ALBERT

Notes: The performance of many wear-resistant materials can be improved further by incorporating diamond into the structure. Diamond that has been coated with titanium is known to adhere well to the matrix particles and also prevents reaction with H2, which often is used in the sintering atmosphere. Two coating methods of coating diamond with titanium have been explored in this study: a sputtering method and a procedure that involves heating the diamond in a mixture of salt and titanium. The latter, which uses a salt mix of NaCl, KCl, and CaCl2 and metallic titanium particles 3 μm in size, heated at a temperature of 750°C in an argon atmosphere, is determined to be the best method.

Notes: Submicrometer-sized, pure calcium hydroxyapatite (HA, (Ca10(PO4)6(OH)2)) and β-tricalcium phosphate (β-TCP, Ca3(PO4)2) bioceramic powders, that have been synthesized via chemical precipitation techniques, were used in the preparation of aqueous slurries that contained methyl cellulose to manufacture porous (70%–95% porosity) HA or β-TCP ceramics. The pore sizes in HA bioceramics of this study were 200–400 μm, whereas those of β-TCP bioceramics were 100–300 μm. The pore morphology and total porosity of the HA and β-TCP samples were investigated via scanning electron microscopy, water absorption, and computerized tomography.

Notes: The general reaction behavior of the 3A process under the thermal explosion mode of synthesis has been investigated via a continuum model. The continuum model uses mass and energy balances to predict temperature difference (Ts,avg−Tf) curves, as well as profile curves of the reactant conversions and sample temperature. In particular, the effect of the dimensionless parameters associated with the rate of local heat generation (β, the thermicity factor), the activation energy (γ, the Arrhenius number), the rate of heat redistribution (α, the modified thermal diffusivity), the rate of heat transfer by convection (Bi, the Biot number or convective heat transfer parameter), and the rate of heat transfer by radiation (Ω, the radiative heat transfer parameter) were investigated. Conditions to control the reaction process, which should produce high-density final products, were determined. It was found that the overall maximum temperature may be reduced for high γ, low β, high α, and high Bi and Ω. In terms of processing conditions, this may be obtained by reducing the initial reactant concentrations, optimizing the particle size, using small sample sizes and high compaction pressure, and increasing the heat loss by using a high thermal conductivity inert gas.

Notes: A solid oxide fuel cell (SOFC) is a complete solid-state energy conversion device with the potential advantages of high efficiency, silent operation, and low emissions. However, the current performance of SOFCs is still limited by a number of problems. Investigations in this field have indicated that it is imperative to fabricate efficient and compatible anodes for SOFCs to minimize polarization loss and to concurrently achieve long-term stability. In this paper, a critical review of previous studies is given and several criteria for the theoretically ideal anode are summarized. Accordingly, a newly developed vapor deposition technique, polarized electrochemical vapor deposition (PEVD), is applied to fabricate composite anodes to meet these criteria. The initial experimental results in the present study show that PEVD is capable of depositing a thin layer of yttria-stabilized zirconia on a porous metallic electrode to form a composite anode. This will not only provide continuous ionic and electronic conducting paths in the anode to reduce the overpotential loss and resistance, but also protect the metallic electrode from further sintering, vapor loss, and poisoning in the harsh SOFC operating conditions.

Notes: Green state joining of SiC was investigated using a paste consisting of polycarbosilane polymer and SiC powder. The joining process and densification were described. Initial experiments resulted in the formation of symmetrical black bands and cracks on both sides of the joint. However, with modifications in processing conditions, the cracks were eliminated and the resulting joints were indistinguishable from the matrix. The flexural strength of joined samples was measured to be 234 MPa, which was comparable to that of the control sample with similar density. As the applied pressure during joining was increased from 34 to 138 MPa, the strength of the joined samples increased from 180 to 250 MPa.

Notes: The dc conductivities of ZrO2–Y2O3 ceramic alloys (in the range 3–12 mol% of Y2O3) have been obtained from ac impedance measurements at temperatures between 250° and 370°C. The Almond–West ac conductivity model has been applied to evaluate hopping rates in this system. The migration enthalpies were evaluated and shown to increase with yttria concentration, but all values determined were shown to be lower than the corresponding activation enthalpies for conductivity. The association enthalpies thus calculated were shown to be very small in 3 mol% Y2O3–ZrO3 and to increase with yttria concentration until the yttria contents were high enough to form fully stabilized cubic zirconia. For these samples the association enthalpies are about 0.19 eV, and no longer sensitive to yttria content. The low hopping rate at high yttria concentration might be attributed to low entropy in the system, which might be attributed to the formation of vacancy clusters and/or an ordering of the structure.

Notes: The dielectric properties of (Ba0.6Sr0.4)TiO3 and Al2O3-doped (Ba0.6Sr0.4)TiO3 have been characterized. The grain size of the specimen is maximum for (Ba0.6Sr0.4)TiO3 that has been doped with 1 wt% Al2O3. The density and the real part of the relative dielectric constant each decrease as the Al2O3 content increases. The loss factor is minimum for (Ba0.6Sr0.4)TiO3 that has been doped with 2 wt% Al2O3. The dielectric constant of the specimens decreases as the applied dc field increases. The influence of the dc field on the loss factor is much less than that on the dielectric constant. The tunability is ∼24% for (Ba0.6Sr0.4)TiO3 that has been doped with 1 wt% Al2O3.

Notes: The standard Gibbs energies of formation of RuO2 and OsO2 at high temperature have been determined with high precision, using a novel apparatus that incorporates a buffer electrode between the reference and working electrodes. The buffer electrode absorbs the electrochemical flux of oxygen through the solid electrolyte from the electrode with higher oxygen chemical potential to the electrode with lower oxygen potential. The buffer electrode prevents polarization of the measuring electrode and ensures accurate data. The standard Gibbs energies of formation (ΔfG°) of RuO2, in the temperature range of 900–1500 K, and OsO2, in the range of 900–1200 K, can be represented by the equations 〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00027820:JACE1745:JACE_1745_mu1"/〉 where the temperature T is given in Kelvin and the deviation of the measurement is ±80 J/mol. The high-temperature heat capacities of RuO2 and OsO2 are measured using differential scanning calorimetry. The information for both the low- and high-temperature heat capacity of RuO2 is coupled with the ΔfG° data obtained in this study to evaluate the standard enthalpy of formation of RuO2 at 298.15 K (ΔfH°298.15K). The low-temperature heat capacity of OsO2 has not been measured; therefore, the standard enthalpy and entropy of formation of OsO2 at 298.15 K (ΔfH°298.15K and S°298.15K, respectively) are derived simultaneously through an optimization procedure from the high-temperature heat capacity and the Gibbs energy of formation. Both ΔfH°298.15K and S°298.15K are treated as variables in the optimization routine. For RuO2, the standard enthalpy of formation at 298.15 K is ΔfH°298.15K(RuO2) =−313.52 ± 0.08 kJ/mol, and that for OsO2 is ΔfH°298.15K(OsO2) =−295.96 ± 0.08 kJ/mol. The standard entropy of OsO2 at 298.15 K that has been obtained from the optimization is given as S°298.15K(OsO2) = 49.8 ± 0.2 J·(mol·K)−1.

Notes: Discrete element modeling was used to establish the effects of size distribution on loose packing fraction during the fall of 5000 to 10 000 agglomerates. Monosized distributions exhibited slightly lower packing fraction than “narrow” distributions. However, broad distributions always produced the lowest packing fraction. The application of radius ratio rules had an effect opposite to that intended. Smaller fines had a disproportionately large effect on packing fraction, an effect attributed to gaslike behavior. Gravity-driven random packing in ceramic agglomerates was governed by a combination of “bridge” formation and kinetic agglomerate–agglomerate interactions, not by geometric constraints.

Notes: The objective of this study was to investigate the effects of temperature and solids loading on the viscosity of two nonaqueous ceramic suspensions. In this article, the viscosity of Al2O3 suspensions with 5%–50% solids loading and hydroxyapatite suspensions with a solids loading of 5%–40% were measured at temperatures of 25°, 45°, 65°, and 75°C. The high-shear Newtonian viscosity at various temperatures was reduced to a single curve by the reduced viscosity and the temperature-adjusted solids volume fraction of the suspensions. The Krieger–Dougherty model, with the intrinsic viscosity corrected for particle geometry, was fitted to the data and was observed to provide a satisfactory description to the solids-loading–viscosity data for both suspensions.

Notes: Accurate quantitative X-ray diffraction analysis of SiC-based ceramics is difficult because of the significant overlap of the Bragg reflections from the different SiC polytypes. In this regard, the Rietveld method is a powerful tool for the accurate and precise analysis of the phase/polytype compositions in these materials. In this study, we have used two different types of Rietveld codes for the quantitative phase/polytype analysis of a liquid-phase-sintered SiC specimen: FULLPROF, which is based on the classical Rietveld approach, and BGMN, which is based on the new fundamental parameter approach. In both cases, the effect of texture corrections on the precision of the analysis also was studied. The accuracy of the analysis, in terms of the weight percentage of SiC (all polytypes) and yttrium aluminum garnet liquid phase, as determined from the starting powder composition, is within the standard deviation of the analysis in both cases (FULLPROF and BGMN), with and without the texture corrections. In addition, in the case of the classical code (FULLPROF), inclusion of the texture corrections has been shown to improve the precision. In contrast, the precision of the analysis using the BGMN code without the texture corrections is better. However, inclusion of the texture corrections is expected to improve the accuracy of the analysis.

