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In situ beam analysis of radiation damage kinetics in MgTiO{sub 3} single crystals at 170-470 K

Description: Radiation damage kinetics in synthetic MgTiO{sub 3} (geikielite) single crystals have been studied using the in situ ion beam facility at Los Alamos National Laboratory. The geikielite samples were irradiated at temperatures of 170, 300, and 470 K with 400 keV xenon ions and the radiation damage was sequentially measured with Rutherford backscattering using a 2 MeV He ion beam along a channeling direction. Threshold doses of I and 5x l0{sup 15} Xe/cm{sup 2} were determined for the crystalline-to-amorphous transformation induced by Xe ion irradiation at 170 and 300 K, respectively. However, geikielite retained its crystallinity up to a dose of 2.5xl0{sup 16}Xe/cm{sup 2} at the irradiation temperature of 470 K. This study has shown that MgTiO{sub 3}, which has a corundum derivative structure, is another radiation resistant material that has the potential for use in radiation environments.
Date: December 31, 1995
Creator: Yu, Ning; Mitchell, J.N.; Sickafus, K.E. & Nastasi, M.
Partner: UNT Libraries Government Documents Department

Synthesis of novel precursors for PMN powders and the thin films obtained from them

Description: Sol-gel processing has been widely used in the preparation of lead zirconate titanate (PZT) thin films. The authors have applied this methodology to the formation of lead magnesium niobate (PMN) spin-cast deposited thin films. Since there is a limited number of soluble, commercially available compounds, the authors have recently synthesized a series of novel metal alkoxides for use as precursors for generation of PMN thin films and powders. The process for generation of the perovskite phase of these PMN powders and films are reported.
Date: March 1, 1995
Creator: Boyle, T.J.; Dimos, D.B. & Moore, G.J.
Partner: UNT Libraries Government Documents Department

Chemically prepared lead magnesium niobate dielectrics

Description: A chemical solution powder synthesis technique has been developed that produces first, uniform powders of lead magnesium niobate (PMN) with 60 to 80 nm crystallite size. The synthesis technique was based on the dissolution of lead acetate and alkoxide precursors in acetic acid followed by precipitation with oxalic acid/propanol solutions. Lead magnesium niobate ceramics fabricated from these chemically derived powders had smaller, more uniform grain size and higher dielectric constants than ceramics fabricated from mixed oxide powders that were processed under similar thermal conditions. Chem-prep PMN dielectrics with peak dielectric constants greater than 22,000 and polarizations in excess of 29 {micro}C/cm{sup 2} were obtained for 1,100 C firing treatments. Substantial decreases in dielectric constant and polarization were measured for chemically prepared PMN ceramics fired at lower temperatures, consistent with previous work on mixed oxide materials.
Date: November 1, 1998
Creator: Tuttle, B.A.; Voigt, J.A.; Sipola, D.L.; Olson, W.R. & Goy, D.M.
Partner: UNT Libraries Government Documents Department

Deposition and Characterization of Highly Oriented Mg(3)(VO(4))(2) Thin Film Catalyst

Description: Magnesium vanadates are potentially important catalytic materials for the conversion of alkanes to alkenes via oxidative dehydrogenation. However, little is known about the active sites at which the catalytic reactions take place. It may be possible to obtain a significant increase in the catalytic efficiency if the effects of certain material properties on the surface reactions could be quantified and optimized through the use of appropriate preparation techniques. Given that surface reactivity is often dependent upon surface structure and that the atomic level structure of the active sites in these catalysts is virtually unknown, we desire thin film samples consisting of a single magnesium vanadate phase and a well defined crystallographic orientation in order to reduce complexity and simplify the study of active sites. We report on the use of reactive RF sputter deposition to fabricate very highly oriented, stoichiometric Mg{sub 3}(VO{sub 4}){sub 2} thin films for use in these surface analysis studies. Deposition of samples onto amorphous substrates resulted in very poor crystallinity. However, deposition of Mg{sub 3}(VO{sub 4}){sub 2} onto well-oriented, lattice-matched thin film ''seed'' layers such as Ti(0001), Au(111), or Pt(111) resulted in very strong preferential (042) crystallographic orientation (pseudo-hexagonal oxygen planes parallel to the substrate). This strong preferential growth of the Mg{sub 3}VO{sub 4}{sub 2} suggests epitaxial (single-crystal) growth of this mixed metal oxide on the underlying metal seed layer. The effects of the seed layer material, deposition temperature, and post-deposition reactive treatments on thin film properties such as stoichiometry, crystallographic orientation, and chemical interactions will be discussed.
Date: October 22, 1999
Creator: RODRIGUEZ,MARK A.; RUFFNER,JUDITH A.; SAULT,ALLEN G. & TISSOT JR.,RALPH G.
Partner: UNT Libraries Government Documents Department

