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Boron nitrides synthesized directly from the elements at high pressures and temperatures

Description: We use angle-resolved synchrotron x-ray diffraction, laser sample heating, and diamond-anvil cells to follow in-situ chemical reactions directly between elemental boron and nitrogen. The structures of the solid reaction products vary with pressure. Below 10 GPa, hexagonal BN is the product; cubic or wurzite BN form at higher pressures. Under nitrogen-rich conditions, another hexagonal allotrope occurs which seems to be a new highly transparent, low density h`-BN. No direct reactions occur at ambient temperature even at pressures as high as 50 GPa, implying that a large activation barrier limits the kinetics of these exothermic processes. Laser heating overcomes the large kinetic activation barrier and initiates spontaneous, self-sustaining exothermic reactions even at moderate pressures.
Date: November 1, 1996
Creator: Nicol, M.; Yoo, C.S.; Akella, J. & Cynn, H.
Partner: UNT Libraries Government Documents Department

Zinc Bromide Combustion: Implications for the Consolidated Incinerator Facility

Description: In the nuclear industry, zinc bromide (ZnBr2) is used for radiation shielding. At Savannah River Site (SRS) zinc bromide solution, in appropriate configurations and housings, was used mainly for shielding in viewing windows in nuclear reactor and separation areas. Waste stream feeds that will be incinerated at the CIF will occasionally include zinc bromide solution/gel matrices.The CIF air pollution systems control uses a water-quench and steam atomizer scrubber that collects salts, ash and trace metals in the liquid phase. Water is re-circulated in the quench unit until a predetermined amount of suspended solids or dissolved salts are present. After reaching the threshold limit, "dirty liquid", also called "blowdown", is pumped to a storage tank in preparation for treatment and disposal. The air pollution control system is coupled to a HEPA pre-filter/filter unit, which removes particulate matter from the flue gas stream (1).The objective of this report is to review existing literature data on the stability of zinc bromide (ZnBr2) at CIF operating temperatures (>870 degrees C (1600 degrees F) and determine what the combustion products are in the presence of excess air. The partitioning of the combustion products among the quencher/scrubber solution, bottom ash and stack will also be evaluated. In this report, side reactions between zinc bromide and its combustion products with fuel oil were not taken into consideration.
Date: December 16, 1998
Creator: Oji, L.N.
Partner: UNT Libraries Government Documents Department

Phase Diagram of Iron, Revised-Core Temperatures

Description: Shock-wave experiments on iron preheated to 1,573 K conducted from 14 to 73 GPa, yield new data for sound velocities of the {gamma}- and liquid-phases. Melting was observed in the highest pressure ({approximately} 71 {+-} 2 GPa) experiments at calculated shock temperatures of 2,775 {+-} 160 K. This single crossing of the {gamma}-liquid boundary measured here agrees closely with the {gamma}-iron melting line determined by Boehler [1993], Saxena et al. [1993], and Jephcoat and Besedin [1997]. This {gamma}-iron melting curve is {approximately} 300 C lower than that of Shen et al. [1998b] at 80 GPa.
Date: January 27, 1999
Creator: Ahrens, T.J.; Chen, G.Q. & Holland, K.G.
Partner: UNT Libraries Government Documents Department

Review of Current Experience on Intermediate Heat Exchanger (IHX) and A Recommended Code Approach