Notes: Detailed analysis of the microstructure of grain boundaries, especially triple-grain and multiple-grain junctions, in ZnO varistor materials has been performed using transmission electron microscopy. Different polymorphs of Bi2O3 are shown to exhibit different wetting properties on ZnO interfaces. Recent investigations suggest that the equilibrium configuration consists of crystalline Bi2O3 in the triple-grain and multiple-grain junctions and an amorphous bismuth-rich film in the ZnO/ZnO grain boundaries. The present investigation supports this suggestion for δ-Bi2O3 and also adds to the microstructural image and wetting properties of α-Bi2O3.

Notes: An anhydrous alumina (Al2O3) sol was prepared from aluminum isopropoxide and an organic solvent, using an acetic acid stabilizer. The complete conversion of the dried sol to α-Al2O3 was accomplished at a temperature of 950°C by a single transition via γ-Al2O3. Al2O3 that was deposited via dip coating resulted in amorphous films, even after annealing at 1100°C, because of the silicon diffusion from the substrate. This phenomenon was avoided using a rapid thermal treatment in a flame after dip coating, which resulted in uniform thin films that are converted to α-Al2O3 via heat treatment.

Notes: The XRD patterns at ambient temperature and at 1500°C showed that the spinel in the Al2O3–MgO castables fired at 1500°C for 3 h has the higher peak intensity, compared to those in Al2O3–spinel castables; the interplanar distance in the set (311) is 2.43 Å for the spinel in Al2O3–MgO castables as well as the spinels in Al2O3–spinel castables using spinels containing 73, 90, and 94 wt% Al2O3, respectively. The corresponding alumina contents of the spinels in these castables were estimated to be around 75 wt%. The smaller grain size of the spinel in Al2O3–MgO castables compared to that in Al2O3–spinel castables is evidenced by the recrystallization of thein situspinel only occurring in Al2O3–MgO castables as revealed by the XRD patterns at ambient temperature and at 1500°C. The larger amount and smaller grain size of thein situ spinel in the matrix mostly account for the better slag resistance of Al2O3–MgO castables, compared to Al2O3–spinel castables.

Notes: We have studied the gelation, consolidation, and rheological properties of boehmite-coated SiC suspensions. A boehmite-coated SiC suspension consists of SiC particles covered with a boehmite layer of a few nanometers in thickness in the suspension. Similar to boehmite suspensions, the boehmite-coated SiC suspension can gel over time. The gelation, as well as the rheological behavior of the boehmite-coated SiC suspension with respect to pH, is shown to be similar to that of a boehmite suspension. However, because of the particle-size difference, a boehmite-coated SiC suspension gels more slowly than suspensions of smaller boehmite particles. The boehmite coating improves the consolidation density of SiC, increasing the sediment density from 39 to 52 vol% and the centrifuged density from 50 to 60 vol%. It, also, makes the consolidation behavior of a boehmite-coated SiC suspension with respect to pH more consistent with the rheological behavior; i.e., lower suspension viscosity and storage modulus correlate with a higher consolidated density. In contrast, suspensions containing SiC particles partially covered with boehmite and individual boehmite particles in the suspensions show no improvement in the sediment density and no systematic correlation between the consolidation density and the rheological properties. This indicates that the complete coating of boehmite on the SiC particles is critical to the improvement in consolidation density.

Notes: Polyelectrolyte species, known as superplasticizers, dramatically affect the rheological properties of dense cement suspensions. We have studied the influence of sulfonated naphthalene formaldehyde condensate (SNF) and carboxylated acrylic ester (CAE) grafted copolymers of varying molecular architecture on the surface (e.g., adsorption behavior and zeta potential) and rheological properties of concentrated cement suspensions of white portland cement and two model compounds, β-Ca2SiO4 and γ-Ca2SiO4. The adsorption of SNF species was strongly dependent on cement chemistry, whereas CAE species exhibited little sensitivity. The respective critical concentrations (Φ*) in suspension required to promote the transition from strongly shear thinning to Newtonian flow (flocculated → stable) behavior were determined from stress viscometry and yield stress measurements. Theoretical analysis of interparticle interactions suggested that only colloidal particles in the size range of ≤1 μm are fully stabilized by adsorbed polyelectrolyte species. Our observations provide guidelines for tailoring the molecular architecture and functionality of superplasticizers for optimal performance.

Notes: Cubic Zr1−xMexOy(Me = Fe, Co, Ni, Cu) metastable solid solutions with metal content significantly higher than equilibrium levels have been synthesized by the self-propagating high-temperature synthesis method based on a thermite reaction between metallic zirconium and the transition-metal oxides CoO, Fe2O3, CuO, and NiO. Through in situ XRD analysis, it was determined that when heated to 1100°C, the cubic solid solution transformed to the tetragonal phase with the concomitant formation of iron oxide. When cooled to lower temperatures, the tetragonal phase transformed to the monoclinic phase at or below 500°C. Results of auxiliary experiments strongly suggest that the formation of the solid solution takes place behind the combustion front by a reaction between zirconia and the metal.

Notes: A new gelcasting system based on aqueous alumina (Al2O3)–poly(vinyl alcohol) (PVA) suspensions cross-linked via titanium ion complexation has been developed as a feedstock for bulk casting and solid freeform fabrication (SFF) routes. Its chemorheological properties, as measured by stress viscometry and oscillatory techniques, exhibited a strong dependence upon polymer hydrolysis and molecular weight. The gelation time of systems of constant PVA volume fraction (φPVAsoln) and cross-linker concentration decreased with increasing degree of hydrolysis and molecular weight, whereas their steady-state elastic modulus (G′) exhibited the opposite dependence. Stress evolution during drying of gelcast layers was measured in situ using a controlled-environment, cantilever deflection apparatus. Both the maximum and residual drying stresses increased with increasing degree of hydrolysis, with only a modest molecular weight effect observed.

Notes: Dense β-Si3N4 with various Y2O3/SiO2 additive ratios were fabricated by hot pressing and subsequent annealing. The thermal conductivity of the sintered bodies increased as the Y2O3/SiO2 ratio increased. The oxygen contents in the β-Si3N4 crystal lattice of these samples were determined using hot-gas extraction and electron spin resonance techniques. A good correlation between the lattice oxygen content and the thermal resistivity was observed. The relationship between the microstructure, grain-boundary phase, lattice oxygen content, and thermal conductivity of β-Si3N4 that was sintered at various Y2O3/SiO2 additive ratios has been clarified.

Notes: The creep behavior of a commercial grade of Si3N4 was studied at 1350° and 1400°C. Stresses ranged from 10 to 200 MPa in tension and from 30 to 300 MPa in compression. In tension, the creep rate increased linearly with stress at low stresses and exponentially at high stresses. By contrast, the creep rate in compression increased linearly with stress over the entire stress range. Although compressive and tensile data exhibited an Arrhenius dependence on temperature, the activation energies for creep in tension, 715.3 ± 22.9 kJ/mol, and compression, 489.2 ± 62.0 kJ/mol, were not the same. These differences in creep behavior suggests that mechanisms of creep in tension and compression are different. Creep in tension is controlled by the formation of cavities. The cavity volume fraction increased linearly with increased tensile creep strain with a slope of unity. A cavitation model of creep, developed for materials that contain a triple-junction network of second phase, rationalizes the observed creep behavior at high and low stresses. In compression, cavitation plays a less important role in the creep process. The volume fraction of cavities in compression was ∼18% of that in tension at 1.8% axial strain and approached zero at strains 〈1%. The linear dependence of creep rate on applied stress is consistent with a model for compressive creep involving solution–precipitation of Si3N4. Although the tensile and compressive creep rates overlapped at the lowest stresses, cavity volume fraction measurements showed that solution–precipitation creep of Si3N4 did not contribute substantially to the tensile creep rate. Instead, cavitation creep dominated at high and low stresses.

Notes: The Templated Grain Growth (TGG) of Al2O3 occurs in three stages: densification, radial growth of individual template grains until template impingement, and template grain thickening. Significant template growth occurs only after densification to ∼90% density. Template loading determines the inter-template spacing and, subsequently, the degree of growth. The spacing distance can be predicted from the initial template concentration and template dimensions. Thermodynamic conditions favorable for template growth occur when the size ratio between the template thickness and matrix grains is ≥1.5. The initial template concentration should be less than a critical template concentration, VT,C, to achieve textured ceramics with a narrow orientation distribution. For this system, which uses 20 ± 5 μm × 2 μm template particles and uniaxial pressing as a forming technique, VT,C is between 5 and 10 vol%.

