Seven kinds of ceramics, β-Si₃N₄, α′/β′-Sialon, TZP, SiC, three kinds of Al₂O₃, were worn using three kinds of abrasive particles having different hardnesses by abrasive water jet (AWJ). Wear mechanisms and wear rates of the worn ceramics depend strongly on the ratio of the hardness of abrasive particles (H_p) to that of target ceramics (H_t) as well as on the fracture toughness of target materials (K_t). K_t affects the wear mechanism and rate more strongly in AWJ than in sand erosion. The erosive wear map, which has been proposed based on the experimental results of sand erosion, was found to be qualitatively applicable to AWJ.

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Rate equations for normal grain growth in a matrix which consisted of spherical grains were formulated. The difference in interfacial energy between a marked grain and other grains in the system was assumed to activate mass transport for grain growth. From the rate equations, abnormal growth rates of one larger grain in a matrix of smaller grains of the same size were calculated. The results showed that the smaller the volume fraction of the larger grain and the larger the difference in grain size became, the faster the larger grain grew.

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The results of this study are summarized as follows:
(1) High density tetragonal PZT ceramics with compositions of {Pb(Zr_xTi_1-x)O₃+0.5mass% MnO₂}, where x=0.10-0.50, were successfully synthesized by hot isostatic pressing.
(2) HIPed samples with x=0.20 had the highest bulk density of 7.82g/cm³, which is 98.2% of the theoretical density.
(3) The Curie temperature T_C for PZT ceramics with x=0.10-0.50 decreased linearly with an increase in Zr content. The rate of linear decrease m calculated from the linear plot of T_C with x was approximately 3.0°C/mol% Zr.
(4) The PZT sample with x=0.20 exhibited the highest figure of merit F.M. of around 2.1×10^-11C·cm/J. Assuming that the volume specific heat C_v of the present sample with x=0.20 and that of PZTZBM ceramic with x=0.30 are the same (3.1J/cm³·K), the F.M. for voltage responsivity of pyroelectric IR sensors fabricated using these ceramics which have the same tetragonal structure should be nearly equal.

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NaX zeolite is used to collect and decompose chlorofluorocarbons (CFCs) and to determine the behavior of CFC-11 molecules in zeolitic pores using various methods. At room temperature, CFC-11 molecules are adsorbed on the micropores of NaX zeolite, and at 400°C CFC-11 molecules were decomposed by the catalytic reaction of NaX zeolite. Approximately 30 CFC-11 molecules are adsorbed and 90 CFC-11 molecules are decomposed per unit cell of NaX zeolite. HCl and HF gases are detected in the outlet gas of the decomposed CFC-11. The results indicate that Al-O bonds in the zeolite crystal structure are destroyed. The destruction of the zeolite crystal structure tends to occur on the selective planes along the hhh, hh0 and 3hhh directions.

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Dissolution behavior of high purity α-alumina particles and adsorption of Mg²⁺ ions onto α-alumina surface were studied in 5vol% solid suspensions containing polyacrylic ammonium (PAA). The amount of alumina dissolved was higher in acidic suspensions than in neutral or basic suspensions. The solubility of alumina in the wide pH range from 2.5 to 9.3 decreased with the addition of PAA. The amount of Mg²⁺ ions adsorbed onto alumina surface depended on two factors of pH and PAA content of suspensions. Negatively charged alumina surface in the pH range from 7.6 to 9.3 adsorbed Mg²⁺ ions of 17.5μmol/m²-alumina surface. Positively charged alumina surface adsorbed little Mg²⁺ ions in acidic suspensions. The amount of Mg²⁺ ions adsorbed onto alumina surface increased in acidic or neutral suspensions and decreased in basic suspensions by addition of PAA.

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Single crystals of (Ba_0.96-xLn_xSr_0.04)TiO₃ (Ln=La, Gd) were grown over a composition range of x=0.001 to 0.03. Electrical resistivities of the single crystals were measured by the DC four-probe method. The temperature dependence of resistivities of these crystals changed from semiconductive to metallic at the Curie temperature (T_C). Although the room temperature resistivities of Gd-doped single crystals were independent of Gd concentration of 1 to 3%, they decreased monotonically with increasing the dopant concentration after annealing in a reducing atmosphere.

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One highly pure θ-Al₂O₃ powder (APA-0.2) with large surface area, but with partial agglomeration, was colloidally processed to prepare samples with uniform microstructure and high strength. A dispersant, semicarbazide hydrochloride (S-HCl) and two preparing methods, ball-milling and turbomixing, were utilized to disperse alumina agglomerates in aqueous solution. With an air-pressure-casting and step-sintering schedule, fine-grain alumina of average grain size 2.5μm, average four-point bending strength of 506MPa, and reproducible Weibull distribution (modulus=12) were obtained. The ζ-potential of APA-0.2 powder, the rheology of the slurries, green density, porosity and sintering properties of the powder were presented and discussed. Properties of green and sintered APA-0.2, including fracture strength, were compared with that of samples prepared from A-16SG powder.

