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Order-disorder behavior in KNbO{sub 3} and KNbO{sub 3}/KTaO{sub 3} solid solutions and superlattices by molecular-dynamics simulations.

Description: We use molecular-dynamics simulation to examine the order-disorder behavior in pure ferroelectric KNbO{sub 3} and in KNbO{sub 3}-KTaO{sub 3} ferroelectric-paraelectric solid solutions and superlattices. We find that the order-disorder behavior is remarkably robust and plays an important role in both the polarization rotation associated with switching of the perfect crystal and in the dynamical behavior of the solid solutions and superlattices.
Date: February 18, 2002
Creator: Phillpot, S. R.; Sepliarsky, M.; Streiffer, S. K.; Stachiotti, M. G. & Migoni, R. L.
Partner: UNT Libraries Government Documents Department

AAA fuels handbook.

Description: PART A of this handbook is for metal alloy fuels. The metal alloy of transuranic elements (i.e., Pu, Np, Am, Cm, etc) in Zr, designated as TRU-Zr, is one of the primary candidate fuel types for the AAA system. The data found in the literature were critically reviewed and assessed to provide the recommended ones. For the convenience of the user, most of the materials properties are given in model correlations; performance models are also provided in mathematical formulas. Tabulations were made in case where these were judged to allow more flexibility for the user. The information for the materials properties of the TRU-Zr alloy, however, is extremely scarce in general. Therefore, where no data exists, the values and models based on theoretical estimations and extrapolations from the U-Zr and U-Pu-Zr data are inevitably recommended. The justifications for this will be possible when sufficient measured data are available in the future. In this respect, this part is subject to modification whenever new data or better methods of deduction become available. The purpose of PART B is to provide the best available fuel materials properties and performance models of the (Pu,Zr)N and (TRU,Zr)N solid-solution fuels for fuel design and safety calculation of the Advanced Accelerator Assisted (AAA) system. PART B parallels PART A, Metal Alloy Fuels, in form and topics. The solid solution of the mononitrides of transuranic elements (i.e., Pu, Np, Am, Cm, etc) with zirconium mononitride, designated as (TRU,Zr)N, is one of the primary candidate fuel types for the AAA system, together with metallic TRU-Zr alloy fuels studied in Argonne National Laboratory. The data found in the literature were critically reviewed and assessed to provide the recommended ones. For the convenience of the user, most of the materials properties are given in model correlations; performance models are also provided ...
Date: March 27, 2003
Creator: Kim, Y. S. & Hofman, G. L.
Partner: UNT Libraries Government Documents Department

The Role of Al on the Thermodynamics of Hydrogen Absorption/Desorption by Some Ternary Pd-M-Al Alloys where M=Rh, Ni, Pt, Cr, Ag.

Description: The solution of hydrogen and hydride formation in FCC substitutional solid solution Pd0.9Rh0.1-xAlx alloys have been examined. In contrast to some other Pd ternary alloys, a linear relation does not obtain between the H capacity and x for the Pd0.9Rh0.1-xAlx alloys investigated here where the H capacity of the alloys is estimated from the H content of the steeply rising part of the isotherms in the hydride phase regions. A linear increase of the dilute phase H solubility with x for these Pd0.9Rh0.1-xAlx alloys does, however, obtain for these alloys. Although Pd-Rh binary alloys have broader plateaux than does Pd itself, small amounts of Al substituted into Pd0.85Rh0.15 or Pd0.80Rh0.20 alloys can reduce or eliminate the two phase regions, the plateaux; there is, however, not much effect on the dilute phase solubilities. For example, small amounts of Al substituted into the Pd0.85Rh0.15 or Pd0.80Rh0.20 alloys eliminate the plateaux. On the other hand, alloying Pd with Al to form binary alloys with Xal equals 0.015 or 0.030 does not eliminate the plateaux which are present in these binary alloys up to Xal equals 0.075 (298 K). Small amounts of Al substitution do not have such a dramatic effect on the plateau widths of the Pd0.90Ni0.10 and Pd0.80Ni0.20 alloys and similarly substitution of Al into Pd-Cr and Pd-Ag alloys does not introduce any anomalous effects into the isotherms.
Date: April 10, 2002
Creator: Shanahan, K.L.
Partner: UNT Libraries Government Documents Department

