bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect Structure and Thermodynamic Properties of the Wustite Phase (Fe1‐yO)
Authors: Nowotny J. , Rekas M.
Published: October 2005

The defect structure model in the wustite phase is considered involving the 4:l cluster as a basic defect structure unit. Interactions between defects are considered in terms of the Debye‐Hückel theory for strong electrolytes. It has been shown that the available data on wustite nonstoichiometry fit well the 4:l cluster model. Above 1173 K the degree of ionization of the cluster is −5. The equilibrium constant of the cluster formation determined in this work is Kc= [((VFe)4Fei)5−][h]5 [FeFe]−6[Vi]−1PO2−3/2f6±= 1.07 × 10−14 exp[396.7 (kJ)/RT]. The equilibrium constant is quite consistent with such thermodynamic parameters as partial molar enthalpy and entropy of oxygen in Fe1‐yO within the entire stability range of the wustite phase.
Retention of Fluorine in Silica Gels and Glass*
Authors: Rabinovich Eliezer M. , Krol Denise M. , Kopylov Nonna A. , Gallagher Patrick K.
Published: October 2005

F− ions enter silica gels as Si‐F bonds and free and hydrogen‐bonded HF. During drying, heating, and sintering, all HF is removed, and a significant portion of the structural fluoride (Si‐F) is also eliminated through reaction with Si—OH, which results in formation of siloxane bonds. Substitution of Si‐Cl bonds for Si—OH bonds assists in retention of fluoride, and up to ∼1 wt% F can be preserved in gels heated to 1000 °C. Introduction of SiF4 into the sintering atmosphere can increase the amount of retained fluoride in the silica glass up to ∼1.8%.
High‐Temperature Failure of an Alumina‐Silicon Carbide Composite under Cyclic loads: Mechanisms of Fatigue Crack‐Tip Damage
Authors: Han Lily X. , Suresh Subra
Published: October 2005

Experimental results are presented on the mechanisms of tensile cyclic fatigue crack growth in an A1203‐33‐vol%‐SiC‐whisker composite at 1400°C. The ceramic composite exhibits subcritical fatigue crack propagation at stress‐intensity‐fator values far below the fracture toughness. The fatigue characterized by the stressintensity‐factor range, ΔK, and crack propagation rates are found to be strongly sensitive to the mean stress (load ratio) and the frequency of the fatigue cycle. Detailed transmission electron microscopy of the fatigue crack‐tip region, in conjunction with optical microscopy, reveals that the principal mechanism of permanent damage ahead of the advancing crack is the nucleation and growth of interfacial flaws. The oxidation of Sic whiskers in the crack‐tip region leads to the formation of a silica‐glass phase in the 1400°C air environment. The viscous flow of glass causes debonding of the whisker‐matrix interface; the nucleation, growth, and coalescence of interfacial cavities aids in developing a diffuse microcrack zone at the fatigue crack tip. The shielding effect and periodic crack branching promoted by the microcracks result in an apparently benefcial fatigue crack‐growth resistance in the A1203—SiC composite, as compared with the unreinforced alumina with a comparable grain size. A comparison of static and cyclic load crack velocities is provided to gain insight into the mechanisms of elevated temperature fatigue in ceramic composites.
Grain Growth During Hot Isostatic Pressing of Presintered Alumina
Authors: Uematsu Keizo , Itakura Kazuhisa , Sekiguchi Masahiko , Uchida Nozomu , Saito Katuichi , Miyamoto Akira
Published: October 2005

Grain growth during hot isostatic pressing is examined at 1373 to 1673 K at 5 to 200 MPa for 0.5 to 4 h on alumina presintered at 1723 to 1873 K. A linear relation is found between logarithms of grain size and porosity. To account for this result, the development of similar microstructures is suggested regardless of the histories of the starting powder and process. Temperature dependences of grain growth and densification must also be equal during hot isostatic pressing. Both grain growth and densification were controlled by the grain‐boundary diffusion of the aluminum ions.
Grain‐Size and R‐Curve Effects in the Abrasive Wear of Alumina
Authors: Cho Seong‐Jai , Hockey Bernard J. , Lawn Brian R , Bennison Stephen J.
Published: October 2005

Results of sliding wear tests on three alumina ceramics with different grain sizes are discussed in the light of crackresistance (R‐curve, or T‐curve) characteristics. The degree of wear increases abruptly after a critical sliding period, reflecting a transition from deformation‐controlled to fracture‐controlled sulface removal. This transition occurs at earlier sliding times for the aluminas with the coarser‐grained microstructures, indicative of an inherent size effect in the wear process. A simplistic fracture mechanics model, incorporating the role of internal thermal expansion mismatch stresses in the crack‐resistance characteristic, is developed. The results suggest an inverse relation between wear resistance and large‐crack toughness for ceramics with pronounced Rcurve behavior.
Effect of Silica and Processing Environment on the Toughness of Alumina Composites
Authors: Smith S. M. , Scattergood R. O. , Singh J. P. , Karasek K.
Published: October 2005

Results are presented for the effect of the hot‐pressing environment and the oxygen content of Sic whiskers on the fracture toughness of an A1203‐matrix composite reinforced with 15 vol% Sic. For the composite with Sic whiskers having a 55 at.% oxygen layer, the fracture toughness (Kic) decreases from 8.03 to 6.64 MPa‐m1/2 when the hot‐pressing environment is changed from argon to a vacuum of ∼6.7 × 10−2 Pa. The results indicate that the decrease in Klc of the composite is related to the degradation of Sic whiskers by reaction with SiO2, which is enhanced in a vacuum environment where the reaction products are constantly removed.
Monolithic Device with Dual Capacitor and Varistor Functions
Authors: Ling Hung C. , Yan Man F. , Rhodes Warren W.
Published: October 2005

