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Sample records for sintered nanocrystalline material

  1. Composites of amorphous and nanocrystalline Zr–Cu–Al–Nb bulk materials synthesized by spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Drescher, P., E-mail: philipp.drescher@uni-rostock.de [Fluidic Technology and Microfluidics, Faculty of Mechanical Engineering and Marine Technology, University of Rostock, 18059 Rostock (Germany); Witte, K. [Physics of New Materials, Institute of Physics, University of Rostock, 18051 Rostock (Germany); Yang, B. [Polymer Physics, Institute of Physics, University of Rostock, 18051 Rostock (Germany); Steuer, R.; Kessler, O. [Chair of Materials Science, Faculty of Mechanical Engineering and Marine Technology, University of Rostock, 18059 Rostock (Germany); Burkel, E. [Physics of New Materials, Institute of Physics, University of Rostock, 18051 Rostock (Germany); Schick, C. [Polymer Physics, Institute of Physics, University of Rostock, 18051 Rostock (Germany); Seitz, H. [Fluidic Technology and Microfluidics, Faculty of Mechanical Engineering and Marine Technology, University of Rostock, 18059 Rostock (Germany)

    2016-05-15

    The fabrication of Zr{sub 70}Cu{sub 24}Al{sub 4}Nb{sub 2} bulk metallic glass composite samples by spark plasma sintering (SPS) process has been successfully realized. The unique characteristics of bulk metallic glasses could lead to the possibility of future applications as new structural and functional materials. The densification of an amorphous Zr{sub 70}Cu{sub 24}Al{sub 4}Nb{sub 2} powder was realized in a systematic study changing the sintering temperature in the SPS process leading to stable composites characteristic of amorphous and nanocrystalline structures. X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) analysis, transmission electron microscopy (TEM) as well as hardness tests were applied to determine the structural and mechanical properties of the sintered materials. A stable amorphous bulk metallic glass based on Zr{sub 70}Cu{sub 24}Al{sub 4}Nb{sub 2} with a low fraction of crystallites could be fabricated applying a nominal sintering temperature of 400 °C. Higher sintering temperatures lead to composites with high fractions of nanocrystalline material with porosities below 0.5%.

  2. Nanocrystalline ceramic materials

    Science.gov (United States)

    Siegel, Richard W.; Nieman, G. William; Weertman, Julia R.

    1994-01-01

    A method for preparing a treated nanocrystalline metallic material. The method of preparation includes providing a starting nanocrystalline metallic material with a grain size less than about 35 nm, compacting the starting nanocrystalline metallic material in an inert atmosphere and annealing the compacted metallic material at a temperature less than about one-half the melting point of the metallic material.

  3. HRTEM and Nanoindentation Studies of Bulk WC Nanocrystalline Materials Prepared by Spark Plasma Sintering of Ball-Milled Powders

    Science.gov (United States)

    Sherif El-Eskandarany, M.; Al-Hazza, Abdulsalam; Al-Hajji, L. A.

    2017-01-01

    In the present work, mechanical milling technique using a high-energy ball mill was employed for preparing of nanoscaled WC grains powders with an average grain size of 7 nm in diameters of WC. The present study demonstrates a successful consolidation process achieved at 1250 °C for sintering of ball-milled WC powders into full dense bulk buttons (above 99.6%), using SPS technique. The as-consolidated WC bulk nanocrystalline buttons revealed high hardness value ( 24 GPa) with low elastic modulus ( 332 GPa). Moreover, they possessed a high fracture toughness (15 MPa m1/2) that has never been reported for pure WC.

  4. Sintering and deformation of nanocrystalline ceramics

    International Nuclear Information System (INIS)

    Hahn, H.; Averback, R.S.; Hofler, H.J.; Logas, J.

    1991-01-01

    Nanocrystalline ceramics have been produced by the method of inert gas condensation of ultra-small particles and in situ consolidation. Sintering characteristics and microstructural parameter such as grain size, porosity and pore size distributions have been investigated by a variety of techniques, including: X-ray diffraction, gravimetry, nitrogen adsorption, scanning electron microscopy and small angle neutron scattering. In pure TiO 2 , the sintering temperatures are drastically lowered compared to conventional ceramics, however, extensive grain growth occurs before full densification is achieved. High density, nanocrystalline ceramics can be prepared by pressure assisted sintering, doping and additions of second phases. High temperature microhardness and creep deformation in compression were measured and it was found that creep processes occur at lower temperatures than in ceramics with larger grain sizes. Nanocrystalline TiO 2 with densities >99% can be deformed plastically without fracture at temperatures below half the melting point. The total strains exceed 0.6 at strain rates as high as 10 -3 s -l . The stress exponent of the strain rate, n, is approximately 3 and the grain size dependence is G -q with q in the range of 1-1.5. In this paper it is concluded that the creep deformation occurs by an interface reaction controlled mechanism

  5. Deformation behavior of sintered nanocrystalline silver layers

    International Nuclear Information System (INIS)

    Zabihzadeh, S.; Van Petegem, S.; Duarte, L.I.; Mokso, R.; Cervellino, A.; Van Swygenhoven, H.

    2015-01-01

    The microstructure of porous silver layers produced under different low temperature pressure-assisted sintering conditions is characterized and linked with the mechanical behavior studied in situ during X-ray diffraction. Peak profile analysis reveals important strain recovery and hardening mechanism during cyclic deformation. The competition between both mechanisms is discussed in terms of porosity and grain size

  6. Hot pressing of nanocrystalline tantalum using high frequency induction heating and pulse plasma sintering

    Science.gov (United States)

    Jakubowicz, J.; Adamek, G.; Sopata, M.; Koper, J. K.; Siwak, P.

    2017-12-01

    The paper presents the results of nanocrystalline powder tantalum consolidation using hot pressing. The authors used two different heating techniques during hot pressing: high-frequency induction heating (HFIH) and pulse plasma sintering (PPS). A comparison of the structure, microstructure, mechanical properties and corrosion resistance of the bulk nanocrystalline tantalum obtained in both techniques was performed. The nanocrystalline powder was made to start from the microcrystalline one using the high-energy ball milling process. The nanocrystalline powder was hot-pressed at 1000 °C, whereas, for comparison, the microcrystalline powder was hot pressed up to 1500 °C for proper consolidation. The authors found that during hot pressing, the powder partially reacts with the graphite die covered by boron nitride, which facilitated punches and powder displacement in the die during densification. Tantalum carbide and boride in the nanocrystalline material was found, which can improve the mechanical properties. The hardness of the HFIH and PPS nanocrystalline tantalum was as high as 625 and 615 HV, respectively. The microstructure was more uniform in the PPS nanomaterial. The corrosion resistance in both cases deteriorated, in comparison to the microcrystalline material, while the PPS material corrosion resistance was slightly better than that of the HFIH one.

  7. High-strength bulk nano-crystalline silver prepared by selective leaching combined with spark plasma sintering

    Czech Academy of Sciences Publication Activity Database

    Marek, I.; Vojtěch, D.; Michalcová, A.; Kubatík, Tomáš František

    2015-01-01

    Roč. 627, March (2015), s. 326-332 ISSN 0921-5093 Institutional support: RVO:61389021 Keywords : Nano-crystalline material * Selective leaching * Silver * Spark plasma sintering * Strength Subject RIV: JK - Corrosion ; Surface Treatment of Materials Impact factor: 2.647, year: 2015 http://dx.doi.org/10.1016/j.msea.2015.01.014

  8. Electric field-assisted sintering of nanocrystalline hydroxyapatite for biomedical applications

    Science.gov (United States)

    Tran, Tien Bich

    consistent during varied heating rate (50--400ºC/min) and varied pressure application (25--90 MPa) studies. While in vitro cytocompatibility studies using MG63 osteoblast-like cells demonstrated the biocompatibility of the FAST-processed specimens, bioactivity was sensitive to processing parameters. Since extensive dehydroxylation reduces the surface charge of the sintered materials, apatite deposition during simulated body fluid immersion only occurred when dehydroxylation was mild---i.e., on specimens sintered at low temperatures (800--900ºC) or for short periods. Microstructural investigations revealed that HA sintered at temperatures above 900ºC under an applied electric field contained nanometric residual pores in grain interiors, as well as micron-sized dehydroxylation-related pores at grain boundaries and grain boundary junctions. These larger pores were responsible for the increasing embrittlement of specimens sintered at higher temperatures. Although grain size dependence could not be found in the 60--100 nm grain size range, fracture toughness (KIC = 1.92 MPa√m, maximum) increased with decreasing sintering temperature. Results from the suite of investigations conducted demonstrate that biocompatible and bioactive nanocrystalline hydroxyapatite with enhanced mechanical properties can be efficiently manufactured by field-assisted sintering under controlled processing conditions.

  9. Morphological analysis and modelling of sintering and of sintered materials

    International Nuclear Information System (INIS)

    Jernot, Jean-Paul

    1982-01-01

    This research thesis addresses the study of solid phase sintering of metallic powders, and aims at describing as precisely as possible the different involved matter transport mechanisms, first by using a thermodynamic approach to sintering. Sintering diagrams are also used to determine prevailing mechanisms. The microstructure of sintered materials has been studied by using image quantitative analysis, thus by using a morphological approach to sintering. Morphological parameters allow, on the one hand, the evolution of powders during sintering to be followed, and, on the other hand, sintered products to be correctly characterised. Moreover, the author reports the study of the evolution of some physical properties of sintered materials with respect to their microstructure parameters. This leads to the development of a modelling of the behaviour of these materials [fr

  10. Method of sintering ceramic materials

    Science.gov (United States)

    Holcombe, Cressie E.; Dykes, Norman L.

    1992-01-01

    A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density.

  11. Structure and thermal stability of nanocrystalline materials

    Indian Academy of Sciences (India)

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

    Taking a cubic unit cell or a regular polyhedron unit cell of nanocrystalline material, the volume fraction of each ... The present article reviews the present states of understanding in these aspects of nanocrystalline materials. ..... Calculations based on the equation of state show 37% reduction in tetragonal shear modulus of ...

  12. Structure and thermal stability of nanocrystalline materials

    Indian Academy of Sciences (India)

    In addition, study of the thermal stability of nanocrystalline materials against significant grain growth is both scientific and technological interest. A sharp increase in grain size (to micron levels) during consolidation of nanocrystalline powders to obtain fully dense materials may consequently result in the loss of some unique ...

  13. Microwave sintering of ceramic materials

    Science.gov (United States)

    Karayannis, V. G.

    2016-11-01

    In the present study, the potential of microwave irradiation as an innovative energy- efficient alternative to conventional heating technologies in ceramic manufacturing is reviewed, addressing the advantages/disadvantages, while also commenting on future applications of possible commercial interest. Ceramic materials have been extensively studied and used due to several advantages they exhibit. Sintering ceramics using microwave radiation, a novel technology widely employed in various fields, can be an efficient, economic and environmentally-friendlier approach, to improve the consolidation efficiency and reduce the processing cycle-time, in order to attain substantial energy and cost savings. Microwave sintering provides efficient internal heating, as energy is supplied directly and penetrates the material. Since energy transfer occurs at a molecular level, heat is generated throughout the material, thus avoiding significant temperature gradients between the surface and the interior, which are frequently encountered at high heating rates upon conventional sintering. Thus, rapid, volumetric and uniform heating of various raw materials and secondary resources for ceramic production is possible, with limited grain coarsening, leading to accelerated densification, and uniform and fine-grained microstructures, with enhanced mechanical performance. This is particularly important for manufacturing large-size ceramic products of quality, and also for specialty ceramic materials such as bioceramics and electroceramics. Critical parameters for the process optimization, including the electromagnetic field distribution, microwave-material interaction, heat transfer mechanisms and material transformations, should be taken into consideration.

  14. Study of the sintering behavior of fine, ultrafine and nanocrystalline WC-CO mixtures obtained by high energy milling; Estudio del comportamiento durante la sinterizacion de mezclas WC-Co finas, ultrafinas y nanocristalinas obtenidas por molienda de alta energia

    Energy Technology Data Exchange (ETDEWEB)

    Salvador, M. D.; Bonache, V.; Amigo, V.; Busquets, D.

    2008-07-01

    In this work the sintering behaviour of fine, ultrafine and nanocrystalline WC-12Co mixtures obtained by high energy milling, as well commercial nano powders, have been studied, in order to evaluate the effect of the particle size and the powder processing, in the densification, microstructural development and mechanical properties of the final product. The consolidation of the mixtures has been made by uniaxial pressing and sintering in vacuum, and by hot isostatic pressing. The sintered materials have been evaluated by measures of density, hardness and indentation fracture toughness, and micro structurally characterized by optical microscopy and scanning and transmission electronic microscopy (SEM and TEM). The results show the improvements in resistant behaviour of the materials obtained from nanocrystalline powders, in spite of the grain growth experienced during the sintering. The best results were obtained for the milling nanocrystalline material, which presents values of hardness higher than 180 HV. (Author) 46 refs.

  15. The progress of nanocrystalline hydride electrode materials

    International Nuclear Information System (INIS)

    Jurczyk, M.

    2004-01-01

    This paper reviews research at the Institute of Materials Science and Engineering, Poznan University of Technology, on the synthesis of nanocrystalline hydride electrode materials. Nanocrystalline materials have been synthesized by mechanical alloying (MA) followed by annealing. Examples of the materials include TiFe - , ZrV 2- , LaNi 5 and Mg 2 Ni-type phases. Details on the process used and the enhancement of properties due to the nanoscale structures are presented. The synthesized alloys were used as negative electrode materials for Ni-MH battery. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. For example, it was found that the respective replacement of Fe in TiFe by Ni and/or by Cr, Co, Mo improved not only the discharge capacity but also the cycle life of these electrodes. The hydrogen storage properties of nanocrystalline ZrV 2 - and LaNi 5 -type powders prepared by mechanical alloying and annealing show no big difference with those of melt casting (polycrystalline) alloys. On the other hand, a partial substitution of Mg by Mn or Al in Mg 2 Ni alloy leads to an increase in discharge capacity, at room temperature. Furthermore, the effect of the nickel and graphite coating on the structure of some nanocrystalline alloys and the electrodes characteristics were investigated. In the case of Mg 2 Ni-type alloy mechanical coating with graphite effectively reduced the degradation rate of the studied electrode materials. The combination of a nanocrystalline TiFe - , ZrV 2 - and LaNi 5 -type hydride electrodes and a nickel positive electrode to form a Ni-MH battery, has been successful. (authors)

  16. Microwave sintering of nanophase ceramics without concomitant grain growth

    Science.gov (United States)

    Eastman, Jeffrey A.; Sickafus, Kurt E.; Katz, Joel D.

    1993-01-01

    A method of sintering nanocrystalline material is disclosed wherein the nanocrystalline material is microwaved to heat the material to a temperature less than about 70% of the melting point of the nanocrystalline material expressed in degrees K. This method produces sintered nanocrystalline material having a density greater than about 95% of theoretical and an average grain size not more than about 3 times the average grain size of the nanocrystalline material before sintering. Rutile TiO.sub.2 as well as various other ceramics have been prepared. Grain growth of as little as 1.67 times has resulted with densities of about 90% of theoretical.

  17. Abrasive wear behaviour of electrodeposited nanocrystalline materials

    Science.gov (United States)

    Jeong, Daehyun

    The effect of grain size refinement on the abrasive wear behaviour of nanocrystalline Ni, Ni-P and Co electrodeposits and the critical materials properties that influence the abrasive wear resistance were studied using the Taber wear test. As the grain size of Ni decreased from 90 mum to 13 nm, the dominant abrasive wear mode changed from ploughing to cutting and the Taber wear resistance was considerably improved by the increases in hardness and surface elastic properties. The abrasive wear behaviour of Ni with various grain sizes can be described using the attack angle model, which takes into consideration the randomly dispersed Al2O3 abrasive particles in the Taber wheel with various sizes, shapes and orientations. Depending on the phosphorus content, the nickel-phosphorus (Ni-P) alloys containing up to 6 wt.% P had nanocrystalline or mixed nanocrystalline-amorphous structures and both regular and inverse Hall-Petch behaviour were observed as a result of the microstructural changes with increasing P content/decreasing grain size. The wear resistance, like hardness, followed the Hall-Petch type behaviour, demonstrating that the smallest grain size does not necessarily provide the best wear resistance. For all Ni-P alloys, the wear resistance was improved by heat treatment due to Ni3P precipitates and, for materials with high P content, nanocrystallization of the amorphous phase. For heat-treated Ni-P alloys, however, the highest hardness did not give the best wear resistance. Despite the grain size reduction of Co from 10 mum to 17 nm, there was no significant change in the wear resistance due to the unusually high degree of plastic deformation of the nanocrystalline material. In addition to hardness and surface elastic properties which are usually considered important material properties that control the abrasive wear resistance, Taber wear ductility was introduced as a new material intrinsic property which can be applied to explain abrasive wear resistance for

  18. Nanocrystalline functional materials and nanocomposites synthesis through aerosol routes

    Directory of Open Access Journals (Sweden)

    Milošević Olivera B.

    2003-01-01

    Full Text Available This paper represents the results of the design of functional nanocrystalline powders and nanocomposites using chemical reactions in aerosols. The process involves ultrasonic aerosol formation (mist generators with the resonant frequencies of 800 kHz, 1.7 and 2.5 MHz from precursor salt solutions and control over the aerosol decomposition in a high-temperature tubular flow reactor. During decomposition, the aerosol droplets undergo evaporation/drying, precipitation and thermolysis in a single-step process. Consequently, spherical, solid, agglomerate-free submicronic particles are obtained. The particle morphology, revealed as a composite structure consisting of primary crystallites smaller than 20 nm was analysed by several methods (XRD, DSC/DTA, SEM, TEM and discussed in terms of precursor chemistry and process parameters. Following the initial attempts, a more detailed aspect of nanocrystalline particle synthesis was demonstrated for the case of nanocomposites based on ZnO-MeO (MeO=Bi Cr+, suitable for electronic applications, as well as an yttrium-aluminum base complex system, suitable for phosphorus applications. The results imply that parts of the material structure responsible for different functional behaviour appear through in situ aerosol synthesis by processes of intraparticle agglomeration, reaction and sintering in the last synthesis stage.

  19. LIGHT-WEIGHT NANOCRYSTALLINE HYDROGEN STORAGE MATERIALS

    Energy Technology Data Exchange (ETDEWEB)

    S. G. Sankar; B. Zande; R.T. Obermyer; S. Simizu

    2005-11-21

    During Phase I of this SBIR Program, Advanced Materials Corporation has addressed two key issues concerning hydrogen storage: 1. We have conducted preliminary studies on the effect of certain catalysts in modifying the hydrogen absorption characteristics of nanocrystalline magnesium. 2. We have also conducted proof-of-concept design and construction of a prototype instrument that would rapidly screen materials for hydrogen storage employing chemical combinatorial technique in combination with a Pressure-Composition Isotherm Measurement (PCI) instrument. 3. Preliminary results obtained in this study approach are described in this report.

  20. Nanocrystalline magnetic materials obtained by flash annealing

    Directory of Open Access Journals (Sweden)

    Murakami R.K.

    1999-01-01

    Full Text Available The aim of the present work was to produce enhanced-remanence nanocrystalline magnetic material by crystallizing amorphous or partially amorphous Pr4.5Fe77B18.5 alloys by the flash annealing process, also known as the dc-Joule heating process, and to determine the optimal conditions for obtaining good magnetic coupling between the magnetic phases present in this material. Ribbons of Pr4.5Fe77B18.5 were produced by melt spinning and then annealed for 10-30 s at temperatures 500 - 640 °C by passing current through the sample to develop the enhanced-remanence nanocrystalline magnetic material. These materials were studied by X-ray diffraction, differential thermal analysis and magnetic measurements. Coercivity increases of up to 15% were systematically observed in relation to furnace-annealed material. Two different samples were carefully examined: (i a sample annealed at 600 °C which showed the highest coercive field Hc and remanence ratio Mr/Ms and (ii a sample annealed at 520 °C which showed phase separation in the second quadrant demagnetization curve. Our results are in agreement with other studies which show that flash annealing improves the magnetic properties of some amorphous ferromagnetic ribbons.

  1. Isotropic and anisotropic nanocrystalline NdFeB-based magnets prepared by spark plasma sintering and hot deformation

    International Nuclear Information System (INIS)

    Liu, Z.W.; Huang, Y.L.; Huang, H.Y.; Zhong, X.C.; Yu, Y.H.; Zeng, D.C.

    2011-01-01

    Isotropic and anisotropic NdFeB permanent magnets were prepared by Spark Plasma Sintering (SPS) and SPS followed hot deformation (HD), respectively, using melt spun NdFeB ribbons with various compositions as starting materials. It is found that, based on RE-rich composition, SPSed magnets sintered at low temperatures (<700 C) almost maintained the uniform fine grain structure inherited from rapid quenching. At higher temperatures, a distinct two-zone (coarse grain and fine grain zones) structure was formed in the SPSed magnets. The SPS temperature and pressure have important effects on the grain structure, which led to the variations in the magnetic properties. By employing low SPS temperature and high pressure, high-density magnets with negligible coarse grain zone and an excellent combination of magnetic properties can be obtained. For single phase NdFeB alloy, because of the deficiency of Nd-rich phases, it is relatively difficult to consolidate micro-sized melt spun powders into high density bulk magnet, but generally a larger particle size is beneficial to achieve better magnetic properties. Anisotropic magnets with a maximum energy product of approx. equal to 38 MGOe were produced by the SPS+HD process. HD did not lead to obvious grain growth and the two-zone structure still existed in the hot deformed magnets. The results indicated that nanocrystalline NdFeB magnets without significant grain growth and with excellent properties could be obtained by SPS and HD processes. (author)

  2. Amorphous and nanocrystalline materials preparation, properties, and applications

    CERN Document Server

    Inoue, A

    2001-01-01

    Amorphous and nanocrystalline materials are a class of their own. Their properties are quite different to those of the corresponding crystalline materials. This book gives systematic insight into their physical properties, structure, behaviour, and design for special advanced applications.

  3. Nanocrystalline NdFeB magnet prepared by mechanically activated disproportionation and desorption-recombination in-situ sintering

    International Nuclear Information System (INIS)

    Xiaoya, Liu; Yuping, Li; Lianxi, Hu

    2013-01-01

    The process of mechanically activated disproportionation and desorption-recombination in-situ sintering was proposed to synthesize highly densified nanocrystalline NdFeB magnet, and its validity was demonstrated by experimental investigation with the use of a Nd 16 Fe 76 B 8 (atomic ratio) alloy. Firstly, the as-cast alloy was disproportionated by mechanical milling in hydrogen, with the starting micron-sized Nd 2 Fe 14 B phase decomposed into an intimate mixture of nano-structured NdH 2.7 , Fe 2 B and α-Fe phases. The as-disproportionated alloy powders were compacted by cold pressing and then subjected to desorption-recombination in-situ sintering. The microstructure of both the as-disproportionated and the subsequently sintered samples was characterized by X-ray diffraction and electron transmission microscopy, respectively. The magnetic properties of the sintered samples were measured by using vibrating sample magnetometer. The results showed that, by vacuum sintering, not only was the powder compact consolidated, but also the as-disproportionated microstucture transformed into nanocrystalline Nd 2 Fe 14 B phase via the well-known desorption-recombination reaction, thus giving rise to nanocrystalline NdFeB magnet. In the present study, the optimal sintering parameters were found to be 780 °C×30 min. In this case, the coercivity, the remanence, and maximum energy product of the magnet sample achieved 0.8 T, 635.3 kA/m, and 106.3 kJ/m 3 , respectively. - Highlights: ► Nano-structured disproportionated NdFeB alloy powders by mechanical milling in hydrogen. ► Highly densified green magnet compact by cold pressing of as-disproportionated NdFeB alloy powders. ► Nanocrystalline NdFeB magnets by desorption-recombination in-situ sintering under vacuum. ► Magnetic properties significantly improved by relative density enhancement and nanocrystallization of Nd 2 Fe 14 B phase. ► The effects of sintering parameters on magnetic properties and the underlying

  4. Nanocrystalline NdFeB magnet prepared by mechanically activated disproportionation and desorption-recombination in-situ sintering

    Energy Technology Data Exchange (ETDEWEB)

    Xiaoya, Liu; Yuping, Li [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Lianxi, Hu, E-mail: hulx@hit.edu.cn [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)

    2013-03-15

    The process of mechanically activated disproportionation and desorption-recombination in-situ sintering was proposed to synthesize highly densified nanocrystalline NdFeB magnet, and its validity was demonstrated by experimental investigation with the use of a Nd{sub 16}Fe{sub 76}B{sub 8} (atomic ratio) alloy. Firstly, the as-cast alloy was disproportionated by mechanical milling in hydrogen, with the starting micron-sized Nd{sub 2}Fe{sub 14}B phase decomposed into an intimate mixture of nano-structured NdH{sub 2.7}, Fe{sub 2}B and {alpha}-Fe phases. The as-disproportionated alloy powders were compacted by cold pressing and then subjected to desorption-recombination in-situ sintering. The microstructure of both the as-disproportionated and the subsequently sintered samples was characterized by X-ray diffraction and electron transmission microscopy, respectively. The magnetic properties of the sintered samples were measured by using vibrating sample magnetometer. The results showed that, by vacuum sintering, not only was the powder compact consolidated, but also the as-disproportionated microstucture transformed into nanocrystalline Nd{sub 2}Fe{sub 14}B phase via the well-known desorption-recombination reaction, thus giving rise to nanocrystalline NdFeB magnet. In the present study, the optimal sintering parameters were found to be 780 Degree-Sign C Multiplication-Sign 30 min. In this case, the coercivity, the remanence, and maximum energy product of the magnet sample achieved 0.8 T, 635.3 kA/m, and 106.3 kJ/m{sup 3}, respectively. - Highlights: Black-Right-Pointing-Pointer Nano-structured disproportionated NdFeB alloy powders by mechanical milling in hydrogen. Black-Right-Pointing-Pointer Highly densified green magnet compact by cold pressing of as-disproportionated NdFeB alloy powders. Black-Right-Pointing-Pointer Nanocrystalline NdFeB magnets by desorption-recombination in-situ sintering under vacuum. Black-Right-Pointing-Pointer Magnetic properties significantly

  5. New materials through a variety of sintering methods

    Science.gov (United States)

    Jaworska, L.; Cyboroń, J.; Cygan, S.; Laszkiewicz-Łukasik, J.; Podsiadło, M.; Novak, P.; Holovenko, Y.

    2018-03-01

    New sintering techniques make it possible to obtain materials with special properties that are impossible to obtain by conventional sintering techniques. This issue is especially important for ceramic materials for application under extreme conditions. Following the tendency to limit critical materials in manufacturing processes, the use of W, Si, B, Co, Cr should be limited, also. One of the cheapest and widely available materials is aluminum oxide, which shows differences in phase composition, grain size, hardness, strain and fracture toughness of the same type of powder, sintered via various methods. In this paper the alumina was sintered using the conventional free sintering process, microwave sintering, Spark Plasma Sintering (SPS), high pressure-high temperature method (HP-HT) and High Pressure Spark Plasma Sintering (HP SPS). Phase composition analysis, by X-ray diffraction of the alumina materials sintered using various methods, was carried out. For the conventional sintering method, compacts are composed of α-Al2O3 and θ-Al2O3. For compacts sintered using SPS, microwave and HP-HT methods, χ-Al2O3 and γ-Al2O3 phases were additionally present. Mechanical and physical properties of the obtained materials were compared between the methods of sintering. On the basis of images from scanning electron microscope quantitative analysis was performed to determine the degree of grain growth of alumina after sintering.

  6. High Temperature Stable Nanocrystalline SiGe Thermoelectric Material

    Science.gov (United States)

    Yang, Sherwin (Inventor); Matejczyk, Daniel Edward (Inventor); Determan, William (Inventor)

    2013-01-01

    A method of forming a nanocomposite thermoelectric material having microstructural stability at temperatures greater than 1000 C. The method includes creating nanocrystalline powder by cryomilling. The method is particularly useful in forming SiGe alloy powder.

  7. Sintered soft magnetic materials. Properties and applications

    Science.gov (United States)

    Bas, J. A.; Calero, J. A.; Dougan, M. J.

    2003-01-01

    A comparison is presented of the characteristics and production requirements of a variety of materials used to produce sintered soft magnetic parts. These include pure iron, phosphorous-iron, silicon-iron, nickel-iron, and cobalt-iron, together with new coated materials based on encapsulated iron powders. In these bonded materials an organic and/or inorganic insulator is used to coat the metallic powder particles giving a magnetic composite. The suitability of the different materials for use in both direct and alternating current applications is reviewed, and examples are provided of their application in both the automotive and other sectors. The results of a comparative study of motors using stators and rotors based on both conventional laminated materials and the insulated iron powders are presented, in which the new materials show advantages of reduced hysteresis losses at high frequencies, and isotropy of magnetic properties. Nevertheless, the applications of these materials in electrical motors requires the modification of existing designs.

  8. Bulk nanocrystalline Al85Ni10La5 alloy fabricated by spark plasma sintering of atomized amorphous powders

    International Nuclear Information System (INIS)

    Sasaki, T.T.; Hono, K.; Vierke, J.; Wollgarten, M.; Banhart, J.

    2008-01-01

    Amorphous Al 85 Ni 10 La 5 powders were consolidated to cylindrical samples by spark plasma sintering (SPS), and their microstructures and mechanical properties were investigated. When the powders were consolidated below the crystallization temperature, an amorphous phase was retained in the consolidated sample. Sintering above the crystallization temperature caused full crystallization. The Vickers hardness of the amorphous-containing sample was about 350 HV in the as-sintered state and increased up to 450 HV by a subsequent heat treatment just below the crystallization temperature. The highest hardness was achieved in a nanocrystalline microstructure. Compression tests revealed the brittle nature of the consolidated samples although the fracture and yield strength was higher than 1 GPa. The brittleness is due to the low relative density of the amorphous-containing samples and the presence of a large amount of intermetallic compounds in the fully crystallized sample

  9. Nanocrystalline Al7075+1 wt % Zr Alloy Prepared Using Mechanical Milling and Spark Plasma Sintering.

    Czech Academy of Sciences Publication Activity Database

    Molnárová, O.; Málek, P.; Veselý, J.; Šlapáková, M.; Minárik, P.; Lukáč, František; Chráska, Tomáš; Novák, P.; Průša, F.

    2017-01-01

    Roč. 10, č. 9 (2017), č. článku 1105. ISSN 1996-1944 R&D Projects: GA ČR(CZ) GA15-15609S Institutional support: RVO:61389021 Keywords : gas atomization * mechanical milling * spark plasma sintering * microstructure * microhardness * recrystallization Subject RIV: JG - Metallurgy OBOR OECD: Materials engineering Impact factor: 2.654, year: 2016 http://www.readcube.com/articles/10.3390/ma10091105

  10. Studies on the synthesis of nanocrystalline Y{sub 2}O{sub 3} and ThO{sub 2} through volume combustion and their sintering

    Energy Technology Data Exchange (ETDEWEB)

    Sanjay Kumar, D. [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Ananthasivan, K., E-mail: asivan@igcar.gov.in [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Venkata Krishnan, R. [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Amirthapandian, S. [Material Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Dasgupta, Arup [Microscopy and Thermo-Physical Property Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India)

    2016-10-15

    Volume combustion was observed in the auto-ignition of the citrate gels containing the nitrates of yttrium/thorium for the first time in mixture with a fuel (citric acid) to oxidant (Y{sup 3+} or Th{sup 4+} nitrate) ratio close to that demanded by the stoichiometry. These nanocrystalline powders were characterized for their bulk density, specific surface area, particle size distribution, carbon residue and X-ray crystallite size and were sintered by both the conventional and the two-step method. The maximum relative sintered density of Y{sub 2}O{sub 3} was 98.9% TD. The sintered density of thoria (97.8% TD) is the highest among the values reported so far, for nanocrystalline ThO{sub 2}. Characterization of the pellets and powders by using scanning electron microscopy and transmission electron microscopy reaffirmed nanocrystallinity and that the sintered pellets comprised faceted sintered grains. The two-step sintering was found to restrict “runaway” sintering. - Highlights: • Scaled-up synthesis of nanocrystalline Y{sub 2}O{sub 3} and ThO{sub 2} using citrate gel-combustion method. • VCR was observed at a fuel to nitrate ratio (R) of 0.125 and 0.17 in mixtures containing Th(NO{sub 3}){sub 4} and Y(NO{sub 3}){sub 3} respectively. • The calcined powders were compacted and sintered by using a novel two-step sintering method. • Sintered densities as high as 97.8% T.D. (ThO{sub 2}, T{sub H} = 0.48) and 98.9% T.D. (Y{sub 2}O{sub 3}, T{sub H} = 0.61) were obtained.

  11. Microstructure and property evolution of isotropic and anisotropic NdFeB magnets fabricated from nanocrystalline ribbons by spark plasma sintering and hot deformation

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Z W; Huang, H Y; Yu, H Y; Zhong, X C; Zeng, D C [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Gao, X X; Zhu, J, E-mail: zwliu@scut.edu.cn [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China)

    2011-01-19

    Isotropic and anisotropic NdFeB magnets were synthesized by spark plasma sintering (SPS) and SPS+HD (hot deformation), respectively, using melt-spun ribbons as the starting materials. Spark plasma sintered magnets sintered at low temperatures (<700 {sup 0}C) almost maintained the uniform fine grain structure inherited from rapid quenching. At higher temperatures, due to the local high-temperature field caused by the spark plasma discharge, the grain growth occurred at the initial particle surfaces and the coarse grain zones formed in the vicinity of the particle boundaries. Since the interior of the particles maintained the fine grain structure, a distinct two-zone structure was formed in the spark plasma sintered magnets. The SPS temperature and pressure have important effects on the widths of coarse and fine grain zones, as well as the grain sizes in two zones. The changes in grain structure led to variations in the magnetic properties. By employing low SPS temperature and high pressure, high-density magnets with negligible coarse grain zone and an excellent combination of magnetic properties can be obtained. An anisotropic magnet with a maximum energy product of {approx}30 MG Oe was produced by the SPS+HD process. HD at 750 {sup 0}C did not lead to obvious grain growth and the two-zone structure still existed in the hot deformed magnets. Intergranular exchange coupling was demonstrated in the spark plasma sintered magnets and was enhanced by the HD process, which reduced the coercivity. Good temperature stability was manifested by low temperature coefficients of remanence and coercivity. The results indicated that nanocrystalline NdFeB magnets without significant grain growth and with excellent properties could be obtained by SPS and HD processes.

  12. Fabrication of 200 mm Diameter Sintering Body of Skutterudite Thermoelectric Material by Spark Plasma Sintering

    Science.gov (United States)

    Tomida, T.; Sumiyoshi, A.; Nie, G.; Ochi, T.; Suzuki, S.; Kikuchi, M.; Mukaiyama, K.; Guo, J. Q.

    2017-05-01

    Filled skutterudite is a promising material for thermoelectric power generation because its ZT value is relatively high. However, mass production of high-performance thermoelectric materials remains a challenge. This study focused on the sintering process of thermoelectric materials. Large-diameter n-type (Yb or La, Ca, Al, Ga, In)0.8(Co, Fe)4Sb12 skutterudite sintering bodies with a small thickness were successfully produced by the spark plasma sintering (SPS) method. When direct current flows through the thermoelectric sintering body during the SPS pulse, the Peltier effect causes a temperature difference within the sintering body. To eliminate the Peltier effect, an electrical insulating material was inserted between the punch (electrode) and the sintering body. In this way, an n-type La-filled skutterudite sample with a diameter of 200 mm, thickness of 21 mm, and weight of 5 kg was successfully produced. The thermoelectric properties and microstructures of the sample were almost the same throughout the whole sintering body, and the dimensionless figure of merit reached 1.0 at 773 K.

  13. Model for temperature-dependent magnetization of nanocrystalline materials

    Energy Technology Data Exchange (ETDEWEB)

    Bian, Q.; Niewczas, M. [Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario L8S4M1 (Canada)

    2015-01-07

    A magnetization model of nanocrystalline materials incorporating intragrain anisotropies, intergrain interactions, and texture effects has been extended to include the thermal fluctuations. The method relies on the stochastic Landau–Lifshitz–Gilbert theory of magnetization dynamics and permits to study the magnetic properties of nanocrystalline materials at arbitrary temperature below the Currie temperature. The model has been used to determine the intergrain exchange constant and grain boundary anisotropy constant of nanocrystalline Ni at 100 K and 298 K. It is found that the thermal fluctuations suppress the strength of the intergrain exchange coupling and also reduce the grain boundary anisotropy. In comparison with its value at 2 K, the interparticle exchange constant decreases by 16% and 42% and the grain boundary anisotropy constant decreases by 28% and 40% at 100 K and 298 K, respectively. An application of the model to study the grain size-dependent magnetization indicates that when the thermal activation energy is comparable to the free energy of grains, the decrease in the grain size leads to the decrease in the magnetic permeability and saturation magnetization. The mechanism by which the grain size influences the magnetic properties of nc–Ni is discussed.

  14. Electron holography of Fe-based nanocrystalline magnetic materials (invited)

    International Nuclear Information System (INIS)

    Shindo, Daisuke; Park, Young-Gil; Gao, Youhui; Park, Hyun Soon

    2004-01-01

    Magnetic domain structures of nanocrystalline magnetic materials were extensively investigated by electron holography with a change in temperature or magnetic field applied. In both soft and hard magnetic materials, the distribution of lines of magnetic flux clarified in situ by electron holography was found to correspond well to their magnetic properties. An attempt to produce a strong magnetic field using a sharp needle made of a permanent magnet, whose movement is controlled by piezo drives has been presented. This article demonstrates that the attempt is promising to investigate the magnetization process of hard magnetic materials by electron holography

  15. Microstructure and mechanical properties of nanocrystalline high strength Al-Mg-Si (AA6061) alloy by high energy ball milling and spark plasma sintering

    International Nuclear Information System (INIS)

    Rana, Jatinkumar Kumar; Sivaprahasam, D.; Seetharama Raju, K.; Subramanya Sarma, V.

    2009-01-01

    In the present paper, the microstructure and mechanical properties of nanostructured Al-Mg-Si based AA6061 alloy obtained by high energy ball milling and spark plasma sintering were reported. Gas atomized microcrystalline powder of AA6061 alloy was ball milled under wet condition at room temperature to obtain nanocrystalline powder with grain size of ∼30 nm. The nanocrystalline powder was consolidated to fully dense compacts by spark plasma sintering (SPS) at 500 deg. C. The grain size after SPS consolidation was found to be ∼85 nm. The resultant SPS compacts exhibited microhardness of 190-200 HV 100g , compressive strength of ∼800 MPa and strain to fracture of ∼15%.

  16. Fabrication of Mg2Si thermoelectric materials by mechanical alloying and spark-plasma sintering process.

    Science.gov (United States)

    Lee, Chung-Hyo; Lee, Seong-Hee; Chun, Sung-Yong; Lee, Sang-Jin

    2006-11-01

    A mixture of pure Mg and Si powders with an atomic ratio 2:1 has been subjected to mechanical alloying (MA) at room temperature to prepare the Mg2Si thermoelectric material. Mg2Si intermetallic compound with a grain size of 50 nm can be obtained by MA of Mg66.7Si33.3 powders for 60 hours and subsequently annealed at 620 degrees C. Consolidation of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies up to 800-900 degrees C under 50 MPa. The shrinkage of consolidated samples during SPS was significant at about 250 degrees and 620 degrees C. X-ray diffraction data shows that the SPS compact from 60 h MA powders consolidated up to 800 degrees C consists of only nanocrystalline Mg2Si compound with a grain size of 100 nm.

  17. A variational multiscale constitutive model for nanocrystalline materials

    KAUST Repository

    Gurses, Ercan

    2011-03-01

    This paper presents a variational multi-scale constitutive model in the finite deformation regime capable of capturing the mechanical behavior of nanocrystalline (nc) fcc metals. The nc-material is modeled as a two-phase material consisting of a grain interior phase and a grain boundary effected zone (GBAZ). A rate-independent isotropic porous plasticity model is employed to describe the GBAZ, whereas a crystal-plasticity model which accounts for the transition from partial dislocation to full dislocation mediated plasticity is employed for the grain interior. The constitutive models of both phases are formulated in a small strain framework and extended to finite deformation by use of logarithmic and exponential mappings. Assuming the rule of mixtures, the overall behavior of a given grain is obtained via volume averaging. The scale transition from a single grain to a polycrystal is achieved by Taylor-type homogenization where a log-normal grain size distribution is assumed. It is shown that the proposed model is able to capture the inverse HallPetch effect, i.e., loss of strength with grain size refinement. Finally, the predictive capability of the model is validated against experimental results on nanocrystalline copper and nickel. © 2010 Elsevier Ltd. All rights reserved.

  18. Preparation and mechanical properties of ultra-high-strength nanocrystalline metals

    Czech Academy of Sciences Publication Activity Database

    Marek, I.; Vojtěch, D.; Michalcová, A.; Kubatík, Tomáš František

    2015-01-01

    Roč. 15, č. 4 (2015), s. 596-600 ISSN 1213-2489 Institutional support: RVO:61389021 Keywords : Mechanical properties * Nanocrystalline materials * Selective leaching * Silver * Spark plasma sintering Subject RIV: JG - Metallurgy

  19. Characterization and Application of Colloidal Nanocrystalline Materials for Advanced Photovoltaics

    Science.gov (United States)

    Bhandari, Khagendra P.

    Solar energy is Earth's primary source of renewable energy and photovoltaic solar cells enable the direct conversion of sunlight into electricity. Crystalline silicon solar cells and modules have dominated photovoltaic technology from the beginning and they now constitute more than 90% of the PV market. Thin film (CdTe and CIGS) solar cells and modules come in second position in market share. Some organic, dye-sensitized and perovskite solar cells are emerging in the market but are not yet in full commercial scale. Solar cells made from colloidal nanocrystalline materials may eventually provide both low cost and high efficiency because of their promising properties such as high absorption coefficient, size tunable band gap, and quantum confinement effect. It is also expected that the greenhouse gas emission and energy payback time from nanocrystalline solar PV systems will also be least compared to all other types of PV systems mainly due to the least embodied energy throughout their life time. The two well-known junction architectures for the fabrication of quantum dot based photovoltaic devices are the Schottky junction and heterojunction. In Schottky junction cells, a heteropartner semiconducting material is not required. A low work function metal is used as the back contact, a transparent conducting layer is used as the front contact, and the layer of electronically-coupled quantum dots is placed between these two materials. Schottky junction solar cells explain the usefulness of nanocrystalline materials for high efficiency heterojunction solar cells. For heterojunction devices, n-type semiconducting materials such as ZnO , CdS or TiO2 have been used as suitable heteropartners. Here, PbS quantum dot solar cells were fabricated using ZnO and CdS semiconductor films as window layers. Both of the heteropartners are sputter-deposited onto TCO coated glass substrates; ZnO was deposited with the substrate held at room temperature and for CdS the substrate was at 250

  20. Magnetic and structural properties of spark plasma sintered nanocrystalline NdFeB-powders

    Energy Technology Data Exchange (ETDEWEB)

    Wuest, H., E-mail: holger.wuest@de.bosch.com [Robert Bosch GmbH, Postfach 10 60 50, 70049 Stuttgart (Germany); Bommer, L., E-mail: lars.bommer@de.bosch.com [Robert Bosch GmbH, Postfach 10 60 50, 70049 Stuttgart (Germany); Weissgaerber, T., E-mail: thomas.weissgaerber@ifam-dd.fraunhofer.de [Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM), Branch Lab Dresden, Winterbergstraße 28, 01277 Dresden (Germany); Kieback, B., E-mail: bernd.kieback@ifam-dd.fraunhofer.de [Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM), Branch Lab Dresden, Winterbergstraße 28, 01277 Dresden (Germany); Technische Universität Dresden, Institute for Materials Science, Helmholtzstraße 7, 01069 Dresden (Germany)

    2015-10-15

    Near-stoichiometric NdFeB melt-spun ribbons have been subjected to spark plasma sintering varying the process temperature T{sub SPS} and pressure p{sub SPS} between 600 and 800 °C and 50–300 MPa, respectively. Produced bulk magnets were analyzed regarding microstructure and magnetic properties. For all samples the intrinsic coercivity H{sub c,J} gradually decreases with increasing sintering temperature and pressure, while residual induction B{sub r} increases simultaneously with sample density. Densities close to the theoretical limit were achieved for p{sub SPS}≥90 MPa and T{sub SPS}≥650 °C. With increasing T{sub SPS} precipitations of Nd-rich and Fe-rich phases have been observed as a result of a decomposition of the hard magnetic Nd{sub 2}Fe{sub 14}B phase. Under optimum sintering conditions of p{sub SPS}=300 MPa and T{sub SPS}=650 °C high-density bulk magnets with H{sub c,J}=652 kA/m, B{sub r}=0.86 T and (BH){sub max}=106 kJ/m{sup 3} have been produced. - Highlights: • Consolidation close to the theoretical density for p{sub SPS}≥90 MPa and T{sub SPS}≥650 °C. • Highest (BH){sub max} of 106 kJ/m{sup 3} for p{sub SPS}=300 MPa and T{sub SPS}=650 °C with 98% theo. • H{sub c,J} gradually decreases with increasing T{sub SPS}, while B{sub r} increases simultaneously with. • With increasing T{sub SPS}, Nd- and Fe-rich precipitations are observed. • Reduction in t{sub SPS} is economic but does not increase (BH){sub max} significantly.

  1. New atom probe approaches to studying segregation in nanocrystalline materials

    Energy Technology Data Exchange (ETDEWEB)

    Samudrala, S.K.; Felfer, P.J.; Araullo-Peters, V.J. [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); The Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); Cao, Y.; Liao, X.Z. [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); Cairney, J.M., E-mail: julie.cairney@sydney.edu.au [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); The Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia)

    2013-09-15

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. - Highlights: ► New data treatment methods allow delineation of grain boundaries, even without segregation. ► Proxigrams calculated from the surfaces accurately show the extent of segregation. ► Tessellation of the data volume can be used to map the Gibbsian interfacial excess.

  2. New atom probe approaches to studying segregation in nanocrystalline materials

    International Nuclear Information System (INIS)

    Samudrala, S.K.; Felfer, P.J.; Araullo-Peters, V.J.; Cao, Y.; Liao, X.Z.; Cairney, J.M.

    2013-01-01

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. - Highlights: ► New data treatment methods allow delineation of grain boundaries, even without segregation. ► Proxigrams calculated from the surfaces accurately show the extent of segregation. ► Tessellation of the data volume can be used to map the Gibbsian interfacial excess

  3. New atom probe approaches to studying segregation in nanocrystalline materials.

    Science.gov (United States)

    Samudrala, S K; Felfer, P J; Araullo-Peters, V J; Cao, Y; Liao, X Z; Cairney, J M

    2013-09-01

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. Copyright © 2013 Elsevier B.V. All rights reserved.

  4. Effective elastic properties of sintered materials with branched cracks

    Science.gov (United States)

    Fedelinski, Piotr

    2018-01-01

    The aim of work is analysis of sintered materials with branched cracks growing from the voids situated at corners of fibers. The material is modelled as a two-dimensional linear-elastic structure using the boundary element method (BEM). The materials without voids and with voids having different shapes are considered. The influence of lengths of cracks and shapes of voids on stress intensity factors (SIF) and effective elastic properties (the Young modulus and the Poisson ratio) are studied. The overall properties of the sintered materials are determined by considering the representative volume element (RVE) with large number of branched cracks. The sensitivity of effective elastic properties on boundary conditions imposed on the RVE is studied.

  5. Properties and processing of nanocrystalline materials. Quarterly report

    Energy Technology Data Exchange (ETDEWEB)

    Valiev, R.Z.

    1996-01-22

    The present Report completes the investigations in the frame of the project for the first year. It is important to estimate our achievements in the investigation of properties of nanocrystalline materials obtained by severe plastic deformation and their production. We think that the main results obtained can be summarized as follows: (1) We performed an improvement of the die-set for equal channel (ECA) pressing and torsion under high pressure with the aim to increase dimensions of the samples produced and to conduct processing of low ductile materials. (2) It was established that in pure metals severe plastic deformation led to the formation of an ultra fine-grained structure with a mean grain size of 100-200 nm, while in alloys due to severe plastic deformation and/or special methods of treatment (a decrease in the temperature of deformation, an increase of the pressure applied etc.) the grain size could be decreased down to a few tens of manometers.

  6. Spark Plasma Sintering (SPS) for Nanostructured Smart Materials

    Science.gov (United States)

    2006-02-05

    ferromagnetic SMA composites, piezo-composites with and without functionally graded microstructure( FGM ), a new active materials such as piezo-SMA composites...without functionally graded microstructure( FGM ), a new active materials such as piezo-SMA composites. These composites will be used for higher performance...g) Sintering Ambience Air. vacuum or inert gas (h) Viewing Windows 0 50mm A O80mm quartz glass with individual protecting plates Wi) Vacuum Neters

  7. Novel sintered ceramic materials incorporated with EAF carbon steel slag

    Science.gov (United States)

    Karayannis, V.; Ntampegliotis, K.; Lamprakopoulos, S.; Papapolymerou, G.; Spiliotis, X.

    2017-01-01

    In the present research, novel sintered clay-based ceramic materials containing electric arc furnace carbon steel slag (EAFC) as a useful admixture were developed and characterized. The environmentally safe management of steel industry waste by-products and their valorization as secondary resources into value-added materials towards circular economy have attracted much attention in the last years. EAF Carbon steel slag in particular, is generated during the manufacture of carbon steel. It is a solid residue mainly composed of rich-in- Fe, Ca and Si compounds. The experimental results show that the beneficial incorporation of lower percentages of EAFC up to 6%wt. into ceramics sintered at 950 °C is attained without significant variations in sintering behavior and physico-mechanical properties. Further heating up to 1100 °C strongly enhances the densification of the ceramic microstructures, thus reducing the porosity and strengthening their mechanical performance. On the other side, in terms of thermal insulation behavior as well as energy consumption savings and production cost alleviation, the optimum sintering temperature appears to be 950 °C.

  8. Effects of Milling Atmosphere and Increasing Sintering Temperature on the Magnetic Properties of Nanocrystalline Ni0.36Zn0.64Fe2O4

    Directory of Open Access Journals (Sweden)

    Abdollah Hajalilou

    2015-01-01

    Full Text Available Nanocrystalline Ni0.36Zn0.64Fe2O4 was synthesized by milling a powder mixture of Zn, NiO, and Fe2O3 in a high-energy ball mill for 30 h under three different atmospheres of air, argon, and oxygen. After sintering the 30 h milled samples at 500°C, the XRD patterns suggested the formation of a single phase of Ni-Zn ferrite. The XRD results indicated the average crystallite sizes to be 15, 14, and 16 nm, respectively, for the 30 h milled samples in air, argon, and oxygen atmospheres sintered at 500°C. From the FeSEM micrographs, the average grain sizes of the mentioned samples were 83, 75, and 105 nm, respectively, which grew to 284, 243, and 302 nm after sintering to 900°C. A density of all the samples increased while a porosity decreased by elevating sintering temperature. The parallel evolution of changes in magnetic properties, due to microstructural variations with changes in the milling atmosphere and sintering temperature in the rage of 500–900°C with 100°C increments, is also studied in this work.

  9. Adjustment of Part Properties for an Elastomeric Laser Sintering Material

    Science.gov (United States)

    Wegner, A.; Ünlü, T.

    2018-03-01

    Laser sintering of polymers is gaining more and more importance within the field of small series productions. Polyamide 12 is predominantly used, although a variety of other materials are also available for the laser sintering process. For example, elastomeric, rubberlike materials offer very different part property profiles. Those make the production of flexible parts like, e.g., sealings, flexible tubes or shoe soles possible because they offer high part ductility and low hardness. At the chair for manufacturing technology, a new elastomeric laser sintering material has been developed and then commercialized by a spin-off from university. The aim of the presented study was the analysis of the new material's properties. Proof was found that Shore hardness can be modified by varying the parameter settings. Therefore, the correlation between process parameters, energy input, Shore hardness and other part properties like mechanical properties were analyzed. Based on these results, suitable parameter settings were established which lead to the possibility of producing parts with different Shore hardnesses.

  10. Spark Plasma Sintering for Nanostructured Smart Materials

    Science.gov (United States)

    2009-03-02

    material. The above relationship shows that at low frequencies a piezoelectric plate can be assumed to behave like a parallel plate capacitor . Hence...predicted load from, Eq.(4.37). By assuming as low frequencies the PZT behaves like a parallel plate capacitor , power available from PZT can be...However, in this case EDAXS analysis showed that the bulges were likely due to agglomeration of NiTi particles in the fiber. The large diameter of the

  11. High Pressure X-Ray Diffraction Studies of Nanocrystalline Materials

    Science.gov (United States)

    Palosz, B.; Stel'makh, S.; Grzanka, E.; Gierlotka, S.; Palosz, W.

    2004-01-01

    Experimental evidence obtained for a variety of nanocrystalline materials suggest that the crystallographic structure of a very small size particle deviates from that in the bulk crystals. In this paper we show the effect of the surface of nanocrystals on their structure by the analysis of generation and distribution of macro- and micro-strains at high pressures and their dependence on the grain size in nanocrystalline powders of Sic. We studied the structure of Sic nanocrystals by in-situ high-pressure powder diffraction technique using synchrotron and neutron sources and hydrostatic or isostatic pressure conditions. The diffraction measurements were done in HASYLAB at DESY using a Diamond Anvil Cell (DAC) in the energy dispersive geometry in the diffraction vector range up to 3.5 - 4/A and under pressures up to 50 GPa at room temperature. In-situ high pressure neutron diffraction measurements were done at LANSCE in Los Alamos National Laboratory using the HIPD and HIPPO diffractometers with the Paris-Edinburgh and TAP-98 cells, respectively, in the diffraction vector range up to 26 Examination of the response of the material to external stresses requires nonstandard methodology of the materials characterization and description. Although every diffraction pattern contains a complete information on macro- and micro-strains, a high pressure experiment can reveal only those factors which contribute to the characteristic diffraction patterns of the crystalline phases present in the sample. The elastic properties of powders with the grain size from several nm to micrometers were examined using three methodologies: (l), the analysis of positions and widths of individual Bragg reflections (used for calculating macro- and micro-strains generated during densification) [I], (2). the analysis of the dependence of the experimental apparent lattice parameter, alp, on the diffraction vector Q [2], and (3), the atomic Pair Distribution Function (PDF) technique [3]. The results

  12. Understanding and controlling low-temperature aging of nanocrystalline materials.

    Energy Technology Data Exchange (ETDEWEB)

    Battaile, Corbett Chandler; Boyce, Brad Lee; Brons, Justin G.; Foiles, Stephen Martin; Hattar, Khalid Mikhiel; Holm, Elizabeth A; Padilla, Henry A.,; Sharon, John Anthony; Thompson, Gregory B.

    2013-10-01

    Nanocrystalline copper lms were created by both repetitive high-energy pulsed power, to produce material without internal nanotwins; and pulsed laser deposition, to produce nan- otwins. Samples of these lms were indented at ambient (298K) and cryogenic temperatures by immersion in liquid nitrogen (77K) and helium (4K). The indented samples were sectioned through the indented regions and imaged in a scanning electron microscope. Extensive grain growth was observed in the lms that contained nanotwins and were indented cryogenically. The lms that either lacked twins, or were indented under ambient conditions, were found to exhibit no substantial grain growth by visual inspection. Precession transmission elec- tron microscopy was used to con rm these ndings quantitatively, and show that 3 and 7 boundaries proliferate during grain growth, implying that these interface types play a key role in governing the extensive grain growth observed here. Molecular dynamics sim- ulations of the motion of individual grain boundaries demonstrate that speci c classes of boundaries - notably 3 and 7 - exhibit anti- or a-thermal migration, meaning that their mobilities either increase or do not change signi cantly with decreasing temperature. An in-situ cryogenic indentation capability was developed and implemented in a transmission electron microscope. Preliminary results do not show extensive cryogenic grain growth in indented copper lms. This discrepancy could arise from the signi cant di erences in con g- uration and loading of the specimen between the two approaches, and further research and development of this capability is needed.

  13. Strengthening of porous matrix materials with evaporation/condensation sintering for composite materials applications

    Science.gov (United States)

    Haslam, Jeffery John

    1998-12-01

    The need for improved fuel economy and reduced environmental emissions from power turbines has prompted the development of high temperature fiber composite materials. One use of these materials is for liners of the hot combustion regions of jet engines and land based power turbines. Stability of the composite materials against oxidative damage during long term use at high temperatures has motivated recent research into fiber composite materials composed entirely of oxide ceramics. All-oxide fiber reinforced composites containing porous, strongly bonded matrices have become of interest. The porosity provides for crack deflection along the fibers to prevent catastrophic failure of the fiber reinforcements. A new application of a processing method that produces evaporation/condensation sintering was employed to prevent shrinkage of the matrix. This processing method and the properties of the matrix, fibers, and composite were evaluated in this work. Producing a matrix without shrinkage is important to prevent undesirable crack-like voids from forming in the matrix. These voids are caused by constraint against shrinkage by the fiber reinforcements. Dry hydrogen chloride gas produced a reactive gas atmosphere that was used to sinter the zirconia particles with minimal shrinkage because the gas promotes evaporation/condensation sintering with zirconia. Sintering of samples that did not contain fiber reinforcements was studied to evaluate the properties of the matrix material. The sintering of monoclinic, tetragonal, and cubic zirconias in the reactive gas atmosphere was compared. Additions of mullite (which did not sinter significantly at processing temperatures) further reduced the shrinkage. The effects of the processing conditions on the sintering shrinkage, microstructure development, and mechanical properties were studied. Cubic and monoclinic zirconia coarsened significantly in the HCl gas sintering atmosphere. The coarsening of the particles during the sintering

  14. Density determination of sintered ceramic nuclear fuel materials

    International Nuclear Information System (INIS)

    Landspersky, H.; Medek, J.

    1980-01-01

    The feasibility was tested of using solids for pycnometric determination of the density of uranium dioxide-based sintered ceramic fuel materials manufactured by the sol-gel method in the shape of spherical particles of 0.7 to 1.0 mm in size and of particles smaller than 200 μm. For fine particles, this is the only usable method of determining their density which is a very important parameter of the fine fraction when it is employed for the manufacture of fuel elements by vibration compacting. The method consists in compacting a mixture of pycnometric material and dispersed particles of uranium dioxide, determining the size and weight of the compact, and in calculating the density of the material measured from the weight of the oxide sample in the mixture. (author)

  15. One step sintering of homogenized bauxite raw material and kinetic study

    Science.gov (United States)

    Gao, Chang-he; Jiang, Peng; Li, Yong; Sun, Jia-lin; Zhang, Jun-jie; Yang, Huan-ying

    2016-10-01

    A one-step sintering process of bauxite raw material from direct mining was completed, and the kinetics of this process was analyzed thoroughly. The results show that the sintering kinetics of bauxite raw material exhibits the liquid-phase sintering behavior. A small portion of impurities existed in the raw material act as a liquid phase. After X-ray diffraction analyses, scanning electron microscopy observations, and kinetics calculations, sintering temperature and heating duration were determined as the two major factors contributing to the sintering process and densification of bauxite ore. An elevated heating temperature and longer duration favor the densification process. The major obstacle for the densification of bauxite material is attributed to the formation of the enclosed blowhole during liquid-phase sintering.

  16. Hot deformed anisotropic nanocrystalline NdFeB based magnets prepared from spark plasma sintered melt spun powders

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Y.H.; Huang, Y.L. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Liu, Z.W., E-mail: zwliu@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Zeng, D.C. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Ma, S.C.; Zhong, Z.C. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China)

    2013-09-01

    Highlights: • Microstructure evolution and its influence on the magnetic properties were investigated. • The increase of stray field and weakening of domain-wall pinning effects were the main reasons of the decrease of the coercivity with increasing the compression ratio. • The influences of non-uniform plastic deformation on the microstructure and magnetic properties were investigated. • Magnetic properties and temperature coefficient of coercivity are indeed very promising without heavy rare earth elements. -- Abstract: Anisotropic magnets were prepared by spark plasma sintering (SPS) followed by hot deformation (HD) using melt-spun powders as the starting material. Good magnetic properties with the remanence J{sub r} > 1.32 T and maximum of energy product (BH){sub max} > 303 kJ/m{sup 3} have been obtained. The microstructure evolution during HD and its influence on the magnetic properties were investigated. The fine grain zone and coarse grain zone formed in the SPS showed different deformation behaviors. The microstructure also had an important effect on the temperature coefficients of coercivity. A strong domain-wall pinning model was valid to interpret the coercivity mechanism of the HDed magnets. The increase of stray field and weakening of domain-wall pinning effects were the main reasons of the decrease of the coercivity with increasing the compression ratio. The influences of non-uniform plastic deformation on the microstructure and magnetic properties were investigated. The polarization characteristics of HDed magnets were demonstrated. It was found out that the HDed magnets had better corrosion resistance than the counterpart sintered magnet.

  17. Nanocrystalline nickel as a material with high hydrogen storage capacity

    Czech Academy of Sciences Publication Activity Database

    Vojtěch, D.; Michalcová, A.; Klementová, Mariana; Šerák, J.; Morťaniková, M.

    2009-01-01

    Roč. 63, č. 12 (2009), s. 1074-1076 ISSN 0167-577X Institutional research plan: CEZ:AV0Z40320502 Keywords : electron microscopy * nanomaterials * nano-crystalline nickel Subject RIV: CA - Inorganic Chemistry Impact factor: 1.940, year: 2009

  18. High Pressure X-Ray Diffraction Studies on Nanocrystalline Materials

    Science.gov (United States)

    Palosz, B.; Stelmakh, S.; Grzanka, E.; Gierlotka, S.; Pielaszek, R.; Bismayer, U.; Werner, S.; Palosz, W.

    2003-01-01

    Application of in situ high pressure powder diffraction technique for examination of specific structural properties of nanocrystals based on the experimental data of SiC nanocrystalline powders of 2 to 30 nrn diameter in diameter is presented. Limitations and capabilities of the experimental techniques themselves and methods of diffraction data elaboration applied to nanocrystals with very small dimensions (nanoparticles of different grain size.

  19. Development of Bulk Nanocrystalline Cemented Tungsten Carbide for Industrial Applicaitons

    Energy Technology Data Exchange (ETDEWEB)

    Z. Zak Fang, H. Y. Sohn

    2009-03-10

    This report contains detailed information of the research program entitled "Development of Bulk Nanocrystalline Cemented Tungsten Carbide Materials for Industrial Applications". The report include the processes that were developed for producing nanosized WC/Co composite powders, and an ultrahigh pressure rapid hot consolidation process for sintering of nanosized powders. The mechanical properties of consolidated materials using the nanosized powders are also reported.

  20. Tool design and materials for electro sinter forging (ESF)

    DEFF Research Database (Denmark)

    Cannella, Emanuele; Nielsen, Chris Valentin

    A near net-shape forming process represents a suitable solution to obtain the final product by avoiding secondary machining processes. In this field, electro sinter forging is capable of accomplishing the advantages of sintering in a reduced amount of time. Classified as a high field mode (HFM...

