bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Intergranular Phase Chemistry on the Microstructure and Mechanical Properties of Silicon Carbide Ceramics Densified with Rare‐Earth Oxide and Alumina Additions
Authors: Zhou You , Hirao Kiyoshi , Toriyama Motohiro , Yamauchi Yukihiko , Kanzaki Shuzo
Published: July 2010

Based on the processing strategy of improving the mechanical properties of liquid‐phase‐sintered materials by modifying the secondary phase chemistry, four rare‐earth oxides (RE2O3, RE = La, Nd, Y, and Yb), in combination with alumina, were used as sintering aids for a submicrometer‐size β‐SiC powder. Doped with 5 vol% RE2O3+ Al2O3 additives, all specimens were hot‐pressed to near full‐densities at 1800°C, and they exhibited similar microstructures and grain size distributions. The SiC grains in all specimens revealed a core‐rim structure after being plasma‐etched, indicating that they were densified via the same solution‐reprecipitation mechanism. It was found that a decrease in the cationic radius of the rare‐earth oxides was accompanied by an increase in Young’s modulus, hardness, and flexural strength of the SiC ceramics, whereas the fracture toughness was improved by incorporating rare‐earth oxides of larger cationic radius. The changes in the mechanical properties were attributed to the difference in the chemistry of the intergranular phases in the four ceramics.
Silicon Nitride Colloidal Probe Measurements: Interparticle Forces and the Role of Surface‐Segment Interactions in Poly(acrylic acid) Adsorption from Aqueous Solution
Authors: Laarz Eric , Meurk Anders , Yanez Joseph A. , Bergström Lennart
Published: July 2010

Direct measurements of forces between silicon nitride surfaces in the presence of poly(acrylic acid) (PAA) are presented. The force‐distance curves were obtained at pH > pHiep with an atomic force microscopy (AFM) colloidal‐probe technique using a novel spherical silicon nitride probe attached to the AFM cantilever. We found that PAA adsorbs onto the negatively charged silicon nitride surface, which results in an increased repulsive surface potential. The steric contribution to the interparticle repulsion is small and the layer conformation remains flat even at high surface potentials or high ionic strength. The general features of the stabilization of ceramic powders with PAA are discussed; we suggest that PAA adsorbs onto silicon nitride by sequential adsorption of neighboring segments (“zipping”), which results in a flat conformation. In contrast, the long‐range steric force found in the ZrO2/PAA system at pH > pHiep arises because the stretched equilibrium bulk conformation of the highly charged polymer is preserved via the formation of strong, irreversible surface‐segment bonds on adsorption.
Nanofiber Formation in the Fabrication of Carbon/Silicon Carbide Ceramic Matrix Nanocomposites by Slurry Impregnation and Pulse Chemical Vapor Infiltration
Authors: Tai Nyan‐Hwa , Chen Che‐Fu
Published: July 2010

The objectives of this work were to investigate the fabrication of carbon‐fiber‐reinforced SiC ceramic nanocomposites using the slurry impregnation process and the pulse chemical vapor infiltration (PCVI) process and to study the influences of processing parameters of the PCVI process on the microstructure variation of the nanocomposites. In this work, SiC nanosized powder was added to the matrix precursor (silicon powder mixed with phenolic resin), followed by the impregnation of the slurry into the preform. In the PCVI process, to densify the nanocomposites, tetramethylsilane (TMS) vapor mixed with hydrogen was used as the vapor precursor for matrix deposition. Fabrication parameters, such as reactant concentrations, pulse number, and holding time, were studied. Morphologies obtained from various processes were compared.
Effect of the Presence of Ammonium Peroxodisulfate on the Direct Precipitation of Ceria and Ceria–Zirconia Solid Solutions from Acidic Aqueous Solutions
Authors: Hirano Masanori , Miwa Toshio , Inagaki Michio
Published: July 2010

Direct precipitation of nanometer‐sized particles of ceria–zirconia (CeO2–ZrO2) solid solutions with cubic and tetragonal structures was successfully attained from acidic aqueous solutions of cerium(III) nitrate (Ce(NO3)3) and zirconium oxychloride (ZrOCl2) through the addition of ammonium peroxodisulfate ((NH4)2S2O8), because of promotion of the hydrolysis via the oxidation of Ce3+ ions, together with the simultaneous hydrolysis of ZrOCl2 under hydrothermal conditions. Ultrafine CeO2 particles also could be formed from relatively concentrated aqueous solutions of the same trivalent cerium salt in the presence of (NH4)2S2O8 via hydrolysis. The crystallite size and lattice strain of as‐precipitated solid solutions varied, depending on the composition within the CeO2–ZrO2 system. Creation of a solid solution of ZrO2 into a fluorite‐type CeO2 lattice clearly introduced lattice strain, as a consequence of the decreasing crystallite size. Both the direct precipitation process and the effectiveness of the presence of (NH4)2S2O8 for the synthesis of CeO2–ZrO2 solid solutions were discussed.
Morphotropic Phase Boundary in the Pb(Zn1/3Nb2/3O3)‐BaTiO3‐PbTiO3 System
Authors: Zhu Weizhong , Kholkin Andrei L. , Mantas Pedro Q. , Baptista Joao L.
Published: July 2010

