bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of the Initial Stage of Sintering from Shrinkage Data: Simultaneous Determination of Activation Energy and Kinetic Model from a Single Nonisothermal Experiment
Authors: Pérez‐Maqueda Luis A. , Criado José Manuel , Real Concepción
Published: July 2010

A new method for the kinetic analysis of the initial stage of sintering for constant‐heating‐rate data has been proposed. Unlike all of the methods previously reported in the literature, this new method proposed here allows the simultaneous determination of the activation energy and the kinetic model from a single dilatometric curve recorded under a linear‐heating‐rate program. The proposed method has been tested with simulated sintering curves and experimental results have been obtained for the sintering of a rutile sample.
Nanocrystalline Maghemite (γ‐Fe2O3) in Silica by Mechanical Activation of Precursors
Authors: Xue Junmin , Zhou Zhaohui , Wang John
Published: July 2010

γ‐Fe2O3 nanocrystallites dispersed in an amorphous silica matrix have been successfully prepared for the first time by mechanical activation of a chemistry‐derived precursor at room temperature. The initial 10 h of mechanical activation triggered the formation of nanocrystallites of Fe3O4 in a highly activated matrix. Increasing the mechanical‐activation time led to a phase transformation from Fe3O4 to γ‐Fe2O3. The γ‐Fe2O3 phase was well established after mechanical activation of the precursor for 30 h. Further increasing the mechanical‐activation time to 40 h induced the formation of α‐Fe2O3. The mechanical‐activation‐grown γ‐Fe2O3 nanocrystallites were ∼10–12 nm in size and well dispersed in the silica matrix, as observed using TEM. They demonstrated superparamagnetic behavior at room temperature when measured using a Mössbauer spectrometer and a vibrating sample magnetometer (VSM). In addition, the γ‐Fe2O3 derived from 30 h of mechanical activation exhibited a value of saturation magnetization as high as 62.6 emu/g.
Microstructural Tailoring and Characterization of a Calcium α‐SiAlON Composition
Authors: Xie Zong‐Han , Hoffman Mark , Cheng Yi‐Bing
Published: July 2010

Three calcium α‐SiAlON microstructures—namely, fine‐grained, bimodal, and large elongated—were developed using powders of the same composition and then characterized. The evolution of grain size and morphology was determined to be a process of nucleation and growth that could be controlled with a two‐step sintering technique. The extent of texture was identified in the as‐hot‐pressed materials as a function of sintering conditions. Samples with different microstructures exhibited different hardness and fracture toughness. The true hardness was derived from the intrinsic relation between applied loads and indent sizes. The effect of microstructure on hardness and fracture toughness was analyzed.
B‐Site Order–Disorder Transition in Pb(Mg1/3Nb2/3)O3–Pb(Mg1/2W1/2)O3 Triggered by Mechanical Activation
Authors: Gao Xingsen , Xue Junmin , Yu Ting , Shen Zexiang , Wang John
Published: July 2010

B‐site cation order–disorder transition induced by mechanical activation was observed in Pb(Mg1/3Nb2/3)O3–Pb(Mg1/2W1/2)O3 (PMN–PMW) solid solution, which was examined using both XRD diffraction and Raman spectroscopic study. The order–disorder transition is composition dependent. Mechanical activation triggers the B‐site disordering, which can be steadily recovered by thermal annealing at elevated temperature, i.e., at temperatures around 600°C. Raman spectroscopy demonstrated that there existed tiny ordered microdomains in 0.4PMN·0.6PMW subjected to up to 20 h of mechanical activation, although they cannot be shown by X‐ray diffraction. This is a result of the equilibrium between the mechanical destruction and temperature‐facilitated recovering at the collision points during mechanical activation. It is therefore unlikely that a complete disordering can be realized in PMN–PMW by mechanical activation. The disordering in PMN–PMW triggered by mechanical activation occurs simultaneously with the refinement in crystallite size at the initial stage of mechanical activation, suggesting that the fragmentation of crystallites is responsible for the order–disorder transition at least during the initial stage of mechanical activation.
Improved Fluorescence from Tm‐Ho‐ and Tm‐Ho‐Eu‐Codoped Transparent PbF2 Glass‐Ceramics for S+‐Band Amplifiers
Authors: Tanabe Setsuhisa , Hayashi Hideaki , Hanada Teiichi
Published: July 2010

Tm3+‐Ho3+‐ and Tm3+‐Ho3+‐Eu3+‐ion‐codoped oxyfluoride transparent glass‐ceramics containing PbF2 nanocrystals were prepared, and the near‐infrared fluorescence properties of the Tm3+ ions were investigated for their potential use as a 1.4 μm amplifier. For all samples, the lifetime of the Tm3+:3H4 level increased with heat treatment because of the decrease of the phonon energy as PbF2 crystals were formed. Moreover, it was revealed that codoping with Ho3+ or Eu3+ was effective in suppressing the lifetime of the Tm3+:3F4 level by energy transfer to the Ho3+:5I7 or Eu3+:7F6 level. For the codoped samples, the heat treatments decreased the Tm3+:3F4 lifetime and increased the Tm3+:3H4 lifetime. This was attributed to the concentration of rare‐earth ions in the fluoride crystallites. These properties improved the population inversion of the 1.4 μm transition.
Oxidation Studies of Aluminum‐Implanted NBD 200 Silicon Nitride
Authors: Mukundhan Priya , Du Henry H. , Withrow Stephen P.
Published: July 2010

