1,095 Matching Results

Search Results

Advanced search parameters have been applied.

Gelcasting of aluminum titanate. Final report

Description: This Cooperative Research and Development Agreement (CRADA) was undertaken to assess the applicability of the gelcasting process for forming automotive exhaust port liner green bodies using Golden Technologies` proprietary aluminum titanate powder composition. A gelcasting process, specifically tailored to Golden Technologies` powder, was developed and used successfully to form green bodies for property evaluation. Using appropriate milling and firing conditions, it was found that the gelcast material had properties which compared favorably with Golden Technologies` baseline material. Tubular gelcast samples simulating exhaust port liners were prepared and shipped to Golden Technologies for final process evaluation.
Date: August 1, 1997
Creator: Nunn, S.D. & Stephan, J.E.
Partner: UNT Libraries Government Documents Department

Advance concepts for conversion of syngas to liquids. Quarterly report No. 3, April 29, 1995--July 28, 1995

Description: The aim of this phase of our study is to demonstrate how cobalt-containing aluminophosphate molecular sieves with structure types AFI and AEL can be synthesized from a clear homogeneous solution. The advantage of beginning with a clear solution is that transient phases, either crystalline or amorphous, can be more easily identified. The nature of these phases and their role in the crystallization process can be seen more easily. HF is used as a mineralizing agent. It has been reported that the presence of F anions in the synthesis mixture can improve considerably the AlPO{sub 4}-5 type crystals.
Date: December 1, 1995
Creator: Szostak, R.; Abotsi, G. & Mitchell, M.
Partner: UNT Libraries Government Documents Department

Investigation of the effect of microstructure on the R-Curve behavior of metal-ceramic composites

Description: An investigation was made into the effect of microstructure on the peak toughness and shape of the crack growth resistance curves for two ceramic-metal composites. An Al{sup 2}O{sup 3}/Al composite formed by Reactive Metal Penetration was used along with an AlN/Al composite formed using a reactive infiltration technique. The results indicate that the toughness increases with an increase in the volume fraction of the metal phase for a particular composite composition, and the peak toughness and shape of the R-Curve also depend on the composite microstructure and metal composition.
Date: July 1, 1995
Creator: Ellerby, D.T.; Flinn, B.D.; Scott, W.D.; Bordia, R.K.; Ewsuk, K.G.; Loehman, R.E. et al.
Partner: UNT Libraries Government Documents Department

POC-scale testing of an advanced fine coal dewatering equipment/technique: Quarterly technical progress report,January--March 1997

Description: Laboratory centrifugal dewatering tests were conducted to study the effects of anionic and cationic flocculants on filtration of PMCC compliance (low sulfur) and non-compliance (high sulfur) ultrafine coal slurry. The results obtained with compliance coal indicated that use of 30 g/t anionic flocculant reduced filter cake moisture from 32. 3 to 29.0 percent and increased solids recovery by two absolute percentage points. Use of cationic flocculant had no effects on solids recovery but lowered cake moisture to 27 percent at a dosage of 15 g/t. With the non-compliance coal slurry addition of 15 g/t anionic flocculant lowered cake moisture from 30 to 28.5 percent with marginal effects on solids recovery; addition of cationic flocculant reduced cake moisture by one absolute percentage point. Both flocculants showed marginal effects on solids recovery. Laboratory vacuum filter leaf filtration studies showed that use of flocculants considerably increased filtration kinetics. For example, addition of 15 g/t anionic flocculant to the compliance coal slurry increased filtration kinetics by 10 times and addition of 15 g/t.
Date: May 7, 1997
Creator: Tao, D.; Grappo, J.G. & Parekh, B.K.
Partner: UNT Libraries Government Documents Department

Local vibrational modes of Se-H complexes in AlSb

Description: Using infrared spectroscopy the authors have observed local vibrational modes (LVMs) arising from Se-H complexes in AlSb. At liquid-helium temperatures, hydrogenated AlSb:Se samples have three stretch mode peaks at 1,606.3, 1,608.6, and 1,615.7 cm{sup {minus}1}, whereas deuterated samples have only one peak at 1,173.4 cm{sup {minus}1}. The anomalous splitting of the se-H stretch mode may be explained by a resonance between the stretch mode and two multi-phonon modes. As the temperature or pressure is increased, the stretch mode and multi-phonon modes show anti-crossing behavior.
Date: September 1, 1996
Creator: McCluskey, M.D.; Hsu, L.; Haller, E.E.; Walukiewicz, W. & Becla, P.
Partner: UNT Libraries Government Documents Department

