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Exploratory development of fusion cast calcium fluoride for 1. 06 micrometer pulsed laser optics. Progress report, December 25, 1976--March 25, 1977

Description: This program is an assessment of fusion cast polycrystalline calcium fluoride for optical components of 1.064 micrometer pulsed laser fusion systems. Task areas include casting of essentially stress-free 33 centimeter diameter, 5 centimeter thick ingots, developing surface finishing techniques for optically figured plane and spherical surfaces, and evaluating state-of-the-art antireflection coatings deposited onto specimens of the cast material. During the third quarter, three casting runs were completed in the large casting furnace, none of which was wholly successful. A decision to limit the remainder of the casting effort to six-inch (15-centimeter) diameter pieces was made. Two chemically homogeneous castings of CaF/sub 2//Nd were made in a second furnace. Diamond abrasive polishing techniques were used successfully to fabricate a 15-centimeter radius convex spherical surface on one polycrystalline casting and a quarter wave plane surface on a second. Both surfaces were free of grain boundary relief which is commonly produced by standard techniques. Antireflection coatings obtained from two vendors were found to be physically durable and optically uniform. The components of these coatings are those also used by the vendors for their laser damage resistant coatings on glass, so it is reasonable to anticipate that they will be damage resistant on the fluoride as well. Damage testing will be carried out during the final quarter of the program.
Date: April 1, 1977
Creator: Willingham, C. B.
Partner: UNT Libraries Government Documents Department

Fundamental studies of metal fluorination reactions. Progress report, May 1, 1976--April 31, 1977

Description: The present research is being undertaken to study some fundamental thermodynamic and transport properties and detailed mechanisms pertinent to metal fluorination reactions. The program consists of determining the following properties using solid-state, CaF/sub 2/-electrolyte galvanic cells: (A) solubility and diffusivity of fluorine in metals, specifically nickel, and (B) the nature of the point defects (type, concentration and mobility) in metal fluorides as a function of fluorine partial pressure, temperature and impurity concentration. The latter study encompasses the study of the electrical conductivity of metal fluorides under thermodynamically well-defined conditions. Another objective of the program is to design and construct a fluorine probe for the measure of fluorine chemical potentials in gaseous environments. The probe must be evaluated in oxygen-containing atmospheres which might limit its accuracy and lifetime. For several technical reasons, the specific experimentation has deviated somewhat from that originally proposed. For two reasons, a probable phase change in CaF/sub 2/ at a temperature around 1175/sup 0/C and a thermal expansion coefficient which differs greatly from solid nickel, CaF/sub 2/ single crystal electrolytes could not yet be interfaced perfectly to solid nickel for electrochemical studies. However, these problems were avoided by the successful substitution of copper for nickel in the studies of solubility and diffusivity. Some problems also arose in the study of the electrical conductivity of NiF/sub 2/, namely, only relatively impure NiF/sub 2/ was available, and NiF/sub 2/ exhibited poor mechanical stability as electrodes. Therefore, the proposed methods were used mostly for the study of B-PbF/sub 2/, for which previous studies also provided values for comparison. With the experience gained from the work reported here, future experimentation with nickel metal and NiF/sub 2/ should be successful.
Date: January 1, 1977
Creator: Rapp, R. A.
Partner: UNT Libraries Government Documents Department

Geologic feasibility of selected chalk-bearing sequences within the conterminous United States with regard to siting of radioactive-waste repositories

Description: Various geologic and hydrologic parameters are evaluated in relation to assessing the potential for repository storage of high-level radioactive wastes within several stratigraphic sequences dominated by chalks and chalky limestones. The former lithology is defined as a carbonate rock consisting mainly of very fine-grained particles of micritic calcite. Although chalks also contain coarser-grained particles such as shells of fossil foraminifera and non-calcitic minerals like quartz, most contain more than 90 percent micritic material. The latter represents broken fossil coccolith plates. The chalk-dominated formations discussed are exposed and underlie two different physiographic provinces which nevertheless display a general similarity in both being regions of extensive plains. The Niobrara Formation occurs mainly within the Great Plains province, while the Austin Chalk of Texas and the Selma Group of Alabama and Mississippi are located in the western and eastern Gulf Coastal Plain, respectively. The preliminary assessment is that chalk-bearing sequences show some promise and are deserving of added consideration and evaluation. Containment for hundreds of thousands of years would seem possible given certain assumptions. The most promising units from the three studied are the Niobrara Formation and Selma Group. Regional and local conditions make the Austin more suspect.
Date: November 1, 1975
Creator: Gonzales, S.
Partner: UNT Libraries Government Documents Department