The effects of aluminum‐ion‐implantation on the oxidation behavior of NBD 200 Si3N4 were investigated over an implant concentration range of 0–30 at.%, at 800°–1100°C, in 1 atm dry O2. Oxidation of both unimplanted and implanted samples follows a parabolic rate law. The parabolic rate constant decreases and the activation energy increases with aluminum concentration. Smooth and crack‐free oxides are formed under the combination of high implant concentrations and low oxidation temperatures. Outward diffusion of Mg2+ from the bulk of NBD 200 to the oxide layer remains the rate‐limiting step for aluminum‐implanted samples. The enhancement of the oxidation resistance of NBD 200 by aluminum implantation is attributed to the retardation of the outward diffusion of Mg2+.
Decomposition of Dolomite Monitored by Neutron Thermodiffractometry
Authors: De Aza Antonio H. , Rodríguez Miguel Angel , Rodríguez José Luis , De Aza Salvador , Pena Pilar , Convert Pierre , Hansen Thomas , Turrillas Xavier
Published: July 2010

Dolomite powder from Coín (Spain) was heated in air at a constant rate of 2°C/min to 1000°C, while neutron diffraction patterns were collected every 150 s. Rietveld refinement was applied and raw intensity data were used to monitor decomposition. The full process happened in two stages: dolomite decomposition to give calcite and periclase, and calcite breakup. The first stage activation energy was 47 kcal·mol−1 from fitting to a contracting sphere model. The dolomite mean thermal expansion coefficients were (6.7 ± 0.4) × 10−6 and (2.7 ± 0.2) × 10−5 K−1 along the a and c axes, respectively. Changes in the Ca–O and Mg–O bond distances were also measured.
Nucleation and Crystallization of a Lead Halide Phosphate Glass by Differential Thermal Analysis
Authors: Zhao Hongsheng , Zhou Wancheng , Li Yanqing , Wu Jingbo
Published: July 2010

The nucleation and crystallization mechanisms of a lead halide phosphate glass [40P2O5·30PbBr2·30PbF2 (mol%)] were investigated by differential thermal analysis (DTA) and X‐ray diffraction analysis. There were two crystalline phases in the crystallized samples: the major phase was PbP2O4, and the minor phase was PbP2O6. The average activation energy for crystallization, E, for two different particle sizes of this glass was determined to be 119 ± 4 kJ/mol by the Kissinger method and 124 ± 4 kJ/mol by the Augis–Bennett method. The Avrami constants were determined to be 1.6 and 2.5 for particle sizes of 203 and 1040 μm, respectively, by the Ozawa equation, and 1.7 and 2.4 for particle sizes of 203 and 1040 μm, respectively, by the Augis–Bennett equation. The decrease in the crystallization peak height in the DTA curve with increasing particle size suggested that the particles crystallize primarily by surface crystallization. A nucleation‐rate type curve was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/Tp, or the height of the crystallization peak, (δT)p, as a function of nucleation temperature, Tn. The temperature where nucleation can occur for this glass ranges from 360°–450°C and the maximum nucleation rate is at 420°± 10°C.
Effects of Transition‐Metal Substitution on the Catalytic Properties of Barium Hexaaluminogallate
Authors: Yamaguchi Toshiaki , Sakamoto Wataru , Yogo Toshinobu , Hirano Shin‐ichi
Published: July 2010

The effects of the substitution of transition‐metal ions and/or reductant gases on the catalytic properties of barium hexaaluminogallate were investigated. Transition‐metal‐substituted hexaaluminogallates (BaM(Al,Ga)11O19, M = transition metal, Al/Ga = 9/3) were synthesized from aqueous metal nitrates and ammonium carbonate by the coprecipitation followed by crystallization at 1100°C. The direct NOx reduction was observed over BaM(Al,Ga)11O19 to be around 10%. The NOx removal activity of BaM(Al,Ga)11O19 powders was improved by addition of C3H6 as a reductant gas. Co‐, Ni‐ and Cu‐substituted BaM(Al,Ga)11O19 catalysts exhibited about 40% NOx reduction with C3H6 in excess oxygen at a high space velocity of 10 000 h−1. The NOx reduction on Mn‐ and Fe‐substituted BaM(Al,Ga)11O19 catalysts was less than 10% even in the presence of C3H6. The temperature of the effective NOx reduction on BaM(Al,Ga)11O19 catalysts could be adjusted from 350° to 500°C by the selection of the transition‐metal substitution in the catalysts. The catalysts hold high activities for NOx reduction even at 500°C in water vapor produced in the combustion system of reductant gases.
Fracture Analyses of Alumina Subjected to Mechanical and Thermal Shock Biaxial Stresses
Authors: Tomba‐Martinez Analía G. , Cavalieri Ana L.
Published: July 2010

Disks of commercial alumina were fabricated by slip casting and sintering. Two surface finishes were performed: coarse (denoted as “C”) using a 70 grit diamond wheel and fine (denoted as “F”) with 120 and 320 grit SiC papers. The machined surfaces were analyzed by SEM, profilometry, and residual stresses measurements. The fracture strength was evaluated in biaxial flexure, and the thermal shock resistance was tested by cooling with a high‐velocity air jet. The fracture of the specimens under both conditions was studied analyzing crack patterns and fracture surfaces in relation to the surface machining and type of loading, i.e., mechanical and thermal stresses.
Effect of Twin‐Plane Reentrant Edge on the Coarsening Behavior of Barium Titanate Grains
Authors: Lee Ho‐Yong , Kim Jae‐Suk , Kim Doh‐Yeon
Published: July 2010

When BaTiO3 ceramics were sintered at relatively low temperatures (≤1250°C), the grains with reentrant edges caused by a (111) double twin grew exclusively. As a result, a microstructure with a bimodal grain‐size distribution composed of platelike large grains and fine matrix grains was obtained. In contrast, at the usual sintering temperature between 1250° and 1350°C, grains containing a (111) double twin did not exhibit any growth advantage. In this case, a coarse and uniform microstructure was obtained. When this coarse‐grained specimen was further heat‐treated at 1365°C, the grains possessing a double twin were observed to grow exclusively again. The results were explained in terms of a coarsening process controlled by two‐dimensional nucleation.
Brillouin‐Scattering Study of the Elastic Constants of ErVO4
Authors: Hirano Yukiko , Guedes Ilde , Grimsditch Marcus , Loong Chun‐Keung , Wakabayashi Nobuyoshi , Boatner Lynn A.
Published: July 2010

