bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Mixed Cobalt‐Molybdenum Oxides Prepared by Evaporative Decomposition of Solutions
Authors: Rossetti George A. , Burger Joseph L. , Sisson Richard D.
Published: March 2005

The synthesis of Co‐Mo oxides by the evaporative decomposition of solutions method has been investigated. The oxides were prepared from atomized metal salt solution precursors decomposed in less than 3 s in air at 700°C. The materials obtained were primarily hollow spheres (1 to 6 μm) composed of fine (100 to 500 Å (10 to 50 nm)) crystallites. CoO, Co2Mo3O8, and CoMoO4 were the major crystalline phases identified. The Co‐Mo oxides were depleted in Mo relative to the precursor solutions and could not be prepared with Co/Mo atom ratios less than unity. A schematic Co‐Mo‐O isothermal section was constructed to explain the compositions, morphologies, and phase distributions observed for materials having different Co/Mo ratios. The loss in Mo was explained by the high vapor pressure of MoO3.
Mechanical Properties of Alumina/Silicon Carbide Whisker Composites
Authors: Lio Satoshi , Watanabe Masakazu , Matsubara Masaru , Matsuo Yasushi
Published: March 2005

The improvement of mechanical properties of Al2O3/SiC whisker composites has been studied with emphasis on the effects of the whisker content and of the hot‐pressing temperature. Mechanical properties such as fracture toughness and fracture strength increased with increasing whisker content up to 40 wt%. In the case of the high SiC whisker content of 40 wt%, fracture toughness of the sample hot‐pressed at 1900° decreased significantly, in spite of densification, compared with one hot‐pressed at 1850°. Fracture toughness strongly depended on the microstructure, especially the distribution of SiC whiskers rather than the grain size of the Al2O3 matrix.
Effect of Residual Surface Stress on the Strenght Distribution of Brittle Materials
Authors: TOjek Monica M. , Green David J.
Published: March 2005

The introduction of residual surface stresses into a material can change the strength distribution simply due to variability in the stress intensity factor of surface cracks. This variability arises from the distribution in surface (critical) crack lengths. A fracture mechanics approach was used to determine the influence of surface compression on the average strength and the standard deviation of the strength distribution. The strengths of the stress‐free samples were assumed to fit a twoparameter Weibull distribution, and the increases in strength resulting from the surface compression were determined using fracture mechanics. It was determined from the analysis that the standard deviation/average strength ratio (coefficient of variation) initially increases, passes through a maximum, and ultimately reaches a plateau value below the initial value, as one increases the depth of surface compression. The maximum increase in the strength scatter occurs when the depth of the surface compression is approximately equal to the characteristic crack size. These changes were found to be dependent on the magnitude of the surface stress, as well as the characteristic strength, Weibull modulus, and fracture toughness of the stress‐free material.
Nucleation in ZBLAN Glasses
Authors: Leede Gerard de , Waal Henk de , Hakkens Frank
Published: March 2005

Nucleation rates were measured in a ZrF4–BaF2–NaF–LaF3–AlF3 glass (ZBLAN) using an optical technique. The results were compared with a similar glass having a slightly different composition. The difference in the nucleation rate is explained by classical nucleation theory using calculated free‐energy differences between the ZBLAN liquid and the BaZrF6 crystal, which is found as the precipitating phase.
Mullite/Alumina Particulate Composites by Infiltration Processing
Authors: Marple Basil R. , Green David J.
Published: March 2005

A method has been developed for incorporating mullite into alumina by infiltrating an alumina preform with a prehydrolyzed ethyl silicate solution, followed by heating to decompose the infiltrant, form mullite, and densify the mullite/alumina composite. It has been found that the major portion of the weight loss of gelled ethyl silicate sols occurs in the 250° to 350°C range. Mullite formed in infiltrated bodies at ∼1475°C and specimens containing 12 to 15 vol% mullite reached 98.5% of the theoretical density after heating for 2 h at 1650°C. The mullite was found to be well dispersed within the alumina matrix and its presence decreased grain growth in the alumina by more than an order of magnitude.
Characterization of Gold—Aluminum Nitride and Gold—Silicon Carbide Interfaces
Authors: Zdaniewski Wieslaw A. , Houser Cheryl A.
Published: March 2005

Aluminum nitride and silicon carbide substrates were screen‐printed with fritless gold and fired at 850°C in air. Interfacial diffusion zones up to 7 αm thick were observed, in which the concentrations of Au, Na impurities, and combined O varied together. Secondary ion mass and photoelectron spectroscopy revealed oxidized Al in the gold conductor supported by AIN. It is suggested that enhanced oxidation accompanies the diffusion of Au into the ceramics.
Nucleation of Flocs in Dilute Colloidal Suspensions
Authors: Agrawal Dinesh C. , Raj Rishi , Cohen Claude
Published: March 2005

In contrast to earlier theories which assume that coagulation of particles in dilute colloidal suspensions occurs by random collisions, we present evidence that coagulation is limited by a nucleation and growth phenomenon, typical of a phase transformation. We show that suspensions of well‐dispersed particles, which are almost indefinitely stable, flocculate rapidly when seeded with pregrown flocs. The nucleation argument is supported further by the observation that flocs which are grown at low ζ potential, where the particle strongly attract, do not peptize when the pH is changed to high ζ potential, where the attraction is weak. The experiments were carried out with aqueous dispersions of alumina particles. The time‐dependent change in cluster sizes was measured by in situ photon correlation spectroscopy. The observations raise the question of agglomeration as a phase transformation, involving a change in entropy, when the system moves from a dispersed to a flocculated state.
Lattice Diffusion Kinetics in Undoped and Impurity‐Doped Sapphire (α‐Al2O3): A Dislocation Loop Annealing Study
Authors: Lagerlof K. Peter D. , Mitchell Terence E. , Heuer Arthur H.
Published: March 2005