Determination of site-occupancies in aluminide intermetallics by ALCHEMI

Description: The site-distributions of Fe in four B2-ordered NiAl-based alloys with Fe concentrations of 10%, 2%, and 0.5% have been determined by ALCHEMI (atom-location by channeling-enhanced microanalysis). Site-distributions have been extracted with standard errors between {approximately} 1.5% (10% Fe concentration) and {approximately} 6% (0.5% Fe concentration). The results show that Fe has no strong site-preference in NiAl and tends to reside on the site of the stoichiometrically deficient host element. An improved ALCHEMI analysis procedure is outlined. The analysis explicitly addresses the phenomenon of ionization delocalization, which previously complicated the determination of site-distributions in aluminide intermetallics, leading to inaccurate and oftentimes nonphysical results. The improved ALCHEMI analysis also addresses the presence of anti-site defects. The data acquisition conditions have been optimized to minimize the sources of statistical and systematic error. This optimized procedure should be suitable for all analyses of B2-ordered alloys. Several analyses at different channeling orientations show that the extracted site-occupancies are robust as long as the data are acquired at orientations that are remote from any major pole of the crystal.
Date: April 1, 1995
Creator: Anderson, I. M.; Bentley, J. & Duncan, A. J.
Partner: UNT Libraries Government Documents Department

III-Sb (001) growth surfaces: Structure and island nucleation

Description: The authors have determined the reconstructions present on AlSb and GaSb(001) under conditions typical for device growth by molecular beam epitaxy. Within the range of Sb flux and temperature where the diffraction pattern is nominally (1 x 3), three distinct (4 x 3) reconstructions actually occur. The three structures are different than those previously proposed for these growth conditions, with two incorporating mixed III-V dimers on the surface. The presence of these hetero-dimers in the top Sb layer leads to an island nucleation and growth mechanism fundamentally different than for other III-V systems.
Date: April 24, 2000
Partner: UNT Libraries Government Documents Department

Inductively Coupled Plasma Etching in ICl- and IBr-Based Chemistries: Part I. GaAs, GaSb and AlGaAs

Description: High density plasma etching of GaAs, GaSb and AIGaAs was performed in IC1/Ar and lBr/Ar chemistries using an Inductively Coupled Plasma (ICP) source. GaSb and AlGaAs showed maxima in their etch rates for both plasma chemistries as a function of interhalogen percentage, while GaAs showed increased etch rates with plasma composition in both chemistries. Etch rates of all materials increased substantially with increasing rf chuck power, but rapidly decreased with chamber pressure. Selectivities > 10 for GaAs and GaSb over AlGaAs were obtained in both chemistries. The etched surfaces of GaAs showed smooth morphology, which were somewhat better with IC1/Ar than with IBr/& discharge. Auger Electron Spectroscopy analysis revealed equi-rate of removal of group III and V components or the corresponding etch products, maintaining the stoichiometry of the etched surface.
Date: November 23, 1998
Creator: Abernathy, C.R.; Cho, H.; Hahn, Y.B.; Hays, D.C.; Hobson, W.S.; Jung, K.B. et al.
Partner: UNT Libraries Government Documents Department

Reactive Ion Beam Etching of GaAs and Related Compounds in an Inductively Coupled Plasma of Cl(2)-Ar Mixture

Description: Reactive ion beam etching (RD3E) of GaAs, GaP, AIGaAs and GaSb was performed in a Cl2-Ar mixture using an Inductively Coupled Plasma (ICP) source. `The etch rates and yields were strongly affected by ion energy and substrate temperature. The RJBE was dominated by ion-assisted etching at <600 eV and by physical sputtering beyond 600 eV. The temperature dependence of the etch rates revealed three different regimes, depending on the substrate temperature: 1) sputtering-etch limited, 2) products-resorption limited, and 3) mass-transfer limited regions. GaSb showed the overall highest etch rates, while GaAs and AIGaAs were etched at the same rates. The etched features showed extremely smooth morphologies with anisotropic sidewalls.
Date: November 23, 1998
Creator: Abernathy, C.R.; Hahn, Y.B.; Hays, D.; Lambers, E.S.; Lee, J.W.; Pearton, S.J. et al.
Partner: UNT Libraries Government Documents Department

