bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the Experimental Climate Prediction Center's fire danger forecasts with remote automated weather station observations
Authors: Reinbold Hauss J. , Roads John O. , Brown Timothy J.
Published: March 2005

The Scripps Experimental Climate Prediction Center has been routinely making regional forecasts of atmospheric elements and fire danger indices since 27 September 1997. This study evaluates these forecasts using selected remote automated weather station observations over the western USA. Bias and anomaly correlations are computed for daily 2-m maximum, minimum, average temperature, 2-m maximum, minimum and average relative humidity, precipitation and afternoon 10-m wind speed, and four National Fire Danger Rating System indices—ignition component, spread component, burning index and energy release component. Of the atmospheric elements, temperature generally correlates well, but relative humidity, precipitation and wind speed are less correlated. Fire danger indices have much lower correlations, but do show useful spatial structure in some areas such as Southern California, Arizona and Nevada.
HLA-restricted epitope identification and detection of functional T cell responses by using MHC–peptide and costimulatory microarrays
Authors: Stone Jennifer D. , Demkowicz Walter E. , Stern Lawrence J.
Published: March 2005

Identification of T cell epitopes is a vital but often slow and difficult step in studying the immune response to infectious agents and autoantigens. We report a spatially addressable technique for screening large numbers of T cell epitopes for both specific antigen recognition and functional activity induced. This system uses microarrays of immobilized, recombinant MHC–peptide complexes, costimulatory molecules, and cytokine-capture antibodies. The array elements act as synthetic antigen-presenting cells and specifically elicit T cell responses, including adhesion, secretion of cytokines, and modulation of surface markers. The method allows facile identification of pertinent T cell epitopes in a large number of candidates and simultaneous determination of the functional outcome of the interaction. Using this method, we have characterized the activation of human CD4+and CD8+T cells responding to vaccinia, influenza, HIV-1, and Epstein–Barr viruses.
Delineation of a unique protein–protein interaction site on the surface of the estrogen receptor
Authors: Kong Eric H. , Heldring Nina , Gustafsson Jan-Åke , Treuter Eckardt , Hubbard Roderick E. , Pike Ashley C. W.
Published: March 2005

Recent studies have identified a series of estrogen receptor (ER)-interacting peptides that recognize sites that are distinct from the classic coregulator recruitment (AF2) region. Here, we report the structural and functional characterization of an ERα-specific peptide that binds to the liganded receptor in an AF2-independent manner. The 2-Å crystal structure of the ER/peptide complex reveals a binding site that is centered on a shallow depression on the β-hairpin face of the ligand-binding domain. The peptide binds in an unusual extended conformation and makes multiple contacts with the ligand-binding domain. The location and architecture of the binding site provides an insight into the peptide's ER subtype specificity and ligand interaction preferences.
In vivo
, an engineered coactivator containing the peptide motif is able to strongly enhance the transcriptional activity of liganded ERα, particularly in the presence of 4-hydroxytamoxifen. Furthermore, disruption of this binding surface alters ER's response to the coregulator TIF2. Together, these results indicate that this previously unknown interaction site represents a bona fide control surface involved in regulating receptor activity.
Cultural Policy and Urban Regeneration in Western European Cities: Lessons from Experience, Prospects for the Future
Authors: García Beatriz
Published: March 2005

This paper reviews the uses of cultural policy and planning as tools of urban regeneration in western European cities. Following a brief assessment of the evolution of European cultural policy in recent decades, the paper studies the origins and development of the European City/Capital of Culture programme and explores the experience of cities considered to have succeeded in re-imaging and regenerating themselves through cultural activity and special events. The paper ends with a reflection on the notion of cultural planning and its potential as an integrated alternative to urban cultural policy, and offers recommendations for further development within the UK context.
Cultural Policy as Urban Transformation? Critical Reflections on Glasgow, European City of Culture 1990
Authors: Mooney Gerry
Published: March 2005

This paper revisits Glasgow, European City of Culture 1990, and considers the main criticisms made of Glasgow's cultural policy as urban renewal strategy. It argues that while many of the criticisms made by opposition groups such as Workers' City were valid, and largely supported by the economic and social problems that have faced the City since 1990, nonetheless it also suggests that this critical response itself needs to be subjected to more thorough scrutiny. The paper claims that flagship cultural events can do little but gloss over and divert attention away from the major structural problems which characterise many ex-industrial cities and concludes by arguing that the lessons of Glasgow's experience are also very relevant for other cities such as Liverpool that are also increasingly embracing cultural policy as a route to urban transformation.
Raf-1 regulates Rho signaling and cell migration
Authors: Ehrenreiter Karin , Piazzolla Daniela , Velamoor Vanishree , Sobczak Izabela , Small J. Victor , Takeda Junji , Leung Thomas , Baccarini Manuela
Published: March 2005

Raf kinases relay signals inducing proliferation, differentiation, and survival. The Raf-1 isoform has been extensively studied as the upstream kinase linking Ras activation to the MEK/ERK module. Recently, however, genetic experiments have shown that Raf-1 plays an essential role in counteracting apoptosis, and that it does so independently of its ability to activate MEK. By conditional gene ablation, we now show that Raf-1 is required for normal wound healing in vivo and for the migration of keratinocytes and fibroblasts in vitro. Raf-1–deficient cells show a symmetric, contracted appearance, characterized by cortical actin bundles and by a disordered vimentin cytoskeleton. These defects are due to the hyperactivity and incorrect localization of the Rho-effector Rok-α to the plasma membrane. Raf-1 physically associates with Rok-α in wild-type (WT) cells, and reintroduction of either WT or kinase-dead Raf-1 in knockout fibroblasts rescues their defects in shape and migration. Thus, Raf-1 plays an essential, kinase-independent function as a spatial regulator of Rho downstream signaling during migration.
Far Infrared Reflection Spectra of Ba(Zn,Ta)O3‐BaZrO3 Dielectric Resonator Material
Authors: WAKINO KIKUO , MURATA MICHIHIRO , TAMURA HIROSKI
Published: March 2005