The shrinkage rates of small prismatic dislocation loops in thin foils of sapphire (α‐Al2O3) have been determined using transmission electron microscopy; between observations the thin foils were annealed ex situ in the temperature range 1200° < T < 1500°C. The shrinkage rates of individual loops were used to determine the diffusivity of the rate‐controlling species, assumed to be oxygen. The loop annealing results agree well with an extrapolation of oxygen self‐diffusion data for undoped crystals obtained by conventional tracer techniques in the temperature range 1400° < T < 1900°C. The oxygen diffusion rate was slower in 600‐ppm‐Ti‐doped and faster in 250‐ppm‐Mg‐doped crystals compared to undoped sapphire, consistent at first sight with a “classical” picture of diffusion via oxygen vacancies in α‐Al2O3. However, consideration of the experimental activation energies in terms of the concentration of free point defects suggests that substantial modification of the classical picture may be necessary.
Aluminum in Rutile [TiO2]: Characterization by Single‐Crystal and Magic‐Angle‐Spinning Nuclear Magnetic Resonance
Authors: Stebbins Jonathan F. , Farnan Ian , Klabunde Ulrich
Published: March 2005

Using both single‐crystal and magicangle‐spinning (MAS) 27Al nuclear magnetic resonance (NMR) spectroscopy, we have characterized the most abundant site for Al dissolved in rutile. The single‐crystal spectrum of the dissolved Al indicates that most Al cations are isolated from each other and from paramagnetic defects, and they are in sites with only two orientations in the crystal. Interstitial octahedra, pairs of Al3+, and “shear planes” can thus be ruled out as the major Al sites, and substitution of Al in Ti sites is suggested. Spectra collected at temperatures up to 600°C show the onset of structural mobility or cation exchange. MAS NMR gives unique values of the quadrupolar coupling constant and asymmetry patameter of the Al site as 2.8 MHz and 1.0, respectively. Combination of both techniques permits the nature and relative proportions of both dissolved and exsolved Al to be determined, even when the latter dominates.
Doping of Pb Ions into Bi‐Sr‐Ca‐Cu‐O Thin Films from PbO Vapor
Authors: Nagata Hirotoshi , Hashiguchi Shoichi , Min Eungi
Published: March 2005

Thin films showing zero resistivity at 103 K were prepared by annealing a Bi‐Sr‐Ca‐Cu‐O film in PbO vapor. Electron probe microanalysis indicated that Pb ions were doped into the film materials up to the amount of maximum solubility. However, experiments on Bi‐Sr‐Ca‐Cu‐O bulks showed that excess amounts of Pb ions formed Ca2PbO4 with decomposition of superconducting phases.
Infant Mortality, Freaks, and Wear‐Out: Application of Modern Semiconductor Reliability Methods to Ceramic Multilayer Capacitors
Authors: Kurtz Stewart K. , Levinson Solomon , Shi Dexiang
Published: March 2005

An overview of the methods of modern semiconductor reliability and accelerated life testing based on the lognormal distribution is given, Bimodal distributions due to the presence of freak failure populations are also discussed, along with the Fowlkes test for a bimodal lognormal distribution. A novel analysis of recent published results on capacitor reliability is given, based on the known properties of the lognormal and Weibull distributions as well as recent experience in their application to semiconductor device reliability. For test periods of 168 and 1000 h, estimates of the required voltages and temperature stresses as well as sample sizes are made to ensure a hazard rate of less than 100 FIT (failures per unit time) per capacitor after 40 yr of operation. The results show that the customary accelerated test at twice the rated voltage and 125°C for 1000 h, is insufficient. Comparison with data from a recent highly accelerated life test (HALT) indicates that the HALT procedures may be useful as an effective screen. Bimodal failure distributions are shown to be due to the presence of freak (early failure) populations of about 10%.
Electromechanical Resonances in Ceramic Capacitors and Their Use for Rapid Nondestructive Testing
Authors: Boser Otmar , Kellawon Paulette , Geyer Richard
Published: March 2005

A rapid nondestructive test method for ceramic multilayer capacitors made from piezoelectric materials such as barium titanate or lead‐containing materials is described and evaluated. The test method is based on the internal excitation of standing acoustic waves in the capacitors. The standing waves are severely dampened by defects such as indentations and delaminations or warped electrodes. An undampened resonance is a good indication of a defect‐free ceramic multilayer capacitor. This finding was used in a nondestructive test setup to evaluate about 1000 capacitors. Through metallographic (cross‐section) examination, a sorting accuracy of 2% false accepts and 8% false rejects was determined for the highspeed test setup. The test setup has the potential to test over 100 000 capacitors an hour. [Key words: capacitors, nondestructive testing, multilayers, mechanical properties, electrical properties.]
Microstructural Aspects of the Fracture of Hardened Cement Paste
Authors: Struble Leslie J. , Stutzman Paul E. , Fuller Edwin R.
Published: March 2005

For microstructural studies, samples of hardened cement paste were fractured, impregnated with epoxy using a procedure that does not produce drying cracks, and examined using a scanning electron microscope. Cracks generally appear to pass around unhydrated cement grains and along calcium hydroxide cleavage planes. Cracks are often branched or forked at their tips, and a few microcracks are sometimes observed just ahead of the tips. Perhaps more importantly, the crack path is often offset, with the interjacent material between these offset crack segments forming a bridge across the crack. Even though the crack plane is most likely continuous in three dimensions, these bridging materials may provide local regions of ligamentary tractions across the crack, thereby providing a plausible explanation for the rising fracture resistance (R ‐curve behavior) of hardened cement paste.
Formation, Defect Structure, and Electrical Properties of La3+ ‐Doped M‐Type Calcium Ferrite Prepared by Coprecipitation
Authors: Fang Tsang‐Tse , Lee Kuo‐Tong
Published: March 2005

