bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Relations at Low Temperatures in the Fe‐Mg‐O System
Authors: KRAWITZ A. , COHEN J. B.
Published: June 2006

Even when magnesiowustite is rapidly cooled in a reducing atmosphere, a small volume fraction of spinel forms. These results provide a basis for understanding the large discrepancies in M‐H curves and the observed quadrupole splitting in Moessbauer spectra reported by various workers. In addition, it is shown that, with modern monochromatic X‐ray diffraction techniques, a volume percent <0.10 can readily be measured.
Translucent Sintered MgAl2O4
Authors: BRATTON R. J.
Published: June 2006

A translucent polycrystalline MgAl2O4 ceramic was prepared from finely divided coprecipitated spinel in which a small amount of CaO added as a sintering aid was uniformly distributed. The CaO promotes densification through the formation of a liquid phase at the sintering temperatures. Depending on the sintering treatment, the relative density of the sintered spinel was 99.7 to ∼100% of theoretical. The in‐line optical transmission was > 10% from 0.3 to 6.5 μm. Total transmission in the visible region was between 67 and 78%.
Analysis of Grain‐Boundary Impurities and Fluoride Additives in Hot‐Pressed Oxides by Auger Electron Spectroscopy
Authors: JOHNSON W. C. , STEIN D. F. , RICE R. W.
Published: June 2006

Auger electron spectroscopy was used to characterize grain‐boundary chemistry in MgO, Al2O3, and MgAl2O4 (spinel) hot‐pressed with LiF or NaF. The presence of additives (F, Na) at the grain boundaries was confirmed; observation of grain‐boundary impurities in MgO extends previous studies.
Silica‐Free Phases with Mullite‐Type Structures
Authors: PERROTTA A. J. , YOUNG J. E.
Published: June 2006

Silica‐free phases which have a structure similar to that of mullite can be crystallized from gels in the Na2O‐Al2O3 and (Na,K)2O‐BaO‐Al2O3 systems. A gelation step appears to be necessary, since a solid‐state reaction between Na2CO3 and Al(OH)3 does not give the mullite‐type phase. Crystallization of this phase requires a high alkali content during formation of the gel. A well‐crystallized phase is formed at 950°C and is stable to at least 1000°C; at higher temperatures (i.e. 1200°C), β‐Al2O3 and corundum are formed. The mullite‐type phase appears to crystallize with an increase in temperature at the expense of a γ‐Al2O3 phase, indicating adsorption of Na on the defect spinel structure, which is then rearranged to give the mullite‐type phases.
Theory of the Dependence of Densification on Grain Growth During Intermediate‐Stage Sintering
Authors: ROSOLOWSKI J. H. , GRESKOVICH C.
Published: June 2006

A semiempirical model for intermediate‐stage sintering is developed based on simultaneously occurring volume and grain‐boundary diffusion mechanisms of mass transport and explicitly incorporating the effects of grain growth. The sintering equation derived depends strongly on the reduction of pore number density associated with grain growth and is independent of the mechanism of grain growth. The time and temperature dependencies of densification predicted by the equation, which are tested using data for metal and ceramic powders, agree well with observations. The data indicate that grain‐boundary diffusion contributes negligibly to densification.
Nernst‐Einstein Relation in Sodium Silicate Glass
Authors: ENGEL JOHN R. , TOMOZAWA MINORU
Published: June 2006

The diffusion coefficient and the electric mobility of sodium (22Na) ions in a sodium silicate glass (25 mol% Na2O) were measured simultaneously at 300°C in an experiment of the type used by Chemla, where the diffusion heat treatment is made in a constant dc electric field. The diffusion coefficient remained unchanged with an applied electric field. The correlation factor in the Nernst‐Einstein relation calculated from the simultaneously measured diffusion coefficient and electric mobility was 0.5±0.05.
Crystallization of a Tetrasilicic Fluormica Glass
Authors: DANIELS W. H. , MOORE R. E.
Published: June 2006

The crystallization of a tetrasilicic synthetic mica glass of nominal composition K2Mg5Si8O20F4 was investigated at selected temperatures from 560° to 1150°C using DTA, density measurements, electron microscopy, and X‐ray diffraction techniques. Crystallization is shown to occur in 2 stages. (1) Initial structural ordering occurs at ∼600°C, as indicated by a strongly exothermic reaction, an increase in density, and the appearance of X‐ray diffraction lines. (This transformation temperature is related to fluorine content.) (2) The crystal morphology of the glass‐ceramic changes at 900° to 1150°C. A mechanism is proposed for the transformation from amorphous to crystalline structure in this synthetic mica system.
Electromagnetic Scattering from Metastable Immiscible Droplets in Glass
Authors: SHETTERLY D. M. , STUBLER R. J.
Published: June 2006

Theoretical calculations of the electromagnetic scattering from a metastable immiscible glass are presented. The calculations assume an assemblage of independently growing spherical droplets sufficiently separated so that interparticle interference is insignificant. The growth of the droplets is controlled by diffusion from the supersaturated matrix. Sharp composition boundaries for the droplets are also assumed. The model is used to predict scattering for a metastable immiscible Na2O‐CaO‐SiO2 glass. This scattering is compared to that predicted by the model of Goldstein. In addition to predicting light scattering for particles larger than those the Goldstein model permits, the present approach also allows calculation of small‐angle X‐ray scattering, which the Goldstein model does not. The compositions of the separating phases and the mechanism of growth can be estimated from electromagnetic scattering data when the present approach is used.
A Nonlinear Structural Relaxation Model for the Glassy State: Application to B2O3
Authors: HSICH HENRY S.‐Y.
Published: June 2006

