bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Particle‐Size Distribution on the Microstructural Evolution in the Intermediate Stage of Sintering
Authors: Shiau Fuh‐Shan , Fang Tsang‐Tse , Leu Tsung‐Hsing
Published: July 2010

The effect of particle‐size distribution on microstructural evolution in the intermediate stage of sintering of powder compacts was investigated. The evolution of pore channels was dominated by particle‐size distribution but independent of sintering temperature. Moreover, a powder compact with a fine particle and uniform size distribution could prolong the intermediate stage of sintering, which in turn effectively inhibited grain growth. The mechanisms of evolution and pinch off of the pore channels of the powder compact with different particle‐size distributions were discussed.
Duplex α,β‐Sialon Ceramics Stabilized by Dysprosium and Samarium
Authors: Ekström Thommy , Falk Lena K. L. , Shen Zhi‐Jian
Published: July 2010

Duplex αβ,‐sialon ceramics with a minimum volume fraction of residual intergranular glass have been prepared using Dy or Sm as the α‐sialon stabilizing element. These microstructures contained high aspect ratio β‐sialon grains homogeneously distributed in an α‐sialon matrix. A number of the larger α‐sialon grains contained dislocations and showed a core/shell structure. Dy gave an α‐sialon which was stable over a wide temperature range (1350–1800°C) for long holding times, while the use of Sm resulted in less stable α‐sialon structures at medium temperatures (1450°C) and the formation of melilite, R2Si3−xAlxO3+xN4−x, β‐sialon, and the 21R sialon polytype during prolonged heating. High α‐phase contents gave a very high hardness (HV10 is approximately 22 GPa) but a comparatively low indentation fracture toughness (around 4.4 MPam1/2). Duplex sialons fabricated from powder mixtures corresponding to an α‐to‐β sialon ratio of around 50:50 resulted in a sialon material with a favorable combination of high hardness (around 22 GPa) and increased toughness (to around 5.5 MPam1/2).
Refractive Index Dispersion of Sodium Magnesium Silicate Glasses for Ultralow‐Loss Fibers
Authors: Todoroki Shin‐ichi , Sakaguchi Shigeki , Peeters Miguel
Published: July 2010

The refractive index dispersion and infrared (IR) reflection spectra of soda magnesium silicate glasses with low Rayleigh scattering were measured to evaluate their potential for use in fabricating ultralow‐loss fibers. The zero‐material dispersion wavelength (λ0) was found to be around 1.5 μm, which is one of the key wavelengths in the present telecommunication system. The compositional dependence of λ0 was found to relate to the population of nonbridging oxygen. Since the oscillation strength and frequency of the Si—O stretching vibrations of the glasses were found to be smaller than those of silica glass, their IR absorption loss was considered to be less than that of silica glass. The minimum loss due to the intrinsic factors, Rayleigh scattering and IR absorption, was estimated to be 0.06 dB/km at 1.6μm.
Application of the SIMS Method in Studies of Cr Segregation in Cr‐Doped CoO: I, Aspects of Quantitative Analysis
Authors: Bernasik Andrzej , Nowotny Janusz , Scherrer Stanislas , Weber Sylvian
Published: July 2010

Aspects of calibration of intensities of SIMS secondary ions vs concentration as well as sputtering time vs depth are considered for Cr‐doped CoO. Advantages and limitations of the SIMS method in quantitative analysis of segregation‐induced concentration profiles in oxide crystals are discussed. The studies indicate a substantial effect due to charging the surface during sputtering. The depth calibration was performed by using the Ta2O5/Ta system as a standard. Good depth resolution was revealed. The calibration dependence of Cr intensities on concentration is characterized by a wide scatter of data caused by charging the surface. Very good shape reproducibility of the intensity ratio vs depth profiles was revealed. Therefore, normalized intensity ratios can be used for calibration.
Dopant Distributions in Rare‐Earth‐Doped Alumina
Authors: Thompson A. Mark , Soni Kamal K. , Chan Helen M. , Harmer Martin P. , Williams David B. , Chabala Jan M. , Levi‐Setti Riccardo
Published: July 2010

The distribution of yttrium and lanthanum dopants has been mapped in yttrium‐ and lanthanum‐doped polycrystalline aluminas using imaging secondary‐ion mass spectrometry (imaging‐SIMS). Both dopants segregate to grain boundaries and pore surfaces. On average, yttrium occupies 7.1%–9.0% of the available grain‐boundary cation sites, whereas lanthanum occupies only 2.0%–5.2%. In 1000‐ppm‐yttrium‐doped alumina, an abundance of yttrium aluminum garnet precipitates also is observed. Implications of these observations to the creep behavior of alumina are discussed. The similarity in the segregation behavior of yttrium and lanthanum highlights the potential of lanthanum‐doped alumina for improved creep properties.
Effect on Electrical Properties of Barium and Strontium Additions in the Lead Lanthanum Zirconate Stannate Titanate System
Authors: Park Seung‐Eek , Markowski Kelley , Yoshikawa Shoko , Cross L. Eric
Published: July 2010

The effect of barium (Ba) and strontium (Sr) additions on the electrical properties of lead lanthanum zirconate stannate titanate (PLZST) ceramics and their electrically induced phase change behavior was examined. Sr additions decreased both the ferroelectric (FE) ↔ antiferroelectric (AFE) transition temperature (TAFE‐FE) and the temperature of the maximum dielectric constant (TMAX). This indicates that Sr additions stabilize the AFE phase. Along with B‐site modifications Sr additions can be used to decrease the switching field and hysteresis. Ba additions caused the temperature range of the AFE phase to narrow by increasing TAFE‐FE and decreasing TMAX. This behavior indicates an ability to lower the switching field and suppress hysteresis. Using a combination of both A‐site and B‐site modifications it is possible to tailor the properties (for example, switching field, hysteresis, and operating temperature range) of this group of phase change materials to meet the requirements of specific applications.
Raman Spectroscopic Investigations of Dicalcium Silicate: Polymorphs and High‐Temperature Phase Transformations
Authors: Remy Corinne , Reynard Bruno , Madon Michel
Published: July 2010