The morphotropic phase boundary (MPB) in the relaxor ferroelectric system Pb(Zn1/3Nb2/3O3)‐BaTiO3‐PbTiO3 (PZN‐BT‐PT) with 15 mol% BT was investigated through dielectric permittivity and high‐temperature X‐ray diffraction measurements. It was revealed that MPB is a broad composition region extending from 12 to 18 mol% PT, within which the temperatures of the permittivity maximum are close to the ending temperatures for the phase transformation from coexisting rhombohedral and tetragonal phases to cubic phase on heating. When the specimen is cooled, the starting temperatures for the rhombohedral‐to‐tetragonal phase transition increase with increasing PT content. The large thermal hysteresis observed by X‐ray diffraction is caused by the phase transformation between rhombohedral and tetragonal phases. On cooling, the MPB curves toward the PT‐rich side, so that ceramics within this composition range undergoe successive phase transitions from cubic to rhombohedral and from rhombohedral to tetragonal phase. The diffuseness of the paraelectric‐to‐ferroelectric phase transition is remarkably decreased by the addition of PT. The enhanced dielectric permittivity peak values for the MPB compositions are correlated with the reduced lattice distortion and phase coexistence.
Electrical Properties of Cerium‐Doped BaTiO3
Authors: Hwang Jin Hyun , Han Young Ho
Published: July 2010

The high‐temperature equilibrium electrical conductivity of Ce‐doped BaTiO3 was studied in terms of oxygen partial pressure, P(O2), and composition. In (Ba1−xCex)TiO3, the conductivity follows the −1/4 power dependence of P(O2) at high oxygen activities, which supports the view that metal vacancies are created for the compensation of Ce donors, and is nearly independent of P(O2) where electron compensation prevails at low P(O2). When Ce is substituted for the normal Ti sites, there is no significant change in conductivity behavior compared with undoped BaTiO3, indicating the substitution of Ce as Ce4+ for Ti4+ in Ba(Ti1−yCey)O3. The Curie temperature (Tc) was systematically lowered when Ce3+ was incorporated into Ba2+ sites, whereas the substitution of Ce4+ for Ti4+ sites resulted in no change in this parameter.
Flaw‐Insensitive Ion‐Exchanged Glass: II, Production and Mechanical Performance
Authors: Sglavo Vincenzo M. , Green David J.
Published: July 2010

A two‐step ion‐exchange process that introduces strengthening and multiple cracking into glasses has been developed. The experimental parameters in the second step must be carefully controlled to avoid spontaneous cracking, because the compressive stress is reduced in the surface region. Control of the near‐surface stress gradient is an important role of the second ion‐exchange step. Double ion exchange leads to strength values as high as those that are obtained after the first ion‐exchange step but remarkably produces multiple cracking on the specimen surface on loading. The multiple cracking, which acts as a failure warning, is initiated at 300 MPa, and the crack spacing decreases as the applied stress increases. The multiple cracking is shown to be a result of the crack stability that is induced by the designed residual‐stress profiles. This behavior has been confirmed, using the measured residual stresses to calculate the apparent‐toughness curves for surface cracks. The duration of the first ion‐exchange step has been shown to be important in determining the degree of strengthening; however, the duration of the second step controls the extent of the crack stability.
Preparation of Highly Oriented Aluminum Nitride Thin Films on Polycrystalline Substrates by Helicon Plasma Sputtering and Annealing
Authors: Akiyama Morito , Xu Chao‐Nan , Kodama Masaya , Usui Ichiro , Nonaka Kazuhiro , Watanabe Tadahiko
Published: July 2010

Highly c‐axis‐oriented aluminum nitride (AlN) thin films were prepared on polycrystalline Si3N4 and SiC substrates by helicon plasma sputtering. The difference in the substrate materials scarcely influenced the crystal structures of the films. The full width at half‐maximum (FWHM) of the X‐ray rocking curves of the films was 3.2°, which is the smallest value for AlN thin films deposited on polycrystalline substrates to our knowledge. Annealing at 800°C in vacuum decreased the FWHM from 3.2° to 2.8°. The structure of the films was densely packed and consisted of many fibrous grains. The films developed c‐axis orientation on the polycrystalline substrates, because the interaction between the films and substrate surfaces was small, and (100) and (110) AlN planes grew preferentially. The films were piezoelectric and generated electrical signals in response to mechanical stress.
Temperature Measurements during Microwave Processing: The Significance of Thermocouple Effects
Authors: Pert Evan , Carmel Yuval , Birnboim Amikam , Olorunyolemi Tayo , Gershon David , Calame Jeff , Lloyd Isabel K. , Wilson Otto C.
Published: July 2010

Reliable and accurate temperature measurement during microwave processing of ceramic bodies is controversial. Although thermocouples are routinely used in conventional thermal furnaces, their presence in microwave furnaces can locally distort the electromagnetic field, conduct heat away from the sample, induce thermal instabilities and microwave breakdown, and lead to serious measurement errors. These thermocouple effects have been studied and found to be more pronounced in low‐ and medium‐loss ceramic materials. To decrease the thermocouple effects during the processing of advanced ceramic materials, an optical, noncontact temperature sensing system has been developed, calibrated, and incorporated into a computer‐controlled microwave furnace.
Synthesis of Pure and Manganese‐, Nickel‐, and Zinc‐Doped Ferrite Particles in Water‐in‐Oil Microemulsions
Authors: Yener Doruk O. , Giesche Herbert
Published: July 2010

In recent years, the materials research focuses toward synthesis of finer and finer microstructural features. The unique properties of nanosized particles outweigh their higher production costs. Precipitation in microemulsion is one technique, which promises to produce small particles of controlled size and morphology at reasonable cost. The present study demonstrates the synthesis of nanocrystalline α‐Fe2O3(hematite), Mn0.5Zn0.5Fe2O4, and Ni0.5Zn0.5Fe2O4 particles in a reverse micellar microemulsion system [water–iso‐octane–AOT (sodium di‐2ethylhexylsulfosuccinate)]. The synthesis of α‐Fe2O3 is performed to obtain baseline data for the synthesis of Mn0.5Zn0.5Fe2O4 and Ni0.5Zn0.5Fe2O4 in the microemulsion system. Nanosized, spherical α‐Fe2O3, Ni‐Zn ferrite, and Mn‐Zn ferrite particles (20–80 nm) with very narrow particle size distribution are synthesized. Crystallization of the particles is obtained at temperatures as low as 300°C.
Ferroelastic Behavior of LaCoO3‐Based Ceramics
Authors: Kleveland Kjersti , Orlovskaya Nina , Grande Tor , Moe Anne Marie Mardal , Einarsrud Mari‐Ann , Breder Kristin , Gogotsi George
Published: July 2010