The dielectric ceramic materiala Ba(Zn1/3Ta2/3)O3–BaZrO3 has extremely low dielectric loss at microwave frequencies. To investigate the lattice vibrations of Ba(Zn,Ta)O3 and Ba(Zr, Zn, Ta)O3 solid solutions, far infrared reflection spectra were measured from 50 to 4000 cm−1 using a Fourier transform infrared spectrometer. These data were analyzed according to the classical dispersion theory. The spectra of Ba(Zn,Ta)O3 are well fitted by using the 14 resonant modes, and the spectra of Ba(Zr, Zn, Ta)O3 solid solution are fitted by assuming the normal distribution on resonant frequencies. The damping constant of these materials is discussed, and the values of tan δ calculated from the dispersion parameters agree with the measured values.
Effect of Shear Stress on Sintering
Authors: RAHAMAN M.N. , DE JONGHE L.C. , BROOK R.J.
Published: March 2005

The effect of small uniaxial stresses on the sintering of CdO powder compacts was studied using a loading dilatometer. Compacts of two different green densities were sintered at 1123 K and subjected to stresses between 0 and 0.25 MPa. Densification and creep occur simultaneously, and the effects of these two processes can be separated. Between relative densities of 0.5 and 0.9, the dependence of the uniaxial creep rate on density can be described in terms of a stress intensification factor which depends exponentially on the porosity but is independent of the grain size. Comparison of the densification and creep rates permits definition of the sintering stress, which is found to decrease with increasing density, and verification of the Zener relation. The stress and grain size dependence of the creep rate, and the grain size dependence of the densification rate, support grain‐boundary diffusion as the rate‐controlling step in both processes.
Stability of ZrO2 Phases in Ultrafine ZrO2‐Al2O3 Mixtures
Authors: MURASE YOSHIO , KATO ETSURO , DAIMON KEIJI
Published: March 2005

Mixtures of ultrafine monoclinic zirconia and aluminum hydroxide were prepared by adding NH4OH to hydrolyzed zirconia sols containing varied amounts of aluminum sulfate. The mixtures were heat‐treated at 500° to 1300°C. The relative stability of monoclinic and tetragonal ZrO2 in these ultrafine particles was studied by X‐ray diffractometry. Growth of ZrO2 crystallites at elevated temperatures was strongly inhibited by Al2O3 derived from aluminum hydroxide. The monoclinic‐to‐tetragonal phase transformation temperature was lowered to ∼500°C in the mixture containing 10 vol% Al2O3, and the tetragonal phase was retained on cooling to room temperature. This behavior may be explained on the basis of Garvie's hypothesis that the surface free energy of tetragonal ZrO2 is lower than that of the monoclinic form. With increasing A12O3 content, however, the transformation temperature gradually increased, although the growth of ZrO2 particles was inhibited; this was found to be affected by water vapor formed from aluminum hydroxide on heating. The presence of atmospheric water vapor elevates the transformation temperature for ultrafine ZrO2. The reverse tetragonal‐to‐monoclinic transformation is promoted by water vapor at lower temperatures. Accordingly, it was concluded that the monoclinic phase in fine ZrO2 particles was stabilized by the presence of water vapor, which probably decreases the surface energy.
Structure and Grain Coarsening During the Sintering of Alumina
Authors: SHAW N.J. , BROOK R.J.
Published: March 2005

The pore surface area (Sp) and grain‐boundary area (Sgb) were measured during the sintering of undoped and doped (100 ppm MgO) alumina compacts. Since the presence of the additive affects only Sgb (raising it at a given value of the density), pinning of the boundaries by solid‐solution drag is the only additive function evidenced by the results. The importance of such pinning even at densities as low as 75% of theoretical is linked to the existence of microstructural inhomogeneities.
Viscosity and Thermal Expansion of Sodium and Potassium Galliosilicate Glasses
Authors: LAPP JOSEF C. , SHELBY JAMES E.
Published: March 2005

The transformation‐range viscosity and thermal expansion behavior of several series of sodium and potassium galliosilicate glasses were studied. The trends observed in the results are similar to those found for alkali aluminosilicate glasses. This result suggests a similarity in the structural roles of aluminum and gallium ions. The present data are discussed in terms of this structural role. In addition, the influence of silica content, alkali content, and alkali identity on the thermal properties of these glasses is discussed.
Synthesis of Silicon Nitride by a Combustion Reaction under High Nitrogen Pressure
Authors: Hlrao Klyoshi , Miyamoto Yoshinari , Koizumi Mltsue
Published: March 2005

Fine Si3N4 powders were prepared by the combustion reaction of an Si powder compact undez 10 MPa nitrogen pressure. Addition of Si3N4 powder to the starting Si promoted conversion of the reactants to homogeneous Si3N4 particles. Submicrometer SisN4powders with a uniform size distribution around 0.5 μm were obtained from a 1.8Si‐0.4Si3N4 mixture (molar ratio); they were free of residual Si.
Precipitation During Controlled Cooling of Magnesia‐Partially‐Stabilized Zirconia
Authors: HUGHAN ROBERT R. , HANNINK RICHARD H.J.
Published: March 2005

