bluuebunny/crossref_metadata_2025 huggingface dataset:
Sintering of Ultrafine Silicon Powder
Authors: MÖLLER H.‐JOACHIM , WELSCH GERHARD
Published: June 2006

The sintering behavior of compacts of ultrafine silicon powder (0.02 to 0.1 μm particle size) was investigated. Two sintering modes occur: normal sintering associated with densification and subnormal sintering without densification. The micro‐structure developed in normal sintering has a fine grain size (0.05 to 0.3 μm) and fine porosity; the grains contain stacking faults and twins. The microstructure developed in subnormal sintering exhibits larger grains (∼1 μm in size) and coarse pores. Green densities >42% of theoretical and temperatures >1100°C are required for densification. Densification follows an exponential time and temperature dependence with an activation energy of 470 kJ/mol, indicating bulk diffusion as the transport mechanism. Grain‐boundary diffusion is thought to be inhibited by grain‐boundary oxide films. The carbon phase‐separates into discrete amorphous regions and is thought to have little effect on sintering behavior.
Reaction between Sodium Carbonate and Silica Sand at 874°C < T < 1022°C
Authors: HRMA PAVEL
Published: June 2006

This paper is concerned with the mechanism of the reaction between sodium carbonate and silica sand at 874° to 1022deg;C. A reaction path which evolves in four stages, i.e., decarbonization, dissolution of orthosilicate, dissolution of metasilicate, and final dissolution of silica, is dealt with in detail, including mass balances. Formulas for dissolution rates in the first two stages are suggested, and the effect of wetting the grains by the melt, amount and distribution of the melt, and nonuniform dissolution (e.g., segregation) on the dissolution rate of silica grains are discussed. The need for more detailed experimental studies is stressed.
NMR Line Shape‐Spin‐Lattice Relaxation Correlation Study of Portland Cement Hydration
Authors: SCHREINER L. J. , MACTAVISH J. C. , MILJKOVIĆ L. , PINTAR M.M. , BLINC R. , LAHAJNAR G. , LASIC D. , REEVES L. W.
Published: June 2006

The proton free induction decay of a portland cement paste in an advanced stage of hydration can be roughly divided into three main components: (1) a component with a very short spin‐spin relaxation time, T2, representing the protons of the solid OH groups and the water of crystallization, (2) a component with an intermediate T, representing the bonded water in the gel phase, and (3) a third component with a relatively long T2 representing the water in the micropores and layers. The dependences of the intensities, T2's, and spin‐lattice relaxation times (T1's) of these three components on the cement hardening time have been determined. The proton spin‐lattice relaxation time of the “solid” component increases with hardening time whereas T1 decreases for the other two components. The observed time dependence of the diffusion coefficient, D, of water in a tricalcium silicate paste supports the findings of the above correlation study.
Sintering and Mechanical Properties of Stoichiometric Mullite
Authors: Kanzaki Shuzo , Tabata Hideyo , Kumazawa Takeshi , Ohta Shigetoshi
Published: June 2006

Stoichiometric mullite powder (3Al2O3·2SiO2) prepared by spray pyrolysis and sintered at 1650°C attained 95% of theoretical density. The flexural strength was 360 MPa at room temperature and decreased slightly at 1400°C. A fairly high KIc value (2.8 MN/m3/2) was obtained. These mechanical properties can be attributed to the highly homogeneous stoichiometric composition of the raw powder.
Effect of Impurity and Carrier Concentrations on Electrical Resistivity and Thermal Conductivity of Sic Ceramics Containing BeO
Authors: Ogihara S. , Maeda K. , Takeda Y. , Nakamura K.
Published: June 2006

Silicon carbide ceramics with BeO as an additive exhibit unusually high electrical resistivity and thermal conductivity compared to conventional SiC ceramics. Studies concerning the effects of carrier concentration in the SiC grains on electrical properties and thermal conductivity are described. The low carrier concentration in this ceramic is responsible for the high electrical resistivity. The thermal conductivity, however, decreases gradually with increasing impurity concentration.
REVIEW—Graphical Displays of the Thermodynamics of High‐Temperature Gas‐Solid Reactions and Their Application to Oxidation of Metals and Evaporation of Oxides
Authors: Lou V. L. K. , Mitchell T. E. , Heuer A. H.
Published: June 2006

The construction and utility of volatility diagrams – isothermal plots showing the partial pressures of two gaseous species in equilibrium with the several condensed phases possible in a system—are demonstrated for simple oxides with reference to the Mg‐0, A1‐0, and Si‐0 systems and compared with Ellingham‐type representations of these same data. Both types of diagrams are useful for providing a condensed format for a great deal of thermodynamic information. Their use is illustrated by analyzing the oxidation of Mg, Al, and Si and the volatilization of MgO, A12O3, and SiO2 in both neutral and reducing gases.
Effect of Physical Nature of Powders and Firing Atmosphere on ZnAI2O4Formation
Authors: OKADA H. , KAWAKAMI H. , HASHIBA M. , MIURA E. , NURISHI Y. , HIBINO T.
Published: June 2006

The rate of ZnA12O4formation for binary powder mixtures of ZnO and α‐Al2O3(dense coarse particles and weak agglomerates of fine powder) fired in air or O2atmospheres was measured and the microstructures of those systems were observed by scanning electron microscopy. With dispersed dense particles of α‐Al2O3, the Al2O3surfaces were covered with ZnO and the spinel grew into the particles maintaining essentially a constant reaction interface area. Calculations based on geometric measurements and use of Jander's equation gave a similar high activation energy, 354 kJ/mol, which corresponds to the activation energy of volume diffusion of Zn2+in ZnAl2O4. An oxygen atmosphere had no effect. With a matrix of fine α‐Al2O3powder and dispersed granules of ZnO, a higher reaction rate occurred because of an increase in reaction interface area due to penetration of the powder compact matrix by ZnO vapor, which was enhanced by an O2atmosphere. The reaction layer grew into the alumina matrix adjoining the ZnO granules with a parabolic rate law. Apparent activation energies below ∼200 kJ/mol were calculated.
Surface Tensions of Alumina‐Containing Liquids
Authors: LIHRMANN J. M. , HAGGERTY J. S.
Published: June 2006

