bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Binders on Interfacial Failure in Sapphire Fiber-reinforced NiAl Composites
Authors: Eldridge Jeffrey I. , Wheeler Donald R. , Bowman Randy R. , Korenyi-Both Andras
Published: March 2008

The influence of organic binders on fiber/matrix bonding during the powder metallurgy fabrication of sapphire fiber-reinforced NiAl matrix composites (sapphire/NiAl) was investigated. One composite panel was fabricated using a poly(methyl methacrylate) (PMMA) fiber binder and a teflon matrix powder binder; another panel was fabricated by binderless powder metallurgy consolidation. The effect of the binders on fiber/matrix bonding was evaluated by fiber push-out testing from room temperature to 900 °C. Examination of mating fiber and matrix-trough fracture surfaces by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) revealed differences in interfacial morphology and chemistry, depending on the use of binders in fabrication. The primary difference between the two composites was the much higher concentration of carbon at the fiber/matrix interface in sapphire/NiAl fabricated with binders. This carbon residue from binder burnout prevented clean contact between the sapphire fiber and NiAl matrix surfaces, resulting in a weak, thermomechanically clamped fiber/matrix interface, in contrast to the stronger, less temperature dependent, interfacial bonding observed without binders.
High Refractive Index Materials of Iron Sulfides and Poly(ethylene oxide)
Authors: Kyprianidou-Leodidou Tasoula , Althaus Hans-Jörg , Wyser Yves , Vetter Daniel , Büchler Michele , Caseri Walter , Suter Ulrich W.
Published: March 2008

High refractive index composites of iron sulfides and poly(ethylene oxide) (PEO) have been prepared by co-precipitation from aqueous solution. Several reaction parameters were varied: inorganic reactants, reactant ratios, reaction temperatures, and reaction times. Selected samples were characterized with organic microelemental analysis, x-ray fluorescence spectroscopy, x-ray diffraction, DSC, and TEM. The nanocomposites with the highest refractive indices have been prepared using PEO, Mohr's salt, and H2S or NaHS. The analyses indicate that the iron sulfides in these materials consist of finely dispersed mackinawite and greigite (“amorphous” FeS) and, partially, also pyrite. The refractive indexes of the resulting composites are clearly above 2 at 632.8 and 1295 nm and can assume values between 2.5 and 2.8.
Ac irreversibility line of bismuth-based high temperature superconductors
Authors: Mehdaoui A. , Beille J. , Berling D. , Loegel B. , Noudem J. G. , Tournier R.
Published: March 2008

We discuss the magnetic properties of lead doped Bi-2223 bulk samples obtained through combined magnetic melt texturing and hot pressing (MMTHP). The ac complex susceptibility measurements are achieved over a broad ac field range (1 Oe < hac < 100 Oe) and show highly anisotropic properties. The intergranular coupling is improved in the direction perpendicular to the applied stress and magnetic field direction, and an intragranular loss peak is observed for the first time. A comparison is made with other bismuth-based compounds and it is shown that the MMTHP process shifts the ac irreversibility line (ac IL) toward higher fields. It is also shown that all the ac IL's for quasi 2D bismuth-based compounds show a nearly quadratic temperature dependence and deviate therefore strongly from the linear behavior observed in quasi 3D compounds and expected from a critical state model.
Annealing induced interdiffusion and crystallization in sputtered amorphous Si/Ge multilayers
Authors: Czigány Zs. , Radnóczi G. , Järrendahl K. , Sundgren J-E.
Published: March 2008

The intermixing and crystallization of amorphous Si/Ge multilayers (with individual layer thickness between 1.5 and 20 nm) and SiGe alloys produced by dc magnetron sputtering have been studied by cross-sectional transmission electron microscopy and x-ray diffraction. Measurement of the crystallization temperature as a function of the Si content showed that multilayers and alloys with equal composition crystallized at the same temperature. This implies that intermixing precedes crystallization in the multilayers. Close to the crystallization temperature, formation of Kirkendall voids was observed in the short-period Si/Ge multilayers. These voids were found at positions corresponding to the original Si layers, indicating that Si diffuses faster in amorphous Ge than Ge in amorphous Si. The Ge layers in short-period Si/Ge multilayers retained their amorphous state to much higher temperatures than thick amorphous Ge layers. This is shown to be due to inhibition of nucleation by the presence of the layer interfaces. A lower estimate for the Si diffusion constant in crystalline Ge is also determined.
Superplastic behavior of a kappa carbide material (Fe3AlCx)
Authors: Kim Woo-Jin , Ruano Oscar A. , Wolfenstine Jeffrey , Frommeyer Georg , Sherby Oleg D.
Published: March 2008

Fine-grained kappa carbide (Fe3AlCx) materials, containing 12.5 and 14% Al, and 3.5% C, were prepared by powder processing and hipping procedures. The creep behavior of the kappa materials was shown to be identical to that observed in superplastic iron carbide, and was shown to follow a grain boundary–diffusioncontrolled grain boundary sliding relation. The tensile fracture strains in kappa, however, were shown to be considerably less than in iron carbide with a maximum elongation of 92% noted. This difference is attributed to either a low stress intensity factor or to contamination of the powder surface in the kappa material. The compression creep strength, at a given strain rate, was shown to be about two times higher than the tension creep strength.
Electrical and microstructural characteristics of Ge/Cu ohmic contacts to n-type GaAs
Authors: Aboelfotoh M. O. , Oktyabrsky S. , Narayan J. , Woodall J. M.
Published: March 2008