An Evaluation of Power Law Breakdown in Metals, Alloys, Dispersion Hardened Materials and Compounds

Description: Creep at high stresses often produces strain rates that exceed those that would be predicted by a power law relationship. In this paper, we examine available high stress creep data for pure metals, solid solution alloys, dispersion strengthened powder metallurgy materials and compounds for power law breakdown (PLB). The results show that, if PLB is observed, then the onset of PLB is generally observed at about {epsilon}/D{sub eff} = 10{sup 13} m{sup -2}, where D{sub eff} is the effective diffusion coefficient incorporating lattice and dislocation pipe diffusion. The common origins of PLB for the various systems studied can be found in the production of excess vacancies by plastic deformation. Anomalous behavior in two pure metals (nickel and tungsten) and a solid solution alloy (Fe-25Cr and Fe-26Cr-1Mo) has been analyzed and provides insight into this excess vacancy mechanism. In metal systems, the onset of PLB is related to a change in the nature of the subgrain structure developed. In the PLB region, subgrains become imperfect containing dislocation tangles adjacent to the sub-boundary, and dislocation cells are evident. The dislocation tangles and cells are the source of excess vacancies and increase the creep rate above that predicted from power law creep. If subgrains do not form then PLB is not observed. In solid solution alloys, in which the dominant deformation resistance results from the interaction of solute atoms with moving dislocations, excess vacancies influence the diffusion of these solute atoms. PLB is not observed in many systems. This is attributed either to the presence of a high equilibrium vacancy concentration (because of a low activation energy for vacancy formation) or to the inability to form subgrains.
Date: October 20, 1999
Creator: Lesuer, D.R.; Syn, C.K. & Sherby, O.D.
Partner: UNT Libraries Government Documents Department

Nickel and manganese interaction with calcite

Description: Many divalent metal cations sorb to calcite surfaces and incorporate into calcite to varying degrees. Since calcite may sorb trace elements in the environment, the factors controlling metal-calcite interactions are critical to understanding element cycling. The interaction of divalent metal cations with calcite can be critical to toxic metal immobilization, nutrient cycling, interpretation of past redox conditions, tracing fluid flow, for example. Sorption of Ni and Mn on calcite surfaces was studied by Zachara et al.. At any particular pH, the sorption of Mn on calcite was greater than Ni. This was attributed in part to the similarity of divalent Mn and Ca with respect to ion size. Although direct spectroscopic evidence was not available, sorption/desorption results suggested that Mn quickly forms a surface precipitate or solid solution while Ni forms a hydrated surface complex that may incorporate into calcite much more slowly via recrystallization. Because Mn(II) ionic radius is similar to that of Ca(II) (0.80 versus 1.0{angstrom}), and because MnCO{sub 3} has a structure similar to calcite, it is likely that Mn can substitute directly for Ca in the calcite structure. The ionic radius of Ni(II) is significantly smaller (0.69{angstrom}) and Ni(OH){sub 2} precipitation is likely to be favored in most systems. For Ni, direct substitution for Ca is less likely or may require more significant calcite lattice deformation.
Date: August 9, 1999
Creator: Doner, H & Zavarin, M
Partner: UNT Libraries Government Documents Department

Fundamental studies of the removal of contaminants from ground and waste waters via reduction by zero-valent metals. 1998 annual progress report