LaCoO3 and La0.8Ca0.2CoO3 ceramics show a nonelastic stress–strain behavior during four‐point bending experiments where hysteresis loops are observed during loading–unloading cycles. Permanent strain is stored in the material after unloading, and a mechanism related to ferroelastic domain switching in the rhombohedral perovskite is proposed. Domain switching in the materials has been confirmed using X‐ray diffractometry. Fracture toughnesses of La0.8Ca0.2CoO3 measured using single‐edge notched beam and single‐edge V‐notched beam methods coincide and are equal to 2.2 MPa·m1/2 at room temperature and decrease to ∼1 MPa·m1/2 at temperatures >300°C. A decrease in fracture toughness is consistent with ferroelastic behavior, because the rhombohedral distortion decreases with increasing temperature.
Bonelike Apatite Formation Induced on Zirconia Gel in a Simulated Body Fluid and Its Modified Solutions
Authors: Uchida Masaki , Kim Hyun‐Min , Kokubo Tadashi , Miyaji Fumiaki , Nakamura Takashi
Published: July 2010

Formation of bonelike apatite on zirconia gel in a simulated body fluid (SBF) with ion concentrations almost equal to those in human blood plasma, in modified SBF solutions to have increased pH values, and modified SBF solutions to have increased concentrations of calcium and phosphate ions has been investigated. The zirconia gel forms apatite on its surface in SBF, indicating that Zr‐OH groups, abundant on the gel, act as effective apatite nucleation centers. Apatite formation is accelerated by increases in pH and in the concentration of calcium and phosphate ions, which is explained by an increase in the ionic activity product of the apatite in the SBF. These results suggest that zirconia ceramics may exhibit a bone‐bonding ability by forming an apatite layer on their surfaces in the living body when they are modified to have many Zr‐OH groups on their surfaces.
Detection of Phase Separation by FTIR in a Liquid‐Crystal‐Display Substrate Aluminoborosilicate Glass
Authors: Kato Yoshinari , Yamazaki Hiroki , Tomozawa Minoru
Published: July 2010

The effect of heat treatment on the Fourier transform infrared spectrometry (FTIR) reflection peak position of the Si–O structural band near 1087 cm−1 of a liquid‐crystal‐display substrate glass was investigated. The FTIR peak position shifted more slowly with heat‐treatment time, and to a greater extent than expected, for the fictive temperature change. The isochronal shift of the FTIR peak as a function of the heat‐treatment temperature exhibited a good correlation with the change of chemical durability in an HCl solution, suggesting that the infrared peak shift was the result of the phase separation induced by the heat treatment. The separated phase, with spherical particles ∼50 nm in diameter, was observed by scanning electron microscopy in a glass sample heat‐treated at 750°C for 2500 h. The FTIR peak shift measurement appears to be a sensitive method for detecting the early stage of the glass‐in‐glass phase separation for borosilicate glasses.
Shrinkage Behavior of Knoop Indentations in Silica and Soda–Lime–Silica Glasses
Authors: Yoshida Satoshi , Isono Shigemi , Matsuoka Jun , Soga Naohiro
Published: July 2010

The annealing characteristics of Knoop‐indented silica and soda–lime–silica glasses were investigated. These glasses were indented using a Knoop indenter in water, and they were annealed at various temperatures below the glass transition temperature. The major diagonal length of the Knoop indentation was measured before and after annealing, and the change of the diagonal length was determined. The change of diagonal length in silica glass was much larger than that in soda–lime–silica glass. This was attributed to the occurrence of more densification around the Knoop indentation in the silica glass. The activation energy of the shrinkage of the Knoop indentation in the silica glass, estimated from the temperature dependence of the relaxation time, was 46 kJ/mol, which was much less than that of viscous flow in silica glass. This suggested that the shrinkage of the Knoop indentation was caused by the structural relaxation of densified glass around the Knoop indentation.
InSitu Densification Behavior in the Pyrolysis Consolidation of Amorphous Si‐N‐C Bulk Ceramics from Polymer Precursors
Authors: Wan Julin , Gasch Matthew J. , Mukherjee Amiya K.
Published: July 2010

In
situ consolidation of amorphous Si‐N‐C ceramics during pyrolysis of polymer precursor provides a way to consolidate bulk silicon nitride based ceramics at lower temperatures. Porosity evolution during polymer‐ceramic conversion has been investigated to clarify the densification process. A densification mechanism based on surface reaction and pyrolysis accommodated by viscous flow has been proposed.
Precursor‐Derived Si‐B‐C‐N Ceramics: Oxidation Kinetics
Authors: Butchereit Elke , Nickel Klaus G. , Müller Anita
Published: July 2010

The oxidation behavior of three precursor‐derived ceramics—Si4.46BC7.32N4.40 (AMF2p), Si2.72BC4.51N2.69 (AMF3p), and Si3.08BC4.39N2.28 (T2/1p)—was investigated at 1300° and 1500°C. Scale growth at 1500°C in air can be approximated by a parabolic rate law with rate constants of 0.0599 and 0.0593 μm2/h for AMF3p and T2/1p, respectively. The third material does not oxidize according to a parabolic rate law, but has a similar scale thickness after 100 h. The results show that at least within the experimental times these ceramics develop extremely thin scales, thinner than pure SiC or Si3N4.
Structure and Electronic Transport Properties of Si‐(B)‐C‐N Ceramics
Authors: Hermann Allen M. , Wang Yao‐Te , Ramakrishnan Padmanabhan A. , Balzar Davor , An Linan , Haluschka Cristoph , Riedel Ralf
Published: July 2010