It is shown that Cu–Ge alloys prepared by depositing sequentially Cu and Ge layers onto GaAs substrates at room temperature followed by annealing at 400 °C form a low-resistance ohmic contact to n-type GaAs over a wide range of Ge concentration that extends from 15 to 40 at. %. The contacts exhibit a specific contact resistivity of 7 × 10−7 Ω cm2 on n-type GaAs with doping concentrations of 1 × 1017 cm−3. The contact resistivity is unaffected by varying the Ge concentration in the range studied and is not influenced by the deposition sequence of the Cu and Ge layers. Cross-sectional high-resolution transmission electron microscopy results show that the addition of Ge to Cu in this concentration range causes Cu to react only with Ge forming the ξ and ε1–Cu3Ge phases which correlate with the low contact resistivity. The ξ and ε1–Cu3Ge phases have a planar and structurally abrupt interface with the GaAs substrate without any interfacial transition layer. It is suggested that Ge is incorporated into the GaAs as an n-type impurity creating a highly doped n+-GaAs surface layer which is responsible for the ohmic behavior. n-channel GaAs metal-semiconductor field-effect transistors using ohmic contacts formed with the ξ and ε1–Cu3Ge phases demonstrate a higher transconductance compared to devices with AuGeNi contacts.
An alternative method for penetration depth determination in nanoindentation measurements
Authors: Woirgard J. , Dargenton J-C.
Published: March 2008

The information provided by the shape of the unloading portion of indentation curves is used to calculate the area of contact between the indenter and the material. Results obtained in fused silica and nickel, including Young's modulus and hardness values, are presented to illustrate the validity of the approach. It is shown that errors of only a few percent are introduced when fitting unloading curves with power laws. The present method is especially useful when direct specimen stiffness measurements can be performed.
Determination of equilibrium cations for the KTiOPO4 structure
Authors: Chani Valery I. , Shimamura Kiyoshi , Fukuda Tsuguo
Published: March 2008

Single crystals with the structure of KTiOPO4 (KTP) were grown from mixtures containing equal concentrations of KSnOPO4 and KGeOPO4 (i), KTiOPO4 and KGeOPO4 (ii), and KTiOPO4 and KTiOAsO4 (iii), respectively. The comparison of the lattice parameters measured and calculated from Vegard's rule shows that structural stability of KTiOAsO4 is higher in comparison with KTiOPO4. It was found that addition of GeO2 to the KTP containing flux is accompanied by increasing all lattice parameters of KTP that correspond to substitution of As5+ by Ge4+.
The standard molar enthalpies of formation of α−Si3N4 and β−Si3N4 by combustion calorimetry in fluorine, and the enthalpy of the α-to-β transition at the temperature 298.15 K
Authors: O'Hare P. A. G. , Tomaszkiewicz Iwona , Seifert H. J.
Published: March 2008

The standard molar enthalpies of formation ΔfH°m of α−Si3N4 and β−Si3N4 have been determined by fluorine combustion calorimetry: ΔfH°m (Si3N4, cr, α, 298.15 K) = − (828.9 ± 3.4) kJ · mol−1 and ΔfH°m (Si3N4, cr, β, 298.15 K) = – (827.8 ± 2.5) kJ · mol−1. These results indicate that the enthalpy of the α-to-β transition, approximately (1 ± 4) kJ · mol−1, is negligible within experimental uncertainty.
Laser micromachining of Al2O3−TiC ceramics
Authors: Oliveira V. , Vilar R. , Conde O. , Freitas P.
Published: March 2008

Al2O3−34 wt.% TiC ceramics have been machined with a KrF (248 nm) excimer laser under normal atmosphere. In the initial steps of the irradiation process both the roughness and the removal rate present a strong variation with the number of pulses. After approximately 200 pulses the process reaches a stationary regime where the roughness and the removal rate become constant. Characterization of the machined areas by scanning electron microscopy showed that the variations in roughness and removal rate are related to the evolution of the surface topography of the samples. Also, as a consequence of laser irradiation, TiC and Al2O3are partially transformed into TiO2, TiC0.7N0.3, and an Al–Ti solid solution.
Superconducting properties and structural stability of Bi2Sr2CaCu2O8+δ compound prepared by electrochemical reduction in protogenic electrolyte
Authors: Matsuda Motohide , Tamada Hideki , Yamashita Kimihiro , Umegaki Takao , Miyake Michihiro
Published: March 2008

Superconducting Bi2Sr2CaCu2O8+δ (Bi-2212) compound was electrochemically reduced in a protogenic electrolyte of benzoic acid dissolved in acetone. The critical temperatures (Tc) of the reduced Bi-2212 were enhanced from 75 K up to ∼90 K, which were reportedly the highest value of Bi-2212 superconductor. In spite of the enhancement of Tc, a diamagnetism of Bi-2212 was weakened after the reduction. This phenomenon was discussed in terms of the flux penetration depth. The electrochemically reduced Bi-2212 had a different structural stability from a partly oxygen-removed Bi-2212 which was prepared by annealing in reducing atmospheres. These results are attributable to injection of protons from the benzoic acid into the Bi-2212 structure.
Scanning and transmission electron microscopies of single-crystal silicon microworn/machined using atomic force microscopy
Authors: Koinkar Vilas N. , Bhushan Bharat
Published: March 2008

