bluuebunny/crossref_metadata_2025 huggingface dataset:
Elevated temperature compressive properties of reaction milled NiAl–AlN and Zr-doped NiAl–AlN composites
Authors: Daniel Whittenberger J. , Luton Michael J.
Published: September 2007

Previous studies of a single lot of NiAl powder which had been ground under high intensity conditions in liquid nitrogen (cryomilling) indicated that this processing leads to a high strength, elevated temperature NiAl–AlN composite. Because this was the first known example of the use of the reaction milling process to produce a high temperature composite, the reproducibility of this technique was unknown. Two additional lots of NiAl powder and a lot of a Zr-doped NiAl powder have been cryomilled, and analyses indicate that AlN was formed within a NiAl matrix in all three cases. Compression testing between 1200 K and 1400 K has shown that the deformation resistance of these heats is similar to that of the first lot of NiAl–AlN; thus cryomilling can improve the creep resistance of NiAl by a factor of six. Based on this work, it is concluded that cryomilling of NiAl powder to form high temperature, high strength NiAl–AlN composites is a reproducible process.
The dissociative adsorption of hydrogen sulfide over nanophase titanium dioxide
Authors: Beck Donald D. , Siegel Richard W.
Published: September 2007

A variety of TiO2 materials, including a nanophase TiO2 powder, were evaluated for their ability to dissociatively adsorb H2S in a H2 environment. A temperature programmed desorption technique was used to determine the rate of sulfide accumulation on the surface of the samples as a measurement of initial activity. The initial activity for the gas condensation-produced nanophase TiO2 with its rutile structure was found to be greater than that for other samples of TiO2 tested. When normalized for surface area, the initial specific activities of the rutile samples studied for the dissociative adsorption of H2S were similar in magnitude, but significantly higher than those of the anatase TiO2 samples investigated. Thus, the improvement in the activity is attributed mainly to the ability of the nanophase synthesis method to produce high surface area rutile TiO2. When evaluated using x-ray photoelectron spectroscopy, the nanophase TiO2 was found to be significantly deficient in oxygen. Annealing this material in oxygen decreased the number of anion vacancies and lowered the activity. Thus, we conclude that oxygen vacancies also contribute to the H2S dissociative adsorption activity.
Laser synthesis of vanadium-titanium oxide catalysts
Authors: Musci M. , Notaro M. , Curcio F. , Casale C. , De Michele G.
Published: September 2007

A laser-induced process has been studied and developed for the synthesis either of pure TiO2 powders for use as a catalyst support or of mixed Ti1−xVxO2 oxides to be used directly as catalysts in the selective catalytic reduction of nitrogen oxides with ammonia. The radiation source is a 600 W cw CO2 laser and the precursors are titanium and vanadium alkoxides whose vapors are carried under the laser beam by controlled flows of an inert gas and of a reaction sensitizer. The study of the process has been mainly devoted to the optimization of the production rate and of the reaction efficiency. The powder characteristics, related to the process parameters, have been investigated through different techniques. The results show that the particles are monodispersed, unaggregated, monocrystalline with anatase structure and their diameters can be as small as 50 A. Vanadium contents up to X = 0.25 have been obtained in Ti1−xVxO2 compounds, without V2O5 segregation. Finally, a comparison between the behavior of surface VOx active sites has been carried out in catalysts prepared by chemical impregnation of TiO2 and in the mixed Ti–V oxide powders.
Expanding heat source model for thermal spalling of TiB2 in electrical discharge machining
Authors: Gadalla A.M. , Bozkurt B.
Published: September 2007

A model is presented to explain the recently reported mechanism of thermal spalling for shaping high melting point ceramics by electrical discharge machining. Since previous models fail to explain the experimental observations completely, an expanding circular heat source created by growth of plasma is assumed to act on the surface. Erosion of materials by spalling is caused by thermally induced compressive stresses during heating-up periods and tensile stresses during cooling-down periods. This model explains material removal for anodic erosion in general (wire-cutting machines) and for cathodic erosion (die-sinking machines) whenever long pulse duration is used. Simulation of the model for TiB2 provides a local melt front that penetrates to a depth of submicrometer, then recedes as pulse duration increases. Spalling develops flakes with thickness correlated to pulse duration. The results were verified by the experimental observations which showed that large flakes having the predicted maximum thickness as well as few quenched spherical droplets containing titanium were obtained.
Crystallization and sintering characteristics of chemically vapor deposited silicon nitride powders
Authors: Gomez-Aleixandre C. , Albella J.M. , Martínez-Duart J.M. , Orgaz F.
Published: September 2007

High purity silicon nitride powders have been obtained by Chemical Vapor Deposition (CVD), through the reaction of SiH4 and NH3 gas mixtures at 1000 °C in a quartz reactor. The crystallization characteristics of the powder have been followed by infrared and x-ray diffraction analysis. The material shows a transition from amorphous to the α-phase after a thermal treatment at about 1300 °C for 1 h, while the β-phase starts to appear at 1725 °C. The sintering properties of the amorphous and crystalline phases were evaluated by measuring the dilatometric curves of compacted powders.
Fiber pullout processes and mechanisms of a carbon fiber reinforced silicon nitride ceramic composite
Authors: Suzuki Takayuki , Sato Masahiro , Sakai Mototsugu
Published: September 2007

