bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ Reaction of B2O3 with AlN and/or Si3N4 to Form BN‐Toughened Composites
Authors: COBLENZ W.S. , LEWIS D.
Published: March 2005

BN‐toughened oxide matrix composites were formed by the in situ reaction of B2O3 with Si3N4 and/or AlN. A lowtemperature transient liquid phase aids densification at <1000°C, and the process tends to produce an intrinsically homogeneous microstructure. Mechanical properties and microstructure of the composites formed in situ were compared to those of composites prepared by conventional means from oxide and BN powders. Fracture toughness and flexural strength of the nearly isotropic in situ formed composites ranged from 2.82 to 3.66 MPa · m1/2 and 130 to 320 MPa, respectively, with Young's moduli of 100 to 110 GPa. Densities achieved ranged from 90% to 97% of estimated theoretical densities. The strength and toughness values are intermediate to the extreme values for the anisotropic composites formed by hot‐pressing mixed powders.
Preparation and Sintering of Colloidal Silica‐Potassium Silicate Gels
Authors: CAO WANQING , GERHARDT ROSARIO , WACHTMAN JOHN B.
Published: March 2005

Porous silica gelled from colloidal silica and potassium silicate mixtures as developed by Shoup has been investigated. Various gels exhibit an average pore size from 50 to 250 nm and a porosity up to 85%. Dealkalization by solution leaching is found to depend on the average pore size and is easier for large pore sizes. A domain model has been proposed for the gel networks to account for the observation of both macropores and mesopores as measured by Hg porosimetry and N2 desorption, respectively. The pore coarsening observed during sintering is explained by the material transport from areas around interdomain pores to those around intradomain pores in order to minimize the total surface energy.
Preparation and Characterization of Machinable Mica Glass‐Ceramics by the Sol‐Gel Process
Authors: HAMASAKI TOSHIO , EGUCHI KATSUYA , KOYANAGI YOSHINORI , MATSUMOTO AKIRA , UTSUNOMIYA TAIZO , KOBA KEIICHIROU
Published: March 2005

The preparation and characterization of machinable mica glass‐ceramics by the sol‐gel process are described. The thermal behavior of the precursor and the optimum conditions for calcination, molding, and sintering are given. Physical, chemical, thermal, electrical, and mechanical properties are investigated, and the machinability of the ceramics is discussed.
Thermal Neutron Irradiation of Y‐Ba‐Cu‐O Superconductor
Authors: Hastings Ian J. , Palmer Brad J. F. , Gin Anne Y. H. , Scoberg Jeff A. , Thatcher Jeff C. , Towner Joanne
Published: March 2005

A Y‐Ba‐Cu‐O superconductor was irradiated at 360 K in the NRX reactor, with a well‐thermalized flux of 1.82 × 1017 n/(m2·s) (E < 1 MeV). Superconducting characteristics at 90 K disappeared by a fluence of 6.6 × 1021 n/m2 (10 h) but were recovered after a postirradiation heat treatment at 760 K in flowing oxygen. The results suggest that suitable shielding will be required for any application which exposes the superconductor to neutron irradiation.
Effect of Pore Distribution on Microstructure Development: I, Matrix Pores
Authors: ZHAO JUNHONG , HARMER MARTIN P.
Published: March 2005

A model has been developed to describe the effect of the matrix (first‐generation) pore distribution on microstructure development in the final stages of sintering. A model of simultaneous densification and grain growth was used to predict the effects of the number of pores per grain and the pore size distribution on microstructure evolution. Increasing the number of pores per grain was predicted to increase the densification rate, the grain growth rate, and the relative densification rate/grain growth rate ratio. Narrowing the pore size distribution was predicted to inhibit grain growth initially and to increase the densification rate indirectly. Overall, the pore distribution was predicted to have a strong influence on microstructure development and sintering kinetics.
Errors in Elastic Constant Measurements in Single Crystals
Authors: INGEL ROBERT P. , III DAVID LEWIS
Published: March 2005

A general analysis is presented of the errors involved in calculations of the elastic constants of single crystals from wave speed measurements. Results are presented graphically for the most probable errors, misorientation of the single‐crystal samples for the wave speed measurements. Specific numerical results are presented for elastic constants typical of yttria‐stabilized zirconia single crystals. These crystals were characterized elastically as cubic, with elastic constants C11, C12, and C44. The results indicate that the measurement of C11 is the least sensitive to alignment errors, while that of C12 is the most sensitive, with approximately a 10% error possible with a 5° misalignment of the crystal.
Reduction of NiO Platelets in a NiO/ZrO2(CaO) Directional Composite
Authors: BONVALOT‐DUBOIS B. , DHALENNE G. , BERTHON J. , REVCOLEVSCHI A. , RAPP R.A.
Published: March 2005

Oriented lamellar eutectic composites of NiO and ZrO2(CaO) platelets were reduced in CO2/CO gaseous atmospheres to form metallic Ni between the zirconia plates. The relatively rapid longitudinal reduction of NiO is described by a local cell electrochemical model whereby oxide ions are conducted from the Ni/NiO internal reaction front to the external surface through the zirconia electrolyte, while electrons are passed through the Ni product. Both the product morphologies and the reaction kinetics are consistent with the model. Apparent “lateral’reduction of NiO platelets indeed corresponds to longitudinal reduction for a platelet inclined to the external surface. Some plastic deformation of the product zone permits partial accommodation of the volume change upon reduction of NiO to Ni.
Dehydration of Hydrous Zirconia with Methanol
Authors: Jones Stanley L. , Norman Colin J.
Published: March 2005