Atomic force microscopy (AFM) is commonly used for microwear/machining studies of materials at very light loads. To understand material removal mechanism on the microscale, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies were conducted on the microworn/machined single-crystal silicon. SEM studies of micromachined single-crystal silicon indicate that at light loads material is removed by ploughing. Fine particulate debris is observed at light loads. At higher loads, cutting type and ribbon-like debris were observed. This debris is loose and can be easily removed by scanning with an AFM tip. TEM images of a wear mark generated at 40 μN show bend contours in and around the wear mark, suggesting that there are residual stresses. Dislocations, cracks, or any special features were not observed inside or outside wear marks using plan-view TEM. Therefore, material is mostly removed in a brittle manner or by chipping without major dislocation activity, crack formation, and phase transformation at the surface. However, presence of ribbon-like debris suggests some plastic deformation as well.
Microwave assisted synthesis of technologically important transition metal silicides
Authors: Vaidhyanathan B. , Rao K. J.
Published: March 2008

A novel, simple, clean, and fast microwave assisted method of preparing important transition metal silicides (MoSi2, WSi2, CoSi2, and TiSi2) has been described. Amorphous carbon is used both as a microwave susceptor and as a preventer of oxidation.
Solid-state mechanical alloying of plastic crystals
Authors: Font J. , Muntasell J. , Cesari E. , Pons J.
Published: March 2008

Ball milling has been used as a solid-state mechanical alloying technique in two binary systems of plastic crystals: neopentylglycol/pentaglycerin (NPG/PG), showing a partial solubility in the ordered phase, and 2-amino-2-methyl-1,3-propanediol/tris(hydroxymethyl) (AMP/TRIS) whose immiscibility in this ordered solid phase is almost total. For the AMP/TRIS system the stable state at room temperature was reached by milling. Contrarily, for NPG/PG, DSC measurements reveal that an annealing period is required after milling. These results have been compared with those of the pentaglycerin/pentaerythritol (PG/PE) binary system, previously studied, whose miscibility is total at room temperature.
Preparation of fine-grained MgO and Gd2O3 stabilized ZrO2 thin films by electron beam physical vapor deposition co-evaporation
Authors: Tcheliebou F. , Boulouz M. , Boyer A.
Published: March 2008

Thin films of ZrO2 doped with MgO and Gd2O3, 1–1.5 μm in thickness are formed onto nickel substrates by reactive thermal evaporation using a dual-hearth electron gun. X-ray diffraction patterns of the deposits show changes in the crystallographic structure and average particle size as a function of the dopant content. A mixture of monoclinic and tetragonal phases gradually disappears to become a single cubic phase with increasing dopant molar fraction. The average crystallite size deduced from diffraction line broadening decreases as the dopant content increases. This observation is strongly confirmed by scanning electron micrographs which reveal a smooth surface topography. Fine-grained materials obtained here are interpreted in terms of high nucleation rate and kinetically limited grain growth. It appears that composition, crystallographic structure, and microstructure relations are of paramount importance in ZrO2-based films prepared by electron-beam evaporation.
Microstructure of liquid phase sintered superplastic silicon carbide ceramics
Authors: Wang Chong-Min , Mitomo Mamoru , Emoto Hideyuki
Published: March 2008

Superplastic silicon carbide ceramics were fabricated at low temperatures by a liquid phase sintering very fine β–SiC powder. The microstructural features of this material, of both before and after the superplastic deformation, have been investigated by transmission electron microscopy. Evaluated from the point of view of phase transformation, dislocation motion, and dynamic grain growth, the materials show very stable microstructures, indicating that the superplastic deformation process was dominated by the liquid phase assisted grain boundary sliding. In addition, the material is also characterized by the formation of clusters of fine SiC particles (5–20 nm) encapsulated in layered graphitized carbon.
The effect of Cr and La on MgTiO3 and MgTiO3–CaTiO3 microwave dielectric ceramics
Authors: Ferreira V. M. , Azough F. , Freer R. , Baptista J. L.
Published: March 2008

Magnesium titanate and MgTiO3–CaTiO3 ceramics were prepared by a chemical (Pechini) route and classical mixed oxide route. Selected specimens were doped with Cr or La. Specimens were sintered at 1350 °C and 1400 °C. Microstructures were examined by optical microscopy, scanning electron microscopy, and transmission electron microscopy. Dielectric properties were determined at 8 GHz by the Hakki and Coleman method. The highest Q values were obtained for undoped, chemically prepared MgTiO3 (20800); any dopants caused the Q value to be degraded. Additions of small amounts of Cr (≤1 mol %) to mixed oxide magnesium titanate increased the density to 97.1% theoretical, and increased the Q value (from 7000) to 13,000. Additions of La led to the formation of La2Ti2O7 second phase and reduction in the Q value for both materials. Both Cr and La acted as effective sintering aids, increasing density (to a maximum of 99% theoretical for 1% mol La in chemically prepared samples) and relative permittivity (to 18.1 for the same specimens). The relative permittivity of MgTiO3–CaTiO3 ceramics increased with calcium content, but the corresponding Q values decreased (∈r = 19.9, Q = 8500 for Mg:Ca = 94: 6). Small additions of La to Mg–Ca titanates enhanced the dielectric Q values but decreased the relative permittivities.
Failure behavior of alumina and alumina/silicon carbide nanocomposites with natural and artificial flaws
Authors: Meschke F. , Alves-Riccardo P. , Schneider G. A. , Claussen N.
Published: March 2008

Alumina/silicon carbide nanocomposites with 5 vol.% SiC nanoparticles were produced by slip casting, pressureless sintering, and hot isostatic pressing. The grain size dependence of both the bend strength and fracture toughness have been investigated. The strength exceeds 1 GPa at a grain size of 1.7 μm. Crack opening displacements (COD) were measured, revealing that crack tip toughness is considerably lower than in pure alumina and an R-curve behavior is unlikely to occur. By introducing artificial pores with a size of 60 μm, the micromechanical fracture process has been studied in both pure alumina and nanocomposites. In contrast to alumina, where an annular precrack forms prior to fracture, it is suggested that precrack formation is strongly impeded in the nanocomposites and failure is controlled by microcrack initiation. The high strength of Al2O3/SiC nanocomposites seems to be the result of an unusually high crack initiation stress.
A descriptive model linking possible formation mechanisms for graphite-encapsulated nanocrystals to processing parameters
Authors: Elliott B. R. , Host J. J. , Dravid V. P. , Teng M. H. , Hwang J-H.
Published: March 2008