Polymorphs and high‐temperature phase transformations of dicalcium silicate (Ca2SiO4) are investigated on powdered samples, using Raman scattering techniques. Raman spectra at room conditions of pure γ‐ and β‐Ca2SiO4 and stabilized β‐, α′L‐, and α‐Ca2SiO4 are presented in the frequency range of 110–1100 cm−1. Each polymorph can be identified by its Raman spectrum, even though strong similarities exist between the β, α′L, and α phases. In‐situ high‐temperature Raman spectroscopic studies in the temperature range of 298–1433 K on heating and cooling also are reported, starting from γ‐Ca2SiO4. Modifications occurring in the Raman spectra recorded in the wavenumber range of 90–1000 cm−1 show up during heating, the irreversible γ→α′L phase transformation. Coexistence of γ and α′L grains is observed in the temperature range of 1091–1119 K at least. The differences observed between the γ‐Ca2SiO4 and α′L‐Ca2SiO4 Raman spectra suggest that this phase transformation is a reconstructive first‐order transition. The reversible α′L⇄β phase transformation also is described. Raman spectra of pure β and α′L phases resemble each other. The transition occurs from 949 K, on cooling, to 960–988 K, on heating, with a hysteresis probably dependent on the thermal history of the starting product. From the Raman scattering observations, this phase transformation also is considered as a first‐order transformation and is probably of a displacive type.
Measurement of Crack Tip Toughness in Alumina as a Function of Grain Size
Authors: Seidel Jürgen , Rödel Jürgen Seidel
Published: July 2010

Crack profile measurements near the crack tip in the SEM were used to measure crack tip toughness of alumina as a function of grain size (average grain size 0.9–16 μm). For comparative tests, two crack configurations were included in the present study: straight cracks (CT specimen) loaded with an in situ device; and radial indentation cracks. The measured crack tip toughness values were independent of crack geometry, and no grain size dependence could be discerned. A mean crack tip toughness of 2.3 MPam1/2 was evaluated. The crack tip toughness determined from crack profile measurements is significantly lower than the toughness evaluated with conventional indentation techniques (e.g., indentation strength bending).
Interfacial Reactions between Sapphire and Silver—Copper—Titanium Thin Film Filler Metal
Authors: Suenaga Seiichi , Nakahashi Masako , Maruyama Miho , Fukasawa Takayuki
Published: July 2010

Wetting and brazing studies of sputtering‐deposited, submicrometer thin film filler metal in an Ag—Cu—Ti/Al2O3 system were performed. The interfacial reaction layer between the filler metal and Al2O3 was investigated. It is possible to make a brazing joint even with a reaction layer of less than 100 nm thickness. Different types of interfacial reaction layers were observed when the Ti content in the filler metal was varied. The Cu—Ti—O system compounds were observed in the samples with high wetting capabilities, but not in the sample with low wetting characteristics. It was found that these compounds are substances that promote effective brazing.
Determination of the Mechanical Response of Sintering Compacts by Cyclic Loading Dilatometry
Authors: Cai Peter Z. , Messing Gary L. , Green David J.
Published: July 2010

Determination of the mechanical response of a powder compact during densification is critical in analyzing defect formation and macroscopic dimensional changes, particularly in systems where constrained sintering is involved. Cyclic loading dilatometry is proposed as a novel approach in evaluating the mechanical response of the sintering compact, including sintering pressure, elastic modulus, and viscosity. The advantage of this technique is that only one experiment is needed to determine the equilibrium elastic and viscous properties of a sintering material at any temperatures for any given heating schedule, and no interrupted tests are necessary. This methodology is demonstrated for sintering compacts of Al2O3, Ce‐TZP, and their composite mixture. The loading dilatometric data showed that the compact behaved elastically prior to the onset of sintering and during the very initial stages of sintering, which was followed by a transition leading to a viscous behavior for the latter part of the densification. Application of different load levels, ranging from 0.25 to 1 MPa, showed that the compact viscosity is essentially linear within the applied stress range at temperatures greater than 1100°C.
Optimization of Dispersion and Viscosity of a Ceramic Jet Printing Ink
Authors: Teng Wan D. , Edirisinghe Mohan J. , Evans Julian R. G.
Published: July 2010

Different amounts (0.5–10.0 wt%) of an oligomeric dispersant were added to a ceramic ink containing 30 vol% of zirconia in butyl acetate. The sediment packing densities of the resulting suspensions were measured. The viscosities of the suspensions were determined using a syringe that was adapted as a capillary viscometer suitable for the measurement of the low viscosities encountered (up to 400 mPas). The highest sediment‐packing density coincided with the lowest viscosity and occurred when 1–2 wt% of dispersant, based on the ceramic, was added. Investigation of the supernatant of the suspensions by thermogravimetric analysis indicated that this amount corresponded to the highest level of adsorption of the dispersant on the ceramic. The sediment from this suspension yielded a high density on subsequent sintering.
Double Cantilever Beam Measurements of Crack Growth in Indium(III) Phosphide
Authors: Braun Linda M. , White Grady S.
Published: July 2010

