1,412 Matching Results

Search Results

Advanced search parameters have been applied.

Absence of antiferromagnetic order in UBe sub 13

Description: The linear magnetostriction ({lambda}{sub //} and {lambda}{sub //}) of a single-crystalline sample of the heavy-fermion compound UBe{sub 13} has been measured for fields B < 8 T (B{sub //}(100)) in the temperature interval 0.3 < T < 12 K. We find neither evidence for the antiferromagnetic order (T{sub N}=8.8 K) nor for the magnetostrictive oscillations, that were reported recently. Instead {lambda} varies proportional to B{sup 2} as expected for a normal paramagnetic metal. 8 refs., 3 figs.
Date: January 1, 1991
Creator: de Visser, A.; van Dijk, N.H.; Franse, J.J.M. (Amsterdam Univ. (Netherlands)); Lacerda, A.; Flouquet, J. (Centre National de la Recherche Scientifique (CNRS), 38 - Grenoble (France). Centre de Recherches sur les Tres Basses Temperatures); Fisk, Z. et al.
Partner: UNT Libraries Government Documents Department

Fundamental studies of metal fluorination reactions. Fourth annual progress report

Description: In order to investigate the effects of oxygen on the electrical characteristics of the bulk and the electrode/electrolyte interface of CaF/sub 2/ electrochemical cells separately, the equivalent electrical circuits for the following cells were determined, and the geometric capacitances, the double-layer capacitances, the bulk conductivities and the interface conductivities were examined: Ni + NiF/sub 2//CaF/sub 2//Ni + NiF/sub 2/, Ni + NiO/CaF/sub 2//Ni + NiO, and Cu + Cu/sub 2/O/CaF/sub 2//Cu + Cu/sub 2/O. After understanding the behavior of oxygen at the electrode/electrolyte interface and in the bulk of a CaF/sub 2/ electrochemical cell, a theory was developed to rationalize the emf values of the Ni + NiO/CaF/sub 2//Cu + Cu/sub 2/O cell.
Date: January 1, 1979
Creator: Rapp, R.A.
Partner: UNT Libraries Government Documents Department

Reaction kinetics and transport properties of the CaO-SO sub 2 -O sub 2 system in absence of intra-particle diffusion

Description: This work examines the CaO-SO{sub 2}-O{sub 2} chemical reaction system, with emphasis on gas diffusivity through the CaSO{sub 4} product layer. A mathematical model was developed to obtain intrinsic chemical kinetics, such as, order of reaction, reaction rate constants and SO{sub 2} gas diffusion coefficient through the CaSO{sub 2} product layer. To obtain the experimental data, equipment and procedures were developed using thermal gravimetric analysis for recording weight changes of a single CaO crystal during the reaction. For three different origins of CaO single crystals, kinetic data for the CaO-SO{sub 2}-O{sub 2} reaction system, such as reaction order, rate constant, and SO{sub 2} diffusion coefficients through the product layer, were obtained experimentally without any numerical fitting technique. 17 refs., 12 figs., 2 tabs.
Date: January 1, 1991
Partner: UNT Libraries Government Documents Department

Electronic structure of defects in oxides. Final report, December 1, 1979-November 30, 1980. [. cap alpha. -Al/sub 2/O/sub 3/; MgAl/sub 2/O/sub 4/]

Description: Details of the electronic structure of F-type centers in the series of oxides SrO, CaO, ..cap alpha..-Al/sub 2/O/sub 3/ and MgAl/sub 2/O/sub 4/ have been determined using measurements of photoconductivity, luminescence, and fluorescence lifetimes. Measurements were made over the spectral range 2 to 6.5 eV and over the temperature range 4 to 350/sup 0/K. The centers were introduced into SrO by electron, on proton or neutron bombardment, into CaO and ..cap alpha..-Al/sub 2/O/sub 3/ by electron a neutron bombardment or thermochemical coloration, and into MgAl/sub 2/O/sub 4/ by particle bombardment. In some cases, notably CaO and ..cap alpha..-Al/sub 2/O/sub 3/, the photoconductivity behaves differently depending on the method used to introduce the centers. In particular, neutron irradiated and some thermochemically colored samples of sapphire contain an effective electron trap with an optical transition energy of approx. 5.0 eV and a thermal excitation energy of 0.72 eV as determined by measurements of photoconductivity, thermoluminescence and phosphorescence. This trap appears to be structural defect consisting of an aggragate of anion vacancies.
Date: January 1, 1980
Creator: Summers, G.P.
Partner: UNT Libraries Government Documents Department

