International Nuclear Information System (INIS)

Augmented plane wave calculation of gadolinium electronic structure crystallized in a hexagonal close-packed lattice is carried out.

International Nuclear Information System (INIS)

... angular momentum cranking model even-even nuclei gadolinium 156 governor

KoreaScience (Korea)

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Energy Technology Data Exchange (ETDEWEB)

Carbide reactions occurring in a precipitation-hardening gamma/gamma-prime Ni-Cr alloy during prolonged high-temperature aging are investigated experimentally. It is found that the decomposition of primary MC carbides, which is accompanied by the precipitation of M23C6 particles, may lead to void nucleation and growth. The effect of carbide transformations on the residual properties of the material at temperatures above the equicohesion temperature is observed at the late stages of aging only. 6 references.

Science.gov (United States)

Beta silicon carbide is an excellent candidate semiconductor material for demanding applications in high power and high temperature electronic devices due to its high breakdown voltage, relatively large band gap, high thermal conductivity and high melting...

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According to the present invention, a joined product is at least two ceramic parts, specifically bi-element carbide parts with a bond joint therebetween, wherein the bond joint has a metal silicon phase. The bi-element carbide refers to compounds of MC, M.sub.2 C, M.sub.4 C and combinations thereof, where M is a first element and C is carbon. The metal silicon phase may be a metal silicon carbide ternary phase, or a metal silicide.

International Nuclear Information System (INIS)

In Pressurised heavy water reactors (PHWRs), neutron poison in the moderator is used to compensate the excess reactivity present in the core on different occasions such as xenon decay during synchronization just after poison out period or start ups from xenon free conditions. It is also used in secondary shutdown system (SDS-2), where required amount of neutron poison is injected directly into the moderator within 2.5 seconds. Further, it is also used for over poisoning the moderator to achieve the guaranteed shutdown state when the regular shutdown systems are taken for maintenance. Generally, two types of moderator poisons are used in power reactors to balance the reactivity of the core and they are boron and gadolinium. Gadolinium is used in the form of gadolinium nitrate (Gd(NO3)3.6H2O). The paper gives the details of estimation of reactivity coefficients of gadolinium for 540 MWe PHWR for different ...

UK PubMed Central (United Kingdom)

Convection-enhanced delivery (CED) has emerged as a promising method of targeted drug-delivery for treating central nervous system (CNS) disorders, but the influence of brain structure on infusate...Full Text Available

UK PubMed Central (United Kingdom)

A new gadolinium chelating NIR fluorescent molecular probe increases T₁ relaxivity of water protons, facilitating combined optical and magnetic resonance imaging.

UK PubMed Central (United Kingdom)

PurposeA major obstacle in glioblastoma (GBM) therapy is the restrictive nature of the blood-brain barrier (BBB). Convection-enhanced delivery (CED) is a novel method...Full Text Available

International Nuclear Information System (INIS)

In order to investigate the relation between the pitting corrosion and precipitated carbides, the heat treatment of specimens was carried out in two ways: Solution treatment and carbides precipitation treatment. The experiment was focused on the polarization curves of specimens immersed in HCL solution and on the microscopic analysis of the corroded specimens through a potentiodynamic method. It was found out that the intergranular and pitting corrosion occurred remarkably in 0.1N and 1N KCL solution when carbides were precipitated around the grain boundary of the 304 stain steel. The intergranular corrosion was noticed in the region of passivation and the pitting was prominent in the region of passivation break-down. The distribution of pits on the solution treated 304 stainless steel was random, while that of pits on carbides precipitated specimen was concentrated around the grain boundary in 0.1N and ...

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This paper reports the presence of face centered cubic cobalt precipitates inside tungsten carbide in nanocomposite of WC-Co synthesized by spray conversion processing. EDS was used to identify the presence and micro-diffraction was employed to determine the nature of the precipitates. There is entrapment of cobalt in tungsten carbide during the spray conversion process used to form WC/Co powder. During consolidation, at high temperatures, the cobalt attains enough mobility to precipitate inside WC. A vanadium containing compound was seen at the interfaces in samples which incorporated VC as a grain growth inhibitor. (orig.)

Science.gov (United States)

cellulose casing material made by Food Products Division,. Union Carbide Corporation. tion of the anode from oxygen generated at the charging electrode. ...

Science.gov (United States)

... Advanced thermal storage systems based on very high temperature solid materials such as boron carbide or graphite have been investigated for ...

Energy Technology Data Exchange (ETDEWEB)

Recently the association of a rare disease named ''nephrogenic systemic fibrosis'' (NSF) with the administration of gadolinium-containing contrast media, especially gadodiamide (Omniscan, GE-Healthcare), was described. NSF is a scleroderma-like disease characterised by widespread tissue fibrosis. Until now, NSF cases were observed only in patients with kidney disease. Almost all patients were suffering from chronic renal insufficiency, 90 % of them required renal replacement therapy. The true incidence of the disease is unknown. First retrospective analyses of selected collectives of patients with end-stage renal disease showed 2 - 5 % cases of NSF after administration of Gadolinium-containing contrast agents with an odds ratio of 20 - 50 in comparison to non-exposed controls. NSF is a serious adverse reaction, which may result in severe disabilities and even death. Therefore all radiologists applying ...

International Nuclear Information System (INIS)

The fission gas xenon bonded in bubbles, in pore, and in the lattice of mixed carbide fuels is measured by electron-probe microanalysis. Radial xenon distribution and release curves are determined and are calibrated by gas chromatography of the bonded fission gas and by burnup analysis in the respective pin sections of the irradiation experiments FR2 6A and 6C, Mol 11/K 2, and DFR 330/1. The results are correlated to the microstructure of the fuel, bonding medium, temperature, and burnup. (Auth.).

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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.

Science.gov (United States)

"Precision manufacture of ceramic parts with CNC machining capability for aerospace, lasers, semiconductors and other industries. Materials include alumina, zirconia, glass, ferrites, silicon carbide, silicon nitride, sapphire, cordierite, mullite and others. A.C.T. has seen the number of applications and demand for high-realiability ceramics (aluminum oxide, zirconia, glass, ferrites, silicon carbide, silicon nitride, sapphire, cordierite, mullite, etc...) increase continually within the aerospace, computer and the industrial markets."

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This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Functionally graded material is an enabling technology for lightweight body armor improvements. The objective was to demonstrate the ability to produce functionally graded ceramic-polymer and ceramic-metal lightweight armor materials. This objective involved two aspects. The first and key aspect was the development of graded-porosity boron-carbide ceramic microstructures. The second aspect was the development of techniques for liquid infiltration of lightweight metals and polymers into the graded-porosity ceramic. The authors were successful in synthesizing boron-carbide ceramic microstructures with graded porosity. These graded-porosity boron-carbide hot-pressed pieces were then successfully liquid-infiltrated in vacuum with molten aluminum at 1,300 C, and with liquid polymers at ...

International Nuclear Information System (INIS)

The optical spectroscopy measurements of gadolinium gallium garnet (GGG) crystals doped with Yb show evidence of the presence of non-equivalent optical centers with very similar radiative decay rates. The energy level schemes of those centers have been determined on the basis of optical absorption, luminescence and Raman experiments. Crystal field fitting resulted in two sets of slightly different crystal field parameters for two non-equivalent Yb centers. Both sets of parameters describe perfectly the experimentally detected Y b3+ energy levels. Correlation between systematic trends in the experimental energy level schemes and crystal field parameters is discussed.

International Nuclear Information System (INIS)

Twenty-three patients with intracranial meningiomas were examined by means of magnetic resonance tomography (MRT). In 13 patients the paramagnetic contrast medium gadolinium DTPA was used. Meningiomas show only slight changes in signal intensity compared with brain in the spin-echo mode, the greatest contrast being found on photon density images (TR 1600 ms, TE 35 ms). In T1 images more than 50% of the patients showed a low signal margin between tumour and brain. Hyperostosis of the calvarium is easily recognised, but MRT is unreliable for showing tumour calcification. After intravenous injection of gadolinium DTPA, there was marked homogeneous uptake in the meningiomas. These signs are useful for the diagnosis of a meningioma by MRT. (orig.).

British Library Electronic Table of Contents (United Kingdom)

In the paper, the effect of Ni content, WC grain size and Mo2C addition on WC-6.25wt%TiC-9.3wt%Ni cemented carbide were investigated to improve the properties of Ni-bonded cemented carbides. The results show that the decrease of Ni content will result in the decrease of transverse rupture strength and increase of hardness; with the decrease of WC particle size, hardness increases due to the refinement of WC grains, however, the transverse rupture strength decrease due to the decrease of Ni binder thickness; Mo2C proves to be an effective grain growth inhibitor. With the increase of Mo2C content, the WC grains are refined and the hardness and transverse rupture strength are improved. Generally, when the Ni content is decreased to 8.4wt%, 13.45mm WC is used and 1.2wt% Mo2C is added, a higher...

Energy Technology Data Exchange (ETDEWEB)

The electrochemical metal dissolution of 100Cr6 steel in sodium chloride solution, applying high electrolyte flow rates and high current densities, has been studied with a view to the influence of material heterogeneities such as carbide segregation lines in the steel matrix. It was shown that the presence of such segregations is responsible for the formation of troughs on the specimen surface during electrochemical dissolution. A mechanism for trough formation was proposed. A dedicated heat treatment applied to the 100Cr6 steel eliminated the carbide segregation lines and established a soft annealed, fine-grained microstructure containing globular carbides. Subsequent electrochemical dissolution did not show any development of surface irregularities as troughs. (orig.)

International Nuclear Information System (INIS)

The examination of the high-temperature properties of the alloy Alloy 800HT has shown that both the creep performance and the microstructure of the material can be purposefully set by the initial heat treatment. At the high temperatures applied, (700-900 C), a rapid softening process sets in induced by carbide precipitation, stabilization, and coarsening. This softening process causes creep velocities strongly accelerating as a function of duration of the heat treatment prior to the creep test. The identified cause of the softening effect is a change in particle size that could be verified by SEM and TEM. It is shown that two different carbide precipitate size classes are responsible for the softening effect. While the precipitates dectable by TEM become effective primarily via interactions with dislocations, the carbide precipitates detectable only by SEM contribute to a hardening of the grain boundaries and the ...

International Nuclear Information System (INIS)

Gadolinium nitrate has been employed in Indian nuclear reactors for the first time as soluble neutron poison in the heavy water moderators of the 540 MWe PHWRs TAPS 3 and 4, as a fast acting secondary shut down system (SDS-2); and also for reactivity shim. For this purpose, the moderator purification system is currently equipped with special ion-exchange columns/schemes, developed by present authors. However, for gadolinium removal from moderator in the post SDS-2 scenario, the two stage ion-exchange - cation bed operation followed by mixed bed operation - results in low pH conditions persisting in the moderator for a few hours, which gives rise to certain operational problems. The present paper describes a mixed bed ion-exchange scheme employing macro-porous strong acid cation and macro-porous weak base anion resins, which has been developed to eliminate acidic conditions and gives a better pH control. The cation to anion capacity ratio in the ...

