic conditions and relate them to spatial variations in provenance signatures from samples collected along an approximately time-correlative source-to-sink pathway in the Permian Cutler Group of the Paradox Basin. Samples proximal to the uplift have a paleoflow direction to the southwest. In the medial basin, paleocurrent direction indicates salt movement caused fluvial pathways divert to the north and northwest on the flanks of anticlines. Channel depth, flow velocity, and discharge calculations were derived from field measurements of grain size and dune and bar cross-stratification indicate that competency of the fluvial system decreased from proximal to the medial basin by up to a factor of 12. Based upon the paleohydraulic calculations, zircon size fractionation would occur along the transect such that the larger zircons are removed from the system prior to reaching the medial basin. Analysis of the size and age distribution of zircons from the proximal and distal fluvial system of the Cutler Group tests if this hydraulic sorting affects the expected Uncompahgre Uplift age distribution.

Effect of cryogenic treatment on tensile behavior of case carburized steel-815M17

International Nuclear Information System (INIS)

Bensely, A.; Senthilkumar, D.; Mohan Lal, D.; Nagarajan, G.; Rajadurai, A.

2007-01-01

The crown wheel and pinion represent the most highly stressed parts of a heavy vehicle; these are typically made of 815M17 steel. The reasons for the frequent failure of these components are due to tooth bending impact, wear and fatigue. The modern processes employed to produce these as high, durable components include cryogenic treatment as well as conventional heat treatment. It helps to convert retained austenite into martensite as well as promote carbide precipitation. This paper deals with the influence of cryogenic treatment on the tensile behavior of case carburized steel 815M17. The impetus for studying the tensile properties of gear steels is to ensure that steels used in gears have sufficient tensile strength to prevent failure when gears are subjected to tensile or fatigue loads, and to provide basic design information on the strength of 815M17 steel. A comparative study on the effects of deep cryogenic treatment (DCT), shallow cryogenic treatment (SCT) and conventional heat treatment (CHT) was made by means of tension testing. This test was conducted as per ASTM standard designation E 8M. The present results confirm that the tensile behavior is marginally reduced after cryogenic treatment (i.e. both shallow and deep cryogenic treatment) for 815M17 when compared with conventional heat treatment. Scanning electron microscopic (SEM) analysis of the fracture surface indicates the presence of dimples and flat fracture regions are more common in SCT specimens than for CHT and DCT-processed material

Sorption of uranyl species on zircon and zirconia

International Nuclear Information System (INIS)

Lomenech, C.; Drot, R.; Simoni, E.; Ehrhardt, J.J.; Mielczarski, J.

2002-01-01

The safety of a long-term storage of radioactive waste in deep geological repositories would be strongly affected by the migration properties of radionuclides through the different barriers to the surface of the earth. Since the main process involved in the retention of radioactive ions is their sorption at the water/ mineral interface, a quantitative description of the sorption reactions is needed. Macroscopic data have for a long time been the only source of information used to propose a modelling of sorption equilibria, although they bring no direct information on the nature of the sorbed species; a microscopic structural investigation of the surface complexes is difficult indeed, because of the small amount of matter sorbed. Thus, in this study, parallel to the macroscopic measurements, different complementary spectroscopic techniques have been used in order to determine the nature of the surface species. As the final purpose of such a study is the simulation of the experimental retention data, the precise structural identification of the sorption equilibria will then be very useful to constrain the data simulation code. In this work, we present the results of both macroscopic and microscopic studies of the sorption of uranyl species on zircon and zirconia. The first part of our macroscopic approach was the surface characterisation of the non-sorbed materials by the determination of the specific areas, of the pH of the isoelectric points, and of the sorption site numbers, while the second part aimed at obtaining the sorption isotherms (percentage of sorption versus pH), which was performed using alpha spectrometry, for different uranyl concentrations, media (NaClO 4 or KNO 3 ) and ionic strengths. The spectroscopic identification of the different surface complexes and sorption sites has been carried out using four different spectroscopies. Whereas tune-resolved laser spectro-fluorimetry gave a direct answer concerning the number of surface species (only for a

Electrochemical characterization of praseodymia doped zircon. Catalytic effect on the electrochemical reduction of molecular oxygen in polar organic solvents

Energy Technology Data Exchange (ETDEWEB)

Domenech, Antonio, E-mail: antonio.domenech@uv.es [Departament de Quimica Analitica, Universitat de Valencia, Dr. Moliner, 50, 46100 Burjassot, Valencia (Spain); Montoya, Noemi; Alarcon, Javier [Departament de Quimica Inorganica, Universitat de Valencia, Dr. Moliner, 50, 46100 Burjassot, Valencia (Spain)

2011-08-01

Highlights: > Electrochemical characterization of Pr centers in praseodymia-doped zircon. > Study of the catalytic effect on the reduction of peroxide radical anion in nonaqueous solvents. > Assessment of non-uniform distribution of Pr centers in the zircon grains. - Abstract: The voltammetry of microparticles and scanning electrochemical microscopy methodologies are applied to characterize praseodymium centers in praseodymia-doped zircon (Pr{sub x}Zr{sub (1-y)}Si{sub (1-z)}O{sub 4}; y + z = x; 0.02 < x < 0.10) specimens prepared via sol-gel synthetic routes. In contact with aqueous electrolytes, two overlapping Pr-centered cathodic processes, attributable to the Pr (IV) to Pr (III) reduction of Pr centers in different sites are obtained. In water-containing, air-saturated acetone and DMSO solutions as solvent, Pr{sub x}Zr{sub (1-y)}Si{sub (1-z)}O{sub 4} materials produce a significant catalytic effect on the electrochemical reduction of peroxide radical anion electrochemically generated. These electrochemical features denote that most of the Pr centers are originally in its 4+ oxidation state in the parent Pr{sub x}Zr{sub (1-y)}Si{sub (1-z)}O{sub 4} specimens. The variation of the catalytic performance of such specimens with potential scan rate, water concentration and Pr loading suggests that Pr is not uniformly distributed within the zircon grains, being concentrated in the outer region of such grains.

Geochronology of Zircon in Eclogite Reveals Imbrication of the Ultrahigh-Pressure Western Gneiss Region of Norway.

Science.gov (United States)

Young, D. J.; Kylander-Clark, A. R.; Root, D. B.

2014-12-01

Eclogite provides the only record of kinematic events at the deepest levels of orogens. Integrating the U-Pb geochronology and trace element chemistry of zircon in eclogite reveals the most complete view of the PTt history, yet low concentrations of uranium and zirconium and drier compositions that hinder zircon growth at peak conditions render it a challenging rocktype for this approach. The iconic Western Gneiss Region (WGR) in Norway is one of the largest terranes of deeply subducted continental rocks in the world, and contains many indicators of ultrahigh-pressure metamorphic conditions (P>2.8 GPa) that developed during the Siluro-Devonian Caledonian Orogeny. A metamorphic transition from amphibolite-facies to ultrahigh-pressure eclogite facies broadly coincides with a km-scale shear zone that underlies the majority of the WGR. A critical unknown is the timing of movement on this feature, which emplaced allochthonous units above the Baltica basement, but might also have accommodated late-orogenic exhumation of the WGR from mantle depths. We carried out laser ablation split-stream ICPMS (LASS) and selected multigrain TIMS analyses of zircons from eleven eclogites across the southern WGR, of which eight are located within or above the shear zone. LASS spots on polished grains mostly yield weakly discordant Proterozoic intrusive ages, and often minimal indication of a Caledonian (U)HP metamorphic overprint. Direct ablation into unpolished zircon reveals thin rims of Caledonian age in some cases. Overall, the dataset shows that all samples began zircon growth at approximately the same time (ca. 430-420 Ma). Eclogite from lower levels of the shear zone does not contain any dates younger than ca. 410 Ma, however, while eclogite from higher levels continued growth until ca. 400 Ma. We interpret this to result from thrusting of the WGR above cooler basement after 410 Ma, terminating new zircon crystallization within the shear zone but allowing limited further growth in

Two age populations of zircons from the Timber Creek kimberlites, Northern Territory, as determined by laser-ablation ICP-MS analysis

International Nuclear Information System (INIS)

Belousova, E.A.; Jackson, S.E.; O'Reilly, S.Y.; Griffin, W.L.

2001-01-01

Two populations of kimberlitic zircon are present in the Timber Creek kimberlites, Northern Territory. Laser-ablation ICP-MS U-Pb dating yields an age of 1483 ± 15 (2σ) Ma for the main group and an age of 179 ± 2 Ma for the other group. This distinction of two age groups is strongly supported by Hf isotope data on the same zircons. Although the trace-element patterns of both populations are typical of mantle-derived zircons, the 'young' population has slightly higher concentrations of most trace elements, but has lower Hf, Nb, Ta and Pb contents. The distinct differences in trace-element contents and Hf isotopic composition of the two zircon populations indicate that they were derived from different magma sources. The dating results indicate that the emplacement age of the Timber Creek kimberlites cannot be older than the age of the 'young' zircon population (i.e. 179 ± 2 Ma). This clarifies the inconsistency between the previously reported SHRIMP age of the Timber Creek zircons (1462 ± 53 Ma) and the much younger age (1200Ma) of the sediments of the Victoria River Basin into which these kimberlites have intruded. The Timber Creek kimberlites are a newly recognised extension of the widespread Jurassic kimberlite activity known in Western Australia and South Australia. Copyright (2001) Geological Society of Australia

L'auto adaptation à des mélanges essence/alcool utilisés comme carburant automobile: le moteur souple The Self-Adapting of Gasoline/Alcohol Mixtures Used As Automotive Fuel: the Flexible Engine

Directory of Open Access Journals (Sweden)

Dorbon M.

2006-11-01

Full Text Available Le moteur souple est un moteur susceptible d'être alimenté par des carburants constitués de mélanges d'une essence classique et d'un alcool léger (méthanol ou éthanol; si la concentration de chacun des composants de ces mélanges varie, les réglages nécessaires au bon fonctionnement du véhicule se font automatiquement. Dans cet article, sont tout d'abord exposées les propriétés caractéristiques en tant que carburant automobile de l'un de ces alcools légers, le méthanol. Puis viennent les descriptions des dispositifs qui font le moteur souple c'est-à-dire d'une part les systèmes de reconnaissance du carburant et d'autre part les appareillages susceptibles de modifier les réglages du moteur (alimentation et allumage en fonction de la qualité du mélange consommé. A flexible engine is one capable of running on fuels consisting of mixtures of conventional gasoline and a light alcohol (methanol or ethanol. If the concentration of each of these components of such mixtures varies, the tuning required for the proper running of the vehicle takes place automatically. This article begins by describing the characteristic properties of one of these light alcohols (methanol as an automotive fuel. Then the equipment is described that makes an engine flexible, i. e. both the fuel recognition systems and the equipment capable of changing engine tuning (feed and ignition as a function of the quality of the mixture burned.

Investigating high zircon concentrations in the fine fraction of stream sediments draining the Pan-African Dahomeyan Terrane in Nigeria

International Nuclear Information System (INIS)

Key, Roger M.; Johnson, Christopher C.; Horstwood, Matthew S.A.; Lapworth, Dan J.; Knights, Katherine V.; Kemp, Simon J.; Watts, Michael; Gillespie, Martin; Adekanmi, Michael; Arisekola, Tunde

2012-01-01

Sixteen hundred stream sediments (<150 μm fraction) collected during regional geochemical surveys in central and SW Nigeria have high median and maximum concentrations of Zr that exceed corresponding Zr concentrations found in stream sediments collected from elsewhere in the World with similar bedrock geology. X-ray diffraction studies on a sub-set of the analysed stream sediments showed that Zr is predominantly found in detrital zircon grains. However, the main proximal source rocks (Pan-African ‘Older Granites’ of Nigeria and their Proterozoic migmatitic gneiss country rocks) are not enriched in zircon (or Zr). Nevertheless, U–Pb LA-ICP-MS dating with cathodoluminescence imaging on detrital zircons, both from stream sediment samples and underlying Pan-African ‘Older Granites’ confirms a local bedrock source for the stream sediment zircons. A combination of tropical/chemical weathering and continuous physical weathering, both by ‘wet season’ flash flooding and ‘dry season’ unidirectional winds are interpreted to have effectively broken down bedrock silicate minerals and removed much of the resultant clay phases, thereby increasing the Zr contents in stream sediments. The strong correlation between winnowing index (Th/Al) and Zr concentration across the study area support this interpretation. Therefore, ‘anomalous’ high values of Zr, as well as other elements concentrated in resistant ‘heavy’ minerals in Nigeria’s streams may not reflect proximal bedrock concentrations of these elements. This conclusion has important implications for using stream sediment chemistry as an exploration tool in Nigeria for primary metal deposits associated with heavy minerals.

Mass spectrographic analysis of selected chemical elements by microbial leaching of zircon

International Nuclear Information System (INIS)

Becker, S.; Dietze, H.J.; Bullmann, M.; Iske, U.

1986-01-01

Spark source mass spectrometry is a useful method for chemical element analysis of geological and biological samples. This sensitive technique (detection limit down to the ppb-range) is used to analyze leaching processes by means of several microorganisms. The problem of microbial leaching of chemical resistent materials was tested under laboratory conditions with regard to possible analytical and technical applications. Leaching of metals with chemolithotrophic and heterotrophic, organic acids producing microorganisms has been investigated with zircon from the Baltic Shield containing 0.7% rare earth elements and 1.67% hafnium. When zircon is leached with strains of thiobacillus ferrooxidans about 80% of the rare earth elements, Hf, Th and U can be recovered. (orig.) [de

Retention capacity of samarium (III) in zircon for it possible use in retaining walls for confinement of nuclear residues

International Nuclear Information System (INIS)

Garcia G, N.

2006-01-01

Mexico, as country that produces part of its electric power by nuclear means, should put special emphasis in the development of technologies guided to the sure and long term confinement of the high level nuclear residuals. This work studies the capacity that has the natural zircon to retain to the samarium (III) in solution, by what due, firstly, to characterize the zircon for technical instrumental to determine the purity and characteristic of the mineral in study. The instrumental techniques that were used to carry out the physicochemical characterization were the neutron activation analysis (NAA), the infrared spectroscopy (IS), the thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), semiquantitative analysis, dispersive energy spectroscopy (EDS), X-ray diffraction (XRD) and luminescence technique. The characterization of the surface properties carries out by means of the determination of the surface area using the BET multipoint technique, acidity constants, hydration time, the determination of the point of null charge (pH PCN ) and density of surface sites (D s ). The luminescence techniques were useful to determine the optimal point hydration of the zircon and for the quantification of the samarium, for that here intends the development of both analysis techniques. With the adjustment of the titration curves in the FITEQL 4 package the constants of surface acidity in the solid/liquid interface were determined. To the finish of this study it was corroborated that the zircon is a mineral that presents appropriate characteristics to be proposed as a contention barrier for the deep geologic confinement. With regard to the study of adsorption that one carries out the samarium retention it is superior to 90% under the described conditions. This investigation could also be applicable in the confinement of dangerous industrial residuals. (Author)

X-ray photoelectron spectroscopy investigation of the carburization of 310 stainless steel

International Nuclear Information System (INIS)

Tabet, N.; Allam, I.; Yin, R.C.

2003-01-01

The surface of 310 stainless steel (310SS) samples was investigated by X-ray photoelectron spectroscopy (XPS) after 500 h cyclic exposure to two carburizing atmospheres: CH 4 (2%)-H 2 (98%) at 800 deg. C, and CH 4 (10%)-H 2 (90%) at 1100 deg. C. The depth distribution of various elements in the surface region was obtained by XPS after successive cycles of argon etching. The microstructure of the alloy was observed by scanning electron microscopy (SEM) and the phases formed during the exposure were analyzed by X-ray diffraction (XRD). The results showed that the major phases that were formed within few micrometer depth during exposure at 800 deg. C include both iron and chromium carbides. (Mn, Cr) oxide was also formed as a result of the reaction with the residual oxygen of the atmosphere. A region of few microns width that was relatively depleted of chromium was formed under the surface as a result of the outwards diffusion of chromium. The exposure to the reducing atmosphere at 1100 deg. C led to the formation of various iron and chromium carbides. No oxide was formed during exposure. In all exposed samples, the surface was Cr enriched while nickel remained buried under the surface region that reacted with the atmosphere

U-Pb zircon and biostratigraphic data of high-pressure/low-temperature metamorphic rocks of the Talea Ori: tracking the Paleotethys suture in central Crete, Greece

Science.gov (United States)

Zulauf, G.; Dörr, W.; Krahl, J.; Lahaye, Y.; Chatzaras, V.; Xypolias, P.

2016-10-01

Inherited deformation microfabrics of detrital quartz grains and U-Pb (Laser ablation (LA)-ICPMS and ID TIMS) ages of detrital zircons separated from the Phyllite-Quartzite Unit s.l. of the Talea Ori, central Crete, suggest strikingly different source rocks. Albite gneiss of the lower Rogdia Beds includes Cambrian and Neoproterozoic rounded zircons with main U-Pb age peaks at 628 and 988 Ma. These and minor Paleoproterozoic and Archean peaks, together with the lack of Variscan-aged and Mesoproterozoic zircons, are similar to the age spectra obtained from the Phyllite-Quartzite Unit s.str. of the Peloponnesus and eastern Crete and from the Taurides. All of these zircons should be derived from the northeastern passive margin of Gondwana (Cimmeria). Metatuffites of the uppermost Rogdia Beds and metasandstone of Bali beach, on the other hand, include euhedral detrital zircons displaying a Variscan U-Pb age spectra at ca. 300 Ma with concordia ages at 291 ± 3, 300 ± 1 Ma (Rogdia) and 286 ± 3, 300 ± 3, 313 ± 2 Ma (Bali). Both types of metasediments and their zircons are similar to those of the pre-Alpine basement and overlying Tyros Beds of eastern Crete, revealing a provenance at the southern active margin of Laurasia. Thus, in central Crete the Paleotethys suture should be situated inside the Rogdia Beds. Magmatic zircons separated from a rhyolite boulder of the lower Achlada Beds yielded a concordant U-Pb zircon age at 242 ± 2 Ma placing a maximum age for the deposition of the (meta)conglomerate from which the boulder was collected. This age is compatible with an Olenekian-early Anisian age of the underlying Vasilikon marble suggested by new findings of the foraminifera Meandrospira aff. pusilla. Both the Achlada Beds and the Vasilikon marble can be attributed to the lower Tyros Beds of eastern Crete. The Alpine deformation led to a pervasive mylonitic foliation, which is affecting most of the studied rocks. This foliation results from D2 top

Contribution to the study of U-Ti and U-Pu-Ti carbides; Contribution a l'etude des carbures U-C-Ti et (U, Pu) - C-Ti

Energy Technology Data Exchange (ETDEWEB)

Milet, C A [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

1968-07-01

After having discussed the reasons to use (U,Pu) carbides as fast reactor fuel, we examine the influence of the addition of titanium to these carbides. A preliminary study has been done on the system of U-C-Ti and some properties have been measured such as: density, thermal expansion, electrical resistivity, atmospheric corrosion and compatibility with stainless steel. The systems U-Pu-C-Ti (Pu/U + Pu equal to 15 per cent) and U-C-Ti have been found to be very similar. There exists a two phases region (U,Pu)C + TiC, an eutectic between (U,Pu)C and TiC for approximately 15 at %. The solubilities of U + Pu in TiC and of Ti in (U,Pu)C is less than 1 % at. The addition of titanium does not markedly change thermal expansion coefficients of (U,Pu)C. However the resistance to atmospheric corrosion and compatibility with stainless steel is improved. Thermal conductivity, calculated from electrical resistivity, has increased. On the other side, the density of fissile material is lowered. The combination of (U,Pu)C + TiC seems to be the most promising alloy for application as nuclear fuel. (author) [French] Apres avoir rappele les problemes poses par un combustible pour les reacteurs a neutrons rapides et l'interet des carbures U-Pu-C comme combustible, on examine l'influence de l'addition de titane dans ces carbures. Une etude preliminaire sur le systeme U-C-Ti a ete effectuee et quelques proprietes sont indiquees: densite, coefficients de dilatation, resistivite electrique, tenue a la corrosion atmospherique, compatibilite avec l'acier inoxydable. Le systeme U-Pu-C-Ti (Pu/U + Pu egal a 15 pour cent) presente de grandes analogies avec le systeme U-C-Ti. Il existe un domaine biphase (U,Pu)C + TiC, un eutectique entre (U,Pu)C et TiC pour environ 15 at % Ti; les solubilites de U + Pu clans TiC et de Ti dans (U,Pu)C sont inferieures a 1 at %. Par rapport a la phase (U,Pu)C, l'addition de titane est sans effets importants sur les coefficients de dilatation. Par contre la tenue a

Phase transformations in lead zirconate-titanate doped with lanthanum

Energy Technology Data Exchange (ETDEWEB)

Ishchuk, V M; Morozov, E M

1979-07-01

Presented are the results of studies on the character of phase transitions of the lead-lanthanum zirconate-titanate (LLZT) system. The replacement of lead by lanthanum leads to the expansion of the region of antisegnetoelectric (ASE) states of solid solutions of lead zirconate-titanate (LZT) in the direction of PbTiO/sub 3/ concentration growth. An intermediate region is revealed between segnetoelectric (SE) and ASE states, material properties in which depend on their prehistory: annealed samples are in the ASE state, whereas the application of electric field exceeding some critical value induces the SE state. A family of phase diagrams obtained at consequent replacement of lead by lanthanum permits to identify phase states in any series of LLZT with a constant ratio of Zr:Ti, in the x/65/35 series in particular. Thermally depolarized state of materials of this series at x<6.5 is shown to be antisegnetoelectric at all the temperatures below the Curie point Tsub(c), and heating causes phase transition of ASE..-->..PE (paraelectric state) at Tsub(c). Polarized samples being heated, a successiveness of phase transitions of SE..-->..ASE takes place at T/sub 0/, and that of ASE reversible PE at Tsub(C) (Tsub(0)..ASE phase transition in the LZT system.

