bluuebunny/crossref_metadata_2025 huggingface dataset:
Microhardness of SiO2 Glass in Various Environments
Authors: HIRAO KAZUYUKI , TOMOZAWA MINORU
Published: March 2005

It was shown in earlier studies that the crack initiation stress of SiO2 glass was stressing‐time dependent only in water while it was time independent in nonaqueous liquids. In order to clarify the roles that various liquids play in the crack initiation of SiO2 glass, Knoop microhardness measurements were made on SiO2 glass in various liquids and FTIR spectroanalysis was performed on the indented SiO2 glass. The microhardness measurements showed a similar loading‐time dependence to the crack initiation stress. The microhardness was separated into two parts: the surface contribution and the volume contribution. The results showed that the volume (or bulk) component was a nearly constant value for glass measured in nonaqueous liquids and that it was lower for glass measured in water. Consistent with these results, FTIR analysis showed that water entered the glass during indentation while nonaqueous liquids did not. The surface component showed a good correlation with the crack initiation stress.
Crystallographic Analysis of the Cubic‐to‐Tetragonal Phase Transformation in the ZrO2‐Y2O3 System
Authors: SHIBATA‐YANAGISAWA MEZAME , KATO MASAHARU , SETO HIROSHI , ISHIZAWA NOBUO , NOBUYASU  , MIZUTANI  , KATO MASANORI
Published: March 2005

The crystallography of diffusion‐induced and diffusionless cubic‐to‐tetragonal phase transformations in the ZrO2‐Y2O3 system is examined on the basis of the phenomenological crystallographic theory by adopting the lsqb;011rsqb; (011) twinning system as the lattice invariant deformation system. Numerical calculation indicates that the principal axes of the cubic phase are not exactly parallel to those of the tetragonal phase and that the habit plane orientation is sensitive to the lattice parameters of the cubic and tetragonal phases. The calculated results are compared with the observed crystallography of the tetragonal precipitates formed by diffusion and of the metastable tetragonal phase formed in a diffusionless manner. In many aspects, the present results were in good agreement with experimental observations. In particular, the crystallography and morphology of the so‐called “herringbone” structure are very well explained by the present analysis.
Structure of Phosphorus Oxynitride Glasses
Authors: BUNKER BRUCE C. , TALLANT DAVID R. , BALFE CAROL A. , KIRKPATRICK R. JAMES , TURNER GARY L. , REIDMEYER MARY R.
Published: March 2005

The structures of phosphourus oxynitride glasses have been determined using a combination of solid‐state 31P, 15N, and 23Na nuclear magnetic resonance and Raman spectroscopies. Raman spectra of model phosphazene compounds with different types of P–N bonding have been used to confirm spectral assignments. Results indicate that nitrogen replaces oxygen in the phosphrus atoms (via one double bond and one single bond) and as nitrogen bonded to three phosphorus atoms via three single bonds. The observed structural features are consistent with data which show that nitrogen influences the chemical durability, thermal expansion, and other properties of phosphate glasses by cross‐linking ploymeric phosphate chain to gether in the glass network.
High‐Pressure Self‐Combustion Sintering of Titanium Carbide
Authors: Yamada Osamu , Miyamoto Yoshinari , Koizumi Mitsue
Published: March 2005

A high‐pressure self‐combusiton sintering process has been applied to the synthesis and simultaneous sintering of titanium carbide. A dense titanium carbide compact was easily fabricated from the constituent elements without sintering aids under 3 GPa. The compact was composed of well‐crystallized grains with a mean diameter of 20 μm at a molar ratio of C/Ti =0.95. The maximum values of the relative density and the Vickers microhardness were 96.5% and 31 GN/m2, respectively, at room temperature.
Effect of Excess PbO on the Sintering Characteristics and Dielectric Properties of Pb(Mg1/3Nb2/3)O3–PbTiO3‐Based Ceramics
Authors: Guha Jyoti P. , Hong Dyllan J. , Anderson Harlan U.
Published: March 2005

Additions of excess PbO to the perovskite Pb[(Mg1/3Nb2/3)0.92Ti0.08]O3 solid solution enhanced the formation of a liquid phase at 840°C, which served as a densification aid for the ceramics. The liquid phase allowed elimination of pores and promoted grain growth during sintering. With additions of 1 to 2 wt% excess PbO, densities in excess of 97% of theoretical were obtained at a sintering temperature of 950°C. The peak dielectric constants of the resulting ceramics were over 18 000 at 30°C and dissipation factors less than 1%. Additions of PbO in excess of 2 wt% resulted in inferior dielectric properties due mainly to the dilution of the ferroelectric phase.
Crack Healing and Bending Strength of Aluminum Titanate Ceramics at High Temperature
Authors: Ohya Yutaka , Nakagawa Zenbe‐e , Hamano Kenya
Published: March 2005

Bending strength and Young's modulus of aluminum titanate ceramics at room temperature to 1300°C were examined. Bending strength increased from 62 MPa at room temperature to 280 MPa at 1100°C. Young's modulus also increased, to 99 GPa at 1100°C. These increments were caused by crack healing. In particular, crack cylinderization occurring at 1000° to 1100°C markedly increased the mechanical strength. The thermal‐hysteresis curves also showed healing of grain‐boundary cracks.
Direct Current Bias Aging Effects in Lead Magnesium Niobate‐Lead Titanate Relaxor Ferroelectric Ceramics
Authors: Pan Wuyi , Zhuang Qiming , Cross Leslie E.
Published: March 2005