International Nuclear Information System (INIS)

Mixed carbide fueled driver assembly experiments will be tested in FFTF fuel driver positions as part of the National Advanced Fuel Program. The design of the experiment flow ducts must assure conformance to FFTF functional requirements in addition to service as a test vehicle for the carbide fuel irradiations. Test goals of damage fluence burnup, and fluence to burnup ratio exceed those of the standard oxide fueled drivers. As a consequence, the 20% cold worked type 316 stainless steel material of construction will experience significant irradiation induced creep and swelling. Additionally, the flow duct design must withstand the enhanced thermal transients produced by the action of carbide fuel during reactor scrams. A major FFTF functional requirement is that adjacent flow ducts do not touch each other except at the load pads. This requires a realistic analysis of the creep and swelling deformation of the flow duct ...

International Nuclear Information System (INIS)

The effect of a mineralizer, magnesium silicate, on the nitridation of compacts consisting of silicon, clay, silica and silicon carbide was examined in terms of their reaction depth, density, porosity, phase composition and microstructure. It was found that addition of mineralizer slowed down the nitridation significantly. The kinetic process of isothermal nitridation in the presence of magnesium silicate obeys a parabolic rate law. Otherwise it obeys a linear rate law. The results suggest that nitrogen transportation is the limiting step during nitridation when mineralizer is added. The mechanism of nitridation is discussed in terms of phase composition and microstructure. Copyright (2000) The Australian Ceramic Society

International Nuclear Information System (INIS)

The 540 MWe PHWR has two fully independent shutdown systems. The first shutdown system (SDS-1) comprises of 28 spring assisted, vertical gravity drop shut-off rods, each consisting of a cadmium absorber sandwiched between stainless steel tubes. The second shutdown system (SDS-2) constitutes six poison tanks connected to respective zircaloy injection tubes. This system is capable of high speed injection of gadolinium nitrate solution (in D2O) into the moderator through these tubes. Theoretical estimation was carried out at different injection pressures and different concentration of gadolinium nitrate solution to arrive at the limiting value of these parameters from reactivity consideration point of view. The plant measurements of SDS-2 actuations at 60 and 80 Kg/cm2 pressure of helium was used to validate and upgrade the estimation model. The paper gives the details of the validation details of SDS-2 actuation. (author)

Energy Technology Data Exchange (ETDEWEB)

The electrochemical dissolution behaviour of armco-iron and of the steels C15, C45, C60 and 100Cr6 in concentrated sodium chloride media has been investigated. Anodic metal dissolution experiments have been carried out using the flow channel cell (parallel plate reactor), the rotating cylinder electrode (RCE) and the capillary cell. The microstructure of the steel has been varied through variation of carbon content and heat treatment (e.g. soft annealed with globular carbides or pearlitic). Current-efficiency values have been obtained by gravimetric measurements in the current-density range from i=5 to 60 A/cm{sup 2}. For the soft annealed steels, the divalent ferrite dissolution in combination with electroless cementite removal dominates. For the pearlitic steels, the occurrence of oxygen evolution electronically conductive metal carbides or trivalent ferrite dissolution, depending on the current density applied, was detected. Microstructure ...

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Intraspinal synovial cysts were diagnosed in six patients during a 5-year period and retrospectively studied. Plain films of the lumbar spine showed degenerative changes in all patients. Lumbar myelography showed a posterior and lateral defect caused by extradural compression. Using CT without contrast enhancement established the diagnosis in five of the six patients. In four cases MRI was performed, three before and after injection of gadolinium diethyline-triamine penta-acetic acid (Gd-DTPA). Including the patient with a false-negative CT, MRI was positive in all patients. (orig.)

International Nuclear Information System (INIS)

The description is presented of binary phase diagrams of titanium alloyed with the following elements: silver, aluminium, arsenic, gold, boron, barium, beryllium, bismuth, carbon, calcium, cadmium, cobalt, chromium, copper, iron, gallium, germanium, hydrogen, hafnium, indium, iridium, potassium, lithium, magnesium, manganese, molybdenum, nitrogen, sodium, niobium, nickel, oxygen, osmium, phosphorus, lead, palladium, platinum, plutonium, rhenium, lanthanium, cerium, preseodymium, neodymium, gadolinium, erbium, terbium, thulium, lutetium, rhodium, ruthenium, scandium, silicon, tin, strontium, tantalum, technetium, thorium, uranium, vanadium, tungsten, yttrium, ytterbium, zinc and zirconium.

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Safety and environmental assessments have been made of conceptual fusion power plant designs employing silicon carbide composites (SiC/SiC) as the first wall and blanket structure material. These have used similar analysis methods to earlier studies of designs based on vanadium alloy or low-activation martensitic steel, allowing direct comparisons. The very low short-term activation of silicon carbide results in an almost insignificant level of decay heat in postulated loss of coolant accidents, and a lower {gamma}-dose rate on the timescale of relevance to handling for maintenance operations. However on the longer time-scale, of interest in possible recycling operations, decommissioning and waste management, SiC/SiC appears to perform no better than vanadium alloy or low-activation martensitic steel, due in part to the activation of impurities in a realistic composition. Furthermore, its increased neutron transparency may result in higher ...

International Nuclear Information System (INIS)

Neutron irradiation embrittlement of reactor pressure vessel (RPV) steels is one of the critical issues on aging management for long term operation of nuclear power plants. Mechanistic understanding of embrittlement is a key to accurate prediction of embrittlement, especially after long term operation where the mechanical test data are sparse. Since matrix hardening is the source of the embrittlement, we focus on matrix hardening of A533B bainitic pressure vessel steel. Bainitic matrix is composed of lath structure made by ferrite and carbides, therefore it is important to understand how this structure affects hardening behavior, and to understand irradiation response of each phase. As the typical dimension of lath structure of A533B is about one micron, nanoindentation technique is suitable for the estimation of hardening of each phase. MV ion accelerators were used for controlled irradiation because MeV ion irradiation can produce defects to the depth greater ...

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In support of the efforts to apply ceramics to advanced heat engines, a study is being performed of the performance of ceramics at the ring/cylinder interface of advanced (low heat rejection) engines. The objective of the study, managed by the Oak Ridge National Laboratory, is to understand the basic mechanisms controlling the wear of ceramics and thereby identify means for applying ceramics effectively. Attempts to operate three different zirconias, silicon carbide, silicon nitride, and plasma-sprayed ceramic coatings without lubrication have not been successful because of excessive friction and high wear rates. Silicon carbide and silicon nitride perform well at ambient temperatures with fully formulated mineral oil lubrication, but are limited to temperatures of 500F because of the lack of suitable liquid lubricants for higher temperatures.

International Nuclear Information System (INIS)

Synthesis, morphology, structural and optical characteristics of SiC NWs and SiC/C nanocomposites with an inverse opal lattice have been investigated. The samples were prepared by carbothermal reduction of silica (SiC NWs) and by thermo-chemical treatment of opal matrices (SiC/C) filled with carbon compounds which was followed by silicon dioxide dissolution. It was shown that the nucleation of SiC NWs occurs at the surface of carbon fibers felt. It was observed three preferred growth direction of the NWs: [111], [110] and [112]. HRTEM studies revealed the mechanism of the wires growth direction change. SiC/C- HRTEM revealed in the structure of the composites, except for silicon carbide, graphite and amorphous carbon, spherical carbon particles containing concentric graphite shells (onion-like particles).

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Microcrystalline silicon carbide ({mu}c-SiC) was prepared at low substrate temperatures using Hot Wire chemical vapor deposition (HWCVD). High crystalline volume fractions were achieved at high hydrogen dilution and high deposition pressure. Without intentional doping, such material shows high dark conductivity and high optical absorption below the band gap. The material prepared at low deposition pressure or low hydrogen dilution, on the other hand, shows much lower conductivity and sub-gap absorption, but high spin densities up to 5 x 10{sup 19} cm{sup -3}. This high absorption can be attributed to free carriers, different to {mu}c-Si:H where a correlation between the sub-gap absorption and the spin density is observed.

British Library Electronic Table of Contents (United Kingdom)

In this work AISI 1045 steel were duplex treated via plasma nitriding of chromized layer. Samples were pack chromized by using a powder mixture consisting of ferrochromium, ammonium chloride and alumina at 1273K for 5h. The samples were then plasma-nitrided for 5h at 803K and 823K, in a gas mixture of 75%N2+25%H2. The treated specimens were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and Vickers micro-hardness test. The thickness of chromized layer before nitriding was about 8mm and it was increased after plasma nitriding. According to XRD analysis, the chromized layer was composed of chromium and iron carbides. Plasma nitriding of chromized layer resulted in the formation of chromium and iron nitrides and carbides. The hardness of the duplex layer...

International Nuclear Information System (INIS)

The study reports the identification of different organic acids that are formed during the pyrohydrolysis of mixed carbide of uranium and plutonium using ion chromatography (IC). The identification of organic acids present in the pyrohydrolysis distillate is required to carry out interference free analysis of Cl and F. The study describes three stage isocratic separations with NaOH eluents having concentrations 2 mM, 10 mM and 50 mM respectively in order to separate and identify both aliphatic and aromatic acids. The present investigation identified formic, acetic, propionic, butyric, tartaric and oxalic acids in the distillate, however, aromatic acids could not be identified. (author)

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This investigation involves a study of the influence of key processing parameters on the heating of materials using microwave energy. Selective and localized heating characteristics of microwaves will be utilized in the sintering of ceramics without hydrostatic pressure. In addition, combustion synthesis will be studied for the production of powders, carbides, and nitrides by combining two or more solids or a solid and a gas to form new materials. The insight gained from the interaction of microwaves with various materials will be utilized in the mobilization and subsequent redeposition of uranium.

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This heat exchanger is a critical step in the development of the Externally Fired Combined Cycle power system, a direct-coal combustion power plant (gas turbine). SiC is the only material with the needed resistance to creep, thermal shock, and oxidation; however a protective coating is needed. Ten candidate materials were identified: alumina-based materials, materials stable with SiO, and low expansion materials. An initial screening study should be performed.

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The development and experimental demonstration of a high-temperature seal for the SHARE ceramic dome cavity receiver is reported. The mechanical contact seal which was tested on one-foot-diameter silicon-carbide ceramic-dome hardware at pressure differentials to four atmospheres and dome temperatures to 2200/sup 0/F (1200/sup 0/C) showed negligible leakage at expected receiver operating conditions. Potential solar receiver applications for the technology are illustrated.