The surface tensions of C02‐ laser‐melted alumina‐containing liquids have been measured by a static, pendant‐drop technique in air, helium, and a 90% helium‐10% hydrogen mixture. The influences of up to 10 wt% Cr203, MgO, and TiO2 have been studied. Surface tension data are also reported throughout the whole concentration range between liquid alumina and zirconia in air. A new analytical technique based on comparing calculated and observed melt contours is reported. Using this technique, more precise surface tension to density ratios can be determined from low length to diameter ratio pendant drops than by previously reported procedures.
Current‐Induced Segregation in Ionic Melts
Authors: PETUSKEY W.T.
Published: June 2006

The criteria for the electrochemically driven demixing of cations in ternary molten salts and silicates are analyzed for two cases of selective ion blocking electrodes. Mathematical expressions are derived for an anion flux case and a cation flux case which relate the concentration profiles and current densities at steady state to the differences of the electrical and chemical potentials applied at the melt surfaces. The analysis can be used to evaluate component demixing if three independent transport coefficients are known as a function of composition. Conversely, demixing experiments are proposed for use in determining such parameters as the inter diffusion coefficient and transference numbers of each ion for the composition range of segregation.
Electrical Conductivity of Polycrystalline A12O3 Doped with Silicon
Authors: LEE C. H. , KRÖGER F. A.
Published: June 2006

Direct current conductivity was measured for polycrystalline Alz03 doped with silicon, which is found to act as a single donor, the donor level lying ∼165 kJ/mol (∼1.7 eV) below the conduction band. Silicon in excess of the solubility limit (∼220 ppm at 1500°C, 300 ppm at 1600°C) is present as a glassy aluminosilicate second phase. Silicon dissolved in Al2O3 tends to segregate at grain boundaries.
Fabrication of Si3N4 Ceramics with Metal Nitride Additives by Isostatic Hot‐Pressing
Authors: Uchida Norimasa , KOIZUMI MITSUE , SHIMADA MASAHIKO
Published: June 2006

High‐density Si3N4 ceramics with nitride additives such as TiN, AlN, ZrN, VN, NbN, YN, TUN, Mg3N2, and HfN were fabricated by isostatic hot‐pressing. The temperature dependence of Vickers microhardness, fracture toughness, and thermal conductivity were measured; these properties, as well as microstructure, were strongly influenced by the additive used.
Interaction of BaCl2 and BaSO4 at Elevated Temperatures
Authors: Chandra Satish
Published: June 2006

The effect of adding BaCl2 to BaSO4 at elevated temperatures was studied. Differential thermal analysis and hot‐stage microscopy revealed that a eutectic occurs at 865°C between BaCl2 and 13.5 mol% BaSO4. The microstructure in the reaction zone indicated that BaS04 recrystallizes from the eutectic melt. Thus, BaCl2 additions can activate BaSO4 at a temperature as low as 865°C.
New Compound in the System La2O3‐Al2O3
Authors: Yamaguchi Osamu , Sugiura Koji , Mitsui Akihiro , Shimizu Kiyoshi
Published: June 2006

A new compound, 5La2O3‐2Al2O3, is formed from an amorphous material prepared by the simultaneous hydrolysis of lanthanum and aluminurn alkoxides. It has an orthorhombic unit cell with a=0.9704 nm, b=0.5967 nm, and c=1.5473 nm. The structure contains tetrahedral AlO4 groups and octahedral AlO6 groups.
A Diffusion‐Compensation Relation for Normal Grain Growth and Grain‐Boundary Diffusion of Oxygen in Oxides
Authors: Joesten Raymond
Published: June 2006

Values of D0/δ and Q for grain‐boundary diffusion, derived from published studies of normal grain growth in Al2O3, BeO, CaO, MgO, SiO2, and CaSiO3, are fit by the linear compensation equation log D0/δ=0.03170Q ‐7.6792 (r2=0.9384). Comparison of grain‐boundary diffusion coefficients derived from grain growth in oxides with those obtained by direct experimental measurement suggests that the kinetics of normal grain growth are controlled by grain‐boundary diffusion of oxygen.
The System Sc2O3‐WO3
Authors: Halum Gary W. , Datta R.K.
Published: June 2006

Phase relations in the system Sc2O3‐WO3 were characterized. Two stable binary compounds were, found. The 1:3 compound, SC2(WO4)3, melts congruently at 1640°±10°C and forms a simple eutectic with WO3 at ∼90 mol% WO3 and 1309°+10°C. The 3 : 1 compound, Sc6WO12, forms a simple eutectic with the 1:3 compound at ‐69 mol% WO2, and 1580°+10°C. The melting temperature of SC6WO12 was >1600°C.
Diffusion of 51Cr in Surface Layers of Magnesia, Alumina, and Spinel
Authors: STUBICAN V. S. , HUZINEC G. , DAMJANOVIĆ D.
Published: June 2006