The effect of aging upon the dielectric properties of MnO‐doped lead magnesium niobate‐lead titantate (0.9PMN·0.1PT) ceramics has been measured for samples aged at room temperature (25°C) both under zero and under high (22 kV/cm) dc fields. In the 0.9PMN·0.1PT composition, 25°C is above the limit for stable remanent polarization, P=0, in the absence of an external field; nonetheless, aging under a high dc bias at 25°C, then cooling to low temperature under zero bias produces a stable remanence at lower temperature and a loss of the dispersive character of the micropolar state. It is suggested that dipolar defects induced by MnO doping in the PMN‐PT can slowly reorient to stabilize the existing domain structure acting like a local bias field. Evidence is presented to show the stabilization of both random (unpoled) and ordered (poled) micropolar states. By comparing the remanent polarization induced by cooling after aging under dc field with that produced by straight dc poling of deaged samples, it appears that the defect ordering is macroscopically equivalent to a field of order 2 kV/cm. This field is in rough accord with the field to be expected from the known defect concentration, when the defects are ordered.
Microwave Sintering of Partially Stabilized Zirconia
Authors: Wilson Jack , Kunz Sarah M.
Published: March 2005

Partially stabilized zirconia has been rapidly sintered in a microwave apparatus to good final densities (95% to 98% of theoretical density). The grain size was not noticeably different from that of conventionally sintered material. Properties of the sintered material are given.
Thermal Expansion of Y2SiO5 Single Crystals
Authors: O'Bryan Henry M. , Gallagher Patrick K. , Berkstresser G.W.
Published: March 2005

The thermal expansion of Y2SiO5 crystals has been measured for the principal crystallographic directions and two orthogonal directions in the (010) plane in the temperature range 25° to 200°C. This monoclinic crystal has strongly anisotropic expansions with coefficients which range from 0.6 × 10−6/°C for [100] to 11.4 × 10−6/°C for [001]. Third‐order polynomials have been calculated from the expansion curves. Data for the β angle and cell volume as a function of temperature are also given. The thermal expansion of Y2SiO5 crystals is not affected by doping with 5% Tb.
Effect of Particle Size Distribution on the Sintering of Alumina
Authors: Yeh Tsung‐Shou , Sacks Michael D.
Published: March 2005

The effect of particle size distribution on the sintering of Al2O3 was investigated. Samples could be sintered to high relative density (∼99%), small average grain size (1 μm), and no growth of exaggerated grains using powders with either broad or narrow particle size distribution. However, the broad particle size distribution provided the advantage that powder compacts could be prepared with higher green density and, therefore, samples could be densified with less total shrinkage.
Indentation Fracture Response and Damage Resistance of Al2O3‐ZrO2 Composites Strengthened by Transformation‐Induced Residual Stresses
Authors: Hansen James J. , Cutler Raymond A. , Shetty Dinesh K. , Virkar Anil V.
Published: March 2005

Indentation fracture behavior of three‐layer Al2O3‐ZrO2 composites with substantial compressive residual stresses was compared with the behaviors of monolithic Al2O3 and Al2O3‐ZrO2 ceramics without intentionally introduced residual stresses. The indentation cracks were smaller in the three‐layer specimens relative to the monolithic specimens in agreement with the predictions of indentation fracture mechanics theory. Indentation and strength testing were used to show that a residual compressive stress of approximately 500 MPa exists in the outer layers of the three‐layer composites. The three‐layer specimens showed excellent damage resistance in that the strength differential between the three‐layer and monolithic indented specimens was maintained at indentation loads up to 1000 N, the maximum indentation load used in the experiments.
X‐ray Powder Study of 2BaO·CuO
Authors: Wong‐Ng Winnie Kwai , Davis K.L. , Roth Robert S.
Published: March 2005

A compound of composition 2BaO·CuO was synthesized during the phase equilibrium study of the BaO‐Y2O3‐CuOx system. Phase characterization has been carried out by using X‐ray powder diffraction. The crystal symmetry was found to be the same as that of Ca2CuO3 and Sr2CuO3. It is orthorhombic with space group Immm and lattice parameters a=12.9655(14) Å (1.29655 nm), b=4.1007(3) Å (0.41007 nm), c=3.9069(5) Å (0.39069 nm), and V=207.72(3) Å3 (0.20772 nm3). The experimental pattern shows good agreement, in general, with intensity values calculated by assuming Ba2CuO3 to have a structure similar to that of Sr2CuO3 and Ca2CuO3. Intensity discrepancy for the h00 reflections might be due to preferred orientation.
Electrical Properties and Site Distribution of Cations in (MnyCo1‐y)0.4Fe2.6O4
Authors: CARTER DANIEL C. , MASON THOMAS O.
Published: March 2005

The high‐temperature electrical properties (conductivity and thermopower) of the Co0.4Fe2.6O4‐Mn0.4Fe2.6O4 join were measured in order to determine the cation intersite distribution and establish the conduction mechanism. The cobalt and manganese site occupancies show a nearly linear composition dependence. Trivalent iron occupancies reflect the transition from an octahedral substituent (Co) to a tetrahedral substituent (Mn), but any influence on the iron distribution reaction is minimal. Small polaron conduction parameters are similar to those for magnetite and vary little across the join.
Role of Particle Substructure in the Sintering of Monosized Titania
Authors: EDELSON LAWRENCE H. , GLAESER ANDREAS M.
Published: March 2005