New and modified mechanisms are proposed to account for detailed observations of carbon encapsulation of Fe, Ni, and Co nanocrystals. The mechanisms are based on aerosol and gas phase chemistry and on the catalytic effects of transition metals. Two parameters are found to qualitatively dominate production: the local-path carbon-to-metal ratio (LCM) and the global carbon-to-metal ratio (GCM). LCM's select which mechanisms are active along each pathway within the reactor. The GCM places bounds upon and determines the weighting between different LCM's and thus determines the distribution of different nanoscale products within the collected, macroscopic product. A two part processing parameter → mechanism → product map links the components. The generality of the model is discussed throughout with reference to related processes and the encapsulation of other materials.
The mechanical behavior of a passivating surface under potentiostatic control
Authors: Bahr D. F. , Nelson J. C. , Tymiak N. I. , Gerberich W. W.
Published: March 2008

Continuous microindentation has been carried out on an iron–3% silicon single crystal in 1 M sulfuric acid. The ability of the material to support elastic loading is directly linked to the presence of thermally grown oxide films and passive films applied through potentiostatic control of the sample. When the passive film is removed, either by chemical or electrochemical means, the iron alloy can no longer sustain pressures on the order of the theoretical shear strength of iron. Instead, the metal behaves in a traditional elastic-plastic manner when no film is present. The oxide film at the edges of the indentation can sustain applied tensile stresses up to 1.2 GPa prior to failure. Indentation in materials undergoing dissolution must account for the rate of material removal over the remote surface and the resulting plastic deformation around the contact of the indentation.
A 133Cs magic angle spinning nuclear magnetic resonance study of cesium environments in barium hollandites and Synroc
Authors: Hartman J. S. , Vance E. R. , Power W. P. , Hanna J. V.
Published: March 2008

Barium aluminum hollandite is a major phase in Synroc, a ceramic designed for the immobilization of high-level waste (HLW) from nuclear fuel reprocessing. Radioactive cesium substitutes into the channel sites, and such hollandites give 133Cs MAS nuclear magnetic resonance (NMR) spectra consisting of a single peak at 211 ppm in the absence of paramagnetic ions. However, the peak shifts to 640 ± 30 ppm and becomes extremely broad when Ti3+ replaces Al3+ in the channel walls of the hollandite structure, apparently because of Fermi contact interaction between the Cs nucleus and the unpaired electron of Ti3+. 133Cs MAS NMR of Synroc and hollandites is very sensitive to the presence of water-soluble CsAlTiO4 which would compromise the aqueous durability of Synroc. 133Cs MAS NMR spectra of Synroc-C, hot-pressed in metal bellows at temperatures as high as 1325 °C, do not indicate significant formation of CsAlTiO4. Synroc samples loaded with Cs and Sr only were shown by MAS NMR as well as electron microscopic techniques to be capable of incorporating nearly 10 wt.% Cs before CsAlTiO4 is formed.
An analytical electron microscopy investigation of municipal solid waste incineration bottom ash
Authors: Krzanowski James E. , Eighmy T. Taylor , Crannell Bradley S. , Eusden J. Dykstra
Published: March 2008

Incinerator bottom ash samples have been characterized using analytical electron microscopy (AEM) techniques, including electron diffraction, energy dispersive spectroscopy, and electron energy loss spectroscopy. The samples were first separated by magnetic properties and density. Three resulting fractions were examined: the magnetic, high-density (MHD) fraction, the nonmagnetic/high-density (NMHD) fraction, and the nonmagnetic, low-density (NMLD) fraction. Examination of these samples revealed a variety of submicron microstructural features. For the MHD fraction, metal oxides, iron silicates, aluminum silicates, and calcium phosphate compounds were found in addition to amorphous material. The NMHD fraction contained elements similar to the MHD fraction but had more amorphous material; crystalline silicates were less common. Compounds such as MgO and chloroapatite were also found. The NMLD fraction contained SiO2 and numerous metal oxides. The results of some of these analyses were used to model leaching behavior of the ash. Based on the AEM results, three mineral phases were chosen as candidates for aqueous geochemical thermodynamic equilibrium modeling of pH-dependent leaching: chromite, chloroapatite, and zincite. In two of these three cases (chromite, chloroapatite), the selected mineral phase provided excellent agreement with the experimentally observed leaching behavior. AEM was shown to be a useful tool for elucidating mineralogy of complex environmental samples.
Evaluation of high resistance to environmental corrosion for excellent car-coating treatment
Authors: Mori Kiyotaka , Okada Takashi , Oguri Kazuya , Sakamoto Kageyoshi , Nishi Yoshitake
Published: March 2008

Using a scanning laser microscope and mercury porosi-meter, we evaluate the effects of an excellent car-coating treatment on resistance to environmental corrosion after aging for three years. The treatment maintains the clear surface. The effect can be explained mainly by the contact angle of sessile drops.
Influence of initial crystal structure and electrical pulsing on densification of nanocrystalline alumina powder
Authors: Mishra R. S. , Risbud S. H. , Mukherjee A. K.
Published: March 2008

