bluuebunny/crossref_metadata_2025 huggingface dataset:
Decomposition of the ZrO2electrolyte in contact with Ni: Structure and chemical composition of the Ni–electrolyte interface
Authors: Wagner Thomas , Duscher Gerd , Kirchheim R.
Published: March 2008

The Ni/(ZrO2+ 9.5 mol% Y2O3) interface was used as a model system to investigate decomposition reactions of a yttria-stabilized ZrO2electrolyte in contact with a metal at elevated temperature. In the present study, the sample was a diffusion-bonded symmetrical galvanic cell Ni‌ZrO2+ 9.5 mol% Y2O3‌Ni. Various electron microscopy techniques were used to study the morphology and structure of the reaction products at the Ni–ZrO2electrolyte phase boundary after current flow. Below a critical oxygen partial pressure of approximately 10−27atm, an intermetallic reaction layer formed at the Ni–electrolyte interface. Between the intermetallic layer and electrolyte a thin Y2O3layer was present, which acted as a diffusion barrier for Zr and Ni, slowing down the overall chemical reaction. At several locations at the interface the Y2O3layer broke up, leading to a morphological instability of the interface between electrolyte and Ni5Zr, allowing further reaction. The thickness of the total reaction layer varied widely as a consequence of such an instability.
Synthesis and characterization of rutile TiO2 nanowhiskers
Authors: Li G. L. , Wang G. H. , Hong J. M.
Published: March 2008

Rutile TiO2 nanowhiskers have been synthesized by annealing a precursor powder in which NaCl and Ti(OH)4 particles were homogeneously mixed. The precursor powder was prepared by mixing three kinds of inverse microemulsions (μE) containing TiCl4 aqueous solution, ammonia, and NaCl aqueous solution, respectively, followed by washing with acetone. Annealing temperature and packing density of Ti(OH)4 in the precursor powder influenced the formation of rutile nanowhiskers. The optimum temperature was 750 °C. TiO2 nanowhiskers obtained by annealing a precursor powder in which the molar ratio of sodium to titanium was 400 at 750 °C for 2 h had diameters of 10–50 nm and lengths of several micrometers. They were straight rods with square cross sections, and the side surfaces were composed of four equivalent {110} planes.
An α–Fe2O3 powder of nanosized particles via precursor dispersion
Authors: Liu Xiangyuan , Ding Jun , Wang John
Published: March 2008

An α–Fe2O3 powder of nanosized particles has been successfully prepared by effectively dispersing the precipitated hydroxide precursor in a sodium chloride matrix. In particular, the hydroxide precursor was converted into crystalline α–Fe2O3 particles approximately 10 nm in size when it was mechanically activated in the sodium chloride matrix for 1 h. The subsequent calcination at 600 °C for 1 h resulted in a limited degree of coarsening in particle size while the crystallinity of α–Fe2O3 was further established. The effectiveness of obtaining ultrafine a–Fe2O3 powders by mechanical activation in the sodium chloride matrix was demonstrated by comparing the powder with those obtained via other routes, such as mechanical activation without sodium chloride as the matrix, calcination at 600 °C, and then mechanical activation in sodium chloride matrix, respectively. None of these processing routes led to a powder comparable in particle characteristics to that derived by the precursor dispersion.
Experimental study of atmospheric pressure chemical vapor deposition of silicon carbide from methyltrichlorosilane
Authors: Papasouliotis George D. , Sotirchos Stratis V.
Published: March 2008

A comprehensive study of the chemical vapor deposition of SiC from methyltrichlorosilane at atmospheric pressure was conducted in this study; its main objectives were to identify the range of operating parameters in which stoichiometric SiC could be deposited and the generation of reliable kinetic data that could be used for the design of atmospheric pressure processes of chemical vapor deposition or chemical vapor infiltration of SiC. Deposition experiments were conducted in a hot-wall, cylindrical reactor at temperature ranging from 1273 to 573 K on flat graphite substrates or thin molybdenum wires aligned with the axis of the reactor. The obtained results showed that the deposition rate and the deposit stoichiometry varied markedly with the distance from the entrance of the reactor. The deposition rate exhibited, depending on the reaction temperature, one or two pronounced maxima before the beginning of the isothermal zone of the reaction, whereas the deposit stoichiometry showed an abrupt transition from almost silicon to stoichiometric silicon carbide after the first maximum. Experiments with HCl added in the feed showed that the presence of HCl could cause complete suppression of the deposition of silicon and lead to smoother variation of the SiC deposition rate with the residence time in the reactor. It is believed that this effect could be exploited to improve the uniformity of SiC deposition in chemical vapor deposition reactors or in the interior of porous preforms.
Synthesis of oxide powders by way of a polymeric steric entrapment precursor route
Authors: Nguyen My H. , Lee Sang-Jin , Kriven Waltraud M.
Published: March 2008

A polymerized organic–inorganic complexion route is introduced for the synthesis of yttrium aluminum garnet, YAG (Y3Al5O12) and cordierite (Mg2Al4Si5O18) powders. Long-chain polymers such as polyvinyl alcohol (–[CH2–CHOH]-nor PVA) or polyethylene glycol (H[O–CH2–CH2]nOH or PEG) were used as the organic carriers for a precursor ceramic gel. Calcined powders were very porous and homogeneous in distribution of components. Experimental studies by differential thermal analysis and thermogravimetric analysis, x-ray diffraction, solid-state nuclear magnetic resonance, and Fourier transform infrared spectrometry indicated that metal-ion chelation is not the primary mechanism for obtaining molecularly homogeneous precursor powders. Water-soluble cations of mixed oxides in the PVA or PEG process were sterically entrapped in the entangled network and resulted in fine and pure, mixed oxide powders.
Synthesis of nickel–chromium–zinc ferrite powders from stainless steel pickling liquors
Authors: López-Delgado Aurora , López Felix A. , de Vidales José L. Martín , Vila Eladio
Published: March 2008

