bluuebunny/crossref_metadata_2025 huggingface dataset:
Bridging and Nonbridging Oxygen Atoms in Alkali Aluminosilicate Glasses
Authors: Onorato Paulette I. K. , Alexander Michael N. , Struck Charles W. , Tasker G. William , Uhlmann D. R.
Published: June 2006

Thallium‐probe ion luminescence spectroscopy and X‐ray photoelectron spectroscopy were used to study the structure of sodium aluminosilicate glasses. It was demonstrated that the O1s spectral envelope for these glasses is comprised of three energetically distinct peaks, two attributed to bridging oxygen atoms (Si‐O‐Si and Al‐O‐Si) and one to nonbridging oxygen atoms (Si‐O‐Na). Both techniques indicate that nonbridging oxygen atoms are present in all sodium aluminosilicate glasses, for which A1 /Na is < 1.
Outstanding Problems in the Kaolinite‐Mullite Reaction Sequence Investigated by 29Si and 27Al Solid‐state Nuclear Magnetic Resonance: I, Metakaolinite
Authors: MacKENZIE K. J. D. , BROWN I. W. M. , MEINHOLD R. H. , BOWDEN M. E.
Published: June 2006

Structural models previously proposed for metakaolinite are examined in light of the most recent published experimental data and new information obtained by solid‐state high resolution 29Si and 27AI NMR. A new model for metakaolinite is proposed, consisting of anhydrous regions of distorted AI‐0 tetrahedra containing randomly distributed isolated residual hydroxyls associated with A1‐0 configurations of regular octahedral and tetrahedpal symmetry. Such a structure, which can readily be formed from kaolinite by the removal of hydroxyls in certain sequences, accounts for the lack of a well‐defined X‐ray pattern and the persistence of ∼10% residual hydroxyls in metakaolinite and is consistent with the most recent density data, bond lengths, and the new 29Si and 27AI NMR data.
Thermochemistry of Sodium Borosilicate Glasses
Authors: HERVIG RICHARD L. , NAVROTSKY ALEXANDRA
Published: June 2006

Glasses synthesized in the system Na20‐B 203−SiO2 were studied by high‐temperature (974 K) solution calorimetry. The sign of the heats of mixing along four joins in the ternary reflects the presence or absence of glass‐glass immiscibility. Calculations of binary phase diagrams using thermochemical data and a configurational entropy model give good agreement with experimental determinations, but complexities arise due to the simplicity of the entropy model used.
Transformation Range Behavior of Lithium Galliosilicate Glasses
Authors: PIGUET JOYCE L. , LAPP JOSEF C. , SHELBY JAMES E.
Published: June 2006

The transformation range viscosity and thermal expansion behavior of lithium galliosilicate glasses were studied. The glass transformation and dilatometric softening temperatures exhibit maxima at gallium to lithium ratios of somewhat greater than one. Similar behavior was observed for the transformation range viscosity. The effect of phase separation on the dilatometric softening temperature is discussed in detail. These results are compared with those obtained for lithium alumino‐silicate glasses in other studies. The results are discussed in terms of the structural role of aluminum and gallium in the glass network.
Crystalline Titanate Ceramic Nuclear Waste Forms: Leaching and Radiation Damage
Authors: DOSCH R. G. , NORTHRUP C. J. , HEADLEY T. J.
Published: June 2006

Leaching in the range 22° to 150°C and pH 2 to 12 was studied to assess the effects of compositional changes and processing variables on the dissolution behavior of titanate ceramic waste forms. Lead‐ion implantation was used to simulate long‐term a‐recoil damage in the crystalline titanate phases. All the titanate phases sustained significant lattice damage at equivalent a‐doses of 1 × 1019/cm3; however, Rutherford backscattering and transmission electron microscopy studies showed that the damage did not result in significant enhancement of matrix dissolution during leaching.
Mixed‐Mode Fracture of Hot‐Pressed Si3N4
Authors: PETROVIC JOHN J.
Published: June 2006

The mixed‐mode fracture of hot‐pressed Si3N4 was investigated using inclined indentation surface flaws in bending and large crack geometries in combined tension/torsion. Non‐coplanar fracture was observed in all cases. Values of KIc, KIIc, and KIIIc stress intensity factors were obtained, with ratios KIIc/KIc= 0.79 and KIIIc/KIc= 1.55 observed. For large cracks, mode II conditions had more of an effect on mode I fracture than mode III conditions. The mixed‐mode I‐II fracture of surface flaws was significantly different from that for large cracks, suggesting surface flaw shear resistance effects. A model describing these effects was derived, based on the ratio of the crack‐opening displacement to the crack surface asperity height.
Demixing of Materials under Chemical Potential Gradients
Authors: ISHIKAWA TAKUMA , SATO HIROSHI , KIKUCHI RYOICHI , AKBAR S. A.
Published: June 2006

A steady‐state demixing of initially homogeneous solid solution which occurs in binary oxides under oxygen partial pressure gradient is treated by the path probability method of irreversible statistical mechanics from an atomistic point of view. The larger the difference between the diffusion coefficients of constituent species is, the larger is the degree of demixing. Essential features of demixing by diffusion, however, do not depend on whether the driving force is the chemical potential gradient, the electric field, or others.
Reversible Optical Change of Amorphous Red Phosphorus in Reduced Phosphate Glasses
Authors: HOSONO HIDEO , SATAKE TAKEHIKO , HOSOE MASAHIRO , ABE YOSHIHIRO
Published: June 2006

