bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Fast Neutron Irradiation on Thermal Conductivity of Li2O and LiAlO2
Authors: Ethridge Jerry L. , Baker Donald E. , Miller Alan D.
Published: March 2005

Li2O and LiAlO2 are two candidates for solid breeder materials in the United States' Fusion Power Program. Critical to breeder design efforts are thermophysical data, the bulk of which have only recently become available, for un‐irradiated lithium ceramics. This paper expands the current limited data base by presenting thermal conductivity data between 373 and 1173 K for both materials following fast neutron irradiation. Samples were irradiated at 773 to 1173 K to lithium burnups ≤11.5 × 1020 captures/cm3. Comparisons are made between these data and those from unirradiated archive samples of these same materials.
Transformation Kinetics of Diphasic Aluminosilicate Gels
Authors: WEI WEN‐CHENG , HALLORAN JOHN W.
Published: March 2005

The formation of mullite in diphasic aluminosilicate gels of stoichiometric composition was studied by quantitative X‐ray diffraction (QXRD) and electron microscopy (AEM and SEM). The transformation is preceded by an incubation time which is apparently an activated process with an activation energy of 236 ± 15 kcal/(g·mol) (∼987 ± 63 kJ/(g·mol)). Microscopic observations show that mullitization occurs via nucleation and growth as a mechanism either interface‐controlled or controlled by short‐range diffusion near the interface. The kinetic time exponent (n), determined by microstructural and QXRD observations, is close to 1.3. The transformation kinetics involve a nearly constant nucleus density, and time‐dependent growth rate for nearly spherical grains. A linear time‐temperature‐transformation diagram is observed.
Microhardness and Fracture Toughness Anisotropy in Cubic Zirconium Oxide Single Crystals
Authors: Pajares Antonia , Guiberteau Fernando , Dominguez‐Rodriguez Arturo , Heuer Arthur H.
Published: March 2005

Vickers and Knoop indentation tests have been used to study the fracture and deformation characteristics of 9.4‐mol%‐Y2O3‐stabilized ZrO2 single crystals. Kc is anisotropic, with values of 1.9 and 1.1 MPa·m1/2 for radial cracks propagating along (100) and (110), respectively. The toughness for these two orientations was also determined using the single‐edge notched‐beam geometry, and yielded values of 1.9 and 1.5 MPa·m1/2.
Thermal Reactions of Hydrated Hexagonal RPO4·nH2O (R=Tb or Dy, n=0.5 to 1)
Authors: Hikichi Yasuo , Sasaki Toshio , Suzuki Suguru , Murayama Kyouhei , Miyamoto Masaaki
Published: March 2005

The thermal reactions of hydrated hexagonal RPO4·nH2O (R=Tb or Dy, n=0.5 to 1) were studied at 20° to 1800°C in air under atmospheric pressure. The hydrated hexagonal forms were dehydrated at 180° to 250°C. Thereafter, no significant changes in structure were seen up to 800°C (R=Tb) or 700°C (R=Dy). The water corresponding to nH2O was zeolitic water. Anhydrous hexagonal RPO4 gradually transformed into the monazite structure at 900°C (R=Tb) or 800°C (R=Dy), then into the xenotime structure at temperatures above 1100°C (R=Tb) or 900°C (R=Dy).
Thermal Expansion Coefficients of Unidirectional Fiber‐Reinforced Ceramics
Authors: Hsueh Chun‐Hway , Becher Paul F.
Published: March 2005

The influence of internal stresses, due to the thermomechanical mismatch between the fiber and the matrix, on the thermal expansion behavior of unidirectional fiber‐reinforced ceramics is considered. Using the composite cylinder model, the effective thermal expansion coefficients of the composite are calculated from the total strains, which consist of the strains due to temperature changes and the strains induced by the presence of internal stresses. The results reveal that when the fiber and the matrix have the same elastic constants, the rule of mixtures approach can be used to obtain the thermal expansion coefficients of the composite, as observed in previous analytical solutions. Also, for the case of low volume fractions of fibers with Young's moduli much larger than those of matrices, and the thermal expansion coefficients lower than those of matrices, the transverse thermal expansion coefficient of the composite is higher than that of either the fiber or the matrix. However, unlike previous studies, the present analysis provides a physical basis for this phenomenon in terms of the internal thermal stress state within the composite.
Determining the Critical Strain Energy Release Rate of Plasma‐Sprayed Coatings Using a Double‐Cantilever‐Beam Technique
Authors: OSTOJIC P. , McPHERSON R.
Published: March 2005

A double‐cantilever‐beam (DCB) method for determining critical strain energy release rate (GIc) values from plasma‐sprayed coatings is described in detail. This approach, involving acoustic emission (AE) methodology, yielded up to 25 results per specimen and was successful in providing cohesive GIc values for plasma‐sprayed coatings of Al2O3‐2.5 wt% TiO2, Ni‐20 wt% Al, as well as two ostensibly identical, 99.5% commercially pure Al2O3 coatings. Adhesive GIc data from Al2O3‐40 wt% TiO2 coatings was also obtained. Results showed a GIc dependence on crack length, and a number of possibilities, based on fractography, the AE response of the coatings during testing, and crack velocity measurements, are advanced to explain this occurrence. Differences in GIc values between coatings were found to correlate with differences in powder/coating properties. The DCB method was also used to investigate batch differences and the effect on toughness of sealing an alumina coating. Problems associated with this method of testing are addressed.
Density of Liquid Rare‐Earth Sesquioxides
Authors: Granier Bernard , Heurtault Serge
Published: March 2005