  1. Synthesis, sintering and optical properties of CaMoO{sub 4}: A promising scheelite LTCC and photoluminescent material

    Energy Technology Data Exchange (ETDEWEB)

    Vidya, S.; Thomas, J.K. [Electronic Materials Research Laboratory, Department of Physics, Mar Ivanios College, Kerala (India); Solomon, S. [Department of Physics, St. John' s College, Anchal, Kerala (India)

    2012-06-15

    The synthesis of nanocrystalline calcium molybdate (CaMoO{sub 4}) through an autoigniting combustion technique is reported in this paper. The structural characterization of the as-prepared nanocrystallites were done by X-ray diffraction (XRD), Fourier transform Raman, and Fourier transform infrared (IR) spectroscopy and the morphological studies using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The studies reveal that the as-prepared powder itself was phase pure with tetragonal structure and of particle size 25 nm. The sample was sintered at a relatively low temperature of 775 C to a high density of {proportional_to}95% for the first time, without the use of any sintering aid. The optical bandgap energy calculated from the ultraviolet-visible absorption spectrum for the as-prepared and annealed sample was 3.72 and 3.99 eV, respectively. The photoluminescence spectra of the sample showed an intense emission in the green region (528 nm). The dielectric constant and loss factor of the sample at 5 MHz was found to be 11.00 and 6.40 x 10{sup -3} at room temperature. The temperature coefficient of dielectric constant was -95.04 pp/ C. These observations reveal that nanostructured CaMoO{sub 4} is a promising scheelite low-temperature co-fired ceramic (LTCC) and also an excellent luminescent material. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Powder-based synthesis of nanocrystalline material components for structural application. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Ilyuschenko, A.F.; Ivashko, V.S.; Okovity, V.A. [Powder Metallurgy Research Inst., Minsk (Belarus)] [and others

    1998-12-01

    Hydroxiapate spray coatings and substrates for implant production as well as multilayered metal ceramic coatings from nanocrystalline materials are a subject of the investigation. The work aims at the improvement of quality of said objects. This study has investigated the processes of hydroxiapatite powder production. Sizes, shapes and relief of initial HA powder surface are analyzed using SEM and TEM. Modes of HA plasma spraying on a substrate from titanium and associated compositions of traditional and nanocrystalline structure are optimized. The quality of the sprayed samples are studied using X-ray phase analysis and metallographic analysis. The results of investigations of bioceramic coating spraying on titanium are theoretically generalized, taking into account obtained experimental data. The results of investigations of ion-beam technology are presented for spraying multilayered coatings consisting of alternating metal-ceramic layers of nanocrystalline structure.

  3. Processing of Nanocrystalline Nitrides and Oxide Composites

    National Research Council Canada - National Science Library

    Ying, Jackie

    1998-01-01

    We have recently begun to investigate the chemical composition, specifically oxygen contamination, and sintering behavior of the nanocrystalline aluminum nitride synthesized in the forced flow reactor...

  4. THERMAL AND ELECTRIC FIELDS AT SPARK PLASMA SINTERING OF THERMOELECTRIC MATERIALS

    Directory of Open Access Journals (Sweden)

    L. P. Bulat

    2014-09-01

    Full Text Available Problem statement. Improvement of thermoelectric figure of merit is connected with the usage of nanostructured thermoelectric materials fabricated from powders by the spark plasma sintering (SPS method. Preservation of powder nanostructure during sintering is possible at optimum temperature modes of thermoelectrics fabrication. The choice of these modes becomes complicated because of anisotropic properties of semiconductor thermoelectric materials. The decision of the given problem by sintering process simulation demands the competent approach to the problem formulation, a correct specification of thermoelectric properties, the properties of materials forming working installation, and also corrects boundary conditions. The paper deals with the efficient model for sintering of thermoelectrics. Methods. Sintering process of the bismuth telluride thermoelectric material by means of SPS-511S installation is considered. Temperature dependences of electric and thermal conductivities of bismuth telluride, and also temperature dependences of installation elements materials are taken into account. It is shown that temperature distribution in the sample can be defined within the limits of a stationary problem. The simulation is carried out in the software product Comsol Multiphysics. Boundary conditions include convective heat exchange and also radiation under Stefan-Boltzmann law. Results. Computer simulation of electric and thermal processes at spark plasma sintering is carried out. Temperature and electric potential distributions in a sample are obtained at the sintering conditions. Determinative role of graphite compression mould in formation of the temperature field in samples is shown. The influence of geometrical sizes of a graphite compression mould on sintering conditions of nanostructured thermoelectrics is analyzed. Practical importance. The optimum sizes of a cylindrical compression mould for fabrication of volume homogeneous samples based on

  5. Implementation Challenges for Sintered Silicon Carbide Fiber Bonded Ceramic Materials for High Temperature Applications

    Science.gov (United States)

    Singh, M.

    2011-01-01

    During the last decades, a number of fiber reinforced ceramic composites have been developed and tested for various aerospace and ground based applications. However, a number of challenges still remain slowing the wide scale implementation of these materials. In addition to continuous fiber reinforced composites, other innovative materials have been developed including the fibrous monoliths and sintered fiber bonded ceramics. The sintered silicon carbide fiber bonded ceramics have been fabricated by the hot pressing and sintering of silicon carbide fibers. However, in this system reliable property database as well as various issues related to thermomechanical performance, integration, and fabrication of large and complex shape components has yet to be addressed. In this presentation, thermomechanical properties of sintered silicon carbide fiber bonded ceramics (as fabricated and joined) will be presented. In addition, critical need for manufacturing and integration technologies in successful implementation of these materials will be discussed.

  6. Mechanically induced self-propagating reaction and consequent consolidation for the production of fully dense nanocrystalline Ti55C45 bulk material

    International Nuclear Information System (INIS)

    Sherif El-Eskandarany, M.; Al-Hazza, Abdulsalam

    2014-01-01

    We employed a high-energy ball mill for the synthesis of nanograined Ti 55 C 45 powders starting from elemental Ti and C powders. The mechanically induced self-propagating reaction that occurred between the reactant materials was monitored via a gas atmosphere gas-temperature-monitoring system. A single phase of NaCl-type TiC was obtained after 5 h of ball milling. To decrease the powder and grain sizes, the material was subjected to further ball milling time. The powders obtained after 200 h of milling possessed spherical-like morphology with average particle and grain sizes of 45 μm and 4.2 nm, respectively. The end-products obtained after 200 h of ball milling time, were then consolidated into full dense compacts, using hot pressing and spark plasma sintering at 1500 and 34.5 MPa, with heating rates of 20 °C/min and 500 °C/min, respectively. Whereas hot pressing of the powders led to severe grain growth (∼ 436 nm in diameter), the as-spark plasma sintered powders maintained their nanograined characteristics (∼ 28 nm in diameter). The as-synthesized and as-consolidated powders were characterized, using X-ray diffraction, high-resolution electron microscopy, and scanning electron microscopy. The mechanical properties of the consolidated samples obtained via the hot pressing and spark plasma sintering techniques were characterized, using Vickers microhardness and non-destructive testing techniques. The Vickers hardness, Young's modulus, shear modulus and fracture toughness of as-spark plasma sintered samples were 32 GPa, 358 GPa, 151 GPa and 6.4 MPa·m 1/2 , respectively. The effects of the consolidation approach on the grain size and mechanical properties were investigated and are discussed. - Highlights: • Room-temperature synthesizing of NaCl-type TiC • Dependence on the grain size on the ball milling time • Fabrication of equiaxed nanocrystalline grains with a diameter of 4.2 nm • Fabrication of nanocrystalline bulk TiC material by SPS with

  7. Nanocrystalline material in toroidal cores for current transformer: analytical study and computational simulations

    Directory of Open Access Journals (Sweden)

    Benedito Antonio Luciano

    2005-12-01

    Full Text Available Based on electrical and magnetic properties, such as saturation magnetization, initial permeability, and coercivity, in this work are presented some considerations about the possibilities of applications of nanocrystalline alloys in toroidal cores for current transformers. It is discussed how the magnetic characteristics of the core material affect the performance of the current transformer. From the magnetic characterization and the computational simulations, using the finite element method (FEM, it has been verified that, at the typical CT operation value of flux density, the nanocrystalline alloys properties reinforce the hypothesis that the use of these materials in measurement CT cores can reduce the ratio and phase errors and can also improve its accuracy class.

  8. Selective laser sintering of calcium phosphate materials for orthopedic implants

    Science.gov (United States)

    Lee, Goonhee

    Two technologies, Solid Freeform Fabrication (SFF) and bioceramics are combined in this work to prepare bone replacement implants with complex geometry. SFF has emerged as a crucial technique for rapid prototyping in the last decade. Selective Laser Sintering (SLS) is one of the established SFF manufacturing processes that can build three-dimensional objects directly from computer models without part-specific tooling or human intervention. Meanwhile, there have been great efforts to develop implantable materials that can assist in regeneration of bone defects and injuries. However, little attention has been focused in shaping bones from these materials. The main thrust of this research was to develop a process that can combine those two separate efforts. The specific objective of this research is to develop a process that can construct bone replacement material of complex geometry from synthetic calcium phosphate materials by using the SLS process. The achievement of this goal can have a significant impact on the quality of health care in the sense that complete custom-fit bone and tooth structures suitable for implantation can be prepared within 24--48 hours of receipt of geometric information obtained either from patient Computed Tomographic (CT) data, from Computer Aided Design (CAD) software or from other imaging systems such as Magnetic Resonance Imaging (MRI) and Holographic Laser Range Imaging (HLRI). In this research, two different processes have been developed. First is the SLS fabrication of porous bone implants. In this effort, systematic procedures have been established and calcium phosphate implants were successfully fabricated from various sources of geometric information. These efforts include material selection and preparation, SLS process parameter optimization, and development of post-processing techniques within the 48-hour time frame. Post-processing allows accurate control of geometry and of the chemistry of calcium phosphate, as well as

  9. Analysis of wear in organic and sintered friction materials used in small wind energy converters

    Directory of Open Access Journals (Sweden)

    Jorge Alberto Lewis Esswein Junior

    2008-09-01

    Full Text Available Wind energy converters of small size used in isolated units to generate electrical energy must present low maintenance cost to such facilities economically viable. The aspect to be analyzed in cost reduction is the brake system, since in isolated systems the use of brake is more frequent reducing the brake pads life time. This study aims at analyzing the wear behavior of some materials used in brake pads. An organic material was analyzed comparing it with a commercial brake pad, and the sintered material was developed and tested. The materials behaviors were evaluated in both wear and friction coefficient. The sintered samples were made by powder metallurgy. The composition was compacted at 550 MPa and sintered in a furnace with controlled atmosphere to avoid oxidation. Despite the different compositions of the two types of materials, they presented a very similar wear; however, the sintered material presented a higher friction coefficient. An adjustment in the braking system of the wind generator might be proposed to use the sintered brake pad, due to its higher friction coefficient. Consequently, the braking action becomes lower, reducing the wear rate of the material.

  10. Grain growth control and transparency in spark plasma sintered self-doped alumina materials

    International Nuclear Information System (INIS)

    Suarez, M.; Fernandez, A.; Menendez, J.L.; Torrecillas, R.

    2009-01-01

    Doping alumina particles with aluminum alkoxides allows dense spark plasma sintered (SPSed) materials to be obtained that have a refined grain size compared to pure materials, which is critical for their transparency. An optical model considering pore and grain size distributions has been developed to obtain information about porosity in dense materials. This work suggests that the atomic diffusion mechanisms do not depend on the sintering technique. A reduction in the activation energy by a factor of 2 has been found in SPSed materials.

  11. Grain boundaries of nanocrystalline materials - their widths, compositions, and internal structures

    International Nuclear Information System (INIS)

    Fultz, B.; Frase, H.N.

    2000-01-01

    Nanocrystalline materials contain many atoms at and near grain boundaries. Sufficient numbers of Moessbauer probe atoms can be situated in grain boundary environments to make a clear contribution to the measured Moessbauer spectrum. Three types of measurements on nanocrystalline materials are reported here, all using Moessbauer spectrometry in conjunction with X-ray diffractometry, transmission electron microscopy, or small angle neutron scattering. By measuring the fraction of atoms contributing to the grain boundary component in a Moessbauer spectrum, and by knowing the grain size of the material, it is possible to deduce the average width of grain boundaries in metallic alloys. It is found that these widths are approximately 0.5 nm for fcc alloys and slightly larger than 1.0 nm for bcc alloys.Chemical segregation to grain boundaries can be measured by Moessbauer spectrometry, especially in conjunction with small angle neutron scattering. Such measurements on Fe-Cu and Fe 3 Si-Nb were used to study how nanocrystalline materials could be stabilized against grain growth by the segregation of Cu and Nb to grain boundaries. The segregation of Cu to grain boundaries did not stabilize the Fe-Cu alloys against grain growth, since the grain boundaries were found to widen and accept more Cu atoms during annealing. The Nb additions to Fe 3 Si did suppress grain growth, perhaps because of the low mobility of Nb atoms, but also perhaps because Nb atoms altered the chemical ordering in the alloy.The internal structure of grain boundaries in nanocrystalline materials prepared by high-energy ball milling is found to be unstable against internal relaxations at low temperatures. The Moessbauer spectra of the nanocrystalline samples showed changes in the hyperfine fields attributable to movements of grain boundary atoms. In conjunction with SANS measurements, the changes in grain boundary structure induced by cryogenic exposure and annealing at low temperature were found to be

  12. Material Evaluation and Process Optimization of CNT-Coated Polymer Powders for Selective Laser Sintering

    Directory of Open Access Journals (Sweden)

    Shangqin Yuan

    2016-10-01

    Full Text Available Multi-walled carbon nanotubes (CNTs as nano-reinforcements were introduced to facilitate the laser sintering process and enhance the thermal and mechanical properties of polymeric composites. A dual experimental-theoretical method was proposed to evaluate the processability and predict the process parameters of newly developed CNT-coated polyamide 12 (CNTs/PA12 powders. The thermal conductivity, melt viscosity, phase transition and temperature-dependent density and heat capacity of PA12 and CNTs/PA12 powders were characterized for material evaluation. The composite powders exhibited improved heat conduction and heat absorption compared with virgin polymer powders, and the stable sintering range of composite powders was extended and found to be favourable for the sintering process. The microstructures of sintered composites revealed that the CNTs remained at the powder boundaries and formed network architectures, which instantaneously induced the significant enhancements in tensile strength, elongation at break and toughness without sacrificing tensile modulus.

  13. Zirconium carbonitride pellets by internal sol gel and spark plasma sintering as inert matrix fuel material

    Science.gov (United States)

    Hedberg, Marcus; Cologna, Marco; Cambriani, Andrea; Somers, Joseph; Ekberg, Christian

    2016-10-01

    Inert matrix fuel is a fuel type where the fissile material is blended with a solid diluent material. In this work zirconium carbonitride microspheres have been produced by internal sol gel technique, followed by carbothermal reduction. Material nitride purities in the produced materials ranged from Zr(N0.45C0.55) to Zr(N0.74C0.26) as determined by X-ray diffraction and application of Vegard's law. The zirconium carbonitride microspheres have been pelletized by spark plasma sintering (SPS) and by conventional cold pressing and sintering. In all SPS experiments cohesive pellets were formed. Maximum final density reached by SPS at 1700 °C was 87% theoretical density (TD) compared to 53% TD in conventional sintering at 1700 °C. Pore sizes in all the produced pellets were in the μm scale and no density gradients could be observed by computer tomography.

  14. Sinterable powders

    International Nuclear Information System (INIS)

    Zanghi, J.S.; Kasprzyk, M.R.

    1979-01-01

    A description is given of sinterable powders and methods of producing sintered products using such powders. The powders consist of (a) a particulate ceramic material, e.g. SiC, having specified particle size and surface area; (b) a carbon source material, e.g. sugar or a phenol-formaldehyde resin; and (c) a residue from a solution of H 3 BO 3 , B 2 O 3 , or mixtures of these as sintering aid. (U.K.)

  15. Sol-gel synthesis of lithium metatitanate as tritium breeding material under different sintering conditions

    Science.gov (United States)

    Lu, Wei; Wang, Jing; Pu, Wenjing; Li, Kaiping; Ma, Shubing; Wang, Weihua

    2018-04-01

    Lithium metatitanate (Li2TiO3) is a promising tritium breeding material candidate for solid blanket of D-T fusion reactors, due to its high mechanical strength, chemical stability, and tritium release rate. In this paper, Li2TiO3 powder with homogeneous crystal structure is synthesized by sol-gel method. The chemical reactions in gel thermal cracking and sintering process are studied by thermo gravimetric/differential scanning calorimetry (TG-DSC). The relationship between the sintering condition and the particle/grain size is characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that below 673 K the gel precursor is completely decomposed and Li2TiO3 phase initially forms. The LiTiO2 by-product formed under the reductive atmosphere in muffle furnace, could be oxidized continually to Li2TiO3 at higher sintering temperature (≥1273 K) for longer sintering time (≥10 h). Both grain and particle sizes rely on a linear growth with the increase of sintering time at 1273 K. Over 1473 K, significant agglomerations exist among particles. The optimal sintering condition is selected as 1273 K for 10 h, for the purer Li2TiO3 phase (>99%), smaller grain and particle size.

  16. Evaluation of Surfactant-stabilized Nanocrystalline Metallic Materials

    Data.gov (United States)

    National Aeronautics and Space Administration — What are the key technical challenges? The materials will be brittle and the microstructural features will be ultrafine. Generating valid data from mechanical...

  17. Spark plasma sintering of pure and doped tungsten as plasma facing material

    Science.gov (United States)

    Autissier, E.; Richou, M.; Minier, L.; Naimi, F.; Pintsuk, G.; Bernard, F.

    2014-04-01

    In the current water cooled divertor concept, tungsten is an armour material and CuCrZr is a structural material. In this work, a fabrication route via a powder metallurgy process such as spark plasma sintering is proposed to fully control the microstructure of W and W composites. The effect of chemical composition (additives) and the powder grain size was investigated. To reduce the sintering temperature, W powders doped with a nano-oxide dispersion of Y2O3 are used. Consequently, the sintering temperature for W-oxide dispersed strengthened (1800 °C) is lower than for pure W powder. Edge localized mode tests were performed on pure W and compared to other preparation techniques and showed promising results.

  18. Formation of nanocrystalline surface layers in various metallic materials by near surface severe plastic deformation

    Directory of Open Access Journals (Sweden)

    Masahide Sato, Nobuhiro Tsuji, Yoritoshi Minamino and Yuichiro Koizumi

    2004-01-01

    Full Text Available The surface of the various kinds of metallic materials sheets were severely deformed by wire-brushing at ambient temperature to achieve nanocrystalline surface layer. The surface layers of the metallic materials developed by the near surface severe plastic deformation (NS-SPD were characterized by means of TEM. Nearly equiaxed nanocrystals with grain sizes ranging from 30 to 200 nm were observed in the near surface regions of all the severely scratched metallic materials, which are Ti-added ultra-low carbon interstitial free steel, austenitic stainless steel (SUS304, 99.99 wt.%Al, commercial purity aluminum (A1050 and A1100, Al–Mg alloy (A5083, Al-4 wt.%Cu alloy, OFHC-Cu (C1020, Cu–Zn alloy (C2600 and Pb-1.5%Sn alloy. In case of the 1050-H24 aluminum, the depth of the surface nanocrystalline layer was about 15 μm. It was clarified that wire-brushing is an effective way of NS-SPD, and surface nanocrystallization can be easily achieved in most of metallic materials.

  19. Neutron scattering from amorphous, disordered and nanocrystalline materials

    International Nuclear Information System (INIS)

    Price, D.L.

    1994-10-01

    The author has described the power of neutron diffraction and inelastic scattering techniques for determining the structure and dynamics of disordered systems, using the archetypal glass SiO 2 as a detailed example. Of course the field of amorphous and disordered systems contains a much greater variety of types of materials exhibiting a wide range of possible types of disorder. The author gives a brief review of the varieties of order and disorder exhibited by condensed matter

  20. A phenomenological variational multiscale constitutive model for intergranular failure in nanocrystalline materials

    KAUST Repository

    Siddiq, A.

    2013-09-01

    We present a variational multiscale constitutive model that accounts for intergranular failure in nanocrystalline fcc metals due to void growth and coalescence in the grain boundary region. Following previous work by the authors, a nanocrystalline material is modeled as a two-phase material consisting of a grain interior phase and a grain boundary affected zone (GBAZ). A crystal plasticity model that accounts for the transition from partial dislocation to full dislocation mediated plasticity is used for the grain interior. Isotropic porous plasticity model with further extension to account for failure due to the void coalescence was used for the GBAZ. The extended model contains all the deformation phases, i.e. elastic deformation, plastic deformation including deviatoric and volumetric plasticity (void growth) followed by damage initiation and evolution due to void coalescence. Parametric studies have been performed to assess the model\\'s dependence on the different input parameters. The model is then validated against uniaxial loading experiments for different materials. Lastly we show the model\\'s ability to predict the damage and fracture of a dog-bone shaped specimen as observed experimentally. © 2013 Elsevier B.V.

  1. Sintered gahnite–cordierite glass-ceramic based on raw materials ...

    Indian Academy of Sciences (India)

    Sci., Vol. 38, No. 7, December 2015, pp. 1731–1736. c Indian Academy of Sciences. Sintered gahnite–cordierite glass-ceramic based on raw materials with different fluorine sources. ESMAT M A HAMZAWY1,∗ and MOHAMMED A BIN HUSSAIN2. 1National Research Centre, Glass Department, Dokki, Cairo 12622, Egypt.

  2. Spark plasma versus conventional sintering in the electrical properties of Nasicon-type materials

    Czech Academy of Sciences Publication Activity Database

    Pérez-Estébanez, Marta; Isasi-Marín, J.; Rivera-Calzada, A.; León, C.; Nygren, M.

    2015-01-01

    Roč. 651, December (2015), s. 636-642 ISSN 0925-8388 R&D Projects: GA MŠk(CZ) LO1219 Keywords : electrode materials * ionic conduction * sintering Subject RIV: BF - Elementary Particles and High Energy Physics Impact factor: 3.014, year: 2015 http://www.sciencedirect.com/science/article/pii/S0925838815308227

  3. The importance of fracture toughness in ultrafine and nanocrystalline bulk materials.

    Science.gov (United States)

    Pippan, R; Hohenwarter, A

    2016-07-02

    The suitability of high-strength ultrafine and nanocrystalline materials processed by severe plastic deformation methods and aimed to be used for structural applications will strongly depend on their resistance against crack growth. In this contribution some general available findings on the damage tolerance of this material class will be summarized. Particularly, the occurrence of a pronounced fracture anisotropy will be in the center of discussion. In addition, the great potential of this generated anisotropy to obtain high-strength materials with exceptionally high fracture toughness in specific loading and crack growth directions will be enlightened. IMPACT STATEMENT Severely plastically deformed materials are reviewed in light of their damage tolerance. The frequently observed toughness anisotropy allows unprecedented fracture toughness - strength combinations.

  4. Syntheses and sintering of materials in view of nuclear waste storage

    International Nuclear Information System (INIS)

    Picot, V.; Glorieux, B.; Montel, J.M.; Deschanels, X.; Jorion, F.

    2005-01-01

    In the context of nuclear waste conditioning, the solid solution monazite-brabantite is extensively studied. Previous works have already shown its potential ability to confine minor actinides with excellent performance in term of chemical durability and structural stability. This present work concerns the synthesis and the sintering of such matrices. The challenge is to propose a synthesis and a sintering processes able to ensure the containment of actinides up to 10%wt. (Am, Cm, Np) in dense matrices (about 95% of the theoretical density). Those processes have to be performed on the equipment similar to that used in a facility dedicated to the high-level radioactive materials studies (glove box and hot cell). The optimized protocols, implying mixer-mill, synthesis by solid reaction at high temperature, uniaxial press compaction and sintering, are presented and discussed. (authors)

  5. Thermal stability of lead sulfide and lead oxide nano-crystalline materials

    Science.gov (United States)

    Nafees, M.; Ikram, M.; Ali, S.

    2017-10-01

    In this study, nano-crystalline lead sulfide (PbS) and lead oxide (PbO) were synthesized using hassle-free and cost-effective chemical route. Lead oxalate (PbC2O4) precursor was thermally decomposed to obtain the nano-crystalline PbO, while PbS nanoparticles were synthesized by microwave irradiation on a mixture of PbC2O4 precursor and sodium thiosulfate. Resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, ultraviolet-visible (UV-Vis) spectrophotometry, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). XRD confirmed the tetragonal structure for PbO and face-centered cubic for PbS with average crystallite sizes varying from 20 to 30 nm for both materials. From UV-Vis spectra, direct band gap energies were calculated to be 2.51 and 2.23 eV for PbO and PbS, respectively. Various decomposition stages during heat treatment of PbO and PbS, as revealed by TGA/DSC, are discussed in detail.

  6. The utilization of mechanochemistry in the extractive metallurgy and at the nanocrystalline materials preparation

    Directory of Open Access Journals (Sweden)

    Boldižárová Eva

    2002-03-01

    Full Text Available The possibility of the application of mechanochemistry in the extractive metallurgy and the nanocrystalline materials preparation is studied. The aim of the experiments is the chloride leaching of a complex sulphidic CuPbZn concentrate (Hodruša-Hámre, the modification of properties of CaCO3 (Yauli, Peru for zinc sorption from model solutions and the mechanochemical reduction of copper sulphide by elemental iron.The chloride leaching of mechanically activated complex sulphidic CuPbZn concentrate is a selective process. While the recoveries of copper, lead and zinc are 65-85 %, the recoveries of silver and gold are less than 7 % and 2 %, respectively.The positive influence of CaCO3 mechanical activation for zinc sorption from ZnSO4 solution was observed. While only 58 % of zinc sorption was determined after 30 minutes for a non-activated sample, 98 % of zinc sorption was determined after 3 minutes sorption for the sample mechanically activated for 15 minutes.By the mechanochemical reduction of copper sulphide with iron, nanocrystalline copper and iron sulphide are formed. This reaction is an example of the new “solid state technology“, where chemical processes in the gaseous and liquid states are excluded.The results can serve as a contribution to the optimization of copper, lead and zinc extraction from complex sulphidic concentrates, the increase of non-ferrous metals sorption efficiency on mineral sorbents as well as to the nanocrystalline copper preparation.The application of mechanical activation has grown in the laboratory research. The Institute of Geotechnics of SAS has also achieved significant theoretical results in study of mechanical activation of sulphides and their reactivity in the different solid-phase reactions with the effect on industrial applications. The Institute has developed the technology of mechanochemical leaching (process MELT which was successfully tested in a pilot plant unit.

  7. An Investigation Into The Viability Of Nanocrystalline Cellulose As A Packaging Material

    Science.gov (United States)

    Glass, John

    The focus of this proposal is to identify unexplored areas of research in the field of packaging science, specifically related to the incorporation of Nanocrystalline Cellulose (NCC) as a functional material in fiber based packaging, as well as to highlight some of potential risks and unknowns in the product lifecycle. This research hypothesizes that incorporating NCC into wood fiber-based c-flute corrugated packaging medium will show a sufficient performance improvement to justify additional research. Nanomaterials, as a whole, are still being understood, including those using naturally occurring bases such as NCC. Further incremental testing with NCC will help provide a performance and safety baseline for the necessary future research prior to mass production. NCC holds great promise for the future: a commonly available, naturally occurring material that's easily recyclable and biodegradable, yet has the strength of steel. Due diligence is required for this material to come to market in a safe and sustainable manner.

  8. Synthesis and properties of nickel-doped nanocrystalline barium hexaferrite ceramic materials

    Science.gov (United States)

    Waqar, Moaz; Rafiq, Muhammad Asif; Mirza, Talha Ahmed; Khalid, Fazal Ahmad; Khaliq, Abdul; Anwar, Muhammad Sabieh; Saleem, Murtaza

    2018-04-01

    M-type barium hexaferrite ceramics have emerged as important materials both for technological and commercial applications. However, limited work has been reported regarding the investigation of nanocrystalline Ni-doped barium hexaferrites. In this study, nanocrystalline barium hexaferrite ceramics with the composition BaFe12- x Ni x O19 (where x = 0, 0.3 and 0.5) were synthesized by sol-gel method and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer and precision impedance analyzer. All the synthesized samples had single magnetoplumbite phase having space group P63/mmc showing the successful substitution of Ni in BaFe12O19 without the formation of any impurity phase. Average grain size of undoped samples was around 120 nm which increased slightly with the addition of Ni. Saturation magnetization ( M s) and remnant magnetization ( M r) increased with the addition of Ni, however, coercivity ( H c) decreased with the increase in Ni from x = 0 to x = 0.5. Real and imaginary parts of permittivity decreased with the increasing frequency and increased with Ni content. Dielectric loss and conductivity showed slight variation with the increase in Ni concentration.

  9. Simultaneous Synthesis and Sintering of a Nanocrystalline AlCr{sub 2}-Al2O{sub 3} Composite by Rapid Heating and Its Mechanical Properties

    Energy Technology Data Exchange (ETDEWEB)

    Kwak, Bong-Won; Lee Seok-Jae; Shon, In-Jin [Chonbuk National University, Jeonju (Korea, Republic of)

    2016-06-15

    A dense nanostuctured AlCr{sub 2}-Al2O{sub 3} composite was sintered by pulsed current activated heating up to 1200 °C within 2 min from mechanically milled powders. The advantage of this process is that it allows very quick densification to near theoretical density and prohibition of grain growth in nanostructured materials. A highly dense AlCr{sub 2}-Al{sub 2}O{sub 3} composite with a relative density of up to 96% was produced under application of a 80 MPa pressure and a pulsed current of 2000 A. The fracture toughness and hardness of the AlCr{sub 2}-Al{sub 2}O{sub 3} composite in this study was better than those of previous studies due to the grain refinement. The microstructure and mechanical properties of the composite were investigated using field emission scanning electron microscopy and a Vickers hardness tester.

  10. Characterizing deformed ultrafine-grained and nanocrystalline materials using transmission Kikuchi diffraction in a scanning electron microscope

    International Nuclear Information System (INIS)

    Trimby, Patrick W.; Cao, Yang; Chen, Zibin; Han, Shuang; Hemker, Kevin J.; Lian, Jianshe; Liao, Xiaozhou; Rottmann, Paul; Samudrala, Saritha; Sun, Jingli; Wang, Jing Tao; Wheeler, John; Cairney, Julie M.

    2014-01-01

    Graphical abstract: -- Abstract: The recent development of transmission Kikuchi diffraction (TKD) in a scanning electron microscope enables fast, automated orientation mapping of electron transparent samples using standard electron backscatter diffraction (EBSD) hardware. TKD in a scanning electron microscope has significantly better spatial resolution than conventional EBSD, enabling routine characterization of nanocrystalline materials and allowing effective measurement of samples that have undergone severe plastic deformation. Combining TKD with energy dispersive X-ray spectroscopy (EDS) provides complementary chemical information, while a standard forescatter detector system below the EBSD detector can be used to generate dark field and oriented dark field images. Here we illustrate the application of this exciting new approach to a range of deformed, ultrafine grained and nanocrystalline samples, including duplex stainless steel, nanocrystalline copper and highly deformed titanium and nickel–cobalt. The results show that TKD combined with EDS is a highly effective and widely accessible tool for measuring key microstructural parameters at resolutions that are inaccessible using conventional EBSD

  11. The porosity effect on properties of sintered materials as their conductivity and Youngs modulus of elasticity

    International Nuclear Information System (INIS)

    Ondracek, G.; Thuemmler, F.

    1979-01-01

    A set of equations derived demonstrates quantitatively the influence of closed pores on the conductivity as well as on Youngsmodulus of elasticity of sintered materials. There are three microstructural parameters following from the theoretical derivation controlling the porosity effect on the properties, which are the total porosity, the form factor and the orientation factor of the pores. By quantitative microstructure analysis these factors become available providing together with the equations the tool - to calculate the conductivity and Youngs modulus of elasticity from microstructural quantities of sintered materials thus substituting direct property measurements by quantitative microstructure analysis if desired - to endeaver technologically optimum microstructures to obtain theoretically predicted special property values and to precalculate property alterations by microstructure variations ('taylor-made-materials') - to supplement the conventional microstructural quality control by calculated property data. (orig.) [de

  12. ADVANCED CERAMIC MATERIALS FOR DENTAL APPLICATIONS SINTERED BY MICROWAVE HEATING

    OpenAIRE

    Presenda Barrera, Álvaro

    2016-01-01

    [EN] Zirconia has become a widely utilized structural ceramic material with important applications in dentistry due to its superb mechanical properties, biocompatibility, aesthetic characteristics and durability. Zirconia needs to be stabilized in the t-phase to obtain improved mechanical properties such as hardness and fracture toughness. Fully dense yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) materials are normally consolidated through the energy-intensive processing of po...

  13. Development of optical ceramic materials for infrared applications by optimizing sintering conditions

    Science.gov (United States)

    Isogai, Masafumi; Sano, Masahiko

    2017-05-01

    The authors developed production process of polycrystalline Zinc Sulfide (ZnS) materials which have been widely applied to windows and domes for infrared sensor systems. Commercially available ZnS powders of ca. 5 um particle sizes were used as a starting material and Spark Plasma Sintering method (SPS) was applied to the powders for firing process. It was found that the densification of the sintered materials was inhibited by outgassing from ZnS powders during the sintering process (ca. 400 Celsius). Thermal desorption spectroscopy analyses revealed the components of outgassing, such as hydrogen sulfide, sulfur oxide and organic molecules. Based on these analyses, the optimum conditions on heating rate and starting temperature of uniaxial pressurization were investigated to remove the outgassing. The polycrystalline ZnS materials fired under the optimized SPS conditions have such characteristics as better transmittance than 65 % and good uniformity in both 3 - 5 um and 8 - 12 um wavelength regions. These results show the importance of removing outgassing from starting materials.

  14. Influence of Chemical Composition Variations on Densification During the Sintering of MOX Materials

    Science.gov (United States)

    Vaudez, S.; Marlot, C.; Lechelle, J.

    2016-06-01

    The mixed uranium-plutonium oxide (MOX) fabrication process is based on the preparation of UO2 and PuO2 powders. The mixture is pelletized before being sintered at 1973 K (1700 °C) in a reducing atmosphere of Ar/4pctH2/H2O. This paper shows how the densification of MOX fuel is affected during sintering by the moisture content of the gas, the plutonium content of the fuel, and the carbon impurity content in the raw materials. MOX densification can be monitored through dilatometric measurements and gas releases can be continuously analyzed during sintering in terms of their quantity and quality. Variations in the oxygen content in the fuel can be continuously recorded by coupling the dilatometer furnace with an oxygen measurement at the gas outlet. Any carbon-bearing species released, such as CO, can be also linked to densification phenomena when a gas chromatograph is installed at the outlet of the dilatometer. Recommendations on the choice of sintering atmosphere that best optimizes the fuel characteristics have been given on the basis of the results reported in this paper.

  15. Sintering of fly ash based composites with zeolite and bentonite addition for application in construction materials

    Directory of Open Access Journals (Sweden)

    Terzić Anja

    2017-01-01

    Full Text Available Due to pozzolanic characteristics, fly ash is commonly used as a cement replacement in construction composites. Addition of natural clays with sorption ability (i.e. zeolite and bentonite in to the fly ash based construction materials is of both scientific and industrial interest. Namely, due to the application of sorptive clay minerals, it is possible to immobilize toxic heavy metals from the composite structure. The thermal compatibility of fly ash and zeolite, as well as fly ash and bentonite, within the composite was observed during sintering procedure. The starting components were used in 1:1 ratio and they were applied without additional mechanical treatment. The used compaction pressure for the tablets was 2 t•cm-2. The sintering process was conducted at 1000ºC and 1200ºC for two hours in the air atmosphere. The mineralogical phase composition of the non-treated and sintered samples was analyzed using X-ray diffraction method. Scanning electron microscopy was applied in the analysis of the microstructure of starting and sintered samples. The thermal behavior was observed via DTA method. The influence of temperature on the properties of fly ash-zeolite and fly ash-bentonite composites was investigated. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 45008 and OI 172057

  16. Identification of Material Parameters for the Simulation of Acoustic Absorption of Fouled Sintered Fiber Felts

    Directory of Open Access Journals (Sweden)

    Nicolas Lippitz

    2016-08-01

    Full Text Available As a reaction to the increasing noise pollution, caused by the expansion of airports close to residential areas, porous trailing edges are investigated to reduce the aeroacoustic noise produced by flow around the airframe. Besides mechanical and acoustical investigations of porous materials, the fouling behavior of promising materials is an important aspect to estimate the performance in long-term use. For this study, two sintered fiber felts were selected for a long-term fouling experiment where the development of the flow resistivity and accumulation of dirt was observed. Based on 3D structural characterizations obtained from X-ray tomography of the initial materials, acoustic models (Biot and Johnson–Champoux–Allard in the frame of the transfer matrix method were applied to the sintered fiber felts. Flow resistivity measurements and the measurements of the absorption coefficient in an impedance tube are the basis for a fouling model for sintered fiber felts. The contribution will conclude with recommendations concerning the modeling of pollution processes of porous materials.

  17. Structural characterization, electrical conductivity and open circuit voltage studies of the nanocrystalline La10Si6O27 electrolyte material for SOFCs

    Science.gov (United States)

    Jena, Paramananda; Jayasubramaniyan, S.; Patro, P. K.; Lenka, R. K.; Sinha, Amit; Muralidharan, P.; Srinadhu, E. S.; Satyanarayana, N.

    2018-02-01

    Nanocrystalline La10Si6O27 apatite-type sample was synthesized by the co-precipitation method. Thermal behavior, phase, structure, morphology and elemental composition of La, O and Si of the synthesized La10Si6O27 sample were investigated through TG/DTA, XRD, FTIR, Raman spectroscopy and SEM-EDX measurements respectively. Formation of phase purity of the nanocrystalline La10Si6O27 sample was confirmed by analysing the measured X-ray powder diffraction (XRD) pattern using Rietveld refinement and the calculated average crystallite size of the La10Si6O27 sample was found to be 33 nm. The electrical conductivity of the sintered La10Si6O27 pellet was investigated as a function of temperature ranging from 200 to 800 °C under air and it was found to be 1.92 × 10-3 S cm-1 at 800 °C. The chemical stability of La10Si6O27 powder under oxidizing and reducing atmospheres was confirmed from the analysis of the measured XRD pattern and Raman spectral results. Open circuit potential of a button cell, made up of the La10Si6O27 sample, was tested up to 800 °C with both oxygen and hydrogen at opposite sides of the cell and was found to 1 V. Hence, the results demonstrate that La10Si6O27 could be a promising solid electrolyte material for the solid oxide fuel cell (SOFC) applications.

  18. Sintered iron biodegradable materials modified by polymer coating

    International Nuclear Information System (INIS)

    Gorejova, R.; Markusova-Buckova, L.; Orinakova, R.

    2017-01-01

    Devices made from biodegradable materials become a promising alternative to a permanent orthopedic implants. Temporary scaffolds made from these materials can provide desirable results in tissue healing and gradually dissolve in vivo by corrosion processes. This work is dedicated to preparation of iron based metallic structures prepared by powder metallurgy which were modified by polyethyleneglycol (PEG) coatings in different concentration. Corrosion behaviour of the prepared samples was observed in the form of static corrosion and dynamic corrosion in Hank's solution. Results show that the rate of degradation of polymer coated samples was greater than rate of degradation of pure iron. The highest rate of degradation was observed in porous structure covered with PEG with a concentration of 10 wt. %. (authors)

  19. Superhard MgB sub 2 bulk material prepared by high-pressure sintering

    CERN Document Server

    Ma, H A; Chen, L X; Zhu, P W; Ren, G Z; Guo, W L; Fu, X Q; Zou Guang Tian; Ren, Z A; Che, G C; Zhao, Z X

    2002-01-01

    Superhard MgB sub 2 bulk material with a golden metallic shine was synthesized by high-pressure sintering for 8 h at 5.5 GPa and different temperatures. Appropriate pressure and temperature conditions for synthesizing polycrystalline MgB sub 2 with high hardness were investigated. The samples were characterized by means of atomic force microscopy and x-ray diffraction. The Vickers hardness, bulk density, and electrical resistivity were measured at room temperature.

  20. Effect of High Speed Sintering on the Properties of Zirconia Oxide Materials

    Science.gov (United States)

    2018-03-22

    purpose of this study was to compare the mechanical properties and translucency of CEREC Zirconia (Dentsply Sirona) sintered using the CEREC...Beam-shaped specimens were designed using an Omnicam (Version 4.4.4; Dentsply Sirona) and milled from CAD /CAM blocks using a MCXL milling unit...zirconia were also compared to a lithium- disilicate material, IPS e.max CAD (lvoclar Vivadent). IPS e.max CAD beams were crystallized in the CEREC

  1. Properties of millimetre wave sintered and oxygenated YBa2Cu3Ox bulk material

    International Nuclear Information System (INIS)

    Hunyar, C.

    1999-12-01

    High temperature superconductors are ceramic materials whose properties strongly depend on the techniques used for their production. The successful use of microwaves for the sintering of other oxidic ceramics suggests the examination of the advantages and disadvantages of that production technique for superconductors. For this purpose pellets of commercially available YBa 2 Cu 3 O x powder from the Solvay company were pressed and sintered by millimetre wave heating (30 GHz, generated in a gyrotron). In various experiments the sintering temperatures were varied between 920 C and 990 C, and the holding times between 15 min and 240 min. The densities of the pellets were measured by the Archimedes method and the material structure was examined with an optical microscope. A strong densification from 86 to 93% of theoretical density could be observed within 30 min at a holding temperature of 960 C. With sintering temperatures above 960 C no significant increase in density occurred. At 950 C, only minor grain growth could be observed, which increased up to 960 C temperature. At higher temperatures a mixture of small grains and crystallites of about 150 μm size established itself. CuO already present in the original powder started to melt along the grain boundaries where it acts as a limiting factor for grain growth. With millimetre wave sintering the same material densities could be achieved in less than one third of the time needed for conventional sintering processes. In addition the effects of millimetre wave heating on the oxygen diffusion in YBCO were investigated with several pairs of identical samples. The pairs were deoxygenated and subsequently oxygenated in an atmosphere of pure O 2 in a conventional tube furnace and by millimetre wave heating respectively. To compare the oxygen concentration of the samples, their specific surface resistance at room temperature, which correlates with the oxygen content, was measured in a cylindrical copper resonator with

  2. Nanostructured Al-ZrAl{sub 3} materials consolidated via spark plasma sintering: Evaluation of their mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, C.; Belzunce, F.J.; Betegon, C. [Escuela Politecnica de Ingenieria (University of Oviedo), Campus Universitario, 33203 Gijon (Spain); Goyos, L. [Centro de Investigacion en Nanomateriales y Nanotecnologia (CINN-CSIC-UNIOVI-PA), Consejo Superior de Investigaciones Cientificas-Universidad de Oviedo-Principado de Asturias, Parque Tecnologico de Asturias, Llanera (Spain); Diaz, L.A., E-mail: la.diaz@cinn.es [Centro de Investigacion en Nanomateriales y Nanotecnologia (CINN-CSIC-UNIOVI-PA), Consejo Superior de Investigaciones Cientificas-Universidad de Oviedo-Principado de Asturias, Parque Tecnologico de Asturias, Llanera (Spain); Torrecillas, R. [Centro de Investigacion en Nanomateriales y Nanotecnologia (CINN-CSIC-UNIOVI-PA), Consejo Superior de Investigaciones Cientificas-Universidad de Oviedo-Principado de Asturias, Parque Tecnologico de Asturias, Llanera (Spain)

    2013-02-15

    Highlights: Black-Right-Pointing-Pointer A surface modification of aluminium powders was carried out by means of a colloidal process. Black-Right-Pointing-Pointer These powders were consolidated and sintered by spark plasma sintering. Black-Right-Pointing-Pointer Regarding the dwell time at the sintering temperature (625 Degree-Sign C), ZrAl{sub 3} intermetallic crystallizes. Black-Right-Pointing-Pointer The mechanical behaviour of this reinforcement was evaluated by Small Punch Test. - Abstract: Aluminium based nanostructured materials with additions of 0.5, 1 and 1.5 wt.% of zirconium have been produced and sintered using the spark plasma sintering technique in order to promote the nucleation of ZrAl{sub 3} platelets. The mechanical behaviour of all these nanocomposites was determined by means of the Small Punch Test. Zirconium additions significantly decrease the mechanical properties of these products when sintering time at the sintering temperature (625 Degree-Sign C) is short (3 min). Nevertheless, when the sintering time increases to 1 h (intermetallic crystallization), the zirconium additions show the expected effect: the stiffness and the yield strength increase while ductility and toughness decrease. The maximum load increases until a 0.5 wt.% Zr is attained and suddenly drops when the Zr content surpasses 1 wt.%.

  3. Sinus Floor Elevation and Augmentation Using Synthetic Nanocrystalline and Nanoporous Hydroxyapatite Bone Substitute Materials: Preliminary Histologic Results.

    Science.gov (United States)

    Belouka, Sofia-Maria; Strietzel, Frank Peter

    To compare the tissue composition of augmented sites after using two different synthetic bone substitute materials, nanocrystalline and nanoporous hydroxyapatite (HA), for sinus floor elevation and augmentation. Forty-four patients received 88 titanium screw implants (Camlog Promote plus) of 4.3-mm diameter and 11- or 13-mm length, placed simultaneously during sinus floor elevation and augmentation. Nanocrystalline (Ostim) or nanoporous (NanoBone) HA were used exclusively. Bone substitute materials and implant lengths were allocated by randomization. Bone biopsy specimens were obtained from the former area of the lateral access window at implant exposure during healing abutment placement after 6 months. Biopsy specimens were prepared and examined histologically and histomorphometrically. All implants were osseointegrated at the time of exposure. Clinically and histologically, no signs of inflammation in the augmented sites were present. The histomorphometric analysis of 44 biopsy specimens revealed 31.8% ± 11.6% newly formed bone for sites augmented with nanocrystalline HA and 34.6% ± 9.2% for nanoporous HA (P = .467). The proportion of remaining bone substitute material was 28.4% ± 18.6% and 30% ± 13%, respectively (P = .453). The proportion of soft tissue within the biopsy specimens was 39.9% ± 11.1% and 35.4% ± 6.8%, respectively (P = .064). No significant differences were found between the area fractions of bone, bone substitute material, and soft tissue concerning the bone substitute material utilized. Within the present study, both synthetic bone substitute materials, nanocrystalline and nanoporous HA, were found to support bone formation in sinus floor elevation and augmentation procedures by osteoconductivity. They were not completely resorbed after 6 months. The amounts of newly formed bone, soft tissue, and bone substitute material remnants were found to be similar, indicating that both materials are likewise suitable for sinus floor elevation and

  4. Magnetic and Mössbauer studies of pure and Ti-doped YFeO {sub 3} nanocrystalline particles prepared by mechanical milling and subsequent sintering

    Energy Technology Data Exchange (ETDEWEB)

    Khalifa, N. O. [University of Khartoum, Physics Department, Faculty of Science (Sudan); Widatallah, H. M., E-mail: hishammw@squ.edu.om; Gismelseed, A. M.; Al-Mabsali, F. N.; Sofin, R. G. S. [Sultan Qaboos University, Physics Department, College of Science (Oman); Pekala, M. [University of Warsaw, Chemistry Department (Poland)

    2016-12-15

    Single-phased nanocrystalline particles of pure and 10 % Ti {sup 4+}-doped perovskite-related YFeO {sub 3}were prepared via mechanosynthesis at 450{sup ∘}C. This temperature is ∼150–350 {sup ∘}C lower than those at which the materials, in bulk form, are normally prepared. Rietveld refinements of the X-ray diffraction patterns reveal that the dopant Ti {sup 4+} ions prefer interstitial octahedral sites in the orthorhombic crystal lattice rather than those originally occupied by the expelled Fe {sup 3+} ions. Magnetic measurements show canted antiferromagnetism in both types of nanoparticles. Doping with Ti {sup 4+} lowers the Néel temperature of the YFeO {sub 3} nanoparticles from ∼ 586 K to ∼ 521 K. The Ti {sup 4+}-doped YFeO {sub 3} nanoparticles exhibit enhanced magnetization and coercivity but less magnetic hyperfine fields relative to the un-doped nanoparticles. The {sup 57}Fe Mössbauer spectra show ∼ 15 % of the YFeO {sub 3} nanoparticles and ∼22 of Ti {sup 4+}-doped YFeO {sub 3} ones to be superparamagnetic with blocking temperatures < 78 K. The broadened magnetic components in the {sup 57}Fe Mössbauer spectra suggest size-dependent hyperfine magnetic fields at the {sup 57}Fe nuclear sites and were associated with collective magnetic excitations. The {sup 57}Fe Mössbauer spectra show the local environments of the Fe {sup 3+} ions in the superparamagnetic nanoparticles to be more sensitive to the presence of the Ti {sup 4+} ions relative to those in the larger magnetic nanoparticles.

  5. Microstructure and thermal properties of Cu-SiC composite materials depending on the sintering technique

    Directory of Open Access Journals (Sweden)

    Chmielewski Marcin

    2017-01-01

    Full Text Available The presented paper investigates the relationship between the microstructure and thermal properties of copper-silicon carbide composites obtained through hot pressing (HP and spark plasma sintering (SPS techniques. The microstructural analysis showed a better densification in the case of composites sintered in the SPS process. TEM investigations revealed the presence of silicon in the area of metallic matrix in the region close to metal-ceramic boundary. It is the product of silicon dissolving process in copper occurring at an elevated temperature. The Cu-SiC interface is significantly defected in composites obtained through the hot pressing method, which has a major influence on the thermal conductivity of materials.

  6. [Determination of major expansion properties of refractory die material compatible with slip casting core of sintered titanium powder].

    Science.gov (United States)

    Chao, Y; Kuang, X; Liao, Y; Wang, H

    1999-02-01

    To determinate major expansion properties of refractory die material. The setting expansion ratio of refractory die material for slip casting core of sintered titanium powder at room temperature was performed, as well as thermal expansion ratio from room temperature to 800 degrees C. The maximum setting expansion ratio in 2 hours reached 0.3407%; The final setting expansion ratio in 24 hours was 0.3117%; The mean thermal expansion coefficient was mainly in range of 8 x 10(-6)-11 x 10(-6)/degree C; The expansion property seemed very stable after sintering repeatedly and the small shrinkage after sintering could be compensated with the die spacer and setting expansion. The expansion properties of the refractory die material that we synthesized can fulfil the application requirements of slip casting core of sintered titanium powder.

  7. Creating bulk nanocrystalline metal.

    Energy Technology Data Exchange (ETDEWEB)

    Fredenburg, D. Anthony (Georgia Institute of Technology, Atlanta, GA); Saldana, Christopher J. (Purdue University, West Lafayette, IN); Gill, David D.; Hall, Aaron Christopher; Roemer, Timothy John (Ktech Corporation, Albuquerque, NM); Vogler, Tracy John; Yang, Pin

    2008-10-01

    Nanocrystalline and nanostructured materials offer unique microstructure-dependent properties that are superior to coarse-grained materials. These materials have been shown to have very high hardness, strength, and wear resistance. However, most current methods of producing nanostructured materials in weapons-relevant materials create powdered metal that must be consolidated into bulk form to be useful. Conventional consolidation methods are not appropriate due to the need to maintain the nanocrystalline structure. This research investigated new ways of creating nanocrystalline material, new methods of consolidating nanocrystalline material, and an analysis of these different methods of creation and consolidation to evaluate their applicability to mesoscale weapons applications where part features are often under 100 {micro}m wide and the material's microstructure must be very small to give homogeneous properties across the feature.

  8. Sintering analysis of 8YSZ electrolyte correlated to the electrical performance

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Cristiane Abrantes da; Furtado, Jose Geraldo de Melo [Centro de Pesquisas de Energia Eletrica (CEPEL), Rio de Janeiro, RJ (Brazil); Miranda, Paulo Emilio Valadao de, E-mail: pmiranda@labh2.coppe.ufrj.br [Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, RJ (Brazil). Departmento de Engenharia Metalurgica e de Materiais

    2010-07-01

    The understanding of the mechanisms associated with densification and sintering of yttria stabilized zirconia (YSZ), a main solid oxide fuel cell electrolyte, enables the improvement of its microstructure. The present work that has the objective to study the sintering and densification processes of polycrystalline nanostructured 8% mol YSZ (8YSZ), correlating the microstructural development with the electrical performance of the material. The sintering behaviors of nanocrystalline 8YSZ powders obtained by two different chemical synthesis techniques (glycine-nitrate combustion process and Pechini method) were studied based on sintering dilatometer method. X-ray diffraction and scanning electron microscopy were used in the microstructural characterization. Full-densified 8YSZ (98.8%) were obtained and it was found that the samples obtained by the Pechini's method showed a higher densification degree in the final stage of sintering and resulted in ceramics with higher final relative density and better electrical behavior. (author)

  9. Microstructural and photoluminescence characterisation of germanium and silicon-germanium nanocrystalline materials

    CERN Document Server

    Kartopu, G

    2003-01-01

    The discovery of the strong room temperature visible photoluminescence (PL) emission from porous Si in 1990 has been the catalyst for much of the recent study on the visible PL emitting semiconductor nanocrystalline materials. Silicon, an indirect bandgap semiconductor, in the form of nanoparticles is thought to emit strong visible light due to quantum confinement effects and, in the near future, will replace GaAs (and the other direct bandgap III-IV semiconductors) as for the light emitting devices such as lasers. On the other hand, mainly due to its much larger exciton Bohr radius, Ge, in the form of nanocrystals, is expected show more pronounced quantum confinement effects compared to Si nanocrystals. SiGe alloys also constitute a more attractive material than Si in terms of both industrial applications and fundamental research: the lifetime of the 'porous Si-like' PL of porous SiGe is observed to be approximately two orders of magnitude faster than that of porous Si. Moreover, the bandgap of Si-Ge alloys ...

  10. Synthesis of CuO nanocrystalline and their application as electrode materials for capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Hongxia [Department of Material Science and Chemical Engineering, Harbin Engineering University, Harbin 150001 (China)], E-mail: zhanghongxia.412@163.com; Zhang Milin [Department of Material Science and Chemical Engineering, Harbin Engineering University, Harbin 150001 (China)], E-mail: zhangmilin@hrbeu.edu.cn

    2008-04-15

    Cauliflower-like, nanobelt-shaped and feather-like CuO nanocrystallines were synthesized by the chemical deposition method. The microstructure and morphology of CuO were characterized by X-ray diffraction (XRD), energy-dispersive spectrum (EDS) and field emission scanning electron microscopy (FESEM). Results showed that the morphology of CuO was affected by property of alkali added into system. The probable mechanisms of the formation of CuO with different morphologies were discussed. The electrochemical properties of CuO as electrode material were enhanced by the improving of morphology. Cauliflower-like CuO exhibited a higher specific capacitance (116.9 F g{sup -1}) than nanobelt-shaped and feather-like CuO, and also showed good reversibility. Specific capacitance of cauliflower-like CuO (115.3 F g{sup -1}) was 343.5% higher than CuO bought (26 F g{sup -1}) at 5 mA cm{sup -2}.

  11. Effect of sintering conditions on the microstructural and mechanical characteristics of porous magnesium materials prepared by powder metallurgy.

    Science.gov (United States)

    Čapek, Jaroslav; Vojtěch, Dalibor

    2014-02-01

    There has recently been an increased demand for porous magnesium materials in many applications, especially in the medical field. Powder metallurgy appears to be a promising approach for the preparation of such materials. Many works have dealt with the preparation of porous magnesium; however, the effect of sintering conditions on material properties has rarely been investigated. In this work, we investigated porous magnesium samples that were prepared by powder metallurgy using ammonium bicarbonate spacer particles. The effects of the purity of the argon atmosphere and sintering time on the microstructure (SEM, EDX and XRD) and mechanical behaviour (universal loading machine and Vickers hardness tester) of porous magnesium were studied. The porosities of the prepared samples ranged from 24 to 29 vol.% depending on the sintering conditions. The purity of atmosphere played a significant role when the sintering time exceeded 6h. Under a gettered argon atmosphere, a prolonged sintering time enhanced diffusion connections between magnesium particles and improved the mechanical properties of the samples, whereas under a technical argon atmosphere, oxidation at the particle surfaces caused deterioration in the mechanical properties of the samples. These results suggest that a refined atmosphere is required to improve the mechanical properties of porous magnesium. © 2013.

  12. Sintering and dielectric properties of a technical porcelain prepared from economical natural raw materials

    Energy Technology Data Exchange (ETDEWEB)

    Kasrani, S.; Harabi, A.; Barama, S.-E.; Foughali, L.; Benhassine, M. T., E-mail: souad478@yahoo.fr, E-mail: harabi52@gmail.com, E-mail: sebarama@usa.com, E-mail: foughali_lazhar@yahoo.fr, E-mail: mtb25dz@gmail.com [Ceramics Lab. Mentouri University of Constantine (Algeria); Aldhayan, D.M., E-mail: aldhayan@ksu.edu.sa [Chemistry Department, Riyadh, King Saud University (Saudi Arabia)

    2016-10-15

    In this study, the production of a technical porcelain, for the ceramic dielectric applications by using economical natural raw materials, was investigated. The basic porcelain composition was selected consisting of 30 wt% kaolin, 45 wt% potash-feldspar and 25 wt% quartz. The obtained phases in the sintered samples were investigated by X-ray diffraction, Fourier transform infrared spectroscopy analysis, and scanning electron microscopy images. It has been confirmed by these techniques that the main crystalline phases were quartz and mullite. Dielectric measurements of technical porcelains have been carried out at 1 kHz from room temperature to 200 °C. The dielectric constant, loss factor, dielectric loss tangent, and resistivity of the porcelain sample sintered at 1160 °C were 22-25, 0.32-1.80, 0.006-0.07, and 0.2-9 x 10{sup 13} Ω.cm, respectively. The value of dielectric constant was significantly high when compared to that of conventional porcelains which did not exceed generally 9. (author)

  13. Characterisation of interfaces in nanocrystalline palladium

    Indian Academy of Sciences (India)

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

    Characterisation of interfaces in nanocrystalline palladium. 49. Interface structures in nanocrystalline materials have been the subject of research from the very beginning. The first indication that the structure of grain boundaries in nanocrystalline materials was different was from the X-ray diffraction (XRD) studies of Zhu et al ...

  14. Non-linear mechanical behavior of a sintered material for braking application using digital image correlation

    Science.gov (United States)

    Mann, Ruddy; Magnier, Vincent; Serrano-Munoz, Itziar; Brunel, Jean-Francois; Brunel, Florent; Dufrenoy, Philippe; Henrion, Michele

    2017-12-01

    Friction materials for braking applications are complex composites made of many components to ensure the various performances required (friction coefficient level, low wear, mechanical strength, thermal resistance, etc.). The material is developed empirically by a trial and error approach. With the solicitation, the material evolves and probably also its properties. In the literature, the mechanical behavior of such materials is generally considered as linear elastic and independent of the loading history. This paper describes a methodology to characterize the mechanical behavior of such a heterogeneous material in order to investigate its non-linear mechanical behavior. Results from mechanical tests are implemented into material laws for numerical simulations. Thanks to the instrumentation, some links with the microstructure can also be proposed. The material is made of a metallic matrix embedding graphite and ceramic particles and is manufactured by sintering. It is used for dry friction applications such as high-energy brake for trains, cars and motorcycles. Compression tests are done with digital image correlation to measure full-filled displacement. It allows to calculate strain fields with enough resolution to identify the material heterogeneity and the role of some of the components of the formulation. A behavior model of the material with plasticity and damage is proposed to simulate the non-linear mechanical behavior and is implemented in an FEM code. Results of mechanical test simulations are compared with two types of experiments showing good agreement. This method thus makes it possible to determine mechanical properties at a virgin state but is extensible for characterizing a material having been submitted to braking solicitations.

  15. Synthesis of Nanocrystalline SnO2 Modified TiO2:a Material for Carbon Monoxide Gas Sensor

    OpenAIRE

    A. B. BODADE; M. ALVI; A. V.KADU; S. V.JAGTAP; S. K. RITHE; P. R. PADOLE; G. N. CHAUDHARI

    2008-01-01

    Nanocrystalline SnO2 doped TiO2 having average crystallite size of 45-50 nm were synthesized by the sol-gel method and studied for gas sensing behavior to reducing gases like CO, liquefied petroleum gas (LPG), NH3 and H2. The material characterization was done by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM). The sensitivity measurements were carried out as a function of different operating temperature in SnO2 doped TiO2....

  16. Synthesis, microstructure and magnetic properties of nanocrystalline MgFe2O4 particles: Effect of mixture of fuels and sintering temperature

    Directory of Open Access Journals (Sweden)

    Osereme Ehi-Eromosele Cyril

    2016-01-01

    Full Text Available The present article reports the results of studies related to the synthesis of MgFe2O4 nanocomposite powder by solution combustion process using mixture of fuels containing urea (U and ammonium acetate (AA. The effect of mixture of fuel and sintering temperature on phase formation, structural, morphological and magnetic properties of MgFe2O4 particles were investigated by X-ray diffraction (XRD, thermogravimetric analysis (TGA, Raman spectroscopy, scanning electron microscopy (SEM, energy dispersive absorption x-ray (EDAX and vibrating sample magnetometer (VSM. Thermodynamic modeling of the combustion reaction shows that by using a mixture of urea and ammonium acetate fuels, the adiabatic flame temperature (Tad, exothermicity and amount of gases produced during the combustion process as well as product characteristics could be controlled. The use of mixture of fuels (U and AA in the synthesis of MgFe2O4 was found to produce ferrites with finer agglomerates, higher crystallinity, higher magnetic properties and smaller crystallite sizes than when only urea was used. It was found that only samples prepared with a mixture of fuels (0.5U + 0.5AA and sintered at 900oC for 2 h produced pure ferrite spinel phase while the auto-combusted and powders sintered at 600oC for 2 h had secondary phases. Apart from giving detailed information about the structural order of the samples, Raman spectroscopy also confirmed that MgFe2O4 is a mixed spinel ferrite.

  17. Spark plasma sintered bismuth telluride-based thermoelectric materials incorporating dispersed boron carbide

    Energy Technology Data Exchange (ETDEWEB)

    Williams, H.R., E-mail: hugo.williams@leicester.ac.uk [Department of Engineering, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); Ambrosi, R.M. [Space Research Centre, Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); Chen, K. [School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, London E1 4NS (United Kingdom); Friedman, U. [Department of Engineering, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); Ning, H.; Reece, M.J. [School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, London E1 4NS (United Kingdom); Robbins, M.C.; Simpson, K. [European Thermodynamics Ltd., 8 Priory Business Park, Wistow Road, Kibworth LE8 0R (United Kingdom); Stephenson, K. [European Space Agency, ESTEC TEC-EP, Keplerlaan 1, 2201AZ Noordwijk (Netherlands)

    2015-03-25

    Highlights: • Nano-B{sub 4}C reinforced Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} p-type thermoelectric produced by SPS. • Addition of B{sub 4}C up to 0.2 vol% to SPS’d material has little effect on zT. • Vickers hardness improved by 27% by adding 0.2 vol% B{sub 4}C. • Fracture toughness of SPS material: K{sub IC} = 0.80 MPa m{sup 1/2} by SEVNB. • Mechanical properties much better than commercial directionally solidified material. - Abstract: The mechanical properties of bismuth telluride based thermoelectric materials have received much less attention in the literature than their thermoelectric properties. Polycrystalline p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} materials were produced from powder using spark plasma sintering (SPS). The effects of nano-B{sub 4}C addition on the thermoelectric performance, Vickers hardness and fracture toughness were measured. Addition of 0.2 vol% B{sub 4}C was found to have little effect on zT but increased hardness by approximately 27% when compared to polycrystalline material without B{sub 4}C. The K{sub IC} fracture toughness of these compositions was measured as 0.80 MPa m{sup 1/2} by Single-Edge V-Notched Beam (SEVNB). The machinability of polycrystalline materials produced by SPS was significantly better than commercially available directionally solidified materials because the latter is limited by cleavage along the crystallographic plane parallel to the direction of solidification.

  18. Grain boundary and triple junction diffusion in nanocrystalline copper

    Energy Technology Data Exchange (ETDEWEB)

    Wegner, M., E-mail: m.wegner@uni-muenster.de; Leuthold, J.; Peterlechner, M.; Divinski, S. V., E-mail: divin@uni-muenster.de [Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Straße 10, D-48149, Münster (Germany); Song, X., E-mail: xysong@bjut.edu.cn [College of Materials Science and Engineering, Beijing University of Technology, 100124 Beijing (China); Wilde, G. [Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Straße 10, D-48149, Münster (Germany); Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, 200444 Shanghai (China)

    2014-09-07

    Grain boundary and triple junction diffusion in nanocrystalline Cu samples with grain sizes, 〈d〉, of ∼35 and ∼44 nm produced by spark plasma sintering were investigated by the radiotracer method using the {sup 63}Ni isotope. The measured diffusivities, D{sub eff}, are comparable with those determined previously for Ni grain boundary diffusion in well-annealed, high purity, coarse grained, polycrystalline copper, substantiating the absence of a grain size effect on the kinetic properties of grain boundaries in a nanocrystalline material at grain sizes d ≥ 35 nm. Simultaneously, the analysis predicts that if triple junction diffusion of Ni in Cu is enhanced with respect to the corresponding grain boundary diffusion rate, it is still less than 500⋅D{sub gb} within the temperature interval from 420 K to 470 K.