A low-temperature method was used to synthesize a nickel–chromium–zinc ferrite from stainless steel pickling liquor, a waste product of the steel industry, which is listed in most industrialized countries as a toxic and hazardous waste. This article reports the recovery (as a valuable ferric product) of the total metal content of this waste (namely, iron, chromium, nickel, and minor manganese), by coprecipitation of the multi-ionic solution and Zn2+ (provided by ZnO) with 1 M n-butylamine at room temperature. The spinel-type ferrite produced was characterized by x-ray diffraction, thermogravimetric analysis and differential scanning calorimetry, and scanning electron microscopy. Its recorded magnetization of 2600 emu cm−3 allows its use in different magnetic applications. Furthermore, the synthesis method is a low-cost technology that yields a more environmentally friendly final effluent.
Crystallite coalescence: A mechanism for intrinsic tensile stresses in thin films
Authors: Nix W. D. , Clemens B. M.
Published: March 2008

We examined the stress associated with crystallite coalescence during the initial stages of growth in thin polycrystalline films with island growth morphology. As growing crystallites contacted each other at their bases, the side-walls zipped together until a balance was reached between the energy associated with eliminating surface area, creating a grain boundary and straining the film. Our estimate for the resulting strain depends only on interfacial free energies, elastic properties, and grain size and predicts large tensile stresses in agreement with experimental results. We also discuss possible stress relaxation mechanisms that can occur during film growth subsequent to the coalescence event.
Shock synthesis of nanocrystalline Si by thermal spraying
Authors: Goswami R. , Sampath S. , Herman H. , Parise J. B.
Published: March 2008

Shock synthesis of nanocrystalline Si was accomplished for the first time using thermal spray in which Si powder is injected into a high-energy flame where the particles melt and accelerate to impact on the substrate. A stream of molten Si particles impacted onto Si wafers of two orientations (100) and (111). The shock wave generated by the sudden impact of the droplets propagated through the underlying Si layer, which experienced a phase transition to a high-pressure form of Si due to propagation of the shock wave. The metastable high-pressure form of Si then transformed to metastable Si-IX, Si-IV (hexagonal diamond-Si), R-8, and BC-8 phases as evidenced by transmission electron microscopy and x-ray diffraction studies. Back-transformed metastable Si grains, with a size range from 2 to 5 nm, were found to be dispersed within Si-I (cubic diamond-Si). The metastable phases formed mostly in deposits on the (100) substrate compared to those of the (111) substrate orientations. This behavior can be correlated with the anisotropic nature of the pressure-induced transformations of Si-I.
Can stress–strain relationships be obtained from indentation curves using conical and pyramidal indenters?
Authors: Cheng Yang-Tse , Cheng Che-Min
Published: March 2008

Applying the scaling relationships developed recently for conical indentation in elastic–plastic solids with work-hardening, we examine the question of whether stress–strain relationships of such solids can be uniquely determined by matching the calculated loading and unloading curves with that measured experimentally. We show that there can be multiple stress–strain curves for a given set of loading and unloading curves. Consequently, stress–strain relationships may not be uniquely determined from loading and unloading curves alone using a conical or pyramidal indenter.
Formation of Bi–Sr–Ca–Cu–O superconducting films by electrodeposition
Authors: Martín-Gonzalez María Soledad , Garci´a-Jaca Javier , Morán Emilio , Alario-Franco Miguel Ángel
Published: March 2008

Superconducting films of the Bi–Sr–Ca–Cu–O family of oxides were prepared by electrodeposition of the constituent metals followed by an oxidative thermal treatment. The influence of water, stirring of the electrolyte, cleaning of the substrate, and deposition time on the quality of the films were studied. Before the thermal treatment, the electrodeposited films consisted of a mixture of different metals and carbonates of the constituent elements. The oxidation of the metallic phases and the decomposition of the carbonates occurred in the ranges 260–280 °C and 400–470 °C, respectively. The final oxides were obtained after an oxidative thermal treatment at 800 °C. Lower temperatures were not sufficient for the preparation of the superconducting oxide films. The prepared Bi-2201 films consisted of a mixture of two phases with different strontium, bismuth, and oxygen contents. The Bi-2212 films were composed of platelike particles with a preference to orientate along the (001) direction. These films showed critical temperatures up to 92 K and critical current densities up to 15,000 A/cm2 (at 77 K and zero field) when the films were pressed before the thermal treatment.
Phase equilibria among the superconductors in the Y2O3–BaO–Cu–O system
Authors: Zhou Zhigang , Navrotsky Alexandra
Published: March 2008

The enthalpy of formation of Y2Ba4Cu7O14.864 at room temperature has been determined by using high-temperature reaction calorimetry. The standard enthalpy of formation of the 247 phase is ΔH°f = −5463 ± 18 kJ mol−1. Phase relationships among the superconductors, namely, the 123, 124, and 247, are assessed. It is intrinsic that impurity phases, such as Y2Cu2O5, BaCuO2, CuO, etc., coexist with the superconductors at equilibrium. Equilibria among the superconductor phases in the Y2O3–BaO–Cu–O system have been determined. The results show that, at the 124 bulk composition, the 247 phase coexists with the excess CuO in a narrow area of pO2 ∼ T space confined by the stability fields of the 124 phase and a mixture of the 123 + CuO. The standard free energies of carbonation and hydration of the 247 phase are also determined, which are −629 ± 13 kJ mol−1 and −873 ± 45 kJ mol−1, respectively. Like the 123 and 124 phases, the 247 phase is thermodynamically unstable for corrosion by water vapor and carbon dioxide in ambient atmosphere.
Oxidation of nanocrystalline Mo–Si–N and nanolayered Mo–Si–N/SiC coatings
Authors: Torri P.
Published: March 2008

