bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Porosity on the Electrical Properties of Polycrystalline Sodium Niobate: I, Electrical Conductivity
Authors: Lanfredi Silvania , Dessemond Laurent , Rodrigues Ana C. M.
Published: July 2009

The electrical behavior of NaNbO3 ceramic samples with different relative densities was investigated by ac impedance spectroscopy in a range of 13 MHz to 10−3 Hz between 400° and 800°C in dry air. Measurements were performed during heating and cooling cycles. The Nyquist impedance diagrams of dense sodium niobate exhibit only one semicircle representing the grain contribution with depression angles as small as 1°, indicating a high homogeneity of the specific electrical properties. In the case of porous samples, the data reveal an additional low‐frequency semicircle related to microstructure. For all studied samples, the Arrhenius conductivity plots show a change in the activation energy around 640°C, attributed to the tetragonal‐cubic phase transition. The electrical conductivity of porous samples appears to be higher than that of dense ones.
Low‐Temperature Processing and Mechanical Properties of Zirconia and Zirconia–Alumina Nanoceramics
Authors: Vasylkiv Oleg , Sakka Yoshio , Skorokhod Valeriy V.
Published: July 2009

The 1.5‐ to 3‐mol%‐Y2O3‐stabilized tetragonal ZrO2 (Y‐TZP) and Al2O3/Y‐TZP nanocomposite ceramics with 1 to 5 wt% of alumina were produced by a colloidal technique and low‐temperature sintering. The influence of the ceramic processing conditions, resulting density, microstructure, and the alumina content on the hardness and toughness were determined. The densification of the zirconia (Y‐TZP) ceramic at low temperatures was possible only when a highly uniform packing of the nanoaggregates was achieved in the green compacts. The bulk nanostructured 3‐mol%‐yttria‐stabilized zirconia ceramic with an average grain size of 112 nm was shown to reach a hardness of 12.2 GPa and a fracture toughness of 9.3 MPa·m1/2. The addition of alumina allowed the sintering process to be intensified. A nanograined bulk alumina/zirconia composite ceramic with an average grain size of 94 nm was obtained, and the hardness increased to 16.2 GPa. Nanograined tetragonal zirconia ceramics with a reduced yttria‐stabilizer content were shown to reach fracture toughnesses between 12.6–14.8 MPa·m1/2 (2Y‐TZP) and 11.9–13.9 MPa·m1/2 (1.5Y‐TZP).
Local Structure of Sodium Aluminum Metaphosphate Glasses
Authors: Schneider José , Oliveira Samuel L. , Nunes Luiz Antônio O. , Panepucci Horácio
Published: July 2009

High‐resolution solid‐state 31P, 27Al, and 23Na nuclear magnetic resonance (NMR), Raman spectroscopy, differential scanning calorimetry, and density measurements were used to characterize the local structure of the glasses (1−x)(NaPO3)3·xAl(PO3)3. A systematic increase in density, glass transition temperature (Tg), and frequencies of P–O stretching vibrations for terminal nonbridging oxygens (NBOs) was observed as the Al content was increased. A change of slope in the behavior of Tg as a function of x was clearly detected around x= 0.25 ± 0.03. Also, changes of behavior in the 23Na NMR line shape and in the Raman band of the PO2 symmetric vibration are detected for concentrations higher than x= 0.17. According to these facts, a reorganization of the network affecting the degree of connectivity between phosphate chains is proposed to explain the observed behaviors of Tg and P–NBO vibrations in these glasses.
Grinding Temperature Measurements in Magnesia‐Partially‐Stabilized Zirconia Using Infrared Spectrometry
Authors: Curry Adam C. , Shih Albert J. , Kong Jin , Scattergood Ronald O. , McSpadden Sam B.
Published: July 2009

Results of temperature measurements by analysis of the thermal emission spectra generated during grinding and subsequently transmitted through partially stabilized zirconia workpieces are presented. Portions of emitted visible and near‐infrared spectra were collected with spectrometers. Source temperatures were determined by fitting the scaled spectrometer output spectra to blackbody curves. Simulations showed that the effective temperatures determined by this method will be strongly biased toward hot‐spot (flash) temperatures, which are expected to occur at the grinding grit–workpiece interface. Hot‐spot temperatures on the order of 3000 K were obtained for grinding with both SiC and diamond wheels. These high temperatures modify the grinding process and the phase content of grinding chips.
Processing, Fracture Toughness, and Vickers Hardness of Allylhydridopolycarbosilane‐Derived Silicon Carbide
Authors: Moraes Kevin V. , Interrante Leonard V.
Published: July 2009

Bulk specimens of precursor‐derived silicon carbide (SiC) suitable for mechanical‐property measurements were prepared from allylhydridopolycarbosilane (AHPCS), which is a commercially available, hyperbranched polycarbosilane. Crack‐free pellets were obtained by cold‐pressing mixtures of finely ground, 1000°C pyrolyzed, “AHPCS‐SiC” with neat AHPCS, followed by pyrolysis to 1000°C and ten subsequent reinfiltration/pyrolysis steps with the neat liquid AHPCS. Then, these pellets were heat‐treated to 1200°, 1400°, and 1600°C, followed by additional reinfiltration/pyrolysis cycles to the final respective maximum temperatures. This fabrication process simulated the production of the matrix phase for ceramic‐matrix composites via successive infiltration/pyrolysis cycles. The density of the material processed at these temperatures, measured via the Archimedes method, was 2.3, 2.5, 2.6, and 2.9 g/cm3, respectively, and the average open porosities of the samples were 2, 0.2, 1, and 9 vol%, respectively. The fracture toughness was measured using the single‐edge V‐notched‐beam method, and the hardness was measured via Vickers indentation. The samples had an average toughness of 1.40 ± 0.08, 1.65 ± 0.09, 1.67 ± 0.07, and 1.46 ± 0.08 MPa·m1/2 for the samples that were treated at 1000°, 1200°, 1400°, and 1600°C, respectively. The Vickers hardness for these samples, measured at a load of 1000 g, was 12 ± 1, 13 ± 2, 11 ± 1, and 9 ± 1 GPa, respectively.
Effect of Titania and Lithia Doping on the Boundary Migration of Alumina under an Electric Field
Authors: Choi Jae‐Il , Han Joo‐Hwan , Kim Doh‐Yeon
Published: July 2009