Description: 'Contaminated groundwater and surface waters are a problem throughout the US and the world. In many instances, the types of contamination can be directly attributed to man''s actions. For instance, the burial of wastes, casual disposal of solvents in unlined pits, and the development of irrigated agriculture have all contributed to groundwater and surface water contamination. The kinds of contaminants include chlorinated solvents and toxic trace elements that are soluble and mobile in soils and aquifers. Oxyanions of selenium, chromium, uranium, arsenic, and chlorine (as perchlorate) are frequently found as contaminants on many DOE sites. In addition, the careless disposal of cleaning solvents, such as carbon tetrachloride and trichloroethylene, has further contaminated many groundwaters at these sites. Oxyanions of selenium, nitrogen, arsenic, vanadium, uranium, chromium, and molybdenum are contaminants in agricultural areas of the Western US. The management of these waters requires treatment to remove the contaminants before reuse or surface water disposal. In one instance in the Central Valley of California, the discharge of selenate-contaminated shallow groundwater to a wildlife refuge caused catastrophic bird deaths and deformities of embryos. A potential remediation method for many of these oxyanions and chlorinated-solvents is to react the contaminated water with zero-valent iron. In this reaction, the iron serves as both an electron source and as a catalyst. Elemental iron is already being used on an experimental basis. Both in-situ reactive barriers and above-ground reactors are being developed for this purpose. However, the design and operation of these treatment systems requires a detailed process-level understanding of the interactions between the contaminants and the iron surfaces. Only limited success has been achieved in the field, partly because the basic surface chemical reactions are not well understood. The authors are performing fundamental investigations of the interactions of the relevant chlorinated solvents, and trace element-containing compounds ...
Date: June 1, 1998
Creator: Yarmoff, J.A. & Amrhein, C.
Partner: UNT Libraries Government Documents Department

Fundamental studies of the removal of contaminants from ground and waste waters via reduction by zero-valent metals. Annual progress report, September 1, 1996--August 31, 1997

Description: 'Contaminated groundwater is a problem throughout the US and the world. In many instances the tvpes of contamination can be directly attributed to man''s actions. For instance, the burial of wastes, casual disposal of solvents in unlined pits, and the development of irrigated agriculture have all contributed to groundwater contamination. The kinds of contaminants include chlorinated solvents and toxic trace elements that are soluble and mobile in soils and aquifers. Oxyanions of selenium. chromium. uranium. arsenic. and chlorine (as perchlorate) are frequently found as contaminants on many DOE sites. In addition. the careless disposal of cleaning solvents. such as carbon tetrachloride and trichloroethylene. has further contaminated many groundwaters at these sites. In agricultural areas of the western US, shallow groundwaters have become contaminated with high levels of selenate, chromate, and uranyl. The management of these waters requires treatment to remove the contaminants before reuse or surface water disposal. In one instance in the Central Valley of California. the discharge of selenate-contaminated shallow groundwater to a wildlife refuge caused catastrophic bird deaths and deformities of embryos. At sites where solid-propellant rocket motors were tested or disposed of, high concentrations of perchlorate and trichloroethylene are being found in the groundwater. A potential remediation method for many of these oxyanions and chlorinated-solvents is to react the contaminated water with zero-valent iron. In this reaction, the iron serves as both an electron source and as a catalyst. Elemental iron is already being used, on an experimental basis, for the reductive dechlorination of solvents and the removal of toxic trace elements. Both in situ reactive barriers and above-ground reactors are being developed for this purpose. However, the design and operation of these treatment systems requires a detailed process-level understanding of the interactions between the contaminants and the iron surfaces. Only limited success has been achieved ...
Date: January 1, 1997
Creator: Yarmoff, J.A. & Amrhein, C.
Partner: UNT Libraries Government Documents Department

Radionuclide immobilization in the phases formed by corrosion of spent nuclear fuel: The long-term assessment. 1998 annual progress report

Description: 'This research program is designed to identify the long-term corrosion products of naturally occurring UO{sub 2}{sup 2+} under oxidizing conditions as an analogue for corrosion of UO2 in spent nuclear fuel. This work will identify the phases that form, the reaction path during their formation, their stability, and their ability to incorporate key radionuclides. As of May 1998, this report summarizes work that has been completed during the first seven months of a 3 year research program. During this period, a post-doctoral fellow, F. Chen, has focused his efforts on the development of a theoretical basis for predicting the Gibbs free energies and enthalpies of formation of uranium (VI) phases. This is quite important, as these uranyl phases are the important alteration products that form during the corrosion of UO{sub 2}. The thermodynamic data base for these uranyl phase is extremely limited and often contradictory.'
Date: June 1, 1998
Creator: Ewing, R.C.
Partner: UNT Libraries Government Documents Department

