bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Codoping on the R‐Line Luminescence of Cr3+‐Doped Alumina
Authors: Yu Haijiang , Clarke David R.
Published: July 2009

The frequency of the R‐line luminescence from Cr3+ ions in aluminum oxide is known to be sensitive to chromium concentration, stress, and temperature. In this work, the effect of simultaneously doping aluminum oxide with both Cr3+ and other ions (Fe, Ti, Ni, or Y) on the R‐line frequency and intensity at room temperature is investigated. It is concluded that ions soluble in aluminum oxide cause systematic shifts in the luminescence frequency and intensity whereas those ions that are insoluble have no effect on the R‐line luminescence. In addition, it is shown that contrary to previous investigations, the ratio of the N1 to R line intensities is not simply related to the chromium concentration and hence cannot be used as a measure of the chromium concentration.
Intrinsic Elastic, Dielectric, and Piezoelectric Losses in Lead Zirconate Titanate Ceramics Determined by an Immittance‐Fitting Method
Authors: Tsurumi Takaaki , Kil Young‐Bae , Nagatoh Kouhei , Kakemoto Hirofumi , Wada Satoshi , Takahashi Sadayuki
Published: July 2009

The material coefficients of “soft” and “hard” lead zirconate titanate (PZT) ceramics were determined as complex values by the nonlinear least‐squares‐fitting of immittance data measured for length‐extensional bar resonators. The piezoelectric d‐constant should be a complex value to obtain a best fitting between observed and calculated results. Because the elastic, dielectric, and piezoelectric losses determined in this process were not “intrinsic” losses, a calculation process to evaluate the “intrinsic” losses was proposed. It was confirmed that the intrinsic losses were smaller than the corresponding extrinsic losses. The intrinsic piezoelectric loss existed in both soft and hard PZTs; ∼50% of the loss of piezoelectric d‐constant was derived from the elastic and dielectric losses. The most notable difference between the soft and hard PZTs was observed in their elastic losses.
In‐Plane Polarized 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films
Authors: Zhou Qifa , Zhang Qingqi , Xu Baomin , Trolier‐McKinstry Susan
Published: July 2009

Ferroelectric 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN‐PT) thin films were deposited on ZrO2/SiO2/silicon substrates using a chemical‐solution‐deposition method. Using a thin PZT film as a seed layer for the PMN‐PT films, phase‐pure perovskite PMN‐PT could be obtained via rapid thermal annealing at 750°C for 60 s. The electrical properties of in‐plane polarized thin films were characterized using interdigitated electrode arrays on the film surface. Ferroelectric hysteresis loops are observed with much larger remanent polarizations (∼24 μC/cm2) than for through‐the‐thickness polarized PMN‐PT thin films (10–12 μC/cm2) deposited on Pt/Ti/Si substrates. For a finger spacing of 20 μm, the piezoelectric voltage sensitivity of in–plane polarized PMN‐PT thin films was ∼20 times higher than that of through‐the‐thickness polarized PMN‐PT thin films.
Preparation and Characterization of Sol—Gel‐Derived Lead Magnesium Niobium Titanate Thin Films with Pure Perovskite Phase and Lead Oxide Cover Coat
Authors: Fan Huiqing , Park Gun‐Tae , Choi Jong‐Jin , Kim Hyoun‐Ee
Published: July 2009

A sol–gel‐derived Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMNT) thin film was prepared using spin coating and a PbO cover coat technique. The amount of lead excess in the precursor solution had significant effects on the phase development and microstructure of the PMNT film. The PbO cover coat proved to be effective on suppressing the formation of pyrochlore phases. PMNT thin films with a pure perovskite structure were obtained by adding 30 mol% excess lead in the precursor solution and coating the PbO layer on the top of the film. The remnant polarization (Pr), the dielectric constant (ɛr), and the dissipation factor (tan δ) of these thin films, which had a thickness of 150 nm, were determined to be 9 μC/cm2, 1370, and 0.031, respectively.
Evidence for Bulk Residual Stress Strengthening in Al2O3/SiC Nanocomposites
Authors: Ferroni Luca Paolo , Pezzotti Giuseppe
Published: July 2009

The fracture behavior of Al2O3/SiC nanocomposites has been studied as a function of the SiC volume fraction and compared to that of the pure Al2O3matrix. A pronounced strengthening effect was only observed for materials with low SiC content (i.e., ≤10 vol%) although no evidence of concurrent toughening was found. Assessment of near‐tip crack opening displacement (COD) could not experimentally substantiate significant occurrence of an elastic crack‐bridging mechanism, in contrast with a recently proposed literature model. Quantitative fractography analysis indicated that transgranular crack propagation in Al2O3/SiC nanocomposites depends on the location of the SiC dispersoids within the matrix texture; the higher the fraction of transgranularly located dispersoids, the more transgranular the fracture mode. Experimental evidence of remarkably high residual stresses arising from thermal dilatation mismatch (upon cooling) between Al2O3and SiC phases were obtained by fluorescence and Raman spectroscopy. A strengthening mechanism is invoked which merely arises from residual stress through strengthening of Al2O3grain boundaries.
Oxidation of Silicon and Silicon Carbide in Ozone‐Containing Atmospheres at 973 K
Authors: Narushima Takayuki , Kato Michihisa , Murase Shin , Ouchi Chiaki , Iguchi Yasutaka
Published: July 2009