Details of fiber pullout processes and mechanisms are addressed for a carbon fiber reinforced silicon nitride ceramic composite. The energy for fiber pullout, γpo, is experimentally measured by the work-of-fracture technique using test specimens with a circumferential notch. A precise determination of the distribution of pullout fibers combined with the experimental results of the pullout energy provides an important insight into the micromechanical processes and mechanisms of the composite fracture. Various energy dissipation processes associated with the composite fracture, the frictional interface shear stress, the Weibull modulus of the reinforcing fibers, and composite designs for improved toughening are discussed.
Effects of the self-bias voltage on crystallinity and superconductivity of a-axis oriented YBa2Cu3O7−δ thin films
Authors: Homma N. , Ito W. , Okayama S. , Morishita T. , Haga T. , Yamaya K.
Published: September 2007

Epitaxial a-axis YBa2Cu3O7–δ thin films have been grown on SrTiO3 (100) by on-axis 94.92 MHz magnetron sputtering using the YBa2Cu5Ox target at a self-bias voltage of −50 V and YBa3Cu7Ox target at a cathode voltage of −100 V adjusted by externally applying a negative dc voltage. Good crystalline quality of the films sputtered at −50 V was confirmed from a full width at half maximum, δω, of 0.04° through the (100) peak by x-ray diffraction and a minimum yield, Xmin, of 4.8% by Rutherford backscattering channeling. Those films, however, have not shown superconductivity. On the other hand, the films sputtered at −100 V were characterized by a δω of 0.12° and a Xmin of 4.3%. Superconductivity occurs in the films only by shifting a self-bias voltage from −50 V on the YBa2Cu5Ox target to −100 V on the YBa3Cu7Ox target. The zero resistance temperature is 33 K at most.
Twinning and faceting in early stages of diamond growth by chemical vapor deposition
Authors: Angus John C. , Sunkara Mahendra , Sahaida Scott R. , Glass Jeffrey T.
Published: September 2007

Flat, hexagonally shaped diamond platelets were observed during the initial stage of microwave plasma assisted deposition of diamond. The platelets are approximately 2.5 μm in linear dimension and are oriented with their large six-sided faces parallel to the silicon substrate. A re-entrant groove, running parallel to the large six-sided face, is present in the small side faces of the platelets. Larger diamond crystals, with a fully developed three-dimensional morphology, all have re-entrant grooves in other directions. The observations support the hypothesis that the growth rate of {111} faceted diamond crystals is greatly enhanced by the presence of microtwins (multiple stacking errors), which give rise to re-entrant corners where they intersect the crystal surface. Fully developed {111} faceting and a strong influence of re-entrant corners is expected when the average lifetime of a carbon atom bonded once to the surface is much less than the average time between addition of adatoms at adjacent surface sites.
The determination of film hardness from the composite response of film and substrate to nanometer scale indentations
Authors: Fabes B.D. , Oliver W.C. , McKee R.A. , Walker F.J.
Published: September 2007

Two equations for determining the hardness of thin films from depth-sensing indentation data are examined. The first equation is based on an empirical fit of hardness versus indenter displacement data obtained from finite element calculations on a variety of hypothetical films. The second equation is based on a model which assumes that measured hardness is determined by the weighted average of the volume of plastically deformed material in the coating and that in the substrate. The equations are evaluated by fitting the predicted hardness versus contact depth to data obtained from titanium coatings on a sapphire substrate. Only the volume fractions model allows the data to be fitted with a single adjustable parameter, the film hardness; the finite element equation requires two thickness-dependent parameters to obtain acceptable fits. It is argued that the difficulty in applying the finite element model lies in the use of an unrealistic area function for the indenter. For real indenters, which have finite radii, the area function must appear explicitly in the final equation. This is difficult to do with the finite element approach, but is naturally incorporated into the volume fractions equation. Finally, using the volume fractions approach the hardnesses of the titanium films are found to be relatively insensitive to film thickness. Thus, the apparent increase in hardness with decreasing film thickness for the titanium films is most likely due to increased interactions between the film and substrate for the thinner films rather than to a change in the basic structure of the titanium films.
Data from recording microhardness testers
Authors: Mason W. , Johnson P.F. , Varner J.R.
Published: September 2007

An apparatus was constructed that measured hardness under load. The instrument measured hardness using a strain-gauge load cell and a linear voltage displacement transducer. Loading rates were less than 1 μm/s. Results were similar to the results of other electronic hardness measurement devices, in that the hardness fell with increasing load. Glasses measured have Meyers indexes from 1.6 to 1.75, while polycrystalline materials showed much more complex behaviors. A model was formulated to explain the data for glasses based on expansion of shear planes.
Role of interface properties on the toughness of brittle matrix composites reinforced with ductile fibers
Authors: Dève H.E. , Schmauder S.
Published: September 2007

The incorporation of ductile fibers in brittle matrices can lead to a significant increase in fracture resistance. The increase in toughness that derives from crack bridging is governed by the properties of the matrix/fiber interface and the ductility of the fibers. The current study addresses the role of interface sliding stress on the toughness of brittle composites reinforced with ductile fibers. The debond length is explicitly related to the interface sliding stress and the properties of the fiber. It is then incorporated into a geometrical model to simulate the bridging tractions versus crack opening under condition of continuous debonding. The implications on the effect of interfaces on the resistance curve are discussed.
Dislocation mediated lattice bending in 1,6-di (N-carbazolyl)-2,4 hexadiyne (DCHD) polydiacetylene droplets
Authors: Wilson Patricia M. , Martin David C.
Published: September 2007

