bluuebunny/crossref_metadata_2025 huggingface dataset:
Process for Buried Metallization in Diamond Film
Authors: Ting Jyh‐Ming , Tang Chi
Published: July 2010

This paper investigates methods of combining chemical vapor deposition diamond growth techniques with a physical vapor deposition technique and an ion‐beam‐enhanced deposition technique, respectively, to produce buried metallization of polycrystalline diamond films. The mechanical and electrical integrity of the insulating and conducting elements following metallization and diamond overgrowth is shown. Both methods are shown to have bonding strength sufficient to withstand tape lift‐off. Diamond overgrowth is also shown, thus enabling buried metallized layers to be created. Electrical resistivity measurements on metallized layers and between metallization separated by diamond films are shown to be sufficient to allow the use of diamond as an insulating interlayer material for multilayer circuit boards.
Fabrication of Silicon Carbide Whisker/Alumina Composite by Thermal‐Gradient Chemical Vapor Infiltration
Authors: Tago Teruoki , Kawase Motoaki , Morita Kenshi , Hashimoto Kenji
Published: July 2010

SiC(w)/Al2O3 composites were made from an AlCl3‐H2‐CO2 mixture by a thermal‐gradient chemical vapor infiltration (CVI) method. Al2O3 was deposited from the reaction of AlCl3 and H2O, which was produced from the oxidation of H2 by CO2. The densification rate was measured at various reactant compositions and total pressures. When the reaction rate or total pressure increased, the rate‐controling step shifted from H2O production to AlCl3 diffusion, which led to premature pore closing. To obtain dense composites in a short infiltration time, the diffusion rate of AlCl3 had to be increased by decreasing the total pressure.
Application of a Two‐Dimensional Computer Simulation to Cake Growth in Slip Casting with Complicated‐Shape Gypsum Molds
Authors: Banno Takumi , Sano Saburo , Oda Kiichi
Published: July 2010

A two‐dimensional computer simulation method, developed by the authors using the method of finite differences, was applied to estimate the cake growth in slip casting of alumina with a triangular gypsum mold and a box‐type gypsum mold with a convex bottom. The cake growth patterns, water penetration patterns, water flow rate distributions, and pressure distributions were simulated in the molds and/or cakes. The simulated cake growth patterns were in good agreement with those observed experimentally in both molds. Moreover, the cake growths could be well understood from the results of the water flow rate distributions in each case. The present method is applicable to cake growth simulation in slip casting with complicated‐shape gypsum molds.
Effect of Polymer Dispersant Structure on Electrosteric Interaction and Dense Alumina Suspension Behavior
Authors: Kamiya Hidehiro , Fukuda Yoshiyuki , Suzuki Yoshio , Tsukada Mayumi , Kakui Toshio , Naito Makio
Published: July 2010

The present paper reports on research on the effect of molecular structure of polymer dispersants on the relationship between the electrosteric interaction of dispersants on solid surfaces and the viscosity of suspensions. Ammonium polyacrylate with different hydrophilic to hydrophobic ratios (m:n) was prepared and added to dense Al2O3 suspensions (40 vol%). The steric interactions and adsorbed structures of dispersants on Al2O3 powders were examined under an atomic force microscope (AFM). An optimum hydrophilic to hydrophobic group ratio, which was obtained from the maximum repulsive force and the minimum viscosity of suspension, was determined at m:n = 3:7. The changing mechanism of the adsorbed structure and the steric interaction of dispersants and the suspension viscosity by the hydrophilic to hydrophobic molecular ratio were discussed by comparing the experimental force curve and DLVO theory.
Bimaterial Composites via Colloidal Rolling Techniques: II, Sintering Behavior and Thermal Stresses
Authors: Menon Mohan , Chen I‐Wei
Published: July 2010

Shrinkage behavior and crack formation during firing have been investigated for Al2O3/Ce‐TZP composites that have been fabricated by colloidal rolling and folding. These composites show improved sinterability and sinter isotropically after repeated rolling. Interface instability in rolling creates corrugated interfaces with large layer waviness; therefore, rolling can substantially alleviate the in‐plane sintering constraints, which leads to improved sinterability. A loss of sintering anisotropy also is observed and is directly correlated to the microstructure instability, which is coincident with the laminate‐cellular transition. Sintering cracks during heating and thermal cracks during cooling both are limited to the thick Ce‐TZP layers in the composites. The critical layer thickness and the normalized crack spacing of the thermal cracks follow the predicted behavior of elasticity theory. Thus, crack‐free, high‐density Al2O3/Ce‐TZP composites with either a laminate or cellular microstructure can be obtained, with a layer thickness of 4‐60 µm, via pressureless sintering.
Influence of Magnesia Addition on the Rheological Properties of Mullite Suspensions
Authors: Galassi Carmen , Roncari Edoardo , Bassarello Carla , Lapasin Romano
Published: July 2010

Water‐based suspensions of mullite that are used to form porous bodies through the impregnation of sponges were investigated. The rheological properties of the suspensions are strongly influenced by the amount of magnesia added, as well as the solid loading and the preparation procedure. Amounts of magnesia higher than 0.15 wt% change both the steady shear behavior from nearly Newtonian to plastic (with an increasing apparent yield stress) and time dependent, as well as the viscoelastic properties (the storage modulus increases more than 5 orders of magnitude). Similar effects are shown for long milling procedures, or solids loadings higher than 25 vol%, while the elastic properties are not strictly related to the total volume fraction. The results of the rheological characterization, under either continuous or dynamic conditions, are discussed in relation to the properties of the structure built up within the suspension. The density of the cast bodies increases with decreasing magnesia content.
Use of a Crack‐Bridging Single‐Fiber Pullout Test to Study Steel Fiber/Cementitious Matrix Composites
Authors: Easley Thomas C. , Faber K. T. , Shah Surendra P.
Published: July 2010