  19. Microwave Sintering of Ceramic Materials for Industrial Application Final Report CRADA No. TC-1116-95

    Energy Technology Data Exchange (ETDEWEB)

    Caplan, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Tandon, R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Callis, R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2017-10-19

    The goal of this project was to develop the commercial capability in the US to sinter alumina oxide ceramic parts for the semiconductor manufacturing equipment industry. We planned to use the millimeter microwave (30 GHz) sintering system first developed by IAP in Russia.

  20. In Operando Mechanism Analysis on Nanocrystalline Silicon Anode Material for Reversible and Ultrafast Sodium Storage.

    Science.gov (United States)

    Zhang, Lei; Hu, Xianluo; Chen, Chaoji; Guo, Haipeng; Liu, Xiaoxiao; Xu, Gengzhao; Zhong, Haijian; Cheng, Shuang; Wu, Peng; Meng, Jiashen; Huang, Yunhui; Dou, Shixue; Liu, Huakun

    2017-02-01

    The electrochemical mechanism of nanocrystalline silicon anode in sodium ion batteries is first studied via in operando Raman and in operando X-ray diffraction. An irreversible structural conversion from crystalline silicon to amorphous silicon takes place during the initial cycles, leading to ultrafast reversible sodium insertion in the newly generated amorphous silicon. Furthermore, an optimized silicon/carbon composite has been developed to further improve its electrochemical performance. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Nanocrystalline BaSnO3 as an Alternative Gas Sensor Material: Surface Reactivity and High Sensitivity to SO2

    Science.gov (United States)

    Marikutsa, Artem; Rumyantseva, Marina; Baranchikov, Alexander; Gaskov, Alexander

    2015-01-01

    Nanocrystalline perovskite-type BaSnO3 was obtained via microwave-assisted hydrothermal route followed by annealing at variable temperature. The samples composition and microstructure were characterized. Particle size of 18–23 nm was unaffected by heat treatment at 275–700 °C. Materials DC-conduction was measured at variable temperature and oxygen concentration. Barium stannate exhibited n-type semiconductor behavior at 150–450 °C with activation energy being dependent on the materials annealing temperature. Predominant ionosorbed oxygen species types were estimated. They were shown to change from molecular to atomic species on increasing temperature. Comparative test of sensor response to various inorganic target gases was performed using nanocrystalline SnO2-based sensors as reference ones. Despite one order of magnitude smaller surface area, BaSnO3 displayed higher sensitivity to SO2 in comparison with SnO2. DRIFT spectroscopy revealed distinct interaction routes of the oxides surfaces with SO2. Barium-promoted sulfate formation favoring target molecules oxidation was found responsible for the increased BaSnO3 sensitivity to ppm-range concentrations of SO2 in air. PMID:28793573

  2. Nanocrystalline BaSnO3 as an Alternative Gas Sensor Material: Surface Reactivity and High Sensitivity to SO2

    Directory of Open Access Journals (Sweden)

    Artem Marikutsa

    2015-09-01

    Full Text Available Nanocrystalline perovskite-type BaSnO3 was obtained via microwave-assisted hydrothermal route followed by annealing at variable temperature. The samples composition and microstructure were characterized. Particle size of 18–23 nm was unaffected by heat treatment at 275–700 °C. Materials DC-conduction was measured at variable temperature and oxygen concentration. Barium stannate exhibited n-type semiconductor behavior at 150–450 °C with activation energy being dependent on the materials annealing temperature. Predominant ionosorbed oxygen species types were estimated. They were shown to change from molecular to atomic species on increasing temperature. Comparative test of sensor response to various inorganic target gases was performed using nanocrystalline SnO2-based sensors as reference ones. Despite one order of magnitude smaller surface area, BaSnO3 displayed higher sensitivity to SO2 in comparison with SnO2. DRIFT spectroscopy revealed distinct interaction routes of the oxides surfaces with SO2. Barium-promoted sulfate formation favoring target molecules oxidation was found responsible for the increased BaSnO3 sensitivity to ppm-range concentrations of SO2 in air.

  3. Nanocrystalline BaSnO₃ as an Alternative Gas Sensor Material: Surface Reactivity and High Sensitivity to SO₂.

    Science.gov (United States)

    Marikutsa, Artem; Rumyantseva, Marina; Baranchikov, Alexander; Gaskov, Alexander

    2015-09-18

    Nanocrystalline perovskite-type BaSnO₃ was obtained via microwave-assisted hydrothermal route followed by annealing at variable temperature. The samples composition and microstructure were characterized. Particle size of 18-23 nm was unaffected by heat treatment at 275-700 °C. Materials DC-conduction was measured at variable temperature and oxygen concentration. Barium stannate exhibited n -type semiconductor behavior at 150-450 °C with activation energy being dependent on the materials annealing temperature. Predominant ionosorbed oxygen species types were estimated. They were shown to change from molecular to atomic species on increasing temperature. Comparative test of sensor response to various inorganic target gases was performed using nanocrystalline SnO₂-based sensors as reference ones. Despite one order of magnitude smaller surface area, BaSnO₃ displayed higher sensitivity to SO₂ in comparison with SnO₂. DRIFT spectroscopy revealed distinct interaction routes of the oxides surfaces with SO₂. Barium-promoted sulfate formation favoring target molecules oxidation was found responsible for the increased BaSnO₃ sensitivity to ppm-range concentrations of SO₂ in air.

  4. Magnetic microstructure and magnetic properties of spark plasma sintered NdFeB magnets

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Y.L., E-mail: hyl1019_lin@163.com [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Wang, Y.; Hou, Y.H.; Wang, Y.L.; Wu, Y.; Ma, S.C. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Liu, Z.W.; Zeng, D.C. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Tian, Y.; Xia, W.X. [Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Zhong, Z.C., E-mail: zzhong2014@sina.com [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China)

    2016-02-01

    Nanocrystalline NdFeB magnets were prepared by spark plasma sintering (SPS) technique using melt-spun ribbons as starting materials. A distinct two-zone structure with coarse grain zone and fine grain zone was formed in the SPSed magnets. Multi-domain particle in coarse grain zone and exchange interaction domain for fine grain zone were observed. Intergranular non-magnetic phase was favorable to improve the coercivity due to the enhancement of domain wall pinning effects and increased exchange-decouple. The remanent polarization of 0.83 T, coercivity of 1516 kA/m, and maximum energy product of 118 kJ/m{sup 3} are obtained for an isotropic magnet. - Highlights: • Nanocrystalline NdFeB magnets were prepared by spark plasma sintering technique. • Multi-domain particle and exchange interaction domain were observed. • Magnetic microstructure and their relation to the properties were investigated.

  5. Furnace for the continuous sintering of pellets of ceramic nuclear fuel material

    International Nuclear Information System (INIS)

    Heyraud, J.

    1977-01-01

    The furnace comprises a hearth for the longitudinal displacement of pellet containers, means for injecting gas at both ends of the furnace, for sucking gas between preheating and sintering zones and for condensing the binder, means for displacing the containers from an introduction lock-chamber to an extraction lock-chamber, a conveyor belt which passes through a glove box and provides a leak-tight connection between the lock-chambers. A station for loading containers with pellet sub-containers prior to sintering and a station for unloading the pellet sub-containers after sintering are juxtaposed within the glove box. 3 claims, 1 drawing figure

  6. THE EFFECT OFCARBON NANOTUBES ON THE SINTERING BEHAVIOR OF ZIRCONIA BASED MATERIALS

    OpenAIRE

    A. M. Zahedi; H. R. Rezaie; J. Javadpour

    2015-01-01

    Different volume fractions (1.3, 2.6, and 7.6 Vol.%) of carbon nanotubes (CNTs) were dispersed within 8Y-TZP nanopowders. Mixed powder specimens were subsequently processed by spark plasma sintering (SPS) and effects of CNTs on the sintering process of 8Y-TZP/CNT composites was studied. Maintenance of CNTs through the SPS process was confirmed using TEM and Raman Spectroscopy. Studies on the sintering profile of zirconia-CNT composites (Z-xC composites) could, to some extent, clarify the effe...

  7. Glass-ceramic coating material for the CO2 laser based sintering of thin films as caries and erosion protection.

    Science.gov (United States)

    Bilandžić, Marin Dean; Wollgarten, Susanne; Stollenwerk, Jochen; Poprawe, Reinhart; Esteves-Oliveira, Marcella; Fischer, Horst

    2017-09-01

    The established method of fissure-sealing using polymeric coating materials exhibits limitations on the long-term. Here, we present a novel technique with the potential to protect susceptible teeth against caries and erosion. We hypothesized that a tailored glass-ceramic material could be sprayed onto enamel-like substrates to create superior adhesion properties after sintering by a CO 2 laser beam. A powdered dental glass-ceramic material from the system SiO 2 -Na 2 O-K 2 O-CaO-Al 2 O 3 -MgO was adjusted with individual properties suitable for a spray coating process. The material was characterized using X-ray fluorescence analysis (XRF), heating microscopy, dilatometry, scanning electron microscopy (SEM), grain size analysis, biaxial flexural strength measurements, fourier transform infrared spectroscopy (FTIR), and gas pycnometry. Three different groups of samples (each n=10) where prepared: Group A, powder pressed glass-ceramic coating material; Group B, sintered hydroxyapatite specimens; and Group C, enamel specimens (prepared from bovine teeth). Group B and C where spray coated with glass-ceramic powder. All specimens were heat treated using a CO 2 laser beam process. Cross-sections of the laser-sintered specimens were analyzed using laser scanning microscopy (LSM), energy dispersive X-ray analysis (EDX), and SEM. The developed glass-ceramic material (grain size d50=13.1mm, coefficient of thermal expansion (CTE)=13.310 -6 /K) could be spray coated on all tested substrates (mean thickness=160μm). FTIR analysis confirmed an absorption of the laser energy up to 95%. The powdered glass-ceramic material was successfully densely sintered in all sample groups. The coating interface investigation by SEM and EDX proved atomic diffusion and adhesion of the glass-ceramic material to hydroxyapatite and to dental enamel. A glass-ceramic material with suitable absorption properties was successfully sprayed and laser-sintered in thin films on hydroxyapatite as well as on

  8. Physics and Technology of Transparent Ceramic Armor: Sintered Al2O3 vs Cubic Materials

    National Research Council Canada - National Science Library

    Krell, Andreas; Hutzler, Thomas; Klimke, Jens

    2006-01-01

    Sintered sub-micrometer alumina (alpha-Al2O3) is the hardest transparent armor. However, its trigonal structure gives rise to a strong thickness effect that makes thicker components translucent. Cubic ceramics (no birefringence...

  9. Sintering of new SiC-Phosphate composite materials for grinding wheels fabrication

    Directory of Open Access Journals (Sweden)

    Silva, R. F.

    2004-04-01

    Full Text Available The effect of several variables such as molar ratio P2O5/B2O3 (X, temperature and heating cycle on the strength of chemically bonded SiC materials for grinding wheels fabrication was studied. It was shown that the highest compressive strength (52.4 MPa could be obtained using an optimal molar ratio X = 4.5 and a multiple step heating cycle up to a sintering temperature of 800oC. DTA, XRD, SEM and dilatometrical analysis were performed to follow the different stages of the structural development.

    Se estudia el efecto de diferentes variables tales como la razón molar P2O5/B2O3(X, temperatura y ciclo de calentamieno sobre la resistencia de materiales de SiC aglomerados quimicamente para la fabricación de muelas arasivas. Se ha comprobado que la más alta resistencia a la compresión (52,4MPa pueda obtenerse usando una razón molar òptima x= 4,5 y un ciclo de calentamiento en múltiples etapas hasta la temperatura de 800º C. Estudios mediante ATD, DRX, MEB y análisis dilatométricos fueron llevados a cabo para seguir las diferentes etapas del desarrollo microestructura.

  10. Yield stress of ultrafine-grained or nanocrystalline materials with a bimodal grain size distribution

    Science.gov (United States)

    Pande, C. S.; DeGiorgi, V. G.; E Moser, A.

    2018-02-01

    An attractive processing route for enhancing the yield strength of high-strength nanocrystalline metals and alloys while maintaining high ductility is to develop a bimodal grain size distribution (GSD), in which, supposedly, the finer grains provide strength, and the coarser grains maintain or even enhance ductility. We present a theoretical model predicting the strength of such a system, and show, analytically, how the yield stress is related to the various parameters of the bimodal GSD, such as volume fraction of the two components of the bimodal distribution and their standard deviations.

  11. Impact of sintering method on certain properties of titanium dioxide nanopowder materials

    Directory of Open Access Journals (Sweden)

    Porozova Svetlana E.

    2017-01-01

    Full Text Available Titanium dioxide nanopowder samples consolidated by method of cold uniaxial compaction at 200 MPa and conventionally sintered in air at 1300°С with isothermal tempering during 60 minutes or spark-plasma sintering at 1300°С and 30 MPа were studied using the method of light combination scattering spectroscopy (Raman spectroscopy and scanning electron microscopy. The samples were found to differ significantly in terms of color, density, phase composition and microstructure.

  12. Main properties of nanocrystalline hydroxyapatite as a bone graft material in treatment of periodontal defects. A review of literature

    International Nuclear Information System (INIS)

    Bayani, Mojtaba; Torabi, Sepehr; Shahnaz, Aysan; Pourali, Mohammad

    2017-01-01

    This study aims to provide a literature review on nanocrystalline hydroxyapatite (n-HA). n-HA constitutes the principle inorganic part of hard tissues. Therefore, preparation of commercial synthetic analogues, the so-called ‘biomimetic’, has gained a lot of attention since it can precisely mimic the physicochemical features of biological apatite compounds. Due to its improved osseointegrative properties, n-HA may represent a promising class of bone graft materials. n-HA binds to the bone and by stimulation of osteoblast activity and enhancing local growth factors it improves bone healing. Periodontitis is an inflammatory condition in response to microbial plaque that leads to periodontal tissue destruction and osseous defects in alveolar bone. A review of the extant literature reveals that n-HA has certain advantages in periodontal tissue regeneration including minimal patient morbidity, better biocompatibility, and lack of toxicity

  13. Synthesis of Nanocrystalline SnO2 Modified TiO2:a Material for Carbon Monoxide Gas Sensor

    Directory of Open Access Journals (Sweden)

    A. B. BODADE

    2008-11-01

    Full Text Available Nanocrystalline SnO2 doped TiO2 having average crystallite size of 45-50 nm were synthesized by the sol-gel method and studied for gas sensing behavior to reducing gases like CO, liquefied petroleum gas (LPG, NH3 and H2. The material characterization was done by using X-ray diffraction (XRD, Fourier transform infrared spectroscopy (FT-IR and scanning electron microscope (SEM. The sensitivity measurements were carried out as a function of different operating temperature in SnO2 doped TiO2. The 15 wt.% SnO2 doped TiO2 based CO sensor shows better sensitivity at an operating temperature 240°C Incorporation of 0.5 wt% Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 240°C to 200°C for CO sensor.

  14. IRON ORE SINTER PRODUCTION USING ELECTRIC ARC FURNACE DUST AS RAW MATERIAL

    Directory of Open Access Journals (Sweden)

    Victor Bridi Telles

    2013-03-01

    Full Text Available The steel production through Electric Arc Furnaces (EAF generates approximately 15% to 20% of Electric Arc Furnace Dust (EAFD. This waste is considered dangerous due to the presence of metals as lead and cadmium that leach in contact with water. Because of this, the EAFD recycling becomes an alternative to diminish the costs with landfills and environmental harms caused by the waste. The iron ore sintering is a process that reuses most part of powders generated by the steelmaking. However the EAFD is not reused in this process because it contains zinc. The zinc is highly detrimental inside blast furnaces causing heavy crusts and affecting the thermodynamic equilibrium of the process. Therefore, this work studies the EAFD reuse in the iron ore sintering process to produce iron ore sinter with zinc contents between the limits established for blast furnaces.

  15. Relationship of microstructure properties to oxygen impurities in nanocrystalline silicon photovoltaic materials

    Science.gov (United States)

    Xu, H.; Wen, C.; Liu, H.; Li, Z. P.; Shen, W. Z.

    2013-03-01

    We have fully investigated the correlation of microstructure properties and oxygen impurities in hydrogenated nanocrystalline silicon photovoltaic films. The achievement has been realized through a series of different hydrogen dilution ratio treatment by plasma enhanced chemical vapor deposition system. Raman scattering, x-ray diffraction, and ultraviolet-visible transmission techniques have been employed to characterize the physical structural characterization and to elucidate the structure evolution. The bonding configuration of the oxygen impurities was investigated by x-ray photoelectron spectroscopy and the Si-O stretching mode of infrared-transmission, indicating that the films were well oxidized in SiO2 form. Based on the consistence between the proposed structure factor and the oxygen content, we have demonstrated that there are two dominant disordered structure regions closely related to the post-oxidation contamination: plate-like configuration and clustered microvoids.

  16. Phase Composition and Microstructure of Hot-Pressing Sintered Ti2AlN Metal-Ceramic Bulk Material

    Directory of Open Access Journals (Sweden)

    LIANG Suying

    2017-06-01

    Full Text Available Ti2AlN metal-ceramic bulk material was fabricated by hot-pressing sintering (HPS using TiN, Ti and Al powder in a stoichiometric ratio of 1:1:1.03 after mechanical mixing. XRD, SEM and TEM were employed to investigate the phase composition and microstructures of the products. The results show that the high purity Ti2AlN can be obtained by HPS at 1300 ℃ for 2.5 h. The sintered Ti2AlN presented a hexagonal system layered structure with an anisotropy. Twins are found in the Ti2AlN. There were a few nano-scale TiN particles in the products.

  17. Electrochemical performance of nanocrystalline Li2CoTiO4 cathode materials for lithium ion batteries

    International Nuclear Information System (INIS)

    Yang, Meng; Zhao, Xiangyu; Ma, Liqun; Yang, Hui; Shen, Xiaodong; Bian, Yajuan

    2015-01-01

    Highlights: • Li 2 CoTiO 4 cathode materials with tunable nanostructures were synthesized. • Small particle or grain size can increase the Li ion diffusion rate. • Li 2 CoTiO 4 with small particle size has good cycle stability and rate capability. - Abstract: Cation disordered Li 2 CoTiO 4 titanate with 3D lithium ion channels could be a promising new cathode material for lithium ion batteries due to its high theoretical capacity. Herein the Li 2 CoTiO 4 materials with tunable nanostructures were synthesized by a sol–gel method and subsequent heat treatment at different temperatures. The microstructure and electrochemical properties of the nanocrystalline Li 2 CoTiO 4 materials have been systematically investigated. The Li 2 CoTiO 4 material synthesized at lower temperature possessed smaller particle size and grain size, and allowed a higher reversible extraction of lithium ions per formula unit. Furthermore, the small particle size enabled insertion of lithium along short diffusion paths, and thus an increase of the lithium ion diffusion coefficient

  18. Influence of the raw-material characteristics on mullite-zirconia composites obtained by reactions sintering

    International Nuclear Information System (INIS)

    Emiliano, J.V.; Segadaes, A.M.B.C.

    1989-01-01

    A number of authors have shown that there are some difficulties in preparing mullite-zirconia composites with good thermomechanical properties through reaction-sintering of Al 2 O 3 and ZrSiO 4 powders. The present work was aimed at investigating the effect of the characteristics of the alumina powders on the reaction-sintering behaviour, microstructural development and final properties of the composites prepared by conventional processes. The results obtained showed that the use of high purity reactive powders, supposed to yield enhanced properties can be overshadowed when conventional techniques of powder processing are used, as these give rise to microstructural inhomogeneities [pt

  19. Effect of Bottom Ash and Fly Ash as a Susceptor Material on The Properties of Aluminium Based Composites Prepared by Microwave Sintering

    Directory of Open Access Journals (Sweden)

    Wan Muhammad Wan Nur Azrina Binti

    2017-01-01

    Full Text Available The use of aluminium as a single material in automotive applications is not suitable without a mixture with reinforcement materials that can support the properties at high temperature. In this study, aluminium based composite were prepared with weight percentage of SiC reinforcement, varying from 5 to 20 wt%. Aluminium powder and reinforcement materials were mixed using ball milling machine with speed of 100 rpm for 2 hours. The powder mixture were then compressed at pressure 4 tonnes with 5 minutes holding time. The compact samples were sintered using microwave sintering technique. Microwave sintering techniques in this study using two different types of susceptor materials that are bottom ash and fly ash. Sintered aluminium based composites using bottom ash susceptor material involving the sintering temperature of 526 °C for 30 minutes whereas for the samples sintered using fly ash susceptor material, involving a temperature of 523 °C for 15 minutes. From the result, the sintered samples using fly ash susceptor material, showed higher density with a value of 2.1933 g/cm3 compared to bottom ash 2.0002 g/cm3 and having the higher hardness value 72.1315 HV compared to bottom ash 50.0511HV. The using of fly ash could affect the heating rate during the sintering process which could influence the properties of aluminium based composites. In conclusion, the type of susceptor could affect the physical and mechanical properties of aluminum-based composite reinforced with silicon carbide.

  20. Amorphous and nanocrystalline titanium nitride and carbonitride materials obtained by solution phase ammonolysis of Ti(NMe2)4

    International Nuclear Information System (INIS)

    Jackson, Andrew W.; Shebanova, Olga; Hector, Andrew L.; McMillan, Paul F.

    2006-01-01

    Solution phase reactions between tetrakisdimethylamidotitanium (Ti(NMe 2 ) 4 ) and ammonia yield precipitates with composition TiC 0.5 N 1.1 H 2.3 . Thermogravimetric analysis (TGA) indicates that decomposition of these precursor materials proceeds in two steps to yield rocksalt-structured TiN or Ti(C,N), depending upon the gas atmosphere. Heating to above 700 deg. C in NH 3 yields nearly stoichiometric TiN. However, heating in N 2 atmosphere leads to isostructural carbonitrides, approximately TiC 0.2 N 0.8 in composition. The particle sizes of these materials range between 4-12 nm. Heating to a temperature that corresponds to the intermediate plateau in the TGA curve (450 deg. C) results in a black powder that is X-ray amorphous and is electrically conducting. The bulk chemical composition of this material is found to be TiC 0.22 N 1.01 H 0.07 , or Ti 3 (C 0.17 N 0.78 H 0.05 ) 3.96 , close to Ti 3 (C,N) 4 . Previous workers have suggested that the intermediate compound was an amorphous form of Ti 3 N 4 . TEM investigation of the material indicates the presence of nanocrystalline regions x (C,N) y crystalline phases

  1. The effect of patient age on bone formation using a fully synthetic nanocrystalline bone augmentation material in maxillary sinus grafting.

    Science.gov (United States)

    Wolf, Michael; Wurm, Alexander; Heinemann, Friedhelm; Gerber, Thomas; Reichert, Christoph; Jäger, Andreas; Götz, Werner

    2014-01-01

    Maxillary sinus floor augmentation is a treatment that has been proposed for patients in whom the alveolar bone height is insufficient. This procedure is commonly used in patients aged 40 to 70 years and older. However, little information exists whether the factor of age might influence the outcome of augmentation procedures. The aim of this study was to investigate whether the patient's age has an effect on bone formation and incorporation in maxillary sinus floor augmentation procedures. A fully synthetic nanocrystalline bone augmentation material (NanoBone, Artoss) was used for sinus floor augmentation in patients with a subantral vertical bone height of at least 3 mm and maximum of 7 mm. After 7 months healing time, biopsy specimens were taken and were divided into two groups according to the patient's age. Exclusion criteria were poor general health (eg, severe renal/and or liver disease), history of a radiotherapy in the head region, chemotherapy at the time of surgical procedure, noncompensated diabetes mellitus, symptoms of a maxillary sinus disease, active periodontal or systemic diseases, smoking, and poor oral hygiene. Histologic analyses with hematoxylin-eosin stain were performed. Multinucleated osteoclast-like cells were identified by histochemical staining (tartrate-resistant acid phosphatase [TRAP]). Quantitative and age-dependent assessment of bone formation, residual bone grafting material, and soft tissue formation following sinus augmentation was performed using histomorphometric analysis and the Bonferroni adjustment of the Student t test. Twenty biopsy specimens from 17 patients were taken and divided into two groups according to age (group 1: 41 to 52 years; group 2: 66 to 71 years) containing 10 specimens each, which were analyzed in triplicate resulting in a total of 30 specimens per group. A regeneration process with varying amounts of newly formed bone surrounded by marrow-like tissue was present in all augmented regions. No signs of

  2. Numerical simulation of electric field assisted sintering

    Science.gov (United States)

    McWilliams, Brandon A.

    A fully coupled thermal-electric-sintering finite element model was developed and implemented to explore electric field assisted sintering techniques (FAST). FAST is a single step processing operation for producing bulk materials from powders, in which the powder is heated by the application of electric current under pressure. This process differs from other powder processing techniques such as hot isostatic pressing (HIP) and traditional press and sinter operations where the powder or compact is heated externally, in that the powder is heated directly as a result of internal Joule heating (for conductive powders) and/or by direct conduction from the die and punches. The overall result is much more efficient heating which allows heating rates of >1000°C/min to be achieved which is desirable for sintering bulk nanocrystalline and other novel high performance materials. Previous modeling efforts on FAST have only considered the thermal-electric aspect of the problem and have neglected densification. In addition to the introduction of a sintering model, a detailed thermal-electric study of process parameters was carried out in order to identify key system variables and quantify their effect on the overall system response and subsequent thermal history of a consolidated sample. This analysis was compared to empirical data from a parallel experimental study and shown to satisfactorily predict the observed trends. This model was then integrated with a phenomenologically based sintering model to capture the densification of the sample. This fully coupled model was used to predict densification kinetics under FAST like conditions and examine the evolution of material properties as the sample transitions from a loose powder to a fully dense compact and the resulting effect on the electrical and thermal fields within the compact. This model was also used to explore the effect of non-uniform thermal, electrical, stress and density fields on the final geometry and local

  3. Nanocrystalline solids

    International Nuclear Information System (INIS)

    Gleiter, H.

    1991-01-01

    Nanocrystalline solids are polycrystals, the crystal size of which is a few (typically 1 to 10) nanometres so that 50% or more of the solid consists of incoherent interfaces between crystals of different orientations. Solids consisting primarily of internal interfaces represent a separate class of atomic structures because the atomic arrangement formed in the core of an interface is known to be an arrangement of minimum energy in the potential field of the two adjacent crystal lattices with different crystallographic orientations on either side of the boundary core. These boundary conditions result in atomic structures in the interfacial cores which cannot be formed elsewhere (e.g. in glasses or perfect crystals). Nanocrystalline solids are of interest for the following four reasons: (1) Nanocrystalline solids exhibit an atomic structure which differs from that of the two known solid states: the crystalline (with long-range order) and the glassy (with short-range order). (2) The properties of nanocrystalline solids differ (in some cases by several orders of magnitude) from those of glasses and/or crystals with the same chemical composition, which suggests that they may be utilized technologically in the future. (3) Nanocrystalline solids seem to permit the alloying of conventionally immiscible components. (4) If small (1 to 10 nm diameter) solid droplets with a glassy structure are consolidated (instead of small crystals), a new type of glass, called nanoglass, is obtained. Such glasses seem to differ structurally from conventional glasses. (orig.)

  4. Low-temperature sintering and phase changes in chromite interconnect materials

    Energy Technology Data Exchange (ETDEWEB)

    Chick, L.A.; Armstrong, T.R.; McCready, D.E.; Coffey, G.W.; Maupin, G.D.; Bates, J.L.

    1993-05-01

    Sintering shrinkage curves and phase changes were compared for calcium-substituted lanthanum chromates with either slight Asite enrichment or depletion. Of the former type, La{sub 0.7}Ca{sub 0.31},CrO{sub 3} that was synthesized by the glycine-nitrate method sintered to high density in air at 1250C, exhibiting two rapid-shrinkage events. Weight loss measurements corroborated XRD data showing that, prior to densiflcation, over half the Ca resided in non-perovskite phases, including CaCrO{sub 4}. In the La{sub 0.7}Ca{sub 0.31}CrO{sub 3}, densification was closely associated with re-dissolution of the Ca into the perovskite.

  5. Low-temperature sintering and phase changes in chromite interconnect materials

    Energy Technology Data Exchange (ETDEWEB)

    Chick, L.A.; Armstrong, T.R.; McCready, D.E.; Coffey, G.W.; Maupin, G.D.; Bates, J.L.

    1993-05-01

    Sintering shrinkage curves and phase changes were compared for calcium-substituted lanthanum chromates with either slight Asite enrichment or depletion. Of the former type, La[sub 0.7]Ca[sub 0.31],CrO[sub 3] that was synthesized by the glycine-nitrate method sintered to high density in air at 1250C, exhibiting two rapid-shrinkage events. Weight loss measurements corroborated XRD data showing that, prior to densiflcation, over half the Ca resided in non-perovskite phases, including CaCrO[sub 4]. In the La[sub 0.7]Ca[sub 0.31]CrO[sub 3], densification was closely associated with re-dissolution of the Ca into the perovskite.

  6. The wetted solid - a generalization of Plateau's problem and its implications for sintered materials

    International Nuclear Information System (INIS)

    Salomon, P.; Berry, R.S.; Carrera-Patino, M.E.; Chicago Univ., IL; Andresen, B.

    1988-01-01

    We introduce a new generalization of the Plateau problem which includes the constraint of enclosing a given region. Physically the problem is important insofar as it bears on sintering processes and on the structure of wetted porous media. Some primal and dual characterizations of the solutions are offered, and aspects of the problem are illustrated in one and two dimensions in order to clarify the combinatorial elements and to demonstrate the importance of numerous local minima. (orig.)

  7. Low-sintering condenser materials on the basis of barium titanate; Niedrig-sinternde Kondensatorwerkstoffe auf der Basis von Bariumtitanat

    Energy Technology Data Exchange (ETDEWEB)

    Naghib zadeh, Hamid

    2010-07-01

    The main objective of this work was the development of new barium titanate capacitor materials, which fully densified at a sintering temperature of 900 C and exhibit a high and almost temperature-independent dielectric constant as well as low dielectric loss. In order to decrease the sintering temperature of barium titanate from ca. 1300 C to 900 C, addition of various types of sintering aids have been tested. Li-containing sintering additives show the best result concerning densification and dielectric properties. By addition of 2 to 3 wt% (SrO-B{sub 2}O{sub 3}-Li{sub 2}O) -, (ZnO-B{sub 2}O{sub 3}-Li{sub 2}O) - or (LiF-SrCO{sub 3})-additive combinations to commercially available barium titanate powder 95 % of the theoretical density was achieved after sintering at 900 C. The sintered capacitor materials with the above mentioned additive combinations possess high dielectric constants from 1800 to 3590. It is well known that for a high temperature stability of dielectric constant the formation of core-shell structure in a fine-grained microstructure is required (average grain size < 1 {mu}m). For BaTiO{sub 3} samples contained 2 wt% LiF-SrCO{sub 3} is temperature coefficient of capacitance (TCC) relatively low. The TCC in temperature range between 0 C and 80 C is less than {+-} 15%. The formation of the core-shell structure in a fine-grained microstructure of this sample, which is required to have low TCC, was detected by TEM / EDX analyses. The significantly higher TCC for the BaTiO{sub 3} samples contained 3 wt% SrO-B{sub 2}O{sub 3}-Li{sub 2}O is due to the strong grain growth during sintering. To reduce the TCC in this sample Nb{sub 2}O{sub 5}-Co{sub 2}O{sub 3} was added. By addition of 1.5 wt% Nb{sub 2}O{sub 5}-Co{sub 2}O{sub 3} the temperature stability of the dielectric constant could be significantly improved as a result of the grain growth inhibition and the core-shell formation during sintering. For BaTiO{sub 3} samples contained ZnO-B{sub 2}O{sub 3}-Li

  8. [Determination of normal temperature properties of refractory die material compatible with slip casting core of sintered titanium powder].

    Science.gov (United States)

    Kuang, X; Liao, Y; Chao, Y; Wang, H

    1999-05-01

    The refractory die is the precondition for developing slip casting core of sintered powder. This study is to determine the normal temperature properties of the refractory die material compatible with slip casting core. to mix the die material at five different ratios (8/1, 7.5/1, 7/1, 6.5/1, and 6/1) and measure their solidification time with self-manufactured Vicker's needle; to prepare five cylindrical specimens (phi 10 x 15 mm) in different drying time for determining their compressive strength, and then to let another five specimens fire at 1000 degrees C four times for measuring the residual compressive strength at room temperature. The setting time was 16.25 minutes (7.5/1), and the lower the powder-liquid ratio, the longer the setting time. The normal compressive strength was 25.32 MPa (drying 24 hours), while the longer the drying time, the higher the compressive strength achieved (P die material meet the demand of slip casting core of sintered powder.

  9. Effect of Ti and C additions on structural and magnetic properties of (Pr,Nd)-Fe-B nanocrystalline magnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, R.K. [Instituto de Fisica, Universidade de Sao Paulo, 05315-970 Sao Paulo, SP (Brazil); Universidade Federal do ABC, R. Santa Adelia, 166, 09210-170 Santo Andre, SP (Brazil)], E-mail: regina.murakami@ufabc.edu.br; Rechenberg, H.R. [Instituto de Fisica, Universidade de Sao Paulo, 05315-970 Sao Paulo, SP (Brazil); Neiva, A.C. [Departamento de Engenharia Quimica, Escola Politecnica da Universidade de Sao Paulo, Sao Paulo, SP (Brazil); Missell, F.P. [Departamento de Fisica e Quimica, Centro de Ciencias Exatas e Tecnologia, Universidade de Caxias do Sul, 95070-560 Caxias do Sul, RS (Brazil); Divisao de Metrologia de Materiais-INMETRO, Av. Nossa Senhora das Gracas, 50 (Xerem), 25250-020 Duque de Caxias, RJ (Brazil); Villas-Boas, V. [Departamento de Fisica e Quimica, Centro de Ciencias Exatas e Tecnologia, Universidade de Caxias do Sul, 95070-560 Caxias do Sul, RS (Brazil)

    2008-07-15

    Effects of titanium carbide (TiC) addition on structural and magnetic properties of isotropic (Pr,Nd)-Fe-B nanocrystalline magnetic materials have been investigated. In this work, we investigate the effect of TiC addition on a (Pr,Nd)-poor and B-rich composition, as well as on a B-poor and (Nd,Pr)-rich composition. Rapidly solidified (Pr,Nd)-Fe-B alloys were prepared by melt-spinning. The compositions studied were (Pr{sub 1-x}Nd{sub x}){sub 4}Fe{sub 78}B{sub 18} (x=0, 0.5, and 1) with addition of 3 at% TiC. Unlike the (Pr{sub x}Nd{sub 1-x}){sub 9.5}Fe{sub 84.5}B{sub 6} materials that present excellent values for coercive field and energy product, the (Pr,Nd)-poor and B-rich composition alloys with TiC addition present lower values. Rietveld analysis of X-ray data and Moessbauer spectroscopy revealed that samples are predominantly composed of Fe{sub 3}B and {alpha}-Fe. For the RE-rich compositions (Pr{sub x}Nd{sub 1-x}){sub 9.5}Fe{sub 84.5}B{sub 6} (x=0.1, 0.25, 0.5, 0.75, and 1) with the addition of 3 at% TiC, the highest coercive field and energy product (8.4 kOe and 14.4 MGOe, respectively) were obtained for the composition Pr{sub 9.5}Fe{sub 84.5}B{sub 6}.

  10. Modeling a material from packing, through sintering and to the final microstructural properties

    DEFF Research Database (Denmark)

    Bjørk, Rasmus; Nielsen, Kaspar Kirstein

    and magnetism known as the magnetocaloric effect. We present a 3-dimensional time-dependent numerical model that spatially resolves samples down to the grain size, and includes the demagnetizing field, chemical inhomogeneity realized as a spatial variation of Curie temperature across the sample, local...... hysteresis and heat transfer. We can thus model how particle size, packing, sintering and chemical inhomogeneity affect the observed properties of magnetocaloric samples. For example, we show that even a modest distribution in Curie temperature (TC) across the sample results in a significant broadening...... and lowering of the total entropy change of the sample around TC. We discuss how clustering of grains with similar values of TC across the sample influences the results....

  11. Microstructure and mechanical properties of a new group of nanocrystalline medical-grade stainless steels prepared by powder metallurgy

    International Nuclear Information System (INIS)

    Javanbakht, M.; Hadianfard, M.J.; Salahinejad, E.

    2015-01-01

    Highlights: • This paper focuses on the structure and mechanical properties of PM alloys. • A eutectic Mn–Si alloy sintering aid was successfully used. • Mechanical properties were improved by adding the sintering aid. - Abstract: This paper focuses on the structure and mechanical properties of powder metallurgy stainless steels (Fe–Cr–Mn–Mo–Si–N–C) developed for biomedical applications. The samples were prepared by mechanical alloying and subsequent liquid-phase sintering with a eutectic Mn–Si alloy additive. By changing the sintering aid content, the pore configuration, compressive strengths, and impact properties of the samples were assessed. The Rietveld X-ray diffraction analysis showed after sintering at 1050 °C for 60 min followed by water-quenching, a nanocrystalline austenitic structure was formed in the material. According to the mechanical experiments, by increasing the additive content from 0 wt% to 6 wt%, sintering densification, yield stress, compression strength, and absorbed impact energy were improved, where spoiling occurred when adding 8 wt% additive. Also, as realized from the impact fracture surface features, despite the presence of some unmelted additive particles, the role of the pore elimination in toughness prevailed over that of these particles

  12. High Performance Nano-Crystalline Oxide Fuel Cell Materials. Defects, Structures, Interfaces, Transport, and Electrochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Barnett, Scott [Northwestern Univ., Evanston, IL (United States); Poeppelmeier, Ken [Northwestern Univ., Evanston, IL (United States); Mason, Tom [Northwestern Univ., Evanston, IL (United States); Marks, Lawrence [Northwestern Univ., Evanston, IL (United States); Voorhees, Peter [Northwestern Univ., Evanston, IL (United States)

    2016-09-07

    This project addresses fundamental materials challenges in solid oxide electrochemical cells, devices that have a broad range of important energy applications. Although nano-scale mixed ionically and electronically conducting (MIEC) materials provide an important opportunity to improve performance and reduce device operating temperature, durability issues threaten to limit their utility and have remained largely unexplored. Our work has focused on both (1) understanding the fundamental processes related to oxygen transport and surface-vapor reactions in nano-scale MIEC materials, and (2) determining and understanding the key factors that control their long-term stability. Furthermore, materials stability has been explored under the “extreme” conditions encountered in many solid oxide cell applications, i.e, very high or very low effective oxygen pressures, and high current density.

  13. A New Class of High Z Nanocrystalline and Textured Oxide-Based Thermoelectric Material, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to develop high figure of merit (ZT) oxide-based thermoelectric materials. This will be accomplished by engineering a novel microstructure that will lead...

  14. Beyond crystallography: the study of disorder, nanocrystallinity and crystallographically challenged materials with pair distribution functions.

    Science.gov (United States)

    Billinge, Simon J L; Kanatzidis, M G

    2004-04-07

    Studying the structure of disordered and partially ordered materials is notoriously difficult. Recently, significant advances have been made using the atomic pair distribution function (PDF) analysis of powder diffraction data coupled with the use of advanced X-ray and neutron sources and fast computers. Here we summarize some of the more spectacular successes of this technique in studying the structure of complex materials and compounds. Our purpose is to make the PDF analysis technique familiar to the chemical community by describing its methodologies and highlighting its potential in solving structural characterization problems that are intractable by any other technique available to this community e.g. single crystal diffraction, Rietveld refinement of powder diffraction data and extended X-ray absorption fine structure analysis (EXAFS).

  15. Nanocrystalline materials for the dosimetry of heavy charged particles: A review

    Science.gov (United States)

    Salah, Numan

    2011-01-01

    Thermally stimulated luminescence or better known as thermoluminescence (TL) is a powerful technique extensively used for dosimetry of ionizing radiations. TL dosimeter (TLD) materials presently in use are inorganic crystalline materials. They are in the form of chips, single crystals or microcrystalline size powder. The most popular are LiF:Mg,Ti, LiF:Mg,Cu,P, CaSO 4:Dy, CaF 2:Dy and Al 2O 3:C. However, these TLD materials are not capable of precisely detecting heavy charged particles (HCP) irradiations in their present forms. The saturation effect is the major problem, which occurs at relatively low fluences (doses). Moreover, there is a significant variation in the TL glow curves structure with increase in doses, which is undesirable for the use in dosimetry. However, with the use of very tiny particles such as nanoscale TLD materials, this problem is overcome to a major extent. The TL results of the recently reported nanomaterials have revealed very imperative characteristics such as high sensitivity and saturation at very high doses. Recent studies on different luminescent nanomaterials showed that they have a potential application in dosimetry of heavy charged particles using TL technique, where the conventional microcrystalline phosphors saturate. This paper is a review on the prepared TLD nanomaterials, studied for their TL response to HCP. These are CaSO 4:Dy, LiF:Mg,Cu,P, K 2Ca 2(SO 4) 3:Eu and Ba 0.97Ca 0.03SO 4:Eu nanomaterials. The important results obtained in these nanomaterials and the possibility of using them as HCP dosimeters are discussed.

  16. Fabrication and properties of dense ex situ magnesium diboride bulk material synthesized using spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Dancer, C E J; Todd, R I; Grovenor, C R M [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Prabhakaran, D [Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Basoglu, M; Yanmaz, E [Department of Physics, Faculty of Arts and Sciences, Karadeniz Technical University, 61080 Trabzon (Turkey); Yan, H; Reece, M, E-mail: claire.dancer@linacre.oxon.or [Department of Materials, Queen Mary, University of London, Mile End Road, London E1 4NS (United Kingdom)

    2009-09-15

    High density ex situ magnesium diboride bulks were synthesized from commercial MgB{sub 2} powder using spark plasma sintering under a range of applied uniaxial pressures between 16 and 80 MPa. The microstructure was characterized using x-ray diffraction, scanning electron microscopy, polarized optical microscopy, Vickers hardness measurements, and density measurements using the Archimedes method. By combining these data with those for other bulk samples we have developed a correlation curve for the hardness and density for magnesium diboride for relative densities of 60-100%. The superconducting properties were determined using magnetization measurements. Comparison to samples of significantly higher porosity indicates a positive correlation between magnetization critical current density and bulk density for magnesium diboride bulks up to around 90% density. Above this level other microstructural processes such as grain growth begin to influence the critical current density, suggesting that full elimination of porosity is not necessary to obtain high critical current density. We conclude that the best superconducting properties are likely to be obtained with a combination of small grain size and minimal porosity.

  17. Colloidal Nanocrystalline Semiconductor Materials as Photocatalysts for Environmental Protection of Architectural Stone

    Directory of Open Access Journals (Sweden)

    Francesca Petronella

    2017-01-01

    Full Text Available Rod-shaped TiO2 nanocrystals (TiO2 NRs, capped by oleic acid molecules (OLEA, were synthesized with controlled size, shape and surface chemistry by using colloidal routes. They were investigated for application as coating materials for preserving architectural stone of monumental and archaeological interest, in consideration of their self-cleaning and protection properties. For this purpose, two different deposition techniques, namely casting and dipping, were tested for the application of a nanocrystal dispersion on a defined stone type, as a relevant example of porous calcarenites, namely the Pietra Leccese, a building stone widely used in monuments and buildings of cultural and historic interest of the Apulia region (Italy. The physical properties of the stone surface were investigated before and after the treatment with the prepared nanostructured materials. In particular, colour, wettability, water transfer properties and stability of the coating were monitored as a function of time and of the application method. The self-cleaning properties of the TiO2 NRs coated surfaces were tested under simulated and real solar irradiation. The obtained results were discussed in the light of the specific surface chemistry and morphology of TiO2 NRs, demonstrating the effectiveness of TiO2 NRs as an active component in formulations for stone protection.

  18. Boric oxide or boric acid sintering aid for sintering ceramics

    International Nuclear Information System (INIS)

    Lawler, H.A.

    1979-01-01

    The invention described relates to the use of liquid sintering aid in processes involving sintering of ceramic materials to produce dense, hard articles having industrial uses. Although the invention is specifically discussed in regard to compositions containing silicon carbide as the ceramic material, other sinterable carbides, for example, titanium carbide, may be utilized as the ceramic material. A liquid sintering aid for densifying ceramic material is selected from solutions of H 3 BO 3 , B 2 O 3 and mixtures of these solutions. In sintering ceramic articles, e.g. silicon carbide, a shaped green body is formed from a particulate ceramic material and a resin binder, and the green body is baked at a temperature of 500 to 1000 0 C to form a porous body. The liquid sintering aid of B 2 O 3 and/or H 3 BO 3 is then dispersed through the porous body and the treated body is sintered at a temperature of 1900 to 2200 0 C to produce the sintered ceramic article. (U.K.)

  19. Synthesis and Sintering Behavior of Cordierite Prepared from Multi-Component Materials Including Alkaline-Earth Minerals

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Suk-In; Kim, Nam-Il; Lee, Sang-Jin [Mokpo National University, Muan (Korea, Republic of)

    2016-10-15

    Cordierite was synthesized using multi-component materials based on a talc-alumina-clay system. The cordierite sintered at 1360 °C showed a high relative density of 98.8% and a low thermal expansion coefficient of 1.59×10{sup -}6/°C. To study the effect of adding alkaline-earth minerals on the cordierite properties, petalite, potash-feldspar, and dicalcium phosphate were added to the synthesized cordierite. In the case of 9 wt% petalite or potash-feldspar addition, the cordierite was more densified; however, the thermal expansion coefficient and the pyroplasticity index were increased. In particular, a 5 μm thick self-glazed coating was formed with the addition of 9 wt% potash-feldspar. In the case of adding dicalcium phosphate, a glass phase was formed at low temperature and gas bubbles formed at high temperature above 1320 ℃. The cordierite synthesized using multi-component materials is expected to be employed as a material for high thermal shock, dense-microstructure flameware.

  20. Titanium carbide-carbon porous nanocomposite materials for radioactive ion beam production: processing, sintering and isotope release properties

    CERN Document Server

    AUTHOR|(CDS)2081922; Stora, Thierry

    2017-01-26

    The Isotope Separator OnLine (ISOL) technique is used at the ISOLDE - Isotope Separator OnLine DEvice facility at CERN, to produce radioactive ion beams for physics research. At CERN protons are accelerated to 1.4 GeV and made to collide with one of two targets located at ISOLDE facility. When the protons collide with the target material, nuclear reactions produce isotopes which are thermalized in the bulk of the target material grains. During irradiation the target is kept at high temperatures (up to 2300 °C) to promote diffusion and effusion of the produced isotopes into an ion source, to produce a radioactive ion beam. Ti-foils targets are currently used at ISOLDE to deliver beams of K, Ca and Sc, however they are operated at temperatures close to their melting point which brings target degradation, through sintering and/or melting which reduces the beam intensities over time. For the past 10 years, nanostructured target materials have been developed and have shown improved release rates of the produced i...

  1. Corrosion Behavior and Strength of Dissimilar Bonding Material between Ti and Mg Alloys Fabricated by Spark Plasma Sintering

    Science.gov (United States)

    Pripanapong, Patchara; Kariya, Shota; Luangvaranunt, Tachai; Umeda, Junko; Tsutsumi, Seiichiro; Takahashi, Makoto; Kondoh, Katsuyoshi

    2016-01-01

    Ti and solution treated Mg alloys such as AZ31B (ST), AZ61 (ST), AZ80 (ST) and AZ91 (ST) were successfully bonded at 475 °C by spark plasma sintering, which is a promising new method in welding field. The formation of Ti3Al intermetallic compound was found to be an important factor in controlling the bonding strength and galvanic corrosion resistance of dissimilar materials. The maximum bonding strength and bonding efficiency at 193 MPa and 96% were obtained from Ti/AZ91 (ST), in which a thick and uniform nano-level Ti3Al layer was observed. This sample also shows the highest galvanic corrosion resistance with a measured galvanic width and depth of 281 and 19 µm, respectively. The corrosion resistance of the matrix on Mg alloy side was controlled by its Al content. AZ91 (ST) exhibited the highest corrosion resistance considered from its corrode surface after corrosion test in Kroll’s etchant. The effect of Al content in Mg alloy on bonding strength and corrosion behavior of Ti/Mg alloy (ST) dissimilar materials is discussed in this work. PMID:28773788

  2. Corrosion Behavior and Strength of Dissimilar Bonding Material between Ti and Mg Alloys Fabricated by Spark Plasma Sintering

    Directory of Open Access Journals (Sweden)

    Patchara Pripanapong

    2016-08-01

    Full Text Available Ti and solution treated Mg alloys such as AZ31B (ST, AZ61 (ST, AZ80 (ST and AZ91 (ST were successfully bonded at 475 °C by spark plasma sintering, which is a promising new method in welding field. The formation of Ti3Al intermetallic compound was found to be an important factor in controlling the bonding strength and galvanic corrosion resistance of dissimilar materials. The maximum bonding strength and bonding efficiency at 193 MPa and 96% were obtained from Ti/AZ91 (ST, in which a thick and uniform nano-level Ti3Al layer was observed. This sample also shows the highest galvanic corrosion resistance with a measured galvanic width and depth of 281 and 19 µm, respectively. The corrosion resistance of the matrix on Mg alloy side was controlled by its Al content. AZ91 (ST exhibited the highest corrosion resistance considered from its corrode surface after corrosion test in Kroll’s etchant. The effect of Al content in Mg alloy on bonding strength and corrosion behavior of Ti/Mg alloy (ST dissimilar materials is discussed in this work.

  3. One-step low temperature reactive consolidation of high purity nanocrystalline Mg{sub 2}Si

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Shaoping, E-mail: chenshaoping@tyut.edu.cn [Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Zhang, Xia [Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024 (China); Fan, Wenhao, E-mail: fanwenhao1979@163.com [Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024 (China); Yi, Tanghong [Department of Chemistry, University of California, Davis, CA 95616 (United States); Quach, Dat V. [Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616 (United States); Bux, Sabah [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Meng, Qingsen [Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Kauzlarich, Susan M. [Department of Chemistry, University of California, Davis, CA 95616 (United States); Munir, Zuhair A. [Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616 (United States)

    2015-03-15

    Highlights: • Bulk nanocrystalline Mg{sub 2}Si were fabricated by one-step reactive sintering. • Use of MgH{sub 2} instead of Mg prevented the formation of MgO. • Presence of the pores contributed to decreasing the thermal conductivity. • Samples with 1 at.% Bi had a maximum ZT of 0.6 at 775. - Abstract: Bulk nanocrystalline Mg{sub 2}Si thermoelectric materials were synthesized and consolidated in a one-step process through a solid-state reaction between magnesium hydride and silicon, using the spark plasma sintering (SPS) method. The hydrogen produced in the process alleviates the problem of the oxidation of Mg. The samples were reactively sintered at temperatures in the range 723–823 K and under a uniaxial pressure in the range of 71–164 MPa in 5 min. Powder X-ray diffraction (XRD) analysis showed the products to be pure Mg{sub 2}Si. The grain size of the consolidated samples was less than 500 nm, as determined by transmission electron spectroscopy (TEM). Residual nano-pores were observed by scanning electron microscopy at grain boundaries; their presence is believed to be the consequence of hydrogen evolution during the reactive sintering. The effect of synthesis temperature and pressure on crystallite size, density, and transport properties was determined. The results showed that use of MgH{sub 2} instead of Mg in the one-step method prevents the formation of MgO. The addition of 1 at.% Bi as a dopant improved the power factor significantly. Samples with 1 at.% Bi had a ZT of 0.6 at 775 K.

  4. Transparent nanocrystalline ZnO films prepared by spin coating

    International Nuclear Information System (INIS)

    Berber, M.; Bulto, V.; Kliss, R.; Hahn, H.

    2005-01-01

    Dispersions of zinc oxide nanoparticles synthesized by the electrochemical deposition under oxidizing conditions process with organic surfactants, were spin coated on glass substrates. After sintering, the microstructure, surface morphology, and electro-optical properties of the transparent nanocrystalline zinc oxide films have been investigated for different coating thicknesses and organic solvents

  5. [Determination of high temperature compressive strength and refractory degree of die material compatible with slip casting core of sintered titanium powder].

    Science.gov (United States)

    Kuang, X; Liao, Y; Chao, Y; Meng, Y

    1999-05-01

    The refractory die is the precondition for developing slip casting core of sintered powder. This study is to determine the high temperature properties of the refractory die material compatible with slip casting core. To prepare three cylindrical specimens (phi 10 x 15 mm) and determine their compressive strength at 1000 degrees C: to make four specimens in flat-topped cone for determining the practical refractory degree by decreasing the pressing temperatures in a sequence of 1420, 1400, 1350 and 1100 degrees C. The compressive strength of this material was 17.8 MPa at 1000 degrees C. Its practical refractory degree was higher than 1100 degrees C. The high temperature properties of the refractory die material that we developed meet the demand of slip casting core of sintered powder.

  6. Fabrication of Tungsten-Rhenium Cladding materials via Spark Plasma Sintering for Ultra High Temperature Reactor Applications

    Energy Technology Data Exchange (ETDEWEB)

    Charit, Indrajit; Butt, Darryl; Frary, Megan; Carroll, Mark

    2012-11-05

    This research will develop an optimized, cost-effective method for producing high-purity tungsten-rhenium alloyed fuel clad forms that are crucial for the development of a very high-temperature nuclear reactor. The study will provide critical insight into the fundamental behavior (processing-microstructure- property correlations) of W-Re alloys made using this new fabrication process comprising high-energy ball milling (HEBM) and spark plasma sintering (SPS). A broader goal is to re-establish the U.S. lead in the research field of refractory alloys, such as W-Re systems, with potential applications in very high-temperature nuclear reactors. An essential long-term goal for nuclear power is to develop the capability of operating nuclear reactors at temperatures in excess of 1,000K. This capability has applications in space exploration and some special terrestrial uses where high temperatures are needed in certain chemical or reforming processes. Refractory alloys have been identified as being capable of withstanding temperatures in excess of 1,000K and are considered critical for the development of ultra hightemperature reactors. Tungsten alloys are known to possess extraordinary properties, such as excellent high-temperature capability, including the ability to resist leakage of fissile materials when used as a fuel clad. However, there are difficulties with the development of refractory alloys: 1) lack of basic experimental data on thermodynamics and mechanical and physical properties, and 2) challenges associated with processing these alloys.

  7. Structural and microstructural characterizations of nanocrystalline hydroxyapatite synthesized by mechanical alloying.

    Science.gov (United States)

    Lala, S; Satpati, B; Kar, T; Pradhan, S K

    2013-07-01

    Single phase nanocrystalline hydroxyapatite (HAp) powder has been synthesized by mechanical alloying the stoichiometric mixture of CaCO3 and CaHPO4 powders in open air at room temperature, for the first time, within 2 h of milling. Nanocrystalline hexagonal single crystals are obtained by sintering of 2h milled sample at 500 °C. Structural and microstructural properties of as-milled and sintered powders are revealed from both the X-ray line profile analysis and transmission electron microscopy. Shape and lattice strain of nanocrystalline HAp particles are found to be anisotropic in nature. Particle size of HAp powder remains almost invariant up to 10h of milling and there is no significant growth of nanocrystalline HAp particles after sintering at 500 °C for 3 h. Changes in lattice volume and some primary bond lengths of as-milled and sintered are critically measured, which indicate that lattice imperfections introduced into the HAp lattice during ball milling have been reduced partially after sintering the powder at elevated temperatures. We could achieve ~96.7% of theoretical density of HAp within 3h by sintering the pellet of nanocrystalline powder at a lower temperature of 1000 °C. Vickers microhardness (VHN) of the uni-axially pressed (6.86 MPa) pellet of nanocrystalline HAp is 4.5 GPa at 100 gm load which is close to the VHN of bulk HAp sintered at higher temperature. The strain-hardening index (n) of the sintered pellet is found to be >2, indicating a further increase in microhardness value at higher load. Copyright © 2013 Elsevier B.V. All rights reserved.

  8. Protocol for Ultralow-Temperature Ceramic Sintering: An Integration of Nanotechnology and the Cold Sintering Process.

    Science.gov (United States)

    Guo, Hanzheng; Baker, Amanda; Guo, Jing; Randall, Clive A

    2016-11-22

    The sintering process is an essential step in taking particulate materials into dense ceramic materials. Although a number of sintering techniques have emerged over the past few years, the sintering process is still performed at high temperatures. Here we establish a protocol to achieve dense ceramic solids at extremely low temperatures (sustainable manufacturing practices.

  9. STUDIES ON THE BEHAVIOR OF THE SINTERED MATERIAL BASED ON IRON POWDER TO MECHANICAL COMPRESSION

    Directory of Open Access Journals (Sweden)

    Cristina IONICI

    2014-05-01

    Full Text Available Compression test at low temperature is 130-150 K range and the conditions set out in the technical execution of the tests carried out at low temperatures. As observed with MS do not behave traction to mechanical stress as compact material. The pore structure of the MS presence influence the mechanical behavior of which have been found in the case of mechanical compression test at room temperature.

  10. Synchrotron X-ray diffraction studies of phase transitions and mechanical properties of nanocrystalline materials at high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Prilliman, Stephen Gerald [Univ. of California, Berkeley, CA (United States)

    2003-01-01

    The behavior of nanocrystals under extreme pressure was investigated using synchrotron x-ray diffraction. A major part of this investigation was the testing of a prototype synchrotron endstation on a bend magnet beamline at the Advanced Light Source for high pressure work using a diamond anvil cell. The experiments conducted and documented here helped to determine issues of efficiency and accuracy that had to be resolved before the construction of a dedicated ''super-bend'' beamline and endstation. The major conclusions were the need for a cryo-cooled monochromator and a fully remote-controllable pressurization system which would decrease the time to change pressure and greatly reduce the error created by the re-placement of the diamond anvil cell after each pressure change. Two very different types of nanocrystal systems were studied, colloidal iron oxide (Fe2O3) and thin film TiN/BN. Iron oxide nanocrystals were found to have a transition from the γ to the α structure at a pressure strongly dependent on the size of the nanocrystals, ranging from 26 GPa for 7.2 nm nanocrystals to 37 GPa for 3.6 nm nanocrystals. All nanocrystals were found to remain in the α structure even after release of pressure. The transition pressure was also found, for a constant size (5.7 nm) to be strongly dependent on the degree of aggregation of the nanocrystals, increasing from 30 GPa for completely dissolved nanocrystals to 45 GPa for strongly aggregated nanocrystals. Furthermore, the x-ray diffraction pattern of the pressure induced α phase demonstrated a decrease in intensity for certain select peaks. Together, these observations were used to make a complete picture of the phase transition in nanocrystalline systems. The size dependence of the transition was interpreted as resulting from the extremely high surface energy of the α phase which would increase the thermodynamic offset and thereby increase the kinetic barrier to transition

  11. Synchrotron X-ray diffraction studies of phase transitions and mechanical properties of nanocrystalline materials at high pressure

    International Nuclear Information System (INIS)

    Prilliman, Gerald Stephen

    2003-01-01

    The behavior of nanocrystals under extreme pressure was investigated using synchrotron x-ray diffraction. A major part of this investigation was the testing of a prototype synchrotron endstation on a bend magnet beamline at the Advanced Light Source for high pressure work using a diamond anvil cell. The experiments conducted and documented here helped to determine issues of efficiency and accuracy that had to be resolved before the construction of a dedicated ''super-bend'' beamline and endstation. The major conclusions were the need for a cryo-cooled monochromator and a fully remote-controllable pressurization system which would decrease the time to change pressure and greatly reduce the error created by the re-placement of the diamond anvil cell after each pressure change. Two very different types of nanocrystal systems were studied, colloidal iron oxide (Fe 2 O 3 ) and thin film TiN/BN. Iron oxide nanocrystals were found to have a transition from the γ to the α structure at a pressure strongly dependent on the size of the nanocrystals, ranging from 26 GPa for 7.2 nm nanocrystals to 37 GPa for 3.6 nm nanocrystals. All nanocrystals were found to remain in the α structure even after release of pressure. The transition pressure was also found, for a constant size (5.7 nm) to be strongly dependent on the degree of aggregation of the nanocrystals, increasing from 30 GPa for completely dissolved nanocrystals to 45 GPa for strongly aggregated nanocrystals. Furthermore, the x-ray diffraction pattern of the pressure induced α phase demonstrated a decrease in intensity for certain select peaks. Together, these observations were used to make a complete picture of the phase transition in nanocrystalline systems. The size dependence of the transition was interpreted as resulting from the extremely high surface energy of the α phase which would increase the thermodynamic offset and thereby increase the kinetic barrier to transition that must be overridden with pressure

  12. Sintering of Synroc D

    International Nuclear Information System (INIS)

    Robinson, G.

    1982-01-01

    Sintering has been investigated as a method for the mineralization and densification of high-level nuclear defense waste powder. Studies have been conducted on Synroc D composite powder LS04. Optimal densification has been found to be highly dependent on the characteristics of the starting material. Powder subjected to milling, which was believed to reduce the level of agglomeration and possibly particle size, was found to densify better than powder not subjected to this milling. Densities of greater than 95% of theoretical could be achieved for samples sintered at 1150 to 1200 0 C. Mineralogy was found to be as expected for Synroc D for samples sintered in a CO 2 /CO atmosphere where the Fe +2 /Fe +3 ratio was maintained at 1.0 to 5.75. In a more oxidizing, pure CO 2 atmosphere a new phase, not previously identified in Synroc D, was found

  13. Sintered gahnite–cordierite glass-ceramic based on raw materials ...

    Indian Academy of Sciences (India)

    1732. Esmat M A Hamzawy and Mohammed A Bin Hussain. Table 1. Chemical composition of the base glass in wt% and the additives. Oxides from raw materials in wt%. Commercial additions. Oxides. SiO2. Al2O3. Fe2O3. CaO MgO Na2O K2O TiO2. ZnO. AlF3 a. MgF2 a. CaF2 a. SCb. 51.36. 34.86. —. —. 13.78. —. —. —.

  14. Glass-ceramic material of the Si-Ca-K system sintered from sugarcane bagasse ash

    International Nuclear Information System (INIS)

    Teixeira, S.R.; Silva, R.A.; Santos, G.C.; Santos, G.T.A.; Romero, M.; Rincon, J.Ma.; Reynoso, V.C.S.

    2009-01-01

    This study analyses the crystallization of glasses obtained from two samples of sugarcane bagasse ash - SCBA (named Cinza 07 and Cinza 08) mixed with carbonates (calcium and potassium). The glasses and their crystallization were examined using differential thermal analysis (DTA), X-ray fluorescence (XRF) and X-ray diffraction (XRD). The characterizations of the ashes show that they consist mainly of crystalline materials, predominantly quartz, with iron, potassium and aluminum oxides as minor elements. For the sample Cinza07 the DTA data presents broad and overlaid crystallization peaks, indicating crystallization of more than two different phases. The DTA results of samples with different grain-size distribution show that the crystallization peak intensities increase as the sample grain-size decreases, suggesting that surface crystallization actively participate on the mechanism of crystallization. For the sample Cinza 08 the DTA data presents two well defined peaks. In this case, the more intense peak was evaluated to obtain kinetic data (Eat= 355 kJ/mol) to the major phase (Wollastonita). (author)

  15. Comparison of Reactive and Non-Reactive Spark Plasma Sintering Routes for the Fabrication of Monolithic and Composite Ultra High Temperature Ceramics (UHTC Materials

    Directory of Open Access Journals (Sweden)

    Roberto Orrù

    2013-04-01

    Full Text Available A wider utilization of ultra high temperature ceramics (UHTC materials strongly depends on the availability of efficient techniques for their fabrication as dense bodies. Based on recent results reported in the literature, it is possible to state that Spark Plasma Sintering (SPS technology offers a useful contribution in this direction. Along these lines, the use of two different SPS-based processing routes for the preparation of massive UHTCs is examined in this work. One method, the so-called reactive SPS (R-SPS, consists of the synthesis and densification of the material in a single step. Alternatively, the ceramic powders are first synthesized by Self-propagating High-temperature Synthesis (SHS and then sintered by SPS. The obtained results evidenced that R-SPS method is preferable for the preparation of dense monolithic products, while the sintering of SHS powders requires relatively milder conditions when considering binary composites. The different kinetic mechanisms involved during R-SPS of the monolithic and composite systems, i.e., combustion-like or gradual solid-diffusion, respectively, provides a possible explanation. An important role is also played by the SHS process, particularly for the preparation of composite powders, since stronger interfaces are established between the ceramic constituents formed in situ, thus favoring diffusion processes during the subsequent SPS step.

