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Task 6.7.3 - Interfacial Mass Transport Effects in Composite Materials

Description: A series of TiNX and Ti(N,O)X films formed from a TiC, N2, H2, and (N2 + 02 ) gas mixture was deposited on aluminum ceramics at 1073 K for 5 hr at atmospheric pressure, according to the procedure described in Dekker et al. These conditions were selected because they offer a reasonable deposition rate and low chlorine content in films. The TiNX films, with two different nonstoichiometries controlled by the ratio of to H2 and two Ti(N,O)X films with different nitrogen and oxygen content were prepared. The N2 and H2 gases were first purified in alkaline pyrogallol and dried over silica gel and further over a copper and palladium catalyst. TiCld concentration in flowing N2 and H2 (70/30) corresponded to its vapor pressure over liquid at 300 K. Film thickness was determined using a multiple interferometer. All of the films obtained were thicker than 1000 nm. Phase analysis and interatomic distances were determined by x-ray diffraction analysis (XRD) at room temperature.
Date: August 1, 1997
Creator: Nowok, Jan W.
Partner: UNT Libraries Government Documents Department

Steady-state creep model for UO$sub 2$

Description: From a review of out-of-pile and in-pile experiments, an analytical model was developed for the steady-state creep of UO$sub 2$: epsilon = [(A$sub 1$ - A$sub 2$F)sigma e/sup -Q$sub 1$/RT/]/[A$sub 3$ + D)G$sup 2$] + [A$sub 4$sigma/ sup 4.5/e/sup -Q$sub 2$/RT/]/[(A$sub 5$ + D)] + A$sub 6$sigma Fe/sub-Q$sub 3$/RT/ , where A$sub 1$ = 9.728 x 10$sup 6$, A$sub 2$ = 3.24 x 10$sup -12$, A$sub 3$ = - 87.7, A$sub 4$ = 1.376 x 10$sup -4$, A$sub 5$ = -90.5, A$sub 6$ = 9.24 x 10$sup - 28$, Q$sub 1$ = 90,000, Q$sub 2$ = 132,000, Q$sub 3$ = 5200 (cal/mole), F = fission rate (8.4 x 10$sup 17$ to 1.18 x 10$sup 20$ f/m$sup 3$s), and G = grain size. (DLC)
Date: January 1, 1975
Creator: Olsen, C.S.
Partner: UNT Libraries Government Documents Department

Sintering of polycrystalline ionic conductors:. beta. ''-Al/sub 2/O/sub 3/ and NASICON

Description: The densification kinetics for both ..beta..''-alumina and NASICON are dramatically different. ..beta..''-Alumina sinters by a reactive liquid process whereas NASICON densifies by a solid state method. More importantly, a qualitative examination of particle and agglomerate distributions, phase composition, linear shrinkage analysis, and heating rate effects can result in a concise determination of sintering processes without recourse to more quantitative techniques. Such a simple procedural method should be a basis for any beginning investigative study into the densification mechanism of new multicomponent ceramic materials.
Date: January 1, 1979
Creator: McEntire, B J; Miller, G R & Gordon, R S
Partner: UNT Libraries Government Documents Department

Thermal plasma chemical synthesis of powders

Description: Thermal plasma processing has been increasingly used to synthesize submicron powders of high-purity ceramics and metals. The high temperatures generated with the plasma provide a vapor phase reaction zone for elements with high boiling points and refractory materials. An overview is presented on the general plasma technology used in synthesis and on the properties of plasma powders.
Date: January 1, 1985
Creator: Vogt, G.J. & Newkirk, L.R.
Partner: UNT Libraries Government Documents Department

Tungsten Cladding of Tungsten-Uranium Dioxide (W-UO2) Composites by Deposition from Tungsten Hexafluoride (WF6)