British Library Electronic Table of Contents (United Kingdom)

Objective To investigate value of magnetic resonance cholangiopancreatography (MRCP) using oral diluted gadolinium (Gd)-diethylenetriamine penta-acetic acid (DTPA) as negative contrast materials in diagnosis of juxtapapillary duodenal diverticulum with atypical imaging features. Methods Nineteen patients with juxtapapillary duodenal diverticula of which imaging findings were atypical underwent MRCP using oral diluted Gd-DTPA as negative contrast materials after conventional MRCP without any oral contrast materials. Results Twenty diverticula were revealed in the 19 patients. At conventional MRCP, the diverticula appeared as rounded lesion with high signal intensity. After oral administration of diluted Gd-DTPA, they disappeared at MRCP. These entities were diagnosed as duodenal diverticula...

Science.gov (United States)

Electron collisional data are required for population kinetics modeling and spectral predictions of highly ionized ions in high-temperature plasmas. Nickel-like ions are especially interesting for their potential use in soft X-ray laser schemes pumped by electron collisional excitation and recombination. For highly stripped ions of moderate to high Z, relativistic effects begin to play a role in the atomic-physics calculations. A relativistic multiconfigurational distored-wave model has been used for the calculation of electron excitation cross sections and rate coefficients between the 3s2 3p6 3d10 Ni-like Gd ground state and the singly excited states with an N-shell electron.

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A real time neutron radiography system has been developed at the University of Michigan Phoenix Memorial Laboratory (PML) and has recently been used to test the imaging capabilities of a neutron imaging device developed by Lixi, Inc. of Downers Grove, Illinois. This device uses an input phosphor that is high in gadolinium to generate a light image which is then sent through an intensifier stage to provide images that can be viewed by eye, video camera, or standard 35 mm camera. It was determined that this device provides images of much higher resolution and sensitivity than those obtained with the imaging system currently being used at PML. Using computerized image enhancement techniques, the images obtained with the Lixi neutron imaging device can then be further enhanced or processed to obtain quantitative information on the object being imaged.

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Three different fuels UO{sub 2}-only, UO{sub 2}-Gd{sub 2}O{sub 3}(5%), and UO{sub 2}-Gd{sub 2}O{sub 3}(10%) were produced by sol-gel technique. Their powder characteristics such as flowability, BET surface area, average pore diameter, and cumulative pore volume were determined. The pore size distributions of powders, green pellets, and sintered fuels were determined by using a mercury porosimeter. The theoretical densities of sintered fuels were found to be 98.01, 95.3, and 95.9 %, respectively. Their ruggedness fractal dimensions were 1.111, 1.044, and 1.042, while the fractal dimensions associated with the size distribution of grains were 1.44, 1.58, and 1.60, respectively. (orig.).

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At the reference plant (Wolsung unit No. 1) a manual poison sampling system is provided to periodically sample gadolinium from each tank and analyze it in the laboratory to provide assurance that adequate poison concentration in each tank is maintained. The AECB required a continuous, on-line monitoring system. On Wolsung unit No. 2, process piping adapter and new instrument loops added to the Liquid Injection Shutdown System(LISS) which is part of SDS2. The new instrument loops continuously monitor SDS2 poison conductivity and initiate an alarm when the poison concentration is too low. 8 refs., 1 fig. (author).

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To assess the utility of magnetic resonance (MR) imaging in the study of pediatric patients with clinical suspicion of pituitary disease. We studied 18 patients aged 7 to 18 years.Fifteen had hormonal disturbances, two presented amenorrhea and 1 complained of headache, fever and symptoms of polyuria and polydipsia. All the patients were examined using a Siemens SP 42 1-Tesla MRI scanner. Sagittal and coronal T1-weighted spin-echo images were obtained; in addition T2-weighted spin-echo or fast spin-echo imaging was performed in ten cases and intravenous gadolinium was administered in nine. We found 9 patients with hypothalamic-pituitary dysgenesis, 2 with germinoma, 2 cases of pituitary hemosiderosis in patients with thalassemia, 2 cases of microadenoma, one abscess, one case of idiopathic central diabetes insipidus and one of Langerhans cell histiocytosis. MR enabled us to assess pituitary structural alterations in children with hypothalamic-pituitary hormone ...

International Nuclear Information System (INIS)

Gadolinium removal during the first approach to criticality of TAPP-4 540 MWe reactor using mixed bed resin (strong acid cation resin and weak base anion resin) topped with strong acid cation exchange resin yielded IX column outlet pH of >6 during the first 6 h of run during which [Gd] decreased from 2.1 to 1 mg/kg. However, the main moderator system pH was between 5.0-5.5. Technical specification for pH of moderator is in the range 5.0-5.5 as long as Gd is present. This is to avoid any precipitation of Gd in the core and a pH of 5.8 or even a pH of 5.6 when carbonate is present is specified as the upper limit of the moderator system pH for this purpose. The situation of IX column outlet pH being #>=# 6 mixing with a system water having Gd results in local mixing zone pH in the range of 6- 5.4. In order to have an iso-pH regime (5-5.5) both with respect to the IX outlet as well as in the system, studies were conducted to modify IX resin composition. Use of ...

International Nuclear Information System (INIS)

Aim: To evaluate magnetic resonance cholangiography (MRC) with high-resolution dynamic gadolinium-enhanced magnetic resonance imaging (MRI) in determining the imaging features of hilar cholangiocarcinoma that relate to tumour extent and influence resectability. Materials and methods: Twenty-six patients that underwent resection were reviewed. Tumour location and extent, lobar atrophy, the degree of portal vein and hepatic artery involvement were recorded. The findings were correlated with surgical and histopathological findings. Results: Biliary assessment was concordant in 14 and discordant in eight of 14 stented and four of 12 non-stented patients. In 63/82 veins and 43/74 arteries results were fully concordant. The mean sensitivity, specificity, positive and negative predictive values (PPV, NPV) in predicting involvement of the main portal vein (MPV) at surgery were 83.3, 100, 100, and 92.5%; of the left main branch of the portal vein (LPV) were 100, 91.6, 93.3, ...

International Nuclear Information System (INIS)

The security of ports and transportation is of utmost importance for the development of economy and the security of a nation. Among the necessary actions to ensure the security of ports and borders, the inspection of containers is one of the most time consuming and expensive procedures. Potential threats are the illegal traffic of radioactive materials that could be employed for the construction of weapons, as uranium and plutonium. New techniques for the inspections of containers should be fast, allow the detection and identification of dangerous materials, and be non-invasive, to reduce costs and delays. We propose to build a large surface photon and neutron detector based on plastic scintillator to identify the presence of fissile or fertile material inside a container. The detector consists of scintillator bars, wrapped in thin foils of reflecting material containing gadolinium for neutron capture and arranged in planes separated by few-millimeter-thick lead ...

Energy Technology Data Exchange (ETDEWEB)

To make the surface composites with hard ceramics particles is an effective means for satisfying the request for the wear-resistance of the casting products. Covering casting is a general method for forming the composites by adding the adhesive into ceramics particles. However, due to the using of adhesive, pore and intermediate are easy to generate, and it is one of the reasons making the wear-resistance unstable. In the present study, it is attempted to form the wear-resistant composite layer by dispersing cast tungsten carbide (CTC) particles on the surface of wear-resistant 7 mass% Mn steel without using adhesives. Subsequently, the experiments on the wear-resistance of the obtained surface composites under several wear conditions are carried out. It is revealed by the results thereof that 7 mass% Mn steel surface composites with CTC particles have the wear-resistance which is even more excellent than those of white cast iron and cast chromium cast iron. It is ...

British Library Electronic Table of Contents (United Kingdom)

TaC and TaC-1wt.% B4C powders were consolidated using spark plasma sintering (SPS) at 1850^oC and varying pressure of 100, 255 and 363MPa. The effect of pressure on the densification and grain size is evaluated. The role of nano-sized B4C as sintering aid and grain growth inhibitor is studied by means of XRD, SEM and high resolution TEM. Fully dense TaC samples were produced at a pressure of 255MPa and higher at 1850^oC. The increasing pressure also resulted in an increase in TaC grain size. Addition of B4C leads to an increase in the density of 100MPa sample from 89% to 97%. B4C nano-powder resists grain growth even at high pressure of 363MPa. The formation of TaB2/Carbon at TaC grain boundaries helps in pinning the grain boundary and inhibiting grain growth. The effect of B4C addition on...

International Nuclear Information System (INIS)

A technique for following sialon formation in situ by high temperature X-ray diffraction (HT-XRD) was developed. The composition chosen for study was an yttrium #alpha#-sialon with x=0.4. Powder compacts containing silicon nitride, aluminum nitride and yttria powders were pre-sintered at 1350 C and then studied by HT-XRD at temperatures between 1450 and 1580 C and nitrogen pressures of 0.11 MPa. The furnace was made from graphite coated with porous silicon nitride/silicon carbide. The coating prevented silicon carbide formation in the sample up to 1600 C. X-ray diffraction results show the formation of a Y_1_0Al_2Si_3O_1_8N_4 phase at 1350 C, which dissolved to form #alpha#-sialon and other phases at higher temperatures. The amounts of #alpha#-sialon formed are similar to the amounts reported by other authors. An empirical method was used for the calculation of activation energy for the silicon nitride to #alpha#-sialon transformation and ...

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Experimental discussions were given on effect of V and W addition on the high temperature strength properties of 12% Cr-15% Mn austenite steels. The test samples were added with W at 0% to 3.5% and V at 0% to 0.5% in addition to C and N, and were given aging treatment or solution treatment. This paper describes the following matters on the results of high-temperature strength measurements and structural observation: A remarkable trend was observed that M23 Cb type carbides precipitate in the aging treatment, wherein aging hardening appears prominently which is attributable to ultra-fine deposits of vanadium nitride (VN) in the V-added material; the V addition is very effective in increasing the high-temperature tensile strength and creep fracture strength as compared with single W addition, wherein the said carbides that accelerate the precipitation as a result of the V addition make a large contribution, in addition to that by ultra-fine VN ...

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The development of a silicon carbide (SiC) heat exchanger is a critical step in the development of the Externally-Fired Combined Cycle (EFCC) power system. SiC is the only material that provides the necessary combination of resistance to creep, thermal shock, and oxidation. While the SiC structure materials provide the thermomechanical and thermophysical properties needed for an efficient system, the mechanical properties of the SiC tubes are severely degraded through corrosion by the coal combustion products. To obtain the necessary service life of thousands of hours at temperature, a protective coating is needed that is stable with both the SiC tube and the coal combustion products, resists erosion from the particle laden gas stream, is thermal shock resistant, adheres to SiC during repeated thermal shocks (start-up, process upsets, shut-down), and allows the EFCC system to be cost competitive. This demanding set of technical performance and cost drivers was used ...