U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration

Energy Technology Data Exchange (ETDEWEB)

Chemale Junior, Farid, E-mail: fchemale@unb.br [Universidade de Brasilia (UnB), DF (Brazil). Inst. de Geociencias; Kawashita, Koji; Dussin, Ivo A. [Universidade de Sao Paulo (USP), SP (Brazil). Centro de Pesquisas Geocronologicas; Avila, Janaina N. [Australian National University, Canberra, (Australia). Research School of Earth Sciences; Justino, Dayvisson; Bertotti, Anelise [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Curso de Pos-Graduacao em Geociencias

2012-06-15

The LA-MC-ICP-MS method applied to U-Pb in situ dating is still rapidly evolving due to improvements in both lasers and ICP-MS. To test the validity and reproducibility of the method, 5 different zircon samples, including the standard Temora-2, ranging in age between 2.2 Ga and 246 Ma, were dated using both LA-MC-ICP-MS and SHRIMP. The selected zircons were dated by SHRIMP and, after gentle polishing, the laser spot was driven to the same site or on the same zircon phase with a 213 nm laser microprobe coupled to a multi-collector mixed system. The data were collected with a routine spot size of 25 {mu}m and, in some cases, of 15 and 40 {mu}m. A careful cross-calibration using a diluted U-Th-Pb solution to calculate the Faraday reading to counting rate conversion factors and the highly suitable GJ-1 standard zircon for external calibrations were of paramount importance for obtaining reliable results. All age results were concordant within the experimental errors. The assigned age errors using the LA-MC-ICP-MS technique were, in most cases, higher than those obtained by SHRIMP, but if we are not faced with a high resolution stratigraphy, the laser technique has certain advantages. (author)

Tracking magmatic processes through Zr/Hf ratios in rocks and Hf and Ti zoning in zircons: An example from the Spirit Mountain batholith, Nevada

Science.gov (United States)

Lowery, Claiborne L.E.; Miller, C.F.; Walker, B.A.; Wooden, J.L.; Mazdab, F.K.; Bea, F.

2006-01-01

Zirconium and Hf are nearly identical geochemically, and therefore most of the crust maintains near-chondritic Zr/Hf ratios of ???35-40. By contrast, many high-silica rhyolites and granites have anomalously low Zr/Hf (15-30). As zircon is the primary reservoir for both Zr and Hf and preferentially incorporates Zr, crystallization of zircon controls Zr/ Hf, imprinting low Zr/Hf on coexisting melt. Thus, low Zr/Hf is a unique fingerprint of effective magmatic fractionation in the crust. Age and compositional zonation in zircons themselves provide a record of the thermal and compositional histories of magmatic systems. High Hf (low Zr/ Hf) in zircon zones demonstrates growth from fractionated melt, and Ti provides an estimate of temperature of crystallization (TTiZ) (Watson and Harrison, 2005). Whole-rock Zr/Hf and zircon zonation in the Spirit Mountain batholith, Nevada, document repeated fractionation and thermal fluctuations. Ratios of Zr/Hf are ???30-40 for cumulates and 18-30 for high-SiO2 granites. In zircons, Hf (and U) are inversely correlated with Ti, and concentrations indicate large fluctuations in melt composition and TTiZ (>100??C) for individual zircons. Such variations are consistent with field relations and ion-probe zircon geochronology that indicate a >1 million year history of repeated replenishment, fractionation, and extraction of melt from crystal mush to form the low Zr/Hf high-SiO2 zone. ?? 2006 The Mineralogical Society.

Decoding a protracted zircon geochronological record in ultrahigh temperature granulite, and persistence of partial melting in the crust, Rogaland, Norway

Science.gov (United States)

Laurent, Antonin T.; Bingen, Bernard; Duchene, Stephanie; Whitehouse, Martin J.; Seydoux-Guillaume, Anne-magali; Bosse, Valerie

2018-04-01

This contribution evaluates the relation between protracted zircon geochronological signal and protracted crustal melting in the course of polyphase high to ultrahigh temperature (UHT; T > 900 °C) granulite facies metamorphism. New U-Pb, oxygen isotope, trace element, ion imaging and cathodoluminescence (CL) imaging data in zircon are reported from five samples from Rogaland, South Norway. The data reveal that the spread of apparent age captured by zircon, between 1040 and 930 Ma, results both from open-system growth and closed-system post-crystallization disturbance. Post-crystallization disturbance is evidenced by inverse age zoning induced by solid-state recrystallization of metamict cores that received an alpha dose above 35 × 1017 α g-1. Zircon neocrystallization is documented by CL-dark domains displaying O isotope open-system behaviour. In UHT samples, O isotopic ratios are homogenous (δ18O = 8.91 ± 0.08‰), pointing to high-temperature diffusion. Scanning ion imaging of these CL-dark domains did not reveal unsupported radiogenic Pb. The continuous geochronological signal retrieved from the CL-dark zircon in UHT samples is similar to that of monazite for the two recognized metamorphic phases (M1: 1040-990 Ma; M2: 940-930 Ma). A specific zircon-forming event is identified in the orthopyroxene and UHT zone with a probability peak at ca. 975 Ma, lasting until ca. 955 Ma. Coupling U-Pb geochronology and Ti-in-zircon thermometry provides firm evidence of protracted melting lasting up to 110 My (1040-930 Ma) in the UHT zone, 85 My (ca. 1040-955 Ma) in the orthopyroxene zone and some 40 My (ca. 1040-1000 Ma) in the regional basement. These results demonstrate the persistence of melt over long timescales in the crust, punctuated by two UHT incursions.

Synthesis, Characterization and Thermal Diffusivity of Holmium and Praseodymium Zirconates

Directory of Open Access Journals (Sweden)

Stopyra M.

2016-06-01

Full Text Available A2B2O7 oxides with pyrochlore or defected fluorite structure are among the most promising candidates for insulation layer material in thermal barrier coatings. The present paper presents the procedure of synthesis of holmium zirconate Ho2Zr2O7 and praseodymium zirconate Pr2Zr2O7 via Polymerized-Complex Method (PCM. Thermal analysis of precursor revealed that after calcination at relatively low temperature (700°C fine-crystalline, single-phase material is obtained. Thermal diffusivity was measured in temperature range 25-200°C, Ho2Zr2O7 exhibits lower thermal diffusivity than Pr2Zr2O7. Additionally, PrHoZr2O7 was synthesized. The powder in as-calcined condition is single-phase, but during the sintering decomposition of solid solution took place and Ho-rich phase precipitated. This material exhibited the best insulating properties among the tested ones.

Detrital zircons from samples of five Neo proterozoic sandstone units deposited on Uruguay and Argentina: about evolution of paleographic Rio de la Plata craton

International Nuclear Information System (INIS)

Gaucher, C.; Poire, D.G.; Pamoukaghlian, K.; Gomez Peral, L.; Finney, S.; Valencia, V.; Blanco, G.

2007-01-01

We report U-Pb ages of detrital zircons from samples of five Neoproterozoic sandstone units deposited on the Rio de la Plata Craton (RPC) in Uruguay and Argentina. Quartz-arenites of the Piedras de Afilar Formation show typical Transamazonian ages, with peaks at 2.00-2.07, 1.87 and 1.78 Ga. However, the most important zircon population is Mesoproterozoic, showing maxima at 1.49, 1.35, 1.25 and 1.0 Ga. Zircons recovered from two sandstone levels in the Arroyo del Soldado Group (Yerbal and Cerros San Francisco formations) are mostly Archean in age, with maxima at 3.2 and 2.7 Ga. Palaeoproterozoic zircons are also prominent in this unit, with peaks at 2.45 and 2.18, with the latter a typical Transamazonian age. Two samples from the Sierras Bayas Group in Tandilia (Argentina) show different age spectra. Sandstones of the Villa Monica Formation show a unimodal zircon population of Transamazonian age (peak at 2.13 Ga). Sandstones of the Cerro Largo Formation are characterized by a dominant Transamazonian zircon population (peaks at 2.15, 2.0 and 1.79), but also important Archean-lowermost Palaeoproterozoic (3.33, 2.99, 2.7, 2.47 Ga) and Mesoproterozoic peaks (1.55, 1.23 and 1.06). The abundance of Mesoproterozoic detrital zircons is surprising. A proto-Andean, Mesoproterozoic belt is suggested as the source of the Mesoproterozoic detritus. Archean rocks of the RPC crop out only in the Nico Perez Terrane in Uruguay, suggesting that the Nico Perez Terrane was much closer to Tandilia than it is today. The sinistral reactivation of the Sarandi del Yi Shear Zone in the Cambrian, as a result of tangential collision of the Cuchilla Dionisio-Pelotas Terrane, may explain this observations. The absence of Neoproterozoic zircons shows that the studied units were deposited in a stable continental margin opening to the East and South. These Neoproterozoic basins had obviously no contribution whatsoever from Brasiliano-Pan African belts, supporting the idea of Cambrian terrane

Zircon and baddeleyite from the economic ultramafic-mafic Noril'sk-1 intrusion (Russia): Hf-isotope constraints on source composition

Science.gov (United States)

Malitch, K. N.; Belousova, E. A.; Badanina, I. Yu.; Griffin, W. L.

2012-04-01

The ultramafic-mafic Noril'sk-1 intrusion in the northwestern part of the Siberian Craton (Russia) represents one of three known Noril'sk-type, ore-bearing intrusions, which host one of the world's major economic sulphide platinum-group-element (PGE)-Cu-Ni deposits. Zircon and baddeleyite dated previously both by SHRIMP (i.e. 248.0 ± 3.7 Ma, Campbell et al. 1992) and ID-TIMS (251.1 ± 3.6 Ma, Kamo et al. 1996) have been restricted to one lithology (e.g. leucogabbro) of the Noril'sk-1 intrusion. To better constrain the age of igneous event and sources involved in its generation our multi-technique study utilized ten rock samples characteristic of unmineralized and mineralized lithologies. The rocks investigated comprise (from top to bottom) gabbro-diorite (sample N1-1), leucogabbro (N1-3), olivine-free gabbro (N1-2 and N1-4), olivine-bearing gabbro (N1-5), olivine gabbro (N1-6), plagiowehrlite and plagiodunite (N1-7), taxitic-textured rocks comprising melanotroctolite, olivine gabbro with relics of ultramafic rocks (N1-8, N1-9) and contact fine-grained gabbro (N1-10). Sulphide PGE-Cu-Ni ores occur in ultramafic (N1-7) and taxitic-textured rocks (N1-8 and N1-9), which have thickness of about 17 m, whereas the low-sulphide horizon of about 1 m thick occurs in the upper part of intrusion (N1-3). In situ U-Pb analyses of zircon from these rocks, combined with detailed study of crystal morphology and internal structure, identify four zircon populations (Malitch et al. 2012). The U-Pb ages of baddeleyite and the defined zircon populations cover a significant time span, from Late Paleozoic to Early Mesozoic (e.g., 290 ± 2.8; 261.3 ± 1.6; 245.7 ± 1.1; 236.5 ± 1.8 and 226.7 ± 0.9 Ma). The established distribution of U-Pb ages implies that crystallization of baddeleyite and zircon corresponds to several stages of protracted evolution of ultramafic-mafic magmas at deep-seated staging chambers and/or probably characterizes interaction of distinct magmas during formation

U-Pb zircon geochronology in the western part of the Rayner Complex, East Antarctica

International Nuclear Information System (INIS)

Horie, Kenji; Hokada, Tomokazu; Motoyoshi, Yoichi; Shiraishi, Kazuyuki; Takehara, Mami; Hiroi, Yoshikuni

2016-01-01

U-Pb zircon geochronology was applied to nine metasedimentary samples collected from Mt. Yuzhnaya, Condon Hills, and Mt. Lira in the inland region of the Rayner Complex of western Enderby Land, East Antarctica, in order to define the eastern limits of the western Rayner Complex that underwent the Pan-African metamorphism and to evaluate potential source areas of metasedimentary rocks. Condon Hills and Mt. Lira revealed metamorphic ages of ∼ 894 and ∼ 934 Ma, respectively, which are consistent with previously reported metamorphism in association with Rayner Structural Episode (RSE). Mt. Yuzhnaya samples affected by the RSE contain zircon grains rejuvenated during 590-570 Ma, which indicates that the Pan-African reworking can be extended up to Mt. Yuzhnaya. On the other hand, the Condon Hills samples include Archean detritus, and the age peaks from 3850 to 2491 Ma are the oldest components in the Rayner Complex of western Enderby Land. There is no evidence of reworked Napier Complex rocks in the studied Rayner samples. (author)

Structural Contribution to the Ferroelectric Fatigue in Lead Zirconate Titanate (PZT) Ceramics

OpenAIRE

Hinterstein , Manuel; Rouquette , Jerome; Haines , J; Papet , Ph; Glaum , Julia; Knapp , Michael; Eckert , J; Hoffman , M

2014-01-01

International audience; Many ferroelectric devices are based on doped lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary (MPB), at which the relevant material's properties approach their maximum. Based on a synchrotron x-ray diffraction study of MPB PZT, bulk fatigue is unambiguously found to arise from a less effective field induced tetragonal-to-monoclinic transformation, at which the degradation of the polarization flipping is detected by a less i...

Carburization behavior under the pits induced by metal dusting in 304L and 347 stainless steels

Energy Technology Data Exchange (ETDEWEB)

Chang, Chia-Hao [Department of Materials Engineering and Science, National Cheng Kung University, Tainan 701, Taiwan (China); Tsai, Wen-Ta, E-mail: wttsai@mail.ncku.edu.tw [Department of Materials Engineering and Science, National Cheng Kung University, Tainan 701, Taiwan (China)

2009-08-15

The metal dusting behavior of Type 304L and 347 stainless steels (SSs) in a flowing mixed CO/H{sub 2}/H{sub 2}O gas stream at 600 deg. C was investigated. After exposure in a 35% CO + 60% H{sub 2} + 5% H{sub 2}O gas for 500 h, large pits were formed on both steel surfaces. The aspect ratio of the pits formed in 304L SS was higher than that of the pits formed in 347 SS. The microstructures and chemical compositions of the reaction products and those of the substrate under the pits were examined by using a scanning electron microscope (SEM) combined with an energy dispersive spectrometer (EDS). A Cr-depleted zone containing voids was formed on the outer surface just beneath the pit. Massive matrix carburization and intergranular carbide precipitation were seen for both steels. The experimental results showed that niobium (Nb) could delay the ingress of carbon and retard the metal dusting reaction.

Electrical fatigue behaviour in lead zirconate titanate: an experimental and theoretical study

International Nuclear Information System (INIS)

Bhattacharyya, Mainak; Arockiarajan, A

2013-01-01

A systematic investigation on electrical fatigue in lead zirconate titanate (PZT) is carried out for different loading frequencies. Experiments are conducted up to 10 6 cycles to measure the electrical displacement and longitudinal strain on bulk ceramics in the bipolar mode with large electrical loading conditions. A simplified macroscopic model based on physical mechanisms of domain switching is developed to predict the non-linear behaviour. In this model, the volume fraction of a domain is used as the internal variable by considering the mechanisms of domain nucleation and propagation (domain wall movement). The measured material properties at different fatigue cycles are incorporated into the switching model as damage parameters and the classical strain versus electric field and electric displacement versus electric field curves are simulated. Comparison between the experiments and simulations shows that the proposed model can reproduce the characteristics of non-linear as well as fatigue responses. (paper)

Electrical fatigue behaviour in lead zirconate titanate: an experimental and theoretical study

Science.gov (United States)

Bhattacharyya, Mainak; Arockiarajan, A.

2013-08-01

A systematic investigation on electrical fatigue in lead zirconate titanate (PZT) is carried out for different loading frequencies. Experiments are conducted up to 106 cycles to measure the electrical displacement and longitudinal strain on bulk ceramics in the bipolar mode with large electrical loading conditions. A simplified macroscopic model based on physical mechanisms of domain switching is developed to predict the non-linear behaviour. In this model, the volume fraction of a domain is used as the internal variable by considering the mechanisms of domain nucleation and propagation (domain wall movement). The measured material properties at different fatigue cycles are incorporated into the switching model as damage parameters and the classical strain versus electric field and electric displacement versus electric field curves are simulated. Comparison between the experiments and simulations shows that the proposed model can reproduce the characteristics of non-linear as well as fatigue responses.

Zircon dating of Devonian-Carboniferous rocks from the Bombala area, New South Wales

International Nuclear Information System (INIS)

Sircombe, K.N.; McQueen, K.G.

2000-01-01

Zircons from two igneous and two sedimentary units in the Bombala area of southeastern New South Wales have been examined by the sensitive high resolution ion microprobe (SHRIMP) to establish a time frame in which to interpret these rocks. Previous studies have correlated these rocks with Late Devonian units of the south coast, solely upon the basis of stratigraphy and lithology as palaeontological evidence was absent. The two igneous units are the Hospital Porphyry and Paradise Porphyry occurring beneath the sedimentary units. Both give a Frasnian age that can be correlated with the Boyd Volcanic Complex. The sedimentary samples are from the basal and upper sections of the Rosemeath Formation, a fluvial 'redbed' consisting of conglomerate, coarse sandstone, and associated red siltstone and mudstone. Detrital zircons from the basal conglomeratic section at Kilbrechin indicate a dominant provenance from local Silurian granites and volcanics and a maximum depositional age that can be correlated with the Frasnian-Famennian Merrimbula Group. However, detrital zircons from the upper coarse sandstone section of the Rosemeath Formation at Endeavour Lookout challenge the positive correlation trend with a lack of Silurian-age grains and a presence of grains ranging from Late Devonian to Early Carboniferous in age. These results imply either that the south coast correlation is not valid for the upper sequences, or that the Merrimbula Group sequences also extend upward into the Carboniferous. The general coarseness of the Rosemeath Formation also suggests a relatively local provenance. No Early Carboniferous source is known in the immediate vicinity suggesting that Early Carboniferous igneous activity in this region of the Lachlan Orogen may have been more extensive than is currently realised. Copyright (1999) Geological Society of Australia

Relict zircon U-Pb age and O isotope evidence for reworking of Neoproterozoic crustal rocks in the origin of Triassic S-type granites in South China

Science.gov (United States)

Gao, Peng; Zheng, Yong-Fei; Chen, Yi-Xiang; Zhao, Zi-Fu; Xia, Xiao-Ping

2018-02-01

Granites derived from partial melting of sedimentary rocks are generally characterized by high δ18O values and abundant relict zircons. Such relict zircons are valuable in tracing the source rocks of granites and the history of crustal anatexis. Here we report in-situ U-Pb ages, O isotopes and trace elements in zircons from Triassic granites in the Zhuguangshan and Jiuzhou regions, which are located in the Nanling Range and the Darongshan area, respectively, in South China. Zircon U-Pb dating yields magma crystallization ages of 236 ± 2 Ma for the Zhuguangshan granites and 246 ± 2 Ma to 252 ± 3 Ma for the Jiuzhou granites. The Triassic syn-magmatic zircons are characterized by high δ18O values of 10.1-11.9‰ in Zhuguangshan and 8.5-13.5‰ in Jiuzhou. The relict zircons show a wide range of U-Pb ages from 315 to 2185 Ma in Zhuguangshan and from 304 to 3121 Ma in Jiuzhou. Nevertheless, a dominant age peak of 700-1000 Ma is prominent in both occurrences, demonstrating that their source rocks were dominated by detrital sediments weathered from Neoproterozoic magmatic rocks. Taking previous results for regional granites together, Neoproterozoic relict zircons show δ18O values in a small range from 5 to 8‰ for the Nanling granites but a large range from 5 to 11‰ for the Darongshan granites. In addition, relict zircons of Paleozoic U-Pb age occur in the two granitic plutons. They exhibit consistently high δ18O values similar to the Triassic syn-magmatic zircons in the host granites. These Paleozoic relict zircons are interpreted as the peritectic product during transient melting of the metasedimentary rocks in response to the intracontinental orogenesis in South China. Therefore, the relict zircons of Neoproterozoic age are directly inherited from the source rocks of S-type granites, and those of Paleozoic age record the transient melting of metasedimentary rocks before intensive melting for granitic magmatism in the Triassic.

