bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Pyrochlore‐Free 0.9Pb(Mg1/3Nb2/3)O3‐0.1PbTiO3 Ceramics via a Soft Mechanochemical Route
Authors: Baek Jong‐Gab , Isobe Tetsuhiko , Senna Mamoru
Published: July 2010

Single‐phase perovskite 0.9Pb(Mg1/3Nb2/3)O3‐0.1PbTiO3 (0.9PMN–0.1 PT) from a stoichiometric mixture of starting materials was synthesized by applying a mechanochemical technique to the stage of a precursor. A stoichiometric mixture of PbO, TiO2, Mg(OH)2, and Nb2O5 was milled for 60 min and heated at temperatures as low as 850°C for 4 h to obtain a single phase. The maximum dielectric constant of the samples from the milled mixture increased as the sintering temperature increased, with the remarkable grain growth, and attained 24600 at 1200°C. In contrast, poor densification and coexistence of the pyrochlore phase were observed on the samples from the nonmilled mixture. Further observation suggested that the pyrochlore phase concentrated near the surface during sintering and then migrated into the PbZrO3 packing powder, leading to a pyrochlore–free phase at 1250°C. The dielectric constant of the latter ceramics was explained by the series mixing rule for the dielectric constant of a diphasic solid.
Phase Diagram and Microstructure in the ZnO–Pr2O3 System
Authors: Chun Sung‐Yong , Wakiya Naoki , Funakubo Hiroshi , Shinozaki Kazuo , Mizutani Nobuyasu
Published: July 2010

The phase diagram of the ZnO–Pr2O3 system with PrO1.83 contents from 0.5 to 98 mol% was studied via differential thermal analysis (DTA). The system ZnOPr2O3 showed a simple eutectic type of phase diagram with no solid solutions and no other compounds. The eutectic temperature was determined to be 1382 ± 5°C. The liquidus line near the eutectic point was determined by a quenching method.
Gel Precursor to Silicon Oxycarbide Glasses with Ultrahigh Ceramic Yield
Authors: Sorar Gian Domenico , Campostrini Renzo , Maurina Stefano , Babonneau Florence
Published: July 2010

This paper reports on the synthesis and the pyrolysis transformation of a sol–gel precursor to an oxycarbide glass with an extremely high ceramic yield (up to 97 wt%). This unusually high ceramic yield is achieved by adding a small amount of boron alkoxide to a precursor gel containing Si—H and Si—CH3 functionalities. The role of boron in the pyrolysis process is investigated using various spectroscopic techniques and by analyzing the pyrolysis gases with a mass spectrometer. The experimental results suggest a catalytic effect of the boron atom in promoting a partial oxidation of the Si—H bonds to Si—O bonds, with a corresponding reduction of the weight losses that are associated with the evolution of silanes during pyrolysis. Chemical analysis and XRD investigation indicate that the presence of boron does not modify the formation of the expected oxycarbide network.
Effect of Weight Loss on Liquid‐Phase‐Sintered Silicon Carbide
Authors: Grande Tor , Sommerset Hkon , Hagen Eirik , Wiik Kjell , Einarsrud Mari‐Ann
Published: July 2010

The evaporation of silicon carbide (SiC) ceramics during sintering has been studied by thermogravimetry in a graphite furnace filled with argon. The SiC powder compacts contained 7.5 wt% eutectic composition of Y2O3–Al2O3 to promote liquid‐phase sintering. A weight loss of 1–11 wt% was observed during sintering, depending on the sintering temperature and sintering time. The weight loss severely influenced the final density and the microstructure of the SiC ceramics. Particularly, the oxide sintering aids, which were homogeneously distributed in the green ceramics, were observed to segregate and form particular patterns that were dependent on the temperature, sintering time, and the total weight loss. Possible heterogeneous reactions evolving volatile species have been discussed in relation to the experimental observations.
Dedensification and Anomalous Grain Growth during Sintering of Undoped Barium Titanate
Authors: Demartin Marlyse , Hérard Claude , Carry Claude , Lemaître Jacques
Published: July 2010

Dedensification (up to 10% of the theoretical density in some instances) occurs at temperatures of .1320°C during the sintering of commercial undoped BaTiO3 powders. The expansion of the rigid, interconnected network of large, rounded grains that grow by the Ostwald ripening effect can explain the dedensification that is observed. The isotropic anomalous grain growth results from the appearance of a liquid phase at } 1320°C and induces tensile stresses on the residual porous fine‐grained matrix. No dedensification was observed at temperatures of, 1320°C, despite anisotropic anomalous grain growth.
Dielectric Measurements on High‐Q Ceramics in the Microwave Region
Authors: Dube Denesh C. , Zurmuhlen Rudolf , Bell Andrew , Setter Nava , Wersing Wolfram
Published: July 2010

The postresonator method proposed by Hakki and Coleman for the measurement of dielectric properties of solids in the microwave region is reexamined. Based on the experiments performed around 10 GHz, the limitations of the method in loss determination for materials with tan δ, 5 × 10−4 are outlined. Alternative techniques for studying high‐Q materials are described. Loss measurements performed on well‐prepared ceramics have been used to draw comparisons among these techniques. Some of the experimental findings are new and are reported for the first time.
Fabrication and Microstructures of MoSi2 Reinforced–Si3N4 Matrix Composites
Authors: Petrovic John J. , Pena Maria I. , Kung H. Harriett
Published: July 2010