Boundary migration under an electric field was investigated for pure, TiO2‐doped, and Li2O‐doped Al2O3 specimens. Boundary migration rates in TiO2‐doped and Li2O‐doped Al2O3 specimens were much faster compared with that of pure Al2O3. In all specimens, the migration rate was observed to depend on the applied bias direction. Compared with pure Al2O3, the dependence of boundary migration on bias direction became more pronounced in TiO2‐doped Al2O3 but less pronounced in Li2O‐doped Al2O3. The results were explained in terms of the variation of grain sizes, mobility, and electrostatic potential of boundaries because of doping.
Influence of Distributed Particle Size on the Determination of the Parabolic Rate Constant for Oxidation by the Powder Method
Authors: Shah Sandeep R. , Saha Atanu , Raj Rishi
Published: July 2009

The established analysis for the study of oxidation using powder specimens is based on the assumption of monosized particles. The experiments, however, are conducted on powders with a distributed particle size. Here we present a statistical approach for the calculation of the rate constant for oxidation. The results of the analysis are applied to new data on oxidation studies of dense powders of silicon carbonitride amorphous ceramics. The monosized model requires a wide range of values for the rate constant to fit the short term and the long‐term data, leading to considerable ambiguity in the estimate of the parabolic rate constant, kp, for oxidation. In contrast the statistical model fits over the entire range of data, yielding a much more reliable value for kp. For example, the monosized approach gave a value in the range 19.7 × 10−18 < kp < 2.7 × 10−18 m2/s. In contrast, the statistical model yields a specific value of 4.5 × 10−18 m2/s.
Synthesis of Nanosized and Microporous Precipitated Hydroxyapatite in Synthetic Polymers and Biopolymers
Authors: Sinha Arvind , Nayar Suprabha , Agrawal Archana , Bhattacharyya Debasish , Ramachandrarao Patcha
Published: July 2009

In situ precipitation of microporous and nanosized hydroxyapatite particles (5–40 nm) has been conducted in poly(vinyl alcohol) and bovine serum albumin gels. The process, which is similar to biomineralization, is highly controlled with respect to microstructural features, such as size and shape, and to precipitation of hydroxyapatite phase having a calcium:phosphorus stoichiometric ratio of 1.67. Nanosized precipitated hydroxyapatite particles show remarkable thermal stability and do not decompose to other calcium phosphate phases, even at higher temperatures.
Crystallite and Grain‐Size‐Dependent Phase Transformations in Yttria‐Doped Zirconia
Authors: Suresh Arun , Mayo Merrilea J. , Porter Wallace D. , Rawn Claudia J.
Published: July 2009

In pure zirconia, ultrafine powders are often observed to take on the high‐temperature tetragonal phase instead of the “equilibrium” monoclinic phase. The present experiments and analysis show that this observation is one manifestation of a much more general phenomenon in which phase transformation temperatures shift with crystallite/grain size. In the present study, the effect of crystallite (for powders) and grain (for solids) size on the tetragonal → monoclinic phase transformation is examined more broadly across the yttria–zirconia system. Using dilatometry and high‐temperature differential scanning calorimetry on zirconia samples with varying crystallite/grain sizes and yttria content, we are able to show that the tetragonal → monoclinic phase transformation temperature varies linearly with inverse crystallite/grain size. This experimental behavior is consistent with thermodynamic predictions that incorporate a surface energy difference term in the calculation of free‐energy equilibrium between two phases.
Interface Structure of an Epitaxial Cubic Ceria Film on Cubic Zirconia
Authors: Wang Chong‐Min , Thevuthasan Suntharampillai , Peden C. H. F.
Published: July 2009

A cubic CeO2 (001) film with a thickness of ∼58 nm was grown epitaxially on Y2O3‐stablized cubic ZrO2 by oxygen‐plasma‐assisted molecular‐beam epitaxy (OPA‐MBE). The interface was characterized using high‐resolution transmission electron microscopy (HRTEM). The interface exhibited coherent regions separated by equally spaced misfit dislocations. When imaged from the [100] direction, the dislocation spacing is 3.3 ± 0.5 nm, which is slightly shorter than the expected value of 4.9 nm calculated from the differences in lattice constants given in the literature, but is fairly consistent with that of 3.9 nm which was calculated using the lattice mismatch measured by electron diffraction. Thus, the results presented here indicate that the lattice mismatch between the film and the substrate is accommodated mainly by interface misfit dislocations above some critical thickness.
α‐SiAlON Ceramics Obtained by Slip Casting and Pressureless Sintering
Authors: Xu Xin , Oliveira Marta I. L. L. , Ferreira José M. F.
Published: July 2009

Dense α‐SiAlON ceramics were obtained by pressureless sintering of green compacts prepared using slip casting. The rheological properties of the reaction SiAlON suspension were optimized to achieve a high degree of dispersion with a high solids volume fraction, which resulted in homogeneous and relatively dense green bodies with high sintering ability, which could be densified by pressureless sintering at 1750°C for 2 h. The sintered samples revealed a high degree of uniformity and almost fully dense microstructures that consisted of many small, elongated grains homogeneously dispersed in the fracture surfaces, which had properties comparable with those of other SiAlONs obtained using hot pressing.
Transparent Sintered Corundum with High Hardness and Strength
Authors: Krell Andreas , Blank Paul , Ma Hongwei , Hutzler Thomas , van Bruggen Michel P. B. , Apetz Rolf
Published: July 2009

