bluuebunny/crossref_metadata_2025 huggingface dataset:
Strengths of Green and Fired Spherical Aluminosilicate Aggregates
Authors: WONG JADE Y. , LAURICH‐McINTYRE SUZANNE L. , KHAUND ARUP K. , BRADT R. C.
Published: March 2005

The strengths of four paired sizes of green and fired spherical aluminosilicate bodies were measured in diametral compression and then compared through their Weibull distributions. Similarities of the strength distributions support the general concept that defects which are created in the green state during the processing of a ceramic body may be propagated to the fired bodies. The results also suggest the genesis of new defects from reactions during firing or during the sintering process and that these reaction/sintering‐generated defects may be of equivalent importance to the processing defects from the overall perspective of the finished body strength.
Weibull Statistics: Tensile and Bending Tests
Authors: Medrano Ricardo E. , Gillis Peter P.
Published: March 2005

Generally, the strength of optical fibers is measured in a tensile test, while their static fatigue is measured in a bending test. A useful comparison can be made if the relationship between tensile stress and maximum bending stress can be interpreted using a “weakest link in the chain” model. This is done for a Weibull strength distribution and for a modification of that function which assumes the existence of upper and lower limits for strength.
Synthesis of Sintered Diamond with High Electrical Resistivity and Hardness
Authors: Akaishi Minoru , Yamaoka Shinobu , Tanaka Junzo , Ohsawa Toshikazu , Fukunaga Osamu
Published: March 2005

Diamond and diamond‐ultrafine Co powder mixtures were sintered at 7.7 GPa and 1800° to 2000°C. A well‐sintered body with a fine‐grained homogeneous microstructure, high hardness, and high electrical resistivity was produced when a diamond‐5 vol% Co powder mixture was used as the starting material.
Crystal Growth of Cadmium Oxide from the Vapor Phase
Authors: Shmada Shiro , Nomura Satoshi , Kodaira Kohei , Matsushita Toru
Published: March 2005

Single crystals of CdO were grown at temperatures of 930° to 1080°C from the vapor phase by air oxidation of Cd vapors which were generated at a constant rate by reaction of CdO with graphite. A prolonged growth up to 70 h at 1030°C produced a crystal conglomerate with a maximum size of 13.5 mm. The electrical resistivity and electron density of the crystal in the direction of (WO) were 5x10‐4°‐cm and 1.3X1020/cm3, respectively, at 20°C.
Structure of Polymeric PbTiO3 Gels
Authors: Dey Sandwip K. , Budd Kenton D. , Payne David A.
Published: March 2005

The structural features of PbTiO3 gels were found to be highly dependent on hydrolysis conditions. Gels formed from acid‐catalyzed solutions were clear and rubbery, whereas base‐catalyzed gels were translucent or cloudy with phase separation. Direct TEM observations determined that acid‐catalyzed gels were fibrous in character and physically homogeneous, whereas base‐catalyzed gels had a coarse texture. Analyses by EDX and SAD indicated that acidic gels were chemically homogeneous and microcrystalline, whereas basic gels were heterogeneous and amorphous.
Theoretical Analysis of Chemical Vapor Deposition of Ceramics in an Impinging Jet Reactor
Authors: REBENNE HELEN , POLLARD RICHARD
Published: March 2005

A mathematical model for chemical vapor deposition in an impinging jet reactor is extended to consider growth of materials that are nonstoichiometric or that contain multiple solid phases. The model treats the fluid flow of the reactant gas mixture, multicomponent heat and mass transfer, and simultaneous gas‐phase and surface reactions. For a given system, insight into the rate‐limiting steps can be obtained by identifying a set of reaction rate constants that gives a match between theoretical results and experimental data. The calculations also provide quantitative information on the relationships between operating conditions, deposition rate, and deposit composition. Results for production of boron carbide from BCI 3, CH4, and H2 are presented as an example. Under typical processing conditions, deposition of By C is found to be controlled primarily by the rate of CH4 decomposition and the extent of surface coverage by CH4 Theoretical calculations are presented for different sets of operating conditions to illustrate the predictive capability of the model. Also, the sensitivity of results to various reaction mechanisms and to values for solid‐phase activities is evaluated. Analogies are drawn between the boron carbide process and deposition of other ceramics in which a carbon‐containing reactant is used.
Effect of Rigid Inclusions on the Sintering of Glass Powder Compacts
Authors: Rahaman M. N. , De Jonghe L. C.
Published: March 2005

The effect of rigid inclusions on the sintering of glass powder compacts has been investigated at 600°C. The densification rates show good agreement with the rule of mixtures for inclusion volume fractions of °0.1 The transient stresses generated during sintering by the presence of the inclusions were evaluated from the sintering data. Below inclusion volume fractions of °0.12, the results are in excellent agreement with Scherer's theory for viscous sintering with rigid inclusions. At higher inclusion volume fractions, interactions between the inclusion particles lead to large deviations from theoretical predictions.
Subcritical Crack Growth along Ceramic‐Metal Interfaces
Authors: Sung Oh Tae , Cannon R. M. , Ritchie R. O.
Published: March 2005

Environmentally assisted subcritical crack growth along glass/copper interfaces is examined in ambient‐temperature gas environments as a function of humidity. Resulting interfacial crack velocities (v), characterised in terms of the crack extension force (G) and approximate solutions for the linear elastic stress intensity factor (K), show ν‐K curve behavior typical of (bulk) ceramics. Subcritical crack growth rates are found to be initially highly sensitive to K for G) and to show evidence of a threshold stress intensity between 0.1 and 0.25 Mp a°m1/2 (region I). At higher crack velocities typically between °10–5 and 10–4 m/s, growth rates display a plateau and tend to become K independent (region II). Although specimen‐to‐specimen scatter is large in region I, interfacial crack velocities in moist environments far exceed those in dry environments and are over 3 orders of magnitude faster (at fixed K) than reported rat's for (bulk) soda‐lime glass.
Raman Spectra of Rare‐Earth Phosphate Glasses
Authors: Morgan Steven H. , Magruder Robert H. , Silberman Enrique
Published: March 2005