Compression wave studies in Blair dolomite

Description: Dynamic compression wave studies have been conducted on Blair dolomite in the stress range of 0-7.0 GPa. Impact techniques were used to generate stress impulse input functions, and diffuse surface laser interferometry provided the dynamic instrumentation. Experimental particle velocity profiles obtained by this method were coupled with the conservation laws of mass and momentum to determine the stress-strain and stress-modulus constitutive properties of the material. Comparison between dynamic and quasistatic uniaxial stress-strain curves uncovered significant differences. Energy dissipated in a complete load and unload cycle differed by almost an order of magnitude and the longitudinal moduli differed by as much as a factor of two. Blair dolomite was observed to yield under dynamic loading at 2.5 GPa. Below 2.5 GPa the loading waves had a finite risetime and exhibited steady propagation. A finite linear viscoelastic constitutive model satisfactorily predicted the observed wave propagation. We speculate that dynamic properties of preexisting cracks provides a physical mechanism for both the rate dependent steady wave behavior and the difference between dynamic and quasistatic response.
Date: February 1, 1976
Creator: Grady, D. E.; Hollenbach, R. E.; Schuler, K. W. & Callender, J. F.
Partner: UNT Libraries Government Documents Department

Recovery of crystallinity in ground calcite

Description: Recovery processes by thermal treatment and recrystallization are examined in a calcite specimen severely disordered by ball milling. As the annealing temperature is increased, restructuring in the bulk lags behind the recovery of crystalline perfection in the surface regions. Surface reordering is significant at temperatures as low as 150 to 175/sup 0/C and is rapidly completed at 400/sup 0/C. Annealing at 600/sup 0/C is required for removal of all lattice strain. Before loss of surface can occur by sintering, the temperature needs to exceed 300/sup 0/C. The corresponding temperature for a high-area precipitated calcite is 400/sup 0/C. Recovery of crystallinity is also promoted by light-etching with aqueous acid when extensive whisker growth occurs. Aging over a period of twelve years has led to loss of the ultrareactive characteristics.
Date: January 1, 1976
Creator: Gammage, R. B. & Glasson, D. R.
Partner: UNT Libraries Government Documents Department

Evaluation of BeO ceramic disks for thermally stimulated exoelectron dosimetry

Description: BeO ceramic disks were evaluated for application as dosimeters for both penetrating and non-penetrating radiation. Response to penetrating radiation was measured as thermoluminescence (TL) and to non-penetrating radiation as thermally stimulated exoelectron emission (TSEE). Field experiments demonstrated that both TSEE and TL responses from BeO can monitor diverse radiation fields. BeO disks in a passive dosimeter were found to be sensitive to a lower exposure level of 100 pCi-day/liter of radon. The depth of the more active exoelectron layer in BeO was found to be 4 ..mu..m. A second less active, exoelectron layer extends to a depth of at least 16 ..mu..m.
Date: November 21, 1975
Creator: Bush, J. R.; Keeler, J. B. & Piret, J. J.
Partner: UNT Libraries Government Documents Department

Recent electroanalytical studies in molten fluorides. [LiF--BeF/sub 2/--ThF/sub 4/ (ZrF/sub 4/)]

Description: This paper summarizes the voltametric and chronopotentiometric studies of Bi, Fe, Te, oxide and U(IV)/U(III) ratio determinations in molten LiF--BeF/sub 2/--ThF/sub 4/ (72-16-12 mole percent) and LiF--BeF/sub 2/--ZrF/sub 4/ (65.6-29.4-5.0 mole percent). 54 references, 11 figures. (DLC)
Date: January 1, 1976
Creator: Manning, D. L. & Mamantov, G.
Partner: UNT Libraries Government Documents Department

Impurity effects on the creep of polycrystalline magnesium and aluminum oxides at elevated temperatures. Technical progress report, December 19, 1974--December 18, 1975