The oxidation behavior of a silicon wafer, chemically vapor‐deposited SiC, and single‐crystal SiC was investigated in an oxygen—2%–7% ozone gas mixture at 973 K. The thickness of the oxide film that formed during oxidation was measured by ellipsometry. The oxidation rates in the ozone‐containing atmosphere were much higher than those in a pure oxygen atmosphere. The parabolic oxidation kinetics were observed for both silicon and SiC. The parabolic rate constants varied linearly with the ozone‐gas partial pressure. Inward diffusion of atomic oxygen formed by the dissociation of ozone gas through the SiO2 film apparently was the rate‐controlling process.
Crystal Structure of Lu4Si2O7N2 Analyzed by the Rietveld Method Using the Time‐of‐Flight Neutron Powder Diffraction Pattern
Authors: Takahashi Junichi , Yamane Hisanori , Shimada Masahiko , Yamamoto Yoshinobu , Hirosaki Naoto , Mitomo Mamoru , Oikawa Kenichi , Torii Shuki , Kamiyama Takashi
Published: July 2009

The crystal structure of a lutetium silicon oxynitride (Lu4Si2O7N2) was analyzed by the Rietveld method using time‐of‐flight (TOF) neutron powder diffraction data. The compound crystallizes in a monoclinic cell, space group P21/c (No. 14‐1) with a= 7.4243(1), b= 10.2728(1), c= 10.6628(1) Å, and β= 109.773(1)° at 297 K. One nitrogen atom in Lu4Si2O7N2 occupies the bridging site between the two Si atoms, and the other one is statistically situated at the terminal sites of Si2O5N2 ditetrahedra. In the local structure, Si2O5N2 ditetrahedra consist of SiO3N and SiO2N2 tetrahedral units sharing the N atom. Lu atoms are in sixfold, sevenfold (×2) and eightfold coordinations of O/N atoms. X‐ray powder diffraction data were also analyzed with the model obtained by the neutron diffraction.
Effect of Germanium Oxide (GeO2) Additive on the Anatase‐to‐Rutile Phase Transition
Authors: Okada Kiyoshi , Katsumata Ken‐ichi , Kameshima Yoshikazu , Yasumori Atsuo
Published: July 2009

The effect of germanium oxide (GeO2) addition on the anatase‐to‐rutile phase transition was investigated by differential thermal analysis (DTA), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). TiO2 xerogels containing up to 20 mol% GeO2 were prepared by refluxing and hydrolyzing titanium tetraisopropoxide (TTIP) and germanium butoxide (GB) using nitric acid as a catalyst. The following occurred with increasing amounts of GeO2 in the xerogels: (i) the crystallization temperature of anatase increased from 410° to 565°C and the DTA temperature of the anatase‐to‐rutile phase transition increased from 676° to 977°C in 20 mol% GeO2‐containing xerogel; (ii) the crystallite size of anatase became smaller; (iii) the lattice a‐parameter of the anatase showed little change, but the c‐parameter decreased up to 20 mol% GeO2; (iv) both the lattice a‐ and c‐parameters of the rutile decreased monotonically. From these results, the added GeO2 is considered to become incorporated into the anatase structure. The following occurred with increasing anatase heating temperature: (i) the lattice c‐parameter of the anatase increased gradually and approached the value of pure anatase; and (ii) the chemical composition of the xerogel surfaces, measured by XPS, showed an increase in GeO2 content, indicating the expulsion of GeO2 from the anatase to form an amorphous surface layer. The formation of this amorphous GeO2 surface layer is thought to play an important role in retarding the anatase‐to‐rutile phase transition by suppressing diffusion between the anatase particles in direct contact, and limiting their ability to act as surface nucleation sites for rutile, as in the case of SiO2 additions. However, GeO2 addition is less effective than SiO2 in retarding the phase transition.
Effect of Phase Transformation on the Densification of Coprecipitated Nanocrystalline Indium Tin Oxide Powders
Authors: Kim Bong‐Chull , Kim Sung‐Min , Lee Joon‐Hyung , Kim Jeong‐Joo
Published: July 2009

Two kinds of nanocrystalline indium tin oxide (ITO) powders with different crystal structures—rhombohedral and cubic—were prepared using a coprecipitation process through the control of aging time of precipitates after coprecipitation. The densification characteristics of the two ITO powders were examined. During sintering the rhombohedral ITO, which is a high‐pressure phase, was transformed to cubic around 900°C. The phase transformation induced coarsening of grains and many voids in the microstructure retarded densification. On the other hand the cubic ITO, which did not experience phase transformation during sintering, was well densified as the sintering temperature increased. Poor densification of the rhombohedral ITO powder is explained from the viewpoint of coarsening of grains during the phase transformation. This result shows the significance of phase transformation during sintering.
Effects of an Electroplated Platinum Interlayer on the Morphology and Phases of Chemically‐Vapor‐Deposited Alumina on Single‐Crystal, Nickel‐Based Superalloy
Authors: Su Yi‐Feng , Torzilli Michele A. , Meyer Justin Daniel , Rawn Claudia J. , Lance Michael J. , Ruppi Sakari , Lee Woo Y.
Published: July 2009

The feasibility of preparing a thin layer of α‐Al2O3 on the surface of a single‐crystal, Ni‐based superalloy was examined using a chloride‐based chemical vapor deposition (CVD) process previously developed for cutting tool applications. A coating directly deposited by this method on the alloy surface consisted of ∼1 μm α‐Al2O3 crystals in a matrix of amorphous Al2O3. When the alloy surface was predeposited with an electroplated Pt layer, the coating was mostly α‐Al2O3, but with the presence of fine microcracks on the coating surface. In comparison to the results observed for pure Pt substrate, the role of the Pt interlayer was apparently to promote the rapid formation of κ‐Al2O3 nuclei, which subsequently transformed to α‐Al2O3 during the CVD growth process.
Preparation and Growth Mechanism of Molybdenum Trioxide Whisker
Authors: Li Jianqiang , Wei Pan , Chen Jian , Rongti Li
Published: July 2009

