bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism for the Peritectic Reaction and Growth of Aligned Grains in YBa2Cu3O6+x
Authors: Bateman Charles A. , Zhang Lijie , Chan Helen M. , Harmer Martin P.
Published: March 2005

It is experimentally observed that the peritectic reaction, 211 + liquid → 123, can be driven essentially to completion in 1 h at an undercooling of only ∽30°C. The kinetic data, together with the observed microstructures, are inconsistent with the normal mechanism of the peritectic reaction. It is proposed that the mechanism of the reaction involves dissolution of 211 particles into the liquid and precipitation of solid 123. The aligned grain structure is explained through sympathetic nucleation of new 123 grains on existing grains.
In Situ Measurement of the Elastic Moduli of Glass‐Ceramic Thick Films
Authors: Ashcroft Ian A. , Lawrence Charles W. , Weihs Timothy P. , Derby Brian
Published: March 2005

A line‐focus acoustic microscope and a depth‐sensing nanoindenter have been used to directly measure the elastic moduli of glass‐ceramic thick films on copper and copper/invar/copper substrates. Both techniques proved successful in determining Young's modulus of the films. Measured moduli of the films were close to those of bulk glass‐ceramic values for both techniques. The nanoindenter produced slightly higher values than the acoustic microscope.
Effects of Surface Modification of Calcined PLZT Powder on Optical Transparency
Authors: Ochi Yasuo , Maekawa Masashi
Published: March 2005

The effects of surface modification of lead lanthanum Zirconate titanate (PLZT) powder on sintering and transparency were investigated by sintering hydrophobic powders modified with various alcohols. When alcohols with longer chain lengths were used for surface treatment, aggregation forces among the particles were reduced, resulting in dense, highly transparent ceramics.
Method for Tensile Experiments with Ceramic Fibers Having a Diameter of a Few Micrometers
Authors: Iwanaga Hiroshi , Iwasaki Takeshi , Reizen Kouji , Matsunami Tadashi , Ichihara Masaki , Takeuchi Shin
Published: March 2005

A method for measuring the tensile strength of whiskers with a diameter of micrometer order has been devised. The method allows us to measure the tensile load in the range of 20 to 1500 mgwt with an accuracy of about 1 mgwt under optical microscope observation. Young's modulus of the whiskers can also be measured. Some examples of measurements are presented.
Near‐Stoichiometric Silicon Carbide from an Economical Polysilane Precursor
Authors: Seyferth Dietmar , Wood Timothy G. , Tracy Henry J. , Robison Jennifer L.
Published: March 2005

Na condensation of CH3SiHCl2 gives polysilanes of the type ((CH3SiH)x (CH3Si)y)n (where x+y= 1) whose pyrolysis in a stream of Ar gives SiC and a substantial amount of elemental Si. Treatment of such polysilanes with catalytic quantities of group‐IV‐metal–organometallic complexes, ((η‐C5H5)2ZrH2)n, (η‐C5H5)2Zr(CH3)2, (η‐C5H5)2ZrHCl, and (η‐C5H5)2‐Ti(CH3)2, results in cross‐linking processes such that pyrolysis of these polysilanes gives close to stoichiometric SiC (≥95 wt %) and only very little elemental Si.
Formation Process and Microstructural Evolution of Sol–Gel‐Derived Ferroelectric Lead Iron Tungstate Ceramics
Authors: Lu Chung‐Hsin , Shinozaki Kazuo , Mizutani Nobuyasu
Published: March 2005

The formation process of Pb(Fe2/3W1/3)O3 was simplified and the synthesis temperatures were reduced because of the improved reactivity and homogeneity in sol–gel‐derived precursors. No liquid phases appeared in the specimens formulated from clear refluxed solution, whereas they were observed in the specimens prepared from turbid solution containing lead tungstate precipitates. The mixing state of reactants in precursors greatly affected the formation of liquid phases. Pb(Fe2/3W1/3) grains with a characteristic cubic shape were formed from the sol–gel process.
Observed and Theoretical Creep Rates for an Alumina Ceramic and a Silicon Nitride Ceramic in Flexure
Authors: Krause Ralph F.
Published: March 2005

Observed creep curvature rates are compared to theoretical rates for both an alumina ceramic at 1000°C and a silicon nitride ceramic at 1200°C in four‐point flexure. The observed rates have been calculated from published rise‐displacement rates, and the theoretical rates have been calculated from published power‐law parameters for compressive and tensile creep, which differ appreciably for these ceramics. Although both compressive and tensile creep measurements are easier to analyze than flexural creep measurements, the latter are usually less expensive and easier to conduct. The present work shows the usefulness of flexural creep tests to verify the accuracy of compressive and tensile creep tests.
Preparation and Physical Properties of Radiofrequency‐Sputtered Amorphous Films in the System AlPO4–TiO2
Authors: Hanada Teiichi , Kato Yoshinari , Tanabe Setsuhisa , Soga Naohiro
Published: March 2005

Amorphous films in the system AlPO4–TiO2 were prepared by an rf‐sputtering method, and their physical properties, such as density, refractive index, and thermal expansion coefficient, and the infrared absorption spectra were measured. The thermal expansion coefficient increased linearly with increasing TiO2 content. The results of the molar refractivity and the infrared absorption spectra indicated that the coordination number of titanium ions in these films is higher than that in SiO2–TiO2 glasses with a negative thermal expansion, in which Ti4+ ions are tetrahedrally coordinated. In order to confirm the coordination state of the titanium ions in these amorphous films, titanium K‐band emission spectra were obtained by X‐ray emission spectroscopy, revealing sixfold coordination. The higher coordination state of Ti4+ was considered to account for these amorphous films not exhibiting negative thermal expansion, as in the SiO2–TiO2 system.
Low‐Temperature Synthesis of β‐Ca2SiO4 from Hillebrandite
Authors: Ishida Hideki , Mabuchi Katsumi , Sasaki Kaori , Mitsuda Takeshi
Published: March 2005