The densities of seven rare‐earth sesquioxides and yttrium sesquioxide were measured in the liquid state in the temperature range from melting point to ∼3200 K. An aerodynamic levitation technique and laser‐heating method were used. The variation of volume at fusion for these oxides was deduced from these results and known data for the solid phases.
Influence of Various Consolidation Techniques on the Green Microstructure and Sintering Behavior of Alumina Powders
Authors: ROOSEN ANDREAS , BOWEN H. KENT
Published: March 2005

Submicrometer alumina powders, of both standard and narrow particle‐size distributions, were consolidated by dry‐pressing and colloidal‐forming techniques. The resulting green compacts were characterized in terms of pore‐size distribution, green density, shrinkage behavior, and sintered density. The interrelationships between powder characteristics, green compact microstructure, and sintering behavior are discussed. There are distinct differences between the characteristics of compacts that were directly consolidated from powder suspensions and those that were dry pressed. Dense microstructures can be achieved at low temperatures using narrow‐sized, well‐dispersed powders with colloidal‐forming techniques.
Mechanism of Sulfate Expansion in Hydrated Portland Cement
Authors: ODLER IVAN , GASSER MICHAEL
Published: March 2005

The origin of sulfate expansion was studied on a series of cements of different compositions and on mixes of pure compounds. The observed data support the theory that the expansion is related to a topochemical formation and/or oriented growth of ettringite. An uptake of water from the environment is not essential for the expansion to take place even though it enhances the extent of expansion. The absence of expansion in iron‐rich cements appears to be due to reduced and delayed ettringite formation in these cements and to an altered morphology of the formed ettringite.
Micromechanical Stresses in SiC‐Reinforced Al2O3 Composites
Authors: Li Zhuang , Bradt Richard C.
Published: March 2005

Applying an Eshelby approach, the internal micromechanical stresses within an SiC‐inclusion‐reinforced (platelet to whisker geometries) polycrystalline alumina matrix composite were calculated. The results are compared to the experimental residual stress measurements of a SiC‐whisker‐reinforced Al2O3 by Predecki, Abuhasan, and Barrett and found to be in excellent agreement. The calculations are then extended to SiC‐reinforced composites with polycrystalline mullite, silicon nitride, and cordierite matrices. It is concluded that the internal stresses are significantly influenced by the inclusion geometry as well as the thermoelastic differences between the inclusion and the matrix and also the volume fraction.
Mechanism of Iron Catalysis of Carbon Monoxide Decomposition in Refractories
Authors: Xu Ming‐Wei Paul , Brown Jesse J.
Published: March 2005

The catalytic effects of selected iron phases (metals, oxides, sulfides, and carbides) on the Boudouard reaction (2CO ⇄ CO2+ C) studied in an effort to more fully understand the disintegration of refractories when exposed to CO for long periods of time. It was found that active Fe atoms generated from the reduction of the iron oxides, especially α‐Fe2O3, are the actual catalysts for the Boudouard reaction. The catalytic process, confirmed by thermodynamic calculations, kinetic data, and X‐ray diffraction data, consists of adsorption and decomposition of CO simultaneously forming carbides of iron. The chemisorption and subsequent decomposition of the iron carbides, rather than diffusion, constitute the rate‐controlling process for carbon deposition.
Effect of Inclusion Size on the Densification of ZnO–Zn7Sb2O12
Authors: Kimura Toshio , Kajiyama Hideto , Kim Jinho , Yamaguchi Takashi
Published: March 2005

Two‐step densification curves, observed in the constant‐rate heating of ZnO–Zn7Sb2O12 composites, have been analyzed in correlation with the effect of inclusion particles (Zn7Sb2O12). In the presence of these inclusion particles, the ZnO matrix is divided into two regions with different densification characteristics depending on the interaction with the particles. The linear shrinkage at the end of the first step depends on the inclusion size as well as on its volume fraction. The fractional volume of the region influenced by the inclusion particles has been estimated from the densification curve, and the size of the region influenced by an inclusion particle is found to increase with increasing inclusion size.
Preparation of Alkoxy‐Derived Tantalum Vanadate
Authors: Yamaguchi Osamu , Mukaida Yasumichi , Shigeta Hiroyasu
Published: March 2005

Compound formation in the system Ta2O5–V2O5 has been studied using amorphous materials prepared by the simultaneous hydrolysis of tantalum and vanadyl alkoxides. Three compounds exist in this system: 9Ta2O5· V2O5, 9Ta2O5·2V2O5, and Ta2O5·V2O5 (TaVO5). Solid solutions of δ‐Ta2O5 are formed at low temperatures up to 10 mol% V2O5. They transform to β‐Ta2O5 solid solutions at higher temperatures; the transformation temperature falls with increasing V2O5 A new compound, 9Ta2O5·V2O5, 670° to 755°. It has an orthorhombic unit cell with a= 0.7859 nm, b= 1.733 nm, and c= 1.766 nm. Orthorhombic TaVO5 crystallized at 535° to 560° decomposes into 9Ta2O5°V2O5 at 1010°.
Dispersion of Silicon Carbide Powders in Nonaqueous Solvents
Authors: Okuyama Masahiko , Garvey Garry J. , Ring Terry A. , Haggerty John S.
Published: March 2005

Thirty‐two pure solvents were used to disperse laser‐synthesized SiC powder, oxidized laser‐synthesized SiC powder, and commercially available SiC powder. Five‐day sedimentation tests were used to screen the solvents. Relative turbidity of the supernatant after 1 month was used as a quantitative measure of the degree of dispersion. Coagulation kinetics were measured by photon correlation spectroscopy to determine the coagulation rate. Stabilized powders were centrifugally cast into ceramic green bodies and their green densities measured. Experimental dispersion results were correlated with various solvent properties including dielectric constant, hydrogen‐bond index, acid dissociation constant (pKa), and Lewis acid/base interaction energy. Microcalorimetry was used to measure the heat of wetting of the powders in various acidic and basic solvents. The heat of wetting was used to determine the Lewis interaction energy parameters for the powder surfaces. Oxidized SiC powder, either laser or commercial, was shown to have an acidic surface and was stabilized by basic solvents. Pure laser‐synthesized SiC powder was shown to have a basic surface and was stabilized by acidic solvents. Solvents with high hydrogen‐bond indices gave high packing densities. Other solvent properties had a much smaller influence on powder dispersibility. Good dispersibility gave ceramic green bodies with high green densities.
Structure and Properties of Long‐Wavelength‐Transmitting Halide Glasses
Authors: Almeida Rui M. , Santos Luis F.
Published: March 2005