Commercial corundum powder and a liquid‐shaping approach are used for manufacturing complex hollow components and large flat windows of sintered and hot isostatically pressed Al2O3 ceramics having grain sizes of 0.4–0.6 μm at relative densities of >99.9%. High macrohardness (HV10 = 20–21 GPa) and four‐point bending strength (600–700 MPa; 750–900 MPa in three‐point bending) are associated with a real in‐line transmission of 55%–65% through polished plates. The submicrometer microstructure and the optical properties can be retained for use at >1100°C using dopants that shift the sintering temperature to high values without additional grain growth.
Kinetics and Mechanism of Formation of Barium Zirconate from Barium Carbonate and Zirconia Powders
Authors: Ubaldini Alberto , Buscaglia Vincenzo , Uliana Claudio , Costa Giorgio , Ferretti Maurizio
Published: July 2009

The formation of BaZrO3from very fine (70–90 nm) ZrO2powders and coarser (∼1 μm) BaCO3powders has been studied in dry and humid air up to 1300°C using TGA/DTA, XRD, SEM, TEM, and EDS microanalysis. In the temperature range 900°–1100°C, barium is rapidly transported at the surface of the ZrO2particles and reacts, forming BaZrO3. The compound grows as a concentric layer with gradual consumption of the central ZrO2particle. The overall formation kinetics of BaZrO3is well described by a diminishing core model, and the most likely rate‐determining step is a phase‐boundary process at the ZrO2–BaZrO3moving interface. The size and shape of the final particles is generally determined by the morphology of the starting ZrO2particles and not by that of the BaCO3. The reaction is faster in humid air than in dry air, and the activation energy decreases from 294 kJ·mol−1(dry air) to 220 kJ·mol−1(humid air). When the fraction reacted is >80–90 mol%, the reaction rate rapidly decreases.
Preparation of SiC/SiC Composites by Hot Pressing, Using Tyranno‐SA Fiber as Reinforcement
Authors: Dong Shaoming , Katoh Yutai , Kohyama Akira
Published: July 2009

The development of advanced Tyranno SA SiC fiber with a near‐stoichiometric composition and a well‐crystallized microstructure has made it possible to prepare SiC/SiC composites even under harsh conditions. To assess the reinforcing effectiveness of Tyranno SA fiber at high temperature under pressure, unidirectional SiC/SiC composites were prepared by hot pressing, using pyrolytic carbon (PyC)‐coated Tyranno SA fiber as a reinforcement and nanopowder SiC with sintering additives for matrix formation. The effects of sintering conditions on the microstructural evolution and mechanical properties of the composites were characterized. As the sintering temperature increased (from 1720° to 1780°C) and the sintering pressure increased (from 15 to 20 MPa), the density of the composites gradually increased. Simultaneously, the elastic modulus, the proportional limit stress, and the strength, under both bend and tensile tests, also improved. At lower temperature and/or pressure, long fiber pullout was a predominant fracture behavior, indicating relatively weak fiber/matrix bonding. However, at high temperature and/or pressure, short fiber pullout became a main fracture characteristic, indicating relatively strong fiber/matrix bonding. These phenomena were also confirmed by the characteristics of the hysteresis loops derived from the stress–strain curves produced by a tensile test with unloading–reloading cycles. In the present investigation, the reinforcement of Tyranno SA fiber is effective for providing noncatastrophic fracture behavior to composites.
Stabilization of Poly(vinylpyrrolidone)‐containing Alkoxide Solutions for Thick Sol‐Gel Barium Titanate Films
Authors: Kozuka Hiromitsu , Higuchi Atsushi
Published: July 2009

The authors previously demonstrated that Ba(CH3COO)2‐Ti(OC3H7i)4‐CH3COOH‐H2O‐i‐C3H7OH solutions containing poly(vinylpyrrolidone) (PVP) can offer crack‐free BaTiO3 coatings >1 μm thick via noncycled, single‐step dip coating. The solutions, however, gelled within a few hours, which cannot be of practicable use in industry. To make the solutions applicable for industrial use, the solution composition has been optimized so that the solutions have sufficient stability in viscosity. Using Ti(OC2H5)4 and C2H5OH instead of Ti(OC3H7i)4 and i‐C3H7OH, respectively, high CH3COOH contents and low H2O contents in solutions were effective in suppressing the variation of viscosity with time. A solution of molar composition, Ba(CH3COO)2:Ti(OC2H5)4:PVP:CH3COOH:H2O:C2H5OH = 1:1:0.5:27:4:5, exhibited great stability in viscosity over 900 h at room temperature. Crack‐free BaTiO3 films as thick as 0.9 μm could be obtained via noncycled gel film deposition and firing at 700°C. However, the dielectric constant of the 0.9‐μm‐thick film was as low as 130 at 1 kHz. The films obtained via stepwise firing at 360° and 700°C, on the other hand, were ∼0.6 μm thick, showed good transparency, and had dielectric constants of ∼290 at 1 kHz.
Effect of the Processing Parameters on the Crystalline Features of the Solid Solution Y(CoxMn1−x)O3, x= 0.6, 0.7
Authors: Moure Carlos , Gutierrez Dionisio , Peña Octavio , Duran Pedro
Published: July 2009

The preparation and crystalline features of perovskite solid solution Y(CoxMn1−x)O3, x= 0.6 and 0.7, belonging to the Co‐rich region of the pseudobinary system YMnO3‐YCoO3 have been studied. Dilatometric experiments performed under different atmospheres have been carried out for determining the best conditions to obtain single‐phase samples. The influence of the thermal cycle and of the sintering density on the appearance of secondary phases has also been established. Firing in O2 atmosphere favors the formation of the pure perovskite. The cooling rate plays an important role for inhibiting the formation of secondary phases. All of the parameters depend ultimately on the final density of the polycrystalline bodies.
Interparticle Potentials in Nonaqueous Silicon Nitride Suspensions
Authors: Gutiérrez Carlos A. , Moreno Rodrigo
Published: July 2009