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The surface layer optimized in resistance of corrosion and wear has been obtained by W + C dual implantation on H13 steel. The electrochemical polarization measurements show that the peak current density I_D is increased and then saturated with increasing of voltage scanning loops. The I_D is 100 times smaller than that of H13 steel, and 2-3 times smaller than that of tungsten. Then influence of dual implantation order on corrosion resistance is also studied. The I_D for W_5C_8 implanted first with W is half of that for C_5W_5 implanted first with C. The corrosion resistance structure of the samples after corrosion is observed by SEM. The X-ray analysis indicates that the structure consists of disperse phases of WC, W_2C, FeW, Fe_2W, FeW_2C and iron carbides. It is shown from Auger analysis that the optimum complex layer for corrosion resistance consists of thin carbon film on surface, disperse phases of these metal compounds in middle and then iron ...

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Mixed Uranium Plutonium Carbide ((U, Pu) C), in the form of pellets encapsulated in stainless steel tubes is the fuel for Fast Breeder Test Reactor (FBTR) at Kalpakkam. For the fabrication of fuel for enlarging the core of this reactor, high burn up plutonium is used. The external exposure in these labs was significantly higher than that with low burn up Pu fuel. Dose evaluation to the organs was carried out using experimental TLDs during various operations of FBTR fuel fabrication to study the dose distribution pattern. (author)

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A study was made of the variation in strength characteristics of group IV transition metal carbon nitrides alloyed with carbides or group V metal nitrides. A complex solid solution of titanium-niobium carbonitride was preliminarily synthesized to a homogeneous equilibrium state and then crushed. The calculated quantity of binder metal was added as elemental powders, the mixture was vibration ball milled in ethanol and the plasticized charge was used to press experimental specimens for mechanical testing. The studies showed that the high-temperature strength properties of the new cermet are superior to standard type KNT. The material is thus promising for use in the manufacture of tools. 8 references, 3 figures.

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A set of materials property data for potential wear resistant materials was collected. These materials are designated for use as the ''core'' materials in the Fibrous Monolith structure. The material properties of hardness, toughness, thermal conductivity and cost were selected as determining factors for material choice. Data for these four properties were normalized, and weighting factors were assigned for each property to establish priority and evaluate the effects of priority fluctuation. Materials were then given a score based on the normalized parameters and weighting values. Using the initial estimates for parameter priority, the highest ranking material was tungsten carbide, with diamond as the second ranked material. Several materials were included in the trade study, and five were selected as promising ''core'' materials to include in this effort. These materials are tungsten ...

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The time-temperature-precipitation diagrams and the resulting time-temperature-sensitization diagrams have been established and are presented for today's current nickel-chromium-molybdenum alloys C-4, C-276, 22 and the recently developed alloy 59. Compared to those materials alloy 625 behaves differently due to its high niobium content. In addition, also the precipitation and sensitization of alloy G-3 has been established. Under the materials considered alloy C-276 has the strongest tendency to precipitate the intermetallics Mu and P together with the carbide M{sub 6}C at intermediate temperatures, followed by the alloys 22 and 59. The tendency to sensitization in the sense of the 50{mu}m (2 mils) intercrystalline penetration criterion when exposed to the ASTM G-28, method A test solution is greatest with alloy C-276, and decreases over the alloys 22, 59 and G-3 to alloy 625. Sensitization is caused by precipitation of the intermetallics {mu} and P and ...

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The current work continues a project completed in 1999 by ReMaxCo Technologies in which a novel, microwave based, VLS Silicon Carbide Fibrils concept was verified. This project continues the process development of a pilot scale commercial reactor. Success will lead to sufficient quantities of fibrils to expand work by ORNL and others on heat exchanger tube development. A semicontinuous, microwave heated, vacuum reactor was designed, fabricated and tested in these experiments. Cylindrical aluminum oxide reaction boats are coated, on the inner surface, with a catalyst and placed into the reactor under a light vacuum. A series of reaction boats are then moved, one at a time, through the reactor. Each boat is first preheated with resistance heaters to 850 C to 900 C. Each reaction boat is then moved, in turn, to the microwave heated section. The catalyst is heated to the required temperature of 1200 C to 1300 C while a mixture of MTS (methyl trichlorosilane) and ...

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A series of Gd-substituted M-type barium hexaferrites has been prepared by the ceramic route, according to the formula (Ba{sub 1-x}Gd{sub x})O.5.25Fe{sub 2}O{sub 3} (x=0-0.30). XRD analysis revealed that all the samples present primarily an M-type structure. Samples x=0 and x=0.05 are single-phase. Hematite (Fe{sub 2}O{sub 3}) and GdFeO{sub 3} were detected in the remaining samples. Coercivity (H{sub c}) shows remarkably high values, {approx}293kA/m for x=0.20 and 0.30 with a maximum of 322kA/m for x=0.25. Specific saturation magnetization ({sigma}{sub sat}) of the samples presents a small increase up to x=0.10. The microstructure examination indicates that Gd may act as a grain growth inhibitor.

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Atomic Energy Regulatory Board carries out the regulatory review of the reactor physics design, commissioning and operational aspects through Project Design Safety Committee and Specialist Group of reactor physicists with wide experience in the design, commissioning and operational safety review of NPPs. TAPP-3 and 4 PHWRs, being the first indigenous design of 540 MWe Units, are quite different than the standard 220 MWe PHWRs. The safety review of reactor physics design was quite complex, as majority of the systems were new. The Reactor Physics Specialist Group carried out extensive safety review of 540 MWe PHWR reactor physics design and made significant contributions of design modifications and improvements in the operational procedures. Some salient contributions include: Monitoring the core during bulk addition of moderator without the availability of shutdown systems. Logics for providing safety cover in case of malfunction of SDS-1, Use of Gadolinium, ...

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Magnetic resonance imaging (MRI) has rapidly attained a major position among the examinations used in the diagnostic approach of multiple sclerosis because it is highly sensitive in demonstrating lesions. However, these lesional images may have several meanings, and there is the problem of distinguishing between oedema, which is said to reflect recent lesions, and gliosis which is thought to betray old lesions. The intrinsic MRI parameters studied (i.e. relaxation times) are unable to make this distinction, whereas it is provided by paramagnetic contrast media such as gadolinium. There is no correlation between the changes observed at MRI and the severity of the disease. Another problem is the accuracy of lesion localization, since visualization is predominantly macroscopic. This raises several questions about the demonstration of correlations between clinical signs and site of the lesion(s). At the moment, several teams of neuroradiologists are trying to find the ...

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This work concerns the study of the nuclear superdeformation phenomenon in the rare earth region (A {approx} 150). The superdeformed (SD) states in Gadolinium and Dysprosium isotopes were produced via heavy-ion induced reactions and studied with the (EUROGAM EUROpean GAmma-ray Microscope) gamma multidetector array. Precise level attenuation method (DSAM). From the derived quadrupole moments, we find large differences in deformation between the yrast bands in neighbour nuclei explained in terms of the case of nuclei corresponding to an axis ratio of 2:1, the shell gaps are not fixed at a specific particle number and deformation. Furthermore the present results indicate that the deformations associated with identical bands are different supporting the picture that mass and deformation changes tend to compensate in SB bands with the same moments of inertia. (author). 114 refs.

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Monoclonal antibodies (MAbs) 19-9 and 73-3 specific for human colon adenocarcinoma were labelled with a high number of gadolinium atoms. Twenty five DTPA were chelated per MAb, with only slight loss of immunoreactivity. The NMR contrast agent Gd-25 DTPA-MAb 19-9 or 73-3 ((Gd) 17 mumole/kg, (MAb) 60 microM) was injected into nude mice bearing human colon adenocarcinoma (SW948). Tumors were removed 24 hr after injection and T1 was measured in vitro. T1 relaxation time varied according to MAb specificity against tumour targets; T1 decreased 20% for MAb 19-9 and MAb 73-3 with SW948 tumor. Imaging was performed with this model. Very good contrast was obtained 24 hr after Gd-25 DTPA-MAb injection.

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Purpose: With intracranial tumors a flat, contrast-enhancing, probably dural structure adjacent to the tumor can occasionally be observed on gadolinium-DTPA enhanced MR images. Therefore we have attempted to evaluate a tumor infiltration of this enthancement on MRI. Material and Methods: This study included 50 patients. 19 patients had a dural thickening at the tumor base (13 meningiomas and 6 metastases), while 31 patients did not (12 meningiomas and 19 metastases). Studies included plane T_2-weighted spin echo (SE) images as well as T_1-weighted axial, coronal, or sagittal plains with and without contrast agent. Histopathological examinations, were done on the tumor base adjacent to the dura mater. Results: 7 of 12 meningiomas showed a meningeal thickening on MRI with histopathologically proven tumor infiltration as did also 5 of 6 metastases. But 3 of 12 meningiomas and 15 of 19 metastases without dural thickening at the tumor base also showed tumor invasion ...

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Cardiac disease research relies increasingly on small animal models and non-invasive imaging methods such as positron emission tomography (PET) and magnetic resonance imaging (MRI). Delayed enhancement magnetic resonance imaging (DE-MRI) using gadolinium-based contrast agents appear to be a visualizing infracted myocardium with high spatial resolution. Polar map (or bull's-eye image) was used to determination of the myocardial infarction area. Polar map is a comprehensive interpretation of the left ventricle. The infarct size was computed as the fraction of the total polar map areas. The threshold was computed as the percentage of mean intensity of the normal region. In other study, 50% predefined threshold value in varying range (30?70%) was most commonly use. However, predefined threshold value isn't acceptance in all case. The purpose of this study was to investigate methodological approach for automatic measurement of rat myocardial infarct size using PET and ...

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Purpose: `Exoscopic` and endoscopic identification of colorectal pathologies via MRI. Methods: 5 patients (36-88 years), two normal and three with different colorectal pathologies (diverticular disease, polyps and carcinoma of the colon), were examined by MRI after colonoscopy. Subsequent to filling of the colon with a gadolinium-water mixture under MRI-monitoring, 3D-data sets of the colon were acquired in prone and supine positions over a 28 sec breathold interval. Subsequently multiplanar T{sub 1}-weighted 2D-sequences were acquired before and following i.v. administration of Gd-DTPA (0.1 mmol/kg BW). All imaging was performed in the coronal orientation. The 3D-data were interactively analysed based on various displays: Maximum intensity projection (MIP), surface shadowed display (SSD), multiplanar reconstruction (MPR), virtual colonoscopy (VC). Results: All of the colorectal pathologies could be interactively diagnosed by MPR. On MIP images some pathologies ...