Amorphous red phosphorus formed in reduced phosphate glasses was found to show a photodarkening effect by illuminating the glasses with light approximately equivalent to its absorption edge; the optical transmission edge shifts toward longer wavelengths on illumination, and then a distinct deepening of the reddish color is observable visually. The photo‐darkened specimen recovers its original transmission when it is heated at 300° to 350°C. This darkening‐restoring process is confirmed to be reversible by repeated illumination and heating. Transmission measurements over a range of elevated temperatures suggest that this optical characteristic of red phosphorus is unique to its amorphous state.
Sharp vs Blunt Crack Hypotheses in the Strength of Glass: A Critical Study Using Indentation Flaws
Authors: LAWN BRIAN R. , JAKUS KARL , GONZALEZ ARMANDO C.
Published: June 2006

The fundamental question as to whether the tip structure of brittle cracks is atomically sharp or has a rounded contour is examined in relation to current descriptions of strength‐controlling flaws. The distinction between the two opposing viewpoints lies in the controlling flaw dimensions in the strength formulation; crack length in the first and tip radius in the second. Definitive evidence on the issue is obtained from aging tests on soda‐lime glass, using indentations as controlled flaws. An increase in the inert strength is observed with increased exposure of the newly created flaws to moist environments prior to stressing to failure. This strength increase saturates after approximately 1 day, depending on the environmental species. The trend mirrors that reported by Mould in an earlier aging study on abrasion flaws. However, whereas Mould concluded that the strengthening must be due to tip rounding, the present tests reveal that the indentation‐induced cracks actually extend during the aging period. A fracture mechanics analysis shows that such extension relaxes residual crack‐opening stresses associated with the central contact deformation zone. It is accordingly concluded that the cracks remain sharp throughout their postindentation evolution; the influence of extraneous conditions on the strength is manifested only through the driving forces on these cracks. Flaws which have been annealed (i.e., which have had their residual driving forces removed) show no such aging effects. The fracture mechanics analysis also shows that in the region of saturated aging, where the indentation cracks appear to stop growing, the fracture driving force is in the region of the zero‐velocity threshold described in the macroscopic crack growth studies by Michalske. Contrary to previous interpretation, the indication is that the cracks do not blunt out in this region, for otherwise the strengthening would steepen rather than level out. Implications of this result concerning the inviolate nature of basic crack growth laws are discussed.
Structure and Ionic Mobility of Zirconia at High Temperature
Authors: ALDEBERT PIERRE , TRAVERSE JEAN‐PIERRE
Published: June 2006

The high‐temperature structure of zirconia was studied by powder neutron diffraction up to 2400°C. The boundaries of the domain of the nonstoichiometric tetragonal form are defined. They are consistent with a tetragonal‐cubic transition at 2350°C for stoichiometric zirconia. The changes in the structural parameters of the tetragonal form (unit‐cell, positional parameters and thermal B factors) with temperature give evidence of medium zirconium and oxygen mobilities. The oxygen ions are, however, always more mobile than the zirconium ions. An enhancement with temperature of the structural an‐isotropy tends to weaken the weaker of the two distinct Zr‐0 bonds of the tetragonal zirconia. It results in the transformation into the cubic form which is accompanied by a change in unit‐cell volume; this change becomes sharper as the composition tends toward stoichiometry. This transition is probably followed by an increase of the ionic mobility.
Gas Sensing Characteristics of Porous ZnO and Pt/ZnO Ceramics
Authors: SAITO SHINICHIRO , MIYAYAMA MASARU , KOUMOTO KUNIHITO , YANAGIDA HIROAKI
Published: June 2006

Changes in resistivity and chemical changes in reducing gases were measured for porous zinc oxide ceramics with and without a platinum catalyst at 300° and 400°C to examine the gas sensing mechanism and the effect of platinum additions. Reducing gases were oxidized to CO2 and Hz2 on the sensor surfaces. Platinum addition promoted the oxidation of reducing gases but did not lead to an increase in the resistivity change at 400°C. The reaction sequences for the gas sensing process are proposed, taking into account partially oxidized intermediates of hydrocarbons and oxidation on platinum without an electron transfer process.
Impact Fracture of Thermally Tempered Glass Helicopter Windshields
Authors: el Leil Mahmoud M. Abou , Camaratta Frank A. , DiGenova Rocco R.
Published: June 2006

In‐service fracture of helicopter windshields was studied. Simulated catastrophic fracture tests were conducted by firing alumina and steel spheres onto stationary tempered and as‐received glass panels. The results were studied by Hertzian analysis and modified Auerbach's relations. Thermally tempered glass shows much higher impact resistance than that estimated from superposition of residual stresses. Subcritical impact sites exhibit slow crack growth in tempered plates, eventually leading to fracture of the entire plate.
Microstructural Characterization of Synroc C and E by Electron Microscopy
Authors: COOPER J. A. , COUSENS D.R. , LEWIS R.A. , MYHRA S. , SEGALL R.L. , SMART R.S.T.C. , TURNER P. S. , WHITE T. J.
Published: June 2006

