320 Matching Results

Search Results

Advanced search parameters have been applied.

Integrated Design and Rapid Development of Refractory Metal Based Alloys for Fossil Energy Applications

Description: One common barrier in the development of new technologies for future energy generating systems is insufficiency of existing materials at high temperatures (>1150oC) and aggressive atmospheres (e.g., steam, oxygen, CO2). To overcome this barrier, integrated design methodology will be applied to the development of refractory metal based alloys. The integrated design utilizes the multi-scale computational methods to design materials for requirements of processing and performance. This report summarizes the integrated design approach to the alloy development and project accomplishments in FY 2008.
Date: July 1, 2008
Creator: Dogan, O.N.; King, P.E. & Gao, M.C.
Partner: UNT Libraries Government Documents Department

A STUDY OF PRECIPITATION IN INTERSTITIAL ALLOYS. I. PRECIPITATION SEQUENCE IN Ta-C ALLOYS

Description: A systematic transmission electron microscopy study of carbide precipitation in quenched-aged tantalum-carbon alloys has clarified the mechanism of precipitation in refractory BCC metal-carbon alloys. Diffraction contrast analysis shows that the precipitate platelets lie on {l_brace}310{r_brace} planes of the matrix, are interstitial in nature, and fully coherent before they thicken further and lose coherency. The precipitation sequence is continuous and involves no renucleation during the formation of the non-coherent phase. Thus, the final orientation relationship of the precipitate with the matrix already is found at the earliest stage at which it is possible to detect it. The interpretation of the results indicates that, as in FCC alloys, vacancies play an important role in the precipitation process during the nucleation and early growth stages and permit the formation of the hexagonal equilibrium M{sub 2}C structure early in the sequence. The model proposed to explain the observations is also consistent with the multistage hardening observed in quenched-aged refractory metal interstitial alloys.
Date: August 1, 1980
Creator: Dahmen, U.; Westmacott, K.H. & Thomas, G.
Partner: UNT Libraries Government Documents Department

Pack cementation diffusion coatings for Fe-base and refractory alloys. Final report

Description: With the aid of computer-assisted calculations of the equilibrium vapor pressures in halide-activated cementation packs, processing conditions have been identified and experimentally verified for the codeposition of two or more alloying elements in a diffusion coating on a variety of steels and refractory metal alloys. A new comprehensive theory to treat the multi-component thermodynamic equilibria in the gas phase for several coexisting solid phases was developed and used. Many different processes to deposit various types of coatings on several types of steels were developed: Cr-Si codeposition for low- or medium-carbon steels, Cr-Al codeposition on low-carbon steels to yield either a Kanthal-type composition (Fe-25Cr-4Al in wt.%) or else a (Fe, Cr){sub 3}Al surface composition. An Fe{sub 3}Al substrate was aluminized to achieve an FeAl surface composition, and boron was also added to ductilize the coating. The developmental Cr-lean ORNL alloys with exceptional creep resistance were Cr-Al coated to achieve excellent oxidation resistance. Alloy wires of Ni-base were aluminized to provide an average composition of Ni{sub 3}Al for use as welding rods. Several different refractory metal alloys based on Cr-Cr{sub 2}Nb have been silicided, also with germanium additions, to provide excellent oxidation resistance. A couple of developmental Cr-Zr alloys were similarly coated and tested.
Date: March 10, 1998
Creator: Rapp, R. A.
Partner: UNT Libraries Government Documents Department