The reaction process and the optimum preparation conditions of the M‐type calcium ferrite by the chemically coprecipitated method were studied using differential thermal, thermogravimetric, and X‐ray analyses. It is found that the formation mechanism using the coprecipitated method is the same as that of the solid‐state reaction, and the precursor CaO·2Fe2O3 cannot be avoided, but it could be formed at lower temperature. The defect structure based on the replacement of Ca2+ by La3+, the charge compensation by Fe2+, and release of oxygen is supported by the DTA/TGA and conductivity data. The conductivity is suggested to occur through a hopping mechanism. The estimated values of the activation energy based on the small‐polaron conduction are 0.34 to 0.44 eV in the high‐temperature region and 0.029 to 0.049 eV in the low‐temperature region. The preexponential factor depends exponentially on the fraction of the M phase in the specimen.
Preparation and Characterization of Superconducting B1‐Type Mo1‐xNbxN Thin Films
Authors: Lai Gao‐Chao , Takahashi Masao , Nobugai Kohji , Kanamaru Fumikazu
Published: March 2005

Solid‐solution thin films, Mo1−xNbxN, with B1 (NaCl) structure have been deposited on substrates at 450°C by reactive sputtering of composite targets with Mo and Nb metals in an equimolar Ar and N2 gas mixture. The lattice parameter of the solid solution increased linearly with an increase of Nb content, x. The superconducting transition temperature, Tc, of the Mo‐rich films (x≦ 0.12) was around 6 K, which was lower than that expected from theoretical prediction. The residual resistivity ratio, r=ρ(300 K)/ρ(20 K), of the films varied with x, and a minimum value of r was observed in the vicinity of x= 0.5.
Influence of Crystalline Secondary Phases on the Densification Behavior of Reaction‐Bonded Silicon Nitride During Postsintering under Increased Nitrogen Pressure
Authors: Kleebe Hans‐Joachim , Ziegler Günter
Published: March 2005

The influence of reaction‐bonded silicon nitride (RBSN) characteristics, especially the crystalline secondary phases formed during the nitridation process, on the densification behavior of RBSN and the resulting microstructure of the sintered material during postsintering under increased nitrogen pressure is discussed. The type and amount of the secondary phases are controlled by the chemical characteristics of the Si starting powder and the additive composition. Three different commercially available Si powders which reveal particular differences in the Fe and Al content were investigated, and a correlation between the microstructural characteristics of RBSN and of the postsintered materials is presented. It is shown that besides micropore size distribution the crystalline secondary phases play an important part in the densification behavior during postsintering and the resulting microstructure of postsintered reaction‐bonded silicon nitride.
Correlation between Grain Size and Thermal Expansion for Aluminum Titanate Materials
Authors: Parker Fred J. , Rice Roy W.
Published: March 2005

Al2TiO5 materials were sintered under different conditions to produce different grain sizes. The resultant microcracked materials exhibited a range of bulk thermal expansions which showed a strong correlation with average grain size. An Al2TiO5 average grain size of 3 to 4 μm was the minimum at which the size and population of microcracks effectively reduced the apparent thermal expansion of the polycrystalline material. Further increases in grain size resulted in a rapid drop in the bulk thermal expansion, followed by diminishing decreases with further increases in grain size. Small amounts of phase stabilizers (<2.1 wt% MgO or Fe2O3) or limited mullite additions in mullite—aluminum titanate composites had no significant effect on this correlation.
Microstructure and Fracture Toughness of Yttria‐Daped Tetragonal Zirconia Polycrystal/Mullite Composites Prepared by an in Situ Method
Authors: Okada Kiyoshi , Ōtsuka Nozomu , Brook Richard J. , Moulson A. J.
Published: March 2005

Yttria‐daped tetragonal zirconia polycrystal (Y‐TZP)/ mullite composites were prepared by three methods: in situ whisker growth (IS), physical mixing (PM) of zirconia powder and mullite whiskers, and reaction sintering (RS). Microstructures and fracture toughness values were compared. All the composites with 15 vol% of mullite could be densified to more than 95% relative density by firing at 1500° to 1500°C for 10 h. The fracture toughness of the composites as measured by the indentation method showed a clear enhancement compared with that of pure Y‐TZP; the ranking was Y‐TZP ≦ RS composite < PM composite < IS composite. Enhancement of the fracture toughness in composites was found to relte strongly to the aspect ratio of mullite particles.
Electrical Conductivity of Cadmium Oxide—Antimony Oxide System Ceramics
Authors: Li Biaorong , Zhang Jingli
Published: March 2005

The electrical conductivity of Cd2Sb2O6.8 and Cd6Sb2O10 semiconductive ceramics was examined from −78° to 1000°C under oxygen, nitrogen, argon, air, methane, and CO /CO2 atmospheres. The existing form of excess CdO in the crystal lattice structure, the relationship between oxygen vacancies and the atmosphere, the conduction mechanism in different temperature regions, the associated defect structure, and phase‐transition properties were analyzed. The activation energy and mobility of the carriers were calculated.
Novel Solution‐Soaking Method for Adding Dopants to YBa2Cu3O7−x to Achieve Higher Sintered Densities
Authors: Umadevi Pottail , Nair K. Ravindran , Damodaran Alathur D.
Published: March 2005