Details of the fabrication and microstructures of hot‐pressed MoSi2 reinforced–Si3N4 matrix composites were investigated as a function of MoSi2 phase size and volume fraction, and amount of MgO densification aid. No reactions were observed between MoSi2 and Si3N4 at the fabrication temperature of 1750°C. Composite microstructures varied from particle–matrix to cermet morphologies with increasing MoSi2 phase content. The MgO densification aid was present only in the Si3N4 phase. An amorphous glassy phase was observed at the MoSi2–Si3N4 phase boundaries, the extent of which decreased with decreased MgO level. No general microcracking was observed in the MoSi2–Si3N4 composites, despite the presence of a substantial thermal expansion mismatch between the MoSi2 and Si3N4 phases. The critical MoSi2 particle diameter for microcracking was calculated to be 3 μm. MoSi2 particles as large as 20 μm resulted in no composite microcracking; this indicated that significant stress relief occurred in these composites, probably because of plastic deformation of the MoSi2 phase.
Reduction and Sintering of a Nickel–Dispersed‐Alumina Composite and Its Properties
Authors: Sekino Tohru , Nakajima Toshio , Ueda Satoru , Niihara Koichi
Published: July 2010

High‐density nickel–dispersed‐alumina (Al2O3/nickel) composites with superior mechanical properties were obtained by the hydrogen reduction and the hot pressing of alumina–nickel oxide (Al2O3/NiO) mixed powders. The mixtures were prepared by using NiO or nickel nitrate (Ni(NO3)2·nH2O) as a dispersion source of nickel metal. Microstructural investigations of the composite fabricated using nitrate powder revealed that fine nickel particles, } 100 nm in diameter, dispersed homogeneously at the matrix grain boundaries, forming the intergranular nanocomposite. High strength (.1 GPa) and high‐temperature hardness were registered for the composite that contained a small amount of nickel dispersion. The ferromagnetic properties of nickel, such as high coercive force, were observed, because of the fine magnetic dispersions, which indicates a functional value of structural composites.
Fundamental Material Aspects Underlying the Preparation of High‐Temperature Superconducting (Bi,Pb)2+xSr2Ca2Cu3O10+d Ceramics
Authors: Majewski Peter J. , Kaesche Stefanie , Aldinger Fritz
Published: July 2010

Phase equilibria of the quasi‐quinary system Bi3O3‐PbO‐SrO‐CaO‐CuO were studied between 650° and 900°C in air with emphasis on the high‐temperature superconducting phase (Bi,Pb)2+xSr2Ca2Cu3O10+d (2223). The 2223 phase lies in equilibrium with a number of nonsuperconducting phases and also with the superconducting phase (Bi,Pb)2Sr2CaCu2O8+d (2212). The single‐phase region was found to be very limited. The Pb solubility of the 2223 phase is strongly temperature dependent. The phase relations are very sensitive to variations of the cation concentration and temperature. This effect significantly influences the preparation of 2223 ceramics.
Grain Boundary Film Thicknesses in Superplastically Deformed Silicon Nitride
Authors: Wang Chong‐Min , Mitomo Mamoru , Nishimura Toshiyuki , Bando Yoshio
Published: July 2010

The thickness of intergranular films in polycrystalline β‐Si3N4 ceramics, both before and after superplastic deformation, has been systematically investigated using high‐resolution transmission electron microscopy. In characterizing the film thickness, care was taken to correlate the grain boundary orientation with the direction of the compressive stress applied during the hot‐pressing and the superplastic deformation. The film thickness shows a dependence on the intersection angle between the grain boundary and the applied force direction, typically ranging from around a characteristic value for most of the boundaries to zero for a boundary which has an overall short length and is perpendicular to the applied force direction. The film thicknesses in the deformed material, as compared with those before deformation, are marked by a wider distribution and an increased fraction of boundaries free of films, unequivocally demonstrating that during the superplastic deformation the liquid phase is redistributed within short ranges, a process governed by the local stress level as well as kinetic factors. Possible consequences of the liquid‐phase redistribution on the deformation behavior are also discussed.
Phase Equilibria Among Acid Calcium Phosphates
Authors: Martin Roger I. , Brown Paul W.
Published: July 2010

The stable ternary system H3PO4‐Ca(OH)2‐H2O has been established further by determining the equilibria among the acidic calcium phosphates. In particular, equilibria involving CaHPO4·2H2O, CaHPO4, Ca(H2PO4)2·H2O, and Ca(H2PO4)2·H2O have been established. In contrast to earlier opinions, Ca(H2PO4)2 is not a stable phase in this system at any temperature below 100°C. Ca(H2PO4)2 can be made only in boiling H3PO4 liquors at 130°C or by dehydration of Ca(H2PO4)2·H2O. Ca(H2PO4)2 converts to Ca(H2PO4)2H2O upon equilibration in calcium phosphate solutions. A liquid region seems to exist between H3PO4 and Ca(H2PO4)2·H2O. Therefore, the related invariant point between H3PO4 and Ca(H2PO4)2·H2O does not exist at 25°C. The most soluble point lies between Ca(H2PO4)2·H2O and H3PO4. The invariant point involving the solids Ca(H2PO4)2·H2O and CaHPO4 is outside its compatibility triangle, and Ca(H2PO4)2·H2O dissolves incongruently. Furthermore, the compatibility line between H2O and Ca(H2PO4)2·H2O intersects the solubility curve of hydroxyapatite, suggesting Ca(H2PO4)2H2O dissolution can form hydroxyapatite initially. The dissolution of Ca(H2PO4)2·H2O in deionized water forms CaHPO4·2H2O, having a very‐thin‐plate morphology below 55°C, and CaHPO4, having a rectangular‐block morphology above 55°C. Over time CaHPO4·2H2O converts to CaHPO4 at temperatures above 36°C. The data obtained in this study have been combined with published data to construct a more complete H3PO4–Ca(OH)2‐H2O diagram at 25°C.
Chemical, Mechanical, and Tribological Properties of Pulsed‐Laser‐Deposited Titanium Carbide and Vanadium Carbide
Authors: Krzanowski James E. , Leuchtner Robert E.
Published: July 2010