Droplets of 1,6–di (N-carbazolyl)-2,4 hexadiyne (DCHD) polydiacetylene were prepared by room temperature evaporation of dilute (0.01 wt. %) solution of the monomer in chloroform onto amorphous carbon-coated mica substrates. High Resolution Electron Microscopy (HREM) and Selected Area Electron Diffraction (SAED) revealed small crystallographically textured droplets (∼1 μm diameter) with cracks parallel to the [001] chain direction. The droplet geometry allowed us to investigate the organization of the polymer near surfaces. It was found that the curvature of the droplet edge caused a local bending of the polymer crystal lattice. Direct imaging of the molecular structure near the droplet surface revealed that the mechanism of lattice bending was by the formation of edge dislocations. Dislocations were etched in some droplets to gain information about perturbations in structure and reactivity near the core.
A new bulge test technique for the determination of Young's modulus and Poisson's ratio of thin films
Authors: Vlassak J.J. , Nix W.D.
Published: September 2007

A new analysis of the deflection of square and rectangular membranes of varying aspect ratio under the influence of a uniform pressure is presented. The influence of residual stresses on the deflection of membranes is examined. Expressions have been developed that allow one to measure residual stresses and Young's moduli. By testing both square and rectangular membranes of the same film, it is possible to determine Poisson's ratio of the film. Using standard micromachining techniques, free-standing films of LPCVD silicon nitride were fabricated and tested as a model system. The deflection of the silicon nitride films as a function of film aspect ratio is very well predicted by the new analysis. Young's modulus of the silicon nitride films is 222 ± 3 GPa and Poisson's ratio is 0.28 ± 0.05. The residual stress varies between 120 and 150 MPa. Young's modulus and hardness of the films were also measured by means of nanoindentation, yielding values of 216 ± 10 GPa and 21.0 ± 0.9 GPa, respectively.
Base electrodes for high dielectric constant oxide materials in silicon technology
Authors: Grill A. , Kane W. , Viggiano J. , Brady M. , Laibowitz R.
Published: September 2007

Several conductive structures which appeared to be usable as base electrodes in VLSI capacitors based on high dielectric materials have been annealed in oxygen at 650 °C. The studied structures were Pt/TiN, Pt/Ta, Au/TiN, Ru, and RuO2/Ru, prepared under a variety of conditions. The structures have been studied by Rutherford backscattering (RBS) and Auger Electron Spectroscopy (AES). It was found that none of the pure metals, Pt, Au, or Ru, can prevent the diffusion of oxygen to the underlying layer and its oxidation, thus causing a possible break in the electrical conduction path to the silicon substrate. Of the investigated materials, in the thickness range ≤ 110 nm only the RuO2/Ru couple preserved its electrical connectivity to the Si substrate and prevented diffusion of silicon to the surface of the electrode.
Hydrotalcite formation on aluminum sheet and powder
Authors: Perrotta A.J. , Tzeng S.Y. , Imbrogno W.D. , Rolles R. , Weather M.S.
Published: September 2007

We have observed the formation of the hydrotalcite-like phase of lithium dialuminate, LiAl2(OH)6OH · 2H2O, and also the carbonate analog, by the oxidation of aluminum sheet and also aluminum powder in aqueous lithium hydroxide or lithium carbonate solutions. A secondary phase, bayerite, was also observed following the oxidation process, except when the aluminum was treated with lithium oxalate solutions where it is the principal phase. Results have been obtained for the time required to form a passivating film to hydrogen formation as a function of temperature and oxidizing solution. Grazing incidence x-ray diffraction of aluminum sheet samples, combined with polycrystalline x-ray diffraction on similarly treated aluminum powder, were used to evaluate the formation of the films. Both transmission and reflectance infrared absorption spectra on powder and sheet samples were used to support the x-ray observations. Scanning and transmission electron microscopies show morphological differences between preparations, film thicknesses of 10–20 μm, and also film defects. Additional SIMS analysis determined the relative lithium and aluminum concentrations in the films, suggesting that a higher concentration of lithium occurs when lithium carbonate is present in the reacting solutions.
Role of particle evaporation during synthesis of lead oxide by aerosol decomposition
Authors: Lyons Shirley W. , Xiong Yun , Ward Timothy L. , Kodas Toivo T. , Pratsinis Sotiris E.
Published: September 2007

The role of product evaporation during lead monoxide (PbO) powder generation by aerosol decomposition (spray pyrolysis) was investigated at various temperatures in a flow reactor. Particles consisting of phase pure litharge and a mixture of litharge and massicot were formed with the dominant phase changing from litharge to massicot as the pyrolysis temperature was increased. Scanning electron microscopy showed particles produced at lower temperatures had a lumpy surface morphology and at higher temperatures appeared to be solid, indicated by the faceted surfaces and a plate-like morphology. Evaporative losses of PbOx, to the reactor walls were observed due to the substantial vapor pressure of PbOx. A simple model was developed that accounts for particle evaporation and mass transfer of lead oxide vapor to the reactor walls. This model suggested that the loss of lead oxide to the reactor walls was limited by diffusional transport of lead oxide vapor to the reactor walls.
Isothermal and nonisothermal sintering kinetics of glass-filled ceramics
Authors: Jean Jau-Ho , Gupta Tapan K.
Published: September 2007

Isothermal and nonisothermal sintering behaviors of glass-filled ceramics are compared in this paper. Equations developed to describe the kinetics of shrinkage for both techniques can be readily used to interpret the experimental data. It is shown that the kinetics of linear shrinkage of powder compacts during isothermal and nonisothermal constant rate of heating are consistent and can be described by the viscous flow of glass.
Structural and textural changes from polyimide Upilex to graphite: Part III
Authors: Bourgerette C. , Oberlin A. , Inagaki M.
Published: September 2007