YBa2Cu3O7−x was doped with various metal ions by a new technique in which a pellet (after binder burnout) was soaked in a solution containing the appropriate ions and then dried. The sintered density of the treated pellets depended on the dopant in the solution, and in many cases it was much higher than that obtained for pure YBa2Cu3O7−x (93% to 96% as compared with 85% to 90%). A study of the microstructure revealed that, in those cases where higher sintered densities were obtained, the grain size was much smaller. The grain morphology, however, did not change. It is likely that the high concentration of dopant adsorbed on the grain surface during solution soaking enhanced the rate of sintering.
Vickers Crack Nucleation of Glass Sheets Coated by Thin Silica Gel Layers
Authors: Maschio Roberto Dal , Pegoretti Alessandro , Rizzo Caterina , Soraru Gian D. , Carturan Giovanni
Published: March 2005

SiO2 gel layers of different thickness have been deposited on glass sheets by dipping from gelling solutions with different concentrations of silicon alkoxide. Some mechanical properties of the coated samples such as hardness (H), elastic modulus (E), crack formation tendency, and tensile stress in the film (σ) have been measured by microindentation techniques and slide deflection. SiO2 films deposited from more dilute solutions had lower H, E, and σ values, accounting for the observed higher resistance to crack nucleation in comparison with that found for samples prepared from more concentrated solutions.
Effect of MgO Addition on the Microstructure Development of 3 mol% Y2O3—ZrO2
Authors: Lu Hong‐Yang , Bow Jong‐Shing
Published: March 2005

MgO addition to 3 mol% Y2O3–ZrO2 resulted in enhanced densification at 1350°C by a liquid‐phase sintering mechanism. This liquid phase resulted from reaction of MgO with trace impurities of CaO and SiO2 in the starting powder. The bimodal grain structure thus obtained was characterized by large cubic ZrO2 grains with tetragonal ZrO2 precipitates, which were surrounded by either small tetragonal grains or monoclinic grains, depending on the heat‐treatment schedule.
Influence of Temperature Gradients on Sintering: Experimental Tests of a Theory
Authors: Beruto Dario , Botter Rodolfo , Searcy Alan W.
Published: March 2005

The H2O‐catalyzed sintering of MgO in temperature gradients between 1303 and 1233 K is compared to sintering of isothermal samples. Both the changes in sample dimensions in planes normal to the temperature gradients and the increases in density for a fixed sintering time are greater than predicted on the assumption that densification in a temperature gradient is a function only of each local temperature in the gradient. Under the conditions used, neither vapor transport nor transport through a liquid phase is important. The results, therefore, support a recent prediction that temperature gradients supplement surface energy changes in driving sintering and related processes not only by vapor transport, as expected from earlier studies, but also by a surface, grainboundary, or bulk diffusion path.
Properties of (Y)ZrO2–Al2O3 and (Y)ZrO2–Al2O3–(Ti or Si)C Composites
Authors: Fukuhara Mikio
Published: March 2005

The effect of Al2O3 and (Ti or Si)C additions on various properties of a (Y)TZP (yttria‐stabilized tetragonal zirconia polycrystal)–Al2O3–(Ti or Si)C ternary composite ceramic were investigated for developing a zirconia‐based ceramic stronger than SiC at high temperatures. Adding Al2O3 to (Y)TZP improved transverse rupture strength and hardness but decreased fracture toughness. This binary composite ceramic revealed a rapid loss of strength with increasing temperature. Adding TiC to the binary ceramic suppressed the decrease in strength at temperatures above 1573 K. The residual tensile stress induced by the differential thermal expansion between ZrO2 and TiC therefore must have inhibited the t‐ →m‐ZrO2 martensitic transformation. It was concluded that a continuous skeleton of TiC prevented grain‐boundary sliding between ZrO2 and Al2O3. In contrast, for the ternary material containing β‐SiC in place of TiC, the strength decreased substantially with increasing temperature because of incomplete formation of the SiC skeleton.
Strengths of Ceramic Fibers at Elevated Temperatures
Authors: Pysher Douglas J. , Goretta Kenneth C. , Hodder Robert S. , Tressler Richard E.
Published: March 2005

Tensile strengths were measured and Young's moduli were estimated for two SiC‐based and three oxide ceramic fibers for temperatures from 25° to 1400°C. The SiC‐based fibers were stronger but less stiff than the oxide fibers at room temperature and retained more of both strength and stiffness to high temperatures. High‐temperature strengths of the SiC‐based fibers were limited by internal void formation and oxidation; those of the oxide fibers were limited by softening of an intergranular glassy phase.
Bonding of Zirconia and Lanthanum Chromite by Co‐firing
Authors: Smith David S. , Sayer Michael , Roeder P. , Smith A. , Odier P.
Published: March 2005

Zirconia has been bonded to lanthanum chromite by co‐firing. The ceramic bodies are joined during sintering with an applied pressure of less than 0.1 MPa. This technique facilitates the formation of a junction phase which involves the impurity silica. During firing at 1500°C, silica is driven from zirconia and lanthanum chromite to the junction region, where it combines with calcia as well as other components to form a liquid phase. The liquid phase relaxes stresses due to differential shrinkage of the two bodies and, on cooling, solidifies, thus bonding lanthanum chromite to zirconia.
Effects of Temperature and Whisker Volume Fraction on Average Residual Thermal Strains in a SiC/Al2O3 Composite
Authors: Majumdar Saurin , Kupperman David
Published: March 2005

Residual thermal strains in a SiC‐whisker‐reinforced/Al2O3‐matrix composite were measured as functions of temperature and volume fraction of whiskers by means of a neutron diffraction technique. The residual strains in both phases decrease with increasing temperature. At room temperature, the residual strains in the whiskers decrease with increasing whisker volume fraction, but the tensile residual strains in the matrix increase. The results agree well with those predicted by an analytical method.
Grain‐Size Dependence of Electrically Induced Microcracking in Ferroelectric Ceramics
Authors: Chung Hun‐Taeg , Shin Byoung‐Chul , Kim Ho‐Gi
Published: March 2005