The fracture process of steel fiber/cementitious matrix composites has been studied using a single‐fiber pullout test that permits detailed measurements of the load‐crack opening displacement relationship during fiber debonding and unloading. Using a suitable analytical model, the interfacial fracture energy and interfacial sliding friction have been calculated for composites incorporating steel fibers with cement paste or mortar matrices. Comparison of theoretical debonding curves with the experimental data show that the model accurately represents the fiber debonding process, except for a decrease in interfacial sliding friction due to wear of matrix asperities at the interface. Differences between the calculated interfacial properties of several specimens are associated with changes in the interfacial microstructure.
Influence of Chemical Reactions in Magnesia‐Graphite Refractories: I, Effects on Texture and High‐Temperature Mechanical Properties
Authors: Baudín Carmen , Alvarez Carlos , Moore Robert E.
Published: July 2010

Four formulations of magnesia‐graphite‐aluminum metal (antioxidant) bricks were prepared from the same raw materials, using the standard commercial practices. Chemical analysis and determination of room‐temperature modulus of rupture and Young's modulus, as well as a complete microstructural characterization of the as‐received materials, were performed. For high‐temperature modulus‐of‐rupture and Young's modulus data, test samples of the four brick compositions were heated to 1000°, 1200°, and 1450°C in flowing argon (<1000 ppm oxygen at 1000°C) and then loaded mechanically in flexure. Modulus‐of‐elasticity values ranged from 3.7 to 16.2 GPa and reflected strong effects of aluminum‐metal concentration and treatment temperature. Young's modulus evolution with temperature was determined by the evolution of the microstructure in the bulk of the specimens. Modulus‐of‐rupture values ranged from 6 to 21 MPa, and their evolution with temperature was determined by the evolution of the microstructure in the bulk of the specimens at the lower testing temperatures (T lessthan equal to 1200°C) and by phase assemblages in the surface regions of the specimens‐essentially by the presence of the dense MgO zone‐at 1450°C.
Model for Fatigue Crack Growth in Grain‐Bridging Ceramics
Authors: Chen I‐Wei , Engineer Mehernosh
Published: July 2010

A model for fatigue crack propagation based on sliding wear of bridging grains is analyzed for polycrystalline ceramics. Taking into account damage development and crack tip energy balance, we have obtained rigorous solutions for equilibrium and compatibility equations in the crack wake under monotonic and cyclic loading/unloading conditions. Fatigue mechanics in ceramics is found to be formally similar to elastic‐plastic mechanics of a path‐dependent hardening material, due to the frictional resistance to reverse sliding. It features a load‐displacement hysteresis causing energy dissipation and wear, and a longer cohesive zone required for supporting the same peak load with the wear‐reduced bridging stresses. The unloading crack opening displacement is more strongly dependent on Kmax than on DeltaK; such displacement causes wear on the bridging grains. Meanwhile, incremental crack growth brings in new bridging grains that has a shielding effect on the crack tip stress field; such an effect is strongly dependent on Kmax but independent of DeltaK. At steady state, when shielding accumulation and shielding degradation are balanced, the fatigue crack growth rate has a form da/dN=A(Kmax)b(DeltaK)c, where A, b, and c are material‐dependent parameters. Fatigue is predicted to have a very high b, a modest c, a higher fatigue resistance for tougher ceramics, and a stronger Kmax dependence for less tough ceramics. These predictions are in agreement with experimental observations.
Porous Alumina Coating with Tailored Fracture Resistance for Alumina Composites
Authors: O'Brien Michael J. , Sheldon Brian W.
Published: July 2010

A porous Al2O3 coating for Al2O3 composites was prepared by aerosol‐spray deposition of submicrometer‐sized Al2O3 powder. A model composite specimen was hot‐pressed to change the coating's porosity and, thereby, change the interphase fracture resistance. The mixed‐mode fracture resistance of the interphase ranged from 0.5 to 14.8 J/m2. The interphase fracture was characterized using electron and acoustic microscopy. Finite‐element analysis (FEA) showed that the testing method possessed a short transient behavior and was immune to asymmetrical cracks. This approach provided a fundamental investigation of the relationships among interphase microstructure, processing, and fracture resistance. The results also provided a detailed test of the He‐Hutchinson criterion for crack deflection.
Interfacial Forces in Si3N4‐ and SiC‐Based Systems and Their Influence on the Joining Process
Authors: Esposito Laura , Bellosi Alida , Landi Spartaco
Published: July 2010

High‐temperature interactions between solid ceramic grains and liquid glass result in final microstructures in which the grain‐to‐grain distance is governed by the specific equilibrium among the interfacial forces. Useful information for many practical applications is obtained by treating the system of interest as a high‐temperature colloidal suspension and studying interactions among the constituents. Si3N4 and SiC silicate systems are investigated in the present study as dispersed suspensions, after liquid‐penetration experiments and long oxidation treatment at high temperature. Dispersed systems by Si3N4 or SiC as solid particles and a silicate glass formed as a liquid phase are studied at high temperature. Particle interactions are described in terms of the surface tensions of the solid‐liquid interface (gammasl) of the grain boundary, both with an intergranular phase (gamma*gb) and without (gamma°gb). Agglomerations of a few particles form in both systems as a result of attractive forces; the needlelike shape of ß‐Si3N4 particles partially inhibits their mutual interaction. The specific equilibrium among the interfacial forces also drives microstructural evolution during penetration experiments of liquid silicates in dense Si3N4 and SiC at high temperature. In fact, at the original ceramic‐glass interface, ß‐Si3N4 grains move easily, and grain boundaries thicken; in contrast, a straight line between the ceramic and the glass characterizes the SiC‐silicate interface. When the same dense materials are heat‐treated in air, a glass layer forms on top of them, as a result of Si3N4 and SiC oxidation. The interface between the so‐formed glass and the original ceramic is similar to those found after the penetration experiments. Finally, knowledge of the specific high‐temperature behavior of these systems is used to produce Si3N4‐Si3N4 and SiC‐SiC joints both with and without a glass interlayer. Direct joints with an average strength of 716 MPa (76% of the strength of the as‐sintered material) are obtained.
Hot‐Isostatic‐Press Joining of Cemented Carbides
Authors: Miodownik Mark , Derby Brian
Published: July 2010