Raman spectra have been recorded for glasses in the binary systems CeO2‐P2O5 and Pr2O3‐P2O5. The cerium phosphate glasses were prepared having different concentrations of CeO2 and the praseodymium phosphate glasses with different ratios of Pr3+ to Pr4+. The spectra indicate that both cerium and praseodymium enter the glass in modifying sites. We see no changes in the Raman spectra with Pr3+/Pr4+ ratio. Measurements of the density and glass transition temperature are also reported.
Enhanced Crystallization of a Glassy Phase in Silicon Nitride by the Addition of Scandia
Authors: Mecartney Martha L.
Published: March 2005

A Sc2O3‐MgO‐Al2O3‐SiO2 melt reacted with bulk pieces of hot‐pressed Si3N4, dissolving Si3N4 at the surface and penetrating into the interior via the grain boundaries. During subsequent cooling, the glass phase in the Si3N4 easily crystallized and fine crystallites were formed, but no phase separation was observed. This behavior contrasts strongly with that observed for a similar melt reaction without Sc2O3.
Influence of Powder Preparation and Compacting Pressure on the Structure of Lithium Silicate Pellets
Authors: Mickelelt Michael
Published: March 2005

This contribution reports on lithium meta‐ and orthosilicates as potential breeder materials for fusion reactors. The preparation of the powder by the spray‐dry technique and the selection of the compacting pressure were important influences on the structure of the “green pellets.”
Effect of Subcritical Crack Growth on Fracture Toughness and Work‐of‐Fracture Tests Using Chevron‐Notched Specimens
Authors: TROCZYNSKI THOMAS B. , NICHOLSON PATRICK S.
Published: March 2005

A correlation between the plane strain stress intensity factor KI, load, and crack extension has been analyzed for constant displacement and constant loading rate experiments, using chevron‐notched, four‐point‐bend specimens. It is assumed that at the beginning of the experiment the chevron triangle tip is not ideally sharp. As loading continues, the crack initially moves with velocity vt at KI equal to a threshold value Kt. Maximum crack velocity is reached at KI= KIC, the fracture toughness. Depending on the type of material tested, a specific displacement or loading rate must be used to correlate the maximum load with KIc. An error in KIC calculation is estimated if different displacement rates are applied. Repeated loading‐unloading work‐of‐fracture (WOF) experiments generate values related to the resistance of the material to fracture initiation, Kt, only when the crack length approaches 100% of the specimen width. Values related to material's fracture toughness, KIC are not generated in WOF tests.
Stress Buildup and Relaxation During Ion Exchange Strengthening of Glass
Authors: SANE AJIT Y. , COOPER A. R.
Published: March 2005

A soda‐lime‐silica glass was subjected to an ordinary ion exchange treatment in molten potassium nitrate at temperatures near and substantially below the strain point of the glass. Stress profiles were measured as a function of exchange temperature and time. At all temperatures, the measurements showed rapid relaxation of the surface stress and the development of a pronounced compression maximum in a short period. A simple viscoelastic model with composition‐independent parameters was used to analyze the stress profiles. Neither Maxwell's nor Michelson's relaxation expression could satisfy both characteristics of the residual stress development. Reasons for discrepancies are discussed.
Effects of pH and Temperature on Sol‐Gel Processing within the Pbo‐TiO2 System
Authors: Lee Moon‐Ho , Park Young‐Ho , Yang Cheul‐Kee
Published: March 2005

Effects of sol formation temperature and pH value on sol‐gel processing within the PbO‐TiO2 system were investigated. PbO‐TiO2 gels were prepared from the mixed solution of lead nitrate and titanium tetrachloride at 30° to 70°C under various pH values of 1.0 to 10.8, and dehydrated at 60° to 80°C for 72 h under vacuum. The dried gels are amorphous. The crystalline phases of the products after calcination at 70°C for 1 h in air are dependent upon the sol formation conditions as follows: (l)TiO2:30°C, pH 1.0 to 4.6; and 40° C, pH l.0 to 2.O. (2) PbTi3O7:50° to 70°C, pH 1.0 to 4.6. (3) PbTiO3: 70°C, pH 8.0 to 10.8. (4) PbTiO3 and traces of PbTi3O7: 30° to60°C, pH 7.1 to 10.8.
New Arsenate Glasses
Authors: VAN UITERT LE GRAND G. , GRODKIEWICZ WILLIAM H. , BRUCE ALLAN J.
Published: March 2005

A variety of new ternary arsenate glasses formed from mixtures of ionic alkali‐metal meta‐arsenates (MAsO3) with somewhat covalent higher valence metal oxides (MOx) have been prepared. From rate‐of‐hydrolysis comparisons, it has been found that bonding in these glasses is enhanced by de‐protonization. The latter is enhanced through processing using alkali‐metal flourides and increases the number of direct oxygen links between the higher valence metals. Stabilization also tends to increase with the covalent bonding or chain‐forming character of the latter metals as well as with the electrostatic binding between alkali‐metal ions and the chain linkage oxygens.
Effect of Surface Tension on the Toughness of Glass
Authors: CHUANG TZE‐JER
Published: March 2005