Pressure dependence of Se absorption lines in AlSb

Description: Using far infrared absorption spectroscopy, the authors have investigated electronic transition spectra of Se donors in AlSb as a function of hydrostatic pressure. At least two distinct ground to bound excited state transition lines, which depend quadratically on the pressure, can be seen. At pressures between 30 and 50 kbar, evidence of an anti-crossing between one of the electronic transitions and a peak which they attribute to the 2 zone center LO phonon mode can be seen.
Date: September 1, 1996
Creator: Hsu, L.; Haller, E.E. & Ramdas, A.K.
Partner: UNT Libraries Government Documents Department

Inorganic-organic composite nanoengineered films using self-assembled monolayers for directed zeolite film growth

Description: This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Zeolites, or molecular sieves, are aluminosilicate cage structures that are typically grown from a heterogeneous mixture of organic template molecules, inorganic salts of alumina and silica, and water. These zeolites are used in industry for catalytic cracking of hydrocarbons (gasoline manufacture from oil), and contaminant removal from chemical production processes. Within one year, we developed a viable method for the deposition of a quaternary ammonium salt amphiphile onto silicon wafer substrates. Using a biomimetic growth process, we were also able to demonstrate the first thin-film formation of a zeolite structure from such an organic template. Additionally, we synthesized the precursor to another amphiphile which was to be for further studies.
Date: October 1, 1997
Creator: Dye, R.C.; Hermes, R.E.; Martinez, M.G. & Peachey, N.M.
Partner: UNT Libraries Government Documents Department

Construction of artificial pigment-protein antennae

Description: Photosynthesis is a complex process which results in the conversion of solar radiation into chemical energy. This chemical energy is then used as the free energy source for all living organisms. In its basic form, photosynthesis can be described as the light-activated synthesis of carbohydrates from the simple molecules of water and carbon dioxide: 6H{sub 2}O + 6 CO{sub 2} light C{sub 6}H{sub 12}O{sub 6} + 6 O{sub 2} This basic mechanism actually requires numerous reaction steps. The two primary steps being: the capture of light by pigment molecules in light-harvesting antenna complexes and the transfer of this captured energy to the so-called photochemical reaction center. While the preferred pathway for energy absorbed by the chromophores in the antenna complexes is transfer to the reaction center, energy can be lost to competing processes such as internal conversion or radiative decay. Therefore, the energy transfer must be rapid, typically on the order of picoseconds, to successfully compete. The focus of the present work is on the construction of light-harvesting antenna complexes incorporating modular pigment-proteins.
Date: January 10, 1997
Creator: Sibbald, J.
Partner: UNT Libraries Government Documents Department

Development of Precipitated Iron Fischer-Tropsch Catalysts.

Description: Four (alumina or silica) supported catalysts with nominal compositions (on mass basis) of synthesized catalysts are: (1) 100 Fe/5 Cu/6 K/139 SiO{sub 2} (2) 100 Fe/10 Cu/6 K/134 SiO{sub 2}, (3) 100 Fe/5 Cu/ K/139 Al{sub 2}0{sub 3} and (4) 100 Fe/10 Cu/6 K/134 Al{sub 2}0{sub 3} were char BET surface area measurements. The surface areas of all four catalysts are between 94 and 136 m{sup 2}/g, whereas the surface areas of alumina and silica support are 213 and 252 m{sup 2}/g, respectively. The decrease in surface area of the supports is due to pore filling and blocking during the impregnation of supports with iron and promoters. During the current reporting period one slurry reactor test (SB-2337) was performed with an alumina supported catalyst with nominal composition 100 Fe/5 Cu/9 K/139 Al{sub 2}0{sub 3}, which was synthesized in our laboratory during the last quarter. The performance of this catalyst was inferior in comparison to our catalysts B (100 Fe/5 Cu/6 K/24 SiO{sub 2}) and C (100 Fe/3 Cu/4 K/16 SiO{sub 2}). Activity of the alumina supported catalyst was lower, and its catalyst deactivation rate was higher than that of the baseline catalysts B and C. The work on testing of alternative catalyst has been completed.
Date: August 29, 1997
Creator: Bukur, D. B.; Ding, Y. & Chokkaram, S.
Partner: UNT Libraries Government Documents Department

Vertical cavity surface emitting lasers emitting near 1.5 {mu}m with Sb-based reflectors

Description: We describe use of AlAsSb/AlGaAsSb lattice matched to InP for distributed Bragg reflectors. These structures are integral to several surface normal devices, in particular vertical cavity surface emitting lasers. The high refractive index ratio of these materials allows formation of a highly reflective mirror with relatively few mirror pairs. As a result, we have been able to show for the first time the 77K CW operation of an optically pumped, monolithic, all-epitaxial vertical cavity laser, emitting at 1.56 {mu}m.
Date: April 1, 1998
Creator: Blum, O.; Klem, J.F. & Vawter, G.A.
Partner: UNT Libraries Government Documents Department