Monosized titania particles (∼0.35‐μ diameter) prepared by controlled hydrolysis of titanium tetraethoxide in ethanol were found to be porous agglomerates of ∼6‐nm primary particles. The sintering behavior of compacts constituted of monodispersed agglomerates was evaluated, and changes in macroscopic dimensions were correlated with changes in particle microstructure and chemistry. The total volume shrinkage during sintering was ≥87%. Five contributions to the total shrinkage and the temperature ranges for the associated processes were identified: removal of chemisorbed water (from ambient to 250°C), crystallization to anatase (between 250° to 425°C), intra‐agglomerate densification (425° to 800°C), conversion of anatase to rutile (600° to 800°C), and inter‐agglomerate densification (>800°C). Approximately one‐half the compact shrinkage was the result of agglomerate substructure changes. Studies of the agglomerate structural evolution indicated the intra‐agglomerate densification and crystallite growth rates are the secondary factors, after compact packing, that influenced microstructure development.
Zirconium Borohydride as a Zirconium Boride Precursor
Authors: Rice Gary W. , Woodin Richard L.
Published: March 2005

Synthesis of zirconium boride, ZrB2, from zirconium borohydride, Zr(BH4)4, has been explored by a variety of methods, including chemical vapor deposition (CVD) in a hot tube, laser CVD with both continuous‐wave (cw) and pulsed lasers, and cw‐laser synthesis of fine powders. In all cases, ZrB2 was the only crystalline product identified. Products made at high temperature contained excess boron, while those made at low temperature were boron‐deficient.
Analytical Microscopy Study of Phases and Fracture in Y2O3‐La2O3 Alloys
Authors: WEI GEORGE C. , EMMA T. , RHODES WILLIAM H. , HORVATH STEVEN , HARMER MARTIN
Published: March 2005

Transmission electron microscopic analyses defined the structures and compositions in single‐phase and two‐phase La2O3‐doped Y2O3 materials fabricated by the transient solid second‐phase sintering. The composition in single‐phase, 10‐mol%‐La2O3‐doped, sintered and annealed samples was found to be uniform, indicating that diffusivity was sufficiently high for homogenization in the single‐phase field. Two‐phase, 16‐mol%‐La2O3‐doped, sintered and annealed samples showed two morphologies: (1) intragranular, lath‐like, monoclinic second‐phase particles (twinned and untwinned) and (2) equiaxed cubic matrix. The second‐phase particles were identified as the monoclinic phase derived from the high‐temperature hexagonal phase through a rapid phase transition. A short, high‐temperature anneal (2200°C for 1 min) of 9 mol% La2O3‐Y2O3 composition was found to retain the hexagonal phase. Microchemical analyses of the phases suggested adjustments to the Y2O3‐La2O3 phase diagram. Observation of the interactions of the intragranular second‐phase particles with crack propagation indicated crack deflection as one of the mechanisms responsible for toughening (1.5 vs 0.9 MPa · m1/2).
Preparation and Properties of Monodispersed Colloidal Particles of Lanthanide Compounds: III, Yttrium(III) and Mixed Yttrium(III)/Cerium(III) Systems
Authors: AIKEN BAR , HSU WAN PETER , MATIJEVIĆ EGON
Published: March 2005

Colloidal dispersions of uniform spherical particles of yttrium basic carbonate and rodlike particles of yttrium ammine carbonate were prepared by aging at elevated temperatures yttrium salt solutions in the presence of urea. Different composition and morphology were achieved by altering the aging temperature and time. Coprecipitation in mixed solutions of yttrium(III) and cerium(III) salts under similar experimental conditions yielded composite spherical particles of basic carbonate. The content of the two metals in the solids followed closely the initial composition of the reacting solutions. On calcination all prepared solids converted to their corresponding oxides while retaining their particle morphology. The so‐prepared powders were characterized by various techniques.
Sol–Gel Coating of Powders for Processing Electronic Ceramics
Authors: SELMI FATHI A. , AMARAKOON VASANTHA R. W.
Published: March 2005

A new technique (sol‐gel coating of powders) was utilized to process electronic ceramics such as Sb‐doped SnO2 and positive‐temperature‐coefficient‐of‐resistance (PTCR) BaTiO3 thermistors. Sol‐gel coatings resulted in the densification via a liquid phase of Sb‐doped SnO2 powders. PTCR thermistors were developed from BaTiO3 powders coated by a sol‐gel composition containing dopants (Y), counterdopants (Mn, F), and additives (Si) with uniform microstructures and improved properties. Incorporation of F via the sol‐gel coating increased the reliability of PTCR devices, making them less sensitive to reducing environments. This process may be extended to the processing of other electronic materials.
Drying Behavior of Colloidal Silica Gels
Authors: Simpkins Peter G. , Johnson David W. , Fleming Debra A.
Published: March 2005

Observations of the drying behavior of thick‐wall colloidal silica gel structures are reported. Various techniques are examined to prevent cracking during the drying of these highstrain viscoelastic materials. Experiments are described which illustrate the effect of relative humidity on the drying rate and on the shrinkage of various samples under isothermal conditions. Surface temperature measurements indicate that evaporation occurs at approximately the wet‐bulb temperature of the surrounding atmosphere. Acoustic detection of the internal strain activity during drying leads to the conclusion that control of the sol‐gel surface tension in the material preparation is crucial to reducing the interior stresses.
Characterization of Silicon Carbide Whiskers
Authors: Karasek Keith R. , Bradley Steven A. , Donner Jeffry T. , Yeh Harry C. , Schienle James L. , Fang Ho T.
Published: March 2005

SiC whiskers from six manufacturers were characterized by bulk chemical techniques, X‐ray photoelectron spectroscopy, X‐ray diffraction, and scanning transmission electron microscopy or scanning electron microscopy. Major component (C, Si, and O) surface chemistries of the whiskers fell into four general categories: high oxygen content with oxide resembling a SiO2, high oxygen content with oxide resembling a Si‐O‐C glass, and hydrocarbon. Several whiskers exhibited significant surface impurities—in particular, Fe. From a morphological viewpoint, significant differences in diameter, debris level, straightness, and types and quantities of defects were observed from one manufacturer to another.
Fabrication of Metal‐Layer (Nickel) Silicate Microcomposite Particles by a Surface‐Nucleated Precipitation Route
Authors: Ohtsuka Kunio , Koga Johji , Suda Mitsuru , Ono Mikiya
Published: March 2005

