bluuebunny/crossref_metadata_2025 huggingface dataset:
Corrosion of Ceramics in Aqueous Hydrofluoric Acid
Authors: Mikeska Kurt R. , Bennison Stephen J. , Grise Steven L.
Published: July 2010

A variety of commercially available ceramic‐based oxides, carbides, nitrides, and borides were evaluated for chemical attack in an azeotropic aqueous hydrofluoric acid (HF) test protocol at 90°C. Weight change measurements and microstructure analysis showed that HF corrosion in polycrystalline ceramics generally occurred at grain boundaries by the dissolution of grain boundary phases although the bulk single crystal may inherently resist attack. Virtually all commercially prepared polycrystalline oxide ceramics (i.e., Al2O3, TiO2, ZrO2) and nonoxide ceramics (i.e., Si3N4, AlN, BN) were extensively corroded while polycrystalline pure carbides (i.e., SiC, TiC, B4C, WC) resisted corrosion. Equilibrium thermodynamic calculations show that these materials are soluble in HF; however, the kinetics of dissolution are slow enough in some cases to permit useful engineering lifetimes.
Microstructure and Oxidation Behavior of Silicon Carbide Fibers Derived from Polycarbosilane
Authors: Takeda Michio , Urano Akira , Sakamoto Jun‐ichi , Imai Yoshikazu
Published: July 2010

Polycarbosilane‐derived SiC fibers (CG Nicalon, Hi‐Nicalon, and Hi‐Nicalon type S) were exposed for 1–100 h at 1273–1673 K in air. Oxide layer growth and changes in tensile strength for these fibers were examined after exposure. The three types of SiC fibers decreased in strength as the oxide layer thickness increased. Fracture origins were located near the oxide layer–fiber interface. The Hi‐Nicalon type S showed better oxidation resistance than the other polycarbosilane‐derived SiC fibers after exposure in air at 1673 K for 10 h. This result was attributed to the nature of the silicon oxide layer on the surface of the SiC fibers.
Tensile Fracture Behavior of Two Types of Silicon Nitride Specimen Geometries Conducted by Ten U.S. Groups
Authors: Tennery Victor J. , Breder Kristin , Ferber Mattison K. , Jenkins Michael G.
Published: July 2010

The work reported was conducted to provide a basis for structural ceramic mechanical property standardization activities under way in the United States, Germany, Japan, and Sweden. All measurements reported here were conducted by 10 U.S. groups on GN‐10 silicon nitride within an International Energy Agency program including the United States, Germany, Japan, and Sweden. This cooperative work included tensile strength studies of two geometries of button‐head tensile specimens. The authors conducted some of the measurements and performed data analyses and interpretation. The tensile fracture behavior of GN‐10 silicon nitride was studied at room temperature. A total of 150 strain‐gaged button‐head tensile specimens were measured. One hundred of a straight collet design and 50 of a tapered collet design were fractured. All specimens were highly strain gaged and the outputs for each were measured during loading to fracture. Bending moments were calculated. Each participating laboratory group fractured 15 tensile specimens, 10 of the straight collet design and 5 of the tapered collet design under rigorously controlled testing conditions. Of 100 straight collet specimens 75 broke in the gage section. Of 50 tapered collet specimens 34 broke within the gage section. Analysis of the Weibullmand σΘestimators at upper and lower confidence bounds of 95% and 5% did not indicate a clear choice between the two designs. For specimens which fractured in the gage section, the unbiased maximum likelihood Weibull estimators formand σΘwere 12.5 and 730 and 10.4 and 716, for the straight and tapered collet configurations, respectively. These are not statistically different at the 95% and 5% confidence levels. Strengths were also analyzed in terms of a three‐parameter Weibull model. The straight collet specimen data fitted the three parameter model well with a threshold stress estimator γ of 506 MPa, while the tapered collet specimens provided a poorer fit to the model and had a threshold stress estimator of 432 MPa, a difference of about 15%. Regression analysis indicated that the straight collet grip provided less bias of strength as a function of bending moment. The straight collet specimens showed essentially little dependence of tensile strength upon bending moment in the range of 0% to 6%, while the tapered collet specimens showed a decrease in strength as the bending moment increased from 0% to 4%. However, the regression parameter was low and no significant statistical conclusion could be made regarding the superiority of either of the grip designs.
Fracture Resistance and Stable Crack‐Growth Behavior of 8‐mol%‐Yttria‐Stabilized Zirconia
Authors: Kumar Amar N. , Sørensen Bent F.
Published: July 2010

The crack‐growth behavior of a yttria‐stabilized zirconia ceramic (8 mol% of cubic‐phase yttria) was studied at room temperature. Double‐cantilever‐beam specimens were loaded with pure bending moments in a specially designed loading fixture inside an environmental scanning electron microscope. Crack‐growth data were obtained from truly sharp (arrested) cracks, bypassing interpretation problems that involve crack initiation from a machined notch. The crack‐growth study was conducted over a range of applied energy‐release rates that allowed crack arrest on one hand and fast fracture on the other. Three energy‐release‐rate values were relevant: initiation of crack growth (3.5 J/m2), crack arrest (2.8 J/m2), and fast fracture (8.0 J/m2). At the macroscopic scale, subcritical crack growth occurred as a continuous process. In situ observations revealed that, at the microscopic scale, crack growth occurred in small jumps. The fracture mode for stable crack growth was identified to be transgranular.
Polishing Behavior and Surface Quality of Alumina and Alumina/Silicon Carbide Nanocomposites
Authors: Kara Hudai , Roberts Steve G.
Published: July 2010

