bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of Copper‐Ruby Glasses by Sputtering: The Effect of Atmosphere on the Growth of Copper Particles
Authors: Akai Tomoko , Yamanaka Hiroshi , Wakabayashi Hajimu
Published: September 2005

Copper‐ruby glasses were prepared by the sputtering method and the effect of reducing treatment was examined. The reducing was carried out either during sputtering or heat treatment. Optical absorption was related to the growth of copper particles. The results are summarized as follows: (i) the volume fraction of copper particles in the glasses which are heat‐treated in air increases with the addition of hydrogen in the sputtering gas. (ii) The copper particles do not grow larger than 8 nm by heat treatment in reducing atmosphere, whereas they grow as large as 12 nm in air. (iii) Reducing during heat treatment gives a pronounced effect only when sputtering was not carried out under reducing conditions. The origin of these phenomena was also discussed, considering the mechanism of nucleation and growth of copper particles.
Fabrication of Optically Transparent Short‐Fiber‐Reinforced Glass Matrix Composites
Authors: Iba Hisayoshi , Chang Tongshik , Kagawa Yutaka , Minakuchi Hiroyoshi , Kanamaru Kuniaki
Published: September 2005

Optically transparent chopped oxynitride glass (SiAlCaON) fiber‐reinforced glass matrix composites have been fabricated by hot‐pressing. Four kinds of glass matrices were candidates in this study. The optical transmission properties of the composites were obtained in UV‐visible and IR wavelength ranges. With selection of the optimal glass matrix and an appropriate processing procedure, an optically transparent glass matrix composite can be obtained. Within the framework of this study, the optical transmittance was strongly dependent on the optical transmittance of the hot‐pressed glass matrix. The well‐fabricated composite with a fiber volume fraction of 0.07 showed measured optical transmittance of 35%–50% in the UV‐visible wavelength region and 80% in the IR wavelength region.
Direct Joining of BSCCO Superconducting Glass‐Ceramics Using a Flame‐Melting Method
Authors: Kasuga Toshihiro , Nakamura Koichi , Inukai Eikichi , Abe Yoshihiro
Published: September 2005

A new method for joining bismuth‐based superconducting glass‐ceramics has been developed; they are joined easily by melting‐annealing with a liquid natural gas (LNG) ‐oxygen flame. Two edge portions of the glass‐ceramics to be joined are melted by a high‐temperature flame, and the molten faces are placed quickly against each other. Subsequently, the joined portion is annealed sufficiently with a soft flame, resulting in a unified product with no cracks. Although the directly unified product is broken electrically, it is converted to a superconductor, with Tc∼ 90 K, by postheating at ∼ 830°C, and its critical current density is almost the same as that of the original glass‐ceramic. This technique is very important for fabrication of large‐sized superconducting ceramics, such as bushing apparatuses.
Porous Silica‐Coated α‐Fe2O3 Ceramics for Humidity Measurement at Elevated Temperature
Authors: Sun Hong‐Tao , Cantalini Carlo , Faccio Marco , Pelino Mario , Catalano Massimo , Tapfer Leander
Published: September 2005

Porous α‐Fe2O3 powder obtained from topotactic decomposition of α‐FeOOH was dispersed in a tetraethyl orthosili‐cate solution. Amorphous silica was coated on the surface of α‐Fe2O3 grains, followed by gelation and sintering. The N2sorption measurement indicates that the pore coalescence is strongly suppressed by coating. For instance, the coated sample sintered at 800°C has a specific surface area of 145.8 m2/g, much greater than the uncoated one, 5.035 m2/g. Furthermore, the hysteresis isotherm implies that thepores of the coated sample have an ink‐bottle type structure. There are O and Si traces in the XPS survey scan, while no Fe peak is found, which confirms that the α‐Fe2O3 grain is totally covered by silica. Organic radicals are also evident in the detail scan of the C1s peak of the fresh fractured surface. The XRD analysis highlights that the coated ceramic is composed of α‐Fe2O3 and amorphous silica. Because of the coating limitation on grain growth, sintering below 950°C hardly increases the grain size as compared with the starting powder, in terms of Scherrer's equation. The HRTEM images of the uncoated and coated samples display a clear layer of the amorphous coating on highly porous grains. Many pores in the 2–5 nm size range seem to be connected in the lattice matrix. The pore number and volume are greatly decreased after sintering, but the silica coating weakens this effect. The complex impedance of the coated sample with porous RuO2 electrode was investigated in the frequency and temperature ranges of 1 Hz‐1 MHz and 20°–400°C, respectively. Artificial dry air was bubbled through deionized water or analytical‐purity ethanol to yield wet air or ethanol vapor condition. The sensitivities, defined as the ratio between impedance under a test and dry air conditions, are 30 for 2.8% water vapor and 2 for 9.3% ethanol vapor at 200°C. A high ethanol vapor sensitivity above 200°C is explained as an “on‐site” water vapor effect arising from the ethanol combustion on a silica catalyst. Various gases like CH4, CO, NOx, and NO2 were introduced into dry and wet air at elevated temperatures. No cross‐sensitivity was found for the gas concentrations up to 5000 ppm. A model of the porous coating structure is proposed for a reason of high humidity sensitivity without gas cross‐sensitivity.
Investigation of the Electronic Structure of Y2Cu2O5–xSx(x — 0.0, 0.25, 0.75) by X‐ray Emission Spectroscopy and Xα Scattered Wave Calculation Methods
Authors: Uvarov Victor N. , Timoshevskaya Liliya V , Obolenskii Michail A.
Published: September 2005