Theoretical modeling of infrared spectra of twinned lead zirconate

Czech Academy of Sciences Publication Activity Database

Dočekalová, Zuzana; Pasciak, Marek; Hlinka, Jiří

2017-01-01

Roč. 90, č. 1 (2017), s. 17-23 ISSN 0141-1594 R&D Projects: GA ČR GA15-04121S Institutional support: RVO:68378271 Keywords : domains * IR spectroscopy * dielectric permittivity * lead zirconate * shell model * Born effective charge Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.060, year: 2016

Episodic growth and homogenization of plutonic roots in arc volcanoes from combined U-Th and (U-Th)/He zircon dating

Science.gov (United States)

Schmitt, Axel K.; Stockli, Daniel F.; Lindsay, Jan M.; Robertson, Richard; Lovera, Oscar M.; Kislitsyn, Roman

2010-06-01

Tracing the fate of unerupted magma is challenging because plutonic roots of young volcanoes are largely inaccessible. Here we develop the use of zircon age spectra to determine crystal provenance and source rocks for volcanic products, in analogy to detrital crystals in sediments. U-Th zircon crystallization ages for the Soufrière Volcanic Complex, Saint Lucia (Lesser Antilles) frequently predate their eruption as determined from combined U-Th and (U-Th)/He zircon dating. The oldest dated eruptions are 273 ± 15 ka and 264 ± 8 ka (1σ uncertainty) for Morne Bonin dacite and Bellevue pumice deposit, respectively. The most recent eruptions formed morphologically pristine domes in the center of the Qualibou depression (Belfond: 13.6 ± 0.4 ka; Terre Blanche: 15.3 ± 0.4 ka). U-Th (U-Pb) zircon crystallization ages determined for crystal rims and interiors range between near-eruption ages to ∼ 600 ka. Older xenocrysts are absent. Zircon crystallization age distributions are complex, yet systematic: crystal rim ages in the most recently erupted volcanic rocks match those of co-erupted plutonic inclusions, whereas crystal interiors are equivalent to the cumulative distribution of zircon ages from older eruptions. This is evidence that silicic lava domes and pyroclastic flows share a common source that is located underneath the Qualibou depression, where the intrusive roots of this long-lived arc volcanic system became homogenized through thermal and mechanical reprocessing of individual batches of unerupted magma from earlier volcanic episodes within timescales of < 100 ka.

Comportement des pots catalytiques en présence de carburants oxygénés Behavior of Catalytic Mufflers in the Presence of Oxygenated Fuels

Directory of Open Access Journals (Sweden)

Degobert P.

2006-11-01

Full Text Available A partir d'un examen critique de la bibliographie disponible, et après un rappel des répercussions sur les émissions de la présence d'alcools dans les carburants, sont successivement examinées les performances d'épurateurs catalytiques multifonctionnels ou d'oxydation appliqués à des véhicules alimentés avec des carburants dont les teneurs en produits oxygénés varient entre 10 et 100 %. Les performances des catalyseurs s'écartent peu de celles constatées dans le cas de l'essence. Elles restent très bonnes vis-à-vis des polluants non réglementés. Par ailleurs, le pot catalytique n'engendre pas, dans ses conditions normales de fonctionnement, de polluants supplémentaires caractéristiques des combustibles oxygènes utilisés. Based on a critical examination of the literature available and after a review of the effects of the presence of alcools in fuels on emissions, this article successively examines the performances of multifunctional or oxidation catalytic scrubbers applied to vehicles fed with fuels containing between 10 and 100% oxygenated products. The performances of catalysts are not very different from those found with gasoline. They remain very good with regard to pollutants not covered by regulations. Furthermore, under normal operating conditions, a catalytic muffler does not produce any supplementary pollutants characteristic of the oxygenated fuels used.

Investigations on microbial leaching of zircon by means of spark source mass spectrometry

International Nuclear Information System (INIS)

Becker, S.; Dietze, H.J.; Bullmann, M.; Iske, U.

1985-01-01

Spark source mass spectrometry is a useful method for chemical element analysis of geological and biological samples. This sensitive technique (detection limit down to the ppb-range) is used to analyze leaching processes by means of several microorganisms. The problem of microbial leaching of chemical resistent materials was tested under laboratory condition with regard to possible analytical and technical applications. Leaching of metalls with chemolithotrophic and heterotrophic, organic acids producing microorganisms has been investigated with zircon from Baltic Shield containing 0.7% rare earth elements and 1.67% hafnium. When zircon is leached with strains of Thiobacillus ferroxidans the rare earth elements, Hf, Th, and U mostly (about 80%) can be recovered. (author)

Reactor modeling of sorption-enhanced autothermal reforming of methane. Part I: Performance study of hydrotalcite and lithium zirconate-based processes

NARCIS (Netherlands)

Halabi, M.H.; Croon, de M.H.J.M.; Schaaf, van der J.; Cobden, P.D.; Schouten, J.C.

2011-01-01

This paper presents a performance analysis for the sorption-enhanced autothermal reforming of CH4 in a fixed bed reformer for pure H2 production with in situ CO2 capture. The process is analyzed for two candidate sorbents of K-promoted hydrotalcite and lithium zirconate in a fixed bed reactor using

The Comparison of Detrital Zircon Ages to Point Count Provenance Analysis for the Pottsville Sandstone in the Northern Appalachian Foreland Basin Venango County, Pennsylvania

Science.gov (United States)

Loveday, S.; Harris, D. B.; Schiappa, T.; Pecha, M.

2017-12-01

The specific sources of sediments deposited in the Appalachian basin prior to and immediately following the Alleghenian orogeny has long been a topic of debate. Recent advances in U-Pb dating of detrital zircons have greatly helped to determine some of the sources of these sediments. For this study, sandstone samples were collected from the Pottsville Formation in the northern Appalachian Foreland Basin, Venango County, Pennsylvania to provide supplementary data for previous work that sought to describe the provenance of the same sediments by point counts of thin sections of the same units. Results of this previous work established that the provenance for these units was transitional recycled orogenic, including multiple recycled sediments, and that a cratonic contribution was not able to be determined clearly. The previous results suggested that the paleoenvironment was a fluvial dominated delta prograding in the northern direction. However, no geochronologic data was found during this study to confirm this interpretation. We sought to verify these results by U-Pb analysis of detrital zircons. Samples were collected from the areas where the previous research took place. U-Pb ages were found from sample at the highest elevation and lowest elevation. In the first sample, sample 17SL01 (younger sample stratigraphically), the zircons yield U-Pb age range peaks at 442-468 ma and 1037-1081 ma. The probability density plot for this specific sample displays a complete age gap from 500 ma to 811 ma. In the second sample, sample 17SL03 (older rock stratigraphically), the zircons yield U-Pb ages range peaks of 424-616 ma and 975-1057 ma. This sample doesn't show any ages younger than 424 ma and it doesn't display the sample age gap as sample 17SL01 does. The ages of zircons are consistent with thin section point counting provenance results from previous research suggesting zircon transport from the northern direction.

Detrital Zircon Geo- and Thermochronologic Constraints on Late Mississippian-Early Pennsylvanian Sediment Transport and Tectonics, Southwestern Kansas and Northwestern Arkansas

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Bidgoli, T. S.; Wang, W.; Moeller, A.; Stockli, D. F.; Watney, L.

2017-12-01

The Late Mississippian to Early Pennsylvanian is a critical time interval across the globe, with major changes in tectonics, climate, and eustacy. Transcontinental sediment transport in North America, from the Appalachians to Great Canyon, has been proposed to initiate at this time (Gehrels et al., 2011). In the midcontinent, clastic influx to the Hugoton Embayment and Arkoma Shelf, during widespread carbonate platform deposition, may record evidence for this model, but the limited number of provenance studies has hindered interpretations. To test this model and further constrain sediment dispersal and source-to-sink systems in the midcontinent, we evaluate the provenance of upper Mississippian to middle Pennsylvanian siliciclastic intervals, in two areas, using sandstone component analysis and detrital zircon U-Pb and (U-Th)/He double dating. (1) For the Hugoton Embayment in southwestern Kansas, we focus on sandstones deposited in two valley-filling intervals, the Chester and Morrow. A total of 1100 zircon U-Pb ages have been acquired from samples from 10 boreholes, 6 from Chester and 4 from Morrow. Preliminary analysis suggests that the Chester is characterized by two major zircon U-Pb age clusters of 900-1295 Ma (Grenville) and 390-475 Ma, consistent with sediment delivery from the Appalachian orogen. Morrow strata record a change in provenance, with the presence of two additional age groups, 1300-1500 Ma (24.5%) and 1600-1800 Ma (17.9%), that correspond well with the age of basement rocks in the Granite-Rhyolite and Yavapai-Maztzal provinces, respectively. We ascribe changes in the zircon age spectra and introduction of these grains to the development of local uplifts, like the Nemaha Ridge, in the early Pennsylvanian. Double dating of zircons from these peaks may reveal additional information about these basement sources and the timing of denudation of these uplifts. (2) For the Arkoma shelf, we are analyzing 11 samples, collected from outcrops in northwestern

The complex systematics of zircons in migmatitic gneisses: An example from an Archean migmatite along the Patos Shear Zone, Borborema Province, NE Brazil

International Nuclear Information System (INIS)

Costa, A.C.D; Hackspacher, P.C; Dantas, E.L; Fetter, A.H.

2001-01-01

The Northem Tectonic Domain Borborema Province, in Northeast of Brazil records a complex history of tectonic activity ranging from 3.4 Ga to 0.6 Ga (Brito Neves, 1995 and Dantas, 1996). U-Pb systematics of zircons from a migmatitic gneiss just north of the Patos Shear Zone provide an excellent example of the difficulties encountered using conventional single-grain U/Pb zircon geochronology in polydeformed gneiss terranes. Our conventional single grain zircon analyses of a migmatite yielded Archean ages between ca. 3.3 at 2.8 a, as well as some highly discordant Paleoproterozoic ages. Subsequent cathodoluminescence images of these zircon grains showed complex internal structures that possibly record up to 4 separate stages of zircon growth. With such internal complexity, is impossible resolve primary crystallization ages as well as the ages of subsequent overgrowth events using conventional single grain analyses. Such resolution will require analyses of the individual grain domains using the SHRIMP method (au)

Air abrasion experiments in U-Pb dating of zircon

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Goldich, S.S.; Fischer, L.B.

1986-01-01

Air abrasion of zircon grains can remove metamict material that has lost radiogenic Pb and zircon overgrowths that were added during younger events and thereby improve the precision of the age measurements and permit closer estimates of the original age. Age discordance that resulted from a single disturbance of the U-Pb isotopic decay systems, as had been demonstrated by T.E. Krogh, can be considerably reduced, and, under favorable conditions, the ages brought into concordancy. Two or more events complicate the U-Pb systematics, but a series of abrasion experiments can be helpful in deciphering the geologic history and in arriving at a useful interpretation of the probable times of origin and disturbances. In east-central Minnesota, U.S.A., Penokean tonalite gneiss is dated at 1869 ?? 5 Ma, and sheared granite gneiss is shown to have been a high-level granite intrusion at 1982 ?? 5 Ma in the McGrath Gneiss precursor. Tonalite gneiss and a mafic granodiorite in the Rainy Lake area, Ontario, Canada, are dated at 2736 ?? 16 and 2682 ?? 4 Ma, respectively. The tonalitic phase of the Morton Gneiss, southwestern Minnesota, is dated at 3662 ?? 42 Ma. ?? 1986.

Effect of the temperature and oxalic acid in the uranyl sorption in zircon; Efecto de la temperatura y acido oxalico en la sorcion de uranilo en circon

Energy Technology Data Exchange (ETDEWEB)

Ordonez R, E.; Almazan T, M. G.; Garcia G, N. [ININ, Departamento de Quimica, Carretera Mexico-Toluca s/n, 52750 Ocoyoacac, Estado de Mexico (Mexico); Hernandez O, R., E-mail: eduardo.ordonez@inin.gob.mx [Instituto Tecnologico de Veracruz, Ingenieria Quimica, Miguel Angel de Quevedo No. 2779, 91860 Veracruz (Mexico)

2012-10-15

In this work the results of the temperature effect study are presented on uranyl solutions adsorbed on zirconium silicate (ZrSiO{sub 4}) and also on the compounds formed in surface with oxalic acid. The adsorption isotherms of uranyl on hydrated zircon with NaClO{sub 4} 0.5 M, show an increase of the uranyl sorption efficiency when increasing the temperature from 20 to 4 C with a sudden descent in this efficiency when changing the temperature at 60 C. The uranyl sorption efficiency increases to hydrate the zircon with a solution of oxalic acid 0.1 M, maintaining the same tendency regarding to the temperatures of the sorption in medium NaClO{sub 4} 0.5 M. The complex formation in the zircon surface with organic acids of low molecular weight increases the fixation of the uranyl in solution due to the formation of ternary systems, in the order Zircon/A. Organic/Uranyl, without altering their response to the temperature. (Author)

Chemical Th-U-total Pb isochron ages of zircon and monazite from granitic rocks of the Negele area, southern Ethiopia

International Nuclear Information System (INIS)

Yihunie, Tadesse

2003-01-01

CHIME (Chemical Th-U-total Pb Isochron Method) age determinations were made on zircon and monazite grains from granitoid samples in the Negele area of southern Ethiopia. A 611±32 Ma zircon age was obtained from a syn-tectonic hornblende-biotite granite of the Alghe domain. A 453±29 Ma zircon age and a 459±16 Ma monazite age were also obtained from post-tectonic two-mica granites of the Alghe domain and the Kenticha domain, respectively. Since these ca. 450 Ma zircon and monazite ages coincide well, as significant post-tectonic granitic magmatism appears to have occurred in southern Ethiopia in early Paleozoid time. The new CHIME age results indicate at least two episodes of granitic magmatism in southern Ethiopia in the late Proterozoic to early Paleozoic, with a ca. 150 Ma interval between syn- and post-tectonic granitic emplacements, and have a important geochronological constraint on the evolution of the East African Orogen. (author)

New SHRIMP zircon results from Broken Hill: towards robust stratigraphic and event timing

International Nuclear Information System (INIS)

Page, R.W.; Stevens, B.P.J.

1999-01-01

Full text: Zircon U-Pb SHRIMP geochronology is a powerful means of elucidating geological ages, providing that it is integrated with unequivocal field constraints, and providing that the fundamental assumptions which are behind any isotopic dating methods are geologically validated. In an attempt to better quantify the timing of Broken Hill's complex history and to reduce some current uncertainties, we report initial results from a new U-Pb SHRIMP investigation. This program was planned within the background of our own disparate stratigraphic and structural approaches to Broken Hill geology, and with objectives to (a) benchmark our new age results with those of previous workers as well as our own previous work in the Broken Hill Group, (b) evaluate and test the evidence for reported Archaean basement terrain, (c) date stratigraphic units in the upper parts of the Willyama Supergroup, (d) better constrain the timing of deformational events. Our U-Pb SHRIMP work on zircons from layered paragneisses in the Redan Geophysical Zone near Farmcote was catalysed by Nutman and Ehlers' (1998a) preferred interpretation that these 'strondhjemitic' gneisses represent an original ∼2650 Ma protolith. Our work finds zircon provenance age signatures typical of almost all ca. 1700 Ma metasediments, whether in the Broken Hill Block or other Australian Palaeoproterozoic settings. This therefore suggests that the rocks are not Archaean basement, but are part of a Thackaringa Group package possibly deposited about 1705-1710 Ma ago. New SHRIMP work on the Alma Gneiss provides a magmatic age of 1704±3 Ma, and a minimum stratigraphic age for host Thackaringa Group. This result is within error of our ages for other granitoids (1703±3 Ma, 1704±3 Ma) in the same stratigraphic position near Farmcote. As the Thackaringa Group is no more than 1000-1500 metres thick and includes 1710-1700 Ma detrital zircons, pan of the Alma Gneiss intrusion may well have been shallowly intruded, and akin to

Study of samarium modified lead zirconate titanate and nickel zinc ferrite composite system

Energy Technology Data Exchange (ETDEWEB)

Rani, Rekha [Department of Physics, SD PG College, Panipat 132103 (India); School of Physics and Materials Science, Thapar University, Patiala 147004 (India); Juneja, J.K., E-mail: jk_juneja@yahoo.com [Department of Physics, Hindu College, Sonepat 131001 (India); Singh, Sangeeta [Department of Physics, GVM Girls College, Sonepat 131001 (India); Raina, K.K. [School of Physics and Materials Science, Thapar University, Patiala 147004 (India); Prakash, Chandra [Solid State Physics Laboratory, Timarpur, Delhi 110054 (India)

2015-03-15

In the present work, composites of samarium substituted lead zirconate titanate and nickel zinc ferrite with compositional formula 0.95Pb{sub 1−3x/2} Sm{sub x}Zr{sub 0.65}Ti{sub 0.35}O{sub 3}–0.05Ni{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} (x=0, 0.01, 0.02 and 0.03) were prepared by the conventional solid state route. X-ray diffraction analysis was carried out to confirm the coexistence of individual phases. Microstructural study was done by using scanning electron microscope. Dielectric constant and loss were studied as a function of temperature and frequency. To study ferroelectric and magnetic properties of the composite samples, corresponding P–E and M–H hysteresis loops were recorded. Change in magnetic properties of electrically poled composite sample (x=0.02) was studied to confirm the magnetoelectric (ME) coupling. ME coefficient (dE/dH) of the samples (x=0 and 0.02) was measured as a function of DC magnetic field. - Highlights: • We are reporting the effect of Sm substitution on PZT–NiZn ferrite composites. • Observation of both P–E and M–H loops confirms ferroelectric and magnetic ordering. • With Sm substitution, significant improvement in properties was observed. • Increase in magnetization for electrically poled sample is evidence of ME coupling. • Electric polarization is generated by applying magnetic field.

Localized rejuvenation of a crystal mush recorded in zircon temporal and compositional variation at the Lassen Volcanic Center, northern California.

Directory of Open Access Journals (Sweden)

Erik W Klemetti

Full Text Available Zircon ages and trace element compositions from recent silicic eruptions in the Lassen Volcanic Center (LVC allow for an evaluation of the timing and conditions of rejuvenation (reheating and mobilization of crystals within the LVC magmatic system. The LVC is the southernmost active Cascade volcano and, prior to the 1980 eruption of Mount St. Helens, was the site of the only eruption in the Cascade arc during the last century. The three most recent silicic eruptions from the LVC were very small to moderate-sized lava flows and domes of dacite (1915 and 27 ka eruptions of Lassen Peak and rhyodacite (1.1 ka eruption of Chaos Crags. These eruptions produced mixed and mingled lavas that contain a diverse crystal cargo, including zircon. 238U-230Th model ages from interior and surface analyses of zircon reveal ages from ∼17 ka to secular equilibrium (>350 ka, with most zircon crystallizing during a period between ∼60-200 ka. These data support a model for localized rejuvenation of crystal mush beneath the LVC. This crystal mush evidently is the remnant of magmatism that ended ∼190 ka. Most zircon are thought to have been captured from "cold storage" in the crystal mush (670-725°C, Hf >10,000 ppm, Eu/Eu* 0.25-0.4 locally remobilized by intrusion of mafic magma. A smaller population of zircon (>730°C, Hf 0.4 grew in, and are captured from, rejuvenation zones. These data suggest the dominant method to produce eruptible melt within the LVC is small-scale, local rejuvenation of the crystal mush accompanied by magma mixing and mingling. Based on zircon stability, the time required to heat, erupt and then cool to background conditions is relatively short, lasting a maximum of 10 s-1000 s years. Rejuvenation events in the LVC are ephemeral and permit eruption within an otherwise waning and cooling magmatic body.