THEORETICAL DIFFUSION PROFILES IN SINGLE PHASE TERNARY SYSTEMS

Description: In order to illustrate the physical meaning of the four independent interdiffusion coefficients which describe a single-phase ternary system, a range of concentration profiles and diffusion paths for the generalized diffusion couple A-10B/A-10C were plotted using three different models of diffusion coefficient behaviour. The shapes of the diffusion paths predicted by these various models were compared with that of an experimentally determined diffusion path from the cobalt solid solution of the substitutional alloy system cobalt-chromium-aluminum. The results indicate that even the most sophisticated dilute solution model fails to predict completely the behaviour of the real system.
Date: February 1, 1980
Creator: Roper, G.W. & Whittle, D.P.
Partner: UNT Libraries Government Documents Department

Investigation of the Peroxovanadate Sol-Gel Process and Characterization of the Gels

Description: In general, the peroxovanadate solution sol-gel process can be thought of as consisting of two parts: (1) the decomposition of the peroxo species and (2) cation hydrolysis leading to gelation. By controlling the synthesis conditions, both layered and amorphous compounds can be created. However, the type of water coordination observed in these gels was found to be identical no matter what the long-range order. The current work clarified many of the discrepancies found in the literature and offered much new valuable information. Highlights include the types of vanadium environments present at various stages of hydration, the role of adsorbed water, oxygen exchange from adsorbed water into the gel sites, and the ability to create metastable VMoO solid solution phases. These results could have a variety of impacts on future catalysis research.
Date: December 2001
Creator: Fontenot, Craig Joseph
Partner: UNT Libraries Government Documents Department

Phase Stability under Irradiation of Precipitates and Solid Solutions in Model ALloys and in ODS Alloys Relevant for Gen IV

Description: The overall objective of this program is to investigate the irradiation-altered phase stability of oxide precipitates in ODS steels and of model alloy solid solutions of associated systems. This information can be used to determine whether the favorable mechanical propertiies of these steels are maintained under irradiation, thus addressing one of the main materials research issues for this class of steels as identified by the GenIV working groups. The research program will also create fundamental understanding of the irradiation precipitation/dissolution problem by studying a "model" system in which the variables can be controlled and their effects understood individually.
Date: October 17, 2007
Creator: Motta, Arthur T. & Birtcher, Robert C.
Partner: UNT Libraries Government Documents Department

THE MEASUREMENT OF OXYGEN TO METAL RATIO IN SOLID SOLUTIONS OF URANIUM AND PLUTONIUM DIOXIDES

Description: A survey was made of methods potentially useful for the determination of the oxygen to metal ratio in mixed oxides of uranium and plutonium. A gravimetric method was selected as being the most promising for adaptation in a short period of time. Development of the technique resulted in a reliable method which meets the requirements for unirradiated mixed oxide fuel samples. The method, based upon an equilibrium weight at 700 deg C in dry hydrogen, was shown to be capable of measurement of O/(Pu + U) ratios in 20% PuO/sub 2/--80% UO/sub 2/ pellets with a standard deviation of plus or minus 0.001. (auth)
Date: May 31, 1963
Creator: Lyon, W.L.
Partner: UNT Libraries Government Documents Department

MATERIALS WITH COMPLEX ELECTRONIC/ATOMIC STRUCTURES

Description: We explored both experimentally and theoretically the behavior of materials at stresses close to their theoretical strength. This involves the preparation of ultra fine scale structures by a variety of fabrication methods. In the past year work has concentrated on wire drawing of in situ composites such as Cu-Ag and Cu-Nb. Materials were also fabricated by melting alloys in glass and drawing them into filaments at high temperatures by a method known as Taylor wire technique. Cu-Ag microwires have been drawn by this technique to produce wires 10 {micro}m in diameter that consist of nanoscale grains of supersaturated solid solution. Organogels formed from novel organic gelators containing cholesterol tethered to squaraine dyes or trans-stilbene derivatives have been studied from several different perspectives. The two types of molecules are active toward several organic liquids, gelling in some cases at w/w percentages as low as 0.1. While relatively robust, acroscopically dry gels are formed in several cases, studies with a variety of probes indicate that much of the solvent may exist in domains that are essentially liquid-like in terms of their microenvironment. The gels have been imaged by atomic force microscopy and conventional and fluorescence microscopy, monitoring both the gelator fluorescence in the case of the stilbene-cholesterol gels and, the fluorescence of solutes dissolved in the solvent. Remarkably, our findings show that several of the gels are composed of similarly appearing fibrous structures visible at the nano-, micro-, and macroscale.
Date: September 1, 2000
Creator: PARKIN, D. M.; CHEN, L. & AL, ET
Partner: UNT Libraries Government Documents Department

