bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Condultion and Polarization in Lead Silicate Glasses
Authors: DUTTA BIPRODAS , MAGRUDER ROBERT H. , WEEKS ROBERT A. , KINSER DONALD L.
Published: March 2005

Thermally stimulated polarization and depolarization current (TSPC/TSDC) and dc conductivity measurements on a series of lead silicate glasses were made between −196° and 190°C. The general composition of the glasses was xPbO·(100 −x)SiO2, where x = 30, 40, 45, 50, and 65. The dc conductivity exhibits a monotonic increase with increasing PbO content. For x > 45, the rise in conductivity with increasing PbO content is much less than for x < 45. Two TSDC peaks have been observed in all the glasses. The smaller of the two TSDC peaks, occurring at lower temperatures, increases linearly in size with increasing concentrations of PbO. The high‐temperature TSDC peak does not saturate from −196° to 190°C. Direct current conductivity in these glasses is ionic and due to the motion of Pb2+ ions. The behavior of the low‐temperature TSDC peak is consistent with the hypothesis that it is caused by short‐range motion (orientational polarization) of Pb2+ ions. The origin of the high‐temperature TSDC peak is tentatively attributed to space charge polarization of Pb2+ ions.
Chemical Interactions in High‐Temperature Ceramic Composites
Authors: LUTHRA KRISHAN L.
Published: March 2005

The useful lives of many ceramic composites will be influenced, if not controlled, by chemical interactions. Thermodynamic and kinetic calculations are invaluable in evaluating them. Composites may contain as many as four constituents: a fiber, its coating, a matrix, and an external coating. The chemical concerns fall into three categories: (i) chemical compatibility between the various constituents, (ii) internal stability of the constituents, and (iii) environmental stability of the composite. Examples are given for each of these concerns. Also included are the approaches useful for evaluating them.
Primary and Secondary Phase Separation in CdF2‐LiF‐AlF3‐PbF2 Glasses
Authors: RANDALL MICHAEL S. , SIMMONS JOSEPH H. , EL‐BAYOUMI OSAMA H.
Published: March 2005

Occurrence of primary and secondary phase separation in the CdF2‐LiF‐AlF3‐PbF2 glass system is observed. A primary phase separation, which is characterized by the formation of a small volume fraction of Cd‐rich, Pb‐deficient spheres whose size is on the order of 5μ is found to form upon cooling. A secondary phase separation initiates with precipitation of Pb‐rich microspheres (about 4nm (40 Å) in diameter) in a Cd‐rich matrix. The Pb‐rich spheres develop with heat treatment 35°C above the glass transition temperature. They increase in volume fraction while changing composition and then grow slightly. As the material is further heat‐treated, the Pb‐rich regions crystallize. A pseudobinary model explaining the occurrence of both primary and secondary decomposition phenomena is presented.
Sintering of Monosized, Spherical Yttria Powders
Authors: SORDELET DANIEL J. , AKINC MUFIT
Published: March 2005

Monosized, spherical Y2O3 was processed from raw commercial Y2O3 by homogeneous precipitation in aqueous solution via urea decomposition. Dry‐pressed pellets of the synthesized and raw powders were sintered to 1500°, 1600°, and 1700°C for 7 to 720 min. Microstructural development was followed with scanning electron microscopy. The differences between sintering behavior of the two powders are discussed.
α‐β Sialon Ceramics Made from Different Silicon Nitride Powders
Authors: EKSTRÖM THOMMY , INGELSTRÖM NILS , BRAGE ROBERT , HATCHER MICHAEL , JOHANSSON THOMAS
Published: March 2005

The present work is concerned with the sintering of an α‐β sialon ceramic using five different silicon nitride powders from a single source. The parameters varied in the silicon nitride were the amount of “free’ silicon, iron content, α:β ratio, and grain size as measured by BET surface. The sintering atmosphere was varied by use of protective powder beds with passive (boron nitride) and active (SiO‐generating) properties. Five sintering temperatures between 1600° and 1800°C were used. Microstructural characterization as well as density, hardness, and fracture toughness measurements were carried out. The sintering conditions were found to be critical for obtaining fully dense materials and low weight change. The optimum sintering temperature was 1750°C. The silicon nitride powder with a high content of free silicon resulted in a material which was more susceptible to the sintering atmosphere conditions. An α‐β sialon made from a silicon nitride powder with a high β‐α phase ratio resulted in a higher β‐α ratio in the sintered material.
Novel Process for the Preparation of Fiber‐Reinforced Ceramic‐Matrix Composites
Authors: Haller Wolfgang , Deshmukh Uday V. , Freiman Stephen W.
Published: March 2005

A procedure for the reproducible production of monofilament/powder composites has been developed. The process consists of making a slurry of the powder in a solventless ultraviolet‐curing resin, and coating the fiber with this slurry in a continuous process whereby the coating solidifies immediately after leaving the coater. The fast curing prevents the breakup of coating into globules, which usually occurs with monofilaments. This technique can be applied to any composite using continuous filaments and matrices available in the form of particulate precursors. The application of the technique for preparing a silicon carbide monofilament/glass composite is demonstrated.
Hydration of Tricalcium Silicate Followed by 29Si NMR with Cross‐Polarization
Authors: RODGER SALLY A. , GROVES GEOFFREY W. , CLAYDEN NIGEL J. , DOBSON CHRISTOPHER M.
Published: March 2005

The use of cross‐polarization (CP) NMR in conjunction with magic angle sample spinning (MASS) to examine the hydration reaction of tricalcium silicate (C3S) is described. In particular the very early stages of the reaction both with and without admixtures has been studied as well as the hydration in a ball mill. The combination of CP and non‐CP 29Si NMR permits the distinction between silicate units associated with protons, i.e., in hydrated material, and those in anhydrous material. It has been found that in paste hydration there is steady formation of a small amount of hydrated monomeric silicate units during the induction period. In ball mill hydration the formation of the crystalline calcium silicate hydrate, afwillite, which contains only hydrated monomeric silicate species, can be monitored. These results are interpreted in terms of possible mechanisms for C3S hydration.
Molten‐Salt Corrosion of Silicon Nitride: I, Sodium Carbonate
Authors: FOX DENNIS S. , JACOBSON NATHAN S.
Published: March 2005