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To clarify the acidic and alkaline Intergranular Stress Corrosion Cracking (IGSCC) mechanism of thermally treated alloy 690 (alloy 690 TT) and shot peened alloy 800 (alloy 800 SP), C-ring tests were conducted in deaerated HCl solutions and in deaerated NaOH solutions at 350degC, compared with the acidic and the alkaline IGSCC susceptibilities of mill-annealed alloy 600 (alloy 600 MA), full-sensitized one (alloy 600 FS) and thermally treated one (alloy 600 TT). Grain boundary characteristics, such as chromium depleted zone and chromium carbide precipitation, were examined using modified Huey test and Transmission Electron Microscopy. Potential-pH diagram for Ni, Cr, Fe-H_2O system at 350degC was constructed and the solubilities of NiO, Cr_2O_3 and Fe_3O_4 were also calculated to evaluate the stability of oxide films which were formed on the surfaces of alloy 690, 800 and 600. Under the acidic condition, the IGSCC susceptibility of alloy 800 SP was high. The ...

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In this paper, the influence of plasma nitriding at temperature 720 deg. C for 20 h on the surface microstructure and interface microstructure of electroplated chromium coating was investigated. In these conditions, interdiffusion, mixing and reaction phenomena of elements originating from the substrate and coating material are more likely to occur, thus increasing the bonding strength between the coating and carbon steel substrate. The change of the structures from the substrate side to the coating surface, and the effect of the substrate steel on the interface structure were studied by cross-sectional transmission electron microscope observation (XTEM). The nitride layer formed on the surface was analyzed by X-ray diffraction method (XRD). After treatment at above conditions a 6-7 #mu#m thick nitride compound layer was formed in surface region and the same thick carbide compound layer was also formed in the interface region between electroplated chromium coating ...

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Microstructure characterization is important for controlling the quality of laser welding. In the present work, a detailed microstructure characterization by transmission electron microscopy was carried out on the laser welding cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft and an unambiguous identification of phases in the weldment was accomplished. It was found that there are #gamma#-FeCrNiC austenite solid solution dendrites as the matrix, (Nb, Ti) C type MC carbides, fine and dispersed Ni_3 Al #gamma#' phase as well as Laves particles in the interdendritic region of the seam zone. A brief discussion was given for their existence based on both kinetic and thermodynamic principles.

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The effect of W and V on the high temperature strength properties of 12%Cr-15%Mn austenitic steels was studied from the view point of precipitation hardening and internal stress. The contribution of W addition to the tensile and creep-rupture strength was not so large. By contrast the combined addition of W and V increased the strength considerably. These are resulted from the precipitation of fine vanadium nitride (VN) within grains and the enhancement of M_2_3C_6 type carbide precipitation at grain boundaries. The V added material had large internal stress value which is considered to be due to dislocation movement disturbed by fine vanadium nitrides. (author).

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The purpose of this study is to investigate the influence of tungsten carbide/carbon (WC/C) coating on the surface durability of casehardened steel gear. Two kinds of WC/C coatings were deposited on the ground gear pair made of chromium molybdenum steel with carburizing and quenching. One is the conventional WC/C coating, and the other is WC/C coating with about 1 ?m CrN interlayer. Here, the WC/C-coated test pinion and the WC/C-coated one with CrN interlayer are represented by WT and ST, respectively. Non-coated test pinion is represented by NT. The surface roughness along the tooth profile direction of WT and ST was almost the same as that of NT. A spur gear test was carried out with an IAE power circulating type gear test rig under EP gear oil lubricating condition. The fatal failure mo...

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In this book are found technical and scientific papers on the main works of the Direction of the Fuel Cycle (DCC) in France. The study fields are: the up-side of the nuclear fuel cycle with theoretical studies (plasma simulation) and technological developments and instrumentation (lasers diodes, carbides plasma projection, carbon 13 enrichment); the down-side nuclear fuel cycle with theoretical studies (ion Eu{sup 3+} complexation simulation, decay simulation, uranium and plutonium diffusion study, electrolyser operating simulation), scenario studies ( recycling, wastes management), experimental studies; dismantling and cleaning (soils cleaning, surface-active agent for decontamination, fault tree analysis); analysis with expert systems and mass spectrometry. (A.L.B.)

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Twelve powders of TiO_2-Y_2O_3-ZrO_2 solid solution of the methodically changed composition were prepared by a coprecipitation-calcination technique. After mixing with phenol-formaldehyde resin, the powders were calcinated for 2 hours at 1200"oC in vacuum. The resultant composite powders contained TiC and non-reacted carbon. Green compacts were sintered in vacuum at 1500"oC for 2 hours. A temperature increase was stopped at 1200"oC to react remains of carbon. There were two carbides in the composites TiC and ZrC. TiC non-stoichiometry depended on carbon content in the system. Phase composition of the depended on of titania and yttria in zirconia solid solution. The majority of the samples showed two tetragonal zirconia phases differing in lattice parameter and tetragonality. (author)

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Advances in nuclear reactor technology and the use of gas-cooled fast reactors require the development of new materials that can operate at the higher temperatures expected in these systems. These include refractory alloys base on Nb, Zr, Ta, Mo, W, and Re; ceramics and composites such as those based on silicon carbide (SiCf-SiC); carbon-carbon composites; and advanced coatings. Besides the ability to handle higher expected temperatures, effective heat transfer between reactor componets is necessary for improved efficiency. Improving thermal conductivity of the materials used in nuclear fuels and other temperature critical components can lower the center-line fuel temperature and thereby enhance durability and reduce the risk of premature failure.

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On the basis of a numerical model, the temperature and liquid fraction of spray-formed H13 tool steel are calculated as a function of time. Results show that a preheated substrate at the appropriate temperature can lead to very low porosity by increasing the liquid fraction in the deposited steel. The calculated cooling rate can lead to a microstructure consisting of martensite, lower bainite, retained austenite, and proeutectoid carbides in as-spray-formed material. In the temperature range between the solidus and liquidus temperatures, the calculated temperature of the spray-formed material increases with increasing substrate preheat temperature, resulting in a very low porosity by increasing the liquid fraction of the deposited steel. In the temperature region where austenite decomposit...

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Transmission electron microscopy studies on solution-annealed Alloy 800 revealed small (100-200 nm), spherical-shaped titanium carbide (face centered cubic structure) and large (200 nm-5 #mu#m), faceted titanium nitride (hexagonal structure) particles randomly distributed in the austenite matrix. The volume fraction of former particles was found to be greater than that of the latter. Corrosion studies of the alloy in acidic, chlorides and acidic chloride environments at room temperature indicated that the passivity of Alloy 800 was adversely affected by the addition Cl"- ions. X-ray photoelectron spectroscopy revealed that the surface film formed on the alloy at the onset of passivity consisted of Cr"3"+ (as Cr_2O_3), without any Fe"3"+/Fe"2"+ or Ni"2"+. Scanning electron microscopy studies indicated initiation of pitting at large, faceted particles, not at small, spherical-shaped ones.

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By applying lock-in thermography imaging, light-beam-induced current imaging, electron-beam-induced current imaging at different stages of sample preparation, and infrared light microscopy in transmission mode, the physical nature of the dominant material-induced shunts in multicrystalline solar cells made from p-type silicon material has been investigated. It turns out that these shunts are due to silicon carbide (SiC) filaments, which grow preferentially in grain boundaries and cross the whole cell. These filaments are highly n-type doped, like the emitter layer on the surface of the cells. They are electrically connected both with the emitter and with the back contact, thereby producing internal shunts in the solar cell.

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The subscale Varestraint test has been used to determine the relative hot cracking susceptibility of the fusion zone in four commercial heats of alloy 800. Although all four heats were susceptible to cracking, one heat exhibited a significant increase in cracking relative to the other three. Optical metallography revealed that nearly all the cracking was localized along fusion zone grain boundaries. Microprobe analysis of the grain boundaries detected high concentrations of titanium, silicon, and niobium resulting from partitioning during solidification. The fusion zone hot cracking mechanism in alloy 800 involves the complex interaction of titanium, silicon, niobium, and carbon along the solidification boundaries. SEM and Auger analyses of the hot crack fracture surfaces revealed the presence of (Ti, Nb)-rich carbides, suggesting that these particles precipitate from the liquid which solidifies last on the fracture surface. 23 references.

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Intergranular corrosion (IGC) resistance of types 304LN and 316LN stainless steels (SS) thermally aged at 823, 873, and 923 K for various durations was assessed by ASTM A262 practice A test (electrolytic etch test) and electrochemical potentiodynamic reactivation (EPR) test. The results indicated that the type 316LN SS has significantly improved IGC resistance compared to 304LN SS. Based on the results of these tests, time-temperature-sensitization (TTS) diagrams were developed for both alloys. The secondary precipitates formed during thermal aging treatments were electrochemically extracted and analyzed by X-ray diffraction (XRD) to determine the types of precipitates formed during the aging treatments. The results indicated that the precipitates were mostly of M_2_3C_6 carbides.

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The tribological properties of gas pressure sintered SiAlON and its composite with 18wt% silicon carbide (SiC) against two different mating materials, i.e., alumina and SiAlON are evaluated. SiAlON and SiAlON-18%SiC composite ceramics were prepared by pressure less sintering and gas pressure sintering. Fretting wear tests were carried out under dry unlubricated ambient conditions (room temperature 23-25^oC; relative humidity 50-55%) with a load of 8N for 45,000 cycles. Friction and wear properties of SiAlON-SiC proved better than the monolithic SiAlON. The formation of silica roll like structure on the composite worn surface was observed.

British Library Electronic Table of Contents (United Kingdom)

The effects of a modifier that contains Rare Earths (RE), low melting point alloy (Al-Bi-Sb) and Ca-Si alloy on an ultrahigh carbon steel containing 1.9wt.% C were studied. Microstructure characterization was carried out with optical microscopy (OM) and scanning electronic microscopy (SEM) combined with energy-dispersive spectrometry (EDS). Upon modification, the continuous eutectic carbide network structure was broken up and changed to a partly isolated and finer blocky structure in the as-cast alloy. Differential scanning calorimetry (DSC) revealed that the eutectoid temperature increased and the eutectic temperature decreased for the modified alloy. Modification also improved the impact toughness of the tempered steel, with a significant increase from 6.5 to 12.6Jcm^-^2, despite the har...

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A rapid combustion unit (Baird and Tatlock) incorporating a combustion chamber provided with baffle plates for complete combustion of the sample without the use of a catalyst has been assembled in a glove box for the determination of carbon and hydrogen in actinide complexes. The unit has been modified employing a movable electric furnace and a proportional temperature controller, for decomposition of the sample at desired heating rates. The set-up was standardised employing various reference materials such as benzoic acid, acetanilide, sulphanilamide and 1-chloro 2:4 dinitrobenzene and the standard deviation in the measurements evaluated. It has also been used successfully for the determination of carbon in uranium carbide and carbon and hydrogen in some uranyl-#beta#-diketone-amine N-oxide complexes and in plutonium(IV) oxalate. (auth.).