Diffusion of 51Cr isotope on MgO (100), Al2O3 (0001, and MgAl2O4 (111) surfaces was investigated by using the edgesource method. The surface diffusion parameter, αD,δ, where α is the segregation factor, D, the surface diffusion coefficient, and δ the thickness of the high‐diffusivity layer, was determined for the temperature region 650° to 1250°C. For calculation of experimental results Whipple's solution was used. Arrhenius plots show a break at ∼1050°C for MgO and at ∼900°C for MgAl2O4. Above these temperatures vapor transport seems to be the overriding diffusion mechanism. Below these temperatures ionic transport predominates. Ionic transport is the predominant mechanism for surface diffusion of 51Cr on Al203 over the entire investigated temperature region. This can be explained by the weak bond between Cr‐vapor species and Al203 surface. The apparent activation energies for ionic transport of 51Cr are 110 ± 12, 121 ± 12, and 119 ± 12 kJ/mol on MgO, Al2O3, and MgAl2O4 surfaces, respectively. They include enthalpy of motion and binding enthalpy and are 2.5 to 2.8 times smaller than the activation energies for volume diffusion. Investigations of surfaces by LEED, Auger, and SIMS indicated structural nonperiodicity and surface segregation of impurities.
Grain‐Boundary Phase Transformations During Aging of a Partially Stabilized ZrO2 ‐ A Liquid‐Phase Analogue of Diffusion‐Induced Grain‐Boundary Migration (DIGM)(?)
Authors: BUTLER E. P. , HEUER A. H.
Published: June 2006

The microchemical/microstructural evolution of grain‐boundary regions in a ternary (Ca, Mg)‐partially‐stabilized ZrO2 during aging at 1400°C has been studied by transmission electron microscopy. Two distinct grain‐boundary transformation products, both of which involve single‐phase cubic (c)‐ZrO2 zones adjacent to grain boundaries, have been identified. An amorphous silicate grain‐boundary phase, whose composition changes during aging, is also present. One of the two grain‐boundary reactions involves grain‐boundary migration by a solution/reprecipitation process and can be termed reactive film migration; it may be a liquid‐phase analogue of diffusion‐induced grain‐boundary migration.
Viscous Sintering on a Rigid Substrate
Authors: SCHERER GEORGE W. , GARINO TERRY
Published: June 2006

Two analyses are presented for the sintering kinetics of a porous glass layer on a rigid substrate. The first treatment uses a continuum model, with constitutive equations and the free strain rate derived from an appropriate microstructural model. Predictions are obtained for the sintering kinetics and the magnitude of the tensile stress in the layer. During sintering, shrinkage is not permitted in the plane of the substrate, but the resulting microstructural anisotropy is ignored by the model. A second treatment represents the sintering layer by tubes whose axes are normal to the substrate. The densification kinetics of this model are in reasonable agreement with the results of the continuum model. Therefore, the effects of microstructural anisotropy (pore orientation) are likely to be small, and either model can be used
Oxygen Pressure Dependence of Lead Ion Transport in PbO‐SiO2 Melts
Authors: Pal Uday B. , DebRoy Tarasankar , Simkovich George
Published: June 2006

The diffusivity of lead in a PbO‐SiO2 melt was determined as a function of oxygen pressure from kinetic data for the oxidation of liquid lead covered by a layer of lead silicate melt which is short‐circuited to facilitate electronic transport. The diffusivity‐oxygen pressure relation thus obtained agreed well with the corresponding prediction based on definitions of the fluxes ofPb2+ and electron holes and an appropriate equilibrium relation.
Barium Titanate Ceramics with High Piezoelectricity Fabricated from Fibrous Particles
Authors: Ohara Yoshinobu , Koumoto Kunihito , Yanagida Hiroaki
Published: June 2006

Barium titanate ceramics with high degrees of c‐axis orientation were fabricated from fibrous particles. The maximum piezoelectric constant, d33, obtained was ≅270 pC/N, which is much higher than values reported previously.
Failure Mechanisms in Ceramic‐Fiber/Ceramic‐Matrix Composites
Authors: MARSHALL D.B. , EVANS A. G.
Published: June 2006

Mechanisms of failure in a unidirectional Sic‐fibe/glass‐ceramic composite are investigated using in situ observations during tensile and flexural loading. These experiments show that failure in tension occurs in several stages (similar to certain other brittle fiber composites): multiple matrix cracking, followed by fiber fracture and pullout. In flexural loading the failure process is more complex. Consequently, the flexural test cannot be used for measurement of tensile strength (although it can be used for measurement of the stress for matrix cracking). The application of conventional fracture mechanics to describe tensile failure is discussed. The in situ observations provide direct indication of the importance of frictional bonding between the matrix and fibers. Some novel methods for measuring the frictional forces and residual stresses are investigated, and the influence of surface damage on strength is assessed.
Thermodynamic Stability of UMoO6 by the Transpiration Method
Authors: TRIPATHI S. N. , CHATTOPADHYAY G. , KERKAR A. S. , CHANDRASEKHARAIAH M. S.
Published: June 2006

The equilibrium vaporization of UMoO6(s) in dry air was studied by the transpiration method in the temperature interval 1110°≤ T (K) ≤ 1250°. Apparent pressure of the trimer measured over the two‐phase mixture UMoO6+ U3O8, with dry air as the carrier gas, was used to calculate the partial pressure of the trimer, (MoO3)3(g). In accordance with the vaporization reaction (UMoO6) = 1/3(U3O8) + 1/6(MoO3)3(g)+ 1/6O2 (g), the free energy of formation of UMoO6)(s) is given by (δ G° in kJ‐mol−1) δ G° (UMoO6) = (−1962 ± 10) + (0.463 ± 0.008) T
Residual Stresses in Meta/Ceramic Bonded Strips
Authors: HSUEH C. H. , EVANS A. G.
Published: June 2006