Corrosion of Si3N4 under thin films of Na2CO3 was investigated at 1000°C. Pure Si3N4 and Si3N4 with various additives were examined. Thermogravimetric analysis and morphology observations lead to the following detailed reaction mechanism: (I) decomposition of Na2CO3 and formation of Na2SiO3, (II) rapid oxidation, and (III) formation of a protective silica layer below the silicate and a slowing of the reaction. For Si3N4 with Y2O3 additions, preferential attack of the grain‐boundary phase occurred. The corrosion of pure Si and SiC was also studied for comparison to Si3N4. The corrosion mechanism generally applies to all three materials. Silicon reacted substantially faster than Si3N4 and SiC.
Molten‐Salt Corrosion of Silicon Nitride: II, Sodium Sulfate
Authors: JACOBSON NATHAN S. , FOX DENNIS S.
Published: March 2005

The corrosion mechanism of Si3N4+ Na2SO4/O2 at 1000°C was investigated. Corrosion of both pure and additive‐containing Si3N4 was studied. The reaction of Si3N4+ Na2SO4 consists of an initial period of slow weight loss due to Na2SO4 vaporization and oxidation‐dissolution. This initial period was the same for all forms of Si3N4. A second region consisted of further oxidation or near termination of reaction, depending on the additive in the Si3N4. A 5‐ to 10‐μm yttrium depletion zone was found after corrosion for the Si3N4 with yttria additives. For comparison, Si and SiC were corroded under similar conditions. These materials corroded substantially faster than all forms of Si3N4.
Crystallization Behavior of a Glass in the Y2O3‐SiO2‐AlN System
Authors: DINGER TIMOTHY R. , RAI RAGHAW S. , THOMAS GARETH
Published: March 2005

Glass formation for a series of 10 glasses on or near the Y2O3‐SiO2‐AIN plane of the Y‐Si‐Al‐O‐N system was found to be strongly dependent on composition with the best glassforming characteristics occurring in a glass having a normalized composition of Y0.26Si0.30Al0.11ON0.11. Crystallization of this glass was found to proceed by a heterogeneous nucleation mechanism, with intermetallic iron silicides acting as nuclei for the columnar dendritic y‐Y2Si2O7 species. Secondary crystallization of a species having a nominal composition of YSi2AIO4N2 occurred in interdendritic regions when crystallization temperatures approached 1200°C. A third stage of crystallization involved the formation of the high‐temperature polymorph of Y2Si2O7 (δ2‐Y2Si2O7) through transformation of the y‐Y2Si2O7 dendrites to an intermediate product (δ2‐Y2Si2O7) followed by recrystallization to the δ1‐Y2Si2O7 polymorph. Convergent‐beam electron diffraction results for the crystal structure determination of y‐Y2Si2O7 showed it to be based on an end‐centered orthorhombic Bravais lattice having unit‐cell dimensions of a= 0.806 nm, b= 0.934 nm, and c= 0.692 nm with a space group of Aba2. A similar determination for δ2‐Y2Si2O7 showed it to be based on a primitive orthorhombic Bravais lattice having unit‐cell dimensions of a=1.36 nm, b= 0.501 nm, and c= 0.815 nm with a space group of Pna21.
Thermal Diffusivity of Partially and Fully Stabilized (Yttria) Zirconia Single Crystals
Authors: YOUNGBLOOD G. E. , RICE ROY W. , INGEL ROBERT P.
Published: March 2005

Laser flash measurements of thermal diffusivity of ZrO2 single crystals partially and fully stabilized with Y2O3 were compared with measurements for polycrystalline cubic ZrO2, and single crystals and polycrystals of Al2O3 and MgAl2O4. In general, the thermal diffusivities of the ZrO2 materials examined initially decrease with increasing temperature, although significantly less than for the Al2O3 and MgAl2O4 materials. The diffusivity subsequently rises with increasing temperature for the single crystals of ZrO2 but not for polycrystalline cubic ZrO2, with this increase for ZrO2 crystals occurring at much lower temperatures than for Al2O3 and MgAl2O4 crystals. As the ZrO2 materials went from fully stabilized with 20 wt% Y2O3 to partially stabilized with 5 wt% Y2O3, the room‐temperature diffusivity increased from 0.70x10‐6 to 0.97x10‐6 m2/s. This indicated that the lattice defects, which increase with Y2O3 content, are more important sources of phonon scattering than are the precipitates which appear at lower Y2O3 compositions. On the other hand, at 1000°C the diffusivity of the fully cubic ZrO2 crystals with 20 wt% Y2O3 was 1.10x10‐6 m2/s while that of the partially stabilized ZrO2 crystals with 5 wt% Y2O3 was 1.05x10‐6 m2/s. The increased diffusivity at higher temperatures can be attributed to radiative heat transfer, with the lower relative diffusivity of the partially stabilized crystals resulting from photon scattering by the precipitate structures present.
Sintering of TiO2–Al2O3 Composites: A Model Experimental Investigation
Authors: BORDIA RAJENDRA K. , RAJ RISHI
Published: March 2005