The effect of the crystal structure of starting alumina powder and electric pulsing on the initial stages of densification has been studied in the temperature range of 1200– 1500 °C. Multiple electric pulsing cycles enhance the densification significantly. The α-alumina powders consolidate more readily in comparison to γ-alumina powders. A high density α-alumina specimen (>98% of theoretical density) was obtained at 1300 °C in less than 10 min.
Improvement of the morphological stability of Ag film on (001)Si with a thin interposing Au layer
Authors: Peng Y. C. , Chen C. R. , Chen L. J.
Published: March 2008

The morphological stability of ultrahigh vacuum deposited Ag film on (001)Si has been drastically improved by the deposition of 1 to 5 nm thick interposing Au layers. In Ag/(001)Si samples, Ag islands were found to form after annealing at 200 °C for 1 h. In contrast, continuous and uniform metal layer persisted after annealing at 500 °C for 1 h in samples with a thin intermediate Au layer. The significantly improved morphological stability is attributed to the strong intermixing between Au and Ag atoms at the metal/Si interface. The intermixing lowers the interface energy between metal layer and (001)Si.
Equilibrium tie-line in PrOy–BaO–CuO ternary phase diagram around peritectic temperature of Pr1+xBa2−xCu3O7−δ
Authors: Tagami Minoru , Kambara Makoto , Umeda Takateru , Shiohara Yuh
Published: March 2008

This paper presents tie-lines between Pr1+xBa2−xCu3O7−δ and liquid on a PrOy –BaO–CuO ternary phase diagram at 965, 970, 975, 980, and 990 °C in air atmosphere, for which knowledge is necessary to fabricate composition controlled Pr1+xBa2−xCu3O7−δ single crystals by the solution growth method. Liquidus faces have been investigated by dipping MgO single crystal rods into the thermal equilibrium melt at various temperatures and analyzing the composition of the adhering melt by ICP. The compositions of Pr1+xBa2−xCu3O7−δ solid solution coexisting with various compositions of liquids were obtained by quantitative EPMA analysis of quenched melts. Tie-lines were calculated by applying the lever rule to these experimental data for solid compositions and liquidus faces. Furthermore, the relationships between solid solubilities and peritectic temperatures of Pr1+xBa2−xCu3O7−δ are reported.
Uniform and rapid nucleation of diamond via bias-assisted hot filament chemical vapor deposition
Authors: Chen Yan , Chen Feng , Wang E. G.
Published: March 2008

A new method was developed to obtain high density, uniform diamond nuclei via bias-assisted hot filament chemical vapor deposition. A negative bias was applied between a mesh (installed above the filament) and the substrate to produce abundant uniform ions at the growth surface. Raman spectroscopy, scanning electron microscopy, and Auger electron microscopy were used to analyze the films obtained. The results show that a layer of diamond film with a nucleation density of 109/cm2 can be obtained after 10 min deposition under 1 Torr.
A micromechanistic model of the combustion synthesis process: Modes of ignition
Authors: He Cheng , Stangle Gregory C.
Published: March 2008

A theoretical model of the combustion synthesis process has been developed to study the ignition of a self-propagating combustion synthesis process in the Nb–C system. Compared with most of the previously published theoretical work on this subject, this model provides a much more detailed description of the combustion synthesis process from a microscale point of view, due to the fact that it takes into consideration the various microprocesses, such as the melting of reactants, the diffusion and mixing of reactants, and the formation of products. Different ignition modes, including constant-temperature ignition, constant-heat-flux ignition, and variable-temperature ignition, are considered in this work. The key parameters that influence the ignition process are also discussed.
Mechanism of the formation of β–Sialon by self-propagating high-temperature synthesis
Authors: Wu Yuanwen , Zhuang Hanrui , Wu Fengying , Dollimore David , Zhang Baolin , Chen Shen , Li Wenlan
Published: March 2008

β–Sialon has been prepared by SHS (Self-propagating High-temperature Synthesis) with Si, Al, Al2O3, and β–Si3N4 under high nitrogen pressure. Rod-like crystals of b–Sialon with an aspect ratio of 4–15 and whiskers with various aspect ratios were obtained in the process. Considering the morphologies of the products, it is concluded that VLS (vapor-liquid-solid) is the predominant mechanism of the formation of rod-like crystals and whiskers.
Metal-organic chemical vapor deposition of Sr–Co–Fe–O films on porous substrates
Authors: Xia Changfeng , Ward Timothy L. , Atanasova Paolina , Schwartz Robert W.
Published: March 2008

Aerosol-assisted chemical vapor deposition using the β-diketonate precursors Sr(tmhd)2 · 2H2O, Fe(tmhd) 3, and Co(tmhd) 3 was investigated for depositing thin films of the mixed-conducting ceramic SrCoyFe1−yO3−δ onto porous α–Al2O3 substrates. Single-phase SrCoyFe1−yO3−δ perovskite films were obtained at a deposition temperature of 550 °C and pressure of 15 mm Hg, whereas deposition at atmospheric pressure produced mixed-phase films. The Co/Fe elemental ratios in the films reflected those in the precursor solution, but the films were depleted in Sr. Reduced-pressure deposition provided a more uniform film morphology than atmospheric pressure, and led to a supported film which was leak-tight to N2 flow.
A study of barium strontium titanate thin films for use in bypass capacitors
Authors: Baumert B. A. , Chang L-H. , Matsuda A. T. , Tracy C. J. , Cave N. G. , Gregory R. B. , Fejes P. L.
Published: March 2008