Processing, Microstructure, and Properties of Multiphase Mo Silicide Alloys

Description: Multiphase Mo silicide alloys containing T2 (Mo{sub 5}SiB{sub 2}), Mo{sub 3}Si and Mo phases where prepared by both melting and casting (M and C) and powder metallurgical (PM) processes. Glassy phases are observed in PM materials but not in M and C materials. Microstructural studies indicate that the primary phase is Mo-rich solid solution in alloys containing {le}(9.4Si+13.8B, at. %) and T2 in alloys with {ge}(9.8Si+14.6B). An eutectic composition is estimated to be close to Mo-9.6Si-14.2B. The mechanical properties of multiphase silicide alloys were determined by hardness, tensile and bending tests at room temperature. The multiphase alloy MSB-18 (Mo-9.4Si-13.8B) possesses a flexure strength distinctly higher than that of MoSi{sub 2} and other Mo{sub 5}Si{sub 3} silicide alloys containing no Mo particles. Also, MSB-18 is tougher than MoSi{sub 2} by a factor of 4.
Date: November 30, 1998
Creator: Heatherly, L.; Liu, C.T. & Schneibel, J.H.
Partner: UNT Libraries Government Documents Department

Redox behavior below 1000K of Pt-impregnated CeO{sub 2}-ZrO{sub 2} solid solutions : an in-situ neutron diffraction study.

Description: The Ce{sup 3+} {leftrightarrow} Ce{sup 4+} redox process in automotive three-way catalysts such as Ce-ZrO{sub 2}/Pt provides an essential mechanism to oxygen storage/release under dynamic air-to-fuel ratio cycling. Such a function requires a metal-support interaction which is not completely understood. We have carried out an in-situ neutron powder diffraction study to monitor the crystal structures (a mixture of a major tetragonal and a minor monoclinic phase) of 10mol% Ce-doped ZrO{sub 2} with and without Pt (1wt%) impregnation under oxidizing and reducing conditions over the temperature range of 25--7000 C. The samples were heated first in flowing 2%O{sub 2}/Ar from room temperature to 400 C and then in 1%CO/Ar to about 700 C. A discontinued increase of the tetragonal unit-cell volume, a decrease of tetragonality (c/a), and a change of color from light yellow to gray when changing from oxidizing to reducing atmosphere were observed only in the sample containing Pt. This result supports the model which assumes the formation of oxygen vacancies initially near the Pt atoms. As more Ce ions are reduced from 4+ to 3+ oxidation states at high temperatures, oxygen vacancies migrate to the bulk of the oxide particles.
Date: January 12, 1998
Creator: Loong, C.-K.; Short, S. M.; Ozawa, M. & Suzuki, S.
Partner: UNT Libraries Government Documents Department

DENSITY-FUNCTIONAL STUDY OF U-Mo AND U-Zr ALLOYS

Description: Density-functional theory previously used to describe phase equilibria in U-Zr alloys [A. Landa, P. Soederlind, P.E.A. Turchi, J. Alloys Comp. 478 (2009) 103-110] is extended to investigate the ground-state properties of U-Mo solid solutions. We discuss how the heat of formation in both alloys correlates with the charge transfer between the alloy components, and how the specific behavior of the density of states in the vicinity of the Fermi level promotes the stabilization of the U{sub 2}Mo compound. Our calculations prove that, due to the existence of a single {gamma}-phase over the typical fuel operation temperatures, {gamma}-U-Mo alloys should indeed have much lower constituent redistribution than {gamma}-U-Zr alloys for which binodal decomposition causes a high degree of constituent redistribution.
Date: November 1, 2010
Creator: Landa, A; Soderlind, P & Turchi, P A
Partner: UNT Libraries Government Documents Department