Hot isostatic pressing (HIPing) is investigated as a technique for joining the cermet WC‐15% Co to itself. Encapsulation of the specimens prior to HIPing was carried out using steel encapsulation, glass encapsulation, and self‐encapsulation. The bonds were evaluated using a four‐point‐bend method. It is shown that the glass and steel encapsulation methods have a number of inherent problems which make them inappropriate for near net shape processing. In contrast the novel self‐encapsulation method, described for the first time in this communication, is both simple and effective, producing joined material with bulk strength. The concept of self‐encapsulation is potentially widely applicable for joining composite materials.
Effect of Surface‐Active Substances on the Rheological Properties of Silicon Carbide Suspensions in Paraffin
Authors: Lenk Reinhard , Ph. Krivoshchepov Alexander
Published: July 2010

In this paper, the possibility of stabilization of SiC suspensions in paraffin (hot‐molding slips) was investigated from the colloid science point of view. By considering the surface properties of finely dispersed silicon carbide, surface‐active agents (fatty amine and alkylsuccinimide) which are suitable for surface modification by chemical adsorption on SiC were selected. Adsorption of fatty amines and alkylsuccinimide was carried out in model experiments in chloroform. Increasing the length of the carbon–hydrogen chain caused the adsorption to decrease, and the adsorption area of one molecule in the saturated adsorption layer to increase. The stabilizing effect of surface‐active agents resulted in improved flow behavior of hot‐molding slips. The efficiency of surface‐active agents increased with increased adsorption layer thickness. In highly concentrated SiC hot‐molding slips, a combination of alkylsuccinimide and fatty amine proved to be very efficient. This synergistic effect of long‐ and short‐chained surface‐active agents is discussed in terms of an adsorption layer model.
Preparation of Nanosized Hematite Particles by Mechanical Activation of Goethite Samples
Authors: Šubrt Jan , Pérez‐Maqueda Luis A. , Criado Jose M. , Real Concepción , Boháček Jaroslov , Večerníková Eva
Published: July 2010

Nanosized single crystals of hematite with a very narrow particle size distribution were prepared by mechanical activation of two different goethite samples. Both goethite samples transformed completely into hematite after 70 h grinding time. Transmission electron microscopy showed that the final particles were spherical in shape and of ∼17 nm average particle size. This particle size was coincident with that estimated from specific surface measurements, indicating that the hematite samples consisted of nonporous and nonaggregated particles. The crystallite size, calculated from the broadening of the XRD peaks, in the hematite samples indicated that particles consisted of single crystals. No influence of the precursor was observed in the products, so both goethite samples yielded identical rounded single crystals with a narrow particle size distribution.
Evaluation of Damage Evolution in Ceramic‐Matrix Composites Using Thermoelastic Stress Analysis
Authors: Mackin Thomas J. , Roberts Mark C.
Published: July 2010

Thermoelastic stress analysis (TSA) has been used to monitor damage evolution in several composite systems. The method is used to measure full‐field hydrostatic stress maps across the entire visible surface of a sample, to quantify the stress redistribution that is caused by damage and to image the existing damage state in composites. Stress maps and damage images are constructed by measuring the thermoelastic and dissipational thermal signatures during cyclic loading. To explore the general utility of the method, test samples of several ceramic‐matrix and cement‐matrix composites have been fabricated and tested according to a prescribed damage schedule. The model materials have been chosen to illustrate the effect of each of three damage mechanisms: a single crack that is bridged by fibers, multiple matrix cracking, and shear bands. It is shown that the TSA method can be used to quantify the effect of damage and identify the operative damage mechanism. Each mechanism is identified by a characteristic thermal signature, and each is shown to be effective at redistributing stress and diffusing stress concentrations. The proposed experimental method presents a new way to measure the current damage state of a composite material.
Kinetics and Microstructural Evolution of Heterogeneous Transformation of θ‐Alumina to α‐Alumina
Authors: Kao Hung‐Chan , Wei Wen‐Chen
Published: July 2010

Ultrafine (<0.1 μm) high‐purity θ‐Al2O3 powder containing 3–17.5 mol%α‐Al2O3 seeds was used to investigate the kinetics and microstructural evolution of the θ‐Al2O3 to α‐Al2O3 transformation. The transformation and densification of the powder that occurred in sequence from 960° to 1100°C were characterized by quantitative X‐ray diffractometry, dilatometry, mercury intrusion porosimetry, and transmission and scanning electron microscopy. The relative bulk density and the fraction of α phase increased with annealing temperature and holding time, but the crystal size of the α phase remained ∼50 nm in all cases at the transformation stage (≤1020°C). The activation energy and the time exponent of the θ to α transformation were 650 ± 50 kJ/mol and 1.5, respectively. The results implied the transformation occurred at the interface via structure rearrangement caused by the diffusion of oxygen ions in the Al2O3 lattice. A completely transformed α matrix of uniform porosity was the result of appropriate annealing processes (1020°C for 10 h) that considerably enhanced densification and reduced grain growth in the sintering stage. The Al2O3 sample sintered at 1490°C for 1 h had a density of 99.4% of the theoretical density and average grain size of 1.67 μm.
Method to Estimate Crack‐Tip Toughness from Bending Tests on Prenotched Bars
Authors: Fett Theo , Munz Dietrich , Thun Gerhard
Published: July 2010