The rheological properties of nonaqueous silicon nitride suspensions are studied. Suspensions were prepared to volume fractions of solids of 0.21, 0.25, 0.29, and 0.33, and dispersed with phosphate ester in a mixture of solvents (methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone). Expanded viscosity curves were obtained by measuring under controlled rate and stress conditions, and the experimental data were fitted to the Cross model that provides the high shear limiting viscosity (η∞). The evolution of viscosity with volume fraction of solids was fitted to the Krieger‐Dougherty equation, to predict the maximum packing fraction (φm). The electrostatic pair potential was calculated based on the DLVO theory by evaluating the dielectric constant of the three‐component solvent and the Hamaker constant of the Si3N4–solvent system. The surface potential was calculated by measuring the elastic modulus through dynamic rheological measurements. The steric potential was also evaluated from the available models. It has been observed that phosphate ester provides a purely steric stabilization at short separation distances (up to 9 nm), while electrostatic forces dominate at larger separation distances.
Novel Method to Manufacture Porous Hydroxyapatite by Dual‐Phase Mixing
Authors: Li Shi Hong , de Wijn Joost R. , Layrolle Pierre , de Groot Klaas
Published: July 2009

We have developed a novel method to construct porous hydroxyapatite (HA) by dual‐phase mixing—in other words, generating a porous ceramic body and pore‐forming template simultaneously. The technique is based on mixing two immiscible phases: HA slurry and polymethylmethacrylate (PMMA) resin. Naphthalene particles are necessary when greater porosity (>50%) is wanted. After shaping in a mold, the mixture is subjected to polymerization, drying, pyrolysis, and sintering. The porous HA has been thoroughly characterized with Fourier transformation infrared spectrometry, X‐ray diffractometry, environmental scanning electron microscopy coupled with energy‐dispersive X‐ray analysis, and image analysis. The demanding specifications for bone ingrowth are met: (i) the size of pores and their fenestrations are adjustable, ∼80% within 300–800 μm; (ii) uniform and isotropic porous structure is observed in three directions; (iii) pores are fully interconnected throughout; (iv) the porosity is adjustable up to 60%; and (v) sufficient mechanical strength is present for cell culture and implantation handling. The porous HA can be applied as either implant material or scaffold for bone‐tissue engineering.
Fabrication of New Cemented Carbide Containing Diamond Coated with Nanometer‐Sized SiC Particles
Authors: Miyamoto Yoshinari , Kashiwagi Takehiko , Hirota Ken , Yamaguchi Osamu , Moriguchi Hideki , Tsuduki Katsunori , Ikegaya Akihiko
Published: July 2009

A simple process for depositing a coating of silicon carbide (SiC) crystallites ∼10 nm in size onto diamond particles has been developed. SiO powders react with diamond in a vacuum at 1350°C to form a uniform β‐SiC polycrystalline layer ∼60 nm thick. The SiC coating improves the oxidation resistance of the diamond. A cemented carbide material containing 20‐vol%‐SiC‐coated diamond particles was sintered to a relative density of 99.5% by pulsed‐electric‐current sintering. A Vickers hardness and indentation fracture toughness of 15 GPa and 16.3 MPa·m1/2, respectively, were obtained. This toughness is two times higher than that of cemented carbide containing no particles. The higher toughness is attributed to deflection and blockage of crack propagation by the diamond particles.
Blocking Grain Boundaries in Yttria‐Doped and Undoped Ceria Ceramics of High Purity
Authors: Guo Xin , Sigle Wilfried , Maier Joachim
Published: July 2009

CeO2 samples doped with 10, 1.0, and 0.1 mol% Y2O3 and undoped CeO2 samples of high purity were studied by impedance spectroscopy at temperatures <800°C and under various oxygen partial pressures. According to microstructural investigations by SEM and analytical STEM (equipped with EDXS), the grain boundaries were free of any second phase, providing direct grain‐to‐grain contacts. An amorphous siliceous phase was detected at only a few triple junctions, if at all; as a result, its contribution to the grain‐boundary resistance was negligible. Nevertheless, the specific grain‐boundary conductivities were still 2–7 orders of magnitude lower than the bulk conductivities, depending on dopant concentration, temperature, and oxygen partial pressure. The charge carrier transport across the grain boundaries occurred only through the grain‐to‐grain contacts, whose properties were then determined by the space‐charge layer. The space‐charge potential in acceptor‐doped CeO2 was positive, causing the simultaneous depletion of oxygen vacancies and accumulation of electrons in the space‐charge layer. The very low grain‐boundary conductivities can be accounted for by the oxygen‐vacancy depletion; the accumulation of electrons became evident in weakly doped and undoped CeO2 at high temperatures and under low oxygen partial pressures.
Effect of the Liquid‐Phase Characteristic on the Microstructures and Dielectric Properties of Donor‐ (Niobium) and Acceptor‐ (Magnesium) Doped Barium Titanate
Authors: Yoon Seok‐Hyun , Lee Je‐Hun , Kim Doh‐Yeon , Hwang Nong M.
Published: July 2009

Changes in the microstructure and dielectric properties with the variation of the donor/acceptor ratio in BaTiO3 ceramics were investigated. In donor‐rich specimens, a liquid that appeared during sintering did not penetrate into grain boundaries. However, in the acceptor‐rich specimens, the grains were separated by a liquid film during sintering. The much higher mobility of the liquid film than that of the grain boundaries was suggested to cause extensive grain growth in acceptor‐rich BaTiO3. The macroscopic homogenization of dopants because of grain growth in acceptor‐rich specimens resulted in changes in the dielectric properties.
Low‐Fire Processing (Ca1−xNd2x/3)TiO3 Microwave Ceramics
Authors: Wei Chih‐Hung , Jean Jau‐Ho
Published: July 2009