Inelastic Neutron Scattering Study of Mn

Description: The authors report zero-field inelastic neutron scattering experiments on a 14-gram deuterated sample of Mn{sub 12}-Acetate consisting of a large number of identical spin-10 magnetic clusters. Their resolution enables them to see a series of peaks corresponding to transitions between the anisotropy levels within the spin-10 manifold. A fit to the spin Hamiltonian H = {minus}DS{sub z}{sup 2} + {mu}{sub B}B{center_dot}g{center_dot}S-BS{sub z}{sup 4} + C(S{sub +}{sup 4} + S{sub {minus}}{sup 4}) yields an anisotropy constant D = (0.54 {+-} 0.02) K and a fourth-order diagonal anisotropy coefficient B = (1.2 {+-} 0.1) x 10{sup {minus}3}K. Unlike EPR measurements, their experiments do not require a magnetic field and yield parameters that do not require knowledge of the g-value.
Date: November 9, 1998
Creator: Zhong, Y.; Sarachik, M.P.; Friedman, J.R.; Robinson, R.A.; Kelley, T.M.; Nakotte, H. et al.
Partner: UNT Libraries Government Documents Department

Defects and metastable structures of MgAl{sub 2}O{sub 4}

Description: This paper presents calculated properties of normal and inverse spinel structures of MgAl{sub 2}O{sub 4} and of point defects in the spinel structure. These results provide information for further study of possible metastable states. Calculated properties of ``amorphous`` structure are also presented. Atomistic simulations show that in MgAl{sub 2}O{sub 4} spinel structure, the exchange of an Mg{sup 2+} ion with an Al{sup 3+} ion has the lowest energy increase, 0. 92eV/atom. The Schottky defect increases the energy by 3.71 eV/atom. Frenkel defects are difficult to form, increasing the energy at least 4.59eV/atom for the Mg{sup 2+} Frenkel defect. Proposed rock salt structure of MgAl{sub 2}O{sub 4} has smaller volume and larger Young modulus, and the amorphosu state has larger volume and smaller Young modulus than the MgAl{sub 2}O{sub 4} spinel.
Date: July 1, 1995
Creator: Chen, S.P.; Yan, M.; Grimes, R.W.; Vyas, S. & Gale, J.D.
Partner: UNT Libraries Government Documents Department

Multi-band Bloch equations and gain spectra of highly excited II-VI semiconductor quantum wells

Description: Quasi-equilibrium excitation dependent optical probe spectra of II-VI semiconductor quantum wells at room temperature are investigated within the framework of multi-band semiconductor Bloch equations. The calculations include correlation effects beyond the Hartree-Fock level which describe dephasing, interband Coulomb correlations and band-gap renormalization in second Born approximation. In addition to the carrier-Coulomb interaction, the influence of carrier-phonon scattering and inhomogeneous broadening is considered. The explicit calculation of single particle properties like band structure and dipole matrix elements using k {center_dot} p theory makes it possible to investigate various II-VI material combinations. Numerical results are presented for CdZnSe/ZnSe and CdZnSe/MnZnSSe semiconductor quantum-well systems.
Date: April 21, 1997
Creator: Girndt, A.; Jahnke, F.; Knorr, A.; Koch, S.W. & Chow, W.W.
Partner: UNT Libraries Government Documents Department