The chemical, mechanical, and tribological properties of pulsed‐laser‐deposited TiC and VC films are reported in this paper. Films were deposited by ablating carbide targets using a KrF (λ= 248 nm) laser. Chemical analysis of the films by XPS revealed oxygen was the major impurity; the lowest oxygen concentration obtained in a film was 5 atom%. Oxygen was located primarily on the carbon sublattice of the TiC structure. The films were always substoichiometric, as expected, and the carbon in the films was identified primarily as carbidic carbon. Nanoindentation hardness tests gave values of 39 GPa for TiC and 26 GPa for VC. The friction coefficient for the TiC films was 0.22, while the VC film exhibited rapid material transfer from the steel ball to the substrate resulting in steel‐on‐steel tribological behavior.
“Classical” Superplasticity of SiAlON Ceramics
Authors: Rosenflanz Anatoly , Chen I‐Wei
Published: July 2010

“Classical” superplasticity of SiAlON ceramics with the nominal composition (YxLiy)0.6/(3x+y)Si8.9Al3.1O2.5N13.5 is reported in this study. During deformation, these materials exhibit little microstructural evolution, with negligible growth of elongated β′‐phase grains and minimal texture formation. Excellent formabilities are obtained in the temperature range of 1500°‐1600°C in compression, where a strain rate of 10−2 s−1 has been achieved, and in punch stretching, where a strain rate of 1.2 × 10−3 s−1 has been used successfully. Flow stresses are found to be dramatically affected by the viscosity of the grain‐boundary phase and decrease as the amount of lithium addition increases. Fracture stress also is compositionally dependent and decreases as the lithium content increases. As the overall formability is determined by the competition between fracture and deformation, maximum formability coincides with a maximum ratio of fracture stress to forming stress at an intermediate lithium composition. Finally, all materials exhibit higher room‐temperature bend strength after postforming annealing. Thus, transient superplastic deformation does not impair the ultimate mechanical properties of the materials.
Spin Coating of a Ca(Ti,Fe)O3 Dense Film on a Porous Substrate for Electrochemical Permeation of Oxygen
Authors: Itoh Hideaki , Asano Hiroshi , Fukuroi Keika , Nagata Makoto , Iwahara Hiroyasu
Published: July 2010

A dense Ca(Ti0.75Fe0.25)O3−α (Ca(Ti,Fe)O3) film, which is a mixed conductor of oxide ions and electrons/holes, was prepared on a porous CaTiO3 substrate by a spin‐coating method. The calcined Ca(Ti,Fe)O3 powder with 2–3 μm grain sizes was mixed with a dispersant in ethanol to form the slurry for spin coating. A uniform Ca(Ti,Fe)O3 green film was obtained at 1000–1500 rpm on the rotating porous CaTiO3 substrate, which had an average pore diameter of a few micrometers. The optimum sintering conditions for the spin‐coated films were a soaking temperature of 1235°C and a holding time of 2 h, in air. A dense, sintered Ca(Ti,Fe)O3 film }20–50 μm thick was prepared by repeating the coatingsintering process. The gas‐tight film prepared on the porous substrate exhibited higher electrochemical permeation of oxygen at an operating temperature of 1000°C compared with that of thicker, sintered Ca(Ti,Fe)O3 disks.
Processing of Piezocomposites by Fused Deposition Technique
Authors: Bandyopadhyay Amit , Panda Raj K. , Janas Victor F. , Agarwala Mukesh K. , Danforth Stephen C. , Safari Ahmad
Published: July 2010

Piezoelectric ceramic/polymer composites were made by a fused deposition (FD) technique, which is a solid‐freeform fabrication (or layered manufacturing) technique where three‐dimensional (3‐D) objects are built layer by layer from a computer‐aided design (CAD) file on a computer‐controlled fixtureless platform. Indirect and direct FD methods were used to fabricate lead zirconate titanate (PZT)/polymer composites. For the indirect method, a CAD file for the negative image of the final part was created. A polymer mold was made via FD using a thermoplastic filament, and composite formation was completed via a lost mold technique. In the direct FD method, a thermoplastic polymeric filament that was filled with 50–55 vol% of PZT powder was used to form a positive image of the desired structure. Three‐dimensional honeycomb (“3‐D honeycomb”) composites and “ladder” composites with 3‐3 connectivity, which were formed via the FD technique, showed excellent electromechanical properties for transducer applications. In addition, the FD technique showed the ability to form composites with controlled phase periodicity, various volume fractions, and a variety of microstructures and macrostructures that are not possible with traditional composite‐forming techniques.
Characterization of Ceramic Materials with BIGDIFF: A Synchrotron Radiation Debye‐Scherrer Powder Diffractometer
Authors: O'Connor Brian H. , Van Riessen Arie , Carter John , Burton Graeme R. , Cookson David J. , Garrett Richard F.
Published: July 2010

Experiments have been conducted to evaluate the potential of the BIGDIFF Debye–Scherrer diffractometer (radius of 573 mm) for characterizing ceramic materials using synchrotron radiation. The instrument has been tested at a wavelength of 0.1538 nm (1.5378), under in vacuo conditions, with standard reference materials and an alumina‐matrix ceramic specimen using capillary‐mounted (diameter of 0.5 mm) powdered material. The diffraction patterns that have been recorded with imaging plates over a period of 15 min provide phase detectability that is clearly superior to Bragg‐Brentano laboratory X‐ray diffractometry data that is collected in 1 h. The superiority of BIGDIFF for the analysis of phase composition becomes very pronounced for trace phases (,1%). The sharper definition of the Bragg peaks with BIGDIFF synchrotron radiation data also leads to improved estimates of nonlinear residual strain and crystallite size data. The superior performance of BIGDIFF is principally due to (i) the intensity of the synchrotron radiation incident beam that is achieved with high collimation and monochromaticity (E/ΔE 104), (ii) the large ratio of the camera radius to the capillary radius, and (iii) the spatial resolution and dynamic range of the imaging plates.
Preceramic Polymer Route to Amorphous and Crystalline Potassium Aluminosilicate Powders and Their Electrorheological Properties
Authors: Baranwal Rita , Laine Richard M.
Published: July 2010