Effects of 3ZnO·2B2O3 (3Z2B) glass addition on densification and microwave properties of (Ca1−xNd2x/3)TiO3(CNT‐X) have been investigated. With the 3Z2B glass content greater than 20 vol%, the densification temperature can be greatly reduced from 1400°C for pure CNT‐X to 850°–900°C for CNT‐X + 3Z2B microwave ceramics. The above result is attributed to a chemical reaction taking place at the interface of 3Z2B/CNT‐X during firing. The Ca in CNT‐X dissolves into 3Z2B, forming a new glass of CaO‐ZnO‐B2O3 at 870°–880°C which enhances the densification kinetics of 3Z2B + CNT‐X microwave ceramics. For the samples with 20–40 vol% 3Z2B, the resulting 3Z2B + CNT‐X microwave ceramics have a dielectric constant (k) of 30–60 and a quality factor (Q) of 200–550 at 1–10 GHz, and a temperature coefficient of resonant frequency of 20–60 ppm/K in the temperature range of 20°–80°C.
Processing of Novel Strontium Titanate‐Based Thin‐Film Varistors by Chemical Solution Deposition
Authors: Ueno Kengo , Sakamoto Wataru , Yogo Toshinobu , Hirano Shin‐ichi
Published: July 2009

Strontium titanate (SrTiO3)‐based multilayered film with varistor characteristics has successfully been fabricated by a chemical solution deposition (CSD) method. Homogeneous precursor solutions of SrTiO3 and Nb:SrTiO3 with long‐term stability could be prepared by optimizing the reaction conditions among strontium ethoxide, titanium isopropoxide, and niobium ethoxide. Films were prepared using the precursor solutions on fused silica substrates at 700°C. Triple layered films with SrTiO3/Nb:SrTiO3/SrTiO3 structure were also successfully crystallized on Pt/Ti/SiO2/Si substrates at 700°C. The current–voltage (I‐V) curve of the multilayered film was characteristic to varistors and the nonlinear coefficient α of the synthesized film was ∼3.0. The varistor voltages (E0.01) of 0.6‐μm‐thick film were 140 kV/cm for the forward direction and −120 kV/cm for the reverse direction, respectively, at room temperature.
Thermal Resistance of Grain Boundaries in Alumina Ceramics and Refractories
Authors: Smith David S. , Fayette Sylvain , Grandjean Sylvie , Martin Christian , Telle Rainer , Tonnessen Thorsten
Published: July 2009

The influence of grain boundaries on heat transfer through polycrystalline alumina has been investigated between 20° and 500°C. The thermal conductivities of small‐grained porous ceramics and large‐grained dense ceramics have been measured using the laser‐flash technique. Two methods have been developed to assess the average thermal resistance of a grain boundary. The first method is based on the comparison of room‐temperature thermal conductivities for dense ceramics that have various average grain sizes. This method yields a value of 0.9 × 10−8 m2·K·W−1. The second method, particularly suitable for porous ceramics, is based on the extrapolation of the inverse of the thermal conductivity versus temperature to give an intercept with the axis at T= 0 K. This value is attributed to the thermal resistance of grain boundaries. By taking into account the influence of the pore content using an effective medium theory, the average thermal resistance of a grain boundary has been evaluated to be 1.3 × 10−8 m2·K·W−1 in dense alumina and 2.2 × 10−8 m2·K·W−1 in alumina containing a pore volume fraction of 0.3.
Substitution of Sodium and Silicon in Tricalcium Aluminate
Authors: Fukuda Koichiro , Inoue Shinji , Yoshida Hideto
Published: July 2009

Four types of tricalcium aluminate solid solutions with different concentrations of Na2O and SiO2 were prepared and examined using an electron probe microanalyzer. The atomic ratios, including those determined in a previous study, were derived from the oxide compositions and provided excellent correlations between Ca and Na + Si (i.e., Ca = 3.003 − 0.48[Na + Si]), and Al and Si (Al = 1.997 − 1.02Si). Because the replacement reactions, Ca2+↔ 2Na+ and Ca2++ 2Al3+↔ 2Si4+, independently occur within the same crystal, these reactions have been simply combined together to generate a new formula, Na2xCa3−x−y(Al1−ySiy)2O6, where x is the amount of Ca substituted by Na, and y is the amount of Al substituted by Si. This formula leads to the equations Ca = 3 − 0.5[Na + Si] and Al = 2 − Si, which nicely account for the constrained chemical variation of the actual solid solutions with 0 ≤x < 0.049 and 0 ≤y < 0.073.
Slow‐Crack‐Growth Behavior of Zirconia‐Toughened Alumina Ceramics Processed by Different Methods
Authors: De Aza Antonio H. , Chevalier Jérôme , Fantozzi Gilbert , Schehl Martin , Torrecillas Ramón
Published: July 2009

A study of slow‐crack propagation in zirconia‐toughened alumina (ZTA) ceramics is presented. Different ZTA composites, using either unstabilized or yttria‐stabilized zirconia, have been tested. The materials were prepared in the range 0–15 vol% ZrO2, using two processing methods: powder mixing and a modified colloidal route. Crack propagation tests have been conducted for crack velocities from 10−12 to 10−2 m/s by means of a double‐torsion method. The influence of the processing conditions and compositions on the microstructures and the effect of these microstructures on the slow‐crack‐growth behavior have been studied. The option that these composites may offer in terms of the lifetime of ceramic joint prostheses is discussed.
Failure Prediction Maps for a Model Al2O3|c‐ZrO2/Al2O3|Al2O3 Brittle Polycrystalline Trilayer Composite
Authors: Barnett‐Ritcey Dwayne D. , Nicholson Patrick S.
Published: July 2009