The lower halides of zinc, namely, ZnCl2, ZnBr2, and ZnI2, may act as network formers in glasses that also contain modifying alkali halides such as KCI, KBr, KI, NaI, or CsI. Compositions which contain only Br− or I− anions are of particular interest because of their extended infrared transmission, which includes the ∼10‐μm region, in addition to full visible transparency. A series of modified zinc halide glasses were prepared and characterized by differential scanning calorimetry, middle and far Fourier transform infrared spectroscopy, and polarized Raman spectroscopy. Tg values were characteristically low, around 40°C. Bulk glass infrared transmission up to 15 to 20 μm was recorded. The most probable glass structures are discussed and compared to oxide glass models. An attenuation of  0.001 dB/km has been projected as a possible intrinsic minimum for optical fibers operating near ∼6 μm.
Healing of Glass in Humid Environments
Authors: Holden Mary Kay Clark , Frechette Van Derck
Published: March 2005

Chill checks of controlled depth were produced in soda‐lime‐silica glass, and an optimum humidity of 30 kPa (300 mbar) water vapor pressure was found to heal these checks in an annealing cycle. Critical factors were found to be a fluxing effect, having a direct dependence on moisture, followed by a drying operation at the annealing temperature. A four‐step model is proposed for crack healing: (1) exposure of the crack surface to moisture at temperatures below Tg, (2) formation of a gel layer, (3) closure of the crack resulting from the relief of stress (a minimum of 10 to 20 MPa applied compressive stress was determined to be necessary for complete closure), and (4) drying in the presence of a controlled atmosphere.
Phase Stability of Ln2BaCuO5 (Ln = Dy, Er, Eu, Gd, Ho, Sm, Yb)
Authors: Nakahigashi Kiyotaka , Tsuboi Tomokazu , Kogachi Mineo , Nakanishi Shigemitsu , Minamigawa Shinnosuke , Sasakura Hiroyuki , Fukuoka Nobuo , Yanase Akira , Yoshiara Kiichi
Published: March 2005

Phase stability of a series of Ln2BaCuO5 (Ln=Dy, Er, Eu, Gd, Ho, Sm, Yb) has been studied as a function of oxygen partial pressure and temperature by X‐ray diffraction, thermal gravimetric, and differential thermal analyses. Above the critical temperature Td, phase decomposition with a decrease in sample weight took place. In the case of Ln=Dy, Er, Ho, and Yb, the Ln2BaCuO5 was decomposed into Ln2O3BaCuO3 and BaCuO2. The critical temperature Td (K) was changed depending heavily on the oxygen partial pressure P (Pa) and the effective ionic radius R (0.1‐nm unit) of the Ln atom which was sevenfold coordinated by oxygen atoms. The observed Td values for all of the systems, together with those of Y2BaCuO5 reported previously, closely followed the relation Td=−17493R2+ 34582R − 15489 + 239.47 In P with a reliability index Rp=0.5%. [Key words: superconductors, barium, phases, X‐ray diffraction, differential thermal analysis.]
Effect of the Heating Rate on the Relative Rates of Sintering and Crystallization in Glass
Authors: Panda Prakash C. , Mobley W. Morris , Raj Rishi
Published: March 2005

The sintering of glass can sometimes be impeded by crystallization. In the optimum process the glass should sinter to full density before the onset of crystallization. In an earlier paper we showed how sinter‐forging experiments can be used to investigate the coupling between densification and crystallization. Here we demonstrate that increasing the heating rate can delay crystallization so that a certain glass can sinter to full density.
Effect of Surface Forces on Subcritical Crack Growth in Glass
Authors: Widerhorn Sheldon M. , Fuller Edwin R.
Published: March 2005

Data on the growth of cracks tested in aqueous solutions were interpreted in terms of surface force theory. For applied stress intensity factors greater than 0.25 MPa · m½, the position and the slope of the curves and their dependence on pH and ion concentration can be explained in terms of surface force theory, provided these forces are of a magnitude and range that are representative of those involved in the cohensive bonding of solids. Weaker forces, such as structural, double‐layer, or dispersion forces, have little effect on crack growth in silica glass for KI > 0.25 MPa · m½.
Toughening of Ceramics through Crack Bridging by Ductile Particles
Authors: Erdogan Fazil , Joseph Paul F.
Published: March 2005

The fracture problem for a brittle matrix reinforced by ductile particles is considered. In the usual manner it is assumed that the crack surface bridging forces provided by the unbroken particles improve the fracture toughness of the matrix. Depending on the relative strength of the interfacial bonding between the matrix and the particles, two particle force models are introduced, namely, a force that is independent of the crack opening displacement (δ) and a force that is a highly non‐linear function of δ. The problem is studied for a penny‐shaped or plane strain crack in an infinite medium and for a surface crack in a semi‐infinite medium under plane strain conditions. The toughness improvement in the matrix is shown to depend on a dimensionless bimaterial constant representing the inherent toughness of the matrix and the yield behavior of the particles. The effective toughness of the composite medium is calculated as a function of the crack size and the bimaterial constant.
Cyclic Fatigue Crack Propagation in Alumina under Direct Tension—Compression Loading
Authors: Reece Michael J. , Guiu Frank , Sammur Mohammad F. R.
Published: March 2005

