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Geometry of some metal halides

Description: Thesis. Two polarizable ion models are developed to describe the gas phase of metal dihalide molecules. Both models use electrostatic and repulsive interactions to predict molecular geometries and molecular constants. The first model is applied to the dihalides of the alkaline earths, group II-b metals, transition metals, group IV-a metals, and europium. In addition to the molecular geometry, bending frequencies are derived for most of these molecules. The second or linear'' model is applied to the alkaline eanth dihalides; equilibrium internuclear bond lengths, stretching force constants, and stretching frequencies are determined. (LK)
Date: July 1, 1973
Creator: Yarnell, P.A.
Partner: UNT Libraries Government Documents Department

Observation of high field DHVA-effect and induced magnetism in single crystal TiBe/sub 2/

Description: Recently much interest has been given to itinerant magnetism in cubic Laves phase or C15 materials. Primarily this stems from the discussion of the relationship of p-state pairing and ferromagnetism in ZrZn/sub 2/ by Enz and Matthias, and the possibility of triplet superconductivity. The most recent work in this field has focused on the isoelectronic, isostructural material TiBe/sub 2/, and the possibility that this material is metamagnetic. That TiBe/sub 2/ is close to some form of magnetic instability can be infered indirectly from the peaked nature of its density of states near the fermi level, but also from the observation of ferromagnetism in TiBe/sub 2-x/Cu/sub x/, when x is greater than about 0.15. In this paper a single crystal of pure TiBe/sub 2/ is considered in fields larger than 15 Tesla (T) and at a temperature of 1.3/sup 0/K.
Date: January 1, 1981
Creator: van Deursen, A.P.J.; van Ruitenbeek, J.M.; Verhoef, W.A.; de Vroomen, A.R.; Smith, J.L.; de Groot, R.A. et al.
Partner: UNT Libraries Government Documents Department

Polar intermetallic compounds of the silicon and arsenic family elements and their ternary hydrides and fluorides

Description: An investigation has been made on the effects of hydrogen and fluoride in the solid state chemistry of alkaline-earth and divalent rare-earth metal pnictide (Pn) and tetrelide (Tt) phases A{sub 5}(Pn,Tt,){sub 3}Z{sub x}, where A = Ca, Sr, Ba, Sm, Eu, Yb; Pn = As, Sb, Bi; Tt = Si, Ge, Sn, Pb and Z = H, F. Several trivalent rare-earth-metal pnictides, RE{sub 5}Pn{sub 3} (RE = Y, La, Gd, Tb, Dy, Ho, Er, Tm) and alkaline-earth-metal trielides, A{sub 5}Tr{sub 3}Z{sub x} (Tr = Ga, In, Tl) have been included in an effort to complete observed structural trends. Two main experimental techniques were followed throughout this work, (a) reactions in absence of hydrogen or under continuous high vacuum, and (b) reactions with binary metal hydrides, AH{sub x}, in closed containers. The results demonstrate that all the phases reported with the {beta}-Yb{sub 5}Sb{sub 3}-type structure in the A{sub 5}Pn{sub 3} systems are hydrogen-stabilized compounds. Reactions in absence of hydrogen lead to compounds with the Mn{sub 5}Si{sub 3}-type structure. The structure type {beta}-Yb{sub 5}Sb{sub 3} (= Ca{sub 5}SB{sub 3}F) was found to be characteristic of ternary systems and inaccurately associated with phases that form in the Y{sub 5}Bi{sub 3}-type. A new series of isomorphous Zintl compounds with the Ca{sub 16}Sb{sub 11}-type structure were prepared and studied as well. All the alkaline-earth-metal tetrelides, A{sub 5}Tt{sub 3}, that crystallize in the Cr{sub 5}B{sub 3}-type structure can be interstitially derivatized by hydrogen or fluoride. Binary and ternary compounds were characterized by Guinier powder patterns, single crystal X-ray and powder neutron diffraction techniques. In an effort to establish property-structure relationships, electrical resistivity and magnetic measurements were performed on selected systems, and the results were explained in terms of the Zintl concepts, aided by extended Hueckel band calculations.
Date: October 17, 1996
Creator: Leon-Escamilla, E.A.
Partner: UNT Libraries Government Documents Department