Residual stresses that develop during cooling of a metal/ ceramic strip are calculated analytically. It is shown that the metal may behave elastically or plastically (with full or partial plasticity) depending on the mechanical properties, the thickness of the two constituents, and the mismatch in thermal expansion. Residual stresses are also calculated for a sequence consisting of constrained undercooling, removal of the constraint, and reheating. It is demonstrated that reheating, which results in elastic stress relaxation, may be used to eliminate the residual stress. The optimum undercooling and reheating conditions needed to produce a stress‐free strip, at the operational temperature, are calculated, and specific results are presented for the system Cu/A2, O2.
Anisotropy of Fracture Toughness of Piezoelectric Ceramics
Authors: PISARENKO G. G. , CHUSHKO V. M. , KOVALEV S. P.
Published: June 2006

The anisotropy of fracture toughness of PZT‐ and barium titanate‐based piezoelectric ceramics was studied using doubletorsion and indentation methods. The influence of elastic anisotropy and the piezoelectric effect in calculating the Kc value are discussed. The fracture toughness in the polarization plane is greater than that in the perpendicular plane. A model is suggested to explain the observed anisotropy; it is based on assumption of a stress‐induced domain reorientation zone near the crack tip.
Parameter‐Free Equation‐of‐State Calculations for MgO and ZrO2
Authors: BOYER L. L. , KLEIN B. M.
Published: June 2006

The electronic band structure of ZrO2 is calculated for the fluorite structure using the self‐consistent augmented‐plane‐wave method in the muffin‐tin approximation. The crystal charge density is then site decomposed by fitting Slater orbitals to the wave functions in the muffin tins. The resultant charge densities for Zr4+ and O2− are then used in the Gordon‐Kim method to derive pair potentials, from which a number of structural, elastic, and thermodynamic properties are calculated and compared with experimental results and similar calculations for MgO.
Solidification Microstructures of Laser‐Melted Alumina Powder Compacts
Authors: Matthiesen David H. , Petuskey William T.
Published: June 2006

Dense, thin sheets of α‐alumina formed after solidification of powder compact surfaces which were melted using CO2 laser radiation. The microstructures and surface topographies varied with the depth of melt. Most significant was a zone of columnar grains oriented in the [661] direction which yielded smooth surfaces for intermediate depths.
Intrinsic Volume Changes of Self‐propagating Synthesis
Authors: Rice Roy W. , McDonough William J.
Published: June 2006

The final product(s) of self‐propagating synthesis are shown to be intrinsically denser than the starting reactants. This behavior results in intrinsic decreases in the sample volume that increase with both the heat of reaction and the adiabatic combustion temperature. Forming of liquid product(s) during reaction simply adds another intrinsic source of porosity, i.e. changes in volume on product solidification. Thus, obtaining fully dense bodies from self‐propagating synthesis requires a mechanism for reducing porosity, e.g. hot‐pressing.
Scandium‐Containing Oxynitride Glasses
Authors: Tredway William K. , Loehman Ronald E.
Published: June 2006

Oxynitride glasses were made by atom‐for‐atom substitution of Sc3+ for Mg2+ in the Mg‐Si‐O‐N and Mg‐Si‐Al‐O‐N systems. Good‐quality glasses containing up to 7 mol% Sc2O3 were obtained. For a constant cation ratio, an increased N/O ratio gives glasses with increased elastic modulus, Vickers microhardness, density, and glass transition temperature.
Ultramicrotoming of Ceramic Powders for Electron Microscopy
Authors: Pickles David G. , Lilley Edward
Published: June 2006

Compacts of monosize TiO2 particles and agglomerates of TiO2 and γ‐alumina were infiltrated with Spurr's epoxy resin, cured, and ultramicrotomed. Transmission electron microscopy of the thin sections revealed the packing of the TiO2 spheres and the structure of the agglomerates.
Preliminary Characterization of Gel Precursors and Their High‐Temperature Products by 27Al Magic‐Angle Spinning NMR
Authors: Komarneni Sridhar , Roy Rustum , Fyfe Colin A. , Kennedy Gordon J.
Published: June 2006

The environment of the Al atom in alumina gels, single‐phase and diphasic mullite gels, and their transformation products was studied by 27Al magic‐angle spinning nuclear magnetic resonance (MASNMR). Alumina gels made from inorganic and organic precursors showed exactly the same 27Al MASNMR spectra. Heat treatment of gels at 500°C caused artial conversion of octahedral Al to tetrahedral Al. The Al in single‐phase mullite gel appears to be highly ordered compared to that in diphasic mullite gel.
High‐Temperature Mechanical Behavior of Fiber‐Reinforced Glass‐Ceramic‐Matrix Composites
Authors: Mah T. , Mendiratta M. G. , Katz A. P. , Ruh R. , Mazdiyasni K. s.
Published: June 2006

Lithium aluminosilicate glass‐ceramic‐matrix composites reinforced with Sic fibers were tested at 900° and 1000°C in flexural and tensile configurations. The composites showed severe thermomechanical degradation when tested in oxidizing atmospheres. This degradation was found to depend on oxygen partial pressure. For Po2≳103 Pa the composites failed in a brittle fashion; a single crack initiated and propagated through the matrix and fibers. At lower Po2, multiple matrix cracking was observed, and the fibers bridged the matrix cracks.
Concentration Dependence of the Diffusion Coefficient of Water in SiO2 Glass
Authors: Tomozawa Minoru
Published: June 2006

The concentration dependence of water diffusion in SiO2 glass was analyzed assuming that both molecular water and hydroxyl water can diffuse and that they are in equilibrium as interstitial and substitutional impurities. The equation obtained appears to be consistent with experimental observations of water diffusion in SiO2 glass.
Effects of α‐Radiolysis on Leaching of a Nuclear Waste Glass
Authors: Weber William J. , Wald John W. , McVay Gary L.
Published: June 2006