Experiments on hydrothermal synthesis were conducted using quartz or silicic acid and lime as starting materials at Ca/Si = 2.0. It is possible to synthesize pure hillebrandite (Ca2(SiO3)(OH)2) having the theoretical composition by heating at 200°C for 10 h or at 250°C for 5 h. The synthesized product is fibrous, open at each end, and has a length of 20 to 30 μm. Calcium silicate hydrate gels are produced at the initial stage of the reaction. These react further with the unreacted lime to give hillebrandite. However, when silicic acid is used as silica, hillebrandite with tricalcium silicate hydrate is observed at 250°C because of the high reaction rate of silica. On heating, hillebrandite starts to decompose at about 500°C and produces low‐crystalline β‐Ca2SiO4, which is stable at room temperature and has a remarkably large specific surface area of about 7 m2/g. The decomposition reaction rate in a single crystal is rapid, and the reaction is considered to proceed topotactically.
Surface Morphology of Heat‐Treated Ceramic Thin Films
Authors: Susnitzky David W. , Carter C. Barry
Published: March 2005

The morphology of surfaces of several ceramic materials has been examined using transmission electron microscopy. The approach used was to prepare a sample for examination in the microscope, carefully clean it, and then heat‐treat it. In the case of the oxides studied (alumina and spinel) the samples were heated in air; the non‐oxides (α‐SiC and β‐SiC) were annealed under vacuum. The morphology in all but one case was such that the surface faceted parallel to the nearest low‐index plane to give well‐defined terraces; these were separated by ledges which also tended to facet parallel to the traces of low‐index planes. The exception was the {1100} alumina surface, which appears to be unstable in air at temperatures close to 1400°C. A computer program using a multislice approach was used to estimate the height of the steps on the (0001) surface; the step heights appear to be multiples of the c lattice parameter. A reconstruction of this surface as a result of this heat treatment is also proposed.
Grain Growth of ZnO during Bi2O3 Liquid‐Phase Sintering
Authors: Dey Debashis , Bradt Richard C.
Published: March 2005

Grain growth of ZnO during the liquid‐phase sintering of binary ZnO–Bi2O3 ceramics has been studied for Bi2O3 contents from 3 to 12 wt% and sintering from 900° to 1400°C. The results are considered in combination with previously published studies of ZnO grain growth in the ZnO–Bi2O3 system. For the Bi2O3 contents of the present study, the rate of ZnO grain growth is found to decrease with increasing Bi2O3. Activation analysis, when combined with the results of similar analyses of the previous studies, reveals a change in the rate‐controlling mechanism for ZnO grain growth. Following a low‐Bi2O3‐content region of nearly constant activation energy values of about 150 kJ/mol, further Bi2O3 additions cause an increase of the activation energy to about 270 kJ/mol. consistent with accepted models of liquid‐phase sintering, it is concluded that the rate‐controlling mechanism of ZnO grain growth during liquid‐phase sintering in the presence of Bi2O3 changes from one of a phase‐boundary reaction at low Bi2O3 levels to one of diffusion through the liquid phase at about the 5 to 6 wt% Bi2O3 level and above.
Highly Reactive β‐Dicalcium Silicate: III, Hydration Behavior at 40–80°C
Authors: Ishida Hideki , Sasaki Kaori , Okada Yoshihiko , Mitsuda Takeshi
Published: March 2005

The effect of curing temperature (40°, 60°, 80°C) on the hydration behavior of β‐dicalcium silicate (β‐C2S) was investigated. The β‐C2S was obtained by decomposition of hillebrandite, Ca2(SiO3)(OH)2, at 600°C, has a specific surface area of about 7 m2/g, and is in the form of fibrous crystals. The dependence of the hydration reaction on temperature continues until the reaction is completed. The hydration is completed in 1 day at 80°C and in 14 days at 14°C. The hydration mechanism is different above and below 60°C, but at a given temperature, the reaction mechanism and the silicate anion structures of C‐S‐H do not change significantly from the initial to the late stages of the reaction. High curing temperature and long curing times after completion of reaction promote silicate polymerization. The Ca/Si ratio of C‐S‐H shows high values, being almost 2.0 above 60°C and 1.95 below 40°C.
High‐Temperature Healing of Cracklike Flaws in Mg‐ and Ca‐Ion‐Implanted Sapphire
Authors: Powers James D. , Glaeser Andreas M.
Published: March 2005

Controlled‐geometry voids were introduced into Mg‐implanted and Ca‐implanted sapphire substrates using microfabrication techniques and ion beam etching, and were subsequently transferred to an internal interface by hot‐pressing. The morphological evolution of cracklike and channel‐like defects in response to anneals at 1700°C was studied. The healing behavior of defects in the Ca‐ and Mg‐ion‐implanted samples differs significantly. Mg additions appear to reduce the directional dependence of the healing characteristics and thus homogenize the evolution. Destabilization of the basal plane by Ca may contribute to the rapid healing of cracks oriented parallel to the basal plane. The healing characteristics of pore channels in Ca‐implanted samples indicate a strong residual energetic barrier to healing stemming from surface energy anisotropy. Despite this, defects in Ca‐implanted sapphire healed more rapidly than crystallographically and geometrically identical defects in Mg‐implanted sapphire. Thus, the results suggest that Ca additions increase transport rates sufficiently to more than compensate for the relatively higher energetic barriers to pore channel breakup.
Transformations during Grinding of Ceria‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Annamalai V. E. , Sornakumar T. , Gokularathnam C. V. , Krishnamurthy R.
Published: March 2005