  16. Study on the mechanical properties, microstructure and corrosion behaviors of nano-WC–Co–Ni–Fe hard materials through HIP and hot-press sintering processes

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Shih-Hsien, E-mail: changsh@ntut.edu.tw; Chang, Po-Yu

    2014-11-17

    This study aims to explore a series of Hot Isostatic Pressing (HIP) and hot-press sintering processes in order to examine the effects on the mechanical properties, microstructures and corrosion behaviors of micro- and nano-WC materials. The experimental results showed that the transverse rupture strength (TRS) values of micro- and nano-WC increased to 1627.3 and 1842.7 MPa after 1250 °C, 125 MPa, 100 min HIP treatments, respectively. Meanwhile, the porosity decreased slightly. The corrosion test results also showed that HIP-treated micro- and nano-WC effectively improved corrosion resistance in a 3.5 wt% NaCl solution. In addition, the lowest porosity (0.21%), highest hardness (91.7 HRA) and highest K{sub IC} (14.7 MPa√m) values appeared in nano-WC after 1250 °C, 15 MPa, 1 h hot-press sintering. Moreover, the hot-press sintering procedure significantly inhibited the grain growth of the tungsten carbide materials.

  17. The Setup Design for Selective Laser Sintering of High-Temperature Polymer Materials with the Alignment Control System of Layer Deposition

    Directory of Open Access Journals (Sweden)

    Alexey Nazarov

    2018-03-01

    Full Text Available This paper presents the design of an additive setup for the selective laser sintering (SLS of high-temperature polymeric materials, which is distinguished by an original control system for aligning the device for depositing layers of polyether ether ketone (PEEK powder. The kinematic and laser-optical schemes are given. The main cooling circuits are described. The proposed technical and design solutions enable conducting the SLS process in different types of high-temperature polymer powders. The principles of the device adjustment for depositing powder layers based on an integral thermal analysis are disclosed. The PEEK sinterability was shown on the designed installation. The physic-mechanical properties of the tested 3D parts were evaluated in comparison with the known data and showed an acceptable quality.

  18. High-quality reduced graphene oxide-nanocrystalline platinum hybrid materials prepared by simultaneous co-reduction of graphene oxide and chloroplatinic acid

    Directory of Open Access Journals (Sweden)

    Wang Yinjie

    2011-01-01

    Full Text Available Abstract Reduced graphene oxide-nanocrystalline platinum (RGO-Pt hybrid materials were synthesized by simultaneous co-reduction of graphene oxide (GO and chloroplatinic acid with sodium citrate in water at 80°C, of pH 7 and 10. The resultant RGO-Pt hybrid materials were characterized using transmission electron microscopy (TEM, powder X-ray diffraction (XRD, X-ray photoelectron spectroscopy (XPS, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Platinum (Pt nanoparticles were anchored randomly onto the reduced GO (RGO sheets with average mean diameters of 1.76 (pH 7 and 1.93 nm (pH 10. The significant Pt diffraction peaks and the decreased intensity of (002 peak in the XRD patterns of RGO-Pt hybrid materials confirmed that the Pt nanoparticles were anchored onto the RGO sheets and intercalated into the stacked RGO layers at these two pH values. The Pt loadings for the hybrid materials were determined as 36.83 (pH 7 and 49.18% (pH 10 by mass using XPS analysis. With the assistance of oleylamine, the resultant RGO-Pt hybrid materials were soluble in the nonpolar organic solvents, and the dispersion could remain stable for several months.

  19. SinterHab

    Science.gov (United States)

    Rousek, Tomáš; Eriksson, Katarina; Doule, Ondřej

    2012-05-01

    This project describes a design study for a core module on a Lunar South Pole outpost, constructed by 3D printing technology with the use of in-situ resources and equipped with a bio-regenerative life support system. The module would be a hybrid of deployable (CLASS II) and in-situ built (CLASS III) structures. It would combine deployable membrane structures and pre-integrated rigid elements with a sintered regolith shell for enhanced radiation and micrometeorite shielding. The closed loop ecological system would support a sustainable presence on the Moon with particular focus on research activities. The core module accommodates from four to eight people, and provides laboratories as a test bed for development of new lunar technologies directly in the environment where they will be used. SinterHab also includes an experimental garden for development of new bio-regenerative life support system elements. The project explores these various concepts from an architectural point-of-view particularly, as they constitute the building, construction and interior elements. The construction method for SinterHab is based on 3D printing by sintering of the lunar regolith. Sinterator robotics 3D printing technology proposed by NASA JPL enables construction of future generations of large lunar settlements with little imported material and the use of solar energy. The regolith is processed, placed and sintered by the Sinterator robotics system which combines the NASA ATHLETE and the Chariot remotely controlled rovers. Microwave sintering creates a rigid structure in the form of walls, vaults and other architectural elements. The interior is coated with a layer of inflatable membranes inspired by the TransHab project. The life-support system is mainly bio-regenerative and several parts of the system are intrinsically multifunctional and serve more than one purpose. The plants for food production are also an efficient part of atmosphere revitalization and water treatment. Moreover

  20. Functional properties of coated by chemical vapour deposition sintered tool materials investigated with use of tribological tests

    Directory of Open Access Journals (Sweden)

    J. Mikuła

    2017-01-01

    Full Text Available The purpose of the work is to present the results of investigations into the structure and properties of sintered carbides with deposited wear resistant coatings after a tribological test carried out with the method of combined examination of abrasion wear resistance and edge fracture resistance.

  1. An Alternative to Clay in Building Materials: Red Mud Sintering Using Fly Ash via Taguchi’s Methodology

    Directory of Open Access Journals (Sweden)

    Suchita Rai

    2013-01-01

    Full Text Available “Red mud” or “bauxite residue” is a highly alkaline waste generated from alumina refinery with a pH of 10.5–12.5 which poses serious environmental problems. Neutralization or its treatment by sintering in presence of additives is one of the methods for overcoming the caustic problem as it fixes nearly all the leachable free caustic soda present in red mud. In the present study, feasibility of reducing the alkaline nature of red mud by sintering using fly ash as an additive via Taguchi methodology and its use for brick production, as an alternative to clay, is investigated. The analysis of variance (ANOVA shows that sintering temperature is the most significant parameter in the process. A pH of 8.9 was obtained at 25–50% of red mud and 50–75% fly ash with water and temperature of . Alternatively 50% of red mud can be mixed with 50% of fly ash with water at temperature of to get a pH of about 8.4. The mechanism of this process has been explained with also emphasis on chemical, mineralogical, and morphological analysis of the sintered red mud. The results would be extremely useful in utilization of red mud in building and construction industry.

  2. Production of sintered alumina from powder; optimization of the sinterized parameters for the maximum mechanical resistence

    International Nuclear Information System (INIS)

    Rocha, J.C. da.

    1981-02-01

    Pure, sinterized alumina and the optimization of the parameters of sinterization in order to obtain the highest mechanical resistence are discussed. Test materials are sinterized from a fine powder of pure alumina (Al 2 O 3 ), α phase, at different temperatures and times, in air. The microstructures are analysed concerning porosity and grain size. Depending on the temperature or the time of sinterization, there is a maximum for the mechanical resistence. (A.R.H.) [pt

  3. Synthesis of nanocrystalline CdS thin films in PVA matrix

    Indian Academy of Sciences (India)

    TECS

    The band gap of the nanocrystalline material is determined from the UV spectrograph. The absorption edge is shifted towards the lower wave length side (i.e. blue ... In recent years nanocrystalline thin films of different II–VI compound semiconductors have been widely synthesized and studied. Nanocrystalline thin films are ...

  4. Nanocrystalline WC-Co HVAF Coatings by Utilizing Novel Powder Manufacturing Route Using Water-Soluble Raw Materials

    Science.gov (United States)

    Karhu, Marjaana; Lagerbom, Juha; Kaunisto, Kimmo; Suhonen, Tomi; Metsäjoki, Jarkko; Turunen, Erja

    2018-01-01

    In this study, nanostructured WC-Co coatings were produced using experimental nanocrystalline WC-12Co and WC-24Co powders produced by a novel chemical synthesis route. Test coatings were produced using HVAF spraying keeping the temperature as low as possible during the deposition in order to avoid decomposition of the nanocarbides. In experimental powders, two different Co incorporation methods were used: a conventional way in which cobalt was incorporated as a metallic Co powder and a chemical synthesis way in which cobalt acetate was used as a cobalt source. When using cobalt acetate, it decomposes to metallic cobalt during the process. Experimental powders in which cobalt acetate has been used as cobalt source resulted poor deposition efficiency. With warmer parameters, powders resulted better DE, but significant WC decarburization and the dissolution into the matrix phase occurred. Powders in which Co has been introduced as Co powder showed enhanced DE enabling spraying with decreased temperature and higher particle velocity, resulting in coatings with less WC decomposition. Especially, an experimental powder in which Co has been incorporated both as Co powder and as Co-Ac results very fine nanocarbide structure with significantly less WC decomposition having a hardness value of 1201 HV0.3, even with 24% Co.

  5. Microscopic appearance analysis of raw material used for the production of sintered UO2 by scanning electron microscope

    International Nuclear Information System (INIS)

    Liu feiming

    1992-01-01

    The paper describes the microscopic appearance of UO 2 , U 3 O 8 , ADU and AUC powders used for the production of sintered UO 2 slug of nuclear fuel component of PWR. The characteristic analysis of the microscopic appearance observed by scanning electron microscope shows that the quality and finished product rate of sintered UO 2 depend on the appearance characteristic of the active Uo 2 powder, such as grade size and its distribution, spherulitized extent, surface condition and heap model etc.. The addition of U 3 O 8 to the UO 2 powder improves significantly the quality and the finished product rate. The mechanism of this effect is discussed on the basis of the microscopic appearance characteristic for two kinds of powder

  6. Sintering additives for zirconia ceramics

    International Nuclear Information System (INIS)

    Wu, S.

    1986-01-01

    This book is an overview of sintering science and its application to zirconia materials including CaO, MgO, and Y/sub 2/O/sub 3/-CeO/sub 2/ doped materials. This book is a reference for first-time exposure to zirconia materials technology, particularly densification

  7. Sintering additives for zirconia ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Wu, S.

    1986-01-01

    This book is an overview of sintering science and its application to zirconia materials including CaO, MgO, and Y/sub 2/O/sub 3/-CeO/sub 2/ doped materials. This book is a reference for first-time exposure to zirconia materials technology, particularly densification.

  8. Grain size and nanoscale effects on the nonlinear pull-in instability and vibrations of electrostatic actuators made of nanocrystalline material

    Science.gov (United States)

    Gholami, R.; Ansari, R.

    2018-01-01

    Presented herein is the study of grain size, grain surface energy and small scale effects on the nonlinear pull-in instability and free vibration of electrostatic nanoscale actuators made of nanocrystalline silicon (Nc-Si). A Mori-Tanaka micromechanical model is utilized to calculate the effective material properties of Nc-Si considering material structure inhomogeneity, grain size and grain surface energy. The small-scale effect is also taken into account using Mindlin’s strain gradient theory. Governing equations are derived in the discretized weak form using the variational differential quadrature method based on the third-order shear defamation beam theory in conjunction with the von Kármán hypothesis. The electrostatic actuation is modeled considering the fringing field effects based upon the parallel plate approximation. Moreover, the Casimir force effect is considered. The pseudo arc-length continuation technique is used to obtain the applied voltage-deflection curve of Nc-Si actuators. Then, a time-dependent small disturbance around the deflected configuration is assumed to solve the free vibration problem. By performing a numerical study, the influences of various factors such as length scale parameter, volume fraction of the inclusion phase, density ratio, average inclusion radius and Casimir force on the pull-in instability and free vibration of Nc-Si actuators are investigated.

  9. Mechanical characteristics of microwave sintered silicon carbide

    Indian Academy of Sciences (India)

    In firing of products by conventionally sintered process, SiC grain gets oxidized producing SiO2 (∼ 32 wt%) and deteriorates the quality of the product substantially. Partially sintered silicon carbide by such a method is a useful material for a varieties of applications ranging from kiln furniture to membrane material.

  10. The Influence of Sintering Temperature of Reactive Sintered (Ti, MoC-Ni Cermets

    Directory of Open Access Journals (Sweden)

    Marek Jõeleht

    2015-09-01

    Full Text Available Titanium-molybdenum carbide nickel cermets ((Ti, MoC-Ni were produced using high energy milling and reactive sintering process. Compared to conventional TiC-NiMo cermet sintering the parameters for reactive sintered cermets vary since additional processes are present such as carbide synthesis. Therefore, it is essential to acquire information about the suitable sintering regime for reactive sintered cermets. One of the key parameters is the final sintering temperature when the liquid binder Ni forms the final matrix and vacancies inside the material are removed. The influence of the final sintering temperature is analyzed by scanning electron microscopy. Mechanical properties of the material are characterized by transverse rupture strength, hardness and fracture toughness.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7179

  11. RELATION BETWEEN PARTICLES SIZE OF RAW MATERIALS AND PROPERTIES OF MULLITE–ZrO2 COMPOSITES PREPARED BY REACTION-SINTERING

    Directory of Open Access Journals (Sweden)

    M. RAHMANI

    2012-09-01

    Full Text Available In this investigation, the mullite–zirconia composites were prepared by reaction-sintering of alumina and zircon powder. Besides, the slip casting method was employed for fabrication of these composites and different times of milling process were used for reducing the particles size of raw materials. Then, the effect of raw materials particles size on the properties of these composites was investigated. The physical properties, fracture toughness, flexural strength, phase composition and microstructure of these composites after firing at 1600°C were studied. The results showed that the milling time and then, particles size of raw materials have a great effect on the phase composition and properties of mullite–zirconia composites. The formation of tetragonal-zirconia is favored by reducing of particle size which, leads to increasing of the fracture toughness and flexural strength of these composites.

  12. Phosphorus containing sintered alloys (review)

    International Nuclear Information System (INIS)

    Muchnik, S.V.

    1984-01-01

    Phosphorus additives are considered for their effect on the properties of sintered alloys of different applications: structural, antifriction, friction, magnetic, hard, superhard, heavy etc. Data are presented on compositions and properties of phosphorus-containing materials produced by the powder metallurgy method. Phosphorus is shown to be an effective activator of sintering in some cases. When its concentration in the material is optimal it imparts the material such properties as strength, viscosity, hardness, wear resistance. Problems concerning powder metallurgy of amorphous phosphorus-containing alloys are reported

  13. The low magnetic field properties of superconducting bulk yttrium barium copper oxide - Sintered versus partially melted material

    Science.gov (United States)

    Hein, R. A.; Hojaji, H.; Barkatt, A.; Shafii, H.; Michael, K. A.; Thorpe, A. N.; Ware, M. F.; Alterescu, S.

    1989-01-01

    A comparison of the low magnetic field properties of sintered (990 C) and partially melted samples (1050 C) has been performed. Changes in the microstructure produced by recrystallization from the melt result in a significant increase in flux pinning at 77 K. Low-frequency (10-100 Hz), low-ac magnetic-field (0.01-9.0 Oe) ac susceptibility data show that gross changes in the loss component accompany the observed changes in microstructure. The effects of applied dc magnetic fields (10-220 Oe) on the ac responses of these microstructures have also been probed.

  14. Sintering and Electrical Characterization of La and Nb Co‐doped SrTiO3 Electrode Materials for Solid Oxide Cell Applications

    DEFF Research Database (Denmark)

    Sudireddy, Bhaskar Reddy; Agersted, Karsten

    2014-01-01

    Single‐phase lanthanum and niobium co‐doped strontium titanate (Sr1–3x/2LaxTi0.9Nb0.1O3; x = 0–0.02) ceramics were prepared. Dilatometry in reducing atmosphere showed an increase in the sintering rate and sintered density with an increase in La amount. Microscopy of fractured surfaces of sintered...

  15. The mechanical properties measurement of multiwall carbon nanotube reinforced nanocrystalline aluminum matrix composite

    International Nuclear Information System (INIS)

    Sharma, Manjula; Pal, Hemant; Sharma, Vimal

    2015-01-01

    Nanocrystalline aluminum matrix composite containing carbon nanotubes were fabricated using physical mixing method followed by cold pressing. The microstructure of the composite has been investigated using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy techniques. These studies revealed that the carbon nanotubes were homogeneously dispersed throughout the metal matrix. The consolidated samples were pressureless sintered in inert atmosphere to further actuate a strong interface between carbon nanotubes and aluminum matrix. The nanoindentation tests carried out on considered samples showed that with the addition of 0.5 wt% carbon nanotubes, the hardness and elastic modulus of the aluminum matrix increased by 21.2 % and 2 % repectively. The scratch tests revealed a decrease in the friction coefficient of the carbon nanotubes reinforced composite due to the presence of lubricating interfacial layer. The prepared composites were promising entities to be used in the field of sporting goods, construction materials and automobile industries

  16. Sintering and densification; new techniques: sinter forging

    International Nuclear Information System (INIS)

    Winnubst, A.J.A.

    1998-01-01

    In this chapter pressure assisted sintering methods will be described. Attention will mainly be paid to sinter forging as a die-wall free uniaxial pressure sintering technique, where large creep strains are possible. Sinter forging is an effective tool to reduce sintering temperature and time and to obtain a nearly theoretically dense ceramic. In this way grain size in tetragonal zirconia ceramics can be reduced down to 100 nm. Another important phenomenon is the reduction of the number density and size of cracks and flaws resulting in higher strength and improved reliability, which is of utmost importance for engineering ceramics. The creep deformation during sinter forging causes a rearrangement of the grains resulting in a reduction of interatomic spaces between grains, while grain boundary (glassy) phases can be removed. The toughness and in some cases the wear resistance is enhanced after sinter forging as a result of the grain-boundary-morphology improvement. (orig.)

  17. Solid state consolidation nanocrystalline copper-tungsten using cold spray

    Energy Technology Data Exchange (ETDEWEB)

    Hall, Aaron Christopher [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sarobol, Pylin [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Argibay, Nicolas [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Clark, Blythe [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Diantonio, Christopher [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    It is well known that nanostructured metals can exhibit significantly improved properties compared to metals with conventional grain size. Unfortunately, nanocrystalline metals typically are not thermodynamically stable and exhibit rapid grain growth at moderate temperatures. This severely limits their processing and use, making them impractical for most engineering applications. Recent work has shown that a number of thermodynamically stable nanocrystalline metal alloys exist. These alloys have been prepared as powders using severe plastic deformation (e.g. ball milling) processes. Consolidation of these powders without compromise of their nanocrystalline microstructure is a critical step to enabling their use as engineering materials. We demonstrate solid-state consolidation of ball milled copper-tantalum nanocrystalline metal powder using cold spray. Unfortunately, the nanocrystalline copper-tantalum powder that was consolidated did not contain the thermodynamically stable copper-tantalum nanostructure. Nevertheless, this does this demonstrates a pathway to preparation of bulk thermodynamically stable nanocrystalline copper-tantalum. Furthermore, it demonstrates a pathway to additive manufacturing (3D printing) of nanocrystalline copper-tantalum. Additive manufacturing of thermodynamically stable nanocrystalline metals is attractive because it enables maximum flexibility and efficiency in the use of these unique materials.

  18. Combustion synthesis of bulk nanocrystalline iron alloys

    Directory of Open Access Journals (Sweden)

    Licai Fu

    2016-02-01

    Full Text Available The controlled synthesis of large-scale nanocrystalline metals and alloys with predefined architecture is in general a big challenge, and making full use of these materials in applications still requires greatly effort. The combustion synthesis technique has been successfully extended to prepare large-scale nanocrystalline metals and alloys, especially iron alloy, such as FeC, FeNi, FeCu, FeSi, FeB, FeAl, FeSiAl, FeSiB, and the microstructure can be designed. In this issue, recent progress on the synthesis of nanocrystalline metals and alloys prepared by combustion synthesis technique are reviewed. Then, the mechanical and tribological properties of these materials with microstructure control are discussed.

  19. Crystal phase evolution, sintering, and strength of anorthite-based LTCC materials by substitution of M2+ (M=Mg, Sr, Ba) for Ca2+

    Science.gov (United States)

    Gu, Sin Il; Shin, Hyo Soon; Yeo, Dong Hun; Nahn, Sahn

    2013-05-01

    LTCC, composed of Ca-Al-Si-O, is well-known for its high strength and phase stability. However research on the correlation of LTCC substrate composition and phase change to strength characteristics has rarely been reported. In this study, an anorthite glass component, group 2 elements, Mg, Sr, and Ba were substituted for Ca, and the resulting changes in the physical properties of the glass were observed. Then, the effect of varying glass composition on the characteristics of LTCCs was investigated. An increase in the Mg content caused an increase in the T g of glass, sintering temperature of the glass/Al2O3 composite material and synthesis temperature of anorthite. The content of Sr and Ba had almost no correlation with T g . Synthesis of BaAlO4 and increased LTCC sintering temperature were observed with the addition of Ba, and high strength of over 320 MPa was demonstrated when glass, Al2O3 and a small amount of anorthite were formed.

  20. Master sintering curve: A practical approach to its construction

    Directory of Open Access Journals (Sweden)

    Pouchly V.

    2010-01-01

    Full Text Available The concept of a Master Sintering Curve (MSC is a strong tool for optimizing the sintering process. However, constructing the MSC from sintering data involves complicated and time-consuming calculations. A practical method for the construction of a MSC is presented in the paper. With the help of a few dilatometric sintering experiments the newly developed software calculates the MSC and finds the optimal activation energy of a given material. The software, which also enables sintering prediction, was verified by sintering tetragonal and cubic zirconia, and alumina of two different particle sizes.

  1. The effect of spark plasma sintering on lithium disilicate glass-ceramics.

    Science.gov (United States)

    Al Mansour, Fatima; Karpukhina, Natalia; Grasso, Salvatore; Wilson, Rory M; Reece, Mike J; Cattell, Michael J

    2015-10-01

    To evaluate the effects of spark plasma sintering (SPS) on the microstructure of lithium disilicate glass-ceramics. IPS e.max CAD glass-ceramic samples were processed using spark plasma sintering (SPS) and conventionally sintered (CS) as a comparison. Specimens were sintered at varying temperatures (T1: 840°C, T2: 820°C, T3: 800°C), heating rates (HR1: 150°C/min, HR2: 300°C/min, HR3: 500°C/min) and pressures (P1: 15MPa, P2: 50MPa, P3: 70MPa). IPS e.max Press glass powder samples were densified at 750 and 800°C (50 or 200MPa pressure). Samples were characterized using XRD, HTXRD, and SEM and quantitative image analysis. There was a significant increase in median crystal size (MCS) between the CS and the SPS T1 groups. A statistical difference (p>0.05) in MCS between SPS T1 and SPS T2 groups was observed. The SPS HR3 sample produced a smaller MCS than the CS, SPS HR1 and HR2 groups (pglass samples resulted in fine fibrils or graduated lithium disilicate crystals. The effects of SPS were used to refine the microstructure of IPS e.max CAD lithium disilicate glass-ceramics. Densification by SPS of IPS e.max Press glass resulted in textured and fine nano-crystalline microstructures. SPS generated glass-ceramic microstructures may have unique properties and could be useful in the production of CAD/CAM materials for dentistry. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  2. THE POLARIZING EFFECTS IN SINTERED KAOLIN

    African Journals Online (AJOL)

    compacted and sintered density of the ceramic have been studied, and a density — pressure relationship for before- and after-sintering conditions obtained. INTRODUCTION. Ceramics have been known to mankind for thousands of years, and have been used in construction materials. In many applications, ceramics have.

  3. NATO Advanced Research Workshop on Properties and Applications of Nanocrystalline Alloys from Amorphous Precursors

    CERN Document Server

    Idzikowski, Bogdan; Miglierini, Marcel

    2005-01-01

    Metallic (magnetic and non-magnetic) nanocrystalline materials have been known for over ten years but only recent developments in the research into those complex alloys and their metastable amorphous precursors have created a need to summarize the most important accomplishments in the field. This book is a collection of articles on various aspects of metallic nanocrystalline materials, and an attempt to address this above need. The main focus of the papers is put on the new issues that emerge in the studies of nanocrystalline materials, and, in particular, on (i) new compositions of the alloys, (ii) properties of conventional nanocrystalline materials, (iii) modeling and simulations, (iv) preparation methods, (v) experimental techniques of measurements, and (vi) different modern applications. Interesting phenomena of the physics of nanocrystalline materials are a consequence of the effects induced by the nanocrystalline structure. They include interface physics, the influence of the grain boundaries, the aver...

  4. Magnetization loss of nanocrystalline soft magnets

    International Nuclear Information System (INIS)

    Flohrer, Sybille; Herzer, Giselher

    2009-01-01

    FeCuNbSiB-ribbons with optimized nanocrystalline microstructure possess a unique combination of near-zero magnetostriction, high saturation induction and low magnetization losses. Due to the absence of distinct intrinsic anisotropies, the magnetization curve can be adjusted by field-annealing to square or flat shape. It is well known that excess losses are an important loss component of soft magnets with square hysteresis loop. Yet, even cores of flat type loop can show significant excess losses. The paper reviews the loss mechanisms for excess losses in nanocrystalline soft magnets on the basis of Kerr-microscopy observation and loss theory and compares it to amorphous materials.

  5. Rapid phase synthesis of nanocrystalline cobalt ferrite

    Energy Technology Data Exchange (ETDEWEB)

    Shanmugavel, T., E-mail: shanmugavelnano@gmail.com [Department of Physics, Paavai Engineering College, Namakkal -637018 (India); Raj, S. Gokul [Department of Physics, Vel Tech University, Avadi, Chennai - 600 062 (India); Rajarajan, G. [Department of Physics, Mahendra Engineering College, Mallasamudram -637503 (India); Kumar, G. Ramesh [Department of Physics, University College of Engineering, Anna University Chennai, Arni- 632317 (India)

    2014-04-24

    Synthesis of single phase nanocrystalline Cobalt Ferrite (CoFe{sub 2}O{sub 4}) was achieved by single step autocombustion technique with the use of citric acid as a chelating agent in mono proportion with metal. Specimens prepared with this method showed significantly higher initial permeability's than with the conventional process. Single phase nanocrystalline cobalt ferrites were formed at very low temperature. Surface morphology identification were carried out by transmission electron microscopy (TEM) analysis. The average grain size and density at low temperature increased gradually with increasing the temperature. The single phase formation is confirmed through powder X-ray diffraction analysis. Magnetization measurements were obtained at room temperature by using a vibrating sample magnetometer (VSM), which showed that the calcined samples exhibited typical magnetic behaviors. Temperature dependent magnetization results showed improved behavior for the nanocrystalline form of cobalt ferrite when compared to the bulk nature of materials synthesized by other methods.

  6. New approach to the synthesis of nanocrystalline boron carbide.

    Science.gov (United States)

    Herth, Simone; Joost, William J; Doremus, Robert H; Siegel, Richard W

    2006-04-01

    The use of nanoparticles in ceramic matrix composites provides lower sintering temperatures and higher densities at a given temperature than common coarse-grained materials. Nanocrystalline B4C was synthesized by an inexpensive carbothermal reduction method using carbon black and B2O3 as precursor. Full conversion was achieved at 1623 K for annealing times of 480 minutes or with a large excess of B2O3 and oxidation of the remaining carbon after 30 minutes of annealing. The average particle size of the synthesized B4C powder was 260 nm, which was reduced to 70 nm after separation of the small particle fraction from the larger particles by sedimentation. A mixture of the as-prepared powder and commercial coarse-grained B4C yielded an increase of the density of low temperature hot pressed samples by 25% in comparison to pure commercial B4C. Possible chemical reactions and mechanisms in the synthesis of B4C were examined with the Gibbs free energies of reactions. The most likely reaction was the reduction of B2O3 vapor at the surfaces of the carbon particles after its vapor transport from the liquid B2O3. An observed reduction of B4C yield above 1623 K was probably caused by loss of B2O3 vapor from the reaction mixture.

  7. Characterization of nanocrystalline cadmium telluride thin films ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 29; Issue 2. Characterization of nanocrystalline ... Structural, electrical and optical characteristics of CdTe thin films prepared by a chemical deposition method, successive ionic layer adsorption and reaction (SILAR), are described. For deposition of CdTe thin films, ...

  8. Immobilazation of aerobic microorganisms on glassy sintered material, illustrated by the example of the production of L leucine using Corynebacterium glutamicum. Immobilisierung von aeroben Mikroorganismen an Glassintermaterial am Beispiel der L-Leucin-Produktion mit Corynebacterium glutamicum

    Energy Technology Data Exchange (ETDEWEB)

    Buechs, J.

    1988-12-01

    The aim of this study was to develop the carrier fixation of aerobic microorganisms on open-pore sintered glass material. The fermentative production of L-leucine from {alpha} cetonic isocaproic acid with Corynebacterium glutamicum was chosen as an example of a microbial process with a high demand of oxygen. (orig.).

  9. Sintering equation: determination of its coefficients by experiments - using multiple regression

    International Nuclear Information System (INIS)

    Windelberg, D.

    1999-01-01

    Sintering is a method for volume-compression (or volume-contraction) of powdered or grained material applying high temperature (less than the melting point of the material). Maekipirtti tried to find an equation which describes the process of sintering by its main parameters sintering time, sintering temperature and volume contracting. Such equation is called a sintering equation. It also contains some coefficients which characterise the behaviour of the material during the process of sintering. These coefficients have to be determined by experiments. Here we show that some linear regressions will produce wrong coefficients, but multiple regression results in an useful sintering equation. (orig.)

  10. Nanocrystalline hydroxyapatite doped with magnesium and zinc: Synthesis and characterization

    International Nuclear Information System (INIS)

    Kalita, Samar J.; Bhatt, Himesh A.

    2007-01-01

    During recent years, there have been efforts in developing nanocrystalline bioceramics, to enhance their mechanical and biological properties for use in tissue engineering applications. In this research, we made an attempt to synthesize nanocrystalline bioactive hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HAp) ceramic powder in the lower-end of nano-range (2-10 nm), using a simple low-temperature sol-gel technique and studied its densification behavior. We further studied the effects of metal ion dopants during synthesis on powder morphology, and the properties of the sintered structures. Calcium nitrate and triethyl phosphite were used as precursors for calcium and phosphorous, respectively, for sol-gel synthesis. Calculated quantities of magnesium oxide and zinc oxide were incorporated as dopants into amorphous dried powder, prior to calcination at 250-550 o C. The synthesized powders were analyzed for their phases using X-ray diffraction technique and characterized for powder morphology and particle size using transmission electron microscopy (TEM). TEM analysis showed that the average particle size of the synthesized powders were in the range of 2-10 nm. The synthesized nano-powders were uniaxially compacted and then sintered at 1250 o C and 1300 o C for 6 h, separately, in air. A maximum average sintered density of 3.29 g/cm 3 was achieved in structures sintered at 1300 o C, developed from nano-powder doped with magnesium. Vickers hardness testing was performed to determine the hardness of the sintered structures. Uniaxial compression tests were performed to evaluate the mechanical properties. Bioactivity and biodegradation behavior of the sintered structures were assessed in simulated body fluid (SBF) and maintained in a dynamic state

  11. Effect of ion-irradiation on the microstructure and microhardness of the W-2Y2O3 composite materials fabricated by sintering and hot forging

    International Nuclear Information System (INIS)

    Battabyal, M.; Spätig, P.; Baluc, N.

    2013-01-01

    Highlights: • W-2Y 2 O 3 material is fabricated using sintering and hot forging method with 99.3 vol.% density. • Microstructure and microhardness of the material after heavy ion irradiation are almost similar irrespective of the sample holder heating temperatures. • Dislocation loops are found on the W grains of irradiated sample where as radiation induced fine voids are observed on yttria particles. • We also observe few radiation loops on yttria particles. • No surface crack at the grain boundary is observed and significant difference in radiation hardening is confirmed. -- Abstract: A W-2Y 2 O 3 material was developed in collaboration with the Plansee Company (Austria). An ingot of the material having approximate dimension of 95 mm × 20 mm was fabricated by mixing the elemental powders followed by pressing, sintering and hot forging. The microstructure of the W-2Y 2 O 3 composite was investigated using transmission electron microscopy (TEM). The microhardness was studied using nano-indentation technique. We observed that the W-grains having a mean size of about 1 μm already formed and these grains contain very low density of dislocations. The size of the yttria particles was between 300 nm and 1 μm and the Berkovich hardness was about 4.8 GPa. The specimens were irradiated/implanted with Fe and He ions at JANNuS facility located at Orsay/Saclay, France. The TEM disks kept were irradiated/implanted at 300 and 700 °C using Fe and He ions with an energy of 24 and 2 MeV, respectively. The calculated radiation dose was about 5 dpa produced by Fe ions and total He content is 75 appm at both 300 and 700 °C. From the TEM investigation of irradiated samples, few radiation loops are present on the W grains, whereas on yttria particles, the radiation induced damages appear as voids. Berkovich hardness of the irradiated sample is higher than that of the non-irradiated sample. Results on the microstructure and microhardness of the ion-irradiated W-2Y 2 O 3

  12. Measurements of the elastic stiffness constants of single-crystal SmCo5 and of liquid-phase sintered SmCo5 permanent magnet material

    International Nuclear Information System (INIS)

    Doane, D.A.

    1977-01-01

    The five elastic stiffness constants were determined for both single-crystal SmCo 5 and for the commercially processed liquid-phase sintered (LPS) SmCo 5 permanent magnet material. The LPS material is an aligned polycrystalline aggregate of SmCo 5 crystallites oriented so that their magnetically easy c axes are approximately parallel. The elastic constants were obtained from the velocities of propagation of ultrasound in various directions in samples of known thickness and density. For the single crystal, the room-temperature values of the constants (in units of 10 12 dyn/cm 2 ) are c 11 =1.968 +- 2%, c 12 =1.032 +- 4%, c 13 =1.049 +- 4%, c 33 =2.398 +- 2%, and c 44 =0.483 +- 2%, and for the LPS permanent magnet material, c 11 =1.330 +- 2%, c 12 =0.616 +- 5%, c 13 =0.485 +- 5%, c 33 =1.659 +- 2%, and c 44 =0.419 +- 2%. The decrease in elastic constants in SmCo 5 relative to cobalt can be related qualitatively to a corresponding decrease in the number of nearest-neighbor cobalt bonds in SmCo 5

  13. Improved compaction of ZnO nano-powder triggered by the presence of acetate and its effect on sintering

    International Nuclear Information System (INIS)

    Dargatz, Benjamin; Gonzalez-Julian, Jesus; Guillon, Olivier

    2015-01-01

    The retention of nanocrystallinity in dense ceramic materials is still a challenge, even with the application of external pressure during sintering. The compaction behavior of high purity and acetate enriched zinc oxide (ZnO) nano-powders was investigated. It was found that acetate in combination with water plays a key role during the compaction into green bodies at moderate temperatures. Application of constant pressure resulted in a homogeneous green body with superior packing density (86% of theoretical value) at moderate temperature (85 °C) in the presence of water. In contrast, no improvement in density could be achieved if pure ZnO powder was used. This compaction behavior offers superior packing of the particles, resulting in a high relative density of the consolidated compact with negligible coarsening. Dissolution accompanying creep diffusion based matter transport is suggested to strongly support reorientation of ZnO particles towards densities beyond the theoretical limit for packing of ideal monosized spheres. Finally, the sintering trajectory reveals that grain growth is retarded compared to conventional processing up to 90% of theoretical density. Moreover, nearly no radial shrinkage was observed after sinter-forging for bodies performed with this advanced processing method. (paper)

  14. Enhanced infrared transmittance properties in ultrafine MgAl2O4 nanoparticles synthesised by a single step combustion method, followed by hybrid microwave sintering

    Science.gov (United States)

    Mathew, C. T.; Vidya, S.; Koshy, Jacob; Solomon, Sam; Thomas, Jijimon K.

    2015-09-01

    Infrared transparent ceramics found to have potential applications as infrared windows and domes in strategic defence and space missions. Synthesis of ultrafine nanostructured MgAl2O4 ceramics by a modified single step auto-igniting combustion technique, followed by sintering of the sample by resistive and resistive-microwave hybrid heating to high density and their excellent infrared transmission characteristics are presented in this paper. Structural characterisations of MgAl2O4 nanoparticles reveal that the as prepared powder is phase pure, with average crystallite size ∼15 nm and possess a cubic structure. Optical band gap calculated using the Kubelka-Munk method is 5.75 eV. The thermal stability of the nanopowder at elevated temperatures has been studied using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). Hybrid heating yield a substantial reduction in sintering temperature and soaking time relative to the conventional resistive heating, and the samples achieved >99% density by microwave-resistive hybrid heating. Scanning electron micrograph (SEM) showed that the pellets are well sintered. The pellet sintered by hybrid heating showed a better transmittance of ∼79% in the UV-Visible region and ∼82% in the mid IR region compared to pellet sintered by resistive heating which has ∼68% in the UV-Visible region and ∼66% in the mid IR region. The results confirm the effective use of nanocrystalline powders from modified combustion synthesis as starting material for the development of high quality IR transparent windows and domes. In addition the microwave hybrid sintering technique employed in the present study also contributes to the results of better transmittance characteristics in highly densified MgAl2O4 ceramic pellets.

  15. Thermal barrier coating resistant to sintering

    Science.gov (United States)

    Subramanian, Ramesh; Seth, Brij B.

    2004-06-29

    A device (10) is made, having a ceramic thermal barrier coating layer (16) characterized by a microstructure having gaps (18) with a sintering inhibiting material (22) disposed on the columns (20) within the gaps (18). The sintering resistant material (22) is stable over the range of operating temperatures of the device (10), is not soluble with the underlying ceramic layer (16) and is applied by a process that is not an electron beam physical vapor deposition process.

  16. Nuclear tracks in sinterized gemstones

    International Nuclear Information System (INIS)

    Espinosa, G.; Rodriguez, L.V.; Golzarri, J.I.; Castano, V.M.

    1993-01-01

    The responses of sinterized gemstones to alpha particles attempt analyzed with the objective of finding new materials for SSNTD, and also to understand their interaction with radiation and the formation of tracks. In this work we present the results of the characterization of these materials as SSNTD. The micro structural changes observed by electron microscopy. The preparation, etching solution concentration, etching time and effects of temperature are discussed. (Author)

  17. Micro-structural, thermal, optical and physical properties nanocrystalline NbSr2Pr1.5Ce0.5Cu2O10-δ material synthesized by mechano-thermal method

    Science.gov (United States)

    Parthiban, P.; Balamurugan, S.; Satya, A. T.; Janaki, J.

    2015-06-01

    We have prepared nanocrystalline NbSr2Pr1.5Ce0.5Cu2O10-δ (Nb1222Pr) material by annealing the ball milled powder at 1000°C for 24h and studied by various characterization techniques such as TG-DTA, XRD, FT-IR, NIR, SEM-EDX, magnetization and electrical resistivity. Significant difference is seen in the TG-DTA curves of the as-milled powder due to ball milling. The annealed Nb1222Pr material is crystallized in tetragonal symmetry with lattice parameters, a = 0.3887(3) nm and c = 2.878(2) nm with reduced average particle size of ˜42.67 nm. Agglomeration of fine spherical particle sizes in the range of ˜180 - 280 nm is seen through SEM micro-image. The variation in the crystalline sizes of the Nb1222Pr phase obtained from XRD and SEM image indicate the polycrystalline characteristic of fine nanocrystalline particles. Neither superconductivity nor magnetic ordering is seen for the Nb1222Pr phase down to 5 K under 100 Oe. The four probe resistivity measurement reveals the semiconducting behavior of the Nb1222Pr phase.

  18. U3O8 microspheres sintering kinetics

    International Nuclear Information System (INIS)

    Godoy, A.L.E.

    1986-01-01

    U 3 O 8 microspheres sintering kinetics was determined using a hot-stage optical microscopy apparatus, able to reach temperature up to 1350 0 C in controlled atmospheres. The sintered material had its microstructure analysed by optical and electron microscopy. The microspheres were characterized initialy utilizing X-ray diffractometry and thermogravimetry. The equation which describes the microspheres shrinkage in function of the time was obtained using finite difference analysis X-ray diffractometry indicated hexagonal structure for the microspheres main starting material, ammonium diuranate thermogravimetric analysis showed reduction of this material to U 3 O 8 at 600 0 C. Ceramography results showed 5 hours sintered microspheres grain sizes G vary with the temperature. Sintered U 3 O 8 micrographs compared with published results for UO 2 , indicate similar homogeneity microstructural characteristics and suggest the processed micorspheres to be potentially useful as nuclear fuels. (Author) [pt

  19. Successive self-propagating sintering process using carbonaceous materials: A novel low-cost remediation approach for dioxin-contaminated solids

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Long, E-mail: zhaolong@craes.org.cn [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Dayangfang 8, Beijing 100012 (China); Hou, Hong, E-mail: houhong@craes.org.cn [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Dayangfang 8, Beijing 100012 (China); Zhu, Tengfei; Li, Fasheng [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Dayangfang 8, Beijing 100012 (China); Terada, Akihiko; Hosomi, Masaaki [Department of Chemical Engineering, Faculty of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588 (Japan)

    2015-12-15

    Highlights: • A SSPSP using carbonaceous materials for removing dioxin pollutants was developed. • Removal and degradation efficiencies of DL-PCBs were higher than those of PCDD/Fs. • Compositions of PCDD/Fs were dependent on the available precursors in raw materials. • Dechlorination of O{sub 8}CDD and formation pathways of PCDFs were deduced. • Dioxin levels in the effluent gas complied with the International emission limit. - Abstract: The disposal of dioxin-contaminated solids was studied using a novel successive self-propagating sintering process (SSPSP) incorporating a carbonaceous material. Among the five types of carbonaceous materials investigated, Charcoal B displayed optimum adsorbent properties and was selected as the best thermal source in the current remediation approach based on economical efficiency aspects. The feasibility of this proposed approach, removal efficiencies, and congener compositions of dioxins were examined using two types of dioxin-contaminated solids (Fugan sediment and Toyo soil) that displayed different characteristics including the initial concentrations of dioxins. The removal efficiencies of DL-PCBs (“dioxin-like” polychlorinated biphenyls) were higher than those of PCDD/Fs (polychlorinated dibenzo-p-dioxins/dibenzofurans), achieving 99.9 and 92% removal in the Fugan sediment and Toyo soil, respectively. In contrast, the degradation efficiencies of DL-PCBs were lower (i.e., 89.3 and 88.8%, respectively). The initial concentrations of dioxins, available precursors, and properties of the solids strongly influenced the congener compositions and removal efficiencies of dioxins. Furthermore, the dechlorination reaction pathways of high-chlorinated PCDDs and potential regeneration pathways of PCDFs from PCBs were deduced using isotope labeling. The proposed novel low-cost remediation approach for the removal of dioxins from solids is a highly efficient and environmentally sound treatment technology.

  20. Novel Approach In Fabrication Of Shielding Composite Materials By Emerging Field Assisted Sintering Technique (FAST), Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — The overall objective of this work is to develop a radiation shielding material system that is sufficiently strong to serve as a load bearing structure. Such a...

  1. Sintered wire cesium dispenser photocathode

    Science.gov (United States)

    Montgomery, Eric J; Ives, R. Lawrence; Falce, Louis R

    2014-03-04

    A photoelectric cathode has a work function lowering material such as cesium placed into an enclosure which couples a thermal energy from a heater to the work function lowering material. The enclosure directs the work function lowering material in vapor form through a low diffusion layer, through a free space layer, and through a uniform porosity layer, one side of which also forms a photoelectric cathode surface. The low diffusion layer may be formed from sintered powdered metal, such as tungsten, and the uniform porosity layer may be formed from wires which are sintered together to form pores between the wires which are continuous from the a back surface to a front surface which is also the photoelectric surface.

  2. Accumulation and recovery of defects in ion-irradiated nanocrystalline gold

    Energy Technology Data Exchange (ETDEWEB)

    Chimi, Y. E-mail: chimi@popsvr.tokai.jaeri.go.jp; Iwase, A.; Ishikawa, N.; Kobiyama, M.; Inami, T.; Okuda, S

    2001-09-01

    Effects of 60 MeV {sup 12}C ion irradiation on nanocrystalline gold (nano-Au) are studied. The experimental results show that the irradiation-produced defects in nano-Au are thermally unstable because of the existence of a large volume fraction of grain boundaries. This suggests a possibility of the use of nanocrystalline materials as irradiation-resistant materials.

  3. Models of current sintering

    Science.gov (United States)

    Angst, Sebastian; Engelke, Lukas; Winterer, Markus; Wolf, Dietrich E.

    2017-06-01

    Densification of (semi-)conducting particle agglomerates with the help of an electrical current is much faster and more energy efficient than traditional thermal sintering or powder compression. Therefore, this method becomes more and more common among experimentalists, engineers, and in industry. The mechanisms at work at the particle scale are highly complex because of the mutual feedback between current and pore structure. This paper extends previous modelling approaches in order to study mixtures of particles of two different materials. In addition to the delivery of Joule heat throughout the sample, especially in current bottlenecks, thermoelectric effects must be taken into account. They lead to segregation or spatial correlations in the particle arrangement. Various model extensions are possible and will be discussed.

  4. Tailoring and patterning the grain size of nanocrystalline alloys

    International Nuclear Information System (INIS)

    Detor, Andrew J.; Schuh, Christopher A.

    2007-01-01

    Nanocrystalline alloys that exhibit grain boundary segregation can access thermodynamically stable or metastable states with the average grain size dictated by the alloying addition. Here we consider nanocrystalline Ni-W alloys and demonstrate that the W content controls the grain size over a very broad range: ∼2-140 nm as compared with ∼2-20 nm in previous work on strongly segregating systems. This trend is attributed to a relatively weak tendency for W segregation to the grain boundaries. Based upon this observation, we introduce a new synthesis technique allowing for precise composition control during the electrodeposition of Ni-W alloys, which, in turn, leads to precise control of the nanocrystalline grain size. This technique offers new possibilities for understanding the structure-property relationships of nanocrystalline solids, such as the breakdown of Hall-Petch strength scaling, and also opens the door to a new class of customizable materials incorporating patterned nanostructures

  5. Production of high-strength Al85Y8Ni5Co2 bulk alloy by spark plasma sintering

    International Nuclear Information System (INIS)

    Surreddi, K B; Scudino, S; Sakaliyska, M; Eckert, J; Srivastava, V C; Uhlenwinkel, V; Kim, J S

    2010-01-01

    Highly dense bulk samples were produced by spark plasma sintering (SPS) through combined devitrification and consolidation of partially amorphous Al 85 Y 8 Ni 5 Co 2 gas atomized powders. The microstructure of the consolidated samples shows a mixed structure containing crystalline, ultrafine-grained and amorphous/nanocrystalline particles. The sintered sample exhibits a remarkable high strength of about 1050 MPa combined with 3.7 % fracture strain.

  6. Science of sintering and its future

    International Nuclear Information System (INIS)

    Ristic, M.M.

    1975-01-01

    Some new books published by M.Yu. Baljshin, V.A. Ivensen, V.V. Skorohod and others are characterized by the wish to give a complete approach to the problems of sintering theory. Bearing just this in mind while writing the book ''An Essay on the Generalization of Sintering Theory'' (G.V.Samsonov, M.M. Ristic with the collaborators) an idea was born: to ask the most eminent scientists in this field to present their own opinions on the theme ''The Science of Sintering and Modern Views on its Future''. There were formed 18 questions, given in the appendix to be answered. The received answers were presented in 10 chapters of this book. The fourth part of the book consists of papers of eminent scientists engaged in the field of sintering science (some of which were published here for the first time). This material is published in the book with the consent of the authors and these original contributions provide a more profound knowledge of sintering. The initial idea, that the book should have a monograph character and in which the answers would serve as some data on the latest notions of the science of sintering, was somewhat changed since the original opinions of individual scientists are given in the book and these, are sometimes very contradictory. This, in fact, gives the book a special charm because the unsolved problems in the science of sintering are most evidently stressed in this way

  7. EVALUATION OF THE TECHNOLOGICAL CHARACTERISTICS OF CLAY WHEN ADDING BUILDING MATERIALS TO MANUFACTURE STRUCTURAL PRODUCTS WITHOUT IMPLEMENTING A SINTERING PROCESS

    Directory of Open Access Journals (Sweden)

    Leonardo Cely Illera

    2016-01-01

    Full Text Available El trabajo hace un estudio sobre el efecto que ejerce la adición de materiales como arena, cemen- to y cal a una arcilla roja, con el objetivo de mejorar las características tecnológicas y eliminando el proceso de cocción. Se compararon los resultados de una pasta standard, con los valores arrojados en diferentes formulaciones, se mejora el desempeño mecánico y propiedades físicas del material, aumentando la densificación en seco y disminuyendo el índice de prensabilidad. Los resultados demostraron que la adición de estos materiales a la arcilla producen incrementos de resistencia mecánica a la flexión entre el 16,9% hasta un 35,5% y una reducción en su contracción en seco de alrededor del 8,3%, siendo la formulación F7 la que obtuvo los mejores resultados. Estos datos contribuirán al desarrollo de productos cerámicos con valor agregado, para ser usados en diversas aplicaciones tecnológicas sin necesidad de sinterizar el material y disminuyendo el gasto energético y la contaminación que estos procesos producen.

  8. Sintering of nonstoichiometric UO2

    International Nuclear Information System (INIS)

    Susnik, D.; Holc, J.

    1983-01-01

    Activated sintering of UO 2 pellets at 1100 deg C is described. In CO 2 atmosphere is UO 2 is nonstoichiometric and pellets from active UO 2 powders sinter at 900 deg C to high density. At 1100 deg C the final sintered density is practically achieved at heating on sintering temperature. After reduction and cooling in H 2 atmosphere which is followed sintering in CO 2 the structure is identical to the structured UO 2 pellets sintered at high temperature in H 2 . Density of activated sintered UO 2 pellets is stable, even after additional sintering at 1800 deg C. (author)

  9. Laser Sintered Calcium Phosphate Bone

    National Research Council Canada - National Science Library

    Vail, Neil

    1999-01-01

    ...) technology selective laser sintering (SLS). BME has successfully implemented a pilot facility to fabricate calcium phosphate implants using anatomical data coupled with the selective laser sintering process...

  10. Effects of sintering atmosphere and initial particle size on sintering of gadolinia-doped ceria

    International Nuclear Information System (INIS)

    Batista, Rafael Morgado

    2014-01-01

    The effects of the sintering atmosphere and initial particle size on the sintering of ceria containing 10 mol% gadolinia (GdO 1.5 ) were systematically investigated. The main physical parameter was the specific surface area of the initial powders. Nanometric powders with three different specific surface areas were utilized, 210 m 2 /g, 36,2 m 2 /g e 7,4 m 2 /g. The influence on the densification, and micro structural evolution were evaluated. The starting sintering temperature was verified to decrease with increasing on the specific surface area of raw powders. The densification was accelerated for the materials with smaller particle size. Sintering paths for crystallite growth were obtained. Master sintering curves for gadolinium-doped ceria were constructed for all initial powders. A computational program was developed for this purpose. The results for apparent activation energy showed noticeable dependence with specific surface area. In this work, the apparent activation energy for densification increased with the initial particle size of powders. The evolution of the particle size distributions on non isothermal sintering was investigated by WPPM method. It was verified that the grain growth controlling mechanism on gadolinia doped ceria is the pore drag for initial stage and beginning of intermediate stage. The effects of the sintering atmosphere on the stoichiometry deviation of ceria, densification, microstructure evolution, and electrical conductivity were analyzed. Inert, oxidizing, and reducing atmospheres were utilized on this work. Deviations on ceria stoichiometry were verified on the bulk materials. The deviation verified was dependent of the specific surface area and sintering atmosphere. Higher reduction potential atmospheres increase Ce 3+ bulk concentration after sintering. Accelerated grain growth and lower electrical conductivities were verified when reduction reactions are significantly present on sintering. (author)

  11. Nanocrystalline Al Composites from Powder Milled under Ammonia Gas Flow

    Directory of Open Access Journals (Sweden)

    J. Cintas

    2014-01-01

    Full Text Available The production of high hardness and thermally stable nanocrystalline aluminium composites is described. Al powder was milled at room temperature in an ammonia flow for a period of less than 5 h. NH3 dissociation during milling provokes the absorption, at a high rate, of nitrogen into aluminium, hardening it by forming a solid solution. Controlled amounts of AlN and Al5O6N are formed during the subsequent sintering of milled powders for consolidation. The pinning action of these abundant dispersoids highly restrains aluminium grain growth during heating. The mean size of the Al grains remains below 45 nm and even after the milled powder is sintered at 650°C for 1 h.

  12. A method for sintering

    DEFF Research Database (Denmark)

    2012-01-01

    The present invention provides a method for sintering, comprising in the following order the steps of: providing a body in the green state or in the pre-sintered state on a support; providing a load on at least one spacer on the support such that the load is located above said body in the green...

  13. Structure and coercivity of nanocrystalline Fe–Si–B–Nb–Cu alloys

    Indian Academy of Sciences (India)

    Unknown

    Fe–Si–B–Nb–Cu alloy; melt-spinning; crystallization; nanocrystalline materials; coercivity. 1. Introduction. Nanocrystalline Fe–Si–B–Nb–Cu alloys have been found to possess a unique combination of soft magnetic properties including high saturation, very low coercivity, high per- meability and high electrical resistivity ...

  14. Sintering behaviour and microstructure of 3Y-TZP + 8 mol% CuO nano-powder composite

    NARCIS (Netherlands)

    Ran, S.; Winnubst, Aloysius J.A.; Koster, H.; de Veen, P.J.; Blank, David H.A.

    2007-01-01

    Nanocrystalline 3Y-TZP and copper-oxide powders were prepared by co-precipitation of metal chlorides and copper oxalate complexation– precipitation, respectively.Asignificant enhancement in sintering activity of 3Y-TZP nano-powders, without presence of liquid phase,was achieved by addition of 8 mol%

  15. Reactive Sintering of Bimodal WC-Co Hardmetals

    OpenAIRE

    Marek Tarraste; Kristjan Juhani; Jüri Pirso; Mart Viljus

    2015-01-01

    Bimodal WC-Co hardmetals were produced using novel technology - reactive sintering. Milled and activated tungsten and graphite powders were mixed with commercial coarse grained WC-Co powder and then sintered. The microstructure of produced materials was free of defects and consisted of evenly distributed coarse and fine tungsten carbide grains in cobalt binder. The microstructure, hardness and fracture toughness of reactive sintered bimodal WC-Co hardmetals is exhibited. Developed bimodal har...

  16. Effect of ball milling process on coercivity of nanocrystalline SmCo5 magnets

    Science.gov (United States)

    Fang, Lei; Zhang, Tianli; Wang, Hui; Jiang, Chengbao; Liu, Jinghua

    2018-01-01

    In this paper, the effect of ball milling process on remanence and coercivity of nanocrystalline SmCo5 magnets was systematically investigated. Nanocrystalline SmCo5 magnets were prepared by high energy ball milling and spark plasma sintering. And their vast difference of remanence and coercivity were analyzed thoroughly. The anisotropic SmCo5 magnets prepared by wet-milling with surfactant (oleylamine, OY) have high remanence, but the coercivity is much lower than the isotropic magnets prepared by dry-milling. Further analysis indicates the milling process induced changes on the size and shape of grains are the key factors influencing the coercivity. The amorphous powders prepared by dry-milling were crystallized during sintering and the magnets have small and homogeneous grains, while the anisotropic nanoflakes prepared by wet-milling could be well oriented but the magnets have lower coercivity due to the larger and inhomogeneous grains.

  17. Determination of platinum, palladium, iridium and gold on selected geological reference materials by radiochemical neutron activation analysis: comparison of procedures based on aqua regia leaching and sodium peroxide sintering

    International Nuclear Information System (INIS)

    Nogueira, C.A.; Figueiredo, A.M.G.

    1995-01-01

    A rapid and sensitive neutron activation method for the determination of platinum, palladium, iridium and gold in rocks is described. The procedure consists of thermal neutron irradiation of about 250 mg of sample, followed by chemical treatment of the rock, precipitation of gold and the platinum group elements with tellurium and high-resolution gamma-ray spectrometry with a hyper-pure Ge detector. Two different methods were used for the chemical treatment of the rock: aqua regia leaching and sintering with sodium peroxide. The procedures were evaluated by analysis of the certified reference material SARM-7 and the reference material CHR-Pt+. (author)

  18. Determination of platinum, palladium, iridium and gold on selected geological reference materials by radiochemical neutron activation analysis: comparison of procedures based on aqua regia leaching and sodium peroxide sintering

    Energy Technology Data Exchange (ETDEWEB)

    Nogueira, C.A.; Figueiredo, A.M.G. [Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, SP (Brazil)

    1995-05-01

    A rapid and sensitive neutron activation method for the determination of platinum, palladium, iridium and gold in rocks is described. The procedure consists of thermal neutron irradiation of about 250 mg of sample, followed by chemical treatment of the rock, precipitation of gold and the platinum group elements with tellurium and high-resolution gamma-ray spectrometry with a hyper-pure Ge detector. Two different methods were used for the chemical treatment of the rock: aqua regia leaching and sintering with sodium peroxide. The procedures were evaluated by analysis of the certified reference material SARM-7 and the reference material CHR-Pt+. (author).

  19. Preparation of Ni-Ti shape memory alloy by spark plasma sintering method

    Czech Academy of Sciences Publication Activity Database

    Salvetr, P.; Kubatík, Tomáš František; Novák, P.

    2016-01-01

    Roč. 16, č. 4 (2016), s. 804-808 ISSN 1213-2489 Institutional support: RVO:61389021 Keywords : Ni-Ti alloy * Powder metallurgy * Reactive sintering * Spark plasma sintering Subject RIV: JK - Corrosion ; Surface Treatment of Materials

  20. Sintering of beryllium oxide

    International Nuclear Information System (INIS)

    Caillat, R.; Pointud, R.

    1955-01-01

    This study had for origin to find a process permitting to manufacture bricks of beryllium oxide of pure nuclear grade, with a density as elevated as possible and with standardized shape. The sintering under load was the technique kept for the manufacture of the bricks. Because of the important toxicity of the beryllium oxide, the general features for the preliminary study of the sintering, have been determined while using alumina. The obtained results will be able to act as general indication for ulterior studies with sintering under load. (M.B.) [fr

  1. Method of manufacturing sintered nuclear fuel

    International Nuclear Information System (INIS)

    Watarumi, Kazutoshi.

    1984-01-01

    Purpose: To obtain composite pellets with an improved strength. Method: A core mainly composed of fuel materials is previously prepared, embedded into the central portion of a pellet, silted therearound with cladding material, and then pressmolded and sintered. For instance, a rugby-ball like core body with the maximum outer diameter of 6 mm and the height of 6 mm is made by compressive molding with uranium dioxide powder, then coating material comprising the same powder incorporated with 0.1 % by weight of SiC fibers is filled around the core body, which is molded into a composite pellet by means of pressing and then sintered at 1600 0 C, to obtain a sintered pellet of 93.5 % theoretical density. As the result of the compression test for the pellet, it showed a strength greater by 15 % than that of the similar mono-layer pellet. (Kamimura, M.)

  2. Mechanical characteristics of microwave sintered silicon carbide

    Indian Academy of Sciences (India)

    Unknown

    tions ranging from kiln furniture to membrane material. Keywords. Microwave sintering; biaxial flexure; silicon carbide. 1. Introduction. Silicon carbide (SiC) ceramics is a very well known candidate material for a structural application. However, due to (i) poor densification due to highly directional bonding, (ii) susceptibility of ...

  3. Synthesis and Characterization of Nanocrystalline Hydroxyapatite by Combustion Method

    International Nuclear Information System (INIS)

    Yin Thu Aye; Su Su Hlaing; Phyu Sin Khaing Oo; Khin Lay Thwe; Nwe Ni Khin

    2011-12-01

    Among various biocompatible materials hydroxyapatite (HAP) is widely used in medical applications.As nanocrystalline Hydroxyapatite is similar in composition and crystal structure of natural bone it can be used as temporary substitute materials for human bone. A simple combustion technique for synthesizing nanocrystalline hydroxyapatite powder from eggshell has been carried out. The resulting powder was characterized using XRD, SEM and FESEM measurements. The particle size was calculated by Debye-Scherrer equation using XRD data. The range of size of resultant HAP powder was between 23nm-75nm. The average particle size was 34 nm.

  4. Co-Sintering behaviour of zirconia-ferritic steel composites

    Directory of Open Access Journals (Sweden)

    Alexander Michaelis

    2016-08-01

    Full Text Available The combination of metallic and ceramic materials allows the combination of positive properties of both and can be applied in various industrial fields. At the moment, the deployment of these composites faces difficult and complex manufacturing. One attempt, which offers a short process route and a high degree of flexibility regarding design is a combined shaping (co-shaping with a combined sintering (co-sintering. The article will show co-sintering results of different metal-ceramic symmetric and asymmetric multi-layered tapes, consisting of yttria stabilized zirconia combined with a ferritic iron chromium steel. Focus is on the densification and co-sintering behaviour of ceramic layers depending on the sintering behaviour of metallic layers. Co-sintered composites were characterized by field emission scanning electron microscopy, x-ray diffraction measurements and in terms of adhesive tensile strength.

  5. Characterization of amorphous and nanocrystalline carbon films

    International Nuclear Information System (INIS)

    Chu, Paul K.; Li Liuhe

    2006-01-01

    Amorphous and nanocrystalline carbon films possess special chemical and physical properties such as high chemical inertness, diamond-like properties, and favorable tribological proprieties. The materials usually consist of graphite and diamond microstructures and thus possess properties that lie between the two. Amorphous and nanocrystalline carbon films can exist in different kinds of matrices and are usually doped with a large amount of hydrogen. Thus, carbon films can be classified as polymer-like, diamond-like, or graphite-like based on the main binding framework. In order to characterize the structure, either direct bonding characterization methods or the indirect bonding characterization methods are employed. Examples of techniques utilized to identify the chemical bonds and microstructure of amorphous and nanocrystalline carbon films include optical characterization methods such as Raman spectroscopy, Ultra-violet (UV) Raman spectroscopy, and infrared spectroscopy, electron spectroscopic and microscopic methods such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, transmission electron microscopy, and electron energy loss spectroscopy, surface morphology characterization techniques such as scanning probe microscopy (SPM) as well as other characterization methods such as X-ray reflectivity and nuclear magnetic resonance. In this review, the structures of various types of amorphous carbon films and common characterization techniques are described

  6. Magnetism in nanocrystalline gold.

    Science.gov (United States)

    Tuboltsev, Vladimir; Savin, Alexander; Pirojenko, Alexandre; Räisänen, Jyrki

    2013-08-27

    While bulk gold is well known to be diamagnetic, there is a growing body of convincing experimental and theoretical work indicating that nanostructured gold can be imparted with unconventional magnetic properties. Bridging the current gap in experimental study of magnetism in bare gold nanomaterials, we report here on magnetism in gold nanocrystalline films produced by cluster deposition in the aggregate form that can be considered as a crossover state between a nanocluster and a continuous film. We demonstrate ferromagnetic-like hysteretic magnetization with temperature dependence indicative of spin-glass-like behavior and find this to be consistent with theoretical predictions, available in the literature, based on first-principles calculations.

  7. The role of nanocrystalline binder metallic coating into WC after additive manufacturing

    Science.gov (United States)

    Cavaleiro, A. J.; Fernandes, C. M.; Farinha, A. R.; Gestel, C. V.; Jhabvala, J.; Boillat, E.; Senos, A. M. R.; Vieira, M. T.

    2018-01-01

    Tungsten carbide with microsized particle powders are commonly used embedded in a tough binder metal. The application of these composites is not limited to cutting tools, WC based material has been increasingly used in gaskets and other mechanical parts with complex geometries. Consequently, additive manufacturing processes as Selective Laser Sintering (SLS) might be the solution to overcome some of the manufacturing problems. However, the use of SLS leads to resolve the problems resulting from difference of physical properties between tungsten carbide and the metallic binder, such as laser absorbance and thermal conductivity. In this work, an original approach of powder surface modification was considered to prepare WC-metal composite powders and overcome these constraints, consisting on the sputter-coating of the WC particle surfaces with a nanocrystalline thin film of metallic binder material (stainless steel). The coating improves the thermal behavior and rheology of the WC particles and, at the same time, ensures a binder homogenous distribution. The feasibility of the SLS technology as manufacturing process for WC powder sputter-coated with 13 wt% stainless steel AISI 304L was explored with different laser power and scanning speed parameters. The SLS layers were characterized regarding elemental distribution, phase composition and morphology, and the results are discussed emphasizing the role of the coating on the consolidation process.