Description: The purpose of the ASME/DOE Gen IV Task 7 Part I is to review the current experience on various high temperature reactor intermediate heat exchanger (IHX) concepts. There are several different IHX concepts that could be envisioned for HTR/VHTR applications in a range of temperature from 850C to 950C. The concepts that will be primarily discussed herein are: (1) Tubular Helical Coil Heat Exchanger (THCHE); (2) Plate-Stamped Heat Exchanger (PSHE); (3) Plate-Fin Heat Exchanger (PFHE); and (4) Plate-Machined Heat Exchanger (PMHE). The primary coolant of the NGNP is potentially subject to radioactive contamination by the core as well as contamination from the secondary loop fluid. To isolate the radioactivity to minimize radiation doses to personnel, and protect the primary circuit from contamination, intermediate heat exchangers (IHXs) have been proposed as a means for separating the primary circuit of the NGNP (Next Generation Nuclear Plant) or other process heat application from the remainder of the plant. This task will first review the different concepts of IHX that could be envisioned for HTR/VHTR applications in a range of temperature from 850 to 950 C. This will cover shell-and-tube and compact designs (including the platefin concept). The review will then discuss the maturity of the concepts in terms of design, fabricability and component testing (or feedback from experience when applicable). Particular attention will be paid to the feasibility of developing the IHX concepts for the NGNP with operation expected in 2018-2021. This report will also discuss material candidates for IHX applications and will discuss specific issues that will have to be addressed in the context of the HTR design (thermal aging, corrosion, creep, creep-fatigue, etc). Particular attention will be paid to specific issues associated with operation at the upper end of the creep regime.
Date: February 2, 2010
Creator: Spencer, Duane & McCoy, Kevin
Partner: UNT Libraries Government Documents Department

Subcritical Crack Growth in Ceramic Composites at High Temperature Measured Using Digital Image Correlation

Description: An in situ experimental technique is described that allows high resolution, high sensitivity determination of displacements and full-field strains during high temperature mechanical testing. The technique is used to investigate elevated temperature crack growth in SiC/Nicalon sub f composites. At 1150 degrees C, the reinforcing fibers have a higher creep susceptibility than the matrix. Fiber creep leads to relaxation of crack bridging tractions, resulting in subcritical crack growth. Differential image analysis is used to measure the crack opening displacement profile u(x) of an advancing, bridged crack. With appropriate modeling, such data can be used to determine the traction law, from which the mechanics of cracking and failure may be determined.
Date: January 11, 1996
Creator: Mumm, D.R.; Morris, W.L.; Dadkhah, M.S. & Cox, B.N.
Partner: UNT Libraries Government Documents Department

High temperature oxidation of Ni{sub 50}(Al,Be){sub 50}

Description: Effect of Be on high-temperature oxidation of NiAl was investigated. From 1 to 10% Be was substituted for Al on a 1 to 1 atomic basis. Oxidation experiments were conducted in pure oxygen. Exposure temperatures ranged from 800 to 1200 C for 16 hours. In addition to thermogravimetry, postexposure analysis involved SEM of intact scales, XRD, XPS, and Rutherford backscattering spectroscopy. At every temperature tested, the Be modified NiAl containing 1, 2, or 5 at.% Be exhibited lower weight gain and comparable or slower oxidation rates than the pure binary material. The surfaces of the Be modified specimens showed minimal topography, with no evidence of the usual transient alumina phases grown on binary NiAl in this temperature range. XRD and surface analysis showed the presence of layers of Al{sub 2}O{sub 3} and ternary oxide phases, primarily BeO*Al{sub 2}O{sub 3}. The growth of this complex scale apparently prevents growth of the transient alumina phases.
Date: December 31, 1996
Creator: Hanrahan, R.J. Jr.; Butt, D.P.; Thoma, D.J.; Taylor, T.N. & Maggiore, C.J.
Partner: UNT Libraries Government Documents Department

Life prediction methodology for ceramic components of advanced vehicular heat engines: Volume 3, Appendices 3, 4, 5, 6, and 7. Final report

Description: The appendices contain: dynamic fatigue testing of MOR specimens in air at Allison from 1000 to 1400 C; dynamic fatigue testing of MOR specimens in air and Ar at ORNL from 1000-1400 C; dynamic fatigue testing of button-head tensile specimens in air at Southern Research Institute; tensile creep curves for dogbone specimens tested at the National Institute of Science and Technology; and oxidation behavior of PY-6 Si nitride between 1000-1400 C in air.
Date: February 1, 1996
Creator: Khandelwal, P.K.; Provenzano, N.J. & Schneider, W.E.
Partner: UNT Libraries Government Documents Department

Energy and environmental research emphasizing low-rank coal: Task 6.2. Joining of advanced structural materials