Description: Work is reported on: 1. Viscous creep of fine-grained MgO doped with iron. 2. The effects of transition metal impurities and grain size on the creep of polycrystalline Al/sub 2/O/sub 3/. 3. The non-viscous creep of large grain size MgO and Al/sub 2/O/sub 3/, pure and doped with transition metal impurities. 4. Stress relaxation tests on polycrystalline MgO and Al/sub 2/O/sub 3/, pure and doped with transition metal impurities. 5. The construction of creep deformation maps for polycrystalline MgO and Al/sub 2/O/sub 3/, pure and doped with iron. 6. Preliminary studies on the effect of grain size on the creep of polycrystalline mullite. Some of the significant findings include: 1. Power law creep (N approx. 3) in polycrystalline MgO is independent of iron doping, grain size, and oxygen partial pressure. 2. Three well-defined regimes have been identified for the diffusional creep of polycrystalline MgO and Al/sub 2/O/sub 3/, pure and doped with transition metal impurities: (1) cation grain boundary diffusion (2) cation lattice diffusion, (3) anion grain boundary diffusion. 3. Coble diffusional creep, which is rate-limited by oxygen grain boundary diffusion, has been identified in reduced iron-doped (2 cation percent) and double doped (1/4 percent Mn and 1/4 percent Ti) polycrystalline Al/sub 2/O/sub 3/. Stress relaxation deformation tests can be used to (1) identify transitions between viscous and non-viscous deformation, and (2) achieve high stresses (approx. 10/sup 3/ kg/cm/sup 2/) and strain rates (1h/sup -1/) without fracture. Good agreement exists between dead-load creep and stress relaxation studies in four point bending. (auth)
Date: December 1, 1975
Creator: Gordon, R. S.
Partner: UNT Libraries Government Documents Department

''Glassy'' low temperature thermal properties in crystalline solids

Description: Amorphous dielectrics are known to exhibit anomalous low temperature properties. An extensive review of these properties is presented with an eye toward an understanding of low-lying excitation modes thought to exist in glasses. Work on these systems is described in which a Zr-20 percent Nb samplewhich would be expected to reduce and redistribute the proposed tunneling states. Indeed, the thermal conductivity becomes similar to that of a quenched Zr-8 percent Nb sample and the ''excess'' specific heat linear in temperature dependence is reduced to half the value found in quenched Zr-20 percent Nb. The coefficient of the T/sup 3/ term in the specific heat unexpectedly increased from 23.3 to 56.9 erg/gm K/sup 4/ and this is attributed to a softening of the lattice due to annealing. The specific heat of this sample was remeasured after it had been dunked in liquid nitrogen. The cubic term was then found to be 19.5 erg/g K/sup 4/, smaller than that in quenched Zr-20 percent Nb, an effect which had been expected due to the chemical diffusion during annealing. Further study of this phenomenon is suggested. Among other relevant measurements performed were the specific heat of a sample of amorphous B/sub 2/O/sub 3/ (presented by Stephens (1976)); thermal conductivities of phase-separated unleached Vycor glass and Pyrex; thermal conductivities above 1.2/sup 0/K of polycrystalline MgO, heat-treated Pyroceram and porous Vycor (presented by Tait (1975)) and of mixed crystal KBr-KI (presented by Nathan, Lou and Tait (1976)). The last sample exhibited density fluctuations on a scale of 1000 A but exhibited thermal properties typical of dielectric crystal. Speed of sound measurements were made on both unleached and porous Vycor.
Date: May 1, 1976
Creator: Nathan, B. D.
Partner: UNT Libraries Government Documents Department

Advanced waste forms research and development. Annual report

Description: Thermogravimetric analysis on cesium aluminosilicates was performed. Pollucite, CsAlSi/sub 2/O/sub 6/, appears to have more than adequate thermal stability for Cs fixation in supercalcine. The possibility of leaving Ru as RuO/sub 2/ during supercalcine crystallization is being assessed. The apatite solid solution (A/sub ss/) phases used in supercalcine phase formation models have been easily prepared as pure phases. Use of Ca instead of Sr as an alkaline earth additive yields a more stable A/sub ss/ phase. Weight ratios have been optimized for two firing temperatures in terms of soxhlet leachability. However, this is not the preferred approach to supercalcine consolidation. The phase formation models developed for PW-4b-type wastes were routinely applied to PW-7, in spite of several significant composition differences in the latter. Uranium oxide remains as a fluorite structure oxide after supercalcine crystallization, but it does seem to have incorporated either or both CeO/sub 2/ or ZrO/sub 2/. Characterization of this F/sub ss/ phase will require further study. Based on observations during several complex compatibility studies, it appears that good overall thermal stability at as high as 1200/sup 0/C might be attainable for nepheline based supercalcine formulations. A thorough literature review of the oxide crystal chemistry of Te has been completed.
Date: June 11, 1976
Creator: McCarthy, G. J.
Partner: UNT Libraries Government Documents Department

Vacuum uv spectra of molecular crystals. Final report, February 1, 1971--June 30, 1975