The response of Al2O3 and Al2O3/SiC nanocomposites to lapping and polishing after initial grinding was investigated in terms of changes in surface quality with time for various grit sizes. The surface quality was quantified by surface roughness (Ra) and by the relative areas of smooth polished surfaces as opposed to rough as‐ground areas. Polishing behavior of the materials was discussed in terms of SiC content and grain size. It was concluded that nanocomposites are more resistant to surface damage than Al2O3, and this behavior does not depend on the amount of SiC in the range 1–5 vol%. SiC addition ≥1 vol% is enough to produce a noticeable improvement in surface quality during lapping and polishing.
Coarsening Behavior of Tricalcium Silicate (C3S) and Dicalcium Silicate (C2S) Grains Dispersed in a Clinker Melt
Authors: Kwon Sang‐Koo , Hong Seong‐Hyeon , Kim Doh‐Yeon , Hwang Nong M.
Published: July 2010

Microstructural evolution during the heat treatment of cement clinker was investigated. Two model specimens, which consisted of faceted tricalcium silicate (C3S) and spherical dicalcium silicate (C2S) grains dispersed in a liquid matrix, were prepared with 5 wt% of large seed particles. The seed particles of faceted C3S grains grew extensively, whereas those of the spherical C2S grains grew rather slowly, relative to the matrix grains. As a consequence, C3S grains exhibited a bimodal size distribution that was typical of exaggerated grain growth, whereas C2S grains retained a uniform and normal size distribution. These results suggest that the growth of faceted C3S grains was controlled by the interface atomic attachment, such as two‐dimensional nucleation, and that of spherical C2S grains was controlled by diffusion through the liquid matrix. The dependence of growth mechanisms on grain morphology has been explained in terms of the atomistic structure of the solid/liquid interface.
Effects of (B2O3, P2O5) Additives on Microstructural Development and Phase‐Transformation Kinetics of Stoichiometric Cordierite Glasses
Authors: Wu Jenn‐Ming , Hwang Shiang‐Po
Published: July 2010

The microstructural development and phase‐transformation kinetics of stoichiometric cordierite glasses containing B2O3 and/or P2O5 additives were highly affected by the microstructural characteristics of the μ‐cordierite and the type of additives. The addition of B2O3 tended to cause the formation of μ‐spherulitic dendrites with thin dendritic arms, which promoted the formation of α‐cordierite, either from crystallization of the residual glass or from transformation of μ‐cordierite. P2O5 had the opposite effect: Increasing the temperature increased the growth rate of α‐cordierite more than that of μ‐cordierite.
Imaging Secondary‐Ion Mass Spectroscopy Observation of the Scavenging of Siliceous Film from 8‐mol%‐Yttria‐Stabilized Zirconia by the Addition of Alumina
Authors: Lee Jong‐Heun , Mori Toshiyuki , Li Ji‐Guang , Ikegami Takayasu , Komatsu Manabu , Haneda Hajime
Published: July 2010

The scavenging of a resistive siliceous phase via the addition of Al2O3 was studied, using imaging secondary‐ion mass spectroscopy (SIMS), given the improved grain‐boundary conductivity in 8‐mol%‐yttria‐stabilized zirconia (8YSZ). The grain‐boundary resistivity in 8YSZ decreased noticeably with the addition of 1 mol% of Al2O3. Strong SiO2 segregation at the grain boundaries was observed in a SIMS map of pure 8YSZ that contained 120 ppm of SiO2 (by weight). The addition of 1 mol% of Al2O3 caused the SiO2 to gather around the Al2O3 particles. The present observations provided direct and visual evidence of SiO2 segregation at the grain boundaries (which had a deleterious effect on grain‐boundary conductivity) and the scavenging of SiO2 via Al2O3 addition.
Synthesis of Yttrium Aluminum Garnet from a Mixed‐Metal Citrate Precursor
Authors: Cinibulk Michael K.
Published: July 2010

Yttrium aluminum garnet (YAG, Y3Al5O12) was synthesized using a polymeric precursor derived from a mixed‐metal citric acid/ethylene glycol/ethanol solution. YAG was found to crystallize directly from an amorphous precursor beginning at temperatures as low as 600°C within 1 h in air. The polymer resin concentration was found to have an effect on the temperature of crystallization initiation. However, all precursors produced a well‐crystallized YAG powder within 1 h at 800°C in air. Formation of phase‐pure YAG in an argon atmosphere did not occur until heating for 1 h at 1000°C. An optimum cation‐to‐resin ratio to maximize reactivity provides a polymeric network to ensure a homogeneous dispersion of cations, yet minimizes cation diffusion distances within the char by limiting excess free carbon after polymer pyrolysis.
Density Gradients and Sintered Dimensional Tolerance in Compacts Formed from Spray‐Dried Alumina
Authors: Lu Peizhen K. , Lannutti John J.
Published: July 2010

This study proves that initial density gradients have lasting detrimental effects on final dimensional tolerances. X‐ray computed tomography has been used to quantify changes in density following sintering; associated dimensional changes have been monitored using a laser micrometer. Nonuniformities present in the green state are still present at an overall relative density of ∼73%; in fact, these nonuniformities are exaggerated. Major losses of dimensional tolerance are triggered by the initial density gradients.
Evaporation of Silver during Cofiring with Barium Titanate
Authors: Chen Chin‐Yi , Tuan Wei‐Hsing
Published: July 2010

Silver and Ag‐Pd alloy are cofired with BaTiO3‐based dielectrics during the manufacturing of capacitors. The diffusion of silver into BaTiO3 during sintering is very slow. However, the vapor pressure of silver is high at temperatures greater than the melting point of silver (960°C). The effect of the evaporation of silver during the sintering with BaTiO3 at 1200°, 1250°, and 1290°C is investigated in the present study. The silver vapor can transport through the pore channel of the dielectrics to a distance of a few hundred micrometers. The melting point of Ag‐Pd alloy is higher than that of silver; therefore, the transportation of silver vapor from Ag‐Pd alloy is hardly observed at temperatures >1200°C.
Short‐Range Ordering in Pb(B′1/3B″2/3)O3‐Type Relaxor Ferroelectrics
Authors: Jang Hyun M. , Cho Seong‐Mok
Published: July 2010