Ce‐TZP is reported to exhibit cyclic transformation during machine grinding. Previous conclusions were based on the results obtained by grinding Ce‐TZP at a single speed and depth of cut. In the present work, grinding parameters were carefully chosen to induce varied stresses. Results show that Ce‐TZP exhibits cyclic transformation, not always, but only under certain favorable grinding conditions. Results are supported by XRD, optical microscopy, and dynamometric observations. Three stages of transformation, namely, a mechanical‐stress‐induced t to m, a frictional‐heat‐driven m to t, and a thermal‐quenching‐stress‐induced t to m, in sequence, are clearly identified.
Controlled Crack Shapes for Indentation Fracture of Soda–Lime Glass
Authors: Smith Stanley M. , Scattergood Ronald O.
Published: March 2005

Radial cracks for indented soda–lime glass aged in distilled water were highly elliptical because of truncation by lateral cracks. Indentation in silicone oil minimized radial/lateral crack interaction but still produced cracks having nominally constant ellipticity during bend testing. Analysis of applied stress/indentation crack length data using stress intensity factors based on half‐penny crack shape resulted in apparent R‐curve behavior and/or overestimation of the fracture toughness. Incorporation of elliptical shape factors eliminated the R‐curve behavior and reduced measured toughness to near the accepted value for soda–lime glass.
Thermodynamic Properties of Alkali Silicates: Heat Capacity of Li2SiO3 and Lithium‐Bearing Melts
Authors: Téqui Christophe , Grinspan Paul , Richet Pascal
Published: March 2005

The heat capacities of liquid Li2SiO3 and Li2Si3O7 have been determined through drop calorimetry measurements to complement available data on lithium, sodium, and potassium silicate melts. The composition and temperature dependences of the heat capacity depends specifically on the nature of the alkali element, indicating that the temperature‐induced structural changes that take place in the melts are specific. The properties of crystalline Li2SiO3 have also been determined above 298 K. The enthalpy of fusion at 1474 K is 71.3 ± 0.6 kJ/mol, in agreement with previous measurements. In contrast to other silicate compounds, and especially the isostructural crystal Na2SiO3, Li2SiO3 shows almost no premelting effects.
Supported Alumina Members by an in‐Situ Sol–Gel Method
Authors: Yu Chunzhe , Klein Lisa C.
Published: March 2005

Alumina membranes were prepared using a sol–gel process. Thin gel layers were grown onto porous alumina support tubes by using the permeation of water through the tube to control the rate of hydrolysis. Optimum coating conditions were found to be an ASB to 2‐propanol volume ratio of 1:25, coating times between 10 and 15 s, and partial drying times between 2.5 and 3 min, depending on whether the water was flowing in the tube or stored in the tube. The coatings remained crack‐free and adherent when fired to 800°C.
Heteroepitaxial Growth of Calcium Silicate Hydrate on Calcium Germanate Hydrate
Authors: Martin Roger I. , Brown Paul W.
Published: March 2005

The hydration of tricalcium silicate at 25°C was accelerated by seeding with 5 wt% tricalcium germanate. Based on heat evolution, seeding resulted in the elimination of the induction period. However, the shape of the hydration peak remained the same. Because tricalcium germanate hydrates first, the microstructure of the calcium silicate hydrate which subsequently forms is influenced by the calcium germanate hydrate morphology. Calcium silicate hydrate formed in the presence of calcium germanate hydrate exhibits the morphology typical of the latter. Acceleration of hydration and morphological variation indicate heteroepitaxial growth.
Composition and Mechanical Properties of rf‐Sputtered Amorphous Silicon Carbide Coating
Authors: Huang Jung‐Sheng , Ohland Matthew , Williams Wendell S.
Published: March 2005

Thin films of amorphous silicon carbide, synthesized by sputtering from Si single‐crystal and high‐purity graphite targets and deposited on Si crystals and fused silica, were studied with respect to their chemical composition and their influence on the mechanical properties of the substrates. Specifically, data were taken for microhardness, static friction, and sliding friction. The results suggest some improvement in these properties from amorphous SiC coatings, though breakup of very thin SiC films under load can be detrimental.
Effect of Pressing Method on Organic Burnout
Authors: Wang Jia
Published: March 2005

Sintered Y‐TZPs formed using cold isostatic compaction exhibit a lower sintered density and more porosity than ceramics formed using conventional uniaxial die compaction, although the isostatically pressed powder compact has a higher and more uniform green density. For the 3 wt% PEG1500‐doped zirconia powder, the sintered density decreases in a near‐linear manner with increasing isostatic pressing pressure. It was identified that the low sintered density and the poor microstructure were due to the incomplete burnout of PEG1500 at the low and intermediate temperatures when the powder compacts were heated at a rate of 3°C/min. The delayed organic burnout at temperatures close to and/or at the sintering temperature results in the formation of largely swollen intergranular pores.
Segregation of Magnesium to the Internal Surface of Residual Pores in Translucent Polycrystalline Alumina
Authors: Sung Changmo , Wei George C. , Ostreicher Kim J. , Rhodes William H.
Published: March 2005

For the first time direct evidence for Mg segregation to the surface of pores within translucent polycrystalline alumina grains has been found using energy dispersive X‐ray spectroscopy (EDXS) and convergent beam electron diffraction (CBED) in an analytical electron microscope (AEM) on a submicrometer scale. This supports the model that MgO dopant increases the surface diffusivity which, in turn, increases the pore mobility. The MgO dopant's role in retarding grain growth in combination with the enhanced pore mobility allows the achievement of nearly full density and translucency in alumina.
Effect of Firing Temperature on Bending Strength of Porcelains for Tableware
Authors: Kobayashi Yuichi , Ohira Osamu , Ohashi Yasuo , Kato Etsuro
Published: March 2005