Notes: The constitution of the ternary system Cr-Si-C is investigated using differential thermal analysis and X-ray diffractometry techniques. Eight invariant reaction temperatures involving the liquid phase are determined. The crystal structures and phase partitions observed for the subsolidus temperature region confirm literature data. Thermodynamic modeling, using a minimum of adjustable ternary parameters and assuming the binary high-temperature phase, β-Cr5Si3, to be stabilized toward lower temperatures as ternary D88-type Cr5Si3Cx, generally reproduces the measured temperatures within 10 K. The calculated liquidus surface contains four ternary eutectics, three transition reactions, three degenerated reactions, and five (pseudobinary eutectics) maxima. The reaction scheme shows that no solid-phase reactions occur in the Cr-Si-C system at 〉1000°C, except for the binary transition β-Cr5Si3↔α-Cr5Si3. The activity diagram along the section Cr-SiC at 1300°C, computed from the optimized data set, agrees with the observed diffusion path.

Notes: Crystals of (Ca1.955□0.045)(Si0.91P0.09)O4, where □ denotes a vacancy, have been prepared and examined by XRD, optical microscopy, SEM, and AFM. At 20°C, the crystals are composed of 38%α′L and 62%β phases. Upon cooling to −185°C, the α′L- to β-phase transformation occurs, which increases the β-phase composition to 72%. The transformation is also accompanied by the formation of platelike surface reliefs. The surface relief angles have been determined from observations (7.9°± 0.2°) and calculations based on a phenomenological analysis (7.84°). The fair agreement of these values indicates that the transformation is martensitic and mainly governed by a shear mechanism.

Notes: Novel approaches for optimized powder processing of advanced ceramics are reviewed with an emphasis on direct-casting methods and solid freeform fabrication techniques. The fundamental principles for green body formation are discussed; a distinction is made between physical and chemical gels based on the nature of the induced gelation. An overview of the properties of dense suspensions is presented, with a focus on the factors controlling the maximum solids loading. Recent work on direct measurements of interparticle forces in ceramic systems is presented and related to rheological properties.

Notes: Air compressibility is important in attaining an accurate quantification of the permeability parameters for refractory castables. Nevertheless, this effect is often neglected in the permeability equations that are found in ceramics literature. The consequences of omitting the compressibility effect in two of the main permeability equations are highlighted and discussed. The permeability to air flow of high-Al2O3 ultra-low-cement refractory castables has been quantified by Darcy's law according to U.S. ASTM C577–96 and European PRE-16th permeability methods, which propose distinct approaches for air compressibility. Forchheimer's equation, which establishes a more realistic dependence between fluid pressure and fluid velocity, also has been used to obtain the permeability constants k1 and k2. Results show that equations proposed by the ASTM and the PRE methods may yield very distinct values of Darcian permeability k1 for the same sample. Forchheimer's equation for compressible fluids provides the best fitting with experimental data.

Notes: Dynamic fatigue data are reported for fine- and coarse-grained micaceous glass-ceramics after contact damage with spheres. The strengths of indented specimens are measured at stressing rates from ∼10−2 to 104 MPa·s−1 in water. The strength degradation is substantially faster in the coarse-grained structure, and is accelerated further by multicycle contact loading. Failures originate from contact sites in all cases but undergo a progressive transition from classical cone cracks to quasi-plastic microcrack zones with increases in the grain size and the number of contact cycles. The results highlight the particularly deleterious effect of quasi-plastic damage accumulation on lifetime.

Notes: The effect of carbon on the sintering of boron-doped SiC was studied. The free carbon present in the green compact was found to react with the SiO2 covering the surfaces of the SiC particles; however, even if no carbon was added, the surface SiO2 reacted with the SiC itself at a slightly higher temperature. This latter reaction was associated with the onset of substantial pore growth in the shrinking green body, which, as the pores continued to grow at higher temperatures, prevented complete densification. Therefore, the reaction of the SiC with the SiO2 may have led to the fracture of interparticle contacts, resulting in the onset of coarsening. Thus, the role of the carbon was to prevent reaction between the SiC and the surface SiO2, by removing the SiO2 at a temperature below that at which this reaction could occur.

Notes: ZrO2 powder is prepared by low-temperature vapor-phase hydrolysis of ZrCl4. TG-DTA, XRD, Raman, BET, and TEM methods are used to investigate the particle size, phase composition, and agglomeration before and after heat treatment. The results show that the as-prepared ZrO2 powder is characterized by large surface area (150 m2/g), fine grain size (5.8 nm), and weak agglomeration. Additionally, the as-prepared ZrO2 powder shows predominantly tetragonal phase attributed to a grain size effect. This route is free of powder drying and calcination processes that are essential for wet chemical preparation, contributing to less agglomeration.

Notes: Two types of titanate derivatives, layered hydrous titanium dioxide (H2Ti4O9·nH2O) and potassium octatitanate (K2Ti8O17) with a tunnellike structure, were synthesized using an ion-exchange reaction. Fibrous potassium tetratitanate (K2Ti4O9·nH2O) was prepared by calcination of a mixture of K2CO3 and TiO2 with a molar ratio of 2.8 at 1050°C for 3 h, followed by boiling-water treatment of the calcined products for 10 h. The material then was transformed to layered H2Ti4O9·nH2O through an exchange of K+ ions with H+ ions using HCl. K2Ti8O17 was formed by a thermal treatment of KHTi4O9·nH2O. Pure KHTi4O9·nH2O phase was effectively produced by a treatment of K2Ti4O9 with 0.005M HCl solution for 30 min. Thermal treatment at 250°–500°C for 3 h resulted in formation of only K2Ti8O17.

Notes: In this study, the microstructural development of AlN during combustion synthesis (CS) in a nitrogen atmosphere was investigated. CS using an aluminum–50 wt% AlN–3 wt% MgCl2 powder compact yielded a mixture of AlN whiskers and powder. The microstructural development during the combustion reaction was studied by heating the compact to various temperatures. Based on the experimental results, the formation mechanisms of the AlN with a whisker morphology were discussed.

Notes: The effects of B2O3 addition on the sintering behavior and the dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 (BST) ceramics were investigated. The dielectric and ferroelectric properties of a BST sample with 0.5 wt% B2O3 sintered at 〈1150°C were as good as those of undoped BST sintered at 1350°C, and the dielectric loss was better. When 〉1.0 wt% B2O3 was added to BST, the overdoped B2O3 did not form a liquid phase or volatilize; it remained in the samples and formed a secondary phase that lowered the sintering behavior and the dielectric and ferroelectric properties of the BST.

Notes: One of the principal modes by which electron-beam-evaporated thermal barrier coatings fail is via the nucleation of local regions of debonding, which grow and link together until reaching a critically sized flaw for spontaneous buckling and spalling. This progressive-failure mode is used as a basis for analyzing the changes that can occur in photostimulated luminescence spectra that have been recorded from the thermally grown oxide. This process also provides a basis for the quantitative determination of the extent of local damage prior to spalling from an analysis of the shape of the luminescence spectra.

Notes: The work reported was conducted to provide a basis for a number of structural ceramic mechanical property standardization activities in the United States, Germany, Japan, and Sweden. A comparison of key property values of a commercial silicon nitride determined in a number of laboratories was a major objective. The work reported was conducted by 10 U.S. laboratories on GN-10 silicon nitride, and represented the U.S. work within an International Energy Agency program including the United States, Germany, Japan, and Sweden. Fracture location analyses showed that fracture location within the inner span often was not a linear function of location within the span. Some of this behavior was explained by random sampling effects based upon simulation predictions, but some was apparently dependent upon friction within the fixtures in spite of efforts to minimize it. Flexural strengths were measured at 25° and 1250°C in air and were analyzed using the two-parameter Weibull model in terms of m and σΘ using both linear regression (LR) and maximum likelihood (ML) methods. Under the measurement conditions for the 10 room-temperature strength sets, the value of the ML estimator for m varied by as much as 36%, while the value for the σΘ parameter estimator varied only 3.3%. The LR estimator for m varied by about 54%. For the high-temperature specimens, the ML estimator for m varied by 48% while the LR estimator varied by 38%. Ranked fracture location analysis showed that the high-temperature fracture locations were more random than those in the room-temperature specimens, and was probably due to friction in the high-temperature fixtures. There was little pin rolling ability in many of the high-temperature fixtures used. Monte Carlo and one-way analysis-of-variance (ANOVA) methods provided insight into the consistency of the strength values. Monte Carlo predictions showed that for room-temperature strength, the maximum likelihood estimator m for all 10 laboratories fit within the 10% and 90% confidence bounds for 30 specimen sets. The dispersion of the high-temperature data was such that the m estimator satisfied the model only at the 1% and 99% confidence levels for the 15 specimen sets. ANOVA results showed that for the room-temperature flexural strength, data from all 10 laboratories were not distinguishable for this evaluator at the 95% confidence level and that scatter within individual data sets was a larger effect than was the variation between the data sets. For the high-temperature data, the results from one laboratory were clearly outside the allowable range at this confidence level.