Traditionally fictive temperature has been used to characterize the structural state of glasses. Since this concept has certain shortcomings, use of a second thermodynamic ordering parameter along with fictive temperature in a nonlinear model is proposed. This model is applied to refractive index relaxation data, from the literature, for B2O3 glass. Data were considered as the refractive index relaxed to a new equilibrium temperature from both higher and lower fictive temperatures.
Loading (L) Factors for the Biaxial Flexure Test
Authors: RADFORD K. C. , LANGE F. F.
Published: June 2006

The dependence of the loading (L) factor on the Weibull modulus (m) was derived for the biaxial flexure test assuming a 2‐parameter Weibull stress function and noninteracting orthogonal stresses. The specimen and test fiture dimensions influence the dependence significantly, whereas little difference is found between a 3‐point or ring specimen support. The L factors are more strongly influenced by the Weibull modulus than in a 3‐point bend test.
Kinetics and Thermodynamics of Decomposition of Dolomite to a Metastable Solid Product
Authors: POWELL ELIZABETH K. , SEARCY ALAN W.
Published: June 2006

The decomposition of dolomite, CaMg(CO3)2, in vacuum was studied by the torsion‐effusion and torsion‐Langmuir methods. Complete decomposition yields poorly crystalline MgO and CaO of high total surface area, but the decomposition product when the reaction is 50% complete does not give coherent X‐ray scattering. Extrapolation of the effusion pressures to pressures for zero orifice area yields thermodynamic data that disagree with well‐established data for dolomite and its thermodynamically stable products. The data are consistent with the interpretation that dolomite and CO2 are at equilibrium with a glasslike solid which has a free energy of formation of (17,600 – 8.8T)cal from O.SCaO + 0.5Mg0. From the torsion‐Langmui data, the apparent activation enthalpy and entropy of decomposition to this product are calculated to be 46.5 kcal and 22.3 cal/degree per mol of CO2. The ratio of the free surface decomposition pressure to the metastable equilibrium pressure is 1 × 10−4 at 850°K. Earlier anomalously low pressures measured for decomposition of Mg(OH)2 are also consistent with the interpretation that the solid product was glasslike.
Recrystallization and Phase Transformation in Reaction‐Sintered Sic
Authors: SHINOZAKI SAMUEL S. , NOAKES JOHN E. , SATO HIROSHI
Published: June 2006

Reaction‐sintered Sic specimens prepared at ∼1500°C and heat‐treated at ∼1850°C in the presence of molten silicon were examined by transmission electron microscopy. The β‐Sic grains in as‐prepared specimens grew to a large size when heat‐treated in the presence of molten Si; the number of growth twins in such °‐Sic crystals was very small. The boundary areas of α‐ and β‐Sic crystals were microsyntactic, consisting of thin strips of α‐ and β‐Sic after heat‐treating. These changes were due mostly to thin lamellar growth of α‐Sic into β‐Sic grains along the basal plane. There is also a high density of similar growth of transformation twins in β‐Sic crystals. The results provide clear evidence of in situ solid‐state transformations in sic.
Resistivity‐Microstructure Relations in Lithia‐Stabilized Polycrystalline β”‐Alumina
Authors: VIRKAR ANIL V. , MILLER GERALD R. , GORDON RONALD S.
Published: June 2006

The sodium ion resistivity of lithia‐stabilized polycrystalline β”‐alumina was measured as a function of temperature for fine‐grained and coarse‐grained specimens with a chemical composition of 8.80 Na20‐0.75 Li2O‐90.45 A12O3 (wt%). A model is presented which explains the dependence of sodium ion resistivity on grain size. Using the model the activation energy was determined for the transport of sodium ions across a grain boundary in this form of sodium β”‐alumina.
Finite Element Analysis and Experimental Verification of the Shape Factor for Narrow Sandwich Seals
Authors: GULATI S. T. , HAGY H. E.
Published: June 2006

Comparison of the results of 3‐dimensional (3D) and 2‐dimensional (2D) finite element analyses (FEA) shows that the 2D analysis is accurate enough for calculating the shape factor for narrow sandwich seals and is considerably less expensive. The 2D analysis confirms the accuracy of an earlier approximate theoretical solution, particularly for seals with skin‐to‐core thickness ratios of 0.5 to 2. For seals with extremely thin or thick skin the use of 2D FEA is recommended. The FEA results show that the shape factor does not change appreciably either with the modulus ratio, Es/Ec, or with the composite Poisson's ratio, v, although it has a marked dependence on the aspect ratio of the core layer. Experimental values of the shape factor show fairly good agreement among theory, FEA, and experiment and provide confidence in the proposed theory and the 2D FEA.
Internal Stresses and Microcrack Formation Caused by Drying in Hardened Cement Pastes
Authors: KAWAMURA MITSUNORI
Published: June 2006

The shrinkage stresses due to drying and the differences of volume changes and rigidities between the two phases of dense Ca(OH), crystals and porous C‐S‐H gel are estimated. High tensile stresses are calculated around the Ca(OH), crystals at a relatively high humidity. It is also shown by a calculation on the basis of some assumptions that the shrinkage stresses may cause microcracks which drastically increase permeability.
Electron Paramagnetic Resonance Spectroscopy Applied to Diffusion of Mn2+ in MgO
Authors: WEEKS R. A. , CHATELAIN ANDRÈ
Published: June 2006

Electron paramagnetic resonance spectroscopy was used to measure the diffusion rates of Mn2+ in MgO single crystals at 1200 to 1520 K. It is shown that the spectral components of Mn2+ must be separated into one due to a high concentration and a set due to a low concentration of Mn2+ ions in the diffusion samples. It was found that the data fit a simple ion‐diffusion model in which the activation energy E = 2.1±0.25 eV and D0= (9.4±s2.8)× 10−6 cm2s−1.
Effect of Forming and Aging Atmospheres on E‐Glass Strength
Authors: MARTIN D. M. , AKINC MUFIT , OH SHIN MOO
Published: June 2006