In recent theoretical work we have shown that the sintering of a composite is strongly affected by the shear deformation of the continuous phase. This phenomenon was studied experimentally in a model system consisting of a TiO2 matrix dispersed with nondensifying agglomerates of Al2O3. The results of this study are reported here. Several interesting results were obtained: (a) The experimentally obtained sintering rate of the composite could be successfully predicted by measuring the concomitant shear and densification rate of the matrix phase in a sinter‐forging experiment and using the developed analysis; (b) the densification rate of the composite changed with the volume fraction of the dispersed phase, but was unaffected by the size of the dispersed phase; and (c) processing flaws appeared to form only when the size of the dispersed phase was greater than about 10 μm. A technique for measuring the parameter β, which was used to correlate theory and experiments, is described. The procedures used for preparation of powders (from alkoxides) and the green compacts are also described in detail.
Surface Coating Technique for Revealing Grain Structures in Alumina
Authors: Bosomworth Paul A. , Harmer Martin P.
Published: March 2005

An alternative technique, not involving heat treatment, has been found to be useful in studying the microstructures of some commercial polycrystalline alumina envelopes used for sodium‐vapor lamps.
Dielectric Dispersion in Polycrystalline Ferrites: Random Network Model
Authors: Jankowski Stanislaw
Published: March 2005

A new approach to the problem of the dielectric permittivity and losses observed in some NiZn polycrystalline ferrites which strongly differs from the Debye form is presented. Because the ferrite sample is considered as a disordered structure where the well‐conducting grains of various shape and size are separated by boundaries of low conductivity, its electric model is in the form of a large three‐dimensional network composed of either resistors with the probability p or capacitors with the probability I–p. These networks are studied by computer simulation. The resulting equivalent admittance and its standard deviation coincide very well with the experimental results obtained for a series of NiZn ferrites. It is shown that a random network model explains the “universal’dielectric behavior of ferrites at constant temperature (e.g., high dielectric permittivity at the low frequency, dielectric dispersion in the wide frequency range from 0.01 Hz to l MHz, and statistical fluctuations of the tangent of losses) due to their inhomogeneous granular structure. Random network models can be applied also to the large class of inhomogeneous dielectrics whose polarization mechanism may be explained by many‐body interactions.
Stress Superposition in High‐Strength Glass
Authors: Roach David H. , Cooper Alfred R.
Published: March 2005

The introduction of surface compression via alkali‐ion exchange is frequently used to strengthen alkali‐containing glass. However, previous investigators found that when starting with high‐strength glass, the strength measured after exchange was significantly less than the sum of the residual compression and the starting fracture strength. Results are presented which suggest that the source of this discrepancy is surface damage produced during the heat treatment accompanying the ion‐exchange process. Further, when the surface damage was removed by shallow hydrofluoric acid etching, the resulting fracture strength did approximately equal the sum of the residual stress and the high starting strength.
Evaluation of Concurrent Flaw Populations in Silicon Carbide in Terms of a Modified Weibull Distribution Function
Authors: Phani Kalyan K. , De Asok K.
Published: March 2005

Concurrent surface‐ and edge‐flaw populations are often observed in strength testing of ceramics The overall strength distribution in such ceramic samples has been analyzed in terms of a modified Weibull distribution function. The junction provides an upper and lower strength limit and is characterized by two shape and location parameters. To evaluate the parameters of the distribution function, the type of flaw that causes failure need not be identified. The applicability of the function has been evaluated in terms of experimental results on SiC specimens. The analysis also shows that the relative values of shape parameters determine which flaw type dominates.
Formation of a Surface Carbide Layer During Sintering of Titanium Diboride
Authors: Walker J.K. , Saha Chandon K.
Published: March 2005

Titanium diboride, vacuum sintered in a graphite furnace, can develop a thin TiC surface layer. A mechanism for carbide formation is proposed which takes into account the changing p(CO2)/p(CO) ratio as a function of temperature. At low temperature, TiB2 is oxidized by CO2 to give a surface oxide layer. As the temperature is increased, the reduced p(CO2)/p(CO) ratio allows formation of TiC via a reaction between the oxide layer and CO. The proposed mechanism is supported by thermochemical calculation and microstructural analysis.
Effects of a Liquid Phase in the Y‐Ba‐Cu‐O Superconductor
Authors: Hwang N.M. , Park Y.K. , Lee H.K. , Hahn J.H. , Bahng G.W. , Lee K.W. , Moon H.G. , Park J.C.
Published: March 2005

Effects of a liquid phase in the YBaCuO ceramic high‐temperature superconductor were studied with respect to densification, grain growth, and critical current density. In addition to the normal 1:2:3 ratio of Y2O3, BaCO3 and CuO, two other ratios of 0.8:2:3 and 1.1:2:2.8 were adopted to prepare the specimen with and without a liquid phase, respectively. The liquid phase enhanced densification and grain growth but penetrated into the grain boundary of the superconducting grains, decreasing the critical current density.
Twinning and Microcracking Associated with Monoclinic Zirconia in the Eutectic System Zirconia–Mullite
Authors: Dravid Vinayak P. , Notis Michael R. , Lyman Charles E.
Published: March 2005

Crystallography and morphology of twins and microcracks in the eutectic system mullite–zirconia are discussed in view of the tetragonal‐to‐monoclinic transformation and associated toughening mechanisms. Specific twin relationships were observed in monoclinic ZrO2. Highly symmetric and crystallographically well‐defined microcracks were observed at the mullite–ZrO2 interface. Microdiffraction revealed closely related crystallography of monnoclinic twins and microcracks. The number of twin variants depend on the monoclinic ZrO2 particle size. A method to calculate twinning shear strain using microcrack morphology is suggested. This parameter is essential in several fracture‐mechanics calculations.
Grain Boundaries in Fine‐Grained Magnesium‐Doped Aluminas
Authors: LARTIGUE SYLVIE , PRIESTER LOUISETTE
Published: March 2005