25 μm thick Upilex films (registered UBE trademark) were carbonized, then graphitized at various temperatures up to 2800 °C and studied by optical and electron microscopies. While the graphitizing behavior of Kapton films is similar to that of anthracites, Upilex graphitization is erratic from one film to the other. The thickness of the better graphitizing Upilex films decreases as the anisotropy increases. Their graphitization occurs at a relatively low temperature (2100 °C), because the oxygen is entirely labile (no cross-linking). Non-graphitizing films are obtained when oxygen remains stable as the heat-treatment temperature (HTT) increases. They stay optically isotropic and microporous without flattening, and even show a limited swelling instead of a thinning. This behavior is attributed to the random mobility of the imide part of the molecule when carbonization starts.
Methyl halides as carbon sources in a hot-filament diamond CVD reactor: A new gas phase growth species
Authors: Bai Benjamin J. , Chu Judith C. , Patterson Donald E. , Hauge Robert H. , Margrave John L.
Published: September 2007

Equal amounts of carbon-12 methyl halides and carbon-13 methane, along with hydrogen, have been introduced into a hot-filament diamond CVD chamber. The isotopic ratios of the as-deposited diamond films on tantalum have been measured by Raman spectroscopy. It was found that methyl chloride yielded carbon-12 enriched diamond films, while the other methyl halides resulted in equal amounts of carbon-13 and carbon-12 in the films. Furthermore, the carbon-12 enrichment was more enhanced as the substrate temperature was lowered. Matrix-isolation FTIR analyses of the gas samples collected during the deposition indicated that there was no straightforward agreement between the 12C/13C ratios of the gas phase species, methane and acetylene, and that of the diamond films. The results imply the presence of a new chlorocarbon radical such as CH2Cl, which is postulated as a more effective growth species than the methyl radical.
Effects of iron impurities in mechanical alloying using steel media
Authors: Yvon P.J. , Schwarz R.B.
Published: September 2007

Mechanical alloying, a high-energy ball-milling technique, is now widely used for preparing alloy powders with metastable phases (crystalline or amorphous). The technique, however, may contaminate the powder with material eroded from the vial and milling media. We report on the analysis and effects of iron contamination on Al25Ge75 powders that we prepared by mechanically alloying mixtures of aluminum and germanium powders, using different mechanical alloying apparatuses.
On the bcc, fcc, hcp, and amorphous polymorphs of Zr3Al
Authors: Yavari A.R. , Gialanella S. , Benameur T. , Cahn R.W. , Bochu B.
Published: September 2007

Rapid solidification of the Zr3Al liquid alloy allows retention of the high temperature β–Zr solid solution with bcc structure. Mechanical grinding is shown to amorphize this metastable phase very easily. Calculations show that the retained bcc phase has a free energy above that of the amorphous phase. The density of bcc Zr3Al at room temperature is found to be 2% lower than that of its equilibrium L12-ordered fcc structure as determined from their respective lattice parameters. The bcc phase thus represents a 2% volume expansion with respect to the fcc structure.
SEM and Auger studies of a PLZT thin film
Authors: No Kwangsoo , Yoon Dae Sung , Kim Jae Myung
Published: September 2007

The microstructure and the composition profile of lead lanthanum zirconate titanate thin film fabricated using the sol-gel method were analyzed using the scanning electron microscope and scanning Auger microscope. The PLZT thin film consists of micron-scale spheroidal perovskite grains and nano-scale pyrochlore grains. The perovskite grain has a higher lead and lower oxygen and zirconium contents than the pyrochlore grain. The Auger spectra of the two phases were similar except for energy shift and extra fine structure of oxygen peaks. The Auger depth profile and SEM observation of the cross-sectional fracture surface showed higher perovskite content near the interface between PLZT and ITO films than the surface of the PLZT film.
Epitaxial growth of BaO and SrO with new crystal structures using mass-separated low-energy O+ beams
Authors: Kita Ryusuke , Hase Takashi , Takahashi Hiromi , Kawaguchi Kenichi , Morishita Tadataka
Published: September 2007

The growth of BaO and SrO on SrTiO3(100) substrates using mass-separated low-energy (50 eV) O+ beams has been studied using x-ray diffraction, reflection high-energy electron diffraction, and high-resolution transmission electron microscopy. It was found that the BaO and SrO films have been epitaxially grown with new structures different from those of corresponding bulk crystals: The BaO films have a cubic structure with a lattice constant of 4.0 Å, and the SrO films have a tetragonal structure with a lattice constant of a = 3.7 Å parallel to the substrate and with c = 4.0 Å normal to the substrate.
Sol-gel synthesis of ferroelectric lithium tantalate ceramics: FTIR investigation of the molecular modification of tantalum ethoxide
Authors: Phulé Pradeep P.
Published: September 2007