Gas flow through porous barriers

Description: In Part I the possibility of CO/sub 2/ surface diffusion through the porous BaO that results from BaCO/sub 3/ decomposition is examined. CO/sub 2/ and He flow rates through a BaO barrier are compared and both are found to exhibit similar behavior. Because He is known not to undergo surface diffusion, it is concluded that CO/sub 2/ goes through BaO by ordinary Knudsen flow. In Part II the decomposition of SO/sub 3/ to SO/sub 2/ and O/sub 2/ in a porous alumina barrier is studied. The goal is to determine if this reaction will equilibrate in the barrier. A stream of SO/sub 3/ is run through the barrier and the exit gas compositions are determined as a function of temperature with a mass spectrometer. These compositions are found to differ considerably from the calculated equilibrium values, indicating the reaction does not equilibrate in the barrier.
Date: October 1, 1978
Creator: Jacobson, N.S.
Partner: UNT Libraries Government Documents Department

Structure, stoichiometry and stability in magnetoplumbite and [beta]-alumina type ceramics

Description: Work has continued on the computer simulation of atomic scale defect complexes in polyaluminates with the magnetoplumbate and [beta]-alumina structures. More stringent criteria have been developed for determining the viability of interatomic potential models for these complex structured materials, details of the cation coordination having been found to be important. It appears that the energetics of point defect complex formation is the reason why Ba hexa-aluminate does not adopt the magnetoplumbate structure, in contrast to Sr hexa-aluminate, which does.
Date: December 1, 1992
Creator: Cormack, A.N. & Park, J.G.
Partner: UNT Libraries Government Documents Department

Kinetics of the desulfurization of molten iron. Final report

Description: Experimental work has involved the fabrication of impervious slip-cast CaO crucibles, measurement of the rate of desulfurization of liquid iron by solid CaO and measurement of the rate of desulfurization of liquid iron by CaO-saturated liquid FeO. Above 0.087 < wt % S < 0.67, the activity of FeS is high enough to form a liquid phase in the system CaO-Fe-S. With lower sulfur levels, CaO does not cause any desulfurization of the liquid iron. When CaO-saturated liquid FeO is brought into contact with a liquid Fe-S alloy a rapid initial rate of desulfurization occurs due to surface tension-induced local convection at the slag-metal interface. After this initial period, the rate of desulfurization is determined by diffusion of sulfur in the metal. No change occurs in the oxygen content of the metal during desulfurization and hence the half cell reactions occurring in the electrochemical transfer process are (Fe) ..-->.. (Fe/sup 2 +/) + 2e/sup -/ and (S) + 2e/sup -/ ..-->.. (S/sup 2 -/). Addition of CaF/sub 2/ to the CaO-saturated slag has no effect on the desulfurization.
Date: March 1, 1981
Creator: Gaskell, D.R.
Partner: UNT Libraries Government Documents Department

A review of metalorganic chemical vapor deposition of high-temperature superconducting thin films

Description: A status report is given on the metalorganic chemical vapor deposition (MOCVD) of high-temperature superconducting thin films. The advantages of MOCVD processing manifest themselves in the quality of the films produced, and in the economy of the process. Metalorganic precursor requirements, deposition parameters and film properties are discussed. Also difficulties have been identified in making MOCVD a manufacturing technology. To solve these problems, future research directions are proposed.
Date: January 1, 1989
Creator: Erbil, A.; Zhang, K.; Kwak, B.S. & Boyd, E.P.
Partner: UNT Libraries Government Documents Department

Glassy thin films. Final report

Description: This report describes the initial results of a long term program to study order-disorder phenomena in dielectric thin films. To achieve this overall goal, an apparatus was constructed to permit the codeposition of a glass-forming additive such as SiO/sub 2/ in a polycrystalline matrix film such as MgO. The extent of crystallinity of mixture films in the MgO-SiO/sub 2/ system was determined using techniques developed for x-ray powder diffraction. With this approach, it was determined that the addition of SiO/sub 2/ in concentrations less than 20 mass % has a relatively small influence on crystallinity. On the other hand, at concentrations greater than 25% SiO/sub 2/ causes the mixture film to become completely disordered.
Date: January 27, 1981
Creator: Haller, W; Sanders, D M & Farabaugh, E N
Partner: UNT Libraries Government Documents Department

Ultraviolet-Spectrograph Lens

Description: A 700-mm f/4.7 spectrograph camera lens was designed for imaging spectral lines in the 200- to 400-nm region on a 120-mm flat image field. Lens elements of fused silica and crystal calcium fluoride give such good achromatization that raytracing calculations predict a resolution limit of 30 lines/mm without refocusing in the 238- to 365-nm region. Light scattering at the polished calcium-fluoride surfaces is avoided by sandwiching the fluoride elements between fused silica and cementing with silicone fluid. The constructed lens makes good spectrograms.
Date: 1981
Creator: Brixner, B. & Winkler, M. A.
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, 1976--December 18, 1977