Zircon trace element and isotopic (Sr, Nd, Hf, Pb) effects of assimilation-fractional crystallization of pegmatite magma: A case study of the Guangshigou biotite pegmatites from the North Qinling Orogen, central China

Science.gov (United States)

Yuan, Feng; Liu, Jia-Jun; Carranza, Emmanuel John M.; Zhang, Shuai; Zhai, De-Gao; Liu, Gang; Wang, Gong-Wen; Zhang, Hong-Yuan; Sha, Ya-Zhou; Yang, Shang-Song

2018-03-01

Evidence for open-system magmatic processes related to wallrock assimilation accompanied by fractional crystallization (AFC) is present in the Guangshigou biotite pegmatites, North Qinling Orogen. The biotite pegmatite-gneiss contacts generally coincide with the greatest enrichment of U and Th. Zircon Usbnd Pb dating constrains the crystallization ages of the biotite pegmatite (rim zone-415 ± 2.6 Ma; internal zone-413.5 ± 2.5 Ma), in line with a pyrite Pbsbnd Pb isochron age (413 ± 22 Ma). Metamict areas in zircon show generally elevated concentrations of trace elements and expulsion of radioactive Pb. Internal zone samples, representing uncontaminated magma, have negative to positive zircon ( 413 Ma) εHf(t) (- 1.53 - + 3.24), low εNd(t) values (- 2.4), and old Hf and Nd model ages (tDM2 = 1.5-1.19 Ga, T2DM = 1.35 Ga, respectively), indicating a dominantly recycled Mesoproterozoic lower crustal material with involvement of some juvenile materials in the source region. The magmatic oxygen fugacity (fO2) and crystallization temperatures ranges from - 24.81 to - 13.34 of log fO2 and 570 °C to 793 °C, respectively. Compared to the internal zone, pegmatite rim samples display a variable and lower εNd(t) values (- 3.9 to - 2.8) and T2DM (1.47-1.37 Ga), but similar Hf isotopic compositions, favouring a three-component isotopic mixing model (recycled Mesoproterozoic lower crust materials, juvenile materials, and host gneiss). Pronounced variations of Ti, Y, U, Th, Hf, and REE concentrations in zircon from grain to grain in individual samples and from area to area within individual grains suggest a fluctuating crystallization environment in hybridized magma from which the rim-hosted zircons crystallized. Variable and high radiogenic Pb ratios of pyrites forming in the hybridized magma were inherited from the matrix. Zircons from both zones exhibit similar Hf isotope patterns, indicating the rim-hosted zircons crystallized during the early stage of hybridization of

High-pressure structural, elastic, and thermodynamic properties of zircon-type HoPO4 and TmPO4

International Nuclear Information System (INIS)

Gomis, O; Lavina, B; Rodríguez-Hernández, P; Muñoz, A; Errandonea, R; Errandonea, D; Bettinelli, M

2017-01-01

Zircon-type holmium phosphate (HoPO 4 ) and thulium phosphate (TmPO 4 ) have been studied by single-crystal x-ray diffraction and ab initio calculations. We report on the influence of pressure on the crystal structure, and on the elastic and thermodynamic properties. The equation of state for both compounds is accurately determined. We have also obtained information on the polyhedral compressibility which is used to explain the anisotropic axial compressibility and the bulk compressibility. Both compounds are ductile and more resistive to volume compression than to shear deformation at all pressures. Furthermore, the elastic anisotropy is enhanced upon compression. Finally, the calculations indicate that the possible causes that make the zircon structure unstable are mechanical instabilities and the softening of a silent B 1u mode. (paper)

Brittle-ductile deformation effects on zircon crystal-chemistry and U-Pb ages: an example from the Finero Mafic Complex (Ivrea-Verbano Zone, western Alps)

Science.gov (United States)

Langone, Antonio; José Alberto, Padrón-Navarta; Zanetti, Alberto; Mazzucchelli, Maurizio; Tiepolo, Massimo; Giovanardi, Tommaso; Bonazzi, Mattia

2016-04-01

A detailed structural, geochemical and geochronological survey was performed on zircon grains from a leucocratic dioritic dyke discordantly intruded within meta-diorites/gabbros forming the External Gabbro unit of the Finero Mafic Complex. This latter is nowadays exposed as part of a near complete crustal section spanning from mantle rocks to upper crustal metasediments (Val Cannobina, Ivrea-Verbano Zone, Italy). The leucocratic dyke consists mainly of plagioclase (An18-24Ab79-82Or0.3-0.7) with subordinate amounts of biotite, spinel, zircon and corundum. Both the leucocratic dyke and the surrounding meta-diorites show evidence of ductile deformation occurred under amphibolite-facies conditions. Zircon grains (up to 2 mm in length) occur mainly as euhedral grains surrounded by fine grained plagioclase-dominated matrix and pressure shadows, typically filled by oxides. Fractures and cracks within zircon are common and can be associated with grain displacement or they can be filled by secondary minerals (oxides and chlorite). Cathodoluminescence (CL) images show that zircon grains have internal features typical of magmatic growth, but with local disturbances. However EBSD maps on two selected zircon grains revealed a profuse mosaic texture resulting in an internal misorientation of ca. 10o. The majority of the domains of the mosaic texture are related to parting and fractures, but some domains show no clear relation with brittle features. Rotation angles related to the mosaic texture are not crystallographically controlled. In addition, one of the analysed zircons shows clear evidence of plastic deformation at one of its corners due to indentation. Plastic deformation results in gradual misorientations of up to 12o, which are crystallographically controlled. Trace elements and U-Pb analyses were carried out by LA-ICP-MS directly on petrographic thin sections and designed to cover the entire exposed surface of selected grains. Such investigations revealed a strong

Stability of Zircon and Its Isotopic Ratios in High-Temperature Fluids: Long-Term (4 months Isotope Exchange Experiment at 850°C and 50 MPa

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Ilya N. Bindeman

2018-05-01

Full Text Available Stability of zircon in hydrothermal fluids and vanishingly slow rates of diffusion identify zircon as a reliable recorder of its formation conditions in recent and ancient rocks. Debate, however, persists on how rapidly oxygen and key trace elements (e.g., Li, B, Pb diffuse when zircon is exposed to silicate melt or hot aqueous fluids. Here, we report results of a nano- to micrometer-scale investigation of isotopic exchange using natural zircon from Mesa Falls Tuff (Yellowstone treated with quartz-saturated, isotopically (18O, D, 7Li, and 11B labeled water with a nominal δ18O value of +450%0 over 4 months at 850°C and 50 MPa. Frontside (crystal rim inwards δ18O depth profiling of zircon by magnetic sector SIMS shows initially high but decreasing 18O/16O over a ~130 nm non-Fickian profile, with a decay length comparable to the signal from surficial Au coating deposited onto zircon. In contrast, backside (crystal interior outwards depth profiling on a 2-3 μm thick wafer cut and thinned from treated zircon by focused ion beam (FIB milling lacks any significant increase in 18O/16O during penetration of the original surface layer. Near-surface time-of-flight (TOF-SIMS frontside profiles of uncoated zircon from 4-month and 1-day-long experiments as well as untreated zircons display similar enrichments of 18O over a distance of ~20 nm. All frontside 18O profiles are here interpreted as transient surface signals from nm-thick surface enrichment or contamination unrelated to diffusion. Likewise, frontside depth profiling of H, Li, and B isotopes are similar for long- and short-duration experiments. Additionally, surface U-Pb dating of zircon from the 4-month experiment returned U-Pb ages by depth profiling with ~1 μm penetration that were identical to untreated samples. Frontside and backside depth-profiling thus demonstrate that diffusive 18O enrichment in the presence of H2O is much slower than predicted from experiments in Watson and Cherniak

Zircons reveal magma fluxes in the Earth's crust.

Science.gov (United States)

Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

2014-07-24

Magma fluxes regulate the planetary thermal budget, the growth of continents and the frequency and magnitude of volcanic eruptions, and play a part in the genesis and size of magmatic ore deposits. However, because a large fraction of the magma produced on the Earth does not erupt at the surface, determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large-scale geological processes. Here we show that age distributions of zircons, a mineral often present in crustal magmatic rocks, in combination with thermal modelling, provide an accurate means of retrieving magma fluxes. The characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the Earth's crust. Our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems. Analysis of existing age population data sets using our method suggests that porphyry-type deposits, plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes. We anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions, and to determine the main factors controlling the distribution of resources on our planet.

The preparation and certification of zirconyl chloride CRM-inhouse from process result of zircon mineral

International Nuclear Information System (INIS)

Samin; Sajimo; Supriyanto; Isman Mulyadi T

2015-01-01

The preparation and certification of the zirconyl chloride certified reference material (CRM) has been carried out from the row material of the zircon mineral. The zircon mineral was processing in the Feeder with the velocity of 17 kg/hour and produced the zircon concentrate. The zircon concentrate was mixed with NaOH, NaF, Na 2 CO 3 and H 2 O. The mixture was melted in the Furnace at 750°C for 2 hours. The results of molten was pressed with aquadest and then was participated for 24 hours. The solid was separated from the filtrate, and then it was dried in the Oven at 105°C for 3 hours, those result was called sodium zirconate. Sodium zirconate was leaching with HCl, it was found the zirconyl chloride solution and then was evaporated it was found the zirconyl chloride concentrated solution. This solution was crystallized, then obtained the zirconyl chloride crystal. It was washed with ethanol, so retrieved the crystal white zirconyl chloride. The crystal white zirconyl chloride was dried in the Oven at 90°C, it was crushed with stainless steel powder and sieved to 200 mesh of the particle size. The crystal white zirconyl chloride was stirred up to homogenous in the Homogenizer. Next was treated the homogenization and the stabilisation testing with statistically method. Zirconyl chloride crystals was standardized by using standard ZrOCl 2 8 H 2 O made in E. Merck, were include the chemical compounds test with XRD Spectrometry, the composition the content of crystals and the specific gravity. From the evaluation of the homogenization and stabilisation testing, the crystal zirconyl chloride was homogeneous, stable and it was fulfil to physically behavior as CRM. Compared with the standard zirconyl chloride, ZrOCl 2 8 H 2 O, the XRD spectra and chemical composition (96,263%), the content of crystals (98,625%). and specific gravity (97,190%) of the zirconyl chloride crystal were nearly same respectively. Certificate of the parameters testing results in the CRM the

1.8 billion years of fluid-crust interaction: A zircon oxygen isotope record for the lower crust, western Churchill Province, Canadian Shield

Science.gov (United States)

Petts, Duane C.; Moser, Desmond E.; Longstaffe, Frederick J.; Davis, William J.; Stern, Richard A.

2014-04-01

The western Churchill Province of the Canadian Shield experienced a prolonged and complex formation history (ca. 4.04 to 1.70 Ga), with evidence for multiple episodes of orogenesis and regional magmatic activity. Here we report on the oxygen isotopic compositions of garnet and zircon recovered from lower crustal xenoliths, which have U-Pb ages between ca. 3.5 and 1.7 Ga. Overall, zircon from four metabasite xenoliths from the Rankin Inlet sample suite have δ18O values ranging from + 5.5 to + 8.6‰. Zircon from three metatonalite/anorthosite xenoliths and five metabasite xenoliths from the Repulse Bay sample suite have δ18O values of + 5.6 to + 8.3‰. High δ18O values (> + 6.0‰) for the oldest igneous zircon cores (ca. 3.5 Ga and 3.0-2.6 Ga) indicate that their metatonalite/anorthosite protolith magmas were generated from, or had assimilated, supracrustal rocks that interacted previously with surface-derived fluids. Igneous zircon cores (ca. 2.9-2.6 Ga) from one metabasite xenolith have δ18O values of + 5.6 to + 6.4‰, which suggests a formation from a mantle-derived basaltic/gabbroic magma. Metamorphic zircon cores (ca. 2.0-1.9 Ga) from one metabasite xenolith commonly have δ18O values between + 6.0 and + 6.3‰, which is indicative of a basalt/gabbro protolith and localized reworking of the lower crust caused by regional-scale plate convergence. The wide range of δ18O values (+ 5.5 to + 8.3‰) for ca. 1.75-1.70 Ga metamorphic zircon rims (identified in all xenoliths) indicates regional transient heating and reworking of mantle- and supracrustal-derived crust, induced by magmatic underplating along the crust-mantle boundary.

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

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Argyrios Kapsiotis

2016-11-01

Full Text Available Several small chromium (Cr ore bodies are hosted within a unit of tectonically thinned dunite in the retired Ayios Stefanos mine of the western Othris ophiolite complex in Greece. Chromium ores consist of tectonically imprinted bodies of semi-massive to massive, podiform and lenticular chromitites composed of chromian spinel [Cr-spinel] with high Cr# [Cr/(Cr + Al = 0.51–0.66] and Mg# [Mg/(Mg + Fe2+ = 0.58–0.76], low Fe3+# [Fe3+/(Fe3+ + Fe2+ ≤ 0.43] and low TiO2 (≤0.21 wt % content. This composition is characteristic of Cr-spinels in equilibrium with melts of intermediate affinity between island-arc tholeiites (IATs and mid-ocean ridge basalts (MORBs. Several Cr-spinel crystals in these ores exhibit imperfect zones made up of spinel hosting oriented lamellae of Mg-silicates (mostly chlorite locally overgrown by porous domains along grain boundaries and fractures. From the Cr-spinel core to the lamellae-rich rim Cr#, Mg# and Fe3+# generally increase (0.68–0.87, 0.78–0.88 and 0.55–0.80, respectively, whereas from the core or the spinel zones with oriented lamellae to the porous domains Mg# and Fe3+# generally decrease (0.45–0.74 and ≤0.51, correspondingly. The lamellae-rich rims formed at oxidizing conditions, whereas the porous rims resulted from a later reducing event. Several tiny (≤30 μm, subhedral to anhedral and elongated Zr-bearing silicate mineral grains were discovered mainly along open and healed fractures cutting Cr-spinel. Most of the Zr-bearing silicate minerals (30 out of 35 grains were found in a chromitite boulder vastly intruded by a complex network of gabbroic dykes. The dominant Zr-bearing silicate phase is by far zircon displaying a homogeneous internal texture in cathodoluminescence (CL images. Raman spectroscopy data indicate that zircons have experienced structural damage due to self-irradiation. Their trace-element contents suggest derivation from a plagioclase-bearing, low-SiO2 intermediate to mafic

Extraction of zirconium from zircon (A new process)

International Nuclear Information System (INIS)

Shahid, K.A.; Saeed, D.; Jan, S.; Masood, A.; Akhtar, J.

1985-10-01

A new process has been used for the extraction of zirconium from zircon. Caustic fritting was done in the presence of magnesium hydroxide carbonate and magnesium oxide. These additives decrease the amount of nitric acid soluble silica less than 1000 ppm. Caustic fritting without any additions results in some nitric acid soluble silica, which is removed by dehydration with concentrated sulphuric acid. The present process eliminates the sulphuric acid dissolution and subsequent precipitation with ammonia which involves difficulty in washing of sulphate ions from the geletinous hydroxide cake and hence makes the direct nitric acid dissolution an attractive option. The effect of excess magnesium was studied and extraction does not seem to be effected by excess magnesium. How the reaction proceeds is not exactly understood but a probable mechanism has been postulated. (authors)

Detrital zircon provenance from three turbidite depocenters of the Middle-Upper Triassic Songpan-Ganzi complex, central China: Record of collisional tectonics, erosional exhumation, and sediment production

Science.gov (United States)

Weislogel, A.L.; Graham, S.A.; Chang, E.Z.; Wooden, J.L.; Gehrels, G.E.

2010-01-01

To test the idea that the voluminous upper Middle to Upper Triassic turbidite strata in the Songpan-Ganzi complex of central China archive a detrital record of Dabie ultrahigh-pressure (UHP) terrane unroofing, we report 2080 single detrital U-Pb zircon ages by sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis from 29 eastern Songpan-Ganzi complex sandstone samples. Low (Th/U zircons, consistent with crystallization under UHP conditions, are rare in eastern Songpan-Ganzi complex zircon, and U-Pb ages of low Th/U zircons are incompatible with a Dabie terrane source. An unweighted pair group method with arithmetic mean nearest-neighbor analysis of Kolmogorov-Smirnov two-sample test results reveals that the eastern Songpan-Ganzi complex is not a single contiguous turbidite system but is instead composed of three subsidiary depocenters, each associated with distinct sediment sources. The northeastern depocenter contains zircon ages characterized by Paleozoic and bimodally distributed Precambrian zircon populations, which, together with south-to southeast-directed paleocurrent data, indicate derivation from the retro-side of the Qinling-Dabie (Q-D) collisional orogen wedge. In the central depocenter, the dominantly Paleozoic detrital zircon signature and south-to southwest-oriented paleocurrent indicators reflect a profusion of Paleozoic zircon grains. These data are interpreted to reflect an influx of material derived from erosion of Paleozoic supra-UHP rocks of the Dabie terrane in the eastern Qinling-Dabie orogen, which we speculate may have been enhanced by development of a monsoonal climate. This suggests that erosional unroofing played a significant role in the initial phase of UHP exhumation and likely influenced the petrotectonic and structural evolution of the Qinling-Dabie orogen, as evidenced by compressed Triassic isotherms/grads reported in the Huwan

An Investigation into the Effects of Process Conditions on the Tribological Performance of Pack Carburized Titanium with Limited Oxygen Diffusion

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Bailey, R.; Sun, Y.

2018-04-01

In the present study, a new pack carburization technique for titanium has been investigated. The aim of this treatment is to produce a titanium carbide/oxycarbide layer atop of an extended oxygen diffusion zone [α-Ti(O)]. The effects of treatment temperature and pack composition have been investigated in order to determine the optimal conditions required to grant the best tribological response. The resulting structural features were investigated with particular interest in the carbon and oxygen concentrations across the samples cross section. The optimization showed that a temperature of 925 °C with a pack composition of 1 part carbon to 1 part energizer produced surface capable of withstanding a contact pressure of ≈ 1.5 GPa for 1 h. The process resulted in TiC surface structure which offers enhanced hardness (2100 HV) and generates a low friction coefficient (μ ≈ 0.2) when in dry sliding contact with an alumina (Al2O3) ball. The process also produced an extended oxygen diffusion zone that helps to improve the load bearing capacity of the substrate.

Evidence From Detrital Zircon U-Pb Analysis for Suturing of Pre-Mississippian Terranes in Arctic Alaska

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Moore, T. E.; Potter, C. J.; O'Sullivan, P. B.; Aleinikoff, J. N.

2007-12-01

Detrital zircon U-Pb ages of pre-Mississippian sandstones were determined using SHRIMP and LA-ICPMS techniques for four key geographic parts of the Arctic Alaska terrane, northern Alaska. In the northeastern Brooks Range, a sample of quartz-rich turbidites from the Proterozoic Neroukpuk Quartzite yielded zircon ages ranging from 980 Ma to 2.9 Ga with clusters at 980-1100 Ma, 1680-1850 Ma and 2220-2660 Ma. Quartz and chert-bearing sandstone in the Tulageak well from Ordovician-Silurian argillite in basement beneath the North Slope yielded a broad spectrum of ages between 1.0 to 2.1 Ga and 2.8 Ga, including peaks at 1.0-1.2 and 1.5-1.7 Ga. Paleozoic zircons cluster at 390 and 440 Ma in this sample, indicating it is Devonian. Lithic sandstone from the Silurian Iviagik Group at Cape Dyer on the Lisburne Peninsula yielded a variety of ages from 450 to 1600 Ma, with a large peak at 475-600 Ma and several grains between 1.9 and 2.5 Ga. In contrast to the broad distributions of the latter two samples, zircons in metamorphosed Proterozoic-Cambrian(?) lithic sandstone from the an unnamed metagraywacke unit near Mt. Snowden on the Dalton Highway in the southern Brooks Range are largely 600-650 Ma with lesser clusters at 1050-1200 Ma and 1600-1900 Ga. Samples of quartz-rich Mississippian sandstone at the base of the unconformably overlying Mississippian to Triassic Ellesmerian sequence near three of the pre-Mississippian sample locations were also analyzed. Mississippian sandstones from the West Dease well (near the Tulageak well) and at Cape Dyer on the Lisburne Peninsula display zircon distributions similar to those found in the underlying pre-Mississippian samples, indicating the Mississippian clastic strata are locally derived and that the observed zircon distributions are representative of a broad area. However, the Mississippian Kekiktuk Conglomerate, which rests on the Neroukpuk Quartzite in the northeastern Brooks Range, also contains a variety of ages between 560 and

U-Pb detrital zircon geochronology from the basement of the Central Qilian Terrane: implications for tectonic evolution of northeastern Tibetan Plateau

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Liu, Changfeng; Wu, Chen; Zhou, Zhiguang; Yan, Zhu; Jiang, Tian; Song, Zhijie; Liu, Wencan; Yang, Xin; Zhang, Hongyuan

2018-03-01

The Tuolai Group dominates the Central Qilian Terrane, and there are different opinions on the age and tectonic attribute of the Tuolai Group. Based on large-scale geologic mapping and zircon dating, the Tuolai Group is divided into four parts: metamorphic supracrustal rocks, Neoproterozoic acid intrusive rocks, early-middle Ordovician acid intrusive rocks and middle Ordovician basic intrusive rocks. The metamorphic supracrustal rocks are the redefined Tuolai complex-group and include gneiss and schist assemblage by faulting contact. Zircon U-Pb LA-MC-ICP-MS dating was conducted on these samples of gneiss and migmatite from the gneiss assemblage, quartzite, two-mica schist and slate from the schist assemblage. The five detrital samples possess similar age spectra; have detrital zircon U-Pb main peak ages of 1.7 Ga with youngest U-Pb ages of 1150 Ma. They are intruded by Neoproterozoic acid intrusive rocks. Therefore, the Tuolai Group belonging to late Mesoproterozoic and early Neoproterozoic. With this caveat in mind, we believe that U-Pb detrital zircon dating, together with the geologic constraints obtained from this study and early work in the neighboring regions. We suggest that the formation age of the entire crystalline basement rocks of metasedimentary sequence from the Central Qilian Terrane should be constrained between the Late Mesoproterozoic and the Late Neoproterozoic, but not the previous Paleoproterozoic. The basement of the Central Qilian Terrane contains the typical Grenville ages, which indicates the Centre Qilian Terrane have been experienced the Grenville orogeny event.

Uranium-lead dating of hydrothermal zircon and monazite from the Sin Quyen Fe-Cu-REE-Au-(U) deposit, northwestern Vietnam

Science.gov (United States)

Li, Xiao-Chun; Zhou, Mei-Fu; Chen, Wei Terry; Zhao, Xin-Fu; Tran, MyDung

2018-03-01

The Sin Quyen deposit in northwestern Vietnam contains economic concentrations of Cu, Au and LREE, and sub-economic concentration of U. In this deposit, massive and banded replacement ores are hosted in Neoproterozoic metapelite. The paragenetic sequence includes sodic alteration (stage I), calcic-potassic alteration and associated Fe-REE-(U) mineralization (stage II), Cu-Au mineralization (stage III), and sulfide-(quartz-carbonate) veins (stage IV). The Sin Quyen deposit experienced an extensive post-ore metamorphic overprint, which makes it difficult to precisely determine the mineralization age. In this study, zircon and monazite U-Pb geochronometers and the Rb-Sr isochron method are used to constrain the timing of mineralization. Zircon grains in the ore are closely intergrown or texturally associated with hydrothermal minerals of stage II (e.g., garnet, allanite, and hedenbergite). They may contain primary fluid inclusions and display irregular zoning in cathodoluminescence (CL) images. Zircon grains are rich in U (688 to 2902 ppm) and poor in Th (0.2 to 2.9 ppm). Their δ18OV-SMOW values range from 11.9 to 14.0‰, higher than those of typical magmatic zircon. These textural and compositional features imply that zircon precipitated from 18O- and U-rich hydrothermal fluids, coeval with the minerals of stage II. Monazite occurs in close association with stage II magnetite and allanite and has low contents of Th (<2700 ppm), indicative of a hydrothermal origin. Hydrothermal zircon and monazite have indistinguishable U-Pb ages of 841 ± 12 and 836 ± 18 Ma, respectively, representing the timing of Fe-REE mineralization. There is no direct isotopic constraint on the timing of the Cu-Au mineralization, but geological observations suggest that the Cu-Au and Fe-REE ores most likely formed within a single evolved hydrothermal process. In the plot of 87Rb/86Sr vs. 87Sr/86Sr, the composition of bulk-ore and biotite separates from ore lie along a reference line for 30 Ma

Outline of Upper Precambrian and Lower Paleozoic evolution of the Iberian Peninsula according to U-Pb dating of zircons

International Nuclear Information System (INIS)

Lancelot, J.R.; Allegret, A.; Iglesias Ponce de Leon, M.