Directed Light Fabrication of Refractory Metals and Alloys

Description: This report covers work performed under Order No. FA0000020 AN Contract DE-AC12-76SN00052 for deposition of refractory pure metals and alloys using the Directed Light Fabrication (DLF) process and represents the progress in depositing these materials through September 1998. In extending the DLF process technology to refractory metals for producing fully dense, structurally sound deposits, several problems have become evident. 1. Control of porosity in DLF-deposited refractory metal is difficult because of gases, apparently present in commercially purchased refractory metal powder starting materials. 2. The radiant heat from the molten pool during deposition melts the DLF powder feed nozzle. 3. The high reflectivity of molten refractory metals, at the Nd-YAG laser wavelength (1.06{micro}m), produces damaging back reflections to the optical train and fiber optic delivery system that can terminate DLF processing. 4. The current limits on the maximum available laser power to prevent back reflection damage limit the parameter range available for densification of refractory metals. The work to date concentrated on niobium, W-25Re, and spherodized tungsten. Niobium samples, made from hydride-dehydride powder, had minimal gas porosity and the deposition parameters were optimized; however, test plates were not made at this time. W-25Re samples, containing sodium and potassium from a precipitation process, were made and porosity was a problem for all samples although minimized with some process parameters. Deposits made from potassium reduced tungsten that was plasma spherodized were made with minimized porosity. Results of this work indicate that further gas analysis of starting powders and de-gassing of starting powders and/or gas removal during deposition of refractory metals is required.
Date: May 14, 1999
Creator: Fonseca, J.C.; Lewis, G.K.; Dickerson, P.G. & Nemec, R.B.
Partner: UNT Libraries Government Documents Department

Fast neutron environments.

Description: The goal of this LDRD project is to develop a rapid first-order experimental procedure for the testing of advanced cladding materials that may be considered for generation IV nuclear reactors. In order to investigate this, a technique was developed to expose the coupons of potential materials to high displacement damage at elevated temperatures to simulate the neutron environment expected in Generation IV reactors. This was completed through a high temperature high-energy heavy-ion implantation. The mechanical properties of the ion irradiated region were tested by either micropillar compression or nanoindentation to determine the local properties, as a function of the implantation dose and exposure temperature. In order to directly compare the microstructural evolution and property degradation from the accelerated testing and classical neutron testing, 316L, 409, and 420 stainless steels were tested. In addition, two sets of diffusion couples from 316L and HT9 stainless steels with various refractory metals. This study has shown that if the ion irradiation size scale is taken into consideration when developing and analyzing the mechanical property data, significant insight into the structural properties of the potential cladding materials can be gained in about a week.
Date: October 1, 2011
Creator: Buchheit, Thomas Edward; Kotula, Paul Gabriel; Lu, Ping; Brewer, Luke N. (Naval Postgraduate School, Monterey, CA); Goods, Steven Howard (Sandia National Laboratories, Livermore, CA); Foiles, Stephen Martin et al.
Partner: UNT Libraries Government Documents Department

Microstructure and High Temperature Oxidation Behavior of Cr-W Alloys

Description: Cr alloys containing 0-30%W by weight were investigated for use in elevated temperature applications. The alloys were melted in a water-cooled, copper-hearth arc furnace. Microstructure of the alloys was characterized using x-ray diffraction, scanning electron microscopy, and light microscopy. A pseudocyclic oxidation test was employed to study scale formation at 1000ºC in dry air. The scale was predominantly chromia and spalled upon cooling. Alloying with aluminum up to 8 weight percent reduced the spalling drastically. Furthermore, aluminizing the surface of the Cr-W alloys completely stopped the spalling.
Date: February 1, 2007
Creator: Dogan, O.N.
Partner: UNT Libraries Government Documents Department

High Pressure - High Temperature Polymorphism in Ta: Resolving an Ongoing Experimental Controversy

Description: Phase diagrams of refractory metals remain essentially unknown. Moreover, there is an ongoing controversy over the high pressure (P) melting temperatures of these metals: results of diamond anvil cell (DAC) and shock wave experiments differ by at least a factor of two. From an extensive ab initio study on tantalum we discovered that the body-centered cubic phase, its physical phase at ambient conditions, transforms to another solid phase, possibly hexagonal omega phase, at high temperature (T). Hence the sample motion observed in DAC experiments is not due to melting but internal stresses accompanying a solid-solid transformation, as explained in more detail in our work. In view of our results on tantalum and previous work on molybdenum, as well as other published data, it is highly plausible that high-PT polymorphism is a general feature of Groups V and VI refractory metals.
Date: April 7, 2010
Creator: Burkovsky, L; Chen, S P; Preston, D L; Belonoshko, A B; Rosengren, A; Mikhaylushkin, A S et al.
Partner: UNT Libraries Government Documents Department