Protective devices are needed in electronic systems to protect against voltage surges. In this paper, a monolithic device incorporating both the functions of a capacitor and a varistor is described. The device has a capacitance of 1 μF and a dissipation factor less than 0.05 between 1 and 100 kHz. At voltages greater than the threshold voltage, V0, of about 15 volts, the device conducts a current, I, according to the power‐law relation of varistors, I=AVα. The nonlinearity index, α, is 11.4. In this device, the capacitor function protects against the lowamplitude and high‐frequency transients while the varistor function protects against the high‐amplitude voltage surges. Appropriate capacitor and varistor composition can be found to have similar sintering temperatures, allowing the fabrication of monolithic devices with a range of sintering temperatures between 900° and 1350°C.
Criteria for Diffusion by a Site‐Interchange Mechanism
Authors: Birnie Dunbar P.
Published: October 2005

Criteria are established for evaluating whether self‐diffusion in a material may be occurring by a site‐interchange diffusion mechanism. The criteria include comparisons between defect formation and migration energies for the site‐interchange model and a normal vacancy diffsion model. These criteria are applied to some material systems to illustrate their utility. A site‐interchange diffusion mechanism is probably occurring in lithium niobate, but this mechanism is not operative in silicon carbide or in some III‐V compound semiconductors.
Anisotropic Ionic Conductivity Observed in Superplastically Deformed Yttria‐Stabilized Zirconia/Alumina Composite
Authors: Drennan John , Swain Michael V. , Badwal Sukhvinder P. S.
Published: October 2005

Ionic conductivity measurements on a yttria‐stabilized tetragonal zirconia polycry stall alumina composite subjected to superplastic deformation demonstrate anisotropic character. Parallel to the pressing direction, the grain‐boundary resistance to oxygen ion mobility is 25% to 30% higher than that measured perpendicular to the pressing direction. The same directional dependency on the volume conductivity is observed but is less pronounced, showing approximately a 9% difference. Microstructural evidence reveals an agglomeration and elongation of alumina particles perpendicular to the pressing direction, and it is suggested that this phenomenon restricts the passage of ions parallel to the compression direction, giving rise to the anisotropic nature of the conductivity measurements.
Decoration of Open Pore Networks in Light‐Colored Ceramics
Authors: Schroth James G. , Druschitz Alan P.
Published: October 2005

A decoration technique was used to determine the positions of open porosity in both ZrO2‐3‐mol%‐Y2O3 and Al2O3. In some instances, deeply penetrating open pore networks were identified even when the sintered bodies investigated contained less than 1% open porosity. The decoration technique could be used in the development of processing procedures for the manufacture of sound ceramic components.
Laser Diagnostics of Zirconium Carbide Vaporization
Authors: Butt Darryl P. , Wantuck Paul J. , Sappey Andrew D.
Published: October 2005

Laser diagnostic methods are developed to study the behavior of laser‐ablated zirconium carbide (ZrC). The optical emission spectra from the Zr‐C plasma plume is measured from 200 to 500 nm. Emission from zirconium atoms dominated the observed spectra. From the spectra, the average plasma temperature was estimated to be 10500 ± 1500 K. Plume formation is characterized using a CCD camera to capture emission at delay times (with respect to the ablation laser pulse) ranging from 1 μs to 1 ms and using planar laser‐induced fluorescence to map Zr atom distributions.
Effect of Sn Substitution on Cation Ordering in (Zr1–xSnx)TiO4 Microwave Dielectric Ceramics
Authors: Christoffersen Roy , Davies Peter K. , Wei Xiaohan , Negas Taki
Published: October 2005

The crystal structure and microwave dielectric properties of (Zr1–xSnx)TiO4 ceramics with x ranging from 0.0 to 0.15 have been investigated to characterize the effect of Sn substitution on cation ordering and the effect of ordering on dielectric loss. The crystal structure of the samples was investigated using high‐resolution transmission electron microscopy and electron diffraction. Although Sn substitution inhibits ordering, the effect is progressive and ordering still proceeds to an observable degree in samples with x= 0.15. The ordered structure of all samples is of the incommensurate modular type previously observed for Sn‐free zirconium titanate compositions. In this structure individual (100) cation layers are observed to switch abruptly from Zr‐rich to Ti‐rich occupancy, indicating that ordering proceeds by the segregation of Zr and Ti into elongate two‐dimensional domains on (100). The domains get smaller as the Sn content of the samples increases and in Zr0.5Sn0.15TiO4 the length scale of the cation correlations is approximately 25–50 Å. We propose that the decrease in the driving energy for the coarsening of the domains during the ordering transformation is due to the preferential segregation of Sn to the Zr‐Ti domain boundaries. Whereas the long‐range cation ordering increases the dielectric loss of Sn‐free ceramics by 30%, it results in a negligible change in the loss properties of Zr0.91Sn0.09TiO4. It is possible that the hypothesized effect of Sn in stabilizing the Zr‐Ti boundaries may also affect the contribution of these sites to the dielectric loss of the ordered structures.
Investigation of Strut Crack Formation in Open Cell Alumina Ceramics
Authors: Brown David D. , Green David J.
Published: October 2005

An investigation was made into the source of strut cracking during the fabrication process of open cell ceramics that are produced by coating a polymeric foam. Several sources for the stress that produces these cracks were considered, viz., differential drying, thermal expansion mismatch between the polymer and the green ceramic coating, and the gas pressure produced by pyrolysis of the organic skeleton. Thermogravimetric analysis of the polymeric foam was used to estimate the gas evolution rate associated with the pyrolysis process, but this was found to be very low compared to the pressures required to cause strut damage. SEM observations on samples taken by interrupting the fabrication procedure showed the cracks were not produced during drying but rather at a temperature near the melting/decomposition point of the polymer and prior to pyrolysis. It was then deduced that the differential thermal expansion between the polymer and the ceramic coating was the source of the stress. The strut cracking is observed to occur primarily in the region of the highly curved strut edges of the polymer foam, at which the ceramic coating is often rather thin. Techniques to change the processing procedure to overcome the strut cracking are discussed.
Kinetics and Deformation during the Reaction of Yttrium‐Aluminum Perovskite and Alumina to Yttrium‐Aluminum Garnet
Authors: Hay Randall S.
Published: October 2005