Conversion of light hydrocarbon gases to metal carbides for production of liquid fuels and chemicals

Description: Light hydrocarbon gases could be reacted with low cost alkaline earth metal oxide (CaO, MgO) in high-temperature plasma reactor to achieve very high ([le]100%) gas conversion to H[sub 2], CO, and the corresponding metal carbides. These carbides could be stored, transported, and hydrolyzed to acetylene or methyl acetylene, which in turn could be upgraded to a wide range of chemicals and premium liquid hydrocarbon fuels. An electric arc discharge reactor was built for converting methane. Literature reviews were made.
Date: February 1, 1993
Creator: Diaz, A.F.; Modestino, A.J.; Howard, J.B. & Peters, W.A.
Partner: UNT Libraries Government Documents Department

Scale formation at various locations in a geothermal operation due to injection of imported waters

Description: The injection of waters that are not native to a geothermal formation generates various physical and chemical problems. The major chemical problem resulting from such injections is the formation of sulfate scales (particularly CaSO4, BaSO4 and SrSO4) at various locations starting from the injection well through the production well to the surface facilities of any geothermal operation. One of the ways to prevent this type of scale formation is by reducing the sulfate concentration of the injection waters. The effect of sulfate deionization on scale formation at various locations of the geothermal operations is studied. Some experimental results on the CaSO4 scale formation in porous media upon heating an injection water with and without addition of scale inhibitors are also given.
Date: June 22, 1982
Creator: Vetter, O.J. & Kandarpa, V.
Partner: UNT Libraries Government Documents Department

Excited state electron transfer in systems with a well-defined geometry. [cyclophane]

Description: The effect of temperature, dielectric strength and ligand on the structure of the mesopyropheophorbide cyclophanes will be studied. ESR, NMR, emission and absorption spectroscopy, as well as circular dichroism will be used. The changes in structure will be correlated with changes in the photochemical activity. Electron acceptors such as benzoquinone will be utilized to stabilize the charge separation. Charge separation in porphyrin quinone dimers will also be studied. It was found that electron transfer in the cyclophane system is relatively slow. This is presumably due to an orientation requirement for fast electron transfer. Solvent dielectric also is important in producing a charge separation. Decreasing the temperature effects the yield of charge transfer, but not the kinetics.
Date: December 1, 1980
Creator: Kaufmann, K.J.
Partner: UNT Libraries Government Documents Department

Hot corrosivity of coal conversion product on high temperature alloys. Final report

Description: This report describes research begun under Contract AS01-76-ET-10577, most of which was continued when the same project was continued under a new number, Contract AC01-79-ET-13547. The areas studied are thermochemistry of high temperature corrosion, hot corrosion of turbine alloys and coatings, and electrochemistry of sulfate melts. A background to the problem of hot corrosion is presented first followed by a description of results obtained in the three areas of this project.
Date: August 29, 1984
Creator: Meier, G.H.
Partner: UNT Libraries Government Documents Department

Transformations of inorganic coal constituents in combustion systems

Description: Results from an experimental investigation of the mechanisms governing the ash aerosol size segregated composition resulting from the combustion of pulverized coal in a laboratory scale down-flow combustor are described. The results of modeling activities used to interpret the results of the experiments conducted under his subtask are also described in this section. Although results from the entire program are included, Phase II studies which emphasized: (1) alkali behavior, including a study of the interrelationship between potassium vaporization and sodium vaporization; and (2) iron behavior, including an examination of the extent of iron-aluminosilicate interactions, are highlighted. Idealized combustion determination of ash particle formation and surface stickiness are also described.
Date: November 1, 1992
Creator: Helble, J.J. (ed.); Srinivasachar, S.; Wilemski, G.; Boni, A.A. (PSI Technology Co., Andover, MA (United States)); Kang, Shin-Gyoo; Sarofim, A.F. et al.
Partner: UNT Libraries Government Documents Department