Modification of Thermal Emission via Metallic Photonic Crystals

Description: Photonic crystals are materials that are periodically structured on an optical length scale. It was previously demonstrated that the glow, or thermal emission, of tungsten photonic crystals that have a specific structure - known as the 'woodpile structure' - could be modified to reduce the amount of infrared radiation from the material. This ability has implications for improving the efficiency of thermal emission sources and for thermophotovoltaic devices. The study of this effect had been limited because the fabrication of metallic woodpile structures had previously required a complex fabrication process. In this project we pursued several approaches to simplify the fabrication of metallic photonic crystals that are useful for modification of thermal emission. First, we used the self-assembly of micrometer-scale spheres into colloidal crystals known as synthetic opals. These opals can then be infiltrated with a metal and the spheres removed to obtain a structure, known as an inverse opal, in which a three-dimensional array of bubbles is embedded in a film. Second, we used direct laser writing, in which the focus of an infrared laser is moved through a thin film of photoresist to form lines by multiphoton polymerization. Proper layering of such lines can lead to a scaffold with the woodpile structure, which can be coated with a refractory metal. Third, we explored a completely new approach to modified thermal emission - thin metal foils that contain a simple periodic surface pattern, as shown in Fig. 1. When such a foil is heated, surface plasmons are excited that propagate along the metal interface. If these waves strike the pattern, they can be converted into thermal emission with specific properties.
Date: July 30, 2012
Creator: Norris, David J.; Stein, Andreas & George, Steven M.
Partner: UNT Libraries Government Documents Department

Manufacturing Ultra-Precision Meso-scale Products by Coining

Description: A method for replicating ultra-precision, meso-scale features onto a near-net-shape metallic blank has been demonstrated. The 'coining' technology can be used to imprint a wide range of features and/or profiles into two opposing surfaces. The instrumented system provides the ability to measure and control the product thickness and total thickness variation (TTV). The coining mechanism relies on kinematic principles to accurately and efficiently produce ultra-precision work pieces without the production of by products such as machining chips, or grinding swarf while preserving surface finish, material structure and overall form. Coining has been developed as a niche process for manufacturing difficult to machine, millimeter size components made from materials that may present hazardous conditions. In the case described in this paper a refractory metal part, tantalum (Ta) was produced with 4 {micro}m peak to valley 50 {micro}m special wavelength sine wave coined into the surface of 50 {micro}m blank. This technique shows promise for use on ductile materials that cannot be precision machined with conventional single crystal diamond tooling and/or has strict requirements on subsurface damage, surface impurities and grain structure. As a production process, it can be used to reduce manufacturing costs where large numbers of ultra-precision, repetitive designs are required and produce parts out of hazardous materials without generating added waste.
Date: February 18, 2010
Creator: Seugling, R M; Davis, P J; Rickens, K; Osmer, J & Brinksmeier, E
Partner: UNT Libraries Government Documents Department

Laser Surface Alloying of Refractory Metals on Aluminum for Enhanced Corrosion Resistance: Experimental and Computational Approaches

Description: Aluminum (Al) and its alloys are widely used in various technological applications, mainly due to the excellent thermal conductivity, non-magnetic, ecofriendly, easy formability and good recyclability. However due to the inferior corrosion resistance its applications are hampered in various engineering sectors. Besides, the corrosion related failures such as leakage of gas from pipeline, catastrophic breakdown of bridges and fire accidents in processing plants further puts the human life in jeopardy. Within the United States over $ 400 billion dollars per year are spent over research to understand and prevent the corrosion related failures. Recently, the development of transition metal(TM) aluminides (AlxTMy, where, TM = Mo, W, Ta, Nb, Cr, Zr and V) has received the global attention mainly due to high strength at elevated temperatures, light-weight, excellent corrosion and wear resistance. In light of this, surface modification via laser surface alloying (LSA) is a promising engineering approach to mitigate the corrosion and wear problems. In the present study the attempts are made to study the Al-Mo, Al-W, Al-Nb, and Al-Ta systems as a potential corrosion resistant coatings on aluminum. The refractory metal (Mo, W, Nb, Ta) precursor deposit was spray coated separately on aluminum substrate and was subsequently surface alloyed using a continuous wave diode-pumped ytterbium laser at varying laser energy densities. Microstructural analysis was conducted using scanning electron microscopy and further X-ray diffractometry was carried out to evaluate the various phases evolved during laser surface alloying. Corrosion resistance of laser alloyed coatings were evaluated using open circuit potential, cyclic potentiodynamic polarization, electrochemical impedance spectroscopy measurements were performed in 0.6 M NaCl solution (pH:6.9±0.2, 23˚C). Open circuit potential measurements indicate the more stable (steady state) potential values over long periods after laser surface alloying. Cyclic polarization results indicated reduction in the corrosion current density, enhancement in the polarization resistance, and ...
Date: December 2014
Creator: Rajamure, Ravi Shanker
Partner: UNT Libraries