The room‐temperature elastic constants of ErVO4 were considerably smaller than those of isostructural silicate and phosphate analogs. The generally “less‐rigid” crystalline lattice and weaker metal‐oxygen bond‐strength in the RVO4 (R = rare earth elements) phases indicates that these materials are of interest for potential applications as an interphase component in toughened oxide ceramic composites.
Paraffin‐Based Process for Producing Layered Composites with Cellular Microstructures
Authors: Dakskobler Aleš , Kosmač Tomaz , Chen I‐Wei
Published: July 2010

A paraffin‐based process that results in high‐strength bimaterial ceramic layered composites is reported. The process facilitates rolling, folding, and shape retention at room temperature and allows the transition from a laminar to a cellular microstructure during deformation. The strength of sintered alumina/zirconia/alumina composites reached 700 MPa, higher than that of conventional zirconia‐toughened alumina composites containing dispersed particles.
Control of Crystal Orientation and Piezoelectric Response of Lead Zirconate Titanate Thin Films Near the Morphotropic Phase Boundary
Authors: Kakimoto Ken‐ichi , Kakemoto Hirofumi , Fujita Shigetaka , Masuda Yoichiro
Published: July 2010

PbZr0.53Ti0.47O3 (PZT) thin films with various preferred crystallographic orientations were synthesized on various substrates using pulsed laser deposition techniques. Larger piezoelectric displacement, which involved the bending vibration of the PZT film/substrate, was observed in randomly oriented PZT thin film than that in (100)‐ and (111)‐preferred texture films. This result was discussed by correlation with the number of effective spontaneous polarization axes in the morphotropic phase boundary of the PZT system. Moreover, polarization fatigue was found to lower the electric‐field‐induced displacement significantly, indicating a large contribution of ferroelectric domain motion to the piezoelectric response of PZT thin films under bipolar drive.
Recent Advances in Mathematical Modeling of Flow and Heat Transfer Phenomena in Glass Furnaces
Authors: Choudhary Manoj K.
Published: July 2010

This paper reviews significant advances in the mathematical modeling of flow and heat transfer phenomena in glass furnaces during the period 1996–2000. It describes developments in both the fundamental/scientific and practical aspects of modeling. The topics reviewed include developments in (a) model formulation and modeling techniques, (b) postprocessing modeling of glass quality and environmental emissions, (c) measurement of thermodynamic and transport properties of melt relevant to modeling, and (d) incorporation of model‐based knowledge into process control schemes. These developments are critically examined and assessed from an industrial perspective, and topics needing further research and development efforts are identified.
Sodium Coordination Environments in Silica Films
Authors: Jupille Jacques , Flank Anne‐Marie , Lagarde Pierre
Published: July 2010

The local structure centered on sodium after diffusion in silica (Na‐SiO2 samples) has been determined by means of extended X‐ray absorption fine structure (EXAFS) studies. The Na‐SiO2 samples are of particular interest because (i) their sodium content can be varied over a wide range of concentration and (ii) their local structure is representative of that of soda–silica glass. EXAFS analyses reveal the existence of a well‐defined local structure involving oxygen, sodium, and silicon neighbors. The Na‐O, Na‐Na, and Na‐Si bonds lengths, which amount to 0.23, 0.30, and 0.38 nm, respectively, do not depend on sodium concentration. This environment closely resembles that found in soda–silica glass. Moreover, it is compatible with the “target site” and “the site memory effect” suggested by recent theories of the ionic conductivity in oxide glasses.
Numerical Simulation of Glass Forming and Conditioning
Authors: Hyre Matthew
Published: July 2010

Advances in numerical simulation capabilities have made the modeling of both glass‐conditioning and glass‐forming processes feasible. Glass‐forming operations include large free surface deformations, conjugate heat transfer, and complex contact phenomena. In this paper, glass‐container forming processes are modeled to provide insight into the impacts of the various stages of forming and conditioning on final container quality. The model uses finite elements and includes the effects of viscoelasticity, surface tension, and time‐varying heat transfer. Special attention is given to areas that require further developments in numerical capabilities and an increased knowledge of boundary conditions and material properties.
Near‐Field Optical Characterization of Nanocomposite Materials
Authors: Novotny Lukas
Published: July 2010

We present a near‐field optical technique which makes use of the strongly enhanced optical field at a laser‐illuminated metal tip. The enhanced field is used to locally excite the sample under investigation by multiphoton absorption. An optical scan image with spatial resolutions down to 20 nm is established by detecting the emitted fluorescence. The principle of the method is described and experimental results are demonstrated for samples of J‐aggregates of PIC dye molecules. Ongoing experiments on nanocomposite, Er3+‐doped oxyfluoride glass‐ceramics are discussed.
Ultrafast Optical Switches and Wavelength Division Multiplexing (WDM) Amplifiers Based on Bismuth Oxide Glasses
Authors: Sugimoto Naoki
Published: July 2010

Glasses with a high refractive index exhibit interesting properties. All optical switching and broadband amplification performances have been demonstrated using glasses based on bismuth oxide (Bi2O3). Optical Kerr shutter (OKS) switching and degenerated four‐wave mixing experiments for nonresonant‐type Bi2O3–B2O3–SiO2 glasses have been performed using femtosecond lasers. This glass exhibits an ultrafast response (<150 fs) in OKS operation. Moreover, terahertz‐range (THz‐range) optical switching has been successfully performed with this glass, using a 1.5‐THz pulse train. Erbium‐doped bismuth‐based oxide glasses also have been prepared for wavelength division multiplexing (WDM) amplifiers. These glasses exhibit broadband emission and negligible concentration quenching, which indicates that the bismuth‐based glass is suitable for broadband amplifiers and highly doped short‐length fiber applications for metro use.
XAFS Investigation of Platinum Impurities in Phosphate Glasses
Authors: Karabulut Mevlut , Marasinghe G. Kanishka , Click Carol A. , Metwalli EzzEldin , Brow Richard K. , Booth Corwin H. , Bucher J. J. , Shuh David K. , Suratwala Tayyab I. , Campbell John H.
Published: July 2010