Description: The research described covers work on: 1. The effect of mixed transition metal (Mn-Ti) impurities on the creep of polycrystalline alumina. 2. Stress relaxation deformation which includes work on (a) the design and construction of an improved experimental apparatus (b) the analysis of stresses and strains in stress relaxation tests and (c) preliminary stress relaxation tests at 1350-1450/sup 0/C on iron-doped (0.53 cation %), polycrystalline MgO.
Date: December 1, 1977
Creator: Gordon, R.S.
Partner: UNT Libraries Government Documents Department

Electron microscopy study of microsegregation and defects in Czochralski grown calcium gallium germanium garnet single crystals

Description: Microstructural defects in single crystal specimens of calcium gallium germanium garnet (CGGG or Ca/sub 3/Ga/sub 2/Ge/sub 3/O/sub 12/) have been investigated using electron microscopy techniques. High voltage transmission electron imaging and diffraction were used to characterize the observed defects with respect to their morphology, structure, and crystallography. Scanning transmission electron microscopy (STEM) with x-ray microanalysis was employed to determine the elemental composition of certain defects.
Date: September 1, 1978
Creator: Roth, T.F.
Partner: UNT Libraries Government Documents Department

Cause of pitting in beryllium

Description: Light microscopy, bare-film radiography, secondary ion mass spectroscopy, electron microprobe and physical testing were used to examine beryllium specimens exhibiting a stratified, pitted, pattern after chemical milling. The objective was to find the cause of this pattern. Specimens were found to have voids in excess of density specification allowances. These voids are attributed, at least in part, to the sublimation of beryllium fluoride during the vacuum hot pressing operation. The origin of the pattern is attributed to these voids and etching out of fines and associated impurities. Hot isostatic pressing with a subsequent heat treatment close residual porosity and dispersed impurities enough to correct the problem.
Date: April 16, 1982
Creator: Kershaw, R.P.
Partner: UNT Libraries Government Documents Department

Nonlinear materials for frequency conversion

Description: Two figures of merit, the threshold power (P/sub th/) and the limiting volume (V/sub min/) can be used to compare the relative efficiency and economy of new harmonic generating crystals. The properties of barium metaborate and L-Arginine phosphate are used to illustrate the effect of nonlinearity, birefringence, and damage threshold on these figures of merit.
Date: March 22, 1988
Creator: Velsko, S.P. & Eimerl, D.
Partner: UNT Libraries Government Documents Department

Isobutanol-methanol mixtures from synthesis gas. Quarterly technical progress report, October 1--December 31, 1995

Description: A series of Cu{sub 0.5}CeMe(II)O{sub x} catalysts (Me refers to Group II alkali earth elements) have been prepared by coprecipitating the corresponding metal nitrates with potassium carbonate. The bulk composition of the catalyst has been determined by atomic absorption (AA) analysis. High-pressure isobutanol synthesis studies have been carried out over a standard BASF Cs-promoted Cu/ZnO/Al{sub 2}O{sub 3} catalyst. At a CO conversion level of 32%, the isobutanol carbon selectivity is about 5%; whereas that of methanol is 40.2%. A 100% selectivity sum has now been obtained as a result of using response factors measured by the laboratory. The reactions of ethanol and acetic acid over a number of catalysts have been investigated using a temperature programmed surface reaction (TPSR) technique. Ethanol and acetone are the only desorption products observed over Cs-promoted Cu/ZnO/Al{sub 2}O{sub 3} catalysts. Surface acetate ion is believed to be the precursor for acetone formation. Over calcined hydrotalcites, i.e., MgO/Al{sub 2}O{sub 3}, ethylene is formed instead of acetone. The amount of ethylene formed decreases as Mg/Al ratio increases, suggesting a role of aluminum ions in ethanol dehydration reactions.
Date: January 10, 1996
Creator: Iglesia, E.
Partner: UNT Libraries Government Documents Department

Scaling of the magnetoresistance of UBe/sub 13/ under pressure

Description: We report magnetoresistance measurements of the heavy electron compound UBe/sub 13/ above the superconducting transition temperature T/sub c/ and below 4 K for pressures P up to 19 kbar and for magnetic fields H up to 9T. We observe strong negative magnetoresistance at all pressures and temperatures. The resistivity /rho/ is quadratic in temperature T from T/sub c/ up to a maximum temperature of 1 K at 1 bar increasing to 2 K at 19 kbar. The slope of the T/sup 2/ term decreases with both H and with P. We find that delta(H) /triple bond/ /minus/ (/rho/(H) /minus/ /rho/(0))/rho/(0) for a given pressure scales as a function of HT and exhibits power law behavior over one decade with an exponent of 1.7. In addition, delta(H) at high pressure shows this same power law over a more limited HT range. 16 refs., 5 figs.
Date: January 1, 1988
Creator: Willis, J.O.; McElfresh, M.W.; Thompson, J.D.; Smith, J.L. & Fish, Z.
Partner: UNT Libraries Government Documents Department