A study has been made of the precipitation and growth processes which occur during cooling from solution treatment and under isothermal hold conditions in a magnesia‐partially‐stabilized zirconia alloy. Three types of precipitate have been identified which develop during cooling or during isothermal hold treatments just above and below the eutectoid temperature. These precipitate forms are termed (i) primary, (ii) large random, and (iii) secondary. Further precipitation, slow growth of existing precipitates, and subeutectoid decomposition result when an additional 1100°C aging treatment is given to the previously cooled material. It is shown that type (iii) secondary precipitates form rapidly within the temperature range of 1300° to 1375°C. The secondary precipitates are largely responsible for the improved room‐temperature strength properties of the heat‐treated samples. The formation and effects on mechanical properties of each type of precipitate are discussed.
Scanning Electron Microscopy and Transmission Electron Microscopy Study of Ferroelectric Domains in Doped BaTiO3
Authors: HU YUNG H. , CHAN HELEN M. , WEN ZHANG XIAO , HARMER MARTIN P.
Published: March 2005

This paper describes the results of detailed studies carried out on Ca‐doped and Nb‐doped BaTiO3 using scanning electron microscopy and transmission electron microscopy. The techniques used were topographical contrast, selected‐area diffraction, and microdiffraction Kikuchi pattern analysis. By these methods it was possible to unambiguously identify the different types of domain boundaries. Also, evidence was obtained for the existence of an unconventional 90% domain boundary which has not previously been reported.
Solid‐State Reactions between CaO Powder and Fe2O3
Authors: BERGMAN BILL
Published: March 2005

Diffusion couples are used to study the reaction between CaO powder and Fe2O3 All heat treatments were performed in air. The growth and morphology of calcium ferrites is studied at different temperatures. It is shown that CaO·2Fe2O3, starts to form at about 1125°C, while the accepted phase diagram for equilibrium with air predicts a temperature of 1155°C.
Stress Corrosion of Ionic and Mixed Ionic/Covalent Solids
Authors: MICHALSKE TERRY A. , BUNKER BRUCE C. , FREIMAN S. W.
Published: March 2005

Slow crack growth data, surface reaction studies, and solubility results for sapphire and magnesium fluoride crystals are used to identify stress corrosion mechanisms for each material. Results suggest that stress corrosion in sapphire proceeds by the dissociative chemisorption of environmental species on strained crack tip bonds. Crack growth rates measured in nonaqueous environments and isotopically labeled water suggest that ion solvation rather than dissociative chemisorption dominates the crack tip interaction in magnesium fluoride.
Strength‐Toughness Relations in Sintered and Isostatically Hot‐Pressed ZrO2‐Toughened Al2O3
Authors: HORI SABURO , YOSHIMURA MASAHIRO , SŌMIYA SHIGEYUKI
Published: March 2005

The fracture toughness of fine‐grained undoped ZrO2‐toughened Al2O3 (ZTA) was essentially unchanged by postsintering hot isostatic pressing and increased monotonically with ZrO2 additions up to 25 wt%. The strength of ZTA with 5 to 15 wt% tetragonal ZrO2, which depended monotonically on the amount of ZrO2 present before hot isostatic pressing, was increased by pressing but became almost constant between 5 and 15 wt% ZrO2 addition. The strength appeared to be controlled by pores before pressing and by surface flaws after pressing; the size of flaws after pressing increased with ZrO2 content. The strength of ZTA containing mostly monoclinic ZrO2 (20 to 25 wt%) remained almost constant despite the noticeable density increase upon hot isostatic pressing because the strength was controlled by preexisting microcracks whose extent did not change on postsintering pressing. These strength‐toughness relations in sintered and isostatically hot‐pressed ZTA are explained on the basis of R‐curve behavior. The importance of the contribution of microcracks to the toughness of ZTA is emphasized.
Surface Characterization of Ultrafine ZrO2‐SiO2 Powders by Electrophoretic Mobility Measurements
Authors: Kagawa Masahiro , Syono Yasuhiko , Imamura Yoko , Usui Shinnosuke
Published: March 2005

Electrophoretic mobilities of ultrafine ZrO2‐SiO2 powders prepared by a modified spray pyrolysis technique with an ultra‐high‐temperature plasma were measured to characterize their surfaces. The surfaces of as‐prepared ZrO2 particles are apparently composed of zirconium hydroxides, which when heated result in a surface which is hydrophobic or slow to hydrate. The surfaces of as‐prepared and heated ZrO2‐SiO2 particles appeared to consist predominantly of SiO2.
Proposed Structure for Calcium Silicate Hydrate Gel
Authors: TAYLOR HARRY F.W.
Published: March 2005

Calcium silicate hydrate gel is a very poorly crystalline material that is the main product of reaction of portland cement with water. Evidence is presented for a disordered layer structure, in which most of the layers are structurally imperfect ones of jennite (Ca9Si6O32H22), and others are similarly related to 1.4‐nm tobermorite (Ca5Si6O26H18), both structures being modified by omission of many of their silicate tetrahedra. The evidence comprises conditions of formation, silicate anion type, Ca/Si ratio, H2O/Ca ratios and densities for various drying conditions, thermogravimetric curve, X‐ray powder and selected‐area electron diffraction patterns, and results of analytical electron microfcopy.
Strengths of Glass Spheres in Compression
Authors: KSCHINKA B.A. , PERRELLA S. , NGUYEN H. , BRADT R.C.
Published: March 2005

The strengths of individual glass spheres of a commercial soda‐lime‐silica composition were measured in diametral compression for an extensive range of sizes. Standard plots for a two‐parameter Weibull distribution yielded m values of ∼5 over a 400‐fold range of volumes corresponding to a 50‐fold range of surface areas. Various techniques related to the Weibull formulation, including normalization to a single specimen size, were applied to demonstrate the existence of a single flaw population in all of the sphere sizes. Dependence of the strengths on volume flaws for the diametral compression mode of testing was also confirmed.
Direct Observation of Cycled Phase Transformations in Zirconia
Authors: Hannink Richard H. J. , Porter John R. , Marshall David B.
Published: March 2005