High‐resolution electron microscopy, analytical electron microscopy, and scanning electron microscopy were used to examine the microstructure and chemistry of the titania‐based nuclear waste ceramics Synroc C and Synroc E. The mineral assemblages of these formulations are dependent upon the level of radwaste incorporation. The principal phases identified are zirconolite, zirkelite, pyrochlore, polymignyte, perovskite, hollandite, magnetoplumbite, and intermetallic alloys. Thin intergranular films and “glassy” triple points were found to exist between different phases. In Synroc formulations containing a large excess of TiO2 the radwaste‐containing minerals are embedded in an inert, continuous rutile matrix; this microencapsulation operates at the level of 10 to 20 nm. Backscattered electron images suggest that the distribution of radwaste ions may not be completely homogeneous throughout the ceramic.
Low‐Activation‐Energy Conduction in Polycrystalline α‐AI2O3 Doped with Si and Na
Authors: LEE C. H. , KRÖGER F. A.
Published: June 2006

Polycrystalline AI2O3 containing a glassy aluminosilicate second phase displays a low‐activation‐energy conductivity when Na is present. The conductivity is ionic in nature at high oxygen pressure and electronic at low oxygen pressure and is attributed to the migration of Na+ ions and electrons through the second phase present at triple junctions. A smaller low‐activation‐energy conductivity is found in the absence of sodium, but in that case the low‐activation‐energy branch has different properties. AI2O3:Na without silicon bas no low‐temperature low‐activation‐energy branch.
Segregation of Isovalent Impurity Cations at the Surfaces of MgO and CaO
Authors: TASKER P. W. , COLBOURN E.A. , MACKRODT W.C.
Published: June 2006

Enthalpies of segregation for isovalent impurities in magnesium and calcium oxide as a function of surface concentration were calculated by using an atomistic computer simulation method. We have considered Be2+, Mg2+, Ca2+, Ba2+, and Ni2+, segregating to both (001) and (110) faces. The results obtained can be extrapolated to predict the behavior of other impurities including Mn2+, Fe2+, and Co2+, We find, for example, that Fe2+, Mn2+, Ca2+, Sr2+, and Ba2+ will concentrate at the (001) surface of MgO, while Ni2+ will be depleted. The enthalpy of segregation is found to vary substantially with coverage particularly for the larger impurities. The enthalpy becomes less negative with increasing impurity concentration due to the increasing lattice strain until the surface is nearly saturated. Then additional stabilization is obtained by restructuring of the surface layer. We predict reconstructed surfaces for both the (001) and (110) faces, which contain a high concentration of a larger impurity ion. The enthalpy of segregation shows a maximum at around 50% surface coverage implying a bimodal surface distribution of segregant. The influence of segregation on surface energy suggests two unusual effects. The (001) surface energy of the impure crystal becomes negative for surface concentrations of impurity greater than 10% Ba2+ or 75% Sr2+ in MgO. This implies a thermodynamic barrier to sintering. At high coverages of Ba2+ in MgO the (110) surface becomes more stable than the (001) face suggesting that facetting may occur.
A New Method of Making Titania Gels and Their Microstructure
Authors: KOMARNENI SRIDHAR , ROY RUSTUM , BREVAL ELSE
Published: June 2006

The reaction of H2O2 with alkoxides results in aerohydro gels of titania. These gels appear to form by a complex polymerization process involving peroxy species. The gels are porous and appear to have a fibrillar microstructure.
Phase Equilibrium in the System Li2O‐Na2O‐Al2O3‐SiO2
Authors: Badger William B. , Hummel Floyd A.
Published: June 2006

To establish phase relations in the quaternary system Li2O‐Na2O‐Al2O3‐SiO2, the 50, 60, 70, 80, and 90 wt% isosilica planes were examined, mainly by quenching of quaternary glass compositions.
Glass Transition Temperatures at Rapid Heating Rates
Authors: Twiggs S.W. , Ringle R.D. , Morena R. , Fairhurst C. W.
Published: June 2006

Glass transition temperatures (Tg) determined at high rates of heating or cooling are essential for applications involving stress relief during cooling from firing of glass‐to‐metal seals and dental restorations. The measurement of Tg at heating rates as high as 600°C min−1 is reported. These high‐rate data, when combined with previously reported low‐rate (≤20°C min‐1) values, indicate that the Arrhenius‐type relation between Tg and heating or cooling rate is maintained into the high‐rate regime.
Preparation of Zirconia‐Alumina Powders by Zirconium Alkoxide Hydrolysis
Authors: Fegley Bruce , White Paul , Bowen H. Kent
Published: June 2006

Zirconia‐alumina powders were prepared by controlled hydrolysis of zirconium propoxide in a dispersion of a‐alumina powder in anhydrous 100% ethanol. Transmission electron micrographs show a “fluffy” zirconia coating on the alumina particles. Chemical analyses by four methods demonstrated that the procedure is reproducible and introduces only low impurity levels.
Analysis of Indentation Crack as a Wedge‐Loaded Half‐Penny Crack
Authors: Shetty Dinesh K. , Rosenfield Alan R. , Duckworth Winston
Published: June 2006

Surface cracks produced by indentation with a Vickers indenter were modeled as half‐penny cracks extended by symmetric disk‐shaped wedges. The wedge diameter was assumed to be equal to the hemispherical plastic zone size, and the wedge thickness was calculated by equating the wedge volume to the hardness‐impression volume. The resulting equilibrium relation between the indentation load and the radius of the half‐penny crack is in good quantitative agreement with similar relations obtained from fracture toughness calibration.
Temperature‐Dependent Phase Boundaries for BaTi409, Ba4Ti13030, and Ba6Ti17040
Authors: O'Bryan Henry M. , Thomson John
Published: June 2006