The investigation of the electronic properties of various copper oxides, containing structural fragments with specific Cu‐O polyhedra, has been carried out. The electronic structure of Y2Cu2O5–xSx compounds (x = 0.0, 0.25, 0.75) has been studied by X‐ray emission spectroscopy and the Xα scattered wave (SW) method of calculation. It is shown that substituting apical oxygen by sulfur in the squarepyramid fragments in high‐temperature superconductors will result in a decrease of the density of hole carriers in “superconducting” grids of CuO2 and in the suppression of superconductivity.
Low Breakdown Voltage Varistors by Grain Boundary Diffusion of Molten Bi2O3 in ZnO
Authors: Barsoum Michel W. , Elkind Alexander , Selim Fadel A.
Published: September 2005

Diffusion of molten Bi2O3 into the grain boundaries of sintered, alumina‐doped (0.23 and 0.7 mol%) ZnO pellets resulted in varistors with breakdown voltages in the 3–5 V range and nonlinearity coefficients of 10–24. The varistors were fabricated by spreading a thin layer of Bi2O3 powder on the surface of ZnO pellets and heating the combination to various temperatures (860–1155°C) and different times. The highest nonlinearity coefficients (20–24) and lowest breakdown voltages (3–5 V) were recorded in samples annealed at 860°C for 35 min. Longer annealing times and/or higher temperatures resulted in progressively higher breakdown voltages. Eventually the devices became insulating, which was attributed to the formation of an insulating Bi2O3 layer between the grains. Separate wetting experiments have shown that the penetration of Bi2O3 into ZnO grain boundaries was a strong function of alumina doping —the penetration rate was decreased by a factor of 5–7 as the ZnO was doped with as little as 0.2 mol% alumina. It is this slowing down of the penetration of the ZnO grain boundaries that is believed to be critical in the development of the low breakdown voltages observed.
Preparation of Monodisperse Zirconia Particles by Thermal Hydrolysis in Highly Concentrated Solutions
Authors: Kato Etsuro , Hirano Masanori , Kobayashi Yuichi , Asoh Keisuke , Mori Makoto , Nakata Masato
Published: September 2005

Monodisperse zirconia particles were prepared by the thermal hydrolysis of mixtures of zirconyl chloride, zirconium hydroxide, and water at high concentrations corresponding to about 5 mol/L Zr. The particles, as first prepared, were temporarily agglomerated spheres composed of primary ultrafine zirconia crystals. The agglomerated particles collapsed and dispersed in water to form a translucent sol. When vacuum dried and followed by heat treatment, they were not dispersible. The size of the agglomerated particles increased with increasing molar ratio of the zirconium chloride in the starting mixture, varying from about 0.2 to 0.6 μm. Using the sample thus obtained, monodisperse tetragonal zirconia particles of about 0.35 μm containing 3 mol% Y2O3 with a relatively uniform composition were obtained by homogeneous precipitation of YOHCO3 by heating with urea and calcination at 800°C.
Surface Chemistry of Lead Titanate and Its Impact on Binder Removal
Authors: Hirakata Keigo , Rhine Wendell E. , Cima Michael J.
Published: September 2005

Carbon residue after binder burnout was characterized for several nonstoichiometric lead titanate powders. Thermal decomposition of the poly(methyl methacrylate) (PMMA) binder was performed in nitrogen at 600°C. A drastic decrease in carbon retention was obtained in the case of the titanium‐rich samples. The amount of carbon retention varies from 0.2 mg/m2 to 1.2 mg/m2 by changing the Pb/Ti molar ratio from 0.92 to 1.08. The surface reaction between PMMA and lead titanate particles was studied by diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). Surface hydroxyls reacted with ester groups in the PMMA or the methylmethacrylate monomer produced upon pyrolysis. The DRIFTS results showed that titaniumrich samples are less reactive and produce less surfacebound organic groups. Interestingly, titanium‐rich samples contained more surface hydroxyls. Isoelectric point measurements, however, show that titanium‐rich samples are more acidic. Thus, the reactivity of the surface hydroxyls is determined primarily by their acid‐base characteristics rather than their concentration. Lead titanate powder was exposed to MMA vapor in a tube furnace at the indicated temperatures using nitrogen carrier gas as a model experiment. DRIFTS difference spectroscopy and Raman spectroscopy were performed on these samples after the exposure. MMA reacts with lead titanate powder in manner similar to PMMA. Analysis for sp2 and sp3 absorbance of Raman spectra of these exposed powders at 400°–600°C showed pyrolysis behavior of surface‐reacted species. The relative amount of sp2 bonded carbon decreases with increasing exposure temperature.
Heteroepitaxial Growth Kinetics in a CVD Process Using Nickel Oxide on MgO as a Model System
Authors: Hoghooghi Bahar , Raj Rishi
Published: September 2005

Three‐dimensional crysallites of NiO were grown on MgO substrates using a CVD process by reacting NiBr2 with oxygen in the presence of water vapor at 600°C. The vapor pressures of oxygen and water vapor were kept at 0.88 and 2.61 kPa, respectively. The growth rate of periodically spaced NiO nuclei was measured. The results, which show a peak in the average deposition rate when plotted against the nuclei spacing, are modeled in terms of an effective diffusion distance for the NiO molecules on the MgO surface, and assuming a negligibly small reaction rate of the precursors on the surface of NiO crystallites. The latter assumption results from the observation that the average growth rate on cleaved MgO surface dropped to a very low value once a continuous film of NiO was formed. An effective diffusion distance was manifested by the observation of characteristic denuded zones surrounding the NiO crystallites when the nucleation rate was increased by increasing the water vapor supersaturation on the surface. The comparison with model is used to estimate the effective diffusion distance.
Morphological Effect of Second Phase on the Thermal Conductivity of AIN Ceramics
Authors: Kim Weon‐Ju , Kim Do Kyung , Kim Chong Hee
Published: September 2005