Cyclically induced crack propagation occurs in alumina subjected to direct tension—compression loading. The crack increment per cycle (da/dN) has a power‐law dependence on the peak stress intensity factor (Kmax). Cyclic crack growth can occur at lower values of Kmax than are required to produce static fatigue effects. Subcritical crack‐growth behavior was found to be dependent on specimen geometry: it is suggested that direct compressive loads and crack length are both factors that affect cyclic fatigue behavior, and that the use of K alone to characterize fatigue crack growth in ceramics may be questionable.
Analytical Modeling of Chemical Vapor Infiltration in Fabrication of Ceramic Composites
Authors: Tai Nyan‐Hwa , Chou Tsu‐Wei
Published: March 2005

A model for chemical vapor infiltration is applied to the study of the growth of alumina from the chemical reaction among AlCl3, H2, and CO2 within a SiC‐fiber bundle which is situated in an isothermal hot‐wall reactor. The pore space between the fibers is simulated by cylindrical capillary tubes. The model considers binary diffusion of CO2 and H2, chemical reaction on the inner surface of the tube, and deposition film growth. Furthermore, diffusion‐controiled and chemical‐reaction‐controlled processes are taken into account to determine the dominating process in chemical vapor infiltration. Both molecular diffusion and Knudsen diffusion are considered sequentially in this model during the infiltration process. Based upon this model, the optimum processing conditions required for chemical vapor infiltration to form a SiC/Al2O3 composite can be predicted for different fiber preform systems.
Low‐Temperature Crack Closure in Fluoride Glass
Authors: Lehman Richard L. , Hill Richard E. , Sigel George H.
Published: March 2005

Radial cracks generated in heavy‐metal fluoride glass (HMFG) by Vickers indentation were found to decrease in length as a function of time when exposed to humid environments in the temperature range of 22° to 80°C. Inspection by optical and electron microscopy indicated that the cracks appear to be closing, leaving little or no evidence of the original crack aperture. The effect was observed to increase with time, temperature, and humidity levels for all conditions studied. Possible explanations for this behavior include viscous relaxation of glass in the region of the crack tip, or the generation and transport of a fluoride gel phase to the crack aperture.
Dielectric Behavior of the Relaxor Pb(Mg1/3Nb2/3)O3—PbTiO3 Solid‐Solution System in the Microwave Region
Authors: Lanagan Michael T. , Yang Ning , Dube Dinesh C. , Jang Sei‐Joo
Published: March 2005

Dielectric behavior of the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3—PbTiO3 solid‐solution system was studied from—50° to 200°C in the 100 to 12 × 109 Hz frequency region, and a broad dielectric relaxation was measured for compositions throughout the system. The relative microwave permittivity of the composition 0.9Pb(Mg1/3Nb2/3)O3·0.1 PbTiO3 decreased by 1 order of magnitude from the 1‐MHz value of 11800, and similar decreases were observed for other compositions in the system. Dielectric loss (tan δ) values ranged from 0.5 to 1.0 at microwave frequency. The temperature of the broad dielectric constant maximum shifts toward higher values with increased frequency.
Synthesis and Crystallography of Sodium Titanium Bronze
Authors: Bamberger Carlos E.
Published: March 2005

An alternative reaction for the preparation of sodium titanium bronze (STB) based on the use of TiN as a reductant has been tested. Crystallographic data for STB available from the literature and from new preparations have been compiled and discussed.
Field‐Forced Antiferroelectric‐to‐Ferroelectric Switching in Modified Lead Zirconate Titanate Stannate Ceramics
Authors: Pan Wuyi , Zhang Qiming , Bhalla Amar , Cross Leslie E.
Published: March 2005

Electric‐field‐forced antiferroelectric‐to‐ferroelectric phase transitions in several compositions of modified lead zirconate titanate stannate antiferroelectric ceramics are studied for ultra‐high‐field‐induced strain actuator applications. A maximum field‐induced longitudinal strain of 0.85% and volume expansion of 0.95% are observed in the ceramic composition Pb0.97La0.02(Zr0.66Ti0.09Sn0.25)O3 at room temperature. Switching from the antiferroelectric form to the ferroelectric form is controlled by the nucleation of the ferroelectric phase from the antiferroelectric phase. A switching time of <1 μs is observed under the applied field above 30 kV/cm. The polarization and strains associated with the field‐forced phase transition decrease with increasing switching cycle, a so‐called fatigue effect. Two types of fatigue effects are observed in these ceramic compositions. In one, the fatigue effects only proceed to a limited extent and the properties may be restored by annealing above the Curie temperature, while in the other, the fatigue effects proceed to a large extent and the properties cannot be restored completely by heat treatment. Hydrostatic pressure increases the transition field and the switching time. But when the applied electric field is larger than the transition field, the induced polarization and strain are not sensitive to increasing hydrostatic pressure until the transition field approaches the applied field.
Dielectric and Pyroelectric Properties of Cadmium Niobate Ceramics
Authors: Swartz Scott L. , Randall C. A. , Bhalla A. S.
Published: March 2005

The low‐temperature dielectric and pyroelectric properties of pyrochlore Cd2Nb2O7 ceramics have been investigated over the temperature range from 10 to 300 K. Dielectric data confirmed that two ferroelectric transitions occurred in the Cd2Nb2O7 ceramics at temperatures near 80 and 192 K. The higher‐temperature ferroelectric transition is complex, with evidence for three separate transitions occurring within a narrow temperature range. The temperature and frequency dependencies of the dielectric constant were consistent with both second‐order (diffuse) and improper ferroelectric (ferroelastic) effects. Pyroelectric data also confirmed the multiple‐transition behavior, with anomalies in the pyroelectric coefficient at temperatures corresponding to the onset of the diffuse ferroelectric transition and the ferroelastic effect. Dielectric loss data (analyzed by both Arrhenius and Cole‐Cole formalisms) indicated the presence of three separate relaxation‐type dielectric loss mechanisms in this temperature range. Unambiguous explanations for the observed dielectric and pyroelectric phenomena could not be made, but domain effects are believed to be responsible for at least part of the complex nature of the ferroelectric transitions in this material.
Silicon‐29 Magic Angle Spinning Nuclear Magnetic Resonance Study of Calcium Silicate Hydrates
Authors: Grutzeck Michael , Benesi Alan , Fanning Barry
Published: March 2005