Crack growth measurements in InP crystals were conducted using an applied‐moment, double cantilever beam (DCB) geometry. Controlled, smooth crack growth was observed in water; however, the crack growth velocities were not constant for constant applied stress intensity (KI). More importantly, there was no clear functional dependence of the crack growth rate (ν) on KI.
Fiber—Matrix Interface Properties of Single‐Fiber Microcomposites as Measured by Fiber Pushin Tests
Authors: Kerans Ronald J. , Rebillat Francis , Lamon Jacques
Published: July 2010

Fiber pushin tests have been performed on single‐fiber microcomposite specimens embedded in glass. The interface properties determined were in agreement with those previously determined by two methods from tensile tests on microcomposites. The uncertainties in the interface properties calculated from the microcomposite pushin tests were not found to benefit from the superior alignment of the microcomposite specimens, as compared to literature results from composite specimens.
Oxidation of the Carbon Interface in Nicalon‐Fiber‐Reinforced Silicon Carbide Composite
Authors: Windisch Charles F. , Henager Charles H. , Springer Gary D. , Jones Russell H.
Published: July 2010

The recession rates for 10‐6‐m‐thick C interfaces in chemical vapor infiltrated SiC reinforced with Nicalon fibers were calculated from thermogravimetric data, assuming all of the mass losses were due to C oxidation, and found to be consistent with the measured recession distances of the C interface, which were surprisingly uniform across the composite. Agreement between the two approaches for a microstructurally complex material indicates thermogravimetric analysis could be an important tool for understanding environmental effects in ceramic composites with reactive interfaces. Mass losses were linear within the first 1.08× 104 s to 2.16× 104 s between 1073 and 1373 K and between 3.1× 102 and 2.5× 103 Pa O2. Calculated reaction orders with respect to O2 were between 0.5 and 1.0 at 1373 K, and activation energies were about 50 kJmol‐1. Analysis of the kinetic data and estimates of gas boundary layer thickness suggest the mechanism for the C‐interface oxidation involved reaction control, but the possibility of diffusion control for some conditions cannot be ruled out.
Effect of Stoichiometry on Mechanical Properties of (Pb0.875Ba0.125)[(Mg1/3Nb2/3)0.5(Zn1/3Nb2/3)0.3Ti0.2]O3 Relaxor Dielectric Ceramic
Authors: Kanai Hideyuki , Fukazawa Takayuki , Furukawa Osamu , Yamashita Yohachi
Published: July 2010

The mechanical and thermal properties of a partially A‐site‐substituted relaxor dielectric ceramic, (Pb0.875Ba0.125)A[(Mg1/3Nb2/3)0.5(Zn1/3Nb2/3)0.3Ti0.2]BO3, were investigated for specimens with A/B ratios ranging from 0.95 to 1.05. Vickers hardness, fracture toughness, and three‐point bending strength altered significantly at an A/B value between 1.00 and 1.01; this was accompanied by a change in the fracture mode from transgranular for A/B# 1.00 to intergranular for 1.01 $A/B. The three‐point bending strength of the relaxor was twice the thermal stress predicted by a simulation of multilayer ceramic capacitors (MLCs) subjected to heat‐cycle tests. However, the tensile strength in the direction normal to the internal electrode layers was much less than the simulated thermal stress. This indicated that mechanical strength was not a critical problem as regarded the MLC dielectric material but, rather, that it was critical to improve the adhesion between dielectric layers and internal electrode layers. Results also showed that it was important to improve the termination structure and solder wettability at the termination.
Sintering of Fine Oxide Powders: II, Sintering Mechanisms
Authors: Chen Pei‐Lin , Chen I‐Wei
Published: July 2010

Conventional and new sintering mechanisms have been investigated using fine powders of CeO2 and Y2O3 of excellent sinterability. We have verified the validity of Herrings scaling law for 60%–84% relative density and found that it is consistent with grain‐boundary‐diffusion control. At lower densities, we have found that pores larger than the critical size, in the sense of Kingery and Francois, can still be sintered readily. This is rationalized by a new sintering mechanism based on particle repacking concurrent with particle coarsening, resulting in a higher packing factor. Very fine, surface‐active powders that coarsen rapidly are uniquely capable of taking advantage of this new sintering mechanism, which along with their propensity to homogenization, accounts for their remarkable sinterability even at very low green densities.
Redistribution of a Grain‐Boundary Glass Phase during Creep of Silicon Nitride Ceramics
Authors: Jin Qiang , Ning Xiao‐Guang , Wilkinson David S. , Weatherly George C.
Published: July 2010

The compressive creep behavior of a high‐purity silicon nitride ceramic with and without the addition of Ba was studied at 1400°C. Two distinct creep stages were observed during high‐temperature deformation of both materials. Transmission electron microscopy (TEM) has been used to characterize the intergranular glass film thickness. Statistical analysis of a number of grain‐boundary films indicates that the film thickness is confined to a narrow range in the as‐sintered materials. However, the mean thickness is greater in the Ba‐doped ceramic than in the undoped material. The standard deviation of the film thickness of a given material is considerably larger after creep than before. We conclude that the grain‐boundary glass phase is redistributed during creep, suggesting that viscous flow of the glass phase is responsible for the first stage of the creep process.
Microstructural Evolution and Mechanical Properties of Si3N4 with Yb2O3 as a Sintering Additive
Authors: Park Hyoungjoon , Kim Hyoun‐Ee , Niihara Koichi
Published: July 2010