Several sol-gel syntheses make use of “additives” in the sol-preparation step. These additives can react with metal alkoxides causing important structural changes. In order to demonstrate the nature of the reactions involved in the molecular modification process, a model system based on Ta(OC2H5)5, acetic acid and acetylacetone (as modifiers), was studied using FTIR spectroscopy. At room temperature, both modifiers react with the ethoxide to cause formation of new organotantalum precursors. The acetic acid modification was observed from the characteristic symmetric and asymmetric vibrations of the COO groups. The average difference in wave numbers (δv = vasymm – vsymm) between the two of 140 cm−1, observed for different ratios of ac/Ta, signifies a bridging nature of the acetate group. For ac/Ta ≥ 1, formation of ethyl acetate, probably as a result of the reaction between ethanol and excess acetic acid, was also observed using FTIR. Results of the acetylacetone modification showed the enol form of acetylacetone which has its v(C–O) and v(C–C) vibrations centered around 1625 cm−1, split into two bands at 1581 and 1518 cm−1, respectively, indicative of chelation of the acetylacetanate ligand to Ta. In the case of acetylacetone modification, the formation of ethanol was confirmed by FTIR analysis of the liquid fraction distilled at ∼80 °C.
Ultra-low density aerogel optical applications
Authors: Hotaling S.P.
Published: September 2007

Despite the extremely low density and the hence low weight of aerogel materials, the applicability of these materials to reflective applications has had little attention due to the high porosities exhibited by the materials. This high porosity yields an intrinsically rough but uniform surface topology for aerogel of density in the low hundreds of milligrams per cubic centimeter and a fractal surface geometry for lower density aerogel (densities of the order of tens of milligrams per cubic centimeter). This paper presents new results of aerogel materials used as ultra-light substrates for reflective coatings by way of surface machining, polishing, and planarization prior to metallization, and the optical characterization thereof.
Modification of high temperature and high performance polymers by ion implantation
Authors: Wang Yongqiang , Mohite S.S. , Bridwell L.B. , Giedd R.E. , Sofield C.J.
Published: September 2007

Several polymers with high temperature and high performance properties have been modified by ion implantation. Ions of As and Xe with energies of 50 keV and 180 keV have been implanted in the dose range of 1015to 1017ions/cm2. Electrical conductivities of these originally insulating polymers have been greatly enhanced after the ion implantation. Structural and compositional changes that accompanied these electrical enhancements were observed using infrared (IR) and Raman spectroscopies, scanning electron microscopy (SEM), Rutherford backscattering spectroscopy (RBS), and elastic recoil detection analysis (ERDA) methods. Our high resolution data reveal a two-component conductivity that depends on both one-dimensional variable range hopping (VRH) and three-dimensional VRH. For lightly damaged samples (e.g., 1015ions/cm2) the 1-D VRH is dominant while for highly damaged samples (e.g., 1017ions/cm2) the 3-D VRH dominates.
TEM study on laser processed intermetallic phases: Al16Ti6(Fe or Ni)7
Authors: Ma Y. , Gj⊘nnes J.
Published: September 2007

The structures of two laser processed ternary intermetallic phases, Al16Ti6(Fe or Ni)7, have been studied by using electron diffraction and microscopy. A convergent beam electron diffraction (CBED) technique for structure determination is described based upon the principle of kinematic interpretation of large angle systematic reflections in CBED disks. The structure type of phases Al16Ti6(Fe or Ni)7 is characterized as the Mn23Th6(cF116)-type, the same as those of relevant phases Cu16Mg6Si7 and Al50Ti25Fe25 etc., by using the CBED technique. Various errors involved in the analyses are also discussed.
Influence of long-range order on tensile properties of Ni3Fe and Ni3Fe—Y2O3 composites
Authors: Bose A. , Camus G. , German R.M. , Duquette D.J. , Stoloff N.S.
Published: September 2007

Ni3Fe is a compound that exhibits long-range ordering below 500 °C and a disordered structure above this temperature. Thus, Ni3Fe allows study of the effect of ordering on mechanical properties. This paper discusses the tensile properties of Ni3Fe produced via powder metallurgical routes. Some samples subsequently were densified by containerless hot isostatic compaction. Ni3Fe was consolidated with elemental nickel and iron powders that were solid state sintered. Composites of Ni3Fe with 5 vol. % Y2O3 were prepared by presintering cold isostatically pressed rods, followed by containerless hot isostatic pressing. The influence of Y2O3 particles on flow stresses of ordered and disordered Ni3Fe was determined. Ordering of Ni3Fe increased both strength and hardness with a small effect on ductility. For the Ni3Fe–Y2O3 composite, the increase in the strength in both ordered and disordered matrix conditions was accomplished by a large reduction in elongation.
Influence of the irradiation temperature on the intracascade ion mixing
Authors: Alurralde M. , Caro A. , Victoria M.
Published: September 2007

We present a description of the thermal behavior of cascades in Cu and Ag over a large energy range and irradiation temperatures. For this purpose the binary collision approximation, which gives the profile of the energy deposition, is coupled to a simplified version of the heat equation. In the present calculations, the original liquid drop model [M. Alurralde, A. Caro, and M. Victoria, J. Nucl. Mater. 183, 33 (1991)] has been extended to the case where the lattice is at finite temperatures. The resulting evolution of the liquid cascade is analyzed for PKA energies up to 1 MeV, and the results are compared to experimental observations of mixing rates. We obtain a temperature dependence that adds to the traditional Radiation Enhanced Diffusion, RED, in very good qualitative agreement with experiments on materials showing thermal spikes.
Fabrication of EuO films by oxidation of Eu metal films
Authors: Yu X.J. , Batalla E. , Wright L.S.
Published: September 2007