Description: A program is being conducted to develop a process for cladding tungsten and tungsten cermet fuels with tungsten deposited from the vapor state by the hydrogen reduction of tungsten hexafluoride. Early work was performed using recrystallized, high purity, commercial tungsten as the substrate material. Temperatures in the range 660 to 12950F (350 to 1700°C) and pressures from 10 to 350 mm Hg were investigated. Hydrogen to WF 6 ratios of 10: 1 to 150: 1 were utilized. Efforts were directed toward optimizing deposition process parameters to attain control of qualities such as coating thickness, uniformity, density, impurity content, and surface quality. Substrate penetration methods have been investigated in the interest of completely eliminating the interface between the fueled substrate and cladding. In addition, the effects of process parameters and post-cladding heat treatments on the fuel retention properties of clad composites at 4500 degrees F (2480 degrees C) in hydrogen for 2 hours have been evaluated. As a result of work performed during the first phase of the program it has been shown that the rate of deposition of tungsten from WF 6 and the uniformity of the deposit can be varied in a predictable and reproducible manner by exercising control over the temperature, pressure, and gas flow rates at which the deposits are produced. A significant result of the study is the discovery that substrate nucleation and epitaxial growth in deposits made on both unfueled tungsten and fueled substrates may be effected by pretreating the substrates in hydrogen. High temperature fuel retention testing of tungsten clad W-U02 at 45000F (2480 degrees C) in hydrogen for 2 hours has demonstrated that the vapor deposited layer effectively and consistently restricts fuel loss.
Date: February 15, 1965
Creator: Lamartine, J.T. & Hoppe, A.W.
Partner: UNT Libraries Government Documents Department

Bonding of WC with an iron aluminide (FeAl) intermetallic

Description: FeAl, which has high oxidation and sulfidation resistance, was shown to be thermodynamically compatible with WC. Calculations indicate that soly. of WC in liq. Fe-40at.%Al at 1450 C is about 2 at.%. Since liquid FeAl wets WC very well, the WC/FeAl system lends itself to liquid-phase sintering, resulting in close to theoretical densities. Almost fully dense cermets with 20.6 wt% FeAl binder were produced. With one-step infiltration, 98% dense cermets with only 7 wt% FeAl binder were fabricated. RT bend strengths and fracture toughness for WC-20.6 wt% FeAl reached 1680 MPa and 22 MPa{center_dot}m{sup 1/2}. Ductile binder fracture was observed on the fracture surfaces. Pores containing oxide inclusions were found, suggesting that improvements in processing are likely to further improve the mechanical properties. Insufficient process control may explain why WC/FeAlNi cermets did not show improved mechanical properties, although Ni strengthens FeAl. For WC bonded with FeAl, mechanical properties were measured at RT and 800 C. Bend strengths at 800 C in air increased with WC volume fraction, and fracture toughness were higher than at RT.
Date: August 1, 1996
Creator: Schneibel, J. H. & Subramanian, R.
Partner: UNT Libraries Government Documents Department

HIP Joining of Cemented Carbides

Description: Hot Isostatic Pressing (HIP) is investigated as a technique for joining the cermet WC-15% Co to itself. Encapsulation of the specimens prior to HIPing was carried out using steel encapsulation, glass encapsulation and self encapsulation. The bonds were evaluated using a four point bend method. It is shown that the glass and steel encapsulation methods have a number of inherent problems which make them inappropriate for near net shape processing. In contrast the novel self encapsulation method, described for the first time in this communication, is both simple and effective, producing joined material with bulk strength. The concept of self encapsulation is potentially widely applicable for joining composite materials.
Date: April 1, 1999
Creator: Derby, B. & Miodownik, M.
Partner: UNT Libraries Government Documents Department

Heavy Vehicle Propulsion Materials Program

Description: The objective of the Heavy Vehicle Propulsion Materials Program is to develop the enabling materials technology for the clean, high-efficiency diesel truck engines of the future. The development of cleaner, higher-efficiency diesel engines imposes greater mechanical, thermal, and tribological demands on materials of construction. Often the enabling technology for a new engine component is the material from which the part can be made. The Heavy Vehicle Propulsion Materials Program is a partnership between the Department of Energy (DOE), and the diesel engine companies in the United States, materials suppliers, national laboratories, and universities. A comprehensive research and development program has been developed to meet the enabling materials requirements for the diesel engines of the future. Advanced materials, including high-temperature metal alloys, intermetallics, cermets, ceramics, amorphous materials, metal- and ceramic-matrix composites, and coatings, are investigated for critical engine applications.
Date: April 26, 1999
Creator: Diamond, Sidney & Johnson, D. Ray
Partner: UNT Libraries Government Documents Department

Development of dense ceramic membranes for hydrogen separation.