Porcelains for tableware in the quartz–feldspar (sericite)–kaolin system were investigated to study the effect of firing temperature on the bending strength. The maximum bending strength of a body was attained at about 75°C below the temperature of complete sintering; therefore, its apparent porosity and the total porosity were almost 0% and 8.0%, respectively. Control of the finely dispersed, round, and isolated pores in the body was found to be necessary to attain strengthening of the body despite its relatively large porosity, and at the same time it was important that a large amount of fine quartz particles remain undissolved. Furthermore, a dense layer, formed close to the surface, was observed to strengthen the body more than that expected from its relative density when the body was fired above 1200°C.
Effect of Microstructure on the Creep of Siliconized Silicon Carbide
Authors: Hockey Bernard J. , Wiederhorn Sheldon M.
Published: March 2005

Mechanisms of creep deformation have been investigated for a commercial grade of siliconized carbide containing ≅33%/silicon. Microstructural studies of both tensile and compressive test specimens indicate dislocation damage generation in both the silicon carbide and the silicon phases as a consequence of creep. In the silicon carbide, dislocation damage was normally restricted to contact sites between the silicon carbide grains resulting from high intergranular contact stresses during deformation. Dislocation damage was also observed in the silicon. Although dislocation damage was heavy in some regions of the specimens, most regions of the specimens, most regions were free of dislocations. This result is consistent with the hypothesis that deformations occurs by the motion of clusters of grains during deformation. In tension, creep at high strain rates,
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1 × 10−8S−1, was accompanied by the formation of cavities at Si/SiC interfaces within the intergranular silicon phase. As cavities were not associated with dislocations, their growth was probably controlled by diffusional processes. Based on observations of the microstructure, a model of deformation is proposed to explain the fact that siliconized silicon carbide creeps faster in tension than in compression, at the same applied stress. The model is based on soil mechanics concepts. It is suggested that creep is controlled by intergranular friction between aggregate particles of the composite.
Measurement of Fiber/Matrix Interfacial Shear Stress at Elevated Temperatures
Authors: Burn Milivoj K.
Published: March 2005

An apparatus for measurement of the fiber/matrix interfacial shear stress at temperatures up to 1100° is described. Equipment was used to measure interfacial properties as a function of temperature in two ceramic‐matrix composites and one metal‐matrix composite. In the composites where the thermal expansion of the matrix was higher than that of the fiber, the interfacial shear stress decreased with temperature. The opposite trend was observed in a system with low matrix thermal expansion. The change of the interfacial shear stress with temperature of all the composites studied can be fully explained by considering the fiber/matrix expansion differences.
Rapid Method for the Preparation of 123 Superconductor Using Microwaves
Authors: Warrier Krishna Gopa Kumara , Varma Hari Krishna , Mani Themanam Veettil , Damodaran Alathoor Damodaran
Published: March 2005

A novel and rapid method to prepare 123 superconductor powder based on microwave processing is reported. A mixture of the nitrates of Y, Ba, and Cu in 123 stoichiometry when subjected to microwaves of frequency 2.45 GHz for 240 s resulted in an appreciable quantity of tetragonal 123 phase. Annealing for a period of 4 h at 940°C in flowing oxygen formed a superconductor having a Tc of 91 K. Sintered pellets of the powder formed by microwave processing have shown transport Jc of 105 A/cm2.
Effects of Particle Size on the Fusion of Soda–Lime–Silicate Glass Containing NaCl
Authors: Savard Michael E. , Speyer Robert F.
Published: March 2005

The coupled effects of particle size and 1 wt% NaCl additions on the sequence of melting reactions in a multicomponent system (sand–soda ash–calcite–dolomite–feldspar) were studied using data from DTA, DTGA, and XRD interactively. Glass batches varied in average particle size from 250 μm to finer than 45 μm. Milestone events in the fusion process of the coarse particle base glass were elucidated. The termination temperature of the last significant reaction associated with CO2 release was 35°C lower in the fine particle size batch than with the coarsest batch. Liquid‐phase formation at ∼523°C in the batch with 1 wt% NaCl occurred to an increasingly sizable extent with decreasing particle size. This contrasts with a similar effect at ∼630°C for a comparable batch without NaCl via eutectic melting between soda ash and dolomite. Sodium chloride additions significantly enhanced dissolution of CaO relic.
Study of Phase Formation in Spray Pyrolysis of ZrO2 and ZrO2─;Y2O3 Powders
Authors: Xiaming Dai , Qingfeng Li , Yuying Tang
Published: March 2005

The phase composition of fine ZrO2 and ZrO─Y2O3 powders prepared by the process of spray pyrolysis was detected using XRD. An interesting phenomenon has been observed. In this paper, the influence of the temperature and carrier gas flux on the phase composition of as‐prepared powders is described. The formation and transformation mechanisms of the powder phase in the process are also discussed.
Lubricated Rolling and Sliding Wear of a SiC‐Whisker‐Reinforced Si3N4 Composite against M2 Tool Steel
Authors: Liu Haiyan , Fine Morris E. , Cheng Herbert S. , Geiger Alan L.
Published: March 2005

Mineral oil lubricated rolling and sliding wear of SiC whisker (SiCw) reinforced Si3N4 composite and monolithic Si3N4 prepared identically against M2 tool steel were investigated using a cylinder‐on‐cylinder apparatus. Wear of this Si3N4 was higher than that of the composite. Wear of the steel against Si3N4 was also higher than that against the composite. Relatively larger scale microfracture occurred in the Si3N4 than in the composite; more pullout and microchipping of carbide particles were observed in the steel against Si3N4 than against the composite. Polishing of the worn surfaces of the steel occurred in both sliding and rolling tests. This was attributed to fine, hard wear debris circulating in the contact area. Spalling was observed in the steel sliding against Si3N4 but not in the steel sliding against the composite.
Improved Mechanical Material Property Definition for Predicting the Thermomechanical Behavior of Refractory Linings of Teeming Ladles
Authors: Schacht Charles A.
Published: March 2005