The effect of the morphology of second phases in sintered microstructure on the thermal conductivity of AIN ceramics was investigated. When an Y2O3‐doped AIN specimen was cooled down slowly at a rate of 3°C/min after sintering at 1850° or 1900°C, the second phases were concentrated in the corners of the AIN grains by an increase of dihedral angle during cooling. On the other hand, the fast‐cooled specimen at a rate of 60°C/min showed a different structure of the second phases interconnected through the triple‐grain junctions. The specimen with isolated second‐phase morphology showed a higher thermal conductivity than those with interconnected second‐phase morphology. The measured thermal conductivity of the specimens with different morphologies of the second phases agreed well with the calculated one derived from modeled microstructures. From the comparison of the measured and calculated thermal conductivity, it was shown that the thermal conductivity of the specimen with interconnected second‐phase morphology decreased steeply with an increase of the amount of the second phases, assuming the content of lattice oxygen to be constant. However, the thermal conductivity of the specimen with isolated second‐phase morphology was rather insensitive to an increase of the amount of the second phases.
Synthesis of Nickel Sulfide by Homogeneous Precipitation from Acidic Solutions of Thioacetamide
Authors: Grau Jason , Akinc Mufit
Published: September 2005

Nickel sulflde powders were precipitated by utilizing the thermal decomposition of thioacetamide in acidic aqueous solutions. Precipitation was induced by a direct reaction between thioacetamide and nickel at 70° and 80°C with thioacetamide concentrations of 0.80M. Precipitation was induced by reaction of sulfide ions with nickel at 90°C and at low pH. Direct reaction products were amorphous and contained significant amounts of carbon, excess sulfur, and hydrogen. Hydrolysis‐controlled precipitation yielded faceted crystalline particles 2 to 4 μm in size. Crystalline, spherical particles with compositions near stoichiometric NiS were precipitated with high yields.
Physical Properties of Quenched Glasses in the Li2O‐ZrO2‐SiO2 System
Authors: Novaes de Oliveira Antonio Pedro , Barbieri Luisa , Leonelli Cristina , Manfredini Tiziano , Pellacani Gian Carlo
Published: September 2005

The behavior and some physical and thermal properties of a 30Li2O‐70SiO2 base glass composition with addition of ZrSiO4 in the as‐quenched state was investigated with the aid of X‐ray diffraction (XRD), differential thermal analysis (DTA), thermal expansion and microhardness measurements, as well as density measurements. Transparent glasses prepared by the addition of ZrSiO4 up to 10.30 mol% were obtained. ZrSiO4 was found to decrease the expansion coefficient of the investigated glasses from 11.0 × 10−6 to 7.96 × 10−6°C−1. The glass transition and softening point temperatures of the glasses showed a reverse behavior. On the other hand, both hardness and density increased for successive increases of the ZrSiO4 amounts, with the highest values of 6.3 GPa and 2.65 g/cm3, respectively.
Molecular Dynamic Simulation in Titanium Dioxide Polymorphs: Rutile, Brookite, and Anatase
Authors: Kim Dae‐Weon , Enomoto Naoya , Nakagawa Zenbe‐e , Kawamura Katsuyuki
Published: September 2005

Molecular dynamic (MD) simulations with a quantum correction were performed on the titanium dioxide polymorphs. Interatomic potential functions of our new model are composed of Coulomb, short‐range repulsion, van der Waals, and Morse interactions. The energy parameters were empirically determined to reproduce the fundamental properties of rutile crystal. The optimized crystal structure of TiO2, rutile, was in very good agreement with experimental data in the literature. For brookite and anatase, our MD simulations reproduced well the crystal structures and several physical properties, including volume thermal expansivity and bulk modulus. The present MD simulations with a new interatomic potential function and parameters successfully predicted the crystal structures of the titanium dioxide polymorphs.
Suppressing the Formation of Cone Structures in Chemical‐Vapor‐Deposited Aluminum Nitride/Titanium Nitride Films
Authors: Liu Yi Jun , Kim Hee Joon , Takeuchi Takashi , Egashira Yasuyuki , Kimura Hisamichi M. , Komiyama Hiroshi
Published: September 2005

Cone structures are sometimes observed in aluminum nitride/titanium nitride (AIN/TiN) composite films formed by chemical vapor deposition (CVD). In this study, we determined the formation mechanism of cone structures by looking at such films deposited on Si substrates. We found that the mechanism can be explained by changes in the deposition rate due to composition differences in the growing surfaces, rather than by inhomogeneities in the original substrate surface. We then used this discovery to develop a technique to suppress cone structure formation, i. e., deposition of an interlayer before the deposition of the composite. To validate our technique, we then successfully suppressed the formation of cone structures in AIN/TiN films by depositing a TiN interlayer on the substrate before the deposition of AIN/TiN.
Spontaneous Formation of Bonelike Apatite Layer on Chemically Treated Titanium Metals
Authors: Kokubo Tadashi , Miyaji Fumiaki , Kim Hyun‐Min , Nakamura Takashi
Published: September 2005

Generally, artificial materials implanted into bone defects are encapsulated by a fibrous tissue isolating them from the surrounding bone. Only limited kinds of ceramics are known to bond to living bone without forming the fibrous tissue, and already they are being used clinically as important artificial bones. However, they cannot be used under highly loaded conditions, since their fracture toughnesses are not so high as that of human cortical bone. The present study shows that even pure titanium metal and its alloys can bond to living bone, if their surfaces are pre‐treated with alkali hydroxide solutions. Thus‐treated metals are believed to be useful as artificial bones even under highly loaded conditions because of their high bone‐bonding ability as well as high fracture toughness.
TEM Investigation of Impurity Phases and the Penetration of Liquid Aluminum in Hot Isostatically Pressed TiB2 Compacts
Authors: Nord‐Varhaug Katrin
Published: September 2005