Cermet crucible for metallurgical processing

Description: A cermet crucible for metallurgically processing metals having high melting points comprising a body consisting essentially of a mixture of calcium oxide and erbium metal, the mixture comprising calcium oxide in a range between about 50 and 90% by weight and erbium metal in a range between about 10 and 50% by weight.
Date: December 31, 1994
Creator: Boring, C.P.
Partner: UNT Libraries Government Documents Department

Chemical vapor deposition of refractory ternary nitrides for advanced diffusion barriers

Description: Refractory ternary nitride films for diffusion barriers in microelectronics have been grown using chemical vapor deposition. Thin films of titanium-silicon-nitride, tungsten-boron-nitride, and tungsten-silicon-nitride of various compositions have been deposited on 150 mm Si wafers. The microstructure of the films are either fully amorphous for the tungsten based films, or nauocrystalline TiN in an amorphous matrix for titanium-silicon-nitride. All films exhibit step coverages suitable for use in future microelectronics generations. Selected films have been tested as diffusion barriers between copper and silicon, and generally perform extremely weH. These fiIms are promising candidates for advanced diffusion barriers for microelectronics applications. The manufacturing of silicon wafers into integrated circuits uses many different process and materials. The manufacturing process is usually divided into two parts: the front end of line (FEOL) and the back end of line (BEOL). In the FEOL the individual transistors that are the heart of an integrated circuit are made on the silicon wafer. The responsibility of the BEOL is to wire all the transistors together to make a complete circuit. The transistors are fabricated in the silicon itself. The wiring is made out of metal, currently aluminum and tungsten, insulated by silicon dioxide, see Figure 1. Unfortunately, silicon will diffuse into aluminum, causing aluminum spiking of junctions, killing transistors. Similarly, during chemical vapor deposition (CVD) of tungsten from ~fj, the reactivity of the fluorine can cause "worn-holes" in the silicon, also destroying transistors. The solution to these problems is a so-called diffusion barrier, which will allow current to pass from the transistors to the wiring, but will prevent reactions between silicon and the metal.
Date: September 22, 1998
Creator: Custer, Jonathan S.; Fleming, James G.; Roherty-Osmun, Elizabeth & Smith, Paul Martin
Partner: UNT Libraries Government Documents Department

Microstructures and oxidation behavior of some Molybdenum based alloys

Description: The advent of Ni based superalloys revolutionized the high temperature alloy industry. These materials are capable of operating in extremely harsh environments, comprising of temperatures around 1050 C, under oxidative conditions. Demands for increased fuel efficiency, however, has highlighted the need for materials that can be used under oxidative conditions at temperatures in excess of 1200 C. The Ni based superalloys are restricted to lower temperatures due to the presence of a number of low melting phases that melt in the 1250 - 1450 C, resulting in softening of the alloys above 1000 C. Therefore, recent research directions have been skewed towards exploring and developing newer alloy systems. This thesis comprises a part of such an effort. Techniques for rapid thermodynamic assessments were developed and applied to two different systems - Mo-Si alloys with transition metal substitutions (and this forms the first part of the thesis) and Ni-Al alloys with added components for providing high temperature strength and ductility. A hierarchical approach towards alloy design indicated the Mo-Ni-Al system as a prospective candidate for high temperature applications. Investigations on microstructures and oxidation behavior, under both isothermal and cyclic conditions, of these alloys constitute the second part of this thesis. It was seen that refractory metal systems show a marked microstructure dependence of oxidation.
Date: December 15, 2010
Creator: Ray, Pratik Kumar
Partner: UNT Libraries Government Documents Department