Ytterbium oxide (Yb2O3) was used as a sintering aid to enhance the mechanical properties of silicon nitride (Si3N4) ceramics. The amount of Yb2O3 had significant effects on microstructural evolution and the composition of secondary phases at the grain boundary. When the Yb2O3 added was less than 8 wt%, small homogeneous grains were formed. At the grain boundary, crystalline Yb2Si2O7 was formed along with a glassy phase. As the amounts of Yb2O3 were increased to higher than 8 wt%, large elongated grains were developed in the fine matrix. In those cases, the grain boundary crystalline phase was changed from Yb2Si2O7 to Yb4Si2O7N2. Mechanical properties were influenced by these changes in microstructure and grain boundary phase. The fracture toughness increased with the Yb2O3 content up to 8 wt% and decreased slightly thereafter. The increase in fracture toughness was apparently due to the formation of the large elongated grains. When more than 8 wt% of Yb2O3 was added, interfacial debonding energy between the elongated grains and grain boundary phase became too large, resulting in a decrease in the fracture toughness. The room‐temperature flexural strength was not significantly affected by the Yb2O3 content or the microstructure, other than in the case of 2 wt% addition. The high‐temperature strength in nitrogen, however, increased steadily with Yb2O3 content. The highest strength, 870 MPa at 1400°C, was observed when 16 wt% of Yb2O3 was added. The increase in the high‐temperature strength with Yb2O3 content was attributed to the formation of crystalline Yb4Si2O7N2 phase at the grain boundary.
Porous Glass‐Ceramics with Bacteriostatic Properties in Silver‐Containing Titanium Phosphates: Control of Release of Silver Ions from Glass‐Ceramics into Aqueous Solution
Authors: Kasuga Toshihiro , Kume Hisashi , Abe Yoshihiro
Published: July 2010

Porous glass‐ceramics with the surface phase consisting predominantly of AgTi2(PO4)3 crystal and the interior phase of LiTi2(PO4)3 crystal are prepared by exchange of Ag+ions for Li+ions. In the present work, the release of Ag+ ions from glass‐ceramics into aqueous solutions was investigated. Exchanged Ag+ ions were chemically stable in water. The as‐exchanged glass‐ceramics released Ag+ ions of 3045 equiv/g into phosphate buffer solution containing Na+ ions. X‐ray diffraction analysis showed that silver‐containing titanium phosphate crystalline phase in the glass‐ceramics did not deteriorate even by heating at 900°C. The amount released from the heated glass‐ceramics into the buffer solution was found to decrease drastically by 1–2 μequiv/g. The heated glass‐ceramics showed excellent bacteriostatic properties. Glass‐ceramics are expected to be novel bacteriostatic materials which have high thermal resistance and are medically safe.
Diamond Synthesis from Graphite in the Presence of MnCO3
Authors: Srikanth Varanasi , Akaishi Minoru , Yamaoka Shinobu , Yamada Hirohshi , Taniguchi Takashi
Published: July 2010

In order to investigate the catalytic effect of MnCO3, a typical transition‐metal carbonate, a graphite and MnCO3 (60:40 by weight) mixture was subjected to temperature and pressure ranges of 6.5–7.7 GPa and 1700°–2100°C, respectively. Diamonds were synthesized from graphite in the presence of MnCO3, at 2000°C and 7.7 GPa, where MnCO3 was confirmed to be in a molten state. Although MnO was found to be decomposed from the samples that were subjected to the aforementioned PT conditions, no diamond formation was detected from an MnO and graphite system for identical experimental conditions. Therefore, it was concluded that MnCO3 solvent catalyzed diamond formation from graphite.
Low‐Temperature Sintering and High‐Strength Pb(Zr,Ti)O3‐Matrix Composites Incorporating Silver Particles
Authors: Hwang Hae Jin , Watari Koji , Sando Mutsuo , Toriyama Motohiro , Niihara Koichi
Published: July 2010

Lead zirconate titanate based composites containing silver particles were fabricated from commercially available PZT and Ag2O powder mixtures. Densification behavior and mechanical and dielectric properties were evaluated as a function of the volume fraction of silver. No unwanted reaction phases between the PZT matrix and silver could be detected in the X‐ray diffraction analysis. The added silver particles were homogeneously dispersed in the matrix. The densification of PZT was substantially accelerated by the addition of silver particles. Mechanical properties, e.g., fracture toughness and fracture strength, were improved by the addition of silver particles. The relative dielectric constant also increased when the volume fraction of silver was increased. This observed enhancement in dielectric constant may be associated with the effective dielectric field developed by the existence of conducting silver particles.
Oxidation‐Induced Toughening and Strengthening of Y2O3/SiC Nanocomposites
Authors: Yoshimura Masashi , Ohji Tatsuki , Niihara Koichi
Published: July 2010

Effects of oxidation on mechanical properties have been investigated for Y2O3/5 vol% SiC nanocomposite. The roomtemperature fracture strength and toughness substantially increased after oxidation around 900–1000°C for 5 h. On the other hand, little improvement was identified for specimens treated in an inert atmosphere under the same conditions. A TEM study of the oxidized specimen surfaces revealed formation of extensive residual strain contours around SiC nanoparticles. The improved strength and toughness could be caused by compressive surface stress, which was generated by volume expansion of the nanoparticles due to oxidation.
Upper‐Phase Stability Limit of Bi‐2212
Authors: MacManus‐Driscoll J. L. , Li Y. H. , Yi Z.
Published: July 2010

The upper stability line for Bi2Sr2CaCu2O8+α (Bi‐2212) was determined over the temperature range 540°–800°C and the oxygen partial pressure range 1.5 ×101‐7.4× 10‐3 atm using coulometric titration and high oxygen pressure annealing. The decomposition products resulting from Bi‐2212 oxidation are CuO, two alkaline‐earth bismuthates, and the Raveau phase, Bi11Sr9Cu5Oy. The main alkaline‐earth bismuthate is a known phase of cation composition Bi:Sr:Ca = 2.00:2.48:1.19 (Bi:Sr:Ca 9:11:5). The other alkaline‐earth bismuthate is a minor phase of cation composition Bi:Sr:Ca = 2.00:0.53:0.39. The kinetics for Bi‐2212 decomposition are very slow; e.g., at 700°C in air, the reaction is incomplete after 7 days.
Preparation of Porous Glass‐Ceramics with a Skeleton of NASICON‐Type Crystal CuTi2(PO4)3
Authors: Yamamoto Kousuke , Kasuga Toshihiro , Abe Yoshihiro
Published: July 2010