Martensitic transformations of zirconia precipitates in magnesia‐partially‐stabilized zirconia (Mg‐PSZ) have been observed directly in a transmission electron microscope. By controlling the electron beam to produce heating and cooling cycles, the precipitates could be repeatedly transformed between monoclinic and tetragonal. Preliminary observations of the resultant precipitate microstructures are presented.
Defect Structure and Dielectric Properties of Nd2O3‐Modified BaTiO3
Authors: SHAIKH AZIZ S. , VEST ROBERT W.
Published: March 2005

The defect structure and dielectric properties of BaTiO3 with 1 to 10 mol% Nd2O3 additions were studied. The results indicated that neodymium occupies the barium site and charge compensation takes place by creation of titanium vacancies. The dependence of inverse electric susceptibility, spontaneous polarization, and specific heat on temperature for samples containing more than 2 mol% of Nd2O3 were characteristic of a diffuse transformation resulting from a disordering of defects. The addition of Nd2O3 leads to a very drastic sfiift in the Curie temperature (Tc) of BaTiO3; 3 mel% Nd2O3 addition moves Tc below room temperature.
Conventionally Sintered (Na0.5,K0.5)NbO3 with Barium Additions
Authors: Ahn Zou Sam , Schulze Walter A.
Published: March 2005

The effect of Ba additions on sodium potassium niobate (NKN) ceramic bodies was investigated with regard to sintering behavior, densification, and electrical properties. Small additions of Ba retard grain growth and increase density. The approximate solubility limit of Ba is 1.5 mol%. During firing the loss of Na and K was very low. Both electrical phase transitions in NKN are lowered with Ba additions. The Ba‐containing bodies show higher permittivity values than hot‐pressed materials, while radial coupling and d33 were similar to or higher than those of the conventionally sintered pure materials.
Combined Mode I‐Mode III Fracture of Fatigue‐Precracked Alumina
Authors: SURESH SUBRA , TSCHEGG ELMAR K.
Published: March 2005

The mixed‐mode fracture behavior of (cyclic) fatigue pre‐cracked ceramic specimens was studied in combined tension‐torsion loading. Circumferentially notched cylindrical rods of polycrystalline alumina were precracked in uniaxiai cyclic compression to introduce a concentric mode I fatigue crack. Subsequently, the rods were quasi‐statically fractured in pure tension, pure torsion, and various combinations of tensile and torsional stresses to obtain the mode I‐mode III fracture envelope. The introduction of torsional loads promotes severe abrasion between the crack faces. The critical stress intensity factor for fracture initiation increases by a factor of °2.3 as the loading mode is changed from pure tension to pure torsion. Fracture surface tortuosity and abrasion “shield” the crack‐tip from the far‐field tensile and torsional loads to cause an apparent toughening effect. The mechanisms of mixed‐mode fracture in alumina are examined and consequences of the breakdown of the similitude concept implicit in the nominal use of fracture mechanics are discussed.
Effect of Sintering Atmosphere on Isolated Pores During the Liquid‐Phase Sintering of MgO‐CaMgSiO4
Authors: KIM JEONG‐JOO , KIM BYUNG‐KI , SONG BYUNG‐MOO , KIM DOH‐YEON , YOON DUK N.
Published: March 2005

The shrinkage behavior of isolated pores during the liquidphase sintering of MgO‐CaMgSiO4 at 1650°C in O2 and N2 atmospheres has been studied. When 90MgO‐ 10Ca MgSiO4 specimens containing artificially produced large spherical pores are sintered in O2, the liquid and grains flow into the pores as oxygen diffuses out. When sintered in N2 the pores remain intact even after a long time, because the N2 gas entrapped in them does not diffuse out. The effect of the sintering atmosphere has also been studied in a fine powder mixture of 80MgO 20CaMgSiO4 composition. Changing the atmosphere from O2 to N2 during the sintering treatment reduces the porosity, probably because of the enhanced oxygen diffusion from the pores. The pores grow when the sintering atmosphere is changed from N2 to O2, probably because of oxygen diffusion into the pores from the specimen surface. The practical implication of these results is that changing the atmosphere from O2 to air during the liquid‐phase sintering of oxide ceramics can greatly reduce the porosity.
Thermal Conductivity/Diffusivity of Silicon Carbide Whisker Reinforced Mullite
Authors: Russell Laura M. , Johnson Lloyd F. , Hasselman D. P. H. , Ruh Robert
Published: March 2005

The thermal conductivity and diffusivity of silicon carbide whisker reinforced mullite was shown to increase with whisker content. This effect was much greater for vapor‐liquid‐solid (VLS) whiskers than for rice‐hull (RH) whiskers. This suggests that the thermal conductivity for the VLS whiskers was significantly higher than for the RH whiskers. Due to preferred orientation of the whiskers, thermal conductivity and diffusivity of the composite samples exhibited significant anisotropy.
Sintering of Ultra‐High‐Purity Alumina Doped Simultaneously with MgO and FeO
Authors: ZHAO JUNHONG , HARMER MARTIN P.
Published: March 2005

The use of ultra‐high‐purity powder processing and multiple solid‐solution additive doping has been evaluated as an effective approach for the fabrication of alumina ceramics. MgO was found to inhibit grain growth more strongly in very pure powders because of its stronger solute drag effect. The degree of inhibition was severe enough to render grain growth insensitive to porosity. By diminishing the dragging influence of pores on grain‐boundary motion, MgO guards against abnormal grain growth due to inhomogeneous densification. FeO acted singly in alumina to promote grain growth more than densification. FeO was not, therefore, an effective sintering additive for undoped alumina. FeO did, however, Ceramic benefit the sintering of MgO‐doped alumina.
Dielectric and Ferroelectric Properties of Ceramics in the Pb(Zn 1/3Nb2/3)O3‐BaTiO3‐PbTiO3 System
Authors: HALLIYAL A. , KUMAR U. , NEWNHAM R. E. , CROSS L. E.
Published: March 2005