A new whisker, α‐MoO3, was fabricated via molybdenum thread oxidation at 973, 1023, and 1173 K. Various morphologies of the whiskers, such as flakelike, platelike, and needlelike, were observed under different fabrication conditions. The lateral surfaces of the whiskers were close‐packed (010) plane, and the growth direction was (001), which related to the unique layered structure of the α‐MoO3 crystal. Growth of the MoO3 whiskers was attributed to a vapor‐liquid‐solid (VLS) mechanism at 1023 and 1173 K, whereas, at 973 K, growth was attributed to a vapor‐liquid (VL) mechanism.
Mechanically Stable Monoclinic Zirconia–Nickel Composite
Authors: Moya José S. , López‐Esteban Sonia , Pecharromán Carlos , Bartolomé José F. , Torrecillas Ramón
Published: July 2009

A dense (>98% theoretical density), residual‐stress‐free m‐ZrO2/40 vol% nickel composite with K IC∼ 5.4 MPa·m1/2 and ςf∼ 225 MPa has been obtained using a simple wet processing route and subsequent sintering at 1430°C in a 90% argon/10% hydrogen atmosphere. The mechanism for release of internal stresses by the composite developed during the t → m transformation on cooling is explained in terms of plastic flow in the infinite nickel cluster formed at the percolation threshold.
Thermal Shock Behavior of Porous Silicon Carbide Ceramics
Authors: She Jihong , Ohji Tatsuki , Deng Zhen‐Yan
Published: July 2009

Using the water‐quenching technique, the thermal shock behavior of porous silicon carbide (SiC) ceramics was evaluated as a function of quenching temperature, quenching cycles, and specimen thickness. It is shown that the residual strength of the quenched specimens decreases gradually with increases in the quenching temperature and specimen thickness. Moreover, it was found that the fracture strength of the quenched specimens was not affected by the increase of quenching cycles. This suggests a potential advantage of porous SiC ceramics for cyclic thermal‐shock applications.
Protective Silica Coatings on Zinc‐Sulfide‐Based Phosphor Particles
Authors: Villalobos Guillermo R. , Bayya Shyam S. , Sanghera Jasbinder S. , Miklos Robert E. , Kung Frederic , Aggarwal Ishwar D.
Published: July 2009

A spray drying approach was used to apply 15‐nm‐thick SiO2 continuous coatings onto ZnS:Ag phosphor particles. A prehydrolyzed TEOS dip coating formula was used as the SiO2 precursor. The phosphor was mixed together with the precursor then atomized without allowing gelation to occur until the droplets containing the particles were in flight. The coating gelled and dried while falling through a graded heat zone. The dried coated particles were captured in a cyclone separator and heat‐treated to further densify the SiO2 coating. The coatings protected the phosphors while in service in field emission display (FED) devices.
Formation of Silica‐Coated Carbon Powder and Conversion to Spherical β‐Silicon Carbide by Carbothermal Reduction
Authors: Jung Yoon Seok , Kwon Ou Jung , Oh Seung M.
Published: July 2009

Spherical β‐SiC powders that are a few micrometers in size have been prepared by heating a mixture of phenolic resin powder and fine‐grained fumed silica at 1600°C in argon. The overall process is composed of two consecutive steps: (i) the formation of silica‐coated spherical carbon powder and (ii) carbothermal reduction. The irregularly shaped resin powder transforms to a spherical‐shaped morphology in the first step, and the resulting silica‐coated spherical carbon powder is converted to β‐SiC in the second step. The key factor in the first step is the utilization of fumed silica that has hydrophobic surface functional groups. Hydrophobic interactions at the point of intimate contact between the resin powder and the silica likely reduce the surface energy of the resin powder, thereby discouraging interparticle coalescence. The resulting β‐SiC powder exhibits a radially developed columnar microstructure. Hollow β‐SiC spheres also can be prepared by controlling the reaction conditions in the carbothermal reduction step.
Constitutive Model for Cold Compaction of Ceramic Powder
Authors: Kim Hyoung Seop , Oh Sung‐Tag , Lee Jai‐Sung
Published: July 2009

Densification behavior of ceramic powder by pressure at room temperature was investigated using the constitutive equation based on plastic deformation theory for porous materials (the Lee‐Kim model). The modified Lee‐Kim constitutive model with two parameters is compared with the Shima model (four parameters) and the Cam‐Clay model (three parameters and one polynomial equation). The calculated yield loci using the modified Lee‐Kim model were compared with the experimental and calculated data for silicon nitride (Si3N4) powder. Contrary to the conclusion of some previous researchers, all three models simulate densification behavior of ceramic powder reasonably well.
Formation of an Environmental Barrier Coating Using DC–RF Hybrid Plasma
Authors: Otsuka Akihiko , Yamamoto Masafumi , Itoh Takashi , Kitagawa Kuniyuki , Hirano Shin‐ichi
Published: July 2009

The characteristics of an Al2O3 coating on a Nb or Mo substrate using a direct current‐radio frequency induction (DC‐RF) thermal plasma of Ar‐H2 were studied. A porous and crystallographically stable coating with highly preferred orientation of {110} planes of α‐Al2O3 crystals was obtained. The preferred orientation was strongly dependent on the diameter of the introduced Al2O3 powder. The formation mechanism of the preferred orientation of the coating is explained by accumulation of charged clusters on the substrate. The coating prepared by this procedure revealed the superior capability of protecting the substrate against high‐temperature oxidation.
Processing and Tribological Properties of Si3N4/Carbon Short Fiber Composites
Authors: Hyuga Hideki , Hirao Kiyoshi , Jones Mark I. , Yamauchi Yukihiko
Published: July 2009