Fabrication of uranium carbide/beryllium carbide/graphite experimental-fuel-element specimens

Description: A method has been developed for fabricating uranium carbide/beryllium carbide/graphite fuel-element specimens for reactor-core-meltdown studies. The method involves milling and blending the raw materials and densifying the resulting blend by conventional graphite-die hot-pressing techniques. It can be used to fabricate specimens with good physical integrity and material dispersion, with densities of greater than 90% of the theoretical density, and with a uranium carbide particle size of less than 10 ..mu..m.
Date: July 6, 1978
Creator: Muenzer, W.A.
Partner: UNT Libraries Government Documents Department

Materials and mechanics of rate effects in brittle fracture. Progress report, October 1979-October 1980

Description: Energy balance methods have been used to find the crack driving force in elastic fractures. The fracture toughness of cracked steel bars have been measured using these techniques. Crack tip dislocations have been shown to protect the crack tip by having a stress intensity value that is opposite in sign from the applied stress intensity value. Thus, crack tip dislocation plasticity shields the crack from the external stress intensity factor. In the fatigue of LiF single crystals a relationship between monotonic and fatigue hardening responses has been established using a statistical model for fatigue deformation.
Date: January 1, 1980
Creator: Burns, S.J.
Partner: UNT Libraries Government Documents Department

Materials for high-temperature hydrogen fluorine environments. Final report, June 1976-December 1978

Description: A determination has been made of the stability of 35 materials under high-temperature, fluorine rich, hydrogen fluoride torch testing. Refractory materials tested included 4 borides, 3 carbides, 3 nitrides, 12 oxides, 1 oxynitride, 1 sulfide, 10 metals, and carbon (10 types). Three materials distinctly performed better than nickel: lanthanum hexaboride, calcium hexaboride, and lanthanum silicon oxynitride. Of these, lanthanum hexaboride is the best candidate tested since it has an estimated upper use temperature > 1726 K, which is above the melting point and more than 300 K above the upper use temperature of nickel.
Date: March 1, 1981
Creator: Holcombe, C.E. Jr. & Kovach, L.
Partner: UNT Libraries Government Documents Department

Sputtering of Be and BeO by light ions

Description: Sputtering yields of Be and BeO using 50 eV to 8 keV H/sup +/, D/sup +/ and He/sup +/ ions are reported. The measurements were made by determining the weight loss of the samples using a microbalance with sub-microgram sensitivity. Zone melted Be and sintered BeO targets were used. For the oxide measurements, the surface charge was compensated by electrons emitted from a hot tungsten filament. The energy dependence of the sputtering yield for both Be and BeO shows a maximum near 1 keV and a sharp decrease to lower energies. The results are discussed in terms of a scaling rule for low energy ion sputtering.
Date: January 1, 1979
Creator: Roth, J.; Bohdansky, J.; Blewer, R.S.; Ottenberger, W. & Borders, J.A.
Partner: UNT Libraries Government Documents Department

Characterization of the adherence of plasma-sprayed ZrO/sub 2/ coatings

Description: Analysis of the microstructure and adherence of ZrO/sub 2/ coatings revealed that the adherence decreased with increasing coating thickness and could be increased by incorporating MgO as a second phase as well as by including noncubic ZrO/sub 2/ in the cubic ZrO/sub 2/ coating. Residual stresses from the plasma spraying process limit adherence (hence the coating thickness dependence) but these can be relieved by plastic flow in the MgO phase during post-spray cooling. Some degree of strength/toughening is also derived by the presence of microcracks and/or from transformation associated with the presence of tetragonal ZrO/sub 2/.
Date: January 1, 1980
Creator: Becher, P.F. & Rice, R.W.
Partner: UNT Libraries Government Documents Department

Predicting diagenetic history and reservoir quality in the Frio Formation of Brazoria County, Texas and Pleasant Bayou test wells