Ladle vessels continue to play a significant role in clean steelmaking. The incorporation of clean‐steel practices imposes severe process environments requiring use of stiffer, stronger refractory linings. As a result, concern has been expressed over the structural integrity of the ladle shell because of the large expansion loads imposed by the stronger linings. Appropriate refractory material properties are required in order to develop accurate and dependable analytical prediction of lining behavior. Analytical results of lining expansion forces using ultrasonic elastic modulus and static elastic modulus (from static compressive stress/strain data) are compared to strain gage measured lining expansion forces
Rise Velocities of Large Bubbles in Viscous Newtonian Liquids
Authors: Li Kang‐Wen K. , Schneider Alfred
Published: March 2005

Rise velocities of large bubbles in high‐viscosity oils and molten simulated waste glass were measured by a newly developed remote technique. Over a range of Reynolds numbers from 2 × 10−4 to 0.6, the experimental data for steady‐state bubble rise velocities agreed better with the Hadamard‐Rybcznski formula than with the Stokes formula.
Synthesis and Irreversibility of Oxygen Weight Loss in 80 K YBa2Cu4O8 Superconductor
Authors: Ravichandran Duraiswamy , Sridharan Varadarajan , Sivasankaran Swaminathan , Biswas Dharani Kanta , Nagarajan Tharmalingam , Balachandran Uthamalingam
Published: March 2005

Synthesis of YBa2Cu4O8 superconductor usually requires oxygen pressure greater than 20 MPa and very long heating schedules at high temperatures. Here we report synthesis of YBa2Cu4O8 superconductor by the standard solid‐state reaction between the precursors BaCu2O3 and Y2O3 in the presence of alkali nitrate. NaNO3, under ambient O2 pressure. The resulting sample showed zero resistance at 78 K. The presence of 124 was confirmed by high‐resolution X‐ray diffraction studies. Irreversibility of oxygen weight loss was studied by thermogravimetric analysis and differential thermal analysis.
Electrophoretic Deposition of Ferroelectric Barium Titanate Thick Films and Their Dielectric Properties
Authors: Nagai Masaharu , Yamashita Kimihiro , Umegaki Takao , Takuma Yasuhisa
Published: March 2005

Barium titanate thick films 10–70 μm thick were obtained using a unique electrophoretic deposition technique, which utilizes a mixed ethanol–acetylacetone suspension as the dispersive medium. The capacitance of the BaTiO3 films was measured as 25–70 nF, at temperatures of up to 200°C, giving a dielectric constant of 4000–12000 and dielectric loss (tan δ) of 0.13–0.51. In the sintered films thus deposited, (111) orientation was observed, and the degree of orientation was found to increase with decrease of the thickness of the films. In so‐oriented films, the Curie point was confirmed to be near 120°C.
Local Structure of Defects on Hydrogen‐ and Vacuum‐Reduced TiO2 Surfaces
Authors: Zhong Qian , Vohs John M. , Bonnell Dawn A.
Published: March 2005

A comparative study was performed on two TiO2 (110) surfaces: one annealed in vacuum, the other annealed in hydrogen. Local geometric and electronic structures were characterized using scanning tunneling microscopy and spectroscopy, in conjunction with conventional surface analytical techniques. Each surface exhibited a distinct pattern of electronic and geometric inhomogeneity. The origin of the defect structure resulting from the two treatments is discussed in terms of reduction mechanisms, defect formation thermodynamics, and chemical reactivity. The implication of local variation in the defect structure to the TiO2 interaction with reactive species is also addressed.
Mechanical Properties and Fracture Toughness of α‐Al2O3‐Platelet‐Reinforced Y‐PSZ Composites at Room and High Temperatures
Authors: Huang Xue‐Ning , Nicholson Patrick S.
Published: March 2005

YPSZ/Al2O3‐platelet composites were fabricated by conventional and tape‐casting techniques followed by sintering and HIPing. The room‐temperature fracture toughness increased, from 4.9 MPa·m1/2 for YPSZ, to 7.9 MPa·m1/2 (by the ISB method) for 25 mol% Al2O3 platelets with aspect ratio = 12. The room‐temperature fiexural strength decreased 21% and 30% (from 935 MPa for YPSZ) for platelet contents of 25 vol% and 40 vol%, respectively. Al2O3 platelets improved the high‐temperature strength (by 110% over YPSZ with 25 vol% platelets at 800°C and by 40% with 40 vol% platelets at 1300°C) and fracture toughness (by 90% at 800°C and 61% at 1300°C with 40 vol% platelets). An amorphous phase at the Al2O3‐platelet/YPSZ interface limited mechanical property improvement at 1300°C. The influence of platelet alignment was examined by tape casting and laminating the composites. Platelet alignment improved the sintered density by >1%dth, high‐temperature strength by 11% at 800°C and 16% at 1300°C, and fracture toughness by 33% at 1300°C, over random platelet orientation.
Compaction‐Induced Anisotropy in Internal Structure of Ceramic Powder
Authors: Shima Susumu , Saleh Mohamed A. E.
Published: March 2005