A novel porous glass‐ceramic with a skeleton of CuTi2(PO4)3 was prepared by controlled crystallization of a glass and subsequent chemical leaching of the resulting dense glass‐ceramic. A volume‐crystallized dense glass‐ceramic composed of CuTi2(PO4)3 and Cu3(PO4)2 whose surface was covered by a CuO thin layer was prepared by reheating a glass with a nominal composition of 50CuO·20TiO230P2O5 (in mol%) glass in air. When the resultant glass‐ceramic was leached with dilute H2SO4, Cu3(PO4)2 and CuO phases were dissolved out selectively, leaving a crystalline CuTi2(PO4)3 skeleton. The specific surface area and the average pore radius of the porous glass‐ceramic obtained were approximately 45 m2g‐1 and 9 nm, respectively. The porous glass‐ceramic showed catalytic activity in the conversion reaction of propene into acrolein.
Interlaboratory Verification of Silicon Nitride Tensile Creep Properties
Authors: Luecke William E. , Wiederhorn Sheldon M.
Published: July 2010

Five laboratories tested NIST‐supplied, pin‐loaded, 76‐mm‐long tensile creep specimens at 1400°C under a 150 MPa load using flag‐based, laser extensometry. The laboratories reported failure time and strain and supplied the individual creep curves. Only one of the laboratories produced failure times that were significantly less than the others. It is likely that their reduced failure times resulted from small load calibration and test temperature errors. After steps were taken to ameliorate these problems, three additional tests yielded failure times that agreed with those of the other four laboratories. Although the times to failure from the four laboratories that initially agreed were statistically indistinguishable, their creep curves exhibited subtle differences. These differences probably arose because the laboratories used different gage length definitions. When we recalculated the creep curves to the same gage length definition, the differences between the four laboratories whose times to failure agreed, vanished. Although a number of the specimens exhibited edge chips, creep cracks, and obvious chemical interactions with the flags, the presence of these defects did not reduce the time or strain to failure. Two additional creep tests in our laboratory, using specimens that were grossly misaligned, yielded failure times and strains that were commensurate with those from well‐aligned specimens.
Microstructure Characterization in Superplastically Deformed Silicon Nitride
Authors: Burger Philippe , Duclos Richard , Crampon Jacques
Published: July 2010

Fully dense silicon nitride (Si3N4) has been produced by hot isostatically pressing α‐Si3N4 powder at 1740°C under 160 MPa, with 0.5 wt% Y2O3 and 0.5 wt% Al2O3 as sintering additives. The sintered material was composed of very fine (0.5 μm) and equiaxed grains, as required for superplasticity. Before deformation, a very small amount of intergranular glassy silicate‐based film was detected by transmission electron microscopy at the two‐grain and triple‐point junctions. Compression tests with a strain value of up to }0.5 were conducted in nitrogen in the temperature range of 1600°–1700°C. The observation of a shear‐thickening phenomenon and the presence of a transition from a mild to a strong strain hardening at 20 MPa were attributed to the occurrence of rigid contacts between the grains. The angular distribution of the observed strain whorls was used to evidence the increase of rigid contacts between the grains, under the local expulsion of the wetting liquid film, with increases in compressive stress.
Young's Modulus, Flexural Strength, and Fracture of Yttria‐Stabilized Zirconia versus Temperature
Authors: Adams Jane W. , Ruh Robert , Mazdiyasni K. S.
Published: July 2010

The flexural strength and elastic modulus of cubic zirconia that was stabilized with 6.5 mol% yttria was determined in the temperature range of 25°–1500°C in air. Specimens were diamond machined from both hot‐pressed and sintered billets that were prepared from alkoxy‐derived powders. The flexural strength of the hot‐pressed material decreased, from }300 MPa at 25°C to 50 MPa at 1000°C, and then increased slightly as the temperature increased to 1500°C. The flexural strength of the sintered material decreased, from 150 MPa at 25°C to 25 MPa at 750°C, and then appeared to increase slightly to }1500°C. Flexural strengths were comparable to other fully stabilized zirconia materials. The overall fracture mode was transgranular at low temperatures, mixed mode at }500°–1000°C, and intergranular at higher temperatures. Pores or pore agglomerates along grain boundaries and at triple points were fracture origins. The value of the porosity‐corrected Youngs moduli was 222 GPa at 25°C, decreased to }180 GPa at 400°C, and then was relatively constant with increasing temperature to 1350°C.
Kinetic Analysis of Combustion Synthesis of Lead Magnesium Niobate from Metal Carboxylate Gels
Authors: Narendar Yeshwanth , Messing Gary L.
Published: July 2010

A combustion synthesis route was developed for direct crystallization of perovskite lead magnesium niobate (PMN) from metal carboxylate gels. Direct PMN formation is attributed to a homogeneous cation distribution in the gel and the rapid heating during exothermic gel decomposition in oxidizing atmospheres. The maximum bed temperature and gel decomposition rate are determined by the combined influence of chemical kinetics, heat, and mass transfer. It is shown that there is a temperature window between 700° and 750°C which favors direct PMN formation, whereas pyrochlore formation is favored below 650°C and PbO volatilization occurs above 800°C. The effects of kinetic and transport parameters including oxygen partial pressure, gas flow rate, and bed geometry on PMN formation are discussed on the basis of a thermal ignition model for heterogeneous reactions.
Dissolution Rate of Silicon Nitride Ceramics into Molten CaO–Al2O3–SiO2 Slags
Authors: Taira Shoichirou , Yamasaki Yasuyuki , Nakashima Kunihiko , Mori Katsumi
Published: July 2010