The phase boundaries of BaTi4O9 and Ba4Ti13O40 are temperature dependent and curve toward BaTiO3 above 1250°C. The appearance of a barium‐rich surface phase during slow cooling is a sensitive indicator of a temperature‐dependent boundary. For both compounds the surface phase which is barium‐rich and has u strong X‐ray peak at d=0.232 nm. No surface phase was detected on Ba6Ti17O40; therefore, its phase boundary is independent of temperature.
Characterization of Corrosion Mechanisms Occurring in a Sintered Sic Exposed to Basic Coal Slags
Authors: FERBER M. K. , OGLE J. , TENNERY V. J. , HENSON T.
Published: June 2006

The high‐temperature reactions occurring between an a‐Sic and a basic coal slag were examined. The resulting corrosion behavior was found to involve at least three mechanisms, including passivation of the Sic via SiO2 formation, dissolution of the SiO2 by the coal slag, and formation of a localized Fe‐Ni silicide. This mechanism, which dominated when the slag thickness exceeded 100 μm, was also responsible for the degradation in high‐temperature strength.
Durability of Glass‐Fiber‐Reinforced Cements with Different Alkali‐Resistant Glass Fibers
Authors: BENTUR A. , BEN‐BASSAT M. , SCHNEIDER D.
Published: June 2006

The durability of glass‐fiber‐reinforced cement composites prepared with different commercial alkali‐resistant glass fiber strands was studied to determine the effect of aging in different environments on the flexural behavior of the composites and on their microstructure. Considerable differences in degradation of mechanical properties could be observed in composites prepared with different glass fiber strands, and they could be correlated with the SEM observations: higher rates of degradation were obtained in composites in which hydration products grew more readily between the glass filaments. It is suggested that during the first year of aging in water at 207deg;C, this growth of hydration products is mainly responsible for the reduction in mechanical properties; chemical degradation of the glass does not play an important role, at least not at this earlier stage.
Crystallization Behavior of a High‐Zinc‐Content Li2O‐ZnO0‐SiO2 Glass‐Ceramic and the Effect of K2O Additions
Authors: CHEN ZU‐XIONG , McMILLAN P. W.
Published: June 2006

The crystallization behavior of an Li2O‐Zn0‐SiO2 glass with a ZnO content of −28.5 wt% and nucleated with P2O5 was investigated by infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. A three‐stage process, consisting of the nucleation, crystallization, and transformation of Li3Zn0.5Si04 and the emergence of a silica phase, occurs during heat treatment of this system. A small addition of K2O varies the sequence of crystallization and the phase composition of the resulting glass‐ceramic.
Interface‐Reaction‐Controlled Kinetics in the Hot Isostatic Pressing of Submicrometer Alumina Powder
Authors: Wills Roger R. , McCoy John Kevin
Published: June 2006

The kinetics of densification of alumina powder compacts at 1000° to 1200°C were studied by using a dilatometer to monitor volumetric changes during hot isostatic pressing. The densification rate is proportional to the square of the applied pressure, and densification does not occur below a threshold pressure. Results are interpreted in terms of an interface‐controlled reaction mechanism involving the movement of grain‐boundary dislocations.
High‐Temperature Mechanical Properties and Microstructures for Hot‐Pressed Silicon Nitrides with Amorphous and Crystalline Intergranular Phases
Authors: Knickerbocker Sarah H. , Zangvil Avigdor , Brown Sherman D.
Published: June 2006

Four‐point flexure tests were performed at 1100° to 1350°C on two hot‐pressed silicon nitrides, one in which the grain‐boundary phase was amorphous and one in which it was largely crystalline. Fracture stress and relative K1c were plotted vs temperature. Fracture regions were analyzed by scanning and transmission electron microscopy. Grain‐boundary phases affected high‐temperature fracture significantly.
Oxidation and Reduction of Palladium in the Presence of Silver
Authors: Cole Sandford S.
Published: June 2006

The silver/palladium ratio, alloy form, and heating rate cause significant changes in the oxidation and reduction behavior of palladium powder as determined by thermogruvimetric analysis. Surface area and airflow had little effect on oxidation and reduction. Possible models to explain the changes are considered.
Kinetics of Liquid Spreading and Penetration with Application to RuO2−Glass Thick‐Film Resistors
Authors: SARMA D. H. R. , VEST R. W.
Published: June 2006

The rate of spreading of a spherical liquid droplet on a flat substrate is analyzed using the time‐dependent contact angle approach. The constants in the contact angle development equation are explicitly related to physical parameters. Normalized rate of spreading is shown to be independent of the volume of the liquid droplet. A general capillary flow equation incorporating the time‐dependent contact angle is used to analyze the kinetics of infiltration of the glass phase into the conductive phase in RuO2/lead‐horosilicate‐glass thick‐film resistors. The dependence of the kinetics on temperature, interparticle separation, and dissolved alumina content of the glass are discussed with reference to microstructure development in these resistors.
Thermal Reactions of Pyrophyllite Studied by High‐Resolution Solid‐state 27Al and 29Si Nuclear Magnetic Resonance Spectroscopy
Authors: MacKENZIE K. J. D. , BROWN I. W. M. , MEINHOLD R. H. , BOWDEN M. E.
Published: June 2006