Improvements in bis(cyclopentadienyl)magnesium purity as determined with gas chromatography-mass spectroscopy

Description: Bis(cyclopentadienyl)magnesium (MgCp2) is used commonly as a source for doping nitride materials with magnesium. Increased oxygen incorporation known to accompany the use of MgCp2 makes the purity of this precursor an important consideration in nitride CVD. Gas chromatography-mass spectroscopy (GCMS) methods have now been developed for the identification of volatile impurities in MgCp2. Diethylether, an oxygen containing organic compound (CH{sub 3}CH{sub 2}OCH{sub 2}CH{sub 3}), and additional organic impurities were found in the MgCp2 supplied by three manufacturers. Subsequent refinements in the synthetic processes by these companies have resulted in the availability of MgCp2 free of ether and other organic impurities as determined by GCMS.
Date: March 8, 2000
Creator: BARTRAM,MICHAEL E.
Partner: UNT Libraries Government Documents Department

ACCEPTABILITY ENVELOPE FOR METAL HYDRIDE-BASED HYDROGEN STORAGE SYSTEMS

Description: The design and evaluation of media based hydrogen storage systems requires the use of detailed numerical models and experimental studies, with significant amount of time and monetary investment. Thus a scoping tool, referred to as the Acceptability Envelope, was developed to screen preliminary candidate media and storage vessel designs, identifying the range of chemical, physical and geometrical parameters for the coupled media and storage vessel system that allow it to meet performance targets. The model which underpins the analysis allows simplifying the storage system, thus resulting in one input-one output scheme, by grouping of selected quantities. Two cases have been analyzed and results are presented here. In the first application the DOE technical targets (Year 2010, Year 2015 and Ultimate) are used to determine the range of parameters required for the metal hydride media and storage vessel. In the second case the most promising metal hydrides available are compared, highlighting the potential of storage systems, utilizing them, to achieve 40% of the 2010 DOE technical target. Results show that systems based on Li-Mg media have the best potential to attain these performance targets.
Date: July 18, 2011
Creator: Hardy, B.; Corgnale, C.; Tamburello, D.; Garrison, S. & Anton, D.
Partner: UNT Libraries Government Documents Department

The influence of fiber/matrix interface on the mechanical behavior of Nicalon SiC fiber reinforced glass-ceramic composites

Description: Mechanical properties of unidirectional Nicalon SiC fiber reinforced Ca aluminosilicate (CAS/SiC) and Mg aluminosilicate (MAS/SiC) glass-ceramic composites were investigated by tensile testing and nondestructive laser-ultrasound technique. The Ba-stuffed MAS was either undoped or doped with 5% borosilicate glass. Degradation of elastic stiffness constant C{sub 11} in transverse direction due to interface damage was monitored in situ by measuring the laser- generated ultrasound wave velocity. The three composite materials show different characteristics of macroscopic deformation behavior, which is correlated strongly to interface degradation. A stronger reduction trend of the elastic constant C{sub 11} is associated with a larger degree of inelastic deformation. The fracture surfaces also reveal the close relation between fiber pullout length and interfacial characteristics. Interfaces of these composites were studied by TEM; their influence on inhibiting and deflecting matrix cracks is discussed.
Date: November 1, 1996
Creator: Liu, Y.M.; Mitchell, T.E. & Wadley, H.N.G.
Partner: UNT Libraries Government Documents Department