E‐glass fibers were drawn in various atmospheres. The specific surface area measured by water vapor adsorption was larger than the geometric area. Specific surface increases with the square root of drawing gas pressure. Exposure of glass fibers to ambient atmosphere decreases the strength and increases the area of macropores (rp> 100 Å). The reciprocal strength of E‐glass filaments aged at ambient humidity for various times is proportional to the square root of macro pore area. This relation is independent of the drawing atmosphere, at least for water and tetrafluoromethane.
Electron Paramagnetic Resonance in R2O‐Al2O3−SiO2 Glass Systems
Authors: KAYASHIMA MITSUTOSHI , SANO NOBUO , MATSUSHITA YUKIO
Published: June 2006

Systematic detection of an EPR signal was conducted for three alkali oxide‐Al2O3−SiO2 glass systems. Observed EPR spectra, having a main line with g=2.03 and a broad and anisotropic shape, are attributed to the unsaturated bridging oxygen bond resulting from the breakup of the SiO2 random network. This signal appears in the area AValkali atom ratio >1 for the Na20 and K2O systems, indicating that the collapse of the Al 4‐coordinated structure begins at an equimolar ratio when alumina is substituted for the alkali oxide, whereas somewhat different behavior was observed for the Li2O system.
Microcracking of Eu2O3=Ta2O5 Bodies
Authors: MALARKEY C. J. , HUNTER O.
Published: June 2006

Europium sesquioxide is of interest as a control material for reactors because it has several large‐cross‐section isotopes which form successively on neutron capture. Pure monoclinic Eu2O3 tends to grow large grains during sintering, causing microcracks to develop and leading to anomalous mechanical properties. The effect of doping the Eu2O3 with the grain growth suppressant Ta2O3 was determined using studies of the elastic properties and internal friction by the sonic resonance technique. Compositions with <3 at.% Ta cation substitution had anomalously low room temperature elastic moduli values and showed a hysteresis on thermal cycling. These specimens also had high internal frictions. The finer‐grained specimens which resulted when the dopant level exceeded 3 at.% Ta did not show these anomalous characteristics.
Solid‐Liquid Equilibria in the System Si3N4‐AlN‐Si02‐A12O3
Authors: NAIK I. K. , GAUCKLER L. J. , TIEN T. Y.
Published: June 2006

Solid‐liquid equilibria at 1750°C and subsolidus phase relations in the system Si3N4−AlN‐SiO2−Al2O3 were determined for the composition region bounded by the β‐Si3N4 solid solution line and silica‐alumina join X‐ray diffraction and optical microscopy were used to determine the phases present in specimens cooled rapidly after equilibration. The extent of a single liquid‐phase region and the tie lines for the βsolid solution + liquid field at 1750°C were established from quantitative X‐ray diffractometry and lattice parameter measurements of βsolid solutions in equilibrium with liquid. The results were corroborated by optical microscopy and melting behavior observations. A new composition, Si12Al18O39N8, is suggested for the x1 phase. The lowest melting temperature in the system is ≅ 1480°C and the corresponding composition is 10 eq% Al‐90 eq%O.
Static and Dynamic Fatigue of a Polymer‐Coated Fused Silica Optical Fiber
Authors: KALISH DAVID , TARIYAL B. K.
Published: June 2006

The dependence of fracture strength on tensile strain rate (dynamic fatigue) was used to establish the characteristic slow‐crack‐growth parameters in ethylene vinyl acetate‐coated optical fibers. Strength was measured with five strain rates at each of four relative humidities (from 2 to 97% rh) on specimens 5 cm long. The inert fracture strength was measured at a low temperature in a dry atmosphere. The results of these tests were incorporated into a fracture mechanics model, including slow crack growth, for static fatigue. An increase in relative humidity promotes dynamic fatigue and leads to a predicted acceleration of static fatigue. Measurements of the static fatigue time‐to‐failure at three applied stress levels (on specimens 61 cm long) in 97% rh agree with the predicted behavior based on dynamic fatigue. The applicability of fracture mechanics crack‐growth laws to fused silica fibers is discussed in terms of the Charles and Hillig stress‐corrosion model.
Fracture of Polycrystalline MgAl2O4
Authors: STEWART R. L. , BRADT R. C.
Published: June 2006

The fracture toughness of stoichiometric polycrystalline MgAl2O4 was measured as a function of grain size and temperature to 1400°C. The room temperature fracture toughnesses are comparable to reported single‐crystal values. No effect of grain size was detected. Two regions of KIc=f(T) were observed, both showing a decreasing KIc with an increasing T. In the low‐temperature region, fracture is of a mixed mode, transgranular and intergranular character. The ∼10−4 MN/m3/2°C (dK10dT) decrease is governed primarily by dE/dT. The high‐temperature region, T >900°C, has a much larger dK10dT decrease, ∼ 10−3 MN/m3/2°C, and a fracture character that is totally intergranular, suggesting dominance by grain‐boundary processes.
Ionic Conductivity and Magnesium Vacancy Mobility in Magnesium Oxide
Authors: SEMPOLINSKI D. R. , KINGERY W. D.
Published: June 2006

The dc conductivity and ionic transference number of MgO single crystals doped with Al, Fe, and Sc were measured as a function of temperature (1200° to 1600°C) and oxygen pressure (10−1 to 10−13 MPa). Magnesium oxide is a mixed conductor with its ionic component directly proportional to the trivalent solute concentration. The activation energy for ionic conduction equals 202 kj/mol and is independent of the specific trivalent solute used. This behavior results from a defect structure for a single trivalent solute for which the charge balance condition is 2[VMg'] =[IMg], where [VMg”] is the Mg vacancy concentration and [IMg] the trivalent solute concentration. At lower temperatures and high Sc concentrations, effects attributed to Sc ionvacancy association are observed. Ionic conduction results from Mg vacancy motion with a diffusion coefficient of VMg' given by