Notes: The room-temperature fracture-resistance behavior (R-curve) of unidirectional silicon-carbide-fiber-reinforced zircon-matrix composites has been studied experimentally and numerically. The composites showed strong rising R-curve behavior from experimental results that used in situ crack-length measurements taken via optical microscopy as well as the compliance method. A numerical calculation, based on the available models, then was performed to determine the bridging-stress function from the experimental R-curve. In addition, the effect of the residual stress and constituent properties on the bridging-stress function also has been considered in the numerical calculations. These results have indicated that the bridging-stress function, which controls the fracture resistance of ceramic composites, can be obtained from the carefully measured R-curve.

Notes: Mullitization from a multicomponent oxide system (alumina–kaolin–quartz–feldspar–talc) was analyzed as a function of firing temperature from 1200° to 1500°C based on quantitative XRD and SEM. In the present study, whisker forms of mullite grew in three characteristic stages. In the first stage (1255°–1295°C), mullitization (nucleation) took place from glass via alumina dissolution into glass under the condition of no apparent change in glass content. The reaction in this stage was rate-limited by alumina dissolution into glass. Extensive mullitization occurred in the 1295°–1335°C range (second stage) directly from glass. Unlike in the sol–gel-based binary system, alumina dissolution into glass was not shown to be the rate-controlling mechanism during this extensive mullitization stage. Finally (〉1335°C, third stage), the reaction was saturated, accompanied by an apparent decrease in glass consumption rate. The impingement of mullite whiskers by other whiskers and crystals was speculated to cause mullite to grow in the transverse direction, yielding a diminished reaction rate in the final stage. Mullitization stages in this work were compared with those of the alumina–silica binary system shown in the literature.

Notes: A triclinic phase of tricalcium silicate (TI) was investigated using transmission electron microscopy (TEM). Electron diffraction patterns were analyzed by introducing a subcell with the cell parameters of a= 7.081 Å, b= 7.043 Å, c= 25.230 Å, α= 89.97°, β= 90.37°, and γ= 119.44°. It was proven that the coordinates of all the reflections can be expressed to be ha*+kb*+lc*±m/6(a*+ 2b*+ 2c*), where m= 0, 1, 2, and 3. The result indicates that the structure modulation in TI is a one-dimensional type with a structural modulation normal to (122). The modulated structure could be observed in a high-resolution TEM image as wavy contrast streaking parallel to the plane with an interval of six times the (122) spacing.

Notes: The effects of high-voltage screening were examined for perpendicularly and parallelly surface-ground titania rectangular bars. A screening field at or below which 30% of titania samples break electrically was applied to each group samples. After high-voltage screening, the surviving samples were subjected to mechanical strength measurement and the resultant strength distribution was compared with the original distribution. After screening, Weibull plots of perpendicularly ground samples bent to become convex curves while plots in the high-strength region remained almost the same, indicating that low-strength samples were selectively eliminated by the high-voltage screening. On the other hand, the screening effect on parallelly surface-ground samples was very small.

Notes: A two-dimensional numerical model that predicts the reliability of multilayer capacitors (MLCs) during soldering and bending is presented. The Weibull parameters used in the model are based on measurements of soldered MLC devices. The preheating and soldering temperatures have a dominant impact on the failure probability, in comparison to the thickness of the nickel layer, the soft solder geometry, and the number of inner electrodes. Comparison of calculated and measured reliability of three MLC sizes leads to the assumption that residual stresses due to the manufacturing process or size-related microstructure are important.

Notes: This paper examined the room-temperature mechanical properties of a mixed-conducting perovskite La1–xSrxCo0.2Fe0.8O3 (x= 0.2–0.8). Powders were made by the combustion synthesis technique and sintered at 1250°C in air. Sintered density, crystal phase, and grain size were characterized. Young's and shear moduli, microhardness, indentation fracture toughness, and biaxial flexure strength were determined. The Young's and shear moduli slightly increased with increasing strontium content. Young's modulus of 151–188 GPa and shear modulus of 57–75 GPa were measured. Biaxial flexure strength of ∼160 MPa was measured for lower strontium content batches. Strength greatly decreased to ∼40 MPa at higher strontium concentrations (x= 0.6–0.8) because of the formation of extensive cracking. Indentation toughness showed a higher value (∼1.5 MPa·m1/2) for low strontium (x= 0.2) content and a lower value (∼1.1 MPa·m1/2) for the other batches (x= 0.4–0.8). Materials with fine and coarse grain size were also tested at various indent loads and showed no dependence of toughness on crack size. In addition, fractography was used to characterize the critical flaw and fracture mode.

Notes: Phase relations within the “V2O3–FeO” and V2O3–TiO2 oxide systems were determined using the quench technique. Experimental conditions were as follows: partial oxygen pressures of 3.02 × 10−10, 2.99 × 10−9, and 2.31 × 10−8 atm at 1400°, 1500°, and 1600°C, respectively. Analysis techniques that were used to determine the phase relations within the reacted samples included X-ray diffractometry, electron probe microanalysis (energy-dispersive spectroscopy and wavelength-dispersive spectroscopy), and optical microscopy. The solid-solution phases M2O3, M3O5, and higher Magneli phases (MnO2n−1, where M = V, Ti) were identified in the V2O3–TiO2 system. In the “V2O3–FeO” system, the solid-solution phases M2O3 and M3O4 (where M = V, Ti), as well as liquid, were identified.

Notes: Studies on scanning electron-beam dielectric microscopy are reported. This microscopy technique is used for determining the temperature coefficient distribution of dielectric materials using an electron beam as a heat source instead of a light beam as in photothermal dielectric microscopy. This microscopy technique, which has the ability to simultaneously observe SEM images and the material composition by EPMA, has a resolution better than that of photothermal dielectric microscopy. To demonstrate the usefulness of this technique, the two-dimensional image of a two-phase composite ceramic composed of TiO2 and Bi2Ti4O11 is measured.

Notes: A MoSi2/reaction-bonded SiC composite was prepared from a preform of petroleum coke and commercial SiC powders (in weight ratios of 0.5 and 0.6), following reactive infiltration of a Si-Mo melt (molybdenum concentration of 7–29 wt%) made from elemental powder. The resulting material had a relative density of 〉90% of the theoretical density and, on a microstructural scale, contained SiC and MoSi2, in addition to unreacted carbon and silicon. The SiC and MoSi2 boundary was smooth and sharp, with no sign of any reaction. The occasional presence of an intermediate zone between SiC and MoSi2 was detected; this zone contained silicon, iron, and aluminum, the formation of which may be related to the presence of impurities in the silicon and SiC.

Notes: Ferroelectric electron emission has two possible sources: rapid polarization switching and surface plasma discharge. The present paper uses an X-ray diffraction (XRD) method to support the theory of rapid polarization switching for lead zirconate titanate samples. A decrease in the 002 peak value and an increase in the 200 peak value were observed after electron emission in two types of samples, which were doped with lanthanum and neodymium. A comparison of the XRD data for the samples showed that a high-density electron emission was related to a high-value polarization switch. These results were consistent with the theory of rapid polarization switching.

Notes: The microstructural development and phase-transformation kinetics of stoichiometric cordierite glasses containing B2O3 and/or P2O5 additives were highly affected by the microstructural characteristics of the μ-cordierite and the type of additives. The addition of B2O3 tended to cause the formation of μ-spherulitic dendrites with thin dendritic arms, which promoted the formation of α-cordierite, either from crystallization of the residual glass or from transformation of μ-cordierite. P2O5 had the opposite effect: Increasing the temperature increased the growth rate of α-cordierite more than that of μ-cordierite.

Notes: The influence of spray parameters on the microstructure and flexural strength of plasma-sprayed alumina was investigated. Coatings were applied using a small-particle plasma spray (SPPS) method, which is a recently patented process that allows submicrometer-sized powders to be sprayed. Using identical starting powders, coatings that were produced using two distinctly different spray conditions exhibited significant differences in both microstructure and strength. Scanning electron microscopy investigations of single lamellae (or splats) revealed that, for one spray condition, melted alumina particles will splash when they contact the substrate. The morphology of the splats that comprised the subsequent layers of the coating also were highly fragmented and thinner than lamellae formed under “nonsplashing” spray conditions. The surface roughness was strongly dependent on the morphology of the lamellae; increased roughness was noted for fragmented splats. Thick coatings that were comprised of splashed splats developed a unique microstructural feature that was responsible for the observed increase in roughness. These microstructural differences greatly influenced the flexure strength, which varied from 75 ± 21 MPa for the nonsplashing spray condition to 17 ± 2.4 MPa for the “splashing” condition.

Notes: Electron-beam physical-vapor-deposited thermal barrier coatings consisting of ZrO2 stabilized by 7 wt% Y2O3 were investigated in regard to phase transformation after annealing. Free-standing ceramic layers were heat-treated in air, for up to 200 h, in the temperature range 1200°—1400°C and then analyzed by X-ray diffractometry. Based on information obtained from the {111} and {400} peaks, the phase composition and the Y2O3 content in the phases were calculated. At the start of transformation, small grains of a low-Y2O3t phase and a c phase formed. After 〉30 h at 1300°C and at 1400°C, a mixture of a t phase deficient in Y2O3, an m phase, and a c phase formed after cooling, with the Y2O3 contents in the phases roughly predicted by the phase diagrams. The results of the present study are discussed here in detail and compared with data for plasma-sprayed coatings.