The distribution and some characteristics of grain boundaries have been determined in three samples of fine‐grained Mg‐doped alumina which had undergone different thermo‐mechanical treatments: as‐pressed at 1500°C, stress‐free annealed, and deformed at the same temperature. The analyses of some particular features point out the role of the grain‐boundary type “special’ or “general’ on the creep deformation mechanisms.
Field‐Induced Strain in Single‐Crystal BaTiO3
Authors: Pan Wuyi , Zhang Qiming , Bhalla Amar S. , Cross Leslie E.
Published: March 2005

The electric‐field‐induced strain in single‐crystal BaTiO3 was investigated. For crystals relatively free of twinning, a longitudinal strain of 0.35% can be induced just above the ferroelectric‐paraelectric phase transition temperature (Tc1) primarily by field‐forced paraelectric‐ferroelectric phase transition. For heavily twinned crystals, 90° domain reorientation under the applied electric field plays an important role in the induced strain below Tc1, and an induced strain of 0.6% is observed a few degrees below Tc1. Above Tc1, the electrostrictive property measured by a weak excitation field is purely intrinsic. When the excitation field is large, so that a field‐forced paraelectric‐ferroelectric phase transition is involved, the x33/P23 value (where x33 and P3 are the induced strain and polarization along the z axis, respectively) is intrinsic at higher temperature, but may be modified at temperatures just at and slightly above Tc1 by residual 90° twin structure.
Microstructure and Crystal Structure of Bismuth Oxide Phases in Zinc Oxide Varistor Ceramics
Authors: CERVA HANS , RUSSWURM WINFRIED
Published: March 2005

The microstructure and crystal structure of bismuth oxide phases of as‐sintered and additionally heat‐treated ZnO varistor ceramics was examined by means of transmission electron microscopy and X‐ray powder diffraction. Grains of β‐Bi2O3 present in as‐sintered samples were found to consist of two types of domains which have the same basic tetragonal lattice. They can, however, be distinguished by the contrast between local strain centers due to microdefects present in one domain. Some multiple‐grain junctions contained both α‐ and β‐Bi2O3 grains. Heat treatment induces a transformation of the α‐ and β‐Bi2O3 phases into γ‐Bi2O3. A clear crystallographic relationship between the transforming phases β to γ is shown. The β‐Bi2O3 phase was also found to transform into the non‐stoichiometric crystalline Bi2O2.33 phase.
Rutherford Backscattering Spectroscopy Study of the Kinetics of Oxidation of (Mg, Fe)2SiO4
Authors: WU TONG , KOHLSTEDT D. L.
Published: March 2005

Single crystals of oilivine, (Mg0.9Fe0.1)2SiO4, have been oxidized in air at temperatures between 700° and 1100°C for times from 0.5 to 100 h. Both an internal and an external oxidation layer developed. Transmission and analytical electron microscopy observations reveal that the internal oxidation layer is composed of precipitates of magnetite plus amorphous silica, which nucleated heterogeneously on dislocations and grew in an Fedepleted matrix of olivine. Rutherford backscattering spec‐trometry (RBS) demonstrates that the thin external oxidation layer is free of Si; that is, it is made up of Mg‐Fe oxide phases. Thus, the oxidation process is primarily controlled by diffusion of Fe2+ and Mg2+ ions toward the surface with Si4+ and O2‐ remaining largely immobile. The kinetics of oxidation, as determined from RBS analyses of the external oxidation layer, are parabolic with an activation energy of 140 kJ/mol. Although this activation energy is lower than that reported for self‐diffusion of Mg in Mg2SiO4, the diffusivity calculated from the reaction rate constant is in good agreement with published values for lattice diffusion of Mg in the limited temperature range in which data overlap. However, the rate of accumulation of Fe in the external layer is more rapid than expected for lattice diffusion, indicating that the transport of Fe is dominated by short‐circuit diffusion along the precipitate complexes which decorate dislocations.
Study of Nonstoichiometry of 〈U1–zGdzO2±x〉
Authors: LINDEMER TERRENCE B. , SUTTON ALFRED L.
Published: March 2005

The extensive nonstoichiometry in the 〈U1–zGdzO2±x〉† phase was investigated experimentally and the data are represented by a chemical thermodynamic method. The experimental ranges of temperature, oxygen potential, and z were 1273 to 1773 K, 0 to −600 kJ/mol, and 0.1 to 0.8, respectively. For hypostoichiometry, ideal‐solution thermodynamics for the equilibrium 3Gd4/3O2+ 4UO2+ (O2) = 6U2/3Gd2/3O8/3 were used to represent the experimental data, while for hyperstoichiometry a nonideal solution was used for the equilibrium 4UO2+ (O2) = 2U2O5. The wide ranges in x and z led to an improvement of the previous analysis of literature data and led to partial molal Gibbs free energy values that are useful for any thermodynamic calculation involving the phase.
Development and Microstructural Characterization of High‐Thermal‐Conductivity Aluminum Nitride Ceramics
Authors: KUROKAWA YASUHIRO , UTSUMI KAZUAKI , TAKAMIZAWA HIDEO
Published: March 2005

The effect of several additives, such as CaC2, CaO, Y2O3, and C, on thermal conductivity of hot‐pressed AlN ceramics was investigated. The addition of CaC2 reductant was found to be useful for achieving high thermal conductivity of 180 W/(m·K) at room temperature. The characterization of AlN ceramics with CaC2 additive was performed by chemical analysis of Ca, C, and O and microstructural analysis using transmission electron microscopes equipped with an energy‐dispersive X‐ray analyzer and an electron energy loss spectrometer. The major influence on high thermal conductivity is the disappearance of a thermal barrier caused by oxygen impurities at the grain boundary.
X‐ray Determination of Transformation Zone Size in Toughened Zirconia Ceramics
Authors: Mori Yuuji , Kitano Yukishige , Akira Ishitani  , Masaki Takaki
Published: March 2005