Description: The broad goal of this work is the characterization of the optical and electronic properties of molecular crystals and biomaterials in the vacuum uv region. Work during the tenure of this contract can be summarized in two general areas: (1) Setting up and implementing a general facility for normal incidence reflection spectroscopy in the vuv region, with accompanying computer analyses for optical constants and derived functions. Detailed results were obtained on two molecular crystals in the form of thin films of tetraphenylporphyrin and its magnesium compound MgTPP. A general program for characterizing the vuv absorption of protein and nucleic acid components was set up, and specific results were obtained for tobacco mosaic virus and its protein in polymerized and unpolymerized configurations. Data were also taken on a synthetic polypeptide, polyglutamic acid in controlled morphologies. (2) Initiating a program to determine the vuv photoemission properties of biomaterials and thereby completely delineate their electronic structure. The requisite ultrahigh vacuum system was finalized and key components designed and fabricated; preliminary data will be taken by the end of the year on the prototype molecular crystal TPP. (auth)
Date: January 1, 1975
Creator: Peterson, C. W.
Partner: UNT Libraries Government Documents Department

Elastic and plastic strains and the stress corrosion cracking of austenitic stainless steels. Progress report, April 30, 1976--December 30, 1976

Description: The influence of homogeneous (uniaxial tension) and heterogeneous (rolling) deformation on the SCC of a transformable (301) and a nontransformable (310) stainless steel in 30 percent MgCl/sub 2/ has been under study. The amount or type of deformation with or without the presence of deformation induced martensite did not appear to influence the electrochemical parameters such as the rest potential or the critical cracking potential. Metallographic studies combined with failure tests and polarization curves identified the pitting potential with the critical cracking potential and indicated that the cracking potential was merely that for initiation of cathodic protection; that is the potential at which the current changes from anodic to cathodic. The failure time at constant applied stress increased significantly with amount of deformation indicating a maximum or optimum amount of plastic deformation. For tests conducted at a fixed percentage of the yield strength, the failure time decreased with increased amounts of deformation, independent of the type of deformation.
Date: February 1, 1977
Creator: Troiano, A. R.
Partner: UNT Libraries Government Documents Department

Thermal conductivity of the V/sub k/ center in CaF/sub 2/

Description: The thermocurrent properties of the V/sub k/ center in CaF/sub 2/ were investigated. The thermocurrent properties during irradiation as a function of temperature indicate that the number of V/sub k/ centers produced per Roentgen decreases with increasing temperatures. The V/sub k/ lifetime and activation energy were determined.
Date: January 1, 1974
Creator: Mayhugh, M. R. & Moran, P. R.
Partner: UNT Libraries Government Documents Department

Study of KLL Auger processes for light elements above Z = 10. [Review]

Description: A comprehensive review is given of the KLL Auger spectrum for members of the third row of the periodic table. This group contains the lightest elements wherein an Auger process can occur without the direct participation of the valence shell. Recent Auger spectra induced by x-ray photoionization on Mg, Al, and Si metals and their oxides are given as well as preliminary results on salts of Na and K, and for comparison, the LMM spectra of RbCl. Results were combined with previous experimental data and theory in order to obtain an overview. Four topics concerned with Auger processes are discussed: Energies, relative intensities, chemical shifts, and satellite structure. Interlaced throughout is a discussion of the role played by the chemical environment and electron correlation.
Date: January 1, 1977
Creator: Carlson, T. A.; Dress, W. B. & Nyberg, G. L.
Partner: UNT Libraries Government Documents Department

DT fusion neutron irradiation of LLL Nb--1 Zr tensile specimens, BNL-LASL superconductor wires, BPNL wire-foil packet, ORNL magnesium oxide crystals, LASL spinel, YAG, Al/sub 2/O/sub 3/ and MgO, and LLL LiF and glass microscope cover slides

Description: The DT fusion neutron irradiation of eight LLL Nb-1Zr tensile specimens, eleven BNL-LASL superconductor wires, one BPNL wire-foil packet, two ORNL magnesium oxide crystals, four LASL high purity single crystals, one each of spinel, YAG, Al/sub 2/O/sub 3/ and MgO, one LLL bicrystal of LiF and several LLL glass microscope cover slides is described. The sample position, beam-on time and dose record are given. The maximum neutron fluence on any sample was 2.51 x 10/sup 17/ neutrons/cm/sup 2/.
Date: March 4, 1977
Creator: MacLean, S. C.
Partner: UNT Libraries Government Documents Department