Water is lost in two overlapping steps from well‐crystallized pyrophyllite from Coromandel, New Zealand. The pyrophyllite structure survives the loss of the first 30% of the total water content, but the loss of a further 60% water in the second step results in the formation of pyrophyllite dehydroxylate, with corresponding changes in both the 29Si and 27Al solid‐state NMR spectra. Detailed analysis of the 29Si chemical shift of the dehydroxylate has allowed the silicate layer structure of this phase to be refined. A similarly detailed interpretation of the 27A1 spectra is not possible because of electric field gradient effects which result in the loss of ∼90% of the A1 spectral intensity due to the formation of five‐coordinate A1 on dehydroxylation. The loss of further water from the dehydroxylate on further heating results in the formation of mullite and cristobalite and is accompanied by changes in the 29Si and 27Al spectra which can be accounted for in terms of coordination changes in the structural regions which contained the residual hydroxyls.
Influence of Gluconate, Lignosulfonate, and Glucose Admixtures on the Hydration of Tetracalcium Aluminoferrite in the Presence of Gypsum with or without Calcium Hydroxide
Authors: Collepardi M. , Monosi S. , Moriconi G. , Pauri M.
Published: June 2006

The influence of 0.3 wt% gluconute, lignosulfonate, or glucose on the hydration of 4CaO·A12O3‐Fe2O3 in the presence of gypsum with or without Ca(OH)2, was examined. In the absence of Ca(OH)2 all the admixtures retard both ettringite production and subsequent conversion of ettringite into the monosulfate in the decreasing order glucose >lignosulfonate >gluconate. In the presence ofCa(OH)2 all the admixtures accelerate early ettringite production but do not affect subsequent conversion of ettringite into the monosulfate, at least up to 28 d.
Reaction Between Ti‐6Al‐4V and Boron
Authors: Steeds John W. , Rhodes Cecil G.
Published: June 2006

The present report describes the investigation by electron diffraction of the reaction between boron and Ti‐6Al‐4V. Plates that are intergrowths of TiB and VB were discovered.
Thermal Expansion Behaviro of single‐Crystal Zirconia
Authors: Adams Jane W. , Nakamura H. Henry , Ingel Robert P. , Rice Roy W.
Published: June 2006

Thermal expansion was measured for skull‐melt‐grown undoped single‐crystal zirconia as well as for crystals containing 2.8 wt% MgO, 4 wt% CaO, and 3 to 20 wt% Y2O3. Samples were cycled in air from room temperature to 1500°C. The partially stabilized samples experienced a phase transformation which was strongly dependent on the composition and phase structures present; fully stabilized materials exhibited uniform behavior throughout the heating/cooling cycle.
Synthesis of Hf1‐x, Zrx02 (O<x<1) with Orthorhombic Symmetry
Authors: Suyama Ryuji , Takubo Hiroshi , Kume Shoichi
Published: June 2006

Three starting materials, Hf1‐xZrxO2 (x =0.24, 0.50, 0.74), were prepared and treated at 600°C and 6 GPa for 30 min. X‐ray powder diffraction patterns of the products indicated only orthorhombic HfO2. The lattice parameters increased linearly as x approached 1 (ZrO2); a continuous solid‐solution series was observed.
Measurement of Cation Diffusion in Silica Light Guides
Authors: Fleming James W. , Kurkjian Charles R. , Paek Un‐Chul
Published: June 2006

Germanium and phosphorus diffusion were studied in binary GeO2‐SiO2 and P2O5‐SiO2 core light guides. Variations in composition profile shape with heat treatment were measured by an energy‐dispersive X‐ray analysis method. These data were fitted to a solution of Fick's second law to obtain diffusion data. No change in germanium profiles was detected for heat treatments of several months at 1200°C, indicating very low Ge mobility. However, phosphorus exhibited significant movement for the heat‐treatment times and temperatures used.
Sintering and Microstructure Formation of β‐Silicon Carbide
Authors: STUTZ DORIS H. , PROCHAZKA SVANTE , LORENZ JOSEF
Published: June 2006

The effect of additions of B, Al, and B + Al on the pressureless sintering of β‐Sic was examined. The influence of the sintering atmosphere and heating schedule on densification behavior, polytype transformation, and microstructure development was also studied. High densities were obtained at 1940°C by the simultaneous addition of B and Al. The decrease in the sintering temperature is attributed to the presence of a liquid phase which results in the formation of platelets (up to 200 # in size) of an α‐polytype, predominantly 4H and 6H. Polytype transformation and exaggerated grain growth could be prevented by annealing the compact at 1650° to 18500°C for 0.5 to 1 h. This procedure results in a better redistribution of the sintering aids, giving a fine‐grained microstructure, constituted primarily of the cubic 3C polytype.
Electrical Conductivity of PbO‐P2O5‐V2O5Glasses
Authors: HIRASHIMA HIROSHI , ARAI DAIKICHI , YOSHIDA TETSURO
Published: June 2006