Attempt to control the interfacial strength

Description: Composites consisting of a B2 iron aluminide matrix and 40 vol.% of TiB{sub 2} particles were processed by liquid phase sintering. In order to encourage segregation of B or Ti at the FeAl/TiB{sub 2} interfaces, the iron aluminide matrix was microalloyed with B or Ti, respectively. Additions of Ti degraded the mechanical properties. However, for composites microalloyed with B, room temperature flexure tests show slight increases in the maximum strength (from 1250 to 1380 MPa) and the fracture toughness. Interfacial segregation of B may have contributed to this result. Significantly improved processing of the composites would be required in order to verify the effect of B conclusively. 15 refs., 6 figs., 2 tabs.
Date: November 1, 1997
Creator: Schneibel, J.H. & Subramanian, R.
Partner: UNT Libraries Government Documents Department

Scoping corrosion tests on candidate waste package basket materials for the Yucca Mountain Project

Description: A scoping corrosion test was performed on candidate waste package basket materials. The corrosion medium was a pH-buffered solution of chemical species expected to be produced by radiolysis. The test was conducted at 90{degrees}C for 96 hours. Samples included aluminum-, copper-, stainless steel-, and zirconium-based metallic materials and several ceramics, incorporating neutron-absorbing elements. Sample weight losses and solution chemical changes were measured. Both corrosion of the host materials and dissolution of the neutron- absorbing elements were studied. The ceramics and the zirconium-based materials underwent only minor corrosion. the stainless steel-based materials performed well except for a welded sample. The aluminum- and copper-based materials exhibited the highest corrosion rates. Boron dissolution depends on it chemical form. Boron oxide and many metal borides dissolve readily in acidic solutions while high- chromium borides and boron carbide, though thermodynamically unstable, exhibit little dissolution in short times. the results of solution chemical analyses were consistent with this. Gadolinium did not dissolve significantly from monazite, and hafnium showed little dissolution from a variety of host materials, in keeping with its low solubility.
Date: March 1, 1998
Creator: Van Konynenburg, R.A.; Curits, P.C. & Summers, T.S.E.
Partner: UNT Libraries Government Documents Department

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

Description: To understand the underlying phenomena when characterizing material performance, we must know the chemistry and physics of the early stages of oxidation, chemistry, and bonding at the substrate/oxide interface, effect of segregants on the strength of bonding, transport processes through the scale formed during corrosion, mechanisms of residual stress generation and relief, and fracture behavior at the oxide/substrate interface. Specific objectives of the program described here are to (a) systematically investigate the relationships among substrate composition and properties and scale/coating adherence, damage tolerance, and micromechanical properties; (b) use results from the investigation to prevent scale/coating failure at elevated temperatures; and (c) identify conditions that lead to coatings that are more damage tolerant and scales that are amenable to legitimate synthesis routes. This report presents experimental data on the microstructural characteristics of alumina scales that have been thermally developed on several Fe-based alumina-forming intermetallic alloys. In addition, data are presented on scale adhesion, along with determinations of strain from data obtained by ruby fluorescence.
Date: November 1996
Creator: Natesan, K.; Renusch, D.; Veal, B. W. & Grimsditch, M.
Partner: UNT Libraries Government Documents Department

Advance concepts for the conversion of syngas to liquids. Quarterly report No. 8, October 1, 1996--December 31, 1996

Description: Large pore Metal Substituted Aluminophosphate Molecular sieves, (H-MAPO-5, H-MnAPO-5, H-CoAPO-5 and H-MAPO-36) were evaluated for the conversion of ethanol in a continuous flow fixed microreactor. At 400{degrees}C, high conversion levels were observed. Ethylene and diethyl ether were the two major products obtained however the catalysts were more selective for ethylene under the reaction conditions. At 500{degrees}C ethylene was the only product detected. The low concentration of acid sites combined with the possibly mild acid strengths of the molecular sieves were speculated to be possible reasons for the absence of higher hydrocarbons form the reaction products. Trends for the catalytic behavior of the various catalysts were unpredictable due to a number of reasons. Among these are (1) differing levels of divalent metal substitution, (2) varying amount of extraframework species which can have tremendous negative impact on catalytic performance, (3) differing levels of H{sup +} exchange, and (4) differing levels of crystallinity and thermal stability.
Date: June 1, 1997
Creator: Szostak, R. & Ingram, C.
Partner: UNT Libraries Government Documents Department