The washing of hydrous zirconia with alcohols to reduce the incidence of hard agglomerates on subsequent drying is well known. The results of methanol dehydration of hydrous zirconia (zirconium hydroxide), [Zr4(μ‐OH)8(OH)8(H2O)8]˙ xH2O, show that only μ‐OH groups are unaffected. This suggests two things: First, the removal of nonbridging hydrooxo groups and water with alcohols such as methanol leads to a reduction/elimination of hard agglomerates. Second, hard agglomerate formation is associated with condensation reactions involving nonbridging hydroxo groups (Zr‐OH+HO‐Zr→Zr‐O‐Zr+H2O).
Bridging and Damage Zones in Crack Growth
Authors: THOULESS M.D.
Published: March 2005

The equivalence between bridging and damage zones that may occur at crack tips during crack propagation is demonstrated. The physical insights provided by both approaches are introduced. Finally, some results for the crack velocity during the creep rupture of a material containing an amorphous phase are discussed.
Volatile Losses from Sphene Glass‐Ceramic and Borosilicate Glass Melts
Authors: Vance E. R. , Hayward Peter J. , Hamon R. F.
Published: March 2005

Heating experiments have been performed with titanosilicate glass melts to investigate possible losses of volatile radionuclides during preparation. The melts are precursors to sphene glass‐ceramics, the latter being candidate materials for immobilization of nuclear fuel recycle wastes. After the titanosilicate melts were heated for up to 24 h at 1300° and 1400°C, weight‐loss measurements and X‐ray fluorescence spectrometry analyses indicated that Cs, Mo, and, to a lesser extent, Na were the main contributors to the observed losses by volatilization. For comparison, similar experiments were performed with an AVM‐type borosilicate glass at temperatures of 1150° and 1250°C, when the viscosities are approximately equal to those of the titanosilicate melts at 1300° and 1400°C, respectively. The losses from the borosilicate glass were predominantly due to Na, B, Cs, and Mo volatilization and were generally higher than the corresponding losses from the titanosilicate glass, typically by factors of ∼4. Possible speciation of the volatile components in these glasses is discussed.
Scanning Tunneling Microscopy and Spectroscopy of Ceramics: Silicon Carbide and Zinc Oxide
Authors: BONNELL DAWN A. , CLARKE DAVID R.
Published: March 2005

The application of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) to the study of ceramic materials is demonstrated with analyses of SiC (6H) single crystals and polycrystalline ZnO both in air and under vacuum. In addition to observations of the surface structure of silicon carbide, mid‐band‐gap electronic states are identified, using STS under vacuum. Surfaces of the sintered ZnO were found to be terraced, having flat areas on the scale of tens of nanometers square, and typical step heights of 1 to 3 nm. The general conditions necessary to enable STM imaging of large‐band‐gap materials typical of most ceramics are discussed. In particular, the effects of doping to create mid‐band‐gap states and induce band bending due to space charging are illustrated in the analyses of SiC and ZnO.
Transformation Plasticity of CeO2‐Stabilized Tetragonal Zirconia Polycrystals: II, Pseudoelasticity and Shape Memory Effect
Authors: REYES‐MOREL PATRICIO E. , CHERNG JYH‐SHIARN , CHEN I‐WEI
Published: March 2005

A macroscopic shape memory effect is demonstrated by first deforming a CeO2‐stabilized tetragonal zirconia polycrystal (Ce‐TZP) between the Mb and As temperatures and then recovering the shape change by heating above Ab. Shape changes effected above Ab are immediately recoverable during unloading, giving rise to a pseudoelastic behavior. Deformation texture is reversible when the shape strain recovers. Both Mb and Ab, along with the associated temperature range for these effects, are depressed to lower temperatures by grain refinement. Prior deformation widens the gap between the transformation temperatures. These observations demonstrate that the shape accommodation in Ce‐TZP arises from twinning and elastic distortions. The operation of pseudoelasticity and shape memory effect is rationalized in terms of martensitic nucleation statistics, the stability of thermoelastic martensite, and internal stresses at the martensitic interface. The implications on transformation plasticity and transformation toughening are explored.
Microstructural Characterization and Fracture Toughness of Cordierite‐ZrO2 Glass‐Ceramics
Authors: McCOY MICHAEL A. , HEUER ARTHUR H.
Published: March 2005

Crystallization of an MgO‐Al2O3‐SiO2‐ZrO2 sintered glass frit was studied. Heat treatment at 850° or 900°C caused initial crystallization of μ‐cordierite and tetragonal (t) ZrO2. The t‐ZrO2 crystallized with an irregular dendritic morphology and could be transformed to monoclinic (m) symmetry under certain conditions; the cordierite underwent the μ→α a transformation with extended annealing. Heat treatments at 1000°C caused crystallization of t‐ZrO2 rods and spheroids in an α‐cordierite matrix; these ZrO2 crystals, however, are resistant to transformation to m‐ZrO2. The beneficial effects of ZrO2 on the fracture toughness of cordierite‐based glass‐ceramics are described.
Li‐(Mg,Zn,Ni) Vanadates
Authors: CHANG LUKE L. Y. , WANG F. Y.
Published: March 2005

Phase relations were determined in the systems of Li‐(Mg,Zn,Ni) vanadates in the temperature range between 500° and 800°C. Each of the ternary systems Li2O‐(Mg, Zn, or Ni)O‐V2O5 is characterized by an orthovanadate: olivine‐type LiMgVO4, phenakite‐type LiZnVO4, and spinel‐type LiNiVO4. Mutual solid solutions form between them. Two solid solutions, a large region of the NiV2O6 type and a complete series between MgV2O6 and ZnV2O6, exist in the system (Mg,Zn,Ni)V2O6. The system (Mg,Zn,Ni)2V2O7 has an extensive solid‐solution region based on Ni2V2O7, whereas the system (Mg,Zn,Ni)3V2O8 is characterized by a complete series.
High‐Temperature Creep and Kinetic Demixing in (Co,Mg)O
Authors: DIMOS DUANE , KOHLSTEDI D.L. , SCHMALZRIED HERMANN
Published: March 2005