The dc conductivities (α) of PbO‐P2O5‐V2O5 glasses containing up to 80 mol% V2O5 were measured at T = 100°C to T = 10°C below the glass transition temperature. Dielectric constants at 1 MHz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism of glasses containing >10 mol% V2O5 was considered to be small‐polaron hopping, as previously reported for other vanadate glasses. The temperature dependence of α was exponential, with α= (αo/T) exp(−W/kT). When the V2O5 content was ≥50 mol%, W decreased and α increased with increasing V2O5 content, and the adiabatic approximation could be applied. In the composition range between 10 and 50 mol% V2O5, α increased with increasing V2O5 content, but W varied little. In this region, the hopping conduction was characterized as nonadiabatic. The effect of dielectric constants and V ion spacing on W is discussed.
Germanium Kα1,2 Shifts Due to Coordination
Authors: FUKUSHIMA SEI , BAI YOU‐ZHAO , GOHSHI YOHICHI , YIN CHENG‐DONG , MORIKAWA HIDEKI , MARUMO FUMIYUKI
Published: June 2006

The K α1,2 lines emitted from Ge in germanium oxide compounds showed energy shifts (∼0.07 eV) resulting from changes in the coordination state of Ge. Based on the results of high‐resolution X‐ray fluorescence spectrometry and theoretical calculations using the molecular orbital theory (DV‐Xα method), it was confirmed that fourfold‐coordinated Ge emits lower energy Kα1,2 lines than sixfold‐coordinated Ge. Theoretical calculations show that this shift is caused by a change in the effective charge of Ge due to the number of nearest‐neighbor atoms.
Pressure‐Temperature Phase Diagram of Zirconia
Authors: BLOCK S. , DA JORNADA J. A. H. , PIERMARINI G. J.
Published: June 2006

The pressure‐temperature phase diagram of zirconia was determined by optical microscopy and X‐ray diffraction techniques using a diamond anvil pressure cell. At room temperature, monoclinic ZrO2 transforms to a tetragonal phase (tII) which is related to the high‐temperature tetragonal structure (tI). The transformation pressure exhibits hysteresis and is cycle dependent. At room temperature, the initial transformation pressure for the monoclinic‐tII transition on a virgin monoclinic crystal can be as high as 4.4 GPa; on subsequent cycling the transition pressure ultimately lowers to 3.29 ± 0.06 GPa. The pressure for the reverse transition is essentially constant at 2.75 ± 0.06 GPa. At pressures > 16.6 GPa, the tII form transforms to the orthorhombic cotunnite (PbCl2) structure. With increasing temperature, the tII form transforms to the high‐temperature tetragonal phase. For increasing P and T, the monoclinic‐tI‐tII triple point is located at T= 596°± 18°C and P= 2.26 ± 0.28 GPa, whereas for decreasing P and T, the triple point is found at T= 535°± 25°C and P= 1.7 ± 0.28 GPa.
Effect of Ba: Ti Ratio on Densification of LiF‐Fluxed BaTiO3
Authors: Tolino DAVID A. , Blum John B.
Published: June 2006

The literature on LiF‐fluxed BaTiO3 has shown substantially lower sintering temperatures compared to that of unfluxed BaTiO3. In an effort to understand densification behavior in this system, shrinkage was studied for various Ba: Ti ratios and 2 wt% LiF additions. Sintering of BaTiO3 with LiF is sensitive to the Ba:Ti ratio. Excess Ba reduced the sintering temperature and increased the fired bulk density. The starting powder stoichiometry, net Ba:Ti ratio, and addition of LiF appear to be independently important.
Microstructure and Electrical Properties of Sodium‐Diffused and Potassium‐Diffused SrTiO3 Barrier‐Layer Capacitors Exhibiting Varistor Behavior
Authors: Fujimoto Masayuki , Chiang Yet‐Ming , Roshko Alexana , Kingery W. David
Published: June 2006

In sodium‐diffused strontium titanate internal‐boundary‐layer capacitors exhibiting good varistor properties, high‐resolution transmission electron microscopy and scanning transmission electron microscopy revealed sodium segregation at grain boundaries in the absence of intergranular phases. The segregation layer is narrow (≅10 nm), unlike much broader diffused boundary layers which have also been observed. The nonohmic behavior in these and in potassium‐diffused specimens suggests that segregated acceptor alkali ions act as grain‐boundary electron traps leading to varistor electrical barriers.
Dopant‐Free Ultraviolet‐Sensitive Calcium Aluminate Glasses
Authors: Hosono Hideo , Yamazaki Koji , Abe Yoshihiro
Published: June 2006

Dopant‐free calcium aluminate glasses are very sensitive to ultraviolet radiation; new optical absorption bands rapidly appear around 400 nm on illumination and are easily bleached when the glass is heated to >100° to 250°C. This coloringbleaching process is reversible when the illumination and heating cycles are repeated, A clear correlation was found between the intensities of the uv‐induced optical absorption and the ESR signal of Al‐OHC.
Duality in the Creep Rupture of a Polycrystalline Alumina
Authors: DALGLEISH B.J. , SLAMOVICH E.B. , EVANS A.G.
Published: June 2006

Creep rupture experiments performed on a polycrystalline alumina have revealed a duality in fracture behavior associated with a crack blunting threshold. At high stresses, or in the presence of large preexisting flaws, fracture is dictated by the slow creep growth of flaws and exhibits substantial statistical variability. At lower stresses, preexisting flaws blunt, and failure is delayed. In this regime, failure occurs by the coalescence of creep damage, manifested as shear bands, and the failure strain becomes inversely dependent on the applied stress.
Grain‐Boundary Characteristics and Their Influence on the Electrical Resistance of Barium Titanate Ceramics
Authors: KOSCHEK GEORG , KUBALEK ERICH
Published: June 2006