The structure and electronic transport properties of polymer‐derived pristine and boron‐doped silicon carbonitride ceramics have been studied, with particular emphasis on understanding the effect of annealing treatments. Structural analysis using the radial distribution function formalism showed that the local structure is comprised of basic building blocks of Si tetrahedra with B, C, and N at the corners. Comparison of the electrical properties of pristine and boron‐doped ceramics shows that boron doping leads to enhanced p‐type conductivity, with a small positive thermopower. The postpyrolysis annealing treatments at elevated temperatures have a significant effect on the conductivity. The conductivity variation with temperature for these ceramics shows Mott's variable range hopping (VRH) behavior, characteristic of a highly defective semiconductor.
Conductive Ceramic Foams from Preceramic Polymers
Authors: Colombo Paolo , Gambaryan‐Roisman Tatiana , Scheffler Michael , Buhler Peter , Greil Peter
Published: July 2010

Ceramic foams in the system Si‐O‐C, possessing different bulk densities and morphologies, were obtained from preceramic polymers using two different direct foaming approaches. The electric properties of the foams were varied by adding suitable fillers to the precursor mixtures in amounts up to 80 wt%. The electrical conductivity of the foams was varied by several orders of magnitude. The effects of the type of filler and preceramic polymer (methylsiloxane or methylphenylsiloxane resins), as well as the used filler precursor, on the properties of the ceramic foams were investigated.
Partially Reduced Cuprous Oxide Nanoparticles Formed in Porous Glass Reaction Fields
Authors: Murase Norio , Yazawa Tetsuo
Published: July 2010

This paper describes the formation of cuprous oxide (Cu2O) particles ∼10 nm in diameter and their reduction by hydrogen gas in porous glasses. Nanoparticles of Cu2O coated with metallic copper are expected to show high third‐order optical nonlinear susceptibilities (χ(3)). The porous glass is a medium in which nanoparticles can be partially reduced without forming agglomerations. Images obtained using transmission electron microscopy showed that particles with the desired core‐shell structure were actually formed, even though some particles were not reduced uniformly from the surface. The χ(3)/α (α: absorbance) values in relevant conditions (10−13 esu·cm) were similar to that of copper because of the formation of a byproduct of copper nanoparticles on reduction.
Formation Mechanism of Hydrous Zirconia Particles Produced by the Hydrolysis of ZrOCl2 Solutions: III, Kinetics Study for the Nucleation and Crystal‐Growth Processes of Primary Particles
Authors: Matsui Koji , Ohgai Michiharu
Published: July 2010

The formation rate and primary particle size of monoclinic, hydrous zirconia particles produced by the hydrolysis of various ZrOCl2 solutions (with and without the addition of HCl, NH4OH, NaCl, CaCl2, or AlCl3) were measured to clarify the effects of the H+ and Cl− ion concentrations on the nucleation and crystal‐growth processes of primary particles of hydrous zirconia. Chemical‐kinetic analyses, to which Avrami–Erofeev's equation was applied, and XRD measurements revealed that both the rate constant and the primary particle size of the hydrous zirconia decreased as the concentrations of H+ and/or Cl− ions produced by hydrolysis increased. The nucleation rate per unit of ZrOCl2 concentration and the crystal‐growth rate of the primary particles of the hydrous zirconia were determined by analyzing the relationships between the rate constant and primary particle size. The nucleation rate per unit of ZrOCl2 concentration revealed almost no change and remained constant as the H+ and/or Cl− ion concentrations increased, except in the case of a slight increase for ZrOCl2 solutions with added HCl. The crystal‐growth rate decreased as the H+ and/or Cl− ion concentration increased. The present kinetic analyses revealed that the decrease in rate constant with increasing H+ and/or Cl− ion concentrations resulted from the decrease in the crystal‐growth rate. The decreasing tendency of the crystal‐growth rate was attributed to interference with crystal growth by the Cl− ions attracted onto the particle surface through the formation of an electric double layer. The formation mechanisms for the primary particles of hydrous zirconia were determined based on the present experimental results.
Microwave‐Hydrothermal Synthesis of Monodispersed Nanophase α‐Fe2O3
Authors: Katsuki Hiroaki , Komarneni Sridhar
Published: July 2010

Synthesis of monodispersed nanophase α‐Fe2O3 (hematite) powder to be used as a red pigment in porcelains was investigated using microwave‐hydrothermal and conventional‐hydrothermal reactions using 0.018M FeCl3·6H2O and 0.01M HCl solutions at 100°–160°C. Acicular and yellow β‐FeOOH (akaganite) particles 300 nm in length and 40 nm in thickness were dominantly formed at 100°C after 2–3 h, while spherical α‐Fe2O3 particles 100–180 nm in diameter were preferentially formed after 13 h using a conventional‐hydrothermal reaction. However, a microwave‐hydrothermal reaction at 100°C led to monodispersed and red α‐Fe2O3 particles 30–66 nm in diameter after 2 h without the formation of β‐FeOOH particles. In this paper, the effect of microwave radiation during hydrothermal treatment at 100°–160°C on the formation yield, kinetics, morphology, phase type, and color of α‐Fe2O3 was investigated.
Ytterbium Cation Diffusion in Yttrium Aluminum Garnet (YAG)—Implications for Creep Mechanisms
Authors: Jiménez‐Melendo Manuel , Haneda Hajime , Nozawa Hoshiteru
Published: July 2010