Ferromagnetic europium (EuO) films have been made by oxidizing europium (Eu) metal films deposited on glass substrates using a thermal evaporation technique. It has been found that the quality of the films is sensitive to substrate temperature. Stable EuO films were formed only if Eu metal films were annealed at temperatures of 320 to 380 °C. Both x-ray diffraction pattern (XRD) and magnetization measurements indicate that a significant amount of EuO phase has been formed in the films. These films undergo a phase transition from paramagnetic to ferromagnetic phase at temperatures between 60 and 70 K and exhibit the magneto-optical Faraday effect. The saturation magnetic moment at 10 K is about 40% of the theoretical value, and the coercive force,Hc, for slow sweeping field is about 70 Oe.
Raman scattering and electrical conductivity in highly disordered activated carbon fibers
Authors: Fung A.W.P. , Rao A.M. , Kuriyama K. , Dresselhaus M.S. , Dresselhaus G. , Endo M. , Shindo N.
Published: September 2007

Because of their unusually large specific surface area (SSA), Activated Carbon Fibers (ACF's) have a huge density of micropores and defects. The Raman scattering technique and low-temperature dc electrical conductivity measurements were used as characterization tools to study the disorder in ACF's with SSA ranging from 1000 m2/g to 3000 m2/g. Two peaks were observed in every Raman spectrum for ACF's and they could be identified with the disorder-induced peak near ∼1360 cm−1 and the Breit–Wigner–Fano peak near ∼1610 cm−1 associated with the Raman-active E2g2 mode of graphite. The graphitic nature of the ACF's is shown by the presence of a well-defined graphitic structure with La values of 20–30 Å. We observed that the Raman scattering showed more sensitivity to the precursor materials than to the SSA of the ACF's. From 4 K to room temperature, the dc electrical resistivity in ACF's is observed to follow the exp [(T0/T)1/2] functional form and it can be accounted for by a charge-energy-limited tunneling conduction mechanism. Coulomb-gap conduction and n-dimensional (n ≤ 3) variable-range hopping conduction models were also considered but they were found to give unphysical values for their parameters.
Analysis of buried oxide layer formation and mechanism of threading dislocation generation in the substoichiometric oxygen dose region
Authors: Nakashima Sadao , Izumi Katsutoshi
Published: September 2007

The structure of SIMOX wafers implanted at 180 keV with doses of 0.1 × 1018-2.0 × 101816O+ cm−2 at 550 °C, followed by annealing over the temperature range of 1050–1350 °C, has been investigated using cross-sectional transmission electron microscopy and a chemical etching. With doses of 0.35 × 1018-0.4 × 1018 cm−2, a continuous buried oxide layer having no Si island inside is formed by high-temperature annealing at 1350 °C. At a dose of 0.7 × 1018 cm−2, multilayered oxide striations appear in the as-implanted wafer. These striations grow into multiple buried oxide layers after annealing at 1150 °C. The multiple layers lead to a discontinuous buried oxide layer, resulting in the formation of a number of Si micropaths between the top Si layer and the Si substrate when the wafer is annealed at 1350 °C. These Si paths cause the breakdown electric field strength of the buried oxide layer to deteriorate. With doses of 0.2 × 1018-0.3 × 1018 cm−2 and of higher than 1.3 × 1018 cm−2, an extremely high density of threading dislocations is generated in the top Si layer after annealing at 1350 °C. The dislocation density is greatly reduced to less than 103 cm−2 when the oxygen dose falls in the range of 0.35 × 1018-1.2 × 1018 cm−2. Here we propose a mechanism that accounts for the threading dislocation generation at substoichiometric oxygen doses of less than 1.2 × 1018 cm−2.
Oxidation behavior of aluminum nitride
Authors: Bellosi A. , Landi E. , Tampieri A.
Published: September 2007

The evaluation of the thermal stability of three different fully dense AlN materials in the temperature range of 600 °C to 1400 °C in air indicates the strong effect of the starting composition on the oxidation process. The oxidation resistance of pure AlN and Y2O3-doped AlN was found to be good up to ≍1350 °C. The kinetics are linear (1100 ≤ T ≤ 1400 °C) and the process is governed by a surface reaction that gives rise to the formation of a porous, nonprotective oxide scale, where Al2O3 and Y-aluminates (i.e., AlN–Y2O3) have been found as crystalline reaction products. For AlN-CaC2, higher oxidation rates indicate that the outward migration of Ca modifies the reaction mechanisms. Linear kinetics in the range 1100 ≤ T ≤ 1200 °C are followed by parabolic kinetics at higher temperatures (T > 1250 °C); with regard to the latter behavior, an activation energy of 160 kJ/mole could indicate the diffusion of oxygen through the oxidation scale as the rate-controlling mechanism.
On the occurrence of a metastable tetragonal t′-phase in a ZrO2−13.6 mole % MgO ceramic and its microscopic thermal evolution
Authors: Caracoche M.C. , Rivas P.C. , Pasquevich A.F. , López García A.R. , Aglietti E. , Scian A.
Published: September 2007

The time-differential perturbed angular correlation technique has been used to investigate the thermal behavior of a ZrO2−13.6 mole % MgO ceramic between room temperature and 1423 K. Two different quadrupole hyperfine interactions corresponding to a tetragonal structure have been found to result on cooling the ceramic from the single-phase cubic field. One of them agrees with that depicting the pure t-ZrO2 tetragonal phase and the other one has been interpreted as describing a high-MgO-content nontransformable t'–ZrO2 phase. As temperature increases, the latter gives rise to a similar but fluctuating interaction related to the oxygen vacancies mobility and which shows a thermal behavior analogous to that already reported for the stabilized cubic ZrO2. Above 1100 K these dynamic t'-sites transform into pure tetragonal ones which behave ordinarily, suffering the t → m phase transition when cooling to room temperature. Differences found between TDPAC results and information drawn from other techniques are discussed.
Selective exchange of divalent transition metal ions in cryptomelane-type manganic acid with tunnel structure
Authors: Tsuji Masamichi , Komarneni Sridhar
Published: September 2007