Notes: The microstructure of the gold decoration layer of bone china was investigated to pinpoint the cause of the gold cracking occurring during the manufacture of high-quality bone china. Using cross-sectional TEM analysis, it was observed that SnO2 crystals from the matting agent underneath the gold underwent abnormal growth. When the few SnO2 crystals grew excessively, the matting oxide burst through the gold layer, resulting in the gold cracking. From this study, we conclude that control of the size distribution of SnO2 crystals is very important to keep a high-quality gold layer.

Notes: Porous Al2O3 and SiC–dispersed-Al2O3 (Al2O3/SiC) nanocomposites with improved mechanical properties were fabricated using pulse electric current sintering (PECS). Microstructures with fine grains and enhanced neck growth, as well as high fracture strength, could be achieved via PECS of Al2O3. The incorporation of fine SiC particles into an Al2O3 matrix significantly increased the fracture strength of porous Al2O3. Based on microstructural observations, it was revealed that the refinement of Al2O3 grains and neck growth occurred by PECS and nanocomposite processing.

Notes: A novel colloid-emulsion process has been used to synthesize nanosized strontium bismuth tantalate (SrBi2Ta2O9) particles. During calcination, the desired bismuth-layered structure phase develops at the expense of the pyrochlore phase. Calcining the precursor powder at 750°C for 2 h leads to the complete formation of single-phase layered-structured SrBi2Ta2O9. The powder that is formed consists of nanoparticles with a narrow size distribution and almost-spherical morphology. The crystallinity of the calcined powder increases as the calcination temperature and heating time increases. The developed colloid-emulsion process significantly reduces the SrBi2Ta2O9 particle size, in comparison to conventional process techniques, and results in a uniform microstructure of the obtained powder.

Notes: A novel dispersant—O-(2-aminopropyl)-O′-(2-methoxyethyl)-polypropylene glycol (AMPG)—was developed to disperse submicrometer-sized Si3N4 powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of 〉0.50) and colloidally stable nonaqueous Si3N4 suspensions can be realized using AMPG.

Notes: The deposition of nano-size titania—silica particles is carried out in a hot-wall CVD reactor by using two premixed precursors, titanium tetraisopropoxide (TTIP) and tetraethyl orthosilicate (TEOS). The deposition occurs mostly in two regions, one near the reactor entrance and the other near the reactor exit. Deposits collected near the reactor entrance are densely packed micrometer-size aggregates/particles of good adhesion to the substrate, while those near the reactor exit are loosely packed nano-size particles with a poor adhesion to the substrate. It is conjectured that the more reactive TTIP reacts first and produces TiO2 particles later covered by SiO2 formed via a catalytic surface reaction of the less reactive TEOS on TiO2 particle surfaces. The presence of surface SiO2 retards the growth of TiO2 particles, leading to deposits formed by micrometer-size aggregates containing nano-size primary particles of 30 to 40 nm in the first deposition region. With less or no SiO2 present on TiO2 particle surfaces, the deposits formed in the first deposition region are densely packed micrometer-size particles. The Ti/Si ratio of the produced particles, for a furnace temperature of 750°C, increases with increasing TTIP/TEOS concentration ratio, and is lower than the Ti/Si ratio of the incoming reactant stream. The Ti/Si ratio of the particles is also found to decrease with increasing furnace temperature.

Notes: Functionally graded materials have designed inhomogeneous distributions of different components on the scale of the material. They can be made by suspension processing, in which particles are stacked in a controlled manner. Segregation effects can be used to obtain the required gradient if the particles in suspension have different velocities. A model is derived for the composition profiles that develop as a result of these effects. The model can be used to determine the most suitable process conditions. The outcome of the model shows fair agreement with experiments found in the literature in which an Al2O3/ZrO2 composite has been produced by uniaxial centrifugal casting.

Notes: NiAl/10-mol%-ZrO2(3Y) composites of almost full density have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The former intermetallic compound, which contains a trace amount of Al2O3, has been prepared via self-propagating high-temperature synthesis. The composite microstructures are such that tetragonal ZrO2 (∼0.2 μm) and Al2O3 (∼0.5 μm) particles are located at the grain boundaries of the NiAl (∼46 μm) matrix. Improved mechanical properties are obtained: the fracture toughness and bending strength are 8.8 MPa·m1/2 and 1045 MPa, respectively, and high strength (〉800 MPa) can be retained up to 800°C.

Notes: Tungsten marker layers and X-ray computed tomography were used to monitor the compaction of spray-dried alumina. Local density changes and compaction curves show that the well-known Stage I—II transition indicates an alteration in the direction of transmitted pressure through the uppermost layer. Stage I pressure is dispersed in local agglomerate contacts until “pockets” of low density are eliminated. In Stage II, these deformed/fragmented agglomerates behave as a continuous body and interact with wall friction to transmit pressure nonuniformly into the bulk. Discrete element simulations reproduced the compaction curves and provided clear explanation of the density distribution development.

Notes: A novel VIMOX (volume identical metal oxidation) route to near-net-shaped calcium hydroxyapatite, Ca10(PO4)6(OH)2, is demonstrated: the oxidation of machinable Ca—Ca2P2O7 precursors. Mechanically alloyed mixtures of Ca and β-Ca2P2O7 were compacted into disk- and bar-shaped preforms. The latter preforms could be machined into cylinders using a metalworking lathe (200 rpm, hardened steel tooling). After oxidation at 600°C in O2, and then postoxidation annealing in H2O/O2 mixtures at 850°C and 1150°C, phase-pure hydroxyapatite was obtained. Because of offsetting volume changes from calcium oxidation and hydroxyapatite formation, porous hydroxyapatite bodies were produced that retained the shapes and dimensions (within 1%) of the machined precursors.

Notes: A simple method for fabricating TiO2-based sensors of CO(g) is demonstrated: the oxidation of Ti-bearing foils. Metallic foils (35 μm thick) were converted into free-standing, porous rutile foils (60 μm thick) by exposure to O2(g) at 800°—965°C. The oxidized foils contained thin (0.5—1 μm thick), regularly spaced oxide layers oriented parallel to the external surface. The exposure of such porous foils to increasing concentrations of CO(g) resulted in a monotonic increase in the steady-state electrical resistance. Rutile foils sensitive to 50 ppm changes in CO(g) content with response times of a few minutes were produced. The effects of oxidation conditions and copper doping on sensing performance are discussed.

Notes: An NiO/yttria-stabilized zirconia (YSZ) layer sintered at temperatures between 1100° and 1500°C onto dense YSZ electrolyte foils forms the precursor structure for a porous Ni/YSZ cermet anode for solid oxide fuel cells. Conflicting requirements for the electrochemical performance and mechanical strength of such cells are investigated. A minimum polarization resistance of 0.09 Ω.cm2at 1000°C in moist hydrogen is obtained for sintering temperatures of 1300°–1400°C. The mechanical strength of the cells decreases with increased sintering temperature because of the formation of channel cracks in the electrode layers, originating in a thermal expansion coefficient mismatch between the layers.

Notes: Structure formation in the combustion synthesis of Al2O3–TiC composites from TiO2, Al, and graphite powders was investigated using cylindrical samples and cone-shaped “quenching samples.” It is shown that the phases Ti and Ti3Al exist as intermediates in the combustion synthesis process. Titanium carbide forms in a secondary step through reactions between graphite and liquid Ti or Ti3Al, then nucleates from a liquid mixture of the three phases Ti, Ti3Al, and alumina. The nucleated particles grow in the postcombustion stage. Liquid alumina, containing TiC as a dissolved phase, solidifies into corundum grains in the postcombustion stage. Moreover, it is shown that the temperature gradient in the postcombustion stage markedly affects the microstructures of the products. Higher-temperature gradients, typical at the surface of the samples, give rise to the formation of corundum whiskers and TiC agglomerates. In contrast, lower gradients, typical in the center of the samples, lead to the formation of relatively large TiC particles and corundum grains.

Notes: Thin films of silica aerogel on a silicon wafer have been synthesized via supercritical drying of wet gel films that were obtained by spin coating the polymeric silica sol, followed by aging in an isopropanol (IPA) or tetraethoxysilane/isopropanol (TEOS/IPA) solution. The viscosity of the sol and the spin rate required to form uniform coating layers were optimized. The film thickness and microstructures could be controlled by adjusting the concentration of the sol, the spin rate, and the aging conditions. The porosities and the dielectric constants of the thin films were in the range of 76%–90% (densities of 0.59–0.22 g/cm3) and 2.0–1.5, respectively. The degree of planarization in the aerogel thin film was ∼100%, and the gap-filling capability on a 0.2 μm tungsten patterning wafer was excellent. In particular, aging the wet gel film in the TEOS/IPA solution was very effective in improving the properties of the aerogel films.