Oxidation of sputter-deposited nanocrystalline Mo–Si–N (MoSi2.2N2.5) coatings in oxygen–water vapor atmosphere has been studied in the temperature range 400–850 °C. In addition, the oxidation properties of nanolayered Mo–Si–N/SiC coatings at 700 °C were studied and compared to those of single-layer coatings of both components. No pest disintegration was observed in Mo–Si–N up to 200 h of oxidation. A preexponential rate constant of (3.7 ± 0.5) × 109 (1015 atoms/cm2)2/h and activation energy 1.03 ± 0.02 eV were determined from an Arrhenius plot for parabolic oxygen buildup on Mo–Si–N. Up to 20% less oxygen was detected in the oxidized nanolayered coatings compared to either of the components as a single layer, indicating an improvement in oxidation resistance.
Microwave dielectric properties of Ca[(Li1/3Nb2/3)1−xMx]O3−δ (M = Sn, Ti) ceramics
Authors: Choi Ji-Won , Kang Chong-Yun , Yoon Seok-Jin , Kim Hyun-Jai , Jung Hyung-Jin , Yoon Ki Hyun
Published: March 2008

The microwave dielectric properties of Ca[(Li1/3Nb2/3)1−xMx]O3−δ (M = Sn, Ti, 0 ≤ x ≤ 0.5) ceramics were investigated. In general, the ceramics prepared were multiphase materials. However, single-phase specimens having orthorhombic perovskite structure similar to CaTiO3 could be obtained in the vicinity of Sn = 0.2 to 0.3, and Ti = 0.2. As Sn concentration increased, the dielectric constant (εr) decreased and the quality factor (Q) significantly increased within the limited Sn concentration. As Ti concentration increased, the dielectric constant (εr) increased, the quality factor (Q) decreased, and the temperature coefficient of resonant frequency (τf) changed from a negative to positive value. The temperature coefficient of resonant frequency of 0 ppm/°C was realized at Ti = 0.2. The Q · fo value and εr for this composition were found to be 26100 GHz and 38.6, respectively.
Effect of nickel on sintering of self-propagating high-temperature synthesis produced titanium carbide
Authors: Mishra (Pathak) S. K. , Das S. K. , Ray A. K. , Ramchandrarao P.
Published: March 2008

A detailed study of the sintering behavior of titanium carbide (TiC) powder synthesized by the self-propagating high-temperature synthesis (SHS) route was carried out with varying percentages of nickel. With an increase in the nickel content, porosity was found to increase along with Ni2.67Ti1.33 secondary phase at grain boundary. A 90–92% dense sintered body of TiC was produced from SHS-produced powder at 1800 °C with 10 wt% nickel.
Preparation and characterization of alumina membranes and alumina–titania composite membranes
Authors: Shi Li , Wong Ning-Bew
Published: March 2008

Supported and unsupported γ-alumina membranes and alumina–titania composite membranes were prepared using the sol-gel method. In the course of preparation, effects of acid concentration, type of acid, alkoxide, and binder on the particle size of the sols and pore size of the membranes were investigated by thermogravimetry and differential thermal analysis, N2 physisorption, and light scattering. It was observed that the particle sizes of all the sols had only a small affect on the pore sizes of the membranes. Qualities of the membranes were improved by addition of polyvinyl alcohol as binder to the boehmite precursor. This resulted in less critical but more controllable drying and calcining procedures. Composite membranes with different pore sizes from 3.2 to 4.8 nm and surface areas retained above 100 m2/g could be regulated by different alumina-to-titania ratios.
Carbon–silicon alloy fibers: Optimizing tensile properties by control of the stabilization stage
Authors: Lu S. , Rand B. , Bartle K. D.
Published: March 2008

The stabilization stage in the processing of carbon–silicon alloy (CSA) precursor fibers is investigated in this study. The critical stabilization parameters are identified and shown to control the mechanical properties of fibers both at the stabilization stage and, after further pyrolysis and controlled oxidation, to produce oxidation-resistant fibers. The attainment of infusibility in the stabilized fibers, necessary for the production of CSA fibers, determines the lowest stabilization degree, whereas the highest stabilization degree can be identified from the relationship between stabilization temperature and tensile properties of CSA fibers, thus enabling the optimum stabilization conditions to be determined. The CSA fibers produced by proper control of stabilization conditions significantly enhance mechanical properties, which are more than double those of CSA fibers obtained previously. Fourier transform infrared spectroscopy and nuclear magnetic resonance studies show that at stabilization temperatures above the optimum there is significant formation of silica in the stabilized fibers. This leads to a higher modulus but lower tensile strength and elongation.
Deposition and mechanical properties of polycrystalline Y2O3/ZrO2 superlattices
Authors: Yashar Philip C. , Barnett Scott A. , Hultman Lars , Sproul William D.
Published: March 2008