Description: We developed novel cermet (i.e., ceramic-metal composite) membranes for separating hydrogen from gas mixtures at high temperature and pressure. The hydrogen permeation rate in the temperature range of 600-900 C was determined for three classes of cermet membranes (ANL-1, ANL-2, and ANL-3). Among these membranes, ANL-3 showed the highest hydrogen permeation rate, with a maximum flux of 3.2 cm{sup 3}/min-cm{sup 2} for a 0.23-mm-thick membrane at 900 C. Effects of membrane thickness and hydrogen partial pressure on permeation rate indicated that bulk diffusion of hydrogen is rate-limiting for ANL-3 membranes. The lack of degradation in permeation rate during exposure to a simulated syngas mixture suggests that ANL-3 membranes are chemically stable and suitable for long-term operation.
Date: November 1, 2000
Creator: Balachandran, U.; Lee, T. H.; Zhang, G.; Dorris, S. E.; Rothenberger, K. S.; Martello, D. V. et al.
Partner: UNT Libraries Government Documents Department

Heavy Vehicle Propulsion Materials: Recent Progress and Future Plans

Description: The Heavy Vehicle Propulsion Materials Program provides enabling materials technology for the U.S. DOE Office of Heavy Vehicle Technologies (OHVT). The technical agenda for the program is based on an industry assessment and the technology roadmap for the OHVT. A five-year program plan was published in 2000. Major efforts in the program are materials for diesel engine fuel systems, exhaust aftertreatment, and air handling. Additional efforts include diesel engine valve-train materials, structural components, and thermal management. Advanced materials, including high-temperature metal alloys, intermetallics, cermets, ceramics, amorphous materials, metal- and ceramic-matrix composites, and coatings, are investigated for critical engine applications. Selected technical issues and planned and ongoing projects as well as brief summaries of several technical highlights are given.
Date: May 14, 2001
Creator: Johnson, D. Ray & Diamond, Sidney
Partner: UNT Libraries Government Documents Department

Characterizing and modeling the apparent anomalous behavior of resistivity in Cr-Si-O thin films

Description: The Cr-Si-O material system is of interest for use as a thin film resistor. The films are sputter deposited onto conducting substrates from metal oxide compacts using a reactive gas mixture. the cermet films composition range from 50 to 100 vol.% SiO{sub 2} as determined from elemental measurements of the Cr, Si and O content. In a wide range of resistivities from 10{sup 1} to 10 {sup 14} {omega}-cm measured through the film thickness, an apparent anomalous behavior is found with the Cr, Si and O composition. The anomaly can be deducted to a discontinuous variation of resistivity with film composition near 80 vol.% SiO{sub 2}. The film microstructure is characterized as a distribution of conducting metal-silicide particles within an insulating matrix. The effective medium theory is used to predict the variation of conductivity and successfully models the anomalous resistivity behavior.
Date: March 1, 1998
Creator: Jankowski, A.F.
Partner: UNT Libraries Government Documents Department

Mo-Al{sub 2}O{sub 3} cermet research and development

Description: This report describes the results to date of a program that was initiated to predict and measure residual stresses in Mo-Al{sub 2}O{sub 3} cermet-containing components and to develop new materials and processes that would lead to the reduction or elimination of the thermal mismatch stresses. The period of performance includes work performed CY95-97. Excessive thermal mismatch stresses had produced cracking in some cermet-containing neutron tube components. This cracking could lead to a loss of hermeticity or decreased tube reliability. Stress predictions were conducted using finite element models of the various components, along with the thermal coefficient of expansion (CTE), Young`s modulus, and strength properties. A significant portion of the program focused on the property measurements for the existing cermet materials, processing conditions, and the measurement technique. The effects of differences in the properties on the predicted residual stresses were calculated for existing designs. Several potential approaches were evaluated for reducing the residual stresses and cracking in cermet-containing parts including reducing the Mo content of the cermet, substituting a ternary alloy with a better CTE match with alumina, and substituting Nb for Mo. Processing modifications were also investigated for minimizing warpage that occurs during sintering due to differential sintering. These modifications include changing the pressing of the 94ND2 alumina and changing to a 96% alumina powder from AlSiMag.
Date: August 1, 1997
Creator: Glass, S.J.; Monroe, S.L.; Stephens, J.J. & Moore, R.H.
Partner: UNT Libraries Government Documents Department

Development of mixed-conducting ceramic membranes for hydrogen separation.