The formation of nonstoichiometric 1:1 ordered nanodomains, which promote B‐site microcompositional fluctuation, is known to be one of the most‐efficient ways of enhancing diffuse phase transition (DPT) characteristics. A new theory regarding the 1:1 short‐range ordering has been developed to account for the observed inability to grow ordered domains beyond the nanometer scale. The dispersion entropy associated with the formation of negatively charged ultrafine domains and the mode of the counter‐ion distribution at the domain/matrix interface both have a significant role in controlling the equilibrium ordered domain size.
Yb:Niobosilicate Glass with High‐Emission Cross Section
Authors: Jiang Chun , Zeng Qingji , Liu Hua , Tang Xiaodong , Zhang Junzhou , Gan Fuxi
Published: July 2010

The emission cross section for the 2F5/2–2F7/2 transition of Yb3+ has been determined from absorption and emission measurements of niobosilicate glasses at room temperature. Using systematic variations in the spectroscopic properties, relative to composition, a glass host with emission cross sections of >2.00 pm2 and fluorescence lifetimes of >0.8 ms is obtained. This glass has advantages over some laser glasses that have been reported in other published papers.
Effects of Barium Substitution on Perovskite Formation, Dielectric Properties, and Diffuseness Characteristics of Lead Zinc Niobate Ceramics
Authors: Ahn Byung‐Yong , Kim Nam‐Kyoung
Published: July 2010

Perovskite‐phase developments in partially/fully substituted (Ba,Pb)(Zn1/3Nb2/3)O3, synthesized via B‐site precursor routes, were investigated. The pyrochlore structure, present at no barium content, was immediately replaced by perovskite with a small amount (≥8 at.%) of barium substitution. Variations in the lattice parameters of the pyrochlore and perovskite structures were studied. The weak‐field radio‐frequency dielectric constants and losses of the system ceramics were examined. A highest maximum dielectric constant of 9000 (76°C, 1 MHz) was observed at 8 at.% barium substitution. The dielectric‐constant spectra were analyzed further in terms of diffuseness characteristics (e.g., diffuseness exponent and degree of diffuseness). The dielectric hysteresis loops of the ceramics were measured. The microstructures of the sintered ceramics also were observed.
Hydrothermal Solidification of Kaolinite–Quartz–Lime Mixtures
Authors: Maenami Hiroki , Watanabe Osamu , Ishida Hideki , Mitsuda Takeshi
Published: July 2010

The strength development of hydrothermally solidified kaolinite–quartz–lime systems with kaolinite as the aluminum source was studied. The starting materials were mixed so that the Ca/(Si + Al) atomic ratio was in the range 0.23 to 0.25, and the Al/(Si + Al) ratio was between 0 to 0.50. Specimens were formed by uniaxial pressing and hydrothermal treatment under saturated steam pressure at 200°C for 2 to 20 h. For quartz‐rich systems with Al/(Si + Al) = 0 and 0.05, strength development by the formation of calcium silicate hydrates, such as C–S–H and tobermorite (Ca5(Si6O18H2)·(4H2O), was observed. On the other hand, in the case of kaolinite‐rich systems with Al/(Si + Al) = 0.24 to 0.50, strength development by the formation of hydrogarnet (Ca3Al2(SiO4)(OH)8) was recognized, resulting in flexural strengths between 15 to 20 MPa. It is proposed that strength development is related to the formation of mesopores (∼0.04 μm) that accompanied formation of the hydrogarnet.
Processing and Sol Chemistry of a Triol‐Based Sol–Gel Route for Preparing Lead Zirconate Titanate Thin Films
Authors: Sriprang Nimit , Kaewchinda Darunee , Kennedy John D. , Milne Steven J.
Published: July 2010

A triol‐based sol–gel system has been developed for the fabrication of thin films of lead zirconate titanate (PZT). Starting reagents were lead acetate, zirconium and titanium isopropoxides, acetylacetone, and 1,1,1‐tris(hydroxymethyl)ethane (THOME), with 2‐methoxyethanol (MOE) being used to dilute the sols for spin coating purposes. Preliminary characterization by NMR spectroscopy suggested that the gels consisted of the metal ions and bound THOME, acetylacetonate, and acetate residues, with some possible M–O–M bridges. Uncracked 0.4 μm single‐layer PZT films of nominal composition PbZr0.53Ti0.47O3 were prepared on platinized substrates. Dielectric and ferroelectric properties were determined for samples made from sols containing 10 and 15 mol% excess lead acetate. Improved values were obtained for samples made from sols containing the higher excess; these exhibited a remanent polarization of 34 μC·cm−1, a coercive field of 54 kV·cm−1, and a relative permittivity of 1000.
Modeling of Laser‐Induced Chemical Vapor Deposition of Silicon Carbide Rods from Tetramethylsilane
Authors: Shaarawi Mohammed S. , Sanchez Juan M. , Kan Honghua , Manthiram Arumugam
Published: July 2010

Finite‐difference fluid‐dynamics modeling has been used to predict deposition rates, fractional amounts of phases, and deposition morphology for the codeposition of silicon carbide and pyrolitic carbon from tetramethylsilane via laser‐induced chemical vapor deposition (LCVD). Calculated results agree fairly well with rod deposition experiments. The morphologic features of rods that have been grown using LCVD are examined and explained using the results of the finite‐difference calculations.
Polymer Effects on the Chemorheological and Drying Behavior of Alumina–Poly(vinyl alcohol) Gelcasting Suspensions
Authors: Huha Marsha A. , Lewis Jennifer A.
Published: July 2010