The lattice and grain‐boundary diffusion coefficients of ytterbium, which substitutes for yttrium, have been determined in high‐purity, stoichiometric yttrium aluminum garnet (YAG) polycrystals in the temperature range 1400°–1550°C, in air. Ytterbium oxide thin films were produced on the YAG surfaces by a dipping method. After diffusion treatments, the penetration profiles were established by secondary ion mass spectroscopy, and the diffusion coefficients were calculated from the thin‐film solution of Fick's equation. The difference between the volume and grain‐boundary diffusion coefficients is ∼5 orders of magnitude in the temperature range studied. The cation activation energies (∼550 kJ/mol) are much larger than those for oxygen (∼300–350 kJ/mol). The effective diffusion coefficient deduced from high‐temperature deformation data reported in the literature for YAG polycrystals, assuming grain‐boundary sliding accommodated by volume diffusion, is in excellent agreement, both in magnitude and activation energy, with the cation diffusion data.
Visualization of Knoop Indentation Damage of Silicon Nitride by Plasma Etching
Authors: Kanematsu Wataru , Miyajima Tatsuya , Sando Mutsuo
Published: July 2010

A visualizing technique for indentation damage of ceramics was developed. Plasma etching was used to enhance the view of cracks and the subsurface microcracking crush zone following Knoop indentation of hot pressed Si3N4. The microcracking zone was readily identified from the surface view of the indented surface as a grain‐falling‐off region (GFOR), defined as a region in which grains were removed by preferential etching using CF4 gas, followed by ultrasonic cleaning. A fissure‐like opening corresponding to the indentation cracks was also observed. It is inferred that the formation of the GFOR region and the fissure‐like opening were caused by the etching/cleaning treatment. Meanwhile, the etching on a section which included diagonals of the impression provided a section view of the microcracking zone.
Lead Zirconate Titanate Thin Films on Base‐Metal Foils: An Approach for Embedded High‐Permittivity Passive Components
Authors: Maria Jon‐Paul , Cheek Kevin , Streiffer Stephen , Kim Seung‐Hyun , Dunn Greg , Kingon Angus
Published: July 2010

An approach for embedding high‐permittivity dielectric thin films into glass epoxy laminate packages has been developed. Lead lanthanum zirconate titanate (Pb0.85La0.15(Zr0.52Ti0.48)0.96O3, PLZT) thin films were prepared using chemical solution deposition on nickel‐coated copper foils that were 50 μm thick. Sputter‐deposited nickel top electrodes completed the all‐base‐metal capacitor stack. After high‐temperature nitrogen‐gas crystallization anneals, the PLZT composition showed no signs of reduction, whereas the base‐metal foils remained flexible. The capacitance density was 300–400 nF/cm2, and the loss tangent was 0.01–0.02 over a frequency range of 1–1000 kHz. These properties represent a potential improvement of 2–3 orders of magnitude over currently available embedded capacitor technologies for polymeric packages.
Mechanical Properties of CoAl Materials with the Combined Additions of ZrO2(3Y) and Al2O3
Authors: Takano Yoshihiko , Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2010

Intermetallic CoAl powder has been prepared via self‐propagating high‐temperature synthesis (SHS). Dense CoAl materials (99.6% of theoretical) with the combined additions of ZrO2(3Y) and Al2O3 have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The microstructures are such that tetragonal ZrO2 (0.3 μm) and Al2O3 (0.5 μm) particles are located at the grain boundaries of the CoAl (8.5 μm) matrix. Improved mechanical properties are obtained; especially the fracture toughness and the bending strength of the materials with ZrO2(3Y)/Al2O3= 16/4 mol% are 3.87 MPa·m1/2 and 1080 MPa, respectively, and high strength (>600 MPa) can be retained up to 1000°C.
Thermal and Electrical Properties in Plasma‐Activation‐Sintered Silicon Carbide with Rare‐Earth‐Oxide Additives
Authors: Zhan Guo‐Dong , Mitomo Mamoru , Xie Rong‐Jun , Mukherjee Amiya K.
Published: July 2010

This study investigates the thermal and electrical properties of SiC ceramics with a combination of Y2O3 and rare‐earth‐oxide additions as sintering additives, by comparing four types of SiC starting powders varying in particle size and chemical composition. The powder mixtures were plasma‐activation sintered to full densities and then annealed at high temperatures for grain growth. The thermal conductivity and electrical resistivity of the SiC ceramics were measured at room temperature by a laser‐flash technique and a current–voltage method, respectively. The results indicate that the thermal conductivity and electrical resistivity of the SiC ceramics are dependent on the chemical composition and particle size of the starting powders. The thermal conductivities observed for all of the annealed materials with a rare‐earth La2O3 sintering additive were >160 W·(m·K)−1, although low electrical resistivity was observed for all materials, in the range 3.4–450 Ω·cm. High thermal conductivity, up to 242 W·(m·K)−1, was achieved in an annealed material using a commercial 270 nm SiC starting powder.
Theoretical Prediction of Post‐Spinel Phases of Silicon Nitride
Authors: Tatsumi Kazuyoshi , Tanaka Isao , Adachi Hirohiko , Oba Fumiyasu , Sekine Toshimori
Published: July 2010

New phases of Si3N4 that may be stable at higher pressure than spinel have been searched using a first‐principles plane‐wave pseudopotential method. The CaTi2O4‐type phase is found to be the prime candidate for the post‐spinel phase among six phases selected on the analogy to high‐pressure oxides. The phase transformation from the spinel is predicted to occur at 210 GPa. All silicon atoms of the new phase are coordinated by six anions, similar to the case of the high‐pressure forms of SiO2 and SiC. Because of its high energy at zero pressure, this new phase may be difficult to quench. The bandgap increases with an increase of pressure when compared in the same polymorph. However, the bandgap and the net charge decrease in the order of β, spinel, and CaTi2O4‐type phases at zero pressure. The theoretical bulk modulus of the CaTi2O4‐type phase is comparable with that of spinel.
Calculation of XANES/ELNES Spectra of All Edges in Si3N4 and Si2N2O
Authors: Ching Wai‐Yim , Mo Shang‐Di , Chen Yu
Published: July 2010