A strain‐gauge procedure that enables determination of the crack‐tip toughness (KI0) from bending‐strength tests is described. The procedure is applied to coarse‐grained alumina and yields an average KI0 value of 2.51 MPa·m1/2, with a standard deviation of 0.16 MPa·m1/2.
Recrystallization of Oxygen Ion Implanted Ba0.7Sr0.3TiO3 Thin Films
Authors: Liedtke R. , Hoffmann S. , Waser R.
Published: July 2010

The crystallization behavior of chemical‐solution‐deposited and amorphous Ba0.7Sr0.3TiO3 (BST) thin films was analyzed with respect to the evolution of the structural and dielectric properties of the films as a function of the annealing temperature. The amorphous films were produced by oxygen ion implantation into crystalline BST thin films. In the amorphous thin films, the crystallization to the perovskite phase occurred at T= 550°C, whereas the as‐deposited CSD films showed the first crystalline XRD‐reflex only after annealing at T= 650°C. Here a carbon‐rich intermediate phase delayed the crystallization process to higher temperatures.
Processing and Mechanical Behavior of CrN/ZrO2(2Y) Composites
Authors: Takano Yoshihiko , Hachiya† Masahiro , Yoshinaka† Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2010

CrN powder consisting of granular particles of ∼3 μm has been prepared by self‐propagating high‐temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2(2Y) composites in the CrN‐rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness (KIC) of 3.3 MPa ·m1/2 and a bending strength (σb) of 400 MPa. In the latter materials almost all of the ZrO2(2Y) grains (0.36–0.41 μm) are located in the grain boundaries of CrN (∼4.6 μm). The values of KIC (6.1 MPa · m1/2) and σb (1070 MPa) are obtained in the composites containing 50 vol% ZrO2(2Y).
Determination of the Oxygen Deficiency in Vacuum‐Hot‐Pressed Ferroelectric Ceramics Using a Thermogravimetric Technique
Authors: Tan Qi , Li Jianxing
Published: July 2010

An attempt to measure the oxygen deficiency in vacuum‐hot‐pressed ferroelectric target materials was made, using a thermogravimetric method. The approach was intended to measure the relative mass increase of oxygen‐deficient sheet samples, with respect to an oxidized reference that was annealed in air. A saturation of mass change was achieved, which indicated a saturated oxidation state and provided a basis for further calculation of the oxygen deficiency in the samples. Results were obtained for barium strontium titanate and lead lanthanum zirconate titanate compositions, which shows the feasibility of applying the thermogravimetric method to ferroelectric materials.
X‐ray Computed Tomography and Mercury Porosimetry for Evaluation of Density Evolution and Porosity Distribution
Authors: Lu Peizhen , Lannutti John J. , Klobes Peter , Meyer Klaus
Published: July 2010

X‐ray computed tomography (CT) and mercury porosimetry were combined to connect density gradients and the distribution of open porosity in a sintered compact. CT clearly showed that open porosity follows the initial distribution of low‐density zones. Mercury porosimetry detected three distinct levels of porosity. Microstructural examination correlated the porosity level with the coordination of (i) two to three or (ii) multiple grains around pores. This combination of techniques provides a novel tool for the study of pore and density‐gradient evolution during sintering.
Rapid Hardening of Cement by the Addition of a Mechanically Activated Al(OH)3–Ca(OH)2 Mixture
Authors: Kitamura Makoto , Kamitani Masataka , Senna Mamoru
Published: July 2010

Rapid hardening of cement was achieved in the present study by adding a mechanically activated Al(OH)3–Ca(OH)2 mixture to the starting cement paste. Among the dominant parameters for hardening were the mechanical treatment time for the Al(OH)3 powder and the Al(OH)3/Ca(OH)2 ratio. The hardening mechanisms are discussed here in terms of the ionic concentration of the solution and the hydration products created when the Al(OH)3–Ca(OH)2 mixture was added to water. Mechanical activation of the Al(OH)3 powder accelerated dissolution into an aqueous alkaline solution and induced the formation of calcium aluminate hydration products. Those hydration products increased the compressive strength of the cement paste at a very early stage of hardening.
Absorption and Emission Spectral Properties of Pr3+, Nd3+, and Eu3+ Ions in Heavy‐Metal Oxide Glasses
Authors: Nachimuthu Ponnusamy , Vithal Muga , Jagannathan Ranga
Published: July 2010