The kinetics of the reaction of directionally solidified eutec‐tics of yttrium‐aluminum perovskite and alumina to yttrium‐aluminum garnet were measured between 1150° and 1550°C for times as long as 20 000 min. Deformation from the 11 vol% increase was observed. Samples were characterized by optical microscopy, SEM, and extensively by TEM. Surface displacements from self‐stress relaxation were measured by atomic force microscopy. YAG nucleated at yttrium silicate impurities as 20‐nm‐thick plates. For nucleation to occur, the 20‐GPa self‐stress must relax. YAG growth was parabolic with a 550‐kJ/mol activation energy. Self‐stress relaxation caused creep polygonization in YAG, forming short‐circuit diffusion pathways that may have increased the growth rate. The maximum flow stress in YAG was estimated to be 1–3 GPa and decreased as the reaction progressed. The inferred flow stresses should not have significantly decreased the reaction driving force. Eventually, off‐axis creep of alumina dominated self‐stress relaxation because its flow stress was much lower than that of YAG.
Impedance Spectroscopy Study of Sintering in Bi‐Doped ZnO
Authors: Kirkpatrick Kelly S. , Mason Thomas O. , Balachandran Uthamalingam , Poeppel Roger B.
Published: October 2005

Solid‐ and liquid‐state sintering kinetics in the (1 – x)ZnO‐xBi2O3 system with 0 ≤x≤ 0.05 over the range 600 ≤T (°C) ≤ 1100 were investigated by impedance spectroscopy. Compositions with x < 0.002 retarded sintering, whereas compositions with x≥ 0.004 accelerated sintering above the eutectic temperature of 740°C. The results could be interpreted in terms of limited solid solubility of Bi2O3 in ZnO (x≃ 0.004 ± 0.002), solid‐state sintering in the subsolidus, and liquid‐state sintering above the solidus. A phase diagram for the ZnO‐rich end of the system is proposed, based on these results.
Microanalytical Determination of ZnO Solidus and Liquidus Boundaries in the ZnO‐Bi2O3 System
Authors: Hwang Jin‐Ha , Mason Thomas O. , Dravid Vinayak P.
Published: October 2005

ZnO solidus and liquidus boundaries in the ZnO‐Bi2O3 system were investigated via analytical electron microscopy (AEM), electron probe microanalysis (EPMA), and secondary ion mass spectrometry (SIMS). The Bi2O3 solubility is highest—0.24 ± 0.04 mol%—at the eutectic temperature of 740°C and decreases rapidly with increasing temperature. Detection limits and quantification procedures of X‐ray microanalysis (AEM, EPMA) and ion microanalysis (SIMS) are discussed with respect to the determination of phase diagrams involving low solubility phases.
Thermal Stress Analysis of Fused‐Cast AZS Refractories during Production: Part I, Industrial Study
Authors: Cockcroft Steven L. , Brimacombe J. Keith , Walrod Dennis G. , Myles Thomas A.
Published: October 2005

A study has been conducted to understand and prevent the formation of cracks in alumina‐zirconia‐silica (AZS) refractory blocks during solidification processing. A fundamental approach has been taken, centered on the development of a three‐dimensional mathematical model to predict heat flow and stress generation in fused‐cast AZS refractory blocks. In the first part of a two‐part study, the “voidless” casting process has been carefully examined in an industrial setting. From a survey of the distribution, frequency of occurrence, and fracture surface morphology of cracks, an attempt was made to link the crack types found in the study to process variables. In‐mold temperature data collected for a single casting throughout the normal cooling period have been used to validate the heat‐flow model which is described in Part 11. The stress analysis, cause of the different cracks, and remedial action are also presented in Part 11.
Thermal Stress Analysis of Fused‐Cast AZS Refractories during Production: Part II, Development of Thermo‐elastic Stress Model
Authors: Cockcroft Steven L. , Brimacornbe J. Keith , Walrod Dennis G. , Myles Thomas A.
Published: October 2005

Mathematical models of heat flow and thermo‐elastic stress, based on the finite‐element method, have been developed and utilized to analyze the “voidless,” fused‐cast, AZS, solidification process. The results of the mathematical analysis, in conjunction with information obtained in a comprehensive industrial study, presented in Part I of this paper, describe the mechanisms for the formation of the various crack types found in the fused‐cast product. Thermal stresses are generated early in the solidification process by rapid cooling of the refractory surface as it contacts the initially cool mold and later in conjunction with the tetrago‐nal‐to‐monoclinic phase transformation which occurs in the zirconia component of the AZS refractory. Applying this model, castings were made using a revised mold design. Preliminary results indicate these castings to be free of objectionable transverse cracks.
Effect of Treatment of Reactive Aggregate by H2O2 on the Alkali‐Silica Reaction
Authors: Hibino Takeshi , Tsuyuki Naomitsu , Ishida Hideki
Published: October 2005