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Deduced values of the Mg‐ion diffusion coefficient lead to the conclusion that the scatter in the published DMg data largely results from differences in impurity content.
Electronic Conductivity of Single Crystalline Magnesium Oxide
Authors: SEMPOLINSKI D. R. , KINGERY W. D. , TULLER H. L.
Published: June 2006

The electronic conductivity of MgO was determined by measuring the dc conductivity and ionic transference number as a function of temperature (1200° to 1600°C), oxygen pressure (10−1 to 10−13 MPa), and trivalent solute concentration (65 to 1500 ppm) using samples doped with Al, Fe, or Sc so that only one dopant controlled the defect structure. The electronic conductivity showed ap‐ to n‐type transition with decreasing oxygen pressure, consistent with a defect structure in which the concentrations of the electronic species are negligible with respect to those of the ionic defects, so that MgO is a fully compensated semiconductor. From the temperature dependence of the electronic conductivity minima, a thermal band gap of 650±50 kj/mol (6.8±0.5 eV/electron) and electron and hole mobilities of 24 and 7 cm2/V·s were determined at 1400°C. From these results, the defect‐reaction equilibrium constants were determined.
Transient Thermal Stresses in Cylinders with a Square Cross Section Under Conditions of Convective Heat Transfer
Authors: SATYAMURTHY K. , SINGH J. P. , HASSELMAN D. P. H. , KAMAT M. P.
Published: June 2006

The transient thermal stresses in a long cylinder with a square cross section resulting from convective heating or cooling by a sudden change in ambient temperature were calculated by the finite element method. On heating, the maximum tensile stresses occur in the center of the rod, whereas the maximum principal stresses occur along the diagonal of the cross section. On cooling, the maximum tensile stresses occur at the center of the faces. The results obtained are discussed in terms of experimental measurement of the thermal stress resistance of brittle ceramics. Possible failure modes during heating and cooling are discussed. Comparison with literature data shows that for a given value of the Biot number the magnitude of the maximum tensile stresses on cooling, in a rod with a square cross section, exceeds those in a rod with a circular cross section.
Effect of Stresses from Thermal Expansion Anisotropy, Phase Transformations, and Second Phases on the Strength of Ceramics
Authors: RICE R. W. , POHANKA R. C. , McDONOUGH W. J.
Published: June 2006

Critical flaws were determined by fractography in several ceramic bodies having internal stresses due to thermal expansion anisotropy, phase transformations, or second phases. Fracture energies calculated using the observed flaw sizes and shapes agreed well with those measured by fracture‐mechanics techniques at large flaw sizes. However, at smaller flaw sizes, calculated fracture energies decreased with decreasing flaw size. This decrease is attributed to internal stresses which increasingly contribute to failure as flaw sizes approach the sizes dominated by tensile components of these internal stresses. These components, in turn, are due to statistical variations of grain orientation. The projected contribution of internal stresses to failure is consistent with simple estimates of their levels as the flaw size decreases to about the grain size. Thus, application of fracture mechanics must take into account an increasing contribution of internal stresses as flaw sizes decrease in bodies in which these stresses can exist.
Fracture Toughness and High‐Temperature Slow Crack Growth inSiC
Authors: McHENRY K. D. , TRESSLER R. E.
Published: June 2006

The subcritical growth of macroscopic cracks in hot‐pressed and in sintered SiC was examined at 900° to 1100°C in oxygen partial pressures of 10−4 and 10−8 atm. The K1‐V data for the hot‐pressed SiC were generated using the double torsion specimen in the incremental displacement rate mode. These data, in addition to earlier results, included three distinct regions in the plot of log V vs logK1,: a low slope region, N∼20, of substantial slow crack growth which was insensitive to testing temperature and environment; a plateau region which shifted to higher velocities with increasing temperature; and a region of very high slope with K values near KIC The results may be described qualitatively by viscous flow of the gram‐boundary phase. No slow crack growth could be detected in the sintered SiC when tested hi the environments described.
Nucleation in Photosensitive Gold Ruby Glass
Authors: FUTATO R. J. , DOREMUS R. H.
Published: June 2006

The numbers of gold particles in a gold ruby glass were calculated as a function of irradiation time, nucleation and irradiation temperature, and cerium concentration. Photonucleation in Ce‐containing glasses and nucleation by X rays in glasses without cerium were similar, suggesting that cerium was not directly involved in nucleating the gold particles. The results were consistent with nucleation by trapped photoelectrons. Temperature of irradiation and cerium concentration influenced production and recombination of the trapped electrons. A decreased number of nuclei as the nucleation temperature increased probably resulted from recombination of the trapped electrons.
Diffusion‐Controlled Attack of Glass Surfaces by Aqueous Solutions
Authors: DAS C. R.
Published: June 2006

Simple binary alkali oxide silica glasses and some ternary glasses derived from the binary compositions by substituting alkaline earth oxides for silica were subjected to the action of water and various aqueous solutions (pH 1.4 to 10.9) and the kinetics of the reactions were studied. In every case a root‐time relation of extraction, suggesting an ion‐exchange controlled diffusion mechanism, was observed, followed by a time relation of extraction. The rate and duration of diffusion depended on the pH of the solution and the reaction temperature. Above a critical pH the hydrogen ion concentration of the attacking solution was so low that the surface sites began to be occupied preferentially by alkali ions, increasing their concentration at the leached layer‐solution boundary and slowing the diffusion process. For potassium glasses only, where alkali ion distribution in the leached layer was exponential, the diffusion coefficients calculated from the concentration profiles agreed well with those calculated from the extraction of potassium ions by a diffusion mechanism.
Applicability of Crack Propagation Data to Failure Prediction in Porcelain
Authors: SOMA T. , MATSUI M. , ODA I. , YAMAMOTO N.
Published: June 2006