A new gelcasting system based on aqueous alumina (Al2O3)–poly(vinyl alcohol) (PVA) suspensions cross‐linked via titanium ion complexation has been developed as a feedstock for bulk casting and solid freeform fabrication (SFF) routes. Its chemorheological properties, as measured by stress viscometry and oscillatory techniques, exhibited a strong dependence upon polymer hydrolysis and molecular weight. The gelation time of systems of constant PVA volume fraction (φPVAsoln) and cross‐linker concentration decreased with increasing degree of hydrolysis and molecular weight, whereas their steady‐state elastic modulus (G′) exhibited the opposite dependence. Stress evolution during drying of gelcast layers was measuredin situusing a controlled‐environment, cantilever deflection apparatus. Both the maximum and residual drying stresses increased with increasing degree of hydrolysis, with only a modest molecular weight effect observed.
Modeling of Ordered Structures of Phase‐Stabilized Cubic Bismuth Oxides
Authors: Wachsman Eric D. , Boyapati Sai , Kaufman Michael J. , Jiang Naixiong
Published: July 2010

Stabilized bismuth oxides undergo a decay in conductivity when subjected to annealing at temperatures of <600°C, because of the formation of an ordered superstructure, which is observed in transmission electron microscopy (TEM) diffraction patterns. Neutron‐diffraction studies of the aged samples indicate that there is a displacement of almost all the anions, from the regular 8c sites to interstitial 32f sites. Based on the TEM patterns and the displacement of the oxygen ions, various structural models for the superstructure have been analyzed. From this work, it can be deduced that the observed decay in conductivity is due to the ordering of the oxygen sublattice, along with a possible concomitant ordering of cations.
Differences in Wetting Characteristics of Bi2O3 Polymorphs in ZnO Varistor Materials
Authors: Elfwing Mattias , Österlund Ragnar , Olsson Eva
Published: July 2010

Detailed analysis of the microstructure of grain boundaries, especially triple‐grain and multiple‐grain junctions, in ZnO varistor materials has been performed using transmission electron microscopy. Different polymorphs of Bi2O3 are shown to exhibit different wetting properties on ZnO interfaces. Recent investigations suggest that the equilibrium configuration consists of crystalline Bi2O3 in the triple‐grain and multiple‐grain junctions and an amorphous bismuth‐rich film in the ZnO/ZnO grain boundaries. The present investigation supports this suggestion for δ‐Bi2O3 and also adds to the microstructural image and wetting properties of α‐Bi2O3.
Sintering of LaFeO3 Ceramics
Authors: Sagdahl Lise T. , Einarsrud Mari‐Ann , Grande Tor
Published: July 2010

The sintering of LaFeO3 has been studied in the temperature interval 1100–1600°C in air. The effect of cation nonstoichiometry on densification, microstructure, and phase composition is emphasized. La2O3 was observed to inhibit both sintering and grain growth. In Fe‐excess materials, exaggerated grain growth occurred, particularly above 1430°C, where a liquid phase was formed. Postsintering swelling was observed in Fe‐excess materials above 1430°C. The swelling mechanism is related to phase equilibria, which are reductive in nature and lead to the evolution of oxygen gas. The density in La‐excess materials remains high up to 1600°C, but the ceramics might disintegrate in air.
Reactive Hot Pressing of ZrB2–SiC Composites
Authors: Zhang Guo‐Jun , Deng Zhen‐Yan , Kondo Naoki , Yang Jian‐Feng , Ohji Tatsuki
Published: July 2010

A ZrB2–SiC composite was prepared from a mixture of zirconium, silicon, and B4C via reactive hot pressing. The three‐point bending strength was 506 ± 43 MPa, and the fracture toughness was 4.0 MPa·m1/2. The microstructure of the composite was observed via scanning electron microscopy; the in‐situ‐formed ZrB2 and SiC were found in agglomerates with a size that was in the particle‐size ranges of the zirconium and silicon starting powders, respectively. A model of the microstructure formation mechanism of the composite was proposed, to explain the features of the phase distributions. It is considered that, in the reactive hot‐pressing process, the B and C atoms in B4C will diffuse into the Zr and Si sites and form ZrB2 and SiC in situ, respectively. Because the diffusion of Zr and Si atoms is slow, the microstructure (phase distributions) of the obtained composite shows the features of the zirconium and silicon starting powders.
Reactive Sintering and Retrograde Densification of Bulk Bismuth‐Based Superconductors
Authors: Thayer Ryan L. , Schmidt Sarah R. , Dorris Stephen E. , Bullard Jeffrey W. , Lanagan Michael T.
Published: July 2010

Densification was observed when bulk ceramic superconductors with a composition of Bi1.8Pb0.4Sr2Ca2Cu3O10+δ were sintered for short times (<4 h) near the incongruent melting temperature. The initial shrinkage of the powder compacts was correlated with the existence of a transient liquid phase. Retrograde densification, which is a decrease in density, occurred for longer sintering times and was attributed to changes in pore structure. The results provide direction for future processing of bulk bismuth‐based superconductors and powder‐in‐tube tapes for the fabrication of long‐length wire.
Fabrication and Crack Deflection in Ceramic Laminates with Porous Interlayers
Authors: Davis Janet B. , Kristoffersson Annika , Carlström Elis , Clegg William J.
Published: July 2010

A simple and general method for making ceramic laminates with porous crack‐deflecting interlayers is demonstrated. Both the strong laminae and the porous interlayers are made by tape casting suitable slurries using the same ceramic powders. Porosity is introduced into the interlayer by adding starch particles to the slurry. The effects of the starch on the burn‐out and sintering behavior of the laminates has been fully described. The influence of resulting porosity on the ability of an interlayer to deflect a growing crack and to remain stable on prolonged heating has also been investigated. For the pore morphologies studied here, it is the volume fraction of pores that controls whether crack deflection takes place. Using existing mechanics solutions, a simple theoretical criterion for this volume fraction of porosity is given and is consistent with all the experimental observations.
Influence of Solids Concentration on the Isoelectric Point of Aqueous Barium Titanate
Authors: Paik Ungyu , Hackley Vincent A.
Published: July 2010