The effects of α‐radiolysis on leaching were studied in compositionally identical Pu‐doped waste glass samples which were prepared at different α‐activities (dose rates) by varying the 239Pu/238Pu isotopic ratio in the Pu dopant. The results of 14‐, 28‐, and 56‐d static leach tests at 40°C, in both deionized water and brine solution, indicate that α‐radiolysis at the samplelsolution interface increased Pu and Si release by a factor of ≅3.
Liquid‐Liquid Immiscibility in Mixed ZrF4‐ThF4 Glass
Authors: Simmons Catherine J. , Simmons Joseph H.
Published: June 2006

Liquid‐liquid phase separation is observed in a mixed ZrF4‐ThF4 glass by the measurement of a double glass transition in the specific heat. This effect, seldom seen before in other glasses and never previously seen in halide glasses, is clear evidence that fluoride glasses are susceptible to subliquidus amorphous phase transitions.
Silicon Nitride Joining
Authors: MECARTNEY M. L. , SINCLAIR R. , LOEHMAN R. E.
Published: June 2006

Hot‐pressed Si3N4 was joined using an Mgo‐A12O3‐SiO2 glass composition chosen to approximate the oxide portion of the grain‐boundary phase in the ceramic. After it has been heated at 1550° to 1650°, the interface of the joined ceramic is an interlocking mixture of Si2N2O, β‐Si3N4, and a residual oxy‐nitride glass. The kinetics of reactions between Si3N4 and the molten joining composition were studied by X‐ray diffraction analysis of the phases present in Si3N4 powder‐glass mixtures quenched after varied heat treatments. Analytical transmission electron microscopy of the composition and micro‐structure of the reaction zone in joined specimens, together with the X‐ray diffraction results, suggests that the driving force for joining is the lowering of the Si3N4 interfacial energy when it is wet by the molten silicate, augmented by the negative Gibbs energy for the reaction SiO2(l) + Si3N4= 2Si2N2O.
Congruent Composition and Li‐Rich Phase Boundary of LiNbO3
Authors: O'BRYAN H. M. , GALLAGHER P. K. , BRANDLE C. D.
Published: June 2006

The congruent composition of LiNbO3 was determined precisely by correlating crystal growth compositions with the Curie temperatures of samples quenched from a melt before and after crystal growth and of various sections of crystals grown from that melt. The initial melt composition was determined by control of Li2CO3 and Nb2O5 contents. The melt compositions were varied from 47 to 49 mol% Li2O. The variation of Te with melt composition was found to follow Te= 9095.2 − 369.05C + 4.228C2, where C is mol% Li2O. High‐temperature DTA was used to determine Te with a precision of ±2°C. Above 1000°C the Li‐rich phase boundary was found to be a function of temperature by determining the weight gain after complete lithiation of congruently grown crystals. This boundary curves slightly toward lower Li2O content as temperature increases. The congruent composition of LiNbO3 contains 48.45 mol% Li2O and has a measured Curie temperature of 1138°± 2°C.
Controlled Transformation and Sintering of a Boehmite Sol‐Gel by α‐Alumina Seeding
Authors: KUMAGAI MASATO , MESSING GARY L.
Published: June 2006

The transformation, microstructural development, and densification of an α‐alumina‐seeded boehmite sol‐gel was studied. α‐Alumina particles are shown to act as nuclei for the trans‐ formation of θ‐ to α‐alumina and to result in an increase in the transformation kinetics and lowering of the transformation temperature by as much as 170°C. By increasing the seed concentration (i.e., nucleation frequency), a submicrometer aggregate‐free microstructure develops, rather than the vermicular microstructure that usually characterizes the α‐alumina transformation. As a result, the transformed α‐alumina sinters to full density with a submicrometer grain size at 1200°C. It is believed that seeding may represent a unique method for microstructure control in the many ceramic systems that transform by nucleation and growth.
Leach Resistance of Nitrogen‐Containing Na2O‐CaO‐SiO2 Glasses
Authors: Frischat Günther H. , Sebastian Klaus
Published: June 2006

The resistance of an Na2O‐CaO‐SiO2 glass containing 1.1 wt% nitrogen to attack by water at 60°C for up to 49 h was compared to that of a nitrogen‐free glass. The attack was followed by weight‐change measurements and solution analysis. The leach resistance of the nitrogen‐containing glass is considerably improved. The leach mechanism is discussed in terms of ion‐exchange and network‐dissolution processes.
Role of Microstructure and Intergranular Phases in Stress Corrosion of TiB2 Exposed to Liquid Aluminum
Authors: Zdaniewski Wieslaw A.
Published: June 2006

The resistance of several polycrystalline TiB2 materials to penetration by liquid aluminum at 970°C was investigated, and their microstructures were characterized. The grain‐boundary properties of individual diborides rather than the intrinsic properties of TiB2 are thought to control stress corrosion susceptibility in liquid metal environments.
Strength and Fatigue Properties of Optical Glass Fibers Containing Microindentation Flaws
Authors: DABBS TIMOTHY P. , LAWN BRIAN R.
Published: June 2006