Physical and electrical characterization techniques have been applied to the problem of developing a lower temperature process for spin-on Ba0.7Sr0.3TiO3 thin films and capacitors compatible with on-chip aluminum metallization. The films were prepared by spin-coating from carboxylate precursors and were processed at temperatures between 650 °C and 450 °C. Capacitors annealed at higher temperatures have a dielectric constant (κ) of 382, a C/A of 20 fF/μm2, and a leakage current density of 2 × 10−7 A/cm2 at 3.3 V. Those processed at 450 °C show occasionally promising but inconsistent results, correlated using TEM images with locally variable crystallization into the perovskite phase. The kinetics of the spin-on solution chemical decomposition and crystallization has been investigated through the use of x-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy.
Initial stages of silicate growth on and oxidation of graphite: A model for composites
Authors: Bonnell Dawn A. , Jiron Darrin , Flinn Timothy
Published: March 2008

The initial stages of silicate growth on graphite are characterized with atomic force microscopy. The morphological development indicates that decomposition of tetra ethyloxysilane at low pressure produces films of 3 nm clusters located at undercoordinated carbon sites. Clusters eventually cover the surface, at which point a second layer grows. In higher pressure deposition multiple layers of clusters grow simultaneously. A comparison of the oxidation behavior of surfaces with defects completely and incompletely terminated with SiOx shows that edge recession is the primary oxidation mechanism and that the site specificity of SiOx is effective in inhibiting oxidation.
Synthesis of thin superconducting HgBa2CaCu2O6+δ films by post-annealing of laser-ablated precursors
Authors: Brazdeikis A. , FlodstrÖm A. S. , Bryntse I.
Published: March 2008

Superconducting HgBa2CaCu2O6+δ (Hg-1212) thin films have been prepared by laser ablation followed by post-annealing at high temperatures. Two synthesis methods were investigated, using (1) direct reaction of Hg–Ba–Ca–Cu–O precursor films in a Hg-controlled ambience, and (2) thermal diffusion of Hg into Ba–Ca–Cu–O precursor films in a controlled atmosphere containing both Hg- and Tl-bearing species. Effects of the annealing temperature, time, and bulk material composition on the Hg-1212 film and residual impurities are presented. Surface morphologies, growth defects, and transport properties of Hg-1212 on SrTiO3 substrates are discussed. Formation of Hg-1212 films on MgO and LaAlO3 substrates is briefly described.
Solidification of YBa2Cu3O6+δ: Part I. Morphology
Authors: Shen Hua , Flemings Merton C. , Cima Michael J. , Haggerty John , Honjo Shoichi , Rigby Karina , Sung Tae Hyun
Published: March 2008

A new quenching technique was used for detailed microstructural examination of quenched YBa2Cu3O6+δ/liquid interfaces. The examination revealed that the growth rate and the amount of excess Y2BaCuO5 (211) had a strong influence on the growth morphology of YBa2Cu3O6+δ (123). The maximum growth rate at which single crystal growth could be obtained increased from 1 μm/s to 1.5 μm/s as excess 211 content increased from 0 to 20 wt. %. It then decreased to 1 μm/s as excess 211 increased to 40 wt. %. Dendritic growth with distinguishable secondary arms occurred for stoichiometric 123 samples in the regime of cellular/dendritic growth. A highly curved 123 envelope was formed on 211 particles located at the 123 growth interface for stoichiometric 123 samples in the regime of single crystal growth. The microscopic 123 growth interface became flat as excess 211 content increased to 20 wt. %. The engulfment of 211 particles into 123 matrix is discussed based on detailed microstructural examination. It is found that the formation of a small highly curved 123 envelope on 211 particles for stoichiometric 123 samples is due to the large 211 particle spacing.
Growth and characterization of (Bi, Pb)2Sr2Ca2Cu3Oxsingle crystals
Authors: Chu Shaoyan , McHenry Michael E.
Published: March 2008

(Bi, Pb)2Sr2Ca2Cu3Ox (2223) single crystals have been grown using a fused-salt reaction of Bi2O3, PbO, SrCl2, CaCl2, CuCl, and KNO3 in a KCl flux. The pristine crystals show regular plate-like morphology with typical dimension of 0.1 × 0.1 × 0.001–0.01 mm3. Crystal orientation, chemical composition, phase purity, and superconductivity of the pristine crystals were determined by SEM, TEM, EDX, x-ray diffraction techniques, and SQUID magnetometry. The relative fraction of the Bi-2223 phase (Tc = 110 K) in as-grown crystals is ~97%. The only impurity phase, Bi-2212, occurs in some selected crystals but is present in amounts less than the detection limit of x-ray diffraction and is unobserved in the diamagnetic signal determined by SQUID magnetometry.
Characterization of superdislocation dissociations in Al66Ti25Cr9with transmission electron microscopy observations and image simulations
Authors: Kumar Mukul , Hemker K. J.
Published: March 2008

The nature of dissociated superlattice dislocation cores in Al66Ti25Cr9, deformed at room temperature, has been characterized by weak-beam transmission electron microscopy (TEM) and comparison of experimental images with computer-simulated images. The displacement fields associated with narrowly dissociated APB- and SISF-dissociated ‹110› superdislocations were calculated to account for the asymmetry in dislocation contrast and led to a better understanding of the formation of images. Such calculations are a powerful aid, when coupled with image simulations, in distinguishing the “real” intensity peaks from the supplementary peaks that can be generated under experimental imaging conditions. While both APB- and SISF-dissociated superdislocations were identified, the vast majority of superdislocations were determined to be APB-dissociated. Corrected values of the fault energies (γAPBand γSISF) have been measured for this alloy. These energies and the observed dissociations are shown to be self-consistent.
Superplastic constitutive equation and rate-controlling process in aluminum matrix composites with discontinuous fiber and particle reinforcements
Authors: Mabuchi Mamoru , Higashi Kenji
Published: March 2008