We report on findings that the particle surface charge is influenced by solids concentration in aqueous suspensions of BaTiO3. Three decades in solids concentration were analyzed by combining results from two different electrokinetic methods. Combined results demonstrate a systematic acidic shift in the isoelectric pH with decreasing solids concentration. The shift is attributed to the development of a Ba‐depleted, TiO2‐rich surface layer. Using kinetic arguments, it is shown that the thickness of this layer will be proportional to the surface‐to‐volume ratio.
Slurry Chemistry Control to Produce Easily Redispersible Ceramic Powder Compacts
Authors: Moon Jooho , Grau Jason E. , Cima Michael J. , Sachs Emanuel M.
Published: July 2010

The slurry‐based Three Dimensional Printing (3DPTM) process requires the production of an easily redispersible powder bed from a well‐dispersed slurry. Understanding and control of the interparticle potential in the dispersed state, as well as in the dry consolidated state, are important. The strength of the particle–particle interactions in the dry state determines the redispersion efficiency. One factor that controls the interparticle strength is the chemical stability of the ceramic powders in the dispersed state. For unstable powders, a partial dissolution and/or hydration of the powders can occur and eventually impede the redispersion by forming insoluble salt bridges at the necks of the particles. Redispersion of the powder bed can be improved substantially by weakening the strength of the particle–particle bonds. The formation of strong chemical bonds between particles should be avoided by adjusting the slurry pH to an appropriate range where the powders are chemically stable in the slurry. Replacement of the chemical bonds by soluble physical bonds, using a low‐molecular‐weight hydrophilic polymer, also reduces the interparticle strength and enhances redispersion.
Processing Effects on the Surface Composition of Glass Fiber
Authors: Palmisiano Marc N. , Boehman Andre L. , Pantano Carlo G.
Published: July 2010

In this study, differences in the surface composition of commercial glass fiber have been characterized as a function of process. The two processes studied were flame attenuation, a high‐temperature combustion‐assisted process, and continuous filament drawing through a bushing. The techniques used to determine the surface compositions were TOF‐SIMS and XPS; the presence of a very thin, boron‐depleted silica‐enriched layer on the flame‐attenuated fibers was most significant. Thermodynamic modeling of the equilibrium vapor pressures at the surface, during fiberization, showed significant differences in the behavior of Na, B, and F species in the two processes. To further test the models, glass fibers were produced under more closely controlled conditions in a laboratory‐scale flame attenuation system. These experiments verified the important effect of flame temperature and residence time in creating the surface layer.
Pyrolysis of Poly(isopropyliminoalane) to Aluminum Nitride
Authors: Saito Yasuo , Sugahara Yoshiyuki , Kuroda Kazuyuki
Published: July 2010

The pyrolysis processes of poly(isopropyliminoalane) ((HAlNiPr)n) were investigated, using mass spectrometry to analyze the gases and infrared spectroscopy to analyze the residual solids. The major mass loss (in the temperature range of 240°–540°C) consisted of two different pyrolysis stages. At the first stage (240°–320°C), (HAlNiPr)6 was detected continuously as a gas, and the precursor was converted to a cross‐linked structure. A polymerization mechanism without a release of organic compounds has been proposed, and the formation of (HAlNiPr)6 during polymerization (besides its evaporation) has been suggested. The second stage (320°–560°C) involved the formation of various organic compounds, and radical processes for their formation were proposed.
Effect of Glass Composition on the Electrical Properties of Thick‐Film Resistors
Authors: Adachi Kenji , Kuno Hiroko
Published: July 2010

Ruthenium‐based thick‐film resistors (TFRs) with lead borosilicate glasses of various compositions have been examined for their electrical properties. A striking increase in resistivity has been observed with lead‐depleted glasses, and analysis of this increase reveals that it is derived from the critical loss of Ru ions/clusters in the glass. With high‐lead‐content glasses, the resistivity decreases by two orders of magnitude, in conjunction with the structural inclination of glass toward PbO·SiO2, 2PbO·SiO2, and 4PbO·B2O3, which are believed to accommodate more Ru ions/clusters. These behaviors substantiate the role of Ru ions/clusters in glass as an indispensable entity for electrical conduction in TFRs.
Microstructure and Current–Voltage Characteristics of Multicomponent Vanadium‐Doped Zinc Oxide Varistors
Authors: Hng Huey‐Hoon , Knowles Kevin M.
Published: July 2010

The effects of the oxide additives MnO2, Co3O4, and Sb2O3, commonly incorporated in commercial Bi2O3‐doped ZnO varistors, on the current–voltage characteristics and microstructure of 0.25 mol% V2O5‐doped ZnO varistors have been studied. MnO2 is the most significant additive in terms of its effects on varistor performance. Varistor performance can also be improved by increasing the V2O5 content to 0.5 mol% in a ZnO ceramic containing 1 mol% MnO2. Further increases in the V2O5 content of 1 mol% MnO2‐doped material cause a deterioration in varistor behavior. The microstructure of the samples consists mainly of ZnO grains with zinc vanadates as the minority secondary phases. Additional spinel phase is formed when Sb2O3 is incorporated.
Oxygen Uptake and Release Mechanism of Lithium Manganese Ferrite in the Low Temperature Range of 573–773 K
Authors: Sano Taizo , Tsuji Masamichi , Gokon Nobuyuki , Kaneko Hiroshi , Tamaura Yutaka
Published: July 2010