A high dc field (1 and 3 kV / mm) was applied to BaTiO3 and PZT ceramics, electrically induced microcracks occur at the grain boundaries and propagate into the grains. The number of cracks becomes larger with increasing grain size and poling field.
Pyrolysis of Preceramic Polymers in Ammonia: Preparation of Silicon Nitride Powders
Authors: Burns Gary T. , Chandra Grish
Published: March 2005

The pyrolysis of cross‐linked polycarbosilanes, polysilanes and polysilazanes in an ammonia atmosphere to 1473 K yields amorphous, low‐carbon silicon nitride powders. The efficacy of carbon removal is independent of the polymer's structure or functionality but is partially dependent on the initial cross‐linking temperature. The amorphous silicon nitride powders partially crystallize to α‐Si3N4 by 1773 K.
Application of the Stepwise‐Regression Method in Calculating High‐Temperature Ceramic Phases
Authors: Wancheng Zhou , Litong Zhang , Hengzhi Fu
Published: March 2005

Phase calculation for nonequilibrium multicomponent systems is attempted using the stepwise‐regression method. The experimental data (the amount and composition of glassy phase in a system of Al2O3–SiO2 ceramics as functions of the state of the original materials, the firing temperature, and the composition of the samples) are treated by the proposed method. The equations obtained are accurate in estimating the amount and composition of glassy phases in the system, showing that the stepwise‐regression method is effective in phase calculation.
Piezoresistivity in Semiconducting Positive Temperature Coefficient Ceramics
Authors: Amin Ahmed
Published: March 2005

The experimental and theoretical aspects of piezoresistivity in semiconducting, positive temperature coefficient (PTC) of resistivity ceramics will be reviewed. Emphasis will be placed on their potential application in sensor technology. Future material and modeling challenges are highlighted.
Dimensionless Load—Displacement Relation and Its Application to Crack Propagation Problems
Authors: Sakai Mototsugu , Inagaki Michio
Published: March 2005

The dimensionless load () and load‐point displacement (û) are introduced to discuss crack propagation problems. The −ũ relation for the case of equilibrium crack propagation in any linear elastic material is demonstrated to lie on a single universal fracture curve independent of the material. The concept of the universal −ũ relation is extended to yield a direct and simple form of the dimensionless total energy (eq(α)) which is applicable to many types of instability problems for crack extension, when the shape factor (Y) of the specimen is known as a function of crack length (a). In addition, by applying the deviation of the experimentally observed —ũ curve and the theoretical universal fracture curve, the evaluation of the nonlinear fracture resistance parameter of a polycrystalline graphite material, as an example, was demonstrated.
Effect of TiO2 on the Sintering and the Electrical Conductivity of Cr2O3
Authors: Nagai Hiroshi , Ohbayashi Ken
Published: March 2005

The effect of TiO2 addition on the sintering behavior and the electrical conductivity of Cr2O3 was studied at 1473 K at various oxygen pressures, 105 > Po2 > 10−10 Pa. TiO2 addition of more than 1 wt% drastically enhanced the sintering of Cr2O3 in the oxygen pressure range 10−3 Pa > Po2 because of the marked increase in the concentration of Vmcr and Vö by introduction of tetravalent titanium ions into Cr2O3. The sintering rate decreased slightly with decreasing Po2 below 10−5 Pa, where the concentration of tetravalent titanium ions is low. The Po2 dependence of the electrical conductivity of Cr2O3 was also drastically altered by TiO2 addition. Undoped Cr2O3 had a p‐type conductivity in the whole Po2 range investigated, while Cr2O3—1% TiO2 passed through a minimum and became an n‐type conductor in the whole Po2 range because of the increase in the concentration of electrons [Ticr] = [e′]. The Po2 dependence and the TiO2 dependence on the sintering rate of the Cr2O3—xTiO2 may be completely explained by the alteration in defect structure.
Improved Process for Making Dense Vitreous Silica from Submicrometer Particles by Sintering Near 1000°C
Authors: Clegg William J. , Alford Neil McN. , Birchall James D. , Kendall Kevin
Published: March 2005

Conventional processes for manufacture of vitreous silica are summarized. The disadvantages of ordinary sintering methods which require too high a firing temperature and of sol–gel systems which self‐destruct on drying are noted. Then a new method for making glassy silica is described which overcomes these problems by mixing fine silica powder with polymer solution, shearing strongly to break down agglomerates, drying, burning out the polymer vehicle followed by firing near 1000°C. The polymer has the combined effect of dispersing the grains of powder to allow facile molding and sintering, while preventig cracking during the drying phase. The properties of the vitreous silica products, and the potential of this process for developing new forms of silica, are discussed.
Chemical Vapor Deposited Sic Matrix Composites
Authors: Veltri Richard D. , Condit David A. , Galasso Francis S.
Published: March 2005

Composites of Sic yarnlchemical vapor deposited Sic matrix and multitei chemical vapor deposited Sic matrix were prepared using methyldichloro‐silane and applying a thermal gradient in a low‐pressure reactor environment. The preparation parameters were selected from an X‐ray study where the pressure and temperature were varied. The Sic‐reinforced composite had a higher strength (450 versus 120 MPu) and exhibited more fiber pullout than the mullite‐reinforced composite.
Melting Apparatus for the Synthesis of Bulk ZrF4‐Based Fluoride Glass
Authors: Broer Matthijs M.
Published: March 2005