A revised method to determine the transformation zone size in ceramics containing tetragonal ZrO2 using X‐ray diffraction technique was described. The zone sizes of tetragonal ZrO2 polycrystals (TZP) and partially stabilized ZrO2 (PSZ) containing 2.0 to 5.0 mol% Y2O3 were found to be larger than those determined by the method previously reported. The maximum zone size of TZP containing 2.0 mol% Y2O3 was estimated to be 6.6 μm, whereas it had been determined to be 2.9 μm by the method previously reported.
Effect of Silicon Dioxide on the Thermal Diffusivity of Aluminum Nitride Ceramics
Authors: Yagi Takeshi , Kazuo Shinozaki  , Ishizawa Nobuo , Mizutani Nobuyasu , Kato Masanori , Tsuge Akihiko
Published: March 2005

The thermal diffusivity of AlN ceramics was significantly decreased by the addition of SiO2. The AlN ceramics with 4 wt% SiO2 could not be densified by pressureless sintering in the temperature range 1400° to 1800°C. The thermal diffusivity of these samples was very low because of their porous structure. The AlN ceramics containing 2, 4, and 8 wt% SiO2 were densified by hot‐pressing and also had low thermal diffusivity. In these samples, the grains of the 27R polytype that resulted from the reaction between AlN and SiO2 were dispersed, obstructing the conduction of heat. The relation between the amount of 27R polytype and the thermal diffusivity of the AlN ceramics was determined.
Ferric Iron Species in Alkali Aluminosilicate Glasses During Fusion
Authors: Knight Diane S. , White Willam B.
Published: March 2005

The luminescence spectra of Fe3+ in alkali aluminosilicate glasses indicate that several species of Fe3+ are present during early stages of melting. When the glass has been heat‐treated for periods of time on the order of 20 h at 1400°C, the luminescence spectra simplify to that of a single species which is interpreted as due to Fe3+ in the glass‐forming framework.
X‐ray Photoelectron Spectroscopy Analysis of Potassium Adsorption onto v‐SiO2: Observation of Reactive Surface Defect Sites
Authors: Caracciolo Robert , Garofalini Stephen H.
Published: March 2005

The adsorption of potassium onto a clean silica surface has been studied by X‐ray photoelectron spectroscopy (XPS). The fracture surface of silica was cleaned by Ar+ sputtering and exposed to potassium metal vapor for 10‐s intervals up to 50 s, resulting in 0.2 to 2 monolayer coverage. High‐resolution XPS spectra were recorded for the K 2p, O 1s, and Si 2p photoelectrons at each potassium exposure. Potassium uptake curves were generated from peak areas which suggest the mechanism of adsorption. Curve synthesis techniques were employed on the O 1s spectra to identify the various chemical states present. A decrease in a reactive state is observed as the number of nonbridging oxygen states increases. Angleresolved XPS was also used to determine the relative position, with respect to depth, of these reactive sites, showing that they are at a higher concentration near the surface.
Phase Relations in the Si3N4‐Rich Portion of the Si3N4–AlN–Al2O3–Y2O3
Authors: Jfukuhara Mlkio
Published: March 2005

The phase relations in the Si3N4‐rich portion of the Si3N4–AlN–Y2O3 rystem were investigated using hot‐pressed bodies. The one‐phase fields of β3 and α, the twophase fields of β+α, β+M (M=melilite), and α+M, and the three‐phase fields of β+α+M were observed in the Si3N4‐rich portion. The α‐ and β‐sialons are not two different compounds but an allotropic transformation phase of the Si–Al–O–N system, and an α solid solution expands and stabilizes with increasing Y2O3 content. Therefore, the formulas of the two sialons should be the same.
Stabilization of Zirconia Sintered with Titanium
Authors: LIN C.L. , GAN D. , SHEN P.
Published: March 2005

Electron and X‐ray diffraction studies show that zirconia sintered with 5 to 15 mol% titanium under a vacuum of 10−1 to 10−2 torr (∼13 to 1.3 Pa) was partially stabilized as cubic and tetragonal phases, whose amounts increase with increasing Ti content. The stabilization of ZrO2 is due to the dissolution of TiO which forms as a second phase in the sintered specimen. The grain size of ZrO2 decreases with increase in Ti. The improvements in strength and thermal shock resistance of ZrO2 sintered with Ti are attributed to the reduction in ZrO2 grain size and the effect of partial stabilization.
Wettability and Work of Adhesion of Nonreactive Liquid Metals on Silica
Authors: SANGIORGI ROBERTO , MUOLO MARIA L. , CHATAIN DOMINIQUE , EUSTATHOPOULOS NICOLAS
Published: March 2005

Wettability of silica by gold, silicon, and lead has been determined by the sessile‐drop method. The contact angle, θ, and the work of adhesion, W, have been found to be 143° and 227 mJ·m−2 for gold at 1353 K, 87° and 869 mJ·m−2 for silicon at 1723 K, and 120° and 203 mJ·m−2 for lead at 1000 K. Thermodynamic adhesion between silica and nonreactive pure metals has been analyzed using models for metal‐oxide bonds. Models based on the assumption that only van der Waals interactions and/or metal‐oxygen chemical bonds exist at the metal‐oxide interface are unsuited for explaining the relative variations in the W values. A valid model can be accomplished by using an empirical equation which takes into account both metal‐oxygen and metal‐oxide chemical bonds. It appears that chemical bonds exist at the interface even for nonreactive metal‐ionocovalent oxide systems.
Preparation and Structure of Lithium‐Ion‐Conducting Mixed‐Anion Glasses in the System LiBO2–LiBS2
Authors: TATSUMISAGO MASAHIRO , YONEDA KAZUYA , MINAMI TSUTOMU
Published: March 2005