The optical properties of the heavy‐metal oxide glasses 70PbO.30TiO2,70PbO.30CdO, and 70PbO.30TeO2doped with Pr3+,Nd3+,and Eu3+ions have been investigated. The transition energies of the absorption spectra of Pr3+and Nd3+ions are analyzed for the Racah parameters, configuration interaction terms, and spin‐orbit coupling. The absorption spectral intensities of Pr3+and Nd3+ions are analyzed for the Judd–Ofelt parameters. The Judd–Ofelt parameter, Ω2,suggests strong covalency for the Ln–O bond in these oxide glass matrices for both Pr3+and Nd3+ions and follow the order 70PbO.30TiO2> 70PbO.30CdO > 70PbO.30TeO2.This trend has been correlated to that of oxide ion polarizabilities, which follow the same order. The radiative parameters, viz., transition probability (A), branching ratios (βR), and stimulated emission cross sections (σp), for laser transitions have been obtained. The high Ω2for Pr3+leads to significantly larger σpfor the3P0→3F2transition in these glass matrices compared to those in fluoride and oxyfluoride glasses. The room‐temperature emission 1D2→3H4transition of Pr3+is much larger in 70PbO.30TiO2than in the other two glass systems. The emission spectra of Pr3+show temperature effects due to the Boltzmann population. The red‐to‐orange intensity ratios in the emission spectra of Eu3+also support strong covalency of the Ln–O bond. The phonon side‐band spectra (PSB) of Eu3+are correlated with the infrared spectra. The electron–phonon coupling strengths and phonon energies have been obtained in all the cases.
Stabilization of Tetragonal ZrO2 in ZrO2–SiO2 Binary Oxides
Authors: del Monte Francisco , Larsen Willa , Mackenzie John D.
Published: July 2010

Gel‐glasses of various compositions in the xZrO2.(10 –x)SiO2system were fabricated by the sol–gel process. Precipitation due to the different reactivities between tetraethyl orthosilicate (TEOS) and zirconium(IV) n‐propoxide has been eliminated through the use of 2‐methoxyethanol as a chelating agent. Thermal treatment of these gels produced crystalline ZrO2particles. While monoclinic is the stable crystalline phase of zirconia at low temperatures, the metastable tetragonal phase is usually the first crystalline phase formed on heat treatment. However, stability of the tetragonal phase is low, and it transforms to the monoclinic phase on further heat treatment. In this study, it has been found that the transformation temperature increases as the SiO2content in the ZrO2–SiO2 binary oxide increases. The most significant results were from samples containing only 2 mol% SiO2, where the metastable tetragonal phase formed at low temperatures and remained stable over a broad temperature range. X‐ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to elucidate the structure of these binary oxides as a function of temperature.
Sintering and Phase Transformation in B2O3/P2O5‐Doped Li2O.Al2O3.4SiO2Glass‐Ceramics
Authors: Shyu Jiin‐Jyh , Chiang Ming‐Tsung
Published: July 2010

The effects of the additives B2O3and P2O5on the sintering and phase transformation in Li2O.Al2O3.4SiO2glass‐ceramics were investigated. The addition of B2O3 enhanced the crystallization of the parent glasses, whereas the addition of P2O5 delayed it; however, both additives improved the sinterability. Glass‐ceramics that contained appropriate amounts of B2O3 and P2O5 showed good sinterability at temperatures as low as 750°C. The phase transformation of metastable high‐quartz solid solution (h‐Q ss) to stable β‐spodumene (β‐S) occurred when the crystallization of parent glass to h‐Q ss was almost complete. Both B2O3 and P2O5 affected the relative amount of β‐S that transformed to h‐Q ss. A glass that contained a larger amount of B2O3 revealed an increase in the relative ratio of β‐S to h‐Q ss with increasing temperature, which was consistent with the generally known phase development in Li2O–Al2O3–SiO2 (LAS) glass‐ceramics. A glass that contained a larger amount of P2O5 showed an anomalous temperature dependence of the transformation of metastable h‐Q ss to stable β‐S; this dependence had not been observed in other LAS glass‐ceramics. A possible explanation for this anomaly is that h‐Q ss (and β‐S) that has been formed at different temperatures may have different phase compositions.
Very Rapid Densification of Nanometer Silicon Carbide Powder by Pulse Electric Current Sintering
Authors: Zhou You , Hirao Kiyoshi , Toriyama Motohiro , Tanaka Hidehiko
Published: July 2010

Rapid densification of a nanometer SiC powder doped with 2.04 wt% Al4C3 and 0.4 wt% B4C was conducted by using a nonconventional sintering technique called pulse electric current sintering (PECS). In all experiments, the sintering temperature and applied pressure were kept to be 1600oC and 47 MPa, respectively, while heating rates varied between 100oC/min and 400oC/min and the holding time was either 2 or 5 min. All of the specimens which were PECS‐sintered under various conditions reached near‐theoretical density. The microstructures of the rapidly densified SiC ceramics consisted of large elongated grains, and the grain size increased with the increase of heating rate. Polytype transformation of SiC occurred during the PECS process, where faster heating favored the formation of 6H polytype while slower heating favored 4H polytype.
Weakly Flocculated Aqueous Alumina Suspensions Prepared by the Addition of Mg(II) Ions
Authors: Dakskobler Aleš , Kosma[c‐breve] Tomaž
Published: July 2010

Well‐dispersed aqueous alumina suspensions were prepared at an inherent pH via the addition of an anionic dispersant. With the addition of an appropriate amount of magnesium acetate to such a suspension, the surface charge of the particles was neutralized, which was reflected in the destabilization of the slurry. Because of the formation of coordinative bonds between the Mg ion and the two dissociated carboxylic groups of the dispersant, a thin neutral layer was formed on the surface of the particles, which established a nontouching particle network and resulted in a weakly flocculated suspension.
Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: I, Surface Chemistry of the Powder
Authors: Wang Liwu , Sigmund Wolfgang , Aldinger Fritz
Published: July 2010

To develop novel dispersants for submicrometer‐sized Si3N4 powder, the surface chemistry of a powder has been investigated using thermodesorption, carrier‐gas heat extraction, X‐ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and zeta potential measurements. This study indicates that the powder surface is composed mainly of silanol groups and exhibits acidic behavior. Furthermore, the interaction affinity of various surface probe molecules with the powder surface has been studied using adsorption isotherms. The detailed description of the surface chemistry can be used as a guide for designing efficient dispersants, as will be presented in part II.
Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the Powder
Authors: Wang Liwu , Sigmund Wolfgang , Aldinger Fritz
Published: July 2010