Four failure zones are defined for the three‐layer model, Al2O3|c‐Zr(8Y)O2/Al2O3|Al2O3 ceramic composite in flexure as a function of inner‐layer composition and geometry. An optimum flexural strength is predicted based on thermal expansion coefficients and elastic moduli. Tunnel‐crack threshold and flexural strength predictions are supported by experimental evidence and displayed in failure‐map form. Many three‐dimensional surface graphs and cutaways of such are used to explain the ramifications (in terms of laminate strength) of choosing various layer thickness values and inner‐layer compositions for a representative trilayer laminate system.
Role of Iron in Mullite Formation from Kaolins by Mössbauer Spectroscopy and Rietveld Refinement
Authors: Soro Nibambin , Aldon Laurent , Olivier‐Fourcade Josette , Jumas Jean Claude , Laval Jean Paul , Blanchart Philippe
Published: July 2009

This paper examines the role of iron in mullite nucleation and growth from kaolins. We chose two typical raw kaolins containing a reduced impurity level and characterized by very different degrees of crystallinity of the kaolinite phase. Both the structural iron in kaolinite and also some iron deposited onto phyllosilicate layers by a chemical route were considered. After firing in the 900–1100°C temperature range, the Fe environment was determined by Mössbauer spectroscopy. From X‐ray spectra of samples fired at 1250°C, mullite stoichiometries were obtained by Rietveld refinements. It was shown that iron contributes to the structural reorganization stage of the material, when mullite is nucleated. Fe atoms are essentially in octahedral sites, which favors an increase of the c parameter of the orthorhombic cell. The iron quantity attains a saturation level for an Fe‐to‐Al ratio between 0.3 and 0.4, depending on the raw kaolinite crystallinity. Besides mullite, the excess iron associates with titanium to form a pseudobrookite phase and hematite.
Scratch Damage in Ceramics: Role of Microstructure
Authors: Xie Zong‐Han , Hoffman Mark , Moon Robert J. , Munroe Paul , Cheng Yi‐Bing
Published: July 2009

Scratch tests were conducted using a standard pyramid indenter against α‐SiAlON ceramics with different microstructures: (i) fine equiaxed grains and (ii) large elongated grains. The formation and propagation of cracks were investigated via focused ion‐beam milling, with an emphasis on the effect of microstructure on material removal. The fine equiaxed microstructure exhibited high resistance to material removal at low loads, because of its high hardness and homogeneous structure. As the load increased, radial and lateral cracks developed, resulting in large‐scale chipping. In contrast, the large elongated microstructure showed a propensity to form microcracks and microabrasion, which is characteristic of partial grain removal, at low loads. With increasing loads, however, the large elongated grains suppressed the propagation of radial and lateral cracks, and, consequently, no large‐scale chipping occurred. Implications for material design in abrasive‐wear conditions have been discussed.
Raman Investigation of the Nitridation of Yttria‐Stabilized Tetragonal Zirconia
Authors: Deghenghi Gianluca , Chung Tai‐Joo , Sergo Valter
Published: July 2009

Raman spectroscopy has been used to obtain Raman spectra of yttria‐stabilized tetragonal zirconia subject to surface nitridation induced by contact with zirconium nitride. Raman spectra recorded from regions at increasing distance from the source of nitridation have been used to obtain diffusion profiles from samples treated at different times and temperatures. The coupling of X‐ray diffraction data previously taken and of the Raman spectra shows that in the samples there is a two‐phase region (tetragonal + cubic) near the nitrided surface and that, at larger distance inside the samples, there is only one phase (tetragonal). Fitting of the diffusive profiles in the single‐phase tetragonal region with an appropriate diffusion function allows the determination of the diffusion coefficient of nitrogen in tetragonal zirconia which is expressed in terms of the preexponential factor, D0= (3.98 ± 0.5) × 10−3 cm2/s, and the activation energy, Q= 170 ± 10 kJ/mol.
Preparation of Titanium Nitride Films from Amide Precursors Synthesized by Electrolysis
Authors: Shimada Shiro , Hasegawa Marika
Published: July 2009

A TiN precursor solution was synthesized by galvanostatic electrolysis of Ti metal and isopropylamine at a current density of 50 mA·cm−2 at room temperature. TiN films were prepared by dip‐coating of the precursor solution on a Si wafer, followed by two‐stage heat treatment at 400°C and a fixed temperature of 800–1200°C in flowing N2, N2/NH3, or NH3 gas. The TiN films were characterized by XRD, chemical analysis, XPS, and electrical resistivity measurements. The TiN films were composed of uniform grains 20 to 200 nm in size with thicknesses ranging from 300 to 400 nm at temperatures of 800–1200°C. The effect of the heat treatment atmosphere (N2 and NH3) on the impurity content, crystallinity, particle size, and electrical resistivity is discussed.
Composition and Crystallization of Hydroxyapatite Coating Layer Formed by Electron Beam Deposition
Authors: Kim Dong‐Hwan , Kong Young‐Min , Lee Su‐Hee , Lee In‐Seop , Kim Hyoun‐Ee , Heo Seong‐Joo , Koak Jai‐Young
Published: July 2009

To improve the biocompatibility of Ti‐based metal implants, a hydroxyapatite (HA) coating layer was formed on the surface by electron‐beam deposition. The dissolution rate of the coating layer was strongly dependent on the layer's calcium/phosphorus (Ca/P) ratio. Layers with a Ca/P ratio close to that of crystalline HA (Ca/P = 1.67) showed good stability in a physiologic saline solution. When the layer was crystallized by heat treatment in air at temperatures between 400° and 500°C, the stability was enhanced further while maintaining good interfacial bonding strength with the substrate. Preliminary in vivotests on rabbits indicated that heat treatment and the resultant enhancement in stability are beneficial for bone attachment to the implants.
Role of the Initial Degree of Ionization of Polyethylenimine in the Dispersion of Silicon Carbide Nanoparticles
Authors: Zhu Xinwen , Tang Fengqiu , Suzuki Tohru S. , Sakka Yoshio
Published: July 2009