Description: SrCeO{sub 3}- and BaCeO{sub 3}-based proton conductors have been prepared and their transport properties have been investigated by impedance spectroscopy in conjunction with open circuit voltage and water vapor evolution measurements. BaCe{sub 0.8}Y{sub 0.2}O{sub 3-{delta}} exhibits the highest conductivity in a hydrogen-containing atmosphere; however, its electronic conductivity is not adequate for hydrogen separation in a nongalvanic mode. In an effort to enhance ambipolar conductivity and improve interfacial catalytic properties, BaCe{sub 0.8}Y{sub 0.2}O{sub 3-{delta}} cermets have been fabricated into membranes. The effects of ambipolar conductivity, membrane thickness, and interfacial resistance on permeation rates have been investigated. In particular, the significance of interfacial resistance is emphasized.
Date: May 18, 1998
Creator: Guan, J.
Partner: UNT Libraries Government Documents Department

Design of Experiments Results for the Feedthru Insulator

Description: A design of experiments (DoE) was performed at Ceramtec to improve the yield of a cermet part known as the feedthru insulator. The factors chosen to be varied in this DoE were syringe orifice size, fill condition, solvent, and surfactant. These factors were chosen because of their anticipated effect on the cermet slurry and its consequences to the feedthru insulator in succeeding fabrication operations. Response variables to the DoE were chosen to be indirect indicators of production yield for the feedthru insulator. The solvent amount used to mix the cermet slurry had the greatest overall effect on the response variables. Based upon this DoE, there is the potential to improve the yield not only for the feedthru insulator but for other cermet parts as well. This report thoroughly documents the DoE and contains additional information regarding the feedthru insulator.
Date: December 1, 1999
Creator: BENAVIDES,GILBERT L.; VAN ORNUM,DAVID J.; BACA,MAUREEN R. & APPEL,PATRICIA E.
Partner: UNT Libraries Government Documents Department

Dense ceramic membranes for hydrogen separation.

Description: We have developed cermet membranes that nongalvanically separate hydrogen from gas mixtures. The highest measured hydrogen flux was 20.0 cm{sup 3} (STP)/min-cm{sup 2} for an ANL-3a membrane at 900 C. For ANL-3 membranes with thickness of 40-500 {micro}m, hydrogen permeation is limited by the bulk diffusion of hydrogen through the metal phase. The effect of hydrogen partial pressure on permeation rate confirmed this conclusion, suggesting that higher permeation rates may be obtained by decreasing the membrane thickness. Permeation rate in a syngas atmosphere for times up to 190 h showed no degradation in performance, which indicates that ANL-3 membranes may be suitable for long-term, practical hydrogen separation.
Date: May 7, 2002
Creator: Balachandran, U.; Lee, T. H.; Wang, S.; Zhang, G. & Dorris, S. E.
Partner: UNT Libraries Government Documents Department

High Temperature Materials Laboratory third annual report

Description: The High Temperature Materials Laboratory has completed its third year of operation as a designated DOE User Facility at the Oak Ridge National Laboratory. Growth of the user program is evidenced by the number of outside institutions who have executed user agreements since the facility began operation in 1987. A total of 88 nonproprietary agreements (40 university and 48 industry) and 20 proprietary agreements (1 university, 19 industry) are now in effect. Sixty-eight nonproprietary research proposals (39 from university, 28 from industry, and 1 other government facility) and 8 proprietary proposals were considered during this reporting period. Research projects active in FY 1990 are summarized.
Date: December 1, 1990
Creator: Tennery, V.J. & Foust, F.M.
Partner: UNT Libraries Government Documents Department

Radiation damage of nonmetallic solids

Description: A review of data and information on radiation damage in nonmetallic solids is presented. Discussions are included on defects in nonmetals, radiation damage processes in nonmetals, electronic damage processes, physical damage processes, atomic displacement, photochemical damage processes, and ion implantation. (JRD)
Date: January 1, 1975
Creator: Goland, A.N.
Partner: UNT Libraries Government Documents Department

Thermal conductivity of $sup 238$PuO$sub 2$ powder, intermediates, and dense fuel forms

Description: The thermal conductivities of porous $sup 238$PuO$sub 2$ powder (calcined oxalate), milled powder, and high-density granules were calculated from direct measurements of steady-state temperature profiles resulting from self- heating. Thermal conductivities varied with density, temperature, and gas content of the pores. Errors caused by thermocouple heat conduction were less than 5 percent when the dimensions of the thermal conductivity cell and the thermocouple were properly selected. (auth)
Date: October 1, 1975
Creator: Bickford, D.F. & Crain, B. Jr.
Partner: UNT Libraries Government Documents Department