A novel dispersant—O‐(2‐aminopropyl)‐O′‐(2‐methoxyethyl)‐polypropylene glycol (AMPG)—was developed to disperse submicrometer‐sized Si3N4 powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of >0.50) and colloidally stable nonaqueous Si3N4 suspensions can be realized using AMPG.
Synthesis In Situ, Characterization, and Photostability of Europium β‐Diketone Chelates in Organically Modified Silicates (ORMOSILs)
Authors: Qian Guodong , Wang Minquan
Published: July 2010

Europium β‐diketonates have desirable optical properties, and transparent inorganic materials that have been doped with these chelates seem to be promising for potential applications in luminescence‐display devices, integrated optical device sources, and new visible lasers. However, these chelates may be decomposed or not dissolved in sol—gel precursor solutions and, thus, cannot be doped in gel glasses that have been prepared via traditional sol—gel processing. An in situ synthesis technique has been used for the first time to synthesize five binary and ternary coordination compounds of europium β‐diketonates in transparent organically modified silicates (ORMOSILs) during heat treatment or during the process of sol‐to‐monolithic ORMOSIL conversion. ORMOSILs that have been doped with in situ europium β‐diketonates exhibit rather‐high fluorescence intensity and good monochromati‐city. These materials result in enhanced red‐light emission under ultraviolet excitation. The chelates that have been synthesized in situ in the ORMOSILs reveal better photostability, in comparison to that of the pure chelates that have been dissolved in ethanol solutions.
Optical Amplification at 1.3 μm in a Praseodymium‐Doped Sulfide‐Glass Fiber
Authors: Tawarayama Hiromasa , Ishikawa Etsuko , Yamanaka Kenji , Itoh Katsuhisa , Okada Keiko , Aoki Hiroshi , Yanagita Hiroaki , Matsuoka Yoshihiko , Toratani Hisayoshi
Published: July 2010

Praseodymium‐doped glasses were prepared in the Ga‐Na‐S (GNS) system and their optical properties were studied. A single‐mode fiber with an attenuation loss of 1.2 dB/m at a wavelength of 1.31 μm was fabricated using an extrusion method, and the amplification characteristics were measured in the bidirectional pumping configuration. We demonstrated a gain coefficient of 0.81 dB/mW at a wavelength of 1.34 μm, which is the highest we have ever reported, and achieved a net gain of 32 dB for a pump power of 90 mW. Highly efficient optical amplification at a wavelength of 1.3 μm was demonstrated in the praseodymium‐doped GNS fiber.
Alternating‐Current Electrical Properties of CaMnO3 below the Néel Temperature
Authors: Jung Woo‐Hwan , Sohn Jeong‐Ho , Lee Joon‐Hyung , Sohn Joon‐Ho , Park Myung‐Sik , Cho Sang‐Hee
Published: July 2010

The alternating‐current electrical properties of polycrystalline CaMnO3 were investigated by alternating current complex‐impedance analysis, and the dielectric properties were analyzed over the temperature and frequency ranges of 10 to 130 K and 20 Hz to 1 MHz, respectively. Direct‐current conductivity and the Seebeck coefficient as a function of temperature also were analyzed. Below 120 K, a Debye‐type dielectric relaxation peak was observed. Experimental results implied that the number of charge carriers, which were generated by Mn3+, were not sufficient to stabilize small polarons, although it induced lattice distortion by the Jahn—Teller effect. Therefore, the thermal motion of Mn3+ between potential minimums produced by lattice distortion in the orthorhombic structure were believed to be the source of dielectric relaxation. The temperature dependence of conductivity of the grain interior (σgi) below 120 K was believed to be due to variable range‐hopping conduction, where σgi∼ exp(−T−1/4).
Fracture Behavior of Alumina/Monazite Multilayer Laminates
Authors: Mawdsley Jennifer R. , Kovar Desiderio , Halloran John W.
Published: July 2010

Monazite (LaPO4) has been proposed as an interphase to promote debonding between the reinforcement and the matrix during the fracture of oxide‐based composites. The correlation between fracture behavior and micromechanical properties in model alumina/monazite (Al2O3/LaPO4) multilayer laminates has been investigated in this study. The delamination fracture energy (Γi) was dependent on crack length, which is consistent with previous results; the initial value of Γi was ∼10 J/m2. The interfacial frictional sliding resistance increased as the normal stress on the interface increased. Using a Coulombic friction model, the coefficient of static friction between the Al2O3 and LaPO4 layers was determined to be 0.63. The influence of Γi and flaw size in the Al2O3 layers on fracture path has been predicted, using an existing model, and confirmed experimentally. The results indicate that, in addition to satisfying energy‐based fracture criteria, several other factors affect whether LaPO4 is a suitable interphase for oxide composites.
Inverse Problem for Composites with Imperfect Interface: Determination of Interfacial Thermal Resistance, Thermal Conductivity of Constituents, and Microstructural Parameters
Authors: Nan Ce‐Wen , Li Xiao‐Ping , Birringer R.
Published: July 2010