Polycrystalline Y2O3/ZrO2 superlattice thin films were deposited using opposedcathode reactive magnetron sputtering. Pulsed direct-current power was used to eliminate arcing on the metallic targets. Radio-frequency power was applied to the substrates to achieve ion bombardment of the growing film. In order to reproducibly deposit at high rates in Ar–O2 mixtures, the Y target voltage was used to indirectly feedback-control the O2 partial pressure. Deposition rates as high as ∼70% of the pure metal rates were achieved, typically 3.5 μm/h. Superlattices with periods ranging from 2.6 to 95 nm were deposited. Y2O3 layer thicknesses were either 75% or 50% of the superlattice period. X-ray diffraction and transmission electron microscopy studies showed well-defined superlattice layers. The ZrO2 layers exhibited the high-temperature cubic-fluorite structure, which was epitaxially stabilized by the cubic Y2O3 layers, for thicknesses ≤7 nm. The equilibrium monoclinic structure was observed for thicker ZrO2 layers. Nanoindentation hardnesses ranged from 11.1 to 14.5 GPa with little dependence on period. The hardness results are discussed in terms of current superlattice hardening theories.
Optical second-order nonlinearity of transparent glass-ceramics containing BaTiO3 precipitated via surface crystallization
Authors: Narazaki Aiko , Tanaka Katsuhisa , Hirao Kazuyuki
Published: March 2008

Second-harmonic generation of transparent glass-ceramics containing BaTiO3 crystalline phase was investigated using Maker fringe method. When 15BaO · 15TiO2 · 70TeO2 glass was heat-treated at 415 °C for 0.5–12 h, (101)- or (110)-oriented BaTiO3 crystals precipitated in the near-surface region. The resultant glass-ceramics exhibit second-harmonic generation. Variation of second-harmonic intensity with angle of incidence, i.e., the Maker fringe pattern changes drastically with an increase in heat treatment time and temperature. No second-harmonic signal was detected in glass-ceramics derived from 15SrO · 15TiO2 · 70TeO2 glass. These facts suggest that BaTiO3 crystal is responsible for the second-order nonlinear phenomenon, although its structure is closer to cubic than tetragonal according to x-ray diffraction measurements. In order to estimate second-order nonlinear optical coefficient d(2), Maker fringe patterns of the BaTiO3-containing glass-ceramics were analyzed. For the glass-ceramic after heat treatment for 0.5 h, d33 and thickness of BaTiO3-crystallized layer, L, are 3.65 pm/V and 3.43 μm, respectively. The value of second-order nonlinear optical coefficient is comparable to those of BaTiO3 films prepared via metalorganic chemical vapor deposition and pulsed-laser deposition. On the other hand, the glass-ceramic heat-treated for 12 h exhibits d15 = 0.31 pm/V and L = 300 μm. The thickness of the layer active in second-order nonlinearity evaluated from the Maker fringe pattern is coincident with the observation by scanning electron microscopy.
Transmission electron microscopy study of barium hexaferrite formation from barium carbonate and hematite
Authors: Steier Hanns P. , Requena Joaquin , Moya José S.
Published: March 2008

The formation of barium hexaferrite from stoichiometric mixtures of BaCO3 and Fe2O3 has been investigated by means of differential thermal analysis and thermogravimetry, x-ray diffraction, and transmission electron microscopy–energy dispersive spectrometry. The first step, which implies decarbonatation and monoferrite formation, includes the formation of various intermediate compounds, which are formed at contact points between BaCO3 and Fe2O3 grains, and implies diffusion of both species. In the second step, barium hexaferrite is formed at interfaces between monoferrite and iron oxide mainly by diffusion of barium through the BF6 lattice into the hematite lattice. This exothermic reaction process leads to nonagglomerated pseudohexagonal platelets with an average particle size very close to the one of the starting powder mixture (∼1 μm).
First-principles study of initial stage of Ni thin-film growth on a TiO2 (110) surface
Authors: Cao P. L. , Ellis D. E. , Dravid V. P.
Published: March 2008

The bonding structure and binding character for the initial stage of thin-film growth of Ni on a rutile (110) surface were studied using first-principles density functional theory. Our results show that, in the first monolayer, Ni atoms are preferentially adsorbed on top of bridging oxygen atoms and upon secondary surface oxygen. The bond strength between Ni adatom and substrate is much stronger than that between Ni adatoms. About 0.3 electrons are transferred from Ni atoms to substrate in low coverage; the adsorption of additional Ni atoms on neighboring sites decreases this transfer. In addition to the ionic bonding component, some covalent character is found in the Ni adatom–substrate bond.
Growth-rate dependence of the thermal conductivity of chemical-vapor-deposited diamond
Authors: Balzaretti Naira M. , Feldman Albert , Etz Edgar S. , Gat Roy
Published: March 2008

The in-plane thermal diffusivity of chemical-vapor-deposited diamond films was measured as a function of diamond-growth rate. The films, 0.1–0.4 mm thick, were prepared in microwave-plasma reactor at growth rates ranging from 1 to 10 μm/h. A modification of Ångstöm's method was used to perform the diffusivity measurements. The thermal conductivity calculated from the thermal diffusivity shows an inverse relationship with growth rate. Analyses of Raman spectra indicate that both the line shifts and the line widths of the diamond Raman peak are practically independent of the deposition rate, except for the specimen grown at the highest growth rate.
Growth and ultraviolet optical properties of KGd1–xREx(WO4)2 single crystals
Authors: Pujol M. C. , Solé R. , Gavaldà Jna. , Massons J. , Aguiló M. , Díaz F. , Nikolov V. , Zaldo C.
Published: March 2008

The suitable conditions for growth of KGd(WO4)2 (KGW) and KGd1–xREx(WO4)2— RE = Nd, Er, Yb, Ho, Tm, Pr—by the top-seeded-solution-growth method, using K2W2O7 as solvent, are discussed. The relation between crystal size, mean growth rate, distribution coefficient of the substituting element, and the presence of macrodefects is analyzed. The optical absorption corresponding to the band-gap transition of KGW has been found to be temperature dependent; the absorption threshold energy changes from 34405 cm−1 at 300 K to 35330 cm−1 at 7 K. Narrow pre-edge absorption bands at about 32000 and 32600 cm−1 have been ascribed to Gd3+ intraconfigurational transitions. The photoluminescence of most RE3+ ions has been observed under ultraviolet (UV) excitation close to the absorption threshold of KGW. This suggests the contribution of charge transfer bands. In Pr-doped samples the presence of a minor concentration of Pr4+ could also contribute in this region. The irradiation with UV light does not introduce any significant coloration of our samples.
Structural characterization of amorphous ceramics in the system Si–B–N–(C) by means of transmission electron microscopy methods
Authors: Heinemann D. , Assenmacher W. , Mader W. , Kroschel M. , Jansen M.
Published: March 2008