A method of controlling the alkali‐silica reaction by treating a reactive aggregate with a solution of hydrogen peroxide was investigated. Mortar bars made using the hydrogen peroxide‐treated aggregate exhibited no expansion after 12 months, indicating that the alkali‐silica reaction was suppressed. Study of the state of bonding of Si in the aggregate using XPS showed that the Si‐O bond energy indicating glassy SiO2 (102.7 eV) before treatment had changed to crystalline SiO2 (103.2 eV) after hydrogen peroxide treatment. This indicates that the strong oxidizing potential of hydrogen peroxide stabilizes the silica in the reactive aggregate and thus suppresses the alkali‐silica reaction.
Phase Transformations in Monoclinic Zirconia Caused by Milling and Subsequent Annealing
Authors: Scian Alberto N. , Aglietti Esteban F. , Caracoche María C. , Rivas Patricia C. , Pasquevich Alberto F. , López García Alberto R.
Published: October 2005

Monoclinic ZrO2 has been milled for various times down to a crystallite size of 145 Å. Using the time‐differential perturbed‐angular‐correlation technique, it was possible to associate the resulting growing amount of disordered material with two different, very distributed and milling‐time‐dependent hyperfine interactions: one (Y) of quadrupole frequency similar to that of tetragonal zirconia after long milling, the other (X) one of a quadrupole frequency similar to that of monoclinic zirconia at shorter milling times. Upon annealing, all samples showed the recovery of the crystalline monoclinic phase at the expense of the disordered structures. In samples milled for shorter times, the (Y) interaction emerges as an ordered crystallization product, upon annealing at temperatures which depend nearly linearly on the crystallite size.
Kinetics of CeO2 Surface Area Reduction in a Mixture of HCI, H2O, and O2
Authors: Gruy Frédéric , Pijolat Michèle
Published: October 2005

Surface area reduction of a cerium dioxide powder is studied at 900 K in a HCI, H2O, and O2 atmosphere. The rate of surface area decrease is determined as a function of the surface chloride content and of the partial pressure of hydrogen chloride. It is shown that particle growth occurs due to the surface diffusion of cerium and hydroxyl ions, which results from hydrogen chloride adsorption. Adsorbed chloride ions react to give gaseous chlorine. The rate‐determining step of the process of initial coarsening is hydrogen chloride fixation at the surface of cerium dioxide particles.
Freudenbergite: A Possible Synroc Phase for Sodium‐Bearing High‐level Waste
Authors: Vance Eric R. , Angel Paul J. , Cassidy David J. , Stewart Martin W. A. , Blackford Mark G. , McGlinn Peter A.
Published: October 2005

Earlier studies have shown that the presence of excess sodium in high‐level nuclear waste can give rise to increased leachability when the waste is incorporated in Synroc‐type titanate ceramics. Freudenbergite (Na2Al2Ti6O16) can incorporate sodium and it exhibits satisfactory leaching resistance in water and reasonable resistance to radiation. From X‐ray diffraction studies, freudenbergite is compatible with the other phases in Synroc. Thus, Synroc containing freudenbergite as an additional phase offers potential for immobilizing sodium accompanying high‐level nuclear fuel reprocessing waste.
Molten Glass Corrosion Resistance of Immersed Combustion‐Heating Tube Materials in Soda‐Lime‐Silicate Glass
Authors: Sundaram S. Kamakshi , Hsu Jen‐Yan , Speyer Robert F.
Published: October 2005

The corrosion resistance of molybdenum, molybdenum disilicide, and a SiC(p)/Al2O3 composite to molten soda‐lime‐silicate glass was studied. The ASTM‐C621–84 corrosion test method was modified because of inherent inaccuracies in the method and Si attack of platinum crucibles. Specimen‐glass interfacial regions were characterized using XRD, SEM, and EDS. After 48 h of exposure at 1565°C, the half‐down corrosion recessions of Mo, MoSi2, and SiC(P)/Al2O3 were 0.11, 0.316, and 0.26 mm, respectively. Mo oxidized to form a MoO2 surface scale which cracked, allowing glass seepage and further oxidation. Silicon was leached out of MoSi2 into the glass, leaving a Mo5Si3 interface and particles of Mo near the interface. For the SiC(P)/Al2O3 composite, bubbles observed at the interfacial regions formed from oxidation of SiC to form CO. Thermodynamic modeling corroborated these experimental observations.
Massive Transformation in the Y2O3‐Bi2O3 System
Authors: Fung Kuan Zong , Virkar Anil V. , Drobeck David L.
Published: October 2005

Cubic solid solutions in the Y2O3‐Bi2O3 system with ∼25% Y2O3 undergo a transformation to a rhombohedral phase when annealed at temperatures ≤ 700°C. This transformation is composition‐invariant and is thermally activated, and the product phase can propagate across matrix grain boundaries, indicating that there is no special crystallo‐graphic orientation relationship between the product and the parent phases. Based on these observations, it is proposed that cubic → rhombohedral phase transformation in the Y2O3‐Bi2O3 system is a massive transformation. Samples of composition 25% Y2O3‐75% Bi2O3 with and without aliovalent dopants were annealed at temperatures ≤ 700°C for up to 10000 h. ZrO2 as a dopant suppressed while CaO and SrO as dopants enhanced the kinetics of phase transformation. The rate of cubic/rhombohedra1 interface migration (growth rate or interface velocity) was also similarly affected by the additions of dopants; ZrO2 suppressed while CaO enhanced the growth rate. Diffusion studies further showed that ZrO2 suppressed while CaO enhanced cation interdiffusion coefficient. These observations are rationalized on the premise that cation interstitials are more mobile compared to cation vacancies in cubic bismuth oxide. The maximum growth rate measured was ∼10−10 m/s, which is orders of magnitude smaller than typical growth rates measured in metallic alloys. This difference is explained in terms of substantially lower diffusion coefficients in these oxide systems compared to metallic alloys.
Effects of α‐Sic versus β‐Sic Starting Powders on Microstructure and Fracture Toughness of Sic Sintered with Al2O3‐Y2O3 Additives
Authors: Lee Seung Kun , Kim Chong Hee
Published: October 2005