Failure probability of porcelain was measured as a function of time under constant stresses in various environments. The experimental results were compared with the theoretical predictions derived from the measured distribution of fracture stress and subcritical crack growth data. The experimental and theoretical results nearly agreed for the short‐term lifetime (less than ∼1000 s), after which failure probability was less than predicted. The applicability of crack propagation data to failure prediction was studied and the very slow crack‐growth data near the fatigue limit were determined to be necessary for predicting the long‐term lifetime of porcelain structures.
STEM Analysis of Grain Boundaries in Cemented Carbides
Authors: SHARMA N. K. , WARD I. D. , FRASER H. L. , WILLIAMS W. S.
Published: June 2006

There is controversy over whether the cobalt binder of liquid‐phase sintered WC forms a continuous skin over the WC particles or whether the carbide grains form a continuous skeleton. It is shown that the atomic Co/W ratio in the 20‐Å grain boundaries is >3 times larger than that in the grains, supporting the former model.
Stresses Arising During the Leaching of a Two‐Phase Glass
Authors: DREXHAGE M. G. , GUPTA P. K.
Published: June 2006

The stresses which arise when one phase of a two‐phase alkali borosilicate glass rod is chemically removed are examined. Three mechanisms which may account for these stresses are described: thermal expansion coefficient differences between the phases, hydration of the porous glass, and ion exchange within the leached layers. The first two effects induce eompres‐sive stresses, whereas the latter causes tension in the clads of partially leached glasses. Expressions for the stresses are developed in terms of glass properties and specimen geometry. Experimental photoelastic data on stress profiles, the effects of clad thickness, and heat‐treatment conditions in two compositions are presented and compared with theoretical predictions. The stresses, whether tensile or compressive, are constant as a function of the radius within the clad, but are strongly dependent on clad thickness. At a given heat‐treatment temperature, compressive stresses increase with time until a constant value is reached. This constant value increases with decreasing heat‐treatment temperature.
Phase Relations in Magnesium Oxysulfate Cements
Authors: URWONGSE LADAWAN , SORRELL CHARLES A.
Published: June 2006

Solubilities of MgO in H2SO4 solutions were measured and X‐ray analyses of over 100 neat cement samples were used to construct an isothermal phase diagram for the system MgO‐H2SO4‐H2O at 23°±3°C. The phases MgO, Mg(OH)2, 3Mg(OH)2 MgSO4·8H2O (3·1·8), MgSO4·7H2O, MgSO4·6H2O, and MgSO4·H2O were stable at 23°C. The phases Mg(OH)2· MgSO4·5H2O (1·1·5) and MgSO4·4H2O were observed but are considered to be metastable, resulting from overheating during reaction. Invariant liquids were located at 8.2±0.2 MgO, 17.4±0.5 wt% H2SO4 in equilibrium with Mg(OH)2 and 3·1·8; at 8.6±0.2 MgO, 21.2±0.5 wt% H2SO4 in equilibrium with 318 and MgSO4·7H2O; at 6.9±0.2 MgO, 42.4±1.0 wt% H2SO4 in equilibrium with MgSO4·7H2O and MgSO4·6H2O; and at 6.0±0.5 MgO, 48±2 wt% H2SO4 in equilibrium with MgSO4·6H2O and MgSO4·H2O. The diagram indicates that cements containing >50 wt% 3·1·8 cannot be made from MgO and MgSO4 solutions at 23°C. Steam curing, however, offers some possibilities for increasing binder‐phase content. Mg(OH)2 formed in the system provides X‐ray patterns which indicate an exaggerated sheet morphology.
Oxidation of Si3N4 Alloys: Relation to Phase Equilibria in the System Si3N4‐SiO2‐MgO
Authors: CLARKE D. R. , LANGE F. F.
Published: June 2006

The oxidation resistance at 1400°C of silicon nitride alloys hot‐pressed with magnesia was investigated as a function of the phase content of the alloys. The extent of oxidation, the products of oxidation, their stratification, and the continuity of the oxide scale are all dependent on the initial composition. Also, the compositions of the alloys themselves change during oxidation. The findings can be interpreted on the basis of compositional paths in the equivalence phase diagram. Reasons for the outward diffusion of Mg and impurities are given and the effect of the secondary phase on oxidation kinetics is discussed.
Disaccommodation of Mn‐Zn Ferrite After Temperature Cycling
Authors: VOGEL E.M. , JOHNSON D.W. , GYORGY E.M.
Published: June 2006

It was shown that cycling Mn‐Zn ferrite through or near the temperature of the zero crossing of the anisotropy constant K1 makes significant changes in the domain patterns and thus changes in disaccommodation rates. For the ferrite studied, with a secondary peak in permeability at—65°C, cycling to −80° or rapid cooling to −40° from room temperature affected the permeability and disaccommodation in a manner very similar to that of an ac demagnetization. Likely mechanisms which may explain these effects are discussed.
Characterization of Particle Orientations in Ceramics by Electron Paramagnetic Resonance
Authors: Mehran F. , Müller K. A. , Fitzpatrick W. J. , Berlinger W. , Fung M. S.
Published: June 2006

It is shown that electron paramagnetic resonance spectroscopy provides an accurate method for measuring the preferential orientation of axial crystallites in ceramics. Since the physical properties of ceramic materials are correlated with the degree of this orientation, EPR can be a convenient and useful tool for the characterization of ceramics.
Densification of Alumina and Silica in the Presence of a Liquid Phase
Authors: Singh Vipin Kant
Published: June 2006

Alumina and silica powders were sintered at 1250° to 1460°C in the presence of liquid phases containing CaO, A12O3, and SiO2. The data were analyzed using the equation D = K log t +C and the Arrhenius equation. The activation energy for sintering decreases with increasing amounts of liquid phase.
Thermal Diffusivities of Molybdenum/Alumina Cermets
Authors: Miller H. Craig
Published: June 2006