Oxysulfide glasses were prepared in a wide range of compositions in the system LiBO2‐LiBS2. Temperatures of glass transition (Tg), crystallization (Tc), and liquidus (Tl) were determined; a maximum of Tg was observed near the composition with 20 mol% LiBS2. The electrical conductivity at 500 K ranges from 5×10−4 to 5×10−3 S·cm−1 with the maxima in conductivity observed near the composition 55LiBO2·45LiBS2. This conductivity enhancement with a mixing of two components, which can be called the mixed‐anion effect, is accompanied by a decrease in the degree of undercooling of glass expressed by the ratio (Tl‐Tg)/Tl. The infrared and Raman spectra showed that the structural units with bridging oxygens B‐O‐B and nonbridging sulfurs B‐S− predominated rather than those with nonbridging oxygens B‐O− and bridging sulfurs B‐S‐B in these glasses.
Mathematical Model for Freeze‐Thaw Durability of Concrete
Authors: BAŽANT ZDENĚK P. , CHERN JENN‐CHUAN , ROSENBERG ARNOLD M. , GAIDIS JAMES M.
Published: March 2005

Although the equations governing the individual basic physical processes involved in freezing and thawing of concrete are known, a mathematical model for this complex phenomenon is unavailable. Its formulation is attempted in the present study. Desorption and absorption isotherms for concrete below 0°C are constructed on the basis of isotherms for concrete above 0°C, using pore size distribution functions. Water movement during freezing or thawing is described as a double diffusion process, involving both macroscopic diffusion through concrete and local diffusion of water into or out of air‐entrained bubbles. Heat conduction is formulated taking into account the latent heat of freezing. Pore pressures are used in a two‐phase material model, which makes it possible to predict the stress in the solid structure of concrete caused simultaneously by freezing and applied loads. This in principle reduces the freeze‐thaw durability problem to the calculation of stresses and strains. However, development of the model to full application would require various new types of tests for calibration of the model, as well as development of a finite element code to solve the governing differential equations. Such a mathematical model could be used to assess the effect of cross‐section size and shape, the effect of cooling rate, the delays due to diffusion of water and of heat, the effect of superimposed stresses due to applied loads, the role of pore size distribution, the role of permeability, and other factors which cannot be evaluated at present in a rational manner.
Application of Roman Spectroscopy for the Study of Phase Transformation in Ti0.65Sn0.35O2
Authors: Cohen R.M. , Drobeck D. , Virkar A.V.
Published: March 2005

Polycrystalline, Al‐doped samples in the TiO2‐SnO2 ceramic system were made and annealed in the two‐phase field above the [001] coherent spinodal. The samples were examined, after various annealing times, using X‐ray diffraction and Raman spectroscopy. It was observed that time constants obtained from X‐ray studies were in good agreement with those obtained from Raman shifts, and both showed similar effects of grain size on the decomposition kinetics. These results suggest that Raman spectroscopy may be a useful technique for the study of phase transformations in ceramics.
Formation of ZnAl2O4 in the Presence of Cl2
Authors: Tsuchida Takeshi
Published: March 2005

The formation of ZnAl2O4 spinel in diffusion couples of Al2O3 and ZnO was investigated between 1000° and 1390°C in air and in air containing 4.8 vol% Cl2 by X‐ray diffraction, electron probe microanalysis, and scanning electron microscopy. The rate of formation of a spinel layer obeyed a parabolic rate law and was accelerated remarkably by the presence of Cl2. The interdiffusion coefficient, D̃, and the activation energy, E, were calculated to be 10−8 to 10−9 cm2/s and 123 kcal/mol (514 kJ/mol) in air and 10−7 cm2/s and 31 kcal/mol (130 kJ/mol) in air containing 4.8 vol% Cl2, respectively.
Spatial Variations in the Sintering Rate of Ordered and Disordered Particle Structures
Authors: Liniger Eric G. , Raj Rishi
Published: March 2005

Local sintering rates were measured in two‐dimensional, ordered and disordered structures constructed from glass spheres. In ordered arrays, made from monosized spheres, the local sintering rates varied from 1/2 to 2 times the average sintering rate. In contrast, disordered arrays, made from bimodal particle sizes, sintered more homogeneously, the local sintering rate deviating less than 15% from the average. The total average densification strain was also greater for the disordered structures. As a result, for the same time and temperature cycle, the disordered structures sintered to near full density while the ordered structures did not. Poor densification in the ordered structure was attributed to packing defects such as domain walls and dislocations. Some evidence was obtained for a correlation between densification and the average coordination number of particles.
Microstrain and Crystallite Size of Natural Microcrystalline Quartz by X‐ray Line Broadening Analysis
Authors: Nagao Hiroyuki , Aikawa Nobuyuki
Published: March 2005

The analysis of X‐ray diffraction line profile broadening reveals the relationship between lattice microstrain and crystallite size for some microcrystalline quartz in natural quartzose rocks which crystallized slowly and statically. The mean microstrain of quartz microcrystallites increases proportionally with the reciprocal of the crystallite size and its magnitude reaches 0.18% (1.8×10−3) for crystallites ∼43 nm in diameter. This large lattice microstrain is ascribed to the internal pressure derived from the surface energy of the quartz microcrystallite.
Thickness Dependence of Fracture Stress in Glass Films Coated on Silicon
Authors: Shimbo Masaru
Published: March 2005

The stress required for spontaneous fracture of glass films on a silicon substrate was found to be proportional to the reciprocal square root of the film thickness. A simple fracture theory, with an assumption of a wedgelike crack shape, explained this relationship well.
Existence of the Ba2Ti5O12 Phase in Ca‐Doped TiO2‐Rich BaTiO3
Authors: Kraševec Viktor , Kolar Drago
Published: March 2005