Mechanical stresses (i.e., surface tension) inherently exist on a general free surface because its atomic structure differs from its bulk counterpart. The effect of surface tension is amplified at a crack tip because of curvature enhancement. An integral equation describing this effect on the toughness of glass is derived and first‐order approximations using a weight function technique were made. The qualitative results indicate that the geometry‐induced toughening is linearly proportional to surface tension and crack tip curvature and to the square root of crack tip zone size. An illustrative example of a recently observed crack tip in SiO2 glass is given which shows that toughness is enhanced by ∼3 times the intrinsic K1C value.
Synthesis of LiAlO2 Powder by Hydrolysis of Metal Alkoxides
Authors: HIRANO SHIN‐ICHI , HAYASHI TAKASHI , KAGEYAMA TOMOYUKI
Published: March 2005

Crystalline fine powders of LiAlO2 can be prepared by hydrolysis of metal alkoxides for application to the breeder blanket in nuclear fusion. The precipitates were fine crystalline particles of β‐LiAlO2of ∼0.1‐μm size under controlled conditions. The transformation from β‐ to γ‐phase was confirmed at temperatures between 700° and 750°C. The microstructure of a sintered body at 1000°C consisted of homogeneous fine particles and pores suitable for the blanket material. A fully dense sintered body could be prepared at 1400°C.
Structural Aspects of the Lattice Thermal Expansion of Hexagonal Cordierite
Authors: PREDECKI PAUL , HAAS J. , FABER JOHN , HITTERMAN R. L.
Published: March 2005

The mechanism of lattice thermal expansion in pure hexagonal cordierite prepared by glass devitrification was investigated by time‐of‐flight neutron powder diffraction at temperatures from 22° to 750°C under vacuum. Full matrix least‐squares refinement of the diffraction spectra was carried out in space group P6/mcc using the Rietveld method. The structural data from the refinements were resolved into components parallel and normal to the c axis. The negative c axis expansion results from two effects: (1) increasing distortion of the T2 tetrahedral (ring tetrahedra) with temperature, primarily due to displacement of the T2 cations toward the c‐axis channels in the structure; (2) decreasing distortion of the T1/M tetrahedra/ octahedra with increasing temperature, due to octahedral I (M‐O1) bond expansion and an associated decrease in torsional distortion of the T1 tetrahedra.
Diffraction Studies of a Highly Metastable Form of Amorphous Silica
Authors: KONNERT JOHN , D'ANTONIO PETER , HUFFMAN MARIA , NAVROTSKY ALEXANDRA
Published: March 2005

An amorphous powder of SiO2 that calorimetric studies indicated to be energetically metastable by 46.9 ± 0.8 kj/mol relative to fused silica was studied by X‐ray diffraction. A calculation of the energetic instability, based on the bond length and bond angle distributions derived from the diffraction data and utilizing the force constants for bond stretching and bending, indicated that 41.3 ± 7.9 kj/mol of the instability may be associated with distortions of the Si‐O bonds, the O‐Si‐O bond angles, and the Si‐O‐Si angles. Analyses of the extensive small‐angle scattering from the porous material suggested that only a small portion of the instability is associated with surface structures.
Theory for Sintering in Temperature Gradients: Role of Long‐Range, Mass Transport
Authors: Searcy Alan W.
Published: March 2005

For a one‐component crystalline solid, the driving force for diffusion in a temperature gradient by any path is the gradient in the equilibrium vapor pressure. A When transport is limited by a surface step, the driving force is the difference in vapor pressures at the extremes of the temperature gradients. Sample calculations suggest that temperature gradients are important in driving densification during fast firing and probably are important during conventional firing.
Demixing of Oxides under a Temperature Gradient
Authors: AKBAR SHEIKH A. , KABURAGI MAKOTO , SATO HIROSHI , KIKUCHI RYOICHI
Published: March 2005

The microscopic mechanism of a demixing of binary oxide solid solution in an oxidizing atmosphere under a temperature gradient is investigated by the path probability method of irreversibly statistical mechanics. The problem is reduced to a steady‐state metal ion transport under the coexistence of an oxygen partial pressure gradient and a temperature gradient. Calculations are performed under two different conditions: (i) demixing in a steady‐state diffusion process under the two driving forces and (ii) a redistribution of constituent metal ions in a closed system under a given temperature gradient (Soret effect). The results can be interpreted as the superposition of the contributions of two driving forces plus a cross term which tends to zero as the driving forces become small. The difference between these two cases is discussed in detail and some controversies in the past work with respect to the difference are pointed out.
Photoluminescence and Absorption of a Zirconium Fluoride Glass and ZrF4
Authors: Ohishi Yasutake , Sakaguchi Shigeki , Takahashi Shiro
Published: March 2005

The glass containing reduced zirconium exhibits a photoemission band at 480 nm and an excitation band from 230 to 370 nm. Reduced zirconium tetrafluoride has broad absorption at 400 nm. Reduction of zirconium tetrafluoride occurs through fluorine or oxygen impurity elimination. When fluorine ion deficiency occurs, emission and excitation bands appear at 440 and 350 nm, respectively. When oxygen deficiency occurs, emission and excitation bands appear at 480 and 300 nm, respectively.
Outgassing of ZrF4‐Based Glasses
Authors: Mathew James , Doremus Robert
Published: March 2005

The nature and quantities of the chemical species evaporating from the surface of fluorozirconate glasses heated to above Tg were investigated. ZrF4 vaporized from a ZBLAN glass whereas ZrF3. ZrF2 and ZrF vaporized from a ZBL glass. Other gases found include HF, HCl, O2, CO2, and atomic fluorine.
State‐Variable Analysis of Inelastic Deformation of TiC Single Crystals
Authors: SURA VIVEK M. , KOHLSTEDT D. L.
Published: March 2005