Notes: Dense PbTiO3 ceramics consisting of submicrometer-sized grains were prepared using the spark-plasma-sintering (SPS) method. Hydrothermally prepared PbTiO3 (0.1 μm) was used as a starting powder. The powder was densified to ≳98% of the theoretical X-ray density by the SPS process. The average grain size of the spark-plasma-sintered ceramics (SPS ceramics) was ≲1 μm, even after sintering at 900°–1100°C, because of the short sintering period (1–3 min). The measured permittivity of the SPS ceramics showed almost no frequency dependence over the range 101–106 Hz, mainly because pores were absent from the ceramics. The coercive field of the SPS ceramics was somewhat higher than that of conventionally sintered ceramics, which could be attributed to the small-grained microstructures of the SPS ceramics.

Notes: The effect of the environment on crack-growth processes in silicon nitride was studied by investigating the static and fatigue crack-growth behavior of small surface cracks, as influenced by testing (i) in the ambient environment, (ii) in distilled water, (iii) under vacuum, and (iv) in toluene. A principal finding was that testing under cyclic conditions led to crack-growth rates that were much higher in air than in toluene, whereas testing under static conditions in air or toluene led to minor differences in the rate of static fatigue crack growth. This difference in sensitivity to the environment under static and cyclic loading conditions was attributed, in part, to a much-greater extent of microcracking at the surface ahead of the main crack in air under cyclic conditions, in comparison to that in other environments. This propensity for microcracking at the surface in air under cyclic conditions also was reflected in the aspect ratios of the crack shapes that developed.

Notes: Fracture and environmentally assisted subcritical crack-growth processes are examined in bulk Y-Si-Al-O-N oxynitride glasses with compositions typical of the grain boundary phase of silicon nitride ceramics. Both long-crack (in compact tension specimens) as well as short-crack behavior (using indentation techniques) were investigated to establish a reliable fracture toughness and to elucidate the anomalous densification behavior of the oxynitride glass. Environmentally assisted subcritical crack-growth processes were studied in inert, moist, and wet environments under both cyclic and static loading conditions. Behavior is discussed in terms of the interaction of the environment with the crack tip. Likely mechanisms for environmentally assisted crack growth are discussed and related to the subcritical crack-growth behavior of silicon nitride ceramics.

Notes: The crystallization of 70Ga2S3.30La2S3(mol%) glasses has been studied using X-ray diffraction and transmission electron microscopy. Two of the glasses were prepared from raw materials with nominally different oxide concentrations. The third was prepared from raw materials aged in an oxygen-depleted, argon-flushed glove box for more than 1 yr. Their oxide/hydroxide impurity content was qualitatively ranked using Fourier transform infrared spectroscopy. The lowest oxide content composition (≤0.5 wt%, supplied information) devitrified readily close to the glass transition temperature, Tg, forming crystallites of a new (GLS) phase with a monoclinic Bravais lattice and a lathlike internal structure. Ga2S3was observed in small quantities between the laths. Samples prepared from nonaged, high oxide (1–3 wt%) content precursors produced the most stable glass. On crystallization, these samples exhibited spherulites composed of intergrown laths of melilite-structured La3.33Ga6S14and the new monoclinic GLS phase. Whiskers of Ga2S3were found in the residual glass between crystallites. Samples prepared from aged raw materials produced spherulites of La3.33Ga6S14on crystallization with no identifiable regions of the new GLS phase.

Notes: Gel-glasses of various compositions in the xZrO2.(10 –x)SiO2system were fabricated by the sol–gel process. Precipitation due to the different reactivities between tetraethyl orthosilicate (TEOS) and zirconium(IV) n-propoxide has been eliminated through the use of 2-methoxyethanol as a chelating agent. Thermal treatment of these gels produced crystalline ZrO2particles. While monoclinic is the stable crystalline phase of zirconia at low temperatures, the metastable tetragonal phase is usually the first crystalline phase formed on heat treatment. However, stability of the tetragonal phase is low, and it transforms to the monoclinic phase on further heat treatment. In this study, it has been found that the transformation temperature increases as the SiO2content in the ZrO2–SiO2 binary oxide increases. The most significant results were from samples containing only 2 mol% SiO2, where the metastable tetragonal phase formed at low temperatures and remained stable over a broad temperature range. X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to elucidate the structure of these binary oxides as a function of temperature.

Notes: Concrete pore solutions are concentrated electrolytes in which the activity of the chemical species must be calculated properly to determine the equilibrium state of such solutions. In this work, the chloride-ion activity coefficients in synthetic concrete pore solutions have been obtained potentiometrically, using different calibrated Cl− ion-selective electrodes (ISEs); also, a discussion about the performance of the different Cl− ISEs in alkaline media is presented. Experimental results are compared with the calculated results, using Pitzer's specific ionic-interaction model, and good agreement is observed between them.

Notes: Rapid densification of a nanometer SiC powder doped with 2.04 wt% Al4C3 and 0.4 wt% B4C was conducted by using a nonconventional sintering technique called pulse electric current sintering (PECS). In all experiments, the sintering temperature and applied pressure were kept to be 1600oC and 47 MPa, respectively, while heating rates varied between 100oC/min and 400oC/min and the holding time was either 2 or 5 min. All of the specimens which were PECS-sintered under various conditions reached near-theoretical density. The microstructures of the rapidly densified SiC ceramics consisted of large elongated grains, and the grain size increased with the increase of heating rate. Polytype transformation of SiC occurred during the PECS process, where faster heating favored the formation of 6H polytype while slower heating favored 4H polytype.

Notes: Crystalline mullite was deposited by chemical vapor deposition (CVD) onto SiC/SiC composites overlaid with CVD SiC. Specimens were exposed to isothermal oxidation tests in high-pressure air + H2O at 1200°C. Unprotected CVD SiC formed silica scales with a dense amorphous inner layer and a thick, porous, outer layer of cristobalite. Thin coatings (∼2 μm) of dense CVD mullite effectively suppressed the rapid oxidation of CVD SiC. No microstructural evidence of mullite volatility was observed under these temperature, pressure, and low-flow-rate conditions. Results of this preliminary study indicate that dense, crystalline, high-purity CVD mullite is stable and protective in low-velocity, high-pressure, moisture-containing environments.

Notes: Well-dispersed aqueous alumina suspensions were prepared at an inherent pH via the addition of an anionic dispersant. With the addition of an appropriate amount of magnesium acetate to such a suspension, the surface charge of the particles was neutralized, which was reflected in the destabilization of the slurry. Because of the formation of coordinative bonds between the Mg ion and the two dissociated carboxylic groups of the dispersant, a thin neutral layer was formed on the surface of the particles, which established a nontouching particle network and resulted in a weakly flocculated suspension.

Notes: Ti(C,N)-based ceramics that contained NbC, TaC, and WC were exposed at 1373 K in air for 10 h to study the effect of these metal carbides on the oxidation resistance. The addition of 10 mol% of NbC and 10 mol% of TaC to Ti(C,N) ceramics improved the oxidation resistance, whereas additions of 10 mol% of WC worsened the oxidation resistance. Weight gain due to the oxidation of Ti(C,N) ceramics with added WC varied in a complicated way, relative to the amount of WC that was involved. There was a competition between weight gain due to the oxidation and weight loss due to the volatile tungsten oxide.

Notes: The effects of silica particle diameter on dispersion and aggregation behavior in water were analyzed, using alkoxide-derived silica powders with particle diameters of 8–260 nm. The present study focused on the relationships between the surface silanol structure and the interaction forces between solid surfaces in water. The surface silanol structure and interaction between particles were determined using Fourier transform infrared spectroscopy, Fourier transform near-infrared spectroscopy, and atomic force microscopy. For relatively large particles (〉30 nm in diameter), the surface silanols primarily were hydrogen-bonded silanols, and isolated silanols disappeared. The hydrogen-bonded silanols formed a hydrogen-bonded water layer on the particle surface; therefore, the additional hydration force was strong between these relatively large particles. In contrast, the surface density of isolated silanols increased as the particle diameter decreased to 〈30 nm, and the additional hydration force between ultrafine powders disappeared. The aggregation behaviors of alkoxide-derived silica powders were dependent on the hydration force, which was changed by the surface silanol structure.

Notes: It is believed that the segregation of oversized dopant ions to grain boundaries in Al2O3 hinders grain-boundary diffusion, thereby reducing the tensile creep rate in this system by ∼2–3 orders of magnitude. In order to explain this improvement in creep behavior, it is helpful to characterize both the effective cation and interstitial volumes at grain boundaries, because the relative openness of some boundary structures suggests a great accommodation of oversized ions. In this study, the boundary volume is determined by a spatially local Voronoi construction, which highlights cation (Al3+) substitutional sites as well as large interstitial voids. In particular, we examine the spatial distribution of free volume near grain boundaries and, in addition, the dependence of the driving force for segregation on misfit strain in doped Al2O3. We interpret our results in light of recent evidence that selective codoping can provide a more efficient means of filling available space near boundaries, thereby further enhancing creep resistance.