Biaxial compaction is carried out for two ceramic powders using a plane‐strain compaction device with various loading paths. It is thus shown that anisotropy is induced into a powder mass undergoing unequal biaxial stresses. A trial to evaluate some experimentally based parameters for the induced anisotropy is carried out. A model for the development of anisotropic powder structure is suggested, and expressions for a measure of the anisotropy are derived. Experimentally measured values of stresses and elastic strains are used to calculate the values of the anisotropic parameters. Anisotropy is also observed in the subsequent sintering behavior.
Molecular Dynamics Study of Na‐Si‐O‐N Oxynitride Glasses
Authors: Unuma Hidero , Kawamura Katsuyuki , Sawaguchi Naoya , Maekawa Hideki , Yokokawa Toshio
Published: March 2005

The structure and properties of Na‐Si‐O‐N oxynitride glasses have been studied by molecular dynamics calculations using a pair potential of the Busing approximation of the Born‐Mayer‐Huggins type. Nitrogen atoms bonded to one, two, and three silicon atoms coexist in the glass structure. The mean of the number of silicon atoms bonded to a nitrogen atom ranges from 2.4 to 2.1, decreasing with increasing Na2O content from 15 to 30 mol%. It has been assumed that nitrogen atoms bonded to two or fewer silicon atoms are formed when nitrogen atoms substitute for non‐bridging atoms. The bond angle ∠Si‐N‐Si exhibits a bimodal distribution around 105–135° and 140–170°, roughly corresponding to the nitrogen atoms bonded to three and two silicon atoms, respectively. The dependences of the density, the bulk thermal expansion, and the bulk modulus on the nitrogen content are consistent with those observed in real systems.
Sol‐Gel Processing of Neodymia–Silica Glass
Authors: Pope Edward J. A. , Mackenzie John D.
Published: March 2005

Neodymia‐doped glasses are currently commercially available for use in laser systems. Typically, these glasses are low‐softening‐temperature borates, phosphates, silicates, and fluorides. With its high softening temperature, high thermal shock resistance, and low nonlinear index of refraction, silica may be an ideal candidate for a neodymia bost glass for high‐power laser applications. Conventional glass processing methods, however, have thus far succeeded in incorporating only low levels of neodymia in silica. In this paper, the fabrication of neodymia–silica glasses with high neodymia content by the sol‐gel route is described. A possible structure for neodymia in silica is discussed.
Measurement of the Fracture Toughness of Ceramic Materials Using a Miniaturized Disk‐Bend Test
Authors: Zhang Jimin , Ardell Alan J.
Published: March 2005

The fracture toughness of several ceramic materials has been measured using a miniaturized disk‐bend test apparatus and methodology based on small disk‐shaped samples 3 mm in diameter. The method involves the Vickers indentation of specimens ranging in thickness from 300 to 700 μm, and testing them in a ring‐on‐ring bending mode. New experiments on a glass‐ceramic (GC) and Si3N4 have been performed to demonstrate the validity of the technique, supplementing the original work on ZnS. The fracture resistances of these materials increase with increasing crack length (R‐curve behavior). The data are analyzed using a specific model for the relationship between fracture resistance and crack length; this model enables the R‐curve behavior to be treated analytically, and the fracture resistance at “infinite” crack length to be evaluated using a straightforward graphical procedure. The resulting values of the fracture toughness for ZnS, GC, and Si3N4 are 0.74 ± 0.02, 2.18 ± 0.09, and 4.97 ± 0.07 MPa‐m1/2, respectively, which are all in very good agreement with values obtained from conventional fracture toughness tests on large specimens. The results verify the utility of the miniaturized diskbend method for measuring the fracture toughness of brittle materials.
High‐Temperature Failure Mechanisms of Hot‐Pressed Si3N4 and Si3N4/Si3N4‐Whisker‐Reinforced Composites
Authors: Chu Cha‐Yang , Singh Jitendra P. , Routbort Jules L.
Published: March 2005

The high‐temperature flexural strength of hot‐pressed silicon nitride (Si3N4) and Si3N4‐whisker‐reinforced Si3N4‐matrix composites has been measured at a crosshead speed of 1.27 mm/min and temperatures up to 1400°C in a nitrogen atmosphere. Load–displacement curves for whisker‐reinforced composites showed nonelastic fracture behavior at 1400°C. In contrast, such behavior was not observed for monolithic Si3N4. Microstructures of both materials have been examined by scanning and transmission electron microscopy. The results indicate that grain‐boundary sliding could be responsible for strength degradation in both monolithic Si3N4 and its whisker composites. The origin of the nonelastic failure behavior of Si3N4‐whisker composite at 1400°C was not positively identified but several possibilities are discussed.
Alumina Prepared from Freeze‐Dried Aluminum Isopropoxide
Authors: Chang Hsiao‐Lan , Lloyd Isabel K.
Published: March 2005

Preliminary experiments show that calcining freeze‐dried aluminum isopropoxide at 300°C produces sinterable amorphous alumina powders. The resultant powders are soft, contain some carbonaceous residue, and have large surface areas (∼100 m2/g). On a micrometer size scale, they are similar in morphology to sulfate‐derived materials although their surface areas are smaller (≤100 m2/g compared to ≥200 m2g for the sulfate‐derived powders). Powders calcined at higher temperatures contain less carbon but are also less sinterable.
Ion‐Beam‐Induced Densification of Zirconia Sol–Gel Thin Films
Authors: Levine Timothy E. , Keddie Joseph L. , Revesz Peter , Mayer James W. , Giannelis Emmanuel P.
Published: March 2005