The inert strength and dynamic fatigue properties of fused‐silica optical fibers are studied using subthreshold indentation flaws, i.e., flaws without radial cracks. These subthreshold properties differ from those obtained in comparative tests on silica rods containing postthreshold indentation flaws in three major respects: (1) the inert strengths are significantly higher than predicted by extrapolation of the postthreshold data; (2) the slopes of the dynamic fatigue plots are likewise greater, indicating a greater susceptibility of the subthreshold flaws to chemical kinetic effects; and (3) the scatter in strengths is wider. These trends reflect the change in mechanical response reported for optical fibers with “natural” flaw populations in going from ordinary to ultra‐high‐strength regions. Direct observations of the indentation sites up to the point of failure indicate that the property differences can be interpreted in terms of a transition from propagation‐controlled to initiation‐controlled fracture instabilities at reduced contact loads. The subthreshold instability condition is modeled qualitatively as a two‐step, deformation‐fracture process, with strong emphasis on the importance of residual stress fields in parametric evaluations. The relevance of the results to the practical issue of fiber reliability, most notably in connection with the potential dangers of using macroscopic crack velocity data to predict long‐lifetime characteristics, is addressed.
Closure and Repropagation of Healed Cracks in Silicate Glass
Authors: MICHALSKE TERRY A. , FULLER E.R.
Published: June 2006

Cracks in soda‐lime‐silica and vitreous silica glass close against a finite load at humidities between 0.01 % and 100%. The force associated with crack closure (0.15 J/m2) can be predicted by a model which involves hydrogen‐bonded linkages of surface‐adsorbed water molecules. The fracture energy to reopen healed cracks in vitreous silica is also in the range of hydrogen‐bonding interactions. In the driest environments used, healed cracks in soda‐lime‐silica glass required 1.7 ± 0.2 J/m2 to reopen. This bonding energy can be attributed to the formation of either cationic bridges or siloxane bonds between fracture surfaces. Since crack healing was observed to be independent of the number of cycles, a cationic bridging model is favored to explain healing effects at room temperature.
Effect of Chloride Incorporation on the Crystallization of Zirconium‐Barium‐lanthanum‐Aluminum Fluoride Glass
Authors: NEILSON GEORGE F. , SMITH GARY L. , WEINBERG MICHAEL C.
Published: June 2006

One aspect of the influence of preparation procedure on the crystallization behavior of a zirconium‐barium‐lanthanum‐aluminum fluoride glass was studied. The crystallization pattern of this glass may be affected by the chlorine concentration within it. In particular, when such glasses are heated at low temperatures, the α‐BaZrF6 crystalline phase forms only in those glasses which contain chloride.
Glass Formation and Properties in the System Calcia‐Gallia‐Germania
Authors: ANGEL PAUL W. , RAY CHANDRA S. , DAY DELBERT E.
Published: June 2006

The critical cooling rate for glass formation, Rc, was measured for four compositions in the system calcia‐gallia‐germania. The activation energy, E, and frequency factor, u, for the crystallization process were determined by reheating the glasses at varied constant heating rates and measuring the temperature of crystallization. Both E and v increased, with increasing germania content of the glass, whereas Rc decreased. The density, refractive index, and Abbe number were also measured; all decreased with increasing GeO2 content. These results are compared with those for calcia‐gallia‐silica glasses of comparable compositions.
The dynamics of injection drug users’ personal networks and HIV risk behaviors
Authors: Costenbader Elizabeth C. , Astone Nan M. , Latkin Carl A.
Published: June 2006

Aims  While studies of the social networks of injection drug users (IDUs) have provided insight into how the structures of interpersonal relationships among IDUs affect HIV risk behaviors, the majority of these studies have been cross‐sectional. The present study examined the dynamics of IDUs’ social networks and HIV risk behaviors over time.

Design  Using data from a longitudinal HIV‐intervention study conducted in Baltimore, MD, this study assessed changes in the composition of the personal networks of 409 IDUs. We used a multi‐nomial logistic regression analysis to assess the association between changes in network composition and simultaneous changes in levels of injection HIV risk behaviors. Using the regression parameters generated by the multi‐nomial model, we estimated the predicted probability of being in each of four HIV risk behavior change groups.

Findings  Compared to the base case, individuals who reported an entirely new set of drug‐using network contacts at follow‐up were more than three times as likely to be in the increasing risk group. In contrast, reporting all new non‐drug‐using contacts at follow‐up increased the likelihood of being in the stable low‐risk group by almost 50% and decreased the probability of being in the consistently high‐risk group by more than 70%.

Conclusions  The findings from this study show that, over and above IDUs’ baseline characteristics, changes in their personal networks are associated with changes in individuals’ risky injection behaviors. They also suggest that interventions aimed at reducing HIV risk among IDUs might benefit from increasing IDUs’ social contacts with individuals who are not drug users.
Near East mtDNA haplotype variants in Roman cattle from Augusta Raurica, Switzerland, and in the Swiss Evolène breed
Authors: Schlumbaum A. , Turgay M. , Schibler J.
Published: June 2006

Typical Near East mitochondrial haplotypes of the T2 lineage were found in one cattle metacarpus sample from the Roman period and in two present‐day Evolène cattle in Switzerland. Sequences from eight additional Evolène and four Raetian Grey aligned to the European haplotype T3. Analysis of nucleotide diversity within the mitochondrial D‐loop of both studied Swiss cattle breeds revealed high haplotype diversity and similar diversity to a European cattle reference group. Mitochondrial T3 haplotypes radiated star‐like from two similarly frequent haplotypes, possibly indicating two different expansion routes. The breed structure of Evolène cattle can be explained either by an introduction of diverse female lineages from the domestication centre or by later admixture. The introduction of the Near East lineage to Switzerland must have happened during the Roman time or earlier.
Cross‐species overgo hybridization and comparative physical mapping within avian genomes
Authors: Romanov M. N. , Dodgson J. B.
Published: June 2006