The reaction products formed in a series of fully “equilibrated,” roomtemperature‐hydrated, fumed colloidal silica plus lime water mixtures were examined using 29Si magic angle spinning nuclear magnetic resonance. The data suggest that two structurally distinct calcium silicate hydrate (C‐S‐H) phases exist in the system CaO–SiO2–H2O. The more silica‐rich C‐S‐H (Ca/Si = 0.65 to 1.0) consists predominantly of long chains of silica tetrahedra (Q2 middle units) similar to those found in 1.4‐nm tobermorite. The studied more lime‐rich C‐S‐H (Ca / Si = 1.1 to 1.3) consists of a mixture of dimer (Q1) and shorter chains (Q1 end units and Q2 middle units) similar to that reported for synthetic jennite. No monomer units (Q0) were detected.
Alternative Prooftester for High‐Strength Optical Fibers
Authors: Brownlow Darryl L. , Iyenger Rama
Published: March 2005

Reproducible, nondestructive methods of prooftesting continuous, multikllometer lengths of high‐strength (>1.4 GPa) optical fiber are important in high‐performance applications of lightguide technology. An alternative prooftester based on the concept of continuously imparting a constant strain rather than a constant weight to the optical fiber has been built and tested. The constant‐strain design is somewhat simpler and has certain advantages over a widely used prooftester. The constant‐strain method is explained, and prooftest data that substantiate the advantages of the design are presented.
Debonding Properties of Residually Stressed Brittle‐Matrix Composites
Authors: Charalambides P. G. , Evans Anthony G.
Published: March 2005

Trends in interface debonding have been calculated during fiber pullout for composites with interfaces subject to residual tension. The debond behavior is shown to depend sensitively on the thermal expansion mismatch. The results are used as the basis for designing a pullout test specimen suitable for measuring the mixed‐mode fracture energy of bimaterial interfaces. The solutions also provide the background needed to assess the role of debonding in the toughening of ceramics by fibers.
Postsintering Hot Isostatic Pressing of Ceria‐Doped Tetragonal Zirconia/Alumina Composites in an Argon–Oxygen Gas Atmosphere
Authors: Sato Tsugio , Endo Tadashi , Shimada Masahiko
Published: March 2005

Ceria‐doped tetragonal zirconia (Ce‐TZP)/alumina (Al2O3) composites were fabricated by sintering at 1450° to 1600°C in air, followed by hot isostatic pressing (postsintering hot isostatic pressing) at 1450°C and 100 MPa in an 80 vol% Ar–20 vol% O2 gas atmosphere. Dispersion of Al2O3 particles into Ce‐TZP was useful in increasing the relative density and suppressing the grain growth of Ce‐TZP before hot isostatic pressing, but improvement of the fracture strength and fracture toughness was limited. Postsintering hot isostatic pressing was useful to densify Ce‐TZP/Al2O3 composites without grain growth and to improve the fracture strength and thermal shock resistance.
Viscoelastic Effects in a Phosphate Glass‐Metal Seal
Authors: Chambers R. S. , Gerstle Frank P. , Monroe S. L.
Published: March 2005

A family of phosphate glasses has been developed with thermal expansion behavior in the elastic range that nearly matches the response of 304 stainless steel. Attempts to make concentric pin‐shell seals consistently have yielded fractures between 400° and 300°C during cooling. Elastic stress analyses which neglect glass transitional behavior and utilize constant glassy (“elastic”) thermal expansion coefficients predict a residual stress state that is compressive. However, viscoelastic computations which include the effects of structural relaxation during glass transtion show that tensile stresses sufficient to cause failure arise during cooldown of the seal.
Influence of Microstructure on the Dielectric and Piezoelectric Properties of Lead Zirconate‐Polymer Composites
Authors: Lee Hyeung Gyu , Kim Ho Gi
Published: March 2005

Composites with 0–3 connectivity were fabricated from lead zirconate titanate (PZT) and phenolic resin powders. These composites were investigated for dielectric and piezoelectric properties with variations in active particle density and PZT‐polymer interface porosity. The dependence of dielectric and piezolectric properties on interface porosity is discussed, especially in terms of porosity factors. The dependence of the piezoelectric constant on interface porosity was greater than that of the dielectric constant. The interface pores play the role of a stress buffer. Thus local stress applied on PZT particles in the composites was remarkably diminished. When particle porosity was high, the dependence of the dielectric and piezoelectric constants on interface porosity decreased.
Technique for Tensile Creep Testing of Ceramics †
Authors: Carroll Daniel F. , Wiederhorn Sheldon M. , Roberts D. E.
Published: March 2005

An experimental technique for measuring tensile creep deformation in ceramic materials to temperatures of 1500°C is described. The technique uses simple flat dog‐bone‐shaped specimens and a hot‐grip design for the loading fixture, which provide good alignment at minimum cost. Creep deformation is measured using laser extensometry to monitor the relative displacement of flags that are attached to the gauge section of the specimen.
Combustion Synthesis of Silicon Carbide in Nitrogen Atmosphere
Authors: Yamada Osamu , Hirao Kiyoshi , Koizumi Mitsue , Miyamoto Yoshinari
Published: March 2005