The dissolution rates of silicon nitride (Si3N4) ceramics into CaOAl2O3SiO2 slags were investigated by using a rotating specimen method in the temperature range of 1773–1873 K. Dissolution rates in the present study increased as the revolution speed and temperature increased and decreased as the SiO2 content of the slags increased. The nitrogen content of the slags increased after the Si3N4 ceramics had been immersed into them. The slags contained two types of nitrogen ions—N3− and CN‐—because a graphite crucible was used for the experiment. N3− ions were confirmed in all the slags that were used in the present work; the CN‐ content was much lower than that of the N3− ions, except in the slag without SiO2. Based on those results, Ficks law of diffusion was used to analyze the dissolution rates. The dissolution mechanism of the Si3N4 ceramics into CaO–Al2O3SiO2 slags has been discussed in this paper.
Synthesis of Submicrometer Titanium Carbide Powders
Authors: Koc Rasit , Folmer Jeffrey S.
Published: July 2010

A novel synthesis process, based on a carbothermal reduction of titania, has been developed for producing high–purity, submicrometer, and nonagglomerated titanium carbide powders. The process utilizes a carbothermic reduction reaction of novel coated precursor powders that has potential as a high–quality (submicrometer and high–purity) powder synthesis route. The precursor is derived from a titania (TiO2) and a hydrocarbon (C3H6) gas and provides high contact area between the reactants. This yields a better distribution of carbon within the titania and inhibits the agglomeration among the titania particles, resulting in a more complete reaction and a purer product at a comparatively low temperature. The TiC powders produced at 1550°C for 4 h under argon gas flow have oxygen content of 0.6 wt% and total carbon content of 22.9 wt%, a very fine particle size (,0.1μm) (surface area of about 20 m2/g), uniform shape, and loose agglomeration.
Effect of Composition on the Electromechanical Properties of (1‐x)Pb(Mg1/3Nb2/3)O3−XPbTiO3Ceramics
Authors: Kelly Joe , Leonard Mark , Tantigate Chutima , Safari Ahmad
Published: July 2010

Ceramic lead magnesium niobate–lead titanate ((1‐x)PMN‐xPT) of different compositions has been prepared by the columbite precursor method. This study discusses compositions ranging from 0.94PMN–0.06PT to 0.60PM–N0.40PT, focusing on two areas of the (1‐x)PMNxPT system: compositions that exhibit electrostrictive behavior, and those that show piezoelectric behavior. In electrostrictive compositions where x is in the range of 0.06–0.20, the dielectric constant and electromechanical coupling factor dependencies on the bias field are evaluated. The optimal electromechanical properties are obtained with the composition 0.82PMN–0.18PT, measured at temperatureT=Tm(the temperature of maximum dielectric constant) = 80°C and with a dc bias of 5 kV/cm. X–ray diffractometry is used to show that the (1‐x)PMN‐xPT system has a compositionally wide two–phase region and that 0.655PMN–0.345PT is the morphotropic phase boundary (MPB) composition. Electromechanical property evaluation shows that the optimal piezoelectric properties (piezoelectric charge coefficient (d33) value of 720 pC/N, dielectric constant (K) value of 5400, and electromechanical planar and thickness coupling coefficient (kpandkt, respectively) values of 62% and 46%, respectively) are obtained at the MPB composition.
Preparation of Spherical Yttria‐Stabilized Zirconia Powders by Reactive‐Spray Atomization
Authors: Belov Vladimir , Belov Irena , Harel Lilian
Published: July 2010

A new inorganic sol–gel process of zirconia (yttri‐stabilized) spherical powders production has been developed. The process is based on spraying zirconia sol into an ammoniawater solution, followed by drying of the gel precipitate and calcination. The gel particles preserve the spherical shape of sprayed droplets, because of a thin solid film that forms on the drop surface via its contact with gaseous ammonia before the impact with the ammonia solution. Being dried and calcined, the gel spheres transform to free–flowing powders composed of the solid, not hollow smooth spheres of zirconia–yttria solid solutions. The particle composition, morphology, and microstructure have been investigated in detail versus the process conditions.
ZrO2–CeO2 Alloys as Candidate Structural Materials for Cryogenic Application
Authors: Li Lai‐Feng , Li Yi‐Yi , Sbaizero Orfeo , Meriani Sergio
Published: July 2010

Zirconia‐based ceramics are considered as support materials for superconducting magnets, and the relationship between composition and mechanical properties at cryogenic temperature is reported. Ce‐TZP materials with CeO2 content between 14.5 and 16.5 mol% can be made with high strength (600 MPa) and high toughness (12 MPa·m1/2) at cryogenic temperatures.
Novel Electrochemical Route for Reduction of Superconducting Bi2Sr2CaCu2O8+δ
Authors: Matsuda Motohide , Tamada Hideki , Yamashita Kimihiro , Umegaki Takao , Miyake Michihiro
Published: July 2010