Si3N4/carbon fiber composites were fabricated using several types of fiber. All the composites had higher fracture toughness compared with monolithic Si3N4 ceramics. Tribological properties were investigated by a ball‐on‐disk method under unlubricated conditions. The composite containing fibers with a high orientation of graphite layers and high graphite content indicated a low friction coefficient. It was identified, by Raman spectroscopy, that graphite was transferred from the composite to the Si3N4 ball of the counterbody during the wear test. This transferred layer was effective for producing the low friction behavior of the composite.
Reaction Synthesis of Magnesium Silicon Nitride Powder
Authors: Lenčéš Zoltán , Hirao Kiyoshi , Yamauchi Yukihiko , Kanzaki Shuzo
Published: July 2009

The synthesis of magnesium silicon nitride (MgSiN2) by direct nitridation of a Si/Mg2Si/Mg/Si3N4 powder mixture is described. A nucleation period at 550°C and stepwise heat‐treatment schedule up to 1350°C was adopted for the synthesis of MgSiN2 powder, based on TG‐DTA measurements. The influence of the ratio of constituents on the final phase composition also has been studied. The content of magnesium and silicon in the starting powder should fulfill the conditions Mg2Si/Mg ≥ 3 and Si3N4/Sitot≥ 0.5 to obtain single‐phase MgSiN2. The silicon particle size of <0.5 μm is preferable to decrease the time of nitridation. The oxygen content of as‐synthesized powders is in the range 0.9–1.2 wt%. However, the oxygen content of MgSiN2 powder decreases further by the addition of 2 wt% CaF2 or 0.75 wt% carbon and reaching the lowest value of 0.45 wt% oxygen after carbothermal reduction in an alumina‐tube furnace.
Critical Evaluation of Hot Forging Experiments: Case Study in Alumina
Authors: Zuo Ruzhong , Aulbach Emil , Bordia Rajendra K. , Rödel Jürgen
Published: July 2009

A new loading dilatometer was successfully developed and applied for hot forging experiments, assisted by two high‐resolution laser beams and providing accurate determination of radial and axial strains. The application of various uniaxial loads linearly increased both radial and axial strain rates of cylindrical specimens if compared at constant density. Microstructural evolution during hot forging was followed with high‐resolution scanning electron microscopy and quantitative analysis of pore size and orientation. Uniaxial loads led to elongated pores oriented in the direction of the applied load. This anisotropic microstructure exhibited an increased densification rate perpendicular to the loading axis, if free sintering was characterized after load removal. The imprinted anisotropy faded out during free sintering.
Nanocrystalline Aluminum Nitride: I, Vapor‐Phase Synthesis in a Forced‐Flow Reactor
Authors: Panchula Martin L. , Ying Jackie Y.
Published: July 2009

A forced‐flow reactor has been designed for the synthesis of nanocrystalline AlN via in situ and ex situ nitridation of aluminum. Various reactor parameters, including evaporation temperature, microwave plasma generation, reactor pressure, gas flow rate, nitriding gas, carrier gas, and crucible purge, have been examined and optimized. Fully nitrided powders with crystallite sizes of 10–100 nm and surface areas of 45–370 m2/g were produced using these techniques. These ultrafine AlN particles were highly moisture‐sensitive, but they could be processed and handled without exposure to air to achieve fully dense materials with low oxygen content.
Nanocrystalline Aluminum Nitride: II, Sintering and Properties
Authors: Panchula Martin L. , Ying Jackie Y.
Published: July 2009

Nanocrystalline aluminum nitride powders obtained from gas condensation and in situ nitridation in a forced‐flow reactor have been sintered successfully without pressure or additives. The resulting densified pellets showed good thermal conductivity and low oxygen content. A comparison of the improvement in densification with micrometer‐size and nanocrystalline yttria additives was undertaken and it was found that the nanocrystalline yttria decreased the sintering temperature significantly. Besides spherical nanoparticles, needle‐shaped nanocrystalline aluminum nitride particles that resulted in highly textured compacts when hot pressed could also be produced.
Reactive‐Templated Grain Growth of Bi1/2(Na,K)1/2TiO3: Effects of Formulation on Texture Development
Authors: West David L. , Payne David A.
Published: July 2009

In this paper we report the effects of formulation on texture development for the “reactive‐templated grain growth” (RTGG) of Bi1/2(Na,K)1/2TiO3 (BNKT). The solids formulation for BNKT was systematically varied by prereacting to well—defined alkali and bismuth titanates (Na2Ti3O7 (N2T3), K2Ti2O5 (K2T2), and Bi2Ti4O11 (B2T4)). Use of these precursors in different BNKT formulations determined that the amount of expansion associated with reacting dry‐pressed compacts at 600−800°C could be influenced by formulation. Lotgering factors (F00l) derived from Θ/2Θ X‐ray diffraction scans indicated that the formulation route strongly affected the {00l} texture development in tape‐cast and sintered specimens. Prereacting alkali carbonates with TiO2 to form N2T3 and K2T2 inhibited texture development in RTGG‐processsed BNKT. However, when Bi2O3 was prereacted to form B2T4, the measured F00l increased from 0.5 to 0.7.
Drying Stages during the Heating of High‐Alumina, Ultra‐Low‐Cement Refractory Castables
Authors: Innocentini Murilo D. M. , Cardoso Fábio A. , Akyioshi Mario M. , Pandolfelli Victor C.
Published: July 2009