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The published literature is reviewed and supplemented by current information from the author's laboratory, to show the influence of various compositional, heat treatment and thermomechanical factors on the structural characteristics of Alloy 800. The features discussed include carbon, aluminium, titanium and boron, solution treatment, ageing treatments with and without applied strain, and cold working. Examples of the aspects reviewed include the effect of heat treatment and service or testing temperature on the austenite grain size, and the relative importance of M_2_3C_6 and TiC, the influence of carbon level on gamma prime, the effect of residual or steady stress combined with time at temperature on changes in carbide or gamma prime morphology, and on the appearance of sigma or other intermetallic phases. The questions posed by these features are discussed generally, in terms of their effect on the mechanical properties at ambient and elevated temperatures and ...

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A study of the magnetic properties and the heat capacity as functions of temperature and magnetic field of two ternary carbides RNiC_2, where R=La and Ce, confirms that LaNiC_2 becomes superconducting at T_c=2.7thinspK, and that CeNiC_2 orders antiferromagnetically below 18thinspK. LaNiC_2 is a conventional superconductor with a critical field of 900 Oe at T=2thinspK. CeNiC_2 obeys the Curie-Weiss law between 50 and 300thinspK showing the nearly full Ce"3"+ magnetic moment, p_e_f_f=2.47(1)#mu#_B, and has a negative paramagnetic Weiss temperature #THETA#_p=-18.3(8)thinspK. A low net magnetic moment in the ordered state, which is far from saturation in a magnetic field of 5thinspT, is consistent with an antiferromagnetic ground state. Below 20thinspK CeNiC_2 shows multiple-step magnetic transitions at 18, 10, and 2.4thinspK. Both LaNiC_2 (in the normal state) and CeNiC_2 have the same electronic heat capacity, #gamma#=6.5(2)thinspmJ/molthinspK"2, which is typical for ...

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Plasma immersion ion implantation (PIII) is an effective materials modification and synthesis technique but has seldom been applied to ceramic materials due to the high electrical resistance that reduces the ion bombardment energy and sometimes causes serious electrical arcing in the instrument. Even in cases where PIII is applicable, the surface properties of the implanted insulating materials can be seriously affected due to the low ion energy and materials damage from electrical arcing. In order to enhance the surface and mechanical properties such as wear resistance of ceramic materials used in many industrial applications, surface modification is needed. In this work, we conduct carbon implantation into sintered #alpha#-SiC (silicon carbides that are widely used in vacuum ceramic bearings) using mesh-assisted plasma immersion ion implantation to enhance the surface properties. The use of a conducting grid is necessitated by the high electrical resistance that ...

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Purpose: With intracranial tumors a flat, contrast-enhancing, probably dural structure adjacent to the tumor can occasionally be observed on gadolinium-DTPA enhanced MR images. Therefore we have attempted to evaluate a tumor infiltration of this enthancement on MRI. Material and Methods: This study included 50 patients. 19 patients had a dural thickening at the tumor base (13 meningiomas and 6 metastases), while 31 patients did not (12 meningiomas and 19 metastases). Studies included plane T{sub 2}-weighted spin echo (SE) images as well as T{sub 1}-weighted axial, coronal, or sagittal plains with and without contrast agent. Histopathological examinations, were done on the tumor base adjacent to the dura mater. Results: 7 of 12 meningiomas showed a meningeal thickening on MRI with histopathologically proven tumor infiltration as did also 5 of 6 metastases. But 3 of 12 meningiomas and 15 of 19 metastases without dural thickening at the tumor base also showed tumor ...

International Nuclear Information System (INIS)

Addition of Gadolinium Nitrate as chemical shim to moderator heavy water of 540 MWe PHWR, at 15 mg/kg level (at a pH of 5.0) is practiced for reactor shutdown purposes. Presently a strong acid cation exchanger column is used for this purpose. During this operation, the moderator pH of 3.8, with the IX column outlet pH of ?3.5-3.6 was observed against the technical specification demand that when Gd is present, the pH of moderator must be in the range of 5.0-5.5. In order to achieve an iso-pH regime during Gd removal, studies were conducted using a mixed bed of strong acid cation resin plus a weak base anion resin (loaded in the volume ratio of 1 : 6), backed up in the same column (bottom most layer) by a 5 % nitric acid loaded weak base resin and topped by a strong acid cation resin (uppermost layer) simulating system flow velocity and percentage loading of resin. Using such a column it is demonstrated that Gd removal could be achieved simultaneously maintaining the ...

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The effect that different chemical and physical atomic environments can have on the relative intensities of radiative electron transitions from the filling of K shell vacancies was investigated. The method used involved the detection of photoionization induced X-ray fluorescence. An experimental system based on a hyper pure germanium detector (HPGE) was used to measure the relative K-L and K-M X-ray yields from the photofluorescence of a series of lanthanide elements and compounds. A background subtraction and peak integration strategy was employed which accounted for scattering in the samples and scattering of the flux from the radioisotope photoionization sources. Analysis of the data resulted in a tabulation of relative K/sub #beta#//K/sub #alpha#/ X-ray intensity ratios. The measured relative K/sub #beta#//K/sub #alpha#/ X-ray intensity ratios were compared to the calculated values predicted by the theoretical development of Scofield and the average of previous experimental values ...

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Two neutron emesis experiments were conducted at the Armed Forces Radiobiology Research Institute (AFRRI). In both experiments (described as Phase I and Phase II) the radiation dose required to cause emesis in 50% of subjects (ED50) was determined for both neutron reactor and gamma reactor source radiation. Emesis onset, offset and duration times post-exposure are reported. Neutrons were maximized from the reactor by passing the beam through a 15.25 cm (6 in.) thick lead wall to filter out gamma photons. Gamma rays were maximized by thermalizing neutrons in 30.5 cm (12 in.) of water, then absorbing the thermal neutrons in a gadolinium-cadmium shield. In Phase I, 28 dogs were exposed to radiation: 12 were exposed to gamma photons at the rate of 0.69 Gy/min and 16 were exposed to neutrons at 1.2 Gy/min. In Phase II, 58 dogs in 3 groups were exposed to radiation: 19 were exposed in the gamma group at 0.75 Gy/min, 20 were exposed in the undrugged neutron group at 1.62 ...

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The photoluminescence spectra of the lanthanum and gadolinium oxynitrates doped with Eu[sup 3+], REONO[sub 3]:Eu[sup 3+] (RE=La and Gd) were measured at 77 and 300 K. The [sup 7]F[sub J] (J=0-5) energy level schemes for the 4f [sup 6] electron configuration were simulated by a C[sub 2v] phenomenological crystal field (CF). The nine non-zero CF parameters for the C[sub 2v] site symmetry reproduce the experimental energy level schemes with rms deviations of 7 and 5 cm[sup -1] for the LaONO[sub 3] and GdONO[sub 3] hosts, respectively. The CF effect is stronger in the lanthanum host although otherwise the CF parameters for the two oxynitrate hosts differ only slightly. The B[sup k][sub 2] (k=2, 4 and 6) values are low indicating only a slight deviation from a higher C[sub 4v] symmetry. The B[sup 2][sub 0], B[sup 4][sub 0] and B[sup 4][sub 4] parameters assume high values which are similar to those obtained previously for the other RE oxy compounds, i.e. oxyhalides, ...

International Nuclear Information System (INIS)

There is significant interest in using computed tomography (CT) for in vivo imaging applications in mouse models of disease. Most commercially available mouse x-ray CT scanners utilize a charge-coupled device (CCD) detector coupled via fibre optic taper to a phosphor screen. However, there has been little research to determine if this is the optimum detector for the specific task of in vivo mouse imaging. To investigate this issue, we have evaluated four detectors, including an amorphous selenium (a-Se) detector, an amorphous silicon (a-Si) detector with a gadolinium oxysulphide (GOS) screen, a CCD with a 3:1 fibre taper and a GOS screen, and a CCD with a 2:1 fibre taper and both GOS and thallium-doped caesium iodide (CsI:Tl) screens. The detectors were evaluated by measuring the modulation transfer function (MTF), noise power spectrum (NPS), detective quantum efficiency (DQE), stability over multiple exposures, and noise in reconstructed CT images. The a-Se ...

Science.gov (United States)

The extensive reserves of mined coal types, their great variety and the complexity of the composition and properties, as well as their important role as an energy fuel and industrial feedstock, cause one to give special attention to their classification. Of course, one of the principal fields of technological processing of coal is coking. In addition to the production of blast furnace coke, in the future specialized plants will be developed for production of coke and other carbonized materials for non-blast-furnace processes (electrothermal processes, production of calcium carbide, ferroalloys, zinc, yellow phosphorus, copper, etc.). One important area is new nonfuel uses, including a number of processes for processing of coal feedstocks to obtain a wide range of carbonaceous materials (coal-graphite products, carbon black, adsorbents, etc.), liquid fuels, and chemical products. In choosing a given area of coal utilization a determining factor is the ...

Energy Technology Data Exchange (ETDEWEB)

The dispersion of more than 20 vol pct submicrometer ceramic particles within a metallic matrix and the deposition of such a cermet to form a thick and tough coating presents problems. Most of the coating techniques have failed in attempting to homogeneously disperse very fine and hard particles in large amounts while avoiding their decomposition or reaction with the metal matrix during the deposition process. A simple and efficient method has been developed for producing ceramic-containing composite coatings. It consists in synthesizing cermet-based materials and in depositing them by a rapid solidification process, such as thermal spraying. Boride- and carbide-based materials have been successfully obtained by plasma spraying reactive powders comprising the basic reagents. These materials, with a microstructure of submicrometer ceramic particles dispersed in a metallic matrix, exhibit good wear-resistant properties (abrasion and sliding wear). Finally, reactive ...

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This paper presents the technical and economic studies performed by CEMIG, Companhia Energetica de Minas Gerais, Brazil, concerning the use of closing resistor in its extra-high voltage (EHV) breakers. The analysis emphasizes the advantages which could be achieved with the elimination of the resistor as far as costs and reliability are concerned. This evaluation was motivated by two 500 kV breaker failures resulting from the breakdown of the closing resistor operation mechanism. These occurrences resulted in operative restriction for CEMIG EHV system. The analysis demanded a review of the capability criteria of silicon carbide (Si C) gap arresters, which are still greatly used in CEMIG EHV System, and of the procedures to be applied when carrying out the transient studies. The investigation resulted in the prompt removal of closing resistors from circuit breakers in CEMIG extra-high voltage system generating an economy of approximately U$ 840,00 and an improvement ...

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Microstructural analyses by several advanced metallographic techniques were conducted on austenitic stainless steel mockup and core shroud welds that had cracked in boiling water reactors. Contrary to previous beliefs, heat-affected zones of the cracked Type 304L, as well as 304 SS core shroud welds and mockup shielded-metal-arc welds, were free of grain-boundary carbides, which shows that core shroud failure cannot be explained by classical intergranular stress corrosion cracking. Neither martensite nor delta-ferrite films were present on the grain boundaries. However, as a result of exposure to welding fumes, the heat-affected zones of the core shroud welds were significantly contaminated by oxygen and fluorine, which migrate to grain boundaries. Significant oxygen contamination seems to promote fluorine contamination and suppress thermal sensitization. Results of slow-strain-rate tensile tests also indicate that fluorine exacerbates the susceptibility of ...