1985-01-01

In the northwestern part of the Iberian Peninsula, recent geological studies have defined the following stratigraphic sequence from bottom to top: basal orthogneiss of Miranda do Douro is overlain by a complex of schist and greywacke which have been assigned to the Cambrian or late Precambrian; these are followed by the Ollo de Sapo gneisses of volcanic-sedimentary origin which in turn are overlain by the fossiliferous layers of the lower Ordovician. The schist and greywacke complex and the lower part of the Ollo de Sapo Formation are transected by granitic dikes (Viana del Bollo orthogneiss). All these rocks were folded, faulted, metamorphosed, and intruded by granite plutons during Variscan times. The emplacement of the Miranda do Douro and Viana del Bollo orthogneisses have been respectively dated at 618+-9 Ma and 465+-10 Ma by the U-Pb method on zircons. These data yield lower and upper limits for the deposition of the Ollo de Sapo Formation and demonstrate the occurrence of a Precambrian basement (''Pan-African'' or ''Cadomian'' orogeny) in the Variscan belt in the northwestern part of the Iberian Peninsula. The emplacement of Viana del Bollo orthogneiss could be genetically related to the main phase of crustal thinning (470-520 Ma) characteristic of the Prevariscan evolution of western Europe. Typology and U-Pb data of the Ollo de Sapo zircons indicate the occurrence of inherited old Precambrian zircons and yield an age of 325+-3 Ma for the Variscan main thermal event in the area considered. Four possible evolutionary models for the U-Pb system of the Ollo de Sapo zircons are discussed. (orig.)

Comment on "Zircon U-Th-Pb dating using LA-ICP-MS: Simultaneous U-Pb and U-Th dating on 0.1 Ma Toya Tephra, Japan" by Hisatoshi Ito

Science.gov (United States)

Guillong, M.; Schmitt, A. K.; Bachmann, O.

2015-04-01

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of eight zircon reference materials and synthetic zircon-hafnon end-members indicate that corrections for abundance sensitivity and molecular zirconium sesquioxide ions (Zr2O3+) are critical for reliable determination of 230Th abundances in zircon. Other polyatomic interferences in the mass range 223-233 amu are insignificant. When corrected for abundance sensitivity and interferences, activity ratios of (230Th)/(238U) for the zircon reference materials we used average 1.001 ± 0.010 (1σ error; mean square of weighted deviates MSWD = 1.45; n = 8). This includes the 91500 and Plešovice zircons, which were deemed unsuitable for calibration of (230Th)/(238U) by Ito (2014). Uranium series zircon ages generated by LA-ICP-MS without mitigating (e.g., by high mass resolution) or correcting for abundance sensitivity and molecular interferences on 230Th such as those presented by Ito (2014) are potentially unreliable.

The lower Mesozoic record of detrital zircon U-Pb geochronology of Sonora, Mexico, and its paleogeographic implications

OpenAIRE

González-León, Carlos M.; Valencia, Víctor A.; Lawton, Timothy F.; Amato, Jeffrey M.; Gehrels, George E.; Leggett, William J.; Montijo-Contreras, Óscar; Fernández, Miguel A.

2009-01-01

Detrital zircon U-Pb geochronology from each of the formations of the Triassic-Lower Jurassic Barranca and El Antimonio groups of central and northwestern Sonora and from the Lower Jurassic Basomari and Middle Jurassic Lily formations of northern Sonora indicate they contain distinctive zircon populations. A Proterozoic population has peak ages near 1.8, 1.7, 1.6, 1.4, and 1.1 Ga. A population of Permo-Triassic grains with important peak ages near 269, 254, 245, 234 and 227 Ma. A third popula...

SHRIMP zircon dating and LA-ICPMS Hf analysis of early Precambrian rocks from drill holes into the basement beneath the Central Hebei Basin, North China Craton

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Yusheng Wan

2014-07-01

Full Text Available The Central Hebei Basin (CHB is one of the largest sedimentary basins in the North China Craton, extending in a northeast–southwest direction with an area of >350 km2. We carried out SHRIMP zircon dating, Hf-in-zircon isotopic analysis and a whole-rock geochemical study on igneous and metasedimentary rocks recovered from drill holes that penetrated into the basement of the CHB. Two samples of gneissic granodiorite (XG1-1 and gneissic quartz diorite (J48-1 have magmatic ages of 2500 and 2496 Ma, respectively. Their zircons also record metamorphic ages of 2.41–2.51 and ∼2.5 Ga, respectively. Compared with the gneissic granodiorite, the gneissic quartz diorite has higher ΣREE contents and lower Eu/Eu* and (La/Ybn values. Two metasedimentary samples (MG1, H5 mainly contain ∼2.5 Ga detrital zircons as well as late Paleoproterozoic metamorphic grains. The zircons of different origins have εHf (2.5 Ga values and Hf crustal model ages ranging from 0 to 5 and 2.7 to 2.9 Ga, respectively. Therefore, ∼2.5 Ga magmatic and Paleoproterozoic metasedimentary rocks and late Neoarchean to early Paleoproterozoic and late Paleoproterozoic tectono-thermal events have been identified in the basement beneath the CHB. Based on regional comparisons, we conclude that the early Precambrian basement beneath the CHB is part of the North China Craton.

Hydrogenation-disproportionation-desorption-recombination in Sm{sub 2}Fe{sub 16}M (M=Al, Ga and Si) and magnetic properties of their carburized powders

Energy Technology Data Exchange (ETDEWEB)

Kubis, M.; Rave, W.; Cao, L.; Gebel, B.; Mueller, K.-H.; Schultz, L. [Institut fuer Festkoerper- und Werkstofforschung Dresden e.V. (Germany)

1998-11-20

The application of the hydrogenation-disproportionation-desorption-recombination (HDDR) process in Sm{sub 2}Fe{sub 16}M (M=Al,Ga and Si) was investigated. The hydrogen absorption behaviour was studied by temperature-pressure analysis (TPA). In the temperature range between 500 and 800 C, Sm{sub 2}Fe{sub 16}M samples with M=Ga and Si show a weaker hydrogen absorption than Sm{sub 2}Fe{sub 16}Al. This was confirmed by X-ray diffraction which showed a complete disproportionation of Sm{sub 2}Fe{sub 16}Al into SmH{sub z} (1.9carburized HDDR powders were studied by VSM measurements and Kerr microscopy. The demagnetization curve of our HDDR processed Sm{sub 2}Fe{sub 16}AlC{sub y} is well shaped, whereas those of Sm{sub 2}Fe{sub 16}GaC{sub y} and Sm{sub 2}Fe{sub 16}SiC{sub y} show a large decrease of the polarization at low fields. The favourable behaviour of Sm{sub 2}Fe{sub 16}AlC{sub y} is due to a homogeneous submicron grain structure. In Sm{sub 2}Fe{sub 16}GaC{sub y} and Sm{sub 2}Fe{sub 16}SiC{sub y} samples, an additional, magnetically soft phase with larger domains was observed which causes the low coercivity. As a consequence, HDDR was only favourable for the preparation of Sm{sub 2}Fe{sub 16}MC{sub y} hard magnets with M=Al but not for M=Ga and Si. Optimization of the HDDR process in Sm{sub 2}Fe{sub 16}Al and subsequent nitrogenation or carburization led to coercivities of {mu}{sub 0j}H{sub c}=2.9 and 2.5 T, respectively. (orig.) 11 refs.

Response of zircon to electron and Ne+ irradiation

International Nuclear Information System (INIS)

Devanathan, R.; Weber, W.J.; Boatner, L.A.

1997-01-01

Zircon (ZrSiO 4 ) is an actinide host phase in vitreous ceramic nuclear waste forms and a potential host phase for the disposition of excess weapons plutonium. In the present work, the effects of 800 and 900 keV electron and 1 MeV Ne + irradiations on the structure of single crystals of ZrSiO 4 have been investigated. The microstructural evolution during the irradiations was studied in situ using a high-voltage electron microscope interfaced to an ion accelerator at Argonne National Laboratory. The results indicate that electron irradiation at 15 K cannot amorphize ZrSiO 4 even at fluences an order of magnitude higher than that required for amorphization by 1.5 MeV Kr + ions. However, the material is readily amorphized by 1 MeV Ne + irradiation at 15 K. The temperature dependence of this amorphization is discussed in light of previous studies of radiation damage in ZrSiO 4

Ferroelectric devices using lead zirconate titanate (PZT) nanoparticles.

Science.gov (United States)

Paik, Young Hun; Kojori, Hossein Shokri; Kim, Sung Jin

2016-02-19

We successfully demonstrate the synthesis of lead zirconate titanate nanoparticles (PZT NPs) and a ferroelectric device using the synthesized PZT NPs. The crystalline structure and the size of the nanocrystals are studied using x-ray diffraction and transmission electron microscopy, respectively. We observe PZT NPs and this result matches dynamic light scattering measurements. A solution-based low-temperature process is used to fabricate PZT NP-based devices on an indium tin oxide substrate. The fabricated ferroelectric devices are characterized using various optical and electrical measurements and we verify ferroelectric properties including ferroelectric hysteresis and the ferroelectric photovoltaic effect. Our approach enables low-temperature solution-based processes that could be used for various applications. To the best of our knowledge, this low-temperature solution processed ferroelectric device using PZT NPs is the first successful demonstration of its kind.

Teaching material for radiation education using zircon sand

International Nuclear Information System (INIS)

Kamata, Masahiro; Okamoto, Miho

2005-01-01

In this paper, we introduced safe and inexpensive student experiment using zircon and containing a uranium series, as well as a similar experiment using several chemicals and foods containing potasium 40. In practice, our experiments were confirmed to be available in classes of Chemistry and/or Earth Science. It should be noted here that they are also expected to be useful in many places other than senior high school because they do not need any dangerous chemicals or special techniques, and can make younger students more interested in radioactivity in their environment. (J.P.N.)

Microstructural and analytical analysis of plasma dissociated zircon

International Nuclear Information System (INIS)

Minnaar, E G; Neethling, J H; Lee, M E; Snyders, E

2012-01-01

The investigation of the microstructure and distribution of impurities was carried out on plasma dissociated zircon (PDZ). The morphology of the PDZ and crystalline nature of the zirconia was determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) while energy dispersive X-ray spectrometry (EDS) provided compositional information. The SEM and TEM results indicate that the morphology and crystalline nature of the zirconia varies as a result of the existence of a thermal gradient. The EDS results show that the majority of the impurities segregates to the silica phase of the PDZ.

Synthesis, microstructural and mechanical properties of ex situ zircon particles (ZrSiO4 reinforced Metal Matrix Composites (MMCs: a review

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Satish Kumar Thandalam

2015-07-01

This review article details the current development on the synthesis, microstructure and mechanical properties of zircon reinforced MMCs, with specific attention on the abrasive wear behavior of the composites. This review also summarizes the work done by various research groups on zircon reinforced MMCs in achieving higher hardness and wear resistance in these composites.

Influence of crystal phases on electro-optic properties of epitaxially grown lanthanum-modified lead zirconate titanate films

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Masuda, Shin; Seki, Atsushi; Masuda, Yoichiro

2010-02-01

We describe here how we have improved the crystal qualities and controlled the crystal phase of the lanthanum-modified lead zirconate titanate (PLZT) film without changing the composition ratio using an oxygen-pressure crystallization process. A PLZT film deposited on a SrTiO3 substrate with the largest electro-optic (EO) coefficient of 498 pm/V has been achieved by controlling the crystal phase of the film. Additionally, a fatigue-free lead zirconate titanate (PZT) capacitor with platinum electrodes has been realized by reducing the oxygen vacancies in the films.

Numerical modeling perspectives on zircon crystallization and magma reservoir growth at the Laguna del Maule volcanic field, central Chile

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Andersen, N. L.; Dufek, J.; Singer, B. S.

2017-12-01

Magma reservoirs in the middle to upper crust are though to accumulate incrementally over 104 -105 years. Coupled crystallization ages and compositions of zircon are a potentially powerful tracer of reservoir growth and magma evolution. However, complex age distributions and disequilibrium trace element partitioning complicate the interpretation of the zircon record in terms of magmatic processes. In order to make quantitative predictions of the effects of magmatic processes that contribute reservoir growth and evolution—such as cooling and crystallization, magma recharge and mixing, and rejuvenation and remelting of cumulate-rich reservoir margins—we develop a model of zircon saturation and growth within a numerical framework of coupled thermal transfer, phase equilibrium, and magma dynamics. We apply this model to the Laguna del Maule volcanic field (LdM), located in central Chile. LdM has erupted at least 40 km3 of rhyolite from 36 vents distributed within a 250 km2 lake basin. Ongoing unrest demonstrates the large, silicic magma system beneath LdM remains active to this day. Zircon from rhyolite erupted between c. 23 and 1.8 ka produce a continuous distribution of 230Th-238U ages ranging from eruption to 40 ka, as well as less common crystal domains up to 165 ka and rare xenocrysts. Zircon trace element compositions fingerprint compositionally distinct reservoirs that grew within the larger magma system. Despite the dominantly continuous distributions of ages, many crystals are characterized by volumetrically substantial, trace element enriched domains consistent with rapid crystal growth. We utilize numerical simulations to assess the magmatic conditions required to catalyze these "blooms" of crystallization and the magma dynamics that contributed to the assembly of the LdM magma system.

Fluids in the Siilinjärvi carbonatite complex, eastern Finland: Fluid inclusion evidence for the formation conditions of zircon and apatite

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Poutiainen, M.

1995-06-01

Full Text Available In the studied zircon and apatite crystals, data recorded two different compositional types of fluid inclusions: Type 1 H2O-CO2, low salinity inclusions (XCO2 = 0.42 to 0.87; XNaCl = 0.001 to 0.005 with bulk densities of 0.73 to 0.87 g/cm3, and Type 2 H2O moderate salinity (XNaCl = 0.03 to 0.06 inclusions with densities of 0.83 to 1.02 g/cm3. The Type 1 inclusions are not present in apatite. In zircon, the observed fluid inclusion types occur in separate domains: around (Type 1 and outside (Type 2 the apparent core. Fluid inclusions are further subdivided into pseudosecondary and secondary inclusions. Using a combination of SEM-EDS, optical characteristics and crushing-stage, various daughter and captive minerals were identified. The fluid inclusion data suggest that the pseudosecondary Type 1 and Type 2 inclusions in zircon and apatite were trapped during the pre-emplacement evolution of the carbonatite at mid-crustal conditions (P≥4 kbar, T≥625°C. The Type 1 fluid was depleted in CO2, during crystal fractionation and cooling leading to a fluid phase enriched in water and alkalies. Fenitization was obviously induced by these saline aqueous fluids. During emplacement of the carbonatite to the present level, zircon phenocrysts were intensively fractured, some Type 1 inclusions were re-equilibrated, and multiphase Type 2 inclusions were trapped. It is assumed that all these inclusions in zircon and the pseudosecondary Type 2 inclusions in apatite have a magmatic origin. In apatite, calcite inclusions occur side-by-side with the secondary Type 2 inclusions. These calcites co-existed with the aqueous fluid during fracturing and metamorphic re-crystallization of apatites. Probably, this metamorphic fluid also is responsible for the transport and deposition of at least some of the calcite at low temperatures (200-350°C.

U-Pb zircon geochronology and evolution of some Adirondack meta-igneous rocks

Science.gov (United States)

Mclelland, J. M.

1988-01-01

An update was presented of the recent U-Pb isotope geochronology and models for evolution of some of the meta-igneous rocks of the Adirondacks, New York. Uranium-lead zircon data from charnockites and mangerites and on baddeleyite from anorthosite suggest that the emplacement of these rocks into a stable crust took place in the range 1160 to 1130 Ma. Granulite facies metamorphism was approximately 1050 Ma as indicated by metamorphic zircon and sphene ages of the anorthosite and by development of magmatitic alaskitic gneiss. The concentric isotherms that are observed in this area are due to later doming. However, an older contact metamorphic aureole associated with anorthosite intrusion is observed where wollastonite develops in metacarbonates. Zenoliths found in the anorthosite indicate a metamorphic event prior to anorthosite emplacement. The most probable mechanism for anorthosite genesis is thought to be ponding of gabbroic magmas at the Moho. The emplacement of the anorogenic anorthosite-mangerite-charnockite suite was apparently bracketed by compressional orogenies.

From Crustal Anatexis to Pluton Emplacement: High-Precision Zircon Geochronology Reveals the Thermal History of the Larderello-Travale Geothermal System (Italy)

Science.gov (United States)

Farina, F.; Dini, A.; Ovtcharova, M.; Davies, J.; Bouvier, A. S.; Baumgartner, L. P.; Caricchi, L.; Schaltegger, U.

2017-12-01

Late Miocene to recent post-collisional extension in Tuscany (Italy) led to the emplacement of shallow-level granitic plutons and to the eruption of small rhyolitic bodies. The intrusion of peraluminous two-mica and tourmaline-bearing granites triggered the formation of the steam-dominated Larderello-Travale geothermal system. In this study, zircon crystals from granite samples obtained from drill holes at 3.0-4.5 km depth were investigated by combining in-situ oxygen isotopes analysis and high-precision CA-ID-TIMS U-Pb age determinations to gain insight into the nature of the magmatic heat source fuelling the geothermal field. Magmatic zircon crystals display δ18O values ranging from 8.6 to 13.5‰ and crystals from individual samples exhibit inter- and intra-grain oxygen isotope variability exceeding 3‰. The geochronological data indicates the existence of three magmatic pulses with ages between 3.637 ± 0.008 and 1.671 ± 0.004 Ma. More importantly, zircon crystals from individual samples exhibit an age spread as large as 200-400 ky. This age dispersion, which is more than one order of magnitude greater than the uncertainty on a single date, suggest that most of the zircon did not crystallize at the emplacement level, but within isolated and isotopically distinct magma batches before large-scale homogenization in a magmatic reservoir at depth. The rate of assembly and final volume of this reservoir is estimated using the distribution of precise U-Pb zircon dates following the approach of Caricchi et al. (2014). Thermal modelling indicates that the heat flow at the surface in the geothermal field cannot be sustained by the inferred reservoir or by heat advection from the mantle. Our data suggest the existence of a younger shallow-level intrusion, whose occurrence also accounts for the existence of confined magmatic fluids at the top of the Larderello-Travale intrusion. We conclude that a multi-disciplinary approach, integrating high-precision zircon dating, in

Archean inheritance in zircon from late Paleozoic granites from the Avalon zone of southeastern New England: an African connection

Science.gov (United States)

Zartman, R.E.; Don, Hermes O.

1987-01-01

In southeastern New England the Narragansett Pier Granite locally intrudes Carboniferous metasedimentary rocks of the Narragansett basin, and yields a monazite UPb Permian emplacement age of 273 ?? 2 Ma. Zircon from the Narragansett Pier Granite contains a minor but detectable amount of an older, inherited component, and shows modern loss of lead. Zircon from the late-stage, aplitic Westerly Granite exhibits a more pronounced lead inheritance -permitting the inherited component to be identified as Late Archean. Such old relict zircon has not been previously recognized in Proterozoic to Paleozoic igneous rocks in New England, and may be restricted to late Paleozoic rocks of the Avalon zone. We suggest that the Archean crustal component reflects an African connection, in which old Archean crust was underplated to the Avalon zone microplate in the late Paleozoic during collision of Gondwanaland with Avalonia. ?? 1987.

Gibbs energies of formation of zircon (ZrSiO4), thorite (ThSiO4), and phenacite (Be2SiO4)

International Nuclear Information System (INIS)

Schuiling, R.D.; Vergouwen, L.; Rijst, H. van der

1976-01-01

Zircon, thorite, and phenacite are very refractory compounds which do not yield to solution calorimetry. In In order to obtain approximate Gibbs energies of formation for these minerals, their reactions with a number of silica-undersaturated compounds (silicates or oxides) were studied. Conversely baddeleyite (ZrO 2 ), thorianite (ThO 2 ), and bromellite (BeO) were reacted with the appropriate silicates. As the Gibbs energies of reaction of the undersaturated compounds with SiO 2 are known, the experiments yield the following data: Δ G 298 , 1 /sub bar/ 0 = -459.02 +- 1.04 kcal for zircon, -489.67 +- 1.04 for thorite, and -480.20 +- 1.01 for phenacite

Zircon, titanite, and apatite (U-Th)/He ages and age-eU correlations from the Fennoscandian Shield, southern Sweden

Science.gov (United States)

Guenthner, William R.; Reiners, Peter W.; Drake, Henrik; Tillberg, Mikael

2017-07-01

Craton cores far from plate boundaries have traditionally been viewed as stable features that experience minimal vertical motion over 100-1000 Ma time scales. Here we show that the Fennoscandian Shield in southeastern Sweden experienced several episodes of burial and exhumation from 1800 Ma to the present. Apatite, titanite, and zircon (U-Th)/He ages from surface samples and drill cores constrain the long-term, low-temperature history of the Laxemar region. Single grain titanite and zircon (U-Th)/He ages are negatively correlated (104-838 Ma for zircon and 160-945 Ma for titanite) with effective uranium (eU = U + 0.235 × Th), a measurement proportional to radiation damage. Apatite ages are 102-258 Ma and are positively correlated with eU. These correlations are interpreted with damage-diffusivity models, and the modeled zircon He age-eU correlations constrain multiple episodes of heating and cooling from 1800 Ma to the present, which we interpret in the context of foreland basin systems related to the Neoproterozoic Sveconorwegian and Paleozoic Caledonian orogens. Inverse time-temperature models constrain an average burial temperature of 217°C during the Sveconorwegian, achieved between 944 Ma and 851 Ma, and 154°C during the Caledonian, achieved between 366 Ma and 224 Ma. Subsequent cooling to near-surface temperatures in both cases could be related to long-term exhumation caused by either postorogenic collapse or mantle dynamics related to the final assembly of Rodinia and Pangaea. Our titanite He age-eU correlations cannot currently be interpreted in the same fashion; however, this study represents one of the first examples of a damage-diffusivity relationship in this system, which deserves further research attention.