The purpose of this work was to investigate the drying kinetics of high‐alumina, ultra‐low‐cement refractory castables under continuous heating conditions. Three main drying stages were identified during the castable heat‐up and were related to the phase change of free water and to the decomposition of hydrated products present in the body. A clear correlation was found between the actual heating profile inside the castable and the dewatering stages under various heating schedules. Thermal analysis was used to assess the drying temperature that represents the highest risk of steam pressure buildup and, thus, of explosive spalling.
Aqueous Combustion Synthesis of Strontium‐Doped Lanthanum Chromite Ceramics
Authors: Deshpande Kishori , Mukasyan Alexander , Varma Arvind
Published: July 2009

An aqueous combustion synthesis is used to produce powders of La0.8Sr0.2CrO3 perovskite. It is shown that interaction between chromium nitrate and glycine controls the process. In addition, it is suggested that glycine reacts with products of nitrate decomposition to yield an intermediate compound, which decomposes exothermically providing high‐temperature conditions for complex oxide formation. It is remarkable that although reaction temperature is high (up to 800°C) and characteristic time is small (∼1 s) for synthesis under the self‐propagating high‐temperature mode, the produced perovskites have high specific surface area (∼40 m2/g) and well‐defined crystalline structure. As a result, ceramics sintered by using these powders are dense (∼96% of theoretical) and possess high electronic and low ionic conductivities, important for interconnect applications in solid oxide fuel cells.
Optimization of a Composite Working Electrode for a New Family of Electrochemical Cell for NO Decomposition
Authors: Matsuda Kazuyuki , Bredikhin Sergei , Maeda Kunihiro , Awano Masanobu
Published: July 2009

The electrochemical properties of a composite (NiO)x−(yttria‐stabilized zirconia (YSZ))1–x working electrode for a new type of electrochemical cell for NO decomposition in the presence of excess oxygen are investigated. It is shown that the dependence of the NO conversion on the value of the current passed through the electrochemical cell with a nanoporous (NiO)x−(YSZ)1–x working electrode is linear and that the value of current efficiency depends on the NO and O2 gas concentrations only (η= [NO] /([NO] + 2[O2]). The optimum NiO addition (35% by volume) to the YSZ resulted in a decrease of the cell operating voltage and, as a result, in a decrease in the electrical power required for NO decomposition. The observed high performance of the composite working electrode at this composition is consistent with the effective medium percolation theory, which predicts the ambipolar transport behavior of the composite mixed ionic−electronic (YSZ–NiO) conductors as a function of the volume fraction of each of the randomly distributed constituent phases.
Effect of Seeding on the Microstructure and Mechanical Properties of α‐SiAlON: III, Comparison of Modifying Cations
Authors: Zenotchkine M. , Shuba R. , Chen I‐Wei
Published: July 2009

Single‐phase in situ toughened SiAlON ceramics containing various modifying cations and single‐crystal seeds were studied. The modifying cations include rare‐earth cations from the smallest to the largest allowed in the α‐SiAlON structure (Yb to Y, to Nd), and from monovalent to trivalent (Li to Ca, to rare earths). At low seeding levels, the aspect ratio of grains increases with the size of modifying cations, giving rise to rather different appearances of the microstructure in different SiAlONs. A one‐to‐one correspondence between seed crystals and large grains at low seeding levels is also observed. An optimal amount of seeds is required to maximize the fracture toughness, which is controlled by grain pullout with the fracture energy that scales with the fraction of elongated grains, their width, and their aspect ratio. The optimal amount of seeds required to reach maximal toughening increases with the aspect ratio of grains and is the lowest (1%) in Y‐ and Yb‐SiAlONs.
Synthesis and Characterization of Nanocrystalline Niobium Nitride Powders
Authors: Li Yaogang , Gao Lian
Published: July 2009

Nanocrystalline NbN powder was synthesized by the direct nitridation of amorphous Nb2O5 powder with high BET surface area. X‐ray diffractometry analysis indicated that the cubic‐phase NbN powder could be obtained by nitridation at 650°–800°C for 3–8 h. Transmission electron microscopy images showed that the particle sizes were in the range of 15–40 nm. The effect of the nitridation temperature and holding time on the powder properties was discussed.
Experimental Design Applied to Silicon Carbide Sintering
Authors: Marchi Juliana , Bressiani José Carlos , Bressiani Ana Helena de A.
Published: July 2009

Silicon carbide is a promising structural ceramic used as abrasives and applied in metallurgical components, due to its low density, high hardness, and excellent mechanical properties. The composition and content of the additive can control liquid‐phase sintering of SiC. Compositions based on the SiO2–Al2O3–RE2O3 system (RE = rare earth) have been largely used to promote silicon carbide densification, but most studies are not systematically presented. The aim of this work is to study the effect of several oxide additives in the SiO2–Al2O3–Y2O3 system on the densification of silicon carbide using experimental design. This technique seems to be effective in optimizing the values of maximum density with minimum weight loss.
Novel Way to Synthesize Nanocrystalline Aluminum Nitride from Coarse Aluminum Powder
Authors: Qiu Yu , Gao Lian
Published: July 2009

A new process has been developed for the synthesis of nanocrystalline AlN powder by the nitridation of coarse aluminum powder in flowing NH3 gas, using NH4Cl and KCl as additives. The resulting powders have been characterized using XRD, TEM, and XRF techniques. XRD‐pure AlN nanoparticles with a diameter of 10–20 nm can be obtained by nitridation at 1273 K for 5 h. NH3 is proved to eliminate the effect of water impurity. The effects of the additives on the conversion of aluminum are also discussed.
Integration of Ceramics Research with the Development of a Microsystem
Authors: Saravanan Rajgopal Arunachalam , Liew Li‐Anne , Bright Victor M. , Raj Rishi
Published: July 2009