  8. Effects of sintering temperature on structural and electrical transport properties of zinc ferrites prepared by sol-gel route

    International Nuclear Information System (INIS)

    Anis-ur-Rehman, M.; Malik, M.A.; Ahmad, I.; Nasir, S.; Mubeen, M.; Abdullah, A.

    2011-01-01

    The effects of sintering temperature on the structural and electrical transport properties of nanocrystalline zinc ferrites are reported. The zinc ferrites were prepared by WOWS sol-gel synthesis route. The prepared sample was sintered at temperatures 500 deg. C, 700 deg. C and 900 deg. C respectively for 2 h. X-ray Diffraction (XRD) technique was used to describe the structural properties. The crystallite size, lattice parameters and porosity of samples were measured from the analysis of XRD data. The average crystallite size for each sample was measured using the Scherrer formula by considering the most intense (3 1 1) peak. The dielectric constant (e), dielectric loss tangent (tan theta ) and AC electrical conductivity of nanocrystalline Zn ferrites are investigated as a function of frequency and sintering temperature. All the electrical properties are explained in accordance with MaxwellWagner model and Koops phenomenological theory. (author)

  9. The Influence of Milling and Spark Plasma Sintering on the Microstructure and Properties of the Al7075 Alloy

    Directory of Open Access Journals (Sweden)

    Orsolya Molnárová

    2018-04-01

    Full Text Available The compact samples of an Al7075 alloy were prepared by a combination of gas atomization, high energy milling, and spark plasma sintering. The predominantly cellular morphology observed in gas atomized powder particles was completely changed by mechanical milling. The continuous-like intermetallic phases present along intercellular boundaries were destroyed; nevertheless, a small amount of Mg(Zn,Cu,Al2 phase was observed also in the milled powder. Milling resulted in a severe plastic deformation of the material and led to a reduction of grain size from several µm into the nanocrystalline region. The combination of these microstructural characteristics resulted in abnormally high microhardness values exceeding 300 HV. Consolidation through spark plasma sintering (SPS resulted in bulk samples with negligible porosity. The heat exposition during SPS led to precipitation of intermetallic phases from the non-equilibrium microstructure of both gas atomized and milled powders. SPS of the milled powder resulted in a recrystallization of the severely deformed structure. An ultra-fine grained structure (grain size close to 500 nm with grains divided primarily by high-angle boundaries was formed. A simultaneous release of stored deformation energy and an increase in the grain size caused a drop of microhardness to values close to 150 HV. This value was retained even after annealing at 425 °C.

  10. Monitoring Sintering Burn-Through Point Using Infrared Thermography

    Directory of Open Access Journals (Sweden)

    Francisco G. Bulnes

    2013-08-01

    Full Text Available Sintering is a complex industrial process that applies heat to fine particles of iron ore and other materials to produce sinter, a solidified porous material used in blast furnaces. The sintering process needs to be carefully adjusted, so that the combustion zone reaches the bottom of the material just before the discharge end. This is known as the burnthrough point. Many different parameters need to be finely tuned, including the speed and the quantities of the materials mixed. However, in order to achieve good results, sintering control requires precise feedback to adjust these parameters. This work presents a sensor to monitor the sintering burn-through point based on infrared thermography. The proposed procedure is based on the acquisition of infrared images at the end of the sintering process. At this position, infrared images contain the cross-section temperatures of the mixture. The objective of this work is to process this information to extract relevant features about the sintering process. The proposed procedure is based on four steps: key frame detection, region of interest detection, segmentation and feature extraction. The results indicate that the proposed procedure is very robust and reliable, providing features that can be used effectively to control the sintering process.

  11. Monitoring sintering burn-through point using infrared thermography.

    Science.gov (United States)

    Usamentiaga, Rubén; Molleda, Julio; Garcia, Daniel F; Bulnes, Francisco G

    2013-08-09

    Sintering is a complex industrial process that applies heat to fine particles of iron ore and other materials to produce sinter, a solidified porous material used in blast furnaces. The sintering process needs to be carefully adjusted, so that the combustion zone reaches the bottom of the material just before the discharge end. This is known as the burn-through point. Many different parameters need to be finely tuned, including the speed and the quantities of the materials mixed. However, in order to achieve good results, sintering control requires precise feedback to adjust these parameters. This work presents a sensor to monitor the sintering burn-through point based on infrared thermography. The proposed procedure is based on the acquisition of infrared images at the end of the sintering process. At this position, infrared images contain the cross-section temperatures of the mixture. The objective of this work is to process this information to extract relevant features about the sintering process. The proposed procedure is based on four steps: key frame detection, region of interest detection, segmentation and feature extraction. The results indicate that the proposed procedure is very robust and reliable, providing features that can be used effectively to control the sintering process.

  12. Monitoring Sintering Burn-Through Point Using Infrared Thermography

    Science.gov (United States)

    Usamentiaga, Rubén; Molleda, Julio; Garcia, Daniel F.; Bulnes, Francisco G.

    2013-01-01

    Sintering is a complex industrial process that applies heat to fine particles of iron ore and other materials to produce sinter, a solidified porous material used in blast furnaces. The sintering process needs to be carefully adjusted, so that the combustion zone reaches the bottom of the material just before the discharge end. This is known as the burn-through point. Many different parameters need to be finely tuned, including the speed and the quantities of the materials mixed. However, in order to achieve good results, sintering control requires precise feedback to adjust these parameters. This work presents a sensor to monitor the sintering burn-through point based on infrared thermography. The proposed procedure is based on the acquisition of infrared images at the end of the sintering process. At this position, infrared images contain the cross-section temperatures of the mixture. The objective of this work is to process this information to extract relevant features about the sintering process. The proposed procedure is based on four steps: key frame detection, region of interest detection, segmentation and feature extraction. The results indicate that the proposed procedure is very robust and reliable, providing features that can be used effectively to control the sintering process. PMID:23939585

  13. Effect of material, process parameters, and simulated body fluids on mechanical properties of 13-93 bioactive glass porous constructs made by selective laser sintering.

    Science.gov (United States)

    Kolan, Krishna C R; Leu, Ming C; Hilmas, Gregory E; Velez, Mariano

    2012-09-01

    The effect of particle size distribution, binder content, processing parameters, and sintering schedule on the microstructure and mechanical properties of porous constructs was investigated. The porous constructs were produced by indirect selective laser sintering (SLS) of 13-93 bioactive glass using stearic acid as a polymeric binder. The binder content and d(50) particle size in the feedstock powders were simultaneously reduced from 22 to 12 wt% and from 20 to 11 μm, respectively, to identify the minimum binder content required for the SLS fabrication. An average particle size of ∼16 μm with a binder content of 15 wt% significantly reduced post-processing time and improved mechanical properties. Increasing the laser power and scan speed at the energy density of 1 cal/cm² maintained the feature sharpness of the parts during the fabrication of green parts and could almost double the mechanical properties of the sintered parts. Changes in the heating rates, ranging from 0.1 to 2 °C/min, during the post-processing of the fabricated "green" scaffolds showed that the heating rate significantly affects the densification and mechanical properties of the sintered scaffolds. The compressive strength of the scaffolds manufactured with the optimized parameters varied from 41 MPa, for a scaffold with a porosity of ∼50%, to 157 MPa, for a dense part. The bioactive scaffolds soaked in simulated body fluids for durations up to 6 weeks were used to evaluate the change in mechanical properties in vitro. Copyright © 2012 Elsevier Ltd. All rights reserved.

  14. Strain rate sensitivity of bulk multi-phase nanocrystalline Al-W-based alloy

    Science.gov (United States)

    Varam, Sreedevi; Narayana, P. V. S. L.; Prasad, Muvva D.; Chakravarty, D.; Rajulapati, Koteswararao V.; Bhanu Sankara Rao, K.

    2014-09-01

    High-energy ball milling of conventional coarse-grained aluminium and nanocrystalline W in an Al-10 at.%W composition results in the formation of a two-phase mixture of Al and W with nanocrystalline features. Subsequent compaction of these powders using spark plasma sintering (SPS) at 748 K resulted in the formation of an Al12W phase in the nanocrystalline aluminium matrix. It is suggested that the mere attainment of nanocrystallinity was not enough to trigger a reaction between Al and W to form Al12W but that sufficient thermal activation was also required, as supplied during SPS. The second-phase particles (~175 nm in size) are uniformly distributed in the nanocrystalline Al matrix having a grain size of ~40 nm. The nanocomposite possessed a high hardness of 5.42 ± 0.33 GPa and an elastic modulus of 145 ± 5 GPa, both measured using depth-sensing nanoindentation. At room temperature, this novel nanocomposite exhibited a strain rate sensitivity (SRS) of 0.024 ± 0.001 and an activation volume in the range of 3.78-3.88 b3. Interfacial regions, viz. grain boundaries and triple junctions in the matrix and the reinforcement, matrix/particle boundaries, etc. could be influential factors in deciding the SRS and the activation volume. A scanning probe microscope image of the nanoindent shows a plastic flow region around the periphery of the indent.

  15. Predicting sintering deformation of ceramic film constrained by rigid substrate using anisotropic constitutive law

    International Nuclear Information System (INIS)

    Li Fan; Pan Jingzhe; Guillon, Olivier; Cocks, Alan

    2010-01-01

    Sintering of ceramic films on a solid substrate is an important technology for fabricating a range of products, including solid oxide fuel cells, micro-electronic PZT films and protective coatings. There is clear evidence that the constrained sintering process is anisotropic in nature. This paper presents a study of the constrained sintering deformation using an anisotropic constitutive law. The state of the material is described using the sintering strains rather than the relative density. In the limiting case of free sintering, the constitutive law reduces to a conventional isotropic constitutive law. The anisotropic constitutive law is used to calculate sintering deformation of a constrained film bonded to a rigid substrate and the compressive stress required in a sinter-forging experiment to achieve zero lateral shrinkage. The results are compared with experimental data in the literature. It is shown that the anisotropic constitutive law can capture the behaviour of the materials observed in the sintering experiments.

  16. Structural elucidation of nanocrystalline biomaterials

    Energy Technology Data Exchange (ETDEWEB)

    Maltsev, S.

    2008-10-23

    Bone diseases, such as osteoporosis and osteoarthritis, are the second most prevalent health problem worldwide. In Germany approximately 5 millions people are affected by arthritis. Investigating biomineralization processes and bone molecular structure is of key importance for developing new drugs for preventing and healing bone diseases. Nuclear magnetic resonance (NMR) was the primary technique used due to its advantages in characterising poorly ordered and disordered materials. Compared to all the diffraction techniques that widely applied in structural investigations, the usefulness of NMR is independent of long range molecular order. This makes NMR an outstanding technique for studies of complex/amorphous materials. Conventional NMR experiments (single pulse, spin-echo, cross polarization (CP), etc.) as well as their modifications and high-end techniques (2D HETCOR, REDOR, etc.) were used in this work. Combining the contributions from different techniques enhances the information content of the investigations and can increase the precision of the overall conclusions. Also XRD, TEM and FTIR were applied to different extent in order to get a general idea of nanocrystalline hydroxyapatite crystallite structure. Results: - A new approach named 'Solid-state NMR spectroscopy using the lost I spin magnetization in polarization transfer experiments' has been developed for measuring the transferred I spin magnetization from abundant nuclei, which is normally lost when detecting the S spin magnetization. - A detailed investigation of nanocrystalline hydroxyapatite core was made to prove that proton environment of the phosphates units and phosphorus environment of hydroxyl units are the same as in highly crystalline hydroxyapatite sample. - Using XRD it was found that the surface of the hydroxyapatite nanocrystals is not completely disordered, as it was suggested before, but resembles the hydroxyapatite structure with HPO{sub 4}{sup 2-} (and some CO{sub 3}{sup

  17. Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

    Directory of Open Access Journals (Sweden)

    Barbara Malič

    2015-12-01

    Full Text Available The potassium sodium niobate, K0.5Na0.5NbO3, solid solution (KNN is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient, lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining phase-pure materials with a high density and a uniform, fine-grained microstructure is a major challenge. For this reason the present paper reviews the different methods for consolidating KNN ceramics. The difficulties involved in the solid-state synthesis of KNN powder, i.e., obtaining phase purity, the stoichiometry of the perovskite phase, and the chemical homogeneity, are discussed. The solid-state sintering of stoichiometric KNN is characterized by poor densification and an extremely narrow sintering-temperature range, which is close to the solidus temperature. A study of the initial sintering stage revealed that coarsening of the microstructure without densification contributes to a reduction of the driving force for sintering. The influences of the (K + Na/Nb molar ratio, the presence of a liquid phase, chemical modifications (doping, complex solid solutions and different atmospheres (i.e., defect chemistry on the sintering are discussed. Special sintering techniques, such as pressure-assisted sintering and spark-plasma sintering, can be effective methods for enhancing the density of KNN ceramics. The sintering behavior of KNN is compared to that of a representative piezoelectric lead zirconate titanate (PZT.

  18. Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

    Science.gov (United States)

    Malič, Barbara; Koruza, Jurij; Hreščak, Jitka; Bernard, Janez; Wang, Ke; Fisher, John G.; Benčan, Andreja

    2015-01-01

    The potassium sodium niobate, K0.5Na0.5NbO3, solid solution (KNN) is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient, lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining phase-pure materials with a high density and a uniform, fine-grained microstructure is a major challenge. For this reason the present paper reviews the different methods for consolidating KNN ceramics. The difficulties involved in the solid-state synthesis of KNN powder, i.e., obtaining phase purity, the stoichiometry of the perovskite phase, and the chemical homogeneity, are discussed. The solid-state sintering of stoichiometric KNN is characterized by poor densification and an extremely narrow sintering-temperature range, which is close to the solidus temperature. A study of the initial sintering stage revealed that coarsening of the microstructure without densification contributes to a reduction of the driving force for sintering. The influences of the (K + Na)/Nb molar ratio, the presence of a liquid phase, chemical modifications (doping, complex solid solutions) and different atmospheres (i.e., defect chemistry) on the sintering are discussed. Special sintering techniques, such as pressure-assisted sintering and spark-plasma sintering, can be effective methods for enhancing the density of KNN ceramics. The sintering behavior of KNN is compared to that of a representative piezoelectric lead zirconate titanate (PZT). PMID:28793702

  19. Topological characterization of nanocrystalline cellulose reinforced Poly (lactic acid) and Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) bionanocomposites

    Science.gov (United States)

    Bhat, A. H.; Dasan, Y. K.; Khan, Ihsan Ullah; Ahmad, Faiz; Ayoub, Muhammad

    2016-11-01

    This study was conducted to evaluate the morphological and barrier properties of nanocrystalline cellulose reinforced Poly (lactic acid) and Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) bionanocomposites. Nanocrystalline cellulose was isolated from waste oil palm empty fruit bunch fiber using Sulphuric acid hydrolysis. Chemical modifications of nanocrystalline cellulose was performed to allow good compatibilization between fiber and the polymer matrices and also to improve dispersion of fillers. Bionanocomposite materials were produced from these nanocrystalline cellulose reinforced Poly (lactic acid) and Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) using solvent casting and evaporation techniques. The properties of extracted nanocrystalline cellulose were examined using FT-IR spectroscopy, X-ray diffractometer, TEM and AFM. Besides that, the properties of bionanocomposites were examined through FESEM and oxygen permeability properties analysis. Better barrier and morphological properties were obtained for nanocrystalline cellulose reinforced bionanocomposites than for neat polymer blend.

  20. Inter- and intra-agglomerate fracture in nanocrystalline nickel.

    Science.gov (United States)

    Shan, Zhiwei; Knapp, J A; Follstaedt, D M; Stach, E A; Wiezorek, J M K; Mao, S X

    2008-03-14

    In situ tensile straining transmission electron microscopy tests have been carried out on nanocrystalline Ni. Grain agglomerates (GAs) were found to form very frequently and rapidly ahead of an advancing crack with sizes much larger than the initial average grain size. High-resolution electron microscopy indicated that the GAs most probably consist of nanograins separated by low-angle grain boundaries. Furthermore, both inter- and intra-GA fractures were observed. The observations suggest that these newly formed GAs may play an important role in the formation of the dimpled fracture surfaces of nanocrystalline materials.

  1. A maximum in the strength of nanocrystalline copper

    DEFF Research Database (Denmark)

    Schiøtz, Jakob; Jacobsen, Karsten Wedel

    2003-01-01

    We used molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper. By varying the grain size between 5 and 50 nanometers, we show that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15...... nanometers. This maximum is because of a shift in the microscopic deformation mechanism from dislocation-mediated plasticity in the coarse-grained material to grain boundary sliding in the nanocrystalline region. The simulations allow us to observe the mechanisms behind the grain-size dependence...

  2. Microstructure evolution during pressureless sintering of bulk oxide ceramics

    Directory of Open Access Journals (Sweden)

    Karel Maca

    2009-06-01

    Full Text Available The author’s experience concerning the infl uence of the choice of different pressureless heating schedules on the fi nal microstructure of oxide ceramic materials is summarized in the paper. Alumina, ceria, strontium titanate, as well as tetragonal (3 mol% Y2O3 and cubic (8 mol% Y2O3 zirconia were cold isostatically pressed or injection moulded and pressureless sintered with different heating schedules – namely with Constant-Rate of Heating with different dwell temperatures (CRH, with Rate-Controlled Sintering (RCS and with Two-Step Sintering (TSS. It was examined whether some of these three sintering schedules, with the same fi nal density achieved, can lead to a decrease of the grain size of sintered ceramics. The results showed that only TSS (and only for selected materials brought significant decrease of the grain size.

  3. Nanocrystalline Aluminum Truss Cores for Lightweight Sandwich Structures

    Science.gov (United States)

    Schaedler, Tobias A.; Chan, Lisa J.; Clough, Eric C.; Stilke, Morgan A.; Hundley, Jacob M.; Masur, Lawrence J.

    2017-12-01

    Substitution of conventional honeycomb composite sandwich structures with lighter alternatives has the potential to reduce the mass of future vehicles. Here we demonstrate nanocrystalline aluminum-manganese truss cores that achieve 2-4 times higher strength than aluminum alloy 5056 honeycombs of the same density. The scalable fabrication approach starts with additive manufacturing of polymer templates, followed by electrodeposition of nanocrystalline Al-Mn alloy, removal of the polymer, and facesheet integration. This facilitates curved and net-shaped sandwich structures, as well as co-curing of the facesheets, which eliminates the need for extra adhesive. The nanocrystalline Al-Mn alloy thin-film material exhibits high strength and ductility and can be converted into a three-dimensional hollow truss structure with this approach. Ultra-lightweight sandwich structures are of interest for a range of applications in aerospace, such as fairings, wings, and flaps, as well as for the automotive and sports industries.

  4. Creep behavior of a nanocrystalline Fe-B-Si alloy

    International Nuclear Information System (INIS)

    Xiao, M.; Kong, Q.P.

    1997-01-01

    The research of nanocrystalline materials has attracted much attention in the world. In recent years, there have been several studies on their creep behavior. Among these, the authors have studied the tensile creep of a nanocrystalline Ni-P alloy (28 nm) at temperatures around 0.5 Tm (Tm is the melting point). The samples were prepared by the method of crystallization of amorphous ribbon. Based on the data of stress exponent and activation energy, they suggested that the creep was controlled by boundary diffusion; while the creep of the same alloy with a larger grain size (257 nm) was controlled by a different mechanism. In the present paper, the authors extend the research to the creep of a nanocrystalline Fe-B-Si alloy. The samples are also prepared by crystallization of amorphous ribbon. The samples such prepared have an advantage that the interfaces are naturally formed without artificial compaction and porosity

  5. Properties enhancement and recoil loop characteristics for hot deformed nanocrystalline NdFeB permanent magnets

    International Nuclear Information System (INIS)

    Liu, Z. W.; Huang, Y. L.; Hu, S. L.; Zhong, X. C.; Yu, H. Y.; Gao, X. X.

    2013-01-01

    Nanocrystalline NdFeB magnets were prepared by spark plasma sintering (SPS) and SPS followed by HD using melt spun ribbons as the starting materials. The microstructure of SPSed and HDed magnets were analyzed. The effects of process including temperature and compression ratio on the microstructure and properties were investigated. High magnetic properties were obtained in anisotropic HDed magnets. The combination of Zn and Dy additions was successfully employed to improve the coercivity and thermal stability of the SPSed magnets. Open recoil loops were found in these magnets with Nd-rich composition and without soft magnetic phase for the first time. The relationship between the recoil loops and microstructure for SPS and HD NdFeB magnets were investigated. The investigations showed that the magnetic properties of SPS+HDed magnets are related to the extent of the aggregation of Nd-rich phase, which was formed during HD due to existence of porosity in SPSed precursor. Large local demagnetization fields induced by the Nd-rich phase aggregation leads to the open loops and significantly reduced the coercivity. By reducing the recoil loop openness, the magnetic properties of HDed NdFeB magnets were successfully improved. (author)

  6. A preliminary study in osteoinduction by a nano-crystalline hydroxyapatite in the mini pig.

    Science.gov (United States)

    Götz, Werner; Lenz, Solvig; Reichert, Christoph; Henkel, Kai-Olaf; Bienengräber, Volker; Pernicka, Laura; Gundlach, Karsten K H; Gredes, Tomasz; Gerber, Thomas; Gedrange, Tomasz; Heinemann, Friedhelm

    2010-12-01

    To test the probable osteoinductive properties of NanoBone, a new highly non-sintered porous nano-crystalline hydroxylapatite bone substitute embedded into a silica gel matrix, granules were implanted subcutaneously and intramuscularly into the back region of 18 mini pigs. After periods of 5 and 10 weeks as well as 4 and 8 months, implantation sites were investigated using histological and histomorphometric procedures. Signs of early osteogenesis could already be detected after 5 weeks. The later periods were characterized by increasing membranous osteogenesis in and around the granules leading to the formation of bone-like structures showing periosteal and tendon-like structures with bone marrow and focal chondrogenesis. Bone formation was better in the subcutaneous than in the intramuscular implantation sites. This ectopic osteogenesis is discussed with regard to the nanoporosity and microporosity of the material, physico-chemical interactions at its surface, the differentiation of osteoblasts, the role of angiogenesis and the probable involvement of growth factors. The results of this preliminary study indicate that this biomaterial has osteoinductive potential and induces the formation of bone structures, mainly in subcutaneous adipose tissue in the pig.

  7. A preliminary study in osteoinduction by a nano-crystalline hydroxyapatite in the mini pig.

    Directory of Open Access Journals (Sweden)

    Karsten K H Gundlach

    2011-04-01

    Full Text Available To test the probable osteoinductive properties of NanoBone, a new highly non-sintered porous nano-crystalline hydroxylapatite bone substitute embedded into a silica gel matrix, granules were implanted subcutaneously and intramuscularly into the back region of 18 mini pigs. After periods of 5 and 10 weeks as well as 4 and 8 months, implantation sites were investigated using histological and histomorphometric procedures. Signs of early osteogenesis could already be detected after 5 weeks. The later periods were characterized by increasing membranous osteogenesis in and around the granules leading to the formation of bone-like structures showing periosteal and tendon-like structures with bone marrow and focal chondrogenesis. Bone formation was better in the subcutaneous than in the intramuscular implantation sites. This ectopic osteogenesis is discussed with regard to the nanoporosity and microporosity of the material, physico-chemical interactions at its surface, the differentiation of osteoblasts, the role of angiogenesis and the probable involvement of growth factors. The results of this preliminary study indicate that this biomaterial has osteoinductive potential and induces the formation of bone structures, mainly in subcutaneous adipose tissue in the pig.

  8. Low power optical limiting studies on nanocrystalline benzimidazole ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 38; Issue 3. Low power optical limiting studies on nanocrystalline benzimidazole thin films prepared by modified liquid phase growth technique. P A Praveen S P Prabhakaran R Ramesh Babu K Sethuraman K Ramamurthi. Volume 38 Issue 3 June 2015 pp 645-651 ...

  9. Pulsed nanocrystalline plasma electrolytic boriding as a novel ...

    Indian Academy of Sciences (India)

    The effect of frequency and duty cycle of pulsed current was investigated. It was found that pulse frequency and duty cycle affect the size and porosity of nanocrystalline borides and by controlling these effective parameters, surface modification can render the CP-Ti material extremely corrosion resistant as a biomaterial.

  10. Fast response time alcohol gas sensor using nanocrystalline F ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 36; Issue 4. Fast response time alcohol gas sensor using nanocrystalline F-doped SnO2 films derived via sol–gel method. Sarbani Basu Yeong-Her Wang C Ghanshyam Pawan Kapur. Volume 36 Issue 4 August 2013 pp 521-533 ...

  11. Light emission, light detection and strain sensing with nanocrystalline graphene

    International Nuclear Information System (INIS)

    Riaz, Adnan; Pyatkov, Feliks; Alam, Asiful; Dehm, Simone; Chakravadhanula, Venkata S K; Flavel, Benjamin S; Kübel, Christian; Krupke, Ralph; Felten, Alexandre; Lemmer, Uli

    2015-01-01

    Graphene is of increasing interest for optoelectronic applications exploiting light detection, light emission and light modulation. Intrinsically, the light–matter interaction in graphene is of a broadband type. However, by integrating graphene into optical micro-cavities narrow-band light emitters and detectors have also been demonstrated. These devices benefit from the transparency, conductivity and processability of the atomically thin material. To this end, we explore in this work the feasibility of replacing graphene with nanocrystalline graphene, a material which can be grown on dielectric surfaces without catalyst by graphitization of polymeric films. We have studied the formation of nanocrystalline graphene on various substrates and under different graphitization conditions. The samples were characterized by resistance, optical transmission, Raman and x-ray photoelectron spectroscopy, atomic force microscopy and electron microscopy measurements. The conducting and transparent wafer-scale material with nanometer grain size was also patterned and integrated into devices for studying light–matter interaction. The measurements show that nanocrystalline graphene can be exploited as an incandescent emitter and bolometric detector similar to crystalline graphene. Moreover the material exhibits piezoresistive behavior which makes nanocrystalline graphene interesting for transparent strain sensors. (paper)

  12. Oxygen reduction on nanocrystalline ruthenia-local structure effects

    DEFF Research Database (Denmark)

    Abbott, Daniel F.; Mukerjee, Sanjeev; Petrykin, Valery

    2015-01-01

    Nanocrystalline ruthenium dioxide and doped ruthenia of the composition Ru1-xMxO2 (M = Co, Ni, Zn) with 0 ≤ x ≤ 0.2 were prepared by the spray-freezing freeze-drying technique. The oxygen reduction activity and selectivity of the prepared materials were evaluated in alkaline media using the RRDE ...

  13. Fast response time alcohol gas sensor using nanocrystalline F

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 36; Issue 4. Fast response time alcohol gas sensor using nanocrystalline F-doped SnO2 films derived via sol–gel method. Sarbani Basu Yeong-Her Wang C Ghanshyam Pawan Kapur. Volume 36 Issue 4 August 2013 pp 521-533 ...

  14. Synthesis and visible light photocatalytic activity of nanocrystalline ...

    Indian Academy of Sciences (India)

    The synthesized materials were characterized by XRD, BET-SA, SEM, HRTEM, XPS, FTIR and UV-DRS techniques to understand their physico-chemical properties. Characterization data reveal the formation of nanocrystalline PrFeO3 perovskite composition with improved physical properties, possibly due to lower ...

  15. Study of ceramics sintering under high pressures

    International Nuclear Information System (INIS)

    Kunrath Neto, A.O.

    1990-01-01

    A systematic study was made on high pressure sintering of ceramics in order to obtain materials with controlled microstructure, which are not accessible by conventional methods. Some aspects with particular interest were: to achieve very low porosity, with fine grains; to produce dispersed metastable and denser phases which can act as toughening agents; the study of new possibilities for toughening enhancement. (author)

  16. Mechanical characterization of microwave sintered zinc oxide

    Indian Academy of Sciences (India)

    Unknown

    Keywords. Zinc oxide; microwave sintering; microhardness. 1. Introduction. The application of microwave energy for the processing of ceramics has become an attractive area of research and innovation recently. The major advantages of the micro- wave processing of ceramic materials are accelerated densification rate as a ...

  17. High-strength CAD/CAM-fabricated veneering material sintered to zirconia copings--a new fabrication mode for all-ceramic restorations.

    Science.gov (United States)

    Beuer, Florian; Schweiger, Josef; Eichberger, Marlis; Kappert, Heinrich F; Gernet, Wolfgang; Edelhoff, Daniel

    2009-01-01

    With this in vitro study the fracture strength of zirconia-based crown copings being veneered with a CAD/CAM generated high-strength ceramic cap by sintering is compared with anatomically identical zirconia-based crowns, which were either overpressed or veneered by the layering technique for completion. A 1.2mm, 360 degrees chamfer preparation was performed on a second maxillary molar and was dublicated 15 times in a cobalt-chromium-alloy. A sample of 45 zirconia copings was produced and divided into three groups. In the first group (VT) zirconia copings received conventional veneering in layering technique, in the second group the veneering porcelain was pressed over the zirconia coping (PT), and for the third group (ST) a CAD/CAM-fabricated high-strength anatomically shaped veneering cap was sintered onto the zirconia coping. All crowns were cemented conventionally onto their dies and tested in the universal testing machine until clinical failure. The fracture load data were compared by a one-way analysis of variance and a multiple comparison posthoc test (alphacrowns and fixed partial dentures with a potential lower risk of chippings.

  18. Selective Laser Sintering And Melting Of Pristine Titanium And Titanium Ti6Al4V Alloy Powders And Selection Of Chemical Environment For Etching Of Such Materials

    Directory of Open Access Journals (Sweden)

    Dobrzański L.A.

    2015-09-01

    Full Text Available The aim of the investigations described in this article is to present a selective laser sintering and melting technology to fabricate metallic scaffolds made of pristine titanium and titanium Ti6Al4V alloy powders. Titanium scaffolds with different properties and structure were manufactured with this technique using appropriate conditions, notably laser power and laser beam size. The purpose of such elements is to replace the missing pieces of bones, mainly cranial and facial bones in the implantation treatment process. All the samples for the investigations were designed in CAD/CAM (3D MARCARM ENGINEERING AutoFab (Software for Manufacturing Applications software suitably integrated with an SLS/SLM system. Cube-shaped test samples dimensioned 10×10×10 mm were designed for the investigations using a hexagon-shaped base cell. The so designed 3D models were transferred to the machine software and the actual rapid manufacturing process was commenced. The samples produced according to the laser sintering technology were subjected to chemical processing consisting of etching the scaffolds’ surface in different chemical mediums. Etching was carried out to remove the loosely bound powder from the surface of scaffolds, which might detach from their surface during implantation treatment and travel elsewhere in an organism. The scaffolds created were subjected to micro- and spectroscopic examinations

  19. Improvement of mechanical strength of sintered Mo alloyed steel by optimization of sintering and cold-forging processes with densification

    Science.gov (United States)

    Kamakoshi, Y.; Shohji, I.; Inoue, Y.; Fukuda, S.

    2017-10-01

    Powder metallurgy (P/M) materials have been expected to be spread in automotive industry. Generally, since sintered materials using P/M ones contain many pores and voids, mechanical properties of them are inferior to those of conventional wrought materials. To improve mechanical properties of the sintered materials, densification is effective. The aim of this study is to improve mechanical strength of sintered Mo-alloyed steel by optimizing conditions in sintering and cold-forging processes. Mo-alloyed steel powder was compacted. Then, pre-sintering (PS) using a vacuum sintering furnace was conducted. Subsequently, coldforging (CF) by a backward extrusion method was conducted to the pre-sintered specimen. Moreover, the cold-forged specimen was heat treated by carburizing, tempering and quenching (CQT). Afterwards, mechanical properties were investigated. As a result, it was found that the density of the PS specimen is required to be more than 7.4 Mg/m3 to strengthen the specimen by heat treatment after CF. Furthermore, density and the microstructure of the PS specimen are most important factors to make the high density and strength material by CF. At the CF load of 1200 kN, the maximum density ratio reached approximately 99% by the use of the PS specimen with proper density and microstructure. At the CF load of 900 kN, although density ratio was high like more than 97.8%, transverse rupture strength decreased sharply. Since densification caused high shear stress and stress concentration in the surface layer, microcracks occurred by the damages of inter-particle sintered connection of the surface layer. On the contrary, in case of the CF load of 1200 kN, ultra-densification of the surface layer occurred by a sufficient plastic flow. Such sufficient compressed specimens regenerated the sintered connections by high temperature heat treatment and thus the high strength densified material was obtained. These processes can be applicable to near net shape manufacturing

  20. The Emergence of Quantitative Sintering Theory from 1945 to 1955

    Science.gov (United States)

    German, Randall M.

    2017-04-01

    Particles flow and pack under stress, allowing shaping of the particles into target engineering geometries. Subsequently, in a process termed sintering, the particles are heated to induce bonding that results in a strong solid. Although first practiced 26,000 years ago, sintering was largely unexplained until recent times. Sintering science moved from an empirical and largely qualitative notion into a quantitative theory over a relatively short time period following World War II. That conceptual transition took place just as commercial applications for sintered materials underwent significant growth. This article highlights the key changes in sintering concepts that occurred in the 1945-1955 time period. This time span starts with the first quantitative neck growth model from Frenkel and ends with the quantitative shrinkage model from Kingery and Berg that includes several transport mechanisms.

  1. Study on selective laser sintering of glass fiber reinforced polystyrene

    Science.gov (United States)

    Yang, Laixia; Wang, Bo; Zhou, Wenming

    2017-12-01

    In order to improve the bending strength of Polystyrene (PS) sintered parts by selective laser sintering, Polystyrene/glass fiber (PS/GF) composite powders were prepared by mechanical mixing method. The size distribution of PS/GF composite powders was characterized by laser particle size analyzer. The optimum ratio of GF was determined by proportioning sintering experiments. The influence of process parameters on the bending strength of PS and PS/GF sintered parts was studied by orthogonal test. The result indicates that the particle size of PS/GF composite powder is mainly distributed in 24.88 μm~139.8 μm. When the content of GF is 10%, it has better strengthen effect. Finally, the article used the optimum parameter of the two materials to sinter prototype, it is found that the PS/GF prototype has the advantages of good accuracy and high strength.

  2. Dilatometric study on sintering mechanism of the WC-10wt%Co cemented carbide doped with tantalum carbide and niobium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Manuel, J.B. [Universidade Federal Rural de Pernambuco (UFRPE), PE (Brazil); Gomes, U.U.; Karimi, M.M. [Universidade Federal do Rio Grande do Norte (UFRN), RN (Brazil)

    2016-07-01

    Full text: Nanocrystalline WC-10wt.%Co powders were prepared by high energy milling and were liquid phase sintered. The powders were milled at 20 hours and characterized by X-ray diffraction, and Scanning electron microscopy. The particle size distribution and mean diameter analysis were characterized by Granulometro Cilas model 920 L and 1180. After sintering the WC-10wt.%Co cemented carbides doped with tantalum carbide and niobium carbide exhibited ultra fine grain sizes. dilatometer study on sintering mechanism detected phase transformations and degassing. (author)

  3. Preparation and mechanism of the sintered bricks produced from Yellow River silt and red mud

    Energy Technology Data Exchange (ETDEWEB)

    He, Hongtao [Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100 (China); Yue, Qinyan, E-mail: qyyue@sdu.edu.cn [Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100 (China); Su, Yuan; Gao, Baoyu; Gao, Yue; Wang, Jingzhou; Yu, Hui [Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100 (China)

    2012-02-15

    Highlights: Black-Right-Pointing-Pointer The best condition was red mud content of 40% and sintering at 1050 Degree-Sign C for 2 h. Black-Right-Pointing-Pointer Bricks' weight loss was caused by the removal of absorbed water and crystal water. Black-Right-Pointing-Pointer Bricks' sintering shrinkage depended on the sodium and iron compounds of red mud. Black-Right-Pointing-Pointer Sintering can strengthen bricks and decrease leaching concentration of toxic metal. - Abstract: The preparation, characteristics and mechanisms of sintered bricks manufactured by Yellow River silt and red mud were studied. The sintering shrinkage, weight loss on ignition, water absorption and compressive strength were tested to determine the optimum preparation condition. Sintering mechanisms were discussed through linear regression analysis. Crystalline components of raw materials and bricks were analyzed by X-ray diffraction. Leaching toxicity of raw materials and bricks were measured according to sulphuric acid and nitric acid method. Radiation safety of the sintered bricks was characterized by calculating internal exposure index and external exposure index. The results showed that at the chosen best parameters (red mud content of 40%, sintering temperature of 1050 Degree-Sign C and sintering time of 2 h), the best characteristics of sintered bricks could be obtained. The weight loss on ignition of sintered bricks was principally caused by the removal of absorbed water and crystal water. The sintering shrinkage of sintered bricks mainly depended on sodium compounds and iron compounds of red mud. The sintering process made some components of raw materials transform into other crystals having better thermostability. Besides, the leaching toxicity and radioactivity index of sintered bricks produced under the optimum condition were all below standards.

  4. Surface-modified nanocrystalline ceramics for drug delivery applications.

    Science.gov (United States)

    Kossovsky, N; Gelman, A; Sponsler, E E; Hnatyszyn, H J; Rajguru, S; Torres, M; Pham, M; Crowder, J; Zemanovich, J; Chung, A

    1994-12-01

    Drug delivery systems comprised of various types of carriers have long been the object of pharmacological investigation. The search has been stimulated by the belief that carriers will lead to reduced drug toxicity, dosage requirements, enhanced cellular targeting and improved shelf-life. Among the carriers investigated are complex polymeric carbohydrates, synthetic proteins and liposomal structures. For the past four years, we have been experimenting with a radically new class of carriers comprised of surface-modified nanocrystalline ceramics. While the ceramics provide the structural stability of a largely immutable solid, the surface modification creates a glassy molecular stabilization film to which pharmacological agents may be bound non-covalently from an aqueous phase with minimal structural denaturation. As a consequence of maintained structural integrity and owing to concentration effects afforded by the surfaces of the nanocrystalline materials, drug activity following surface immobilization is preserved. We have used successfully surface-modified nanocrystalline ceramics to deliver viral antigens for the purpose of evoking an immune response, oxygenated haemoglobin for cell respiration and insulin for carbohydrate metabolism. The theoretical principles, technical details and experimental results are reviewed. Surface-modified nanocrystalline materials offer an exciting new approach to the well-recognized challenges of drug delivery.

  5. Electrophoretic deposition of nanocrystalline TiO2 films on Ti substrates for use in flexible dye-sensitized solar cells

    International Nuclear Information System (INIS)

    Tan Weiwei; Yin Xiong; Zhou Xiaowen; Zhang Jingbo; Xiao Xurui; Lin Yuan

    2009-01-01

    Nanocrystalline TiO 2 films were prepared on flexible Ti-metal sheets by electrophoretic deposition followed by chemical treatment with tetra-n-butyl titanate (TBT) and sintering at 450 deg. C. X-ray diffraction (XRD) analysis indicates that TBT treatment led to the formation of additional anatase TiO 2 , which plays an important role in improving the interconnection between TiO 2 particles, as well as the adherence of the film to the substrate, and in modifying the surface properties of the nanocrystalline particles. The effect of TBT treatment on the electron transport in the nanocrystalline films was studied by intensity-modulated photocurrent spectroscopy (IMPS). An increase in the conversion efficiency was obtained for the dye-sensitized solar cells with TBT-treated nanocrystalline TiO 2 films. The cell performance was further optimized by designing nanocrystalline TiO 2 films with a double-layer structure composed of a light-scattering layer and a transparent layer. The light-scattering effect of the double-layer nanocrystalline films was evaluated by diffuse reflectance spectra. Employing the double-layer nanocrystalline films as the photoelectrodes resulted in a significant improvement in the incident photo-to-current conversion efficiency of the corresponding cells due to enhanced solar absorption by light scattering. A high conversion efficiency of 6.33% was measured under illumination with 100 mW cm -2 (AM 1.5) simulated sunlight.

  6. Quartz crystal reinforced quartz glass by spark plasma sintering

    International Nuclear Information System (INIS)

    Torikai, D.; Barazani, B.; Ono, E.; Santos, M.F.M.; Suzuki, C.K.

    2011-01-01

    The Spark Plasma Sintering presents fast processing time when compared to conventional sintering techniques. This allows to control the grain growth during sintering as well as the diffusion rate of a multi-material compounds, and make possible obtainment of functionally graded materials and nanostructured compounds. Powders of high purity silica glass and crystalline silica were sintered in a SPS equipment at temperatures around 1350° C, i.e., above the softening temperature of silica glass and below the melting temperature of quartz crystal. As a result, glass ceramics with pure silica glass matrix reinforced with crystalline alpha-quartz grains were fabricated at almost any desired range of composition, as well as controlled size of the crystalline reinforcement. X-ray diffraction and density measurements showed the possibility to manufacture a well controlled density and crystallinity glass-ceramic materials. (author)

  7. Ferromagnetism appears in nitrogen implanted nanocrystalline diamond films

    Czech Academy of Sciences Publication Activity Database

    Remeš, Zdeněk; Sun, S. J.; Varga, M.; Chou, H.; Hsu, H.S.; Kromka, A.; Horák, Pavel

    2015-01-01

    Roč. 394, Nov (2015), s. 477-480 ISSN 0304-8853 R&D Projects: GA ČR(CZ) GBP108/12/G108; GA MŠk(CZ) LD14011 EU Projects: European Commission(XE) COST Action MP1202 HINT Institutional support: RVO:68378271 ; RVO:61389005 Keywords : diamond * nonmetallic ferromagnetic materials * fine-particle systems * nanocrystalline materials Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.357, year: 2015

  8. Nanocrystalline sp{sup 2} and sp{sup 3} carbons: CVD synthesis and applications

    Energy Technology Data Exchange (ETDEWEB)

    Terranova, M. L. [Università degli Studi di Roma “Tor Vergata,” via Della Ricerca Scientifica, Dipartimento di Scienze e Tecnologie Chimiche—MinimaLab (Italy); Rossi, M. [Università degli Studi di Roma “Sapienza,” via A. Scarpa, Dipartimento di Scienze di Base e Applicate per l’Ingegneria and Centro di Ricerca per le Nanotecnologie Applicate all’Ingegneria (CNIS) (Italy); Tamburri, E., E-mail: emanuela.tamburri@uniroma2.it [Università degli Studi di Roma “Tor Vergata,” via Della Ricerca Scientifica, Dipartimento di Scienze e Tecnologie Chimiche—MinimaLab (Italy)

    2016-11-15

    The design and production of innovative materials based on nanocrystalline sp{sup 2}- and sp{sup 3}-coordinated carbons is presently a focus of the scientific community. We present a review of the nanostructures obtained in our labs using a series of synthetic routes, which make use of chemical vapor deposition (CVD) techniques for the selective production of non-planar graphitic nanostructures, nanocrystalline diamonds, and hybrid two-phase nanostructures.

  9. Self-composite comprised of nanocrystalline diamond and a non-diamond component useful for thermoelectric applications

    Science.gov (United States)

    Gruen, Dieter M [Downers Grove, IL

    2009-08-11

    One provides nanocrystalline diamond material that comprises a plurality of substantially ordered diamond crystallites that are sized no larger than about 10 nanometers. One then disposes a non-diamond component within the nanocrystalline diamond material. By one approach this non-diamond component comprises an electrical conductor that is formed at the grain boundaries that separate the diamond crystallites from one another. The resultant nanowire is then able to exhibit a desired increase with respect to its ability to conduct electricity while also preserving the thermal conductivity behavior of the nanocrystalline diamond material.

  10. Spark plasma sintering and mechanical properties of $ZrO_{2} (Y_{2}O_{3})-Al_{2}O_{3}$ composites

    CERN Document Server

    Jin Sheng H; Dalla Torre, S; Miyamoto, H; Miyamoto, K

    2000-01-01

    Spark plasma sintering (SPS) was conducted on nanocrystalline ZrO/sub 2/(Y/sub 2/O/sub 3/)-20 mol% Al/sub 2/O/sub 3/ powder at a heat rate of 600 degrees C/min with a short holding time. Full density was obtained at sintering temperatures >1300 degrees C. Considerable grain growth occurred relative to the initial powder particles, but smaller grain size and higher density can be obtained as compared to hot-pressing. High flexural strength and fracture toughness were also achieved for the SPS-resulted composite. (8 refs).

  11. Sintering of B4C by pressureless liquid phase sintering

    International Nuclear Information System (INIS)

    Rocha, Rosa Maria da; Melo, Francisco Cristovao Lourenco de

    2009-01-01

    The effect of three different sintering additive systems on densification of boron carbide powder was investigated. The sintering additives were Al 2 O 3 :Y 2 O 3 , AlN:Y 2 O 3 and BN:Y 2 O 3 compositions. Powder mixtures were prepared with 10 vol% of sintering aids following conventional powder technology processes. Samples were sintered by pressureless sintering at 2050 deg C/30min in argon atmosphere. Sintered samples were compared to a sintered B 4 C without sintering additive. Samples were characterized by XRD to analyze the crystalline phases after sintering and SEM to observe the microstructure and the second phase distribution. YB 4 and YB 2 C 2 were identified in all samples, indicating a reaction between Y 2 O 3 , B 4 C and B 2 O 3 present at the B 4 C particle surface. The best densification result was achieved with Al 2 O 3 :Y 2 O 3 additive system, showing 92.0 % of theoretical density, low porosity and 15.2 % of linear shrinkage. But this sample showed the highest weight loss. (author)

  12. Sintering behavior of LZSA glass-ceramics

    Directory of Open Access Journals (Sweden)

    Oscar Rubem Klegues Montedo

    2009-06-01

    Full Text Available The LZSA glass-ceramic system (Li2O-ZrO2-SiO2-Al2O 3 shows interesting properties, such as good chemical resistance, low thermal expansion, high abrasion resistance, and a low dielectric constant. However, in order to obtain a high performance material for specific applications, the sintering behavior must be better understood so that the porosity may be reduced and other properties improved. In this context, a sintering investigation for a specific LZSA glass-ceramic system composition was carried out. A 18.8Li2O-8.3ZrO2-64.2SiO2-8.7Al 2O3 glass was prepared by melting the solids, quenching the melt in water, and grinding the resulting solid in order to obtain a powder (3.68 μm average particle diameter. Subsequently, the glass powder was characterized (chemical analysis and determination of thermal properties and the sintering behavior was investigated using optical non-contact dilatometry measurements. The results showed that the crystallization process strongly reduced the sintering in the temperature interval from 785 to 940 °C, and a maximum thermal shrinkage of 15.4% was obtained with operating conditions of 1020 °C and 180 minutes.

  13. Laser Sintering Technology and Balling Phenomenon.

    Science.gov (United States)

    Oyar, Perihan

    2018-02-01

    The aim of this review was to evaluate the balling phenomenon which occurs typically in Selective Laser Sintering (SLS). The balling phenomenon is a typical SLS defect, and observed in laser sintered powder, significantly reduces the quality of SLS, and hinders the further development of SLS Technology. Electronic database searches were performed using Google Scholar. The keywords "laser sintering, selective laser sintering, direct metal laser melting, and balling phenomenon" were searched in title/abstract of publications, limited to December 31, 2016. The inclusion criteria were SLS, balling phenomenon, some alloys (such as Cr-Co, iron, stainless steel, and Cu-based alloys) mechanical properties, microstructure and bond strength between metal-ceramic crown, laboratory studies, full text, and in English language. A total of 100 articles were found the initial search and yielded a total of 50 studies, 30 of which did not fulfill the inclusion criteria and were therefore excluded. In addition, 20 studies were found by screening the reference list of all included publications. Finally, 40 studies were selected for this review. The method in question is regulated by powder material characteristics and the conditions of laser processing. The procedure of formation, affecting factors, and the mechanism of the balling effect are very complex.

  14. Sintering Behavior, Microstructure, and Mechanical Properties: A Comparison among Pressureless Sintered Ultra-Refractory Carbides

    Directory of Open Access Journals (Sweden)

    Laura Silvestroni

    2010-01-01

    Full Text Available Nearly fully dense carbides of zirconium, hafnium, and tantalum were obtained by pressureless sintering at 1950°C with the addition of 5–20 vol% of MoSi2. Increasing the amount of sintering aid, the final density increased too, thanks to the formation of small amounts of liquid phase constituted by M-Mo-Si-O-C, where M is either Zr, Hf, or Ta. The matrices of the composites obtained with the standard procedure showed faceted squared grains; when an ultrasonication step was introduced in the powder treatment, the grains were more rounded and no exaggerated grains growth occurred. Other secondary phases observed in the microstructure were SiC and mixed silicides of the transition metals. Among the three carbides prepared by pressurless sintering, TaC-based composites had the highest mechanical properties at room temperature (strength 590 MPa, Young's modulus 480 GPa, toughness 3.8 MPa·m1/2. HfC-based materials showed the highest sinterability (in terms of final density versus amount of sintering aid and the highest high-temperature strength (300 MPa at 1500  °C.

  15. Research Update: Phonon engineering of nanocrystalline silicon thermoelectrics

    Directory of Open Access Journals (Sweden)

    Junichiro Shiomi

    2016-10-01

    Full Text Available Nanocrystalline silicon thermoelectrics can be a solution to improve the cost-effectiveness of thermoelectric technology from both material and integration viewpoints. While their figure-of-merit is still developing, recent advances in theoretical/numerical calculations, property measurements, and structural synthesis/fabrication have opened up possibilities to develop the materials based on fundamental physics of phonon transport. Here, this is demonstrated by reviewing a series of works on nanocrystalline silicon materials using calculations of multiscale phonon transport, measurements of interfacial heat conduction, and synthesis from nanoparticles. Integration of these approaches allows us to engineer phonon transport to improve the thermoelectric performance by introducing local silicon-oxide structures.

  16. Toughness and strength of nanocrystalline graphene

    Science.gov (United States)

    Shekhawat, Ashivni; Ritchie, Robert O.

    2016-01-01

    Pristine monocrystalline graphene is claimed to be the strongest material known with remarkable mechanical and electrical properties. However, graphene made with scalable fabrication techniques is polycrystalline and contains inherent nanoscale line and point defects—grain boundaries and grain-boundary triple junctions—that lead to significant statistical fluctuations in toughness and strength. These fluctuations become particularly pronounced for nanocrystalline graphene where the density of defects is high. Here we use large-scale simulation and continuum modelling to show that the statistical variation in toughness and strength can be understood with ‘weakest-link' statistics. We develop the first statistical theory of toughness in polycrystalline graphene, and elucidate the nanoscale origins of the grain-size dependence of its strength and toughness. Our results should lead to more reliable graphene device design, and provide a framework to interpret experimental results in a broad class of two-dimensional materials. PMID:26817712

  17. Sintering and electrical properties of strontium-doped lanthanum manganite

    Energy Technology Data Exchange (ETDEWEB)

    Tarrago, Diego Pereira; Sousa, Vania Caldas de [Universidade Federal do Rio Grande do Sul (LABIOMAT/PPGEM/UFRGS), Porto Alegre, RS (Brazil). Programa de Pos-Graduacao em Engenharia de Minas, Metalurgica e de Materiais. Lab. de Biomateriais], Email: dptarrago@gmail.com; Moreno Buriel, Berta; Chinarro Martini, Eva; Jurado Egea, Jose Ramon [Consejo Superior de Investigaciones Cientificas (ICV/CSIC), Madrid (Spain). Inst. de Ceramica y Vidrio; Malfatti, Celia de Fraga [Universidade Federal do Rio Grande do Sul (LAPEC/PPGEM/UFRGS), Porto Alegre, RS (Brazil). Programa de Pos-Graduacao em Engenharia de Minas, Metalurgica e de Materiais. Lab. de Pesquisa em Corrosao

    2010-07-01

    Lanthanum strontium manganites (LSM) are potential materials for cathode applications in solid oxide fuel cells (SOFC) due to their good catalytic activity, chemical stability and compatibility with electrolyte materials in high temperatures. The sinterability of single phase La{sub 1-x}Sr{sub x}Mn{sub O3} (x=0.18) perovskite powders and the electrical properties of the resulting samples are analyzed in this study. Using a heating microscope, the powders were pressed and sintered at different pressures and temperatures, resulting in an open porosity of 33.36% when compacted at 125 MPa and sintered at 1200 degree C. Top and cross-section s canning electron microscopy (SEM) micrographs revealed interconnected pores in the sintered body and, hence, a suitable microstructure for the application. The activation energy for conductance was 0.04 eV and the tested LSM bulk started to exhibit adequate electrical properties at about 500 degree C. (author)

  18. Non-pressurized sintered silicon carbide with titanium carbide reinforcement

    International Nuclear Information System (INIS)

    Adler, J.

    1992-01-01

    A non-pressurized compression of SiC-TiC composite materials can be achieved via liquid phase sintering by the application of oxidic additives. Materials with TiC proportions up to 40% by volume of TiC and densities of 97 to 98% TD were produced at sintering temperatures around 1875 C. With SiC sintered in the liquid phase an increase of toughness at fracture of 80% compared with conventionally non-pressurized sintered SiC was achieved with B/C additive. No further increase could be achieved by the addition of TiC particles. However, the oxidation resistance at 1200 C was worsened. (orig.) [de

  19. Nanocrystalline magnetic alloys and ceramics

    Indian Academy of Sciences (India)

    Ultrafine particles of both ferro- and ferrimagnetic systems show superparamagnetic behaviour at room temperature. Coercivity ( H c ) and maximum energy product ( B H ) max of the magnetic particles can be changed by controlling their sizes. The present paper reviews all these aspects in the case of nanocrystalline ...

  20. `Joint Research and Development of Industrial Technology,` an international research collaboration for fiscal 1997. Research and development for practical application of low-temperature sinterable, highly heat-radiating materials for ceramics; 1997 nendo kokusai kenkyu kyoryoku jigyo `sangyo kiban gijutsu kyodo kenkyu kaihatsu`. Teion shoketsu kohonetsusei ceramics kiban zairyo no jitsuyoka gijutsu no kenkyu kaihatsu seika hokokusho

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-03-01

    A highly heat-conducting AlN ceramic substrate is developed for the cooling of semiconductor integrated circuit devices and power controlling semiconductor devices. In the development of a low-temperature sinterable ceramic texture, a sintering assistant is selected. In this process various assistants are tested for the effect of their presence on the occurrence of AlN oxidation and on the magnitude of standard energy for aluminate compound formation. The volatility at high temperatures of the components of the assistants are also examined. The sintering assistant developed for this project (mixture of Y2O3, CaO, LaB6, and WO3) is used in the sintering of an AlN material powder developed by The Dow Chemical Co., and then it is demonstrated that highly heat-conducting AlN substrates are mass-produced by continuous sintering at 1600degC in a nitrogen atmosphere, the product having a relative density of 100%, average heat conductivity of 154W/mK, bend resisting strength of 440MPa, and a fracture toughness value of 3.8MPam{sup 1/2}. 6 refs., 92 figs., 10 tabs.

  1. The effects of surface finish and grain size on the strength of sintered silicon carbide

    Science.gov (United States)

    You, Y. H.; Kim, Y. W.; Lee, J. G.; Kim, C. H.

    1985-01-01

    The effects of surface treatment and microstructure, especially abnormal grain growth, on the strength of sintered SiC were studied. The surfaces of sintered SiC were treated with 400, 800 and 1200 grit diamond wheels. Grain growth was induced by increasing the sintering times at 2050 C. The beta to alpha transformation occurred during the sintering of beta-phase starting materials and was often accompanied by abnormal grain growth. The overall strength distributions were established using Weibull statistics. The strength of the sintered SiC is limited by extrinsic surface flaws in normal-sintered specimens. The finer the surface finish and grain size, the higher the strength. But the strength of abnormal sintering specimens is limited by the abnormally grown large tabular grains. The Weibull modulus increases with decreasing grain size and decreasing grit size for grinding.

  2. Nanocrystalline SiC and Ti3SiC2 Alloys for Reactor Materials: Thermal and Mechanical Properties

    Energy Technology Data Exchange (ETDEWEB)

    Henager, Charles H. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Alvine, Kyle J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Roosendaal, Timothy J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Shin, Yongsoon [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Nguyen, Ba Nghiep [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Borlaug, Brennan A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Jiang, Weilin [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2014-04-01

    SiC-polymers (pure polycarbosilane and polycarbosilane filled with SiC-particles) are being combined with Si and TiC powders to create a new class of polymer-derived ceramics for consideration as advanced nuclear materials in a variety of applications. Compared to pure SiC these materials have increased fracture toughness with only slightly reduced thermal conductivity. Future work with carbon nanotube (CNT) mats will be introduced with the potential to increase the thermal conductivity and the fracture toughness. At present, this report documents the fabrication of a new class of monolithic polymer derived ceramics, SiC + SiC/Ti3SiC2 dual phase materials. The fracture toughness of the dual phase material was measured to be significantly greater than Hexoloy SiC using indentation fracture toughness testing. However, thermal conductivity of the dual phase material was reduced compared to Hexoloy SiC, but was still appreciable, with conductivities in the range of 40 to 60 W/(m K). This report includes synthesis details, optical and scanning electron microscopy images, compositional data, fracture toughness, and thermal conductivity data.

  3. Microstructures and mechanical properties of nanocrystalline NiTi intermetallics formed by mechanosynthesis

    Science.gov (United States)

    Arunkumar, S.; Kumaravel, P.; Velmurugan, C.; Senthilkumar, V.

    2018-01-01

    The formulation of nanocrystalline NiTi shape memory alloys has potential effects in mechanical stimulation and medical implantology. The present work elucidates the effect of milling time on the product's structural characteristics, chemical composition, and microhardness for NiTi synthesized by mechanical alloying for different milling durations. Increasing the milling duration led to the formation of a nanocrystalline NiTi intermetallic at a higher level. The formation of nanocrystalline materials was directed through cold fusion, fracturing, and the development of a steady state, which were influenced by the accumulation of strain energy. In the morphological study, uninterrupted cold diffusion and fracturing were visualized using transmission electron microscopy. Particle size analysis revealed that the mean particle size was reduced to 93 μm after 20 h of milling. The mechanical strength was enhanced by the formation of a nanocrystalline intermetallic phase at longer milling time, which was confirmed by the results of Vickers hardness analyses.

  4. Sintering techniques for microstructure control in ceramics

    Science.gov (United States)

    Rosenberger, Andrew T.

    Sintering techniques can be manipulated to enhance densification in difficult to sinter materials and to produce property enhancing microstructures. However, the interplay between materials, sintering techniques, and end properties is not fully understood in many material systems, and some fundamental aspects of sintering such as the nature of the effects of electric fields remains unknown. The processing property relationships were examined in two classes of materials; zirconium diboride ultra high temperature ceramic composites, and all solid lithium-ion battery phosphate materials. Investigation of zirconium diboride ceramics focused on the effects of zirconium carbide as a secondary or tertiary phase in ZrB2 and ZrB2 -- SiC. Addition of zirconium carbide was observed to increase flexural strength of composites up to 590MPa at 50wt% ZrC, significantly higher than the flexural strength of 380MPa observed in similarly prepared ZrB2 -- SiC. This difference was attributed to the absence of CTE mismatch induced residual stresses in the ZrB2 -- ZrC composites. A high temperature reaction between ZrB2 and TiC producing Zr1-xTixB2 -- ZrC composites was discovered and found to enhance densification while reducing the average grain size to as small as 1.4mum, lower than the starting powder size of 1.8mum. While a high flexural strength of 670MPa was observed, a strength dependence on the ZrC grain size indicative of CTE mismatch residual stresses was also seen. Finally, the oxidation and ablation resistance of ZrB2 -- ZrC -- SiC composites as a function of ZrC fraction and ZrC:SiC ratio was investigated. Above 5vol% ZrC, the oxidation and ablation resistance of the composites was significantly reduced due to ZrC oxidation, regardless of SiC content. While ZrC can significantly enhance the mechanical properties of the composite, the volume fraction must be kept low to avoid an undesirable reduction in the oxidation resistance. The influence of applied electrical fields

  5. Embrittling Components in Sintered Steels: Comparison of Phosphorus and Boron

    Science.gov (United States)

    Danninger, Herbert; Vassileva, Vassilka; Gierl-Mayer, Christian

    2017-12-01

    In ferrous powder metallurgy, both boron and phosphorus have been known to be sintering activators for a long time. However, the use has been widely different: while P is a standard additive to sintered iron and steels, boron has been frequently studied, but its use in practice is very limited. Both additives are also known to be potentially embrittling, though in a different way. In the present study the differences between the effects of both elements are shown: while P activates sintering up to a certain threshold, in part by stabilizing ferrite, in part by forming a transient liquid phase, boron is the classical additive enhancing persistent liquid phase, being virtually insoluble in the iron matrix. The consequence is that sintered steels can tolerate quite a proportion of phosphorus, depending on composition and sintering process; boron however is strongly embrittling in particular in combination with carbon, which requires establishing a precisely defined content that enhances sintering but is not yet embrittling. The fracture mode of embrittled materials is also different: while with Fe-P the classical intergranular fracture is observed, with boron a much more rugged fracture surface appears, indicating some failure through the eutectic interparticle network but mostly transgranular cleavage. If carbon is added, in both cases transgranular cleavage dominates even in the severely embrittled specimens, indicating that no more the grain boundaries and sintering necks are the weakest links in the systems.

  6. Sintering of magnesia: effect of additives

    Indian Academy of Sciences (India)

    % was studied on the sinter- ing and microstructural developments of the chemically pure magnesia using the pressureless sintering technique between 1500 and 1600◦C. Sintering was evaluated by per cent densification and microstructural ...

  7. Nanocrystalline SiC and Ti3SiC2 Alloys for Reactor Materials: Annual Report

    Energy Technology Data Exchange (ETDEWEB)

    Henager, Charles H. [pnnl; Alvine, Kyle J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Roosendaal, Timothy J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Shin, Yongsoon [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Nguyen, Ba Nghiep; Borlaug, Brennan A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Jiang, Weilin [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Arreguin, Shelly A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2015-01-15

    A new dual-phase nanocomposite of Ti₃SiC₂/SiC is being synthesized using preceramic polymers, ceramic powders, and carbon nanotubes (CNTs) designed to be suitable for advanced nuclear reactors and perhaps as fuel cladding. The material is being designed to have superior fracture toughness compared to SiC, adequate thermal conductivity, and higher density than SiC/SiC composites. This annual report summarizes the progress towards this goal and reports progress in understanding certain aspects of the material behavior but some shortcomings in achieving full density or in achieving adequate incorporation of CNTs. The measured thermal conductivity is adequate and falls into an expected range based on SiC and Ti₃SiC₂. Part of this study makes an initial assessment for Ti₃SiC₂ as a barrier to fission product transport. Ion implantation was used to introduce fission product surrogates (Ag and Cs) and a noble metal (Au) in Ti₃SiC₂, SiC, and a synthesized at PNNL. The experimental results indicate that the implanted Ag in SiC is immobile up to the highest temperature (1273 K) applied in this study; in contrast, significant out-diffusion of both Ag and Au in MAX phase Ti₃SiC₂ occurs during ion implantation at 873 K. Cs in Ti₃SiC₂ is found to diffuse during post-irradiation annealing at 973 K, and noticeable Cs release from the sample is observed. This study may suggest caution in using Ti₃SiC₂ as a fuel cladding material for advanced nuclear reactors operating at very high temperatures. Progress is reported in thermal conductivity modeling of SiC-based materials that is relevant to this research, as is progress in modeling the effects of CNTs on fracture strength of SiC-based materials.

  8. Hot Superplastic Powder Forging for Transparent nanocrystalline Ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Cannon, W. Roger

    2006-05-22

    The program explored a completely new, economical method of manufacturing nanocrystalline ceramics, Hot Superplastic Powder Forging (HSPF). The goal of the work was the development of nanocrystalline/low porosity optically transparent zirconia/alumina. The high optical transparency should result from lack of grain boundary scattering since grains will be smaller than one tenth the wavelength of light and from elimination of porosity. An important technological potential for this process is manufacturing of envelopes for high-pressure sodium vapor lamps. The technique for fabricating monolithic nanocrystalline material does not begin with powder whose particle diameter is <100 nm as is commonly done. Instead it begins with powder whose particle diameter is on the order of 10-100 microns but contains nanocrystalline crystallites <<100 nm. Spherical particles are quenched from a melt and heat treated to achieve the desired microstructure. Under a moderate pressure within a die or a mold at temperatures of 1100C to 1300C densification is by plastic flow of superplastic particles. A nanocrystalline microstructure results, though some features are greater than 100nm. It was found, for instance, that in the fully dense Al2O3-ZrO2 eutectic specimens that a bicontinuous microstructure exists containing <100 nm ZrO2 particles in a matrix of Al2O3 grains extending over 1-2 microns. Crystallization, growth, phase development and creep during hot pressing and forging were studied for several compositions and so provided some details on development of polycrystalline microstructure from heating quenched ceramics.