The creep behavior of fine‐grained (Co0.5Mg0.5)O and (Co0.25Mg0.75)O has been characterized as part of an investigation of kinetic demixing in solid‐solution oxides due to a nonhydrostatic stress. (i) For low stresses and small grain sizes, the dominant deformation mechanism for both compositions is diffusional creep limited by the transport of oxygen along grain boundaries. The oxygen grain‐boundary diffusivity, Dob is independent of oxygen partial pressure. The values of ωDob, where ω is the grain‐boundary width, that have been determined from the steady‐state diffusional creep rates are given by ωDob=4.7×10−8 exp[‐230 (kJ/mol)/RT] (cm3/s) for (Co0.5Mg0.5)O in the range 950° to 1200°C and ωDob=7.4 × 10−8 exp[‐263 (kJ/mol)/RT] (cm3/s) for (Co0.25Mg0.75)O in the range 1100° to 1250°C. Since oxygen diffusion controls the rate of diffusional creep, kinetic demixing is not observed in deformed samples of either composition. (ii) For high stresses and large grain sizes, the dominant deformation mechanism in both cases is dislocation‐climb‐controlled creep, where the rate of dislocation climb is controlled by oxygen lattice diffusion. Based on the positive dependence of creep rate on oxygen partial pressure, it is concluded that oxygen diffuses through the lattice by an interstitial mechanism.
Phase Relationships in the Silicon Carbide‐Aluminum Nitride System
Authors: ZANGVIL AVIGDOR , RUH ROBERT
Published: March 2005

Phase relationships in the SiC‐AlN system were determined by analytical electron microscopy of local equilibria among adjacent phases in hot‐pressed samples and in diffusion couples. At 2100° to 2300°C, a 4H–2H equilibrium exists, the 4H field extending from ∼2 mol% AlN to an upper limit of 11 to 14 mol% AlN. The wurtzite‐type 2H (δ) solid solution extends from an impurity‐sensitive lower limit of 17 to 24 mol% AlN up to 100 mol% AlN. Semiquantitative Auger electron spectroscopy and energy dispersive X‐ray spectroscopy ultrathin‐window detector measurements confirmed the assumption that the solid solutions have the general formula (SiC)1‐x(AlN)x and belong to the SiC‐AlN pseudobinary system. The existence of a miscibility gap below 1950°C was confirmed, but its limits were not determined accurately. A faulted metastable cubic phase, β′, exists below ∼2000°C and contains up to ∼4 mol% AlN. The transformations into the stable a structures occur through diffusion‐controlled stacking rearrangements.
Thermorheological Simplicity in the Glass Transition
Authors: NARAYANASWAMY O. S.
Published: March 2005

Thermorheological simplicity (TRS) in the glass transition is derived from the principle of temperature (actual and fictive)‐time equivalence. Methods of formulating structural relaxation models consistent with TRS are given. Nonlinear dependence of properties on glass structure (Tf) and temperature (T) is taken into account by modifying the traditional definition of fictive temperature (Tf).
Bistable Optical Information Storage Using Antiferroelectric‐Phase Lead Lanthanum Zirconate Titanate Ceramics
Authors: LAND CECIL E.
Published: March 2005

A recently discovered photostorage effect in antiferroelectric‐phase (AFE‐phase) lead lanthanum zirconate titanate (PLZT) compositions appears to be particularly applicable to binary optical information storage. The basis for bistable optical information storage is that exposure to near‐UV or visible light shifts the electric field threshold of the phase transition between the field‐induced ferroelectric (FE) phase and the stable AFE phase in the direction of the initial AFE → FE phase transition. Properties of this photoactivated shift of the FE → AFE phase transition, including preliminary photosensitivity measurements and photostorage mechanisms, are presented. Photosensitivity enhancement by ion implantation is also discussed.
Chemical States of Copper and Tin in Copper Glazes Fired under Various Atmospheres
Authors: Wakamatsu Mitsuru , Takeuchi Nobuyuki , Nagai Hiroki , Ishida Shingo
Published: March 2005

R—O, N—R, and O—R firing operations produce copper red glazes resulting from the formations of Cu2O, metallic copper, and both Cu2O and metallic copper, respectively. The symbols O, N, and R denote oxidizing, neutral, and reducing atmospheres, respectively, and in the set of symbols, the former corresponds to the heating atmosphere and the latter to the successive cooling atmosphere. All other firing operations such as R—R and R—N fail to produce red glazes. The formation mechanisms of metallic copper and Cu2O are postulated from a microscopic viewpoint.
Metastability of the Martensitic Transformation in a 12 mol% Ceria‐Zirconia Alloy: I, Deformation and Fracture Observations
Authors: Hannnink Richard H. J. , Swain Michael V.
Published: March 2005

A single‐phase tetragonal zirconia polycrystal containing 12 mol% cerium dioxide was found to readily undergo the tetragonal‐to‐monoclinic phase transformation on deformation, fracture, or cooling below 150 K. Deformation tests, primarily indentation studies, indicated that an extensive transformation zone developed about the impression. The transformation zone increased in dimension as the temperature approached the martensitic start temperature for the tetragonal‐to‐monoclinic transformation. Associated with flexure tests at room temperature “Luders”‐like transformation bands propagated entirely across the tensile surface perpendicular to the applied stress. Transmission electron microscopy and X‐ray diffraction were used to monitor the extent and form of the transformation. The reverse transformation was also examined using X‐ray diffraction while heating and compared with in situ transmission electron microscopy observations.
Organic Silanes and Titanates as Processing Additives for Injection Molding of Ceramics
Authors: Lindqvist Karin , Carlström Elis , Persson Michael , Carlsson Roger
Published: March 2005