207Pb-206Pb zircon ages of eastern and western Dharwar craton, southern India : Evidence for contemporaneous Archaean crust

Science.gov (United States)

Maibam, B.; Goswami, J. N.; Srinivasan, R.

2009-04-01

Dharwar craton is one of the major Archaean crustal blocks in the Indian subcontinent. The craton is comprised of two blocks, western and eastern. The western domain is underlain by orthogneisses and granodiorites (ca. 2.9-3.3 Ga) collectively termed as Peninsular Gneiss [e.g., 1] interspersed with older tracts of metasedimentary and metamorphosed igneous suites (Sargur Group and Dharwar Group; [2]). The eastern part of the craton is dominated by Late Archaean (2.50-2.75 Ga) granitoids and their gneissic equivalents. They are interspersed with schist belts (also of Sargur Group and Dharwar Group), which are lithologically similar to the Dharwar Supergroup in the western block, but are in different metamorphic dress. Here we report 207Pb-206Pb age of zircons separated from the metasedimentary and gneissic samples from the two blocks to constrain the evolution of the Dharwar craton during the early Archaean. Detrital zircons of the metasedimentary rocks from both the blocks show a wide range of overlapping ages between ~2.9 to >3.5 Ga. Zircon ages of the orthogneisses from the two blocks showed that most of the analysed grains of the eastern Dharwar block are found to be of the age as old as the western Dharwar gneisses. Imprints of younger events could be discerned from the presence of overgrowths in zircons from the studied samples throughout the craton. Our data suggest that crust forming cycles in the two blocks of the Dharwar craton occurred contemporaneously during the Archaean. References [1] Beckinsale, R.D., Drury, S.A., Holt, R.W. (1980) Nature 283, 469-470. [2] Swami Nath J., Ramakrishnan M., Viswanatha M.N. (1976) Rec. Geol. Surv. Ind., 107, 149-175.

Analysis of monazite, zircon, and apatite from the southeastern Piedmont. National uranium resource evaluation program

International Nuclear Information System (INIS)

Karfunkel, B.S.; Fay, W.M.; Price, V. Jr.

1981-12-01

Two hundred sixty-three monazite, 191 zircon, and 16 apatite grains from 52 stream-sediment locations in the Southeastern Piedmont were analyzed by electron microprobe for one of the following suites of elements: Ca, La, Ce, Pr, Nd, Sm, Eu, Gd, Er, Dy, Y, Th, U, P, and F, or Ca, La, Ce, Fe, Er, Hf, Y, Th, U, P, Zr, Mg, Al, and Si. Monazite samples that had high uranium or thorium content and zircon samples that had high hafnium or iron content from a total of six locations were reanalyzed to confirm the initial results. This report contains a description of sample collection and preparation procedures, analytical methods, tables of analyses, and a statistical summary of analyses

U-Pb Detrital Zircon Geochronologic Constraints on Depositional Age and Sediment Source Terrains of the Late Paleozoic Tepuel-Genoa Basin

Science.gov (United States)

Griffis, N. P.; Montanez, I. P.; Isbell, J.; Gulbranson, E. L.; Wimpenny, J.; Yin, Q. Z.; Cúneo, N. R.; Pagani, M. A.; Taboada, A. C.

2014-12-01

The late Paleozoic Ice Age (LPIA) is the longest-lived icehouse of the Phanerozoic and the only time a metazoan dominated and vegetated world transitioned from an icehouse climate into a greenhouse. Despite several decades of research, the timing, extent of glaciation and the location of ice centers remain unresolved, which prohibits reconstruction of ice volume. The Permo-Carboniferous sediments in the Tepuel-Genoa Basin, Patagonia contains a near complete record of sedimentation from the lower Carboniferous through lower Permian. Outsized clasts, thin pebble-rich diamictites and slumps represent the last of the late Paleozoic glacially influenced deep-water marine sediments in the Mojón de Hierro Fm. and the Paleozoic of Patagonia. U-Pb analysis of detrital zircons separated from slope sediments reveal groupings (20 myr bins, n≥5 zircons) with peak depositional ages of 420, 540 to 660 and 1040 Ma. Zircon age populations recovered from the Mojón de Hierro Fm. compare well with bedrock ages of the Deseado Massif of SE Patagonia, suggesting this may be a potential source of sediments. The maximum depositional age of the sediments is 306.05 ± 3.7 Ma (2σ) as determined by the median age of the two youngest concordant zircons that overlap in error. The youngest zircon from the analysis yields a 238U/206Pb age of 301.3 ± 4.5 Ma (2σ; MSWD = 2.3). Younger zircons from the analysis compare well with the age of granite bedrock exposed along the basin margin to the E-NE suggesting they may reflect a more proximal source. These data, which indicate a maximum age of late Carboniferous for the Mojón de Hierro Fm, provide the first geochemical constraints for the timing of final deposition of glaciomarine sediments in the Tepuel-Genoa Basin, and contributes to the biostratigraphic correlation of the late Paleozoic succession in Patagonia with other key LPIA basins that has thus far been hindered by faunal provincialism.

Electron probe micro analyser chemical zircon ages of the Khetri granitoids, Rajasthan, India: records of widespread late palaeoproterozoic extension-related magmatism

International Nuclear Information System (INIS)

Kaur, Parampreet; Chaudhri, Naveen; Biju-Sekhar, S.; Yokoyama, K.

2006-01-01

A number of granitoid plutons were emplaced in the northernmost entity of the Aravalli craton, the Khetri Copper Belt (KCB). We report here Th-U-Pb electron probe micro analyser chemical ages for zircon and monazite from two granitoid plutons of the north KCB, the Biharipur and Dabla. Zircons occurring in the granitoids depict well-developed magmatic zoning and are chronologically unzoned. Both the plutons and their diverse granitoid facies are coeval and provide ages around 1765-1710 Ma. Geochemical attributes of the studied plutons are typical of A-type within-plate granites and consistent with an extensional tectonic environment. Our new age data are comparable to the petrologically similar A-type granitoids of the Alwar region, which have provided zircon chemical ages around 1780-1710 Ma. These analogous ages imply a widespread late palaeoproterozoic extension-related plutonism in the northern part of the Aravalli craton. The monazites, which were recovered only from the mafic magmatic rocks of the Biharipur pluton, yielded an isochron age of 910 ±10 Ma, signifying an over- print of a younger neoproterozoic thermal event in the region. (author)

Zircon U-Pb age of the Pescadero felsite: A late Cretaceous igneous event in the forearc, west-central California Coast Ranges

Science.gov (United States)

Ernst, W.G.; Martens, U.C.; McLaughlin, R.J.; Clark, J.C.; Moore, Diane E.

2011-01-01

Weathered felsite is associated with the late Campanian-Maastrichtian Pigeon Point Formation near Pescadero, California. Poorly exposed, its age and correlation are uncertain. Is it part of the Pigeon Point section west of the San Gregorio-Hosgri fault? Does it rest on Nacimiento block basement? Is it dextrally offset from the Oligocene Cambria Felsite, ~185 km to the southeast? Why is a calc-alkaline hypabyssal igneous rock intrusive into the outboard accretionary prism? To address these questions, we analyzed 43 oscillatory-zoned zircon crystals from three incipiently recrystallized pumpellyite ?? prehnite ?? laumontite-bearing Pescadero felsite samples by sensitive high-resolution ion microprobe-reverse geometry (SHRIMPRG) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) techniques. Thirty-three zircons gave late Mesozoic U-Pb ages, with single-grain values ranging from 81 to 167 Ma; ten have pre-Mesozoic, chiefl y Proterozoic ages. A group of the four youngest Pescadero zircons yielded an apparent maximum igneous age of ca. 86-90 Ma. Refl ecting broad age scatter and presence of partly digested sandstone inclusions, we interpret the rest of the zircons (perhaps all) as xenocrysts. Twenty-three zircons were separated and analyzed from two samples of the similar Cambria Felsite, yielding a unimodal 27 Ma U-Pb age. Clearly, the origin of the Upper Oligocene Cambria Felsite is different from that of the Upper Cretaceous Pescadero felsite; these rocks are not correlated, and do not constrain displacement along the San Gregorio-Hosgri fault. Peak ages differ slightly, but relative probability curves for Mesozoic and pre-Mesozoic Pescadero zircons compare well, for example, with abundant U-Pb age data for detrital zircons from Franciscan metaclastic strata ~100 km to the east in the Diablo Range- San Francisco Bay area, San Joaquin Great Valley Group turbidites, Upper Cretaceous Nacimiento block Franciscan strata, and Upper Cretaceous

Triassic North American paleodrainage networks and sediment dispersal of the Chinle Formation: A quantitative approach utilizing detrital zircons

Science.gov (United States)

Blum, M. D.; Umbarger, K.

2017-12-01

The Triassic Chinle Formation is a fluvial succession deposited in a backarc setting across the present-day Colorado Plateau of the southwestern United States. Existing studies have proposed various mechanisms responsible for the unique stratigraphic architecture and depositional sequences of the Chinle. However, these studies lack necessary age control to correlate stratigraphic patterns with contemporaneous mechanisms. This study will collect new samples for detrital zircon analysis, as well as upgrade existing samples (to n=300) from Dickinson and Gehrels (2008), to improve the resolution of Triassic sediment provenance from source-to-sink. The improved dataset allows appraisal of the multiple provenance terranes that contributed to the Chinle depositional system to delineate and reconstruct paleodrainage patterns. The additional samples will be collected systematically from the base of the Chinle, and vertically throughout the section to capture a regional story of how the continental scale drainage reorganized through time. U-Pb ages of detrital zircons will be utilized to provide quantitative fingerprinting information to constrain interpretations for the origin and transport history of the Chinle fluvial succession in time and space.

Quantitative analysis method for niobium in lead zirconate titanate

International Nuclear Information System (INIS)

Hara, Hideo; Hashimoto, Toshio

1986-01-01

Lead zirconate titanate (PZT) is a strong dielectric ceramic having piezoelectric and pyroelectric properties, and is used most as a piezoelectric material. Also it is a main component of lead lanthanum zirconate titanate (PLZT), which is a typical electrical-optical conversion element. Since these have been developed, the various electronic parts utilizing the piezoelectric characteristics have been put in practical use. The characteristics can be set up by changing the composition of PZT and the kinds and amount of additives. Among the additives, niobium has the action to make metallic ion vacancy in crystals, and by the formation of this vacancy, to ease the movement of domain walls in crystal grains, and to increase resistivity. Accordingly, it is necessary to accurately determine the niobium content for the research and development, quality control and process control. The quantitative analysis methods for niobium used so far have respective demerits, therefore, the authors examined the quantitative analysis of niobium in PZT by using an inductively coupled plasma emission spectro-analysis apparatus which has remarkably developed recently. As the result, the method of dissolving a specimen with hydrochloric acid and hydrofluoric acid, and masking unstable lead with ethylene diamine tetraacetic acid 2 sodium and fluoride ions with boric acid was established. The apparatus, reagents, the experiment and the results are reported. (Kako, I.)

Detrital zircon typology and U/Pb geochronology for the Miocene Ladrilleros-Juanchaco sedimentary sequence, Equatorial Pacific (Colombia): New constraints on provenance and paleogeography in northwestern South America

Energy Technology Data Exchange (ETDEWEB)

Osorio-Granada, E.; RESTREPO-MORENO, S.A.; MUÑOZ-VALENCIA, J.A.; TREJOS-TAMAYO, R.A.; PARDO-TRUJILLO, A.; BARBOSA-ESPITIA, A.A.

2017-11-01

Typology and internal texture analyses were performed on detrital zircons obtained from the Miocene sandstones of the Ladrilleros-Juanchaco sedimentary sequence (Colombia, Equatorial Pacific). This analysis was complemented with zircon U/Pb dating to identify typology-age associations as indicators of sediment provenance. Our results show that zircons with S and P dominant typologies have internal structures/zoning indicative of igneous, and potentially also metamorphic, origins. Morphometric results suggest limited transport from source areas. Both typology and U/Pb data point to the western Cordillera as the principal source of detrital materials for this sedimentary sequence. A paleogeographic reconstruction shows that, during the Late Miocene, significant portions of the western Cordillera were uplifted and actively eroding, thereby forming a fluvio-topographic barrier that prevented sediments from the central Cordillera reaching the Pacific basins. Exhumed Miocene plutons located along the axis of the western Cordillera may also have played a role as geomorphologically active massifs. This study demonstrates that typologic analysis on detrital zircon grains is a useful tool for establishing provenance and paleogeography in complex litho-tectonic areas where overlapping U/Pb signatures can lead to contradictory results.

Hydrozirconation of lithium alkynylselenolate anions. Generation and reactions of alpha-zirconated vinyl selenide intermediates

Science.gov (United States)

Dabdoub; Begnini; Guerrero; Baroni

2000-01-14

Lithium alkynylselenolate anions react completely with 1.0 equiv of Cp(2)Zr(H)Cl in THF at room temperature to give exclusively the alpha-zirconated vinylselenolate intermediates 23-27, which by treatment with an alkyl halide afforded the alpha-zirconated vinyl alkylselenide intermediates 29-33. Reaction of 29-33 with butyltellurenyl bromide results in the formation of ketene telluro(seleno) acetals 35-39 with total control of the regio- and stereochemistry. The synthetic utility of the ketene telluro(seleno) acetals obtained here was demonstrated by reaction of 36 with butyllithium. This promotes the exclusive and stereospecific removal of the tellurium moiety and enables formation of the corresponding selenium-containing allylic alcohol of type 44, alpha-(alkylseleno)-alpha,beta-unsaturated aldehyde 45, ester 46, or carboxylic acid 47, after reaction with different types of electrophiles.

Zircon U-Pb ages and geochemistry of migmatites and granites in the Foping dome: Evidence for Late Triassic crustal evolution in South Qinling, China

Science.gov (United States)

Zhang, He; Li, Shuang-Qing; Fang, Bo-Wen; He, Jian-Feng; Xue, Ying-Yu; Siebel, Wolfgang; Chen, Fukun

2018-01-01

Migmatites provide a record of melt formation and crustal rheology. In this study we present zircon U-Pb ages and geochemical composition of migmatites from the Foping dome and granites from the Wulong pluton. U-Pb results from migmatite zircons indicate two episodes of partial melting. Rim domains from a leucosome in the Longcaoping area yield an age of ca. 209 Ma. Migmatites collected from the Foping dome yield U-Pb zircon ages of 2910 to 190 Ma, suggesting the involvement of meta-sedimentary source components. Rim domains of the zircons with low Th/U ratios (pluton can be subdivided into high Sr/Y and low Sr/Y granites. U-Pb zircon ages vary from 219 to 214 Ma for the high Sr/Y granites and from 214 to 192 Ma for the low Sr/Y granites. High Sr/Y granites have higher Na2O and Sr contents than the low Sr/Y granites. They also lack negative Eu anomalies and are depleted in HREE compared to the low Sr/Y granites. Initial 87Sr/86Sr ratios and εNd values of all the samples roughly overlap with those of Neoproterozoic basement rocks exposed in South Qinling. Including previous studies, we propose that the high and low Sr/Y granites formed by melting of thickened and normal crust, respectively. Close temporal-spatial relationship of the high and low Sr/Y granites with the two-stage migmatization events implies variation of crustal thickness and thermal overprints of the orogenic crust in post-collisional collapse. Following the collision of South Qinling and the Yangtze block prior to 219 Ma, partial melting of the deep crust occurred. The melts migrated upwards to form the high Sr/Y granites. This process occurred rapidly and caused collapse of the thickened crust and carried heat upwards, leading to further partial melting within the shallower crust and formation of the low Sr/Y granites.

Zircon provenance of SW Caledonian phyllites reveals a distant Timanian sediment source

Czech Academy of Sciences Publication Activity Database

Sláma, Jiří; Pedersen, R. B.

2015-01-01

Roč. 172, č. 4 (2015), s. 465-478 ISSN 0016-7649 Institutional support: RVO:67985831 Keywords : East-European-Craton * LA-ICP-MS * Norwegian Caledonides * detrial zircon * U-PB * Scandinavian Caledonides * LU-HF * Cambrian papaeogeography * South Norwey * Oslo region Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.473, year: 2015

Structural contribution to the ferroelectric fatigue in lead zirconate titanate ceramics

Science.gov (United States)

Hinterstein, M.; Rouquette, J.; Haines, J.; Papet, Ph.; Glaum, J.; Knapp, M.; Eckert, J.; Hoffman, M.

2014-09-01

Many ferroelectric devices are based on doped lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary (MPB), at which the relevant material's properties approach their maximum. Based on a synchrotron x-ray diffraction study of MPB PZT, bulk fatigue is unambiguously found to arise from a less effective field induced tetragonal-to-monoclinic transformation, at which the degradation of the polarization flipping is detected by a less intense and more diffuse anomaly in the atomic displacement parameter of lead. The time dependence of the ferroelectric response on a structural level down to 250 μs confirms this interpretation in the time scale of the piezolectric strain response.

Preparation of lead titanate zirconate from metal citrates

International Nuclear Information System (INIS)

Bastos, C.M.R.

1994-01-01

Lead titanate zirconate (PZT) preparation from its metal constituent citrates have been investigated. Metal citrates were obtained by forced precipitation using a dehydration alcohol mixture. Salt solutions of lead nitrate and octahydrated zirconyl chloride, and titanium tetrachloride were treated separately with citric acid and ammonium hydroxide. Zirconium, titanium and lead oxides resulted from thermal decomposition of corresponding citrates at 500 0 C, 450 0 C and 250 0 C, respectively. Lead titanate (PT) and lead zirconate (P Z) were obtained by calcining at 450 0 C and 500 0 C, respectively, after adequate heating of citrates mechanically mixed in ethyl ether. PZT samples were obtained with different starting stoichiometry. Rhombohedral PZT-1 53/47 sample was prepared from co precipitating zirconyl ammonium and ammonium lead citrates in presence of ethanolic titanium oxide dispersion, and calcinating at 800 0 C. Rhombohedral PZT-q 52/48 sample was obtained from heating at 500 0 C for 2 hours a mixture of metal citrates coprecipitated by dehydration mixture of acetone-ethanol-formic acid (2:1:0,06). Tetragonal PZT-m stoichiometry 53/47 sample were obtained by calcining at after 600 0 C for 2 hours after heating a mechanically mixed metal citrates. PT phase arose at 400 0 C. PZT-m powders obtained in a range of 400 0 C-800 0 C were isostatically pressed, and sintered at 1100 0 C and 1200 0 C in saturated Pb O atmosphere. Rhombohedral sintered PZT was obtained with 7,78 g.cm -3 at 1200 0 C. (author). 123 refs, 53 figs, 32 tabs

New U-Pb zircon ages and the duration and division of Devonian time

Science.gov (United States)

Tucker, R.D.; Bradley, D.C.; Ver Straeten, C.A.; Harris, A.G.; Ebert, J.R.; McCutcheon, S.R.

1998-01-01

Newly determined U-Pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the Devonian time-scale. They are: 1) 417.6 ?? 1.0 Ma for an ash within the conodont zone of Icriodus woschmidti/I. w. hesperius Lochkovian); 2) 408.3 ?? 1.9 Ma for an ash of early Emsian age correlated with the conodont zones of Po. dehiscens--Lower Po. inversus; 3) 391.4 ?? 1.8 Ma for an ash within the Po. c. costatus Zone and probably within the upper half of the zone (Eifelian); and 4) 381.1 ?? 1.3 Ma for an ash within the range of the Frasnian conodont Palmatolepis punctata (Pa. punctata Zone to Upper Pa. hassi Zone). U-Pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites-lepidophyta spore zone, are dated at 363.8 ?? 2.2 Ma and 363 ?? 2.2 Ma and 363.4 ?? 1.8 Ma, respectively, suggesting an age of ~363 Ma for a level within the late Famennian Pa. g. expansa Zone. These data, together with other published zircon ages, suggest that the base and top of the Devonian lie close to 418 Ma and 362 Ma, respectively, thus lengthening the period of ~20% over current estimates. We suggest that the duration of the Middle Devonian (Eifelian and Givitian) is rather brief, perhaps no longer than 11.5 Myr (394 Ma-382.5 Ma), and that the Emsian and Famennian are the longest stages in the period with estimated durations of ~15.5 Myr and 14.5 Myr, respectively.