Modeling of the phase evolution in Mg1-xAlxB2 (0<x<0.5) and its experimental signatures

Description: Despite the chemical and structural simplicity of MgB{sub 2}, at 39 K this compound has the highest known {Tc} of any binary compound. Electron doping by substituting Al for Mg leads to decreasing Tc and the observed concentration dependent rate of decrease has been proposed to arise from the non-ideal character of MgB{sub 2}-AIB{sub 2} solid solutions, which derives from the existence of an ordered Mg{sub 0.5}Al{sub 0.5}B{sub 2} compound. Heterogeneous nano-scale structure patterns in solid solutions have emerged as an important concept for complex materials, ranging from actinide alloys and oxides to high-temperature cuprate superconductors and mallganite-based materials exhibiting colossal magnetoresistivity. In this work we investigate the formation of structural heterogeneities in Mg{sub 1-x}AI{sub x}B{sub 2}, which take the form of nano-scale AI-AI and AI-Mg domains of different geometry and size, using molecular statics/dynamics simulations and in particular we study the corresponding signatures in diffraction experiments. In order to undertake this task we first derive appropriate Mg-AI-B semi-empirical potentials within the Modified Embedded Atom Method formalism. These potentials are also applied to explore the equilibrium Mg{sub 1-x}AI{sub x}B{sub 2} phase diagram for 0 &lt; x &lt; 0.5. Additionally, density functional theory calculations were utilized to study the influence of heterogeneities on the electronic structure and charge distribution in Mg{sub 1-x}AI{sub x}B{sub 2}.
Date: January 1, 2009
Creator: Andersson, Anders David; Casillas, Luis; Lezama Pacheco, Juan & Conradson, Steven D
Partner: UNT Libraries Government Documents Department

Fabrication of Dual Phase Magnesia-Zirconia Ceramics Doped with Plutonia and Erbia

Description: Dual phase magnesia-zirconia ceramics doped with plutonia and erbia are being evaluated as an inert matrix fuel (IMF) for light water reactors (LWR). The motivation for this work is to develop an IMF with a thermal conductivity superior to that of the fuels based on single-phase yttria stabilized zirconia. The innovative fuel developed at INL is comprised of two major phases: pure MgO and quaternary solid solution consisting of MgO, ZrO{sub 2}, Er{sub 2}O{sub 3} and PuO{sub 2}. Pure MgO phase acts as an efficient heat conductor. It has been shown [1] that dual phase MgO-ZrO{sub 2} ceramics have the thermal conductivity superior to that of UO{sub 2} and have notable chemical resistance to water at the temperature of 573 K and pressure 8.6 MPa, which makes them attractive for use as an IMF matrix in LWRs.
Date: June 1, 2006
Creator: Lessing, Paul A. & Hyde, Timothy A.
Partner: UNT Libraries Government Documents Department

Fabrication of dual phase magnesia-zirconia ceramics doped with plutonia and erbia

Description: Dual phase magnesia-zirconia ceramics doped with plutonia and erbia are being evaluated as an inert matrix fuel (IMF) for light water reactors (LWR). The motivation for this work is to develop an IMF with a thermal conductivity superior to that of the fuels based on single-phase yttria stabilized zirconia. The innovative fuel developed at INL is comprised of two major phases: pure MgO and quaternary solid solution consisting of MgO, ZrO{sub 2}, Er{sub 2}O{sub 3} and PuO{sub 2}. Pure MgO phase acts as an efficient heat conductor. It has been shown [1] that dual phase MgO-ZrO{sub 2} ceramics have the thermal conductivity superior to that of UO{sub 2} and have notable chemical resistance to water at the temperature of 573 K and pressure 8.6 MPa, which makes them attractive for use as an IMF matrix in LWRs.
Date: June 1, 2006
Creator: Medvedev, P. G.; Jue, J. F. & Frank, S. M.
Partner: UNT Libraries Government Documents Department