Description: Silicon carbide (SiC) is considered an attractive material for structural applications in fossil energy systems because of its corrosion and wear resistance, high thermoconductivity, and high temperature strength. These same properties make it difficult to sinter or join SiC. Conventional sintering techniques require applying pressure and heating to temperatures near 2000{degree}C, or the use of binders with lower melting temperatures, or pressureless sintering with the aid of carbon and boron to near full density about 2100{degree}C. The sintering temperature can be reduced to 1850{degree}--2000{degree}C if SiC is sintered with the addition of small quantities of Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3} {plus} Y{sub 2}O{sub 3}. In addition, reaction sintering has been used by mixing Si and C with SiC powder and heating the mixture to 1400{degree}C to cause the Si and C to react and form SiC, which bonds the aggregate together. Work proposed for this year was to center on determining gas compositions that could be used to increase the sinterability of oxide binders and on using the binder and gas combinations to join bars of SiC, alumina, and mullite (3Al{sub 2}O{center_dot}2SiO{sub 2}). During the course of the year the focus was shifted to SiC joining alone, because it was felt that alumina and mullite are too prone to thermal shock for use in structural applications in fossil energy systems. Because of a thermal expansion mismatch between alumina and SiC, only SiC and mullite were investigated as joining aides for SiC. Therefore, the objectives of this work evolved into examining the sintering phenomena of SiC and mullite-derived binders at and below 1500{degree}C in various atmospheres and determining which conditions are suitable to form strong joints in monolithic SiC structures to be used at temperatures of 1000{degree}--1400{degree}C.
Date: March 1, 1995
Creator: Nowok, J.W. & Hurley, J.P.
Partner: UNT Libraries Government Documents Department

High-temperature deformation of ZrO{sub 2}-Al{sub 2}O{sub 3}/SiC whisker composites fabricated by two techniques

Description: ZrO{sub 2} {minus} Al{sub 2}0{sub 3}/SiC whisker-reinforced composites, with whisker volume fractions of 0 to 28%, fabricated both by powder and precursor processing, have been deformed at temperatures of 1300--1500 C under constant compression rates of 1.7 {times} 10{sup {minus}5} to 6.8 {times} 10{sup {minus}5} s{sup {minus}1}. Above 1400 C, a stress at which the work-hardening rate became zero could be measured and correlated with whisker content. On the other hand, at 1300 C all samples broke within the elastic.regime. At 1350 C, increased whisker content appeared to inhibit fracture, so plastic behavior was obtained for samples containing 28% SiC. In the range of temperatures and compression rates, noted above, stress exponents were determined and tentatively correlated with microstructural features and their evolution during plastic deformation.
Date: March 1, 1995
Creator: Calderon Moreno, J.M.; DeArellano-Lopez, A.R.; Dominguez-Rodriguez, A. & Routbort, J.L.
Partner: UNT Libraries Government Documents Department

Time resolved studies of phase transformations using high temperature powder diffraction

Description: A high temperature furnace (up to 1500 C) has been designed specifically for use with high-energy synchrotron radiation using Debeye-Scherrer transmission geometry. This allows for full bulk sampling and a low thermal gradient (< 1 C/mm) and a controlled environment (inert to oxidizing). Unlike flat plate geometry, the transmission geometry allows for solid-liquid as well as solid-solid phase transitions to be explored. A comparison between image plate and charged-coupled detector (CCD) system will be discussed. The potential is to collect quantifiable powder patterns under a second. Data collected on the tetragonal to cubic transition in the RhTi systems demonstrate the capabilities for performing quantitative time resolved high temperature powder diffraction.
Date: October 12, 1999
Creator: Kramer, M.J.; Margulies, L.; McCallum, R.W.; Zhao, H.L.; Goldman, A.I.; Kycia, S. et al.
Partner: UNT Libraries Government Documents Department

Some effects of metallic substrate composition on degradation of thermal barrier coatings