Radiation-Induced Phase Transformations in Ilmenite-Group Minerals

Description: Transmission electron microscopy (TEM) is a powerful tool for characterizing and understanding radiation-induced structural changes in materials. We have irradiated single crystals of ilmenite (FeTiO{sub 3}) and geikielite (MgTiO{sub 3}) using ions and electrons to better understand the response of complex oxides to radiation. Ion irradiation experiments of bulk single crystals at 100 K show that ilmenite amorphized at doses of less than 1x10(exp15) Ar(2+)/sq cm and at a damage level in the peak damage region of 1 displacement per atom (dpa). Transmission electron microscopy and electron diffraction of a cross-sectioned portion of this crystal confirmed the formation of a 150 am thick amorphous layer. Geikielite proved to be more radiation resistant, requiring a flux of 2x10(exp 15) Xe(2+)/sq cm to induce amorphization at 100 K. This material did not amorphize at 470 K, despite a dose of 2.5 x10(exp 16) Xe(2+)/sq cm and a damage level as high as 25 dpa. Low temperature irradiations of electron- transparent crystals with 1 MeV Kr(+) also show that ilmenite amorphized after a damage level of 2.25 dpa at 175 K.Similar experiments on geikielite show that the microstructure is partially amorphous and partially crystalline after 10 dpa at 150 K. Concurrent ion and electron irradiation of both materials with 1 MeV Kr(+) and 0.9 MeV electrons produced dislocation loops in both materials, but no amorphous regions were formed. Differences in the radiation response of these isostructural oxides suggests that in systems with Mg-Fe solid solution, the Mg-rich compositions may be more resistant to structural changes.
Date: December 31, 1997
Creator: Mitchell, J. N.
Partner: UNT Libraries Government Documents Department

A background subtraction routine for enhancing energy-filtered plasmon images of MgAl{sub 2}O{sub 4} implanted with Al{sup +} and Mg{sup +} ions

Description: MgAl{sub 2}O{sub 4}, a candidate fusion reactor material, was irradiated with Al{sup +} or Mg{sup +} ions; electron energy-loss spectra and energy-filtered plasmon images showed that metallic Al colloids are present in the ion-irradiated regions. This paper shows the subtraction of the spinel plasmon component in images using 15-eV-loss electrons in some detail.
Date: June 1995
Creator: Evans, N. D.; Kenik, E. A.; Bentley, J. & Zinkle, S. J.
Partner: UNT Libraries Government Documents Department

Evaluation of field enforced antiferroelectric to ferroelectric phase transition dielectrics and relaxor ferroelectrics for pulse discharge capacitors

Description: Discharge capacitors were designed based on materials with antiferroelectric (AFE) to ferroelectric (FE) field enforced transitions that had 10 times the capacitance of relaxor ferroelectric or state of the art BaTiO{sub 3} materials in the voltage range of interest. Nonlinear RLC circuit analysis was used to show that the AFE to FE materials have potentially more than 2 times the peak discharge current density capability of the BaTiO{sub 3} or lead magnesium niobate (PMN) based relaxor materials. Both lead lanthanum zirconium tin titanate (PLZST) AFE to FE field enforced phase transition materials and PMN based relaxor materials were fabricated and characterized for Sandia`s pulse discharge capacitor applications. An outstanding feature of the PLZST materials is that there are high field regimes where the dielectric constant increases substantially, by a factor of 20 or more, with applied field. Specifically, these materials have a low field dielectric constant of 1,000, but an effective dielectric constant of 23,000 in the electric field range corresponding to the FE to AFE transition during discharge. Lead magnesium niobate (PMN) based relaxor materials were also investigated in this project because of their high dielectric constants. While the PMN based ceramics had a low field dielectric constant of 25,000, at a field corresponding to half the charging voltage, approximately 13 kV/cm, the dielectric constant decreases to approximately 7,500.
Date: September 1, 1997
Creator: Hoover, B.D.; Tuttle, B.A.; Olson, W.R.; Goy, D.M.; Brooks, R.A. & King, C.F.
Partner: UNT Libraries Government Documents Department

High temperature alkali corrosion of dense SiC and Si{sub 3}N{sub 4} coated with CMZP and Mg-doped Al{sub 2}TiO{sub 5} in coal gas. Quarterly progress report No. 10, October 1, 1996--December 31, 1996