Fine SiC powders were synthesized by burning the mixed reactionts Si and C in a nitrogen atmosphere of 3 to 10 MPa. The exothermic synthesis reaction propagated spontaneously after igniting the reactants at room temperature. The SiC powders obtained had a uniform size distribution of about 0.2 μm. The combustion velocity was 0.8 to 1.5 mm / s. The maximum temperature measured at the reaction was 2500 K, which was higher than the adiabatic combustion temperature of SiC, but slightly lower than the decomposition temperature of Si3N4 under nitrogen pressure.
Role of Oxygen in Bonding Copper to Alumina
Authors: Yoshino Yuichi
Published: March 2005

Although the Cu—Cu2O eutectic bonding of copper to alumina has been studied, the effect of oxygen on the bond strength is not well understood. In this study, eutectically bonded copper‐alumina joints are subjected to deoxidation and reoxidation in an atmosphere with varying oxygen potential. The bond strength changes reversibly with the interface oxygen concentration. There is a critical concentration of oxygen far less than the eutectic concentration, above which bond strength shows no further increase. The role of oxygen and the practical significance of eutectic reaction are considered and discussed.
Lattice Parameters, Ionic Conductivities, and Solubility Limits in Fluorite‐Structure MO2 Oxide [M = Hf4+, Zr4+, Ce4+, Th4+, U4+] Solid Solutions
Authors: Kim Dae‐Joon
Published: March 2005

Changes in the lattice parameters of fluorite type MO2 oxides (M = Hf4+, Zr4+, Ce4+, Th4+, U4+) due to the formation of solid solutions can be predicted by proposed empirical equations. The equations show the generalized relationship between dopant size and ionic conductivity in the binary systems of these oxides, illustrating that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity. The solubility limit of the same periodic group elements in fluorite‐structure MO2 oxides decreaes linearly with the square of Vegard's slope for each solute as determined from the proposed equations.
Reaction of Zirconium Fluoride Monohydrate and Ammonium Bifluoride: Its Effect on Fluoride Glass Preparation and Quality
Authors: Ewing Kenneth J. , Sanghera Jasbinder S. , Miklos Robert E. , Sachon Maria G. , Peitersen Laura , Hart Patricia , Aggarwal Ishwar
Published: March 2005

The products obtained from the roomtemperature reaction of ammonium bifluoride and zirconium fluoride monohydrate are ammonium heptafluorozirconate ((NH4)3ZrF2), liquid water, and hydrogen fluoride. Ammonium bifluoride and zirconium fluoride monohydrate were reacted prior to glass batching, producing dry ammonium heptafluorozirconate which was used to prepare a high‐quality ZBLAN fluoride glass.
Low‐Temperature Ionic Conductivity of 9.4‐mol%‐Yttria‐Stabilized Zirconia Single Crystals
Authors: de Dios Solier Juan , Pérez‐Jubindo Miguel A. , Dominguez‐Rodriguez Arturo , Heuer Arthur H.
Published: March 2005

Direct current and alternating current electrical conductivity measurements are used to determine the activation energies for the formation of oxygen vacancies by breakup of bound defect complexes (0.32 eV) and their migration (0.84 eV) at low temperatures (<600°C) in Y2O3‐fully‐stabilized ZrO2 single crystals. The defect clusters break up between 360° and 450°C.
Core‐Shell Structures in ZrO2‐Modified BaTiO3 Ceramic
Authors: Lu Hong‐Yang , Bow Jong‐Shing , Deng Wen‐How
Published: March 2005

Pure BaTiO3 exhibits a paraelectric‐to‐ferroelectric phase transition at 130°C. When stoichiometric BaTiO3 is combined with 10 mol% ZrO2, the relative permittivity (ε) changes to a broad, relatively insignificant temperature dependence, and the Curie point, Tc, is not sharply defined. However, the transition sharpens at T= 95°C when these samples are sintered for a longer period of 60 h. SEM, EDAX analysis coupled with TEM observation gives three types of core‐shell structures of different microstructural characteristics which are related to the diffuse phase transition. Chemical inhomogeneity, due to Zr4+ distribution in the core‐shell structure, is proposed to account for the diffuse phase transition behavior.
Microstructure of 96% Alumina Ceramics: II, Crystallization of High‐Magnesia Boundary Glasses
Authors: Powell‐Doǧan Cynthia A. , Heuer Arthur H.
Published: March 2005

Development of the grain‐boundary microstructure with heat treatment at 800° to 1500°C was examined for a group of 96% Al2O3 ceramics containing a high‐MgO boundary phase. Using a combination of analytical and conventional electron microscopy techniques, eight different crystalline phases were detected at the boundaries following annealing. Despite the extensive devitrification, however, a residual glass remained in all samples examined, and is believed to be continuous.
Effect of Particle Size Distribution on the Melting of Soda‐Lime‐Silica Glass
Authors: Sheckler Chad A. , Dinger Dennis R.
Published: March 2005

Research has been conducted on the effects of the particle size distribution of a glass batch on the reaction path leading up to the first glassy phase. The research has involved DTA/TGA, X‐ray diffraction, and SEM/EDS studies of particle size effects on the reaction path. The results of the studies were compiled to give a description of the reaction path for three soda‐lime‐silica batches, each with a different silica particle size distribution. The purpose of this work was to determine the effect of the silica particle size distribution on the reaction path and to determine the feasibility of building a predictive computer model consistent with these results.
Ceramic‐Metal Composite Produced by Melt Infiltration
Authors: Toy Cetin , Scott William D.
Published: March 2005