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Nanocrystalline cemented tungsten carbide has attracted considerable interests for use in cutting tool because of its superior mechanical properties. In this study, nano-sized powders of mixed WC and Co were prepared from attrition-milled oxides by a gas reduction-carburization process. The effects of compacting pressure, heating schedule, additional ball-milling, and the presence of a grain growth inhibitor on the sintering properties of the nano-sized WC-Co powders were examined. The grain size and phases in WC-Co alloy were clearly affected by compacting pressure. Because of the trapped gases and the lower melting point of the cobalt binder, when a compact of nano-sized WC-Co powder was sintered through a heating schedule with holding steps, the sintered alloy maintained the small size of WC grains without any {eta} phase. In addition, the additional ball-milling improved the microstructure and mechanical properties of the nano-sized WC-Co powder by producing a ...

Energy Technology Data Exchange (ETDEWEB)

Silver zeolite is used to capture radioiodines from air cleaning systems in some nuclear facilities at the Idaho National Engineering Laboratory. It may become radioactively contaminated and/or poisoned by hydrocarbon vapors, which diminishes its capacity for iodine. Silver zeolite contains up to 38 wt% silver. A pyrometallurgical process was developed to reclaim the silver before disposing of the unserviceable zeolite as a radioactive waste. A flux was formulated to convert the refractory aluminosilicate zeolite structure into a low-melting fluid slag, with Na{sub 2}O added as NAOH instead of Na{sub 2}CO{sub 3} to avoid severe foaming due to CO{sub 2} evolution. A propane-fired furnace was built to smelt 45 kg charges at 1300C in a carbon-bonded silicon carbide crucible. A total of 218 kg (7000 tr oz) of silver was reclaimed from 1050 kg of unserviceable zeolite. Silver recoveries of 97% were achieved, and the radioisotopes were fixed as stable silicates in a ...

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A major problem in the maintenance and rehabilitation of pipelines is the removal of the original coating system, particularly in cases where the coating contains sticky components or adhesives. It has been found that such coatings can be removed by use of a cleaning machine with a plurality of counter-rotating carbide-tipped tools mounted to an oscillating head embracing the pipe, and which is operable at the same time to travel along the length of the pipe. Such a machine can be designed to effect a positive, gentle milling operation on the pipe surface to remove the coating efficiently and at relatively low power consumption. A particular advantage of the pipe cleaning machine of the invention is that its design and manner of operation allows it to be used in the field to clean an uncovered section of pipeline, for example a natural gas pipeline, without the requirement of removing the pipeline section from the ditch in which it is seated. The machine of the ...

International Nuclear Information System (INIS)

Nanodimensional powders of cubic copper ferrite are synthesized by two-steps procedure of co-precipitation of copper and iron hydroxide carbonates, followed by mechanochemical treatment. X-ray powder diffraction, Moessbauer spectroscopy and temperature-programmed reduction are used for the characterization of the obtained materials. Their catalytic behavior is tested in methanol decomposition to hydrogen and CO and total oxidation of toluene. Formation of nanosized ferrite material is registered even after one hour of milling time. It is established that the prolonging of treatment procedure decreases the dispersion of the obtained product with the appearance of Fe2O3. It is demonstrated that the catalytic behavior of the samples depends not only on their initial phase composition, but on the concomitant ferrite phase transformations by the influence of the reaction medium. -- Graphical abstract: It is demonstrated that the catalytic behavior of the obtained copper ferrites depends not ...

International Nuclear Information System (INIS)

Buried silicon carbide (SiC) microstructures with lateral dimensions in the #mu#m range were formed by high-dose projection of 1.5 MeV C"2"+ ions in Si(100) at different doses and temperatures and subsequent annealing for 10 h at 1250 deg. C. Sections of individual SiC microstructures were prepared for cross-sectional transmission electron microscopy (TEM) analysis using a focused ion beam (FIB). Besides the possibility to select an individual microstructure, the FIB technique has the advantage of producing specimen foils of uniform thickness. Therefore, it was possible to map the carbon concentration of microstructures by energy filtered TEM (EFTEM) using the C_K absorption edge without the need of any sample thickness correction. Local overstoichiometric (>50%) carbon concentrations are shown to be correlated to the formation of an amorphous phase in the SiC and to significant swelling visible at the Si wafer surface 2 #mu#m above.

Energy Technology Data Exchange (ETDEWEB)

The interrelationship between the testing temperature and HfC strength increment of an arc-melted W-3.6Re-0.4HfC was determined from 1950 K to 2980 K in a vacuum of better than 1.3{times}10{sup {minus}5} Pa (10{sup {minus}7} torr). The present research was focused on the characteristic temperature at which the rapid coarsening of HfC particles occurred and the effect of the second-phase particle size on the high temperature strength properties of this material. It was found that the HfC particle strengthening was effective in a W-Re matrix up to a characteristic temperature of 2450 K in the short-term tensile test. Carbon was found to be the rate-limiting solute in the HfC particle growth. The strength of HfC strengthened alloy at temperature above 0.5 T{sub m} is proportional to the square root of particle volume fraction. The yield strengths of W-3.6Re-0.26HfC calculated based on the particle statistical distribution had good agreement with the experimental values from 1950 K to 2980 ...

International Nuclear Information System (INIS)

Past elastic-plastic fracture studies for leak-before-break (LBB) assessment of low alloy steel pipings have been focused mostly on the behavior of base metals and their weld metals. In contrast, the heat-affected zone (HAZ) of a welded pipe has not been studied in detail primarily because the size of the HAZ is too small to make specimens for mechanical properties measurements. In this study, microstructural analyses, microhardness tests, tensile tests and J-R tests have been conducted as a function of distance from a fusion line and temperature for HAZ materials of SA106Gr.C low alloy piping steels. For the ferrite-pearlite steels such as SA106Gr.C, the HAZ specimens showed a higher yield strength and fracture toughness compared with those of its base metal. These characteristics, despite of grain coarsening, can be explained by cleaner microstructures of HAZ materials with a finer morphology of carbides compared with pearlitic-ferritic base metals. However, the ...

International Nuclear Information System (INIS)

In the heat-affected zones (HAZ) of low alloy steels used for nuclear pressure vessel, microstructural changes, such as grain coarsening, carbide precipitation, and martensite formation, generally occur and cause a deterioration of toughness and an increase in sensitivity to brittle fracture. Metallographic analyses of low alloy steel welds reveal significantly different regions in HAZ microstructures. In 2-pass welds, there were seven characteristic regions in the HAZ determined by the peak temperature, to which the region was exposed during the weld thermal cycle: a coarse-grained region, a fine-grained region, an intercritical region, and subcritical region. The coarse-grained region can be categorized into four zones according to the reheating temperature as follows : an unaltered coarse-grained zone (UCGHAZ), a supercritically reheated coarse grained zone (SCRCGHAZ), an intercritically reheated coarse-grained zone (ICRCGHAZ), and an subcritically reheated ...

International Nuclear Information System (INIS)

The effects of Fe and B_4C on the sintering behavior and mechanical properties of TiB_2 ceramics have been studied. Sintering was performed in an Ar atmosphere at 2000 degrees C using attrition-milled TiB_2 powder. When a small amount of Fe (0.5 wt%) was added, abnormal grain growth occurred and the sintered density was low. In the case of B_4C added along with 0.5 wt% Fe, however, abnormal grain growth was remarkably suppressed, and the sintered density was increased up to 95% of theoretical. But with excess Fe addition (5 wt%), B_4C grains did not act as a grain growth inhibitor, and B_4C grains were frequently trapped in large TiB_2 grains. The best mechanical properties were obtained for the TiB_2-10 wt% B_4C-0.5 wt% Fe ceramics, which exhibited a three-point bending strength of 400 MPa and a fracture toughness of 5.5 MPa #centre dot# m"1"/"2.

International Nuclear Information System (INIS)

Displacements per atom (DPA) is a widely used damage unit for displacement damage in nuclear materials. Calculating the DPA for SiC irradiated in a particular facility requires a knowledge of the neutron spectrum as well as specific information about displacement damage in that material. In recent years significant improvements in displacement damage information for SiC have been generated, especially the energy required to displace an atom in an irradiation event and the models used to describe electronic and nuclear stopping. Using this information, numerical solutions for the displacement functions in SiC have been determined from coupled integro-differential equations for displacements in polyatomic materials and applied in calculations of spectral-averaged displacement cross sections for SiC. This procedure has been used to generate spectrally averaged displacement cross sections for SiC in a number of reactors used for radiation damage testing of fusion materials, as well as the ...

Energy Technology Data Exchange (ETDEWEB)

In this work, an attempt was made to develop a novel type of wear-resistant composite employing a TiNi alloy matrix reinforced by hard particles. Titanium carbide was chosen as the reinforcing phase because of its high hardness and TiNi alloy as the matrix due to its pseudoelasticity and good toughness. TiC particles may sustain external load, while the TiNi matrix may accommodate deformation, absorb impact energy and retain the hard particles. Such a combination is expected to lead to an enhanced wear resistance, compared to TiNi alloy. As a matter of fact, some efforts were previously made to develop TiNi-matrix composite reinforced by ceramic particles. However, the emphasis of those studies was put on effects of the reinforcing particles on the phase transformation behavior, shape memory effect and some mechanical properties of the composite; no attempt was made to explore the potential benefit of the material for wear application.

International Nuclear Information System (INIS)

The microstructures of so called high temperature alloys, which have been developed for service temperatures up to 800"0C, are not necessarily stable at higher temperatures. The mobility of alloying elements is very high in FeCrNi alloys at 950 "0C e.g. iron, chromium or nickel can diffuse up to 0.1 mm distance in one year, which is about a grain diameter. Interstitials like carbon or nitrogen show a four orders of magnitude higher diffusivity than the alloying elements. In addition, the carbon solubility in this type of alloy is reported to be very low. Therefore the alloys are supersaturated with carbon after heat treatment above 1100 "0C and water quenching although the absolute carbon content is very low. At service temperatures around 800"0C the solubility of carbon is still about one order of magnitude lower than at heat treatment temperature. This will lead, together with the high mobility of elements, to precipitation of carbides even after short times and ...

Energy Technology Data Exchange (ETDEWEB)

Aluminum-containing intergranular phases, forming intergranular films and secondary phase particles at triple-junctions in SiC hot-pressed with aluminum, boron, and carbon additions, were studied by transmission electron microscopy. Statistical high-resolution electron microscopy study of intergranular films indicated that a large fraction of the vitreous intergranular films in the s-hot-pressed SiC crystallized during postannealing in argon above 1000 C. However, brief heating to 1900 C indeed re-melted 25 percent of the crystallized intergranular films. The structural transitions were reflected in the statistical width distributions of the amorphous grain boundary layers. At triple-junctions, Al2O3, Al2OC-SiC solid solution, and mullite phases were newly identified. These phases,together with others reported before are represented in a quaternary phase diagram for 1900 C. It is proposed that a SiC-Al2OC liquid domain is to be included in this phase diagram.