Dense Sic ceramics were obtained by pressureless sintering of β‐Sic and α‐Sic powders as starting materials using Al2O3‐Y2O3 additives. The resulting microstructure depended highly on the polytypes of the starting SiC powders. The microstructure of SiC obtained from α‐SiC powder was composed of equiaxed grains, whereas SiC obtained from α‐SiC powder was composed of a platelike grain structure resulting from the grain growth associated with the β→α phase transformation of SiC during sintering. The fracture toughness for the sintered SiC using α‐SiC powder increased slightly from 4.4 to 5.7 MPa.m1/2 with holding time, that is, increased grain size. In the case of the sintered SiC using β‐SiC powder, fracture toughness increased significantly from 4.5 to 8.3 MPa.m1/2 with holding time. This improved fracture toughness was attributed to crack bridging and crack deflection by the platelike grains.
Evidence for Anelastic Creep Recovery in Silicon Carbide‐Whisker‐Reinforced Alumina
Authors: Gu Weizhong , Porter John R. , Langdon Terence G.
Published: October 2005

Experiments were conducted on monolithic Al2O3 and Al2O3 composites reinforced with SiC‐whiskers in which the load was removed during high‐temperature creep. The monolithic material exhibited no anelastic recovery on load removal, but the composites showed a significant anelastic recovery which was reproducible and essentially independent of the total creep strain at which the load was removed. The results were consistent with the hypothesis that an interconnecting whisker network may develop during processing of the composites.
Doped Perovskite Oxide, PrMnO3, as a New Cathode for Solid‐Oxide Fuel Cells that Decreases the Operating Temperature
Authors: Ishiham Tatsumi , Kudo Takanari , Matsuda Hideaki , Takita Yusaku
Published: October 2005

Cathodic overpotentials of Ln0.6Sr0.4MnO3 (Ln is La, Pr, Nd, Sm, Gd, Yb, and Y) were studied for a new cathode for solid‐oxide fuel cells (SOFCs) with low overpotentials in a relatively‐low‐temperature region. Cathodic overpotentials strongly depended on the rare‐earth cations in the A sites of the perovskite oxide. In particular, overpotentials of a Sr‐doped PrMnO3 cathode maintained low values despite decreased operating temperature. Consequently, almost the same power density of a SOFC with Ln0.6Sr0.4MnO3 cathode was obtained at about 100 K lower operating temperature by using Sr‐doped PrMnO3 as the cathode.
Formation and Sintering of Yttria‐Doped Tetragonal Zirconia with 50 mol% Alumina Prepared by the Hydrazine Method
Authors: Kimoto Shinya , Hirota Ken , Yamaguchi Osamu , Kume Hideki , Inamura Suguru , Miyamoto Hiroki
Published: October 2005

Al2O3/Y2O3‐doped ZrO2 composite powders with 50 mol% Al2O3 are prepared by the hydrazine method. As‐prepared powders are mixtures of AlO(OH) gel and amorphous ZrO2 solid solutions containing Y2O3 and Al2O3. The formation process leading to α‐Al2O3‐t‐ZrO2 composite powders is examined. Hot isostatic pressing is performed for 2 h at 1400°C under 196 MPa using θ‐Al2O3‐t‐ZrO2 composite powders. The resulting dense, sintered α‐Al2O3‐t‐ZrO2 composites show excellent mechanical strength.
Particle‐Inhibited Grain Growth in Al2O3‐SiC: II, Equilibrium and Kinetic Analyses
Authors: Stearns Laura C. , Harmer Martin P.
Published: October 2005

The grain‐growth data presented in a companion paper for the Al2O3‐SiC system are analyzed. Central to the analysis is the experimentally observed relationship between the fraction of particles on grain boundaries, φ, and the average grain size, G. This relationship is included in both the equilibrium‐grain‐size expression originally formulated by Zener and classical grain‐growth rate equations. The modified expression for equilibrium grain size, GL, as a function of volume fraction of pinning particles, f, contains a power‐law dependence for GL on f that has been developed using the relationship between φ and G during microstructure evolution. The expressions for the grain‐growth kinetics are similarly developed. The equilibrium and kinetic relationships are used to describe the experimental data from the companion paper and predict grain‐growth behavior. A new type of map is constructed to predict the time required to approach equilibrium as afunction of volume fraction and annealing temperature. This map reveals that extreme experimental conditions (very long times and high annealing temperatures) are necessary for the system to reach equilibrium, especially for smaller volume fractions, and that the attainment of equilibrium is experimentally quite difficult.
Synthesis of Nd:YVO4 Thin Films by a Sol‐Gel Method
Authors: Hirano Shin‐ichi , Yogo Toshinobu , Kikuta Ko‐ichi , Sakamoto Wataru , Koganei Hirosada
Published: October 2005

Nd: YVO4 powders and thin films were successfuly synthesized by the sol–gel method using metal alkoxides. A homogeneous and stable solution was prepared by the reaction of Y(OEt)3, VO(OiPr)3, and Nd(OEt)3 in 2‐methoxyethanol. The precursor was a mixture of vanadium and yttrium double alkoxide. Precursor films were prepared by dip coating and crystallization to single‐phase YVO4 at 500°C. Nd:YVO4 films were crystallized with (200) preferred orientation on glass substrates, which showed the characteristic optical absorption of neodymium.
Short‐Crack Toughness and Abrasive Machining of Silicon Nitride
Authors: Xu Hockin H. K. , Jahanmir Said , Ives Lewis K. , Job Lenox S. , Ritchie Kevin T.
Published: October 2005