Organic silanes and titanates were added to a system of polyethylene and silicon nitride intended for injection molding and to a model system of paraffin oil and silicon nitride. The effect of the additions on viscosity was studied. Results from the model system agree comparatively well with the results from the system intended for injection molding. The model system can be used for screening tests. A glycidoxytrimethoxysilane reduces the viscosity of the polyethylene‐silicon nitride system. In combination with tetrabutyl titanate, the effect is more pronounced.
Stoichiometry of the C + SiO2 Reaction
Authors: Biernacki J. J. , Wotzak G. P.
Published: March 2005

The reaction of one‐to‐one molar carbon/silica powder mixtures was studied using simultaneous thermogravimetric analysis and mass spectroscopy with crystalline and amorphous silica. Reaction proceeded via a two‐stage path in which there are at least three identifiable competing global reactions. During the first stage, silicon carbide is formed along with small amounts of silicon monoxide. The most likely reaction path during this stage is the following: SiO2(s) + C(s) → SiO(g) + CO(g); SiO(g) + 2C(s) → SiC(s) + CO(g). The second stage consists of reactions between silica with silicon carbide which form silicon monoxide and, where conditions permit, may also form silicon metal. The major reaction during this stage is 2SiO2(g) + SiC(s) → 3SiO(g) + CO(g).
Effects of Powder Processing on the Green Compacts of High‐Purity BaTiO3
Authors: Hsieh Huey‐Lin , Fang Tsang‐Tse
Published: March 2005

Two processing methods have been used to prepare different green compacts of high‐purity BaTiO3. The substructures of agglomerates have been examined by SEM, and the strength of the agglomerates was interpreted in a plot of the logarithm of the pressure versus the relative density, which is consistent with the structures of cut surfaces of green compacts. The Hg‐penetration results have been used to compare the uniformity of the powder compacts. The wer method (wet milling and subsequent wet pressing) was used to produce uniform green compacts.
Binder Evolution from Powder Compacts: Thermal Profile for Injection‐Molded Articles
Authors: Shukla Vishwa N. , Hill David C.
Published: March 2005

Binder evolution information generated using thermal analysis techniques is used along with microstructural information to define a thermal cycle for debinderizing injection‐molded articles. In addition, the roles of binder chemistry, powder morphology, binder loading, article size, heating rate, and environmental conditions in determining a satisfactory thermal cycle are investigated. Major binder evolution events and types of defects generated are identified. An improved binder removal cycle is developed from this evaluation for organics elimination of a honeycomb structure.
Longitudinal Electrooptic Effects and Photosensitivities of Lead Zirconate Titanate Thin Films
Authors: Land Cecil E.
Published: March 2005

The feasibility of storing and reading high‐density optical information in lead zirconate titanate (PZT) and in lead lanthanum zirconate titanate (PLZT) thin films depends on both the longitudinal electrooptic coefficients and the photosensitivities of the films. This paper describes the methods used to measure the longitudinal electrooptic effects and the photosensitivities of the films. The results of these measurements were used to evaluate a longitudinal quadratic electrooptic R coefficient, a longitudinal linear electrooptic rc coefficient, and the wavelength dependence of the photosensitivity of a composition of PZT polycrystalline thin film. The longitudinal electrooptic R and rc coefficients are about an order of magnitude less than the transverse R and rc coefficients of bulk ceramics of similar compositions. This is attributed to clamping of the film by the rigid substrate. The large birefringence of the films after poling (>10−2) suggests that the optic axes of the films are preferentially oriented normal to the film surface. The techniques used in this paper for evaluating the photosensitivities of thin films are based on measuring the photocurrent generated rather than the reduction in coercive voltage (as in bulk ceramics) when the film is exposed to light. The thin film photosensitivities appear to be significantly higher than those of bulk ceramics of similar compositions. The high photosensitivities coupled with the substantial longitudinal electrooptic coefficients combine to establish the feasibility of using PZT or PLZT thin films for optical information storage applications.
Novel Composite Microstructure and Mechanical Behavior of Mollusk Shell
Authors: Laraia Vincent J. , Heuer Arthur H.
Published: March 2005

Preliminary investigations of the microstructure/mechanical properties relationship in a mollusk shell—the large conch, Strombus gigas—are reported. Strombus gigas has the well‐ordered “crossed lamellar” microstructure and, in four‐point bending, is remarkably tough in certain orientations, permitting noncatastrophic (“graceful”) failure. Fractography indicates that several toughening mechanisms are acting in concert, including crack bridging, microcracking, fiber pullout, and microstructurally induced crack arrest branching. Microindentation studies show that this material is very resistant to cracking; the damage zones around the indents strongly reflect the lamellar character of the microstructure.
Interface Debonding and Fiber Cracking in Brittle Matrix Composites
Authors: Evans Anthony G. , He Ming Y. , Hutchinson John W.
Published: March 2005

Analyses of debonding along interfaces and of the kinking of interface cracks into a fiber have been used to define the role of debonding in fiber‐reinforced, brittle matrix composites. The results reveal that, for fibers aligned with the tensile stress axis, debonding requires an interface fracture energy, Γi, less than about one‐fourth that for the fiber, Γf. Further‐more, once this condition is satisfied, it is shown that fiber failure does not normally occur by deflection of the debond through the fiber. Instead, fiber failure is governed by weakest‐link statistics. The debonding of fibers inclined to the stress axis occurs more readily, such that debonds at acutely inclined fibers can deflect into the fiber, whereupon the failure of fibers is dominated by their toughness.
Preparation of Semiconducting Barium Titanate by Excimer Laser Irradiation
Authors: Igarashi Kaoru , Saito Hideaki , Fujioka Tomoo , Fujitsu Satoru , Koumoto Kunihito , Yanagida Hiroaki
Published: March 2005