The coordination environments of Pt impurities in a ternary K‐aluminophosphate (KAP) glass and commercial K,Mg‐aluminophosphate (KMAP) laser glasses have been investigated by Pt LIII‐edge X‐ray absorption fine structure (XAFS) spectroscopy. Pt valence in the KAP glass depends on the melt preparation atmosphere. Pt4+ ions form in melts that are bubbled with oxygen, whereas metallic Pt particles form when these same samples are remelted in air. Residual chlorine in KMAP glasses has an effect on Pt bonding. In chlorine‐free samples, Pt4+ ions are coordinated with ∼5.4 (8) oxygen atoms with an average distance of 2.02 (1) Å. For glasses with low chlorine contents (<200 ppm Cl), the Pt4+ ions have both O and Cl atoms in the first coordination shell. As the Cl concentration increases, the number of O nearest neighbors decreases and for Cl:Pt > 5, only Cl nearest neighbors are observed. Pt4+ ions in these latter glasses are coordinated by ∼5.5 (8) Cl atoms at an average distance of 2.27 (2) Å.
Role of Liquid Phase in PTCR Characteristics of (Ba0.7Sr0.3)TiO3 Ceramics
Authors: Lee Jung‐Kun , Park Jong‐Sung , Hong Kug‐Sun , Ko Kyung‐Hyun , Lee Byung‐Chan
Published: July 2010

The role of liquid phase in the enhancement of the PTCR (positive temperature coefficient of resistance) effect in (Ba0.7Sr0.3)TiO3 (BST) with the addition of AST (4Al2O3· 9SiO2· 3TiO2) is investigated in this paper. The AST–BST samples were characterized with optical microscopy, transmission electron microscopy, energy‐dispersive spectroscopy, and impedance spectroscopy. Microscopic observations showed that slower cooling might facilitate the precipitation of the (Ba,Sr)TiO3 phase from the liquid phase on matrix grains since the amount of liquid phase was reduced with a decreasing cooling rate. Impedance spectroscopy indicated that this variation accompanied the change in the intrinsic properties of grain boundaries, which could not be explained by well‐known oxidation effects. With the aid of a brick‐layer model and high‐resolution transmission electron microscopy (HRTEM), it appeared that the change in electrical characteristics of grain boundaries with decreasing cooling rate originated from the precipitation of (Ba,Sr)TiO3. Finally, the effect of precipitated (Ba,Sr)TiO3 on the PTCR characteristics is discussed in terms of the acceptor‐state density and the polarization state at grain boundaries.
Superplastic Deformation in Fine‐Grained YBa2Cu3O7−x
Authors: Yun Jondo , Chou Ye T. , Harmer Martin P.
Published: July 2010

The superplastic behavior of YBa2Cu3O7−x ceramic superconductors was studied. Large compressive deformation over 100% strain was measured in the temperature range of 775°–875°C, with a strain rate of 1 × 10−5 to 1 × 10−3/s, and a grain size of 0.5–1.4 μm. The nature of the deformation was investigated in terms of three deformation parameters: the stress exponent (n), the grain size exponent (p), and the activation energy (Q). The measured values of these parameters were n= 2 ± 0.3, p= 2.7 ± 0.7, and Q= 745 ± 100 kJ/mol. With the aid of the deformation map, the deformation mechanism was identified as grain boundary sliding accommodated by grain boundary diffusion. The conclusion is consistent with the microstructural observations made by SEM and TEM: the invariance of equiaxed grain shape, the absence of significant dislocation activity, no grain boundary second phases, and no significant texture development.
Evaluation of Electric Fracture Properties of Piezoelectric Ceramics Using the Finite Element and Single‐Edge Precracked‐Beam Methods
Authors: Shindo Yasuhide , Murakami Heihachiro , Horiguchi Katsumi , Narita Fumio
Published: July 2010

Single‐edge precracked‐beam (SEPB) tests were performed on a commercial lead zirconate titanate (PZT) ceramic. Mechanical loading was applied by the crosshead displacement control of a screw‐driven electromechanical test machine. The fracture toughness parameter KC was determined for various electric fields. A finite element analysis was also done to calculate the total potential energy release rate, mechanical strain energy release rate, and stress intensity factor for three‐point flexure piezoceramic specimens with permeable and impermeable cracks under displacement and load control conditions. Numerical investigation and comparison with test data indicate that the energy release rate, upon application of the permeable model, is useful for predicting crack growth in PZT ceramic under electromechanical loading. Based on current findings, we suggest that the energy release rate criteria for the permeable crack are superior to fracture criteria for the impermeable crack.
Effect of Seeding on the Microstructure and Mechanical Properties of α‐SiAlON: II, Ca‐α‐SiAlON
Authors: Shuba Roman , Chen I‐Wei
Published: July 2010

Seeding effects on the microstructure and mechanical properties of single‐phase Ca‐α‐SiAlON ceramics have been investigated. Whereas a small amount of seeds can transform the microstructure from one of fine equiaxed grains to one consisting of many needle‐like grains, the highest fracture toughness of 8 MPa·m1/2 is not reached until 8% seeding. This contrasts with the much higher seed efficiency in Y‐SiAlON, where the peak toughness is reached at 1% seeding. The difference and the general trend of mechanical properties of seeded α‐SiAlONs are discussed in terms of α‐SiAlON formation and toughening mechanisms.
Microstructural Evolution of Titanium Carbide–Chromium Carbide (TiC–Cr3C2) Composites Produced via Combustion Synthesis
Authors: Kunrath Augusto O. , Reimanis Ivar E. , Moore John J.
Published: July 2010