Amorphous ceramics with the chemical composition Si3B3N7 and SiBN3C were produced from single-source molecular precursors by polymerization and pyrolysis. The powder and fiber materials were investigated by means of energy filtering transmission electron microscopy. The intensity of elastically scattered electrons is recorded to calculate the pair distribution function of these ceramics. In the pair distribution function of Si3B3N7 three significant maxima at 0.144, 0.172, and 0.291 nm are clearly resolved and are assigned to the pair distances B–N, Si–N, and Si–Si (N–N), respectively, by comparison to crystalline materials. The predominant structural units of the ceramic are trigonal planar BN3 and tetrahedral SiN4 groups, which are close to their regular symmetry. The overall pair distribution function of SiBN3C is very similar to that of Si3B3N7; however, the maxima are broadened due to the incorporation of carbon into the network. High-resolution mapping of the elements Si, B, N, and C with electron spectroscopic imaging reveals a homogeneous distribution on a subnanometer scale without precipitation or separation of, for example, carbon-rich clusters. Similarly, elemental mapping of Si3B3N7 reveals a random distribution of the elements Si, B, and N at the same scale. Both new ceramics consist of an amorphous network with bonds and coordinations as preformed in the precursor.
Physical properties of nearly zero magnetostriction Co-rich glass-coated amorphous microwires
Authors: Cobeño A. F. , Zhukov A. , de Arellano-López A. R. , Elías F. , Blanco J. M. , Larin V. , González J.
Published: March 2008

Magnetic and mechanical properties of Co-rich amorphous microwires of nominal compositions (Co1–xMnx)75Si10 B15 (0.08 < x < 0.11) and Co56.5Fe6.5Ni10B16Si11 with nearly zero magnetostriction constant have been studied. Drastic changes of the hysteresis loop with the decrease of x from rectangular to flat shape were observed at x < 0.1, while the Co56.5Fe6.5Ni10B16Si11 microwire showed rectangular hysteresis loops. Compositions with x ≥ 0.1 have small but positive magnetostriction constant while negative λs values have been observed at x ≤ 4 0.09, indicating rectangular character of the hysteresis loop in samples with nearly zero and even for small negative λs. External stress dependence of switching field, H*, showed an increase of H*; with s for samples with x = 0.11 and a decrease of H* with σ for x = 0.1. Besides, microwires of the same composition but with different dimensions showed different H*(σ) dependencies.
Indentation model and strain gradient plasticity law for glassy polymers
Authors: Lam David C. C. , Chong Arthur C. M.
Published: March 2008

Plastic deformation of metals is generally a function of the strain. Recently, both phenomenological and dislocation-based strain gradient plasticity laws were proposed after strain gradients were experimentally found to affect the plastic deformation of the metal. A strain gradient plasticity law is developed on the basis of molecular theory of yield for glassy polymers. A strain gradient plasticity modulus with temperature and molecular dependence is proposed and related to indentation hardness. The physics of the strain gradient plasticity in glassy polymer is then discussed in relation to the modulus.
High-temperature phases in ternary Zr–O–N systems
Authors: Dreizin Edward L. , Hoffmann Vern K. , Vicenzi Edward P.
Published: March 2008

Zirconium aerosol was ignited and burned in atmospheric pressure air in microgravity using a 2.2-s drop tower. Combustion products were collected and analyzed using electron microscopy. The elemental composition analyses indicated that combustion product compositions fell along two linear traces on a ternary Zr–O–N diagram. Currently, the equilibrium Zr–O–N phases are not characterized at temperatures above 2000 °C, typical of zirconium combustion in air, and it is suggested that the phases detected in zirconium combustion products can serve as a guide to further studies of the Zr–O–N system at high temperatures. It is also suggested that experimental metal combustion techniques can be adopted for studying high-temperature metal–gas phase equilibria.
High-temperature phase relationships for YxNd1–xBa2Cu3Oy(0 ≤ x ≤ 0.5) superconductors via containerless processing
Authors: Olive J. R. , Hofmeister W. H. , Bayuzick R. J. , Vlasse M.
Published: March 2008

This paper presents the results of drop-tube experiments performed on YxNd1–xBa2Cu3Oy (0 ≤ x ≤ 0.5) to understand some of the effects of partial substitutions of Nd for Y on the phase relationships in these systems at elevated temperatures. Powders from 50 to 100 μm in diameter were processed in pure O2 at furnace temperatures from 1400 to 1800 °C, every 25 °C. The resulting samples were examined microstructurally using scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy. Powder x-ray diffraction was performed for phase identification. It was verified that Nd substitution alters phase selection by introducing at least one new phase and allowing for solidification of the superconducting composition directly from the melt via undercooling to below the peritectic transformation temperature. In addition, solidification pathways are altered for samples processed at temperatures just below the liquidus temperature. Microstructural and x-ray diffraction evidence was used to map the liquidus with increasing Nd substitution. It was found that a minimum in this liquidus occurs at or near the composition Y0.1Nd0.9Ba2Cu3Ox and at a temperature of 1500 °C (±25 °C).
Influence of solidification rate on precipitation and microstructure of directional solidification IN792 + Hf superalloy
Authors: Sun W. R. , Hu Z. Q. , Lee J. H. , Ceo S. M. , Choe S. J.
Published: March 2008