Dynamic response of porous calcium carbonate minerals

Description: A theoretical study of the shock-loaded response of calcium carbonate materials is presented in which both dry and water-saturated samples with porosities up to 50 percent are considered. Data are presented for the unloading response from 15.0 and 18.5 GPa, and calculations from a mixture model using a Mie-Grueneisen equation of state with volume-dependent parameters are compared to both the Hugoniot and the isentropic unloading response.
Date: January 1, 1985
Creator: Drumheller, D.S. & Grady, D.E.
Partner: UNT Libraries Government Documents Department

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

Cyclic fatigue-crack propagation in ceramics: Long and small crack behavior

Description: Stress/life (S/N) and cyclic fatigue-crack growth properties are studied in a Mg-PSZ, with particular reference to the role of crack size. S/N data from unnotched specimens show markedly lower lives under tension-compression compared to tension-tension loading; fatigue limits'' (at 10{sup 8} cycles) for the former case approach 50% of the tensile strength. Under tension-tension loading, cyclic crack-growth rates of long'' (> 3 mm) cracks are found to be power-law dependent on the stress-intensity range {Delta}K with a fatigue threshold, {Delta}K{sub TH}, of order 50% K{sub c}. Conversely, naturally-occurring small'' (1 to 100 {mu}m) surface cracks were observed to grow at {Delta}K levels some 2 to 3 times smaller than {Delta}K{sub TH}. The implications of such data for structural design with ceramics is briefly discussed. 21 refs., 3 figs., 1 tab.
Date: December 1, 1989
Creator: Steffen, A.A.; Dauskardt, R.H. & Ritchie, R.O (Lawrence Berkeley Lab., CA (United States) California Univ., Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering)
Partner: UNT Libraries Government Documents Department

Secondary grain-boundary dislocations in (001) twist boundaries in MgO. II. Extrinsic structures

Description: Extrinsic secondary grain boundary dislocation (GBD) structures were observed by weak beam transmission electron microscopy in a variety of (001) twist boundaries in MgO. These structures were derived from segments of lattice dislocations embedded in the boundaries and could be interpreted as the result of the decomposition of the lattice dislocations into extrinsic GBDs and the subsequent interaction of the product GBDs with the intrinsic boundary structure. The results demonstrate that lattice dislocations in MgO are attracted to grain boundaries over a wide range of conditions and tend to remain embedded in the boundaries as extrinsic GBD structures.
Date: December 1, 1981
Creator: Sun, C.P. & Balluffi, R.W.
Partner: UNT Libraries Government Documents Department

Multimode fiber interferometry and several-mode fiber polarimetry via phase conjugation

Description: While the simplest fiber optics are realized by transmission intensity modulations impressed on multimode fibers, great enhancements in sensitivity are achieved by interferometric or polarimetric methods with light propagated through single-mode fibers. In this paper we report preliminary experiments on retaining the sensitivity of interferometric and/or polarimetric measurements while using only multimode fiber components. The utility of success in this endeavor can be measured by greater experimental simplicity (light injection and alignment tolerances), by cost factors (cheaper fiber optics components), or by larger intensity transmission limits (which can be translated to higher time resolution for a given signal-to-noise ratio). 14 refs., 3 figs.
Date: January 1, 1989
Creator: Forman, P.R.; Jahoda, F.C.; Mason, B.L. & Netterfield, C.B.
Partner: UNT Libraries Government Documents Department

Improvements in geothermometry. Final technical report. Rev

Description: Alkali and alkaline earth geothermometers are useful for estimating geothermal reservoir temperatures, though a general theoretical basis has yet to be established and experimental calibration needs improvement. Equilibrium cation exchange between feldspars provided the original basis for the Na-K and Na-K-Ca geothermometers (Fournier and Truesdell, 1973), but theoretical, field and experimental evidence prove that neither equilibrium nor feldspars are necessary. Here, evidence is summarized in support of these observations, concluding that these geothermometers can be expected to have a surprisingly wide range of applicability, but that the reasons behind such broad applicability are not yet understood. Early experimental work proved that water-rock interactions are slow at low temperatures, so experimental calibration at temperatures below 150/sup 0/ is impractical. Theoretical methods and field data were used instead for all work at low temperatures. Experimental methods were emphasized for temperatures above 150/sup 0/C, and the simplest possible solid and solution compositions were used to permit investigation of one process or question at a time. Unexpected results in experimental work prevented complete integration of the various portions of the investigation.
Date: August 1, 1982
Creator: Potter, J.; Dibble, W.; Parks, G. & Nur, A.
Partner: UNT Libraries Government Documents Department