A new ceramic‐metal composite with continuous interconnected ceramic and metal phases has been fabricated from sintered aluminum nitride infiltrated with aluminum metal. A dense, lightweight, hard material with high strength has been obtained. Advance of the infiltration front was linear with time. The activation energy of the process was very high (330 kJ/mol), suggesting that a chemical interaction rather than viscous flow was rate‐controlling. The infiltration rate was observed to be inversely proportional to the pore size. Thermal and mechanical properties of the composite were promising.
Impedance Spectra During Solid‐State Powder Reactions of Oxide Superconductors
Authors: Cooper Elizabeth A. , Mason Thomas O. , Biznek Mark E. , Balachandran Utham
Published: March 2005

Complex impedance spectra over the frequency range of 5 Hz to 13 MHz were measured during the solid‐state reaction of La2CuO4 (with and without Sr doping) from the constituent oxides or carbonate (Sr). A single bulk arc was observed which could be modeled as a simple resistor‐capacitor network. The resistance falls continuously with time, spanning several orders of magnitude. Complex impedance measurements appear to be quite sensitive to small volume fractions of an electronically conductive product phase, especially during the early stages of solid‐state reaction. Impedance spectroscopy should therefore be a useful tool for the investigation of processing reactions in electronic ceramics.
Preparation of Ba2YCu3O7‐δ Thin Films with Preferred Orientation through an Organometallic Route
Authors: Hirano Shin‐ichi , Hayashi Takashi , Miura Masashi
Published: March 2005

Superconducting Ba2YCu3O7‐δ thin films were prepared through an organometallic route. Single‐phase Ba2YCu3O7‐δ thin films with preferred orientation were successfully prepared on SrTiO3 (100) single‐crystal substrates at 800°C by a dip coating method using partially hydrolyzed Ba‐Y‐Cu organometallic solutions. Preferentially oriented Ba2YCu3‐O7‐δ thin films were also prepared on MgO (100) substrates. By controlling the partial hydrolysis conditions, a coating solution for precursor thin films was kept accurately at the stoichiometric composition. The use of ozone gas during the pyrolysis of the precursor thin films was found to suppress the formation of BaCO3. Ba2YCu3O7‐δ thin films with c‐axis orientation perpendicular to a SrTiO3 (100) substrate, which were heat‐treated at 900°C for 15 min, exhibited a superconductivity transition with an onset of 90 K and an end of 75 K.
Repeated Indentation Method for Studying Cyclic Fatigue in Ceramics
Authors: Reece Michael , Guiu Frank
Published: March 2005

A new method for studying cyclic fatigue in ceramics in proposed. It is based on the repeated indentation of the ceramic surface with a sharp indenter and on the relation between the indentation load and the number of indentation cycles needed to produce chipping. The technique is analyzed on the basis of observations on the development of the lateral cracks produced below the identation cavity in a high‐grade alumina and on the model of elastic/plastic indentation damage. It is shown that cyclic compressive forces across the lateral crack faces are needed to produce chipping and that a fatigue limit exists in terms of these forces. The scope and limitations of the technique are discussed.
Oxygen Pressure Effect on the Y2O3—Bao—Cuo Liquidus
Authors: Lay Kenneth W. , Renlund Gary M.
Published: March 2005

Concurrent DTA, TGA, and oxygen pressure measurement were used to determine liquidus temperature for compositions near YBa2Cu3Ox. Liquidus temperatures were measured for oxygen partial pressures from 2 × 10−4 to 1 bar. Liquidus temperatures decreased for lowered oxygen pressure. The ternary eutectic is 930°C for 1 bar and 854°C for 0.02 bar oxygen pressure. Incongruent melting of YB2Cu3Oxoccurs at 1034°C for 1 bar and 938°C for 2 × 10−4 bar oxygen pressure. Some implications for processing are also discussed.
Solid‐State Bonding of Silicon Nitride Ceramics with Nickel‐Chromium Alloy Interlayers
Authors: Nakamura Mamoru , Peteves Stathis D.
Published: March 2005

Si3N4 ceramics with Al2O3 and Y2O3 as additives were joined with an 80 wt% Ni‐20 wt% Cr alloy sheet as an insert layer. Joining was performed by hot‐pressing between 1000° and 1350°C in argon, and under uniaxial pressures in the range of 50 to 100 MPa. The average joint strength, evaluated by four‐point bending, was large enough (>300 MPa) for some industrial applications. However, the scatter in strength was relatively large, because of the formation of interfacial pores, which were not distributed uniformly at the bond interface. The effects of joining pressure and N2 gas partial pressure on the formation of the pores were confirmed microscopically. Cr coating on the Si3N4 ceramic before joining contributed to reduce the joint strength scatter. The major interfacial reaction products were Cr nitrides.
Order‐Disorder Phenomenon in Lead Scandium Tantalate
Authors: Wang Hui‐Chieh , Schulze Walter A.
Published: March 2005

Lead scandium tantalate (PST) is a ferroelectric relaxor with the perovskite structure of A(B′B″)O3. By suitable heat treatment, the B‐site cations can be brought from a stucturally disordered state into various degree of ordering. The degree of ordering is strongly affected by the amouth of vacancies present in the materials. To suppress PbO loss during the sintering or annealing process, a PbO‐rich atmosphere is supplied by materials having high PbO vapor pressure, such as PbZrO3. For PST ceramics with nearly zero weight loss, very long annealing times and higher annealing temperatures are required for ordering. The higher Pbo‐loss materials are found to be easily ordered. The introduction of a reducing atmosphere during annealing enhances the ordering process. The ordering process is characterized quantitatively by X‐ray diffraction and qualitatively by Raman spectroscopy.
Thermal Expansion of Compounds of Zircon Structure
Authors: Subbarao Eleswarapu C. , Agrawal Dinesh K. , McKinstry Herbert A. , Sallese Christopher W. , Roy Rustum
Published: March 2005