Heavy‐metal fluoride glasses are currently prepared by melting of the solid fluoride precursors. We have constructed a melting facility for the synthesis of ZrF4‐based fluoride glass cullet. This stand‐alone system provides a controlled (dry and reactive) atmosphere and in situ quenching of the melts. The glass is melted in a vitreous carbon crucible, which is mounted in a silica tube flow reactor. The reactor is resistively heated with a tube furnace and purged with He and SF6 or Cl2. It was found that of the latter two halogenating species only Cl2 prevents effectively the formation of black inclusions in the melt (ZrF3 and ZrF2 particles). With this melting apparatus we have routinely melted 250‐g batches of optically clear ZrF4–BaF2–LaF3–AlF3–NaF glass samples.
Dispersion Methods of Yttria in Silicon Nitride by Comminution
Authors: Zarnon Linda C. , Drew Robin A. L.
Published: March 2005

Sintering additives were incorporated into Si3N4 by attrition and ball milling using both Si3N4 and Al2O3 media. Dispersion of Y2O3 was observed by backscattered electron imaging. Attrition milling for only 15 min using an Si3N4 medium, was equivalent to 24 h of ball milling. Minimal contamination by the Si3N4 was encountered. [Key words: silicon nitride, yttria, comminution, sintering, dispersion.
Phase Equilibria and Phase Transformation in the Aluminum Nitride‐Aluminum Oxycarbide Pseudobinary System
Authors: Kuo Shih‐Yee , Virkar Anil V.
Published: March 2005

Samples in the pseudobinary AIN–AI2OC were fabricated by hot‐pressing mixtures of ANI, AI4C3, and AI2O3 powders in graphite dies in an atmosphere of nitrogen. The resulting dense samples were subjected to thermal treatments over a range of temperatures from 1550° to 1950°C. The hot‐pressed as well as annealed samples were examined using optical microscopy, scanning transmission electron microscopy, and X‐ray diffraction. An electron microprobe was used to determine composition. X‐ray diffraction showed that AI2OC dissolved in AIN up to 44 mol% at 1800°C. Thermal treatment at lower temperatures led to the decomposition of the solid solution into two isostructural phases. In samples containing ∼14 to 60 mol% AIN, the morphology of the precipitates was lenticular. Diffraction contrast analysis showed that the precipitates were rich in ANI. Lattice images showed that the (001) planes of the 2H structure were continuous between the matrix and the precipitates. These precipitates appear to be similar to Guinier‐Preston zones observed in metallic alloys. When annealed for long periods of time, interface dislocations formed, signifying partial loss of coherency. In some compositions (∼61 to 64 mol% AIN), a lamellar microstructure developed similar to that observed in cellular phase separation. Also, in some of the compositions, an additional phase was observed whose composition and structure were not determined.
Characterization of the AIN–W Interface in a Cofired Multilayer AIN Substrate
Authors: Kurokawa Yasuhiro , Toy Cetin , Scott William D.
Published: March 2005

The AIN–W Interfaces in a cofired multilayer AIN substrate were observed using an optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). Optical and SEM observations showed an intricate intricatelocking AIN‐W grain structure at the interface. After the W pad was removed from the substrate with a NaOH etchant, the surface morphology of the W metal at the interface side was found to be very rough, with a small‐grain microstructure compared with that at the free surface side. Electron microprobe analyses using SEM revealed that there was no diffusion of either W or Al at the interface at the order of a few micrometer's resolution. Bright‐field images, dark‐field images and selected area electron diffraction (SAD) patterns using TEM indicated there was no secondary phase between AIN and W. However, scanning transmission electron microscopy using an energy dispersive X‐ray detector revealed that there was a 200‐nm thick W diffusion layer from the interface into the AIN ceramics. It was concluded that the high adhesion strength between the W conductor and the AIN substrate (>20 MPa) was not due to any secondary phase but to mechanical interlocking of AIN and W during cofiring.
Silicon Carbide Whisker Stability During Processing of Silicon Nitride Matrix Composites
Authors: Bradley Steven A. , Karasek Keith R. , Martin Michael R. , Yeh Harry C. , Schienle James L.
Published: March 2005

The effects of two different sources of SiC whiskers on the chemistry and microstructure of the SiC‐whisker—Si3N4 composites were evaluated using scanning transmission electron microscopy. Analyses were performed after presintering in N2 and after encapsulated hot isostatic pressing. Significant differences in the porosity, α‐ to β‐Si3N4 conversion, and whisker degradation were observed after presintering. It was also noted that whiskers containing surface iron impurities were converted to Si3N4 during processing. Whiskers from the source having low surface iron exhibited little reaction. After hot isostatic pressing, some oxidation of the cleaner whiskers was observed.
Preparation of Bi‐Sr‐Ca‐Cu‐O Thin Films by Sputtering under a Variable Magnetic Field
Authors: Nagata Hirotoshi , Takano Akihiro , Kawasaki Masashi , Yoshimoto Mamoru , Koinuma Hideomi
Published: March 2005

Bi‐Sr‐Ca‐Cu‐O thin films were deposited on MgO(100) substrates by a new sputtering method which controls the film composition with magnetic fields over the target. Films having compositions close to Bi2Sr2Ca2Cu3Ox were annealed at 880°C to show superconductivity at moderately high Tc's. Auger electron spectroscopy indicated a chemical interaction between the film and the substrate during the annealing, and this information was utilized to improve the annealing conditions.
Coaxial Lines Containing Ceramic High‐Tc Superconducting‐Center Conductors
Authors: Peterson George E. , Stawicki Robert P.
Published: March 2005