The ion-exchange selectivity of divalent transition metal ions on cryptomelane-type manganic acid (CMA) with tunnel structure has been studied using the distribution coefficients (Kd) at a small fractional exchange in nitrate media. All metal ions studied showed linear relationships with a slope of −2 on the log-log plot of Kd vs [HNO3] which clearly indicated that the adsorption process is an “ideal” ion-exchange. The selectivity increased in the following order: Pb ≫ Mn > Co > Cu > Hg > Cd > Zn > Ni. The high selectivity of the manganic acid was successfully utilized in the removal of Co2+ from seawater and tap water.
Investigation of cured hydridopolysilazane-derived ceramic fibers via dynamic nuclear polarization
Authors: Lewis Russell H. , Wind Robert A. , Maciel G.E.
Published: September 2007

During the pyrolysis of cured hydridopolysilazane (HPZ) polymer to form Si–C–N ceramic fibers, large quantities of unpaired electrons are produced. For such materials dynamic nuclear polarization (DNP) provides a means of enhancing the intensity of the NMR signal, and supplies information on the localization or delocalization of unpaired electrons. 29Si, 1H, and 13C DNP gives enhancements of 250 for 13C and at least 800 for 29Si. 13C and 29Si DNP-DPMAS experiments yield the following results: (i) there are at least two distinct types of carbon, sp2 and sp3; (ii) there is a distribution of sp3 silicon environments; (iii) the unpaired electrons behave as fixed paramagnetic centers; and (iv) the unpaired electrons are distributed homogeneously throughout the sample. Proton DNP spectra can be obtained even though hydrogen is only a trace element in the finished ceramic.
Void distribution and susceptibility differences in ceramic materials using MRI
Authors: Wallner Anton S. , Ritchey William M.
Published: September 2007

Magnetic Resonance Imaging (MRI) is applied to porous ceramic materials to study structural properties. In ceramics, processing differences create inhomogeneous binder distribution in the materials which can cause the formation of regions with differing densities and voids. These defects can be observed with MRI using solvent permeation. Fractional porosity obtained by using image intensity measurements and weight gain due to solvent permeation can be correlated. Dark regions in the image are due to defects such as closed voids, pockets of binder, or agglomerates. Defects such as voids or agglomerates usually have different magnetic susceptibilities. This difference causes artifacts in the image. By exploiting the increase in signal loss using a gradient-echo sequence, apparent enhancement of voids in ceramics is achieved.
The effect of Y2Ba1Cu1O5 addition on microstructure and formation of microcracks in the partially melted Y–Ba–Cu–O oxides
Authors: Kim Chan-Joong , Kim Ki-Baik , Chang In-Soon , Won Dong-Yeon , Moon Hong-Chul , Suhr Dong-Soo
Published: September 2007

In order to investigate microstructural variation by 2-1-1 addition in partially melted Y–Ba–Cu–O, a specimen resulting from 2-1-1 added to 1-2-3 was heat-treated through the peritectic temperature. Microstructure was observed on the directionally solidified region near the interface of the two samples. The 2-1-1 addition results in a homogeneous microstructure where no remnant liquid phase is present. It reduced the 1-2-3 plate thickness, as well as suppressed the formation of microcracks due to the tetragonal-to-orthorhombic phase transition or the thermal contraction during cooling from the peritectic temperature. The formation of microcracks induced by the phase transition seems to be closely related to the process of oxygen diffusion into a sample. We discuss the formation of microcracks in terms of the oxygen diffusion along the plate boundaries and of the thickness of 1-2-3 plates. The decrease in the plate thickness and the fine dispersion of 2-1-1 particles contribute suppression of the formation of microcracks and their propagation.
Characteristics of TlBa2Ca2Cu3O9+δ powder as-synthesized and after grinding
Authors: Kung P.J. , Maley M.P. , Wahlbeck P.G. , Peterson D.E.
Published: September 2007

Crystal structure and superconductivity of the Tl–Ba–Ca–Cu–O powder prepared by a solid-state reaction were studied. The results of x-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses indicate that the powder of a major single 1223 phase was synthesized with a cauliflower-like morphology; by grinding, the powder was partially transformed to an amorphous phase. The measurement of magnetic hysteresis was also performed in the temperature range of 7–75 K up to 5 T from which the weak field-dependent behavior of critical current density was observed. The as-synthesized powder, with Tc = 110 K measured from magnetometer and susceptometer, is considered to consist of weak-linked regions. The results obtained from comparing the as-synthesized and the ground powder imply that in the Tl-1223 system, the Ag-sheathed tapes fabricated by the powder-in-tube process may be benefited by forming other intermediate phases with plate-like morphologies to give better densification or grain alignment.
Structural studies on Tl–Ca–Ba–Cu−0 superconducting thin films
Authors: Morosin Bruno , Norton Grant M. , Carter Barry C. , Venturini E.L. , Ginley D.S.
Published: September 2007