Rapid implementation of new materials into engineering systems may require a paradigm shift in our approach to materials research. One option is to obtain fundamental material properties from experimental systems that can also serve as devices. This concept is applied to the measurement of Young's modulus of a novel ceramic, a polymer‐derived silicon carbonitride (SiCN), directly from the performance of a microelectromechanical system (MEMS) device. The device is an electrostatic actuator. The flexure resistance of the arms of the actuator is measured and analyzed for the elastic modulus of SiCN. The comparison between theory and experiment yields a value for Young's modulus in the range 130–155 GPa.
Pu, U, and Hf Incorporation in Gd Silicate Apatite
Authors: Vance Eric R. , Ball Clifford J. , Begg Bruce D. , Carter Melody L. , Day R. Arthur , Thorogood Gordon J.
Published: July 2009

Trivalent Pu can be incorporated in the silicate apatite structure to form Ca2Pu8(SiO4)6O2 by sintering under reducing conditions, while the incorporation of tetravalent Pu in the Ca/rare earth sites in oxidizing or neutral conditions is limited to only 0.6 formula units (f.u.). The d‐spacings and intensities of the X‐ray pattern of hexagonally structured Ca2Pu8(SiO4)6O2 after firing at 1250°C are given, and the a and c lattice parameters are 0.95611 and 0.70281 nm, respectively. The respective solid solubility limits of U and Hf in Ca2Gd8–x(U/Hf)x(SiO4)6O2 apatite samples were 0.3 and 0.2 f.u.
Pressureless Sintering of Boron Carbide
Authors: Lee Hyukjae , Speyer Robert F.
Published: July 2009

B4C powder compacts were sintered using a graphite dilatometer in flowing He under constant heating rates. Densification started at 1800°C. The rate of densification increased rapidly in the range 1870°–2010°C, which was attributed to direct B4C–B4C contact between particles permitted via volatilization of B2O3 particle coatings. Limited particle coarsening, attributed to the presence or evolution of the oxide coatings, occurred in the range 1870°–1950°C. In the temperature range 2010°–2140°C, densification continued at a slower rate while particles simultaneously coarsened by evaporation–condensation of B4C. Above 2140°C, rapid densification ensued, which was interpreted to be the result of the formation of a eutectic grain boundary liquid, or activated sintering facilitated by nonstoichiometric volatilization of B4C, leaving carbon behind. Rapid heating through temperature ranges in which coarsening occurred fostered increased densities. Carbon doping (3 wt%) in the form of phenolic resin resulted in more dense sintered compacts. Carbon reacted with B2O3 to form B4C and CO gas, thereby extracting the B2O3 coatings, permitting sintering to start at ∼1350°C.
Formation of Lead Zirconate Titanate Powders by Spray Pyrolysis
Authors: Nimmo William , Ali Naseef J. , Brydson Rik M. , Calvert Clair , Hampartsoumian Edward , Hind David , Milne Steven J.
Published: July 2009

Twin‐fluid atomization spray pyrolysis (SP) has been investigated for the production of lead zirconate titanate (PZT) powders, using aqueous solutions of lead acetate and zirconium and titanium alkoxide precursor reagents. The particle size distribution of the PZT powder showed a d50 value of 0.3 μm, but with a small fraction of relatively large particles, several micrometers in size. Most particles were spherical but many of the largest particles, in the size range ca. 1–5 μm, were irregular. It was demonstrated that the morphology of the final PZT powder was controlled by decomposition processes occurring during the initial drying stages, at ≤200°C. A pyrochlore or fluorite‐type intermediate crystalline phase was present in the final powders, but when the maximum reactor temperature was raised, and/or when the levels of excess lead in the starting solutions were increased, the proportion of the desired perovskite phase increased. However, at the highest process temperatures studied, ∼900°C, small crystallites of another phase formed on the surface of the PZT particles; these were probably lead oxide carbonate particles. Overall, a starting solution composition containing around 5 mol% excess Pb, and a maximum reactor temperature of 800°C, were selected as offering the most suitable conditions for producing PZT (52/48) powder, with minimal secondary phases(s). Preliminary densification studies showed that the powders could be sintered at 1150°–1200°C to give pellets of 95%–96% theoretical density.
Preparation and Characterization of Macroporous α‐Alumina
Authors: Sokolov Sergey , Bell David , Stein Andreas
Published: July 2009

α‐Al2O3 powders with three‐dimensionally ordered or randomly positioned macropores were synthesized by templating with poly(methyl methacrylate) colloidal crystals. Aluminum nitrate was precipitated with ammonium hydroxide within the interstices of the template; calcination removed the polymer and converted the inorganic precursors into a macroporous skeleton of α‐Al2O3. Subsequent calcination at higher temperatures and hot stage transmission electron microscopy experiments were performed to study sintering effects on the product morphology. These materials combine the thermal and chemical stability of corundum with a very open structure of uniform macropores that can permit facile transport of guest molecules in potential catalysis, filtration, and sensing applications.
Vaporization Processes and Pressure Buildup during Dewatering of Dense Refractory Castables
Authors: Innocentini Murilo D. M. , Miranda Marcela F. S. , Cardoso Fábio A. , Pandolfelli Victor C.
Published: July 2009

This work describes an experimental investigation on the dewatering kinetics of high‐alumina refractory bodies under several heating conditions. The drying stages involving the removal of unbound water have been correlated with the two consecutive thermal processes by which liquid water transforms into vapor during heating: evaporation and ebullition. Thermogravimetric data have been used as the basis for a discussion of the parameters that affect the performance of both vaporization processes and guide the design of suitable heating schedules aimed at minimizing the drying time and the risk of harmful pore pressurization.
Effect of Alumina Addition on the Distribution of Intergranular‐Liquid Phase during Sintering of 15‐mol%‐Calcia‐Stabilized Zirconia
Authors: Lee Jong‐Heun , Lee Je Hun , Jung Young‐Soo , Kim Doh‐Yeon
Published: July 2009