Notes: Mullite ceramics have been produced by reaction sintering of powders prepared using pseudoboehmite–colloidal silica and aluminum sulfate–colloidal silica mixtures. The microstructural development of these mullites was studied by a number of transmission electron microscopy based techniques including diffuse dark field, Fresnel fringe defocus imaging, and high-resolution transmission electron microscopy. This characterization procedure showed that mullite ceramics free from glassy phases at triple junctions and grain boundaries could be produced from both mixtures using suitable sintering temperatures and alumina/silica ratios. The wetting of grain boundaries by glass, occurring in the mullite ceramics from either incomplete reaction between alumina and silica components or release of silica from the mullite structure with increasing temperature, was found to depend on the prior thermal history of the ceramics.

Notes: Sol–gel-derived powder samples of zirconia (ZrO2) prepared via the dissolution of zirconium n-propoxide in methanol, ethanol, and 2-propanol have been characterized mainly using perturbed angular correlations spectroscopy, as a function of temperature. Results indicate that the nanostructures and subsequent thermal evolution are alcohol dependent: the shorter the alcohol chain, the more hydrolyzed the product. ZrO2 powder that has been obtained using ethanol as the solvent is the product that exhibits the better stabilization of the metastable tetragonal phase (t-phase). It undergoes a clear and detailed t1-form →t2-form → monoclinic ZrO2 thermal transformation and shows the highest activation energy against the transformation to the monoclinic phase.

Notes: The microstructures of niobium-based alumina composites prepared by pressureless sintering of compacts of attrition milled Al2O3, Nb, and Al powder mixtures were studied. The addition of a small amount of Al is assumed to assist in rapid sintering. X-ray diffraction analyses show that Al2O3, Nb, NbO, and the intermetallics AlNb2 and AlNb3 are present in the composites. Electron microscopy studies confirm the existence of these phases and reveal dense, fine-grained (≤500 nm) composites. Al2O3 and Nb grains form the matrix. NbO occurs as grains and additionally as small particles within Al2O3 grains and at Al2O3/Al2O3 grain boundaries. The intermetallic AlNb2 and AlNb3 phases do not exceed 300 nm in size if they occur at grain boundaries, and possess even smaller dimensions when occluded within Al2O3 grains or located at Al2O3 triple junctions. While the niobium intermetallics are expected to form during the heating cycle before reaching the sintering temperature, the NbO is assumed to form during the cooling cycle due to precipitation of oxygen dissolved in the niobium.

Notes: A strain-gauge procedure that enables determination of the crack-tip toughness (KI0) from bending-strength tests is described. The procedure is applied to coarse-grained alumina and yields an average KI0 value of 2.51 MPa·m1/2, with a standard deviation of 0.16 MPa·m1/2.

Notes: Silicon nitride has been researched intensively, largely in response to the challenge to develop internal combustion engines with hot-zone components made entirely from ceramics. The ceramic engine programs have had only partial success, but this research effort has succeeded in generating a degree of understanding of silicon nitride and of its processing and properties, which in many respects is more advanced than of more widely used technical ceramics. This review examines from the historical standpoint the development of silicon nitride and of its processing into a range of high-grade ceramic materials. The development of understanding of microstructure–property relationships in the silicon nitride materials is also surveyed. Because silicon nitride has close relationships with the SiAlON group of materials, it is impossible to discuss the one without some reference to the other, and a brief mention of the development of the SiAlONs is included for completeness.

Notes: Colloidal stability of concentrated aqueous BaTiO3 suspensions with ammonium salts of poly(acrylic acid) (PAA-NH4) and poly(methacrylic acid) (PMAA-NH4) as a function of pH and solids loading is investigated. For suspensions with solids loading less than 40 vol%, the required polyelectrolyte concentration to stabilize aqueous BaTiO3 suspensions decreases with increasing pH, but remains relatively unchanged with increasing solids loading. As the solids loading continuously increases (e.g., 〉50 vol%), the required amount of polyelectrolyte increases, but exhibits a minimum at pH ∼ 9.2. The critical amount of polyelectrolyte needed to achieve colloidal stability of aqueous BaTiO3 suspensions as a function of pH and solids loading is summarized in a three-dimensional stability map.

Notes: The optical properties of the heavy-metal oxide glasses 70PbO.30TiO2,70PbO.30CdO, and 70PbO.30TeO2doped with Pr3+,Nd3+,and Eu3+ions have been investigated. The transition energies of the absorption spectra of Pr3+and Nd3+ions are analyzed for the Racah parameters, configuration interaction terms, and spin-orbit coupling. The absorption spectral intensities of Pr3+and Nd3+ions are analyzed for the Judd–Ofelt parameters. The Judd–Ofelt parameter, Ω2,suggests strong covalency for the Ln–O bond in these oxide glass matrices for both Pr3+and Nd3+ions and follow the order 70PbO.30TiO2〉 70PbO.30CdO 〉 70PbO.30TeO2.This trend has been correlated to that of oxide ion polarizabilities, which follow the same order. The radiative parameters, viz., transition probability (A), branching ratios (βR), and stimulated emission cross sections (σp), for laser transitions have been obtained. The high Ω2for Pr3+leads to significantly larger σpfor the3P0→3F2transition in these glass matrices compared to those in fluoride and oxyfluoride glasses. The room-temperature emission 1D2→3H4transition of Pr3+is much larger in 70PbO.30TiO2than in the other two glass systems. The emission spectra of Pr3+show temperature effects due to the Boltzmann population. The red-to-orange intensity ratios in the emission spectra of Eu3+also support strong covalency of the Ln–O bond. The phonon side-band spectra (PSB) of Eu3+are correlated with the infrared spectra. The electron–phonon coupling strengths and phonon energies have been obtained in all the cases.

Notes: The cyclic fatigue life of zirconia bioceramic was determined under biaxial flexion using disk-shaped specimens. The fatigue life was not reduced by subjecting the material to a simulated physiological environment nor was it affected by testing at different loading frequencies. Tests performed at different stress ratios produced a large degree of scatter in the data but a statistical analysis proved that there was no significant effect on the fatigue life of the material. Failure of disk specimens was initiated either by flaws introduced during manufacturing or by the more typical inherent flaws commonly observed in ceramics. The former generally resulted in premature, low-stress failures on initial loading whereas the latter acted as initiating defects for fatigue cracks that then propagated to failure. The distributions of the two categories of flaw were analyzed using two- and three-parameter Weibull probability functions. It became clear that the Weibull modulus for the fatigue failures was consistent with previously reported work on other ceramics.

Notes: R-curves, process zones, and shielding stresses of barium titanate (BaTiO3) and partially stabilized zirconia (PSZ) have been studied using compact-tension (CT) specimens. BaTiO3 and PSZ exhibited pronounced R-curves that rose over similar crack lengths and showed steady-state toughnesses of 0.7 and 6.4 MPa·m1/2, respectively. Both steady-state toughnesses were ∼80% larger than the initial fracture toughnesses. Ferroelastic domain switching was the main toughening mechanism in BaTiO3, whereas, in PSZ, transformation toughening was the main toughening mechanism. The crack process zone and crack-opening-displacement (COD) profile of each material was studied in detail using atomic force microscopy. Crack-closure-stress distributions were extracted from the COD profiles, using weight-function methods. The resulting stress profiles indicated that compressive residual stresses of 40 MPa in BaTiO3 and 400 MPa in PSZ acted in a limited region behind the crack tip. In the PSZ, crack bridging seemed to be a competing mechanism to transformation toughening.

Notes: Phase stability and effects of sintering atmosphere on the crystalline structure of Np-doped yttria-stabilized zirconia (YSZ) were evaluated in comparison with those same properties and conditions for Ce-doped YSZ. Different sintering atmospheres for Ce-doped YSZ led to differences in phase formation through reduction of the dopant from Ce4+ to Ce3+. On the other hand, YSZ specimens containing up to 40 mol% Np formed only a fluorite-structure phase regardless of sintering atmosphere. Yttria-stabilized zirconia thus seems to accommodate Np within a wide range of concentrations and to have excellent phase stability under both oxidizing and reducing atmospheres.

Notes: The effect of oxygen annealing on the dielectric aging of manganese-doped Pb(Fe2/3W1/3)O3 (PFW) ceramics is investigated in an attempt to clarify the role of defects on aging. Evident relaxor-type aging is observed in as-sintered manganese-doped PFW samples. The degree of aging gradually decreases as the annealing time increases, and no aging is observed for 100 h of annealing, which supports the correlation between oxygen vacancies and aging.

Notes: We present a new approach, namely ball milling, to synthesize amorphous boron nitride (a-BN). The amorphization kinetics are revealed by X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS). HRTEM investigations indicate that, in the early stage of milling, the thick sp2 layers are sliced into many thinner sheets because of cleavage along the basal planes. In the intermediate stage of milling, deformation is accommodated primarily by simultaneous shearing along the basal planes. As a result of sustained shearing, a number of defects, such as stacking faults, (0002) [11¯20] twinning, simultaneous shearing of lattice planes, and half Frank loops with Burgers vectors of 1/2[0001], are introduced in the hexagonal BN (h-BN) grains. Simultaneous shearing also causes significant change in the lattice symmetry of most grains. In the final stage of milling, the fiberlike tightly bonded sp2 sheets are broken and refined further, until a nanocrystalline and amorphous mixture is formed. XRD of the sample milled for 180 h exhibits an amorphous halo pattern; nevertheless, HRTEM demonstrates that the end product is essentially a nanocrystalline and amorphous mixture. The grain sizes of the nano-crystals are 〈3 nm, and their stacking is turbostratic. EELS investigations of the a-BN indicate that bonding is primarily sp2, but a small fraction of sp3a-BN is also found, which is assumed to be the nuclei of the cubic phase (c-BN) in the high-pressure and high-temperature experiments and thus facilitates the hexagonal to cubic transition. The present a-BN fabrication method can provide an effective way to facilitate the synthesis of sintered bulk c-BN materials.