Description: Comparisons have been made in laboratory isothermal and cyclic oxidation tests of the degradation of oxide scales grown on single crystal superalloy substrates and bond coating alloys intended for use in thermal barrier coatings systems. The influence of desulfurization of the superalloy and bond coating, of reactive element addition to the bond coating alloy, and of oxidation temperature on the spallation behavior of the alumina scales formed was assessed from oxidation kinetics and from SEM observations of the microstructure and composition of the oxide scales. Desulfurization of nickel-base superalloy (in the absence of a Y addition) resulted in an increase in the lifetime of a state-of-the-art thermal barrier coating applied to it compared to a Y-free, non-desulfurized version of the alloy. The lifetime of the same ceramic coating applied without a bond coating to a non-desulfurized model alloy that formed an ideal alumina scale was also found to be at least four times longer than on the Y-doped superalloy plus state-of-the-art bond coating combination. Some explanations are offered of the factors controlling the degradation of such coatings.
Date: December 1997
Creator: Wright, I. G.; Pint, B. A.; Lee, W. Y.; Alexander, K. B. & Pruessner, K.
Partner: UNT Libraries Government Documents Department

Microstructural and mechanical characterization of alumina scales thermally developed on iron aluminide alloys

Description: Several alumina-forming Fe-Al intermetallic alloys have been oxidized in oxygen for 100 h at 1000 C to understand the scaling kinetics, scale morphology, scale adhesion, and strain accommodation in the scales. Oxidation studies were conducted by thermogravimetry, followed by analyses of the surfaces of oxide scales. In addition, samples were cooled to 77 K and then fractured; then, their scale/metal interfaces were analyzed. Some of the scales were adhesion-tested by applying a tensile load to pull the scale away from the substrate. Finally, ruby fluorescence was used to measure in-plane strains in the oxide scales and values correlated with scale microstructures.
Date: May 1, 1996
Creator: Natesan, K.; Klug, K.L.; Renusch, D.; Grimsditch, M. & Veal, B.W.
Partner: UNT Libraries Government Documents Department

Determination of the compatibility between structural alloys and molten metals at high temperatures

Description: The experimental methods for determining high-temperature compatibility between structural alloys and molten metals, particularly braze alloys, have been established. The structural alloys of interest are formed or machined into small crucibles into which the metal to be melted is placed. This system is placed in a furnace which typically will have a vacuum or inert gas environment; other atmospheres are possible as well. Multiple crucibles are exposed for various times and temperatures. Following cooling, a visual examination for loss of containment is performed. Each crucible is then sectioned and examined metallographically to document any loss in thickness of the crucible or any reactions between the materials. These procedures are fairly simple and require only common laboratory equipment; costs, therefore, are kept low. These experimental techniques were refined for use in determining the compatibility of both commercially pure vanadium and 21-6-9 stainless steel with a 92.5% Pb-5% In-2.5% Ag braze alloy. Both the vanadium and the stainless steel contained the molten Pb-In-Ag alloy for exposures ranging from 1000C for 10 minutes up to 1200C for 2 hours.
Date: August 9, 1993
Creator: Henshall, G. A.; Wagner, L. M.; Westfall, B. A. & Kershaw, R. P.
Partner: UNT Libraries Government Documents Department

Effect of high-temperature loading on mechanical properties of Nicalon fibers and Nicalon fiber/SiC matrix composites

Description: Results of an investigation into the effect of elevated temperature exposure on the strength distribution of Nicalon fibers as well on mechanical properties of Nicalon/SiC composites are reported in this paper. Single-fiber strength distribution of as-fabricated Nicalon fibers was obtained from bundle tests. Strength distributions of fractured fibers in as-fabricated Nicalon/SiC composites and after elevated temperature exposure of composites were assessed from measurements of fracture mirror radii. Variations in the mechanical properties of composites evaluated as a function of test temperatures are compared with those evaluated at room temperature and are correlated to the fiber strength characteristics. Limited tests were also conducted to investigate the effect of long term exposure at elevated temperatures on composite ultimate strength.
Date: January 1993
Creator: Singh, Dileep & Singh, Jitendra P.
Partner: UNT Libraries Government Documents Department

Plastic anisotropy in MoSi{sub 2} single crystals

Description: Single crystals Of MoSi{sub 2} are an order of magnitude stronger when compressed along [001] than along any other orientation. This is because the easy slip systems, <101><100> and <110><111>, have a zero Schmid factor acting on them so that harder slip systems are forced into operation. We find that [001] crystals compressed at 1OOO{degree}C yield by slip on <103><331>. TEM shows that the 1/2<331> dislocations tend to decompose into 1/2<111> and <110> dislocations. This decomposition process apparently inhibits the mobility of 1/2<331> dislocations at higher temperatures and another system, <101><1ll>, becomes operative at 1300{degree}C and above. [021] crystals have been tested for comparison and are found to yield at much lower stresses on the easy systems. In the design of advanced high temperature structural materials based on MOSi{sub 2}, the large plastic anisotropy should be used to advantage.
Date: May 1, 1993
Creator: Mitchell, T. E. & Maloy, S. A.
Partner: UNT Libraries Government Documents Department