Description: Good-quality geothermal reservoirs displaying secondary porosity exist on the upper Texas coast (Brazoria County), site of the Pleasant Bayou No. 1 and No. 2 wells, and are attributed to a moderately stable mineral assemblage, normal geothermal gradients, and low in situ pH. Major authigenic minerals are calcite, quartz, and kaolinite. Detrital feldspar has been extensively albitized at depth. Major diagenetic events overlapped, occurring in the general order-precipitation of calcite, formation of quartz overgrowths, albitization, leaching of calcite to form secondary porosity, and precipitation of kaolinite. Seventeen Brazoria County water analyses including two from the Pleasant Bayou No. 2 well were thermodynamically tested. Predictions based on equilibrium thermodynamics add new insight on mineral stabilities and are consistent with the paragenetic sequence developed from petrographic data. Early precipitation of calcite at shallow depths of burial is predicted. Low temperture and low in situ pH explain the general absence of chlorite. The use of solution-mineral equilibria as a predictor of reservoir quality is inconclusive, but well-defined clustering of waters indicates that identification of regional trends will probably be possible. Shallow waters may be the key to predicting reservoir quality at depth.
Date: January 1, 1981
Creator: Kaiser, W.R. & Richmann, D.L.
Partner: UNT Libraries Government Documents Department

Continuing development of regenerable sorbents for fluidized-bed combustion. Semiannual technical progress report No. 2, April 1-September 30, 1980

Description: Our efforts were directed primarily to preparation for and/the initial operation of the laboratory-scale hot fluidized bed test system (LSHFB). The initial test sequence in the LSHFB system was performed with a fixed-bed of 100 grams of barium titanate synthetic sorbent. The sorbent bed was alternately sulfated and regenerated five times. Sulfation was accomplished at 900/sup 0/C, with a synthetic flue gas mixture comprising 10.1% CO/sub 2/, 4.95% O/sub 2/, 0.2435% SO/sub 2/ and 84.7% N/sub 2/. Regeneration was performed at 1025/sup 0/C with a gas containing 8.0% CO and 92.0% N/sub 2/. After an initial drop in sulfation performance after the first sulfation/regeneration cycle, performance held steady, or was shown to be improving, during the succeeding four cycles. Although the initial operation of this system proceeded relatively smoothly, the reactor was found to have been irreparably damaged by the end of the initial test sequence. A new reactor was subsequently designed, fabricated, and installed in the unit. Concurrently, sorbent pellet preparation by extrusion was investigated in the Catalyst Preparation Facility at the Baton Rouge Laboratory of Exxon Research and Engineering Company. Preparation of sorbent pellets for use in the LSHFB operation was continued on a laboratory-scale at Linden throughout the reporting period. Cost and time estimates were prepared for operation of the bench-scale fluidized bed coal combustion and regeneration facilities, including preparation of the requisite volumes of synthetic sorbent pellets needed for that program.
Date: January 1, 1980
Creator: Kalfadelis, C D
Partner: UNT Libraries Government Documents Department

Sintering theory for crystalline solids

Description: A thermodynamic model for vacancy partitioning among sites of different bonding environments, yields a more satisfactory expression for the driving forces for sintering and for grain growth at constant temperature than traditional theories. This expression is shown to be also a logical consequence of classical thermodynamic theory for faceted particles. Then the driving force for sintering in a temperature gradient is evaluated in terms of gradients in equilibrium vapor pressures. 26 refs., 6 figs.
Date: November 1, 1986
Creator: Searcy, A.W.
Partner: UNT Libraries Government Documents Department

Removal of plutonium from high-level caustic waste solutions using bone char: pilot study

Description: Pilot studies have been completed using 275-..mu..m bone char as an adsorbent for the removal of plutonium, in concentrations ranging up to 8 mg/liter, from caustic waste solutions. These waste solutions were adjusted to an approximate pH of 8 before they were passed through columns of the bone char. Overall decontamination factors of about 5 x 10/sup 9/ were obtained. A tentative design of a caustic waste treatment system utilizing cartridge filters and bone char columns was made. Its advantages and possible cost saving benefits are assessed.
Date: October 2, 1978
Creator: Blane, D.E. & Herald, W.R.
Partner: UNT Libraries Government Documents Department