The log σ‐log ɛ data obtained from load relaxation experiments on TiC single crystals, at 900° to 1400°C, were analyzed in terms of Hart's two‐branch rheological model. The analysis verified the existence of a mechanical equation of state within the ranges of stress, strain rate, and temperature employed. Straight and clustered dislocations dominated the micro‐structure of samples at low temperatures, while well‐developed cell structures dominated the microstructure of samples at high temperatures. The observed changes in log σ‐log ɛ curves and the dislocation structure both indicate that, in addition to the glide‐controlled mechanisms, climb/cross‐slip‐controlled mechanisms contribute significantly to the plastic flow with increasing temperature.
Measurement of Residual Stresses in Coatings on Brittle Substrati by Indentation Fracture
Authors: GRUNINGER MARK F. , LAWN BRIAN R. , FARABAUGH EDWARD N. , WACHTMAN JOHN B.
Published: March 2005

A method for evaluating stresses in coatings on brittle substrates by indentation is described. The basis for evaluations is fracture mechanics model of the radial crack system in the Vickers geometary, incorpeorating the effects of a thin surface demonstrate the methodology. The crack size on these coated specimens are found to be considerebly small than those on uncoated controls, indicating substantial (∼50 MPa) in‐plane expansions observed after applying the coatings to already indented sufaces, are found to make an unexpectedly large contribution to the fracture susceptibility. The procedure offers a simple means for quantifying the mechanical integrity of coating configuration for ceramic components.
Liquid‐Phase Bonding of Silicon Nitride Ceramics
Authors: BAIK SUNGGI , Raj Rishi
Published: March 2005

Mg‐Si‐O‐N glasses were used to bond dense Si3N4 ceramic pieces by a liquid‐phase diffusion bonding mechanism. In this case, it was difficult to achieve defect‐free bonding because, at low nitrogen content in the glass, a large mismatch in thermal expansion coefficient produced cracks perpendicular to the bonding glass layer. With an increase in nitrogen content, the glass layer became frothy and contained “bubbles.” However, when a small amount of elemental silicon was added to the glass, volatile reaction was suppressed and intimate bonding was achieved without thermal cracks.
Comparison of the Properties of Oxycarbide and Oxynitride Glasses
Authors: Homeny Joseph , Nelson Gregory G. , Paulik Steven W. , Risbud Subhash H.
Published: March 2005

Oxycarbide glasses in the Mg‐Al‐Si‐O‐C system and oxynitride glasses in the Mg‐Al‐Si‐O‐N system were synthesized by conventional melting techniques, chemically analyzed, and evaluated for selected mechanical properties as a function of carbon or nitrogen content. Both glass systems exhibited increases in density, Young's elastic modulus, microhardness, and fracture toughness with increasing anionic substitutions. Carbon substitutions were found to be more effective than nitrogen additions for improving glass properties.
Study of Tetraethyl Orthosilicate Hydrolysis by in Situ Generation of Water
Authors: Jada Sivananda S.
Published: March 2005

The effect of acetic acid on acid‐catalyzed tetraethyl orthosilicate (TEOS) hydrolysis has been followed with 1H NMR. The changes in [CH2] and [CH3] of TEOS, [OH] of ethanol, and the formation of ethyl acetate are observed during the sequential addition of acetic acid. Mixed SNl and SN2 reaction mechanisms are proposed to explain the TEOS hydrolytic behavior by the esterification process.
Growth and Coalescence of Indentation Cracks in Glass
Authors: Yoda Mitsuo , Yoshikawa Yoshio
Published: March 2005

Indentation cracks show the initial decrease and subsequent increase in crack velocity with the stress intensity factor whether the cracks are single or coalescent. The decrease in crack velocity is mainly due to the residual stress effects. For two collinear cracks, the individual cracks before coalescence show crack velocity much higher than would be expected on the basis of the stress intensity factor for single or coalescent cracks.
Deposition and Sintering of Particle Films on a Rigid Substrate
Authors: Garino Terry J. , Bowen H. Kent
Published: March 2005

Experimental techniques for the deposition and sintering of ceramic particle films on a rigid substrate have been investigated. Three representative systems (SiO2, ZnO‐Bi2O3, and Al2O3) were chosen to determine the validity of the conceptual processing model. Crack‐free, sintered films 1 to 50 μm thick were produced using single or multiple deposition/sintering cycles.
Oxide Thickness Measurement in the Electron Probe Microanalyzer
Authors: Blachere J. R. , Klimovich D. F.
Published: March 2005

An X‐ray method for the measurements of the thickness of supported thin films in the microprobe is modified for silica films on silicon nitride and silicon carbide. The intensities of the oxygen Kα line are measured on bulk SiO2 and on the film. The derivation of the caliboration curve giving the thickness of the film from the ratio of these intensities is outlined. The method has been used for silica films thinner than 1 μm with a lateral resolution of a few micrometers.
Sintering and Mechanical Properties of Yttria‐Doped Tetragonal ZrO2 Polycrystal/Mullite Composites
Authors: Ishitsuka Masayuki , Sato Tsugio , Endo Tadashi , Shimada Masahiko
Published: March 2005

Yttria‐doped tetragonal ZrO2 polycrystal (Y‐TZP)lmullite composites were sintered at 1450° to 1500°C in air to disperse rodlike mullite grains at the grain boundary of Y‐TZP and the mechanical and thermal properties were investigated. The aspect ratios of mullite grain were >2. High fracture strength of 1000 MPa and fracture toughness of 12 MPa·m1/2 were obtained by dispersing <20 vol% of mullite into Y‐TZP. The thermal expansion coefficient of Y‐TZP/mullite composites decreased with increasing mullite content. The thermal shock resistance of Y‐TZP was greatly improved by dispersion of rodlike mullite grains.
Crack Initiation and Arrest in a SiC Whisker/A12O3 Matrix Composite
Authors: JENKINS MICHAEL G. , KOBAYASHI ALBERT S. , WHITE KENNETH W. , BRADT RICHARD C.
Published: March 2005