Clay complexes with surface‐grown nickel(II) basic salts were produced from nickel(II) nitrate solutions containing dispersed layer silicate by homogeneous precipitation using hydrolysis of urea. These clay—nickel(II) salt complexes were obtained with clay having cation‐exchange properties; in contrast, using clay without these properties caused formation of a separate precipitate. Metal‐layer (Ni) silicate microcomposite powders, consisting of layer silicate uniformly covered with metal particles, were derived by reduction of these products; the metal/clay weight ratio was varied from 0.76 to 8.01. At a low metal/clay ratio (=0.76), highly divided fine metal (<10 nm) was fixed on the clay surface.
Incorporation of Cesium by Hydrating Calcium Aluminosilicates
Authors: Hoyle Susan L. , Grutzeck Michael W.
Published: March 2005

The leach behavior of cesium from a series of cement‐based waste forms has been modeled in terms of pore solution concentration and phase formation data. Cement‐based Materials enriched in alumina and silica, and compositionally related glasses, were hydrated in the presence of cesium hydroxide to gauge the degree of partitioning of cesium by the developing hydrates. The compositions of the pore solutions extracted from the cement‐based waste forms were compared both pore solution and leachates, the retention of cesium was found to be directly related to the bulk composition of the waste form; the degree of partitioning of cesium by the hydrated phases increased as more alumina and/or silica were added to the formulation, suggesting that cesium‐containing phases were forming. Additionally, the leachate concentration of cesium for any given composition was also found to be related to the pore solution concentration. This observation led to the development of a leaching model for cement‐based waste forms in which the concentration of cesium in the leachate could be described in terms of pore solution concentration, diffusion, dissolution, and development of cesium host phases. Using this model, effective diffusion coefficients for cesium were calculated to be ∼2 × 10−7 cm2· s−1. Pollucite and cesium‐substituted herschelite were identified as two of the hydration products of the studied glasses. The ability of these zeolites to strongly partition cesium suggests that small quantities of zeolitic phases may also be forming in the cement‐based waste forms, thus explaining their compositionally related leach behavior.
Aqueous Precipitation of Spherical Zinc Oxide Powders for Varistor Applications
Authors: Haile Sossina M. , Johnson David W. , Wiseman Gary H. , Bowen H. Kent
Published: March 2005

Aqueous precipitation has been used to prepare spherical ZnO particles. These powders have been shown to be suitable for use in the preparation of varistors. The uniform size distribution and uniform coating of these powders with the appropriate dopants allowed fabrication of varistors with improved properties over those fabricated from conventionally ball‐milled and calcined powders. The improved properties were a high coefficient of nonlinearity (∼44) in the nonohmic region, a sharp change in electrical behavior from ohmic to nonohmic, and a high resistivity (5×1012 SOM°m) at low voltages.
Preparation, Sintering, and Properties of Translucent Er2O3‐Doped Tetragonal Zirconia
Authors: Durán Pedro , Recio Paloma , Jurado José R. , Pascual Carmen , Moure Carlos
Published: March 2005

Tetragonal zirconia doped with 3 mol% Er2O3 was prepared by the gel‐precipitation wet‐chemical method. The compaction response of ultrafine (∼8.5 nm), calcined, deagglomerated powders was studied. Initial sintering was studied using both isothermal and nonisothermal techniques, and an activation energy of 270 ± 40 kJ/mol was obtained; therefore, grain‐boundary diffusion was probably the predominant mechanism in the sintering stage. The microstructural development in the high‐temperature‐aged, sintered samples and its effect on density and mechanical properties were also studied. A theoretically dense body of tetragonal zirconia solid solution of 3 mol% Er2O3–ZrO2, obtained from sintering below 1400°C, was translucent.
Construction of Chemical Potential Diagrams for Metal‐Metal‐Nonmetal Systems: Applications to the Decomposition of Double Oxides
Authors: Yokokawa Harumi , Kawada Tatsuya , Dokiya Masayuki
Published: March 2005

A chemical potential diagram for A‐B‐O (A, B = metallic elements) systems has been constructed to make visually clear the thermodynamic stability of double oxides; the stability area of metallic elements, their binary oxides, and double oxides can be presented as convex polygons in a log (aA/aB) vs log P(O2) plot, a and P(O2) being the activity of metallic elements and the oxygen partial pressure, respectively; the axis variable, log (aA/aB), is used to treat two metallic elements equivalently. The Co‐Ti‐O and La‐Co‐O systems have been chosen as examples to demonstrate how the present diagram can provide complicated phase relations in a compact and visualized manner. An attempt has also been made to utilize this diagram to present graphically products of kinetic decomposition of double oxides placed in an oxygen potential gradient.
Radio‐Frequency Plasma Spraying of Ceramics
Authors: Okada Tomohisa , Hamatani Hideki , Yoshida Toyonobu
Published: March 2005

This study was aimed at developing a novel spraying process using a radio‐frequency (rf) plasma. Experiments of Al2O3 and ZrO2–8 wt% Y2O3 spraying showed that the initial powder size was the most important parameter for depositing dense coatings. The optimum powder sizes of Al2O3 and ZrO2–8 wt% Y2O3 were considered to be around 100 and 80 μm, respectively. The use of such large‐size powders compared with those used by conventional dc plasma spraying made it possible to deposit adherent ceramics coatings of 150 to 300 μm on as‐rolled SS304 substrates. It was also shown that low particle velocity of about 10 m/s, which is peculiar to rf plasma spraying, was sufficient for particle deformation, though it imposed a severe limitation on the substrate position. These experimental results have proved that rf plasma spraying is an effective process and must be a strong candidate to open new fields of spraying applications.
Electrochemical Boundary Conditions for Resistance Degradation of Doped Alkaline‐Earth Titanates
Authors: Waser Rainer M.
Published: March 2005