Using a recently developed first‐principles supercell method that includes the electron and core‐hole interaction, the XANES/ELNES spectra of Si‐L2,3, Si‐K, and N‐K edges in α‐Si3N4, β‐Si3N4, spinel c‐Si3N4, and Si2N2O were calculated and compared. The difference in total energies between the initial ground state and the final core‐hole state provides the transition energy. The calculated spectra are found to be in good agreement with the experimental measurements on β‐Si3N4 and c‐Si3N4. The differences in the XANES/ELNES spectra for the same element in different crystals are explained in terms of differences in local bonding. The use of orbital‐decomposed local density of states to explain the measured spectra is shown to be inadequate. These results reaffirm the importance of including the core‐hole effect in any XANES/ELNES spectral calculation.
Effective Doping in Cubic Si3N4 and Ge3N4: A First‐Principles Study
Authors: Oba Fumiyasu , Tatsumi Kazuyoshi , Tanaka Isao , Adachi Hirohiko
Published: July 2010

First‐principles calculations have been conducted to investigate impurities in cubic Si3N4 and Ge3N4. Impurity species suitable for n‐ and p‐type doping are suggested, in terms of the formation and ionization energies. The suggested species are P and O as n‐type dopants and Al as a p‐type dopant for c‐Si3N4, and Sb and O as n‐type dopants and Al as a p‐type dopant for c‐Ge3N4. The dependence of the formation energies on the chemical potentials indicates that a proper choice of growth conditions is mandatory for suppressing the incorporation of these impurities into anti and interstitial sites, where the impurities can be charged to compensate carriers.
Theoretical Study on the Chemistry of Intergranular Glassy Film in Si3N4–SiO2 Ceramics
Authors: Yoshiya Masato , Tatsumi Kazuyoshi , Tanaka Isao , Adachi Hirohiko
Published: July 2010

The intergranular glassy film (IGF) composed of silicon oxynitride in a Si3N4 ceramic material has been studied by molecular dynamics calculations. Structural analyses showed that the presence of an IGF having both nitrogen and oxygen reduces the number of dangling bonds at the junction between the IGF and adjacent Si3N4 grains, which reduces the interface energy at the grain boundary. More dangling bonds were generated at the junction when the N/(N + O) ratio of the IGF was decreased due to the larger chemical and structural mismatch between the IGF and the adjacent grain. On the other hand, the increase in the N/(N + O) ratio of the IGF caused a greater energy penalty in the IGF. The balance of these two contributions should determine the chemistry of the IGF.
Preparation of Nanometer‐Sized α‐Alumina Powders by Calcining an Emulsion of Boehmite and Oleic Acid
Authors: Lin Chih‐Peng , Wen Shaw‐Bing , Lee Ting‐Tai
Published: July 2010

This study proposes a method to form ultrafine α‐Al2O3 powders. Oleic acid is mixed with Al(OH)3 gel. The gel is the precursor of the Al2O3. After it is mixed and aged, the mixture is calcined in a depleted oxygen atmosphere between 25° and 1100°C. Oleic acid evaporates and decomposes into carbon during the thermal process. Residual carbon prevents the growth of agglomerates during the formation of α‐Al2O3. The phase transformation in this process is as follows: emulsion →γ‐Al2O3→δ‐Al2O3→θ‐Al2O3→α‐Al2O3. This process has no clear θ phase. Aging the mixed sample lowers the formation temperature of α‐Al2O3 from 1100° to 1000°C. The average crystallite diameter is 60 nm, measured using Scherrer's equation, which is consistent with TEM observations.
Growth of High‐Quality Pb((Zn1/3Nb2/3)0.91Ti0.09)O3 Single Crystals by Excess ZnO Addition
Authors: Harada Kouichi , Shimanuki Senji , Kobayashi Tsuyoshi , Yamashita Yohachi , Saitoh Shiroh
Published: July 2010

A high‐quality single crystal of Pb((Zn1/3Nb2/3)0.91Ti0.09)O3 (PZNT 91/9), 40 mm in diameter and 20 mm in length, was successfully grown using the solution Bridgman method with a slight excess amount of ZnO. High‐quality wafers were sliced from the light‐brown single crystal. No PbO inclusions or opaque areas were observed in the transparent wafers. An array probe for echocardiography was constructed with the single‐crystal wafer, and its superior performance was demonstrated.
Constrained Densification Kinetics of Alumina/Borosilicate Glass + Alumina/Alumina Sandwich Structure
Authors: Lin Yun‐Chiang , Jean Jau‐Ho
Published: July 2010

The densification kinetics and mechanism of a low‐temperature cofirable borosilicate glass (BSG) + alumina during the constrained sintering of a sandwich structure of alumina/(BSG + alumina)/alumina has been studied. The densification kinetics becomes slower when the BSG + alumina tape is constrained during firing. However, a viscous flow‐controlling mechanism of the BSG also is still operative during free and constrained sintering. The densification behavior of constrained sintering can be mathematically described by free sintering, using the viscous analogy for the constitutive equations of a porous sintering glass.
Microstructure and Microwave Dielectric Properties of Ba(Zn1/3Ta2/3)O3 Ceramics with ZrO2 Addition
Authors: Yang Jung‐In , Nahm Sahn , Choi Chang‐Hack , Lee Hwack‐Joo , Park Hyun‐Min
Published: July 2010

The effect of ZrO2 on crystallographic order, microstructure, and microwave dielectric properties of Ba(Zn1/3Ta2/3)O3 (BZT) ceramics was investigated. A small amount of ZrO2 disturbed the 1:2 cation ordering. The average grain size of the BZT significantly increased with the addition of ZrO2, which was attributed to liquid‐phase formation. The relative density increased with the addition of a small amount of ZrO2, but it decreased when the ZrO2 content was increased. Variation of the dielectric constant with ZrO2 addition ranged between 27 and 30, and the temperature coefficient of resonant frequency increased abruptly as the ZrO2 amount exceeded 2.0 mol%. The Q value of the BZT significantly improved with the addition of ZrO2, which could be explained by the increased relative density and grain size. The maximum Q×f value achieved in this investigation was ∼164 000 GHz for the BZT with 2.0 mol% ZrO2 sintered at 1550°C for 10 h.
Decoupling between Enthalpy Relaxation and Viscous Flow and Its Structural Origin in Fragile Oxide Glass‐Forming Liquids
Authors: Komatsu Takayuki , Aida Kazuya , Honma Tuyoshi , Benino Yasuhiko , Sato Ryuji
Published: July 2010