Oxygen uptake and release of (Li,Mn) ferrite [LMF; (Li0.60Mn1.20Fe1.20)1−δO4; δ= 0.007 to 0.033] was investigated concerning the relations between redox reactions of ferrite and cation migration. Mössbauer spectroscopy and X‐ray diffractometry showed that some of the Li+ and Fe3+ ions migrated from the A sites to the B sites of the spinel‐type structure and Mn4+ ions migrated from the B sites to the A sites during oxygen uptake at 573 K. The cation‐deficient LMF formed by the oxygen uptake released oxygen molecules in He gas only at 660 K. The cation migration during the oxygen release was in the opposite direction of the movement during oxygen uptake at 573 K.
Effect of Density Gradients on Dimensional Tolerance During Binder Removal
Authors: Lu Peizhen K. , Lannutti John J.
Published: July 2010

The present work utilized X‐ray computed tomography (CT) and in situ laser dilatometry to correlate internal structural changes with dimensional variation during thermally driven binder removal. Nonuniform agglomerate arrangement and deformation introduced during compaction provide density gradients that drive binder migration. Simultaneously, density undergoes a slight decrease accompanied by a 1.0% loss in dimensional tolerance. This loss and CT difference images show that capillary forces generated during binder melting can change internal density distribution. This change in density has important implications for the binder removal process.
The Wulff Shape of Alumina: II, Experimental Measurements of Pore Shape Evolution Rates
Authors: Kitayama Mikito , Narushima Takayuki , Glaeser Andreas M.
Published: July 2010

The rate at which a facetted tetragonal cavity of nonequilibrium shape approaches a cubic equilibrium (Wulff) shape via surface diffusion was modeled. The shape relaxation rate of a facetted “stretched cylinder” was also modeled. For the first geometry, only an approximate solution based on linearizing the mean potential difference between the source and sink facets was obtained. For the stretched cylinder, both an approximate and an exact solution can be obtained; the approximate solution underestimates the evolution rate by a factor of ∼2. To assess the applicability of the models, nonequilibrium shape pores of identical initial geometry (∼20 μm × 20 μm × 0.5 μm) were introduced into (0001), {10[Onemacr]2}, {1120}, and {100} surfaces of sapphire single crystals using microfabrication techniques, ion‐beam etching, and hot pressing. The large (∼20 μm × 20 μm) faces of the pore are low‐index surfaces whose nature is dictated by the wafer orientation. A series of anneals was performed at 1900°C, and the approach of the pore shape to an equilibrium shape was monitored. The kinetics of shape evolution are highly sensitive to the crystallographic orientation and stability of the low‐index surface that dominates the initial pore shape. The measured variations of the pore aspect ratio were compared to those predicted by the kinetic model. The observations suggest that when the initial bounding surface is unstable, shape relaxation may be controlled by diffusion. However, surface‐attachment‐limited kinetics (SALK) appears to play a major role in determining the pore shape evolution rate in cases where the initial bounding surfaces have orientations that are part of the Wulff shape.
Microstructural Changes during the Reduction/Reoxidation Process in Donor‐Doped BaTiO3 Ceramics
Authors: Makovec Darko , Drofenik Miha
Published: July 2010

Microstructural changes occurring during oxidation of the reduced form of donor‐doped BaTiO3 (Ba1−XDX.Ti1−X4+TiX3+O3) and during reduction of the oxidized form of donor‐doped BaTiO3 (Ba1−XDX.Ti1−X/44+(VTi)X/4O3) were studied using TEM. Samples of both types of solid solutions, containing different La concentrations (from 2 to 20 mol% La), were prepared by sintering under reducing conditions and in air, respectively. The reduced form of donor‐doped BaTiO3 was oxidized by annealing at high temperatures (1150° and 1350°C) in air, while the oxidized form was reduced by annealing under reducing conditions. Because of oxidation of the reduced phase of donor‐doped BaTiO3, the Ti‐rich phases Ba6Ti17O40 and BaLa2Ti4O12 were precipitated. Reduction of the oxidized form caused precipitation of the Ba‐rich phase Ba2TiO4 preferentially inside the matrix grains. All precipitates had well‐defined orientational relationships with the perovskite matrix.
Long‐Lasting Phosphorescence of Transparent Surface‐Crystallized Glass‐Ceramics
Authors: Fu Jie
Published: July 2010

Transparent surface‐crystallized glass‐ceramics with molar compositions of 43SiO2–2B2O3–30SrO–25MgO–0.05Eu2O3–0.8Dy2O3 (sample GC‐A) and 43SiO2–2B2O3–24SrO–6CaO–25MgO–0.05Eu2O3–0.8Dy2O3 (sample GC‐B) were prepared by heat‐treating the mother glasses at 850°C for 10 h. The precipitated phases in both glass‐ceramics were (Sr1−xCax)2MgSi2O7, in which Eu2+ and Dy3+ ions were incorporated. Phosphorescence with emission peaks at 470 and 480 nm that is due to the 4 f65 d–4 f7 transition of Eu2+ ions was observed from samples GC‐A and GC‐B, respectively. The phosphorescence lasted for >5 h at room temperature.
Influence of Undercooling and Nd4Ba2Cu2O10 Content on the Growth Rate of Large‐Grain Bulk Nd‐Ba‐Cu‐O Superconductor
Authors: Babu Nadendla Hari , Lo Wai , Cardwell David A.
Published: July 2010

The dependence of growth rate on isothermal undercooling and composition has been investigated for Nd‐Ba‐Cu‐O single grains containing various amounts of nonsuperconducting Nd4Ba2Cu2O10 (Nd‐422) phase inclusions and fabricated under a 1% O2 in N2 atmosphere using a top seeded melt growth technique. The growth rate along the crystallographic c‐direction is observed to exceed that along the a/b direction at all undercooling temperatures and exhibits a maximum for a Nd‐422 content of ∼10 mol%. The samples have been examined by optical microscopy and the results interpreted within an established planar solidification model.
Templated Grain Growth of Barium Titanate Single Crystals
Authors: Rehrig Paul W. , Messing Gary L. , Trolier‐McKinstry Susan
Published: July 2010