The oxide one‐pot synthesis (OOPS) process was used to synthesize a polymer precursor to potassium aluminosilicate, KAlSiO4 (KASp). A KAlSiO4 gel (KASg) also was produced via a solgel route using the same precursor. The two routes to KAlSiO4 were explored to compare the effects of the two processing methods on powder properties. The KASp and KASg powders both transformed on heating (.500°C) to amorphous, high‐surface‐area powders with narrow pore‐size distributions (4–24 nm). These anhydrous, amorphous powders were intrinsic electrorheological (ER) materials. Both materials crystallized at } 1070°C, and thermogravimetric analysis, differential thermal analysis, and X‐ray diffractometry suggested that they were identical. Diffuse reflectance infrared Fourier transform spectroscopy and scanning electron microscopy proved that the KASp powders were homogeneous, whereas the KASg powders were heterogeneous and segregated. The KASg powders exhibited better ER properties that were associated with the segregated phases.
Domain‐Related Phase Transitionlike Behavior in Lead Zinc Niobate Relaxor Ferroelectric Single Crystals
Authors: Mulvihill Maureen L. , Cross L. Eric , Cao Wenwu , Uchino Kenji
Published: July 2010

The relaxor ferroelectric lead zinc niobate (Pb(Zn1/3Nb2/3)O3) has been intensively investigated, because of its large dielectric and piezoelectric properties for applications in actuators and transducers. In this study, the in‐situ behavior of the domains in Pb(Zn1/3Nb2/3)O3 single crystals has been observed using optical microscopy in combination with a charge‐coupled device (CCD) camera. The temperature of the sample has been cycled between −185°C and −200°C, while applying an electric field of up to ±10 kV/cm. Many characteristics, such as the induction of birefringence, the transition between the microdomains and macrodomains, and the “freeze‐in” of the macrodomains, have been optically observed. The optical and dielectric data have been collected and plotted as a function of temperature and electric field. An electric‐fieldtemperature diagram showing five domain‐related regions has been proposed. The microdomain‐to‐macrodomain phase transitionlike behavior seems to be an analog of a martensitic phase transition.
Microhardness of Sputter‐Deposited Zirconia Films on Silicon Wafers
Authors: Pakala Mahendra , Walls Heather , Lin Ray Y.
Published: July 2010

Calcia‐stabilized zirconia films were deposited on the surface of silicon 111 wafers using radio frequency (rf) magnetron sputter deposition. Deposition was conducted at substrate temperatures that varied in the range of 80°–900°C. X‐ray diffractometry results showed that all the films consisted of cubic zirconia. The fracture surface morphology and etched surfaces of the films were studied using scanning electron microscopy (SEM). Depending on the deposition temperature, the structure of the film was either columnar or equiaxed. The transition temperature from the columnar structure to the equiaxed structure was at a ratio of deposition temperature to melting temperature of } 0.42. The microhardness of the films was evaluated using a developed model that is based on the plastic zone analysis below a diamond (Vickers) indentor. From this model, the microhardness was found to increase as the deposition temperature increased, which was probably because the hardness of ceramic materials decreases as the defect concentration increases.
Phase Equilibria of the Bismuth Oxide–Calcium Oxide–Copper Oxide System in Oxygen at 1 atm
Authors: Tsang Chi‐Fo , Meen James K. , Elthon Don
Published: July 2010

Phase equilibria in the bismuth oxide‐calcium oxide‐copper oxide system have been determined at 1 atm pressure in oxygen over the temperature range of 750°–1000°C. The phases found to be stable at 750°C are Bi2CuO4, CuO, Ca2CuO3, CaO, Bi2Ca2O5, Bi6Ca4O13, Bi14Ca5O26, a rhombohedral Bi‐Ca oxide solid solution (Rhss), and a face‐centered cubic Bi‐Ca oxide solid solution (Fccss) that includes Bi2O3. At 800°C, the stable phases are Bi2CuO4, CuO, Ca2CuO3, CaO, Bi2Ca2O5, Bi6Ca4O13, a hexagonal Bi‐Ca oxide solid solution (δss), Rhss, Fccss, and liquid. The phases found to be stable at 850°C are CuO, Ca2CuO3, CaO, Bi2Ca2O5, Bi6Ca4O13, Fccss, and liquid. The phases found to be stable at 900°C are CuO, Ca2CuO3, CaO, Bi2Ca2O5, a body‐centered cubic Bi‐Ca oxide solid solution (Bccss), and liquid. The stable phases at 950°C are CuO, Ca2CuO3, CaO, and liquid. At 1000°C, the stable phases are CuO, Ca3Cu7O10, Ca2CuO3, CaO, and liquid.
Sintering Behavior of Cadmium‐Doped Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 Ceramics
Authors: Cho Jeong‐Ho , Park In‐Kil , Kim Ho‐Gi , Chung Hoon‐Taek
Published: July 2010

Substituting Cd2+ ions into the A and B sites in a Pb(Ni1/3Nb2/3)O3PbZrO3PbTiO3 (PNNPZPT) ternary perovskite material made it possible to determine the effects of the Cd2+ ion substitution site on sintering behavior. The substitution site of the Cd2+ ion was identified by using X‐ray photoelectron spectroscopy spectra. Although Cd2+ ions were substituted into the A and B sites in PNNPZPT, the Cd2+ ions preferred the A site over the B site. When Cd2+ ions replaced Pb2+ ions, a weight gain was observed during sintering. On the other hand, replacing Ni2 ions with Cd2+ ions promoted weight loss. Those weight changes indicated that Cd2+ ions change the bonding strength between the B‐site cations and the oxygen of the octahedron in a perovskite structure. Density was influenced by the Cd2+ ion substitution site, and the A‐site‐doped compositions had higher densities than the B‐site‐doped compositions.
Application of Weakest‐Link Fracture Statistics to Fiber‐Reinforced Ceramic‐Matrix Composites
Authors: McNulty John C. , Zok Frank W.
Published: July 2010