A calcium oxide sorbent process for bulk separation of carbon dioxide

Description: This research project is investigating the technical feasibility of a high-temperature, high-pressure process for the bulk separation of CO[sub 2] from coal-derived gas. Phase I consisted of 6 tasks. Phase II added a seventh task to the project. This report is limited to a description of the final experimental results obtained in Phase I, Task 5 (multicycle tests), and a brief overview of justification and plans for Phase II, Task 7.
Date: April 1, 1992
Creator: Harrison, D.P.
Partner: UNT Libraries Government Documents Department

Ceramic heat recuperators for industrial heat recovery. Final report

Description: Development of a GTE ceramic recuperator, designed for relatively small furnaces with firing rates of 0.3 to 0.6 MM Btu/h and with exhaust gas temperatures of 1500 to 2600 F, is described. The ceramic selected as the material of construction is cordierite, a magnesium aluminum silicate. Details of the ceramic recuperator design are presented in Chapter 2. Also results of tests and measurements, system economics, and cost performance analyses are presented. Five demonstration programs were performed to determine the heat transfer performance of the recuperator, establish the energy savings by recuperation, demonstrate minimum maintenance requirements in typical furnace operation, determine the durability of the ceramic core, determine the operating requirements of the burners and controls with recuperation, and establish the overall system costs and payback period. Demonstration programs and results of the Bliss Mill Furnace, Tungsten Reduction Furnace, Glass Tank, Pilot Plant US Smelting Furnace, and Rotary Calciner Furnace are given in Chapter 3. Chapter 4 develops the methodology and shows how an impact analysis may be performed. Industrial applications are implied and a process flow diagram for smelting and refining primary copper is shown. Concluding chapters present conclusions and recommendations, a bibliography, and additional information in appendices. (MCW)
Date: August 1, 1980
Creator: Cleveland, J.J.; Gonzalez, J.M. & Kohnken, K.H.
Partner: UNT Libraries Government Documents Department

A novel approach to highly dispersing catalytic materials in coal for gasification

Description: This project seeks to develop a technique, based on coal surface properties, for highly dispersing catalysts in coal for gasification and to investigate the potential of using potassium carbonate and calcium acetate mixtures as catalysts for coal gasification. The lower cost and high catalytic activity of the latter compound will produce economic benefits by reducing the amount of K{sub 2}CO{sub 3} required for high coal char reactivities. The work is focused on the elucidation of coal-catalyst precursor interactions in solution and the variables which control the adsorption and dispersion of coal gasification metal catalysts. In order to optimize coal-metal ion interactions and hence maximize catalyst activity, the study examines the surface electrochemistry of a lignite, a subbituminous, and a bituminous coals and their demineralized and oxidized derivatives prior to loading with the catalytic materials. The surface electrical properties of the coals are investigated with the aid of electrophoresis, while the effects of the surface charge on the adsorption of K{sup +} and Ca{sup 2+} are studied by agitating the coals with aqueous solutions of potassium and calcium. A zeta meter, a tube furnace, and other equipment required for the investigation have been acquired and installed. Preliminary work shows that the lignite (Psoc 1482) is negatively charged between pH 1.8 and pH 11.0 and has an isoelectric point of pH 1.8.
Date: January 1, 1989
Creator: Abotsi, G.M.K. & Bota, K.B.
Partner: UNT Libraries Government Documents Department

Grain boundaries in complex oxides

Description: A quantitative comparison was achieved between space charge theory and segregation at grain boundaries in the model system TiO[sub 2]. The ionic space charge can be titrated from negative to positive potential. A space charge model was developed that includes the lattice defect chemistry. Defect formation energies in the Frenkel pair for TiO[sub 2] were studied. Grain boundary enthalpy was measured during coarsening. It was shown that it is the barium vacancy that forms near surfaces in donor-doped BaTiO[sub 3] electroceramics during oxidative-cooling.
Date: May 1, 1993
Creator: Chiang, Yet-Ming.
Partner: UNT Libraries Government Documents Department