A microstructural analysis of compounds produced by combustion synthesis coupled with hot pressing, for reactions between titanium, chromium, and carbon, was conducted. The reactions were aimed to produce composites of Cr3C2 and TiC at three different volume fractions of each carbide (25/75, 50/50, and 75/25). Large amounts of chromium and carbon were found to be in solution in the B1 rock‐salt structure of TiC. The materials with 25 and 50 vol% of Cr3C2 consisted of 100% (Ti,Cr)Css solid solution, while the composition with 75 vol% Cr3C2 was formed by Cr3C2+ (Ti,Cr)Css. Some precipitation of Cr3C2 was achieved by annealing, but a minimum of 20 wt% was always in solution. The 50 vol% Cr3C2–50 vol% TiC composition was the most affected by the heat treatments. Discontinuous and general precipitation were observed, depending on the annealing conditions. A TTT‐type diagram was plotted for this material.
Synthesis of Nanocrystalline Chromium Nitride Powders by Direct Nitridation of Chromium Oxide
Authors: Li Yaogang , Gao Lian , Li Jingguo , Yan Dongsheng
Published: July 2010

Nanocrystalline CrN powder was synthesized by the direct nitridation of nanosized Cr2O3 powder. Powder X‐ray diffractometry patterns indicated that pure cubic‐phase CrN powder could be obtained by nitridation at 800°C for 8 h. Transmission electron microscopy images showed that the particle sizes were 40–80 nm. The effect of the nitridation temperature and holding time on the powder properties was studied.
Calcium Silicate Hydrates Studied by Small‐Angle Neutron Scattering (SANS)
Authors: Popova Alla , Geoffroy Ghita , Gartner Ellis M. , Lapp A.
Published: July 2010

Small‐angle neutron scattering (SANS) was used to study calcium silicate hydrate (C‐S‐H) formed via pozzolanic reaction between calcium oxide and ultrafine silica in water or polymer solutions at a temperature of 20°C. The SANS profile of this product was consistent with a structure that consisted of platelets with maximum diameters of ∼20 nm (± 5 nm) in the x–y plane, which was similar to a structure that had been deduced in previous work via X‐ray diffractometry. The presence of two different types of superplasticizer in solution (at a concentration of 10 g/L) had no significant effect on its formation kinetics or its SANS profile.
Surface Finishing of Alumina Ceramics by Means of Abrasive Jet Machining
Authors: Wakuda Manabu , Yamauchi Yukihiko , Kanzaki Shuzo
Published: July 2010

Abrasive jet machining (AJM) is proposed as a new approach to surface finishing of structural ceramics. The effect of AJM on the material removal behavior of a commercially available alumina ceramic, and its effect on mechanical properties, was characterized and compared with identical material subjected to conventional finishing processes. Conventional grinding of the ceramic resulted in a surface that was dominated by intergranular fracture, whereas, during AJM, impact by the abrasives led to material removal in a manner resembling ductile behavior, and the resulting surface appearance was much smoother. A significant improvement in flexural strength was attained, compared with the strength of both the ground and lapped samples, because of an induced compressive residual stress.
Microstructural Development of Natural Hydroxyapatite Originated from Fish‐Bone Waste through Heat Treatment
Authors: Ozawa Masakuni , Suzuki Suguru
Published: July 2010

The morphologic and microstructural development of natural fish bone through heat treatment is examined in view of fish‐waste management and as a possible route for hydroxyapatite ceramics. Fish bone heated at temperatures ≤1300°C maintains a porous structure, with a sintered wall and a major crystalline phase of hydroxyapatite. Fish‐originated ceramics are potentially useful as bioactive media as well as for environmentally compatible materials.
Synthesis of Platinum/Silica Nanocomposite Particles by Reverse Micelle and Sol–Gel Processing
Authors: Bae Dong‐Sik , Han Kyong‐Sop , Adair James H.
Published: July 2010

Pt/SiO2 nanosized particles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethoxysilane (TEOS) within the microemulsion. The average size of synthesized particles was in the size range of 21–42 nm. The effects of synthesis parameters, such as the molar ratio of water to TEOS and the molar ratio of water to surfactant, are discussed.
State of Magnesia in Magnesia (10.4 mol%)‐Doped Zirconia Powder Prepared from Coprecipitation
Authors: Rong Tian Jun , Huang Xiao Xian , Wang Shi Wei , Zhao Shi Ke , Guo Jing Kun
Published: July 2010

MgO (10.4 mol%)‐doped ZrO2 powder, which was prepared by coprecipitation and calcination at 750°C, was leached and milled, respectively. The powders were characterized by Auger electron scanning microprobe and XRD technologies. Only the 2.3 mol% MgO was soluble in ZrO2; it stabilized ZrO2 as the metastable tetragonal phase (crystallite size ∼45 nm) at room temperature. The rest of the MgO (8.1 mol%) existed on the surface of the ZrO2 grains in the prepared powder.
Microwave Dielectric Properties of CaTiO3‐CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4
Authors: Kucheiko Sergey , Yeo Dong‐Hun , Choi Ji‐Won , Yoon Seok‐Jin , Kim Hyun‐Jai
Published: July 2010

The microwave dielectric properties of CaTi1−x(Al1/2Nb1/2)xO3 solid solutions (0.3 ≤x≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO3. The substitution of Ti4+ by Al3+/Nb5+ improved the quality factor Q of the sintered specimens. A small addition of Li3NbO4 (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x= 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛr) of 48, a Q×f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τf) of −2 ppm/K. Li3NbO4 as a sintering additive had no harmful influence on τf of ceramics.
Fracture Toughness of Spray‐Dried Powder Compacts
Authors: Zhang Zhiye , Green David J.
Published: July 2010