In a 15‐mol%‐CaO‐stabilized zirconia (CSZ) specimen, the grain boundaries at the surface region exhibited a lower electrical resistance than those at the inner region. However, when up to 1.5 mol% Al2O3 was added, the grain boundaries at the surface showed a higher resistance. These results were explained in terms of redistribution of the intergranular‐liquid phase during CSZ sintering.
Increase in Phase Transition Temperature of Activated Alumina with Nano‐Zirconia Synthesized by Pulsed Wire Discharge
Authors: Kinemuchi Yoshiaki , Mouri Hiroshi , Suzuki Tsuneo , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: July 2009

Activated alumina powders have been synthesized by using a novel dry process of pulsed wire discharge. The temperature of phase transition from activated alumina to α‐alumina and its variation caused by adding zirconia have been investigated. A mixture of activated alumina and zirconia was formed by mixing zirconium plasma with aluminum plasma and cooling together in an oxygen atmosphere. It was found that the transition temperature increased when the zirconia content ratio was increased. On the other hand, results of X‐ray diffraction and X‐ray photoelectron spectroscopy analysis indicated no substitution of zirconium in an alumina lattice. Thus, most of the zirconium atoms were located in zirconia particles on the surface and/or the grain boundary of alumina grains. Thus, it appears that the increase in the phase transition was caused by retardation of atomic diffusion at zirconia particles.
Crystallization Measurements Using DTA Methods: Applications to Zerodur®
Authors: Davis Mark J. , Mitra Ina
Published: July 2009

Differential thermal analysis (DTA) experiments described herein apply two methodologies by which to estimate absolute nucleation rates and/or temperature dependencies using a low‐expansion, commercially relevant, multicomponent glass‐ceramic as a test material. In particular, the Marotta and the Ray et al. methods were applied to Zerodur® and both provided valuable insight into a relatively complicated crystallization process. Previous nucleation and crystal growth rate data were used in a comparative manner. Although the Marotta method accurately predicted the maximum nucleation temperature, the nature of the technique precluded an estimation of absolute nucleation rates. The Ray et al. technique provided reasonable nucleation rates, but failed to provide useful estimates of the number of quenched‐in nuclei, in part because of a substantial “blank” contribution coming from additional, unwanted nucleation during heating and cooling stages of the DTA technique.
Formation of β‐Silicon Nitride Crystals from (Si,Al,Mg,Y)(O,N) Liquid: I, Phase, Composition, and Shape Evolutions
Authors: Wang Lingling , Tien Tseng‐Ying , Chen I‐Wei
Published: July 2009

Precipitation, growth, and coarsening of Si3N4 crystals in (Si,Al,Mg,Y)(O,N) liquids at 1680°C has been studied. The initial nucleation of β‐Si3N4 occurs mostly on α‐Si3N4 because of the very high supersaturation of the liquid. After a brief period of growth, the crystals then undergo accelerated coarsening, decreasing the crystal concentration by almost 100 times with little change in the total crystal volume. Meanwhile, the crystals gradually transform from β‐Si3N4, by substituting Si‐N with Al‐O, to β′‐SiAlON of various compositions. The evolution of aspect ratio strongly depends on the Si/(Al,Mg,Y) ratio, which is rationalized by cation segregation to the interface driven by the acidity‐basicity differential between the liquid and the crystal.
Hydrothermal Chemistry of Silicates: Low‐Temperature Synthesis of y‐Yttrium Disilicate
Authors: Becerro Ana I. , Naranjo Moisés , Perdigón Ana C. , Trillo José M.
Published: July 2009

The synthesis of crystalline y‐Y2Si2O7 has been achieved at a temperature as low as 365°C. This has been accomplished by following a hydrothermal method and using a layered clay as silicon source, whose structure‐directing character facilitates the nucleation process. The structural characterization of the y‐Y2Si2O7 polymorph is conducted with special emphasis on the MAS‐NMR spectrum. Extending this finding to other binary silicate compounds allows revising the phase diagrams of these systems in the low‐temperature range.
Characterization of Precursor‐Derived Silicon‐Carbon‐Nitrogen Ceramics after Creep Testing
Authors: Cai Ye , Zimmermann André , Bauer Arndt , Aldinger Fritz
Published: July 2009

Precursor‐derived Si‐C‐N ceramics after creep testing in air were characterized using X‐ray diffractometry (XRD) and transmission electron microscopy (TEM). XRD analysis showed that the crept Si‐C‐N ceramics were covered by an α‐cristobalite layer. TEM observations revealed that the precipitated nanocrystallites in the crept Si‐C‐N ceramics were β‐SiC. Between α‐cristobalite and crept Si‐C‐N ceramic, there was an intermediate zone in which Si2N2O nanocrystallites were distributed homogeneously. Moreover, Si2N2O nanocrystallites were often found covering the surface of nanosized gas channels in the crept Si‐C‐N ceramics, where no α‐cristobalite phase was detected. Based on these observations, a two‐step oxidation mechanism of Si‐C‐N ceramics during creep testing in air was proposed.
Use of the Retarded Solution‐Reprecipitation Process to Attain a Higher Initial Permeability in MnZn Ferrites
Authors: Drofenik Miha , Žnidaršič Andrej , Makovec Darko
Published: July 2009