Immiscibility in the NiFe2O4-NiCr2O4 Spinel Binary

Description: The solid solution behavior of the Ni(Fe{sub 1-n}Cr{sub n}){sub 2}O{sub 4} spinel binary is investigated in the temperature range 400-1200 C. Non-ideal solution behavior, as exhibited by non-linear changes in lattice parameter with changes in n, is observed in a series of single-phase solids air-cooled from 1200 C. Air-annealing for one year at 600 C resulted in partial phase separation in a spinel binary having n = 0.5. Spinel crystals grown from NiO, Fe{sub 2}O{sub 3} and Cr{sub 2}O{sub 3} reactants, mixed to give NiCrFeO{sub 4}, by Ostwald ripening in a molten salt solvent, exhibited single phase stability down to about 750 C (the estimated consolute solution temperature, T{sub cs}). A solvus exists below T{sub cs}. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n values of 0.2 and 0.7 at 300 C. The extrapolated solvus is shown to be consistent with that predicted using a primitive regular solution model in which free energies of mixing are determined entirely from changes in configurational entropy at room temperature.
Date: August 13, 2004
Creator: Ziemniak, S
Partner: UNT Libraries Government Documents Department

Final Report for Department of Energy Grant No. DE-FG02-02ER45997, "Alloy Design of Nanoscale Precipitation Strengthened Alloys: Design of a Heat Treatable Aluminum Alloy Useful to 400C"

Description: A creep resistant high temperature Al base alloy made by conventional processing procedures is the subject of this research. The Ni-based superalloys have volume fractions of cubic L1{sub 2} phase precipitates near 50%. This is not attainable with Al base alloys and the approach pursued in this research was to add L1{sub 2} structured precipitates to the Al-Ni eutectic alloy, 2.7 at. % Ni-97.3 at. % Al. The eutectic reaction gives platelets of Al{sub 3}Ni (DO{sub 11} structure) in an almost pure Al matrix. The Al{sub 3}Ni platelets give reinforcement strengthening while the L1{sub 2} precipitates strengthen the Al alloy matrix. Based on prior research and the extensive research reported here modified cubic L1{sub 2} Al{sub 3}Zr is a candidate. While cubic Al{sub 3}Zr is metastable, the stable phase is tetragonal, only cubic precipitates were observed after 1600 hrs at 425 C and they hardly coarsened at all with time at this temperature. Also addition of Ti retards the cubic to tetragonal transformation; however, a thermodynamically stable precipitate is desired. A very thorough ab initio computational investigation was done on the stability of L1{sub 2} phases of composition, (Al,X){sub 3}(Zr,Ti) and the possible occurrence of tie lines between a stable L1{sub 2} phase and the Al alloy terminal solid solution. Precipitation of cubic (Al{sub (1-x)}Zn{sub x}){sub 3}Zr in Al was predicted by these computations and subsequently observed by experiment (TEM). To test the combined reinforcement-precipitation concept to obtain a creep resistant Al alloy, Zr and Ti were added to the Al-Ni eutectic alloy. Cubic L1{sub 2} precipitates did form. The first and only Al-Ni-Zr-Ti alloy tested for creep gave a steady state creep rate at 375 C of 8 x 10{sup -9} under 20MPa stress. The goal is to optimize this alloy and add Zn to achieve a thermodynamically stable ...
Date: May 6, 2006
Creator: Fine, Morris E.; Ghosh, Gautam; Isheim, Dieter; Vaynman, Semyon; Knipling, Keith & Liu, Jefferson Z.
Partner: UNT Libraries Government Documents Department