The microstructure of materials compacted from commercially produced TiB2 powders was investigated using transmission electron microscopy. A number of impurity phases that are introduced during the various processing stages were identified. After exposure to liquid aluminum, grain boundaries and triple junctions of TiB2 were found to be penetrated by aluminum. In the penetrated regions pure aluminum, two aluminum oxides, and an (Al2OC)1‐x(AlN)x. phase were identified. A SiO2 glass phase, introduced during hot isostatic pressing, is believed to be responsible for the formation of alumina. None of the other impurity phases were found to react with aluminum.
Solute Segregation and Grain‐Boundary Impedance in High‐Purity Stabilized Zirconia
Authors: Aoki Makoto , Chiang Yet‐Ming , Kosacki Igor , Lee L. Jong‐Ren , Tuller Harry , Liu Yaping
Published: September 2005

Solute segregation at grain boundaries has been correlated with grain‐boundary conductivity in high‐purity 15‐mol%‐CaO‐stabilized ZrO2. STEM measurements of solute coverage show that the segregation of impurity silicon (present at bulk levels <80 ppm) is grain‐size dependent. The boundary coverage of silicon can be systematically varied by varying grain size at concentrations low enough that a discrete siliceous film does not form. The cosegregation of calcium and silicon is observed. The grain‐boundary solute coverage (Tsi+Ca) has been correlated with the specific grain‐boundary conductivity (σspgb) determined using impedance spectroscopy. At monolayer segregation levels, the specific boundary conductivity is less than the bulk conductivity by a factor >103 at 500°C. At the lowest levels of segregation achieved, <0.1 monolayer, σspgb remains ∼102 less, and possibly represents an “intrinsic” limiting value for the grain boundary. Comparison with Y2O3‐doped ZrO2 suggests similar behavior in this system. The control of grain‐boundary segregation through purity, microstructure, and thermal history is discussed from the objective of engineering the grain‐boundary impedance of polycrystalline ionic conductors.
Microstructural Evolution during the Sintering of Nanostructured Ceramic Oxides
Authors: Allen Andrew J. , Krueger Susan , Skandan Ganesh , Long Gabrielle G. , Hahn Horst , Kerch Helen M. , Parker John C. , All Mohammad N.
Published: September 2005

Using small‐angle scattering, together with density measurements, X‐ray diffraction, nitrogen adsorption, and both transmission and scanning electron microscopy, the microstructural evolution during sintering in nanostructured ceramic oxides has been studied. The availability of samples with sufficient size and uniformity has permitted absolute calibration of the scattering data and made possible determinations of microstructural parameters and surface areas that are statistically representative of the undisturbed nanophase morphologies. A fully quantitative microstructural model has been developed, and the effects of varying processing parameters during powder synthesis and sintering have been assessed. Predictions are made regarding the achievable sintered full‐density microstructures.
Fracture Behavior of Directionally Solidified Y3Al5O12/Al2O3 Eutectic Fiber
Authors: Yang Jenn‐Ming , Jeng S. M. , Chang Sekyung
Published: September 2005

The strength and fracture of a directionally solidified Y3Al5O12/Al2O3 eutectic fiber were investigated. The fiber was grown continuously by an edge‐defined film‐fed growth technique. The microstructure was characterized using X‐ray diffraction, scanning electron microscopy, and energy‐dispersive spectroscopy. The tensile strength and Weibull's modulus of the eutectic fibers were determined in the as‐fabricated state and after extended thermal exposure at 1460°C in air. Fractographic analysis was used to identify and classify the strength‐limiting mechanisms. The fracture toughness and crack growth behavior were characterized by an indentation technique. A fracture mechanics analysis was also used to establish the relationships between surface flaw size, tensile strength, and fracture toughness of the fiber.
Role of Particle Dissolution in the Stability of Binary Yttria‐Silica Colloidal Suspensions
Authors: Yasrebi Mehrdad , Ziomek‐Moroz Margaret , Kemp William , Sturgis David H.
Published: September 2005

The stability of yttria‐silica binary aqueous colloidal suspensions is examined as a function of time. It has been observed that initially stable silica particles go through a flocculation period and then restabilize. This phenomenon is attributed to slow dissolution and the specific adsorption of trivalent yttrium cation and its hydroxo complexes on the surface of silica. Furthermore, it is shown that the kinetics of flocculation and restabilization can be controlled by pH adjustment.
Preloading Technique in Dynamic Fatigue Testing of Glass and Ceramics with an Indentation Flaw System
Authors: Choi Sung R. , Salem Jonathan A.
Published: September 2005

The solution of fatigue strength as a function of preloading in dynamic fatigue testing was obtained numerically for an indentation flaw system. The dynamic fatigue strength is dependent on preloading and fatigue parameter (K). The effect of preloading on dynamic fatigue strength decreases with increasing fatigue parameter: for n 20 the effect is negligible up to a preloading of 90%. The solution was verified by dynamic fatigue experiments conducted with soda‐lime glass and alumina specimens with as‐indented flaws in room‐temperature distilled water. The result indicates that one can apply a preloading corresponding up to 90% of fatigue strength for most glass and ceramic materials with no change in fatigue strength, resulting in a dramatic saving of testing time.
Formation of Sm2+ lons in Sol‐Gel‐Derived Glasses of the System Na2 O‐Al2O3‐SiO2
Authors: Nogami Masayuki , Hayakawa Naoya , Sugioka Naoya , Abe Yoshihiro
Published: September 2005