In order to improve the understanding of de‐field‐induced resistance degradation, ceramic capacitors made from perovskite‐type titanates are formally treated as solidelectrolyte cells. Based on the consideration of the interfaces in these cells, the degradation process can be unambiguously deduced from the well‐known defect structure and transport properties of the titanates. Additional information is obtained from in situ impedance analyses and transport calculations as well as from comparisons between the degradation rate in single crystals and ceramics of different grain size. [Key words: capacitors, titanates, grain boundaries, dielectrics, electrical conductivity.]
Retrograde Densification in Bi2Sr2CaCu2O8 Superconductors
Authors: Johnson David W. , Rhodes Warren W.
Published: March 2005

Bi2Sr2CaCu2O8 was prepared using the mixed oxide‐carbonate method and sintered at temperatures ranging from 850° to 911°C. The samples were characterized for density, mechanical strength, phase composition, microstructure, and superconducting transition temperatures. A unique retrograde densification characteristic is demonstrated in the temperature range 850° to 890°C whereby the material first becomes less dense as the sintering temperature is raised, and only in a narrow temperature range from 900° to 905°C does the material densify then with the formation of a liquid phase. The retrograde densification mechanism is shown to be that of the formation of thin platelike crystallites which grow in a randomly oriented fashion, thus pushing the structure apart. This retrograde densification, coupled with a narrow sintering range overlapping the melting temperature, makes this compound a difficult one to process.
Two‐Dimensional Whisker Percolation in Ceramic Matrix–Ceramic Whisker Composites
Authors: Holm Elizabeth A. , Cima Michael J.
Published: March 2005

A computer model that treats ceramic‐powder matrix–ceramic whisker composites as a percolative network of whiskers has been developed. The model calculates the critical fraction of whiskers at the percolation threshold for a two‐dimensional random network of whiskers. The computed critical fraction was found to display an inverse dependence on whisker aspect ratio. In addition, the computed critical fraction (27 vol% for a whisker aspect ratio of 7) agreed well with the zero‐shrinkage whisker fraction of 30 vol% in the densification of a colloid‐pressed alumina–silicon carbide composite that exhibited a two‐dimensional orientation of such whiskers.
Electrostrictive and Dielectric Response in Lead Magnesium Niobate–Lead Titanate (0.9PMN · 0.1PT) and Lead Lanthanum Zirconate Titanate (PLZT 9.5/65/35) under Variation of Temperature and Electric Field
Authors: Zhang Qiming , Pan Wuyi , Bhalla Amar , Cross Leslie E.
Published: March 2005

In situ measurements of electrostrictive strain and effective dielectric constant for two ferroelectric relaxor materials, lead magnesium niobate–lead titanate (0.9PMN · 0.1PT) and lead lanthanum zirconate titanate (PLZT 9.5/65/35), were performed in the temperature ranges near their respective mean Curie points under the variation of applied electric field. The measurement results show that the polarization‐related electrostrictive coefficients Qij are not constant under variation of temperature and electric field. The observed anomaly in Qij indicates the dynamic behavior of the existing micropolar domains and its coupling to local defect structure. The data also support the idea that at temperatures far above the mean Curie point, there is still a substantial amount of micropolar domain and the response of the relaxor materials at the experimental temperature range is from the combined contributions due to induced polarization and micropolar domain flipping.
In Vitro Aging of Yttria‐Stabilized Zirconia
Authors: Drummond James L.
Published: March 2005

Yttria‐stabilized zirconia was aged in distilled water, saline, and Ringer's solution for 140, 304, and 453 d. The significant decreases in strength (13% to 22%) is attributed to the phase transformation of zirconia from tetragonal to monoclinic. The effect of aging stabilized zirconia in physiological media is still unresolved.
Effects of Annealing Temperature on Microstructure and Electrical and Optical Properties of Radio‐Frequency‐Sputtered Tin‐Doped Indium Oxide Films
Authors: Na Jong‐Gab , Cho Young‐Rae , Kim Young‐Ho , Lee Taek‐Dong , Park Soon‐Ja
Published: March 2005

Indium tin oxide (ITO) films (0.3 μm thick), with a doping level of 28 mol% SnO2, were prepared by a radio frequency magnetron sputtering mehthod. The effects of postannealing on the microstructure and the electrical properties of the ITO films were investigated. The as‐sputtered film showed an amorphous structure, whereas the films annealed at 350° and 510°C exhibited crystalline structures with grain sizes of 0.12 and 0.14 μm, respectively. Examination by TEM showed that the postannealing treatment induced SnO2 precipitates along the grain boundaries. The resistivity increased with increasing postannealing temperatures. The mobility of carriers appears to be responsible for the resistivity increase in these specimens. The mobility change is discussed in connection with the SnO2 precipitates.
Slip Casting of SiC‐Whisker‐Reinforced Si3N4
Authors: Hoffmann Michael J. , Nagel Alwin , Greil Peter , Petzow Günter
Published: March 2005