The thermal diffusivities of several molybdenum/alumina cermets were measured using a transient heat‐flow, semi‐infinite plate method. The cermets had thermal diffusivities significantly greater than those of 94% A12O3 alumina. A 50150 wt% cermet had a thermal diffusivity of 0.102 cm2/s at 313 K, while the alumina had a value of 0.067 cm2/s.
Influence of Microcracking and Slow Crack Growth on the Planar Coupling Coefficient in PZT
Authors: Chiang S. S. , Fulrath R. M. , Pask J. A.
Published: June 2006

The difference in the planar coupling coefficient, kp, of two PZT specimens with different grain sizes under the same poling treatment was attributed to a greater tendency for microcracking in the large grain‐size specimens. In the absence of microcracking, as shown in small grain‐size specimens, the decrease in kp and failure of the poled specimens is attributed to slow crack growth. The optimum poling conditions for small grain‐size specimens were evaluated in terms of reducing the slow crack‐growth effect.
Effect of Microstructure on the PTCR Effect in Semiconducting Barium Titanate Ceramics
Authors: KUWABARA MAKOTO
Published: June 2006

The microstructural influence on the PTCR effect in semiconducting barium titanate ceramics was studied and a method for preparing the ceramic bodies exhibiting a PTCR effect of more than seven orders of magnitude was established. Commercial barium titanyl oxalate was used as a starting material and Sb2O3 was added as a doping substance. The average grain sizes of the ceramic bodies prepared were 2 to 5 μm over a sintering range of 60 to 92%, to examine in detail the microstructural influence on the PTCR effect. No extra element, such as Mn or Cr, was added to develop the PTCR effect in the present PTCR materials.
Effect of Corrosion Processes on Subcritical Crack Growth in Glass
Authors: SIMMONS C. J. , FREIMAN S.W.
Published: June 2006

Crack‐growth studies were conducted on soda‐lime‐silica, soda borosilicate, and two binary soda‐silica glasses immersed in solutions of 1M Li+, 1M Cs+, or deionized water at different pH values. A definite effect of the Li+ and Cs+ was observed on the V‐K1 curves in all but the soda‐lime glass. A plateau in crack velocity in the range 10‐8 to 10‐10 m/s was measured on the binary soda‐silica glasses for K1<0.35 MPa.m1/2. These data are analyzed in terms of both the ion exchange and SiO2 dissolution steps of the corrosion process. A model of crack growth in corrosive conditions is proposed.
Fracture Toughness of Chalcogenide Glasses of the System Se‐Ge‐As
Authors: Michels B. ‐D. , Frischat G. H.
Published: June 2006

Measurements of the critical stress‐intensity factor, K10 are reported for eight glasses of the chalcogenide system Se‐Ge‐As. The K10 values are between 5.5 and 9.4 N.mm‐3/2. The dependence on glass composition can be understood qualitatively according to different short‐range order units of the Se‐Ge‐As glasses. A relation between fracture toughness, K10, microhardness, L2VH, and Young's modulus, E, may not be excluded for these glasses.
Electrical Conduction in Pure and Li‐Substituted Co3O4
Authors: KOUMOTO KUNIHITO , YANAGIDA HIROAKI
Published: June 2006

Electrical conductivity and thermoelectric power measurements on pure and Li‐substituted Co3O4 were performed at 200° to 900°C. Impurity‐induced p‐type semiconduction was observed at low temperatures and intrinsic behavior at high temperatures. A hopping scheme for electron hole conduction was confirmed, and site exchange of cations in the spinel structure was proposed to explain the electrical conduction at high temperatures.
Reaction Mechanism of H3BO3‐ZnO Bonding Material Under Hot‐Pressing and Heat Treatment
Authors: Utsumi Yoshikazu , Murakami Tadaki , Ishii Isao
Published: June 2006

The bonding material H3BO3‐ZnO was used to form a composite with fiberglass mats. The composite is formed by hot‐pressing at 180°C and is then heat‐treated for durability. The bonding material becomes liquid during hot‐pressing. Heat treatment promotes the reaction between H3BO3 and ZnO and converts the bonding phase to a primarily amorphous state containing a small amount of crystalline material.
Analytical Electron Microscopy of Cement Pastes: IV, β‐Dicalcium Silicate Pastes
Authors: MOHAN K. , TAYLOR H.F.W.
Published: June 2006

Analyses of 225 particles of C‐S‐H in ground and redispersed pastes of β‐Ca2SiO4 hydrated for 7 days to 22 years gave a mean Ca/Si ratio of 1.38 with a range of 1.1 to 1.6. The mean Ca/Si ratio is substantially constant over the period studied and is lower than that of 1.52 found by the same method for Ca3SiO5 pastes.
Delayed Failure of Plasma‐Sprayed Al2O3 Applied to Metallic Substrates
Authors: FERRER M. K. , BROWN S. D.
Published: June 2006

Aluminum oxide coatings were applied to the ends of cylindrical metal samples of both 316L stainless steel and TS–6Al‐4V ELI by a plasma spray process. These samples, fabricated into 4‐point bend specimens, were used to determine both the strength and slow crack growth characteristics. The data obtained indicated that both systems were susceptible to stress corrosion. When the substrate was the titanium alloy, the delayed failure behavior was characterized by two parallel stress‐corrosion reactions: one at the ceramic‐metal interface and one in the coating itself. The latter became dominant at low stresses. Finally, the nature of the epoxy adhesive used to fabricate the 4‐point bend samples was found to strongly influence the fatigue behavior at long failure times.
Evaluation of Bimodal Concurrent Flaw Distributions
Authors: Jakus K. , Ritter J.E. , Service T. , Sonderman D.
Published: June 2006