Energy Technology Data Exchange (ETDEWEB)

We report on a recent search for {bar {nu}}{sub e} appearance from stopped {pi}{sup +} {yields} {mu}{sup +}{nu}{sub {mu}} and {mu}{sup +} {yields} e{sup +}{nu}{sub e}{bar {nu}}{sub {mu}} decay made by the LAMPF experiment E645. The appearance of {bar {nu}}{sub e} may occur from {bar {nu}}{sub {mu}} {yields} {bar {nu}}{sub e}, {nu}{sub e} {yields} {bar {nu}}{sub eL}, or {nu}{sub {mu}} {yields} {bar {nu}}{sub eL} oscillations. Appearance may also occur from rare {mu}{sup +} {yields} e{sup +}{bar {nu}}{sub e}{nu}{sub {mu}} decay, which is allowed by a multiplicative lepton charge conservation law. The neutrino energies range from E{sub {nu}} = 0 to 52.8MeV. The neutrino detector, which is located 26.1 meters from the neutrino source, consists of a segmented liquid scintillator and proportional drift tube central detector surrounded by both active and passive shielding. The central detector detects {bar {nu}}{sub e} through the {bar {nu}}{sub e}p {yields} ne{sup +} Charge Current (CC) ...

Energy Technology Data Exchange (ETDEWEB)

An approach to the ductile fracture of ultra high strength steels has been evaluated. According to this approach the critical crack tip opening, delta/sub IC/, will scale with X/sub 0/(R/sub V//R/sub I/vertical bar/sub R//sub 0/. X/sub 0/ is an average inclusion spacing and (R/sub V/R/sub I/)vertical bar/sub R//sub 0/ is the void radius divided by the radius of the inclusion nucleating the void evaluated at the average inclusion size. AF1410 was selected to test this approach because it has exceptionally high fracture toughness on aging at 510/sup 0/C and because its toughness varies markedly with aging temperature. The results from this and earlier work showed a linear relationship exists between delta/sub IC/ and X/sub 0/(R/sub V//R/sub I/)vertical bar /sub R//sub 0/ for values of delta/sub IC/ ranging from about 8 ..mu..m to 60 ..mu..m. The values of (R/sub V//R/sub I/)vertical bar /sub R//sub 0/ for AF1410 aged at 425/sup 0/C and 510/sup 0/C differed by a factor of two. Because the ...

Energy Technology Data Exchange (ETDEWEB)

Exploratory experiments of laser welding cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft were conducted. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. The corresponding mechanisms were discussed in detail. Results showed that the laser-welded seam had non-equilibrium solidified microstructures consisting of FeCr{sub 0.29}Ni{sub 0.16}C{sub 0.06} austenite solid solution dendrites as the dominant and some fine and dispersed Ni{sub 3}Al {gamma}' phase and Laves particles as well as little amount of MC short stick or particle-like carbides distributed in the interdendritic regions. The average microhardness of the welded seam was relatively uniform and lower than that of the base metal due to partial ...

Energy Technology Data Exchange (ETDEWEB)

Out of the R and D of mesoscopic metal group composite materials, the paper described the fiscal 1997 results. In the in-situ method as a composite material making method, elucidated to some degree were chemical composition of Fe-C-Cr-V-Nb-Mo-W-Ni base multi-dimensional alloys, and wear resistance and oxidation resistance of MC type carbide dispersion multi-phase texture crystallizing as primary crystal and eutectic. In the composite material making with ceramic fiber and alloy by the pressure infiltration method, the paper clarified the texture formation mechanism in solidification/heat treatment by a combination of Al alloys and alumina long fiber, and the relation between fiber configuration and wear resistance. By MA and MG methods as the powder metallurgy composite material making method, a composed body of {alpha}-stainless steel of Fe-12%Cr composition and M23C6 of 40-90vol% are designed for alloy composition, and powder of amorphous or hyperfine texture was ...

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The availability of reactor-produced radioisotopes in the United States for use in medical research and nuclear medicine has traditionally depended on facilities which are an integral part of the US national laboratories and a few reactors at universities. One exception is the reactor in Sterling Forest, New York, originally operated as part of the Cintichem (Union Carbide) system, which is currently in the process of permanent shutdown. Since there are no industry-run reactors in the US, the national laboratories and universities thus play a critical role in providing reactor-produced radioisotopes for medical research and clinical use. The goal of this survey is to provide a comprehensive summary of these production capabilities. With the temporary shutdown of the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR) in November 1986, the radioisotopes required for DOE-supported radionuclide generators were made available at the Brookhaven ...

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We have demonstrated in this work (1) that methane is readily activated at mild conditions (100{degree}C, 1 torr) over a relatively noble metal, Pd. This was observed using a stepped and kinked Pd(679) crystal (1), and other crystal faces are now being investigated to establish whether the cracking of the C-H bond of methane on Pd is structure sensitive or structure insensitive. Oxygen chemisorption is extremely structure sensitive: weakly bonded, highly reactive oxygen overlayers form on Pd(100) surface (2), while strongly bonded, moderately reactive oxygen overlayers form on Pd(111) and Pd(679). Reaction of the weakly bonded oxygen with surface carbide gives rise to CO{sub 2} over clean Pd(100) but to CO over halogen-doped Pd(100) (3--5). The effect of halogens is primarily ensemble-controlling, or oxygen-supply restricting, but long range influence of surface Cl on the strength of the Pd-O bond has also been observed (3). Because the overall chemistry of methane ...

International Nuclear Information System (INIS)

Thermo-reactive diffusion chromizing followed by pulsed plasma nitriding were carried out on AISI 52100 and 8620 bearing steels. The chromized samples were pulse-plasma nitrided for 5 h at 500 deg. C in various N_2-H_2 gas mixtures. The coated steels were characterized using scanning electron microscopy, X-ray diffraction and microhardness testing. The unlubricated wear behaviors of only chromized and duplex treated steels were investigated in ball-on-disc system tests at room temperature. X-ray diffraction patterns of the duplex treated samples containing H_2 indicated the formation of dominant CrN and Cr_2N nitrides as well as the formation of Cr_3C_2 and Cr_7C_3 carbides. Gas mixtures in the plasma nitriding, which was performed after chromizing, have a significant influence on the wear rate of the duplex treated steels. The wear and friction tests showed that the lowest friction coefficient and wear rates were observed for the samples duplex treated in a 50%N_2 ...

International Nuclear Information System (INIS)

Experiments of autogenous laser full penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 3.5 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser welding velocity, flow rate of side-blow shielding gas, defocusing distance were investigated. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. Results show that high quality full penetration laser-welded joint can be obtained by optimizing the welding velocity, flow rate of shielding gas and defocusing distance. The laser-welded seam have non-equilibrium solidified microstructures consisting of #gamma#-FeCr_0_._2_9Ni_0_._1_6C_0_._0_6 austenite solid solution dendrites as the dominant and very small amount ...

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Since 1991, secondary side cracking has become a major concern in EDF steam generators. At 350 C, IGSCC of Alloy 600 was found in pure NaOH solutions from 4 to 500 g/l, with a maximum at 100 g/l. From the present results and available data, IGSCC of Alloy 690 occurred in pure NaOH solutions from 40 to 500 g/l, but the greatest sensitivity was observed at 100 g/l. TG/IGSCC of Alloy 800 became more severe with increasing NaOH solutions, from 10 to 500 g/l. On the whole, the ranking for SCC-resistance was Alloy 600 < Alloy 800 < Alloy 690. A significant improvement was still obtained with 690TT with intergranular carbides (industrial tubes) and perhaps with Alloy 800 NG (nuclear grade), but both alloys cracked at the highest stresses. IGSCC susceptibility of Alloy 600 MA was higher for the tubes with the lowest values of the yield stress. The depth of IGA in the case of Alloy 600 was higher than for Alloy 690; for this alloy, it appeared to be general oxidation. ...

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Purpose: The aim of this study was to demonstrate the typical appearance of ganglioneuromas in computer-assisted tomography (CT), and magnetic resonance imaging (MRI). Material and methods: Retrospective analysis of diagnostic imaging (9 CT, 6 MRI) in 9 children aged 3 to 15 years with the histological diagnosis of ganglioneuroma. Results: The tomographies showed large (max. 13.4 cm in diameter) round or oval tumors with sharp delineation. The sites of the tumors were the retroperitoneum (5), the mediastinum (3), and the adrenal gland (1). Intraspinal tumor involvement occurred in 4 cases. On comparing CT with MRI, MRI was more accurate in defining the intraspinal involvement. The ganglioneuromas were of hypodense appearance in the native CT scan and showed moderate enhancement upon administration of contrast media. In five patients tumor calcifications with a disseminated sprinkled pattern were seen in CT. In MRI T{sub 1}-weighted scans the tumors were homogeneous and hypointense, ...

Energy Technology Data Exchange (ETDEWEB)

The extensive research and development effort was initiated by the U.S. Department of Energy (DOE) in 2002 at West Virginia University (WVU) in order to investigate practical ways of reducing the structural weight and increasing the durability of heavy vehicles through the judicious use of lightweight composite materials. While this project was initially focused on specific Metal Matrix Composite (MMC) material, namely Aluminum/Silicon Carbide (Al/SiC) commercially referenced as ''LANXIDE'', the current research effort was expanded from the component level to the system level and from MMC to other composite material systems. Broadening the scope of this research is warranted not only by the structural and economical deficiencies of the ''LANXIDE'' MMC material, but also by the strong coupling that exists between the material and the geometric characteristics of the structure. Such coupling ...

International Nuclear Information System (INIS)

SiC-AlN and SiC-SiAlON refractory composites were obtained by means of nitridation of the mixtures of silicon carbide (SiC) powder with a broad granulometric distribution and powders of aluminium (Al) and aluminium-silicon (Al-Si) mixtures. The mixtures of the composition Al-25% Si, Al-50% Si and Al-75% Si were previously prepared by means of 'mechanical alloying' technique. Thermodynamic analysis was accomplished in order to evaluate the viability of SiC-SiAlON and SiC-AlN refractories production by the chosen processing method, and the results confirmed viability of such. Investigation of nitridation of Al and Al-Si powder compacts in order to obtain the AlN and #beta#-SiAlON matrix phases of the composite was accomplished by means of differential thermal analysis (DTA) and thermogravimetric analysis (TG). The results of the thermal analysis show that nitridation of the Al-25% Si, Al-50% Si and Al-75% Si resulting in p-SiAlON formation occur at temperatures of ...