The use of Pb(Zn1/3Nb2/3)O3 ceramics is restricted by the formation of a pyrochlore phase detrimental to both dielectric and piezoelectric properties. Recently it has been shown that a 6 mol% addition of BaTiO3 to PZN suppresses the formation of pyrochlore phase. Phase relations and dielectric properties of ceramics in the PZN‐BT‐PT system are reported here. Compositions with the perovskite structure, having high dielectric constant and low temperature coefficient of capacitance, have been identified.
Cavity Development During Creep Deformation in Alumina with a Bimodal Grain Size Distribution
Authors: CHOKSHI ATUL H. , PORTER JOHN R.
Published: March 2005

An alumina sample, codoped with equimolar proportions of magnesia and zirconia, exhibited a bimodal grain size distribution after hot‐pressing. Flexural creep experiments were performed on this material at temperatures of 1673 and 1773 K in air. Inspection of the deformed specimens revealed extensive creep cavitation, with cavities developing preferentially in the coarse‐grained regions. The nucleation, growth, and interlinkage of the cavities led to the formation of cracks. Crack growth occurred in the coarse‐grained regions by the linkage of cavities with the crack tip. However, several cracks were observed to terminate after extending up to a fine‐grained region of a specimen. A model has been developed to rationalize the observation that preferential cavitation occurs in the coarse‐grained regions of a specimen undergoing creep deformation.
Spinodal Decomposition in Tetragonal Systems: SnO2‐Tio2
Authors: FLEVARIS NIKOS K.
Published: March 2005

Expressions are given for the coherency‐strain elastic free energy of systems with tetragonal symmetry in the framework of the continuum theory. This theory is applied for SnO2‐TiO2 and the results are compared with known experimental observations. Calculations for other tetragonal systems are also presented. Finally, the results of these calculations for systems of tetragonal symmetry are discussed in the light of the Cahn and Hilliard theory of spinodal decomposition.
Oxygen Partial Pressure and Grain Growth in Donor‐Doped BaTiO3
Authors: DROFENIK MIHA
Published: March 2005

The grain growth of donor‐doped BaTiO3 at different oxygen partial pressures was studied. Results showed that the oxygen pressure had a pronounced influence on the grain growth and related effects. A model for the grain size anomaly during sintering of donor‐doped BaTiO3 in the presence of a TiO2‐rich liquid phase is proposed.
Quantitative Analysis of Polymorphic Mixes of Zirconia by X‐ray Diffraction
Authors: SCHMID H. K.
Published: March 2005

Nonlinear calibration curves of weight fraction vs integrated intensity ratio arc obtained for polymorphic mixtures of ZrO2 by means of powder X‐ray diffraction. The (C + M) and (T + M) ZrO2 systems are analyzed using the {111} reflections. Intensity ratios in mixtures prepared with an ultrafine m‐ZrO2 powder agree well with theoretical values. The observed nonlinearity of the intensity‐concentration curve is explicable from the differences in reflecting power of corresponding reflections in the three polymorphs. Considerable deviations from theoretical intensity ratios are observed in mixtures prepared with coarser commercially available m‐ZrO2 powders. This effect is attributed to an anomalously high absorption behavior of those monoclinic materials and can be suppressed by quenching in liquid nitrogen, which is believed to cause the particles to shatter. The (C + T) ZrO2 system is analyzed using the {200} reflections rather than the more usual high‐angle reflections and the derived nonlinear calibration curve agrees well with theoretical prediction. In the ternary system (C + T + M) ZrO2 the presence of tetragonal phase can be confirmed by microphotometric tracing of the {111} and {200} reflection profiles on Guinier photographs, but in this case a quantitative analysis would be difficult.
High‐Temperature Mechanical Properties of a Ceramic Matrix Composite
Authors: LUH ELLICE Y. , EVANS ANTHONY G.
Published: March 2005

The change in mechanical properties of a fiber‐reinforced ceramic from notch insensitivity at room temperature to notch sensitivity at elevated temperature has been investigated. The change in behavior has been attributed primarily to a correspondingly large variation in the shear resistance of the fiber/matrix interface caused by oxidation effects at that interface. The transition in behavior has been correlated with a fracture model based on the incidence of fiber failure in the crack wake.
Effect of Polyaxial Stress States on Fracture Strength of Soda‐Lime Glass
Authors: IKEDA KIYOHIKO , IGAKI HISASHI
Published: March 2005

Triaxial stress tests of soda‐lime glass were carried out by four‐point bending of plates under hydrostatic pressure and by concentric‐ring loading of disks under hydrostatic pressure. The triaxial data for fracture stresses plotted in principal stress space were compared with the theoretical fracture predictions. The Weibull statistical theory could not provide a good description on the data, but underestimated the effect of hydrostatic stress on the increase of the fracture strength. The deviation of the experimental data from the Weibull statistical prediction could be explained by assuming that subcritical crack growth enhanced at the same surface flaws in the specimen tested at atmospheric pressure was restricted under hydrostatic pressure.
Eletrical Conductivity of Antimony‐Doped Tin Dioxide Prepared by Hot Isostatic Pressing
Authors: Uematsu Keizo , Kato Zenzi , Uchida Nozomu , Saito Katukazu
Published: March 2005

High‐purity and high‐density tin dioxide doped with 1 × 1020/cm3 antimony was prepared by hot isostatic pressing, and its electrical conductivity was measured over the temperature range 20° to 1200°C in various atmospheres. The conductivity decreased with increasing temperature and reached the value found in specimens normally sintered under the same conditions at normal pressure. The effect of microstructure on the carrier transport is discussed. Grain boundaries only slightly affect carrier transport at high temperatures.
Effect of Flux Materials on the Reaction of Y2O3and SiO2
Authors: Leskelä Markku , Jyrkäs Kauko
Published: March 2005