The strength and reliability of fiber‐reinforced ceramic‐matrix composites (CMCs) are dependent on whether conditions of local or global load sharing prevail. Global load sharing is promoted by a low interfacial sliding stress and is manifested in a zero‐tangent modulus at the point of tensile failure along with random fiber failures and extensive fiber pullout. In this paper, it is demonstrated that conditions of global load sharing are not present in two commonly studied CMCs, despite the fibrous appearance of their fracture surfaces. This behavior is manifested in a volume‐dependent strength, as evidenced by strength differences measured in tension and flexure (accounting for the nonlinear stress distribution in flexure). Methods of weakest‐link statistics are used to relate the strengths measured in the two test configurations. Estimates for the Weibull moduli of the two systems are obtained from the experiments and compared with values obtained through Monte Carlo simulations based on a three‐dimensional‐lattice Greens function method. The implications of these results on the strength of large components and of small regions of high stress concentration are discussed briefly.
Mullite Transformation Kinetics in P2O5‐, TiO2‐, and B2O3‐Doped Aluminosilicate Gels
Authors: Hong Seong‐Hyeon , Messing Gary L.
Published: July 2010

Mullite transformation kinetics of sol‐gel‐derived diphasic mullite gels doped with P2O5, TiO2, and B2O3 were studied using quantitative X‐ray diffraction and differential thermal analysis (DTA). The mullite transformation temperature initially increased with P2O5 doping because of phase separation and formation of α‐alumina and cristobalite. In TiO2‐doped samples, the mullite transformation temperature decreased with TiO2 doping, and the transformation rate increased with decreasing TiO2 particle size. Kinetic studies showed that titania reduced the activation energy for both nucleation and growth relative to pure diphasic mullite gels by lowering the glass viscosity and/or enhancing the solid‐state mass transport through lattice defects. B2O3 doping decreased the mullite transformation temperature and lowered the activation energy for both nucleation and growth but especially affected the mullite nucleation process, as indicated by the much smaller grain size.
Unusual Immiscibility Structures in Tellurite Glasses
Authors: Kashchieva Elena P. , Dimitriev Yanko B.
Published: July 2010

Unusual droplet microaggregates are observed in TeO2‐rich glasses of the systems TeO2–B2O3, TeO2–GeO2, TeO2–B2O3–GeO2, and TeO2–GeO2–V2O5. A decrease of the TeO2 content is established in the aggregates in comparison with the matrix. Their appearance is related to the process of metastable liquid‐phase separation at high viscosity of the melts.
Preparation and Characterization of Chemically Vapor Deposited ZrO2 Coating on Nickel and Ceramic Fiber Substrates
Authors: Borst Mark A. , Lee Woo Y. , Zhang Ying , Liaw Peter K.
Published: July 2010

Monoclinic ZrO2 was deposited on several metallic and ceramic substrates by reacting ZrCl4, CO2, and H2 at temperatures of 800° to 1050°C. Ni substrates reacted significantly in the ZrO2 coating environment since the coating was porous and contained a considerable amount of Ni. In contrast, the coating deposited on SiC and aluminoborosilicate fibers was highly crystalline, faceted, and dense without any apparent interaction with the substrate materials.
Anisotropic Thermal Expansion of β‐Ca2SiO4 Monoclinic Crystal
Authors: Fukuda Koichiro , Maki Iwao , Ito Suketoshi
Published: July 2010

Crystals of β‐Ca2SiO4 (space group P121/n1) were examined by high‐temperature powder X‐ray diffractometry to determine the change in unit‐cell dimensions with temperature up to 645°C. The temperature dependence of the principal expansion coefficients (αi) found from the matrix algebra analysis was as follows: α1= 20.492 × 10−6+ 16.490 × 10−9 (T ‐ 25)°C−1, α2= 7.494 × 10−6+ 5.168 × 10−9(T ‐ 25)°C−1, α3=−0.842 × 10−6− 1.497 × 10−9(T ‐ 25)°C−1. The expansion coefficient α1, nearly along [302] was approximately 3 times α2 along the b‐axis. Very small contraction (α3) occurred nearly along [01]. The volume changes upon martensitic transformations of β↔αL′ were very small, and the strain accommodation would be almost complete. This is consistent with the thermoelasticity.
Strain‐Dependent Electrical Conduction in the System NiO–CaO
Authors: Nakamura Yoshinobu , Ogawa Hiroshi , Nakashima Tetsuya , Kishimoto Akira , Yanagida Hiroaki
Published: July 2010

Strain‐dependent electrical conduction has been observed in the system NiO–CaO.xNiO·(1 ‐ x)CaO solid solutions are fabricated by a traditional solid‐reaction method. When the 0.03NiO·0.97CaO solid solution is annealed at 1000°C, excess NiO is excluded and precipitates on the surface or intergrain layers. When compressive stress is applied to the specimen, the electrical conductivity increases with an increase in the applied stress. The magnitude of the conductivity change exceeds 50% during 15 MPa loading at 800°C. The presence of a precipitated NiO layer over the xNiO (1 ‐ x)CaO phase is suggested to be the origin of the applied stress‐dependent electrical conductivity.
A Natural Ceramic/Polymer Layered Composite
Authors: Sobel Howard L. , Williams Wendell S.
Published: July 2010