The thermal expansion behavior of 13 members of ABO4 compounds of the zircon family is examined in terms of crystal chemical (size, charge, and mass of cations) and crystallographic (a and c) parameters. The systematic trend in the thermal expansion coefficients, αa and αc, with the ionic radii, rA and rB, can be explained in terms of the unique arrangement of M‐O polyhedra along a and c directions of this lattice. In the zircon structure, edge‐sharing ZrO8 dodecahedra form a chain along the a direction while the chain along the c direction consists of alternate edgesharing SiO4 tetrahedra and ZrO8 triangular dodecahedra. Substitution in the A sites affects a and αa more than c and αc and the reverse is true for replacements in the B sites. Unequal valencies on the A and B sites affect thermal expansion coefficients, particularly αc.
Low‐Temperature Preparation of Ultrafine Rare‐Earth Iron Garnets
Authors: Sankaranarayanan Vellancheri K. , Gajbhiye Namdeo S.
Published: March 2005

Ultrafine rare‐earth iron garnets, (R3Fe5O12 where R = Sm, Tb, Dy, Ho, Er, Yb, (YGd), and (YNd)) have been prepared by thermal decomposition of a citrate precursor, R3Fe5(cit)25· (36 +n)H2O. The precursors decompose at lower temperatures, below 450°C, and are characterized using DTA, DSC, TG, and IR spectroscopy. Ultrafine amorphous garnets having particle size 10 to 35 nm and surface area 30 to 75 m2/g have been obtained and characterized by XRD, TEM, Mössbauer spectra, particle size analysis, and magnetic and surface area measurements. Superparamagnetism indicates the ultrafine characteristics of the garnet materials. The nature of crystallite aggregates and agglomerates is of special interest because it represents finite clusters. An intercrystallite bond exists between crystallites having 1.0‐ to 1.5‐nm size. The rupture of intercrystallite bonds during crystallization leads to monolith formation.
Electrical Properties of Gallium‐Doped Zinc Oxide Films Prepared by RF Sputtering
Authors: Choi Byung Ho , Im Ho Bin , Song Jin Soo
Published: March 2005

Ga‐doped polycrystalline ZnO films on glass substrates were prepared by sputtering the targets, which had been prepared by sintering disks consisting of ZnO powder and various amounts of Ga2O3, to investigate the effects of gallium doping and sputtering conditions on electrical properties. Optimizing the RF power density, argon gas pressure, and gallium content, transparent Ga‐doped ZnO films with resistivity less than 10−3Ω·cm were obtained. Electron concentrations for undoped and Ga‐doped ZnO films were on the order of 1018 and 1021/cm3, respectively. The Ga‐doped ZnO films became degenerate when the electron concentration exceeded ∼ 1019/cm3, and the optical band gap increased with increasing carrier concentration because of the increase of Fermi energy in the conduction band.
Fracture Toughness of Graded Metal‐Particulate/Brittle‐Matrix Composites
Authors: Jessen Todd L. , Lewis David
Published: March 2005

A series of 0, 10, and 25 vol% metal‐particulate/glass‐matrix composites were prepared, with the composite volume fraction both constant and graded across the specimen bulk. Applied‐moment double‐cantilever‐beam (AMDCB) fracture toughness results show, in general, that the graded composites had equivalent values when compared with the constant fraction specimens. This equivalence in toughness occurred despite lower overall volume fraction particulate phase and composite density for the graded composites. Additionally, these results indicate the necessity of a minimum composite layer thicknes for optimization of toughening.
Potassium Vapor Attack in Refractories of the Alumina–Silica System
Authors: Scudeller Luis A. M. , Longo Elson , Varela Jose A.
Published: March 2005

A graphite chamber was used for the reaction between samples of 45 or 55 wt% alumina and a mixture of metallurgical coke and potassium carbonate. Thermal treatments were conducted at 1000°C. The results suggest that the potassium attack in silica‐alumina bricks is controlled by the following reactions: K2O + SiO2→ K2O → SiO2 in the glassy matrix; 3(K2O · 2SiO2) + 3Al2O3→ 2SiO2· 3(K2O · Al2O3· 2SiO2) + 2SiO2 for short times; and K2O → Al2O3· 2SiO2+ 2SiO2· K2O · Al2O3· 4SiO2 for long times. In 55 wt% alumina bricks containing corundum and tridymite, potassium also attacks those phases forming a glassy phase. The formation of kaliophilite at the matrix/mullite grain interface causes a volumetric expansion of 55.5%, resulting in cracks in the matrix. Because the kaliophilite phase is not in equilibrion with mullite, the former will react with free silica to form leucite that is more thermodynamically stable.
Effect of Aspect Ratio and Liquid‐Phase Content on Densification of Alumina‐Silicon Carbide Whisker Composites
Authors: Tiegs Terry N. , Dillard D. Matt
Published: March 2005

Densification of alumina‐SiC whisker composites by pressureless sintering is inhibited as a result of whisker interference with particle rearrangement and composite shrinkage. Reduction of the aspect ratio improves densification by improving particle/whisker packing for increased green densities and enhances the ability of the whiskers to rearrange themselves during sintering. Increasing the amount of liquid phases present during sintering also improves densification by aiding whisker rearrangement.
Carbon Dioxide Sensor Mechanism of Porous Hydroxyapatite Ceramics
Authors: Nagai Masayuki , Saeki Tatsuya , Nishino Tadashi
Published: March 2005

Hydroxyapatite and Cl− ‐containing hydroxyapatite powders are prepared and characterized. Reversible substitution of CO2‐3 for OH− at the surface is presumed to be responsible for the sensor function. The role of Cl−, which is necessary to realize the sensor function and is incorporated during soaking treatment, is considered as follows. It may reduce the strain caused by the incorporation of CO2‐3 (which is larger than OH−), and, hence, promote the reversible substitution reaction. This behavior is presumed because Cl− ‐containing hydroxyapatite samples exhibit sensor characteristics typical of CO2 without any treatment.