A superconducting line should be essentially lossless and dispersionless and have a purely resistive impedance up to at least 10 GHz. In fact we expect that a long (>1 km) line could carry nanosecond rise time pulses with zero distortion and low loss (<1 dB/km). We have measured the losses in some short sections of coaxial line containing ceramic high‐Tc superconducting‐center conductors over the frequency range from 5 to 50 MHz. There is only a slight improvement over a completely copper coaxial line.
Preparation of Stoichiometric Crystalline Lithium Niobate Fibers by Sol‐Gel Processing with Metal Alkoxides
Authors: Hirano Shin‐ichi , Hayashi Takashi , Nosaki Katsutoshi , Kato Kazumi
Published: March 2005

Homogeneous and stoichiometric crystalline LiNbO3 fibers were successfully prepared above 450°C by sol‐gel processing with metal alkoxides. Controlling the concentration of alkoxide solution and the amount of water used for partial hydrolysis made it possible to draw gel fibers having uniform diameters (10 to 100 μm) from the metal alkoxide solution. The gel fibers withdrawn crystallized directly to single‐phase LiNbO3 fibers by heating from 450° to 600°C. The density of the crystalline LiNbO3 fibers was higher than 4.22 g/cm3, and the dielectric constant at room temperature was about 10 at 10 MHz.
Glasses as Nonlinear Photonic Materials
Authors: Vogel Eva M.
Published: March 2005

The success of photonic switching depends on the development of the materials and devices that are capable of processing light signals without converting them to electronic forms. Glasses are promising materials for these all‐optical devices because of their fast‐responding nonlinearities and low absorption. The aim of this paper is to apprise the ceramic community of the development of nonlinear optics research. The relative merits and trade‐offs of glasses as nonlinear photonic material are discussed.
Effect of Crack Velocity on Crack Resistance in Brittle‐Matrix Composites
Authors: Jessen Todd L. , Lewis David
Published: March 2005

Fast‐ and slow‐fracture studies were conducted on a glass matrix–metal particle composite system, using the appliedmoment double‐cantilever‐beam technique. At 10 vol % metal, the fracture toughness (KIc) was seen to increase 71% over that of the matrix alone, as compared to an increase of only 40% in the stress intensity (KI) for the same system in slow fracture. This difference was corroborated by fracture surface stereology work, which showed 9.6% metal on the fast‐fracture surface as compared to only 5.3% for the slowfracture specimens. This indicates that in slow fracture, the crack “chooses” its path of propagation, thus resulting in a lowering of the expected increase in crack resistance.
Synthesis of Uniform Titanium and 1:1 Strontium‐Titanium Carboxyhydrosols by Controlled Hydrolysis of Alkoxymetal Carboxylate Precursors
Authors: Riman Richard E. , Landham Rowena R. , Bowen H. Kent
Published: March 2005

Uniform inorganic carboxyhydrosols containing titanium or strontium and titanium cations were precipitated from isopropyl alcohol solutions by the controlled hydrolysis of metal alkoxycarboxylate precursors. The hydrolysis of various triisopropoxytitanium carboxylate compounds yielded the capability to control particle size. Spherical particles of carboxyhydrosols were prepared in mean sizes from 0.4 to 2.9 μm. Controlled hydrolysis of quintaisopropoxystrontium titanium octanoate resulted in slightly agglomerated, uniform 1‐μm spheres in a solvent medium in which controlled precipitation of uniform powders was not previously possible. Conversion of the hydrous oxide carboxylate precipitate to the oxide via calcination or hydrothermal treatment was possible.
Hot Isostatic Pressing of Silicon Nitride with Boron Nitride, Boron Carbide, and Carbon Additions
Authors: Mieskowski Diane M. , Sanders William A.
Published: March 2005

Si3 N4 test bars containing additions of BN, B4C, and C, were hot isostatically pressed in Ta cladding at 1900° and 2050°C to 98.9% to 99.5% theoretical density. Room‐temperature strength data on specimens containing 2 wt% BN and 0.5 wt% C were comparable to data obtained for Si3 N4 sintered with Y2O3, Y2O3 and Al2O3, or ZrO2. The 1370°C strengths were less than those obtained for additions of Y2O3 or ZrO2 but greater than those obtained from a combination of Y2O3 and Al2O3. Scanning electron microscope fractography indicated that, as with other types of Si3N4, roomtemperature strength was controlled by processing flaws. The decrease in strength at 1370°C was typical of Si3N4 having an amorphous grainboundary phase. The primary advantage of non‐oxide additions appears to be in facilitating specimen removal from the Ta cladding.
Dependence of YBaCuO Superconductor Properties on Constituent Oxide Preparation: I, CuO and BaCO3 Pretreatment
Authors: Goodman Peter , Grigg Mark , Opat Geoffrey , Peele Andrew , Drennan John , Rohan Patrick
Published: March 2005

A systematic study has been made of the influence of different solid‐state decomposition preparations of copper oxide and barium carbonate on the synthesis of YBa2Cu3O7−x superconductor. Considerable morphological control on the end product can be achieved through a monitored calcining of starting materials. The ceramic particle size is found to be primarily dependent on initial CuO morphology, whereas uniformity of the ceramic and the occurrence of an intergranular phase is sensitive to the form of the BaO precursor. The use of accoustic testing for characterizing the ceramic quality is suggested.
Large‐Deformation Strength Analysis of Chemically Strengthened Glass Disks
Authors: Connolly Derry , Stockton Allen C. , O'Sullivan Timothy C.
Published: March 2005

A large‐deformation stress analysis of a ring‐on‐ring bending fracture test, using the finite‐element method, was used to derive the strength of chemically strengthened and nonstrengthened glass disks from experimental test data. Agreement between measured and predicted disk deflections was very good. The predicted strength data were analyzed using Weibull statistics.
Solid‐Phase Epitaxy of Boehmite‐Derived α‐Alumina on Hematite Seed Crystals
Authors: McArdle James L. , Messing Gary L. , Tietz Lisa A. , Carter C. Barry
Published: March 2005