A novel electrochemical route was developed for reduction of the superconducting Bi2Sr2CaCu2O8+δ compound (Bi‐2212) in the over‐hole‐doped state, which was undertaken employing an electrolyte solution consisting of benzoic acid dissolved in acetone. The reduction gave rise to enhancement of the critical temperature (TC) of Bi‐2212 up to 90 K. This reduction effect on TC corresponded to the effect of annealing at elevated temperatures in reducing atmospheres. It appears that protons from the benzoic acid carboxyl groups were responsible for the reduction of the Bi‐2212. Structural stability of the electrochemically reduced Bi‐2212 was different from that of Bi‐2212 annealed in reducing atmospheres.
Scaling Analysis for the Axial Displacement and Pressure of Flextensional Transducers
Authors: Shih Wan Y. , Shih Wei‐Heng , Aksay Ilhan A.
Published: July 2010

We have examined the axial displacement, Δh, and maximum axial pressure, Pmax, of flextensional transducers such as the moonies and the rainbows with both scaling and mechanical analyses. For a constant electric field E across the transducer, Δh/t∝E/t2 where t is the thickness of the rainbow or the thickness of the metal end cap of the moonie and Δh/t, the relative axial displacement. Thus, for a constant voltage V across the transducer, Δh/t∝V/t3. As for the maximum pressure, Pmaxt2 for the rainbows and Pmax∝wt for the moonies where t is the thickness of the rainbow or the thickness of the metal end cap of the moonie and w the thickness of the piezoelectric disk of the moonie. These predictions agree well with the experimental results found in the rainbows and the moonies. Our analysis showed that although the rainbows and the moonies differ in design and processing, the underlying physics for the enhancement in the axial displacement are essentially the same: The nonuniform distribution of d31 through the thickness of the transducer causes the transducer to arch or flatten with an applied electrical field, which leads to the enhancement in the axial displacement. The only difference is that, for the transducer to arch, the applied field is in the opposite direction to the polarization in the rainbows but in the same direction as the polarization in the moonies.
Thermodynamic Assessment of the Bismuth–Strontium–Oxygen Oxide System
Authors: Hallstedt Bengt , Risold Daniel , Gauckler Ludwig J.
Published: July 2010

The experimental data on the oxide portion of the Bi–Sr–O system have been reviewed, and an optimized thermodynamic description is presented. There are at least seven stable ternary oxide phases, two of which show considerable solid‐solution ranges. At least two phases—δ‐Bi2O3 and the rhombohedral β‐phase—are good oxygen‐ion conductors. Most of the phases are confined to the Bi2O3‐SrO line at ambient oxygen partial pressure; however, in the SrO‐rich portion, there are at least two phases with oxygen in excess, i.e., with bismuth in the oxidation state Bi5+ instead of the usual Bi3+. There are rather large differences between different experimental data sets; nevertheless, a reasonably consistent set of data can be chosen for the optimization.
Space‐Charge Distribution across Internal Interfaces in Electroceramics Using Electron Holography: I, Pristine Grain Boundaries
Authors: Ravikumar Venkataraman , Rodrigues Richard P. , Dravid Vinayak P.
Published: July 2010

The role and importance of interface charge and the associated space‐charge in governing the electrical activity of interfaces are well appreciated, and have been the focus of a large number of investigations. Despite a considerable progress in this area, the direct determination of the sign, magnitude of the interface charge, and the space‐charge potential associated with the interface double‐Schottky barrier has remained elusive. We propose electron holography as a bulk sensitive tool with subnanometer resolution to obtain direct real‐space evidence of space‐charge, as well as determine the electrical activity of individual grain boundaires (GBs) in electroceramics. Part I of this investigation is focused on the theory and practice of electron holography of interfaces, in the context of pristine (undoped) GBs in SrTiO3. We show that pristine GBs exhibit very little electron phase change, and that the phase change is associated with a reduction in the mean inner potential and with any residual charge, both present by the virtue of the GB. This investigation forms the basis for the electron holography investigation of doped (charged) GBs in Part II. It is shown that quantitative information about the magnitude, sign, and spatial extent of electrical potential and charge, as well as defect densities across individual GBs in electroceramics, can be obtained using transmission electron holography.
Structural Analysis of Inclusions in β‐Silicon Carbide Whiskers Grown from Rice Hulls
Authors: Knowles Kevin M. , Ravichandran Maharajapuram V.
Published: July 2010

Microcrystalline inclusions in the core of β‐SiC whiskers derived from the pyrolysis of rice hulls have been studied by transmission electron microscopy using conventional brightfield and dark‐field imaging. The electron diffraction patterns from the whiskers show extra reflections arising from these inclusions. Dark‐field images from these reflections are consistent with the presence of three different variants of inclusions, all of which are oriented with their [001] axes parallel to the heavily faulted [111] growth axis of the whiskers. A structural model for these inclusions is proposed which accounts satisfactorily for the extra reflections in the electron diffraction patterns.
Effect of Hydroxyl Content on Thermally Induced Change in Surface Morphology of Lithium Niobate (0001) Substrates
Authors: Nagata Hirotoshi , Shima Kaori , Ichikawa Junichiro
Published: July 2010

Two types of LiNbO3(0001) single‐crystal substrates (LN), a conventional LN containing .1019 cm−3 OH ions, and a dehydrated LN were annealed in a dry O2 atmosphere, and their surface morphologies were investigated using atomic force microscopy. For the conventional LN with more OH ions, the surface was significantly roughened in the temperature range of 600°–800°C, accompanied by a large outward diffusion of OH, and then it evolved to a steplike morphology at higher temperatures. However, the dehydrated LN surface changed gradually at temperatures of .700°C to flat terraces without any roughening process. The step heights of the annealed surfaces corresponded to n/6 (where n is an integer) of the c‐axis length of the LN crystal. The dehydrated LN substrate, along with the dry‐annealing process, achieved fairly flat surfaces.
Titania as a Sintering Additive in Indium Oxide Ceramics
Authors: Nadaud Nicolas , Kim Doh‐Yeon , Boch Philippe
Published: July 2010