A drastic drop of the electrical resistivity was observed on a ferroelectric insulator BaTiO3 surface, after KrFlaser irradiation in air at atmospheric pressure. The temperature dependence of the resistivity was employed to demonstrate semiconducting behavior. Such behavior was seen when the resistance was measured in nitrogen. When measured in air, the semiconducting layer was oxidized and the insulating behavior restored.
Degradation Mechanisms of ZrO2–8 wt% Y2O3/Ni‐22Cr‐10Al‐1Y Thermal Barrier Coatings
Authors: Wu Bo‐Chen , Chang Edward , Chang Shih‐Feng , Tu David
Published: March 2005

Duplex ZrO2–8 wt% Y2O3/Ni‐22Cr‐10Al‐1Y thermal barrier coatings (TBCs) on Mar‐M247 superalloy were tested under different operating conditions within the temperature range 1000° to 1150°C. Results of experiments in this study show that oxidation of bond coatings is the dominant TBC degradation mechanism whereas the operationally induced stresses exert a conjugate effect. The mechanisms of sintering and phase transformation of top coatings do not contribute to failure of TBCs within the temperature range studied. NiO and Ni(Cr,Al)2O4 grown on the surfaces of the bond coatings seem to accelerate spalling of the top coatings along a top coating/bond coating out‐grown oxide interface. However, it is also concluded that the lifetime of TBCs is not directly related to a critical specific weight gain under thermal cycling conditions.
Prevention of Low‐Temperature Surface Transformation by Surface Recrystallization in Yttria‐Doped Tetragonal Zirconia
Authors: Whalen Philip J. , Reidinger Franz , Antrim Robert F.
Published: March 2005

The low‐temperature (100° to 400°C) tetragonal to monoclinic transformation in yttria‐doped tetragonal zirconia (Y‐TZP) can be inhibited by a postsintering grinding and annealing treatment. The surface region so treated contains fine tetragonal grains which have recrystallized from the severely damaged ground surface. The various features of the recrystallized surface that may affect the lowtemperature transformation are analyzed.
Effects of Aspect Ratios of Ellipsoidal Inclusions on Elastic Stress Transfer of Ceramic Composites
Authors: Hsueh Chun‐Hway
Published: March 2005

The elastic stress transfer from a ceramic matrix to aligned elliposidal inclusions is analyzed for the case where the axis of the applied load is parallel to the axis of the ellipsoid. Perfect bonding between the matrix and inclusions is assumed. The calculation is based on Eshelby's model for loading of an infinite matrix containing an ellipsoidal inclusion, and the modification developed by Mori and Tanaka to account for the effect of finite volume fractions of inclusions. The results show that the transfer of the axial stress from the matrix to inclusions increases with the increase in the aspect ratio of the ellipsoid, and decreases with the increase in the volume fraction of inclusions when Young's modulus of the inclusion is higher than that of the matrix.
Reactive‐Electrode Submerged‐Arc Process for Producing Fine Non‐Oxide Powders
Authors: Kumar Amitabh , Roy Rustum
Published: March 2005

The reactive‐electrode submerged‐arc (RESA) method utilizes metal electrodes submerged in a dielectric fluid to produce fine ceramic powders. An arc is struck and causes localized vaporization of the electrode and reaction of the metal with the fluid vapor. This paper reports the extension of this process from oxide to non‐oxide powders. Fine particles of TiC and SiC have been synthesized and characterized by SEM, TEM, and XRD.
Thermal Expansion of Tungsten Carbide at Low Temperature
Authors: Krawitz Aaron D. , Reichel Daniel G. , Hitterman Richard
Published: March 2005

The thermal expansion of WC from 20 to 900 K was measured in the a and c axial directions using high‐resolution neutron powder diffraction. Third‐order polynomials have been calculated from the expansion curves. The results complement and are compared with prior data in the 293 to 900 K region.
Synthesis and Characterization of Catalysts in the System A12O3‐MgO‐NiO‐Ni for Methane Reforming with CO2
Authors: Gadalla Ahmed M. , Sommer Michael E.
Published: March 2005

Compositions to yield solid solutions were prepared by coprecipitation and firing. Fine active clusters of nickel were obtained by reduction. Phase changes were followed by thermal analysis, X‐rays, electron microscopy, surface area measurements, and reforming methane with CO2. Nickel on periclase remained active over 125 h with nearly 100% conversion. The catalysts suppressed carbon deposition which occurred only immediately upstream and downstream of the catalyst. Nickel on spinel solid solution caused the catalyst to shatter with a drastic increase in surface area due to formation of NiAl2O4. The pressure drop decreased the flow rate, making this catalyst infeasible.
Processing of Boron Carbide‐Aluminum Composites
Authors: Halverson Danny C. , Pyzik Aleksander J. , Aksay IIhan A. , Snowden William E.
Published: March 2005

The processing problems associated with boron carbide and the limitations of its mechanical properties can be significantly reduced when a metal phase (e.g., aluminum) is added. Lower densification temperatures and higher fracture toughness will result. Based on fundamental capillarity ther modynamics, reaction thermodynamics, and densification kinetics, we have established reliable criteria for fabricating B4C–Al particulate composites. Because chemical reactions cannot be eliminated, it is necessary to process B4C–AI by rapidly heating to near 1200°C (to ensure wetting) and subsequently heat‐treating below 1200°C (for microstructural development).
Electrochemical Techniques for Corrosion Rate Determination in Ceramics
Authors: Divakar Ramesh , Seshadri Srinvasa G. , Srinivasan Makuteswarc
Published: March 2005