Si3N4 composite materials containing up to 20 vol% SiC whiskers were slip cast and pressureless sintered at 1820°C and 0.13 MPa of N2. Viscosimetry showed no influence of whisker loading on the rheology of the highly concentrated aqueous slips up to 15 vol% whiskers. During casting the whiskers were preferentially aligned parallel to the mold surfaces. Depending on the whisker loading, green densities of 0.64 to 0.69 fractional density could be achieved. Strong anisotropic shrinkage occurred during sintering with a maximum linear shrinkage of 21% perpendicular but only 7% parallel to the whisker plane. With increasing whisker content from 0 to 20 vol% sintered densities decreased from 0.98 to 0.88, respectively.
Fabrication of Titanium Carbide Ceramics by High‐Pressure Self‐Combustion Sintering of Titanium Powder and Carbon Fiber
Authors: Adachi Seiji , Wada Takahiro , Mihara Toshihiro , Miyamoto Yoshinari , Koizumi Mitsue , Yamada Osamu
Published: March 2005

Titanium carbide ceramics have been fabricated from the reactants titanium powder and carbon fiber by the highpressure self‐combustion sintering method (HPCS) under two pressure conditions (65 MPa and 3 GPa). Porous TiC with a density of about 50% of theoretical was obtained under a pressure of 65 MPa. A possible model accounting for the formation mechanism of TiC is proposed on the basis of observation of the microstructure of the products formed from the incomplete reaction. On the other hand, dense TiC (>95% of theoretical) was fabricated under 3 GPa. The mean grain size varied, depending on the mixing molar ratio of the reactants. The influence of differences in the carbon (powder and fiber forms) on the structure of TiC compacts is discussed.
Problems in the Shock Compaction of Diamond Using Fine‐Particle Additives
Authors: Kondo Ken‐ichi , Sawai Sumiichi
Published: March 2005

Shock compaction experiments for diamond powder with an initial size of 2 to 4 μm, respectively. The difference in the mechanical properties of SiC and diamond improves the densification, and Si is available to join diamond particles via chemical reaction. The difference of the constituent particle radii, however, causes serious problems with the distribution of shock energy.
Partial Bi‐Sr‐Cu‐O Subsolidus Diagram at 800°C with and without Lithium Carbonate
Authors: Saggio J. A. , Sujata K. , Hahn J. , Hwu S. J. , Poeppelmeier K. R. , Mason T. O.
Published: March 2005

Solid‐phase relationships have been determined for the Bi2O3–SrO–CuO system at 800°C in air with and without Li2CO3 mineralizer. Two ternary compounds were detected with Bi:Sr:Cu ratios of approximately 2:2:1 and a solid‐solution phase 11−;x:9+x:5 with 0x0.4. The solid‐solution phase is a 9 K super‐conductor at x=0.4. Two additional compounds with Bi:Sr:Cu ratios of approximately 4:9:1 and 2:7:2 are apparently stabilized by the presence of Li2CO3, but do not form without it. X‐ray crystallographic data are provided for each compound. Ramifications for quaternary Bi:Sr:Ca:Cu‐O superconductors are discussed.
Adhesion of Electrolessly Deposited Nickel on Lead Zirconate Titanate Ceramic
Authors: Baumgartner Charles E.
Published: March 2005

The adhesion of electrolessly deposited Ni onto lead zirconate titanate (PZT) ceramic has been measured as a function of both the ceramics surface preparation prior to metalization and the plated Ni thickness. A maximum in NI/PZT interfacial adhesion of approximately 27 kg/cm2, as measured by a pull test, occurs when the ceramic grain boundaries are chemically etched, thereby providing points to mechanically anchor the Ni deposit. The adhesion decreases with overetching as the ceramic grains are undercut and drops off dramatically with increasing plated Ni thickness.
Determination of the Fe2+/Fe3+ Ratio in Nuclear Waste Glasses
Authors: Hunter R. Todd , Edge Mark , Kalivretenos Aristotle , Brewer Kathy M. , Brock Nancy A. , Hawkes Alice E. , Fanning James C.
Published: March 2005

The Fe2+/Fe3+ ratios of 47 simulated nuclear waste glass samples with ratios varying from 0.01 (oxidized) to 1.6 (reduced) were determined by wet‐chemical and Mössbauer spectral analyses. The wet‐chemical method involved the spectrophotometric determination of Fe2+ and total iron using remote spectroscopy with fiber optic chemical sensing. Interferences from other species present in these glasses were examined and alternative analytical techniques were investigated. Results of wet‐chemical and Mössbauer spectral analysis were comparable; however, the wet‐chemical method is probably preferable for the analysis of highly radioactive glasses until such glasses have been shown to have satisfactory Mössbauer spectra.
Hot Isostatic Pressing of a Presintered Yttria‐Stabilized Zirconia Ceramic
Authors: Druschitz Alan P. , Schroth James G.
Published: March 2005

The effect of hot isostatic pressing on the bend strength of ZrO2–3 mol% Y2O3 was critically dependent on the presintering process. Optimally sintered bodies contained no open porosity and exhibited large increases in strength following hot isostatic pressing. When open porosity of as little as 0.3% persisted after sintering, hot isostatic pressing increased the bulk density, but little or no increase in strength was realized. Two‐parameter Weibull analysis of the strength data was used to quantify the strength improvement obtained following hot isostatic pressing. Typical fracture‐initiating flaws were identified through optical and electron microscopy.
Effect of Dispersants on the Rheological Properties and Slip Casting of Concentrated Alumina Slurry
Authors: Chou Kan‐Sen , Lee Li‐Jun
Published: March 2005

Slip casting is one of the most common forming techniques used in the fabrication of ceramics. To obtain successful casting results, one need first to fully deagglomerate the ceramic powders and get concentrated slurries with good rheological properties. In this work, the rheological properties of concentrated alumina slurries were studied as functions of solid contents and quantities of two different dispersants, i.e., sodium pyrophosphate and diammonium hydrogen citrate. It was found that these properties could be satisfactorily related to the maximum packing fractions which were determined from sedimentation experiments. Our results also indicated that an optimum deflocculation process can always lead to optimal casting and sintering results.
Formation of Acicular Monoclinic Zirconia Particles under Hydrothermal Conditions
Authors: Li Chunting , Yamai Iwao , Murase Yashio , Kato Etsuro
Published: March 2005