A TEM investigation was conducted on the structure of a second phase precipitated between the grains of a polycrystalline TiO2‐rich BaTiO3 which was doped with 8 mol% Ca. This phase was identified as Ca‐stabilized Ba2Ti5O12 with a 10‐layer orthorhombic structure and unit‐cell parameters a=0.990, b=1.131, and c=2.330 nm.
Investigation of the Phase Diagram for the Pseudobinary System Li2SO4–La2(SO4)3 and Its Ionic Conductivity
Authors: Zhang Chai , Jing‐Kui Liang , Xian‐ting Xu
Published: March 2005

The phase diagram of the pseudobinary system Li2SO4–La2(SO4)3 has been investigated by means of X‐ray diffraction and differential thermal analysis. LiLa(SO4)2 is formed by a peritectic reaction in this system; the peritectic temperature is 653±3°C. The eutectic reaction of Li2SO4 and LiLa(SO4)2 occurs at 553±3°C; the composition at the eutectic point is 17 mol% La2(SO4)3. LiLa(SO4)2 is monoclinic with a=1.375 nm, b=0.6744 nm, c=0.7068 nm, and β=105.4°. The ionic conductivity of LiLa(SO4)2 has been studied from room temperature to 350°C and is found to be relatively low at room temperature or at lower temperatures. Its activation energy is 0.66 eV. Thus it is not suitable as a fast ion conductor.
Creep Deformation of Ceramics in Four‐Point Bending
Authors: JAKUS KARL , WIEDERHORN SHELDON M.
Published: March 2005

Flexural testing was investigated as a method of studying the creep of ceramic materials at elevated temperatures. Three techniques were used to evaluate the steady‐state stress exponent: two of them were based on the measurement of the surface curvature of a flexure specimen after testing; the third was based on the more conventional technique of measuring displacement rate as a function of applied load and exposure time. Applied to a grade of commercial vitreous‐bonded alumina, the techniques yielded disparate results for the steady‐state stress exponent. This discrepancy in results is believed to be a consequence of the fact that ceramics tend to creep more readily in tension than in compression, leading to a shift in the neutral plane for stress and strain in flexural specimens, which results in extended primary creep. A local enhancement of creep under the loading points of the test specimens was observed in the materials tested; this creep enhancement was attributed to contact stresses at the loading points.
Formation and Properties of 2Tb2O3· Al2O3
Authors: Jero Paul D. , Kriven Waltraud M.
Published: March 2005

The compound 2Tb2O3· Al2O3 was fabricated, and selected properties were investigated. The room‐temperature X‐ray diffraction pattern was indexed and the lattice parameters were calculated. Powder density was determined and used to calculate the number of molecules per unit cell (Z). This allowed calculation of a theoretical density. The material was characterized with regard to thermal expansion and indentation hardness and toughness. It was found to exhibit a rapid and reversible polymorphic transformation at high temperature.
Magnetic Inducement of Texture in Ba2YCu3O6.9 Particle Assemblies under Cryogenic Conditions
Authors: Peterson Simone C. , Cima Michael, J.
Published: March 2005

The properties of Ba2YCu3O6.9 in the superconducting state and anisotropic behavior can be used to texture polycrystalline samples. Application of a relatively small magnetic field while a particle assembly is immersed in liquid nitrogen preferentially orients the particles so that their c axes are perpendicular to the direction of the applied field.
High‐Temperature Optical Absorption Measurement of Single‐Crystal, Yttria‐Stabilized Zirconia
Authors: Park Jong‐Hee , Blumenthal Robert N.
Published: March 2005

High‐temperature optical absorption measurements were performed on single‐crystal yttria‐stabilized zirconia. The optical band gap (Eg) can be represented in the temperature range 15° to 1010°C as Eg(T)=3.40‐5.16x10−4T(K)(eV).
Transition Temperatures for the Tetragonal‐Orthorhombic Phase Transition in the 123 Superconductor
Authors: Wang Hong , Li Dong X. , Thomson William J.
Published: March 2005

Transition temperatures for the reversible orthorhombic‐tetragonal phase transition in the “123′’superconductor have been measured using dynamic X‐ray diffraction. Results are reported for heating/cooling rates up to 180°C/min and in oxygen partial pressures from 3.2 to 21 kPa and are consistent with a rapid second‐order (order‐disorder) transition. In air and at cooling rates ≤12°C/min, the transition is perfectly reversible with no detectable hysteresis. At higher heating or cooling rates and at lower oxygen pressures the transition has a definite hysteresis and a measurable dependence on time.
Strength Distribution in Commercial Silicon Carbide Materials
Authors: Dutta Sunil
Published: March 2005

Four types of commercial silicon carbide samples from different sources were characterized in terms of baseline strength and strength distribution (reliability). Four‐point flexural strength of each material was determined on 30 test bars, 5.1 by 0.64 by 0.32 cm, for a reliable estimate of the Weibull modulus values. The results show that the average strength of these sintered silicon carbide samples ranged from 380 to 482 MPa (55 to 69 ksi) at room temperature and 307 to 470 MPa (45 to 68 ksi) at 1370°C (2500°F). Considerable variations in strength were found among specimens of each material. Baseline Weibull modulus values ranged from 8 to 11 at room temperature and 7 to 11 at 1370°C (2500°F). The strength scatter clearly reflected flaw variability, which must be minimized to improve reliability in sintered silicon carbide materials.
Black Color in Partially Stabilized Zirconia
Authors: Moya J. S. , Moreno R. , Requena J. , Soria J.
Published: March 2005

The exsolution of iron (ppm) from the bulk of yttria‐partially‐stabilized zirconia (Y‐PSZ) polycrystals caused by a change in oxidation of Fe was found to be responsible for the darkening of the PSZ material. The movement of Fe2+ under reducing conditions to the grain boundary has been detected using electron spin resonance techniques.
Thermodynamics of Nitride Formation in Thorium‐Uranium‐Tin Alloys
Authors: SLIVINSKY SANDRA H. , PARLEE NORMAN A.D.
Published: March 2005