Densification of sol–gel zirconia films was achieved using ion implantation instead of conventional heat treatment. Densification was observed with Xe+‐ion doses as low as 1014 ions/cm2. Ion implantation resulted in hydrogen and carbon losses as measured by forward recoil elastic spectrometry (FRES) and Rutherford backscattering spectrometry (RBS) using 12C(α,α)12C resonance, respectively. The density and chemical composition of the highest‐dose implanted sol–gel films were comparable with those obtained by high‐temperature sintering. The chemical and microstructural modifications in the films were attributed to both electronic interactions and nuclear collisions between the Xe+ ions and the target atoms.
Local Measurements of Temperature Changes Associated with the Stress‐Induced Tetragonal to Monoclinic Transformation in Zirconia
Authors: Sergo Valter , Schmid Chiara , Accardo Patrizio , Meriani Sergio
Published: March 2005

An experimental arrangement capable of monitoring temperature changes from 0.01 to 0.1 K has been successfully tested for registering the temperature evolution occurring during the tetragonal to monoclinic transformation of an alumina/ceria‐stabilized tetragonal zirconia polycrystal (Al2O3/Ce‐TZP). The arrangement is based on a very small thermistor. The data obtained have been used for evaluating the thermal diffusivity of the Al2O3/Ce‐TZP composites.
Nonisothermal Microwave Processing of Reaction‐Bonded Silicon Nitride
Authors: Thomas Jeffrey J. , Christensen Renee. J. , Johnson D. Lynn , Jennings Hamlin M.
Published: March 2005

The size and density of reaction‐bonded silicon nitride (RBSN) specimens are limited by the reduction in pore size and pore volume associated with the nitridation reaction. In particular, under conventional heating, pores at the surface of dense compacts close before the center has reacted fully. Microwave heating offers a unique advantage over conventional heating for the processing of RBSN. A temperature gradient can be maintained within the compact, which causes the reaction to occur preferentially in the interior. This increases the amount of silicon converted to Si3N4 because the center of compacts with a high green density finishes reacting before the porosity near the surface closes. This study follows the reaction process and shows that partially nitrided silicon compacts have composition gradients in the radial direction. Microwave processing also facilitates control of the reaction rate.
Effect of Stoichiometry on the Dielectric Properties and Life Performance of (Pb0.875Ba0.125) [(Mg1/3Nb2/3)0.5 (Zn1/3Nb2/3)0.3 Ti0.2]O3 Relaxor Dielectric Ceramic: Part I, Dielectric Properties
Authors: Kanai Hideyuki , Furukawa Osamu , Nakamura Shin‐ichi , Yamashita Yohachi
Published: March 2005

Effects of stoichiometry (A/B mole ratio, i.e., the ratio of elements on the A‐site to those on the B‐site in the perovskite structure) on the dielectric properties and microstructure of a partially A‐site substituted relaxor, (Pb0.875Ba0.125)A [(Mg1/3Nb2/3)0.5(Zn1/3Nb2/3)0.3 Ti0.2]BO3 were investigated in the A/B range between 0.95 and 1.05. Specimens, with A/B equal to or greater than 1.01, were sintered at lower temperatures than those with A/B equal to or less than 1.00. A maximum dielectric constant (Kmax) value of 13300 was obtained when A/B was 1.01. When A/B was less than 1.01, Kmax decreased, due to the formation of pyrochlore phase. Kmax also decreased with A/B values greater than 1.01, probably due to a grain boundary phase. Resistivity measurements did not suggest a stoichiometry dependence. However, breakdown voltage decreased with an increase in A/B, possibly due to the segregation of PbO with low dielectric constant at grain boundaries.
Predicting the Incidence of Voids in the Injection Molding of Thick Ceramic Sections
Authors: Zhang Tao , Evans Julian R. G.
Published: March 2005

A numerical method is used to calculate the temperature distributions and specific volumes of finite elements in a short cylindrical molding in order to find the time at which the pressure in the molten core reaches zero. The criterion for the formation of a void is that this event should precede the time needed for the center of the cylinder to solidify. The results of the prediction compare favorably with experiment. Further calculations are made in order to show the effects of material and machine parameters on the incidence of voids.
Mechanical Behavior of Alumina–Silicon Carbide „Nanocomposites”
Authors: Zhao Junhong , Stearns Laura C. , Harmer Martin P. , Chan Helen M. , Miller Gary A. , Cook Robert F.
Published: March 2005

The fracture behavior of Al2O3 containing 5 vol% 0.15μm SiC particles was investigated using indentation techniques. A significant increase in strength was achieved by the addition of SiC particles to the base Al2O3. Specifically, the strength increased from 560 MPa for Al2O3 to 760 MPa for the composite samples (average values for unindented hotpressed bars tested in four‐point bending). After annealing for 2 h at 1300°C, the average strength of the composite samples increased to about 1000 MPa. Toughness was estimated using indentation‐strength data. While there was a slight increase in toughness, the increase was not sufficient to account for the increase in the unindented strength on SiC particle addition. It is suggested that the observed strengthening and apparent toughening were due to a machining‐induced compressive surface stress.
Batch Rotary Kiln Calcination of YBaCuO Precursor Powders
Authors: Shelukar Suhas D. , Sundar H. G. Keshava , Semiat Raphael , Richardson James T. , Luss Dan
Published: March 2005

Precursor powders of Y1Ba2Cu3O6+x (123) derived from spray roasting were calcined in a batch rotary kiln. The optimum conditions were 15 min in air at temperatures between 920° and 940°C for 1.5 vol% solid loading. Pure 123 was formed in a single calcination step from homogeneous, micrometer‐sized precursor material containing Y2O3, CuO, and BaCO3. Rotation speed did not affect the product quality, but longer calcination times are needed at higher loadings. Product agglomeration increased with increasing loading and decreasing rotation speed. In nitrogen, 123 decomposed so that a pure product could not be obtained. The BaCO3 decomposition is the rate‐limiting step in the calcination. The presence of Ba(NO3)2 in the precursor led to formation of intermediate phases.
Testing of High‐Strength Ceramics with the Split Hopkinson Pressure Bar
Authors: Staehler James M. , Predebon William W. , Pletka Bruce J. , Lankford James
Published: March 2005