Description: In high temperature engineering applications, commercially available silicon nitride non-oxide ceramics have retained special attention because of their superior thermal, mechanical, and chemical properties. These properties mainly include a high fracture strength and toughness, a low coefficient of thermal expansion relative to other ceramics, good thermal shock resistance, and good chemical stability. With silicon carbide, silicon nitride was the second material selected for heat exchangers in the High Temperature Advanced Furnace being developed under the DOE Combustion 2000 program. Their potential use in heat exchangers is, however, limited in time since both materials corrode severely in high temperature coal combustion atmospheres containing alkali compounds. Thus, this research will first focus on enhancing the performance of Si{sub 3}N{sub 4} ceramics by coating them with alkali corrosion resistant materials such as CMZP and Mg-doped Al{sub 2}TiO{sub 5} oxide ceramics.
Date: January 15, 1997
Creator: Thierry, N. & Brown, J.J.
Partner: UNT Libraries Government Documents Department

High temperature alkali corrosion of dense SiC and Si{sub 3}N{sub 4} coated with CMZP and Mg-doped Al{sub 2}TiO{sub 5} in coal gas. Quarterly progress report No. 4, April 1, 1995--June 30, 1995

Description: High temperature alkali corrosion has been known to cause premature failure of ceramic components used in advanced high temperature coal combustion systems such as coal gasification and clean-up, coal fired gas turbines, and high efficiency heat engines. Non-oxide ceramics, such as SiC and Si{sub 3}N{sub 4}, are applied in HITAF systems for their well-known and desirable high temperature thermal and mechanical properties. However, these materials are prone to rapid corrosion under some types of high temperature coal combustion conditions. The objective of this research is to apply CMZP and Mg-stabilized Al{sub 2}TiO{sub 5} as coatings to SiC and Si{sub 3}N{sub 4} to improve the corrosion resistance under coal combustion atmospheres as well as to improve high temperature mechanical properties. The research will not only develop and characterize CMZP and Mg-Al{sub 2}TiO{sub 5} coatings but will also strive to expand the existing knowledge of the mechanism of coal combustion corrosion of SiC and Si{sub 3}N{sub 4} in the temperature range of 1000-1400{degrees}C.
Date: June 30, 1995
Creator: Yang, S. & Brown, J.J.
Partner: UNT Libraries Government Documents Department

High temperature alkali corrosion of dense SiC and Si{sub 3}N{sub 4} coated with CMZP and Mg-doped Al{sub 2}TiO{sub 5} in coal gas. Quarterly report, July 1, 1995--September 30, 1995

Description: SiC samples coated with CMZP and Mg-Al{sub 2}TiO{sub 5}, respectively, were tested in a 100-hour slagging combustion test at the Energy and Environmental Research Center at the University of North Dakota. Results of measurements and analysis indicate that CMZP and Mg-Al{sub 2}TiO{sub 5} coatings improved the high temperature alkali corrosion resistance under coal combustion atmospheres. It is clearly shown that it is important to obtain a homogeneous and crack-free coating and good adhesion of the coating to the surface of the substrate for the best corrosion resistance. Some measures to improve the coating procedure are presented.
Date: October 2, 1995
Creator: Yang, Shaokai & Brown, J.J.
Partner: UNT Libraries Government Documents Department

REFINING OF MgX AND OTHER URANIUM-BEARING MATERIALS. Quarterly Progress Report

Description: Investigations on problems related to the use of MgX and other feed materials in the Plant 6 U refinery at St. Louis, Mo., have continued, with emphasis on the extraction of process feeds by neutral ether. Results of Scheibel column extraction tests wtth neutral ether on a variety of pitchblende, MgX, and V-20 soda salt feed materials indicate that the addition of Fe to complex interfering elements can reduce U losses in raffinates to lower levels than are attainable with acid ether in the absence of Fe. The beneficial effect of neutral ether on transfer of contaminants, especially Mo, to the ether extract was substantiated. It is indicated that the inclusion of V-20 soda salt in a feed tends to increase U losses in extraction; the addition of Fe was shown to be advantageous here also. Sources and costs of added Fe are considered. (G.Y.)
Date: June 30, 1951
Creator: Ewing, R.A.; Kiehl, S.J. Jr.; Sharpe, R.E. & Bearse, A.E.
Partner: UNT Libraries Government Documents Department