The strengths and fracture toughness values were measured for alumina powder compacts containing two different binder systems. Diametral compression was used to measure both the tensile strength and the fracture toughness (through‐thickness notch). This methodology was very useful in linking processing parameters, such as binder choice and compaction stress, to the quality of the green bodies. Observations of the compact structure before and after fracture showed that the binders segregated to the region between the spray‐dried granules. The presence of the excess binder in this region was linked to both the failure mode and the creation of secondary cracks.
Structure and Electrical Properties of A‐site‐Deficient Perovskite Compounds in the La2/3TiO3‐La1/3NbO3 System
Authors: Yoshioka Hideki
Published: July 2010

The structure and electrical properties of an A‐site‐deficient perovskite compound found in the La2/3TiO3‐La1/3NbO3 system were investigated. The composition of the perovskite compound seemed to be very close to La0.633(Ti0.90Nb0.10)O3. X‐ray diffraction analysis revealed a superstructure with a doubled c‐axis parameter, resulting from an ordered arrangement of the A‐site cation vacancies. Impedance measurements on the compound showed that La0.633(Ti0.90Nb0.10)O3 had high ionic conductivity at relatively low temperature (<770 K) and increased electronic conduction at high temperature (>770 K). The bulk ionic conductivity was comparable with that of La0.683(Ti0.95Al0.05)O3, which has the highest ionic conductivity among the La‐(Ti,Al)‐O perovskite compounds.
Bismuth Oxide Nanoparticles by Flame Spray Pyrolysis
Authors: Mädler Lutz , Pratsinis Sotiris E.
Published: July 2010

Bismuth oxide nanostructured particles were made via the flame spray pyrolysis (FSP) of bismuth nitrate that had been dissolved in a solution of ethanol/nitric acid or in acetic acid. These self‐sustaining spray flames produced tetragonal β‐Bi2O3. The use of ethanol/nitric acid solutions resulted in a mixture of hollow, shell‐like, and solid nanograined particles. The particle homogeneity was improved as the content of acetic acid in the precursor solution increased. Solid bismuth oxide nanoparticles were prepared consistent with percolation theory, accounting for the specific volume of the product and the precursor. Using pure acetic acid as the solvent, the effect of FSP variables on spray flame and product powder characteristics was investigated. The specific surface area of the Bi2O3 particles could be controlled over a range of 20–80 m2/g by the liquid feed and oxygen gas flow rates for powder production rates of 6–46 g/h.
Formation of Nanocrystalline Transition‐Metal Ferrites inside a Silica Matrix
Authors: Rajić Nevenka , C̆eh Miran , Gabrovšek Roman , Kauc̆ic̆ Venc̆eslav
Published: July 2010

Nanocrystalline transition‐metal ferrites were synthesized inside an amorphous silica matrix by the sol–gel method. The formation of spinel ferrites began above 400°C, giving fine particles of about 10 nm at 800°C. This is associated with a specific role of the silica matrix, which facilitates the diffusion of the reacting cations, enhancing the ferrite formation. Above 1000°C the MnFe2O4 and CuFe2O4 nanoparticles lost their fine nature. The dried gels and crystalline materials were characterized by X‐ray diffraction, thermal, FTIR, and BET analyses as well as by high‐resolution scanning transmission electron microscopy.
Biaxial Flexure Strength and Dynamic Fatigue of Soda–Lime–Silica Float Glass
Authors: Krohn Matthew H. , Hellmann John R. , Shelleman David L. , Pantano Carlo G. , Sakoske George E.
Published: July 2010

The strength and dynamic fatigue behavior of float glass was investigated using biaxial flexure tests. The samples were tested using the ring‐on‐ring (ROR) biaxial flexure test geometry, and the data analyzed using a conventional two‐parameter Weibull distribution. The as‐received samples revealed that the air side exhibits a higher characteristic strength (243 MPa) compared with the tin side (114 MPa); fractographic analysis confirmed the presence of significantly larger flaws on the tin side of the specimens, presumably due to contact damage by the rollers in the float glass process. Dynamic fatigue results for as‐received and indented samples were performed to assess whether differences in the stress corrosion behavior of float glass exist because of tin penetration. No statistical difference in the stress corrosion exponent was found between the air (n= 21.7) and tin (n= 21.6) sides of the float glass. This indicates either that the tin penetration (which extends ∼25 μm) plays no role in altering the stress corrosion susceptibility of float glasses because the native flaw size is larger than the tin penetration depth or that the tests do not have the required sensitivity to distinguish the effect of the tin. Alternative test methods for direct observation of slow crack growth in tin‐doped bulk glasses are planned to investigate this in the future.
Effect of Substituent Ions on Martensitic Transformation Temperatures in Dicalcium Silicate Solid Solutions
Authors: Fukuda Koichiro , Taguchi Hiroyuki , Fukuda Tetsuya
Published: July 2010

Five types of Ca2SiO4 solid solutions, doped with either P5+, Ge4+, Fe3+, Mg2+, or Ba2+, were prepared and examined by high‐temperature X‐ray diffractometry up to 800°C. The starting and finishing temperatures were determined for the α′L‐to‐β martensitic transformation during cooling and the reverse (β‐to‐α′L) transformation during heating. These four types of transformation temperatures for the preparations doped with either P5+ or Ge4+ steadily decreased with increasing substituted fraction. The effect of the substitution on the decrease for each transformation temperature was quantitatively evaluated by ΔT/x, where ΔT is the difference in the transformation temperatures between the solid solutions and pure Ca2SiO4, and x represents the fraction substituted for Si4+ or Ca2+ in the α′L‐phase structure. The evaluated value for the substitution of P5+ was more than 3 times that of Ge4+. The effect of the substituent ions mentioned above, together with Na+ and Sr2+, on the lowering of the starting temperature of the α′L‐to‐β transformation was principally determined by the differences in the ionic radius between the interchanging cations.
Anomalous Temperature Dependence of the Growth Rate of the Reaction Layer between Silica and Molten Aluminum
Authors: Yoshikawa Noboru , Kikuchi Atsushi , Taniguchi Shoji
Published: July 2010