The examination of natural materials at the microscopic and microchemical level from a materials science perspective can occasionally suggest advances in modern materials engineering. The present paper reports on such a case: an analytical study of the detailed structure and composition of sea urchin teeth.
Formation Kinetics of MoSi2 and Mo5Si3 by the Reactive Diffusive Siliciding of Molybdenum
Authors: Hillig William B. , Usta Metin
Published: July 2010

The formation kinetics of products formed by the reaction between dense molybdenum and vapor‐supplied silicon at an activity approximating that of solid silicon under open flowing gas conditions was studied at 1200°3C. An outer MoSi2 layer overlaid the much thinner Mo5Si3 that formed on the molybdenum. Both phases obeyed parabolic growth laws over a 22 h period, having parabolic rate constants of 6.8 times 10‐10 cm2/s for the MoSi2 and 1.3 times 10‐13 cm2/s for the Mo5Si3 phases. These results were ∼2 orders of magnitude less than prior results, mostly obtained by another processing route. Possible explanations include enhanced growth rates from chemical contamination. Gross distortion and abnormal layer thicknesses at specimen edges and the 159% volume increase during siliciding suggest that the kinetics also are strain dependent.
Synthesis of Ba2NaNb5O15 Powders and Thin Films Using Metal Alkoxides
Authors: Yogo Toshinobu , Sakamoto Wataru , Isaji Tadayuki , Kikuta Koichi , Hirano Shin‐ichi
Published: July 2010

Transparent and highly oriented Ba2NaNb5O15 (BNN) thin films have been prepared by using metal alkoxides. A homogeneous precursor solution was prepared by the controlled reaction of NaOC2H5, Nb(OC2H5)5, and barium metal. The BNN precursor included a molecular‐level mixture of NaNb(OC2H5)6 and Ba[Nb(OC2H5)6]2 in ethanol. The alkoxy‐derived powder crystallized to a low‐temperature phase, and then transformed to orthorhombic BNN (tungsten bronze) at 600°3C. BNN precursor films on substrates crystallized to orthorhombic BNN at 800°3C via the low‐temperature phase. Highly (002) oriented BNN films of tungsten bronze structure were successfully prepared on MgO (100) substrates at 700°3C by using BNN underlayer.
In Situ Reacted Rare‐Earth Hexaaluminate Interphases
Authors: Cain Markys G. , Cain Rebecca L. , Lewis Michael H. , Gent John
Published: July 2010

A novel in situ reaction between a ceria‐doped zirconia interphase coating on Saphikon fibers and an outer alumina coating has resulted in the formation of oriented hexaaluminate platelets which can act as a low fracture energy interface barrier for crack deflection in oxide—oxide ceramic‐matrix composites (CMCs). The reaction proceeds only in reducing environments where the reduction of the cerium and zirconium ions to their 3+ valent state causes a destabilization phenomenon consistent with previously reported findings. The diffusion of the cerium from the zirconia into solid solution with the alumina can stabilize the layered hexaaluminate structure. Preferred orientational growth of the hexaaluminate parallel to the coating interface was observed which is the required orientation for enhanced debonding at the fiber/matrix interface in long‐fiber‐reinforced CMCs.
Differential Negative Resistance and Piezoresistivity in Thin Semiconducting BaTiO3 Ceramic Bars
Authors: Kuwabara Makoto , Matsuda Hirofumi , Hamamoto Koichi
Published: July 2010

Thin, semiconducting barium titanate (BaTiO3) ceramic bars, with a diameter of 10 to 20 μm, consisting of single grains joined together in series have been prepared to investigate the piezoresistivity in the materials, which was evaluated from their current (I)‐voltage (V) characteristics under the loading condition of various bending stresses. I‐V characteristics of single grain boundaries in some of the materials were found to exhibit distinct differential negative resistance (DNR) at room temperature with its feature changing with stress. The DNR appeared on the I‐V curves at an electric field of several volts per one grain, and has been confirmed to be connected with the transition of current between two conduction states in the grain boundary region. The obtained results indicate that this phenomenon cannot be interpreted by a rise in the temperature of the materials up to their positive temperature coefficient of resistivity (PTCR) region above the Curie point by Joule heating due to current flow, that is their self‐heating effect. This newly observed DNR phenomenon has thus been tentatively interpreted by the morphological change in the ferroelectric domain structure in the vicinity of grain boundaries under mechanical and electric stresses, on an assumption that different configurations of ferroelectric domains yield different conduction states in the grain boundary due to a difference in the degree of surface acceptor charge compensation or the anisotropic carrier mobilities in the crystal.
A Discernible Dielectric Aging Effect in the Undoped, N2‐H2‐Annealed Lead Magnesium Niobate—Lead Titanate Ceramic
Authors: Wang Yu , Chan Yan Cheong , Gui Zhi Lun , Li Long Tu , Straw Andrew
Published: July 2010

It is well known that the undoped Pb(Mg1/3Nb2/3)O3‐PbTiO3 ceramics, prepared through conventional ceramic processing, present no evident aging effect. In this paper, however, a discernible aging phenomenon was observed in an undoped, N2‐H2‐annealed ceramic. When this sample was later annealed again in air, this effect became negligible again just like that of a normally prepared PMN—PT ceramic. The valence states of Ti ions, which may be changeable in different annealing atmospheres, were assumed to be responsible for the different degrees of aging.
Model Experiment on Thermodynamic Stability of Retained Intergranular Amorphous Films
Authors: Ackler Harold D. , Chiang Yet‐Ming
Published: July 2010

To test the stability of intergranular amorphous films against crystallization, a model experiment was conducted wherein a thin SiO2 film was deposited on a single‐crystal TiO2 substrate, annealed to form a eutectic liquid in equilibrium with the substrate, then quenched and crystallized below the eutectic temperature. This geometry is free of residual stresses and capillary effects proposed by others as kinetic limitations to complete crystallization. Furthermore, using a binary system removes solute rejection barriers to complete crystallization. A remnant amorphous film ∼1.5 nm thick retained at the hetero‐interface shows unequivocally that the amorphous film is thermodynamically preferred to a crystal/crystal interface in this system.
Fracture Toughness Evaluation of Small Thin Ceramic Specimens
Authors: Sherman Dov
Published: July 2010

A test method to evaluate the fracture toughness, KIC, of thin, small, precracked ceramic specimens is described. The method is applicable for thin plates, wafers, self‐supported layers, etc., especially when a large amount of material is not available for testing. The method consists of bonding a small, thin single‐edge notched beam on one side of a metallic beam. A stress‐free precrack with a square root singularity is achieved when the assembly is deformed in three‐point bending.