Acicular monoclinic ZrO2, particles were prepared by hydrothermal treatmentat 250°C using sulfuric acid solutions containing zirconium ions. The formation process and morphology of the ZrO2, particles were investigated. Two types of acicular monoclinic Zr02, particle morphologies were obtained, both elongated in the 〈001〉 direction, and the range of acicular ZrO2, particle sizes changedfrom 0.3 to 1.3 μ m with hydrothermal conditions. Addition of MgSO4, to the starting solution promoted the crystallization of the monoclinic ZrO2, particles.
Interplay of Sintering Microstructures, Driving Forces, and Mass Transport Mechanisms
Authors: Cannon Rowland M. , Carter W. Craig
Published: March 2005

The equilibrium shapes of segments of a row of sintering particles are calculated for the case where interparticle distances are constrained and, in particular, for only vapor‐phase transport or surface diffusion active. These equilibrium states are contrasted with those obtained by mechanisms which allow densification. The sintering potentials and surface curvatures are calculated for the equilibrium shapes as a function of dihedral angle. Expressions for the rate of shrinkage are presented and, for the case of equilibrium structures, calculated exactly.
Stabilization of Cubic Zirconia by Aluminum Nitride
Authors: Mukerji Joydeb
Published: March 2005

Cubic ZrO2 is stabilized at room temperature by the addition of AIN. The percentage of c‐ZrO2 in the mixture of c‐ZrO2 and m‐ZrO2 increases linearly with the addition of up to 20 mol% AIN and decreases thereafter. Stabilization becomes complete at 50 mol% AIN. The lattice spacing of the cubic phase gradually expands up to 20 mol% AIN. A displacement reaction ZrO2+ AIN → ZrN+Al2O3 occurs above 20 mol% AIN and is completed at 50 mol% AIN.
Characterization of β‐Silicon Nitride Whiskers
Authors: Homeny Joseph , Neergaard Lynn J. , Karasek Keith R. , Donner Jeffry T. , Bradley Steven A.
Published: March 2005

The physical, chemical, and structural properties of a commercially available β‐Si3N4 whisker were characterized. Bulk chemical analysis indicated that the whiskers were close to stoichiometric silicon nitride, with oxygen and yttrium as the major impurities. Surface chemistry analysis by XPS analysis revealed that the surfaces consisted primarily of silicon nitride, with the oxygen and yttrium impurities concentrated at the surfaces. SEM and STEM studies indicated that the whiskers were dimensionally straight with relatively featureless surfaces, although some whiskers had Y‐rich particles attached. The whiskers were also found to be of extreme crystallographic perfection, as determined by TEM analysis.
Effect of Magnesia Solute on Surface Diffusion in Sapphire and the Role‐of Magnesia in the Sintering of Alumina
Authors: Bennison Stephen J. , Harmer Martin P.
Published: March 2005

Surface diffusion in sapphire and sintering of Al2O3 have been studied under identical firing conditions (1593°C, N2) as a function of MgO solute additions. The effect of MgO on surface diffusion has been investigated directly using the technique of multiple scratch smoothing on the (1123) surface of sapphire. For these conditions MgO additions enhance the decay of periodic profiles by a factor of 4; that is interpreted as reflecting an increase in the surface diffusivity by the same amount. Measurements of the grain sizedensity trajectory during final stages of sintering of Al2O3 reveal that MgO enhances the densification rate/coarsening rate ratio by a modest factor of 1.8. Since an increase in surface diffusivity alone would decrease the ratio, it is deduced that the primary role of MgO in the sintering of Al2O3 is other than the influence on surface diffusion. These observations in conjunction with independent measurements of the effect of MgO on grain‐boundary mobility confirm that the primary role of MgO is the suppression of grainboundary motion.
Formation of a High‐Temperature Liquid Phase During the Sintering of PbFe2/3W1/3O3
Authors: Mizutani Nobuyasu , Lu Chung‐Hsin , Shinozaki Kuzuo , Kato Masanori
Published: March 2005

A high‐temperature liquid phase (rather than a low‐temperature liquid phase at 690°C as reported recently) has been demonstrated to form at 860°C on heating and to solidify at 840°C on cooling in PbFe2/3O3. This liquid phase not only promotes densification, but also induces the formation of rounded PbFe2/3W1/3O3 grains during sintering at 870°C. Through slow cooling at a rate of 25°C/h after sintering, platelike grains, designated G phase, are found to form in a thin surface layer of specimens. This formation of platelike G phase is considered to be related to the solidification and recrystallization of the liquid phase exuded from the interior. The amount of the G phase on the surfaces decreases with the increase of cooling rates, indicating that fast cooling will lead the liquid phase to be solidified in the bulk of specimens. These results reveal that the microstructure of PbFe2/3W1/3O3 is greatly affected by the high‐temperature liquid phase; additionally, the slow cooling treatment seems to be a direct and effective method for removing the residual liquid phase from PbFe2/3W1/3O3.
New Fluorination Reactions of Ammonium Bifluoride
Authors: Sanghera Jasbinder S. , Hart Patricia , Sachon Maria G. , Ewing Ken J. , Aggarwal Ishwar
Published: March 2005