The molten ternary system Th‐U‐Sn was investigated, leading to a selective nitriding separation scheme. The analysis of the data led to a determination of the activity coefficients whose values agree with thermodynamic data.
Crack Growth Resistance of Textured Alumina
Authors: Salem Janathan A. , Shannon John L. , Brad Richard C.
Published: March 2005

The crack growth resistance of a textured, extruded alumina body was compared with that of an isotropic, isopressed body of similar grain size, density, and chemistry. R‐curve levels reflected the preferred orientation; however, R‐curve slopes (dKIR/dΔa) were the same in all instances, implying a similar crack growth resistive mechanism. Three orthongonal orientations of crack growth in the two structures exhibited similar forms of KIR versus Δa curves, for which a schematic diagram for polycrystalline ceramics is proposed.
Admittance—Frequency Response in Zinc Oxide Varistor Ceramics
Authors: Alim Mohammad A.
Published: March 2005

The lumped parameter/complex plane analysis technique revealed several contributions to the terminal admittance of the ZnO—Bi2O3 based varistor grain‐boundary ac response. The terminal capacitance has been elucidated via the multiple trapping phenomena, a barrier layer polarization, and a resonance effect in the frequency range 10−2≤f≤ 109 Hz. The characterization of the trapping relaxation behavior near ∼ 105 Hz (∼ 10−6 s) provided a better understanding of a previously reported loss‐peak. The possible nonuniformity in this trapping activity associated with its conductance term observed via the depression angle of a semicircular relaxation in the complex capacitance (C*) plane has been postulated.
Effects of Chemical Inhomogeneities on Grain Growth and Microstructure in Al2O3
Authors: Handwerker Carol A. , Morris Patricia A. , Coble Robert L.
Published: March 2005

Effects of chemical inhomogeneities and single‐crystal seeds on normal and discontinuous grain growth were investigated in both undoped and MgO‐doped Al2O3. The chemical impurities in the samples were exsolved at a lower temperature than the sintering temperature and measured by SEM/EDS to determine the correlation between the distribution of impurities and the microstructure in Al2O3. A feature of this study was the use of clean‐room processing and firing procedures to maintain sample composition at the levels initially present in the starting powders. As the local concentrations of chemical impurities (i.e., Si, Ca) increased, the grain boundary–grain boundary dihedral angle distribution widened, with many angles at 180°, the grain‐size distribution widened, and pore–boundary separation was enhanced. Discontinuous grain growth was observed in regions of undoped Al2O3 containing the largest Ca and Si concentrations. It is suggested that doping with MgO solute reduces the effects of impurities on grain growth by increasing the bulk solubility and decreasing interfacial segregation of impurities, especially Si, and by narrowing the distribution of grain boundary–grain boundary dihedral angles.
Positive Temperature Coefficient of Resistivity Effect in Undoped, Atmospherically Reduced Barium Titanate
Authors: Alles Aldo Bologna , Amarakoon Vasantha R. W. , Burdick Vernon L.
Published: March 2005

A sharp positive temperature coefficient of resistivity effect for undoped, fluorinated BaTiO3−x samples was observed. The qualitative agreement between the behavior of BaTiO3−x and La‐doped BaTiO3, with respect to the trap density at the boundaries, suggests that in the absence of counterdopants such as Mn, the main origin of surface acceptor states is chemisorbed gases. Impedance analysis indicates that, under the conditions of the present work, fluorine seems not to diffuse in significant amounts into the lattice. The treatment of the fluorinated samples in inert/reducing atmospheres did not markedly decrease the resistivity jump, suggesting that fluorine might be chemisorbed more strongly than oxygen. The composition of two different liquid phases, produced by excess titania and silica additions, did not have an important effect on the resulting properties.
Thermodynamic Regularities in Perovskite and K2NiF4 Compounds
Authors: Yokokawa Harumi , Kawada Tatsuya , Dokiya Masayuki
Published: March 2005

It has been found that the enthalpy of formation of perovskite compounds, ΔfH° (ABO3, B = transition metais), from binary oxides can be well characterized in terms the tolerance factor, t≡(rA+ ro)√2 (rB+ ro), where rA and rB are the radii of A‐site ions with 12‐coordination and B‐site ions with 6‐coordination, respectively, and ΔfH°=−168 + 270(1 − t) kJ·mol−1 for AIBVO3, ΔfH°=−125 + 1000(1 − t) kJ·mol−1 for AIIBIVO3, and ΔfH°=− 90 + 720(1 − t) kJ·mol−1 for AIIIBIIIO3. Although the thermodynamic data of K2NiF4 compounds are not extensive, a similar regularity can be found when use is made of the radii of A‐site ions with 9‐coordination for the K2NiF4 compounds. These correlations will be quite useful in predicting.
Thermodynamic and Experimental Study of High‐Purity Aluminum Nitride Formation from Aluminum Chloride by Chemical Vapor Deposition
Authors: Nickel Klaus G. , Riedel Ralf , Petzow Günter
Published: March 2005

Thermodynamic calculations in the systems Al‐Cl, Al‐Cl‐N, and H‐Al‐Cl‐N were used to assess the capabilities of AlCl3 or mixtures of AlCl3 with Al to produce AlN by chemical vapor deposition (CVD) techniques. Direct nitridation (N2 as reaction agent) is possible only at high temperatures (≥1500 K), using AlCl3–Al mixtures. Reaction with NH3 at equilibrium gives low yields but the suppression of NH3 dissociation yields near 100%, which makes the method suitable for powder production, coating, and single‐crystal growth. AlN with less than 1 wt% oxygen was obtained from technical grade AlCl3 by this process. The formation of both amorphous AlN powder and crystalline AlN coatings was observed. It is assumed that the formation of AlCl3·xNH3 adducts by mixing of Al‐Cl vapor and NH3 at temperatures ≤1273 K prevents NH3 dissociation and favors the production of amorphous AlN.