The solid‐state reaction between yttrium oxide and amorphous silicon oxide with a molar ratio 1:1 has been studied. The effect of several flux materials on conversion at different temperatures (900° to 1300°C) has been investigated. Lithium compounds and especially fluoride gave the highest conversions. Fluorides of cations other than lithium were also powerful fluxes. The purity of the oxyorthosilicate formed was studied by different methods.
Oxygen Potential in the System UMoO6/UMoO5 by the Solid Oxide Electrolyte Emf Method
Authors: Swaminathan K. , Mallika C. , Sreedharan O. M.
Published: March 2005

The emf of the galvanic cell Pt|UMoO6UMoO5|ZrO2‐Y2O3|O2(air, Po2=0.21 atm)|Pt, measured from 776 to 1127 K, was determined to be E = 751.7−0.4909 ±4.3 mV. Using the standard Gibbs energy of formation, fΔG°, for UMoO6 reported in the literature from transpiration studies, the fΔG° for UMoO5 is calculated to be fΔG°〈UMoO5〉=−1816.9+0.3748T±6.0 U‐mol−1 The magnitudes of the standard entropies of formation, fΔS°, for UMoO6 and UMoO5 were evaluated from those values reported for the binary oxides which constitute the ternary compounds.
Measurement of Interfacial Mechanical Properties in Fiber‐Reinforced Ceramic Composites
Authors: MARSHALL DAVID B. , OLIVER W. C.
Published: March 2005

Properties of the fiber/matrix interface in a SiC/glass‐ceramic composite were investigated using an indentation method in Which a pyramidal indenter is used to push on the fibers and cause sliding at the interface. An ultralow‐load indentation instrument was used to measure force and displacement continuously during loading, unloading, and load cycling. Frictional sliding and combined debonding/frictional sliding at the interface were analyzed. The analyses enabled the results to be used to provide a measure of the debond fracture energy, the magnitude of the frictional sliding stress, a measure of the uniformity of the frictional stress, and an indication of the sensitivity of the frictional stress to repeated sliding, varying load rate, and exposure to high temperatures.
Mechanism of Oxide Nucleation in Lithium Aluminosilicate Glass‐Ceramics
Authors: Maier Veronika , Müller Gerd
Published: March 2005

A commercial lithium aluminosilicate glass‐ceramic material is investigated by high‐resolution transmission electron microscopy after different heat treatments. Evidence is presented that epitaxy of β‐quartz crystals on ZrTiO4‐type crystallites is the critical step initiating silicate crystallization.
Grain‐Boundary Microcracking Due to Thermal Expansion Anisotropy in Aluminum Titanate Ceramics
Authors: Ohya Yutaka , Nakagawa Zenbe‐e , Hamano Kenya
Published: March 2005

The relation between grain size and grain‐boundary microcracking during cooling in aluminum titanate ceramics was studied. Microcracking temperature was determined by the measurement of thermal contraction and expansion, which was accompanied by acoustic emission. When the ceramics were cooled at a rate of 6°C/min, stress relaxation did not occur below the sintering temperature of 1500°C. The relation between the temperature difference from the sintering temperature to the microcracking temperature and the grain size showed good agreement with the prediction based on the energy criterion of grain‐boundary microcracking.
Molecular Dynamics Simulation of the Structure of Borate Glasses
Authors: INOUE HIROYUKI , AOKI NORIAKI , YASUI ITARU
Published: March 2005

The structures of borate glasses have been simulated by use of molecular dynamics. A new type of potential calculated by means of the intermediate neglect of differential overlap (INDO) method and a three‐body potential were introduced into the molecular dynamics simulation. Boroxyl rings and diborate groups have been successfully reproduced in the structure models obtained from the present molecular dynamics simulation. Calculated radial distribution functions agreed well with the observed one obtained from X‐ray diffraction data. The distribution of O–B–O and B–O–B bond angles is also given.
Effect of Grain Growth on Hot‐Pressed Optical Magnesium Fluoride Ceramics
Authors: Lin Whai‐Yuh , Hon Min‐Hsiung , Yang Sheng‐Jenn
Published: March 2005

An optical MgF2 ceramic was hot‐pressed at 838 to 983 K with 241‐MPa pressure. The maximum mechanical strength (>180 MPa) developed in the resulting ceramic within the grain‐growth range μ/μ0= 7 to 10, where μ is the grain size of the hot‐pressed article and μ0 that of the starting powder. In the early stages of grain growth (μ/μ0<7), however, mechanical strength was directly proportional to grain size, which appeared to contradict the expectations of the Petch and Knudsen relations. Optical transmission was inversely proportional to grain size, especially in the visible wavelength. This study thus demonstrates a particular case in which increasing grain size promotes higher mechanical strength but lower optical transmission.
Occurrence of Pseudotetragonal Mullite
Authors: Schneider Hartmut , Rymon‐Lipinski Tadeusz
Published: March 2005

Mullite‐type phases with about 74 wt% Al2O3 and 26 wt% SiO2 were prepared from tetraethyl orthosilicate and aluminum butylate between 950° and 1000°C. The lack of 120/210, 240/420, 041/401, and 250/520 reflection pair splitting on the X‐ray diffractograms indicates tetragonal symmetry, whereas normal mullite is orthorhombic. We believe that the tetragonal character of the phase is due to twinning and/or domain formation of orthorhombic structural units in an elementary cell scale. Therefore, the mullite‐type phase should be designated as pseudotetragonal rather than tetragonal. According to our present knowledge, pseudotetragonal mullite is formed from highly reactive metal organic compounds only. The phase is metastable and transforms gradually to orthorhombic mullite at temperatures above 1000°C.
Electrical Properties and Cation Valencies in Mn3O4
Authors: DORRIS S.E. , MASON T.O.
Published: March 2005