The structural relaxation kinetics at the glass transition in tellurium oxide (TeO2)‐based glasses has been examined from viscosity and heat‐capacity measurements to clarify the features of the structural relaxation in fragile oxide glass‐forming liquids. A large decoupling between enthalpy relaxation and viscous flow, i.e., a large discrepancy between the activation energies for the enthalpy relaxation (recovery), ΔH, and viscous flow, Eη, has been demonstrated in TeO2‐based glasses. The values in xK2O·xMgO·(100 − 2x)TeO2 glasses, for example, are ∼919–1051 kJ/mol for ΔH and ∼ 577–701 kJ/mol for Eη, given the ratio of ΔH/Eη≈ 1.44–1.59. Some viscosity and heat‐capacity data (all data have been reported previously) obtained from similar experiments in Sb2O3–B2O3 glasses belonging to the category of strong glass‐forming liquids have been reanalyzed in this paper for comparison; a strong coupling was found to exist between ΔH and Eη, i.e., ΔH/Eη≈ 0.98–1.18. An origin of decoupling between ΔH and Eη in fragile glass‐forming systems such as TeO2‐based glasses has been discussed by considering the glass structure model for fragile glasses; strongly bonded correlated (highly constrained) regions are surrounded or connected by weakly bonded noncorrelated (unconstrained) parts.
Alkaline Activation of Metakaolin: Effect of Calcium Hydroxide in the Products of Reaction
Authors: Granizo Maria Luz , Alonso Santiago , Blanco‐Varela Maria T. , Palomo Angel
Published: July 2010

The alkali activation of metakaolin (MK) leads to the production of high‐mechanical‐performance network‐structure materials. Adding calcium hydroxide (Ca(OH)2) to the raw MK produces a somewhat different reaction: a network structure and C‐S‐H gel form. In the present study, MK and (MK + Ca(OH)2) mixes were activated with 5M and 12M NaOH solutions and cured at 45°C. A 5M concentration, in the absence of Ca(OH)2, did not produce MK activation within the test time. An activator concentration of 12M resulted in complete activation and the formation of a network structure. When Ca(OH)2 was present in the raw mix, a small amount of C‐S‐H gel formed.
Manufacturing Silicon Carbide Microrotors by Reactive Hot Isostatic Pressing within Micromachined Silicon Molds
Authors: Li Jing‐Feng , Sugimoto Shinya , Tanaka Shuji , Esashi Masayoshi , Watanabe Ryuzo
Published: July 2010

A novel ceramic microfabrication process—based on the idea of silicon carbide (SiC) reaction sintering within a micromachined silicon mold—has been developed to produce a SiC microroter for miniaturized gas turbines. The new process involves the micromachining of silicon molds; filling the molds with powder mixtures of α‐SiC, graphite, and phenol resin; bonding the molds with an adhesive; reaction sintering by hot isostatic pressing (HIP); and the releasing of a reaction‐sintered workpiece from the mold by wet etching. Using this process, we have successfully fabricated SiC microrotors with a diameter of 5 mm, whose complicated geometry was well transferred from the negative shape of the micromachined silicon mold. The reaction‐HIPed SiC ceramics within Si molds showed reasonably good mechanical properties, which are comparable to those of the commercialized reaction‐sintered SiC ceramics.
High‐Strength Porous Alumina Ceramics by the Pulse Electric Current Sintering Technique
Authors: Jayaseelan D. Doni , Kondo N. , Brito M. E. , Ohji T.
Published: July 2010

High‐strength porous alumina has been fabricated with a microstructure control using the pulse electric current sintering (PECS) technique. During sintering the discharge, which is assumed to take place in the voids between the particles, is thought to promote the bridging of particles by neck growth in the initial stages of sintering, leaving high porosity. The effect of dopants (MgO, 200 ppm; TiO2, 1000 ppm) and of secondary inclusions (3 vol% 3Y‐TZP) on the constrained densification and the improvement in the mechanical behavior of porous alumina ceramics has been reported. The porosity of the fabricated porous alumina was controllable between 30% and 50% depending on the sintering temperature. The flexural strength of alumina having 30% and 42% porosity showed impressive values of 250 and 177 MPa, respectively. The dominance of the preferential neck growth of grains over densification significantly improved the mechanical properties of porous alumina, besides leaving high porosity.
Low‐Voltage Varistor Based on (Sn,Ti)O2 Ceramics
Authors: Bueno Paulo R. , Cassia‐Santos Maria R. , Simões Luis G. P. , Gomes José W. , Longo Elson , Varela José A.
Published: July 2010

A description is given of the nonohmic behavior obtained in (SnxTi1−x)O2‐based systems. A matrix founded on (SnxTi1−x)O2‐based systems doped with Nb2O5 leads to a low‐voltage varistor system with nonlinear coefficient values of ∼9. The presence of the back‐to‐back Schottky‐type barrier is observed based on the voltage dependence of the capacitance. When doped with CoO, the (SnxTi1−x)O2‐based system presents higher nonlinear coefficient values (>30) than does the SnO2‐based varistor system.
Cement‐Based 0‐3 Piezoelectric Composites
Authors: Li Zongjin , Zhang Dong , Wu Keru
Published: July 2010