The fracture toughness of a thin, alumina single‐edge precracked beam was evaluated experimentally using this method, and compared with that obtained for similar specimens having a 0.3‐mm‐wide machined notch. Comparison with previously reported fracture toughness values suggests that even a very sharp machined notch overestimates the evaluated fracture toughness.
Kinetics and Formation of the 110 K Phase in the Bismuth–Lead–Strontium–Calcium–Copper–Oxygen System
Authors: Zhu Wen , Kuo C. K. , Nicholson Patrick S.
Published: July 2010

The kinetics and formation of the 110 K superconducting phase in the Bi‐Pb‐Sr‐Ca‐Cu‐O system have been analyzed via Avrami theory, high‐temperature X‐ray diffractometry, scanning and transmission electron microscopy, and differential thermal analysis techniques. The kinetic study indicates that the reaction is diffusion controlled for oxygen partial pressures of ˜1‐35 kPa (0.01‐0.35 atm). The appearance of liquid increases the contact area of the reactant particles, thus accelerating mass transport and the phase formation kinetics. The 110 K phase forms via reaction between the 80 K phase, secondary phases that are rich in calcium and copper, and the liquid that contains lead, calcium/strontium, and copper.
Low‐Temperature Sintering and Influence of the Process on the Dielectric Properties of Ba(Zn1/3Ta2/3)O3
Authors: Tolmer Véronique , Desgardin Gilbert
Published: July 2010

By controlling the granulometric distribution of the powders, a density of >96% of the theoretical density has been attained for Ba(Zn1/3Ta2/3)O3 that has been sintered at a low temperature (1450°C) for a short soaking time (2 h). Attrition milling produces a very fine and monomodal powder that allows for good densification. The attrition conditions result from a compromise between granulometric distribution and the risk of pollution. We have found a great influence of the origin of the raw materials on the temperature coefficient of frequency, allowing a modulation in the range of 0‐15 ppm/°C. Finally, we have studied the influence of each step of the process on the dielectric properties and identified the secondary phases that form with the evaporation of zinc: an eight‐layered hexagonal perovskite and a tetragonal tungsten‐bronze‐type phase.
Microstructure and Flow Behavior of Fresh Cement Paste
Authors: Lei Wei‐Guo , Struble Leslie J.
Published: July 2010

A rheological technique (creep/recovery) was used, in combination with scanning electron microscopy, to study the effects of hydration on both the microstructure and flow properties of fresh cement paste during the induction period, which is the first few hours after cement and water are mixed. The principal hydration product was calcium silicate hydrate (C‐S‐H), which was first observed in the neck areas between cement particles. At the same time, yield stress increased progressively, which reflected a strengthening of bonds between particles attributed to the C‐S‐H. Failure strain also increased, which reflected a fundamental change in the nature of that bond. Based on rheological measurements, the activation energy of the hydration process during this time period was estimated to be 5.2 kcal/mol (˜22 kJ/mol).
Thermal Degradation of Fiber Coatings in Mullite‐Fiber‐Reinforced Mullite Composites
Authors: Schmücker Martin , Schneider Hartmut , Chawla Krishan K. , Xu Zheng R. , Ha Jung‐Soo
Published: July 2010

The thermal degradation behavior of single‐layer BN and of double‐layer BN/SiC chemically vapor‐deposited fiber coatings in mullite‐fiber‐reinforced mullite composites was investigated by means of transmission electron microscopy after processing and heat treatment of the composites at 1000°, 1200°, and 1300°C for 6 h in air. The single‐layer BN coatings were ˜0.7 mu m thick and consisted of turbostratic BN with (0001) basal planes lying parallel to the surfaces of the fibers plus nanosized areas that had no preferential orientation. This microstructure remained unchanged up to 1000°C; however, distinct coarsening of the randomly oriented BN crystallites occurred in the temperature range of 1000°‐1200°C. The single‐layer BN coatings were stable against oxidation, up to 1200°C. At higher temperatures, degradation of the coatings via oxidation occurred. Double‐layer BN/SiC coating systems consisted of BN that was 0.08 mu m thick and SiC layers that were 0.16 mu m thick and deposited onto the mullite fibers. The turbostratic BN was highly anisotropic and did not undergo any microstructural change, up to 1300°C. The outer SiC layer of the double‐layer coating system improved the oxidation resistance of BN in the 1200°‐1300°C temperature range, despite a partial oxidation of SiC to SiO2.
Glycothermal Reaction of Rare‐Earth Acetate and Iron Acetylacetonate: Formation of Hexagonal ReFeO3
Authors: Inoue Masashi , Nishikawa Toshihiro , Nakamura Tomohiro , Inui Tomoyuki
Published: July 2010

The reaction of a mixture of iron acetylacetonate and rare‐earth (Tm‐Lu) acetate in 1,4‐butanediol at 300°C yielded a novel phase of ReFeO3 having a hexagonal crystal system (a0 = 6.06, c0= 11.74 A) together with small amounts of Fe3O4and/or the garnet phase. The particle size of the product distributed in a narrow range and selected area electron diffraction from a particle having apparent polycrystalline outlines suggested that each particle was actually a single crystal grown from one nucleus. On calcination, the hexagonal phase irreversibly transformed into the perovskite phase at around 980°C. The use of ethylene glycol in place of 1,4‐butanediol of the present procedure afforded Fe3O4, while hydrothermal reaction of the same starting materials yielded a mixture of Fe2O3and an amorphous rare‐earth phase.
Tensile Creep of Alumina‐Silicon Carbide “Nanocomposites”
Authors: Thompson A. Mark , Chan Helen M. , Harmer Martin P.
Published: July 2010