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Two kinds of hydroxyapatite powder (HAp) were prepared by wet syntheses using cattle bones (r-HAp) and reagents (s-HAp). The physicochemical natures of the two HAp's juring heating in air or a stream of water vapor were compared within the temperature range of 273-1073K. The white powders obtained commonly gave a single phase of HAp and were commonly characterized within the two temperature regions of 273-673K (Region I) and 673-1073K (Region II), regardless of the gas atmosphere. The crystallite size (C_S), the specific surface area (S_A) and the total pore volume (V_T) changed little in Region I, whereas they varied considerably in Region II. The adsorption of bovine serum albumin (BSA) on these HAp's in phosphoric acid buffer solutions was satisfied with the Langmuir isotherm equation. The saturated amount (A_SA) of the adsorption and the heat of adsorption (Q) for BSA linearly increased and decreased, respectively, with increasing C_S, with the slope of the lines differing between the r-HAp and s-HAp cases. Based on these results, it was concluded that the adsorption behavior of BSA on the C-site of HAp is strongly controlled by the crystallite size rather than the pore structure. r-HAp had a 157% higher Q in Region I and 22-44% larger ASA in Region II than s-HAp, indicating an advantage as an adsorbent for biopolymers.

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Langmuir monolayers of DHP were confirmed to induce oriented crystallization of HAp in the present study. Both electrostatic and stereochemical interactions at the inorganic-organic interface were of vital importance for the oriented growth of HAp crystals. Organic surfaces with highly ordered functional groups would in general have potential to catalyze inorganic crystallization in a controlled manner through molecular recognition.

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ZnO films were prepared on silica glass substrates by the sol-gel method from Zn(CH₃COO)₂⋅2H₂O-2-methoxyethanol solutions containing monoethanolamine (MEA) or diethanolamine (DEA). Smooth and transparent ZnO films were obtained by heating at temperatures from 200 to 500°C for 10min after each coating and finally at the same temperatures for 1h. The films prepared from coating solutions containing MEA were strongly oriented along the (002) plane. The effects of heating temperature and ethanolamines on the film morphology, grain size distribution and crystallographic orientation are discussed based on X-ray diffraction and scanning electron microscopy.

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Crystallization of Al₂O₃-SiO₂ glass fiber (AS) and the effect of ZrO₂ and Cr₂O₃ addition on the crystallization were investigated by PTA, XRD and density measurement. Mullite crystallized in the AS at 995°C. The mullite crystal grew and its amount increased with rising temperature. Cristobalite crystallized in the AS at 1450°C and above. Mullite crystallized at 1015°C with t-ZrO₂ and spinel phase in fibrous glass containing ZrO₂ (ASZ). The mullite crystal grew and its amount increased with rising temperature. At 1500°C, cristobalite crystallized and the t-ZrO₂ partly transformed into m-ZrO₂. The amount of cristobalite in this fibers was larger than that in the AS. Only spinel phase crystallized at 990°C in fibrous glass containing Cr₂O₃ (ASC). The amount of spinel phase increased up to 1100°C, but slightly decreased at 1200°C and disappeared at 1300°C. Mullite appeared from 1100°C and increased with rising temperature. Cr₂O₃ dissolved in the mullite and suppressed the crystallization rate and grain growth. The addition of Cr₂O₃ raised the temperature at which the amount of mullite reached the calculated value by 105°C compared to that of the AS. Although the amount was smaller than that of the AS, cristobalite also crystallized in the ASC by firing at 1500°C.

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The effect of liquid-forming additives (CaO+SiO₂) on the microstructure of particulate reinforced Al₂O₃ ceramics, e.g., Al₂O₃-5vol% ZrO₂ and Al₂O₃-5vol% SiC, was investigated. When the liquid phase was not formed during sintering (CaO+SiO₂≤0.05mol%), the shape of Al₂O₃ grains was equi-axed. As the content of additives increased and these additives reacted with Al₂O₃ to produce the liquid phase along grain boundaries, abnormal grain growth occurred and reinforced particles could not prevent this abnormal growth.

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Densification process, phase component and mechanical strength of the feldspathic porcelain bodies were investigated. Packing ratio and flexural strength showed a linear correlation and its gradient (k-value) indicated a degree of the effect for the reinforcement during densification. The k-value was greatly influenced by mullite/glass ratio, and needlelike crystals of mullite was considered to accelerate the reinforcement of bodies. Fracture toughness increased with the residual amount of quartz. It is considered that, although the mechanisms are different, mullite and quartz strengthen the body.