Notes: R-curves of lead zirconate titanate (PZT) have been measured with compact tension (CT) specimens for different poling conditions and grain sizes. Depending on poling direction the plateau value of the R-curves ranged from 1.13 to 1.54 MPa·m1/2 for a grain size of 6.4 μm and from 1.14 to 1.30 MPa·m1/2 for a grain size of 5.2 μm. Poling in the thickness direction yielded the material with the highest fracture toughness while the direction parallel to the loading direction led to the lowest fracture toughness.

Notes: A benzene–thermal reaction of TiCl4 and NaN3 at 350°–380°C was conducted for the preparation of nanocrystalline TiN. Powder X-ray diffractometry patterns indicated that the powder was cubic-phase TiN with a lattice constant a= 4.23656 Å. Transmission electron microscopy images showed the TiN powders consisted of uniform spherical particles with an average diameter of 50 nm. The binding energies of Ti 2p3/2 and N 1s core levels at the positions of 454.85 and 397.1 eV, respectively, and the Ti:N atomic ratio of 1.08:1.00 were detected by X-ray photoelectron spectra. A possible formation mechanism of TiN was proposed.

Notes: Grinding lanthanum oxide (La2O3) with Al2O3 was conducted to investigate their mechanochemical reactions to form lanthanum aluminate (LaAlO3) powder using a planetary ball mill. Grinding for 120 min allowed us to obtain single-phase LaAlO3 with a large surface area when transition alumina was used, whereas no formation of LaAlO3 was achieved when α-Al2O3 was used. The mechanochemical process can be applied to synthesize other rare-earth (RE) aluminates (REAlO3) from mixtures of a rare-earth oxide and transition alumina.

Notes: CrN powder consisting of granular particles of ∼3 μm has been prepared by self-propagating high-temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2(2Y) composites in the CrN-rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness (KIC) of 3.3 MPa ·m1/2 and a bending strength (σb) of 400 MPa. In the latter materials almost all of the ZrO2(2Y) grains (0.36–0.41 μm) are located in the grain boundaries of CrN (∼4.6 μm). The values of KIC (6.1 MPa · m1/2) and σb (1070 MPa) are obtained in the composites containing 50 vol% ZrO2(2Y).

Notes: Synthesis of hexacelsian barium aluminosilicate (BaAl2Si2O8 or BAS) from BaCO3, Al2O3, and amorphous SiO2 was examined. BaCO3 can react with SiO2 and Al2O3 to form barium silicates (Ba2SiO4 or B2S, BaSiO3 or BS, and BaSi2O5 or BS2) and barium aluminate (BaAl2O4 or BA). It is shown that there are two competitive reactions leading to the formation of hexacelsian BAS. One involves a reaction between BS2 and Al2O3 and the other involves a reaction between BA and SiO2. In experiments with the model BS2–Al2O3 and BA–SiO2 systems it is shown that the reaction between BS2 and Al2O3 is much faster than the reaction between BA and SiO2. However, in the BAS system, Al2O3 suppresses the reactions which form BS2 and instead reacts with B2S and BS to form BA. The kinetics of hexacelsian BAS formation are greatly enhanced when BS2 is made separately and fired with Al2O3 to yield BAS.

Notes: Strength and dynamic fatigue behavior of silica fibers has been measured as a function of ambient humidity. Bare and polymer-coated fibers were compared to determine the influence of the coating. The results verify earlier work that suggests the degradation reaction is approximately second order with respect to humidity. However, we verify this result using rigorous data analysis techniques and, unlike the earlier work, the result is shown to be independent of the form of the kinetic model for crack growth. Trends in the calculated fatigue parameters illustrate that a simple exponential crack growth law best describes the humidity data. No significant differences were found between coated and bare fibers, provided the coated fibers were properly equilibrated. A data analysis methodology is given for obtaining valid reaction orders independently of the crack growth law form.

Notes: Microstructural evolution in a model triaxial porcelain was studied by X-ray diffractometry and electron microscopy of quenched samples after firing for 3 h at 600°–1500°C. The clay component dehydroxylated to metakaolin at ∼550°C. Metastable sanidine formed from decomposition of the feldspar at 〉600°C and dissolved at 〉900°C. Liquid formation at ∼1000°C was associated with melting of feldspar and silica discarded from metakaolin formation via the K2O–Al2O3–SiO2 eutectic. Liquid content increased at 1000°–1200°C with further feldspar melting and additionally at 〉1200°C because of quartz dissolution. Small (≤7 nm) mullite and γ-alumina crystals precipitated in pure clay relicts and larger (≤30 nm) mullite crystals in mixed clay-feldspar relicts at 1000°C. In the evolving microstructures, three regions were observed. These regions were derived from pure clay relicts containing primary (type-I) mullite; feldspar-penetrated clay relicts, also containing secondary (granular type-II) mullite; and the matrix of fine clay, feldspar, and quartz, containing secondary (granular type-II and elongated type-III) mullite. In addition to shape, the mullite size changed, increasing from regions containing type-I to type-III mullite, because the increasingly fluid liquid enhanced crystal growth. Below 1300°C, primary mullite was richer in Al2O3 than the secondary mullite, and the glass composition was inhomogeneous, with the K2O and Al2O3 contents varying throughout the microstructure. Above 1400°C, mullite began to dissolve.

Notes: The binary systems Ca5[PO4]3F–CaAl2Si2O8 and Ca5[PO4]3F–CaMgSi2O6 have been investigated, via annealing and quenching in the experimental method, direct observation of the melting behavior of the samples, X-ray diffraction analysis, petrography, and transmission electron microscopy. Phase equilibrium in the ternary system Ca5[PO4]3F–CaAl2Si2O8–CaMgSi2O6 was determined by combining information from the structure of the binary boundary systems and additional experimental data that were obtained from ternary compositions. The glass-formation region of the fluorapatite–anorthite–diopside system was studied, and the glass compositions for the development of glass-ceramics for technical and medical applications were identified.

Notes: The single-edge V-notched-beam fracture testing method was used to measure the short-crack R-curve behavior of a 90-vol%-alumina–10-vol%-ceria-doped zirconia multilayered composite. The initiation and extension of short cracks from the V-notch tip were observed in situ via optical microscopy. Initial crack lengths of 15–50 μm were obtained repeatedly. The resulting R-curve was similar to the R-curve that was measured using the surface-crack-in-flexure testing method. The ability to control the position of the V-notch tip within a material permits study of the influence of specific microscopic features on the fracture behavior.

Notes: A layered, zircon–molybdenum functionally graded material was obtained by starting from commercial powders of molybdenum (median particle size (d50) of ∼3 μm) and zircon (d50∼ 0.8 μm). Conventional processing led to a material that was free of internal residual stress. The sintering behavior of green compacts with compositions that corresponded to the different layers was studied via dynamic sintering. The thermal expansion coefficients of each layer were measured using conventional dilatometry. The presence of residual stresses was determined using Vickers indentations. Both thermal expansion mismatch and differential shrinkage between the layers were negligible.

Notes: The sessile drop method has been used to determine the time dependence of the contact angle at 850°C in vacuo for Ag–28 wt% Cu, Ag–35 wt% Cu–1.5 wt% Ti, and Ag–27 wt% Cu–12 wt% In–2 wt% Ti on vitreous and devitrified fused quartz substrates. Nonwetting behavior (θ 〉 90°) was observed for Ag–28 wt% Cu on both substrates with no evident effect of time at temperature. The silica substrate structure, whether crystalline or amorphous, as well as its surface condition, whether smooth or rough, made no significant difference. In contrast, with Ag–35 wt% Cu–1.5 wt% Ti and Ag–27 wt% Cu–12 wt% In–2 wt% Ti the contact angle continuously decreased with time for both silica substrates, and the structure and surface condition of the substrates had a negligible effect in the case of Ag–27 wt% Cu–12 wt% In–2 wt% Ti, which produced essentially the same contact angles on both silica substrates at a given time of hold at 850°C. The contact angles produced by Ag–35 wt% Cu–1.5 wt% Ti on devitrified fused quartz were consistently higher than those produced on the vitreous substrates, with increasing holding time at 850°C. This is attributable to the presence of extensive cracks in the α-cristobalite layer at the surface of the devitrified substrates, which obstruct wetting and spreading. These results, when correlated with the wettability of preoxidized silicon carbide by the same alloys reported in previous work, could account for the adverse effect on wetting of the high-temperature silica films formed on the surface of the SiC in that work.