The integral and spectral cathodoluminescence (CL) properties of grain‐boundary zones in positive‐temperature‐coefficient‐type barium titanate ceramics were investigated with respect to typical sintering parameters in the spectral range 300 to 1800 nm at room temperature. Spatially resolved CL micrographs for the wavelength range 300 to 850 nm show dark grain‐boundary zones and light grain interiors. Corresponding micrographs for the infrared wavelength range 800 to 1800 nm show just the opposite CL contrast. The CL properties of the grain‐boundary zone can be correlated to doubly ionized barium vacancies. Therefore, grain‐boundary zones which are visible in integral CL images of both wavelength ranges represent the theoretically predicted grain‐boundary zone of high barium vacancy concentrations. The width of these grain‐boundary zones varies characteristically with sintering time and cooling rate. Additional measurements of the electrical conductivity of the specimens confirmed the theoretically assumed correlation between grain‐boundary‐zone width and electrical resistance of the samples.
Acoustic and Elastic Properties of PZT Ceramics with Anisotropic Pores
Authors: KAHN M.
Published: June 2006

It has been shown that anisotropic porosity in PZT reduces the d31/d33, ratio, raising the hydrostatic piezoelectric response of PZT significantly. In the present work, this behavior is related to Poisson's ratio by applying the Gibbs thermodynamic energy function, literature data for dense PZT ceramics and for materials with hexagonal crystal symmetry, and experimental results for PZT with anisotropic porosity. Acoustic as well as mechanical tests of PZT ceramics with anisotropic pores demonstrate the elastic anisotropies that cause the reduction in Poisson's ratio. The dependence of d31/d33 on Poisson's ratio is also detailed. In addition, a close relation between d31/d33 and the longitudinal acoustic velocity is demonstrated. Flexural strength tests indicate that anisotropic pores provide dhn‐enhanced PZT ceramics with significantly greater strength than isotropic pores.
An evaluation of a brief motivational intervention among young ecstasy and cocaine users: no effect on substance and alcohol use outcomes
Authors: Marsden John , Stillwell Garry , Barlow Helen , Boys Annabel , Taylor Colin , Hunt Neil , Farrell Michael
Published: June 2006

Aims  To investigate whether a stimulant‐ and alcohol‐focused brief motivational intervention induces positive behaviour change among young, regular users of MDMA (‘ecstasy’), cocaine powder and crack cocaine.

Design and measurements  A randomized trial of the intervention versus a control group who received written health risk information materials only. All participants completed a baseline self‐assessment questionnaire before randomization. Outcome measures were self‐reported period prevalence abstinence from ecstasy, cocaine powder and crack cocaine and the frequency and amount of stimulant and alcohol use in the previous 90 days, recorded at 6‐month follow‐up via self‐completion questionnaire and personal interview.

Participants and setting  A total of 342 adolescent and young adult stimulant users (aged 16–22 years) were recruited and 87% were followed‐up. The intervention was delivered by a team of 12 agency youth drug workers and two researchers at five locations in Greater London and south‐east England.

Findings  There were no significant differences in abstinence for ecstasy, cocaine powder or crack cocaine use between the experimental and control groups. Contrasting follow‐up with baseline self‐reports, there were no between‐group effects for changes in the frequency or amount of stimulant or alcohol use. Participant follow‐up data suggested that the baseline assessment was a contributing factor in within‐group behaviour change among experimental and control condition participants.

Conclusions  Our brief motivational intervention was no more effective at inducing behaviour change than the provision of information alone. We hypothesize that research recruitment, baseline self‐assessment and contact with study personnel are influences that induce positive reactive effects on stimulant use.
A match–mismatch test of a stage model of behaviour change in tobacco smoking
Authors: Dijkstra Arie , Conijn Barbara , De Vries Hein
Published: June 2006

Aims  An innovation offered by stage models of behaviour change is that of stage‐matched interventions. Match–mismatch studies are the primary test of this idea but also the primary test of the validity of stage models. This study aimed at conducting such a test among tobacco smokers using the Social Cognitive Stage Model.

Design  A match–mismatch field‐experiment was conducted in which smokers and ex‐smokers in different stages were assigned randomly to one of three information conditions.

Participants  Smokers in the pre‐contemplation stage, the contemplation stage and the preparation stage, and ex‐smokers in the action stage (n = 481), who were recruited through mass media, were assigned randomly to one of three information conditions.

Intervention  In each of the three information conditions, participants received a four‐ to six‐page computer‐tailored letter designed to: (1) increase the positive outcome expectations of quitting, (2) decrease the negative outcome expectations of quitting or (3) increase self‐efficacy.

Measurements  Forward stage transition was the primary outcome measure, which was assessed 2 months after the participants received the information.

Findings  At the 2‐month follow‐up, the matched interventions were significantly more effective in stimulating forward stage transition (44.7%) than were mismatched interventions (25.8%; odds ratio = 2.78; confidence interval = 1.85–4.35).