The fracture initiation and arrest stress intensity factors were determined for a SiC‐whisker‐reinforced AI2O3 matrix composite. A chevron‐notched, three‐point‐bend specimen was used to genera e the load/displacement curve, which exhibited repeated crack initiation, followed by crack arrest behavior. Corresponding stress intensity factors were determined for both situations using the compliance technique. Calculated crack arrest positions were in agreement with fractographic observations. Both the crack arrest and the crack initiation stress intensity factors exhibited a rising R ‐curve with increasing crack length, suggesting the presence of wake toughening effects on the crack growth resistance.
A Modified Chevron Specimen for Ceramic Materials
Authors: Hlvisolt Günther , Munz Dietrich , Fett Theo
Published: March 2005

The well‐known chevron notch is modified by introducing a starter crack in a Knoop indentation test. An evaluation formula is given for the KIc determination, and first results are reported.
Effect of Silicon Carbide Fiber or Whisker Reinforcement on the Thermal Diffusivity/Conductivity of an Osumilite Glass‐Ceramic
Authors: Johnson Lloyd F. , Hasselman D. P. H. , Chyung Kenneth
Published: March 2005

The thermal diffusivity of silicon carbide fiber‐ and whisker‐reinforced osumilite glass‐ceramic was determined by the laser‐flash method. The thermal conductivity was calculated from the data of thermal diffusivity, density, and specific heat measured by differential scanning calorimetry. Because of the much higher thermal conductivity of the crystalline silicon carbide whiskers compared to the corresponding value for the amorphous fibers, the whisker‐reinforced composites exhibited significantly higher thermal diffusivity and thermal conductivity than the fiber‐reinforced composites.
Corrosion of a Silica‐Bearing Ceramic in Sulfur‐Oxygen Atmospheres
Authors: VAN DER BIEST OMER O. , BARNES JOHN , CORISH JOHN , NORTON JAMES FRANK
Published: March 2005

Experimental observations and thermodynamic calculations are described which show that formation of SiS vapor from SiO2 in a high‐sulfur, low‐oxygen atmosphere is a viable corrosion mechanism. This mechanism will become more important than the well‐known decomposition of SiO2 to SiO in those sulfur‐bearing atmospheres where the oxygen activity is close to the Si/SiO2 phase boundary on a volatility diagram.
Combined Effect of Flaw Distribution and Diameter Variation on the Statistics of Glass Fiber Strength
Authors: GUPTA PRABHAT K.
Published: March 2005

This paper examines the combined effects of flaw‐severity distribution and fiber diameter distribution on the fracture statistics of glass fibers. The approach adopted is to assume specific forms (Gaussian and Weibull) for the diameter distribution, a Weibull distribution for the true strength, and then to calculate the measured strength distributions. Exact analytical results are obtained in the cases of flawless fibers, uniform size flaws, and when true strength and fiber diameter are Weibull distributed. Approximate analytical expressions have been derived for the general case. A procedure is described to obtain the parameters of the true strength distribution from the knowledge of measured strength distribution and the coefficient of variation of fiber diameters. Implications of these results for the fracture statistics of high‐strength glass fibers are discussed.
Early Hydration of Tetracalcium Aluminoferrite in Gypsum and Lime‐Gypsum Solutions
Authors: BROWN PAUL WENCIL
Published: March 2005

Based on product compositions and on the compositional changes occurring in the aqueous phase, a mechanism for the early hydration of C4AF in solutions containing gypsum or lime and gypsum is suggested. According to this mechanism, early formation of AFt is preceded by the formation of alumina gel or C2AH8. Early AFt formation occurs through solution, and the early AFt product contains little or no iron. The solution chemistry also suggests that an amorphous, iron‐rich gel forms and that calcium is associated with this gel.
Enhancement of Strength through Sinter Forging
Authors: VENKATACHARI K. R. , RAJ R.
Published: March 2005

Packing defects in powder compacts can develop into microcracks during the sintering process. For example, an agglomerate which sinters differently than its surroundings can open up large, cracklike defects which are difficult to remove in free sintering. Traditionally, hot‐pressing or hot isostatic pressing has been used to prevent the formation of such defects. Here we show that processing defects can be virtually eliminated by sinter forging. In sinter forging the powder preform is compacted under a uniaxial compressive stress without any lateral constraint. In this way both densification and shear strain are imposed on the specimen. We have found that the shear strain can eliminate large pores by changing their shape. Eventually the flattening of the pore under compressive strain causes it to disintegrate into small pores which are then removed by sintering, leading to an increase in the strength of the ceramic. In alumina, a sigmoidal curve for the change in strength with strain is obtained where the strength begins to increase at 20% shear strain and reaches a maximum value at 60% strain. The shear strain required for the improvement in strength is compared with theoretical estimates.
Phase Relations and Ordering in the System ZrO2‐MgO
Authors: SIM SOO MAN , STUBICAN VLADIMIR S.
Published: March 2005

The Phase relationships in the system ZrO2‐MgO were reinvestigated over a wide range of temperatures and compositions. The extent of the cubic solid solution field was determined with precise lattice parameter measurements and a high‐temperature X‐ray furnace using analyzed samples. DTA results show that the addition of MgO to ZrO2 decreases the transition temperature for monoclinic ⇌ tetragonal ZrO2 and 1 mol% of MgO is soluble in the monoclinic zirconia at ∼1070°C.The invariant eutectiod point is at 13.5 ± 0.3 mol% MgO at 1406°± 7°C, which is in fair agreement with previous results by Grain. The ordered phase Mg2Zr5O12 (δ‐phase) can form metastably in cubic solid solutions at temperatures as low as 800°C after prolonged annealing. Evidence for the existence of the ordered phase MgZr6O13(γ‐phase) was obtained by electron diffraction technique. Conditions for the formation of this phase are described. The ordered phases in this system are metastable and their formation is an intermediate step in the eutectoid decomposition of the cubic phase.
Preparation of Larnthanum β‐Alumina with High Surface Area by Coprecipitation
Authors: Kato Akira , Yamashita Hisao , Kawagoshi Hiroshi , Matsuda Shimpei
Published: March 2005