Multiaxial deformation and life prediction model and experimental data for advanced silicon nitride ceramics

Description: This paper summarizes recent experimental results on creep and creep rupture behavior of a commercial grade of Si{sub 3}N{sub 4} ceramic in the temperature range of 1150 to 1300C obtained at ORNL; and introduces a tentative multiaxial deformation and life prediction model for ceramic materials under general thermomechanical loadings. Issues related to the possible standardization of the data analysis methodology and possible future research needs for high temperature structural ceramics in the area of development of data base and life prediction methodology are also discussed.
Date: June 1, 1993
Creator: Ding, J. L.; Liu, K. C. & Brinkman, C. R.
Partner: UNT Libraries Government Documents Department

BAC-G2 Predictions of Thermochemistry for Gas-Phase Aluminum Compounds

Description: A self-consistent set of thermochemical data for 55 molecules in the Al-H-C-O-F-Cl system are obtained from ab initio quantum-chemistry calculations using the BAC-G2 method. Calculations were performed for both stable and radical species. Good agreement is found between the calculations and experimental heats of formation in most cases where data are available for comparison. Electronic energies, molecular geometries, moments of inertia, and vibrational frequencies are provided in the Supporting Information, as are polynomial fits of the thermodynamic data (heat of formation, entropy, and heat capacity) over the 300--3000 K temperature range.
Date: October 2001
Creator: Allendorf, Mark D.
Partner: UNT Libraries Government Documents Department

Microwave annealing of ion implanted 6H-SiC

Description: Microwave rapid thermal annealing has been utilized to remove the lattice damage caused by nitrogen (N) ion-implantation as well as to activate the dopant in 6H-SiC. Samples were annealed at temperatures as high as 1,400 C, for 10 min. Van der Pauw Hall measurements indicate an implant activation of 36%, which is similar to the value obtained for the conventional furnace annealing at 1,600 C. Good lattice quality restoration was observed in the Rutherford backscattering and photoluminescence spectra.
Date: May 1996
Creator: Gardner, J. A.; Rao, M. V.; Tian, Y. L.; Holland, O. W.; Kelner, G.; Freitas, J. A., Jr. et al.
Partner: UNT Libraries Government Documents Department

The effect of microstructure and temperature on the oxidation behavior of two-phase Cr-Cr{sub 2}X (X = Nb, Ta) alloys

Description: The oxidation behavior of Cr(X) solid solution (Cr{sub ss}) and Cr{sub 2}X Laves phases (X = Nb, Ta) was studied individually and in combination at 950--1,100 C in air. The Cr{sub ss} phase was significantly more oxidation resistant than the Cr{sub 2}X Laves phase. At 950 C, two-phase alloys of Cr-Cr{sub 2}Nb and Cr-Cr{sub 2}Ta exhibited in-situ internal oxidation, in which remnants of the Cr{sub 2}X Laves phase were incorporated into a growing chromia scale. At 1,100 C, the Cr-Cr{sub 2}Nb alloys continued to exhibit in-situ internal oxidation, which resulted in extensive O/N penetration into the alloy ahead of the alloy-scale interface and catastrophic failure during cyclic oxidation. IN contrast, the Cr-Cr{sub 2}Ta alloys exhibited a transition to selective Cr oxidation and the formation of a continuous chromia scale. The oxidation mechanism is interpreted in terms of multiphase oxidation theory.
Date: November 1, 1998
Creator: Brady, M.P. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