We investigated the effect of various amounts of liquid phase on microstructure development during sintering and the resulting magnetic permeability of MnZn ferrite (MZF) samples. Our results revealed that the microstructure and the final magnetic permeability depend on the thickness of the liquid‐phase film during sintering. The solution‐reprecipitation (S‐R) process, which is associated with an intensive microstructure development in MZF, starts when a continuous liquid‐phase film of critical thickness δo, which wets the MZF grains, is formed. The solid‐state sintering that takes place before the formation of the continuous liquid‐phase film is essential for the final microstructure of MZF.
Current–Voltage Characteristics of Cobalt‐Doped Inversion Boundaries in Zinc Oxide Bicrystals
Authors: Oba Fumiyasu , Sato Yukio , Yamamoto Takahisa , Ikuhara Yuichi , Sakuma Taketo
Published: July 2009

Undoped and cobalt‐doped basal inversion boundaries were fabricated in ZnO bicrystals to investigate their current–voltage characteristics. High‐resolution transmission electron microscopy observations and energy‐dispersive X‐ray spectroscopy analyses for a cobalt‐doped bicrystal revealed that the boundary was highly coherent and free from intergranular phases and precipitates, but a certain amount of cobalt was present near the boundary. The cobalt‐doped bicrystals exhibited nonlinear characteristics that depended on cooling rates from annealing temperature, in contrast to linear characteristics of the undoped bicrystals. It is suggested that the presence of cobalt impurities enhances the formation of acceptor‐like native defects near the boundaries to generate electrostatic potential barriers.
Strength of Silicon Nitride after Thermal Shock
Authors: She Jihong , Yang Jian‐Feng , Jayaseelan Daniel Doni , Ueno Shunkichi , Kondo Naoki , Ohji Tatsuki , Kanzaki Shuzo
Published: July 2009

A water‐quenching technique was used to evaluate the thermal‐shock strength behavior of silicon nitride (Si3N4) ceramics in an air atmosphere. When the tensile surface was shielded from air during the heating and soaking process, the quenched specimens showed a gradual decrease in strength at temperatures above 600°C. However, the specimens with the air‐exposed surface exhibited a ∼16% and ∼29% increase in strength after quenching from 800° and 1000°C, respectively. This is because of the occurrence of surface oxidation, which may cause the healing of surface cracks and the generation of surface compressive stresses. As a result, some preoxidation of Si3N4 components before exposure to a thermal‐shock environment is recommended in practical applications.
Fabrication of NiO Nanoparticle‐Coated Lead Zirconate Titanate Powders by the Heterogeneous Precipitation Method
Authors: Xiang Ping‐Hua , Dong Xian‐Lin , Feng Chu‐De , Wang Yong‐Ling
Published: July 2009

NiO nanoparticle‐coated lead zirconate titanate (PZT) powders are successfully fabricated by the heterogeneous precipitation method using PZT, Ni(NO3)2·6H2O, and NH4HCO3 as the starting materials. The amorphous NiCO3·2Ni(OH)2·2H2O are uniformly coated on the surface of PZT particles. XRD analysis and the selected‐area diffraction (SAD) pattern indicate that the amorphous coating layer is crystallized to NiO after being calcined at 400°C for 2 h. TEM images show that the NiO particles of ∼8 nm are spherical and weakly agglomerated. The thickness of the nanocrystalline NiO coating layer on the surface of PZT particle is ∼30 nm.
Prognostic impact of immunohistochemical biomarkers in diffuse large B‐cell lymphoma in the rituximab era
Authors: Seki Ritsuko , Ohshima Koichi , Fujisaki Tomoaki , Uike Naokuni , Kawano Fumio , Gondo Hisashi , Makino Shigeyoshi , Eto Tetsuya , Moriuchi Yukiyoshi , Taguchi Fumihiro , Kamimura Tomohiko , Tsuda Hiroyuki , Ogawa Ryosuke , Shimoda Kazuya , Yamashita Kiyoshi , Suzuki Keiko , Suzushima Hitoshi , Tsukazaki Kunihiro , Higuchi Masakazu , Utsunomiya Atae , Iwahashi Masahiro , Imamura Yutaka , Tamura Kazuo , Suzumiya Junji , Yoshida Minoru , Abe Yasunobu , Matsumoto Tadashi , Okamura Takashi
Published: July 2009

We evaluated the usefulness of prognostic markers in patients with diffuse large B‐cell lymphoma (DLBCL) treated with cyclophosphamide, vincristine, doxorubicin, and prednisolone (CHOP) ± rituximab (R‐CHOP) in Japan. We studied 730 patients with DLBCL; 451 received CHOP and 279 R‐CHOP. We analyzed biopsy samples immunohistochemically for markers of germinal center B cells (CD10, Bcl‐6), postgerminal center B cells (Multiple myeloma‐1), and apoptosis (Bcl‐2). The median follow‐up period for surviving patients was 56.4 months for the CHOP group and 25.2 months for the R‐CHOP group. DLBCL were categorized as germinal center B (GCB) subtype (352/730; 48.2%) or non‐GCB subtype (378/730; 51.8%). In the CHOP group, the high expression of CD10 (P = 0.022) or Bcl‐6 (P = 0.021), or GCB subtype (P = 0.05) was associated with better overall survival, whereas the high expression of Bcl‐2 (P = 0.001) or MUM1 (P = 0.011), or non‐GCB subtype (P = 0.05) was associated with worse overall survival. In the R‐CHOP group, however, these biomarkers except Bcl‐6 were not significant prognostic factors. The patients with non‐GCB subtype showed improved survival in the R‐CHOP group (P = 0.756). The International Prognostic Index was a useful clinical marker of survival in the CHOP group (P < 0.001) and also in the R‐CHOP group (P < 0.001). Results of improved survival with rituximab addition indicate that the relevance of previously recognized prognostic factors should be re‐evaluated. (Cancer Sci 2009; 100: 1842–1847)