Mixtures of La2O3 and Al2O3 with various La contents were prepared by co‐precipitation from La(NO3)3 and Al(NO3)3 solutions and calcined at 800° to 1400°C. The addition of small amounts of La2O3 (2 to 10 mol%) to Al2O3 gives rise to the formation of lanthanum β‐alumina (La2O3·11–14Al2O3) upon heating to above 1000°C and retards the transformation of γ‐Al2O3 to α‐Al2O3 and associated sintering.
Formation Process of Metastable Phase (δ) of Alkaline‐Earth Carbonate
Authors: Nishino Tadashi
Published: March 2005

The metastable phase (δ‐phase) of SrCO3 or BaCO3 is obtained by quenching from the phase transition temperature of each carbonate for the admixture of a few mol% of BaSO4. The present paper concerns the δ‐phase formation process in the systems SrCO3‐BaSO4 and BaCO3‐BaSO4 by comparing the “dissolution” tendency of incorporated BaSO4 in an aqueous suspension containing a cation‐exchange resin. A mixture of CaCO3 and BaSO4 was also examined for comparison as a system which does not participate in δ‐phase formation.
Crystallization Kinetics of Lithia‐Silica Glasses: Effect of Composition and Nucleating Agent
Authors: RAY CHANDRA S. , HUANG WENHAI , DAY DELBERT E.
Published: March 2005

The kinetics of crystallization of a 25Li2O · 75SiO2 (wt%) glass doped with Pt, Cu, Au, TiO2, and P2O5 were studied using nonisothermal techniques. The activation energy, E, and the frequency factor, v, for the overall crystallization process depended directly on the critical cooling rate for the glass formation, Rc, of these glasses. The crystallization kinetics of several other glasses in the lithia‐silica system were also studied as a function of composition, critical cooling rate, and liquidus temperature, Tm. E and v for these glasses were more dependent on the liquidus temperature than on Rc.
Formation of AlVO4 Solid Solution from Alkoxides
Authors: Yamaguchi Osamu , Uegaki Tatsuji , Miyata Yutaka , Shimizu Kiyoshi
Published: March 2005

Solid solutions of AlVO4 crystallize at lower temperatures than amorphous materials between 50 and 70 mol% Al2O3 prepared by the simultaneous hydrolysis of aluminum and vanadyl alkoxides. They decompose into α‐Al2O3, and V2O5, at 775° to 800°C. The compound AlVO4 prepared from 50 mol% Al2O3 has a triclinic unit cell with a = 0.6471 nm, b = 0.7742 nm, c = 0.9084 nm, α= 96.848°, β= 105.825°, and γ= 101.399°. The volume of the unit cell increases continuously with increases in Al2O3 content. The structure contains tetrahedral AlO4, octahedral AlO6, and tetrahedral VO4 groups.
Metastable Retention of a High‐Pressure Phase of Zirconia
Authors: DA JORNADA J. A. H. , PIERMARINI G. J. , BLOCK S.
Published: March 2005

A high‐pressure phase of zirconia, stable above 3.3 GPa at room temperature, can be retained metastably, at ambient room conditions of pressure and temperature by appropriate thermal/pressure treatments. The amount of high pressure phase retained depends on the thermal treatment, hydrostatic environment, and particle size of the starting powder. The results support the idea that the high‐pressure transformation in zirconia is initiated at nucleation centers whose population can be minimized by appropriate thermal treatments. The results also point out the importance of high pressure as a source of controllable driving force to induce the transformation in zirconia, thus permitting the use of annealing treatments to change the population of defects involved in nucleating the transition.
Nonlinear Electrical Properties of Grain Boundaries in an Oxygen‐Ion Conductor (CeO2· Y2O3)
Authors: TANAKA JUNZO , BAUMARD JEAN‐FRANCOIS , ABELARD PIERRE
Published: March 2005

The ceria‐yttria solid solution is a good anionic conductor. In polycrystalline ceramics, the complex impedance spectroscopy shows clearly the existence of a significant additional resistance associated with the grain boundaries. In this paper a theoretical analysis of the ac response in the nonlinear regime is developed. In particular the current‐voltage and capacitance‐voltage characteristics of the grain boundaries are derived. For the material investigated the former is well fitted by the Poole‐Frenkel law while the capacitance is voltage independent. These results are in agreement with microscopic STEM observations of a silica‐rich second phase.
Dielectric Properties of Ceramics in Ba (Co1/3 Nb2/3)O3–Ba(Zn1/3Nb2/3)O3 Solid Solution
Authors: Endo Kazuaki , Fujimoto Kenji , Murakawa Kyohei
Published: March 2005

The dielectric properties of the Ba (Co1/3 Nb2/3)O3–Ba(Zn1/3Nb2/3)O3 system were determined. Ba (Co1/3 Nb2/3)O3–Ba(Zn1/3Nb2/3)O3 has a complex perovskite structure, a high dielectric constant, a low dielectric loss, and a low temperature coefficient of the resonant frequency. A solid‐solution ceramic with 0.7Ba (Co1/3 Nb2/3)O3·0.3 Ba(Zn1/3Nb2/3)O3 has a dielectric constant of K=33.5, Q=11000 at 6.5 GHz, and a temperature coefficient of the resonant frequency of τf=0 ppm/°C. The temperature coefficient of resonant frequency can be varied by changing the composition. The Q values of the ceramics can be increased by annealing in a nitrogen atmosphere. These ceramics can be used for resonant elements and stabilized oscillators.
Admittance Spectroscopy of Polycrystalline ZnO‐Bi2O3 and ZnO‐BaO Systems
Authors: SHIM YOUNGJAE , CORDARO JAMES F.
Published: March 2005