Samarium ions (Sm2+) incorporated into aluminosilicate glasses by a sol‐gel process showed persistent spectral hole burning at room temperature. Gels of the system Na2O‐Al2O3SiO2 synthesized by the hydrolysis of Si(OC2H5)4, Al(OC4H9)3, CH3 COONa, and SmCl3·6H2O were heated in air at 500°C, then reacted with H2 gas to form Sm2+ ions. Whereas Al3+ ions effectively dispersed the Sm3+ ions in the glass structure, Na+ ions were not effective. The Al2O3‐SiO2 glasses proved appropriate for reacting the Sm3+ ions with H2 gas and exhibited the intense photoluminescence of Sm2+ ions. The reaction of Sm3+ ions with H2 in the Al2O2‐SiO2 glasses was determined by first‐order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm2+ ions was achieved within 20 min.
Investigation of SiC‐AlN: Part II, Mechanical Properties
Authors: Huang Jow‐Lay , Jih Jyh‐Ming
Published: September 2005

SiC/AIN composites with controlled interfacial solid solution were employed in the present work for investigating the effects of interfacial bonding and A1N polytypes on the mechanical properties. Platelike A1N polytypes and interfacial bonding were found to have substantial effects on the flexural strength, hardness, and fracture toughness.
Ferroic Phase Transitions in (Na1/2Bi1/2)TiO3 Crystals
Authors: Park Seung‐Eek , Chung Su‐Jin , Kim In‐Tae
Published: September 2005

The ferroic phase‐transition behavior of two (Na1/2Bi1/2)TiO3(NBT) crystals grown by flux and by the Czochralski method has been investigated in the present study. Although both the tetragonal and the rhombohedral phases of NBT are expected to be ferroelastic, these crystals exhibit different ferroelastic behavior. The two NBT crystals also show differences in the amount of temperature hysteresis and the thermal expansion coefficients. These differences can be attributed to nonstoichiometry and structural variations dependent on the growing method. The present investigation has revealed a second maximum at −450°C in dielectric constant ((T)) curves, which could indicate that the intermediate tetragonal phase is either polar or antipolar. This maximum, however, originates from space‐charge polarization and interaction between the charge carrier and the electrode, such that the tetragonal phase, in fact, is para‐electric. The diffuse phase transition (DPT) of the NBT crystal, therefore, is from a paraelectric and ferroelastic tetragonal phase to a ferroelectric and ferroelastic rhombohedral phase. The crystallographic supergroup‐subgroup relationships in the ferroic phase transitions of NBT crystals are discussed.
Influence of Grain Size on the Grinding Response of Alumina
Authors: Xu Hockin H. K. , Wei Lanhua , Jahanmir Said
Published: September 2005

The effect of grain size on the grinding response, i. e., grinding forces, surface roughness, and grinding‐induced subsurface damage, is investigated in a series of alumina ceramics with the average grain size ranging from 3 to 35 μm. The grinding forces are measured as a function of depth of cut in surface grinding. It is found that the grinding forces decrease as the grain size is increased from 3 to 9 μm. But at larger grain sizes, the grinding forces are independent of the grain size. Subsurface damage in grinding is observed using a bonded‐interface sectioning technique. The subsurface damage is found to consist of intragrain twin/slip bands and intergranular microcracks. The density of grinding‐induced subsurface microcracks increases with the grain size. In addition to using optical microscopy on the sections of the ground specimens, a nondestructive thermal wave measurement technique is used directly on the ground surfaces for the detection of grinding‐induced subsurface microcracks. The grain size dependence of the microcrack density estimated from the thermal images is found to agree with the results obtained using the bonded‐interface technique.
Microstructural Characterization of ZrO2/O'‐SiAION Composites
Authors: Cheng Yi‐Bing , Drennan John
Published: September 2005

Zirconia has demonstrated a very moderate toughening effect in nitrogen‐based ceramic composites because the reaction between tetragonal zirconia (t‐ZrO2) and nitrogen results in additional zirconia stabilization to a nontrans‐formable t' or cubic structure. In O'‐SiAlON matrices, the oxygen concentration increases and the oxygen‐rich inter‐granular glassy phase prevents zirconia from nitridation. As a result, tetragonal ZrO2 is maintained and is transformable in the O'‐SiAlON materials. The present study has provided transmission electron microscopy (TEM) evidence of the zirconia transformation and the associated toughening effect in a ZrO2/O'‐SiAlON composite. The implications and limitations of the transformation on toughening of the material are discussed.
Properties of As40S(60–x) Sex Glasses for IR Fiber Optics
Authors: Sanghera Jas S. , Nguyen Vinh Q. , Aggarwal Ishwar D.
Published: September 2005

The physical and optical properties of glasses in the As40S((60‐x:)Sex system where x= 0, 5,10,15, and 20 at. % Se have been investigated. The changes in the glass transition temperature, density, hardness, IR edge, and refractive index can be attributed to the presence of Se, which simply replaces S in these glasses. The glasses do not exhibit crystallization under the conditions used in this study, which is a desirable property from the viewpoint of flberization. Appropriate core and cladding glass compositions have been identified for fabrication of optical fibers with known numerical apertures. Furthermore, it has been shown that these glasses will not impart additional thermal or mechanical stresses in optical fibers made from these compositions.
Leachability of Molybdenum from Ternary Phosphate Glasses
Authors: Pyare Ram , Lai Lai Ji , Joshi V C. , Singh V K.
Published: September 2005