An aluminum/Al2O3 composite body is produced by a displacement reaction between SiO2 and molten aluminum. The growth rate of the reaction layer possesses negative (anomalous) temperature dependence at 1000–1300 K. This study compared reported reaction‐kinetic data and investigated causes for this temperature dependence. The reaction product, Al2O3, changed from the γ‐/θ‐Al2O3 phase to the α‐Al2O3 phase in this temperature range and α‐Al2O3 became the dominant phase at >1273 K. Isothermal transformation of the γ‐/θ‐Al2O3 product phases to the α‐Al2O3 phase was also observed. Morphologies and scales of the Al2O3 phases change drastically at 1173 K; this transition occurred in a spatially discontinuous manner. Reaction‐rate retardation was interpreted in terms of occurrence of the competitive and simultaneous reactions to produce different Al2O3 phases in this temperature range. It was also found that the hydrogen release from the raw SiO2 and the SiO2 phase transformation were not related to the negative temperature dependence.
Equilibrium Shape of Internal Cavities in Ruby and the Effect of Surface Energy Anisotropy on the Equilibrium Shape
Authors: Choi Jung‐Hae , Kim Doh‐Yeon , Hockey Bernard J. , Wiederhorn Sheldon M. , Blendell John E. , Handwerker Carol A.
Published: July 2010

Cavities formed in ruby (99.46Al2O3·0.54Cr2O3) by the healing and annealing of indentation cracks at 1600°C are more equiaxed than similar cavities in sapphire. Surface energies for the observed facet planes (R, S, and A) relative to the surface energy of the basal plane, C, were γA/C= 1.00 ± 0.03, γR/C= 1.05 ± 0.07, and γS/C= 1.02 ± 0.04, with the uncertainty representing 95% confidence limits. Thus, the surface energies of all observed facets were statistically indistinguishable. Unlike sapphire, P‐plane facets were not observed. The substantial rounding of the cavities in ruby indicated that portions of the Wulff shape were above the roughening transition temperature. Thus, even though Cr2O3 and Al2O3 form ideal solutions, Cr3+ ions are sufficiently surface active to modify the relative free energy of the surfaces.
Preparation and Aging Behavior of Chemical‐Solution‐Deposited (Pb(Mg1/3Nb2/3)O3)1‐x–(PbTiO3)x Thin Films without Seeding Layers
Authors: Hoffmann† Marcus , Hofer† Christiane , Schneller† Theodor , Böttger† Ulrich , Waser†‡ Rainer
Published: July 2010

The aging behavior of the solid‐solution series (Pb(Mg1/3Nb2/3)O3)1−x–(PbTiO3)x (PMN1−x−PTx) prepared by chemical‐solution deposition without seeding layers was investigated. A strong influence of the rapid thermal annealing step on the film density was determined. The best nucleation and density of the thin films occurred when each deposited layer was separately pyrolyzed and crystallized. The thin‐film microstructure was investigated using scanning electron microscopy. Conventional capacitance‐voltage and hysteresis measurements were performed. For the first time, investigations on the fatigue performance and the leakage current for alternating‐current and direct‐current voltage were executed, which are important for the reliability in device applications.
Laser Sintering of Bismuth Germanate (Bi4Ge3O12) Ceramics
Authors: Macedo Zélia Soares , Hernandes Antonio Carlos
Published: July 2010

A solid‐state route to synthesize bismuth germanate (Bi4Ge3O12, or BGO) ceramics, and the optimum conditions for the laser sintering of these ceramics, were investigated. Special emphasis was placed on the influence of laser power and irradiation time on densification and microstructure evolution. The procedure that was used involved preheating the samples and a laser‐irradiation program, which resulted in sintered, crack‐free BGO ceramics with good pore shrinkage and a relative density of 95% (±3%).
Experimental Archaeology: Investigation on the Copper–Aluminum–Silicon–Oxygen System
Authors: Woelk Hans‐Joerg , Hoffmann Bettina , Mestl Gerhard , Schloegl Robert
Published: July 2010

The behavior of the Cu‐Al‐Si‐O system was investigated in the temperature range of 800°–1150°C. X‐ray diffraction, infrared spectroscopy, diffusive reflectance, and electron microscopy were applied to obtain information about the influence of sintering, crystallization, and chemical reaction, each of which determines the color of the material. Definition of the artificial term “engobe,” opposite to the term “glaze,” was possible using copper(II) oxide (CuO) as its indicator. The detected chemical processes render possible explanations about the traditional way of ceramic painting during the 16th century and support the knowledge transfer from the viewpoint of history and that of natural science, as attempted by “archaeometry.”
Synthesis and Properties of Porous Single‐Phase β′‐SiAlON Ceramics
Authors: Yang Jian‐Feng , Beppu Yoshihisa , Zhang Guo‐Jun , Ohji Tatsuki , Kanzaki Shuzo
Published: July 2010

Single‐phase β′‐SiAlON (Si6−zAlzOzN8−z, z= 0–4.2) ceramics with porous structure have been prepared by pressureless sintering of powder mixtures of á‐Si3N4, AlN, and Al2O3 of the SiAlON compositions. A solution of AlN and Al2O3 into Si3N4 resulted in the β′‐SiAlON, and full densification was prohibited because no other sintering additives were used. Relative densities ranging from 50%–90% were adjusted with the z‐value and sintering temperature. The results of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses indicated that single‐phase β′‐SiAlON free from a grain boundary glassy phase could be obtained. Both grain and pore sizes increased with increasing z‐value. Low z‐value resulted in a relatively high flexural strength.
High‐Strain‐Rate Superplasticity in Y2O3‐Stabilized Tetragonal ZrO2 Dispersed with 30 vol% MgAl2O4 Spinel
Authors: Morita Koji , Hiraga Keijiro , Sakka Yoshio
Published: July 2010