  9. Low temperature synthesis of nanocrystalline lanthanum monoaluminate powders by chemical coprecipitation

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, C.-L. [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Wang, C.-L. [Department of Materials Science and Engineering, I-Shou University, 1 Section 1, Hsueh-Cheng Road, Ta-Hsu Hsiang, Kaohsiung 840, Taiwan (China); Chen, T.-Y. [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Chen, G.-J. [Department of Materials Science and Engineering, I-Shou University, 1 Section 1, Hsueh-Cheng Road, Ta-Hsu Hsiang, Kaohsiung 840, Taiwan (China); Hung, I-M. [Department of Chemical Engineering and Materials Science, Yuan Ze University, 135 Yuan-Tung Road, Chungli, Taoyuan 320, Taiwan (China); Shih, C.-J. [Faculty of Fragrance and Cosmetics, Kaohsiung Medical University, 100 Shi-Chuan 1st Road, Kaohsiung 807, Taiwan (China)]. E-mail: CJShih@kmu.edu.tw; Fung, K.-Z. [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China)

    2007-08-16

    Nanocrystalline lanthanum monoaluminate (LaAlO{sub 3}) powders were prepared by chemical coprecipitation using 25 vol.% of NH{sub 4}OH, 0.05 M La(NO{sub 3}){sub 3}.6H{sub 2}O and 0.05 M Al(NO{sub 3}){sub 3}.9H{sub 2}O aqueous solutions as the starting materials. Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analyses (TGA/DTA), X-ray diffraction (XRD), Raman spectrometry, specific surface area (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) were utilized to characterize the LaAlO{sub 3} powders prepared by chemical coprecipitation. The crystallization temperature of the LaAlO{sub 3} precursor gels precipitated at pH 9 is estimated as 810 deg. C by TG/DTA. The XRD pattern of the LaAlO{sub 3} precursor gels precipitated at pH 8-12 and calcined at 700 deg. C for 6 h shows a broad arciform continuum exist between 24{sup o} and 32{sup o} and sharp peaks of LaAlO{sub 3} except the precursor gels precipitated at pH 9. For the LaAlO{sub 3} precursor gels precipitated at pH 9 and calcined at 700 deg. C for 6 h, the formation of the perovskite LaAlO{sub 3} phase occurs and the presence of crystalline impurities is not found. The crystallite size of LaAlO{sub 3} slightly increases from 37.8 to 41.5 nm with calcination temperature increasing from 700 to 900 deg. C for 6 h. The LaAlO{sub 3} powders prepared by chemical coprecipitation have a considerably large specific surface of 30 m{sup 2}/g. The relative density greater than 97% is obtained when these nanocrystalline LaAlO{sub 3} powders are sintered at 1550 deg. C for 2 h.

  10. Effect of Sr substitution on the room temperature electrical properties of La1-xSrxFeO3 nano-crystalline materials

    Science.gov (United States)

    Kafa, C. A.; Triyono, D.; Laysandra, H.

    2017-07-01

    LaFeO3 is a material with Perovskite structure which electrical properties got investigated a lot, because as a p-type semiconductor it showed good gas sensing behavior through resistivity comparison. Sr doping on LaFeO3 is able to improve the electrical conductivity through structural modification. Using the Sr atoms doping concentration (x) from 0.1 to 0.4, La1-xSrxFeO3 nanocrystal pellets were synthesized using sol-gel method, followed by gradual heat treatment and uniaxial compaction. Structural analysis from XRD characterization shows that the structure of the materials is Orthorhombic Perovskite. The topography of the sample by SEM reveals grain and grain boundary existence with emerging agglomeration. The electrical properties of the material, as functions of frequency, were measured by Impedance Spectroscopy method using RLC meter. Through the Nyquist plot and Bode plot, the electrical conductivity of La1-xSrxFeO3 is contributed by grain and grain boundaries. It is reported that La0.6Sr0.4FeO3 sample has the most superior electrical conductivity of all samples, and the electrical permittivity of both La0.8Sr0.2FeO3 and La0.7Sr0.3FeO3 are the most stable.

  11. Ferroelectric Polarization in Nanocrystalline Hydroxyapatite Thin Films on Silicon

    Science.gov (United States)

    Lang, S. B.; Tofail, S. A. M.; Kholkin, A. L.; Wojtaś, M.; Gregor, M.; Gandhi, A. A.; Wang, Y.; Bauer, S.; Krause, M.; Plecenik, A.

    2013-01-01

    Hydroxyapatite nanocrystals in natural form are a major component of bone- a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics. PMID:23884324

  12. Raman and Rietveld structural characterization of sintered alkaline earth doped ceria

    Energy Technology Data Exchange (ETDEWEB)

    Siqueira Junior, Jose Marcio; Brum Malta, Luiz Fernando; Garrido, Francisco M.S. [Departamento de Quimica Inorganica, Instituto de Quimica, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 149, Centro de Tecnologia, Bloco A, room 632, CEP 68563, 21941-909 Rio de Janeiro, RJ (Brazil); Ogasawara, Tsuneharu [Programa de Engenharia Metalurgica e de Materiais, Coordenacao dos Programas de Pos - Graduacao de Engenharia, Centro de Tecnologia, Universidade Federal do Rio de Janeiro, Ilha do Fundao, CEP 68505, 21941-972 Rio de Janeiro, RJ (Brazil); Medeiros, Marta Eloisa, E-mail: chico@iq.ufrj.br [Departamento de Quimica Inorganica, Instituto de Quimica, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 149, Centro de Tecnologia, Bloco A, room 632, CEP 68563, 21941-909 Rio de Janeiro, RJ (Brazil)

    2012-08-15

    Nanocrystalline calcium and strontium singly doped ceria and co-doped ceria materials for solid electrolytes were prepared via a hydrothermal route. The effect of the hydrothermal treatment time on the solid solution composition was evaluated. Sr doped ceria was the most difficult to form, due to the Sr{sup 2+} large ionic radius. The small crystal size (12-16 nm) of powders allowed sintering into dense ceramic pellets at 1350 Degree-Sign C for 5 h. Raman spectroscopy evidenced a great lattice distortion for Sr doped and co-doped ceria materials, explaining the deterioration of the electrical properties for these ceramics. Besides that, a second phase was detected for Sr doped ceria pellet by using X-ray powder diffraction and Rietveld refinement of XRD data. Impedance measurements showed that Ca-doped ceria behaves as the best ionic conductor ({sigma}{sub g} 390 Degree-Sign C = 1.0 Multiplication-Sign 10{sup -3} S cm{sup -1}) since the nominal composition was achieved; on the other hand, Sr doped ceria performed as resistive materials since Sr incorporation into ceria lattice was critical. These results enhance the close interlace between electrical performance and chemical composition of alkaline earth doped ceria. -- Highlights: Black-Right-Pointing-Pointer Hydrothermally synthesized calcium doped ceria nanoparticles. Black-Right-Pointing-Pointer Incorporation of alkaline earth dopant into ceria lattice. Black-Right-Pointing-Pointer Raman and Rietveld structural characterization. Black-Right-Pointing-Pointer Calcium doped ceria ceramic pellets with high ionic conductivity. Black-Right-Pointing-Pointer Problems associated with the Sr{sup 2+} incorporation into ceria lattice.

  13. Nanocrystalline SiC and Ti3SiC2 Alloys for Reactor Materials: Diffusion of Fission Product Surrogates

    Energy Technology Data Exchange (ETDEWEB)

    Henager, Charles H. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Jiang, Weilin [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2014-11-01

    MAX phases, such as titanium silicon carbide (Ti3SiC2), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti3SiC2 has been suggested in the literature as a possible fuel cladding material. Prior to the application, it is necessary to investigate diffusivities of fission products in the ternary compound at elevated temperatures. This study attempts to obtain relevant data and make an initial assessment for Ti3SiC2. Ion implantation was used to introduce fission product surrogates (Ag and Cs) and a noble metal (Au) in Ti3SiC2, SiC, and a dual-phase nanocomposite of Ti3SiC2/SiC synthesized at PNNL. Thermal annealing and in-situ Rutherford backscattering spectrometry (RBS) were employed to study the diffusivity of the various implanted species in the materials. In-situ RBS study of Ti3SiC2 implanted with Au ions at various temperatures was also performed. The experimental results indicate that the implanted Ag in SiC is immobile up to the highest temperature (1273 K) applied in this study; in contrast, significant out-diffusion of both Ag and Au in MAX phase Ti3SiC2 occurs during ion implantation at 873 K. Cs in Ti3SiC2 is found to diffuse during post-irradiation annealing at 973 K, and noticeable Cs release from the sample is observed. This study may suggest caution in using Ti3SiC2 as a fuel cladding material for advanced nuclear reactors operating at very high temperatures. Further studies of the related materials are recommended.

  14. Laser sintering of copper nanoparticles

    International Nuclear Information System (INIS)

    Zenou, Michael; Saar, Amir; Ermak, Oleg; Kotler, Zvi

    2014-01-01

    Copper nanoparticle (NP) inks serve as an attractive potential replacement to silver NP inks in functional printing applications. However their tendency to rapidly oxidize has so far limited their wider use. In this work we have studied the conditions for laser sintering of Cu-NP inks in ambient conditions while avoiding oxidation. We have determined the regime for stable, low-resistivity copper (< ×3 bulk resistivity value) generation in terms of laser irradiance and exposure duration and have indicated the limits on fast processing. The role of pre-drying conditions on sintering outcome has also been studied. A method, based on spectral reflectivity measurements, was used for non-contact monitoring of the sintering process evolution. It also indicates preferred spectral regions for sintering. Finally, we illustrated how selective laser sintering can generate high-quality, fine line (<5 µm wide) and dense copper circuits. (paper)

  15. Reinforced plastics and aerogels by nanocrystalline cellulose

    Energy Technology Data Exchange (ETDEWEB)

    Leung, Alfred C. W.; Lam, Edmond; Chong, Jonathan; Hrapovic, Sabahudin; Luong, John H. T., E-mail: john.luong@cnrc-nrc.gc.ca [National Research Council Canada (Canada)

    2013-05-15

    Nanocrystalline cellulose (NCC), a rigid rod-like nanoscale material, can be produced from cellulosic biomass in powder, liquid, or gel forms by acid and chemical hydrolysis. Owing to its unique and exceptional physicochemical properties, the incorporation of a small amount of NCC into plastic enhances the mechanical strength of the latter by several orders of magnitudes. Carbohydrate-based NCC poses no serious environmental concerns, providing further impetus for the development and applications of this green and renewable biomaterial to fabricate lightweight and biodegradable composites and aerogels. Surface functionalization of NCC remains the main focus of NCC research to tailor its properties for dispersion in hydrophilic or hydrophobic media. It is of uttermost importance to develop tools and protocols for imaging of NCC in a complex matrix and quantify its reinforcement effect.

  16. Onset conditions for flash sintering of UO2

    Science.gov (United States)

    Raftery, Alicia M.; Pereira da Silva, João Gustavo; Byler, Darrin D.; Andersson, David A.; Uberuaga, Blas P.; Stanek, Christopher R.; McClellan, Kenneth J.

    2017-09-01

    In this work, flash sintering was demonstrated on stoichiometric and non-stoichiometric uranium dioxide pellets at temperatures ranging from room temperature (26 °C) up to 600 °C . The onset conditions for flash sintering were determined for three stoichiometries (UO2.00, UO2.08, and UO2.16) and analyzed against an established thermal runaway model. The presence of excess oxygen was found to enhance the flash sintering onset behavior of uranium dioxide, lowering the field required to flash and shortening the time required for a flash to occur. The results from this study highlight the effect of stoichiometry on the flash sintering behavior of uranium dioxide and will serve as the foundation for future studies on this material.

  17. Verification of the Skorohod-Olevsky Viscous Sintering (SOVS) Model

    Energy Technology Data Exchange (ETDEWEB)

    Lester, Brian T. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-11-16

    Sintering refers to a manufacturing process through which mechanically pressed bodies of ceramic (and sometimes metal) powders are heated to drive densification thereby removing the inherit porosity of green bodies. As the body densifies through the sintering process, the ensuing material flow leads to macroscopic deformations of the specimen and as such the final configuration differs form the initial. Therefore, as with any manufacturing step, there is substantial interest in understanding and being able to model the sintering process to predict deformation and residual stress. Efforts in this regard have been pursued for face seals, gear wheels, and consumer products like wash-basins. To understand the sintering process, a variety of modeling approaches have been pursued at different scales.

  18. Fabrication of a Ti-Al2O3 functionally graded material by dry-jet spraying of ultrafine particles and subsequent temperature-gradient sintering; Chobiryushi funsha sekisoho oyobi ondo keisha fuka shoketsuho ni yoru Ti-Al2O3 keisha kino zairyo no shisaku

    Energy Technology Data Exchange (ETDEWEB)

    Otsuka, A.; Tanizaki, H.; Iwasaki, K. [Nisshin Steel Co. Ltd., Tokyo (Japan)

    1997-04-15

    Investigations are conducted and efforts are exerted for the prevention of some problems from arising in the process of sintering of films formed by dry jet spraying of ultrafine particles. Such problems involve the exfoliation of films from the substrate, emergence of voids in the functionally graded material (FGM) when the composition of the material is altered, and initiation of cracks. A Ti-Al2O3-base stepped cylinder shape FGM is tentatively fabricated by the lamination-forming ultrafine particle dry-jet spraying method and temperature-gradient sintering method. The occurrence of defects during the sintering process may be avoided by the following steps. Addition of ultrafine hydride particles to the powder which is to be compacted into a base substrate makes the shrinkage rate of this substrate slightly higher than that of the FGM layer, and this prevents cracks due to difference in shrinkage rate. The size of pores in the FGM can be reduced if the high shrinkage rate range r=1 through r=0.5 (r=Ti/(Ti+Al2O3)) is skipped in the laminate deposition process. When the compacting pressure is appropriately chosen after lamination, cracks are prevented from occurring in parts of extraordinary shape of the substrate before it is subjected to sintering. 7 refs., 10 figs.

  19. Low temperature sintering of fluorapatite glass-ceramics.

    Science.gov (United States)

    Denry, Isabelle; Holloway, Julie A

    2014-02-01

    Fluorapatite glass-ceramics have been shown to be excellent candidates as scaffold materials for bone grafts, however, scaffold production by sintering is hindered by concurrent crystallization of the glass. Objective, our goal was to investigate the effect of Ca/Al ratio on the sintering behavior of Nb-doped fluorapatite-based glasses in the SiO2-Al2O3-P2O5-MgO-Na2O-K2O-CaO-CaF2 system. Methods, glass compositions with Ca/Al ratio of 1 (A), 2 (B), 4 (C) and 19 (D) were prepared by twice melting at 1525°C for 3h. Glasses were either cast as cylindrical ingots or ground into powders. Disk-shaped specimens were prepared by either sectioning from the ingots or powder-compacting in a mold, followed by heat treatment at temperatures ranging between 700 and 1050°C for 1h. The density was measured on both sintered specimens and heat treated discs as controls. The degree of sintering was determined from these measurements. Results and Significance XRD showed that fluorapatite crystallized in all glass-ceramics. A high degree of sintering was achieved at 775°C for glass-ceramic D (98.99±0.04%), and 900°C for glass-ceramic C (91.31±0.10). Glass-ceramics A or B were only partially sintered at 1000°C (63.6±0.8% and 74.1±1.5%, respectively). SEM revealed a unique microstructure of micron-sized spherulitic fluorapatite crystals in glass-ceramics C and D. Increasing the Ca/Al ratio promoted low temperature sintering of fluorapatite glass-ceramics, which are traditionally difficult to sinter. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  20. Nanocrystalline silicon in biological studies

    Czech Academy of Sciences Publication Activity Database

    Fučíková, A.; Valenta, J.; Pelant, Ivan; Kůsová, Kateřina; Březina, Vítězslav

    2011-01-01

    Roč. 8, č. 3 (2011), s. 1093-1096 ISSN 1862-6351 R&D Projects: GA AV ČR KAN400100701; GA AV ČR(CZ) IAA101120804; GA MŠk LC510; GA ČR GD202/09/H041 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z60870520 Keywords : nanocrystalline * silicon * biocompatibility * quantum dot * fluorescence label Subject RIV: BM - Solid Matter Physics ; Magnetism

  1. Effect Of Compaction Pressure And Sintering Temperature On The Liquid Phase Sintering Behavior Of Al-Cu-Zn Alloy

    Directory of Open Access Journals (Sweden)

    Lee S.H.

    2015-06-01

    Full Text Available The liquid phase sintering characteristics of Al-Cu-Zn alloy were investigated with respect to various powder metallurgy processing conditions. Powders of each alloying elements were blended to form Al-6Cu-5Zn composition and compacted with pressures of 200, 400, and 600 MPa. The sintering process was performed at various temperatures of 410, 560, and 615°C in N2 gas atmosphere. Density and micro-Vickers hardness measurements were conducted at different processing stages, and transverse rupture strength of sintered materials was examined for each condition, respectively. The microstructure was characterized using optical microscope and scanning electron microscopy. The effect of Zn addition on the liquid phase sintering behavior during P/M process of the Al-Cu-Zn alloy was also discussed in detail.

  2. A study of the structure and crystallisation of nanocrystalline zirconia

    International Nuclear Information System (INIS)

    Tucker, M.

    1999-12-01

    Nanocrystalline zirconia, prepared via, calcination of the hydroxide, has been studied using a variety of experimental techniques. Two chemical routes, a precipitation and a sol-gel route, were used to prepare the hydroxide. Neutron and X-ray diffraction, EXAFS, NMR and SANS have been used to study the structure and crystallisation, during in-situ and ambient condition measurements. The structural information from the diffraction data has been complimented by the other techniques to provide information on the short, medium and longer range structure of nanocrystalline zirconia. Pure and yttrium doped samples were studied, this enabled the affects of doping and preparation routes to be investigated. The amorphous hydroxide was found to have a, monoclinic-like structure for all samples, independent of preparation route or yttrium content. The crystallisation temperature was lowest for the pure precipitation sample and was increased by the addition of yttrium or by preparation via, the sol-gel route. For the precipitation samples, in addition to the crystallisation temperature being raised, doping with yttrium also had an effect on the size of the crystallites obtained at high temperatures. Due to the different incorporation method of the yttrium into the sol-gel samples the effect on crystallite size and crystallisation temperature, as seen for the precipitation samples, were not evident for the sol-gel samples. The neutron and NMR data clearly show hydrogen remains in the samples well after crystallisation has become evident. The structural picture of nanocrystalline zirconia consisting of small crystallites surrounded by material containing, or terminated by, hydroxyl groups, is supported by all the results and methods used in this thesis. The in-situ and ambient conditions data is combined into a coherent growth picture of the nanocrystalline material from the hydroxide until at high enough temperatures the bulk or polycrystalline material is formed. (author)

  3. Experimental and finite element modeling study of co-sintering of multilayer, multifunctional ceramics

    Science.gov (United States)

    Wu, Kuan

    2007-12-01

    The co-sintering behavior of low temperature co-fired ceramics (LTCC) is investigated by combining experiment and simulation methods. The numerical method offers a way to provide quantitative information regarding the final sintered shape of multilayer ceramics, which can be used to optimize the design of multilayer, multifunctional components and help reduce tedious and expensive empirical design iterations. To predict the sintering behavior of LTCC, parameters in the viscoplastic constitutive equations for single materials (such as shear viscosity G, bulk viscosity K, and sintering stress sigma s, etc.) need to be known. An apparatus was constructed for in situ measurements of the longitudinal and radial shrinkage during free sintering and sinter forging experiments. Cylindrical samples of individual LTCC materials (DuPont 951AX, Heraeus CT-800, Ferro A6-S) were made. Free sintering and sinter-forging experiments have been performed at various heating rates and under different intermittently applied axial loads. Various methods for analyzing the data were used to extract those parameters and their dependence on temperature and relative density. The constitutive parameters obtained from experiments were then implemented in the user subroutine UMAT of the general-purpose finite element program ABAQUS to simulate the free sintering behavior of bi-layer structures (DU951/CT800) with different thickness ratios. The simulation results were then compared with the actual experimental results, which were obtained by free co-sintering bi-layer planar samples with different thickness ratios. Simulation results showed the finite element analysis was successful in predicting the shape changes and the stresses at different positions during sintering of bi-layer structures. This finite element model was also used to examine the sensitivity to various parameters of the sintering results, such as elastic Poisson's ratio v, Young's modulus E, sintering stress sigmas, shear and

  4. The sintering of dioxide pellets (UO2) in an oxidizing atmosphere (CO2)

    International Nuclear Information System (INIS)

    Santos, G.R.T.; Riella, H.G.

    1993-06-01

    In this study the process of sintering of U O 2 pellets in oxidative atmosphere has been evaluated. Temperature and time of study have been varied in order to determine the influence of these parameters on final density and microstructure of the material. The NIKUSI process, allows to work in a temperature range below to those that have been employed in the conventional process, lowering in up to 50% the sintering cycle because it is possible to decrease the time of sintering. (author)

  5. Analysis of Laser Sintering Technology

    Directory of Open Access Journals (Sweden)

    Vladislav Markovič

    2014-02-01

    Full Text Available The new, high-tech development and customization is one ofthe most important factors in promoting the country‘s economicgrowth indicators. The economic downturn in the industryrequires technology and equipment using a minimumof raw materials and providing maximum performance. Thisstatement perfectly describes the innovative, forward-looking,cost-effective laser powder sintering (SLS technology. Here,thanks to the latest engineering achievements, product surfacesare modified and improved, they gain new characteristics. SLSis viable in automobile, engineering, construction, aerospace,aircraft, printing, medical and other areas.In order to create a product which meets the standards andtechnical documentation it is necessary to use and ensure highquality of raw materials, high-end equipment, qualified personnel,the working environment with proper climatic conditions, ergonomics,etc. But all of these, the quality of the product becomesthe decisive indicators meaningless if know how to properly selectthe laser processing operation. Scanning speed, beam power,pulse frequency, protective gases, powder layer thickness – allof them are the physical and mechanical characteristics of thechange in a small range changes the quality of the product of thefuture, the field of application and performance characteristics.

  6. Dye-Sensitized Solar Cells Based on High Surface Area Nanocrystalline Zinc Oxide Spheres

    Directory of Open Access Journals (Sweden)

    Pavuluri Srinivasu

    2011-01-01

    Full Text Available High surface area nanocrystalline zinc oxide material is fabricated using mesoporous nanostructured carbon as a sacrificial template through combustion process. The resulting material is characterized by XRD, N2 adsorption, HR-SEM, and HR-TEM. The nitrogen adsorption measurement indicates that the materials possess BET specific surface area ca. 30 m2/g. Electron microscopy images prove that the zinc oxide spheres possess particle size in the range of 0.12 μm–0.17 μm. The nanocrystalline zinc oxide spheres show 1.0% of energy conversion efficiency for dye-sensitized solar cells.

  7. Production of pure sintered alumina

    International Nuclear Information System (INIS)

    Rocha, J.C. da; Huebner, H.W.

    1982-01-01

    With the aim of optimizing the sintering parameters, the strength of a large number of alumina samples was determined which were produced under widely varying sintering conditions and with different amounts of MgO content. The strength as a function of sintering time or temperature was found to go through a maximum. With increasing time, this maximum is shifted to lower temperatures, and with decreasing temperature to longer times. Data pairs of sintering times and temperatures which yeld the strength maximum were determined. The value of the strength at the maximum remains unchanged. The strength is high (= 400 MN/m 2 , at a grain size of 3 um and a porosity of 2 per cent) and comparable to foreign aluminas produced for commercial purposes, or even higher. The increase in the sintering time from 1 h to 16 h permits a reduction of the sintering temperature from 1600 to 1450 0 C without losing strength. The practical importance of this fact for a production of sintered alumina on a large scale is emphasized. (Author) [pt

  8. A fundamental study on measurement of internal residual stress of sintered Fe-Cr/TiN composite material with neutron diffraction

    International Nuclear Information System (INIS)

    Takago, Shigeki; Sasaki, Toshihiko; Hirose, Yukio; Minakawa, Nobuaki; Morii, Yukio

    2001-01-01

    The Neutron diffraction technique was applied for the internal stress measurements of a composite material consisted of chromium alloy and titanium nitride manufactured by the powder metallurgy. The material has been developed for the valve seat insert of diesel engines in automobiles, because material has high wear-resistance and heat-resistance. In this study, the influence of the titanium nitride on the stresses in each phase was investigated. The Fe-Cr 200 diffraction peak occurs at 2θ=93.4 deg. and the TiN 311 diffraction peak at 2θ=109.5 deg are available. Neutron diffraction data obtained from both phases were compared to the Micromechanics model based on Eshelby's approach and the Mori-Tanaka theorem. It was found that experimental phase stress agrees well with the theoretical estimation. It has been shown that neutron diffraction method is suitable to determine the residual stress of composite materials. (author)

  9. Microwave-assisted sintering of non-stoichiometric strontium bismuth niobate ceramic: Structural and dielectric properties

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Rajveer [Department of Physics and Astrophysics, University of Delhi, New Delhi 110007 (India); Department of Physics, Atmaram Sanatan Dharma College, University of Delhi, Dhaula Kuan, New Delhi 110021 (India); Luthra, Vandna [Department of Physics, Gargi College, University of Delhi, Siri Fort Road, New Delhi 110049 (India); Tandon, R.P., E-mail: ram_tandon@hotmail.com [Department of Physics and Astrophysics, University of Delhi, New Delhi 110007 (India)

    2016-11-01

    In recent years the microwave sintering has been utilized for the synthesis of materials in enhancement of the properties. In this paper strontium bismuth niobate (Sr{sub 0.8}Bi{sub 2.2}Nb{sub 2}O{sub 9}:SBN) bulk ceramic has been synthesized by microwave reactive sintering and conventional heating techniques. A relative density of 99.6% has been achieved for microwave sintered SBN, which is higher than that of (98.81%) conventionally sintered SBN. The phase formation of SBN synthesized by both processes has been confirmed by X-ray diffraction (XRD). The surface morphology of SBN was observed by scanning electron microscopy (SEM). The microstructure was found to be more uniform in case of SBN sintered by microwave sintering. The dielectric properties of SBN were studied as a function of frequency in the temperature range of 30–500 °C. Both the samples synthesized by two different processes were found to follow Curie–Weiss law above the transition temperature. The Curie temperature was found to be higher for microwave sintered SBN. The dielectric constant and the transition temperature were observed to be higher for SBN ceramic synthesized by microwave sintering technique. The ac and dc activation energy values were also found to be higher for microwave sintered SBN as compared to conventional sintering technique.

  10. Bending Behavior of Porous Sintered Stainless Steel Fiber Honeycombs

    Science.gov (United States)

    Zou, Shuiping; Wan, Zhenping; Lu, Longsheng; Tang, Yong

    2017-02-01

    A novel porous honeycomb-type substrate has been developed using solid-state sintering stainless steel fibers. The porous sintered stainless steel fiber honeycombs (PSSSFH) are composed of a skeleton of sintered stainless steel fibers, three-dimensionally interconnected porous structures and multiple parallel microchannels. The bending behavior of the PSSSFH is investigated using three-point bending tests. Four stages, including an elastic stage, a yielding stage with a plateau, a hardening stage and a failure stage, are observed during the bending process of the PSSSFH. In the initial yielding stage, the bending forces increase slowly with displacement increasing, and then a yielding plateau follows, which is unique compared with other porous materials. Moreover, the structure parameters of the PSSSFH are varied to investigate the influence on the bending strength. It is determined that the multiple parallel microchannels can enhance the bending strength of porous stainless steel fiber sintered substrates (PSSFSS) and do not influence the variation trend of bending strength of PSSFSS with porosity increasing. The open ratio is conducive to increasing the bending strength, and the microchannel diameters ranging from 0.5 mm to 1.5 mm have little influence on the bending strength. In addition, both the increasing of sintering temperature and sintering time can strengthen the PSSSFH.

  11. Manufacture of sintered bricks of high density from beryllium oxide

    International Nuclear Information System (INIS)

    Pointud, R.; Rispal, Ch.; Le Garec, M.

    1959-01-01

    Beryllium oxide bricks of nuclear purity 100 x 100 x 50 and 100 x 100 x 100 mm of very high density (between 2.85 and 3.00) are manufactured by sintering under pressure in graphite moulds at temperatures between 1,750 and 1,850 deg. C, and under a pressure of 150 kg/cm 2 . The physico-chemical state of the saw material is of considerable importance with regard to the success of the sintering operation. In addition, a study of the sintering of a BeO mixture with 3 to 5 per cent of boron introduced in the form of boric acid, boron carbide or elementary boron shows that high densities can only be obtained by sintering under pressure. For technical reasons of manufacture, only the mixture based on boron carbide is used. The sintering is carried out in graphite moulds at 1500 deg. C under 150 kg/cm 2 pressure, and bricks can be obtained with density between 2,85 and 2,90. Laboratory studies and the industrial manufacture of various sinters are described in detail. (author) [fr

  12. Low temperature sintering of fluorapatite glass-ceramics

    Science.gov (United States)

    Denry, Isabelle; Holloway, Julie A.

    2014-01-01

    Fluorapatite glass-ceramics have been shown to be excellent candidates as scaffold materials for bone grafts, however, scaffold production by sintering is hindered by concurrent crystallization of the glass. Our goal was to investigate the effect of Ca/Al ratio on the sintering behavior of Nb-doped fluorapatite-based glasses in the SiO2-Al2O3-P2O5-MgO-Na2O-K2O-CaO-CaF2 system. Glass compositions with Ca/Al ratio of 1 (A), 2 (B), 4 (C) and 19 (D) were prepared by twice melting at 1525°C for 3h. Glasses were either cast as cylindrical ingots or ground into powders. Disc-shaped specimens were prepared by either sectioning from the ingots or powder-compacting in a mold, followed by heat treatment at temperatures ranging between 700 and 1050°C for 1h. The density was measured on both sintered specimens and heat treated discs as controls. The degree of sintering was determined from these measurements. XRD showed that fluorapatite crystallized in all glass-ceramics. A high degree of sintering was achieved at 775°C for glass-ceramic D (98.99±0.04%), and 900°C for glass-ceramic C (91.31±0.10). Glass-ceramics A or B were only partially sintered at 1000°C (63.6±0.8% and 74.1±1.5%, respectively). SEM revealed a unique microstructure of micron-sized spherulitic fluorapatite crystals in glass-ceramics C and D. Increasing the Ca/Al ratio promoted low temperature sintering of fluorapatite glass-ceramics, which are traditionally difficult to sinter. PMID:24252652

  13. Properties of Bulk Sintered Silver As a Function of Porosity

    Energy Technology Data Exchange (ETDEWEB)

    Wereszczak, Andrew A [ORNL; Vuono, Daniel J [ORNL; Wang, Hsin [ORNL; Ferber, Mattison K [ORNL; Liang, Zhenxian [ORNL

    2012-06-01

    This report summarizes a study where various properties of bulk-sintered silver were investigated over a range of porosity. This work was conducted within the National Transportation Research Center's Power Device Packaging project that is part of the DOE Vehicle Technologies Advanced Power Electronics and Electric Motors Program. Sintered silver, as an interconnect material in power electronics, inherently has porosity in its produced structure because of the way it is made. Therefore, interest existed in this study to examine if that porosity affected electrical properties, thermal properties, and mechanical properties because any dependencies could affect the intended function (e.g., thermal transfer, mechanical stress relief, etc.) or reliability of that interconnect layer and alter how its performance is modeled. Disks of bulk-sintered silver were fabricated using different starting silver pastes and different sintering conditions to promote different amounts of porosity. Test coupons were harvested out of the disks to measure electrical resistivity and electrical conductivity, thermal conductivity, coefficient of thermal expansion, elastic modulus, Poisson's ratio, and yield stress. The authors fully recognize that the microstructure of processed bulk silver coupons may indeed not be identical to the microstructure produced in thin (20-50 microns) layers of sintered silver. However, measuring these same properties with such a thin actual structure is very difficult, requires very specialized specimen preparation and unique testing instrumentation, is expensive, and has experimental shortfalls of its own, so the authors concluded that the herein measured responses using processed bulk sintered silver coupons would be sufficient to determine acceptable values of those properties. Almost all the investigated properties of bulk sintered silver changed with porosity content within a range of 3-38% porosity. Electrical resistivity, electrical conductivity

  14. Sintering, camber development of layer composites and a new ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 37; Issue 1. Sintering ... To eliminate or decrease the camber, a new method semi-fixed uniaxial pressure technique (SUP) was proposed. ... Department of Materials Science and Engineering, Xi'an University of Science and Technology, Xi'an 710054, P. R. China ...

  15. Sintering of titanium alloy by powder metallurgy

    Energy Technology Data Exchange (ETDEWEB)

    Cosme, C.R.M. [Universidade de Brasilia (UnB), DF (Brazil); Henriques, V.A.R.; Cairo, C.A.A.; Taddei, E.B. [Centro Tecnico Aeroespacial (CTA), Sao Jose dos Campos, SP (Brazil)

    2009-07-01

    Full text: Titanium alloys are suitable for biomaterial applications, considering its biocompatibility and low elastic modulus compared to steel. Bone resorption in this case can be reduced by load sharing between the implant and natural bone.Starting powders were obtained by hydride method, carried out under positive hydrogen pressure at 500 deg C for titanium and 800 deg C for Nb, Zr and Ta powders. After reaching the nominal temperature, the material was held for 3h, with subsequent cooling to room temperature and milling of the friable hydride. Samples were produce by mixing of initial metallic powders followed by and cold isostatic pressing. Subsequent densification by sintering was performed at temperature range between 900 and 1700 deg C. Characterization was carried out with scanning electron microscopy, X-ray diffractometry and microhardness measurements. Microstructural examinations revealed higher amount of &⧣946;-phase for higher sintering temperature and dissolution of Ta and NB particles. In vitro tests revealed low cytotoxicity of sintered samples. (author)

  16. Low sintering temperature glass waste forms for sequestering radioactive iodine

    Science.gov (United States)

    Nenoff, Tina M.; Krumhansl, James L.; Garino, Terry J.; Ockwig, Nathan W.

    2012-09-11

    Materials and methods of making low-sintering-temperature glass waste forms that sequester radioactive iodine in a strong and durable structure. First, the iodine is captured by an adsorbant, which forms an iodine-loaded material, e.g., AgI, AgI-zeolite, AgI-mordenite, Ag-silica aerogel, ZnI.sub.2, CuI, or Bi.sub.5O.sub.7I. Next, particles of the iodine-loaded material are mixed with powdered frits of low-sintering-temperature glasses (comprising various oxides of Si, B, Bi, Pb, and Zn), and then sintered at a relatively low temperature, ranging from 425.degree. C. to 550.degree. C. The sintering converts the mixed powders into a solid block of a glassy waste form, having low iodine leaching rates. The vitrified glassy waste form can contain as much as 60 wt % AgI. A preferred glass, having a sintering temperature of 500.degree. C. (below the silver iodide sublimation temperature of 500.degree. C.) was identified that contains oxides of boron, bismuth, and zinc, while containing essentially no lead or silicon.

  17. The sintering of nitrogen ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Hampshire, S.

    1986-01-01

    The mechanism of densification with oxide additives and the role of the ..cap alpha..-BETA phase transformation is investigated in a detailed kinetic study. Selected compositions in the Si-Al-O-N system are detailed, with and without additives. Although the work is mainly concerned with the identification of the mechanisms of sintering, some property measurements on a sintered BETA-sialon are reported and the feasibility of preparing pure ..cap alpha..-sialon phases is explored.

  18. Pressure sintering and creep deformation: a joint modeling approach

    International Nuclear Information System (INIS)

    Notis, M.R.

    1979-10-01

    Work related to microchemical and microstructural aspects of the joint modeling of pressure sintering and creep in ceramic oxides is reported. Quantitative techniques for the microchemical analysis of ceramic oxides and for the examination of impurity segregation effects in polycrystalline ceramic materials were developed. This has included fundamental absorption corrections for the oxygen anion species as a function of foil thickness. The evolution in microstructure during the transition from intermediate stage to final stage densification during hot pressing of cobalt oxide and preliminary studies with doped oxides were studied. This work shows promise in using time-integrated microstructural effects to elucidate the role of impurities in the sintering of ceramic materials

  19. Pressure sintering and creep deformation: a joint modeling approach

    Energy Technology Data Exchange (ETDEWEB)

    Notis, M.R.

    1979-10-01

    Work related to microchemical and microstructural aspects of the joint modeling of pressure sintering and creep in ceramic oxides is reported. Quantitative techniques for the microchemical analysis of ceramic oxides and for the examination of impurity segregation effects in polycrystalline ceramic materials were developed. This has included fundamental absorption corrections for the oxygen anion species as a function of foil thickness. The evolution in microstructure during the transition from intermediate stage to final stage densification during hot pressing of cobalt oxide and preliminary studies with doped oxides were studied. This work shows promise in using time-integrated microstructural effects to elucidate the role of impurities in the sintering of ceramic materials.

  20. Method and apparatus for radio frequency ceramic sintering

    Science.gov (United States)

    Hoffman, Daniel J.; Kimrey, Jr., Harold D.

    1993-01-01

    Radio frequency energy is used to sinter ceramic materials. A coaxial waveguide resonator produces a TEM mode wave which generates a high field capacitive region in which a sample of the ceramic material is located. Frequency of the power source is kept in the range of radio frequency, and preferably between 60-80 MHz. An alternative embodiment provides a tunable radio frequency circuit which includes a series input capacitor and a parallel capacitor, with the sintered ceramic connected by an inductive lead. This arrangement permits matching of impedance over a wide range of dielectric constants, ceramic volumes, and loss tangents.

  1. Sintering of MSW fly ash for reuse as a concrete aggregate.

    Science.gov (United States)

    Mangialardi, T

    2001-10-12

    The sintering process of municipal solid waste (MSW) fly ash was investigated in order to manufacture sintered products for reuse as concrete aggregates. Four types of fly ash resulting from different Italian MSW incineration plants were tested in this study. A modification of the chemical composition of MSW fly ash--through a preliminary four-stage washing treatment of this material with water--was attempted to improve the chemical and mechanical characteristics of sintered products.The sintering treatment of untreated or washed fly ash was performed on cylindrical compact specimens (15 mm in diameter and 20mm in height) at different compact pressures, sintering temperatures and times.The sintering process of untreated MSW fly ashes proved to be ineffective for manufacturing sintered products for reuse as a construction material, because of the adverse chemical characteristics of these fly ashes in terms of sulfate, chloride, and vitrifying oxide contents.A preliminary washing treatment of MSW fly ash with water greatly improved the chemical and mechanical characteristics of sintered products and, for all the types of fly ash tested, the sintered products satisfied the Italian requirements for normal weight aggregates for use in concretes having a specified strength not greater than 12 and 15N/mm(2), when measured on cylindrical and cubic specimens, respectively.A compact pressure of 28 N/mm(2), a sintering temperature of 1140 degrees C, and a sintering time of 60 min were the best operating conditions for manufacturing sintered products of washed MSW fly ash.

  2. Fracture toughness of yttria-stabilized zirconia sintered in conventional and microwave ovens.

    Science.gov (United States)

    Marinis, Aristotelis; Aquilino, Steven A; Lund, Peter S; Gratton, David G; Stanford, Clark M; Diaz-Arnold, Ana M; Qian, Fang

    2013-03-01

    The fabrication of zirconium dioxide (ZrO2) dental prosthetic substructures requires an extended sintering process (8 to 10 hours) in a conventional oven. Microwave sintering is a shorter process (2 hours) than conventional sintering. The purpose of this study was to compare the fracture toughness of 3 mol % Y2O3-stabilized ZrO2 sintered in a conventional or microwave oven. Partially sintered ZrO2 specimens from 3 manufacturers, KaVo, Lava 3M, and Crystal HS were milled (KaVo Everest engine) and randomly divided into 2 groups: conventional sintering and microwave sintering (n=16 per group). The specimens were sintered according to the manufacturers' recommendations and stored in artificial saliva for 10 days. Fracture toughness was determined by using a 4-point bend test, and load to fracture was recorded. Mean fracture toughness for each material was calculated. A 2-way ANOVA followed by the Tukey HDS post hoc test was used to assess the significance of sintering and material effects on fracture toughness, including an interaction between the 2 factors (α=.05). The 2-way ANOVA suggested a significant main effect for ZrO2 manufacturer (P.05). The main effect of the sintering process (Conventional [5.30 MPa·m(1/2) ±1.00] or Microwave [5.36 MPa·m(1/2) ±0.92]) was not significant (P=.76), and there was no interaction between sintering and ZrO2 manufacturer (P=.91). Based on the results of this study, no statistically significant difference was observed in the fracture toughness of ZrO2 sintered in microwave or conventional ovens. Copyright © 2013 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

  3. Solid freeform fabrication of biological materials

    Science.gov (United States)

    Wang, Jiwen

    functionally graded materials. The volume and composition of the suspensions printed in droplets at a small area are controlled by the inkjet Cyan-Magenta-Yellow-Black color printing principle. The potential of this newly-developed method for fabricating FGMs with arbitrarily designed three-dimensional composition profiles is demonstrated. Sintering investigation focuses on dental porcelain and hydroxyapatite (HA) bodies. Proper sintering conditions have been established for dental porcelain bodies to maintain dimensional accuracy and to prevent slumping. For sintering of HA bodies, a novel approach for sintering of HA bodies at temperatures as low as 900°C has been developed. Low temperature sintering of HA bodies is critical for the success of fabricating functionally graded HA/Ti-6Al-4V materials for orthopedic implant applications because co-sintering of HA and Ti-4Al-4V at temperatures above 950°C can result in the formation of soluble tricalcium phosphate and severe oxidation of Ti-6Al4V. The low temperature sintering of nanocrystalline HA developed in this study, based on the morphology driven anisotropic crystal coarsening mechanism, opens up the opportunity to fabricate functionally graded HA/Ti-6Al-4V materials with no decomposition of HA and oxidation of Ti-6Al-4V and to improve the quality of HA coatings on Ti alloys.

  4. The Influence of Sintering Temperature toward Density and Strength of Plastic-Ruber Composite

    Directory of Open Access Journals (Sweden)

    Heru Sukanto

    2012-11-01

    Full Text Available The research investigates the effect of sintering temperature on density and mechanical properties of HDPE-rubbercomposite which was produced by pressured sintering methodThe materials that were used are HDPE plastic waste of oilbottle and unused tire. These materials were powdered via mechanical grinding manually. The powder size of -20 mesh wasselected as a raw material for specimen. Producing the specimens involved powder technology. Pressured sintering processwas commited for 5 minutes under pressure load of 1 MPa. The sintering temperature was variated along 110 to 140oC byincreasing 10oC incrementally. Specimen testing involved density, bending strength and izot impact strength. All of testingwas conducted on ASTM standard testing.The result reveals that increasing sintering temperature will grow up the density,bending strength and impact strength of specimen up to 10%, 12% and 72% respectively. The extreme increasing ofspecimen properties occurs at the temperature range of 120 to 130oC..

  5. Uncertainty propagation in a multiscale model of nanocrystalline plasticity

    International Nuclear Information System (INIS)

    Koslowski, M.; Strachan, Alejandro

    2011-01-01

    We characterize how uncertainties propagate across spatial and temporal scales in a physics-based model of nanocrystalline plasticity of fcc metals. Our model combines molecular dynamics (MD) simulations to characterize atomic-level processes that govern dislocation-based-plastic deformation with a phase field approach to dislocation dynamics (PFDD) that describes how an ensemble of dislocations evolve and interact to determine the mechanical response of the material. We apply this approach to a nanocrystalline Ni specimen of interest in micro-electromechanical (MEMS) switches. Our approach enables us to quantify how internal stresses that result from the fabrication process affect the properties of dislocations (using MD) and how these properties, in turn, affect the yield stress of the metallic membrane (using the PFMM model). Our predictions show that, for a nanocrystalline sample with small grain size (4 nm), a variation in residual stress of 20 MPa (typical in today's microfabrication techniques) would result in a variation on the critical resolved shear yield stress of approximately 15 MPa, a very small fraction of the nominal value of approximately 9 GPa. - Highlights: → Quantify how fabrication uncertainties affect yield stress in a microswitch component. → Propagate uncertainties in a multiscale model of single crystal plasticity. → Molecular dynamics quantifies how fabrication variations affect dislocations. → Dislocation dynamics relate variations in dislocation properties to yield stress.

  6. Dynamic recovery in nanocrystalline Ni

    International Nuclear Information System (INIS)

    Sun, Z.; Van Petegem, S.; Cervellino, A.; Durst, K.; Blum, W.; Van Swygenhoven, H.

    2015-01-01

    The constant flow stress reached during uniaxial deformation of electrodeposited nanocrystalline Ni reflects a quasi-stationary balance between dislocation slip and grain boundary (GB) accommodation mechanisms. Stress reduction tests allow to suppress dislocation slip and bring recovery mechanisms into the foreground. When combined with in situ X-ray diffraction it can be shown that grain boundary recovery mechanisms play an important role in producing plastic strain while hardening the microstructure. This result has a significant consequence for the parameters of thermally activated glide of dislocations, such as athermal stress and activation volume, which are traditionally derived from stress/strain rate change tests

  7. Effect of surface roughness on grain growth and sintering of alumina

    Indian Academy of Sciences (India)

    Administrator

    quality of the final product. Ceramic material shrinks linearly around 20% during sintering. In general, sintered ceramic product having accurate ..... Marshall D B, Evans A G, Yakub B T K, Tien J W and Kino G. S 1983 Proc. R. Soc. London A385 461. Mendelson M I 1969 J. Am. Ceram. Soc. 52 443. Narayan P and Hancock ...

  8. Sputtered tungsten-based ternary and quaternary layers for nanocrystalline diamond deposition.

    Science.gov (United States)

    Walock, Michael J; Rahil, Issam; Zou, Yujiao; Imhoff, Luc; Catledge, Shane A; Nouveau, Corinne; Stanishevsky, Andrei V

    2012-06-01

    Many of today's demanding applications require thin-film coatings with high hardness, toughness, and thermal stability. In many cases, coating thickness in the range 2-20 microm and low surface roughness are required. Diamond films meet many of the stated requirements, but their crystalline nature leads to a high surface roughness. Nanocrystalline diamond offers a smoother surface, but significant surface modification of the substrate is necessary for successful nanocrystalline diamond deposition and adhesion. A hybrid hard and tough material may be required for either the desired applications, or as a basis for nanocrystalline diamond film growth. One possibility is a composite system based on carbides or nitrides. Many binary carbides and nitrides offer one or more mentioned properties. By combining these binary compounds in a ternary or quaternary nanocrystalline system, we can tailor the material for a desired combination of properties. Here, we describe the results on the structural and mechanical properties of the coating systems composed of tungsten-chromium-carbide and/or nitride. These WC-Cr-(N) coatings are deposited using magnetron sputtering. The growth of adherent nanocrystalline diamond films by microwave plasma chemical vapor deposition has been demonstrated on these coatings. The WC-Cr-(N) and WC-Cr-(N)-NCD coatings are characterized with atomic force microscopy and SEM, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and nanoindentation.

  9. Reactive Sintering of Bimodal WC-Co Hardmetals

    Directory of Open Access Journals (Sweden)

    Marek Tarraste

    2015-09-01

    Full Text Available Bimodal WC-Co hardmetals were produced using novel technology - reactive sintering. Milled and activated tungsten and graphite powders were mixed with commercial coarse grained WC-Co powder and then sintered. The microstructure of produced materials was free of defects and consisted of evenly distributed coarse and fine tungsten carbide grains in cobalt binder. The microstructure, hardness and fracture toughness of reactive sintered bimodal WC-Co hardmetals is exhibited. Developed bimodal hardmetal has perspective for demanding wear applications for its increased combined hardness and toughness. Compared to coarse material there is only slight decrease in fracture toughness (K1c is 14.7 for coarse grained and 14.4 for bimodal, hardness is increased from 1290 to 1350 HV units.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7511

  10. In-situ TEM observation of the response of ultrafine- and nanocrystalline-grained tungsten to extreme irradiation environments.

    Science.gov (United States)

    El-Atwani, O; Hinks, J A; Greaves, G; Gonderman, S; Qiu, T; Efe, M; Allain, J P

    2014-05-06

    The accumulation of defects, and in particular He bubbles, can have significant implications for the performance of materials exposed to the plasma in magnetic-confinement nuclear fusion reactors. Some of the most promising candidates for deployment into such environments are nanocrystalline materials as the engineering of grain boundary density offers the possibility of tailoring their radiation resistance properties. In order to investigate the microstructural evolution of ultrafine- and nanocrystalline-grained tungsten under conditions similar to those in a reactor, a transmission electron microscopy study with in situ 2 keV He(+) ion irradiation at 950 °C has been completed. A dynamic and complex evolution in the microstructure was observed including the formation of defect clusters, dislocations and bubbles. Nanocrystalline grains with dimensions less than around 60 nm demonstrated lower bubble density and greater bubble size than larger nanocrystalline (60-100 nm) and ultrafine (100-500 nm) grains. In grains over 100 nm, uniform distributions of bubbles and defects were formed. At higher fluences, large faceted bubbles were observed on the grain boundaries, especially on those of nanocrystalline grains, indicating the important role grain boundaries can play in trapping He and thus in giving rise to the enhanced radiation tolerance of nanocrystalline materials.

  11. Effect of compacting pressure, powder degassing and thermobaric treatment on densification and properties of nanocrystalline titanium nitride

    Directory of Open Access Journals (Sweden)

    Andrei V. Kapylou

    2009-09-01

    Full Text Available The effects of compacting pressure, powder degassing and high pressure sintering temperature and time on the densification and properties of nanocrystalline titanium nitride have been investigated. For this reason, TiN powder with a mean particle size of 55 nm was pressed in the range of compacting pressure from 0.2 to 1.0 GPa and sintered under static pressure of 3.5 GPa in the temperature range of 900–1600°C for 45–120 s. Some of green bodies were degassed in vacuum before sintering. It was shown that samples compacted in the pressure range of 0.2–0.6 GPa have the highest density after the thermobaric treatment. The maximum density (about 97.3 %TD was obtained with degassed samples. Microhardness and microstructure investigations have shown that recrystallization of the TiN nanopowder begins at the sintering temperatures of 1100–1200°C and sintering time less than one minute. The maximum microhardness obtained was 23.2±1.0 GPa and themaximum Young modulus was 370 GPa.

  12. Selective laser sintering in biomedical engineering.

    Science.gov (United States)

    Mazzoli, Alida

    2013-03-01

    Selective laser sintering (SLS) is a solid freeform fabrication technique, developed by Carl Deckard for his master's thesis at the University of Texas, patented in 1989. SLS manufacturing is a technique that produces physical models through a selective solidification of a variety of fine powders. SLS technology is getting a great amount of attention in the clinical field. In this paper the characteristics features of SLS and the materials that have been developed for are reviewed together with a discussion on the principles of the above-mentioned manufacturing technique. The applications of SLS in tissue engineering, and at-large in the biomedical field, are reviewed and discussed.

  13. Effect of Co-Zr doping on structural and magnetic properties of nanocrystalline strontium hexaferrite SrCoxZrxFe(12-2x): a neutron diffraction study

    International Nuclear Information System (INIS)

    Meena, Sher Singh; Jain, Anil; Yusuf, S.M.; Kaur, Prabhjyot; Chawla, S.K.

    2016-01-01

    Extensive research is being carried out on strontium hexaferrites (SHF) to optimize its structural and macroscopic magnetic properties for its use in microwave devices, recording media with high density magnetic recording, multiferroic, bioceramics and nanoscience and technology. The current focus is to synthesize ferrites with well controlled shape and size, fine morphology, uniform composition and desired magnetic properties at lower sintering temperatures for their use in electronic material industry. Tailoring of magnetic properties has been realized by the substitution of one or more cations at Fe or Sr sites. Citrate precursor solgel technique is simple and ensures a lower sintering temperature because the decomposition of precursor is extremely exothermic. We employed this route to accomplish the synthesis of Co-Zr doped nanocrystalline M-type hexaferrites SrCo x Zr x Fe (12-2x )O 19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) with a purpose to investigate the structural properties and dependence of magnetic properties on the occupancy of five cystallographic positions by dopant ions. Correlation between the distribution of dopant cations over five crystallographic positions and magnetic properties of strontium hexaferrites are probed by Neutron diffraction and Mössbauer spectroscopy studies. Neutron powder diffraction experiments at room temperature were carried out using neutron powder diffractometer-1 at Dhurva reactor, Trombay, India. Rietveld refinements of room temperature neutron diffraction patterns confirm the formation of pure single phase hexagonal ferrites at 800°C. Upon Co-Zr doping both the lattice constants a and c are increased. Room temperature Mössbauer spectra show five sextets (Zeeman splitting patterns) belongs to five Fe sites. Hyperfine filed of all five sextets are decreased with doping at Fe site. Neutron diffraction results are also supported by the Mössbauer data. (author)

  14. Two steps sintering alumina doped with niobia; Sinterizacao em duas etapas de alumina aditivada com niobia

    Energy Technology Data Exchange (ETDEWEB)

    Gomes, L.B.; Hatzfeld, J.; Heck, M.; Pokorny, A.; Bergmann, C.P., E-mail: lucas.gomes@ufrgs.br [Universidade Federal do Rio Grande do Sul (LACER/UFRGS) Porto Alegre, RS (Brazil). Laboratorio de Materiais Ceramicos

    2014-07-01

    In this work, high surface area commercial alumina was doped with niobia and sintered in two steps in order to obtain dense materials with lower processing temperatures. The powders were milled and uniaxially pressed (200 MPa). The first step of sintering took place at 1100°C for 3, 6, 9 and 12 hours, followed by the second step at 1350°C for 3 hours. The relative density, porosity and water absorption of the samples were determined by the Archimedes method. The crystalline phases were analyzed by X-ray Diffraction (XRD) and the morphology of the samples after sintering, evaluated by Scanning Electron Microscopy (SEM). The results indicate that the use of niobia combined with the two steps sintering promotes an increase in the density of the material, even at lower sintering temperatures. (author)

  15. Report on in-situ studies of flash sintering of uranium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Raftery, Alicia Marie [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-01-24

    Flash sintering is a novel type of field assisted sintering that uses an electric field and current to provide densification of materials on very short time scales. The potential for field assisted sintering techniques to be used in producing nuclear fuel is gaining recognition due to the potential economic benefits and improvements in material properties. The flash sintering behavior has so far been linked to applied and material parameters, but the underlying mechanisms active during flash sintering have yet to be identified. This report summarizes the efforts to investigate flash sintering of uranium dioxide using dilatometer studies at Los Alamos National Laboratory and two separate sets of in-situ studies at Brookhaven National Laboratory’s NSLS-II XPD-1 beamline. The purpose of the dilatometer studies was to understand individual parameter (applied and material) effects on the flash behavior and the purpose of the in-situ studies was to better understand the mechanisms active during flash sintering. As far as applied parameters, it was found that stoichiometry, or oxygen-to-metal ratio, has a significant effect on the flash behavior (time to flash and speed of flash). Composite systems were found to have degraded sintering behavior relative to pure UO2. The critical field studies are complete for UO2.00 and will be analyzed against an existing model for comparison. The in-situ studies showed that the strength of the field and current are directly related to the sample temperature, with temperature-driven phase changes occurring at high values. The existence of an ‘incubation time’ has been questioned, due to a continuous change in lattice parameter values from the moment that the field is applied. Some results from the in-situ experiments, which should provide evidence regarding ion migration, are still being analyzed. Some preliminary conclusions can be made from these results with regard to using field assisted sintering to

  16. Mineral Phases and Release Behaviors of As in the Process of Sintering Residues Containing As at High Temperature

    Directory of Open Access Journals (Sweden)

    Xingrun Wang

    2014-01-01

    Full Text Available To investigate the effect of sintering temperature and sintering time on arsenic volatility and arsenic leaching in the sinter, we carried out experimental works and studied the structural changes of mineral phases and microstructure observation of the sinter at different sintering temperatures. Raw materials were shaped under the pressure of 10 MPa and sintered at 1000~1350°C for 45 min with air flow rate of 2000 mL/min. The results showed that different sintering temperatures and different sintering times had little impact on the volatilization of arsenic, and the arsenic fixed rate remained above 90%; however, both factors greatly influenced the leaching concentration of arsenic. Considering the product’s environmental safety, the best sintering temperature was 1200°C and the best sintering time was 45 min. When sintering temperature was lower than 1000°C, FeAsS was oxidized into calcium, aluminum, and iron arsenide, mainly Ca3(AsO42 and AlAsO4, and the arsenic leaching was high. When it increased to 1200°C, arsenic was surrounded by a glass matrix and became chemically bonded inside the matrix, which lead to significantly lower arsenic leaching.

  17. Sintering diagrams of UO2

    International Nuclear Information System (INIS)

    Mohan, A.; Soni, N.C.; Moorthy, V.K.

    1979-01-01

    Ashby's method (see Acta Met., vol. 22, p. 275, 1974) of constructing sintering diagrams has been modified to obtain contribution diagrams directly from the computer. The interplay of sintering variables and mechanisms are studied and the factors that affect the participation of mechanisms in UO 2 are determined. By studying the physical properties, it emerges that the order of inaccuracies is small in most cases and do not affect the diagrams. On the other hand, even a 10% error in activation energies, which is quite plausible, would make a significant difference to the diagram. The main criticism of Ashby's approach is that the numerous properties and equations used, communicate their inaccuracies to the diagrams and make them unreliable. The present study has considerably reduced the number of factors that need to be refined to make the sintering diagrams more meaningful. (Auth.)

  18. Synthesis and Processing of Nanocrystalline Aluminum Nitride

    OpenAIRE

    Duarte, Matthew Albert

    2016-01-01

    Synthesis, processing and characterization of nanocrystalline aluminum nitride has been systematically studied. Non-carbon based gas nitridation was used to reduce nanocrystalline γ-alumina, having a grain size of ~80 nm. Single phase aluminum nitride powder was obtained at firing temperatures of 1200°C. Further processing of AlN powders was performed by CAPAD (Current Activated Pressure Assisted Densification) to obtain dense single phase aluminum nitride. Dense bulk aluminum nitride was ob...

  19. Effect of sintering temperature and time on the mechanical ...

    Indian Academy of Sciences (India)

    Administrator

    partial sintering of the alloy particles on the cell walls. Pore size and pore interconnectivity are critical factors in porous material for tissue engineering. Micropores are scale to provide pathways for body fluid and nutrient transpor- tation, needed for bone regeneration and growth.25 In addition, these kinds of pores provide ...

  20. Diffusion of silver during sintering in high permittivity COG dielectrics

    NARCIS (Netherlands)

    Mikkenie, R.; Groen, W.A.; Drift, R. van der

    2010-01-01

    To achieve cost reduction in multi-layer ceramic capacitors and actuators, which use a silver-palladium alloy as internal electrode, the trend is to use alloys with the highest silver content possible. This requires ceramic materials which must be sintered at a relative low temperature. Goal is to

  1. Synthesis and electrical field-assisted sintering behaviour of yttria ...

    Indian Academy of Sciences (India)

    Synthesis and electrical field-assisted sintering behaviour of yttria-stabilized tetragonal ZrO2 nanopowders by polyacrylamide gel method. XINGHUA SU. ∗. , BENPAN WANG, JIE ZHOU and HAOYU SUN. School of Materials Science and Engineering, Chang'an University, Xi'an 710061, China. MS received 5 May 2015; ...

  2. Joining of β-SiC by spark plasma sintering

    Czech Academy of Sciences Publication Activity Database

    Grasso, S.; Tatarko, Peter; Rizzo, S.; Porwal, H.; Hu, Ch.; Katoh, Y.; Salvo, M.; Reece, M. J.; Ferraris, M.

    2014-01-01

    Roč. 34, č. 7 (2014), s. 1681-1686 ISSN 0955-2219 EU Projects: European Commission(XE) 264526 - GLACERCO Institutional support: RVO:68081723 Keywords : β-SiC * joining * Spark plasma sintering Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass Impact factor: 2.947, year: 2014

  3. Micromechanical modelling of nanocrystalline and ultrafine grained metals: A short overview

    DEFF Research Database (Denmark)

    Mishnaevsky, Leon; Levashov, Evgeny

    2015-01-01

    and nanoscale properties are discussed and compared. The examples of incorporation of peculiar nanocrystalline effects (like large content of amorphous or semi-amorphous grain boundary phase, partial dislocation GB emission/glide/GB absorption based deformation mechanism, diffusion deformation, etc.......) into the continuum mechanical approach are given. The possibilities of using micromechanical models to explore the ways of the improving the properties of nanocrystalline materials by modifying their structures (e.g., dispersion strengthening, creating non-equilibrium grain boundaries, varying the grain size...

  4. Magnetic properties of sintered high energy sm-co and nd-fe-b magnets

    Directory of Open Access Journals (Sweden)

    Talijan Nadežda M.

    2006-01-01

    Full Text Available Magnetic properties of permanent magnetic materials based on intermetallic compounds of Sm-Co and Nd-Fe-B are in direct dependence on the microstructure. In the first part of this paper, having in mind the importance of the regime of sintering and heat treatment to obtain the optimal magnetic structure, yet another approach in defining the most adequate technological parameters of the sintering process for applied heat treatment conditions was made. The goal of these investigations was to use the correlation that exists between sintering conditions (temperature and time and intensity of the diffraction peak of the (111 plane of the SmCo5 phase to optimize. In the second part a brief overview of high energy magnetic materials based on Nd-Fe-B is presented with special emphasis to the current research and development of high remanent nanocomposite magnetic materials based on Nd-Fe-B alloys with a reduced Nd content. Part of experimental results gained during research of the sintering process of SmCo5 magnetic materials were realized and published earlier. The scientific meeting devoted to the 60th anniversary of Frankel’s theory of sintering was an opportunity to show once more the importance and role of sintering in optimization of the magnetic microstructure of sintered Sm Co5 magnetic materials.

  5. Consolidation of metallic hollow spheres by electric sintering

    Science.gov (United States)

    Mironov, V.; Tatarinov, A.; Lapkovsky, V.

    2017-07-01

    This paper considers peculiarities of the technology of production of structures from metallic hollow spheres (MHS) using magnetic fields and electric sintering. In these studies, the raw material was MHS obtained by burning of polystyrene balls coated by carbon steel. MHS had an outer diameter of 3-5 mm and a steel wall thickness of 70-120 microns. Pulsed current generators were used for electric sintering of MHS to obtain different spatial structures. Since MHS have small strength, the compressive pressure during sintering should be minimal. To improve the adhesion strength and reduce the required energy for sintering, hollow spheres were coated with copper by ion-plasma sputtering in vacuum. The coating thickness was 10-15 microns. The ferromagnetic properties of MHS allowed using of magnet fields for orientation of the spheres in the structures, as well as using of perforated tapes acting as orienting magnetic cores. Ultrasonic testing of MHS structures has been tried using through propagation of ultrasound in low kilohertz frequency range. Sensitivity of the propagation parameters to water filling of inter-spheres space and sintering temperature was demonstrated.

  6. Transformation of Goethite to Hematite Nanocrystallines by High Energy Ball Milling

    Directory of Open Access Journals (Sweden)

    O. M. Lemine

    2014-01-01

    Full Text Available α-Fe2O3 nanocrystallines were prepared by direct transformation via high energy ball milling treatment for α-FeOOH powder. X-ray diffraction, Rietveld analysis, TEM, and vibrating sample magnetometer (VSM are used to characterize the samples obtained after several milling times. Phase identification using Rietveld analysis showed that the goethite is transformed to hematite nanocrystalline after 40 hours of milling. HRTEM confirm that the obtained phase is mostly a single-crystal structure. This result suggested that the mechanochemical reaction is an efficient way to prepare some iron oxides nanocrystallines from raw materials which are abundant in the nature. The mechanism of the formation of hematite is discussed in text.