The role of the initial degree of ionization (αi) of polyethylenimine (PEI) in the dispersion of SiC nanopartilces in water was investigated by sedimentation and rheological measurements. The ionization of PEI was characterized by potentiometric titration, which indicated a pH‐dependent conformational transition. The dispersion of SiC particles in the presence of PEI was found to strongly depend on the αi. In the presence of 0.4% by weight PEI, the 23.8% SiC by volume (ΦSiC= 23.8) slurries showed a Newtonian behavior for αi= 0.12–0.4 values, whereas a shear‐thinning behavior was observed for αi > 0.4 in the optimal pH range of around pH 4. The rheological behavior of the slurries exhibited a strong dependence on the concentration of PEI of αi= 0.12–0.4 and the slurry showed a Newtonian behavior at an optimal concentration of 0.4% by weight. The stabilization may be dominated by an electrosteric effect arising from the adsorbed PEI of αi= 0.12–0.4. The flocculation mechanism of the slurries with PEI of αi > 0.4 is also discussed.
Preparation of 0.95Bi1/2Na1/2TiO3·0.05BaTiO3Ceramics by an Aqueous Citrate‐Gel Route
Authors: West David L. , Payne David A.
Published: July 2009

This report details development of a route to solution‐derived (1−x)Bi1/2Na1/2TiO3·xBaTiO3powders. The method developed was the citrate‐gel method—an evaporative, aqueous technique. When applied to 0.95Bi1/2Na1/2TiO3·0.05BaTiO3(BNBT‐5), the method produced perovskite phase powders that readily densified in the temperature range of 1000°C. The grain size of the sintered materials was on the order of 1 μm, and the weak‐field dielectric properties at 1 MHz were similar to those reported for conventionally prepared materials sintered at higher temperatures (e.g., 1200°C).
Microstructure Tailoring for High Thermal Conductivity of β‐Si3N4 Ceramics
Authors: Yokota Hiroshi , Ibukiyama Masahiro
Published: July 2009

β‐Si3N4 ceramics sintered with Yb2O3 and ZrO2 were fabricated by gas‐pressure sintering at 1950°C for 16 h changing the ratio of “fine” and “coarse” high‐purity β‐Si3N4 raw powders, and their microstructures were quantitatively evaluated. It was found that the amount of large grains (greater than a few tens of micrometers) could be drastically reduced by mixing a small amount of “coarse” powder with a “fine” one, while maintaining high thermal conductivity (>140 W·(m·K)−1). Thus, this work demonstrates that it is possible for β‐Si3N4 ceramics to achieve high thermal conductivity and high strength simultaneously by optimizing the particle size distribution of raw powder.
A Novel Processing Route to Develop a Dense Nanocrystalline Alumina Matrix (<100 nm) Nanocomposite Material
Authors: Zhan Guo‐Dong , Kuntz Joshua , Wan Julin , Garay Javier , Mukherjee Amiya K.
Published: July 2009

A dense 3‐mol%‐yttria‐stabilized tetragonal zirconia polycrystalline (3Y‐TZP) toughening alumina matrix nanocomposite with a nanocrystalline (<100 nm) matrix grain size has been successfully developed by a novel processing method. A combination of very rapid sintering at a heating rate of 500°C/min and at a sintering temperature as low as 1100°C for 3 min by the spark‐plasma‐sintering technique and mechanical milling of the starting γ‐Al2O3 nanopowder via a high‐energy ball‐milling process can result in a fully dense nanocrystalline alumina matrix ceramic nanocomposite. The grain sizes for the matrix and the toughening phase were 96 and 265 nm, respectively. A great increase in toughness almost 3 times that for pure nanocrystalline alumina has been achieved in the dense nanocomposite. Ferroelastic domain switching without undergoing phase transformation in nanocrystalline t‐ZrO2 is likely as a mechanism for enhanced toughness.
Tetragonal Nanocrystalline Barium Titanate Powder: Preparation, Characterization, and Dielectric Properties
Authors: Xu Huarui , Gao Lian
Published: July 2009

Nanocrystalline tetragonal‐BaTiO3 powder was prepared using a hydrothermal method, under moderate conditions, and with a high precursor concentration. Characterization via X‐ray diffractometry and differential scanning calorimetry confirmed that the average particle size and tetragonal content of the prepared powder were 70 nm and 80%, respectively. The sintered sample made from the prepared powder had a room‐temperature dielectric constant of 6900, which was high for BaTiO3.
Reduction‐Nitridation Synthesis of Titanium Nitride Nanocrystals
Authors: Yang Xiaogang , Li Cun , Yang Lihua , Yan Yan , Qian Yitai
Published: July 2009

Titanium nitride (TiN) particles (8 nm) were prepared via a reduction‐nitridation route in an autoclave at 500°C, using TiCl4, NH4Cl, and metal Na as reactants. X‐ray powder diffraction indicated that the product was a NaCl‐type of TiN with a cell constant a= 4.242 Å. Transmission electron microscopy images showed that the TiN particles were 5–10 nm. Raman spectra showed the defect‐induced first‐order shifts in the TiN nanocrystals.
Metabolic adaptation of Phytophthora infestans during growth on leaves, tubers and artificial media
Authors: JUDELSON HOWARD S. , TANI SHUJI , NARAYAN REENA D.
Published: July 2009