BaTiO3 single crystals were grown via templated grain growth (TGG), which is a process in which a single‐crystal “template” is placed in contact with a sintered polycrystalline matrix and then heated to migrate the single‐crystal boundary into the matrix. Millimeter‐sized, stoichiometric single crystals of BaTiO3 were produced by heating polycrystalline matrix with a relative density of 97% and a Ba/Ti ratio of <1.00, which was bonded to a BaTiO3 single crystal, at temperatures above the eutectic temperature. Growth rates of 590–790, 180–350, and 42–59 μm/h were observed for {111}‐, {100}‐, and {110}‐oriented single‐crystal templates, respectively. Lower‐surface‐energy facets were formed for {111}‐ and {100}‐oriented templates, whereas {110} crystals maintained a {110} growth front, which indicated that this plane orientation was the lowest‐energy surface in this system. SrTiO3 also was shown to be a suitable substrate for TGG of BaTiO3.
Microstructures and Properties of Three Composites of Alumina, Mullite, and Monoclinic SrAl2Si2O8
Authors: Chinn Richard E. , Haun Michael J. , Kim Chan Young , Price David B.
Published: July 2010

Three composites that were 96% alumina were mixed and uniaxially dry‐pressed into bars and pellets; all had monoclinic SrAl2Si2O8 as an intergranular phase. The diffraction patterns, microstructure, density, dielectric properties, strength, and toughness were measured. The first composition, which contained crystalline SrCO3, Al2O3, and SiO2, in a 1:1:2 molar ratio, as the 4% component, densified but was generally inferior to the second and third compositions, which contained strontium aluminosilicate (SrAlxSiyOz, SAS) glass as the 4% component, in terms of mechanical properties, defects, and monoclinic SrAl2Si2O8 transformation. The second composition, which lacked B2O3, was very tough and was comparable to commercial alumina, in terms of the dielectric constant. The third, which contained 0.068% of B2O3 that was dissolved in the SAS glass as a sintering aid, had high strength and toughness and no macroscopically visible defects. Mullite formed, in addition to monoclinic SrAl2Si2O8 in all three composites. Alumina–monoclinic SrAl2Si2O8 composites of the third composition had room‐temperature properties that were comparable to commercial aluminas that contained 96% alumina and also had potential for mechanical and refractory applications.
Effect of Atmosphere on Weight Loss in Sintered Silicon Carbide during Heat Treatment
Authors: Nagano Takayuki , Kaneko Kenji , Zhan Guo‐Dong , Mitomo Mamoru
Published: July 2010

Heat treatment was performed on β‐SiC with different sintering additives in the temperature range 1873–2073 K, in both argon and nitrogen‐gas atmospheres. In the case of the specimens heat‐treated at 2073 K in argon, the weight loss was more than the total weight of the sintering additives, except for B,C‐doped β‐SiC. On the other hand, weight loss was suppressed by about one‐third to one‐half in nitrogen gas. Weight loss depended mainly on the reaction at the interface between the SiC grains and the grain‐boundary phase.
Phase Analysis and Thermal Stability of Hot Isostatically Pressed Zirconia–Hydroxyapatite Composites
Authors: Adolfsson Erik , Alberius‐Henning Peter , Hermansson Leif
Published: July 2010

Composites of zirconia and hydroxyapatite (OHAp) have been processed via hot isostatic pressing (HIP) or sintering in air. When the composites were sintered in air at a temperature of 950°C, decomposition of the OHAp to tricalcium phosphate occurred. Using the HIP technique, composites without any detectable degradation of the OHAp phase were produced at 1200°C. The reactivity between zirconia and OHAp was dependent on both the amount of water lost from OHAp and the geometry of the interaction. The phase composition of the materials prepared was evaluated from their powder X‐ray diffraction patterns, and their microstructures were studied via electron microscopy.
Effect of Simulated Radioactive Liquid Waste on the Microstructure of Cementitious Materials: Portlandite Orientation and Saturation Factors in the Pore Solution
Authors: Guerrero Ana , Hernández María‐Soledad , Goñi Sara
Published: July 2010

The microstructural implications of the preferred orientation of portlandite crystals and portlandite saturation factors in the pore solution of a fly‐ash–pozzolanic‐cement mortar that is used in Spain for the disposal of low‐ and medium‐level radioactive waste have been discussed. Changes in the saturation of portlandite, which were promoted by the interaction of two types of simulated radioactive liquid waste (SRLW) with the mortar, were evaluated during a period of 365 d at a temperature of 40°C. The mortar was immersed in two SRLW materials, whose main ions were SO42− (0.68M), PO43− (0.89M), and Cl− (0.51M) in one case and SO42− (2.05M) and Na+ (4.1M) in the other case. The diffusion of those ions through the porous mortar microstructure and related dissolution–precipitation reactions influenced both the quantity and the degree of orientation of portlandite crystals at the paste/sand and paste/fly‐ash interfaces. All these effects will lead to a pore refinement of the mortar that improves the strength and durability of a mixture of fly ash and cement mortar.
Refined Continuum Model on the Behavior of Intergranular Films in Silicon Nitride Ceramics
Authors: Choi Heon‐Jin , Kim Gyeung‐Ho , Lee June‐Gunn , Kim Young‐Wook
Published: July 2010