Superplastic behavior of aluminum matrix composites with discontinuous reinforcements has been investigated in a temperature range below the melting temperature measured by differential scanning calorimetry. The experimental results of the mechanical properties revealed that the rate-controlling process of superplastic flow was associated with dislocation movement controlled by lattice self-diffusion. The strengthening due to the presence of reinforcements was retained. It is suggested that the strongest strengthening process of the dislocation-pileup mechanism and the diffusional relaxation-limitation or dislocation bypass mechanism affects the rate-controlling process.
Semiconducting BaTiO3 ceramic prepared by low temperature liquid phase sintering
Authors: Zajc I. , Drofenik M.
Published: March 2008

Donor-doped BaTiO3 ceramics were prepared by adding PbO B2O3 SiO2 as a sintering aid. Semiconducting BaTiO3 was obtained at a sintering temperature of 1100 °C. The sintered samples exhibit the Positive Temperature Coefficient of Resistivity (PTCR) effect, which depends on the amount of liquid phase, the concentration of the donor-dopant, and the sintering temperature. The cold resistivity of the samples decreases when the sintering temperature increases. The increase of the grain boundary resistivity and hence of the cold resistivity at lower sintering temperatures was explained by applying the diffusion grain boundary layer model.
High temperature epitaxial growth and structure of Nb films on α–Al2O3(0001)
Authors: Wagner Thomas
Published: March 2008

Epitaxial Nb thin films were grown via molecular beam epitaxy (MBE) at different substrate temperatures on α–Al2O3(0001) substrates. For temperatures of 900 °C to 1100 °C, it was found that Nb grows in the Volmer–Weber growth mode (formation of three-dimensional crystallites). Depending on the growth temperature, different epitaxial orientations of Nb films can be found. At a growth temperature of 900 °C, the Nb{111} planes are parallel to the sapphire basal plane whereas at 1100 °C the Nb grows with the {110} planes on the basal plane of sapphire. These orientations are present even in the initial stages of growth at both temperatures. The formation of two different epitaxial orientations of thick Nb films can be conclusively explained only by considering both the change in the total density of Nb islands with temperature and the influence of island size on the total energy of the islands. The Nb island growth process has been investigatedin situusing reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). Scanning electron microscopy (SEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM) were employed to determine the morphology and structure of Nb islands, Nb films, and Nb/α–Al2O3interfaces.
Passivation of nanocrystalline Al prepared by the gas phase condensation method: An x-ray photoelectron spectroscopy study
Authors: Sánchez-López J. C. , González-Elipe A. R. , Fernández A.
Published: March 2008

Nanocrystalline aluminum powders have been prepared by the gas phase condensation method. Samples have been synthesized in a conventional preparation chamber for gas phase condensation and also in the pretreatment chamber of an XPS (x-ray photoelectron spectroscopy) spectrometer so that in situ studies of the passivation process of nanocrystalline aluminum can be performed. For the range of particle sizes (12–41 nm) studied in the present work, we found a universal behavior during passivation with oxygen of the nanocrystalline Al0. An Al2O3 overlayer of 4 nm, which protects the material from further oxidation, was obtained for all samples independently of the route of oxygen dosage. A careful analysis of the photoelectron parameters (binding energy and Auger parameters) for Al and O shows that in the early stages of passivation the alumina overlayer is so thin (<2.5 nm thickness) that the Al2O3 –Al interface induces an increase in the relaxation energy of the photoholes as compared to that of bulk alumina. Conclusions have been drawn about the best way to proceed during passivation of Al ultrafine particles before exposure to an air atmosphere.
On the reactivity of organic solvents on the particle surface of metal pigment
Authors: Ohshima Kazushi
Published: March 2008

For very fine, acicular particles of α–Fe prepared for audio/video magnetic recording media, the relationship between their chemical property and surface flatness of the tape material made from the particles was investigated experimentally. It was found that adsorption capacity of acidic resin on the particle surface can be a very good index to predict the flatness of the magnetic tape. Because this index depends strongly on the acidic and basic properties of the particle surface, the tape performance can be well controlled by chemically designing the particle surface of α–Fe.
TiN prepared by plasma source ion implantation of nitrogen into Ti as a diffusion barrier for Si/Cu metallization
Authors: Wang W. , Booske J. H. , Liu H. L. , Gearhart S. S. , Shohet J. L. , Bedell S. , Lanford W.
Published: March 2008

A method of forming TiN films for Si/Cu metallization by using plasma source ion implantation (PSII) of nitrogen into Ti is described. The PSII process utilizes a dose of 1 × 1017 ions/cm2 and peak voltages of –10, –15, and –20 kV. The properties of such TiN films as diffusion barriers between Cu and Si were investigated by annealing Cu(2000 A)/TiN/Ti/Si films in vacuum from 500 °C to 700 °C, and by analyzing with four-point probe sheet resistance measurements, Rutherford backscattering spectrometry (RBS), and Auger electron spectroscopy (AES). The TiN films made at peak voltages of –15 and –20 kV were stable barriers against Cu diffusion after annealing at temperatures higher than 600 °C.
Spinning deposition of silica and silica-titania optical coatings: A round robin test
Authors: Guglielmi M. , Martucci A. , Almeida R. M. , Vasconcelos H. C. , Yeatman E. M. , Dawnay E. J. C. , Fardad M. A.
Published: March 2008