The chicken genome sequence facilitates comparative genomics within other avian species. We performed cross‐species hybridizations using overgo probes designed from chicken genomic and zebra finch expressed sequence tags (ESTs) to turkey and zebra finch BAC libraries. As a result, 3772 turkey BACs were assigned to 336 markers or genes, and 1662 zebra finch BACs were assigned to 164 genes. As expected, cross‐hybridization was more successful with overgos within coding sequences than within untranslated region, intron or flanking sequences and between chicken and turkey, when compared with chicken‐zebra finch or zebra finch‐turkey cross‐hybridization. These data contribute to the comparative alignment of avian genome maps using a ‘one sequence, multiple genomes’ strategy.
Evolution of the late Cenozoic Chaco foreland basin, Southern Bolivia
Authors: Uba Cornelius Eji , Heubeck Christoph , Hulka Carola
Published: June 2006

Eastward Andean orogenic growth since the late Oligocene led to variable crustal loading, flexural subsidence and foreland basin sedimentation in the Chaco basin. To understand the interaction between Andean tectonics and contemporaneous foreland development, we analyse stratigraphic, sedimentologic and seismic data from the Subandean Belt and the Chaco Basin. The structural features provide a mechanism for transferring zones of deposition, subsidence and uplift. These can be reconstructed based on regional distribution of clastic sequences. Isopach maps, combined with sedimentary architecture analysis, establish systematic thickness variations, facies changes and depositional styles. The foreland basin consists of five stratigraphic successions controlled by Andean orogenic episodes and climate: (1) the foreland basin sequence commences between ∼27 and 14 Ma with the regionally unconformable, thin, easterly sourced fluvial Petaca strata. It represents a significant time interval of low sediment accumulation in a forebulge‐backbulge depocentre. (2) The overlying ∼14–7 Ma‐old Yecua Formation, deposited in marine, fluvial and lacustrine settings, represents increased subsidence rates from thrust‐belt loading outpacing sedimentation rates. It marks the onset of active deformation and the underfilled stage of the foreland basin in a distal foredeep. (3) The overlying ∼7–6 Ma‐old, westerly sourced Tariquia Formation indicates a relatively high accommodation and sediment supply concomitant with the onset of deposition of Andean‐derived sediment in the medial‐foredeep depocentre on a distal fluvial megafan. Progradation of syntectonic, wedge‐shaped, westerly sourced, thickening‐ and coarsening‐upward clastics of the (4) ∼6–2.1 Ma‐old Guandacay and (5) ∼2.1 Ma‐to‐Recent Emborozú Formations represent the propagation of the deformation front in the present Subandean Zone, thereby indicating selective trapping of coarse sediments in the proximal foredeep and wedge‐top depocentres, respectively.

Overall, the late Cenozoic stratigraphic intervals record the easterly propagation of the deformation front and foreland depocentre in response to loading and flexure by the growing Intra‐ and Subandean fold‐and‐thrust belt.
Lost in transition? Between paediatric and adult services
Authors: Reading Richard
Published: June 2006

.
 
McDonagh J.E. &
Viner R.
(
2006
)

,
332
,
435
–
436
.
Racial and socioeconomic disparity in perforated appendicitis among children: where is the problem?
Authors: Jacobson Robert M.
Published: June 2006

Nwomeh B.C.,
Chisolm D.J.,
Caniano D.A. &
Kelleher K.J.
(
2006
)

,
117
,
870
–
875
.

Objective  Significant racial, ethnic and socio‐economic disparities have been observed in the rates of perforated appendicitis among children, by using large administrative databases. This study evaluated whether these factors had an impact on the care of patients with appendicitis at a major children’s hospital in the USA with a well‐established, comprehensive and primary referral system.

Methods  A retrospective analysis was performed for all children between the ages of 2 and 20 years old who were treated for appendicitis between 1 January 2001 and 31 December 2003. Demographic variables included patient age, gender, race, insurance status, parental educational status and income level. Coding data were used to identify patients with perforated appendicitis. The use of radiologic imaging was also analysed.

Results  During the 3‐year period, 788 patients were treated for appendicitis. The racial distribution (white: 81%; black: 12%; other: 7%) was consistent with the demographic composition of the local population. The overall perforation rate was 25%, and the rate was significantly greater in the age group of <6 years, compared with older children. However, there were no significant differences in the perforation rate with respect to race, insurance status, educational level, or income status. Rates of radiologic imaging use were similar among all racial and socio‐economic groups.

Conclusions  Although racial and socio‐economic disparities in the rates of perforated appendicitis among children have been reported, we found no significant evidence for such inequality at our institution. This may reflect improved access, early diagnosis and referral by primary care physicians in the community. Pooled national and multiple‐state administrative databases have been used to highlight persistent disparities in health care. This study illustrates how single‐institution data sources can be used to test a local hypothesis generated by national data, with surprisingly different results.
Treatment with chitin microparticles is protective against lung histopathology in a murine asthma model
Authors: Ozdemir C. , Yazi D. , Aydogan M. , Akkoc T. , Bahceciler N. N. , Strong P. , Barlan I. B.
Published: June 2006

Background
Chitin, a natural polysaccharide extracted from shrimp, is a potent T and B cell adjuvant when delivered in the form of chitin microparticles and can shift a polarized T‐helper type 2 (Th2) immune response towards a Th1 response.

Objective
We investigated the beneficial effects of the intranasal application of chitin microparticles in newborn mice before and after the establishment of a model of allergic asthma.

Methods
Mice were grouped as asthma (A), primary prevention (PP), treatment (T), primary prevention+treatment (PPT) and control (C) groups. All mice except controls were sensitized with ovalbumin intraperitoneally and challenged intratracheally to establish the asthma model. Mice in the PP and PPT groups received chitin microparticles intranasally during the newborn period before sensitization. Mice in the PPT and T groups received intranasal chitin microparticles after challenge. Airway histopathology was evaluated in all groups.