Standard electrochemical test procedures have been successfully applied to determine the corrosion rates of SiC‐based ceramics in aqueous reagents. Direct‐current polarization measurements in HCI solutions indicate that the corrosion rate of α‐SiC is 0.0050 ± 0.0002 mil/yr and is fairly independent of HCI concentration. The corrosion rates of α‐SiC are significantly lower than those for reaction‐sintered SiC in all of the electrolytes used including HCI, HNO3, H3, H3PO4, and aqua regia. It is believed that the free Si contained in the reaction‐sintered SiC is responsible for the higher corrosion rates. It has been shown that electrochemical techniques are reproducible and eminently suitable for determining very low corrosion rates encountered in ceramics.
Structural and Thermodynamic Variation in Nickel Aluminate Spinel
Authors: Mocala Krzysztof , Navrotsky Alexandra
Published: March 2005

New structural and calorimetric data for samples of NiAl2O4 quenched from 600° to 1560°C are presented The spinel remains stoichiometric for all heat treatments. Based on the refinement of X‐ray powder patterns, it is shown that the degree of disorder, defined as the mole fraction of tetrahedral sites occupied by Al3+, changes from x = 0.82 at 600°C to 0.78 at 1560°C. Simultaneously, the lattice parameter and enthalpy vary in a complex manner with quench temperature. The largest lattice parameter (0.80500 ± 0.00004 nm) and most exothermic enthalpy of annealing (heat released when sample is equilibrated at 780°C; ‐10.1 kJ/mol) occur for the sample quenched from 1100°C. A linear correlation exists between the heat of annealing and the lattice parameter. The results have been interpreted as a superposition of at least two effects: (1) the disordering of Ni2+ and Al3+ ions between octahedral (16d) and tetrahedral (8a) sites and (2) a second process, which may be a small amount of the disordering of ions into the usually empty (16c) sites.
Densification of Alumina‐Silicon Carbide Powder Composites: I, Effects of a Polymer Coating on Silicon Carbide Particles
Authors: Jang Hyun M. , Rhine Wendell E. , Bowen H. Kent
Published: March 2005

One possible approach to improving the densification of powder composites containing a major crystalline phase which densifies (e.g., Al2O3) and a difficult‐to‐sinter phase (e.g., SiC) is to accommodate the matrix volume shrinkage with a “disappearing” polymer coating. A polymer coating prevents contact between the nonsinterable particles and the surrounding matrix. The coating can be burned off before sintering, allowing the matrix phase to “shrink‐fit” around the nonsinterable particles during sintering. The effects of a polymer coating on the densification of a two‐phase particle system were tested using SiC powder dispersed in an Al2O3 matrix. The composites processed with a polymer coating showed more densification during equivalent firing cycles than did those processed without a polymer coating. Densification during sintering was approximately proportional to the amount of polymer adsorbed on SiC, suggesting that the Al2O3 matrix did shrink‐fit into the gaps between the SiC particles and the surrounding Al2O3 matrix. Differences in the pore‐size distributions of polymercoated green compacts and uncoated compacts indicated a perturbation of the green microstructure by the gaps. The estimated average thickness of the gap is approximately 20 nm, ∼8% of the average radius of the SiC powder used in this study.
Dielectric, Piezoelectric, and Pyroelectric Properties of Lead Zirconate—Lead Zinc Niobate Ceramics
Authors: Takenaka Tadashi , Bhalla Amar S. , Cross L. Eric , Sakata Koichiro
Published: March 2005

New piezoelectric and pyroelectric ceramics consisting of antiferroelectric lead zirconate (PZ) and relaxor ferroelectric lead zinc niobate (PZN) are studied from an application view‐point of the field‐induced antiferroelectric‐to‐ferroelectric phase transition. An antiferroelectric‐ferroelectric phase boundary exists in PbZrx(Zn1/3Nb2/3)1−xO3 (PZZN‐1000x) close to x = 0.93 to 0.94 at room temperature. A new ferroelectric rhombohedral phase change, Fα–F′α, at low temperature is found and studied by the temperature dependence of the pyroelectric coefficient. Electrical poling in these ceramics is easy, and the coercive field Ec∼8 to kV/cm is rather low. Samples with compositions in the range PZZN‐86 to PZZN‐92 have a large electromechanical coupling constant, k (kt and k15∼50% to 60%), and a low dielectric constant, ɛs (ɛT33/ɛ0= 260 to 320, ɛT11/ɛ0= 380). PZZN ceramics appear to be potential candidates for high‐frequency ultrasonic transducers used in the thickness shear mode. The pyroelectric figure of merit (Fv) of these ceramics is comparable to the values published for the PZT‐based or PbTiO3‐based materials.
Microstructures of Simulated Nuclear Waste
Authors: Chan Hing Wah , Howitt David G. , Harker Alan B.
Published: March 2005

The microstructures of simulated tailored ceramic forms for the Idaho Chemical Processing Plant (ICPP) high‐level waste were characterized by TEM. The ceramic forms were consolidated from simulated ICPP waste calcines with either silicayttria‐based or silica–lithia‐based additives by hot isostatic pressing. The hot isostatically pressed ceramic waste forms are composed of cubic CaF2, monoclinic ZrO2, stabilized cubic ZrO2, tetragonal ZrSiO4, and amorphous silicate phases which can be phase separated. The phaseseparated glass is a result of phase immiscibility in the soda aluminosilicate glass to the compositions of albite and mullite.
Microstructure and Mechanical Properties of Mullite–Silicon Carbide Composites
Authors: Osendi M. Isabel , Bender Barry A. , Lewis David
Published: March 2005

Mullite‐SiC‐whisker composites were prepared by powder processing using two commercial SiC whiskers. These composites were prepared by sintering rather than hot‐pressing. A mulliteSlC‐powder composite and a base line mallite material were also prepared for comparison with the two whisker composite materials. Fracture toughness measurements showed significant enhancement in only one of the whisker composite materials. The microstructure of the four materials was examined by scanning electron microscopy and transmission electron microscopy to assist in the explanation of the mechanical behavior of these composites. The examinations suggested that most of the toughening results from second‐phase particles, with only limited toughening from effects associated with whiskers per se. In one case, higher toughness was partially associated with the formation of sialon phase by reaction with the whiskers and the furnace environment.
Structural and Microstructural Changes in Zirconia in Dilute Chlorine Atmosphere
Authors: Pasquevich Daniel M. , Francisco Lovey  , Caneiro Alberto
Published: March 2005