The seeded transformation of boehmite‐derived alumina was studied by transmission electron microscopy. Crystallographic analysis confirmed that the growth of α‐Al2O3 on α‐Fe2O3 seed crystals occurs by solid‐phase epitaxy, with the orientation relationship [0001]Al2O3||[0001]Fe2O3 and [1120]Al2O3||[1120Fe2O3.
Densification of Alumina‐Silicon Carbide Powder Composites: II, Microstructural Evolution and Densification
Authors: Jang Hyun M. , Rhine Wendell E. , Bowen H. Kent
Published: March 2005

Microstructural evolution adn densification kinetics of Al2O3‐SiC powder composites were studied using two different SiC powders. Examination of the microstructural evolution of Al2O3‐fine SiC powder composites showed three well‐defined stages of densification: the first was characterized by constant pore size and no grain growth; the second involved rapid pore coarsening and grain growth; the third was characterized by pore shrinkage and slow grain growth. Studies of the densification kinetics of Al2O3‐coarse SiC powder composites exhibited two stages of densification: in the first stage there were no significant differences in densification rate between pure Al2O3 compacts and composites; in the second stage, however, differences in densification behavior between pure Al2O3 compacts and composites became pronounced.
Plasticity and Microcracking in Shock‐Loaded Alumina
Authors: Longy F. , Cagnoux J.
Published: March 2005

Using a 110‐mm‐diameter compressed‐gas gun, we performed two types of experiments on alumina samples. The first involved plate impacts with wave profile measurements made with a VISAR velocity interferometer. The second type was plate‐impact recovery experiments. SEM, TEM, and X‐ray diffraction analysis showed that grain plasticity begins below the Hugoniot elastic limit (HEL), leading to a compaction of the material. This compaction is not accompanied by microcracking in pure alumina up to 2 × HEL. In the case of alumina with an intergranular glassy phase, the deformation of the sample is accompanied by a microcracking of the glass. However, the microcracks are not interconnected at a stress level equal to 2 × HEL for an alumina with about 10% glassy phase.
Effect of Residual Strain on the Electronic Structure of Alumina and Magnesia
Authors: Song Huesup , French Roger H. , Coble Robert L.
Published: March 2005

The reflectance spectra of polycrystalline Al2O3 and singlecrystal MgO, with different surface treatments were measured using vacuum ultraviolet (VUV) spectroscopy to determine the effect of residual stresses and strains. The bulk stresses were estimated using the R‐line flourescence of trace Cr3+ in Al2O3. No grain‐size dependence was observed for the residual thermal expansion anisotropy stresses in polycrystalline Al2O3. The effects of mechanical‐polishing‐induced damage in Al2O3 shifted the band‐to‐band and exciton transitions to higher energies, compared with those of chemically polished Al2O3. There was little difference in peak positions between cleaved and chemically polished surfaces of MgO. However, mechanically polished MgO surfaces exhibited band‐to‐band and exciton‐peak shifts to higher energies. The VUV technique of determining the exciton‐peak and band‐gap shifts was used with knowledge of the band‐gap strain coefficient to estimate the magnitudes of residual surface stresses in the 1‐μm surface layer probed. The polishing‐damage‐induced residual surface stress is 2.2 GPa for Al2O3 and 1.1 GPa for MgO. These values are based on band‐gap strain coefficients of 700 meV/(lin% strain) derived for Al2O3 and 400 meV/(lin% strain) estimated for MgO.
Characterization and Sintering Behavior of Alkoxide‐Derived Aluminosilicate Powders
Authors: Hirata Yoshihiro , Sakeda Kazuyoshi , Matsushita Yumi , Shimada Kinji , Ishihara Yoshimi
Published: March 2005

Submicrometer SiO2‐Al2O3 powders with compositions of 46.5 to 76.6 wt% Al2O3 were prepared by hydrolysis of mixed alkoxides. Phase change, mullite composition, and particle size of powders with heating were analyzed by DTA, XRD, IR, BET, and TEM. As‐produced amorphous powders partially transformed to mullite and Al‐Si spinel at around 980°C. The compositions of mullite produced at 1400° and 1550°C were richer in Al2O3 than the compositions of stable mullite solid solutions predicted from the phase diagram of the SiO2‐Al2O3 system. Particle size decreased with increasing Al2O3 content. The sintered densities depended upon the amount of SiO2‐rich glassy phase formed during sintering and the green density expressed as a function of particle size.
Combustion Synthesis of the Titanium‐Aluminum‐Boron System
Authors: Taneoka Yutaka , Odawara Osamu , Kaieda Yoshinari
Published: March 2005

TiB2 and Al base composite powders, which will offer a weight‐saving improvement in stiffness, were produced by combustion synthesis of Ti, Al, and B ternary powder mixtures. Finely dispersed TiB2 was synthesized by reacting a mixture of Ti, Al, and B in the molar ratio of 1:1:4. The grain size of the TiB2 formed was <0.5 μm, which was much smaller than that obtained from the reaction of a mixture of Ti, Al, and B in the molar ratio 1:1:2. These results are discussed in light of the reaction propagating velocity and heat removal during the combustion synthesis process.
Fragmentation of Glass Bottles by Impact
Authors: Freéchette Van Derck , Yates Sharon L.
Published: March 2005

Three sizes of water‐filled generic soft‐drink containers were impacted against a blunt steel rod striking the middle sidewall. The fracture origins of the containers were in hinge breaks. The containers showed a linear relation between the number of mature primary cracks and the energy of impact.