With a view to use glasses as a source of molybdenum, which is one of the micronutrients required by plants, a systematic study of the leachability of molybdenum from ternary phosphate glasses having molar compositions of 25MoO3‐25X50P2Os (where X = Li2O, Na2O, K2O, CaO, B2O3, or SiO2) was carried out. Leaching of molybdenum ions has been studied as a function of pH, which shows that leaching increases with increasing pH of the solutions. The concentration of molybdenum ions in the leachate decreases with increasing bond strength between nonbridging oxygen ions and the cations in glasses. Leaching increases with an increase in leaching time and decreases with an increase in the particle sizes of the glasses. P2O5 was also leached along with MoO3. The leaching characteristics of P2O5 from the glasses are also reported.
Using Simultaneous Deposition and Rapid Growth to Produce Nanostructured Composite Films of AIN/TiN by Chemical Vapor Deposition
Authors: Liu Yi Jun , Kim Hee Joon , Egashira Yasuyuki , Kimura Hisamichi , Komiyama Hiroshi
Published: September 2005

Brittleness has been the major obstacle in using ceramics. Previous research has shown, however, that ceramic materials that have small grain size show plasticity. We therefore propose two methods to produce nanostructured ceramic films by chemical vapor deposition (CVD): (1) high‐speed deposition and (2) simultaneous deposition of insoluble materials (contained in a mixture of insoluble solids). These methods were successfully applied to aluminum nitride/ titanium nitride (AlN/TiN) films produced by CVD. The AlN/TiN nanostructured composite films were synthesized by atmospheric‐pressure CVD (APCVD), using aluminum chloride (AlC13), titanium chloride (TiCl4), and ammonia (NH3) as reactant gases at temperatures ranging from 923 to 1123 K in a horizontal tubular reactor. For the highspeed deposition strategy, we obtained growth rates as high as 1.2 mm/h. Using either method, we were able to attain AlN/TiN composite films that had a grain size of 8 nm (AlN crystals) and 6 nm (TIN crystals), showing that these methods are effective in producing nanostructured composite films by CVD. Measurements of the fracture toughness of the prepared materials indicated that these strategies can be used to improve the ductility of ceramics.
Thermodynamics of the Si‐O‐N System: I, High‐Temperature Study of the Vaporization Behavior of Silicon Nitride by Mass Spectrometry
Authors: Rocabois Philippe , Chatillon Christian , Bernard Claude
Published: September 2005

Si3N4(s) powders are vaporized in effusion cells, and the gaseous phase, analyzed by mass spectrometry, is composed of N2, Si, Si2, Si3, SiN, and Si2N. Owing to retarding vaporization of N2, effusion cells with different orifice sizes are used in order to determine the evaporation coefficient for this species, which is then compared with previous Knudsen or Langmuir studies. Enthalpies of formation for SiN(g) and Si2N(g) are determined.
Mechanism of LaFeO3 Perovskite‐Type Oxide Formation from the Thermal Decomposition of d‐f Heteronuclear Complex La[Fe(CN)6]‐5H2O
Authors: Traversa Enrico , Sakamoto Masatomi , Sadaoka Yoshihiko
Published: September 2005

Nanosized, single‐phase perovskite‐type LaFeO3 powders are synthesized by the thermal decomposition at 600°C of d‐f heteronuclear complex La[Fe(CN)6]‐5H2O. The mechanism of the formation of LaFeO3 has been studied by simultaneous thermogravimetric and differential thermal analysis (TG/DTA), Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The formation of LaFeO3 from the complex involves the formation of a carbonated, orthorhombic transition phase, which facilitates the formation of the LaFeO3 orthorhombic structure at low temperatures with a peculiar morphology.
Effect of Grain Size on Diffusion‐Induced Grain‐Boundary Migration in Ba(Zn1/3Nb2/3)O3 Ceramics
Authors: Park Jong‐Keuk , Kim Doh‐Yeon
Published: September 2005

Diffusion‐induced grain‐boundary migration (DIGM) in Ba(Zn1/3Nb2/3)O3 (BZN) ceramics was investigated with small (3.0 μm) and large (31. 4 μm) grain size specimens. The specimens were embedded in Nb2O5 or ZnO powders and then heat‐treated at 1250° and 1310°C, respectively. The grain boundaries of the small grain size specimens were immobile, while those of the large grain size specimens migrated away from their centers of curvature. From the observed difference in migration behavior depending on grain size, the magnitude of the driving force for the DIGM was estimated.
Microwave‐Hydrothermal Processing of BiFeO3 and CsAl2PO6
Authors: Komarneni Sridhar , Menon V C. , Li Q. H. , Roy Rustum , Ainger F.
Published: September 2005

Microwave‐hydrothermal (M‐H) processing was compared with conventional‐hydrothermal (C‐H) processing in the crystallization of BiFeO3 and CsAl2PO6 phases. The presence of the microwave field led to accelerated kinetics of the crystallization of both these phases as detected by powder X‐ray diffraction. The acceleration of reaction rates under microwave field is expected to lead to energy savings during ceramic processing.
Hardness Variations in Multilayered ZrO2‐Al2O3 Composites
Authors: Mumm Daniel R. , Marshall David B. , Griffin Alair , Griffin Curtis W , Turner Colleen S.
Published: September 2005

The hardness of zirconia‐alumina laminar composites has been measured over contact size scales ranging from much smaller to much larger than the layer thicknesses. The results correlate with a weighted average of the hardnesses of the two layer constituents based on the volume of the plastic zone; and they deviate significantly from a similar average based on the contact area.
Effects of Sulfate, Pyrophosphate, and Citrate Ions on the Physicochemical Properties of Cements Made of β‐Tricalcium Phosphate‐Phosphoric Acid‐Water Mixtures
Authors: Bohner Marc , Lemaitre Jacques , Ring Terry A.
Published: September 2005