High‐strain‐rate superplasticity is attained in a 3‐mol%‐Y2O3‐stabilized tetragonal ZrO2 polycrystal (3Y‐TZP) dispersed with 30 vol% MgAl2O4 spinel: tensile elongation at 1823 K reached >300% at strain rates of 1.7 × 10−2– 3.3 × 10−1 s−1. The flow behavior and the microstructure of this material indicate that the MgAl2O4 dispersion should enhance accommodation processes necessary for grain boundary sliding. Such an effect is assumed to arise from an enhancement of the cation diffusion by the dissolution of Al and Mg ions into the ZrO2 matrix and from stress relaxation due to the dispersed MgAl2O4 grains.
Properties of Ionic‐Conducting β‐Bi2O3 Containing Mixed Dopants
Authors: Nunn Stephen D. , Payzant E. Andrew
Published: July 2010

β‐Bi2O3 compositions were prepared to evaluate the effect on properties of using mixed dopants. Baseline compositions containing 28 mol% of the alkaline‐earth oxides CaO, SrO, or BaO were used for comparison. When the alkaline earths were combined in pairs to dope the bismuth oxide, the resulting properties were intermediate between the baseline end members. The data suggest that the transformation temperature for forming the high‐conductivity β1 phase can be varied continuously over a temperature range of about 565° to 750°C. Utilization of additional additives having different ionic size or valence charge compared with the alkaline earths resulted in no observed property changes that could be attributed to the additive alone. The most important variables influencing the conductivity level and phase transformation temperature of β‐Bi2O3 were the type and the amount of the alkaline‐earth dopant in the composition.
Study of the Mixed‐Conducting SrFeCo0.5Oy System
Authors: Ma Beihai , Victory Nicole I. , Balachandran U. , Mitchell Brian J. , Jr. Richardson J. W.
Published: July 2010

Mixed‐conducting Sr‐Fe‐Co oxides have potential applications in dense ceramic membranes for high‐purity oxygen separation and/or methane conversion to produce syngas (CO + H2), because of their combined high electronic/ionic conductivity and significant oxygen permeability. SrFeCo0.5Oy has been synthesized by the solid‐state reaction method. Conductivities were measured at elevated temperatures in various gas environments and increased as temperature and oxygen partial pressure (pO2) increased in the surrounding environment. Neutron powder diffraction experiments revealed that in a high pO2 environment the SrFeCo0.5Oy material consists of three different phases. The relative concentration of each component phase is dependent on temperature and pO2 in the surrounding environment. In air, Sr2(Fe, Co)3Oy (236‐phase) is the majority phase and consists of >75 wt% of the total, whereas the perovskite and rocksalt phases account for ∼20 and <5 wt%, respectively. However, in a reducing environment, the 236‐phase decomposes and converts to perovskite and rocksalt phase at high temperature. In an environment of pO2 < 10−12.2 atm, the 236‐phase is completely converted into perovskite (brownmillerite) and rocksalt phases.
Porous Yttrium Aluminum Garnet Fiber Coatings for Oxide Composites
Authors: Cinibulk Michael K. , Parthasarathy Triplicane A. , Keller Kristin A. , Mah Tai‐Il
Published: July 2010

A porous oxide fiber coating was investigated for Nextel™ 610 fibers in an alumina matrix. Polymeric‐solution‐derived yttrium aluminum garnet (YAG, Y3Al5O12) with a fugitive carbon phase was used to develop the porous fiber coating. Ultimate tensile strengths of tows and minicomposites following heat treatments in argon and/or air were used to evaluate the effect of the porous fiber coating. The porous YAG fiber coatings did not reduce the strength of the tows when heated in argon, and they degraded tow strength by only ∼20% after heating in air at 1200°C for 100 h. Minicomposites containing porous YAG‐coated fibers were nearly twice as strong as those containing uncoated fibers. However, after heating at 1200°C for 100 h, the porous YAG coatings densified to >90%, at which point they were ineffective at protecting the fibers, resulting in identical strengths for minicomposites with and without a fiber coating.
Processing‐Dependent Microstructural Factors Affecting Cavitation Damage and Tensile Ductility in a Superplastic Alumina Dispersed with Zirconia
Authors: Hiraga Keijiro , Nakano Keishi , Suzuki Tohru S. , Sakka Yoshio
Published: July 2010

Superplastic tensile ductility in Al2O3–10 vol% ZrO2 (3 mol% Y2O3) exhibits processing dependence when the grain size is reduced to 0.45 μm for a given relative density of ∼99.5%. The reduced grain size leads to largely enhanced ductility in a material prepared by colloidal processing, but does not in a material prepared by conventional dry processing. This result is explained from cavity‐damage accumulation sensitive to a rather small variation in a few processing‐dependent factors: the numerical densities of residual defects and ZrO2 particles. The rate of damage accumulation is shown to depend mainly on the former and additionally on the latter.
Determining Crystal Habits from Observations of Planar Sections
Authors: Saylor David M. , Rohrer Gregory S.
Published: July 2010

A method is described for reconstructing the habits of crystals embedded in a second phase from observations of random planar sections of known orientation. We have generated simulated observations based on five assumed crystal habits and found that it is possible to reconstruct the shape from 100‐1000 planar sections, depending on the relative area of each facet. Habit planes comprising as little as 3% of the crystal's area have been detected and axial ratios accurately determined.