Hardness and toughness are often used to analyze the abrasive machining behavior of ceramic materials. However, toughness values of silicon nitride ceramics with microstructures containing elongated grains increase with crack extension. The present study investigates the effect of toughness on the process of abrasive machining to determine which value of toughness should be used in the analysis. The toughness curves (i.e., toughness as a function of crack length) of ten different silicon nitride materials are characterized by an indentation‐strength technique and an indentation technique. The forces in surface grinding are measured as a function of the depth of cut. Examination of ground surfaces by scanning electron microscopy indicates that the material‐removal processes in grinding follows the formation of short cracks (i.e., microcracks) and grain‐scale material dislodgement. An indentation fracture model for material removal in abrasive machining is used to correlate the grinding forces with toughness and hardness of the materials. An agreement is obtained between the experimental results and the indentation model only when the toughness associated with short cracks is used. This study shows the importance of using appropriate toughness values corresponding to the microfracture processes in analyzing abrasive machining results for materials possessing rising toughness curves.
Oxygen Nonstoichiometry and Defects in Mn‐Doped Gd2Ti2O7+x
Authors: Porat Ofer , Tuller Harry L.
Published: October 2005

The oxygen nonstoichiometry in Mn‐doped Gd2Ti2O7, Gd2(Ti0.975Mn0.025)2O7+x, was measured electrochemically, as a function of temperature and oxygen partial pressure, with the aid of an oxygen titration cell. The analysis of the data shows that the defect equilibrium can be described by considering the dominant point defects to be neutral oxygen interstitials, doubly charged oxygen vacancies, and trivalent and quadrivalent Mn ions substituted in the Ti sites. The enthalpies for the formation of neutral oxygen interstitials and trivalent Mn are determined.
Grain‐Size Dependence of Sliding Wear in Tetragonal Zirconia Polycrystals
Authors: He Yingjie , Winnubst Louis , Burggraaf Anthonie J. , Verweij Henk , van der Varst Paul G. Th. , de With Bert
Published: October 2005

Using a pin‐on‐plate tribometer with the reciprocating motion of SiC against yttria‐doped tetragonal zirconia polycrystal (Y‐TZP) plates, the friction and wear of Y‐TZP ceramics were investigated as a function of grain size in dry N2 at room temperature. The results showed that the overall wear resistance increased as the grain size of Y‐TZP ceramics decreased. For grain sizes ≤0.7 μm, the wear results revealed a Hall‐Petch type of relationship (d−1/2) between wear resistance and grain size. In this case, the main wear mechanisms were plastic deformation and microcracking. For grain sizes ≥0.9 μm, the wear resistance was proportional to the reciprocal of the grain diameter. In this regime, delamination and accompanying grain pullout were the main mechanisms. In this case, the phase transformation to monoclinic zirconia had a negative effect on the wear resistance of TZP ceramics. The coefficient of friction tended to be higher for fine‐grained TZP‐SiC couples than for coarse‐grained TZP‐SiC couples, whereas, for a specific regime of grain size, the coefficient of friction was almost independent of the grain size.
Self‐Propagating High‐Temperature Synthesis Flammable Range and Dominant Parameters for Synthesizing Several Ceramics and Intermetallic Compounds under Heat‐Loss Condition
Authors: Makino Atsushi , Law Chung K.
Published: October 2005

Extensive comparisons have been conducted between experimental and theoretical results for the nonadiabatic self‐propagating high‐temperature synthesis combustion characteristics of many solid‐solid systems subjected to volumetric heat loss. The nonadiabatic flame propagation theory‐which describes the premixed mode of bulk flame propagation supported by the nonpremixed reaction of dispersed nonmetal (or higher‐melting‐point metal) particles in the liquid metal, with finite‐rate reaction at the particle surface and temperature‐sensitive Arrhenius‐type condensed‐phase mass diffusivity‐is used to compare with experimental results with heat loss. Systems examined are ceramics (TiC, TiB2, and ZrB2) and intermetallic compounds (NiAl, TiCo, and TiNi). By using a consistent set of physicochemical parameters for these systems, satisfactory quantitative agreement is demonstrated for the flammable range (defined in terms of the mixture ratio, degree of dilution, particle size, and/or compact diameter.
Densification and Thermal Conductivity of AIN Doped with Y2O3, CaO, and Li2O
Authors: Watari Koji , Valecillos Maria Cecilia , Brito Manuel E. , Toriyama Motohiro , Kanzaki Shuzo
Published: October 2005

Small amounts of Li2O result in sintering in the AIN‐Y2O3‐CaO and AIN‐CaO systems at firing temperatures <1600°C. The effect is ascribed to reduction of the liquidus temperature. Furthermore, Li2O is removed by volatization at temperatures from 1300° to 1600°C, and its content decreases several ppm from the initial 0.3 wt%. Li2O‐doped AIN specimens containing Y2O3 and CaO additives are well densified by firing at 1600°C for 6 h, and their thermal conductivity is 135 W.m−1.K−1.The effect of Li2O addition on sintering and thermal conductivity also is discussed through thermo‐dynamic considerations.
X‐ray Photoelectron Spectroscopy Investigation on the Low‐Temperature Degradation of 2 mol% Y2O3‐ZrO2 Ceramics
Authors: Li Jing‐Feng , Watanabe Ryuzo , Zhang Bo‐Ping , Asami Katsuhiko , Hashimoto Koji
Published: October 2005

2 mol% Y2O3‐ZrO2 polycrystals were annealed in water and under vacuum to highlight the effect of the presence of H2O on the low‐temperature degradation transformation. The specimen surfaces with monoclinic phases transformed during annealing in the different environments were analyzed by X‐ray photoelectron spectroscopy with special interest on the electron binding energy change of the constituent ions of the 2 mol% Y2O3‐ZrO2 ceramics after the degradation transformation. It was found that no change occurred for the electron‐bonding energies of core levels of zirconium ions after the transformation, whereas Y‐OH bonds were formed during annealing in water. This result suggested a possibility that the preferred hydration of yttrium took place at the surface of Y2O3‐partially‐stabilized ZrO2, which is likely to be the reason for the low‐temperature degradation accelerated by the presence of H2O.
Microstructure, Electrical Conductivity, and Piezoelectric Properties of Bismuth Titanate
Authors: Shulman Holly S. , Testorf Martin , Damjanovic Dragan , Setter Nava
Published: October 2005