Dating Metasomatism: Monazite and Zircon Growth during Amphibolite Facies Albitization

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Cailey B. Condit

2018-04-01

Full Text Available We present coupled textural observations and trace element and geochronological data from metasomatic monazite and zircon, to constrain the timing of high-grade Na-metasomatism (albitization of an Archean orthogneiss in southwest Montana, USA. Field, mineral textures, and geochemical evidence indicate albitization occurred as a rind along the margin of a ~3.2 Ga granodioritic orthogneiss (Pl + Hbl + Kfs + Qz + Bt + Zrn exposed in the Northern Madison range. The metasomatic product is a weakly deformed albitite (Ab + Bt + OAm + Zrn + Mnz + Ap + Rt. Orthoamphibole and biotite grew synkinematically with the regional foliation fabric, which developed during metamorphism that locally peaked at upper amphibolite-facies during the 1800–1710 Ma Big Sky orogeny. Metasomatism resulted in an increase in Na, a decrease in Ca, K, Ba, Fe, and Sr, a complete transformation of plagioclase and K-feldspar into albite, and loss of quartz. In situ geochronology on zoned monazite and zircon indicate growth by dissolution–precipitation in both phases at ~1750–1735 Ma. Trace element geochemistry of rim domains in these phases are best explained by dissolution–reprecipitation in equilibrium with Na-rich fluid. Together, these data temporally and mechanistically link metasomatism with high-grade tectonism and prograde metamorphism during the Big Sky orogeny.

Subduction Initiation Existed Along the Ancient Continent Margins? Evidence of U-Pb ages of zircons from the Bonin Trench, Japan

Science.gov (United States)

Li, Y. B.; Pearce, J. A.; Ryan, J. G.; Li, X. H.; Haraguchi, S.; Iizuka, T.; Kon, Y.; Yamamoto, S.; Sawaki, Y.; Ishii, T.; Maruyama, S.

2017-12-01

Although it is not cleanly known when and where the subduction initiation began on the Paleo-Izu-Bonin-Mariana (IBM) Trench, Jurassic and Cretaceous plutonic rocks, such as gabbroic, granitic and metamorphic rocks had been sampled from the Amami Plateau-Daito Ridge-Okidaito Ridge (ADO) in the Philippine Sea Plate. Furthermore, Mesozonic to Paleozonic ages zircons were obtained from volcaniclastic sandstones collected from northern Izu-Bonin forarc (Tani et al., 2012). We present U-Pb ages, Hf-O isotopes and trace element compositions of zircon grains separated from sediment, volcanic rock, dolerite and gabbro, collected from Chichijima Island and Bonin forearc seafloor (KH03-3, KT04-28 cruise of the University of Tokyo, IODP Leg 352). In the zircon age histogram, several age groups were identified. The age peaks are 0-3 Ma and 13 Ma (Hahajima Seamount: soft mud and volcanic tuff); 38 Ma (Oomachi Seamount: sandstone); 45 Ma (Chichijima Island: volcanic rock); 40 Ma, 48 Ma and 52 Ma (Hahajima Seamount: dolerite and gabbro); 45 Ma and 164-165 Ma (IODP Leg 352: volcanic rock), respectively. Zircon U-Pb ages ranging 0-52 Ma correspond well to the multi-stages of magmatism in the IBM. However, 164-165 Ma maybe represent the ages of zircon xenocryst including in forearc volcanic rock , which pre-existing in ancient continent crustal materials (SE China Continent Crust?) as the basement of Paleo-IBM. It seems reasonable to suppose that the subduction initiation of IBM existed along the ancient SE China Continent margins. The initiation of subduction zone is a consequence of lateral compositional buoyancy contrast within the lithosphere, that advocated by Niu et al. (2003, 2016).

Uranium determinations by 133Xe in terrestrial zircon, apatite and chromite; comparative study of thermal releases of fissiogenic xenon from terrestrial and meteoritic minerals

International Nuclear Information System (INIS)

Sakamoto, K.; Hamajima, Y.; Itoh, K.; Yamazaki, K.

1980-01-01

Terrestrial zircon and apatite, as examples of uranium rich refractory minerals, and chromite, also highly refractory but uranium poor, were neutron-irradiated for their 133 Xe release studies. Uranium determination by 133 Xe was found not to be successful in these refractory samples, due to incomplete fissiogenic-xenon release at 1600 deg C as revealed by stepwise heating experiment. In these terrestrial materials the high temperature release peaks appeared at >=1500 deg C, but in meteoritic whitlockite and chromite values of 1000 approximately 1200 deg C were reported. (author)

Differential lead retention in zircons: implications for nuclear waste containment.

Science.gov (United States)

Gentry, R V; Sworski, T J; McKown, H S; Smith, D H; Eby, R E; Christie, W H

1982-04-16

An innovative ultrasensitive technique was used for lead isotopic analysis of individual zircons extracted from granite core samples at depths of 960, 2170, 2900, 3930, and 4310 meters. The results show that lead, a relatively mobile element compared to the nuclear waste-related actinides uranium and thorium, has been highly retained at elevated temperatures (105 degrees to 313 degrees C) under conditions relevant to the burial of synthetic rock waste containers in deep granite holes.

Preparation of high quality zirconium oxychloride from zircon of Vietnam

International Nuclear Information System (INIS)

Ngo Van Tuyen; Vu Thanh Quang; Trinh Giang Huong; Vuong Huu Anh

2007-01-01

This paper introduces a sodium hydroxide decomposition method for zirconium oxychloride production from zircon sand of Vietnam such as Ha Tinh, Hue, Binh Thuan seaside. Techniques for separation of impurities in ZOC final product such as SiO 2 , Fe 2 O 3 , TiO 2 , rare earths, uranium, and thorium have also been introduced. Content of uranium and thorium in the final product of ZOC is less than 1 ppm. (author)

Early cretaceous zircon SHRIMP U-Pb age of the trachyte and its significances of the Gan-Hang belt

International Nuclear Information System (INIS)

Liu Feiyu; Wu Jianhua; Liu Shuai

2009-01-01

The Shixi basin was located at Gan-Hang tectonic volcanic uranium deposit of rock-magma belt which belong to a part of the Mesozoic volcanic rocks in the northeastern of China. The appearance of the trachyte in Shixi basin have the majoy elements characteristic of the shoshonite series volcanic rocks. To determine the geological age of trachyte have very important significance on the geodynamics research and the study on the cause of uranium mineralization. The zircons of the trachyte have clear ring and high Th/U ratio which belong to the typical magmatic zircons. The zircon SHRIMP U-Pb dating resules show that 14points' age range is very smaller is 132-144 Ma and the weighted average age is (137.00±0.94)Ma which represents the diagenetic age of volcanic rocks. Accronding to the latest International Stratigraphic Chart the boundary of Jurassic and Cretaceous is (145.4±4.0)Ma. So the trachyte of Shixi Group belong to early Cretaceous. The large-scale acidic volcanic activity occurred in the Early Cretaceous in Southeastern China, and the Volcanic uranium deposit of Gan-Hang tectonic belt relate to Alkali metasomatism Uranium mineralization also occurred in the Early Cretaceous (120-130 Ma). The determined of trachyte in Shixi Group in the Early Cretaceous show that the acidic volcanic activity have connection with magma activity and the early Uranium mineralization consistent with the Alkali magma activity. (authors)

Petrologic and zircon U-Pb geochronological characteristics of the pelitic granulites from the Badu Complex of the Cathaysia Block, South China

Science.gov (United States)

Zhao, Lei; Zhou, Xiwen; Zhai, Mingguo; Liu, Bo; Cui, Xiahong

2018-06-01

The recognition of the Indosinian Orogeny in the South China block has been controversial and difficult because of strong weathering and thick cover. High temperature (HT) and high pressure (HP) metamorphic rocks related to this orogeny were considered to be absent from this orogenic belt until the recent discovery of eclogite and granulite facies meta-igneous rocks, occurring as lenses within the meta-sedimentary rocks of the Badu Complex. However, metamorphic state of these meta-sedimentary rocks is still not clear. Besides, there have been no geochronological data of HT pelitic granulites previously reported from the Badu Complex. This paper presents petrographic characteristics and zircon geochronological results on the newly discovered kyanite garnet gneiss, pyroxene garnet gneiss and the HT pelitic granulites (sillimanite garnet gneiss). Mineral assemblages are garnet + sillimanite + ternary feldspar + plagioclase + quartz + biotite for the HT pelitic granulite, kyanite + ternary feldspar + garnet + sillimanite + plagioclase + quartz + biotite for the kyanite garnet gneiss, and garnet + biotite + pyroxene + plagioclase + ternary feldspar + quartz for the pyroxene garnet gneiss, respectively. Decompressional coronas around garnet grains can be observed in all these pelitic rocks. Typical granulite facies mineral assemblages and reaction textures suggest that these rocks experienced HP granulite facies metamorphism and overprinted decompression along a clockwise P-T loop. Results from integrated U-Pb dating and REE analysis indicate the growth of metamorphic zircons from depleted heavy REE sources (100-50 chondrite) compared with detrital zircons derived from granitic sources (typically > 1000 chondrite). Metamorphic zircons in HP granulite exhibit no or subdued negative Eu anomalies, which perhaps indicate zircon overgrowth under eclogite facies conditions. The zircon overgrowth ages range from 250 to 235 Ma, suggesting that HP granulite (eclogite) to

U-Pb dating of large zircons in low-temperature jadeitite from the Osayama serpentinite melange, southwest Japan: insights into the timing of serpentinization

Science.gov (United States)

Tsujimori, T.; Liou, J.G.; Wooden, J.; Miyamoto, T.

2005-01-01

Crystals of zircon up to 3 mm in length occur in jadeitite veins in the Osayama serpentinite mélange, Southwest Japan. The zircon porphyroblasts show pronounced zoning, and are characterized by both low Th/U ratios (0.2-0.8) and low Th and U abundances (Th = 1-81 ppm; U = 6-149 ppm). They contain inclusions of high-pressure minerals, including jadeite and rutile; such an occurrence indicates that the zircon crystallized during subduction-zone metamorphism. Phase equilibria and the existing fluid-inclusion data constrain P-T conditions to P > 1.2 GPa at T > 350°C for formation of the jadeitite. Most U/Pb ages obtained by SHRIMP-RG are concordant, with a weighted mean 206Pb/238U age of 472 ± 8.5 Ma (MSWD = 2.7, n = 25). Because zircon porphyroblasts contain inclusions of high-pressure minerals, the SHRIMP U-Pb age represents the timing of jadeitite formation, i.e., the timing of interaction between alkaline fluid and ultramafic rocks in a subduction zone. Although this dating does not provide a direct time constraint for serpentinization, U-Pb ages of zircon in jadeitite associated with serpentinite result in new insights into the timing of fluid-rock interaction of ultramafic rocks at a subduction zone and the minimum age for serpentinization.

Correlation between radionuclides associated with zircon and monazite in beach sand of Rosetta, Egypt

International Nuclear Information System (INIS)

Nada, A.; Abd El-Maksoud, T.M.; Abu Zeid, H.; Abd El-Azeem, S.A.; Mostafa, S.M.I.

2012-01-01

The study aims to evaluate the activity concentrations of 238 U, 232 Th, 40 K and 137 Cs along Rosetta beach, Egypt. Non-destructive assay techniques were carried out using HP-Ge spectrometer and binocular microscope. The results of this study serve as a database for radioactivity levels of the mineral sand deposits of Rosetta area. The activity concentrations of 238 U, 232 Th and 40 K ranged from 5.39 to 134.2, 6.6 to 160.8 and 57.6 to 492 Bq kg -1 respectively. The range of activity concentrations of 137 Cs is between 0.05 and 0.91 Bq kg -1 . The total gamma absorbed dose rates varied from 11.59 to 160.01 nGyh -1 with a mean value of 50.53 nGyh -1 . These values correspond to an annual effective dose equivalent of 0.01-0.2 mSvy -1 with a mean of 0.07 mSvy -1 , which is in agreement with the worldwide average. Also, a correlation between the calculated zircon and monazite radioactive mineral contents with the measured radioactive isotopes was carried out to determine the contribution of each mineral for radioactivity. These correlations predicted that both zircon and monazite minerals are the main contributors for radioactivity in the Egyptian beach black sands. Also the present study ensured that area under investigation is to be safe for public. (author)

L'or, le zircon et la tourmaline : Traceurs de l'origine des materiaux ...

African Journals Online (AJOL)

The thick lateritic cover of tropical zones are often considered as old soils which have undergone several evolutionary cycles throughout time. Nevertheless, they contain some resistant minerals like gold, zircon and tourmaline which remain after surficial processes.These residual minerals, used as tracers of the genesis ...

Estimating the formation age distribution of continental crust by unmixing zircon ages

Science.gov (United States)

Korenaga, Jun

2018-01-01

Continental crust provides first-order control on Earth's surface environment, enabling the presence of stable dry landmasses surrounded by deep oceans. The evolution of continental crust is important for atmospheric evolution, because continental crust is an essential component of deep carbon cycle and is likely to have played a critical role in the oxygenation of the atmosphere. Geochemical information stored in the mineral zircon, known for its resilience to diagenesis and metamorphism, has been central to ongoing debates on the genesis and evolution of continental crust. However, correction for crustal reworking, which is the most critical step when estimating original formation ages, has been incorrectly formulated, undermining the significance of previous estimates. Here I suggest a simple yet promising approach for reworking correction using the global compilation of zircon data. The present-day distribution of crustal formation age estimated by the new "unmixing" method serves as the lower bound to the true crustal growth, and large deviations from growth models based on mantle depletion imply the important role of crustal recycling through the Earth history.

Nanostructural Evolution of Hard Turning Layers in Carburized Steel

Science.gov (United States)

Bedekar, Vikram

The mechanisms of failure for components subjected to contact fatigue are sensitive to the structure and properties of the material surface. Although, the bulk material properties are determined by the steel making, forming and the heat treatment; the near surface material properties are altered during final material removal processes such as hard turning or grinding. Therefore, the ability to optimize, modulate and predict the near surface properties during final metal removal operations would be extremely useful in the enhancement of service life of a component. Hard machining is known to induce severely deformed layers causing dramatic microstructural transformations. These transformations occur via grain refinement or thermal phenomena depending upon cutting conditions. The aim of this work is to engineer the near surface nanoscale structure and properties during hard turning by altering strain, strain rate, temperature and incoming microstructure. The near surface material transformations due to hard turning were studied on carburized SAE 8620 bearing steel. Variations in parent material microstructures were introduced by altering the retained austenite content. The strain, strain rate and temperature achieved during final metal cutting were altered by varying insert geometry, insert wear and cutting speed. The subsurface evolution was quantified by a series of advanced characterization techniques such as transmission electron microscopy (TEM), glancing angle X-ray diffraction (GAXRD), X-ray stress evaluation and nanoindentation which were coupled with numerical modeling. Results showed that the grain size of the nanocrystalline near surface microstructure can be effectively controlled by altering the insert geometry, insert wear, cutting speed and the incoming microstructure. It was also evident that the near surface retained austenite decreased at lower cutting speed indicating transformation due to plastic deformation, while it increased at higher cutting

Conductivity and hydration trends in disordered fluorite and pyrochlore oxides: A study on lanthanum cerate–zirconate based compounds

DEFF Research Database (Denmark)

Besikiotis, Vasileios; Ricote, Sandrine; Jensen, Molly Hjorth

2012-01-01

In the present contribution we discuss the influence of order/disorder on the concentration and mobility of ionic charge carriers in undoped and acceptor (calcium) doped fluorite and pyrochlore structured lanthanum cerate–zirconate solid solutions: (La1−yCay)2(Ce1−xZrx)2O7−δ (y=0, 0.02, 0.10; x=0...... enthalpy becomes more exothermic with higher cerium content, i.e. with more disordered materials. The proton conductivity decreases upon acceptor substitution of La3+ with Ca2+ which is attributed to trapping of the charge carriers by the effectively negative acceptor....

Electron Backscatter Diffraction (EBSD) Analysis and U-Pb Geochronology of the Oldest Lunar Zircon: Constraining Early Lunar Differentiation and Dating Impact-Related Deformation

Science.gov (United States)

Timms, Nick; Nemchin, Alexander; Grange, Marion; Reddy, Steve; Pidgeon, Bob; Geisler, Thorsten; Meyer, Chuck

2009-01-01

The evolution of the early moon was dominated by two processes (i) crystallization of the Lunar Magma Ocean (LMO) and differentiation of potassium-rare earth element-phosphorous-rich residual magma reservoir referred to as KREEP, and (ii) an intense meteorite bombardment referred to as lunar cataclysm . The exact timing of these processes is disputed, and resolution relies on collection and interpretation of precise age data. This study examines the microstructure and geochronology of zircon from lunar impact breccias collected during the Apollo 17 mission. A large zircon clast within lunar breccia 72215,195 shows sector zoning in optical microscopy, cathodoluminescence (CL) imaging and Raman mapping, and indicates that it was a relict fragment of a much larger magmatic grain. Sensitive high resolution ion microprobe (SHRIMP) U-Pb analysis of the zircon shows that U and Th concentration correlate with sector zoning, with darkest CL domains corresponding with high-U and Th (approx.150 and approx.100 ppm respectively), and the brightest-CL sectors containing approx.30-50 ppm U and approx.10-20 ppm Th. This indicates that variations in optical CL and Raman properties correspond to differential accumulation of alpha-radiation damage in each sector. Electron backscatter diffraction (EBSD) mapping shows that the quality of electron backscatter patterns (band contrast) varies with sector zoning, with the poorest quality patterns obtained from high-U and Th, dark-CL zones. EBSD mapping also reveals a deformation microstructure that is cryptic in optical, CL and Raman imaging. Two orthogonal sets of straight discrete and gradational low-angle boundaries accommodate approx.12 misorientation across the grain. The deformation bands are parallel to the crystallographic {a}-planes of the zircon, have misorientation axes parallel to the c-axis, and are geometrically consistent with formation by dislocation creep associated with {010} slip. The deformation bands are unlike curved

SHRIMP zircon U-Pb age and its significances of volcanic rocks from banshi basin in south jiangxi province

International Nuclear Information System (INIS)

Wang Baofeng; Wu Jianhua

2011-01-01

SHRIMP zircon U-Pb dating is applied to geochronological study for tuff of original Jilongzhang formation and rhyolite of original Banshi formation in Banshi basin, located in the Sannan (Longnan, Dingnan, Quannan) -Xunwu volcanic rocks belts in the south of Jiangxi. The result shows that zircon SHRIMP U-Pb age of the tuff is (142.5 ± 1.3) Ma and the age of the rhyolite is (131.4 ± 1.3) Ma. According to the latest international stratigraphic chart, the boundary between Jurassic and Cretaceous is (145.4 ± 4.0) Ma. So original Jilongzhang Formation and original Banshi Formation in Banshi basin were formed during early Early Cretaceous. The volcanic series in Banshi basin belongs to only one volcanic cycle. The features of the rock associations consistent with Wuyi group on the Xiajiang-Guangfeng volcanic rocks belts in the north of Jiangxi, so original Jilongzhang formation falls under E'huling formation and original Banshi formation falls under Shixi formation. (authors)

Reducing uranium and thorium level in Zircon: effect of heat treatment on rate of leaching

International Nuclear Information System (INIS)

Meor Yusoff Meor Sulaiman

2002-01-01

Considerable amount of uranium and thorium are found in Malaysian zircon and the level is much higher than the minimum value adopted by many importing countries. Selective leaching had been applied as an important technique to reduce these elements. An initial study was carried out using hydrochloric acid leaching system but the result was not favourable. The rate of uranium and thorium leached can be further improved by introducing a heat pretreatment process prior to leaching (Author)

The Sr:Ba:Rb ratio and zircon typology in granitoid complexes of Sao Paulo, Parana and Minas Gerais states (Brazil)

International Nuclear Information System (INIS)

Wernick, E.; Galembeck, T.M.B.; Artur, A.C.; Rigo Junior, L.; Weber-Diefenbach, K.

1990-01-01

Chemical (Sr: Ba: Rb) and zircon typology data from the Nazare Paulista, Mairipora/Cantareira, Cunhaporanga, Tres Corregos, Morungaba, Socorro, Itu, Graciosa and Serra Carambei granitoid complexes from the states of Minas Gerais, Sao Paulo and Parana (SE/S Brazil) are presented and discussed. By the zircon typology method these complexes are reffered, respectively, to the 2nd crustal, 3rd crustal/low temperature C-A, low temperature C-A, medium temperature C-A, medium/high temperature C-A, K-SA/Alkaline and alkaline serie which are considered as generated under increasing temperature associated with a progressive major participation of mantellic material. All these series, with the exception of the medium to high temperature calc-alkaline complexes Socorro and Morungaba whose chemical data come from several laboratories, display different positions and behaviour in the Sr: Ba: Rb diagram which reinforce the use of the zircon typology method in the study of granitoids. From the 2nd crustal serie up to the medium temperature C-A serie the complexes show a regular shift in their chemical composition which became progressively richer in Sr and depleted in Rb. The highly differentiades hypersolvus Serra do Carambei granite is strongly enriched in Rb and impoverish in Ba with respect to the Itu and the Graciosa complex which itself is slighly more depleted in Sr than the Itu granite. (author)

CL-imaging and ion microprobe dating of single zircons from a high-grade rock from the Central Zone, Limpopo Belt, South Africa: Evidence for a single metamorphic event at ˜2.0 Ga

Science.gov (United States)

Mouri, H.; Brandl, G.; Whitehouse, M.; de Waal, S.; Guiraud, M.