The electrical conductivity and thermopower of Mn3O4 were measured in the temperature range 920° to 1530°C. Electrical conduction in cubic Mn3O4 is explained by the small polaron hopping of electron holes between Mn4+ and Mn3+ on octahedral sites. The concentrations of Mn4+ and Mn3+ are governed by the disproportionation equilibrium 2Mnoct3+⇄Mnoct4++ Mnoct2+. This model also explains the electrical behavior of NiMn2O4 and CuMn2O4.
Oxycarbide Glasses in the Mg‐Al‐Si‐O‐C System
Authors: HOMENY JOSEPH , NELSON GREGORY G. , RISBUD SUBHASH H.
Published: March 2005

Oxycarbide glasses in the Mg‐Al‐Si‐O‐C system were produced at initial carbon levels of 0.0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt%. Carbon was incorporated into the glass melts by means of SiC additions. The glasses were melted between 1750° and 1800°C under nitrogen atmospheres. The limit of carbon incorporation was reached at the 2.5% carbon level, as these glasses crystallized (predominantly cordierite, 2MgO˙2Al2O3˙5SiO2) upon gradual cooling from the meit. Glasses containing less than 2.5% carbon were amorphous according to standard X‐ray diffraction methods. Further examination of these oxycarbide glasses by transmission electron microscopy indicated the lack of microcrystalline phases and the potential for producing clear inclusion‐free glasses. The Mg‐Al‐Si‐O‐C glasses showed significant increases in density, Young's elastic modulus, shear modulus, Vickers hardness, and fracture toughness with increasing carbon content.
Lead Galliate Glasses
Authors: Shelby James E.
Published: March 2005

Glasses have been formed in the binary system PbO–Ga2O3 within the compositional range extending from 60 to 80 mol% PbO. These glasses exhibit infrared cutoff values near 7.75 μm. The glasses are orange‐red as a result of a cutoff in visible transmission near 500 nm. The glass transformation temperature decreases with increasing PbO concentration, whereas the thermal‐expansion coefficient and density increase with increasing PbO content. Glasses containing 70 to 75 mol% PbO are good glass formers, with little tendency to crystallize, and exhibit good weathering behavior on exposure to normal atmosphere.
Crack‐Resistance Curves of Surface Cracks in Alumina
Authors: Steinbrech Rolf W. , Schmenkel Olaf
Published: March 2005

The resistance of coarse‐grained alumina to stable crack growth, initiated from “naturally’occurring surface flaws, was studied in strength tests with a bend‐bar technique. The surface cracks experienced R‐curve behavior over the first few hundred micrometers; i.e., the applied crack driving force had to be increased with crack extension. Compared to R curves generated from long cracks in standard single‐edge‐notched‐bend specimens, the surface‐crack curves have lower initial values. The possible influence of localized residual stresses, counteracting the applied crack driving force, is discussed.
Solubility of Hydrogen Defects in Doped and Undoped BaTiO3
Authors: WASER R.
Published: March 2005

Thermal desorption studies and electrical conductivity measurements have been used to investigate the solubility of hydrogen defects in barium titanate ceramics in oxidizing atmospheres. Hydrogen is found to dissolve in the perovskite lattice of undoped and acceptor‐doped BaTiO3 by the formation of hydroxide ions on regular oxygen ion sites. The hydrogen defects act as mobile donors and may substitute the oxygen vacancies in compensating fixed acceptors. From the dependence of the solubility on the water vapor pressure and the dopant concentration, the incorporation/desorption equilibrium reaction is deduced. A defect model is derived which consistently extends previously proposed models. The influence of Ba2TiO4 and Ba6Ti17O40 second phases on the solubility of hydrogen defects is discussed.
Experimental Analysis and Modeling of Slip Casting
Authors: HAMPTON J. HOLLY D. , SAVAGE STUART B. , DREW ROBIN A.L.
Published: March 2005

The filtration mechanics of slip casting is extended to account for the filtrate transporting the finer particles to the bottom of the cake. Scanning electron micrographs of alumina (Al2O3) green microstructures illustrate that a higher concentration of fine particles can accumulate at the bottom section of a cake. The rheological behavior of alumina suspensions with different solids loadings, particle‐size distributions, and amounts of deflocculant is discussed. Slip‐casting experiments demonstrate that the rheology of a suspension greatly affects the green density and growth rate of the cake.
Processing of Highly Concentrated Aqueous α‐Alumina Suspensions Stabilized with Polyelectrolytes
Authors: CESARANO JOSEPH , AKSAY ILHAN A.
Published: March 2005

Stability and rheology of aqueous α‐Al2O3 suspensions with poly(methacrylic acid) and poly(acrylic acid) polyelectrolytes were studied as a function of pH, solids loading, and molecular weight. Past work has found polyelectrolyte‐stabilized suspensions to be fairly pH independent at low (e.g., 20 vol%) solids loadings. However, we now show that the effective pH range to provide dispersed and fluid suspensions narrows as the concentration of solids increases as related to interparticle forces. At high solids levels, the presence of excess polymer in solution has detrimental effects on stability, which increases as the molecular weight increases. Finally, with knowledge of these concepts, highly concentrated fluid suspensions of 60 vol% Al2O3 (>85 wt%) with submicrometer‐size particles have been processed. Higher consolidated densities and reduced sintering temperatures are attained when compared with more conventional processing techniques.
Corrosion of Silicon Nitride Ceramics in Aqueous Hydrogen Chloride Solutions
Authors: SATO TSUGIO , TOKUNAGA YASUKI , ENDO TADASHI , SHIMADA MASAHIKO , KOMEYA KATSUTOSHI , KOMATSU MICHIYASU , KAMEDA TSUNEJI
Published: March 2005