The tetragonal‐to‐monoclinic phase transition in zirconia powders when exposed to different gas mixtures was studied. Analysis was done at 940°C in the presence of argon and a chlorine–argon mixture. X‐ray diffraction shows that the phase transition is accelerated in the presence of chlorine. Transmission electron microscopy reveals changes in the microstructure of the particles subjected to the gaseous mixtures.
Equilibrium and Transport Properties of Gases in E‐Glass Melts
Authors: Schreiber Henry D. , Kozak Samuel J. , Balazs G. Bryan , Fritchman Ann L. , Schreiber Charlotte W.
Published: March 2005

The solubility and diffusion coefficients of oxygen, sulfur dioxide, and water were determined (and those for nitrogen, carbon dioxide, and argon were estimated) in commercial E‐glass melts as a function of melt temperature and atmosphere. Knowledge of these fundamental constants of gases in glass melts is required for the development of models for bubble growth and elimination within the melt. The effectiveness of fining agents can be traced to the production of those gases in the melt which possess the greatest variation in solubility and diffusion as a function of the temperature and atmosphere. Accordingly, oxygen through multivalent elements and sulfur are the best fining agents for glass production.
Secondary Ion Mass Spectrometer Analysis of Potash–Lime–Silica Glasses Leached in Hydrochloric and Sulfuric Acids
Authors: Schreiner Manfred
Published: March 2005

Secondary ion mass spectrometry investigations were performed on leached K2 O–CaO–SiO2 glass with a chemical composition similar to that of medieval stained glass. The results reveal that the type and concentration of the acid used definitely influence the kinetics of the leaching process. In addition to hydrogen, an enrichment of Cl and S was observed in the leached layers of glass treated with HCl and H2 SO4, respectively.
Laser‐Sintered Barium Titanate
Authors: Kasai Toshihiro , Ozaki Yoshiharu , Noda Hideki , Kawasaki Kenji , Tanemoto Kei
Published: March 2005

Laser sintering of alkoxy‐derived ultrafine BaTiO3 powders was investigated. The temperature increases of the sample with laser irradiation were measured with a thermocouple. It was found that laser irradiation could generate enough heat to sinter ceramics. A slurry was prepared by mixing an alkoxy‐derived BaTiO3 powder, binder additives, solvent, and plasticizer. The slurry was tape cast and dried to give a green sheet. The green sheet was laser sintered and was then characterized by SEM, XRD, and density measurements. The effect of burnout before laser irradiation and the characteristic microstructure of laser‐sintered BaTiO3 are described.
β‐Sialon Ceramics Prepared at 1700°C by Hot Isostatic Pressing
Authors: Ekström Thommy , Olsson Per‐Olof
Published: March 2005

Dense, single‐phase β‐sialon ceramics were sintered at 1700°C and 200 MPa using the glass‐encapsulated hot isostatic pressing technique. The materials were very hard, 1500 to 1700 kg / mm2 (98 N load), but were fairly brittle, with an indention fracture toughness of about 3 MPa · m1/2. The addition of 1 wt% Y2O3 before sintering had a positive effect on the toughness, especially at the low x compositions of Si3‐xAlxOxN4‐x, where KIC∼4 MPa · m1/2.
Carbon Inclusions in Sintered Silicon Carbide
Authors: Hamminger Rainer
Published: March 2005

The carbon additions in the pressureless sintering of SiC are commonly used for the removal of SiO2 layers on the starting powders. In practice, it is common to add more C than is necessary for stoichiometric removal to ensure a complete deoxidation. As a result, inclusions of excess free C are a general feature of the microstructure of sintered SiC. This phenomenon was studied by high‐resolution Auger electron spectroscopy on ultra‐high‐vacuum‐exposed fracture surfaces as well as by high‐resolution transmission electron microscopy of B‐ and C‐doped materials.
Cyclic Fatigue Behavior of an Alumina Ceramic with Crack‐Resistance Characteristics
Authors: Lathabai Srinivasarao , Yiu‐Wing Mai , Lawn Brian R.
Published: March 2005

The behavior under cyclic tension—tension loading of an alumina ceramic with pronounced crack‐bridging (R‐curve) characteristics is studied. Tests on disk specimens with indentation cracks reveal no failures below the static fatigue limit. Theoretical predictions of the stress‐lifetime response, based on the premise that environmentally assisted slow crack growth is the sole factor determining lifetime, are consistent (within experimental scatter) with the data. The results indicate that there is no significant cyclic degradation from potential damage to the bridges, at least in the short‐crack region pertinent to strength properties.
High‐Temperature Passive Oxidation of Chemically Vapor Deposited Silicon Carbide
Authors: Narushima Takayuki , Goto Takashi , Hirai Toshio
Published: March 2005

The oxidation behavior of chemically vapor deposited (CVD) SiC at high temperature was investigated using a thermogravimetric technique in the temperatures range of 1823 to 1948 K. The specimens were prepared by chemical vapor deposition using SiCl4, C3H8, and H2 as source gases. The oxidation behavior of the CVD‐SiC indicated “passive” oxidation and a two‐step parabolic oxidation kinetics over the entire temperature range. The crystallization of the SiO2 film formed may have caused this two‐step parabolic behavior. The parabolic oxidation rate constant (Kp) varied with the square root of the oxygen partial pressure (P1/2O2). The activation energy for the oxidation was determined to be 345 and 387 kJ · mol−1. These values suggest that the diffusion process of the oxygen ion which passes through the SiO2 film is rate‐controlling.
Volatilization of 137Cs and 106Ru from Borosilicate Glass Containing Actual High‐Level Waste
Authors: Kamizono Hiroshi , Kikkawa Shizuo , Togashi Yoshihiro , Tashiro Shingo
Published: March 2005