Method for adjusting temperature-time fading characteristics in TL phosphors: applications in wide range thermal dose monitoring

Description: Thermal fading of TL phosphors can be used to monitor thermal dose over some temperature-time range. For practical use the TL activation energy must be matched to the temperature-time characteristic desired. Simple criteria can be derived to establish the approximate glow peak peaking temperature, Tm, necessary to ensure the appropriate effective activation energy. How the complex, composite, glow curves of many common TL phosphors can be modified substantially by controlling the initial radiation dose, its quality, and by varying initial preannealing are described. This enables one to adjust Tm to any desired value over a reasonably wide range.
Date: January 1, 1976
Creator: Moran, P. R.
Partner: UNT Libraries Government Documents Department

New thermoluminescence techniques for mineral exploration

Description: The thermoluminescence of carbonate host rock in the vicinity of known lead-zinc and lead-zinc-fluorite mineralization was reexamined for possible development as an exploration technique. The measurements were made with equipment for determining the thermoluminescence spectrum at closely spaced temperature intervals. Radiation-induced thermoluminescence was also measured. Samples were studied from five localities in Mexico, Southwest Africa, and the United States. Four thermoluminescence properties were found to vary with ''distance-from-ore'' in a systematic manner. These include the glow peak intensity and temperature and the emission spectrum peak energy and full width at half-maximum. For example, in both limestone and dolomite, the high-temperature glow peak intensities are low or negligible within the ore and as the distance from the contact increases the intensity rises rapidly to a maximum, or maxima, and then decreases irregularly to constant value slightly above that in the ore. Depending on the thickness of the ore, the thermoluminescence characteristics associated with the mineralization extended from ten to a hundred or so meters from the ore host rock contact. 5 figures. (DLC)
Date: January 1, 1977
Creator: Levy, P W; Holmes, R J; Ypma, P J; Chen, C C & Swiderski, H S
Partner: UNT Libraries Government Documents Department

Application of borehole geophysics to fracture identification and characterization in low porosity limestones and dolostones

Description: Geophysical logging was conducted in exploratory core holes drilled for geohydrological investigations at three sites used for waste disposal on the US Department of Energy's Oak Ridge Reservation. Geophysical log response was calibrated to borehole geology using the drill core. Subsequently, the logs were used to identify fractures and fractured zones and to characterize the hydrologic activity of such zones. Results of the study were used to identify zones of ground water movement and to select targets for subsequent piezometer and monitoring well installation. Neutron porosity, long- and short-normal resistivity, and density logs exhibit anomalies only adjacent to pervasively fractured zones and rarely exhibit anomalies adjacent to individual fractures, suggesting that such logs have insufficient resolution to detect individual fractures. Spontaneous potential, single point resistance, acoustic velocity, and acoustic variable density logs, however, typically exhibit anomalies adjacent to both individual fractures and fracture zones. Correlation is excellent between fracture density logs prepared from the examination of drill core and fractures identified by the analysis of a suite of geophysical logs that have differing spatial resolution characteristics. Results of the study demonstrate the importance of (1) calibrating geophysical log response to drill core from a site, and (2) running a comprehensive suite of geophysical logs that can evaluate both large- and small-scale rock features. Once geophysical log responses to site-specific geological features have been established, logs provide a means of identifying fracture zones and discriminating between hydrologically active and inactive fracture zones. 9 figs.
Date: January 1, 1986
Creator: Haase, C. S. & King, H. L.
Partner: UNT Libraries Government Documents Department

Carbon-14 immobilization via the Ba(OH)/sub 2/8H/sub 2/O process

Description: The airborne release of /sup 14/C from various nuclear facilities has been identified as a potential biohazard due to the long half-life of /sup 14/C (5730 yrs) and the ease in which it may be assimilated into the biosphere. At Oak Ridge National Laboratory, technology is under development, as part of the Airborne Waste Management Program, for the removal and immobilization of this radionuclide. Prior studies have indicated that the /sup 14/C will likely exist in the oxidized form as CO/sub 2/ and will contribute slightly to the bulk CO/sub 2/ concentration of the gas stream, which is airlike in nature (approx. 330 ppMv CO/sub 2/). The technology under development utilizes the CO/sub 2/ - Ba(OH)/sub 2/ 8H/sub 2/O gas-solid reaction with the mode of gas-solid contacting being a fixed bed. The product, BaCO/sub 3/, possessing excellent thermal and chemical stability, prerequisites for the long-term disposal of nuclear wastes. For optimal process operation, studies have indicated that an operating window of adequate size does exist. When operating within the window, high CO/sub 2/ removal efficiency (effluent concentrations < 100 ppBv), high reactant utilization (> 99%), and an acceptable pressure drop across the bed (3 kPa/m at 13 cm/s superficial velocity) are possible. This paper will address three areas of experimental investigation. These areas are (1) micro-scale studies on 150-mg samples to provide information concerning surface properties, kinetics, and equilibrium vapor pressures, (2) macro-scale studies on large fixed beds (4.2 kg reactant) to determine the effects of humidity, temperature, and gas flow-rate upon bed pressure drop and CO/sub 2/ breakthrough, and (3) the design, construction, and initial operation of a pilot unit capable of continuously processing a 34 m/sup 3//h (20 ft/sup 3//min) air-based gas stream.
Date: January 1, 1982
Creator: Haag, G. L.; Nehls, J. W. Jr. & Young, G. C.
Partner: UNT Libraries Government Documents Department