The split Hopkinson pressure bar was used to study the failure of a high‐strength alumina at strain rates on the order of 103 s‐1. There appears to be a critical strain rate above which the traditional method of using the transmitter bar signal to calculate the stress in the specimen is no longer valid. To compute the correct stress in the specimen it was necessary to use the strain signal from a gage mounted directly on the specimen.
Effects of SiF4 and NH3 Concentrations on the Low‐Pressure CVD of Polycrystalline α‐Si3N4
Authors: Lee Woo Y. , Strife James R.
Published: March 2005

The effects of SiF4 and NH4 concentrations on the growth rate of polycrystalline α‐Si3N4 were examined in the pressure range of 1.5 to 10.0 torr (1 torr ∽ 1.33 × 102 Pa). At low SiF4 partial pressures, the growth rate increased almost linearly with the SiF4 partial pressure. The relationship appeared to become zeroth‐order at high SiF4 partial pressures. Under excess NH3 conditions, the growth rate was not significantly affected in any consistent manner by changes in the NH3 partial pressure. A surface kinetic rate mechanism which qualitatively described the observed deposition behavior was postulated and discussed.
Effects of Sintering Atmosphere on Densification Behavior and Piezoelectric Properties of Pb(Ni1/3Nb2/3)O3–PbZrO3 Ceramics
Authors: Moon Jong H. , Jang Hyun M.
Published: March 2005

Densification of polycrystalline Pb(Ni1/3Nb2/3)O3–PbTiO3–PbZrO3 (PNN–PT–PZ) specimens was enhanced as the partial pressure of O2 in the sintering atmosphere was increased. This observation was attributed to the increase in the internal pressure of a closed pore due to the thermal decomposition of PbO at a low partial pressure of O2. The relative dielectric permittivity (εr), d33, kp, and grain size of sintered specimens were also increased as the partial pressure of O2 in the sintering atmosphere was increased. The observed dependence of piezoelectric properties on the partial pressure of O2 was discussed in terms of the enhanced formation of the A‐site vacancy (V″Pb) or the suppression of the B‐site defect (V¨O) as the oxygen potential increased.
Flexural Stress Rupture and Creep of Selected Commercial Silicon Nitrides
Authors: Sanders William A. , Groseclose Lance E.
Published: March 2005

Four commercial Si3N4 compositions were compared with regard to flexural stress rupture and creep in ambient air as functions of temperature from 1100° to 1400°C and stress from 200 to 350 MPa. One Si3N4, SN252, was found to be more resistant to time‐dependent deformation in both stepped‐temperature stress rupture tests and creep tests than a very similar Si3N4 composition and two other dissimilar Si3N4 compositions. Materials were compared on the bases of percent final strains, creep rates, and posttest microscope examinations. The latter revealed tensile face transverse cracking, and slow crack growth. The superior behavior of the SN252 Si3N4 was related to its microstructure.
Mechanical Properties of Unidirectionally Oriented SiC‐Whisker‐Reinforced Si3N4 Fabricated by Extrusion and Hot‐Pressing
Authors: Goto Yasuhiro , Tsuge Akihiko
Published: March 2005

SiC‐whisker‐reinforced Si3N4 was fabricated by extrusion and hot‐pressing. A unidirectional alignment of the whiskers was achieved through sheet forming by extrusion. The degree of whisker orientation changed with the thickness of the green sheets. Unidirectionally oriented whiskers increased fracture strength and toughness compared to samples with more randomly oriented whiskers. Anisotropy of fracture strength was observed. Bridging by whiskers impeded crack propagation when the whisker orientation was perpendicular to the crack plane.
Microcomposite and Nanocomposite Structures from Chemical Vapor Deposition in the Silicon–Titanium–Carbon System
Authors: Touanen Muriel , Teyssandier Francis , Ducarroir Michel , Maline Mohammed , Hillel Roger , Derep Jean Luc
Published: March 2005

Microcomposite and nanocomposite structures composed of SiC‐TiC and C have been prepared by chemical vapor deposition at atmospheric pressure (APCVD) from an initial gaseous mixture with the composition C4H10‐SiH2Cl2‐TiCl4‐H2. Transmission electron microscopy reveals that deposits with a nanocomposite structure consist of a network of 10‐nm‐thick needles surrounded by small areas of amorphous carbon. The relative amounts of TiC and SiC as well as the microstructure depend on the SiH2Cl2 and TiCl4 content in the initial gas‐phase mixture. The variations of composition of the deposits are in good accordance with the thermodynamic calculations. Amorphous carbon is always present in the deposits. This amount can be lowered to 1 at.% at low deposition temperatures but, at such a concentration, still has a great influence on microhardness. The variation of the preferred orientation of crystals is also discussed with respect to the composition of the samples and the deposition temperature.
Preparation of Stoichiometric Fine Lead Barium Titanate Powder
Authors: Saegusa Kunio , Rhine Wendell E. , Bowen H. Kent
Published: March 2005

Lead barium titanate powder with 0.03–0.15 μm particle sizes was prepared from lead barium titanyl oxalate which was previously prepared by reacting high‐purity ammonium titanyl oxalate with barium and lead acetate. The critical factor in preparing the barium titanyl oxalate was the reaction time. It was necessary to allow 2–4 h to synthesize the oxalate to get a single‐phase barium titanate. The critical factors in preparing the lead titanyl oxalate were pH and the concentration of the solution. It was necessary to adjust the pH to around 0.5 and the concentration to <0.08M. When lead barium titanyl oxalate is prepared, low pH, low concentration, and a long reaction time are necessary.