Bimodal concurrent flaw distributions are often observed in strength testing of ceramics. A technique is proposed to evaluate the appropriate Weibull parameters of the individual concurrent distributions where the type of flaw causing failure can be identified. This technique involves separating the data according to flaw origin and then analyzing each of these two censored data sets.
Hydrothermal Preparation of Ultrafme Monoclinic ZrO2 Powder
Authors: Tani Eiji , Yoshimura Masahiro , Somiya Shigeyuki
Published: June 2006

Ultrafine powder of single‐phase manoclinic ZrO2 was prepared by hydrothermal treatments of amorphous hydrated zirconia with 8 wt% KF solution under 100 MPa at 200° to 500°C for 24 h. The process yielded well‐crystallized particles 16 nm and 22 nm in size at 200° and 500°C, respectively.
Effect of H2O Vapor on the Internal Friction of Binary Alkali Silicate Glasses
Authors: Zdaniewski Wieslaw A. , Rindone Guy E.
Published: June 2006

Internal friction and shear modulus of Na, K, and Li disiticate glasses were measured by a torsional pendulum as a function of H2O vapor treatment at T=300°C. H2O produced changes in the acoustic spectra (between—100° and 400°C and f=0.5 Hz) similar to the mixed‐alkali effect which appears upon introduction of a second alkali to a single‐alkali glass. An Na2O·2SiO2 glass free from the common nonbridging oxygen relaxation was produced.
Infection induced inflammation is associated with erectile dysfunction in men with diabetes
Authors: Blans M. C. A. , Visseren F. L. J. , Banga J. D. , Hoekstra J. B. L. , Van Der Graaf Y. , Diepersloot R. J. A. , Bouter K. P.
Published: June 2006

Background  In diabetic patients with erectile dysfunction, endothelial dysfunction is a major underlying cause. Infection‐induced inflammation may be associated with endothelial dysfunction. The goal of this study was to determine whether erectile dysfunction in patients with diabetes is associated with infections of Chlamydia pneumoniae or cytomegalovirus and/or with low‐grade inflammation.

Materials and methods  Diabetic patients, 57 with and 33 without erectile dysfunction, were enrolled in a case–control study. Both groups of patients consists of type 1 and type 2 diabetics. Serum antibodies against cytomegalovirus and C. pneumoniae and markers of inflammation, including high‐sensitivity C‐reactive protein and fibrinogen, were measured.

Results  Adjusted odds ratios for erectile dysfunction in cytomegalovirus IgG, C. pneumoniae IgG and C. pneumoniae IgA seropositive men were 2·4 (95%CI; 1·0–6·0), 3·0 (95%CI; 1·2–8·1) and 1·8 (95%CI; 0·7–4·6), respectively. Odds ratios for the highest tertiles of high‐sensitivity C‐reactive protein and fibrinogen concentrations compared to the lowest tertile were 4·3 (95%CI; 1·4–13·1) and 6·6 (95%CI; 2·1–21·2), respectively.

Conclusion  Elevated high‐sensitivity C‐reactive protein or fibrinogen serum levels and infection with cytomegalovirus or C. pneumoniae were associated with erectile dysfunction in diabetes. The relation between cytomegalovirus and erectile dysfunction is markedly present in patients with elevated high‐sensitivity C‐reactive protein and fibrinogen levels, suggesting a modifying effect by the inflammation.
Cardiac troponin I and ventricular arrhythmia in patients with chronic heart failure
Authors: Liu Z. , Cui L. , Wang Y. , Guo Y.
Published: June 2006

Background  Both detectable serum cardiac troponin I (cTnI) and ventricular dysrhythmias are common in patients with chronic heart failure (CHF) and are paralleled with the severity of the CHF. However, the relationship between serum cTnI and ventricular arrhythmia severity in patients with CHF remains unknown; the mechanism of the ventricular arrhythmia in the CHF patients also remains unclear.

Materials and methods  The study group included 218 patients with CHF who had cTnI assay drawn at the time of initial presentation. Patients with acute myocardial infarction or myocarditis were excluded from the analysis. The patients were divided into two groups: cTnI‐positive with serum cTnI > 0·5 ng mL−1 (n = 98) and cTnI‐negative with serum cTnI ≤ 0·5 ng mL−1 (n = 120). The severity of ventricular dysrhythmias was assessed by 24‐h Holter monitoring, using prospectively defined measures of ventricular arrhythmic burden.

Results  Prevalence of risk factors for ventricular dysrhythmias was equal in both groups. All measures of ventricular ectopy were much higher in patients of the cTnI‐positive groups. Mean hourly ventricular pairs (13·59 ± 10·3 vs. 11·1 ± 6·01, P = 0·027), mean hourly repetitive ventricular beats (26·01 ± 13·67 vs. 22·01 ± 13·56, P = 0·032), and the frequency of ventricular tachycardia episodes per 24 h (12·54 ± 16·68 vs. 7·68 ± 11·54, P = 0·012) were higher in patients with detectable cTnI levels. After inclusion of clinical variables and drug therapies in a multivariate analysis, the positive relationship between cTnI and the frequency of ventricular pairs (P = 0·03), repetitive ventricular beats (P = 0·037), and ventricular tachycardia (P = 0·03) remained independent. In multivariate logistic regression, the risk of developing ventricular tachycardia was higher in patients with detectable cTnI levels with an adjusted odds ratio (OR) of 2·31 (95% CI, 1·22–2·65, P = 0·003).

Conclusions  In patients with CHF, serum cTnI is closely related to increased occurrence of ventricular dysrhythmias and could identify a subgroup of patients with ventricular tachycardia. The minimal myocardial injury detected by serum cTnI might be the abnormal substrate for ventricular dysrhythmias.
TGF‐β1 generates a specific multicomponent extracellular matrix in human coronary SMC
Authors: Schmidt A. , Lorkowski S. , Seidler D. , Breithardt G. , Buddecke E.
Published: June 2006

Background  Transforming growth factor (TGF‐β1) is postulated to play an important role in maintaining the structure and function of arterial tissue and protection against development of arteriosclerosis. The TGF‐β1‐induced production of a stable extra‐cellular matrix‐rich plaque phenotype is suggested to be part of the protection against a switch to an unstable rupture‐prone arteriosclerotic plaque.