A study was conducted on the effects of microstructure, atmosphere, and several dopants on the electrical conductivity of bismuth titanate (Bi4Ti3O12, BIT). Increased grain size increased the conductivity in undoped BIT as did acceptor dopants that substituted for either Bi (Ca and Sr) or Ti (Fe). A donor dopant (Nb) decreased the conductivity in BIT by as much as 3 orders of magnitude. The increased resistivity of Nb‐doped BIT improved the polarization in an electric field. A piezoelectric coefficient, d33, of 20.0 pC/N was achieved with a Nb‐doped BIT composition corresponding to Bi4Ti2.86 Nb0.14 O12.
R‐Curve Behavior of In‐Situ‐Toughened Al2O3:CaAl12O19 Ceramic Composites
Authors: An Linan , Chan Helen M.
Published: October 2005

The mechanical behavior of reaction‐sintered alumina: 30 vol% calcium hexaluminate (Al2O3:CaAl12O19,or A12O3: CA6) composites was evaluated using the indentation strength in bending technique. A composite in which the hexaluminate (CA6) phase possessed a platelike morphology showed more‐pronounced R‐curve behavior than a composite in which the CA6 phase consisted of equiaxed grains. Toughness curves derived from the indentation‐strength data exhibited a “crossover,” such that the platelet composite exhibited the lower toughness at small flaw sizes, but the higher toughness at large flaw sizes. Incorporation of the platelet CA6 resulted in enhanced toughening, compared to single‐phase alumina of comparable grain size, thus demonstrating the viability of the in‐situ‐toughening approach. A simple grain‐pullout model was used to estimate the toughening increment due to bridging by the platelet grains; the value obtained was in good agreement with toughness curves derived from indentation‐strength measurements. Finally, fabrication of trilayer specimens, whereby outer layers of equiaxed A12O3:CA6 composite were strongly bonded to the platelet A12O3:CA6 composite, demonstrated high strength over the range of tested flaw sizes.
Heat Generation in Multilayer Piezoelectric Actuators
Authors: Zheng Jiehui , Takahashi Sadayuki , Yoshikawa Shoko , Uchino Kenji , de Vries J. W. C.
Published: October 2005

Multilayer piezoelectric actuators when driven under high frequency, generate significant heat, which influences the reliability and other piezoelectric properties. In this paper, heat generation in various types of multilayer PZT‐based actuators was studied. Experimental results showed that heat generation is mainly caused by ferroelectric hysteresis loss in the stress‐free state. A simplified analytic method was established to evaluate the temperature rise, which is useful for the design of multilayer and other high‐power actuators.
Domain Structure‐Second Harmonic Generation Correlation in Potassium Niobate Thin Films Deposited on a Strontium Titanate Substrate
Authors: Gopalan Venkatraman , Raj Rishi
Published: October 2005

The experimental measurement of second harmonic generation (SHG) and theoretical correlation of the SHG output to domain microstructure is presented for ferroelectric KNbO3 (110) thin films on a SrTiO3 (100) substrate. From X‐ray diffraction, four possible domain variants in the film growth plane were determined to be KNbO3 [110]∥SrTiO3 [001], [001], [010], or [010] denoted as variants X+, X−, Y+, and Y−, respectively. From theoretical modeling of the SHG output from the film, the ratios of nonlinear coefficients do/d32 and d24/d0 in the film were determined to be 2.19 ± 0.12 and 0.46 ± 0.26, respectively, in good agreement with the bulk KNbO3 crystals. The term d0 is defined as d15+ (d31+d33)/2. The SHG can also distinguish between X+ and X–, as well as Y+ and Y–, domains, which was not possible by X‐ray diffraction. The ratio of net area fraction (|AX+−AX−|/|AY+−AY−|) was determined to be 2.76 ± 1.06 in the probe area (2.25π mm2) where Ax+, Ax‐, AY+, and AY− are the area fractions of domain variants X+, X−, Y+, and Y−, respectively, in the film growth plane.
Effect of Compositional Variations in the Lead Lanthanum Zirconate Stannate Titanate System on Electrical Properties
Authors: Markowski Kelley , Park Seung‐Eek , Yoshikawa Shoko , Cross L. Eric
Published: October 2005

The purpose of this work was to evaluate the effect of compositional modifications on the electrical properties of lead lanthanum zirconate stannate titanate (PLZST) ceramics, as well as to examine their electrically induced phasechange behavior. Variations in the Ti:Sn ratio were evaluated. Increased Ti4+ content produced the following: decreased switching field, related to an increased antiferro‐electric‐ferroelectric (AFE‐FE) transition temperature; constant hysteresis (ΔE) correlated with a constant temperature of the maximum dielectric constant (Tmax); a sharper dielectric‐constant maximum peak; and increased room‐temperature dielectric constant (K). Variations in the Zr:Sn ratio also were evaluated. Increased Zr4+ content produced the following: increased hysteresis with increased Tmax, decreased maximum dielectric constant, and decreased switching field with increased AFE‐FE transition temperature (TAFE_FE). From these results, with respect to compositional modifications, the AFE‐FE switching field (EAFE_FE) and ΔE were observed to be dependent strongly on TAFE_FE and Tmax, respectively. Negligible change existed in the strain achievable at the switching field, which remained constant for all compositions at ∼0.16%. The significance of this research was the ability demonstrated to tailor the properties of phase‐change materials through compositional modifications.
Formation of Expandable Mica from Talc Using the Intercalation Procedure
Authors: Tateyama Hiroshi , Tsunematu Kinue , Noma Hideaki , Adachi Yasuo , Takeuchi Hideaki , Kohyama Norihiko
Published: October 2005