2008-02-01

The combination of ion microprobe dating and cathodoluminescence (CL) imaging of zircons from a high-grade rock from the Central Zone of the Limpopo Belt were used to constrain the age of metamorphic events in the area. Zircon grains extracted from an orthopyroxene-gedrite-bearing granulite were prepared for single crystal CL-imaging and ion microprobe dating. The grains display complex zoning when using SEM-based CL-imaging. A common feature in most grains is the presence of a distinct core with a broken oscillatory zoned structure, which clearly appears to be the remnant of an original grain of igneous origin. This core is overgrown by an unzoned thin rim measuring about 10-30 μm in diameter, which is considered as new zircon growth during a single metamorphic event. Selected domains of the zircon grains were analysed for U, Pb and Th isotopic composition using a CAMECA IMS 1270 ion microprobe (Nordsim facility). Most of the grains define a near-concordant cluster with some evidence of Pb loss. The most concordant ages of the cores yielded a weighted mean 207Pb/ 206Pb age of 2689 ± 15 (2 σ) Ma, interpreted as the age of the protolith of an igneous origin. The unzoned overgrowths of the zircon grains yielded a considerably younger weighted mean 207Pb/ 206Pb age of ˜2006.5 ± 8.0 Ma (2 σ), and these data are interpreted to reflect closely the age of the ubiquitous high-grade metamorphic event in the Central Zone. This study shows clearly, based on both the internal structure of the zircons and the data obtained by ion microprobe dating, that only a single metamorphic event is recorded by the studied 2.69 Ga old rocks, and we found no evidence of an earlier metamorphic event at ˜2.5 Ga as postulated earlier by some workers.

New phase transitions in lead zirconate-titanate

International Nuclear Information System (INIS)

Ishchuk, V.M.; Morozov, E.M.; Klimov, V.V.

1977-01-01

Processes of disordering are considered in the paraelectric phase of lead zirconate-titanate. Te investigations were carried out on poly- and single-crystal specimens of the composition PbZrsub(1-x)Tisub(x)O 3 (0< x(<=)0.5). The results are presented of measurements of the temperature dependence of the dielectric constant and the dependence of the polarization on the temperature and the electric field. Anomaly is observed of the investigated characteristics above the Curie point due to a first-type phase transition. The results are interpreted within the framework of the model proposed by Coms, Lambert, and Guiniot, according to which this transition is due to the disordering of chains of unit cells existing above the Curie point

Studies on the production of zirconia from Indian zircon - Part I : CaCo/sub 3/-ZrSiO/sub 4/ system

Energy Technology Data Exchange (ETDEWEB)

Reddy, S R; Mandal, G [Indian Inst. of Tech., Bombay. Dept. of Chemical Engineering

1974-09-01

With a view to developing a process for the manufacture of zirconia from Indian zircon CaCO/sub 3/ and ZrSiO/sub 4/ were used in different molar ratios and fires between 1100-1450/sup 0/C for varied lengths of time. The optimum conditions for the production of zirconia were suggested and the probable course of reactions was investigated with the help of X-ray, microscopic and chemical analysis.

Zircons and fluids: An experimental investigation with applications for radioactive waste disposal: Progress report, June 1, 1988--March 1, 1989

International Nuclear Information System (INIS)

Sinha, A.K.; Hewitt, D.A.; Ribbe, P.H.; Wayne, D.

1989-01-01

Experimental hydrothermal investigations of natural zircons have shown significant variations in loss of uranium. The percent loss is related to the composition of the fluid used in the experimental changes, rather than pressure and temperature alone. Development of microfractures provide an increase in surface area, and may be critical in developing adsorption models for actinides associated with radioactive waste storage. Zircons are being synthesized with various elemental substitution schemes prior to hydrothermal stability tests. 55 refs., 3 figs., 6 tabs

Using the methods of radiospectroscopy (EPR, NMR) to study the nature of the defect structure of solid solutions based on lead zirconate titanate (PZT)

Czech Academy of Sciences Publication Activity Database

Bykov, I. P.; Zagorodniy, A.Y.; Yurchenko, L.P.; Korduban, A.M.; Nejezchleb, K.; Trachevsky, V.V.; Dimza, V.; Jastrabík, Lubomír; Dejneka, Alexandr

2014-01-01

Roč. 61, č. 8 (2014), 1379-1385 ISSN 0885-3010 R&D Projects: GA TA ČR TA01010517; GA ČR GAP108/12/1941 Institutional support: RVO:68378271 Keywords : lead zirconate titanate ( PZT ) * EPR * NMR * XPS spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.512, year: 2014

Cross-poling textures in a lead zirconate titanate piezoelectric material

International Nuclear Information System (INIS)

Wan, Shan; Bowman, Keith J.

2000-01-01

Tetragonal ferroelectric materials are polarized to induce the anisotropy necessary for the piezoelectric effect. This poling of the material is inherently an orientation process. Pole figure texture measurements of poling and cross-poling in a lead zirconate titanate Navy VI material show domain motion. The resulting axisymmetric and three-dimensional textures demonstrate the contribution of 90 degree sign domain motion to piezoelectricity. Cross-poling results in strong orientations with lower applied fields than in the initial poling steps. (c) 2000 Materials Research Society

Significance of detrital zircons in upper Devonian ocean-basin strata of the Sonora allochthon and Lower Permian synorogenic strata of the Mina Mexico foredeep, central Sonora, Mexico

Science.gov (United States)

Poole, F.G.; Gehrels, G.E.; Stewart, John H.

2008-01-01

U-Pb isotopic dating of detrital zircons from a conglomeratic barite sandstone in the Sonora allochthon and a calciclastic sandstone in the Mina Mexico foredeep of the Minas de Barita area reveals two main age groups in the Upper Devonian part of the Los Pozos Formation, 1.73-1.65 Ga and 1.44-1.42 Ga; and three main age groups in the Lower Permian part of the Mina Mexico Formation, 1.93-1.91 Ga, 1.45-1.42 Ga, and 1.1-1.0 Ga. Small numbers of zircons with ages of 2.72-2.65 Ga, 1.30-1.24 Ga, ca. 2.46 Ga, ca. 1.83 Ga, and ca. 0.53 Ga are also present in the Los Pozos sandstone. Detrital zircons ranging in age from 1.73 to 1.65 Ga are considered to have been derived from the Yavapai, Mojave, and Mazatzal Provinces and their transition zones of the southwestern United States and northwestern Mexico. The 1.45-1.30 Ga detrital zircons were probably derived from scattered granite bodies within the Mojave and Mazatzal basement rocks in the southwestern United States and northwestern Mexico, and possibly from the Southern and Eastern Granite-Rhyolite Provinces of the southern United States. The 1.24-1.0 Ga detrital zircons are believed to have been derived from the Grenville (Llano) Province to the east and northeast or from Grenvilleage intrusions or anatectites to the north. Several detrital zircon ages ranging from 2.72 to 1.91 Ga were probably derived originally from the Archean Wyoming Province and Early Paleoproterozoic rocks of the Lake Superior region. These older detrital zircons most likely have been recycled one or more times into the Paleozoic sandstones of central Sonora. The 0.53 Ga zircon is believed to have been derived from a Lower Cambrian granitoid or meta-morphic rock northeast of central Sonora, possibly in New Mexico and Colorado, or Oklahoma. Detrital zircon geochronology suggests that most of the detritus in both samples was derived from Laurentia to the north, whereas some detritus in the Permian synorogenic foredeep sequence was derived from the

Zircon Hf-O isotopic constraints on the origin of Late Mesozoic felsic volcanic rocks from the Great Xing'an Range, NE China

Science.gov (United States)

Gong, Mingyue; Tian, Wei; Fu, Bin; Wang, Shuangyue; Dong, Jinlong

2018-05-01

The voluminous Late Mesozoic magmatism was related to extensive re-melting of juvenile materials that were added to the Central East Asia continent in Phanerozoic time. The most favoured magma generation mechanism of Late Mesozoic magmas is partial melting of underplated lower crust that had radiogenic Hf-Nd isotopic characteristics, but this mechanism faces difficulties when interpreting other isotopic data. The tectonic environment controlling the generation of the Late Mesozoic felsic magmas is also in dispute. In this study, we obtained new U-Pb ages, and geochemical and isotopic data of representative Jurassic (154.4 ± 1.5 Ma) and Cretaceous (140.2 ± 1.5 Ma) felsic volcanic samples. The Jurassic sample has inherited zircon cores of Permian age, with depleted mantle-like εHf(t) of +7.4 - +8.5, which is in contrast with those of the magmatic zircons (εHf(t) = +2.4 ± 0.7). Whereas the inherited cores and the magmatic zircons have identical mantle-like δ18O composition ranges (4.25-5.29‰ and 4.69-5.54‰, respectively). These Hf-O isotopic characteristics suggest a mixed source of enriched mantle materials rather than ancient crustal components and a depleted mantle source represented by the inherited Permian zircon core. This mechanism is manifested by the eruption of Jurassic alkaline basalts originated from an enriched mantle source. The Cretaceous sample has high εHf(t) of +7.0 - +10.5, suggesting re-melting of a mafic magma derived from a depleted mantle-source. However, the sub-mantle zircon δ18O values (3.70-4.58‰) suggest the depleted mantle-derived mafic source rocks had experienced high temperature hydrothermal alteration at upper crustal level. Therefore, the Cretaceous felsic magma, if not all, could be generated by re-melting of down-dropped supracrustal volcanic rocks that experienced high temperature oxygen isotope alteration. The two processes, enriched mantle-contribution and supracrustal juvenile material re-melting, are new

Improved microstructure and properties of 12Cr2Ni4A alloy steel by vacuum carburization and Ti + N co-implantation

Science.gov (United States)

Dong, Meiling; Cui, Xiufang; Jin, Guo; Wang, Haidou; Cai, Zhaobing; Song, Shengqiang

2018-05-01

The carburized 12Cr2Ni4A alloy steel was implanted by Ti + N double elements implantation. The microstructure, nano-hardness and corrosion properties were investigated by EPMA, TEM, XPS, nano-hardness and electrochemistry tests in detail. The results showed that the Ti + N co-implanted layer is composed of FCC TiN and TiC phases with BCC martensite. Compared with the un-implanted layer, the Ti + N implanted layer has higher nano-hardness and better corrosion resistance. In addition, the higher nano-hardness was presented below the surface of 1800 nm compared with un-implanted layer, which is far beyond the thickness of the implanted layer. The results also indicated that the generation of nanoscale ceramic phase and structures are not the only factor to impose the influence on the nano-hardness and corrosion resistance, but the radiation damage and lattice distortion will play an important role.

Late Archaean-early Proterozoic source ages of zircons in rocks from the Paleozoic orogen of western Galicia, NW Spain

Energy Technology Data Exchange (ETDEWEB)

Kuijper, R P; Priem, H N.A. [Laboratorium voor Isotopen-Geologie, Amsterdam (Netherlands); Den Tex, E [Rijksuniversiteit Utrecht (Netherlands). Inst. voor Aardwetenschappen

1982-08-01

U-Pb data are reported for nine suites of zircons and three monazites from the Paleozoic orogen in western Galicia: one paragneiss and six orthogneisses from the early Paleozoic basement, and two Carboniferous (ca. 310 Ma old) intrusions of two-mica granite. New whole-rock Rb-Sr analyses, along with earlier data, indicate an age of ca. 470-440 Ma (Ordovician) for the emplacement of the granitic precursors of the orthogneisses. Monazite from the paragneiss also yields an U-Pb age of ca. 470 Ma. From the high initial /sup 87/Sr//sup 86/Sr ratios an involvement of Precambrian continental crust material is evident in the generation of the early Paleozoic suite of granites, while the zircon U-Pb data give evidence of the presence of about 3.0-2.0 Ga old (late Archaean-early Proterozoic) components in the source material. Zircons from the oldest sedimentary rocks in the area, now present as catazonal paragneisses and a likely source for the granites, likewise reveal a provenance age of 3.0-2.0 Ga.

Automation Of An Analogue Temperature Control System For Chlorination Process Of Zircon Sand In A Bricket Form

International Nuclear Information System (INIS)

Triyono; Wasito, Bangun; Aryadi

2000-01-01

Automation of an analogue temperature control system for chlorination process of zircon sand in a bricket form has been carried out. Principally, automation of an analogue temperature control is a simple and a closed loop system model controller. The used controller system is an ON-OFF model thermocople probe as a sensor. The output system is in the form of ON-OFF relay which is connected to contactor relay, so that it is able to serve the chlorination furnace. The prepared automatic temperature control system for chlorination process of zircon sand has been continuously tested at temperatures between 800 to 1050 o C. This required heating times between 8 to 17 minutes

Tectonic implications of U-Pb (zircon) Geochronology of Chor Granitoids of the Lesser Himalaya, Himachal Pradesh, NW Himalaya

Science.gov (United States)

Singh, P.; Bhakuni, S. S.

2017-12-01

Granitoids of various ages ranging from Proterozoic to Tertiary occur throughout the Himalayan fold-thrust belt. The occurrence of the Neoproterozoic granitoids are very less in the Himalayan orogen. One of the best example of Neoproterozoic granitoids is Chor granitoids, which are the intrusive granite bodies in the Paleoproterozoic of the Lesser Himalayan Crystallines of the Jutogh Group. In the central part these granites are non-foliated homogeneous that are porphyritic and peraluminous in nature (Singh et al., 2002; Bhargava et al., 2014, 2016), whereas in the peripheral part these are foliated showing south directed shear sense of movement. In this work we present the U-Pb (zircon) geochronology of two different granites samples of the Chor granitoids of Himachal Pradesh, NW Himalaya. The Jutogh Group of rocks is thrust over the Lesser Himalayan Sequence along the Jutogh Thrust or MCT. The geochronology of the Chor Granitoids and Lesser Himalayan Crystallines and their relationship with each other, including with the Indian shield are sparsely obscure. U-Pb zircon geochrnological age populations from these granitoids yield ages between 780 and 980 Ma. One sample gives the prominent age spectra for 206Pb/238U with weighted mean age of 908.3 ± 6.7 Ma (2σ) MSWD = 2.4 (n = 18). Similarly another sample gives the age of crystallization with weight mean age of 917 ± 17 Ma (2σ) MSWD = 3 (n = 11) and Th/U ratios of both samples are >0.1, indicating their magmatic origin. As a result of ductile shearing of granites along the MCT during the Cenozoic Himalayan Orogeny, the age has reduced to 780 Ma. The Neoproterozoic age of Chor granite matches with the Neoproterozoic detrital zircon age (800 to 1000 Ma by Parrish and Hodges 1996, Decelles et al., 2000) of the HHC. On the basis of U-Pb (zircon) geochronological ages, it is revealed that the source of zircons of the Chor granite and HHC rocks was the northern margin of the Pan-African orogen. The Chor granitoids was

Excess hafnium-176 in meteorites and the early Earth zircon record

DEFF Research Database (Denmark)

Bizzarro, Martin; Connelly, James; Thrane, Kristine

2012-01-01

The long-lived Lu-to- Hf decay system is a powerful tool to understand ancient chemical fractionation events associated with planetary differentiation. Detrital Hadean zircons (>3.8 Gyr) from the Jack Hills metasedimentary belt of Western Australia record extremely enriched Hf-isotope signals sug...... crust prior to ~4.4 Gyr. This new view suggests continuous juvenile crustal growth and recycling throughout the Hadean and Archean eras, perhaps analogous to modern plate tectonics....

Provenance analysis of the Late Triassic Yichuan Basin: constraints from zircon U-Pb geochronology

Directory of Open Access Journals (Sweden)

Meng Xianghong

2018-03-01

Full Text Available Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS U-Pb dating has been performed on detrital zircons from the Chunshuyao Formation sandstone of Yichuan Basin. The ages of 85 detrital zircon grains are divided into three groups: 252-290 Ma, 1740-2000 Ma, and 2400-2600 Ma. The lack of Early Paleozoic and Neoproterozoic U-Pb ages indicates that there is no input from the Qinling Orogen, because the Qinling Orogen is characterized by Paleozoic and Neoproterozoic material. In combination with previous research, we suggest that the source of the Chunshuyao Formation is most likely recycled from previous sedimentary rocks from the North China Craton. In the Late Triassic, the Funiu ancient land was uplifted which prevented source material from the Qinling Orogen. Owing to the Indosinian orogeny, the strata to the east of the North China Craton were uplifted and eroded. The Yichuan Basin received detrital material from the North China Craton.

Dielectric behaviors of lead zirconate titanate ceramics with coplanar electrodes

International Nuclear Information System (INIS)

Wang, Y.; Cheng, Y.L.; Zhang, Y.W.; Chan, H.L.W.; Choy, C.L.

2003-01-01

This paper reports on the dielectric behaviors of lead zirconate titanate (PZT) capacitors with coplanar electrodes. Usually a ferroelectric device has a metal-ferroelectric-metal configuration (parallel plate capacitor); when both the electrodes are on one side of a ceramic to form a coplanar capacitor, different dielectric behaviors will be anticipated because of the change in the distribution of the test field inside the dielectrics. This paper describes how the capacitance and dielectric loss of PZT-based coplanar capacitors change with electrode distance, area and test frequency

LA-ICP-MS and SIMS U-Pb and U-Th zircon geochronological data of Late Pleistocene lava domes of the Ciomadul Volcanic Dome Complex (Eastern Carpathians

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Réka Lukács

2018-06-01

Full Text Available This article provides laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS and secondary ionization mass spectrometry (SIMS U-Pb and U-Th zircon dates for crystals separated from Late Pleistocene dacitic lava dome rocks of the Ciomadul Volcanic Dome Complex (Eastern Carpathians, Romania. The analyses were performed on unpolished zircon prism faces (termed rim analyses and on crystal interiors exposed through mechanical grinding an polishing (interior analyses. 206Pb/238U ages are corrected for Th-disequilibrium based on published and calculated distribution coefficients for U and Th using average whole-rock and individually analyzed zircon compositions. The data presented in this article were used for the Th-disequilibrium correction of (U-Th/He zircon geochronology data in the research article entitled “The onset of the volcanism in the Ciomadul Volcanic Dome Complex (Eastern Carpathians: eruption chronology and magma type variation” (Molnár et al., 2018 [1].

Occupational exposure to natural radioactivity in a zircon sand milling plant

International Nuclear Information System (INIS)

Ballesteros, Luisa; Zarza, Isidoro; Ortiz, Josefina; Serradell, Vicente

2008-01-01

Raw zirconium sand is one of the substances (naturally occurring radioactive material, NORM) which is widely used in the ceramic industry. This sand contains varying concentrations of natural radionuclides: mostly U-238 but also Th-232 and U-235, together with their daughters, and therefore may need to be regulated by Directive 96/29/EURATOM. This paper describes the method used to perform the radiological study on a zircon sand milling plant and presents the results obtained. Internal and external doses were evaluated using radioactivity readings from sand, airborne dust, intermediate materials and end products. The results on total effective dose show the need for this type of industry to be carefully controlled, since values near to 1 mSv were obtained

Occupational exposure to natural radioactivity in a zircon sand milling plant

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Ballesteros, Luisa [Laboratorio de Radioactividad Ambiental, Universidad Politecnica de Valencia, Apartado 22012, E-46071 Valencia (Spain)], E-mail: lballest@upvnet.upv.es; Zarza, Isidoro [Laboratorio de Radioactividad Ambiental, Universidad Politecnica de Valencia, Apartado 22012, E-46071 Valencia (Spain)], E-mail: iszarpe@upvnet.upv.es; Ortiz, Josefina [Laboratorio de Radioactividad Ambiental, Universidad Politecnica de Valencia, Apartado 22012, E-46071 Valencia (Spain)], E-mail: jortiz@iqn.upv.es; Serradell, Vicente [Laboratorio de Radioactividad Ambiental, Universidad Politecnica de Valencia, Apartado 22012, E-46071 Valencia (Spain)], E-mail: vserradell@iqn.upv.es

2008-10-15

Raw zirconium sand is one of the substances (naturally occurring radioactive material, NORM) which is widely used in the ceramic industry. This sand contains varying concentrations of natural radionuclides: mostly U-238 but also Th-232 and U-235, together with their daughters, and therefore may need to be regulated by Directive 96/29/EURATOM. This paper describes the method used to perform the radiological study on a zircon sand milling plant and presents the results obtained. Internal and external doses were evaluated using radioactivity readings from sand, airborne dust, intermediate materials and end products. The results on total effective dose show the need for this type of industry to be carefully controlled, since values near to 1 mSv were obtained.

U-Pb SHRIMP ages of detrital zircons from Hiriyur formation in Chitradurga Greenstone belt and its implication to the Neoarchean evolution of Dharwar craton, South India

International Nuclear Information System (INIS)

Nasheeth, A.; Okudaira, T.; Horie, K.; Hokada, T.; Satish Kumar, M.

2016-01-01

We report newly obtained U-Pb SHRIMP ages of detrital zircons from metagreywackes in the Hiriyur Formation (Chitradurga Group, Dharwar Supergroup) from the central eastern part of the Chitradurga greenstone belt. U-Pb analyses yield three major Neoarchean age populations ranging from 2.70 - 2.54 Ga with some minor age population of Mesoarchean. The maximum age of deposition is constrained by the youngest detrital zircon population at 2546 Ma. This is the first report of the occurrence of supracrustal rocks less than 2.58 Ga in the central part of Chitradurga greenstone belt. Close evaluation of detrital ages with the published ages of surrounding igneous rocks suggest that the youngest detrital zircons might be derived from rocks of the Eastern Dharwar craton and the inferred docking of the western and eastern Dharwar cratons happened prior to the deposition of the Hiriyur Formation. The Chitradurga shear zone, dividing the Dharwar craton into western and eastern blocks, probably developed after the deposition. Furthermore, the lower intercept is interpreted as evidence for the Pan-African overprints in the study area. (author)

Fracture mechanisms in lead zirconate titanate ceramics