  7. High-pressure X-ray diffraction study of bulk- and nanocrystalline GaN

    DEFF Research Database (Denmark)

    Jorgensen, J.E.; Jakobsen, J.M.; Jiang, Jianzhong

    2003-01-01

    Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, while...... the wurtzite phase was retained up to 60 GPa in the case of nanocrystalline GaN. The bulk moduli for the wurtzite phases were determined to be 187 ( 7) and 319 ( 10) GPa for the bulk- and nanocrystalline phases, respectively, while the respective NaCl phases were found to have very similar bulk moduli [ 208...... ( 28) and 206 ( 44) GPa]....

  8. Synthesis of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 powder and sintered ferrites by high energy ball-milling process

    International Nuclear Information System (INIS)

    Shi, X.L.; Yang, H.; Shao, G.Q.; Duan, X.L.; Xiong, Z.; Sun, P.; Wang, T.G.

    2007-01-01

    (Mg 0.476 Mn 0.448 Zn 0.007 )(Fe 1.997 Ti 0.002 )O 4 nanocrystalline powder prepared by high energy ball-milling process were consolidated by microwave and conventional sintering processes. Phases, microstructure and magnetic properties of the ferrites prepared by different processes were investigated. The (Mg 0.476 Mn 0.448 Zn 0.007 )(Fe 1.997 Ti 0.002 )O 4 nanocrystalline powder could be prepared by high energy ball-milling process of raw Fe 3 O 4 , MnO 2 , ZnO, TiO 2 and MgO powders. Prefired and microwave sintered ferrites could achieve the maximum density (4.86 g/cm -3 ), the average grain size (15 μm) was larger than that (10 μm) prepared by prefired and conventionally sintered ferrites with pure ferrite phase, and the saturation magnetization (66.77 emu/g) was lower than that of prefired and conventionally sintered ferrites (88.25 emu/g), the remanent magnetization (0.7367 emu/g) was higher than that of prefired and conventionally sintered ferrites (0.0731 emu/g). Although the microwave sintering process could increase the density of ferrites, the saturation magnetization of ferrites was decreased and the remanent magnetization of ferrites was also increased

  9. Recycling of mill scale in sintering process

    Directory of Open Access Journals (Sweden)

    El-Hussiny N.A.

    2011-01-01

    Full Text Available This investigation deals with the effect of replacing some amount of Baharia high barite iron ore concentrate by mill scale waste which was characterized by high iron oxide content on the parameters of the sintering process., and investigation the effect of different amount of coke breeze added on sintering process parameters when using 5% mill scale waste with 95% iron ore concentrate. The results of this work show that, replacement of iron ore concentrate with mill scale increases the amount of ready made sinter, sinter strength and productivity of the sinter machine and productivity at blast furnace yard. Also, the increase of coke breeze leads to an increase the ready made sinter and productivity of the sintering machine at blast furnace yard. The productivity of the sintering machine after 5% decreased slightly due to the decrease of vertical velocity.

  10. Modeling Macroscopic Shape Distortions during Sintering of Multi-layers

    DEFF Research Database (Denmark)

    Tadesse Molla, Tesfaye

    Ceramic multi-layered composites are being used as components in various technologies ranging from electronics to energy conversion devices. Thus, different architectures of multi-layers involving ceramic materials are often required to be produced by powder processing, followed by sintering...... the camber development during co-firing. The effect of extrinsic factors (e.g. gravity, thickness ratio and friction) on the shape evolution of bi-layers during co-firing has been studied using the developed model and experiments. Furthermore, a new analytical model describing stresses during sintering...... of tubular bi-layer structures has been developed by using the direct correspondence between elasticity and linear viscous problems. The finite element model developed in this study and sintering experiments of tubular bi-layer sample have been used to verify and validate the developed analytical model...

  11. CdS sintered films: growth and characteristics

    International Nuclear Information System (INIS)

    Sharma, Monika; Kumar, Sushil; Sharma, L.M.; Sharma, T.P.; Husain, M.

    2004-01-01

    Cadmium sulphide finds extensive applications in a variety of optoelectronic devices. CdS, with a band gap of 2.43 eV, is a suitable window material in heterojunction solar cells that employ CdTe, Cu 2 S or CuInSe 2 as an absorber. Polycrystalline films of CdS, thickness ∼15 μm, were grown onto chemically clean and optically plane glass substrates by sintering process. A 10 min sintering time and 500 deg. C sintering temperature were found to be optimum. As deposited films were characterized through optical, structural and electrical transport properties using optical reflection spectroscopy, X-ray diffractometry and I-V characteristics techniques

  12. Corrosion behaviour of sintered duplex stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    Utrilla, M. Victoria; Urena, Alejandro; Otero, Enrique; Munez, Claudio Jose [Escuela Superior de Ciencias Experimentales y Tecnologia, Universidad Rey Juan Carlos, C/ Tulipan s/n, 28933 Mostoles, Madrid (Spain)

    2004-07-01

    Duplex austenite-ferrite stainless steels were prepared by mixing austenitic (316L) and ferritic (434L) atomized powders. Although different 316L/434L ratios were prepared, present work centred its study on 50% ferrite - 50% austenite sintered steel. The powders were mixed and pressed at 700 MPa and sintered at 1250 deg. C for 30 min in vacuum. The cooling rate was 5 deg. C/min. Solution treatment was carried out to homogenize the microstructure at 1100 deg. C during 20 min. A microstructural study of the material in solution was performed, evaluating the microstructure, proportion and shape of porosity, and ferrite percentage. This last was measured by two methods, quantitative metallography and Fischer ferrito-metry. The materials were heat treated in the range of 700 to 1000 deg. C, for 10, 30 and 60 min and water quenched, to study the microstructural changes and the influence on the intergranular corrosion resistance. The method used to evaluate the sensitization to the intergranular corrosion was the electrochemical potentio-kinetic reactivation procedure (EPR). The test solution was 0.5 M H{sub 2}SO{sub 4} + 0,01 M KSCN at 30 deg. C. The criterion used to evaluate the sensitization was the ratio between the maximum reactivation density (Ir) and the maximum activation density (Ia). The results of the electrochemical tests were discussed in relation with the microstructures observed at the different heat treatments. (authors)

  13. Sintering and mechanical properties of porcelains prepared from algerian raw materials Sinterização e propriedades mecânicas de porcelanas preparadas com matéria-prima argelina

    Directory of Open Access Journals (Sweden)

    S. Kitouni

    2011-12-01

    Full Text Available Porcelain is a type of ceramics highly valued for its beauty and strength. The overall goal of this work is to utilize local raw materials within the following fractions: 37 wt.% kaolin, 35 wt.% feldspar and 28 wt.% quartz. This composition has been selected on the basis of the ternary phase diagrams (kaolin-feldspar-quartz. The densification behaviour indicated that specimens sintered at 1200 °C for 2 h with a heating rate of 5 °C/min, have a bulk density of about 2.50 g/cm³. This value is slightly higher than that reported for the conventional porcelain products (2.45 g/cm³. Porcelain specimens with and without calcination sintered at 1200 °C for 2 h have tensile strength values of about 45 and 73 MPa, respectively (equivalent flexural strength values of about 122 and 197 MPa, respectively. The flexural strength values of both specimens are much higher than those reported for conventional porcelains (ranged between 60 and 80 MPa. Furthermore, the value of micro-hardness of the fired samples without calcination at 1200 °C is 9.3 ± 0.2 GPa which is higher than the commercial porcelain products (5.5 GPa.A porcelana é um tipo de cerâmica altamente valorizada pela sua beleza e resistência mecânica. O objetivo geral deste trabalho é utilizar matérias-primas locais nas seguintes frações: 37% em peso de caulim, feldspato 35% em peso e 28% em peso de quartzo. Esta composição foi escolhida com base em diagramas de fase ternários (caulim, feldspato-quartzo. O comportamento de densificação indicou que amostras sinterizadas a 1200 °C por 2 h com taxa de aquecimento de 5 °C/min, tem uma densidade de cerca de 2,50 g/cm³. Este valor é ligeiramente superior ao relatado para os produtos de porcelana convencional (2,45 g/cm³. Espécimes de porcelana, com e sem calcinação sinterizadas a 1200 °C por 2 h têm valores de resistência à tração de cerca de 45 e 73 MPa, respectivamente (valores equivalentes de resistência à flexão de

  14. Nanocrystalline sol-gel Nb{sub 2}O{sub 5} coatings. Preparation, characterisation and application to photovoltaic cell, lithium battery and eletrochromic device

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yeping

    2002-07-01

    Thick and thin films of Nb{sub 2}O{sub 5} have been prepared by the sol-gel process using cheap niobium pentachloride as precursor and a new synthesis route. The microstructure of the films was tailored by adding poly(ethylene glycol) (PEG) and carbon soot into the sol and varying the sintering temperature. The thesis describes the properties of the sols and their influence on the properties of the resulting nanocrystalline Nb{sub 2}O{sub 5} films as electrodes in dye sensitised solar cells, electrochromic devices and rechargeable lithium batteries. A solar light-to-electric conversion efficiency of Ru(II) sensitised Nb{sub 2}O{sub 5} solar cell as high as 7% under 120 W/m{sup 2} illumination was obtained. An equivalent electric circuit of the dye sensitised electrode/electrolyte interface based on the electrochemical impedance spectroscopy was modelled and found to fit all the results. The values obtained for the electric elements from the simulation of the results were found to relate material parameters to the cell performance and their influence on the cell performance are illustrated. The electrochromism and Li{sup +}-charge and discharge of the Nb{sub 2}O{sub 5} films exhibited also good performance. (orig.)

  15. Phase-pure Nanocrystalline Li4Ti5O12 for Lithium ion Battery

    Czech Academy of Sciences Publication Activity Database

    Kalbáč, Martin; Zukalová, Markéta; Kavan, Ladislav

    2003-01-01

    Roč. 8, č. 1 (2003), s. 2-6 ISSN 1432-8488 R&D Projects: GA MŠk OC D14.10 Institutional research plan: CEZ:AV0Z4040901 Keywords : phase purity * Li4Ti5O12 * nanocrystalline materials Subject RIV: CG - Electrochemistry Impact factor: 1.195, year: 2003

  16. High-pressure X-ray diffraction study of bulk- and nanocrystalline GaN

    DEFF Research Database (Denmark)

    Jorgensen, J.E.; Jakobsen, J.M.; Jiang, Jianzhong

    2003-01-01

    Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, whi...

  17. Controllable chemical vapor deposition of large area uniform nanocrystalline graphene directly on silicon dioxide

    DEFF Research Database (Denmark)

    Sun, Jie; Lindvall, Niclas; Cole, Matthew T.

    2012-01-01

    Metal-catalyst-free chemical vapor deposition (CVD) of large area uniform nanocrystalline graphene on oxidized silicon substrates is demonstrated. The material grows slowly, allowing for thickness control down to monolayer graphene. The as-grown thin films are continuous with no observable pinhol...

  18. An investigation into the room temperature mechanical properties of nanocrystalline austenitic stainless steels

    International Nuclear Information System (INIS)

    Eskandari, Mostafa; Zarei-Hanzaki, Abbas; Abedi, Hamid Reza

    2013-01-01

    Highlights: ► Strength of nanocrystalline specimens follows a trend of a remarkable rise along with a small drop in ductility in comparison to the coarse-grained one. ► Universal correlation of linear type (UTS = mτ max ) between shear punch test data and the tensile strength may be unreliable for the nanocrystalline materials. ► Actual relation between the maximum shear and ultimate tensile strength follows an empirical formula of UTS=0.013τ max 2 -25.62τ max +13049. -- Abstract: The present work has been conducted to evaluate the mechanical properties of nanostructured 316L and 301 austenitic stainless steels. The nanocrystalline structures were produced through martensite treatment which includes cold rolling followed by annealing treatment. The effect of equivalent rolling strain and annealing parameters on the room temperature mechanical behavior of the experimental alloys have been studied using the shear punch testing technique. The standard uniaxial tension tests were also carried out to adapt the related correlation factors. The microstructures and the volume fraction of phases were characterized by transmission electron microscopy and feritscopy methods, respectively. The results indicate that the strength of nanocrystalline specimens remarkably increases, but the ductility in comparison to the coarse-grained one slightly decreases. In addition the strength of nanocrystalline specimens has been increased by decreasing the annealing temperature and increasing the equivalent rolling strain. The analysis of the load–displacement data has also disclosed that the universal correlation of linear type (UTS = mτ max ) between shear punch test data and the tensile strength is somehow unreliable for the nanocrystalline materials. The results suggest that the actual relation between the maximum shear strength and ultimate tensile strength follows a second order equation of type UTS=aτ max 2 -bτ max +c.

  19. Application of printed nanocrystalline diamond film for electron emission cathode

    International Nuclear Information System (INIS)

    Zhang Xiuxia; Wei Shuyi; Lei Chongmin; Wei Jie; Lu Bingheng; Ding Yucheng; Zhu Changchun

    2011-01-01

    The low-cost and large area screen-printed nano-diamond film (NDF) for electronic emission was fabricated. The edges and corners of nanocrystalline diamond are natural field-emitters. The nano-diamond paste for screen-printing was fabricated of mixing nano-graphite and other inorganic or organic vehicles. Through enough disperse in isopropyl alcohol by ultrasonic nano-diamond paste was screen-printed on the substrates to form NDF. SEM images showed that the surface morphology of NDF was improved, and the nano-diamond emitters were exposed from NDF through the special thermal-sintering technique and post-treatment process. The field emission characteristics of NDF were measured under all conditions with 10 -6 Pa pressure. The results indicated that the field emission stability and emission uniformity of NDF were improved through hydrogen plasma post-treatment process. The turn-on field decreased from 1.60 V/μm to 1.25 V/μm. The screen-printed NDF can be applied to the displays electronic emission cathode for low-cost outdoor in large area.

  20. Sintering of ultra high molecular weight polyethylene

    Indian Academy of Sciences (India)

    ... involves compaction of polymeric powder under pressure and sintering of the preforms at temperature above its melting point. In this study, we report our results on compaction and sintering behaviour of two grades of UHMWPE with reference to the powder morphology, sintering temperatures and strength development.

  1. Bulletin of Materials Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    ... on the sintering temperature. Two photon processes were mainly responsible for green and red upconversion emissions. pp 1153-1160. Effect of variation of precursor concentration on structural, microstructural, optical and gas sensing properties of nanocrystalline TiO2 thin films prepared by spray pyrolysis techniques.

  2. Master Sintering Surface: A practical approach to its construction and utilization for Spark Plasma Sintering prediction

    Directory of Open Access Journals (Sweden)

    Pouchly V.

    2012-01-01

    Full Text Available The sintering is a complex thermally activated process, thus any prediction of sintering behaviour is very welcome not only for industrial purposes. Presented paper shows the possibility of densification prediction based on concept of Master Sintering Surface (MSS for pressure assisted Spark Plasma Sintering (SPS. User friendly software for evaluation of the MSS is presented. The concept was used for densification prediction of alumina ceramics sintered by SPS.

  3. Basic monolithic materials containing zirconium sinters

    International Nuclear Information System (INIS)

    Kloska, A.; Miaczynska, H.; Strama, J.; Seifert, H.

    1997-01-01

    The presented proposals and results of investigation deal with the new types of basic refractory concrete. Refractory ceramic composites of the system CaO-MgO-ZrO 2 -SiO 2 have a key role in the production technology of these types of concrete. Such types of concrete possess useful characteristics, especially good corrosion resistance and thermomechanical properties. Preliminary analysis of the application possibilities for the new concrete types suggests that they can be useful in modern steel-making processes, including secondary metallurgy. (author)

  4. Sintering of Multilayered Porous Structures: Part II – Experiments and Model Applications

    DEFF Research Database (Denmark)

    Ni, De Wei; Olevsky, Eugene; Esposito, Vincenzo

    2013-01-01

    for the determination of the shear viscosities ratio of the layer fully dense materials. This original technique enables the derivation of all the input parameters for the bilayer sintering modeling from one set of optical dilatometry measurements, including the conversion between real and specific times of sintering......, the layers’ relative sintering intensity, and the shear viscosities ratio of the layer fully dense materials. These optical dilatometry measurements are conducted simultaneously for each individual layer and for a symmetric trilayered porous structure based on the two layers utilized in the bilayered system...

  5. Thermal conductivity of amorphous and nanocrystalline silicon films prepared by hot-wire chemical-vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Jugdersuren, B.; Kearney, B. T.; Queen, D. R.; Metcalf, T. H.; Culbertson, J. C.; Chervin, C. N.; Stroud, R. M.; Nemeth, W.; Wang, Q.; Liu, Xiao

    2017-07-01

    We report 3..omega.. thermal conductivity measurements of amorphous and nanocrystalline silicon thin films from 85 to 300 K prepared by hot-wire chemical-vapor deposition, where the crystallinity of the films is controlled by the hydrogen dilution during growth. The thermal conductivity of the amorphous silicon film is in agreement with several previous reports of amorphous silicon prepared by a variety of deposition techniques. The thermal conductivity of the as-grown nanocrystalline silicon film is 70% higher and increases 35% more after an anneal at 600 degrees C. They all have similarly weak temperature dependence. Structural analysis shows that the as-grown nanocrystalline silicon is approximately 60% crystalline, nanograins and grain boundaries included. The nanograins, averaging 9.1 nm in diameter in the as-grown film, are embedded in an amorphous matrix. The grain size increases to 9.7 nm upon annealing, accompanied by the disappearance of the amorphous phase. We extend the models of grain boundary scattering of phonons with two different non-Debye dispersion relations to explain our result of nanocrystalline silicon, confirming the strong grain size dependence of heat transport for nanocrystalline materials. However, the similarity in thermal conductivity between amorphous and nanocrystalline silicon suggests the heat transport mechanisms in both structures may not be as dissimilar as we currently understand.

  6. Growth and Characterization of Cd1−XZnXTe-Sintered Films

    Directory of Open Access Journals (Sweden)

    V. Kumar

    2007-01-01

    Sintering is a very simple and viable method compared to other cost-intensive methods. The results of the present investigation will be useful in characterizing the material CdZnTe for its applications in photovoltaics.

  7. Structural comparison of sintering products made of "TiC + Ti" composite powders and "Ti + C" powder mixtures

    Science.gov (United States)

    Krinitcyn, Maksim G.; Pribytkov, Gennadii A.; Korosteleva, Elena N.; Firsina, Irina A.; Baranovskii, Anton V.

    2017-12-01

    In this study, powder composite materials comprised of TiC and Ti with different ratios are processed by sintering of Ti and C powder mixtures and self-propagating high-temperature synthesis (SHS) in "Ti+C" system followed by sintering. The microstructure and porosity of obtained composites are investigated and discussed. The dependence of porosity on sintering time is explained theoretically. Optimal regimes that enable to obtain the most homogeneous structure with the least porosity are described.

  8. Improvement of mechanical properties by additive assisted laser sintering of PEEK

    International Nuclear Information System (INIS)

    Kroh, M.; Bonten, C.; Eyerer, P.

    2014-01-01

    The additive assisted laser sintering was recently developed at IKT: A carbon black (CB) additive is used to adjust the polymer's laser absorption behavior with the aim to improve the interconnection of sintered powder layers. In this paper a parameter study, Polyetheretherketone (PEEK) samples were prepared with different contents of carbon black and were laser sintered with varying thermal treatment. The samples were mechanically tested and investigated by optical light and transmission electron microscopy. An influence on the morphology at the border areas of particles and intersections of laser sintered layers was found. Depending on the viscosity of the raw material and CB content, different shapes of lamellae were observed. These (trans-) crystalline or polymorph structures, respectively, influence the thermal and mechanical behavior of the virgin PEEK. Moreover, the thermal treatment during the sintering process caused an improvement of mechanical properties like tensile strength and elongation at break

  9. High frequency magnetic properties of Fe-based nanocrystalline alloy powder cores

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Y.K. [Seoul National University of Technology, Seoul 139-743 (Korea); Korea Institute of Science and Technology, Seoul 136-791 (Korea); Kim, Yoon B.; Jee, K.K. [Korea Institute of Science and Technology, Seoul 136-791 (Korea); Choi, G.B. [R and D Center, Changsung Corporation, Incheon (Korea)

    2007-12-15

    Toroidal shape Fe-based nanocrystalline alloy powder cores were prepared from the melt spun Fe{sub 73.5}Cu{sub 1}Nb{sub 3}Si{sub 15.5}B{sub 7} ribbons by cold pressing using silicon and phenol resin as an insulating material, respectively. The effect of the insulating materials and their content on the high-frequency magnetic properties of the compacted cores were investigated. The Fe-based nanocrystalline alloy powder cores using phenol resin exhibit stable permeability over 1 MHz, showing excellent high-frequency characteristics. The core loss was reduced significantly and the dc-bias property was improved by using phenol resin. Uniform and good insulation by phenol resin leads to the excellent high-frequency characteristics of the cores. Silicon resin as an insulating material was also effective in improving the high frequency characteristics of the Fe-based nanocrystalline alloy powder cores. However, an appropriate coating process for silicon resin should be applied in order to achieve more improved high frequency characteristics of the nanocrystalline alloy powder cores by controlling the thickness of coated layer. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Microstructure evolution of SiC sintered bodies activated by boron and carbon

    International Nuclear Information System (INIS)

    Gubernat, A.; Stobierski, L.

    2003-01-01

    Investigation on the role of sintering aids on densification of silicon carbide indicate that boron and carbon modify mass transport mechanisms. It leads to changes of microstructure of polycrystalline silicon carbide. In the present work the influence of varying proportions of sintering aids on the material microstructure was studied. The microstructural changes were related to the changes of the selected properties of the resulting materials. (author)

  11. Processing and Properties of Distaloy Sa Sintered Alloys with Boron and Carbon

    Directory of Open Access Journals (Sweden)

    Karwan-Baczewska J.

    2015-04-01

    Full Text Available Prealloyed iron-based powders, manufactured in Höganäs Company, are used in the automotive parts industry. The properties and life time of such sintered parts depend, first of all, on their chemical composition, the production method of the prealloyed powder as well as on the technology of their consolidation and sintering. One of simpler and conventional methods aimed at increasing the density in sintered products is the process of activated sintering, performed, for example, by adding boron as elementary boron powder. Under this research project obtained were novel sintered materials, based on prealloyed and diffusion bonded powder, type: Distaloy SA, with the following chemical composition: Fe-1.75% Ni-1.5%Cu- 0.5%Mo with carbon (0.55%; 0.75% and boron (0.2%, 0.4% and 0.6%. Distaloy SA samples alloyed with carbon and boron were manufactured by mixing powders in a Turbula mixer, then compressed using a hydraulic press under a pressure of 600 MPa and sintered in a tube furnace at 1473 K, for a 60 minute time, in the hydrogen atmosphere. After the sintering process, there were performed density and porosity measurements as well as hardness tests and mechanical properties were carried out, too. Eventually, analyzed was the effect of boron upon density, hardness and mechanical properties of novel sintered construction parts made from Distaloy SA powder.

  12. Analysis and modeling of sintering of Sr-hexaferrite produced by PIM technology

    Directory of Open Access Journals (Sweden)

    Zlatkov B.S.

    2011-01-01

    Full Text Available The powder injection moulding (PIM technology is lately becoming more and more significant due to complex design possibilities and good repeatability. This technology requires optimization of all steps starting with material and binder, injection, debinding and sintering parameters. Sintering is one of the key links in this technology. The powder injection moulding process is specific as during feedstock injection powder particles mixed into the binder do not come into mechanical contact. Shrinkage during sintering of PIM samples is high. In this work we have analyzed and modeled the sintering process of isotropic PIM samples of Sr-hexaferrite. The Master Sintering Curve (MSC principle has been applied to analyze sintering of two types of PIM Sr-hexaferrite samples with completely removed binder and only the extraction step of the debinding procedure (thermal debinding proceeding simultaneously with sintering. Influence of the heating rate on resulting sample microstructures has also been analyzed. Influence of the sintering time and temperature was analyzed using three different phenomenological equations.

  13. Field assisted sintering of refractory carbide ceramics and fiber reinforced ceramic matrix composites

    Science.gov (United States)

    Gephart, Sean

    The sintering behaviors of silicon carbide (SiC) and boron carbide (B4C) based materials were investigated using an emerging sintering technology known as field assisted sintering technology (FAST), also known as spark plasma sintering (SPS) and pulse electric current sintering (PECS). Sintering by FAST utilizes high density electric current, uniaxial pressure, and relatively high heating rate compared to conventional sintering techniques. This effort investigated issues of scaling from laboratory FAST system (25 ton capacity) to industrial FAST system (250 ton capacity), as well as exploring the difference in sintering behavior of single phase B4C and SiC using FAST and conventional sintering techniques including hot-pressing (HP) and pressure-less sintering (PL). Materials were analyzed for mechanical and bulk properties, including characterization of density, hardness, fracture toughness, fracture (bend) strength, elastic modulus and microstructure. A parallel investigation was conducted in the development of ceramic matrix composites (CMC) using SiC powder impregnation of fiber compacts followed by FAST sintering. The FAST technique was used to sinter several B4C and SiC materials to near theoretical density. Preliminary efforts established optimized sintering temperatures using the smaller 25 ton laboratory unit, targeting a sample size of 40 mm diameter and 8 mm thickness. Then the same B4C and SiC materials were sintered by the larger 250 ton industrial FAST system, a HP system, and PL sintering system with a targeted dense material geometry of 4 x 4 x 0.315 inches3 (101.6 x 101.6 x 8 mm3). The resulting samples were studied to determine if the sintering dynamics and/or the resulting material properties were influenced by the sintering technique employed. This study determined that FAST sintered ceramic materials resulted in consistently higher averaged values for mechanical properties as well as smaller grain size when compared to conventionally sintered

  14. Liquid phase sintered SiC. Processing and transformation controlled microstructure tailoring

    Directory of Open Access Journals (Sweden)

    V.A. Izhevskyi

    2000-10-01

    Full Text Available Microstructure development and phase formation processes during sintering of silicon carbide based materials with AlN-Y2O3, AlN-Yb2O3, and AlN-La2O3 sintering additives were investigated. Densification of the materials occurred by liquid-phase sintering mechanism. Proportion of alpha- and beta-SiC powders in the initial mixtures was a variable parameter, while the molar ratio of AlN/RE2O3, and the total amount of additives (10 vol. % were kept constant. Shrinkage behavior during sintering in interrelation with the starting composition of the material and the sintering atmosphere was investigated by high temperature dilatometry. Kinetics of b-SiC to a-SiC phase transformation during post-sintering heat treatment at temperatures 1900-1950 °C was studied, the degree of phase transformation being determined by quantitative x-ray analysis using internal standard technique. Evolution of microstructure resulting from beta-SiC to alpha-SiC transformation was followed up by scanning electron microscopy on polished and chemically etched samples. Transformation-controlled grain growth mechanism similar to the one observed for silicon nitride based ceramics was established. Possibility of in-situ platelet reinforced dense SiC-based ceramics fabrication with improved mechanical properties by means of sintering was shown.

  15. Strain-enhanced sintering of iron powders

    Energy Technology Data Exchange (ETDEWEB)

    Amador, D.R.; Torralba, J.M. [Universidad Carlos III de Madrid, Departamento de Ciencias de Materiales e Ingenieria Metalurgica, Leganes, Madrid (Spain); Monge, M.A.; Pareja, R. [Universidad Carlos III de Madrid, Departamento de Fisica, Madrid (Spain)

    2005-02-01

    Sintering of ball-milled and un-milled Fe powders has been investigated using dilatometry, X-ray, density, and positron annihilation techniques. A considerable sintering enhancement is found in milled powders showing apparent activation energies that range between 0.44 and 0.80 eV/at. The positron annihilation results, combined with the evolution of the shrinkage rate with sintering temperature, indicate generation of lattice defects during the sintering process of milled and un-milled powders. The sintering enhancement is attributed to pipe diffusion along the core of moving dislocations in the presence of the vacancy excess produced by plastic deformation. Positron annihilation results do not reveal the presence of sintering-induced defects in un-milled powders sintered above 1200 K, the apparent activation energy being in good agreement with that for grain-boundary diffusion in {gamma}-Fe. (orig.)

  16. Effect of degassing temperature on the microstructure of a nanocrystalline Al-Mg alloy

    International Nuclear Information System (INIS)

    Ahn, Byungmin; Newbery, A. Piers; Lavernia, Enrique J.; Nutt, Steven R.

    2007-01-01

    The microstructural evolution of a nanocrystalline Al-Mg alloy was investigated to determine the effects of degassing temperature. Al 5083 powder was ball-milled in liquid nitrogen to obtain a nanocrystalline structure, then vacuum degassed to remove contaminants. The degassed powder was consolidated by cold isostatic pressing and then forged to produce bulk, low-porosity material. The material microstructure was analyzed at different stages using optical microscopy, transmission electron microscopy, and density measurements. The impurity concentration of the final product was also measured. The forged material exhibited a bimodal grain size distribution, consisting of both ultra fine and coarse grains. The bimodal distribution was attributed to the presence of residual coarse grains in the as-milled powder. Higher degassing temperatures resulted in higher density values and lower hydrogen content in the consolidated materials, although these materials also exhibited more extensive grain growth

  17. Microwave Sintering and Its Application on Cemented Carbides

    OpenAIRE

    Rumman Md Raihanuzzaman; Lee Chang Chuan; Zonghan Xie; Reza Ghomashchi

    2015-01-01

    Cemented carbides, owing to their excellent mechanical properties, have been of immense interest in the field of hard materials for the past few decades. A number of processing techniques have been developed to obtain high quality carbide tools, with a wide range of grain size depending on the application and requirements. Microwave sintering is one of the heating processes, which has been used to prepare a wide range of materials including ceramics. A deep understanding ...

  18. Physical chemistry and modelling of the sintering of actinide oxides

    International Nuclear Information System (INIS)

    Lechelle, Jacques

    2013-01-01

    This report gives a synthesis of the work I have carried out or to which I have numerically contributed to from 1996 up to 2012 in the Department of Plutonium Uranium and minor Actinides in Cadarache CEA Center. Their main goal is the study and the modeling of the sintering process of nuclear fuels which is the unifying thread of this document. Both in order to take into account the physical and chemical features of the actinide bearing oxide material and in order to combine the different transport phenomena leading to sintering, a sub-granular scale model is under development. Extension to a varying chemical composition as well as exchanges with the gaseous phase are foreseen. A simulation on a larger scale (pellet scale) is ongoing in the framework of a PhD thesis. Validation means have been tested with (U,Pu)O 2 material on the scale of the pellet (Small Angle Neutron Diffusion), on the scale of powder granules (X-Ray High Resolution Micro-Tomography) and with CeO 2 at the 'Institut de Chimie Separative' in Marcoule on a single crystal scale (Environmental Scanning Electron Microscope). The required microstructure homogeneity for nuclear fuels has led to a campaign of experimental studies about the role of Cr 2 O 3 as a sintering aid. Whole of these studies improve our understanding of fuel sintering and hence leads to an improved mastering of this process. (author) [fr

  19. The radiation response of mesoporous nanocrystalline zirconia thin films

    Energy Technology Data Exchange (ETDEWEB)

    Manzini, Ayelén M.; Alurralde, Martin A. [Comisión Nacional de Energía Atómica, Centro Atómico Constituyentes, Av. General Paz 1499, 1650 San Martin, Provincia de Buenos Aires (Argentina); Giménez, Gustavo [Instituto Nacional de Tecnología Industrial - CMNB, Av. General Paz 5445, 1650 San Martín, Provincia de Buenos Aires (Argentina); Luca, Vittorio, E-mail: vluca@cnea.gov.ar [Comisión Nacional de Energía Atómica, Centro Atómico Constituyentes, Av. General Paz 1499, 1650 San Martin, Provincia de Buenos Aires (Argentina)

    2016-12-15

    The next generation of nuclear systems will require materials capable of withstanding hostile chemical, physical and radiation environments over long time-frames. Aside from its chemical and physical stability, crystalline zirconia is one of the most radiation tolerant materials known. Here we report the first ever study of the radiation response of nanocrystalline and mesoporous zirconia and Ce{sup 3+}-stabilized nanocrystalline zirconia (Ce{sub 0.1}Zr{sub 0.9}O{sub 2}) thin films supported on silicon wafers. Zirconia films prepared using the block copolymer Brij-58 as the template had a thickness of around 60–80 nm. In the absence of a stabilizing trivalent cation they consisted of monoclinic and tetragonal zirconia nanocrystals with diameters in the range 8–10 nm. Films stabilized with Ce{sup 3+} contained only the tetragonal phase. The thin films were irradiated with iodine ions of energies of 70 MeV and 132 keV at low fluences (10{sup 13} - 10{sup 14} cm{sup −2}) corresponding to doses of 0.002 and 1.73 dpa respectively, and at 180 keV and high fluences (2 × 10{sup 16} cm{sup −2}) corresponding to 82.4 dpa. The influence of heavy ion irradiation on the nanocrystalline structure was monitored through Rietveld analysis of grazing incidence X-ray diffraction (GIXRD) patterns recorded at angles close to the critical angle to ensure minimum contribution to the diffraction pattern from the substrate. Irradiation of the mesoporous nanocrystalline zirconia thin films with 70 MeV iodine ions, for which electronic energy loss is dominant, resulted in slight changes in phase composition and virtually no change in crystallographic parameters as determined by Rietveld analysis. Iodine ion bombardment in the nuclear energy loss regime (132–180 keV) at low fluences did not provoke significant changes in phase composition or crystallographic parameters. However, at 180 keV and high fluences the monoclinic phase was totally eliminated from the GIXRD

  20. Kiln furniture for sintering electronic ceramics. Ceramics shosei jigu (doguzai) ni tsuite

    Energy Technology Data Exchange (ETDEWEB)

    Fushimi, T.; Shibata, S. (Toshiba Ceramics Co. Ltd., Tokyo (Japan))

    1994-05-01

    This paper summarizes refractory jigs used in manufacturing electronic ceramics. Jigs used vary with types of sintering kilns. Sintering kilns include pusher kiln, trolley kiln, roller hearth kiln, batch kiln, and HIP. The paper describes jigs by electronic ceramics materials. Ferrites are sintered in a pusher kiln, where such jigs are used as a base plate, stanchions, shelf plates, saggers, and a setter. Jigs that contact with ferrite are demanded not to give such adverse effects to materials to be sintered as crystal growth. Soft ferrites of Mn/Zn and Ni/Zn systems use jigs of pure alumina and zirconia nature, while large-size soft ferrites use setters with rough surface. A barium titanate system as a ceramic dielectric uses a zirconia jig, and materials containing Pb and Bi such as for varistors use magnesia and spinel jigs. Alumina porcelain substrates use mullite or high-alumina pusher kilns and alumina jigs. 4 refs., 1 fig., 4 tabs.

  1. Comparative studies on mechanical properties of WC-Co composites sintered by SPS and conventional techniques

    Directory of Open Access Journals (Sweden)

    Pristinskiy Yuri

    2017-01-01

    Full Text Available Spark plasma sintering (SPS is an extremely fast solidification technique for compounds that are difficult to sinter within the material group metals, ceramics, or composites thereof, SPS uses a uniaxial pressure and a very rapid heating cycle to consolidate these materials. With SPS the main benefit is the ability to control the WC grain size due to the short sintering times at high temperature. Additionally, its allows to avoid negative reactions between WC and cobalt and to minimize the formation of undesirable phases in sintered composites. The WC-6wt.% Co cermet prepared by SPS processing achieves the enhanced mechanical properties with the hardness of 18.3 GPa and the fracture toughness of 15.5 MPa·m1/2 in comparison to standard reference tungsten carbide/cobalt material.

  2. Influence of grain boundaries on elasticity and thermal conductivity of nanocrystalline diamond films

    International Nuclear Information System (INIS)

    Mohr, Markus; Daccache, Layal; Horvat, Sebastian; Brühne, Kai; Jacob, Timo; Fecht, Hans-Jörg

    2017-01-01

    Diamond combines several outstanding material properties such as the highest thermal conductivity and highest elastic moduli of all materials. This makes diamond an interesting candidate for a multitude of applications. Nonetheless, nanocrystalline diamond films, layers and coatings, usually show properties different to those of single crystalline diamond. This is usually attributed to the larger volume fraction of the grain boundaries with atomic structure different from the single crystal. In this work we measured Young's modulus and thermal conductivity of nanocrystalline diamond films with average grain sizes ranging from 6 to 15 nm. The measured thermal conductivities are modeled considering the thermal boundary conductance between grains as well as a grain size effect on the phonon mean free path. We make a comparison between elastic modulus and thermal boundary conductance of the grain boundaries G k for different nanocrystalline diamond films. We conclude that the grain boundaries thermal boundary conductance G k is a measure of the cohesive energy of the grain boundaries and therefore also of the elastic modulus of the nanocrystalline diamond films.

  3. Recent developments in hard magnetic bulk materials

    International Nuclear Information System (INIS)

    Fidler, Josef; Schrefl, Thomas; Hoefinger, Sabine; Hajduga, Maciej

    2004-01-01

    The importance of newly developed permanent magnetic materials in many electromechanical, magnetomechanical and electronic applications is attributed to the drastic improvement in microstructure related properties, such as the remanence, the magnetic energy density product and the coercive field. The influence of the microstructure on the magnetic properties of the magnets will be discussed, where special emphasis is laid on rare earth permanent magnets. Highest performance, anisotropic Nd-Fe-B magnets with J r >1.5 T (BH) max >450 kJm -3 and J H c > 750 kAm -1 , which are produced by the powder metallurgy route, show a strong influence of composition and processing parameters on the magnetic properties. The magnetic properties of Sm(Co,Cu,Fe,Zr) z sintered magnets, which are used nowadays for high temperature applications between 300 and 500 deg. C, are determined by the cellular precipitation microstructure, which is developed during a complex heat treatment and by the microchemistry. Special hard magnetic powder materials, such as Sm 2 Fe 17 N 3 and nanocrystalline, composite Nd 2 Fe 14 B /(α-Fe,Fe 3 B) materials have been developed especially for usage in bonded magnetic materials, which show the strongest annual increase in the production of permanent magnets. The phenomenon of the enhancement of remanence, occurring in single phase and composite Nd 2 Fe 14 B based magnets with isotropic grain alignment, is attributed to intergrain exchange interactions

  4. PRESSURELESS SINTERING OF B4C-NANOTiB2 NANOCOMPOSITE BY ADDITION OF Fe AND Ni AS SINTERING AIDS

    Directory of Open Access Journals (Sweden)

    M. M. Mohammadi Samani

    2014-12-01

    Full Text Available B4C and its composites with TiB2 as second phase continues to be extensively used as the preferred ceramic material in military applications as armor systems for absorbing and dissipating kinetic energy from high velocity projectiles. It also exhibits a high melting point (2427 °C, and high neutron absorption cross section. Pressureless sintering of the B 4C-nanoTiB2 nanocomposite using small amount of Fe and Ni (≤3 Wt% as sintering aids was investigated in order to clarify the role of Fe and Ni additions on the mechanical and microstructural properties of B4C-nanoTiB2 nanocomposites. Different amount of Fe and Ni, mainly 1 to 3 Wt% were added to the base material. Pressureless sintering was conducted at 2175, 2225 and 2300 °C. It was found that Addition of 3 Wt% Fe and 3 wt% Ni and sintering at 2300 °C resulted in improving the density of the samples to about 99% of theoretical density. The nanocomposite samples exhibited high density, hardness, and microstructural uniformity.

  5. Impedance and AC conductivity study of nano crystalline, fine grained multiferroic bismuth ferrite (BiFeO3, synthesized by microwave sintering

    Directory of Open Access Journals (Sweden)

    Jayant Kolte

    2015-09-01

    Full Text Available In this paper, major reduction in sintering time,temperautre and significant improvement over final density of sitnered sample is reported for the microwave sintered nanocrystalline BiFeO3 (BFO ceramic. Also, different sintering time and temperatures have been used to tailor the grain size and the final density of the resulting BFO ceramics synthesized from phase pure BFO nanoparticles ( d ̄   ≈ 10   n m . Microwave sintering resulted in reducing the sintering time substantially (by 1h, and has resulted in submicron sized grains and high resistivity ∼1.8 GΩ-cm. The AC conductivity is seen to follow the Jonscher’s power law behavior, suggesting correlated barrier hopping (CBH mechanism in the sample. The role of oxygen vacancies at high temperature, due to volatility of bismuth, in dielectric and conductivity behavior is also discussed. Further, the sample displayed dielectric anomaly near magnetic transition temperature (∼180 °C indicating bearing of magnetic moments on the dielectric properties. Using Impedance Spectroscopy (IS we have established, the electrical heterogeneity of the ceramic BFO reavealing semiconducting nature of grains and insulating nature of grain boundary. This, formation of network of insulating grain boundaries and semiconducting grains could lead to formation of internal barrier layer capacitance (IBLC leading to high dielectric constant in microwave sintered BFO.

  6. Ceramic-intermetallic composites produced by mechanical alloying and spark plasma sintering

    CERN Document Server

    Cabanas-Moreno, J G; Martínez-Sanchez, R; Delgado-Gutierrez, O; Palacios-Gomez, J; Umemoto, M

    1998-01-01

    Nano-and microcomposites of intermetallic (Co/sub 3/Ti, AlCo/sub 2 /Ti) and ceramic (TiN, Ti(C, N), Al/sub 2/O/sub 3/) phases have been produced by spark plasma sintering (SPS) of powders resulting from mechanical alloying of Al-Co-Ti elemental powder mixtures. The mechanically alloyed powders consisted of mixtures of nanocrystalline and amorphous phases which, on sintering, transformed into complex microstructures of the intermetallic and ceramic phases. For Al contents lower than about 30 at% in the original powder mixtures, the use of SPS led to porosities of 1-2% in the sintered compacts and hardness values as high as ~1700 kg/mm/sup 2/; in these cases, the composite matrix was TiN and Ti(C, N), with the Al/sub 2/O/sub 3/ phase found as finely dispersed particles in the matrix and the Co /sub 3/Ti and AlCo/sub 2/Ti phases as interdispersed grains. (19 refs).

  7. Small-angle neutron scattering investigations on sintering behavior in the powder compacts of ceria (CeO2)

    International Nuclear Information System (INIS)

    Bedekar, Vinila; Patra, A.K.; Sen, D.; Mazumder, S.; Tyagi, A.K.

    2008-01-01

    Nano-crystalline ceria powders have been synthesized by gel combustion process. The effect of sintering temperature on the pore morphology of the powder compacts has been investigated by small-angle neutron scattering (SANS) in the accessible scattering wave vector 'q' range of 0.003-0.17 nm -1 of a double crystal based instrument. The scattering profiles do not follow normal 'q -4 ' power law at higher q-values. The X-ray diffraction and light scattering results indicate that the ceria nano-powders are in the form of porous agglomerates. The porosity of the sintered compacts has been attributed to inter-agglomerate, inter-aggregate and intra-aggregate pores. Scattering profiles have been modeled by using a tri-modal size distribution of pores

  8. Ice sintering timescales at the surface of Europa and implications for surface properties

    Science.gov (United States)

    Phillips, C. B.; Molaro, J.; Meirion-Griffith, G.

    2017-12-01

    The planned exploration of Europa by NASA's Europa Clipper Mission and the possibility of a future Europa lander have driven the need to characterize its surface strength, roughness, porosity, thermal conductivity, and regolith depth in order to accurately interpret remote sensing data and develop appropriate spacecraft landing systems. Many processes contribute to Europa's landscape evolution, such as sputtering, mass wasting, thermal segregation, and impact gardening, driving the creation and distribution of icy regolith across the surface. While the efficacy of these processes are not well constrained, any amount of regolith emplaced at the surface will undergo subsequent processing due to sintering. Ice sintering is a form of frost metamorphism whereby contacting ice grains experience the diffusion of material into their contact region, forming a "neck" between them and densifying over time. Over long enough timescales, ice aggregates will sinter into solid material, which may contribute to the incorporation of non-ice material into Europa's subsurface and help to drive subsurface chemistry. Sintering also interacts with other processes, adding to the complexity of icy surface evolution. For example, sputtering preferentially removes larger grains and may enhance sintering rates, and changes in ice porosity may affect the response of the surface to micrometeorite impacts. Quantifying the effects of ice sintering will allow us to predict the microstructural properties of Europa's surface at spacecraft scales. To this end, we have modeled pressure-less (no overburden) sintering of spherical water-ice grains and validated the results with a laboratory experiment. We also modeled ice at the surface of Europa to obtain a first-order approximation of the sintering timescale and surface properties. Preliminary results indicate that ice grains will experience neck growth but not significant densification over Europa's surface age, suggesting that loose surface ice

  9. Synergistic Sintering of Lignite Fly Ash and Steelmaking Residues towards Sustainable Compacted Ceramics

    Directory of Open Access Journals (Sweden)

    V. G. Karayannis

    2017-01-01

    Full Text Available The development of value-added ceramic materials deriving only from industrial by-products is particularly interesting from technological, economic, and environmental point of views. In this work, the synergistic sintering of ternary and binary mixtures of fly ash, steelmaking electric arc furnace dust, and ladle furnace slag for the synthesis of compacted ceramics is reported. The sintered specimens’ microstructure and mineralogical composition were characterized by SEM-EDS and XRD, respectively. Moreover, the shrinkage, apparent density, water absorption, and Vickers microhardness (HV were investigated at different sintering temperatures and raw material compositions. The characterization of the sintered compacts revealed the successful consolidation of the ceramic microstructures. According to the experimental findings, the ceramics obtained from fly ash/steel dust mixtures exhibited enhanced properties compared to the other mixtures tested. Moreover, the processing temperature affected the final properties of the produced ceramics. Specifically, a 407% HV increase for EAFD and a 2221% increase for the FA-EAFD mixture were recorded, by increasing the sintering temperature from 1050 to 1150°C. Likewise, a 972% shrinkage increase for EAFD and a 577% shrinkage increase for the FA-EAFD mixture were recorded, by increasing the sintering temperature from 1050 to 1150°C. The research results aim at shedding more light on the development of sustainable sintered ceramics from secondary industrial resources towards circular economy.

  10. Science at the interface : grain boundaries in nanocrystalline metals.

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, Mark Andrew; Follstaedt, David Martin; Knapp, James Arthur; Brewer, Luke N.; Holm, Elizabeth Ann; Foiles, Stephen Martin; Hattar, Khalid M.; Clark, Blythe B.; Olmsted, David L.; Medlin, Douglas L.

    2009-09-01

    Interfaces are a critical determinant of the full range of materials properties, especially at the nanoscale. Computational and experimental methods developed a comprehensive understanding of nanograin evolution based on a fundamental understanding of internal interfaces in nanocrystalline nickel. It has recently been shown that nanocrystals with a bi-modal grain-size distribution possess a unique combination of high-strength, ductility and wear-resistance. We performed a combined experimental and theoretical investigation of the structure and motion of internal interfaces in nanograined metal and the resulting grain evolution. The properties of grain boundaries are computed for an unprecedented range of boundaries. The presence of roughening transitions in grain boundaries is explored and related to dramatic changes in boundary mobility. Experimental observations show that abnormal grain growth in nanograined materials is unlike conventional scale material in both the level of defects and the formation of unfavored phases. Molecular dynamics simulations address the origins of some of these phenomena.

  11. Extension of the master sintering curve for constant heating rate modeling

    Science.gov (United States)

    McCoy, Tammy Michelle

    The purpose of this work is to extend the functionality of the Master Sintering Curve (MSC) such that it can be used as a practical tool for predicting sintering schemes that combine both a constant heating rate and an isothermal hold. Rather than just being able to predict a final density for the object of interest, the extension to the MSC will actually be able to model a sintering run from start to finish. Because the Johnson model does not incorporate this capability, the work presented is an extension of what has already been shown in literature to be a valuable resource in many sintering situations. A predicted sintering curve that incorporates a combination of constant heating rate and an isothermal hold is more indicative of what is found in real-life sintering operations. This research offers the possibility of predicting the sintering schedule for a material, thereby having advanced information about the extent of sintering, the time schedule for sintering, and the sintering temperature with a high degree of accuracy and repeatability. The research conducted in this thesis focuses on the development of a working model for predicting the sintering schedules of several stabilized zirconia powders having the compositions YSZ (HSY8), 10Sc1CeSZ, 10Sc1YSZ, and 11ScSZ1A. The compositions of the four powders are first verified using x-ray diffraction (XRD) and the particle size and surface area are verified using a particle size analyzer and BET analysis, respectively. The sintering studies were conducted on powder compacts using a double pushrod dilatometer. Density measurements are obtained both geometrically and using the Archimedes method. Each of the four powders is pressed into ¼" diameter pellets using a manual press with no additives, such as a binder or lubricant. Using a double push-rod dilatometer, shrinkage data for the pellets is obtained over several different heating rates. The shrinkage data is then converted to reflect the change in relative

  12. Reactive Spark Plasma Sintering: Successes and Challenges of Nanomaterial Synthesis

    Directory of Open Access Journals (Sweden)

    Dina V. Dudina

    2013-01-01

    Full Text Available Spark plasma sintering (SPS, initially developed as an advanced sintering technique for consolidating nanopowders into nanostructured bulk materials, has been recently looked at in much broader perspective and gained a strong reputation of a versatile method of solid state processing of metals, ceramics, and composites. The powders in the SPS-dies experience the action of pulsed electric current and uniaxial pressure; they are heated at very high rates unachievable in furnace heating and sintered within shorter times and at lower temperatures than in conventional methods. The principle of SPS and convenient design of the facilities make it attractive for conducting solid state synthesis. In this paper, based on our own results and the literature data, we analyze the microstructure formation of the products of chemical reactions occurring in the SPS in an attempt to formulate the requirements to the microstructure parameters of reactant mixtures and SPS conditions that should be fulfilled in order to produce a nanostructured material. We present successful syntheses of nanostructured ceramics and metal matrix composite with nanosized reinforcements in terms of microstructure stability and attractive properties of the materials and discuss the challenges of making a dense nanostructured material when reaction and densification do not coincide during the SPS. In the final part of the paper, we provide an outlook on the further uses of reactive SPS in the synthesis of nanostructured materials.

  13. Characterization of Sintered and Sintered/Plasma-Nitrided Fe-1.5% Mo Alloy by SEM, X-Ray Diffraction and Electrochemical Techniques

    Directory of Open Access Journals (Sweden)

    Alves Neto José de Pinho

    2002-01-01

    Full Text Available Electrochemical experiments together with SEM and X-Ray techniques were carried out in order to evaluate the corrosion resistance, to analyze the surface condition and to characterize the nitride layer of the sintered and sintered/plasma-nitrided Fe-1.5% Mo alloy in Mg(NO32 0.5mol.L-1 solution (pH 7.0. The sintered/plasma-nitrided samples presented a higher corrosion resistance, indicating that the surface treatment improved the electrochemical properties of the sintered material. In addition, the nitride layer formed at 500 °C showed better corrosion resistance that the layers formed at higher temperatures. This difference can be ascribed to the nitrogen content in the nitride layer, which at 500°C is higher due to the formation of a phase rich in nitrogen (epsilon phase while at higher temperatures a phase poor in nitrogen (gamma' phase is formed.

  14. Sinterização ultra-rápida de materiais cerâmicos usando radiação laser Ultra-fast laser sintering of ceramic materials

    Directory of Open Access Journals (Sweden)

    Z. S. Macedo

    2000-12-01

    Full Text Available Nessa comunicação apresentamos nossos primeiros resultados de sinterização ultra-rápida em materiais cerâmicos óxidos usando a radiação de um laser de CO2 como fonte de aquecimento. Os compostos Bi4Ti3O12 (BIT e Bi4Ge3O12 (BGO foram sintetizados via reação do estado sólido, conformados em corpos cerâmicos cilíndricos de 12 mm de diâmetro e 2 mm de espessura e, posteriormente, levados ao laser para o processo de sinterização. A análise dos pós reagidos, efetuada por difratometria de raios X, confirmou a presença de fase cristalina única em cada um dos sistemas investigados. A potência máxima do laser necessária para a sinterização apresentou forte dependência com a estratégia usada na irradiação. A análise da microestrutura, realizada por microscopia eletrônica de varredura (MEV, revelou um alto grau de eficiência do processo desenvolvido. Em alguns casos, pudemos verificar que a sinterização ocorreu a uma profundidade de até 1 mm, apontando para a viabilidade de obtenção de corpos cerâmicos sinterizados como um todo.In this communication we present our first results on ultra-fast laser sintering of oxide ceramics employing a CO2 laser as the heating source. The Bi4Ti3O12 (BIT and Bi4Ge3O12 (BGO compounds were synthesized following a solid state route in air atmosphere. Cylindrical ceramic bodies with 12 mm in diameter and 2 mm in thickness were shaped and sintered under laser irradiation. The X-ray diffraction of the calcined powders confirmed the presence of single phase in each of the investigated systems. The maximum laser power required to the sintering process showed to have a strong dependency on the strategy used for irradiation. The microstructure analysis of the samples, performed by scanning electron microscopy (SEM, revealed the high efficiency of the process. In some cases we could verify that the sintering occurred until a depth of 1mm, indicating the feasibility of obtaining the ceramic bodies

  15. On the Mechanism of Microwave Flash Sintering of Ceramics

    Directory of Open Access Journals (Sweden)

    Yury V. Bykov

    2016-08-01

    Full Text Available The results of a study of ultra-rapid (flash sintering of oxide ceramic materials under microwave heating with high absorbed power per unit volume of material (10–500 W/cm3 are presented. Ceramic samples of various compositions—Al2O3; Y2O3; MgAl2O4; and Yb(LaO2O3—were sintered using a 24 GHz gyrotron system to a density above 0.98–0.99 of the theoretical value in 0.5–5 min without isothermal hold. An analysis of the experimental data (microwave power; heating and cooling rates along with microstructure characterization provided an insight into the mechanism of flash sintering. Flash sintering occurs when the processing conditions—including the temperature of the sample; the properties of thermal insulation; and the intensity of microwave radiation—facilitate the development of thermal runaway due to an Arrhenius-type dependency of the material’s effective conductivity on temperature. The proper control over the thermal runaway effect is provided by fast regulation of the microwave power. The elevated concentration of defects and impurities in the boundary regions of the grains leads to localized preferential absorption of microwave radiation and results in grain boundary softening/pre-melting. The rapid densification of the granular medium with a reduced viscosity of the grain boundary phase occurs via rotation and sliding of the grains which accommodate their shape due to fast diffusion mass transport through the (quasi-liquid phase. The same mechanism based on a thermal runaway under volumetric heating can be relevant for the effect of flash sintering of various oxide ceramics under a dc/ac voltage applied to the sample.

  16. AC susceptibility in amorphous and nanocrystalline Fe-Zr-B alloys

    International Nuclear Information System (INIS)

    Slawska-Waniewska, A.; Pont, M.; Lazaro, F.J.; Garcia, J.L.; Nowicki, P.; Munoz, J.S.

    1995-01-01

    AC susceptibility measurements show that in Fe 89 Zr 7 B 4 amorphous material the ferromagnetic-reentrant spin-glass transition follows the paramagnetic-ferromagnetic transition as the temperature is lowered, whereas the behavior of nanocrystalline sample is characteristic of ferromagnetic material. The results are interpreted in terms of a non-collinear magnetic structure in amorphous alloy which changes considerably after crystallization. ((orig.))

  17. High-level radioactive waste fixation in sintered vitreous matrix

    International Nuclear Information System (INIS)

    Russo, D.O.; Messi de Bernasconi, N.; Audero, M.A.

    1987-01-01

    The safe storage of high-level wastes from fuel elements reprocessing includes, as a first step, the fixation of the same in materials having a good resistance to the leaching in aqueous medium, such as borosilicate glass. As an alternative to the usual method of the molten glasses, a procedure for the sintering of a powdered glass and waste mixture at lower temperatures (600-700 deg C) has been developed, which minimizes the volatilization of active compounds during the process. Two glasses matrices of different composition and characteristics were used, to which the simulated wastes were added in the ratio of a 10% in weight of oxides. Two sintering techniques were employed 1: cold pressing and further sintering; 2: hot pressing and sintering under pressure. The densities were measured, the microstructure of the samples was analyzed and leaching essays were made in distilled water. The pellet's microstructure was observed by means of optical microscopy, by reflection in polished samples and by transparency in thin slices. The presence of crystalline compounds was analyzed by means of x rays and electron microprobe. The results have shown the convenience to continue with hot pressing essays, because a denser product with a higher resistance to the leaching is thus obtained. (M.E.L.) [es

  18. Microstructural optimization of solid-state sintered silicon carbide

    Science.gov (United States)

    Vargas-Gonzalez, Lionel R.

    Silicon carbide armor, manufactured through solid-state sintering, liquid-phase sintering, and hot-pressing, is being used by the United States Armed Forces for personal and vehicle protection. There is a lack of consensus, however, on which process results in the best-performing ballistic armor. Previous studies have shown that hot-pressed ceramics processed with secondary oxide and/or rare earth oxides, which exhibit high fracture toughness, perform well in handling and under ballistic impact. This high toughness is due to the intergranular nature of the fracture, creating a tortuous path for cracks and facilitating crack deflection and bridging. However, it has also been shown that higher-hardness sintered SiC materials might perform similarly or better to hot-pressed armor, in spite of the large fracture toughness deficit, if the microstructure (density, grain size, purity) of these materials are improved. In this work, the development of theoretically-dense, clean grain boundary, high hardness solid-state sintered silicon carbide (SiC) armor was pursued. Boron carbide and graphite (added as phenolic resin to ensure the carbon is finely dispersed throughout the microstructure) were used as the sintering aids. SiC batches between 0.25--4.00 wt.% carbon were mixed and spray dried. Cylindrical pellets were pressed at 13.7 MPa, cold-isostatically pressed (CIP) at 344 MPa, sintered under varying sintering soaking temperatures and heating rates, and varying post hot-isostatic pressing (HIP) parameters. Carbon additive amounts between 2.0--2.5 wt.% (based on the resin source), a 0.36 wt.% B4C addition, and a 2050°C sintering soak yielded parts with high sintering densities (˜95.5--96.5%) and a fine, equiaxed microstructure (d50 = 2.525 mum). A slow ramp rate (10°C/min) prevented any occurrence of abnormal grain growth. Post-HIPing at 1900°C removed the remaining closed porosity to yield a theoretically-dense part (3.175 g/cm3, according to rule of mixtures). These

  19. Structural, electrical and dielectric properties of nanocrystalline Mg-Zn ferrites

    International Nuclear Information System (INIS)

    Anis-ur-Rehman, M.; Malik, M.A.; Nasir, S.; Mubeen, M.; Khan, K.; Maqsood, A.

    2011-01-01

    The nanocrystalline Mg-Zn ferrites having general formula Mg/sub 1-x/Zn/sub x/Fe/sub 2/O/sub 4/ (x=0, 0.1, 0.2, 0.3, 0.4, 0. 5) were prepared by WOWS sol-gel route. All prepared samples were sintered at 700 deg. C for 2 h. X-ray powder diffraction (XRD) technique was used to investigate structural properties of the samples. The crystal structure was found to be spinel. The crystallite size, lattice parameters and porosity of samples were calculated by XRD data analysis as function of zinc concentration. The crystallite size for each sample was calculated using the Scherrer formula considering the most intense (3 1 1) peak and the range obtained was 34-68 nm. The dielectric constant, dielectric loss tangent and AC electrical conductivity of nanocrystalline Mg-Zn ferrites are investigated as a function of frequency. The dielectric constant, dielectric loss tangent increased with increase of Zn concentration. All the electrical properties are explained in accordance with Maxwell Wagner model and K/sub oops/ phenomenological theory. (author)

  20. A novel route for synthesis of nanocrystalline hydroxyapatite from eggshell waste.

    Science.gov (United States)

    Siva Rama Krishna, D; Siddharthan, A; Seshadri, S K; Sampath Kumar, T S

    2007-09-01

    The eggshell waste has been value engineered to a nanocrystalline hydroxyapatite (HA) by microwave processing. To highlight the advantages of eggshell as calcium precursor in the synthesis of HA (OHA), synthetic calcium hydroxide was also used to form HA (SHA) following similar procedure and were compared with a commercially available pure HA (CHA). All the HAs were characterized by X-ray powder diffraction (XRD) method, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and specific surface area measurements. Nanocrystalline nature of OHA is revealed through characteristic broad peaks in XRD patterns, platelets of length 33-50 nm and width 8-14 nm in TEM micrograph and size calculations from specific surface area measurements. FT-IR spectra showed characteristic bands of HA and additionally peaks of carbonate ions. The cell parameter calculations suggest the formation of carbonated HA of B-type. The OHA exhibits superior sinterability in terms of hardness and density than both SHA and CHA may be due to larger surface area of its spherulite structure. The in vitro dissolution study shows longer stability in phosphate buffer and cell culture test using osteoblast cells establishes biocompatibility of OHA.

  1. Transparent Yttrium Aluminium Garnet Obtained by Spark Plasma Sintering of Lyophilized Gels

    Directory of Open Access Journals (Sweden)

    M. Suárez

    2009-01-01

    Full Text Available Lyophilized YAG gel, synthesized by the coprecipitation technique, has been sintered to transparency by spark plasma sintering method at 1500∘C. Whereas conventionally dried gels show large agglomerates, over 1 μm, powders from lyophilized gels show no agglomeration with an average particle size below 100 nm. The absence of agglomerates affects on the optical properties of the sintered materials: conventionally dried powders are opaque after sintering, whereas 0.8 mm thick transparent YAG materials with in-line transmittances close to 60% at 680 nm and over 80% in the infrared range have been obtained for the lyophilized gels.

  2. Titanium Powder Sintering in a Graphite Furnace and Mechanical Properties of Sintered Parts

    OpenAIRE

    Changzhou Yu; Peng Cao; Mark Ian Jones

    2017-01-01

    Recent accreditation of titanium powder products for commercial aircraft applications marks a milestone in titanium powder metallurgy. Currently, powder metallurgical titanium production primarily relies on vacuum sintering. This work reported on the feasibility of powder sintering in a non-vacuum furnace and the tensile properties of the as-sintered Ti. Specifically, we investigated atmospheric sintering of commercially pure (C.P.) titanium in a graphite furnace backfilled with argon and stu...

  3. Fabrication and Characterization of Thermoelectric CrSi2 Compound by Mechanical Alloying and Spark Plasma Sintering.

    Science.gov (United States)

    Lee, Chung-Hyo

    2015-07-01

    A mixture of elemental Cr-Si powders has been subjected to mechanical alloying (MA) at room temperature to prepare CrSi2 thermoelectric compound.The MA powders were sintered at 800-1000 °C Cunder 60 MPa using spark plasma sintering (SPS) technique. Due to the observed larger loss of Si relative Cr during ball milling, the starting composition was modified to Cr30Si70, Cr31.5Si68.5 and Cr33Si67 to get a single phase of CrSi2 compound. The single phase CrSi2 has been obtained by MA of Cr31.5Si68.5 mixture powders for 70 h and subsequently sintered at 1000 °C. X-ray diffraction data shows that the SPS compact sintered at 1000 °C consists of only nanocrystalline CrSi2 compound with a grain size of 250 nm. The value of Seebeck coefficient of CrSi2 compound increases with temperature and reaches maximum value of 245 µV/K at 300 °C.

  4. Study of effect of sintering time on the 2223 phase growth Bi-Pb-Sr-Ca-Cu-O superconductor by Rietveld method

    International Nuclear Information System (INIS)

    Parikin; Prasuad, W; Gunawan

    1996-01-01

    It has been reported that the sintering time is as important for the preparation of superconductor as the sintering temperature and method. This paper reports on the finding of the optimum sintering time in the preparation of the 2223 phase bismuth (Bi) superconductor. The samples were synthesized with nominal composition 1.84 : 0.34 : 1.91 : 2.03 : 3.06 from raw materials by solid state reaction and sintered at 860 o C for five days. The resintering were done three times, i.e. 24, 48 and 96 hours. The Rietveld analysis shows that the 2223 phase grows continuously as a function of the sintering time. The highest percentage of the 2223 phase (80.64%) were obtained at 96 hours sintering time. The result suggests that the 2223 phase can be obtained effectively by sintering with sufficiently long time

  5. Advanced Magnetic Materials for Aircraft Power Applications

    National Research Council Canada - National Science Library

    McHenry, Michael

    2003-01-01

    ... new materials with improved magnetic and mechanical properties at high temperature. The group worked on the refinement of existing soft bulk materials while conducting research on novel nanocrystalline magnets in parallel...