THE CHOICE OF THE PROPER REFRACTORY FOR THE CASTING OF HIGHMELTING ELECTROPOSITIVE METALS

Description: As titanium, zirconium, and other of the high melting electropositive metals become more important, the problem of using suitable refractory materials for their casting becomes more important. This paper discusses the method of choosing and testing possible container materials. To make the discussion more specific, titanium is used as an example. As titanium melt at 2000 {+-} 10 K, it is immediately clear that one is restricted to refractory materials melting considerably above 2000 K. This greatly limits the possible materials that might be considered. The possibility of using any pure high melting element can be quickly eliminated as titanium reacts quite vigorously with non-metals such as carbon and due to its high boiling point and therefore high internal pressure, one can predict that it dissolves even the most refractory metals. Examination of phase diagrams confirms that even metals such as tantalum, tungsten, and rhenium would not be able to resist attack by titanium. One is thus limited to high melting compounds such as the oxides, sulfides, nitrides, carbides, silicides, and borides. The first consideration is that, if possible, one would use a compound which is thermodynamically stable in the presence of titanium metal at 2000 K. Titanium should not be able to react with the refractory to form a titanium compound. Thus all compounds less stable than the titanium compound which can exist in equilibrium with titanium metal are excluded.
Date: June 20, 1950
Creator: Brewer, Leo
Partner: UNT Libraries Government Documents Department

Characterization of Niobium Oxide Films Deposited by High Target Utilization Sputter Sources

Description: High quality, refractory metal, oxide coatings are required in a variety of applications such as laser optics, micro-electronic insulating layers, nano-device structures, electro-optic multilayers, sensors and corrosion barriers. A common oxide deposition technique is reactive sputtering because the kinetic mechanism vaporizes almost any solid material in vacuum. Also, the sputtered molecules have higher energies than those generated from thermal evaporation, and so the condensates are smoother and denser than those from thermally-evaporated films. In the typical sputtering system, target erosion is a factor that drives machine availability. In some situations such as nano-layered capacitors, where the device's performance characteristics depends on thick layers, target life becomes a limiting factor on the maximizing device functionality. The keen interest to increase target utilization in sputtering has been addressed in a variety of ways such as target geometry, rotating magnets, and/or shaped magnet arrays. Also, a recent sputtering system has been developed that generates a high density plasma, directs the plasma beam towards the target in a uniform fashion, and erodes the target in a uniform fashion. The purpose of this paper is to characterize and compare niobia films deposited by two types of high target utilization sputtering sources, a rotating magnetron and a high density plasma source. The oxide of interest in this study is niobia because of its high refractive index. The quality of the niobia films were characterized spectroscopically in optical transmission, ellipsometrically, and chemical stoichiometry with X-ray photo-electron spectroscopy. The refractive index, extinction coefficients, Cauchy constants were derived from the ellipsometric modeling. The mechanical properties of coating density and stress are also determined.
Date: January 29, 2007
Creator: Chow, R; Ellis, A D; Loomis, G E & Rana, S I
Partner: UNT Libraries Government Documents Department

Refractory metal welding using a 3.3 kW diode pumped Nd:YAG laser.

Description: Recent developments in multi-kilowatt continuous wave lasers allow fiber optic delivery to high-purity controlled atmosphere chambers and challenge electron beam welding with improvements in cost, complexity, beam quality and flexibility. Questions remain with respect to the performance of these lasers for refractory alloy welding regarding damaging back reflections, laser-plume interactions, and sufficiency of beam intensity and coupled energy. System performance for the welding of various refractory metal alloys and comparisons to electron beam welds will be presented.
Date: January 1, 2001
Creator: Carpenter, R. W. (Robert W.); Piltch, M. S. (Martin S.); Nemec, R. B. (Ronald B.) & Milewski, J. O. (John O.)
Partner: UNT Libraries Government Documents Department