Regenerative process for desulfurization of high temperature combustion and fuel gases. Quarterly progress report No. 3, October 1--December 31, 1976

Description: A regenerative process based on using carbon in coal ashes for lime regeneration has been studied. Ten sulfation/regeneration cycles using Greer limestone have been conducted in a TG system and there was no sign of weakening of the SO/sub 2/ sorption activity. Work on the regenerative process based on silicates is being continued. For pure silicates, the sulfation rate of the monocalcium silicate appeared to be higher than that of the calcined Greer limestone and dicalcium silicate; the latter two being similar. Procedures for particle strength test and for generating coal ash with controlled carbon content are being established. A micro-, semi-pilot plant for studying the regenerative processes is being constructed.
Date: January 1, 1976
Creator: Shen, M. S.; Kainz, F. B.; Farber, G. & Smol, R.
Partner: UNT Libraries Government Documents Department

Hydration-dehydration cycling of MgO--Mg(OH)/sub 2/ for application to solar heat storage systems

Description: A method for storing heat energy by utilizing reversible chemical reactions of inorganic oxides with water is under investigation at Atomics International. The system design requires a knowledge of rates of the dehydration and hydration reactions, and, in order that these rates be significant for practical applications, it must be shown that these rates are maintained as the material is cycled repeatedly through the anhydrous and hydrated condition. For solar heat storage operating on a daily cycle, for example, a 3-yr life requires somewhat more than 1000 cycles. Besides the effect of cycling on reaction kinetics, the extent of corrosion by the inorganic oxide/hydroxide on its containment vessel during cycling is an important parameter. Also, since one form of the active material that appears to have some advantages is that of granules held together by an inorganic cement, it is important in this case to know if the granules are broken down by cycling.
Date: September 30, 1976
Creator: Ervin, G.
Partner: UNT Libraries Government Documents Department

Advanced Thermionic Technology Program progress report No. 3

Description: Research progress is reported. A BaO collector was subjected to Auger and scanning electron microprobe analyses. Experiments measuring the work function of promising collector materials at high cesium impingement rates were continued. Evaluation of the tungsten oxide converter, barium oxide converter, and guarded converter continued. Results are given and discussed. (WHK)
Date: September 1, 1975
Partner: UNT Libraries Government Documents Department

Pressure sintering and creep deformation: a joint modeling approach. Progress report, January 1, 1977--December 31, 1977

Description: The joint modeling of creep deformation and pressure sintering, previously developed for the final and intermediate stages, has now been refined to include a ''transition stage'' that accounts for a decreasing ''connectivity'' for the cylindrical-open porosity and a smooth transition to spherical porosity as pinch-off occurs. As in the final and intermediate stages, this transition stage takes into account three major contributions to densification: lattice diffusional flow, grain boundary flow, and power law deformation; effects of grain growth have also been included. The model has been extensively tested and compared to experimental results on hot-pressed CoO, and is now being tested against earlier experimental data that we have obtained on MgAl/sub 2/O/sub 4/. Work has continued on creep studies of NiO and CoO, comparing the similarities and differences in creep behavior and relating these to dislocation structures observed in TEM. Finally, work has been completed on the grain growth of CoO as a function of porosity level, and also the effects of impurities (Cr, Li) on the creep and densification rates of CoO and NiO. These studies have provided specific information required for the intermediate stage modeling. They have also led to initial work on grain boundary segregation effects studied by STEM that we hope to continue and extend to a quantitative approach during the next year.
Date: July 1, 1977
Creator: Notis, M. R.
Partner: UNT Libraries Government Documents Department