A round robin test has been performed on sol-gel processing for the deposition of silica and silica-titania films on silicon substrates by spin-coating. Three solution preparation processes for silica coatings and three for silica-titania coatings were used to prepare samples at each of the participating laboratories. The films have been characterized mainly by thickness (profilometry and ellipsometry measurements), refractive index, porosity, and optical scattering. Different processes gave different thicknesses. Thickness differences were found in films prepared by the same process and by the same deposition parameters, but in different laboratories, when heat-treated at 500 °C. Variations were reduced in samples annealed at 1000 °C. Refractive index and porosity measurements suggest that variations were due to structural differences, particularly porosity. Furthermore, films heat-treated at 500 °C were not completely stabilized, and showed index and porosity variations after six months.
An x-ray photoelectron spectroscopic study of the chemical states of fluorine atoms in calcium silicate glasses
Authors: Hayakawa Satoshi , Nakao Akira , Ohtsutki Chikara , Osaka Akiyoshi , Matsumoto Shuji , Miura Yoshinari
Published: March 2008

X-ray photoelectron spectroscopy has been used to examine the chemical states of fluorine in the glasses of composition xCaF2(50 – x)CaO · 50SiO2 (x = 5, 10, 15, 20, and 25 mol %) and xCaF2(50 – x/2)CaO(50 – x/2)SiO2 (x = 5, 10, 15, and 20 mol %). The analysis of the F1s spectra indicated that Ca2+ and F- ions introduced as CaF2 are favorably located among the Si–O skeleton forming Ca–F clusters. The fraction of the bridging and nonbridging oxygen atoms was derived from the O1s spectra, and the network of the fluorine-containing glasses was concluded to depend only on the ratio CaO/SiO2.
Layered mixed tin-titanium phosphates
Authors: Trobajo Camino , Rodríguez Maria L. , Suárez Marta , García José R. , Rodríguez Julio , Parra José B. , Salvadó Miguel A. , Pertierra Pilar , García-Granda Santiago
Published: March 2008

Mixed crystalline tin-titanium phosphates with variable tin-to-titanium molar ratio have been prepared by precipitation of soluble salts of the metal (IV) with phosphoric acid and refluxing the amorphous solids in 17 M H3PO4. The new materials are characterized by chemical textural and thermal analysis and x-ray powder diffraction. The tin-titanium phosphates are solid solutions showing an isomorphic substitution of tin by titanium in the α-tin phosphate lattice and tin substitution in the γ-titanium phosphate lattice. In both cases, the solubility is partial. The coexistence of both saturated phases is observed in samples of composition between the solubility limits.
Soft chemical preparation and electrochemical oxygen doping of La2Can−1CunO2n+2
Authors: Kikkawa Shinichi , Taya Noriko , Kanamaru Fumikazu
Published: March 2008

La2CaCu2O6 (n = 2) was obtained at temperatures as low as 800 °C by firing the coprecipitates from a mixed aqueous solution of La, Ca, and Cu acetates which were titrated with tartaric acid. The firing temperature was much lower than that in solid state reactions which are usually conducted above 1000 °C. Both La2Ca2Cu3O8 (n = 3) and La2Ca3Cu4O10 (n = 4) were obtained at 700 °C in a similar preparation method. Low temperature firing was very important for these preparations. A porous sintered body of La2CaCu2O6 with a relative density of about 15% was also obtained using this preparation method. This porous sintered body could be effectively oxygen-doped by electrochemical oxidation showing the presence of a new superconducting phase with Tc around 30 K.
Sinterability of SiC powder coated uniformly with Al ions
Authors: Sameshima Soichiro , Miyano Keisuke , Hirata Yoshihiro
Published: March 2008

SiC particles coated uniformly with Al ions (0.25 mass% Al2O3) in an aluminum nitrate solution were consolidated by filtration through a gypsum mold. Hot-pressing in vacuum gave dense SiC (above 99% relative density) in the temperature range of 1900–1950 °C under a pressure of 39 MPa. The microstructures of dense SiC consisted of 2–5 μm grains of low aspect ratios (below 2). The fracture toughness and flexural strength of SiC increased gradually as the hot-pressing temperature became higher and were 4.3 Mpa m0.5 and 350 MPa, respectively, with hot-pressing at 1950 °C. Crack propagation in SiC shifted from intergrain to intragrain with increasing hot-pressing temperature.
New hydrogenation systems of unsaturated organic compounds using noble metal-deposited palladium sheet electrodes with three-dimensional structures
Authors: Iwakura Chiaki , Yoshida Yasuki , Ogata Setsuro , Inoue Hiroshi
Published: March 2008

A successive hydrogenation system was constructed using a two-compartment cell separated by a Pd sheet. The hydrogenation rate changed greatly, depending on the kind of substrates used. For the purpose of improving the hydrogenation rate, the surface of a Pd sheet was modified with highly active catalysts such as Pd black, Pt, and Au by using active hydrogen passing through the Pd sheet as a reducing agent. As a result, the hydrogenation rate of unsaturated organic compounds such as 4-methylstyrene was markedly increased by the surface modification with these catalysts due to the increase in reaction zone and appearance of new active sites.
Electrochemical preparation of cobalt oxide using an autoclave electrolytic cell
Authors: Koinuma Michio , Hirae Tomohiko , Matsumoto Yasumichi
Published: March 2008

Polycrystalline films of cobalt oxides (Co3O4and CoOOH) with and without Sm were fabricated on platinum substrates by electrochemical oxidation in an autoclave. The cobalt oxides were directly crystallized at temperatures higher than about 100 °C during electrolysis. The composition of the cobalt oxides strongly depended on the electrode potential; i.e., Co3O4and CoOOH were formed in non-noble and relatively noble potential regions, respectively. When Sm was incorporated in the CoOOH by the electrolysis in solutions containing Sm3+, only theclattice constant was increased due to an expansion in the layer structure.