The effect of solidification rate on the precipitation and microstructure of directional solidification IN792 + Hf alloy was studied. The solidification sequence and the initial precipitation temperature of different phases were determined by the observation of the quenched microstructure combined with the differential thermal analysis measurement. The script carbide was turned into faceted carbide with the drop of solidification rate. It was concluded by microstructure analysis that the faceted carbide was pushed by the γ solid front before it was captured. The incorporation of γ phase into the faceted carbide was due to the dendrite growth of the carbide toward one point and the mergence of the dendrites. Some long carbide bars were formed along the grain boundaries by continual reaction of eutectic (γ + MC carbide) at a solidification rate of 0.5 μm/s. Two zones, the γ′ forming elements enriched zone and depleted zone, were found in the residual liquid area. Eutectic γ/γ′ nucleated in the γ′ forming elements enriched zone. The η-phase precipitation was controlled by the ratio of (Ti + Hf + Ta + W)/Al in the residual liquid. The growth of eutectic γ/γ′ increased the ratio and induced the η-phase precipitation. A lower solidification rate decreased the ratio by sufficient diffusion and hence efficiently suppressed the η-phase precipitation.
High-temperature lead-free SnSb solders: Wetting reactions on Cu foils and phased-in Cu–Cr thin films
Authors: Jang J. W. , Kim P. G. , Tu K. N. , Lee Michael
Published: March 2008

We report the soldering behaviors of high-temperature (300 °C) lead-free SnSb alloys on Cu foils and phased-in Cu–Cr thin films. By increasing the Sb content from 5 to 15 wt%, the solder surface became rougher and the wetting angle decreased from 50° to 20° on the Cu foils. Interfacial compounds were found to be Cu6Sn5 and Cu3Sn. The Cu6Sn5 showed a scallop-type morphology, whereas the Cu3Sn had a layer-type morphology. The growth of the latter was found to be diffusion limited. On phased-in Cu–Cr thin films, the solders showed much lower wetting angles than on the Cu foils, but the dewetting phenomenon was observed after 1 min of reflow time in the 85Sn15Sb alloy. In comparison, we found no dewetting of the high-temperature 95Pb5Sn solder.
Nanocrystalline MnFe2O4 produced by niobium doping
Authors: Kundu T. K. , Chakravorty D.
Published: March 2008

Nanosized MnFe2O4 phase with diameters in the range 13.7 to 100 nm were produced by calcination and sintering treatments in the system zNb2O5 · (50 – z)MnO · 50Fe2O3 with z having values between 0 and 20. Nb5+ ions are believed to give rise to vacancies in the Mn2+ sites, which break up the coupling of ferrimagnetically active oxygen polyhedra. The Curie temperature decreases as the size of the MnFe2O4 phase is reduced. This is explained on the basis of a decrease in the number of exchange pairs of the type Mn2+–Fe3+. The coercivity increases with a decrease in the size of the ferrimagnetic phase. This is believed to arise due to a decrease in saturation magnetization as the size of the MnFeO4 phase is reduced.
Mechanical, tribological, and stress analyses of ion-beam-deposited boron-rich boron nitride films with increasing N content
Authors: Chan K. F. , Ong C. W. , Choy C. L. , Kwok R. W. M.
Published: March 2008

Boron (B) films and B-rich BNx films with different N contents (4.1–40.3 at.%.) were deposited by dual ion-beam deposition. The films consist of a B-rich phase constructed of icosahedral atomic clusters and a graphitelike boron nitride phase. The films with N content ≤20.3 at.% is dominated by the B-rich phase. Their hardness rises with increasing N content to reach a maximum value of 18.8 GPa. The hardness-to-elastic modulus ratio (H/E) and the critical load of the films also increase, showing stronger wear resistance of the films. These results can be explained if some N–B–N chains are formed at the interstitial sites in the network of the B-rich phase, which cross-link different icosahedral atomic clusters in the B-rich phase and strengthen the rigidity of the structure. For the films with higher N contents, the volume fraction of the graphitelike boron nitride phase becomes higher, and the hardness drops as a consequence. However, the change in the H/E ratio is rather mild. This implies that the wear resistance of the films is not altered and explains why the critical load of the films remains almost unchanged. In addition, the friction coefficient μ of all the films depends on the normal load L in the form of μ = aLy, where a and y are numerical parameters and are insensitive to the change in the N content. Furthermore, compressive stress was found to increase from about 0.12 to 1.7 GPa when the N content increased from 4.1 to 40.3 at.%.
Oriented calcium metaphosphate glass-ceramics
Authors: Yue Yuanzheng , Keding Ralf , Rüssel Christian
Published: March 2008

Highly oriented calcium metaphosphate glass-ceramics were obtained directly from the corresponding melt. On the interface between the Ca(PO3)2 melt and an Al2O3 rod, the nucleation could easily be induced. The dependence of the crystal growth rate on the crystallization temperature was determined. The crystal growth rates observed were up to 71 μm/s. The c axes of most crystals were oriented in the direction perpendicular to the surface of the Al2O3 rod as illustrated by scanning electron microscope and pole figures. The degree of crystal orientation increased with increasing crystallization temperature. At higher temperatures (e.g., at 892 °C), even single-crystal-like dendrites were formed.
Temperature effect on nonhydrolytic foaming process
Authors: Grader G. S. , Hazan Y. de , Natali G. , Dadosh T. , Shter G. E.
Published: March 2008