Oxidation and Volatilization from Tantalum Alloy During Air Exposure

Description: Tantalum alloys are one of the refractory metals with renewed consideration for high temperatures in fusion reactor applications. Tantalum alloys perform well in protective environments but are oxidized readily in gases containing higher oxygen levels. In addition, the radioactive isotope Ta-182 would be produced in tantalum and could be a significant contributor to dose if mobilized. Other isotopes of importance are produced from tungsten and hafnium. Mobilization of activated products during an accident with air ingress is therefore a safety issue. In this study, we measured the extent of oxidation and mobilization from tantalum alloy T-222 oxidized in flowing air between 500 and 1200 degrees C. This alloy nominally contains 10 wt% tungsten, 2.5 wt% hafnium and 0.01 wt% carbon. We found that the mobilization of Ta and Hf was closely linked to the occurrence of oxide spalling. These elements showed no migration from the test chamber. Some W was mobilized by volatilization as evidenced by transport from the chamber. Tungsten volatilization could occur primarily during initial stages of oxidation before the formation of an oxide scale impedes the process. The mobilization of Ta and W are presented in terms of the mass flux (g/m2-h) as a function of test temperature. These measurements along with specific designs, activation calculations, and accident scenarios provide information useful for dose calculations of future fusion devices.
Date: October 1, 2000
Creator: Smolik, Galen Richard; Petti, David Andrew & Schuetz, Stanley Thomas
Partner: UNT Libraries Government Documents Department

Preliminary Design of Pinhole camera for NSLS-II Project.

Description: The NSLS-II Light Source being built at Brookhaven National Laboratory is expected to provide very small emittances and electron beam sizes. High resolution imaging systems are required in order to provide robust measurements. The pinhole camera will utilize 6-fold magnification with a pinhole placed inside a crotch absorber. The pinhole is protected from high power synchrotron radiation with a filter made of refractory metal. In this paper we provide resolution analyses, heat load calculations, and optimization details for the NSLS-II pinhole camera, including beamline design.
Date: May 4, 2009
Creator: Pinayev,I.; Kosciuk, B. & Singh, O.
Partner: UNT Libraries Government Documents Department

Elevated Temperature Sensors for On-Line Critical Equipment Health Monitoring

Description: The objective of this research program is to improve high temperature piezoelectric aluminum nitride (AlN) sensor technology to make it useful for instrumentation and health monitoring of current and future electrical power generation equipment. The program will extend the temperature range of the sensor from approximately 700 C to above 1000 C, and ultrasonic coupling to objects at these temperatures will be investigated and tailored for use with the sensor. The chemical vapor deposition (CVD) AlN deposition process was successfully transferred from film production on tungsten carbide substrates to titanium alloy and silicon carbide (SiC) substrates. Further evaluation of the piezoelectric films on titanium caused it to be discarded as a candidate material due to an excessive thermal expansion coefficient mismatch, causing film failure upon reheating from room temperature. Deposition on SiC is proceeding well, with a highly conductive grade of silicon carbide required for practical use. Additional substrate materials, including refractory metals and conductive ceramics, have been considered but are generally not promising in light of the experience with titanium. Pulsed laser deposition (PLD) was investigated as an alternate means of creating the films as an alternative to CVD. A concurrent effort has focused on investigation of means of coupling ultrasound from the sensor into the test object at high temperature. A literature search combined with preliminary experimentation has resulted in the selection of two methods for coupling: low melting point glasses and metal foil- pressure couplant. The work in the next two years of the program will include continued improvement of the CVD deposition process, experimental testing of films and coupling at high temperatures, and a laboratory demonstration of the sensor in a simulated industrial application
Date: September 29, 2003
Creator: Sebastian, James
Partner: UNT Libraries Government Documents Department