An explicit method is introduced to solve inverse problems for composites with imperfect interfaces. We apply the method to determine the thermal conductivity of constituents and the interfacial thermal resistance in SiC‐particulate‐reinforced aluminum‐matrix composites and to estimate the whisker thermal conductivity, the interfacial thermal resistance, and the whisker alignment distribution in two types of SiC‐whisker‐reinforced lithium aluminosilicate glass‐ceramic composites from their measured effective thermal conductivity reported in the literature. Certain bounds for these three properties of both SiC‐whisker‐reinforced glass‐ceramic composites are obtained, and reasonable estimates for their exact values from room temperature to 500°C are made. The inverse problem is quite sensitive to noise in the measurements. We also comment on existing estimates.
Physical Properties of Chalcogenide and Chalcohalide Glasses
Authors: Nguyen Vinh Q. , Sanghera Jas S. , Aggarwal Ishwar D. , Lloyd Isabel K.
Published: July 2010

The physical properties of glasses in the Ge30As10Se(60—x)Tex system with x= 25, 28, 30, and 35 at.% Te, the Ge30As10Se30Te(30—y)Iy system with y= 5, 10, 20, and 30 at.% I, the Ge30As10Se35Te(25—z)Iz system with z= 2, 6, 10, and 20 at.% I, and the [Ge30As10Se30Te30](100—w)Iw system with w= 0, 5, 10, and 20 at.% I have been investigated. The changes in the glass transition temperature, density, coefficient of thermal expansion, hardness, and viscosity are attributed to the delocalized metallic bonding character of Te in the substitution of Te for Se in the Ge‐As‐Se‐Te glass system and the network‐terminating role of iodine in the substitution of I for Te in the Ge‐As‐Se‐Te‐I glass system, respectively.
Thermodynamic Solubility Constant of Ca(OH)2 in Simulated Radioactive Sulfate Liquid Waste
Authors: Guerrero Ana , Goñi Sara , Hernández María‐Soledad
Published: July 2010

The thermodynamic solubility product constant (Ksp) of Ca(OH)2 in simulated radioactive sulfate liquid waste was experimentally determined at temperatures of 25° and 40°C. Synthetic solutions were prepared with pH ranging from 12.6 to >14 and ionic strength ranging from 0.25M to 3.7M. All the solutions were saturated in CaO and contained Na2SO4 to simulate the salts accompanying radioactive liquid waste. The Bromley model was applied to estimate the global ionic activity coefficients, and the Ksp value was compared with those found in the literature. The stability ranges of the different compounds formed as a function of pH were determined by X‐ray diffractometry analysis, and their quantification was conducted by thermal analysis.
Low‐Temperature Fabrication of Transparent Yttrium Aluminum Garnet (YAG) Ceramics without Additives
Authors: Li Ji‐Guang , Ikegami Takayasu , Lee Jong‐Heun , Mori Toshiyuki
Published: July 2010

A carbonate precursor of yttrium aluminum garnet (YAG) with an approximate composition of NH4AlY0.6(CO3)1.9(OH)2·0.9H2O was synthesized via a coprecipitation method from a mixed solution of ammonium aluminum sulfate and yttrium nitrate, using ammonium hydrogen carbonate as the precipitant. The precursor precipitate was characterized using chemical analysis, differential thermal analysis/thermogravimetry, X‐ray diffractometry, and scanning electron microscopy. The sinterability of the YAG powders was evaluated by sintering at a constant rate of heating in air and vacuum sintering. The results showed that the precursor completely transforms to YAG at ∼1000°C via the formation of a yttrium aluminate perovskite (YAP) phase. YAG powders obtained by calcining the precursor at temperatures of ≤1200°C were highly sinterable and could be densified to transparency under vacuum at 1700°C in 1 h without additives.
Preparation of ZnGa2O4 Spinel Fine Particles by the Hydrothermal Method
Authors: Hirano Masanori , Imai Mikimasa , Inagaki Michio
Published: July 2010

ZnGa2O4 fine particles with a single phase of spinel were synthesized from a mixed solution of gallium sulfate and zinc sulfate in the presence of aqueous ammonia under hydrothermal conditions above 180°C. The effects of treatment temperature and ZnO/Ga2O3 molar ratio in the starting solution on the crystallite size, morphology, lattice parameter, and chemical composition of the ZnGa2O4 spinel particles were examined. Spinel with different morphologies, cubic nanoparticles, and elongated rodlike particles were thought to be formed based on the structure of amorphous gallium hydroxide and needlelike GaO(OH) particles, respectively. By treatment at a higher temperature, these particles with nonstoichiometric composition grew large and thick, and their composition approached ZnO/Ga2O3= 1. With an increase in the starting ZnO/Ga2O3 molar ratio, the lattice parameter of the synthesized ZnGa2O4 spinel approached the reported value for the stoichiometric composition and reached a= 0.8335 nm at ZnO/Ga2O3= 1.95 by treatment at 240°C for 50 h.
Effects of M3+ Ions on the Conductivity of Glasses and Glass‐Ceramics in the System Li2O—M2O3—GeO2—P2O5 (M = Al, Ga, Y, Dy, Gd, and La)
Authors: Fu Jie
Published: July 2010

Glasses with compositions Li1.2M0.2Ge1.8(PO4)3 (M = Al, Ga, Y, Gd, Dy, and La) were prepared and converted to glass‐ceramics by heat treatment. The effects of the M3+ ions on the conductivity of the glasses and glass‐ceramics were studied. The main phase present in the glass‐ceramics was the conductive phase LiGe2(PO4)3. Al3+ and Ga3+ ions entered the LiGe2(PO4)3 structure by replacing Ge4+ ions, but lanthanide ions did not. The glass‐ceramics exhibited much higher conductivity than the glasses. With increased ionic radius of the M3+ ions, the conductivity remained almost unchanged at ∼3 × 10−12 S/cm for the glasses, but it decreased from 1.5 × 10−5 to 8 × 10−9 S/cm for the glass‐ceramics at room temperature. The higher conductivity for Al3+‐ and Ga3+‐containing glass‐ceramics was suggested to result from the substitutions of Al3+ and Ga3+ ions for Ge4+ ions in the LiGe2(PO4)3 structure.
Single‐Step Dip Coating of Crack‐Free BaTiO3 Films >1 μm Thick: Effect of Poly(vinylpyrrolidone) on Critical Thickness
Authors: Kozuka Hiromitsu , Kajimura Masahiro
Published: July 2010