Volatility of 137 Cs and 106Ru from borosilicate glass containing actual high‐level waste was measured in an almost closed stainless‐steel canister. The temperature dependence of the volatility of 137Cs was close to that obtained in our previous study using 134Cs. The volatility of 106Ru was about one‐fifth that of 137Cs at 600° and 800°C. The air contamination by 137Cs and 106Ru in the canister at 400°C was estimated at 1.8 × 102 and 2 × 10 Bq/cm3, respectively, when it was assumed that the glass contained a realistic amount of 137Cs and 106Ru expected in commercial waste glass. These results are useful for predicting safety in a storage facility under operation.
Zirconia Coating on Stainless Steel Sheets from Organozirconium Compounds
Authors: Izumi Keiji , Murakami Megumi , Deguchi Takenori , Morita Arihiko , Tohge Noboru , Minami Tsutomu
Published: March 2005

The stability and the coating characteristics of a variety of organozirconium compounds have been investigated to coat ZrO2 films on stainless steets for the improvement of heat resistance against oxidation. Zirconium tetraoctylate and zirconium tetrakis(acetylacetonate) were found to be more stable than zirconium alkoxides in an ambient atmosphere. The ZrO2 films from zirconium alkoxides became white and discontinuous when the thickness of the films exceeded about 200 Å (20 nm). On the other hand, transparent ZrO2 films were obtained from zirconium tetraoctylate and zirconium tetrakis(acetylacetonate). The IR spectra of the films showed that the heat treatment at 400°C for 5 min produced organic‐free ZrO2 films. The heat resistance of stainless steel sheets against oxidation was improved by the ZrO2 coating, depending on the film thickness.
Tensile Strengths of Se, As2S3, As2Se3, and Ge30As15Se55 Glass Fibers
Authors: McEnroe David J. , LaCourse William C.
Published: March 2005

The strengths of as‐drawn, abraded, and pristine Se, As2Se3, As2S3, and Ge30As15Se55 fibers are reported. Pristine strength values range from an average of 80 MPa for Se and Ge30As15Se55 to 100 and 180 MPa for As2Se3 and As2S3, respectively. Although these values are considerably higher than those reported previously for bulk samples, in no case does the maximum observed strength reach more than about 6% of that expected from simple theoretial calculations. Several factors that can control the strength are discussed. The overall behavior is interpreted in terms of the glass structures which permit localized stress relaxation effects in regions of weak, nondirectional bonds. These effects occur at temperatures well below the glass‐transition region.
Ball‐on‐Ring Test Revisited
Authors: de With Gijsbertus , Wagemans Harrie H. M.
Published: March 2005

A literature survey indicates that the ball‐on‐ring test is the best biaxial strength testing method. There is, however, some controversy in the calculation of the strength. In this communication, the theroretical controversy of the ball‐on‐ring test is resolved by strain and deflection analysis. Consequently, the ball‐on‐ring test can be used as a reliable method for testing the strength of flat brittle specimens.
Dependence of the Crystal Structure on Particle Size in Barium Titanate
Authors: Uchino Kenji , Sadanaga Eiji , Hirose Terukiyo
Published: March 2005

The effect of the sample particle size on the crystal structure and the Curie temperature of BaTiO3 powder has been investigated in the particle size range 0.1 to 1.0 μm. The transformation from tetragonal to cubic symmetry occurs at a critical particle size of 0.12 μm at room temperature, and the Curie temperature drops below room temperature at the critical particle size.
Effect of Praseodymium and Uranium Addition on the Jc of Ba2 YCu3O7
Authors: O'Bryan H. M. , Gyorgy E. M. , Rhodes W. W.
Published: March 2005

Ba2YCu3O7 ceramics doped with either Pr or U at 0.000 17 to 1.7 wt% levels have been prepared. For each sample Jc (magn) has been measured with a vibrating sample magnetometer. No improvement in Jc was found for either dopant and it is concluded that neither provides the clusters necessary to produce suitable pinning sites.
Synthesis of V2O3 Powder by Evaporative Decomposition of Solutions and H2 Reduction
Authors: Sullivan Robert J. , Srinivasan Thallam T. , Newnham Robert E.
Published: March 2005

The evaporative decomposition of solutions method was used to form V2O5. Spraying above the congruent melting temperature of V2O5 (690°C) resulted in dense spherical particles with a smooth surface. Spraying below the V2O5 melting temperature yielded porous V2O5 powder with a rough surface. Reduction of the V2O5 to V2O3 was done in a H2 atmosphere. Spherical V2O3 powder was attained when the reduction temperature was low enough to reduce the V2O5 surface before partial sintering (necking) between V2O5 particles occurred. The resulting V2O3 particle size was smaller than the precursor V2O5 powder as expected by the differences in densities between V2O5 (p= 3.36 g/cm3) and V2O3 (p= 4.87 g/cm3).
Glass Strengthening by Polymer‐Derived Ceramic Coatings
Authors: Blum Yigal D. , Platz Robert M. , Crawford Edward J.
Published: March 2005

Polysilazane‐derived ceramic coatings in the form of thin films (0.1 to 4 μm) — fabricated by dipcoating soda‐lime rods with preceramic polymer solutions, followed by pyrolysis — increased the strength of the glass rods. Strengths up to 414 ± 57 MPa were obtained, 2.3 and 3.3 times higher than the strengths of uncoated/annealed and as‐received rods, respectively. As‐received coated glass was stronger than coated annealed glass. Microstructural damage was not observed in the optimal coatings.