Thermophotovoltaic emitter material selection and design

Description: Thermophotovoltaics (TPV) is a potentially attractive direct energy conversion technology. It reduces the need for complex machinery with moving parts and maintenance. TPV generators can be run from a variety of heat sources including waste heat for smaller scale operations. The US Naval Academy`s goal was to build a small experimental thermophotovoltaic generator powered by combustion gases from a General Electric T-58 helicopter gas turbine. The design of the generator imposes material limitations that directly affect emitter and structural materials selection. This paper details emitter material goals and requirements, and the methods used to select suitable candidate emitter materials for further testing.
Date: July 1, 1997
Creator: Saxton, P.C.; Moran, A.L.; Harper, M.J. & Lindler, K.W.
Partner: UNT Libraries Government Documents Department

Materials research and development for fusion energy applications

Description: Some of the critical issues associated with materials selection for proposed magnetic fusion reactors are reviewed, with a brief overview of refractory alloys (vanadium, tantalum, molybdenum, tungsten) and primary emphasis on ceramic materials. SiC/SiC composites are under consideration for the first wall and blanket structure, and dielectric insulators will be used for the heating, control and diagnostic measurement of the fusion plasma. Key issues for SiC/SiC composites include radiation-induced degradation in the strength and thermal conductivity. Recent work has focused on the development of radiation-resistant fibers and fiber/matrix interfaces (porous SiC, SiC multilayers) which would also produce improved SiC/SiC performance for applications such as heat engines and aerospace components. The key physical parameters for dielectrics include electrical conductivity, dielectric loss tangent and thermal conductivity. Ionizing radiation can increase the electrical conductivity of insulators by many orders of magnitude, and surface leakage currents can compromise the performance of some fusion energy components. Irradiation can cause a pronounced degradation in the loss tangent and thermal conductivity. Fundamental physical parameter measurements on ceramics which are of interest for both fusion and non-fusion applications are discussed.
Date: November 1, 1998
Creator: Zinkle, S.J. & Snead, L.L.
Partner: UNT Libraries Government Documents Department

Fused-salt-liquid-metal corrosion of refractory alloys in the presence of hot cell impurities

Description: The pyrochemical conditioning of spent nuclear fuel for the purpose of final disposal is currently being demonstrated at Argonne National Laboratory (ANL). One aspect of this program is to develop a lithium preprocessing stage for the Fuel Conditioning Facility (FCF). Furthermore, a pilot scale of this preprocessing stage is being designed by ANL-W to demonstrate the in situ hot cell capability of this process. In this pilot scale system, fused lithium chloride salt is saturated with molten lithium to form a powerful fluxing compound with a vigorous reducing agent. During this stage of the fuel conditioning, the reduction will take place at a nominal temperature of 650 C in an argon-cell atmosphere contaminated with up to 10,000 ppm nitrogen, 100 ppm oxygen and 100 ppm of moisture. The maximum local temperature was calculated to be 725 C on the inner shell of the reduction vessel during operation. One of the significant concerns of this project is the system`s corrosion response in the presence of irradiated commercial fuel as well as atmospheric impurities. The purpose of this work was to demonstrate the potential corrosivity of the salt matrix in a worse case environment as well as provide a boundary for allowable impurities in the system during operation.
Date: September 1, 1997
Creator: Eberle, C.S.; Raraz, A.G.; Mishra, B. & Olson, D.L.
Partner: UNT Libraries Government Documents Department

Dry etch development of W/WSi short Gate MESFETs

Description: The use of refractory metal thin films in the fabrication of high-speed, high-density GaAs field effect transistors (FETs) are prominent with applications as interconnects, via plugs, and ohmic and Schottky contacts. Tungsten and tungsten silicide can be used in a self-aligned gate process as the ion implantation mask during the formation of source and drain regions for metal-semiconductor FETs (MESFETs). The gate etch must be highly anisotropic to accurately define the implant region. Reactive ion etch (RIE) techniques have been used to etch W and WSi films in fluorine-based discharges. The etch mechanism tends to be very chemical and often results in severe undercutting of the feature due to the lateral attack of the refractory metal. The undercut is often so severe that critical dimensions are not maintained and gate profiles do not properly align to the implant region resulting in poor device characteristics. As device design rules shrink, the etch requirements and patterning techniques become even more critical.
Date: January 1, 1996
Creator: Shul, R.J.; Sherwin, M.E.; Baca, A.G.; Zolper, J.C. & Rieger, D.J.
Partner: UNT Libraries Government Documents Department