This paper describes the effect of temperature on the formation of nonhydrolytic alumina foams. The foams are generated by heat treatment of crystals of the aluminum chloride isopropyl ether complex [AlCl3(Pri2O)], with the release of isopropyl chloride (PriCl). The chlorine content in the foams was determined by titration, and their weight loss during sintering was measured by thermogravimetric and differential thermal analysis. Based on these measurements, the condensation degree (CD) in the foams was modeled. The foaming time ranged from several minutes at 70 °C to several seconds at 160 °C. It was found that the chlorine-to-aluminum ratio of the foam (Cl/Al) decreased from 1.79 at 70 °C to 1.56 at 160 °C. Thermogravimetric analysis data confirm that the smaller Cl content gives rise to a smaller weight loss during thermal decomposition, consistent with a higher CD in the foams created at higher temperatures. Finally, about 80% of the PriCl produced during complex decomposition and subsequent –Al–O–Al– condensation reactions is lost during foaming.
Initial hillock formation and changes in overall stress in Al–Cu films and pure Al films during heating
Authors: Kylner C. , Mattsson L.
Published: March 2008

The effect of adding a few percent (3 at.%) Cu to Al films on the initial hillock formation and the changes in overall film stress were studied. Al films were evaporated by an electron-beam gun onto Si wafers in an ultrahigh vacuum deposition system and Al–Cu films were coevaporated with a thermally heated source used for the Cu. The as-deposited samples were radiatively heated at 3 °C/s in an air environment. During heating, the initial hillocking and the changes in overall stress were measured simultaneously and in real time with a specially designed optical instrument. The measurement principle of this instrument is based on laser beam deflection, caused by wafer bending due to film stress, and collection of the laser light scattered off from the hillocks appearing on the film surface. The experimental results show that Cu alloying has a strengthening effect on Al films, resulting in delayed and considerably reduced hillock formation. Before heating, the as-deposited Al–Cu samples were investigated by total integrated scattering and atomic force microscopy. These investigations showed that Al–Cu films are considerably smoother and have smaller grains than Al films of similar thickness (340 nm). It was found that the small grains of Al–Cu films contribute to increasing the tensile stress–temperature slope. In addition, Al–Cu films can withstand higher compressive stresses than Al films.
A novel bulk sol-gel process to prepare monolithic silica materials
Authors: Wang Ce , Zhang Yahong , Lu Yunfeng , Wei Yen
Published: March 2008

A bulk sol-gel process has been developed to prepare monolithic silica materials at room temperature. The process involves an acid-catalyzed hydrolysis of tetraethyl orthosilicate in tetrahydrofuran containing aqueous HC1 catalyst, followed by neutralization with carbonate salts, extraction with aliphatic nonpolar solvents, molding, gelation, and drying. This method shortens the processing time from weeks for the conventional sol-gel process to several days. The silica objects prepared from the process are transparent, crack-free, and of relatively low volume shrinkage (e.g., 52%) and high silica content (e.g., 82%).
Solvent-induced stresses in glassy polymer: Elastic model
Authors: Wang Wei-Lung , Chen J. R. , Lee Sanboh
Published: March 2008

The solvent-induced stresses in glassy polymers were investigated. The mass transport accounts for case I, case II, and anomalous transport. Case I transport is attributed to the concentration gradient, whereas case II transport is attributed to stress relaxation. Anomalous transport is the mixture of case I and case II. Both one-side and two-side mass transports with the boundary condition of constant surface concentration are considered. The stresses and longitudinal displacement arising from the mass transport are formulated based on the linear elasticity theory. The maximum stress is always located at the surface at the initial time. The stresses are a function of the partial molal volume, Young's modulus, and Poisson's ratio. From the longitudinal displacement data, the partial molal volume was determined.
Nanoprobe analysis of core–rim structure of carbides in TiC–20 wt% Mo2C–20 wt% Ni cermet
Authors: Yamamoto T. , Jaroenworaluck A. , Ikuhara Y. , Sakuma T.
Published: March 2008

In order to get detailed information of the core–rim interface of carbides in TiC–20 wt% Mo2C–20 wt% cermet, chemical analysis in the vicinity of the interface was carried out by energy dispersive x-ray spectroscopy equipped with a high-resolution transmission electron microscope (HRTEM) with a field-emission-type gun. It was found that the chemical composition discretely changed across the core–rim interface at a nanoscale level, whereas HRTEM observation revealed that the interface is highly coherent. The discrete change in molybdenum content at the interface may suggest the existence of a miscibility gap between TiC and MoC systems at the sintering temperature.
Evidence of transition metal diffusion during hydrothermal ceramic film growth: Ba(Ti,Zr)O3on layered Ti–Zr alloy
Authors: Alvarez Alejandra V. , Fuenzalida V. M.
Published: March 2008

Ti–Zr alloy thin films of 20–60 nm in thickness were evaporated on Pt-coated silicon wafers. The films exhibited a layered Ti–Zr depth distribution. The films were then treated hydrothermally in 0.25 M Ba(OH)2at 150 and 200 °C for 4–8 h. Films treated at 150 °C did not exhibit reflections from the Ba(TixZr1−x)O3perovskite structure by x-ray diffraction, although a slight barium content was detected by x-ray photoelectron spectrometry. On the other hand, the films treated hydrothermally at 200 °C revealed reflections corresponding to perovskite Ba(TixZr1−x)O3. These films exhibited a homogeneous titanium and zirconium depth distribution, as shown by x-ray photoelectron spectroscopy and Auger depth profiles, proving that either titanium or zirconium ions diffuse during the hydrothemal treatment. The initial Ti–Zr film was completely consumed during the hydrothermal process, leading to a film of homogeneous composition (Ba, Ti, and Zr) up to the interface with the platinum layer.
A solvothermal decomposition process for fabrication and particle sizes control of Bi2S3 nanowires
Authors: Yu Shu-Hong , Shu Lei , Yang Jian , Han Zhao-Hui , Qian Yi-Tai , Zhang Yu-Heng
Published: March 2008