A refined continuum model has been proposed, based on the bond‐strength consideration between cations and anions in the film, to address the effect of sintering additives on the behavior of intergranular glassy films (IGFs) in silicon nitride ceramics. The refined model indicates that the incorporation of additive ions in the film will modify the attractive van der Waals and repulsive steric forces. The model also implies that the charge and size of the ions, which determine the bond strength between cations and anions, and the amount of ions are important parameters to the force balance and behavior of the IGFs. Experimental evidence for (i) the effect of sintering additives on the thickness of IGFs in Si3N4 ceramics and (ii) the occurrences of the “squeezing out” of IGFs in hot‐pressed Si3N4 under a moderate external pressure (e.g., 25 MPa) are discussed, to confirm the validity of the present model.
Effect of Dislocations on Grain Growth in Strontium Titanate
Authors: Chung Sung‐Yoon , Kang Suk‐Joong L.
Published: July 2010

Two series of experiments were done to investigate the effect of dislocations on grain growth in SrTiO3. In the first series, we observed the growth behavior of a single‐crystal plate toward a TiO2‐excess SrTiO3 powder compact, containing different dislocation densities on two equivalent {100} surfaces. The surface with a higher dislocation density exhibited faster growth, showing interface mobility enhancement by dislocation. In the second series, a polycrystalline SrTiO3 sample which had been plastically deformed by hot pressing was embedded in a TiO2‐excess SrTiO3 powder compact, and its growth behavior toward the powder compact was compared with that of a sample without hot pressing. As with a single crystal, the grains with the higher dislocation density in the plastically deformed sample grew faster. In addition, some grains in the plastically deformed sample showed the characteristic of abnormal grain growth. The transmission electron microscopy (TEM) observations on a sintered TiO2‐excess SrTiO3 showed that the abnormally large grains contained many dislocations while the fine matrix grains contained practically no dislocations. This result suggests that the uneven distribution of dislocations between grains is possibly one of the causes of the abnormal grain growth in polycrystalline SrTiO3.
Effect of 20°–200oC Fabrication Temperature on Microstructure of Hydrothermally Prepared LiCoO2 Films
Authors: Song Seung‐Wan , Han Kyoo‐Seung , Yoshimura Masahiro
Published: July 2010

Films of LiCoO2 were directly fabricated by hydrothermal treatment of a cobalt metal plate in a 4M LiOH aqueous solution at 20°–200°C, with no subsequent annealing, and the effect of fabrication temperature on the film microstructure was investigated for the films. Micro‐Raman studies have indicated that increasing the fabrication temperature produces a phase change in LiCoO2 from spinel to hexagonal. This change is revealed by a variation in the film thickness and the film surface morphology, as seen in the micrographs. The present scanning electron microscopy results showed a growth of spinel LiCoO2 particles up to 125°C and the formation of hexagonal particles at >125°C, in good agreement with the Raman and X‐ray photoemission spectroscopy results. A film‐formation mechanism based on the dissolution of cobalt metal, followed by precipitation, as LiCoO2, onto the cobalt substrate, is proposed. The mechanism is supported by experimental data, such as the one‐step potential evolution (0 → 0.6 V, with respect to the Ag/AgCl reference electrode) of the cobalt electrode during hydrothermal treatment and the detection of dissolved cobalt species by atomic absorption and ultraviolet–visible‐light absorption spectroscopic analyses. Apparently, the evolution of the film structure arises from different nucleation and growth rates of LiCoO2 particles on the film, caused by the dissolution–precipitation mechanism, and a phase selection of spinel or hexagonal as the fabrication temperature increases.
Thermal Expansion Characteristics of Alumina–Magnesia and Alumina–Spinel Castables in the Temperature Range 800°–1650°C
Authors: Ko Yung‐Chao , Lay Jinn Tsang
Published: July 2010

The thermal expansion of Al2O3–MgO castables containing 5.5 wt% MgO and 1.36 wt% CaO and Al2O3–spinel castables containing 20 wt% spinel having 95 wt% Al2O3 and 1.7 wt% CaO was measured in the temperature range of 800–1650°C by dilatometry. A sharp increase in expansion from around 1425° to 1525°C, followed by a sharp decrease with further increasing temperature, is characteristic of Al2O3–MgO castables. The sharp increase in expansion is believed to be caused by the bond linkage between the CA6 and spinel grains in the bonding matrix, while the sharp decrease is apparently related to liquid‐phase sintering. The sharp increase and decrease in expansion were not observed in Al2O3–spinel castables because of the much lower MgO (around 1 wt% MgO) and impurity contents. The magnitude of thermal expansion of calcium aluminate bonded castables containing self‐forming or preforming spinels or both is dictated by the MgO content of the castables.
Consolidation of Eutectic Powder of Al2O3–GdAlO3
Authors: Omori Mamoru , Isobe Toshinori , Hirai Toshio
Published: July 2010

A eutectic solid of Al2O3–GdAlO3 was prepared by arc discharge and crushed to a eutectic powder of 3–125 μm. The powder was consolidated by the spark plasma system (SPS). The consolidated powder duplicated the eutectic structure: Al2O3 and GdAlO3 were joined to each crystal. There were no flaws such as cracks or pores in the eutectic composite. The bending strength was half that of the eutectic composite prepared by unidirectional solidification.
Formation Mechanism and Synthesis of Apatite‐Type Structure Ba2+xLa8−x(SiO4)6O2−δ
Authors: Takeda Hiroaki , Ohgaki Masataka , Kizuki Takashi , Hashimoto Kazuaki , Toda Yoshitomo , Udagawa Shigekazu , Yamashita Kimihiro
Published: July 2010

The formation process of Ba2La8(SiO4)6O2 was clarified using thermogravimetry–differential thermal analysis (TG‐DTA) and a high‐temperature powder X‐ray diffraction (HT‐XRD) method. Phase changes identified from the HT‐XRD data surprisingly corresponded to the weight loss and/or endothermic peaks observed in the TG‐DTA curves. Raw material with the composition Ba2La8(SiO4)6O2 was completely reacted at 1400°C and produced only an apatite‐type compound without a secondary phase. Moreover, the synthesis of Ba2+xLa8−x(SiO4)6O2−δ crystals with x= 0–2 was attempted using a solid‐state reaction.