The influence of TiO2 additives on the sintering behavior of In2O3 ceramics has been investigated. TiO2 increases the densification rate, decreases the grain growth during the intermediate stage of sintering, and hinders the pore/boundary breakaway that can affect the final stage of sintering. For a given grain size, TiO2 shifts the grain size/density trajectory toward higher densities. TiO2 mainly acts by a second‐phase mechanism, but it also may decrease the decomposition rate of In2O3.
Effect of Product Conductivity on Field‐Activated Combustion Synthesis
Authors: Feng Aigou , Munir Zuhair A.
Published: July 2010

Experimental and modeling results on the field‐activated combustion synthesis (FACS) of Nb5Si3 are reported. In the absence of an electric field and without reactant preheating, Nb5Si3 cannot be prepared by self‐propagating high‐temperature synthesis (SHS). Under the influence of a field a self‐sustaining combustion wave is established whose rate of propagation decreases with traveled distance. For relatively low field values, the wave propagation mode changes from a continuous (smooth) to a spin mode. The product of synthesis depends on the mode of propagation. Synthesis during continuous wave propagation results in the formation of Nb5Si3, primarily in the α‐modification. In contrast, when the wave propagates in a spin mode, the product is NbSi2 with unreacted niobium. The present observations demonstrate a case where the field effect is not localized, as was the case in previous studies. The difference in behavior is attributed to differences in the electrical conductivities of the product phases.
Comparison of Solid‐State and Spray‐Pyrolysis Synthesis of Yttrium Aluminate Powders
Authors: Nyman May , Caruso James , Hampden‐Smith Mark J. , Kodas Toivo T.
Published: July 2010

The influence of precursor characteristics and synthesis conditions on the formation of yttrium aluminum garnet, Y3Al5O12 (YAG), was investigated using “single‐source” precursors (cohydrolyzed yttrium and aluminum alkoxides and yttrium aluminum glycolates) and “multiple‐source” precursors (mixtures of metal nitrates and mixtures of separately hydrolyzed yttrium and aluminum alkoxides). Phase‐pure YAG was formed only in the solid‐state thermal decomposition experiments. The lack of formation of YAG in all the spray‐pyrolysis experiments was ascribed to the short heating times and fast heating rates, which resulted in the formation of kinetic products. In the case of the metal nitrates, an additional factor that influenced product formation was the difference in thermal reactivity of the precursors. It was concluded that the formation of complex metal oxide materials by conventional or aerosol routes is not necessarily achieved by the use of a chemically homogeneous precursor, such as a single‐source precursor. It also was necessary to ensure that the precursors and intermediates have similar thermal decomposition temperatures to avoid phase segregation in the initial stages of thermal decomposition.
Microwave Synthesis of Ultrafine Silicon Carbide Whiskers
Authors: Dai Changhong , Zhang Xianpeng , Zhang Jinsong , Yang Yongjin , Cao Lihua , Xia Fei
Published: July 2010

Silicon carbide (SiC) whiskers were formed by microwave and conventional heating in the present study. SiC whiskers with diameters in the nanometer range were synthesized by reducing silica (SiO2) with various forms of carbon in a microwave furnace. Ultrafine SiO2 powder, char, phenolformaldehyde resin, and carbon black were used as starting materials. The effects of temperature and type of heating on the production of SiC whiskers, as well as the role of carbon, are discussed here.
A Test Method to Measure Shear Strength of Ceramic Joints at High Temperatures
Authors: Ünal Özer , Anderson Iver E. , Maghsoodi Sina I.
Published: July 2010

The asymmetrical four‐point bend (AFPB) method, which provides a pure shear stress state in the middle of the test specimen, was utilized to measure the shear strength of the joints between Nicalon‐fiber‐reinforced SiC composites. The small test specimens were prepared as butt‐joints with uniform depth (no notch). It was shown experimentally that the position of loading points is critical to induce shear fracture at the joint without the failure of base material. The appropriate positions for the present test specimen were determined and, as a result, an articulated ceramic fixture was designed. This test method is economical and involves small test specimens with simple geometry, and can be used at high temperatures.
Carbon Coating of Nextel 550 and 720 by Pitch–Toluene Pyrolysis
Authors: Moore Edmund H. , Mah Tai‐il , Brown Peter W.
Published: July 2010

The carbon coatings on Nextel 550™ and 720™ were studied in batch (furnace) and continuous (solution fiber coating apparatus) modes, and in an inert atmosphere. Ashland Aerocarb 240™ pitch in toluene was used as the precursor material for carbon coating. The effect of processing variables (i.e., pitch concentration, Nextel fiber sizing, and oxidative curing) was studied. Characterization was done by tactile, scanning electron microscopy (SEM), and thermal gravimetric–differential thermal analysis (TG‐DTA). Coating adherence, thickness, and uniformity were investigated. Applied carbon coatings adhered well onto the filaments; however, the thickness and uniformity of the carbon coatings were not good, mainly because of melting and wicking of the pitch inside the tow prior to pyrolysis.
Stiffness of Grain‐Bridging Elements in a Monolithic Alumina
Authors: Hay Jack C. , White Kenneth W.
Published: July 2010

The postfracture tensile (PFT) technique isolates the crack wake to characterize the mechanical behavior of the grain‐bridging elements as a function of crack‐opening displacement. Incorporating the PFT stiffnesses into a Hooke's law‐based model provides insight to the nature of the active bridging mechanism. The conventional model, which presumes to extract prismatic grains from sockets in the mating fracture face, is not consistent with the low wake stiffnesses presented here. In conjunction with fractographic evidence, such low wake stiffnesses suggest the strong influence from other, more compliant, mechanisms such as grain rotation, asperity loading, and ligament bending.