Tensile properties of as-cast iron-aluminide alloys

Description: Room-temperature tensile properties of as-cast Fe{sub 3}Al-based FA-129 alloy were investigated. Tensile properties were obtained in the as-cast condition in air, oxygen, and water-vapor environments, and after homogenization at 700, 900, and 1200{degrees}C. Transmission electron microscopy (MM) was used to characterize ordered phases and dislocation structure, and optical metallography and scanning electron microscopy (SEM) were used to characterize the grain microstructure and fracture morphology. Tensile properties in the as-cast condition exhibited an environmental effect; tensile ductilities in oxygen atmosphere were greater than those obtained in laboratory air. Homogenized samples of FA-129 alloy exhibited almost twice the ductility found in the as-cast condition. Microstructural characterization of the homogenized samples and comparison of the as-cast and homogenized microstructures provided clues that helped to explain the poor ductility in the as-cast state.
Date: January 1, 1995
Creator: Viswanathan, S.; McKamey, C.G. & Maziasz, P.J.
Partner: UNT Libraries Government Documents Department

Tensile and cyclic fatigue behavior of SiC whisker-reinforced Al{sub 2}O{sub 3} at room and elevated temperatures

Description: Uniaxial tensile and cyclic fatigue data are reported for a commercial grade of silicon carbide whisker-reinforced alumina matrix composite (SiC{sub w}/Al{sub 2}O{sub 3}) tested at room and elevated temperatures. The data show that addition of short SiC{sub w} (30 vol%) in Al{sub 2}O{sub 3} can significantly increase room temperature tensile strength and resistance to cyclic fatigue of monolithic Al{sub 2}O{sub 3} by {approximately} 40% and {approximately} 100%, respectively, bringing the high-cycle fatigue strength (> 10{sup 5} cycle range) to {approximately} 95% of its tensile strength. These dramatic improvements in tensile and fatigue behavior were attributed to the presence of SiC{sub w} which effectively inhibited cyclic fatigue crack growth. The composite further exhibited excellent retention of tensile and cyclic fatigue strengths at elevated temperatures as high as 1,000 C for practical engineering applications.
Date: June 1, 1996
Creator: Liu, K.C.; Stevens, C.O. & Brinkman, C.R.
Partner: UNT Libraries Government Documents Department

Ultrahigh temperature intermetallic alloys

Description: A new family of Cr-Cr{sub 2}Ta intermetallic alloys based on Cr-(6--10)Ta (at.%) is under development for structural use in oxidizing environments in the 1,000-1,300 C (1,832--2,372 F) temperature range. Development objectives relate to high temperature strength and oxidation resistance and room temperature fracture toughness. The 1,200 C (2,192 F) strength goals have been met: yield and fracture strengths of 275 MPa (40 ksi) and 345 MPa (50 ksi), respectively, were achieved. Progress in attaining reasonable fracture toughness of Cr-Cr{sub 2}Ta alloys has been made; current alloys exhibit room-temperature values of about 10--12 MPa{radical}m (1.1 MPa{radical}m = 1 ksi{radical}in.). Oxidation rates of these alloys at 950 C (1,742 F) in air are in the range of those reported for chromia-forming alloys. At 1,100 C (2,012 F) in air, chromia volatility was significant but, nevertheless, no scale spallation and positive weight gains of 1--5 mg/cm{sup 2} have been observed during 120-h, 6-cycle oxidation screening tests. These mechanical and oxidative properties represent substantial improvement over Cr-Cr{sub 2}Nb and Cr-Cr{sub 2}Zr alloys previously developed.
Date: November 1, 1998
Creator: Brady, M.P.; Zhu, J.H.; Liu, C.T.; Tortorelli, P.F.; Wright, J.L. & Carmichael, C.A.
Partner: UNT Libraries Government Documents Department

High temperature alkali corrosion of dense SiC and Si{sub 3}N{sub 4} coated with CMZP and Mg-doped Al{sub 2}TiO{sub 5} in coal gas. Quarterly progress report No. 7, January 1, 1996--March 31, 1996

Description: Objective is to apply CMZP and Mg-Al{sub 2}TiO{sub 5} as coatings to SiC to improve corrosion resistance under coal combustion atmospheres as well as to improve high temperature mechanical properties. The research will also study the mechanism of coal combustion corrosion of SiC at 1000-1400 C. 16 figs, 8 tabs.
Date: March 31, 1996
Creator: Yang, Shaokai & Brown, J.J.
Partner: UNT Libraries Government Documents Department