  6. Electrical relaxation, optical and magnetic studies of nanocrystalline lithium ferrite synthesized by different chemical routes

    Science.gov (United States)

    Cheruku, Rajesh; Govindaraj, G.; Vijayan, Lakshmi

    2017-12-01

    The nanocrystalline lithium ferrite was synthesized by wet chemical methods such as solution combustion technique, sol-gel, and hydrothermal for a comparative study. Different characterization techniques like x-ray powder diffraction and thermal analysis were employed to confirm the structure and phase. Temperature-dependent Raman analysis was employed to classify the phonon modes associated with precise atomic motions existing in the synthesized materials. Morphology of sample surface was explored by scanning electron microscopy, and elemental analysis was done by energy dispersive spectroscopy analysis. The nanocrystalline nature of the materials was confirmed through transmission electron microscopy. Magnetic properties of these samples were explored through a vibrating sample magnetometer. Ac electrical impedance spectroscopy data were investigated using two Cole-Cole functions, and activation energies were calculated for all materials. Among them, solution combustion prepared lithium ferrite shows the highest conductivity and lowest activation energy.

  7. Small-angle neutron scattering investigations of nanocrystalline alloy chips obtained by machining

    Directory of Open Access Journals (Sweden)

    Elwyn Rebello

    2014-12-01

    Full Text Available Ultrafine-grained (UFG materials exhibit significantly enhanced mechanical properties. This has brought renewed attention on the use of large strain or severe plastic deformation as a means for achieving microstructural refinement in metals and alloys. Large plastic strains imposed in a machine chip result in significant microstructural refinement, including the creation of UFG and nanocrystalline materials. It looks to be an economical route for realizing nanocrystalline materials. In the present study, small-angle neutron scattering (SANS was employed to investigate the modifications in the microstructure of the chips produced via machining. Double crystal-based medium resolution SANS instrument has been used for this purpose. Significant scattering intensity at small enough angles reveals the presence of mesoscopic density fluctuations produced because of the machining. Atomic force microscopy images also corroborate the existence of such small length scale density fluctuations.

  8. Computational materials science: Nanoscale plasticity

    DEFF Research Database (Denmark)

    Jacobsen, Karsten Wedel; Schiøtz, Jakob

    2002-01-01

    How does plastic deformation of polycrystalline materials with grain sizes less than 100 nm look at the atomic scale? A large-scale molecular dynamics simulation of nanocrystalline alluminium reveals some surprising behaviour.......How does plastic deformation of polycrystalline materials with grain sizes less than 100 nm look at the atomic scale? A large-scale molecular dynamics simulation of nanocrystalline alluminium reveals some surprising behaviour....

  9. Spark plasma sintering and porosity studies of uranium nitride

    Science.gov (United States)

    Johnson, Kyle D.; Wallenius, Janne; Jolkkonen, Mikael; Claisse, Antoine

    2016-05-01

    In this study, a number of samples of UN sintered by the SPS method have been fabricated, and highly pure samples ranging in density from 68% to 99.8%TD - corresponding to an absolute density of 14.25 g/cm3 out of a theoretical density of 14.28 g/cm3 - have been fabricated. By careful adjustment of the sintering parameters of temperature and applied pressure, the production of pellets of specific porosity may now be achieved between these ranges. The pore closure behaviour of the material has also been documented and compared to previous studies of similar materials, which demonstrates that full pore closure using these methods occurs near 97.5% of relative density.

  10. Liquid Phase Sintering of Highly Alloyed Stainless Steel

    DEFF Research Database (Denmark)

    Mathiesen, Troels

    1996-01-01

    of boride to AISI 316L type steels have previously been studied, but were found to be sensitive to intergranular corrosion due to formation of intermetallic phases rich in chromium and molybdenum. In order to improve this system further, new investigations have focused on the use of higher alloyed stainless......Liquid phase sintering of stainless steel is usually applied to improve corrosion resistance by obtaining a material without an open pore system. The dense structure normally also give a higher strength when compared to conventional sintered steel. Liquid phase sintrering based on addition...... calculations, made by use of the computer programme Thermo-Calc, were also correlated with the observed microstructure. Corrosion measurements by electrochemical techniques show no signs of intergranular corrosion in contrast to the case of AISI 316L based steel. Furthermore most of the material showed...

  11. Alternative sintering methods compared to conventional thermal sintering for inkjet printed silver nanoparticle ink

    NARCIS (Netherlands)

    Niittynen, J.; Abbel, R.; Mäntysalo, M.; Perelaer, J.; Schubert, U.S.; Lupo, D.

    2014-01-01

    In this contribution several alternative sintering methods are compared to traditional thermal sintering as high temperature and long process time of thermal sintering are increasing the costs of inkjet-printing and preventing the use of this technology in large scale manufacturing. Alternative

  12. Qualitative mineralogical characterization of the sinter by X-ray diffraction

    International Nuclear Information System (INIS)

    Greca, M.C.; Pietroluongo, L.R.V.; Baliza, S.V.; Costa Pereira, E.A. da

    1987-01-01

    This paper aims the qualitative mineralogical characterization of sinters and raw materials employed on its fabrication, via X-ray diffraction technique. Thus, sample with constant coke breeze content and variable contents of sand, limestone, dunite and dolomite were prepared to obtain current sinter compositions, with variable basicity. The tests were performed at the research of the following institutions: Companhia Siderurgica Nacional, Centro de Tecnologia Mineral and Instituto Nacional de Tecnologia. (author) [pt

  13. Dilatometric study of anisotropic sintering of alumina/zirconia laminates with controlled fracture behaviour

    Czech Academy of Sciences Publication Activity Database

    Maca, K.; Pouchlý, V.; Drdlík, D.; Hadraba, Hynek; Chlup, Zdeněk

    2017-01-01

    Roč. 37, č. 14 (2017), s. 4287-4295 ISSN 0955-2219 R&D Projects: GA ČR(CZ) GA15-06390S; GA MŠk(CZ) LQ1601 Institutional support: RVO:68081723 Keywords : Alumina/zirconia laminate * Crack deflection * Master sintering curve * Sintering shrinkage Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass OBOR OECD: Ceramics Impact factor: 3.411, year: 2016

  14. An investigation in texturing high Tc superconducting ceramics by creep sintering

    International Nuclear Information System (INIS)

    Regnier, P.; Deschanels, X.; Maurice, F.; Schmirgeld, L.; Aguillon, C.; Senoussi, S.; Mac Carthy, M.; Tatlock, G.J.

    1991-01-01

    We study in detail the possibility of high-T c superconducting ceramics texturing by high pressing them during sintering. We show texture variations as a function of the applied load, of the deformation, of the temperature, and of the sintering stage length, of the rate of variation of temperature, of the material nature in contact with ceramic and of the original powder quality. We present results obtained by optical microscopy, electronic microscopy, X-rays, and local chemical analysis

  15. Review on Sintering Process of WC-Co Cemented Carbide in Metal Injection Molding Technology

    Science.gov (United States)

    Prathabrao, M.; Amin, Sri Yulis M.; Ibrahim, M. H. I.

    2017-01-01

    The objective of this paper is to give an overview on sintering process of WC-Co cemented carbides in metal injection molding technology. Metal injection molding is an advanced and promising technology in producing cemented nanostructured carbides. Cemented tungsten carbide (WC-Co) hard metal is known for its high hardness and wear resistance in various applications. Moreover, areas include fine grained materials, alternative binders, and alternative sintering techniques has been discussed in this paper.

  16. Synthesis and characterization of a nanocrystalline diamond aerogel

    Energy Technology Data Exchange (ETDEWEB)

    Pauzauskie, Peter J.; Crowhurst, Jonathan C.; Worsley, Marcus A.; Laurence, Ted A.; Kilcoyne, A. L. David; Wang, Yinmin; Willey, Trevor M.; Visbeck, Kenneth S.; Fakra, Sirine C.; Evans, William J.; Zaug, Joseph M.; Satcher, Jr., Joe H.

    2011-07-06

    Aerogel materials have myriad scientific and technological applications due to their large intrinsic surface areas and ultralow densities. However, creating a nanodiamond aerogel matrix has remained an outstanding and intriguing challenge. Here we report the high-pressure, high-temperature synthesis of a diamond aerogel from an amorphous carbon aerogel precursor using a laser-heated diamond anvil cell. Neon is used as a chemically inert, near-hydrostatic pressure medium that prevents collapse of the aerogel under pressure by conformally filling the aerogel's void volume. Electron and X-ray spectromicroscopy confirm the aerogel morphology and composition of the nanodiamond matrix. Time-resolved photoluminescence measurements of recovered material reveal the formation of both nitrogen- and silicon- vacancy point-defects, suggesting a broad range of applications for this nanocrystalline diamond aerogel.

  17. Mesoporous nanocrystalline film architecture for capacitive storage devices

    Science.gov (United States)

    Dunn, Bruce S.; Tolbert, Sarah H.; Wang, John; Brezesinski, Torsten; Gruner, George

    2017-05-16

    A mesoporous, nanocrystalline, metal oxide construct particularly suited for capacitive energy storage that has an architecture with short diffusion path lengths and large surface areas and a method for production are provided. Energy density is substantially increased without compromising the capacitive charge storage kinetics and electrode demonstrates long term cycling stability. Charge storage devices with electrodes using the construct can use three different charge storage mechanisms immersed in an electrolyte: (1) cations can be stored in a thin double layer at the electrode/electrolyte interface (non-faradaic mechanism); (2) cations can interact with the bulk of an electroactive material which then undergoes a redox reaction or phase change, as in conventional batteries (faradaic mechanism); or (3) cations can electrochemically adsorb onto the surface of a material through charge transfer processes (faradaic mechanism).

  18. Microwave combustion and sintering without isostatic pressure

    International Nuclear Information System (INIS)

    Ebadian, M.A.

    1998-01-01

    In recent years interest has grown rapidly in the application of microwave energy to the processing of ceramics, composites, polymers, and other materials. Advances in the understanding of microwave/materials interactions will facilitate the production of new ceramic materials with superior mechanical properties. One application of particular interest is the use of microwave energy for the mobilization of uranium for subsequent redeposition. Phase III (FY98) will focus on the microwave assisted chemical vapor infiltration tests for mobilization and redeposition of radioactive species in the mixed sludge waste. Uranium hexachloride and uranium (IV) borohydride are volatile compounds for which the chemical vapor infiltration procedure might be developed for the separation of uranium. Microwave heating characterized by an inverse temperature profile within a preformed ceramic matrix will be utilized for CVI using a carrier gas. Matrix deposition is expected to commence from the inside of the sample where the highest temperature is present. The preform matrix materials, which include aluminosilicate based ceramics and silicon carbide based ceramics, are all amenable to extreme volume reduction, densification, and vitrification. Important parameters of microwave sintering such as frequency, power requirement, soaking temperature, and holding time will be investigated to optimize process conditions for the volatilization of uranyl species using a reactive carrier gas in a microwave chamber

  19. Damage Behavior of Sintered Fiber Felts

    Directory of Open Access Journals (Sweden)

    Nicolas Lippitz

    2015-04-01

    Full Text Available The reduction of aircraft noise is important due to a rising number of flights and the growth of urban centers close to airports. During landing, a significant part of the noise is generated by flow around the airframe. To reduce that noise porous trailing edges are investigated. Ideally, the porous materials should to be structural materials as well. Therefore, the mechanical properties and damage behavior are of major interest. The aim of this study is to show the change of structure and the damage behavior of sintered fiber felts, which are promising materials for porous trailing edges, under tensile loading using a combination of tensile tests and three dimensional computed tomography scans. By stopping the tensile test after a defined stress or strain and scanning the sample, it is possible to correlate structural changes and the development of damage to certain features in the stress-strain curve and follow the damage process with a high spatial resolution. Finally, the correlation between material structure and mechanical behavior is demonstrated.

  20. Nanocrystalline diamond films for biomedical applications

    DEFF Research Database (Denmark)

    Pennisi, Cristian Pablo; Alcaide, Maria

    2014-01-01

    performance of nanocrystalline diamond films is reviewed from an application-specific perspective, covering topics such as enhancement of cellular adhesion, anti-fouling coatings, non-thrombogenic surfaces, micropatterning of cells and proteins, and immobilization of biomolecules for bioassays. In order...

  1. Synthesis and characterization of nanocrystalline zinc ferrite

    DEFF Research Database (Denmark)

    Jiang, J.S.; Yang, X.L.; Gao, L.

    1999-01-01

    Nanocrystalline zinc ferrite powders with a partially inverted spinel structure were synthesized by high-energy ball milling in a closed container at ambient temperature from a mixture of alpha-Fe2O3 and ZnO crystalline powders in equimolar ratio. From low-temperature and in-field Mossbauer...

  2. Multiphase Nanocrystalline Ceramic Concept for Nuclear Fuel

    International Nuclear Information System (INIS)

    Mecartnery, Martha; Graeve, Olivia; Patel, Maulik

    2017-01-01

    The goal of this research is to help develop new fuels for higher efficiency, longer lifetimes (higher burn-up) and increased accident tolerance in future nuclear reactors. Multiphase nanocrystalline ceramics will be used in the design of simulated advanced inert matrix nuclear fuel to provide for enhanced plasticity, better radiation tolerance, and improved thermal conductivity

  3. Chemical vapor deposition of nanocrystalline diamond films

    International Nuclear Information System (INIS)

    Vyrovets, I.I.; Gritsyna, V.I.; Dudnik, S.F.; Opalev, O.A.; Reshetnyak, O.M.; Strel'nitskij, V.E.

    2008-01-01

    The brief review of the literature is devoted to synthesis of nanocrystalline diamond films. It is shown that the CVD method is an effective way for deposition of such nanostructures. The basic technological methods that allow limit the size of growing diamond crystallites in the film are studied.

  4. Synthesis of nanocrystalline fluorinated hydroxyapatite by ...

    Indian Academy of Sciences (India)

    Fluorinated hydroxyapatite, (FHA, Ca10(PO4)6(OH)2-F), possesses higher corrosion resistance in biofluids than pure HA and reduces the risk of dental caries. The present work deals with the synthesis of nanocrystalline FHAs by microwave processing. The crystal size and morphology of the nanopowders were ...

  5. Multiphase Nanocrystalline Ceramic Concept for Nuclear Fuel

    Energy Technology Data Exchange (ETDEWEB)

    Mecartnery, Martha [Univ. of California, Irvine, CA (United States); Graeve, Olivia [Univ. of California, San Diego, CA (United States); Patel, Maulik [Univ. of Liverpool (United Kingdom)

    2017-05-25

    The goal of this research is to help develop new fuels for higher efficiency, longer lifetimes (higher burn-up) and increased accident tolerance in future nuclear reactors. Multiphase nanocrystalline ceramics will be used in the design of simulated advanced inert matrix nuclear fuel to provide for enhanced plasticity, better radiation tolerance, and improved thermal conductivity

  6. Characterisation of interfaces in nanocrystalline palladium

    Indian Academy of Sciences (India)

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

    Alternatively, it is possible to calculate power spectrum from each of the nanocrystalline grains in images scanned or recorded online using a framestore. Peak detection algorithms can then be applied to detect peak positions corresponding to the lattice periodicity in the grain. Advantages are that the process can be made ...

  7. Phonon density of states in nanocrystalline Fe

    Indian Academy of Sciences (India)

    Abstract. The Born–von Karman model is used to calculate phonon density of states (DOS) of nanocrystalline bcc Fe. It is found that there is an anisotropic stiffening in the interatomic force constants and hence there is shrinking in the nearest-neighbour distances in the nanophase. This leads to additional vibrational modes ...

  8. Characterization of nanocrystalline silicon germanium film and ...

    African Journals Online (AJOL)

    The nanocrystalline silicon-germanium films (Si/Ge) and Si/Ge nanotubes have low band gaps and high carrier mobility, thus offering appealing potential for absorbing gas molecules. Interaction between hydrogen molecules and bare as well as functionalized Si/Ge nanofilm and nanotube was investigated using Monte ...

  9. Structural, optical and photoluminescence study of nanocrystalline ...

    Indian Academy of Sciences (India)

    Undoped SnO2 thin films prepared by spray pyrolysis method reveal polycrystalline nature with prominent peaks along (110), (101) and (211) planes. All the films are nanocrystalline with particle size lying in the range of 3.14–8.6 nm calculated by DS formula. Orientation along plane (200) decreases continuously as molar ...

  10. Sintering of micro-trusses created by extrusion-3D-printing of lunar regolith inks

    Science.gov (United States)

    Taylor, Shannon L.; Jakus, Adam E.; Koube, Katie D.; Ibeh, Amaka J.; Geisendorfer, Nicholas R.; Shah, Ramille N.; Dunand, David C.

    2018-02-01

    The development of in situ fabrication methods for the infrastructure required to support human life on the Moon is necessary due to the prohibitive cost of transporting large quantities of materials from the Earth. Cellular structures, consisting of a regular network (truss) of micro-struts with ∼500 μm diameters, suitable for bricks, blocks, panels, and other load-bearing structural elements for habitats and other infrastructure are created by direct-extrusion 3D-printing of liquid inks containing JSC-1A lunar regolith simulant powders, followed by sintering. The effects of sintering time, temperature, and atmosphere (air or hydrogen) on the microstructures, mechanical properties, and magnetic properties of the sintered lunar regolith micro-trusses are investigated. The air-sintered micro-trusses have higher relative densities, linear shrinkages, and peak compressive strengths, due to the improved sintering of the struts within the micro-trusses achieved by a liquid or glassy phase. Whereas the hydrogen-sintered micro-trusses show no liquid-phase sintering or glassy phase, they contain metallic iron 0.1-2 μm particles from the reduction of ilmenite, which allows them to be lifted with magnets.

  11. Synthesis and characteristic of nanocrystalline La{sub 0.7}Sr{sub 0.3}MnO{sub 3} manganites by solid state reaction route

    Energy Technology Data Exchange (ETDEWEB)

    Astik, Nidhi, E-mail: nidhiastik2002@gmail.com; Jha, Prafulla K. [Department of physics, Faculty of Science, The M. S. University of Baroda, Vadodara (India); Patil, Swapnilkumar, E-mail: patilswapnilkumar@yahoo.co.in [Department of Physics, M. K. Bhavnagar University, Bhavnagar (India); Bhargava, Parag [Department of Metallurgical Engineering & Material Science, IIT-Bombay (India)

    2016-05-06

    Nanocrystalline stoichiometric La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (x=0.3) manganites have been synthesized through solid-state reaction by ball milling mechanical method at two different sintering temperatures 1250°C and 1350°C. The synthesized samples were characterized using X-ray diffraction (XRD) and found to have rhombohedral crystal structure (R-3c). The calcined samples exhibited a pure single phase perovskite, had a crystallite size of about 47-51 nm. The morphology of the prepared nanocrystalline manganites were recorded by the field emission gun-scanning electron microscope (FEG-SEM) and EDAX.

  12. NEUTRON IRRADIATION EFFECTS ON SPARK PLASMA SINTERED BORON CARBIDE

    OpenAIRE

    Buyuk, Bulent; Cengiz, Meral; Tugrul, A. Beril

    2015-01-01

    In this study, spark plasma sintered boron carbide (B4C) was examined against neutrons. The specimens were irradiated by reactor neutrons (include both thermal and fast neutrons) up to fluence of 1.37x1021n m-2. Thermal and fast neutrons cause swelling by different interactions with boron (10B) atoms in the related materials. X-Ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images were investigated for initial and irradiated samples. In addition, lattice parameters and ...

  13. Preparation and properties of low cement castable sintered at different temperatures

    Directory of Open Access Journals (Sweden)

    Sanja Martinović

    2009-12-01

    Full Text Available The low cement high alumina castable (LCC studied in this paper was synthesised, cured and then treated at different sintering temperatures. Since any inhomogeneity introduced during the castable preparation can remain inside the material degrading its properties and therefore the quality during service life, particular attention was given to the processing procedure in order to produce the material with the optimum characteristics. Composition of the castable regarding particle size distribution was adjusted according to the Andreassen’s packing model. The samples were sintered at 1100, 1300 and 1600°C for three hours. Influence of the different sintering temperatures on the castable properties is discussed. Compressive and flexural strengths were determined by destructive testing method, while the water immersion method was used for determination of the bulk density and the water absorption. Changes of elastic properties and microstructure (porosity were observed by the non-destructive testing methods, ultrasonic measurements and image analysis. Based on the results, it can be concluded that sintering temperature has strong influence on the properties of the LCC. Exceptionally good properties were obtained for the sample sintered at 1600°C, but it should be highlighted that the samples treated at 1100 and 1300°C were provided with good properties, too. This should not be neglected because of the energy saving importance, in cases where the material sintered at lower temperature satisfies the application requirements.

  14. Record-low sintering-temperature (600 °C) of solid-oxide fuel cell electrolyte

    Energy Technology Data Exchange (ETDEWEB)

    Dasari, Hari Prasad, E-mail: energyhari@nitk.edu.in [High-Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Chemical Engineering Department, National Institute of Technology Karnataka, Mangalore 575025, Karnataka (India); Ahn, Kiyong; Park, Sun-Young; Hong, Jongsup; Kim, Hyoungchul; Yoon, Kyung Joong; Son, Ji-Won; Kim, Byung-Kook; Lee, Hae-Weon [High-Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Lee, Jong-Ho, E-mail: jongho@kist.re.kr [High-Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of)

    2016-07-05

    One of the major problems arising with Solid-Oxide Fuel Cell (SOFC) electrolyte is conventional sintering which requires a very high temperature (>1300 °C) to fully density the electrolyte material. In the present study, the sintering temperature of SOFC electrolyte is drastically decreased down to 600 °C. Combinational effects of particle size reduction, liquid-phase sintering mechanism and microwave sintering resulted in achieving full density in such a record-low sintering temperature. Gadolinium doped Ceria (GDC) nano-particles are synthesized by co-precipitation method, Lithium (Li), as an additional dopant, is used as liquid-phase sintering aid. Microwave sintering of this electrolyte material resulted in decreasing the sintering temperature to 600 °C. Micrographs obtained from Scanning/Transmission Electron Microscopy (SEM/TEM) clearly pointed a drastic growth in grain-size of Li-GDC sample (∼150 nm) than compared to GDC sample (<30 nm) showing the significance of Li addition. The sintered Li-GDC samples displayed an ionic conductivity of ∼1.00 × 10{sup −2} S cm{sup −1} at 600 °C in air and from the conductivity plots the activation energy is found to be 0.53 eV. - Highlights: • Sintering temperature is drastically decreased to 600 °C. • Key factors: Particle size reduction, liquid-phase and microwave sintering. • Nano-Li-GDC sample has ionic conductivity of ∼1.00 × 10{sup −2} S cm{sup −1} at 600 °C in air.

  15. In-situ anatase phase stabilization of titania photocatalyst by sintering in presence of Zr4+ organic salts

    Science.gov (United States)

    Strini, Alberto; Sanson, Alessandra; Mercadelli, Elisa; Bendoni, Riccardo; Marelli, Marcello; Dal Santo, Vladimiro; Schiavi, Luca

    2015-08-01

    The direct in-situ stabilization of an anatase-based nanocrystalline photocatalyst (Degussa P25) was obtained by sintering the catalyst powder in presence of Zr4+ organic salts. This approach allows the doping of an already-formed nanocrystalline photocatalyst instead of introducing the dopant in the crystal lattice during the catalyst synthesis. The procedure was demonstrated by the production of thick ceramic layers using the screen printing technique. This new method allows to easily stabilize the anatase phase 200 °C higher than the undoped P25 maintaining the same photocatalytic activity. The process was studied using specifically formulated screen-printing inks added with Zr4+ organic salt at 1% and 2% Zr/Ti molar ratio. The anatase phase stability was investigated in the 500-900 °C temperature range analysing the resulting catalysts with XRD, TEM and (S)TEM-EDS. The catalytic activity of the screen-printed layers was assessed by measuring the degradation of toluene in air at ambient concentration (500 nmol m-3) and low UV-A irradiance (180 μW cm-2). The described in-situ stabilization method could be potentially applied to any deposition process involving already formed anatase photocatalyst, allowing higher sintering temperature and then an improved mechanical stability of the active layers without photocatalytic activity degradation.

  16. The role of the native oxide shell on the microwave sintering of copper metal powder compacts

    International Nuclear Information System (INIS)

    Mahmoud, Morsi M.; Link, Guido; Thumm, Manfred

    2015-01-01

    Highlights: • Thin oxide native layer had a critical role on microwave sintering of copper. • Explain why microwaves interact with copper powder differently than its bulk. • Abnormal expansion in copper is due to the plastic deformation and crack formation. • In-situ setup gives important insight about the microwave sintering of metals. • Microwave sintering is a promising candidate technology in powder metallurgy. - Abstract: Successful microwave sintering of several metal powders had been reported by many researchers with remarkable improvements in the materials properties and/or in the overall process. However, the concept behind microwave heating of metal powders has not been fully understood till now, as it is well known that bulk metals reflect microwaves. The progress of microwave sintering of copper metal powder compacts was investigated via combining both in-situ electrical resistivity and dilatometry measurements that give important information about microstructural changes with respect to the inter-particle electrical contacts during sintering. The sintering behavior of copper metal powders was depending on the type of the gas used, particle size, the initial green density, the soaking sintering time and the thin oxide layer on the particles surfaces. The thin copper oxide native layer (ceramics) that thermodynamically formed on the particles surfaces under normal handling and ambient environmental conditions had a very critical and important role in the microwave absorption and interaction, the sintering behavior and the microstructural changes. This finding could help to have a fundamental understanding of why MW’s interact with copper metal powder in a different way than its bulk at room temperature, i.e. why a given metal powder could be heated using microwaves while its bulk reflects it

  17. Magnetic ageing study of high and medium permeability nanocrystalline FeSiCuNbB alloys

    Energy Technology Data Exchange (ETDEWEB)

    Lekdim, Atef, E-mail: atef.lekdim@univ-lyon1.fr; Morel, Laurent; Raulet, Marie-Ange

    2017-04-15

    increasing the energy efficiency is one of the most important issues in modern power electronic systems. In aircraft applications, the energy efficiency must be associated with a maximum reduction of mass and volume, so a high components compactness. A consequence from this compactness is the increase of operating temperature. Thus, the magnetic materials used in these applications, have to work at high temperature. It raises the question of the thermal ageing problem. The reliability of these components operating at this condition becomes a real problem which deserves serious interest. Our work takes part in this context by studying the magnetic material thermal ageing. The nanocrystalline materials are getting more and more used in power electronic applications. Main advantages of nanocrystalline materials compared to ferrite are: high saturation flux density of almost 1.25 T and low dynamic losses for low and medium frequencies. The nanocrystalline Fe{sub 73.5}Cu{sub 1}Nb{sub 3}Si{sub 15.5}B{sub 7} alloys have been chosen in our aging study. This study is based on monitoring the magnetic characteristics for several continuous thermal ageing (100, 150, 200 and 240 °C). An important experimental work of magnetic characterization is being done following a specific monitoring protocol. Elsewhere, X-Ray Diffraction and magnetostriction measurements were carried out to support the study of the anisotropy energies evolution with ageing. This latter is discussed in this paper to explain and give hypothesis about the ageing phenomena. - Highlights: • The magnetic ageing of the nanocrystalline materials is related to their annealing. • The degradations with ageing are not related to a change of the grain size diameter. • The amount of anisotropies introduced with ageing depends just on ageing conditions.

  18. Master sintering curves of two different alumina powder compacts

    Directory of Open Access Journals (Sweden)

    Vaclav Pouchly

    2009-12-01

    Full Text Available Concept of Master Sintering Curve is a strong tool for optimizing sintering schedule. The sintering behaviour can be predicted, and sintering activation energy can be calculated with the help of few dilatometric measurements. In this paper an automatic procedure was used to calculate Master Sintering Curves of two different alumina compacts. The sintering activation energies were determined as 640 kJ/mol for alumina with particle size of 240 nm, respective 770 kJ/mol for alumina with particle size of 110 nm. The possibility to predict sintering behaviour with the help of Master Sintering Curve was verified.

  19. Sintering characteristics of nano-ceramic coatings

    NARCIS (Netherlands)

    de Hosson, J.T.M.; Popma, R.

    2003-01-01

    This paper concentrates on sintering characteristics of nano-sized ceramic SiO2 particles. The sintering process is studied as a function of temperature using a conventional furnace and using a laser beam. The underlying idea is to combine the nanoceramic sol-gel concept with inkjet technology and

  20. Kinetic analysis of boron carbide sintering

    International Nuclear Information System (INIS)

    Borchert, W.; Kerler, A.R.

    1975-01-01

    The kinetics of the sintering of boron carbide were investigated by shrinkage measurements with a high-temperature dilatometer under argon atmosphere in dependence on temperature, grain size, and pressure. The activation energies and the reaction mechanisms of the different stages of sintering were determined. (orig.) [de

  1. Electro sinter forging of titanium disks

    DEFF Research Database (Denmark)

    Cannella, Emanuele; Nielsen, Chris Valentin; Bay, Niels Oluf

    Electro sinter forging (ESF) is a new sintering process based on the principle of electrical Joule heating. In the present work, middle frequency direct current (MFDC) was flowing through the powder compact, which was under mechanical pressure. The main parameters are the high electrical current,...

  2. Sintering of ultra high molecular weight polyethylene

    Indian Academy of Sciences (India)

    Abstract. Ultra high molecular weight polyethylene (UHMWPE) is a high performance polymer having low coefficient of friction, good abrasion resistance, good chemical ... In this study, we report our results on compaction and sintering behaviour of two grades of UHMWPE with reference to the powder morphology, sintering ...

  3. Sintered-to-size FBR fuel

    International Nuclear Information System (INIS)

    Rasmussen, D.E.; Schaus, P.S.

    1984-04-01

    Fabrication of sintered-to-size PuO 2 -UO 2 fuel pellets was completed for testing of proposed FBR product specifications. Approximately 6000 pellets were fabricated to two nominal diameters and two densities by cold pressing and sintering to size. Process control and correlation between test and production batches are discussed

  4. Sintering of zirconia in high-pressure

    International Nuclear Information System (INIS)

    Kunrath, A.O.; Strohaecker, T.R.; Pereira, A.S.; Jornada, J.A.H. da; Piermarini, G.J.

    1989-01-01

    A systematic study about the sintering of zirconia hyperfines powders in high-pressure is presented. The differents conditions effect of sintering in microstructure and in hardness and tenacity properties of zirconia samples with a very fine grain is also studied. (C.G.C.) [pt

  5. Modeling the microstructural evolution during constrained sintering

    DEFF Research Database (Denmark)

    Bjørk, Rasmus; Frandsen, Henrik Lund; Tikare, V.

    A numerical model able to simulate solid state constrained sintering of a powder compact is presented. The model couples an existing kinetic Monte Carlo (kMC) model for free sintering with a finite element (FE) method for calculating stresses on a microstructural level. The microstructural respon...

  6. Modeling the Microstructural Evolution During Constrained Sintering

    DEFF Research Database (Denmark)

    Bjørk, Rasmus; Frandsen, Henrik Lund; Pryds, Nini

    2015-01-01

    A numerical model able to simulate solid-state constrained sintering is presented. The model couples an existing kinetic Monte Carlo model for free sintering with a finite element model (FEM) for calculating stresses on a microstructural level. The microstructural response to the local stress as ...

  7. Mechanical characteristics of microwave sintered silicon carbide

    Indian Academy of Sciences (India)

    Unknown

    Central Glass and Ceramic Research Institute, Kolkata 700 032, India. Abstract. The present work deals with the sintering of ... recently become an attractive area of research and deve- lopment. The major advantages of ... without the usage of sintering aids (Lee and Case 1999;. Goldstein et al 1999). Several studies have ...

  8. Evaluation of the Cutting Force Components and the Surface Roughness in the Milling Process of Micro- and Nanocrystalline Titanium

    Directory of Open Access Journals (Sweden)

    Habrat W.

    2016-09-01

    Full Text Available Nanocristalline pure titanium in comparison to microcrystalline titanium is characterized by better mechanical properties which influence its wider usability. The aim of the research was to evaluate whether the grain size of pure titanium (micro- and nanocrystalline has influence on the cutting force components and the surface roughness in the milling process. Models of cutting force components for both materials were prepared and differences between the results were examined. The feed rate effect on selected parameters of surface roughness after milling of micro- and nanocrystalline pure titanium was determined.

  9. Mix-solvent-thermal method for the synthesis of anatase nanocrystalline titanium dioxide used in dye-sensitized solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Lao, Chunfeng; Chuai, Yutao; Su, Li; Liu, Xiao; Huang, Lan; Cheng, Humin; Zou, Dechun [Department of Polymer Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 (China)

    2005-01-31

    Nanocrystalline TiO{sub 2} with almost pure anatase form has been synthesized through the Mix-solvent-thermal method (MST) by using TiCl{sub 4} as the starting material. The mean size of the synthesized TiO{sub 2} is 10nm with narrow distribution. High-performance dye-sensitized solar cell with nanocrystalline TiO{sub 2} electrode formed from MST was achieved. Its Isc and Voc values reached 21.62mA/cm{sup 2} and 727.9mV, respectively, and the photovoltaic conversion efficiency reached 9.13%, i.e. 7.5% higher than those of solar cells with TiO{sub 2} made from the traditional precursor of titanium alkoxides. To our knowledge they are the highest values obtained from the solar cells with nanocrystalline TiO{sub 2} electrode formed from the hydrolysis of TiCl{sub 4}.

  10. Sintered ceramics having controlled density and porosity

    International Nuclear Information System (INIS)

    Brassfield, H.C.; DeHollander, W.R.; Nivas, Y.

    1980-01-01

    A new method was developed for sintering ceramic uranium dioxide powders, in which ammonium oxalate is admixed with the powder prior to being pressed into a cylindrical green body, so that the end-point density of the final nuclear-reactor fuel product can be controlled. When the green body is heated, the ammonium oxalate decomposes and leaves discrete porosity in the sintered body, which corresponds to the ammonium oxalate regions in the green body. Thus the end-point density of the sintered body is a function of the amount of ammonium oxalate added. The final density of the sintered product is about 90-97% of the theoretical. The addition of ammonium oxalate also allows control of the pore size and distribution throughout the fuel. The process leaves substantially no impurities in the sintered strucuture. (DN)

  11. Consolidation & Factors Influencing Sintering Process in Polymer Powder Based Additive Manufacturing

    Science.gov (United States)

    Sagar, M. B.; Elangovan, K.

    2017-08-01

    Additive Manufacturing (AM) is two decade old technology; where parts are build layer manufacturing method directly from a CAD template. Over the years, AM techniques changes the future way of part fabrication with enhanced intricacy and custom-made features are aimed. Commercially polymers, metals, ceramic and metal-polymer composites are in practice where polymers enhanced the expectations in AM and are considered as a kind of next industrial revolution. Growing trend in polymer application motivated to study their feasibility and properties. Laser sintering, Heat sintering and Inhibition sintering are the most successful AM techniques for polymers but having least application. The presentation gives up selective sintering of powder polymers and listed commercially available polymer materials. Important significant factors for effective processing and analytical approaches to access them are discussed.

  12. Determinants of the quality of sintered steel for the automotive industry

    Directory of Open Access Journals (Sweden)

    Barbara Lisiecka

    2016-03-01

    Full Text Available The increasing demand on components obtained using powder metallurgy is driven by economic changes that have turned product quality into the most basic criterion which affects the interest in a component and its successful use. The improvement in quality should be expected in the beginning of the planning of the technological process and selection of adequate raw materials. High requirements concerning product quality management and production improvement stimulates the development of the current automotive industry where sintered steels represent the highest percentage of products. The multiphase sinters investigated in the study were prepared from two types of water–atomized steel powders: 316L and 409L. Optical microscopy, X–ray phase analysis and examinations of microhardness were performed in order to determine the microstructure and basic properties of sintered steels. The main assumption for this study was to analyse the microstructure and mechanical properties of sintered steels used for manufacturing of various car parts.

  13. Effect of sintering temperatures on titanium matrix composites reinforced by ceramic particles

    Energy Technology Data Exchange (ETDEWEB)

    Romero, F.; Amigo, V.; Busquets, D.; Klyatskina, E. [Mechanical and Materials Engineering Department. Polytechnical University of Valencia, Valencia (Spain)

    2005-07-01

    Titanium and titanium composites have a potential use in aerospace and biotechnology industries, and nowadays in others like sports and fashion ones. In this work composite materials, based on titanium matrix reinforced with ceramic particles, have been developed. PM route is used to obtain compact and sintered samples. TiN and TiAl powders, are milled with Ti powder in different volumetric percentages in a ball mill. These mixtures are pressed in a uniaxial press and sintered in a vacuum furnace at different temperatures between 1180 to 1220 deg. C. Porosity of samples is analysed, before and after the sintering process, by Archimedes technique and by image analysis. Mechanical properties and the reinforcement particles influence in the titanium matrix are studied by flexion test in green and sintered states, and by hardness and microhardness tests. Complimentarily, a microstructural analysis is carried out by optical and electron microscopy, and the reactivity between the reinforce particles and titanium matrix are studied. (authors)

  14. Comparative optical investigations of sintered and monocrystalline black and green silicon carbide (SiC)

    International Nuclear Information System (INIS)

    Werheit, H.; Schwetz, K.A.

    2004-01-01

    Crystalline SiC appears in many different polytypes of cubic, hexagonal, and rhombohedral structures. These polytypes are colorless transparent or exhibit various colors evoked by doping with different elements. Dense sintered S-SiC (solid-state sintered) and LPS-SiC (liquid-phase sintered) were known in black color only, but recently a new liquid-phase sintering process was developed to achieve green LPS-SiC as well. Whereas in S-SiC the polycrystalline grains are homogeneously doped with 0.2 wt% boron, in the LPS-types the SiC grains contain up to 1.2 wt% Al, 0.3 wt% N and 0.1% O having a structure comprising a SiC(Al,N,O) mixed crystal shell and a pure SiC core. The difference in color of polycrystalline SiC bodies seems to result from small amounts of carbon in the sintered specimens (0.2-0.5 wt% C). Green sintered LPS-SiC is obtained, after free carbon has largely been removed by a suitable oxidation process prior to sintering. To get information on the various types of sintered SiC, the optical extinction and absorption spectra of black and green sintered SiC and green Acheson-SiC single crystals were quantitatively measured in the spectral range between about 1.4 and 4.1 eV. While the absorption coefficients of the single crystals vary between about 50 and 200 cm -1 , the extinction coefficients of the sintered materials are between 2000 and 7000 cm -1 . Nevertheless the absorption bands in the more or less transparent region of the green and black materials can easily be attributed to one another. Hence, the reason for these absorption processes must be assumed to be the same. In the same way, position and slope of the absorption edges are correlated amongst green or black SiC, irrespective of, whether the material is single crystal or sintered

  15. Synthesis of Nanocrystalline MgO Particles by Combustion Followed by Annealing Method Using Hexamine as a Fuel

    Directory of Open Access Journals (Sweden)

    S. Balamurugan

    2014-01-01

    Full Text Available In this work, nanocrystalline MgO particles were prepared through combustion method using magnesium nitrate as oxidizer and hexamine as a fuel. The materials obtained by combustion method were subsequently annealed at 800°C for 3 h to improve the crystallinity and phase purity. The obtained MgO nanomaterials were characterized by powder X-ray diffraction analysis (XRD, infrared (IR spectroscopy, photoluminescence (PL, near-infrared (NIR spectroscopy, and scanning electron microscopy (SEM. The cubic crystal structure with lattice parameter, a = 0.4210(4 nm with average crystalline size of 22 nm, is obtained for the nano-MgO particles. The PL emission spectrum of nanocrystalline MgO materials exhibits three emission peaks at 432, 465, and 495 nm which are due to various structural defects. The SEM results expose the fact that the MgO nanomaterials are seemingly porous and highly agglomerated with fine particles. Owing to the higher reflectance of prepared nanocrystalline MgO, it can be used as NIR reflective pigments. The present results prove that the combustion technique using hexamine can produce the materials with high crystallinity. To the best of our knowledge, this is the first report on the synthesis of nanocrystalline MgO materials by combustion method using hexamine as a fuel.

  16. Comment on "Mitigating grain growth in binary nanocrystalline alloys through solute selection based on thermodynamic stability maps"

    Czech Academy of Sciences Publication Activity Database

    Lejček, Pavel; Hofmann, S.

    2015-01-01

    Roč. 107, Sep (2015), s. 235-237 ISSN 0927-0256 R&D Projects: GA ČR GBP108/12/G043 Institutional support: RVO:68378271 Keywords : nanocrystalline materials * grain size * grain boundary energy * grain boundary segregation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.086, year: 2015

  17. THERMALLY STABLE NANOCRYSTALLINE TIO2 PHOTOCATALYSTS SYNTHESIZED VIA SOL-GEL METHODS MODIFIED WITH IONIC LIQUID AND SURFACTANT MOLECULES

    Science.gov (United States)

    Recently, sol-gel methods employing ionic liquids (ILs) have shown significant implications for the synthesis of well-defined nanostructured inorganic materials. Herein, we synthesized nanocrystalline TiO2 particles via an alkoxide sol-gel method employing a water-immi...

  18. A nanocrystalline Sm-Co compound for high-temperature permanent magnets.

    Science.gov (United States)

    Zhang, Zhexu; Song, Xiaoyan; Qiao, Yinkai; Xu, Wenwu; Zhang, Jiuxing; Seyring, Martin; Rettenmayr, Markus

    2013-03-21

    The inherently high magnetic anisotropy and nanoscale grain size in a Sm5Co19 compound result in an intrinsic coercivity far higher than those of known Sm-Co compounds prior to orientation treatment. The combination of ultrahigh intrinsic coercivity, high Curie temperature and low coercivity temperature coefficient of nanocrystalline Sm5Co19 as a single phase material shows it to be a very promising compound to develop outstanding high-temperature permanent magnets.

  19. Nanostructured CoSi Obtained by Spark Plasma Sintering

    Science.gov (United States)

    Longhin, Marco; Viennois, Romain; Ravot, Didier; Robin, Jean-Jacques; Villeroy, Benjamin; Vaney, Jean-Baptiste; Candolfi, Christophe; Lenoir, Bertrand; Papet, Philippe

    2015-06-01

    Cobalt monosilicide is a cheap, environmentally friendly thermoelectric material for medium temperatures (200-700°C). While its power factor is similar to the state-of-the-art thermoelectric materials, its thermal conductivity is too large to reach high ZT values. Nanostructuring might be an interesting strategy to reduce the phonon mean free path thereby improving the thermoelectric performance. In this paper, we report on a 35% reduction of the thermal conductivity of n-type CoSi by a nanostructuring approach. CoSi nanostructured powders were synthesized by arc melting, followed by 4° h mechanical milling. By optimizing the spark plasma sintering thermal and pressure cycle, pellets with 5â€"10% porosity were obtained. During sintering, a small amount of Co2Si extra phase appeared and grains coarsened. After sintering, the pellets remained nanostructured, with an averaged grain size of 70 nm. The reduction of thermal conductivity is ascribed to a decrease in both the electronic and lattice contributions. The former is directly related to a decrease in the electrical conductivity, which appears to be the limiting factor preventing nanostructured CoSi from reaching enhanced thermoelectric performances.

  20. PRODUCTION OF PROTOTYPE PARTS USING DIRECT METAL LASER SINTERING TECHNOLOGY

    Directory of Open Access Journals (Sweden)

    Josef Sedlak

    2015-08-01

    Full Text Available Unconventional methods of modern materials preparation include additive technologies which involve the sintering of powders of different chemical composition, granularity, physical, chemical and other utility properties. The technology called Rapid Prototyping, which uses different technological principles of producing components, belongs to this type of material preparation. The Rapid Prototyping technology facilities use photopolymers, thermoplastics, specially treated paper or metal powders. The advantage is the direct production of metal parts from input data and the fact that there is no need for the production of special tools (moulds, press tools, etc.. Unused powder from sintering technologies is re-used for production 98% of the time, which means that the process is economical, as well as ecological.The present paper discusses the technology of Direct Metal Laser Sintering (DMLS, which falls into the group of additive technologies of Rapid Prototyping (RP. The major objective is a detailed description of DMLS, pointing out the benefits it offers and its application in practice. The practical part describes the production and provides an economic comparison of several prototype parts that were designed for testing in the automotive industry.

  1. Mineralogy and microstructure of sintered lignite coal fly ash

    Energy Technology Data Exchange (ETDEWEB)

    Marina Ilic; Christopher Cheeseman; Christopher Sollars; Jonathan Knight [Faculty of Technology and Metallurgy, Belgrade (Yugoslavia)

    2003-02-01

    Lignite coal fly ash from the 'Nikola Tesla' power plant in Yugoslavia has been characterised, milled, compacted and sintered to form monolithic ceramic materials. The effect of firing at temperatures between 1130 and 1190{sup o}C on the density, water accessible porosity, mineralogy and microstructure of sintered samples is reported. This class C fly ash has an initial average particle size of 82 {mu}m and contains siliceous glass together with the crystalline phases quartz, anorthite, gehlenite, hematite and mullite. Milling the ash to an average particle size of 5.6 m, compacting and firing at 1170{sup o}C for 1 h produces materials with densities similar to clay-based ceramics that exhibit low water absorption. Sintering reduces the amount of glass, quartz, gehlenite and anhydrite, but increases formation of anorthite, mullite, hematite and cristobalite. SEM confirms the formation of a dense ceramic at 1170{sup o}C and indicates that pyroplastic effects cause pore formation and bloating at 1190{sup o}C. 23 refs., 6 figs., 2 tabs.

  2. Strain rate dependency of laser sintered polyamide 12

    Directory of Open Access Journals (Sweden)

    Cook J.E.T.

    2015-01-01

    Full Text Available Parts processed by Additive Manufacturing can now be found across a wide range of applications, such as those in the aerospace and automotive industry in which the mechanical response must be optimised. Many of these applications are subjected to high rate or impact loading, yet it is believed that there is no prior research on the strain rate dependence in these materials. This research investigates the effect of strain rate and laser energy density on laser sintered polyamide 12. In the study presented here, parts produced using four different laser sintered energy densities were exposed to uniaxial compression tests at strain rates ranging from 10−3 to 10+3 s−1 at room temperature, and the dependence on these parameters is presented.

  3. Nanocrystalline hydroxyapatite prepared under various pH conditions

    Science.gov (United States)

    Palanivelu, R.; Mary Saral, A.; Ruban Kumar, A.

    2014-10-01

    Hydroxyapatite (HAP) has sovereign biomedical application due to its excellent biocompatibility, chemical and crystallographic similitude with natural human bone. In this present work, we discussed about the role of pH in the synthesis of calcium phosphate compound using calcium nitrate tetrahydrate and di-ammonium hydrogen phosphate as starting materials by chemical precipitation method assisted with ultrasonic irradiation technique. 5% polyethylene glycol (PEG600) is added along with the precursors under various pH condition of 7, 9 and 11 respectively. The functional group analysis, crystallized size and fraction of crystallized size are confirmed using Fourier Transformation Infra-Red spectroscopy and X-ray diffraction pattern. Morphological observations are done by scanning electron microscope. The results revealed the presence of nanocrystalline hydroxyapatite at pH above 9.

  4. Nanocrystalline metal-superconductor powders produced by aerosol decomposition

    International Nuclear Information System (INIS)

    Carim, A.H.; Doherty, P.; Kodas, T.T.

    1990-01-01

    This paper reports on composite silver---YBa 2 Cu 3 O 7-δ powders with nanocrystalline and larger sizes produced by aerosol techniques at 1000 degrees C and 930 degrees C. Silver is incorporated primarily in the elemental form, although particles of hexagonal Ag 2 O are also observed when the reactor is operated below the Ag-O eutectic temperature (939 degree C). Longer reactor residence times (>35 s, as opposed to c > 90K) can still be obtained in the composite powders. Aerosol decomposition of Y-Ba-Cu nitrate precursors with Pt additions did not produce superconductive material; instead, most of the resultant particles were Pt-Y-Ba-Cu-O compounds

  5. Liquid phase sintered SiC ceramics from starting materials of different grade Cerâmicas à base de SiC sinterizadas via fase líquida a partir de matérias-primas de diferentes purezas

    Directory of Open Access Journals (Sweden)

    V. A. Izhevskyi

    2004-09-01

    Full Text Available Possibility of high performance ceramics manufactured from commercial SiC powder of technical grade has been shown. Sintering behavior and microstructure formation under conditions of liquid phase sintering (LPS with oxynitride sintering aids (AlN-Y2O3 of three SiC-based compositions have been investigated. Two of the compositions were based on Alcoa 1000 SiC powder of technical grade, and the third one, which was used as a reference, was based on H.C. Starck UF-15 fine grade commercial powder. Milling process used for Alcoa 1000 SiC powder granulometry improvement has been investigated in detail, while chemical treatment of milled SiC powders has been used for pick-up impurities removal. Dilatometric experiments showed that SiC powder of technical grade after appropriate treatment exhibits sinterability comparable with the fine grade SiC. Microstructural investigations performed on sintered samples showed that the final microstructure of the Alcoa 1000 SiC based materials was practically identical with the H.C. Starck SiC based reference ones. Preliminary investigations of hardness and fracture toughness were carried out revealing excellent results for the materials produced from cheaper, nationally produced starting powder.Neste trabalho é apresentada a possibilidade de obtenção de cerâmicas de SiC de alto desempenho a partir de matéria-prima comercial de grau técnico. Foi realizado o estudo de sinterização via fase líquida e desenvolvimento microestrutural de três composições à base de SiC tendo como aditivos de sinterização AlN e Y2O3 . Duas destas composições são à base de SiC-1000 da Alcoa, grau técnico, e a terceira, utilizada como referência, à base do UF-15 da H.C. Starck - Alemanha, pó comercial de granulometria fina. O processo de moagem do pó SiC-1000 da Alcoa foi acompanhado por medidas de distribuição granulométrica e posterior ataque químico, para remoção de impurezas. Os pós de grau técnico, ap

  6. Effect of phase transitions on thermoluminescence characteristics of nanocrystalline alumina

    International Nuclear Information System (INIS)

    Rani, Geeta; Sahare, P.D.

    2013-01-01

    Highlights: •Synthesis of Al 2 O 3 nanocrystalline TLD phosphor. •Material characterizations by XRD, TEM and TL. •Change in structure and morphology of the phase transition alumina. •Change in glow curve structures and trapping parameters on phase transitions. -- Abstract: Nanocrystalline boehmite (γ-AlOOH) was synthesized by hydrothermal method using AlCl 3 ·6H 2 O and Urea as precursors. The material gets decomposed to form the γ-Al 2 O 3 phase at around 873 K on annealing in air. On annealing further at higher temperatures it gets converted into different phases, such as, δ, θ and the most stable α-phase. Not only the phase changes but the annealing has also changed the morphology of the nanomaterial, i.e. it has changed from spindle like edges to vermicular structures and also grew bigger in sizes. The formations of different phases were confirmed by the X-ray diffraction (XRD) patterns and the changes in the morphology were seen through the TEM images. Further the effect of different phases on the thermoluminescence (TL) glow curve structures was studied and it is also shown that the TL glow curves structures do change due to phase transformations. To investigate further and to determine trapping parameters, different glow curves have been theoretically deconvoluted using computerized glow curve deconvolution (CGCD method) into simple glow peaks. The values of different trapping parameters also change as the glow curve structures on phase transformations due to reorganization of energy levels and the stress/strain generated by some intermediate phases

  7. Titanium Powder Sintering in a Graphite Furnace and Mechanical Properties of Sintered Parts

    Directory of Open Access Journals (Sweden)

    Changzhou Yu

    2017-02-01

    Full Text Available Recent accreditation of titanium powder products for commercial aircraft applications marks a milestone in titanium powder metallurgy. Currently, powder metallurgical titanium production primarily relies on vacuum sintering. This work reported on the feasibility of powder sintering in a non-vacuum furnace and the tensile properties of the as-sintered Ti. Specifically, we investigated atmospheric sintering of commercially pure (C.P. titanium in a graphite furnace backfilled with argon and studied the effects of common contaminants (C, O, N on sintering densification of titanium. It is found that on the surface of the as-sintered titanium, a severely contaminated porous scale was formed and identified as titanium oxycarbonitride. Despite the porous surface, the sintered density in the sample interiors increased with increasing sintering temperature and holding time. Tensile specimens cut from different positions within a large sintered cylinder reveal different tensile properties, strongly dependent on the impurity level mainly carbon and oxygen. Depending on where the specimen is taken from the sintered compact, ultimate tensile strength varied from 300 to 580 MPa. An average tensile elongation of 5% to 7% was observed. Largely depending on the interstitial contents, the fracture modes from typical brittle intergranular fracture to typical ductile fracture.

  8. Room-temperature saturated ferroelectric polarization in BiFeO3 ceramics synthesized by rapid liquid phase sintering

    International Nuclear Information System (INIS)

    Wang, Y.P.; Zhou, L.; Zhang, M.F.; Chen, X.Y.; Liu, J.-M.; Liu, Z.G.

    2004-01-01

    Single-phased ferroelectromagnet BiFeO 3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 deg. C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm 2 , 4.0 μC/cm 2 , and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe 2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials

  9. Ultrafast Terahertz Conductivity of Photoexcited Nanocrystalline Silicon

    DEFF Research Database (Denmark)

    Cooke, David; MacDonald, A. Nicole; Hryciw, Aaron

    2007-01-01

    The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described by a class......The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described...... by a classical Drude–Smith model, suitable for disorder-driven metal–insulator transitions. In this work, we explore the time evolution of the frequency dependent complex conductivity after optical injection of carriers on a picosecond time scale. Furthermore, we show the lifetime of photoconductivity...

  10. Effects of sintering atmosphere and initial particle size on sintering of gadolinia-doped ceria; Efeitos da atmosfera de sinterizacao e do tamanho de particula na sinterizacao da ceria-gadolinia

    Energy Technology Data Exchange (ETDEWEB)

    Batista, Rafael Morgado

    2014-07-01

    The effects of the sintering atmosphere and initial particle size on the sintering of ceria containing 10 mol% gadolinia (GdO{sub 1.5}) were systematically investigated. The main physical parameter was the specific surface area of the initial powders. Nanometric powders with three different specific surface areas were utilized, 210 m{sup 2}/g, 36,2 m{sup 2}/g e 7,4 m{sup 2}/g. The influence on the densification, and micro structural evolution were evaluated. The starting sintering temperature was verified to decrease with increasing on the specific surface area of raw powders. The densification was accelerated for the materials with smaller particle size. Sintering paths for crystallite growth were obtained. Master sintering curves for gadolinium-doped ceria were constructed for all initial powders. A computational program was developed for this purpose. The results for apparent activation energy showed noticeable dependence with specific surface area. In this work, the apparent activation energy for densification increased with the initial particle size of powders. The evolution of the particle size distributions on non isothermal sintering was investigated by WPPM method. It was verified that the grain growth controlling mechanism on gadolinia doped ceria is the pore drag for initial stage and beginning of intermediate stage. The effects of the sintering atmosphere on the stoichiometry deviation of ceria, densification, microstructure evolution, and electrical conductivity were analyzed. Inert, oxidizing, and reducing atmospheres were utilized on this work. Deviations on ceria stoichiometry were verified on the bulk materials. The deviation verified was dependent of the specific surface area and sintering atmosphere. Higher reduction potential atmospheres increase Ce{sup 3+} bulk concentration after sintering. Accelerated grain growth and lower electrical conductivities were verified when reduction reactions are significantly present on sintering. (author)

  11. Characterization of Uranium Oxide and Ln-bearing Uranium Oxide during Sintering

    Energy Technology Data Exchange (ETDEWEB)

    Henderson, J.B. [Netzsch Instruments, Inc., Estes Park, CO (United States); Byler, D.D.; Stanek, C.R.; Dunwoody, J.T.; Luther, E.P.; Volz, H.M.; Vogel, S.C.; McClellan, K.J. [Los Alamos National Laboratory, Los Alamos, NM (United States)

    2009-06-15

    In support of the transmutation fuel development as part of the effort to close the fuel cycle, research has been carried out to gain an in-depth understanding of the evolution of material properties during sintering as well as the properties of post-sintered oxide fuels. Of course the effects of material and test parameters such as starting powder O/M, green density, particle size distribution, heating rate and atmosphere on the densification of oxide and mixed oxide fuels have been widely studied, sometimes with conflicting results. However, the evolution of thermophysical properties such as specific heat and thermal conductivity during densification is not well known. Further, the effects of lanthanides on densification as well as on other thermodynamic and transport properties during sintering have not been widely studied. The purpose of this work was to characterize the effects of key material and test parameters on the thermophysical properties during sintering (both surface and volume transport) and on post-sintered UO{sub 2+x} and UO{sub 2+x} + lanthanide samples. Mixtures of UO{sub 2+x} and lanthanide component powder as well as pre-synthesized solid solutions have been studied. In addition to the standard bulk characterization methods such as dilatometry (thermal expansion / densification), laser flash (thermal diffusivity / thermal conductivity), differential scanning calorimetry (specific heat and transformation energetics) and thermogravimetric analysis (mass change), we have employed ancillary techniques such as neutron scattering, laboratory X-ray diffraction and scanning electron microscopy to help evaluate phases, lattice parameters and microstructure during sintering. The experimental data from the methods mentioned above have been cross-correlated to help explain the physics which govern the sintering process as well as those which govern the development of the thermophysical properties of these materials. The results of this work will be

  12. Thermodynamics and mechanisms of sintering

    International Nuclear Information System (INIS)

    Pask, J.A.

    1978-10-01

    A phenomenological overview and exploration of the thermodynamic and geometric factors play a role in the process of densification of model compact systems consisting of crystalline spheres of uniform size in regular and irregular packing that form grain boundaries at every contact point. A further assumption is the presence of isotropic surface and grain boundary energies. Although such systems are unrealistic in comparison with normal powder compacts, their potential sintering behavior can be analyzed and provided with a limiting set of behavior conditions which can be looked upon as one boundary condition. This approach is logically realistic since it is easier to understand and provide a basis for understanding the more complex real powder systems

  13. Melting and Sintering of Ashes

    DEFF Research Database (Denmark)

    Hansen, Lone Aslaug

    1997-01-01

    , the biggest deviations being found for salt rich (i.e. straw derived) ashes.A simple model assuming proportionality between fly ash fusion and deposit formation was found to be capable of ranking deposition rates for the different straw derived fly ashes, whereas for the fly ashes from coal/straw co......-firing, the model only had a qualitative agreement with the measured ash deposit formation rates.Sintering measurements were carried out by means of compression strength testing of ash pellets. This method showed to not be applicable for the salt rich fly ash derived from straw combustion. For the fly ashes...... have been employed in a simple model for prediction of ash deposit formation, the results of which have been compared to ash deposition formation rates measured at the respective boilers.The ash fusion results were found to directly reflect the ash compositional data:a) Fly ashes and deposits from...

  14. Vacuum-sintered body of a novel apatite for artificial bone

    Science.gov (United States)

    Tamura, Kenichi; Fujita, Tatsushi; Morisaki, Yuriko

    2013-12-01

    We produced regenerative artificial bone material and bone parts using vacuum-sintered bodies of a novel apatite called "Titanium medical apatite (TMA®)" for biomedical applications. TMA was formed by chemically connecting a Ti oxide molecule with the reactive [Ca10(PO4)6] group of Hydroxyapatite (HAp). The TMA powders were kneaded with distilled water, and solid cylinders of compacted TMA were made by compression molding at 10 MPa using a stainless-steel vessel. The TMA compacts were dried and then sintered in vacuum (about 10-3 Pa) or in air using a resistance heating furnace in the temperature range 1073-1773 K. TMA compacts were sintered at temperatures greater than 1073 K, thus resulting in recrystallization. The TMA compact bodies sintered in the range 1273-1773 K were converted into mixtures composed of three crystalline materials: α-TCP (tricalcium phosphate), β-TCP, and Perovskite-CaTiO3. The Perovskite crystals were stable and hard. In vacuum-sintering, the Perovskite crystals were transformed into fibers (approximately 1 µm in diameter × 8 µm in length), and the fiber distribution was uniform in various directions. We refer to the TMA vacuum-sintered bodies as a "reinforced composite material with Perovskite crystal fibers." However, in atmospheric sintering, the Perovskite crystals were of various sizes and were irregularly distributed as a result of the effect of oxygen. After sintering temperature at 1573 K, the following results were obtained: the obtained TMA vacuum-sintered bodies (1) were white, (2) had a density of approximately 2300 kg/m3 (corresponding to that of a compact bone or a tooth), and had a thermal conductivity of approximately 31.3 W/(m·K) (corresponding to those of metal or ceramic implants). Further, it was possible to cut the TMA bodies into various forms with a cutting machine. An implant made of TMA and inserted into a rabbit jaw bone was covered by new bone tissues after just one month because of the high

  15. X-ray interference by nanocrystalline domains.

    Science.gov (United States)

    Gelisio, Luca; Scardi, Paolo

    2012-11-01

    Regular arrangement of nanocrystalline domains can introduce interference effects which alter considerably the powder diffraction pattern. Role of nanocrystal alignment (local texture) and mutual positioning are different, with the latter much more effective in controlling the interference effect. While it is demonstrated that these effects are unlikely to be observed on a conventional laboratory instrument, coherence conditions available at modern synchrotron radiation beamlines might support further investigations of interference in systems made of very fine nanocrystals.

  16. Solubility of Carbon in Nanocrystalline -Iron

    OpenAIRE

    Kirchner, Alexander; Kieback, Bernd

    2012-01-01

    A thermodynamic model for nanocrystalline interstitial alloys is presented. The equilibrium solid solubility of carbon in -iron is calculated for given grain size. Inside the strained nanograins local variation of the carbon content is predicted. Due to the nonlinear relation between strain and solubility, the averaged solubility in the grain interior increases with decreasing grain size. The majority of the global solubility enhancement is due to grain boundary enrichment however. Therefor...

  17. Nanocrystalline diamond growth on different substrates

    Czech Academy of Sciences Publication Activity Database

    Kulisch, W.; Popov, C.; Vorlíček, Vladimír; Gibson, P. N.; Favaro, G.

    2006-01-01

    Roč. 515, - (2006), s. 1005-1010 ISSN 0040-6090 Grant - others:EC Framework(XE) MEIF-CT-2004-500038; NATO(XE) CBP.EAP.CLG 981519 Institutional research plan: CEZ:AV0Z10100520 Keywords : nanocrystalline diamond * growth mechanisms * nucleation mechanisms * mechanical properties Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.666, year: 2006

  18. Highly defective oxides as sinter resistant thermal barrier coating

    Science.gov (United States)

    Subramanian, Ramesh

    2005-08-16

    A thermal barrier coating material formed of a highly defective cubic matrix structure having a concentration of a stabilizer sufficiently high that the oxygen vacancies created by the stabilizer interact within the matrix to form multi-vacancies, thereby improving the sintering resistance of the material. The concentration of stabilizer within the cubic matrix structure is greater than that concentration of stabilizer necessary to give the matrix a peak ionic conductivity value. The concentration of stabilizer may be at least 30 wt. %. Embodiments include a cubic matrix of zirconia stabilized by at least 30-50 wt. % yttria, and a cubic matrix of hafnia stabilized by at least 30-50 wt. % gadolinia.

  19. Immobilization of Uranium Silicides in Sintered Glass

    International Nuclear Information System (INIS)

    Mateos, P.; Russo, D.O.; Heredia, A.D.; Sanfilippo, M.

    2003-01-01

    High activity nuclear spent fuels vitrification by fusion is a well known technology which has industrial scale in France, England, Japan, EEUU. Borosilicates glasses are used in this process.Sintered glasses are an alternative to the immobilization task in which there is also a wide experience around the world.The available technics are: cold pressing and sintering , hot-pressing and hot isostatic pressing.This work compares Borosilicates and Iron silicates sintered glasses behaviour when different ammounts of nuclear simulated waste is added

  20. Solidification of HLLW into sintered ceramics

    International Nuclear Information System (INIS)

    O-Oka, K.; Ohta, T.; Masuda, S.; Tsunoda, N.

    1979-01-01

    Simulated HLLW from the PNC reprocessing plant at Tokai was solidified into sintered ceramics by normal sintering or hot-pressing with addition of some oxides. Among various ceramic products obtained so far, the most preferable was nepheline-type sintered solids formed with addition of SiO 2 and Al 2 O 3 to the simulated waste calcine. The solid shows advantageous properties in leach rate and mechanical strength, which suggest that the ceramic solids were prepared with additions of ZrO 2 or MnO 2 , and some of them showed good characteristics