This paper describes a novel route for the production of low‐oxygen‐containing fluorozirconate glasses. The process involves the use of a hitherto unknown solid‐state chemical reaction between ammonium bifluoride and specific anhydrous and hydrated metal fluoride salts. The products are defined as ammonium fluoride–metal fluoride complexes. The kinetics of their formation and subsequent dissociation were followed by thermogravimetric analysis. It was observed that these complexes decompose with the evolution of HF above temperatures at which ammonium bifluoride decomposes and where its supply may be exhausted. These materials have been used to melt fluorozirconate glasses. The oxygen contents of these glasses have been dramatically reduced to approximately 10 ppm. The glass stability, as defined by the lack of devitrification on reheating, also appears to increase with a lowering of the oxygen content. This implies that the mechanism of nucleation and growth is predominantly heterogeneous and not homogeneous nucleation. Furthermore, the production of long lengths of crystal‐free fluoride fibers for transcontinental optical communication systems appears to be a realistic goal, especially if the heterogeneities can be eliminated.
Dihedral Angles in Magnesia and Alumina: Distributions from Surface Thermal Grooves
Authors: Handwerker Carol A. , Dynys Joseph M. , Cannon Rowland M. , Coble Robert L.
Published: March 2005

Dihedral angles, Ψs, from surface thermal grooves were measured using a metal reference line technique for polycrystalline MgO, undoped Al2O3, and MgO‐doped Al2O3. The values of Ψs span the following ranges: 89° to 116° for MgO at 1520 K, 76° to 166° for undoped Al2O3 at 1870 K, and 90° to 139° for MgO‐doped Al2O3 at 1870 K. For all three systems, the median Ψs values are 105° to 113°, implying that the median γgb/γs is 1.1 to 1.2, in contrast to metals where γgb/γs ranges typically from 1/4 to 1/2. The widths in Ψs distributions were different for the three materials with the width increasing in the following order: MgO, MgO‐doped Al2O3, undoped Al2O3. For all three materials, the grainboundary grooves and their corresponding Ψs were not symmetrical with respect to the surface normal. The asymmetry for MgO was due to the pinning of the grain boundaries by the surface thermal grooves. The range of inclination angles of the grain boundary to the surface was a function of Ψs, with the maximum inclination angles of ∼13°, in quantitative agreement with theory.
Causes of Instability and Aging of Piezoelectric Power Ceramics
Authors: Eyraud Lucien , Gonnard Paul , Claudel Bernard
Published: March 2005

A simple model of substituted perovskites of the PZT type involving the presence of centers which can act both as donors and acceptors provides an explanation of the cancellation of space charge density (ρ=−div ) in polarized ceramics. A cause of instability can be avoided by incorporating substitutions in the cation lattice to form these centers and lock them in position. These substitutions insure the nonconductive state of the material although they allow a short‐range electron transfer between the centers.
Phase Diagram of the BaO‐CuO Binary System
Authors: Zhang Wei , Osamura Kozo , Ochiai Shojiro
Published: March 2005

The phase diagram of the BaO‐CuO binary system has been investigated in air and in a mixed gas of Ar + 0.21 atm of O2. The existence of two compounds, BaCuO2 and Ba2CuO3, was confirmed. The phase transition of Ba2CuO3 from an orthorhombic to a tetragonal phase was observed to occur at 1083 K. The lattice constants of the tetragonal Ba2CuO3 phase were determined to be a= 1.2975 nm and b= 0.3992 nm. BaCuO2 was shown to melt incongruently by a synthetic reaction at 1289 K. Furthermore, the existence of two eutectic reactions and a peritectic reaction in the present system was confirmed.
Static Fatigue Behavior of Polycrystalline Beryllia
Authors: Ferber Mattison K. , Becher Paul F.
Published: March 2005

The delayed failure/static fatigue behavior of a polycrystalline BeO ceramic was examined by measuring the time to failure as a function of the static stress level. Using this technique, curves were generated over a temperature range of 8° to 50°C. The test environment consisted of a fluorocarbon fluid containing small quantities of water. The measured fatigue life was a strong function of both stress and temperature. The data also provided evidence of a fatigue limit which was insensitive to the temperature. These results were consistent with data generated from direct V–KI measurements. The fatigue data were used to examine the applicability of a generalized slow crack growth model relating the subcritical crack velocity to the stress intensity factor. Initially, agreement between the experimental and predicted behavior could be obtained only by assuming that the activation volume for the stress‐assisted crack growth reaction was negligible. This result implies that the major stress dependency was associated with the preexponential term in the crack growth equation. However, an alternate and more reasonable description of the experimental data was obtained by assuming that the activation volume exhibited a linear dependence upon the mechanical stress.
Determination of Residual Stress Profile Using a Strain Gage Technique
Authors: Virkar Anil V.
Published: March 2005

A simple beam theory analysis is presented for the determination of residual stress patterns in beams or plates using a strain gage technique. The analysis is valid for a general stress distribution which need not be symmetric with respect to the neural axis. The experimental approach consists of attaching a strain gage on the surface of a beam or a plate and then grinding off the other side. The recorded strain vs thickness ground off data can be used to determine the corresponding stress profile.
Kinetics of Titanium(IV) Chloride Oxidation
Authors: Pratsinis Sotiris E. , Bai Hebi , Biswas Pratim , Frenklach Michael , Mastrangelo Sebastian V. R.
Published: March 2005

The oxidation rate of TiCl4 vapor was measured by FTIR spectroscopy between 700° and 1000°C in a furnace aerosol reactor. The reaction rate was found to be first order with respect to TiCl4 and to follow the Arrhenius form. The apparent activation energy for the reaction was 88.8 ± 3.2 kJ/mol and the preexponential factor 8.26 × 104 s−1. A kinetic mechanism for the oxidation of TiCl4 was proposed that was consistent with the observed dependence of oxygen concentration on the apparent rate constant.