ENGINEERING EXPERIENCE AT BROOKHAVEN NATIONAL LABORATORY IN HANDLING FUSED CHLORIDE SALTS

Description: Two fused chloride salt eutectics, binary LiCl-KCl and ternary NaCl- KCl- MgCl/sub 2/, were used in fuel processing studies as part of the Liquid Metal Fuel Reactor research and development program. Results of engineering work done at Brookhaven since 1950 are summarized. It was demonstrated that fused chloride salt technology is sufficiently developed so that loops and other experimental equipment can be designed and operated at 500 deg C with a high degree of confidence. The equipment, which was operated for many hours, included a large forced-circulation loop and many thermal-convection loops and tanks. The specifications used for the fabrication, cleaning, and testing of equipment for salt service are described. All welded systems, welded by the usual inert-arc procedures, are preferred, but ring type joint stainless-steel flanged connections were found satisfactory, mainly for connecting melt tanks to experimental equipment and for mounting orifice flowmeters. The surfaces of equipment to be used with fused salts were cleaned satisfactorily prior to assembly by several different methods, but sandblasting was found applicable to all types of equipment. Radiography was used to check all welds in contact with fused salt for flaws and, during operation, to locate and determine the cause of any malfunction. Components tested at the normal operating temperature of 500 deg C included pumps, valves, agitators, sightports, samplers, and filtens. Salt samples were usually taken by the thief method. Both stationary and movable resistance type, liquid-level probes were used and were reliable so long as the salt surface remained quiescent; otherwise, splashing and short-circuiting occurred. Nullmatic, pilot-operated pressure transmitters gave good service in conjunction with both orifice and Venturi flowmeters. A procedure is described for preparing pound quantities of pure eutectics, which, in the case of the ternary eutectic, differs from that used in preparing gram quantities. Both eutectics were pretreated ...
Date: June 1, 1960
Creator: Raseman, C.J.; Susskind, H.; Farber, G.; McNulty, W.E. & Salzano, F.J.
Partner: UNT Libraries Government Documents Department

Remarkable Strontium B-Site Occupancy in FerroelectricPb(Zr1-xTix)O3 Solid Solutions Doped with Cryolite-Type StrontiumNiobate

Description: New high-performance ferroelectric materials based on Pb(Zr{sub 1-x}Ti{sub x})O{sub 3} (PZT) that are doped with cryolite-type strontium niobate (SNO, Sr{sub 4}(Sr{sub 2-2y/3}Nb{sub 2+2y/3})O{sub 11+y}V{sub 0,1-y} with 0 {le} y {le} 1), hence denoted PZT:SNO, and their microscopic structure are described. The combination of exceptional piezoelectric properties, i.e. a piezoelectric strain constant of d{sub 33} {approx} 760 pm/V, with excellent stability and degradation resistance makes ferroelectric PZT:SNO solid solutions very attractive for use in novel and innovative piezoelectric actuator and transducer applications. Extended X-ray absorption fine-structure (EXAFS) analyses of PZT:SNO samples revealed that {approx}10 % of the Sr cations occupy the nominal B-sites of the perovskite-type PZT host lattice. This result was supported by EXAFS analyses of both a canonical SrTiO{sub 3} perovskite and two SNO model and reference compounds. Fit models that do not account for Sr cations on B-sites were ruled out. A clear Sr-Pb peak in Fourier transformed EXAFS data visually confirmed this structural model. The generation of temporary oxygen vacancies and the intricate defect chemistry induced by SNO-doping of PZT are crucial for the exceptional materials properties exhibited by PZT:SNO materials.
Date: April 26, 2007
Creator: Feltz, A.; Schmidt-Winkel, P.; Schossman, M.; Booth, C.H. & Albering, J.
Partner: UNT Libraries Government Documents Department

Correlating Observations of Deformation Microstructures by TEM and Automated EBSD Techniques

Description: The evolution of the deformed microstructure as a function of imposed plastic strain is of interest as it provides information on the material hardening characteristics and mechanism(s) by which cold work energy is stored. This has been extensively studied using transmission electron microscopy (TEM), where the high spatial and orientational resolution of the technique is used to advantage to study local phenomenon such as dislocation core structures and interactions of dislocations. With the recent emergence of scanning electron microscope (SEM) based automated electron backscatter diffraction (EBSD) techniques, it has now become possible to make mesoscale observations that are statistical in nature and complement the detailed TEM observations. Correlations of such observations will be demonstrated for the case of Ni-base alloys, which are typically non-cell forming solid solution alloys when deformed at ambient temperatures. For instance, planar slip is dominant at low strain levels but evolves into a microstructure where distinct crystallographic dislocation-rich walls form as a function of strain and grain orientation. Observations recorded using both TEM and EBSD techniques are presented and analyzed for their implication on subsequent annealing characteristics.
Date: June 5, 2000
Creator: Schwartz, A.J. & King, W.E.
Partner: UNT Libraries Government Documents Department