To meet the requirements of development for smart or intelligent structures in civil engineering, new functional materials that have good compatibility with civil engineering structural materials are needed. In this study, for the first time in the field of piezoelectric materials, cement‐based 0‐3 piezoelectric (PZT) composites were fabricated by the normal mixing and spreading method. The new materials have very good compatibility with portland cement concrete. The cement‐based 0‐3 piezoelectric composites were shown to have a slightly higher piezoelectric factor and electromechanical coefficient than those of 0‐3 PZT/polymer composites with a similar content of PZT particles; thus, they are adequate for sensor application. There is potential for the application of cement‐based 0‐3 PZT composites in civil engineering because of their better piezoelectric properties and good compatibility with portland cement concrete.
Dispersion and Grinding of Oxide Powders into an Aqueous Slurry
Authors: Houivet David , El Fallah Jaâfar , Haussonne Jean‐Marie
Published: July 2010

The present paper deals with a comprehensive analysis of the dispersion behavior of oxide powders to determine accurate conditions for mixing and grinding dense slurries without the use of steric dispersing agents. The experimental support of the work was the synthesis of (Zr,Sn)TiO4 microwave dielectric ceramics by the solid‐state reaction of raw materials mixed and ground by attrition milling. Zeta potential measurements were performed on the raw materials versus pH to determine the optimum pH of the slurry, allowing a good dispersion of all the species: the absolute value of the zeta potential of every powder >20 mV, with all potentials having the same sign. During the grinding process, as the surface of the materials increases due to the breakup of the grains, surface reaction occurs with the dispersion liquid, and pH must be continuously adjusted to be maintained at an adequate level. We have correlated these characterizations of the optimal processing conditions with the rheological behavior of the slurries, thus providing an analysis of the flocculated or deflocculated state. When applied to synthesizing (Zr,Sn)TiO4 microwave dielectric ceramics, these conclusions made it possible to produce reproducible resonators with a k= 37 dielectric constant and characterized by a quality factor, Q×F > 60 000 GHz measured at 3 GHz, the highest value reported for this composition.
Synthesis of Lead Nickel Niobate–Barium Titanate System by Oxidation of Polyethylene Glycol–Cation Complex
Authors: Uekawa Naofumi , Sukegawa Takashi , Kakegawa Kazuyuki , Sasaki Yoshinori
Published: July 2010

The complex between polyethylene glycol (PEG) and cations (Ni2+,Nb5+) was used for the preparation of compound lead nickel niobate (Pb(Ni1/3Nb2/3)O3) and a (1 −x)Pb(Ni1/3Nb2/3)O3–xBaTiO3 solid solution system. The sintering of the powder mixture of PbO and the oxide obtained by the oxidation of the PEG–(Ni2+, Nb5+) complex at 1023 K for 1 h formed a greater amount of the perovskite phase than when the solid‐phase reaction method was used for the preparation. The (1 −x)Pb(Ni1/3Nb2/3)O3–xBaTiO3 system was prepared by sintering the mixture of the oxide obtained by the oxidation of the PEG–(Ni2+,Nb5+) complex, PbO, and BaTiO3 at 1373 K for 1 h. When PEG with a molecular weight of 1000 and PEG with a molecular weight of 7500 were used, the pure perovskite phase was obtained by a 7.5 mol% and a 1 mol% addition of BaTiO3, respectively. The formation behavior of perovskite phase depended on the amount of NiNb2O6 (columbite) in the oxide obtained by oxidation of PEG–(Ni2+,Nb5+) complex. When the solid‐phase reaction method was used, only a small amount of NiNb2O5 was obtained. The formed amount of NiNb2O6 with a columbite structure increased with an increase in the molecular weight of the PEG. The increase of the formation of NiNb2O6 showed that the effective formation of the perovskite phase occurred with the smallest addition of BaTiO3.
Stress Development during Constrained Sintering of Alumina/Glass/Alumina Sandwich Structure
Authors: Tzeng Shin‐Yu , Jean Jau‐Ho
Published: July 2010

Stress development during the constrained sintering of a sandwich structure of alumina/glass/alumina has been studied. Stress distribution in the glass layer was calculated using a finite element method. The shear stress exhibited a maximum at the edge of the alumina/glass interface. The in‐plane tensile stress, formed during constrained sintering, decreased from the interface of the alumina/glass to the middle of the glass in thez‐direction, but increased from the edge to the center of glass in thex−ydirection. This in‐plane tensile stress reduces the driving force of densification, resulting in a largerx−yshrinkage and higher densification in the middle of the glass.
High‐Temperature Oxidation Behavior of High‐Purity α‐, β‐, and Mixed Silicon Nitride Ceramics
Authors: Backhaus‐Ricoult M. , Guerin V. , Huntz A.‐M. , Urbanovich V. S.
Published: July 2010

High‐temperature oxidation behavior, microstructural evolution, and oxidation kinetics of additive‐free α‐, β‐, and mixed silicon nitride ceramics is investigated. The oxidation rate of the ceramics depends on the allotropic ratio; best oxidation resistance is achieved for ceramics rich in α‐phase. Variations in the oxidation kinetics are directly related to average grain size and glass distribution in the oxidation scale. The oxygen contents incorporated into the Si3N4 phase before its dissolution at the oxidation front affects the local glass composition and thereby yields nucleation and growth rates of SiO2 crystallites within the glass phase and a final oxidation scale microstructure, which depend on the incorporated oxygen contents. For the α‐polymorph, the dynamic oxygen solubility is found to remain negligible; therefore, a nitrogen‐rich glass forms at the oxidation front, which promotes devitrification and yields a scale with small grain size and thin intergranular glass films. β‐Si3N4 is observed to form oxygen‐rich solid solutions on oxidation, which are in contact with silicon oxynitride or oxygen‐rich glass. Nucleation of cristobalite in the latter is sluggish, yielding coarse‐grained oxidation scales with thick intergranular glass film.