Results
All of the airway histopathologic parameters of small and medium‐sized airways of the T and PPT groups were significantly ameliorated when compared with the asthma model group. In the large airways, thicknesses of basement membrane, epithelium and subepithelial smooth muscle layers of the PPT group and basement membrane thicknesses of the T group were also significantly lower compared with the asthma model group. Comparison of the PP group with the asthma model group revealed significantly reduced goblet cell numbers and significantly reduced epithelial and basement membrane thicknesses in small and medium airways, in addition to significantly reduced basement membrane thicknesses in the medium‐sized airways.

Conclusion
Intranasal application of microgram quantities of chitin microparticles had a beneficial effect in preventing and treating histopathologic changes in the airways of asthmatic mice.
In silico identification of potential new latex allergens
Authors: Guarneri F. , Guarneri C. , Guarneri B. , Benvenga S.
Published: June 2006

Background
Allergy to latex of Hevea brasiliensis is a frequent problem. In spite of the significant progress of research, the identity and cross‐reactivity of some latex allergens are unknown.

Objective
To identify, among the fully characterized latex proteins, those with a higher probability to be allergenic.

Methods
We used in silico techniques (amino acid sequence comparison and molecular modelling) to identify potential new allergens among the known proteins of H. brasiliensis.

Results
Cu/Zn superoxide dismutase, heat shock protein and calmodulin of H. brasiliensis show highly significant (E<10−9) amino acid sequence homologies with known allergens.

Conclusions
On the basis of our data, Cu/Zn superoxide dismutase, heat shock protein and calmodulin are the most probable allergens among fully characterized proteins of H. brasiliensis, and could potentially explain, at least in part, the multiple cross‐reactivities of latex with vegetable foods and other plant‐derived products. Consequently, we think that the above proteins should be particularly considered in the future laboratory and clinical research.
Very early prophylactic thyroid surgery for infants with a mutation of the RET proto‐oncogene at codon 634: evaluation of the implementation of international guidelines for MEN type 2 in a single centre
Authors: Piolat Christian , Dyon Jean‐François , Sturm Nathalie , Pinson Stéphane , Bost Michel , Jouk Pierre‐Simon , Plantaz Dominique , Chabre Olivier
Published: June 2006

Objective  Genetic diagnosis available since 1993 established germinal mutations of the RET proto‐oncogene at codon 634 as the main cause of inherited medullary thyroid carcinoma (MTC). International guidelines established in 1999 recommend that children with such mutations undergo a total thyroidectomy before age 5, with unspecified cervical neck dissection. Since 1993, only 41 of 275 thyroidectomies reported in RET 634 children were performed before age 5 (15%). The aim of this study was to evaluate the implementation of these guidelines in a single centre.

Design and patients  Genetic diagnosis was proposed to the parents of all eight children born after 1992 from two RET 634 families. Total thyroidectomy was proposed before age 5 if the child carried a mutation.

Results  Genetic diagnosis was performed in all the children (aged 1–3) and thyroidectomy in the five who carried a mutation (aged 2–5). Cervical lymph node dissection varied from lymphadenectomy of central and lateral compartments in the eldest child to pickings in the youngest. There was no permanent hypoparathyroidism or recurrent nerve paralysis. C‐cell hyperplasia, medullary thyroid carcinoma and lymph node metastasis were present in 5/5, 3/5 and 0/5, respectively. Undetectable pentagastrin‐stimulated CT levels were achieved and maintained postoperatively in all five children (average follow‐up 3·6 years).

Conclusions  MEN 2 guidelines on thyroidectomy can be efficiently and safely implemented by a multidisciplinary team operating in a single centre. The lack of guidelines on cervical neck dissection remains a problem; this could be solved by determining an age under which this procedure would be deemed unnecessary.
Fate of airborne metal pollution in soils as related to agricultural management. 1. Zn and Pb distributions in soil profiles
Authors: Fernandez C. , Labanowski J. , Cambier P. , Jongmans A. G. , Van Oort F.
Published: June 2006

The fate of airborne metal pollutants in soils is still relatively unknown. We studied the incorporation of such airborne metal pollution in two soils under long‐term permanent pasture (PP) and conventional arable land (CA). Both soils were located at an almost equal distance from a former zinc smelter complex and developed under comparable pedogenetic conditions. Profiles of total concentrations of Zn, chosen as a mobile, and Pb as a little‐ or non‐mobile element, were examined and compared with macro‐ and micromorphological soil characteristics (soil colour, biological activity). The two soils showed different profiles of total Zn and Pb concentrations, with a marked decrease of concentrations of both elements under the plough layer in CA, whereas the decrease was more progressive in PP. However, the stocks of Zn and Pb for the 1‐m soil profiles of CA and PP were comparable. Correlation of Zn and Pb concentration at different depths with total Fe contents and comparison with estimated data for the local geochemical background (LGCB), suggests transport of Zn from the surface to depth in CA and PP, and Pb movement in PP. In CA, 53% of Zn and 92.5% of Pb stocks derived from airborne metal pollution were located at depths < 26 cm. In PP, only 40% of Zn and 82% of Pb, derived from airborne pollution, were found in the A11 and A12 horizons (< 26 cm), the remaining 18% of the Pb stock being incorporated until 50 cm depth; one‐third of total Zn stock ascribed to airborne pollution was found at depths > 50 cm. Studies of the composition of gravitational water collected in soils from the same study area suggest two mechanisms for metal movement. First, mobile metal ions (Zn2+) move in the soil solution and are intercepted by iron‐clay complexes in deeper soil horizons. Second, observed only in PP, simultaneous movement of Zn and Pb is ascribed to bioturbation by earthworms.