Efficient nutrient acquisition is critical to the fitness of plant pathogens. To address how the late blight agent Phytophthora infestans adapts to nutrients offered by its hosts, genes in glycolytic, gluconeogenic and amino acid pathways were mined from its genome and their expression in different plant tissues and artificial media was measured. Evidence for conventional glycolytic and gluconeogenic processes was obtained, although several steps involved pyrophosphate‐linked transformations which are uncommon in eukaryotes. In media manipulation studies, nearly all genes in the pathways were subject to strong transcriptional control. However in rye–sucrose media, tomato leaflets, potato tubers and, at both early and late stages of infection, most glycolytic genes were expressed similarly, which indicated that each plant tissue presented a nutrient‐rich environment. Biochemical analyses also demonstrated that sporulation occurred from host material in which sugars were abundant, with fructose and glucose increasing at the expense of sucrose late in the disease cycle. The expression of only a few genes changed late in infection, with the most notable example being lower invertase levels in the sucrose‐reduced leaves. Interestingly, most gluconeogenic genes were up‐regulated in tubers compared with other tissues. Rather than reflecting a starvation response, this probably reveals the role of such enzymes in converting carbon skeletons from the abundant free amino acids of tubers into citric acid cycle and glycolysis intermediates, as genes involved in amino acid catabolism were also more highly expressed in tubers. The corresponding enzymes also displayed higher activities in defined media when amino acids were abundant, as in tubers.
Pliocene onset of rapid exhumation in Taiwan during arc–continent collision: new insights from detrital thermochronometry
Authors: Kirstein L. A. , Fellin M. G. , Willett S. D. , Carter A. , Chen Y.‐ G. , Garver J. I. , Lee D. C.
Published: July 2009

The Coastal Range in eastern Taiwan contains the remnants of the Pliocene–Pleistocene retro‐foredeep basin of the ongoing Penglai orogeny. These sedimentary successions record the earliest exhumation of the Central Range, Taiwan. We dated detrital Plio‐Pleistocene sediments in the Coastal Range using multiple thermochronometers [fission‐track, zircon (U–Th)/He and U/Pb dating] to document changes in exhumation rate through time. Fission‐track grain ages in 2–4‐Myr‐old sediments were not reset by the Penglai orogeny and reflect the early stage removal of the sedimentary cover. This early stage, when exhumation rates were low, could encompass both the accretionary wedge phase of the orogen and the early arc–continent collision. Sediments younger than 2‐Myr‐old yield Pliocene zircon fission‐track grain ages and suggest that exhumation, transport and deposition occurred within 0.4–1.5 Myr. The recorded onset of rapid exhumation in the Pliocene is contemporaneous with other major tectonic changes in the region, including an increase in subsidence rate in both the pro‐ and retro‐foredeep basins and a change in the wedge kinematics from internal shortening to underplating.
Association of G‐protein‐coupled receptor 154 with asthma and total IgE in a population of the Caribbean coast of Colombia
Authors: Vergara C. , Jiménez S. , Acevedo N. , Martínez B. , Mercado D. , Gusmão L. , Rafaels N. , Hand T. , Barnes K. C. , Caraballo L.
Published: July 2009

Background
G protein‐coupled receptor 154 was described as an asthma susceptibility gene by positional cloning. It has been subsequently associated with asthma and other inflammatory diseases in several populations with different ethnic origin. Replication of associations adds reliability to these findings.

Objective
To analyze the association of G protein‐coupled receptor 154 with asthma and total and mite‐specific IgE levels in a population of the Caribbean Coast of Colombia.

Methods
We genotyped seven single nucleotide proteins (SNPs) in GPR154 in 475 asthmatics, 394 controls and 116 families from Cartagena, Colombia using either SnaPshot or TaqMan. Total and specific IgE against Blomia tropicalis and Dermatophagoides pteronyssinus were determined by ELISA. Hardy–Weinberg equilibrium was assessed and case–control and family‐based analyses were performed to evaluate the association between the SNPs and their haplotypes and asthma and IgE. Association analyses in the case–control dataset were corrected by population stratification using 52 ancestry informative markers.

Results
Allelic distribution was similar to that described in other populations. Two SNPs were associated with the same direction of the effect in both datasets. Allele A of Hopo546333 was protective for asthma (case–control OR: 0.42; 95% CI: 0.17–0.99, P=0.042; P=0.043; families Z score=−2,236; P=0.025). Similarly, allele C of rs740347 conferred low risk for asthma (OR: 0.44; 95% CI: 0.28–0.70, P=0.00017; Pc=0.00037) and total IgE (OR: 0.29; 95% CI: 0.09–0.88, P=0.015; Pc=0.030) in the case–control study and families (Z score=−3.207, P=0.0013; Z score=−3.182, P=0.0014, respectively). Haplotype CCAGGT was associated with total IgE (OR: 1.76; 95% CI: 1.14–2.71, P=0.006, Pc=0.007) in the case–controls group and CGCGGT with both phenotypes (P=0.044 and P=0.032, respectively) in families. Neither SNPs nor haplotypes were associated with levels of mite‐specific IgE.

Conclusions
Our findings in a sample of asthmatics from Colombia suggest a relevant role of G protein‐coupled receptor 154 in the pathogenesis of asthma and allergy.
On the putative role of transient receptor potential cation channels in asthma
Authors: Colsoul B. , Nilius B. , Vennekens R.
Published: July 2009

The mammalian transient receptor potential (TRP) superfamily consists of 28 mammalian TRP cation channels, which can be subdivided into six main subfamilies: the TRPC (‘Canonical’), TRPV (‘Vanilloid’), TRPM (‘Melastatin’), TRPP (‘Polycystin’), TRPML (‘Mucolipin’) and the TRPA (‘Ankyrin’) groups. Increasing evidence has accumulated during the previous few years that links TRP channels to the cause of several diseases or to critically influence and/or determine their progress. This review focuses on the possible role of TRP channels in the aetiology of asthmatic lung disease.