Several additives were selected to increase the setting time of calcium phosphate cements made of β‐tricalcium phosphate (β‐TCP; β‐Ca3(PO4)2)‐phosphoric acid‐water mixtures. The effects of the additives, i.e., sulfate, pyrophosphate, and citrate ions, are presented in this study. The results show that they all increased the setting time of the cement. Their effectiveness at increasing the setting time is in the order pyrophosphate > citrate > sulfate. The effect of sulfate ions on the setting time is increasingly large below a concentration of 0.1M. Above that concentration, calcium sulfate dihydrate (CSD; CaSO4‐2H2O) crystals nucleate and act as nuclei for dicalcium phosphate dihydrate (DCPD; CaHPO4‐2H2O) crystals, which are the normal product of the setting reaction. This decreases the setting time and decreases the DCPD crystal size, resulting in an increase of the tensile strength of the cement.
Constitutive Law for the Densification of Fused Silica, with Applications in Polishing and Microgrinding
Authors: Lambropoulos John C. , Xu Su , Fang Tong
Published: September 2005

We discuss a constitutive model describing the permanent densification of fused silica under large applied pressures and shear stresses. The constitutive law is assumed to be rate‐independent and uses a yield function coupling hydrostatic pressure and shear stress, a flow rule describing the evolution of permanent strains after initial densification, and a hardening rule describing the dependence of the incremental densification on the levels of applied stresses. Normality, or lack thereof, of the permanent strain increments to the current yield surface in stress space allows for various relative contributions of densification and shear flow in the ensuing deformation. The constitutive law accounts for multiaxial states of stress, since during polishing and grinding operations complex stress states, with large shear components due to friction and abrasion, occur in a thin surface layer due to the action of abrasive particles. We apply the constitutive law in estimating the extent of the densified layer during the mechanical interaction of an abrasive grain and a flat surface under polishing and grinding conditions. The grain is assumed to be spherical and in Hertz contact with the surface, or sharp and in point contact. The effect on the densified depth of stress relaxation due to densification is discussed.
Dielectric Dispersion of Polycrystalline Aluminum Nitride at Microwave Frequencies
Authors: Nakayama Akira , Nambu Shinji , Inagaki Masahiro , Miyauchi Masahiko , Itoh Nobuyuki
Published: September 2005

Complex permittivity of polycrystalline AlN was measured over the frequency range 100 MHz to 13 GHz using reflection coefficient and cavity resonator methods. Dielectric relaxation peaks of loss tangent were observed in the frequency range 200 MHz to 3 GHz. The maximum value of loss tangent was ∼200 × 10−4. Relative permittivities decreased by ∼4% with increased frequency at the region of relaxation peaks. It was shown that these dispersion frequencies were inversely proportional to the grain sizes of AlN and independent of purities and processes. Model calculations for elastic vibration of a single‐crystal grain of AlN were performed to investigate the origin of the dielectric dispersion due to piezoelectric effect. The calculated results of elastic sphere and 14‐faced‐polyhedron models showed a good quantitative agreement with the observed dispersion frequencies, which suggested that the dispersion was due to a piezoelectric vibration of a single grain of AlN ceramics at microwave frequencies.
Novel Plutonium Titanate Compounds and Solid Solutions Pu2Ti2O7‐Ln2Ti2O7: Relevance to Nuclear Waste Disposal
Authors: Shoup Shara S. , Bamberger Carlos E. , Haire Richard G.
Published: September 2005

The compounds SrPu2Ti4O12, Pu2Ti3O8.79, and Pu2Ti2O7, where plutonium is in the (III) oxidation state, were prepared and identified via X‐ray diffraction (XRD). The solid solubility limit of Pu2Ti2O7 in Ln2Ti2O7 (Ln = Gd, Er, or Lu) was also studied via XRD; it was determined that the solubility of Pu2Ti2O7 increased as the radius of the lanthanide ion in the host compound decreased. Attempts to synthesize Sr2Pu2 Ti5O16 and Sr2Ce2–yPuyTi5O16 solid solutions, where plutonium is in the (IV) oxidation state, were unsuccessful.
Preparation of Mullite Fiber
Authors: Chen Lifu , Wang Baowei , Liu Shujie , Yan Yongjun
Published: September 2005

Transparent mullite fibers have been prepared using aluminum carboxylates (ACs) and tetraethyl orthosilicate (TEOS) as starting materials. The ACs are derived from the catalyzed dissolution of elemental aluminum in a mixture of formic acid and acetic acid. The solubility of aluminum in the acids is influenced by the concentrations of the acids, water, and additives and the preparation temperature. A 1:4:3:24 molar ratio of aluminum, formic acid, acetic acid, and water dissolves the aluminum completely to give a colorless, clear solution suitable for fiber synthesis. The mixture of the ACs and TEOS, in the presence of ethyl alcohol as a mutual solvent at 50°–60°C, is concentrated to give a spinnable dope, from which mullite precursor fibers can be drawn. Heat treatment of the precursor at 1250°C yields crystallized and transparent mullite fibers.
Varistor Performance of ZnO‐Based Ceramics Related to Their Densification and Structural Development
Authors: Nobrega Maria Cecilia S. , Mannheimer Walter A.
Published: September 2005