The leaching behavior of pressureless sintered and hotpressed Si3N4 containing Y2O3, Al2O3, and AlN and hot isostatically pressed Si3N4 without additives was studied in 0.1M to 10M HCl aqueous solutions at 50° to 100°C. Y and Al ions contained in the grain‐boundary phase dissolved in HCl solutions, but dissolution of the Si ion from the matrix was negligible. The dissolution of Y and Al ions in HCl solutions was adequately described by a surface‐chemical‐reaction‐controlled, shrinking‐core model in <1M HCl solutions and by a diffusion‐controlled, shrinking‐core model in >5M HCl solutions. The rates of dissolution of both Y and Al ions decreased as the degree of crystallinity of the grain‐boundary phase increased. The fracture strength of the corroded samples linearly decreased with increasing degree of dissolution of soluble Y and Al ions.
Mixing and Flow Characteristics in the Alumina/Thermoplastic Resin System
Authors: TAKAHASHI MINORU , SUZUKI SUGURU , NITANADA HIDETO , ARAI EIKI
Published: March 2005

Rheological properties were investigated for combinations of six different alumina and three thermoplastic resins of polyethylene, polypropylene, and polystyrene. The curves of torque versus time in the alumina/resin mixture systems could be classified into four patterns depending on both the mixing properties of each of the resins and the solid concentration. It was verified through infrared spectroscopy and gel permeation chromatography measurements that the behavior of the mixtures could be explained by taking the degradation of each resin into account. Flow was characterized as shear thinning in both the alumina/resin and resin systems. A simple parameter, V¯p= (ρcr− V¯)/ρcr, a kind of corrected liquid volume concentration, was introduced to express the dependence of relative viscosity ηr of the mixture on the solid concentration V¯ and the relative compaction density ρcr. The relation ηr=αV¯−βp could be useful for estimation of the flow properties of ceramic powder/resin mixture systems.
Aminoborane Polymers as Precursors of C‐N‐B Ceramic Materials
Authors: MAYA LEON
Published: March 2005

Aminoborane polymers were prepared via condensation reactions between polyfunctional amines and either triethylborane or tris(dimethylamino)borane. The products were characterized by chemical and spectroscopic analyses. The thermal degradation of these materials was studied to establish pyrolytic pathways and to evaluate their potential as precursors to C‐N‐B ceramic materials. The borane condensation products with 4,4′‐methylenedipyrazole, o‐phenylenediamine, and 3,3′‐diaminobenzidine produced relatively high ceramic yields at 800°C, whereas that with diethylenetriamine decomposed into partially volatile oligomers.
Formation and Transformation of Cubic ZrO2 Solid Solutions in the System ZrO2—Al2O3
Authors: Yamaguchi Osamu , Shirai Masakazu , Yoshinaka Masaru
Published: March 2005

In the system ZrO2‐Al2O3, cubic ZrO2 solid solutions containing up to 40 mol% Al2O3 crystallize at low temperatures from amorphous materials prepared by the simultaneous hydrolysis of zirconium and aluminum alkoxides. The values of the lattice parameter, a, increase linearly from 0.5095 to 0.5129 nm with increasing Al2O3 content. At higher temperatures, the solid solutions transform into tetragonal ZrO2 and α‐Al2O3. Pure ZrO2 crystallizes in the tetragonal form at 415° to 440°C.
Transformation Toughening in Large‐Grain‐Size CeO2‐Doped ZrO2 Polycrystals
Authors: Coyle Thomas W. , Coblenz William S. , Bender Barry A.
Published: March 2005

The fracture and transformation behavior of tetragonal polycrystalline ZrO2 alloys containing 18 mol% CeO2 (Ce‐TZP) was investigated. In the absence of applied stress the tetragonal phase was found to be stable in large‐grained (>30 μm) samples at room temperature. The monoclinic phase was detected in regions of high residual stress near hardness indentations although no evidence of a wake of monoclinic phase along the fracture surface was observed. The fracture toughness increased from 4 to 7 MPa · m1/2 as density and/or grain size increased. It is proposed that the relatively high toughness of these materials is due to the occurrence of stress‐driven tetragonal‐to‐monoclinic transformation near the crack tip, which reverses when the crack has passed.
Preparation of Cerium Dioxide Powders for Catalyst Supports
Authors: Powell Bob R. , Bloink Raymond L. , Eickel Carolyn C.
Published: March 2005

Studies of the mechanisms by which cerium dioxide enhances automotive catalyst performance would be facilitated by the use of pure, high‐surface‐area forms of cerium dioxide. A cerium dioxide powder with a BET area of 50 m2·g−1 has been prepared by spray drying an aqueous solution of cerium nitrate, citric acid, and nitric acid. The thermal stability of the BET area at temperatures from 500° to 1100°C has been determined and compares favorably to other CeO2 powders. Microstructure evolution during thermal treatments is discussed and pelleting procedures are reported.
Reactions between α‐Silicon Carbide Ceramic and Nickel or Iron
Authors: Schiepers René C. J. , van Loo Frans J. J. , de With Gijsbertus
Published: March 2005

The interactions of very pure and practically 100% dense α‐SiC with nickel and iron at 850°C were investigated. Large reaction zones, consisting of carbon and silicides of Ni and Fe, were examined by microprobe analysis. By means of marker experiments, the diffusion mechanisms were investigated: only Ni and Fe migrate through the reaction layer. Isothermal sections of the ternary phase diagrams Ni‐Si‐C and Fe‐Si‐C at 850°C are presented.