The microstructure of mixed phase, c-axis oriented Tl–Ca–Ba–Cu–O thin films, exhibiting excellent superconducting properties, has been examined by transmission electron microscopy and x-ray diffraction. Although the stoichiometry of the as-deposited films corresponds to the Tl2Ca2Ba2Cu3O10 phase (Tl-2223, c = 3.6 nm), x-ray diffraction showed these films contain up to 50% of the Tl2CaBa2Cu2O8 phase (Tl-2122, c ≍ 2.9 nm). The x-ray diffraction peaks of the 3.6 nm phase are noticeably broader than those of the 2.9 nm phase, suggesting a smaller coherent size along the c-axis for the 3.6 nm phase Lattice-fringe images of the 2.9 nm phase typically show only an occasional or no defect layer; however, such layer defects are more abundant in the 3.6 nm phase and, though random, occur with sufficiently wide separation and regularity to be consistent with an average coherency of ∼40 nm. The coherent sizes along the c-axis, as determined by x-ray line profile analysis, were 140 nm and 40 nm, respectively, for the 2.9 nm and 3.6 nm phases, in good agreement with those determined by electron microscopy. The estimated width of the layer defects observed in the lattice-fringe images is suggestive, for the most part, of the four Cu-layered phases (Tl-1324 or Tl-2324) and to a lesser degree the two Cu-layered phases (Tl-1122 or Tl-2122).
Effects of Cr+ ion implantation on the oxidation of Ni3Al
Authors: Chen M. , Patu S. , Shen J.N. , Shi C.X.
Published: September 2007

Ni3Al samples were implanted with different doses of 150 keV Cr+ ions to modify the surface region. The high temperature oxidation behavior was tested. The surface layer structure was investigated by AES, TEM, XRD, and optical microscope before and after the test. The experimental results show that chromium ions turn a small amount of ordered superlattice Ni3Al phase into a disordered Ni–Al–Cr phase. Also there is a bcc chromium phase in the implanted sample. Implanted Ni3Al alloy has better oxidation resistance than the unimplanted one at 900 °C. The oxide layer is of a multilayer structure after 50 h oxidation, composed of a NiO inner layer, Cr2O3, spinel NiAl2O4 intermediate layers, and an α–Al2O3 external layer at the oxide/air interface. The α-Al2O3 and Cr2O3 are independent scale-like layers. The two protective layers improve the oxidation resistance significantly. The effects of implanted elements and possible reaction mechanisms are discussed.
Growth kinetics and characterizations of gallium nitride thin films by remote PECVD
Authors: Choi S.W. , Bachmann K.J. , Lucovsky G.
Published: September 2007

Thin films of GaN have been deposited at relatively low growth temperatures by remote plasma-enhanced chemical-vapor deposition (RPECVD), using a plasma excited NH3, and trimethylgallium (TMG), injected downstream from the plasma. The activation energy for GaN growth has been tentatively assigned to the dissociation of NH groups as the primary N-atom precursors in the surface reaction with adsorbed TMG, or TMG fragments. At high He flow rates, an abrupt increase in the growth rate is observed and corresponds to a change in the reaction mechanism attributed to the formation of atomic N. X-ray diffraction reveals an increased tendency to ordered growth in the 〈0001〉 direction with increasing growth temperature, He flow rate, and rf plasma power. Infrared spectra show the fundamental lattice mode of GaN at 530 cm−1 without evidence for vibrational modes of hydrocarbon groups.
Phases and crystallization in the system Li2O–B2O3–H2O under hydrothermal conditions
Authors: Byrappa K. , Shekar K.V.K.
Published: September 2007

The Li2O–B2O3–H2O system has been studied under hydrothermal conditions (T= 250 °C,P< 100 bars). The phases crystallizing in this system are Li4B7O12Cl, Li2B4O7, Li3B5O8(OH)2, LiH2B5O9, and Li2HBO3. Some of these phases are new ones. Their fields of crystallization are shown in the composition diagram. The growth and characterization of these lithium borates obtained in the system Li2O–B2O3–H2O under lowerPTconditions have been discussed in brief.
Structure property relationships in core-shell BaTiO3–LiF ceramics
Authors: Randall C.A. , Wang S.F. , Laubscher D. , Dougherty J.P. , Huebner W.
Published: September 2007

A sintering, microstructural development and dielectric property study of BaTiO3–LiF ceramics was performed to assess the potential application of low-fired multilayer capacitors. Not only does LiF allow for sintering below 1000 °C, it also allows for the manipulation of dielectric properties and interfaces within BaTiO3–LiF ceramics. Using mixing laws, a model of the dielectric properties of the core-shell microstructures is presented that agrees well with the observed experimental data.
New fluoroindate glass compositions
Authors: Messaddeq Y. , Delben A. , Aegerter M.A. , Soufiane A. , Poulain M.
Published: September 2007

The limits of glass formation of new fluoroindate glass compositions have been determined for the basic systems InF3–BaF2–GdF3−20ZnF2−20SrF2–2XFn where × = Na, La and InF3–BaF2−20ZnF2−20SrF2−2GdF3–XFn, where × = Ca and Y. The incorporation of small amounts of GaF3 and/or GdF3 increases strongly the thermal glass stability. All the fluoroindate compositions studied are highly transparent in the mid-infrared range; their transmission edge is shifted beyond 7 μm and the theoretical attenuation coefficient, extrapolated at the CO laser wavelength emission, is typically α = 100 dB/km. Large bulks and preforms have been prepared allowing the drawing of optical fibers.
Processing of electroceramic-polymer composites using the electrorheological effect
Authors: Randall C.A. , Miller D.V. , Adair J.H. , Bhalla A.S.
Published: September 2007

This paper presents a novel approach that demonstrates the usefulness of electrorheological fibril formation to form 1-3 connected ceramic-polymer composites. These fillers include ferroelectric, polar, metal, semiconductor, and superconductor crystallite powders. Patterned distributions of ceramic fillers within the polymer matrix can be induced by electric fields applied between patterned electrodes.