Electrical potential barriers are often observed in ZnO‐based ceramics. Earlier studies on ZnO photoconduction have shown that the narrow regions, where the sintered grains have grown together, control the resistance of the entire sample. In those regions, the surface/volume ratio is sufficiently high for the acceptor concentration (which occurs because of adsorbed oxygen) to exceed the donor concentration inside the ZnO grains. More recent works have shown that Schottky barriers result from interface states because of the chemisorbed oxygen ion at the ZnO‐ceramic grain boundaries. The work reported in this paper involves the relationship between the densification of the microstructure and the varistor performance of ZnO ceramics. The emphasis of densification percentage as an indicator of the degree of sintering shows the desirability of continuity across ZnO grain boundaries, without the presence of voids or films of second phases, in optimizing varistor behavior. The effect of oxygen partial pressure on the development of varistor microstructure and electrical properties, as well the kinetics of grain growth, during the sintering process have been determined and are discussed.
Densification Behavior and Properties of Y2O3‐Containing α‐SiAlON‐Based Composites
Authors: Bandyopadhyay Siddharta , Hoffmann Michael J. , Petzow Günter
Published: September 2005

Different SiAION composites based on α′‐SiAION are investigated, with respect to the phase relationships, densification behavior, and mechanical properties. The compositions are located on a phase‐diagram line parallel to the Si3N4‐Y2O3 9AIN compound in the Si3N4‐SiO2‐AlN‐Al2O3‐Y2O3‐YN system. Analysis of the reaction sequences shows that the formation of the composites is associated with the transient appearance of Y4A12O9 (YAM), yttrium‐aluminum‐garnet (YAG), melilite, and a nitrogen‐rich liquid phase. The small shift of compositions on the Si3N4‐Y2O3‐9AIN compound phase‐diagram line toward the Al2O3‐rich side offers the advantage of a higher sinterability and the removal of the melilite phase from a wide range of compositions containing α′‐SiAlON and polytypes. The α′/β′‐SiAlON composites show better mechanical properties in comparison to pure α′‐SiAlON and composites of α′‐SiAION and polytypes. A post‐heat‐treatment causes the crystallization of YAG as a grain‐boundary phase and leads to excellent strength retention up to temperatures of 1350°C.
Preparation and Characterization of BaxSr1‐x, TiO3Thin Films by a Sol‐Gel Technique
Authors: Tahan Danielle M. , Safari Ahmad , Klein Lisa C.
Published: September 2005

Barium strontium titanate, (Bax,Sr1‐xTiO3, thin films of various compositions were prepared by a sol‐gel method. Solutions consisting of acetate powders and titanium IV isopropoxide in a mixture of acetic acid and ethylene glycol were spin‐coated onto silicon and platinum‐coated silicon substrates. Processing parameters were optimized to develop stable solutions which yielded films with relatively low crystallization temperatures. It was determined that ethylene glycol was a necessary component of the solution to increase stability to precipitation and to decrease the crystallization temperature of the films. The grain size of the films varied with annealing temperature and atmosphere and directly affected the dielectric properties. A dielectric constant of 400 and a dissipation factor of 0.04 were measured at 1 kHz for (Ba0.8,Sr0.2) TiO3films heated to 700°C for 1 h with a thickness of approximately 400 nm. Films of this composition maintained low leakage current densities for extended time periods when measured at an applied field of 75 kV/cm.
Fabrication of Textured Silicon Carbide via Seeded Anisotropic Grain Growth
Authors: Sacks Michael D. , Scheiffele Gary W , Staab Greg A.
Published: September 2005

Highly textured silicon carbide was fabricated via anisotropic grain growth. Large, platelike grains were grown from a fine‐grained sintered matrix which had been seeded with ≤2% SiC platelets. The seeds were initially incorporated with preferred orientation during the green‐state forming process and this resulted in oriented growth of the platelike grains. The development of texture in the samples was evident from microstructure observations and X‐ray diffraction analysis.
Discontinuous Dissolution and Grain‐Boundary Migration in Al2O3‐Fe2O3 by Oxygen Partial Pressure Change
Authors: Lee Ho‐Yong , Rhee Young‐Woo , Kang Suk‐Joong L.
Published: September 2005

When sintered 95Al2O3‐5Fe2O3 (wt%) specimens constituting corundum grains and iron aluminate spinel precipitates were annealed under high oxygen partial pressure (Po2) where only a corundum phase is stable, fast dissolution of particulate spinel precipitates occurred, together with the migration of corundum grain boundaries. Behind the migrating boundaries, a corundum solid solution enriched with Fe2O3 formed. Discontinuous dissolution (DD) of particulate spinel precipitates thus occurred by Po2 increase. In contrast, when 95Al2O3‐5Fe2O3 specimens constituting only corundum grains were annealed under low Po2 where both corundum and spinel phases are stable, grain boundaries migrated without spinel precipitation, leaving behind a corundum phase depleted of Fe2O3, similar to chemically induced grain‐boundary migration (CIGM) observed during solute depletion. The volatilization of Fe2O3 appeared to cause the boundary migration without precipitation. The observed CIGM and DD would suggest various possibilities of microstructure control in other oxide systems through oxygen partial pressure change.
Viability of Oxide Fiber Coatings in Ceramic Composites for Accommodation of Misfit Stresses
Authors: Kerans Ronald J.
Published: September 2005

The C and BN fiber coatings used in most ceramic composites perform a less obvious but equally essential function, in addition to crack deflection; they accommodate misfit stresses due to interfacial fracture surface roughness. Coatings substituted for them must also perform that function to be effective. However, in general, oxides are much less compliant materials than C and BN, which raises the question of the feasibility of oxide substitutes. The viability of oxide coatings for accommodating misfit stresses in Nicalon fiber/SiC composites was investigated by calculating the maximum misfit stresses as functions of coating properties and geometries. Control of interfacial fracture path was also briefly considered. The implications regarding composite properties were examined by calculating properties for composites with mechanically viable oxide coatings.