DEVELOPMENT AND PRODUCTION OF URANIUM 10 wt.% MOLYBDENUM AS-CAST SLUGS FOR HNPF PHYSICS EXPERIMENT

Description: A multiple casting process was developed for the production of 0.590 plus or minus 0.005-in. diam. by 12-in. long solid right cylinders. The process involves vacuum induction melting in MgZrO/sub 3/ coated graphite crucibles and casting into coated graphite molds. Thirty-eight hundred fifty 90 wt.% U of 1.5 wt.% enrichment-10 wt.% Mo as-cast pins were produced for HNPF Exponential Experiments. (auth)
Date: April 1, 1960
Creator: Stanley, J.A. & Binstock, M.H.
Partner: UNT Libraries Government Documents Department

MOISTURE MONITOR TESTING AND CALIBRATION

Description: ABS>Electrolytic moisture monitors which continuously analyze the moisture content of gases are commercially available. After a period of operation, these instruments may give erroneous readings, frequently because of damage to the electrolytic cell. A gas with a known and reproducible moisture content within the operating range would be useful for making operational response tests on these monltors and for checking their calibration. A paired- hydrate system of a chemical compound exhibits a water vapor pressure that is constant at a constant temperature. ff an unreactive gas is allowed to equilibrate with a paired-hydrate system, the moisture content of the gas is determined by the vapor pressure of the hydrate pair, the total pressure, and the temperature. Hydrated magnesium perchlorate was prepared which contained between four and six moles of water per mole of perchlorate. This material was pulverized lightly then packed into a stainless steel column and 100 cc/minute of air at atmospheric pressure was passed through the bed. The exit air from the column was analyzed with a moisture monitor. A gas residence time of two minutes in the column was found to be sufficient for establishing moisture equilibrium in the exit flow. The moisture content of the exit air was found to vary from 34 to 70 ppm by volume as the temperature of the paired-hydrate system varied from 20 to 28 un. Concent 85% C. Other paired-hydrate systems can extend this range to higher moisture levels. (auth)
Date: March 14, 1963
Creator: Montgomery, C.D.; Googin, J.M. & Phillips, L.R.
Partner: UNT Libraries Government Documents Department

Influence of irradiation spectrum and implanted ions on the amorphization of ceramics

Description: Polycrystalline Al2O3, magnesium aluminate spinel (MgAl2O4), MgO, Si3N4, and SiC were irradiated with various ions at 200-450 K, and microstructures were examined following irradiation using cross-section TEM. Amorphization was not observed in any of the irradiated oxide ceramics, despsite damage energy densities up to {similar_to}7 keV/atom (70 displacements per atom). On the other hand, SiC readily amorphized after damage levels of {similar_to}0.4 dpa at room temperature (RT). Si3N4 exhibited intermediate behavior; irradiation with Fe{sup 2+} ions at RT produced amorphization in the implanted ion region after damage levels of {similar_to}1 dpa. However, irradiated regions outside the implanted ion region did not amorphize even after damage levels > 5 dpa. The amorphous layer in the Fe-implanted region of Si3N4 did not appear if the specimen was simultaneoulsy irradiated with 1-MeV He{sup +} ions at RT. By comparison with published results, it is concluded that the implantation of certain chemical species has a pronounced effect on the amorphization threshold dose of all five materials. Intense ionizing radiation inhibits amorphization in Si3N4, but does not appear to significantly influence the amorphization of SiC.
Date: December 31, 1995
Creator: Zinkle, S.J. & Snead, L.L.
Partner: UNT Libraries Government Documents Department