BaTiO3 coating films were prepared from Ba(CH3COO)2–Ti(OC3H7i)4–H2O–CH3COOH–C3H7iOH solutions containing poly(vinylpyrrolidone) (PVP) via single‐step, nonrepetitive dip coating. The critical thickness—i.e., the maximum film thickness achieved without crack formation via nonrepetitive dip coating—was successfully increased by incorporation of PVP in the precursor solution. Relatively dense, crack‐free BaTiO3 films >1 μm in thickness were achieved via single‐step deposition using a solution containing PVP of average molecular weight of 630 000. Incorporation of an excess amount of PVP, however, led to a decrease in the critical thickness. Higher‐molecular‐weight PVP was more effective in increasing the critical thickness, whereas N‐vinyl‐2‐pyrrolidone monomers did not affect the critical thickness. Stepwise heating of the gel films resulted in increased optical transmittance of the films, accompanied by film densification.
Synthesis of Titanate Derivatives Using Ion‐Exchange Reaction
Authors: Lee Chul‐Tae , Um Myeong‐Heon , Kumazawa Hidehiro
Published: July 2010

Two types of titanate derivatives, layered hydrous titanium dioxide (H2Ti4O9·nH2O) and potassium octatitanate (K2Ti8O17) with a tunnellike structure, were synthesized using an ion‐exchange reaction. Fibrous potassium tetratitanate (K2Ti4O9·nH2O) was prepared by calcination of a mixture of K2CO3 and TiO2 with a molar ratio of 2.8 at 1050°C for 3 h, followed by boiling‐water treatment of the calcined products for 10 h. The material then was transformed to layered H2Ti4O9·nH2O through an exchange of K+ ions with H+ ions using HCl. K2Ti8O17 was formed by a thermal treatment of KHTi4O9·nH2O. Pure KHTi4O9·nH2O phase was effectively produced by a treatment of K2Ti4O9 with 0.005M HCl solution for 30 min. Thermal treatment at 250°–500°C for 3 h resulted in formation of only K2Ti8O17.
Enhanced Magnetization of 3 mol% Yttria‐Doped Zirconia/Barium Hexaferrite by Post‐Plastic Deformation
Authors: Suzuki Yoshikazu , Awano Masanobu , Kondo Naoki , Ohji Tatsuki
Published: July 2010

A 3‐mol%‐Y2O3‐doped tetragonal‐ZrO2 polycrystal/BaFe12O19 composite was fabricated by powder metallurgical processes, and its mechanical and magnetic properties were evaluated. Post‐plastic deformation (i.e., hot‐forging) on the composite improved its magnetic properties—that is, saturation magnetization and coercivity—probably because of the alignment of the hexaferrite platelet particles. Post‐plastic deformation may represent a new process to complement conventional slurry‐pressing under a magnetic field, for obtaining good magnetic properties in a magnetic‐particle‐dispersed composite.
Aluminum Nitride Whisker Formation during Combustion Synthesis
Authors: Lee Kyung‐Jae , Ahn Do‐Hwan , Kim Yong‐Seog
Published: July 2010

In this study, the microstructural development of AlN during combustion synthesis (CS) in a nitrogen atmosphere was investigated. CS using an aluminum–50 wt% AlN–3 wt% MgCl2 powder compact yielded a mixture of AlN whiskers and powder. The microstructural development during the combustion reaction was studied by heating the compact to various temperatures. Based on the experimental results, the formation mechanisms of the AlN with a whisker morphology were discussed.
Equilibrium Point Defect and Electronic Carrier Distributions near Interfaces in Acceptor‐Doped Strontium Titanate
Authors: McIntyre Paul C.
Published: July 2010

A mathematical model based on Frenkel's theory for charged defect segregation at interfaces is used to calculate the equilibrium grain boundary depletion layer widths and conductivity profiles in acceptor‐doped SrTiO3 ceramics. The calculations examine the effect of oxygen vacancy equilibration during annealing at moderate temperatures (∼1000 K) on the development of interfacial charge that influences grain boundary electrical properties at lower temperatures. Good agreement is demonstrated between the model predictions and experimental results reported in the literature.
Effect of the Interfacial Transition Zone on the Conductivity of Portland Cement Mortars
Authors: Shane John D. , Mason Thomas O. , Jennings Hamlin M. , Garboczi Edward J. , Bentz Dale P.
Published: July 2010

The electrical conductivity of portland cement mortars was determined experimentally as a function of the volume fraction of sand and the degree of hydration. The results were analyzed using theoretical models that represent the mortars as three‐phase, interactive composites. The three phases are the matrix paste, the aggregate, and the thin interfacial transition zone between the two. The microstructure and properties of the conductive phases (the transition zone and the matrix paste) were determined by a micrometer‐scale microstructural model, and were used in conjunction with random‐walk algorithms and differential‐effective medium theory to determine the overall mortar conductivities. The presence of the transition zone was not found to significantly affect the global electrical conductivity of the mortar. However, there were significant differences in conductivity between the transition zone and matrix pastes when examined on a local level. These differences were found to vary with hydration and were most significant when the degree of hydration was between 0.5 and 0.8.