Admittance spectroscopy was used to characterize the bulk electron traps in polycrystalline ZnO‐Bi2O3 and ZnO‐BaO systems. Temperatures from 30 to 350 K and a frequency range from 1.0 to 33.3 kHz were used. Admittance spectra for the ZnO‐Bi2O3 system showed large variations with sintering atmosphere and heat treatment. A trap is observed at 0.33 eV below the conduction band edge in both systems. This trap is likely to be associated with an ionized oxygen vacancy. A possible explanation of primitive varistor characteristics in terms of the roles of the electronic defects is presented.
Sintering of Si3N4 with the Addition of Rare‐Earth Oxides
Authors: Hirosaki Naoto , Okada Akira , Matoba Kazuo
Published: March 2005

The effect of rare‐earth oxide additives on the densification of silicon nitride by pressureless sintering at 1600° to 1700°C and by gas pressure sintering under 10 MPa of N2 at 1800° to 2000°C was studied. When a single‐component oxide, such as CeO2, Nd2O3, La2O3, Sm2O3, or Y2O3, was used as an additive, the sintering temperature required to reach approximate theoretical density became higher as the melting temperature of the oxide increased. When a mixed oxide additive, such as Y2O3–Ln2O3 (Ln=Ce, Nd, La, Sm), was used, higher densification was achieved below 2000°C because of a lower liquid formation temperature. The sinterability of silicon nitride ceramics with the addition of rare‐earth oxides is discussed in relation to the additive compositions.
Analysis of a Chevron‐Notch Four‐Point‐Bend Specimen by the Three‐Dimensional Finite‐Element Method
Authors: Joch J. , Zemánková J. , Kazda J.
Published: March 2005

This paper deals with a computation of the stress intensity factor (KI) for a four‐point‐bend chevron‐notch specimen of preselected geometry by the three‐dimensional finite‐element method. In addition, there is a comparison with the straight‐through crack assumption and Bluhm models. The dependence of KI on Poisson's ratio (v) is discussed for one of the crack lengths.
Fracture of Si3N4–SiC Whisker Composites under Cyclic Loads
Authors: Suresh Subra , Han Lily X. , Petrovic John J.
Published: March 2005

This communication demonstrates the role of cyclic compressive loads in inducing mode I fatigue crack growth at room temperature in Si3N4 matrix–SiC whisker composite materials containing stress concentrations. The characteristics of stable, cyclic fracture are examined for several volume fractions of the SiC whisker and are compared with those of the matrix material. It is found that the composites with higher volume fractions of SiC whiskers exhibit an inferior resistance to fracture under cyclic compressive loads despite improvements in fracture toughness values.
Liquid‐Phase‐Assisted Transformation of Seeded γ‐Alumina
Authors: SHELLEMAN RICHARD A. , MESSING GARY L.
Published: March 2005

α‐Al2O3‐seeded, boehmite‐derived γ‐Al2O3 was transformed in the presence of V2O5, resulting in a 205°C decrease in the α‐Al2O3 transformation temperature and a 74% reduction in the apparent activation energy for the γ‐ to α‐Al2O3 transformation at temperatures greater than 850°C. These changes are attributed to the lowered energy barrier for nucleation by seeding and the lowered activation energy for material transport through the liquid relative to the unseeded, solid‐state transformation. Growth of the transforming alumina yielded fine‐grained α‐Al2O3 particles which exhibited a highly faceted morphology. It is proposed that the combined control of both nucleation and growth during liquid‐phase‐assisted transformation provides a potentially powerful technique for tailoring powder characteristics in many material systems which undergo nucleation and growth processes.
Evaluation of Fracture Toughness for Ceramic Materials by a Single‐Edge‐Precracked‐Beam Method
Authors: NOSE TETSURO , FUJII TOSHIMITSU
Published: March 2005

As a substitute for the fatigue‐cracked‐beam method prescribed in ASTM E399 A2, a recently devised precracking method was applied to the evaluation of fracture toughness of ceramic materials. Straight‐through precracks proved to be easily introduced into rectangular beams of several ceramic materials. This method gives Kic values almost identical with those of the fatigue‐cracked‐beam method. The Kic values are almost constant over wide ranges of the pop‐in precrack length and the loading rate of the three‐point bend test. The test can be easily performed even at elevated temperatures although its validity should be further examined.
Melt Growth of High‐Critical‐Temperature Superconducting Fibers
Authors: MORRIS PATRICIA A. , BAGLEY BRIAN G. , TARASCON JEAN MARIE , GREEN LAURA H. , HULL GEORGE W.
Published: March 2005

To determine the intrinsic properties of the newly discovered high‐critical‐temperature oxide superconductors, their single crystals are necessary. Using the float‐zone technique with CO2 laser heating, coarse‐grained polycrystalline superconducting La‐Sr‐Cu‐O fibers have been grown directly from the melt of a sintered compact. Cu‐O is lost from the liquid and can be compensated by the addition of an excess of CuO in the compact. Superconducting properties (including Tc and Meissner effect), X‐ray diffraction, and EDAX indicate that the La/Sr stoichiometry is not maintained from the sintered compact to the melt‐grown material. Attempts to grow an analogous fiber in the Y‐Ba‐Cu‐O system were unsuccessful because the very high evaporation rates of the constituents precluded the maintenance of a molten zone. The results also indicate that patterning of circuits on thin films of the Y‐Ba‐Cu‐O superconductor can be achieved using laser irradiation.
Critical Appraisal of Diffusivity Determinations from Experimental Creep Data
Authors: Chokshi Atul‐H.
Published: March 2005