Conclusion  The present study provides experimental support for the benefits of stage‐matching and for the validity of the Social Cognitive Stage Model.
The long and the short of it: evidence that FGF5 is a major determinant of canine ‘hair’‐itability
Authors: Housley D. J. E. , Venta P. J.
Published: June 2006

Hair length in dogs has been known for many years to be primarily controlled by a limited number of genes, but none of the genes have been identified. One of these genes produces a recessively inherited long‐haired phenotype that has been thought to explain the bulk of hair‐length variation among many breeds. Sequence analysis of the FGF5 gene in short and long‐haired corgis resulted in the identification of two coding region differences: a duplication in a relatively non‐conserved region of the gene and a missense mutation, resulting in the substitution of Phe for Cys, in a highly conserved region. Genotyping of 218 dogs from three breeds fixed for long hair, eight breeds fixed for short hair and five breeds in which long hair is segregating provided evidence that the missense mutation is associated with the hair‐length differences among these breeds.
Chicken major histocompatibility complex class II molecules of the B19 haplotype present self and foreign peptides
Authors: Cumberbatch J. A. , Brewer D. , Vidavsky I. , Sharif S.
Published: June 2006

The chicken major histocompatibility complex (MHC), or B‐complex, mediates genetic resistance and susceptibility to infectious disease. For example, the B19 haplotype is associated with susceptibility to Marek's disease. Here, we describe the sequencing and analysis of peptides presented by B19 MHC class II molecules. A B19/B19 B‐cell line was used for the immunoaffinity purification of MHC class II molecules, which was followed by acid elution of the bound peptides. The eluted peptides were then analysed using tandem mass spectrometry. Thirty peptide sequences were obtained, ranging from 11 to 25 amino acids in length. Source protein cellular localization included the plasma membrane, cytosol and endosomal pathway. In addition, five peptides from the envelope glycoprotein of chicken syncytial virus (CSV) were identified. Chicken syncytial virus had been used as a helper virus along with reticuloendotheliosis virus strain T for transformation of B19/B19B cells. Alignment and analysis of the peptide sequence pool provided a putative peptide‐binding motif for the B19 MHC class II.
Health, economy and social capital in Nordic children and their families: a comparison between 1984 and 1996
Authors: Berntsson L. , Köhler L. , Vuille J.‐C.
Published: June 2006

Objective  The aim of the study was to analyse the development in the health of children that occurred in the five Nordic countries (Denmark, Finland, Iceland, Norway and Sweden) between 1984 and 1996 and relate it to the changes in economic growth and social capital in these countries during the same period.

Methods  Two cross‐sectional studies covered a representative sample of children, aged 2–17 years in each country, a total of 10 291 in 1984 and 10 317 in 1996. The data were collected by mailed questionnaires. Statistical associations between a health indicator (the absence of psychosomatic complaints), economic indicators (social class, housing and disposable income) and social capital indicators (parents’ and children’s organized group activities, parents playing with their children and the absence of bullying) within samples and between corresponding values in different samples across subgroups (defined by country and area of residence) were evaluated using multiple linear regression.

Results  In both surveys, there was a statistically highly significant association between the health indicator and the social capital indicators, whereas the economy indicators were not related to either of the other two types of measure. Change in health was associated positively with change in social capital and negatively with change in economy.

Conclusion  The study provides strong support for the concept of social capital as an important determinant of children’s health.
Children’s cortisol levels and quality of child care provision
Authors: Sims M. , Guilfoyle A. , Parry T. S.
Published: June 2006

Background  Cortisol levels are increasingly being used as an indicator of stress levels. Research suggests that children who attend child care demonstrate higher cortisol levels than children in their homes, suggesting that child care acts as a risk factor for poor child outcomes. However, it is also suggested that quality influences outcomes.

Methods  Cortisol levels were measured through samples of saliva taken from children (3–5 years of age) attending long‐day care centres in Perth, Western Australia. Quality of the programme was measured using industry national quality assurance indicators designed for child care centres. The analysis employed a 2 (time of collection: average am cortisol, average pm cortisol) by 3 (centre quality: high, satisfactory, unsatisfactory) split plot anova with repeated measures on the time factor.

Results  Cortisol levels of children attending high‐quality programmes demonstrated a decline across the child care day. Levels in children attending unsatisfactory programmes demonstrated an increase across the day.

Conclusions  Although we do not yet know how high, and for how long, cortisol levels need to be elevated for risk of undesirable outcomes to increase, this research signals the importance of emphasizing the need for high‐quality care for young children.
Towards a typology of specific language impairment
Authors: Cundall David
Published: June 2006

.
 
Van Weerdenburg M.,
Verhoeven L. &
Van Balkom H.
(
2006
)

,
47
,
176
–
189
.

Background  The population of children with specific language impairments (SLI) is heterogeneous.

Objective  To examine this heterogeneity more closely, by identifying and describing subgroups within the population of children with SLI in the Netherlands.

Method  A broad battery of language tests and language‐related cognitive tests were administered to 147 6‐year‐old and 136 8‐year‐old children with SLI.

Results  Factor analysis revealed four factors indicating four distinct linguistic domains for both age samples: (i) lexical‐semantic abilities; (ii) auditory conceptualization; (iii) verbal sequential memory; and (iv) speech production. These empirical findings were further validated by the positive correlations found between the language factors and the judgements of teachers and speech therapists. Finally, a cluster analysis revealed four distinct clusters of SLI children for each sample with specific language profiles based on the four clusters.

Conclusions  The language problems that emerged from the two samples of children with SLI could be described as falling into four types. Based on these language types, four subgroups of children with SLI could be distinguished, each with a separate profile. Some subgroups had severe problems on one specific type of language problem; others had severe problems in more than one type of language problem when compared with the other subgroups in the same age sample. The different profiles may indicate a more dynamic approach is needed in intervention, considering the presence of both compensating and restricting factors within each child with SLI.