To investigate the transformation process from talc to expandable micas, mixtures of talc and Na2SiF6 were heated from 600° to 900°C and air‐quenched at 50°C intervals. The air‐quenched product at 800°C mainly consisted of expandable micas with a basal spacing of 1.25 nm, nonexpandable materials with a basal spacing of 0.96 nm, and a small amount of talc used as the starting material. A lattice fringe image by HRTEM of the product shows that the layer spacing at the edges surfaces is about 1.2 nm, but the layer spacing inside of the particles is close to that of talc. Such a nanostructure indicates a topotactic reaction from talc to expandable micas and confirms that Na+ ions intercalate into the structure from the edge to the core.
Effect of Boron Nitride on the Phase Stability and Phase Transformations in Silicon Carbide
Authors: Turan Servet , Knowles Kevin M.
Published: October 2005

High‐resolution transmission electron microscopy has been used to study the effect of hexagonal boron nitride (h‐BN) on the stability of SiC polytypes in Si3N4‐particulatereinforced SiC composites in which h‐BN particles appeared as a trace contaminant. In contrast to previous transmission electron microscopy work on SiC‐BN composites, our results imply that there is no clear preference for a particular SiC polytype to be stabilized by h‐BN nearby. Instead, we propose that previous observations suggesting that the 3C SiC polytype is stabilized by h‐BN can be simply explained in terms of it being stabilized indirectly by nitrogen arising from BN dissociation during processing.
Novel Method for Zirconium Oxide Synthesis from Aqueous Solution
Authors: Yao Takeshi , Inui Takashi , Ariyoshi Akira
Published: October 2005

A novel method for zirconium oxide crystal synthesis from an aqueous solution at ordinary temperature and pressure has been discovered. Boric acid was added to a sodium hexafluorozirconate solution, fluoride ion was consumed by the formation of BF−4 complex ion, then the hexafluorozirconate ion was hydrolyzed to zirconium oxide in order to increase the amount of fluoride ion. The formation of zirconium oxide crystal was confirmed by clear X‐ray diffraction peaks. This method is promising for preparing zirconium oxide films in various applications
Oxidative stress and nitric oxide synthase in skeletal muscles of rats with post‐infarction, compensated chronic heart failure
Authors: Rush J. W. E. , Green H. J. , MacLean D. A. , Code L. M.
Published: October 2005

Aim:  Involvement of oxidative stress and nitric oxide synthase (NOS) isoforms in skeletal muscle cellular adaptations to chronic heart failure (CHF) is controversial, and possible muscle fibre‐type heterogeneity in the oxidative stress and NOS responses to CHF have not been examined. Consequently, we hypothesized that the changes in determinants of elevated oxidative and nitrosylative stress associated with CHF would occur in skeletal muscle and would be similar in predominantly type I slow twitch muscle (soleus) and type II fast twitch muscle (plantaris) of rats.

Methods:  The purpose of this study was to measure NOS isoforms (endothelial, inducible and neuronal NOS) and antioxidant enzymes (SOD‐1, SOD‐2, catalase) by protein immunoblot as well as markers of oxidative stress by biochemical assays in soleus and plantaris muscle sections of the rat hind limb. This was performed for control and post‐infarction, compensated CHF rats.

Results:  Twelve weeks after coronary artery ligation‐induced moderate CHF, soleus exhibited decreased SOD‐1, SOD‐2 and eNOS, but increased iNOS and nNOS isoforms assessed by immunoblot. This was associated with elevated lipid and DNA oxidative damage assessed by biochemical assays. In contrast, plantaris muscle exhibited no changes in antioxidant enzymes or NOS isoforms, and had lower lipid and DNA oxidative damage.

Conclusion:  These observations suggest a heretofore unreported muscle fibre‐type‐specific response of oxidative stress and NOS isoforms to CHF is of importance in understanding the cellular mechanisms of skeletal muscle dysfunction in CHF.
Saline‐induced natriuresis and renal blood flow in conscious dogs: effects of sodium infusion rate and concentration
Authors: Sandgaard N. C. F. , Andersen J. L. , Holstein‐Rathlou N.‐H. , Bie P.
Published: October 2005

Aim:  This study focused on static and dynamic changes in total renal blood flow (RBF) during volume expansion and tested whether a change in RBF characteristics is a necessary effector mechanism in saline‐induced natriuresis.

Methods:  The aortic flow subtraction technique was used to measure RBF continuously. Identical amounts of NaCl (2.4 mmol kg−1) were given as slow isotonic (Iso, 120 min), slow hypertonic (Hyper, 120 min), and rapid isotonic loads (IsoRapid, 30 min).

Results:  During Iso and IsoRapid, arterial blood pressure increased slightly (6–7 mmHg), and during Hyper it remained unchanged. Iso and Hyper increased sodium excretion (4 ± 1 to 57 ± 27 and 10 ± 4 to 79 ± 28 μmol min−1, respectively) and decreased plasma renin activity (by 38% and 29%), angiotensin II (by 56% and 58%) and aldosterone (by 47% and 65%), while RBF remained unchanged. IsoRapid caused a similar increase in sodium excretion (to 72 ± 19 μmol min−1), a similar decrease in renin system activity, but a 15% elevation of RBF (282 ± 22 to 324 ± 35 mL min−1). Selected frequency domain parameters of RBF autoregulation did not change in response to any load.

Conclusions:  In response to slow saline loading simulating daily sodium intake, the rate of sodium excretion may increase 10–20‐fold without any change in mean arterial blood pressure or in RBF. Regulatory responses to changes in total body NaCl levels appears, therefore, to be mediated primarily by neurohumoral mechanisms and may occur independent of changes in arterial pressure or RBF.