The tensile creep behavior of an (Al2O3‐SiC) nanocomposite that contains 5 vol% of 0.15 μm SiC particles is examined in air under constant‐load conditions. For a stress level of 100 MPa and in the temperature range of 1200°–1300°C, the SiC reduces the creep rate of Al2O3 by 2–3 orders of magnitude. In contrast to Al2O3, the nanocomposite exhibits no primary or secondary stages, with only tertiary creep being observed. Microstructural examination reveals extensive cavitation that is associated with SiC particles that are located at the Al2O3 grain boundaries. Failure of the nanocomposite occurs via growth of subcritical cracks that are nucleated preferentially at the gauge corners. A modified test procedure enables creep lifetimes to be estimated and compared with creep rupture data. Several possible roles of the SiC particles are considered, including (i) chemical alteration of the Al2O3 grain boundaries, (ii) retarded diffusion along the Al2O3‐SiC interface, and (iii) inhibition of the accommodation process (either grain‐boundary sliding or grain‐boundary migration).
Synthesis of Silicon Carbide Thin Films with Polycarbosilane (PCS)
Authors: Colombo Paolo , Paulson Thomas E. , Pantano Carlo G.
Published: July 2010

Polycarbosilane (PCS) thin films were deposited on silicon (and other) substrates and heat treated under vacuum (∼10‐‐6>torr)at temperatures in the range of 200°–1200°C. At temperatures in the range of 1000°–1200°C, the initially amorphous PCS films transformed to polycrystalline ß‐silicon carbide (ß‐SiC). Although PCS films could be deposited at thickness up to 2 μm, the films with thicknesses >1 μm could not be transformed to SiC without extensive cracking. The resulting SiC coatings were characterized using Fourier transform infrared spectroscopy, glancing‐angle X‐ray diffractometry, secondary‐ion mass spectroscopy, Raman spectoscopy, transmission electron microscopy, and scanning electron microscopy. The temperature and time dependence of the amorphous‐to‐crystalline transition could be associated with the evolution of free carbon, oxygen, and hydrogen in the films.
Viscous Slip along Grain Boundaries in Chlorine‐Doped Silicon Nitride
Authors: Pezzotti Giuseppe , Ota Ken'ichi , Kleebe Hans‐Joachim
Published: July 2010

The effect of chlorine doping on the anelastic‐relaxation and torsional‐creep behavior of a silicon nitride (Si3N4) polycrystalline body was studied. Two model polycrystals—one undoped and the other doped with a small fraction of chlorine—were investigated. Their microstructures consisted of equiaxed and well‐faceted Si3N4 grains whose boundaries were separated by a continuous, nanometer‐sized film of silica (SiO2) glass. The actual presence of chlorine in the doped polycrystal was ascertained by ion chromatography and is thought to be enriched at the grain boundaries. The effect of chlorine on the intergranular film structure was characterized by high‐resolution electron microscopy. The micromechanical response of the SiO2 grain boundary under shear stress was monitored up to very high temperatures (i.e., ∼2000°C) by internal‐friction and torsional‐creep experiments. The presence of the chlorine dopant, which is a network modifier of SiO2 glass that also causes a widening of the grain‐boundary film, significantly lowered the bulk viscosity of the residual glass. As a consequence of the change in grain‐boundary chemistry, the internal‐friction curve of the chlorine‐doped material shifted toward lower temperatures and the torsional‐creep rate markedly increased, as compared to the undoped material. According to a viscoelastic model of the Si3N4 polycrystal, the internal‐friction data resulted as a superposition of two individual components: (i) a relaxation peak that is related to the anelastic slip mechanism along grain boundaries and (ii) a background component that results from an irreversible diffusional‐creep mechanism.
Acoustic Emission Studies of Alumina‐13% Titania Free‐Standing Forms during Four‐Point Bend Tests
Authors: Lin Chung‐Kwei , Berndt Christopher C. , Leigh Sang‐Ha , Murakami Kenji
Published: July 2010

Free‐standing alumina‐13% titania samples were manufactured with a water‐stabilized plasma spray gun to a thickness of ∼5 mm. A thin layer of aluminum was arc sprayed prior to depositing the thick coating and etched away using hydrochloric acid. The so‐obtained free‐standing plate was cut into four‐point‐bend‐test specimens with dimensions of ∼5 mm × 5 mm × 50 mm. The as‐sprayed material consisted of a supersaturated solid solution, where titania was frozen inside the alumina matrix. Heat treatment was performed at 1450°C for 24 h and then at 1100°C for another 24 h. After heat treatment, titania precipitates were observed. The major phases of the as‐sprayed and heat‐treated samples were γ‐ and α‐alumina, respectively. The porosity was ∼10% for as‐sprayed samples; this value was reduced to ∼3% after heat treatment. Four‐point bend tests were performed on the as‐sprayed and heat‐treated specimens in cross‐section and in‐plane directions. An acoustic emission technique was used to examine the cracking during the tests in situ. Microcracking prior to failure was observed for as‐sprayed samples that were tested in the cross‐section direction. However, when tested in the in‐plane direction, catastrophic failure with less evidence of microcracking occurred. For heat‐treated specimens, microcracks were usually observed when tests were performed in either of the orientations. Energy and amplitude distributions for each testing condition were examined. These distributions changed after heat treatment; however, no significant differences were distinguished when tests were performed in the cross‐section or in‐plane directions.