Materials and methods  This study addresses the question of whether the expression profile and the type of extra‐cellular matrix (ECM) generated by TGF‐β1 stimulation have the structural feature of a fibril‐rich stable matrix. Seventeen genes codings for ECM components of human coronary smooth muscle cells (SMCs) after a 24‐h stimulation by TGF‐β1 have been analyzed.

Results  Real‐time RT‐PCR was used to quantify the mRNA of genes under investigation. It was found that after TGF‐β1 stimulation (a) the up‐regulation of COL1A1‐specific mRNA was associated with increased [3H]proline incorporation into the α‐1 and ‐2 chains of collagen type I, (b) the up‐regulation of biglycan‐ and syndecan‐1‐specific mRNA corresponded to an increased [35S]sulphate and [4,5‐3H]leucine incorporation into the biglycan molecule and to an increase of syndecan‐1 protein, (c) the up‐regulated FGF‐2 gene accounted predominantly for the ECM‐bound subfraction of FGF‐2‐protein and (d) fibronectin and thrombospondin exhibited a significantly higher mRNA level. In contrast collagen XIV, a minor collagen type, and the proteoglycan decorin were down‐regulated. The down‐regulated decorin changed its structure by elongation and reduced GlcA to IdoA epimerization of the dermatan sulphate side‐chain as judged by [35S]sulphate metabolic labelling experiments. No significant changes in response to TGF‐β1 were observed for the collagen types III, VI and XVI, for versican, perlecan and the syndecans‐2 and ‐4.

Conclusions  It was concluded from the data that the TGF‐β1‐induced formation of a highly specific multicomponent extra‐cellular matrix on coronary arterial SMCs could provide in vivo mechanical strength to the neointima in arteriosclerotic lesions and to the fibrous cap overlying the lipid core.
The immunology of parasite infections in immunocompromised hosts
Authors: EVERING T. , WEISS L. M.
Published: June 2006

Immune compromise can modify the severity and manifestation of some parasitic infections. More widespread use of newer immnosuppressive therapies, the growing population of individuals with immunocompromised states as well as the prolonged survival of these patients have altered the pattern of parasitic infection. This review article discusses the burden and immunology of parasitic infections in patients who are immunocompromised secondary to congenital immunodeficiency, malnutrition, malignancy, and immunosuppressive medications. This review does not address the literature on parasitic infections in the setting of HIV‐1 infection.
Membrane lipid alteration during phosphate starvation is regulated by phosphate signaling and auxin/cytokinin cross‐talk
Authors: Kobayashi Koichi , Masuda Tatsuru , Takamiya Ken‐ichiro , Ohta Hiroyuki
Published: June 2006

During phosphate (Pi) starvation in plants, membrane phospholipid content decreases concomitantly with an increase in non‐phosphorus glycolipids. Although several studies have indicated the involvement of phytohormones in various physiological changes upon Pi starvation, the regulation of Pi‐starvation induced membrane lipid alteration remains unknown. Previously, we reported the response of type B monogalactosyl diacylglycerol synthase genes (atMGD2 and atMGD3) to Pi starvation, and suggested a role for these genes in galactolipid accumulation during Pi starvation. We now report our investigation of the regulatory mechanism for the response of atMGD2/3 and changes in membrane lipid composition to Pi starvation. Exogenous auxin activated atMGD2/3 expression during Pi starvation, whereas their expression was repressed by cytokinin treatment in the root. Moreover, auxin inhibitors and the axr4 aux1 double mutation in auxin signaling impaired the increase of atMGD2/3 expression during Pi starvation, showing that auxin is required for atMGD2/3 activation. The fact that hormonal effects during Pi starvation were also observed with regard to changes in membrane lipid composition demonstrates that both auxin and cytokinin are indeed involved in the dynamic changes in membrane lipids during Pi starvation. Phosphite is not metabolically available in plants; however, when we supplied phosphite to Pi‐starved plants, the Pi‐starvation response disappeared with respect to both atMGD2/3 expression and changes in membrane lipids. These results indicate that the observed global change in plant membranes during Pi starvation is not caused by Pi‐starvation induced damage in plant cells but rather is strictly regulated by Pi signaling and auxin/cytokinin cross‐talk.
Factors predicting loss and gain of red cell volume in cardiac surgery patients
Authors: Slight R. D. , Bappu N. J. , Nzewi O. C. , Lee R. J. , McClelland D. B. L. , Mankad P. S.
Published: June 2006

summary.  Haemoglobin may be a poor indicator of changes in red cell volume (RCV) because of factors such as haemodilution. This study has been designed to analyse what peri‐operative variables may be associated with loss or gain in RCV due to bleeding or transfusion.

Prospective observational study.

Single centre study based in a regional cardiac surgery centre.

Twenty‐nine elective adult cardiac surgery patients.

Loss and gain of RCV were measured in theatre and for the first 24 h post‐operatively. Patient and operative factors analysed were age, sex, height, weight, body surface area (BSA), induction haematocrit (Hct), estimated pre‐operative RCV and antiplatelet therapy taken less than 7 days before operation, cardiopulmonary bypass (CPB) time, aortic occlusion time, minimum and maximum CPB temperatures and fluid administered.

Age, sex, height, weight, BSA and induction Hct were found to predict red cell transfusion but not RCV loss. The total number of red cells transfused was significantly associated with RCV lost when expressed as a percentage reduction in the estimated pre‐operative RCV but not the absolute RCV lost.

Pre‐operative RCV, as predicted by the variables outlined above, is more important than RCV lost in triggering red cell transfusion.