The procedures used to obtain diffusion coefficients from experimental creep data are analyzed in detail. Using experimental data for polycrystalline alumina, it is demonstrated that, in general, it is impossible to correctly determine the diffusion coefficients from experimental creep data.
Singular Nature of Preferential Conducting Paths at High Electric Fields in ZnO‐Based Varistors
Authors: Alim Mohammad A. , Seitz Martin A.
Published: March 2005

The ac electrical response of ZnO‐based varistors was monitored as a function of frequency (50 Hzf2 MHz) and electric field (60% ElmA/cm2EElmA/cm2, ElmA/cm2 in the critical field at 1 mA/cm2) at room temperature, and these data were represented in the complex impedance (Z*) plane. The finite depression angle observed in this plane was rationalized in terms of nonuniformity in the measured reactance between the terminals. The singular nature of the series‐parallel combination of the uniform conducting paths between the electrodes was suggested when this depression angle diminished to 0° at high electric fields (EElmA/cm2).
Effect of Lead Compounds on the Properties of Stannous Fluorophosphate Glasses
Authors: Shaw Cathy M. , Shelby James E.
Published: March 2005

The effects of PbO or PbF2 additions on the density, thermal‐expansion behavior, and chemical durability of stannous fluorophosphate glasses have been determined. Lead compounds dramatically improve the chemical durability of these glasses in water, resulting in low‐melting‐temperature glasses (Tg<150°C) which have durabilities approaching those of commercial soda–lime–silica glasses. Possible causes of these effects are discussed.
Barium Metaplumbate Ceramic Electrodes for Ceramic Capacitors
Authors: Skeele Frank P. , Newnham Robert E. , Cross Leslie E.
Published: March 2005

A novel approach to reduce electrode costs in ceramic capacitors is presented. Barium metaplumbate (BaPbO3) was fired onto sintered commercial (Ba, Sr)TiO3 disk capacitors as external electrodes. Samples were compared to disk capacitors of the same composition with electrodes made of sputtered gold and air‐dried silver. The ceramic electrode led to substantial changes in the insulation resistance and dc breakdown strengths, but other properties remained the same. The feasibility of using BaPbO3 electrodes strongly depends on chemical reactions between the electrode and dielectric.
Rhombohedral Phase in Y2O3‐Partially‐Stabilized ZrO2
Authors: Kitano Yukishige , Mori Yuuji , Ishitani Akira , Masaki Takaki
Published: March 2005

Tetragonal‐to‐rhombohedral stress‐induced phase transformation was studied by X‐ray diffraction on the ground surfaces of tetragonal zirconia polycrystals and partially stabilized zirconia containing 2.0 to 5.0 mol% Y2O3 prepared by hot isostatic pressing. The rhombohedral phase increased with Y2O3 content and also with hot isostatic pressing temperature. The stability of the rhombohedral phase was studied with regard to surface finish and thermal annealing. The subsequent heat treatment of the specimens was found to cause the reverse rhombohedral‐to‐tetragonal transformation.
Compensation Effect in Semiconducting Barium Titanate
Authors: Peng Cheng‐Jien , Lu Hong‐Yang
Published: March 2005

Donor‐doped, stoichiometric BaTiO3 sintered at 1350°C for 1 h exhibits a maximum room‐temperature conductivity at [La3+]∼0.15 mol%. Elements of lower valence than Ba2+ or Ti4+, when incorporated into semiconducting BaTiO3, are regarded as poisoning impurities, i.e., acceptors. They tend to increase the room‐temperature resistivity of the semiconducting BaTiO3. For insulating BaTiO3 resulting from high Mg2+ acceptor doping levels, the semiconductivity can be restored by introducing higher La3+ donor‐dopant concentrations. This behavior is interpreted as a compensation effect based on the defect chemistry of the acceptor‐ and donor‐doped BaTiO3.
Preparation of Uniform Colloidal Strontium Ferrite Particles
Authors: Fan Xi‐Jing , Matijević Egon
Published: March 2005

A procedure is described that yields uniform ferrite particles containing strontium. The process consists of crystallizing the solids from a ferrous hydroxide gel in the presence of SrCl2 and a mild oxidizing agent (KNO3) at 90°C. The amount of Sr2+ in the particles can be varied with the concentration of the SrCl2 in the original system, but its content decreases with extensive washings. Calcination of the powder partially inhibits the leaching of Sr2+. Magnetic properties of such materials are also given.
Possible Alternative Transformation Tougheners to Zirconia: Crystallographic Aspects
Authors: KRIVEN WALTRAUD M.
Published: March 2005

Several new potential alternative transformation tougheners to zirconia have been identified on the basis of crystallographic considerations and experimental observations. Examples can be found in ceramics, minerals, and components of glass and of cement. The displacive transformations exhibit martensitic characteristics of dusting or self‐disintegration, and a critical particle size effect operates. Large positive volume changes (< 12%) accompany the transformations on cooling, in the lanthanide sesquioxides (Ln2O3), dicalcium silicate (Ca2SiO4), and nickel sulfide (NiS). High Ms temperatures (<2000°C) in the Ln2O3 compounds also suggest the possibility of high‐temperature transformation toughening. Detrimental negative volume changes are seen in composites with enstatite (MgO · SiO2) and the lanthanide borates (LnBO3). The relative effects of volume change, X‐ray unit‐cell shape change, and the (martensitic) macroscopic shape change on the mechanical properties of a composite ceramic can thus be investigated.