A novel one-step solvothermal decomposition process (SDP) was successfully developed for fabrication of Bi2S3 nanowires via a reaction between BiCl3 and thiourea in polar solvents at 140 °C for 6–12 h. The influence of solvents, reaction temperature, and reaction time on the formation of Bi2S3 nanowires was investigated. The yield was as high as 98%. The particle sizes of Bi2S3 nanowires are controlled by the choice of solvents. The possible formation mechanism of Bi2S3 nanowires via the so-called SDP method is proposed. The present technique is expected to synthesize other nanostructural metal chalcogenides under mild conditions.
Photoacoustic spectrum of porous silicon irradiated by light
Authors: Kawahara Toshio , Kiyotoo Takaharu , Morimoto Jun , Koga Ritsuyasu , Iwane Sinsui , Tahira Kenichi , Miyakawa Toru
Published: March 2008

The photoacoustic (PA) spectra for the porous silicon samples irradiated during or after anodization are reported. The difference between the spectra for the irradiation conditions is discussed. The light irradiation time dependence of the PA spectra is shown. The irradiation after anodization causes the samples to luminesce in the blue region and enhances the photoluminescence signal intensity around 600 nm. It also reduces the PA signal intensity in the shorter wavelength region. The irradiation during the anodization causes enhancement only in the red-region luminescence.
On the indexing and reciprocal space of icosahedral quasicrystal
Authors: Singh Alok , Ranganathan S.
Published: March 2008

Important features of the icosahedral reciprocal space have been brought out. All reciprocal vectors up to sixth generation (by addition of icosahedral vectors) have been considered. Some more relationships for indexing the icosahedral phase are derived, and it is shown that the zone law using Cahn indices is also analogous to that valid for crystals. All important vectors, i.e., up to fourth generation and sixth generation, have been identified. Poles of all these vectors have been determined and shown to be one of the zone axes formed by these vectors. The types of indices that the planes and axes will have in three-dimensional and six-dimensional coordinates is discussed.
Laser-processing-induced phase transformation in Zn–Al-based alloy
Authors: Zhu Y. H. , Chavez-Carvayar J. A. , Man H. C. , Villagran M.
Published: March 2008

Microstructure and phase transformation of a furnace-cooled eutectoid Zn–Al-based alloy were studied after laser beam bombardment using low-angle x-ray diffraction (XRD) and backscattered scanning electron microscopy (BSEM). It was found that the microstructure of the laser-beam-treated specimen consisted mainly of the supersaturated Zn-rich β′s phase particulates of about 1−2 μm in diameter. Three structure morphologies were observed. Microcracking occurred in the laserbeam-affected zone during laser processing. Two laser-processing-induced phase transformations, i.e., decomposition of the η′FC phase and a four-phase transformation, were detected using XRD and BSEM techniques, similar to phase transformations that occurred in the same eutectoid Zn–Al-based alloy after various thermal and thermomechanical processing procedures.
Comparison of the crystallographic and magnetic properties between Tb2Fe16.46Cr1.23 and Tb3(Fe,Cr)29 single crystals
Authors: Yang C. P. , Wang Y. Z. , Wu G. H. , Hu B. P. , Han X. F. , Jiang Z. L. , Ma C. L. , Zhu J.
Published: March 2008

A novel Tb3(Fe,Cr)29 single crystal, which has a monoclinic Nd3(Fe,Ti)29-type structure, is obtained using the Czochralski method by performing a proper heat treatment on the Tb2Fe16.46Cr1.23 crystal with a Th2Ni17-type structure. Thermomagnetic curves along the easy axis and magnetization curves along the easy and hard axes are presented for both crystals. The lattice parameters are a = 1.058 nm, b = 0.848 nm, c = 0.968 nm, α = γ = 90°, and β = 96.93° for the Tb3(Fe,Cr)29 single crystal. The Curie temperatures, saturation magnetizations, and magnetocrystalline anisotropy constants are compared between the Tb-2:17 and Tb-3:29 crystals. The magnetization behavior along the hard axis is quite different as a first-order magnetization process (FOMP) of type I for the Tb-2:17, but a FOMP of type II for the Tb-3:29 crystal is observed below room temperature. At low temperatures, magnetohistory effects are detected for both crystals.
Fabrication and thermal stability of a nanocrystalline Ni–Al–Cr alloy: Comparison with pure Cu and Ni
Authors: Oh-ishi Keiichiro , Horita Zenji , Smith David J. , Valiev Ruslan Z. , Nemoto Minoru , Langdon Terence G.
Published: March 2008

A Ni–Al–Cr alloy with an initial grain size of ∼60 μm was subjected to torsion straining to a strain of ∼7 at room temperature, thereby reducing the grain size to ∼34 nm. Similar torsion straining with samples of pure Cu and pure Ni gave grain sizes of ∼170 and ∼130 nm, respectively. Inspection of the Ni–Al–Cr alloy after torsion straining revealed highly strained regions containing dislocations associated with lattice distortions but with an absence of any Ni3Al ordered phase. The ultrafine grains in the Ni–Al–Cr alloy were extremely stable at high temperatures, and it was possible to retain a grain size of less than 100 nm after annealing at temperatures up to ∼900 K. By contrast, there was rapid grain growth in the samples of pure Cu and Ni at annealing temperatures in the vicinity of ∼500 K. The stability of the grains in the Ni–Al–Cr alloy is attributed to the formation of a Ni3Al-based ordered phase after annealing at ∼650–700 K. The presence of this phase also leads to an apparent negative slope in the standard Hall–Petch relationship.