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Characteristics of slurry-coated Ni/YSZ cermet anode for solid oxide fuel cells (SOFCs) were investigated for the optimization of the anode microstructure. The anodic polarization of Ni/YSZ cermet was strongly affected by the particle-diameter ratio of raw materials rather than the particle size itself. The plot of polarization versus particle-diameter ratio of YSZ to Ni yielded a minimum at a particle-diameter ratio of around 2×10^-2. From the density measurement of Cermet green bodies and EDX analysis, it was found that there was a strong correlation between the distribution of Ni in the cermet and the particle-diameter ratio. At the particle-diameter ratio which gave the minimum anodic polarization, Ni particles distributed most uniformly.

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By codoping Dy³⁺ into the SrAl₂O₄:Eu²⁺ phosphor, long persistent phosphorescence was observed and its afterglow characteristics were investigated. The excitation wavelength suitable for long persistent phosphorescence was 200-250nm, much shorter than the wavelength of 4f⁷-4f⁶5d absorption of the Eu²⁺ ions, suggesting that the energy levels of electron traps are higher than the 4f⁶5d level. The phosphorescence intensity and its lifetime increased with increasing temperature. The depth of the electron traps was calculated from the Hoogenstraaten's plot of glow curves at about 0.3 and 0.6eV. From the temperature dependence of decay curves, the deeper trap is considered to contribute to the long-lasting afterglow.

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The influence of the three parameters (composition, firing temperatures and the duration of heat treatment) on the synthesis of two crystallographic phases characterized by T_c-85K (L-phase) and -110K (H-phase) in the Sr-Bi-Ca-Cu-O and Sr-Bi-Pb-Ca-Cu-O systems was investigated. It has been shown that, with a correct starting composition and thermal conditions, pure H-phase can be obtained without foreign crystalline phase. The H-phase solid-solution ranges and its synthetic conditions were determined as follows; Sr₅Bi₆Ca_mCu_3+mO_17+2m 6<m<8 865°C/100h, Sr₇(Bi₆Pb)Ca_mCu_4+mO_21+2m 7<m<12 850°C/100h

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The TiB₂-TiN_xC_y composite ceramics, which have high hardnesses and electrical conductivities, and can be used for electric discharge machining, were fabricated by the reaction sintering of B₄C and TiN powders. The TiN powders containing 0-20mass% B₄C-additives were pressed under a pressure of 100MPa, and then sintered at 2100°C for 3.6ks in an ambient Ar gas of normal pressure. As a result, the 27.5mass% TiB₂-TiN_xC_y composite, for example, was obtained by the reaction sintering of TiN powders containing 8mass% B₄C-additive. The composite had a maximum relative density of 96.1% and showed improved hardness by -1.5 times, fracture toughness of K_IC by -1.7 times, Young's modulus by -1.3 times, electrical conductivity by -1.7 times compared with those of pure TiN ceramics with a relative density of 87.7%. The hardness and electrical conductivity of the 67.0mass% TiB₂-TiN_xC_y composite obtained from the TiN powders containing 20mass% B₄C-additive were 2.0 and 2.2 times higher than those of pure TiN ceramics, respectively, in spite of the lower relative density of 90.9%.

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Sintering behavior of (Ni, Co) O was investigated measuring linear shrinkage as a function of Al₂O₃ addition. Morphological study was also attempted for the samples sintered at 1280°C for 10h. The added Al₂O₃ reacted with the (Ni, Co) O matrix to form (Ni, Co) Al₂O₄ spinel from 800 to 1200°C. The addition of Al₂O₃ inhibited the growth of (Ni, Co) O particles, and then decreased the linear shrinkage from 800 to 1100°C. Above 1150°C, in contrast to the constant linear shrinkage of (Ni, Co) O, (Ni, Co) O with Al₂O₃ showed steep linear shrinkage behavior. Furthermore, at 1400°C, the linear shrinkage for (Ni, Co) O without Al₂O₃ and with Al₂O₃ was 14 and 18%, respectively. The microstructure of the quenched samples showed that number of (Ni, Co) Al₂O₄ spinel precipitates decreased above 1150°C. The average grain size of the samples sintered at 1280°C for 10h decreased from 11 to 4μm with increasing Al₂O₃ additive from 0.5 to 8mass%; the addition of Al₂O₃ inhibited the grain growth of matrix in the final stage of sintering.

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The strengths of zirconia-to-zirconia joints formed by glasses with diopside (Diop), and eutectic diopside and anorthite (Diop-An) compositions were measured by a shear strength method. The concentration distributions of several elements in the vicinity of the joint interface were observed by SEM and EPMA. When the Diop glass was used as the insert material, the optimum joining temperature was around 1350°C and the maximum joint strength was 22MPa. When the Diop-An glass was used, the optimum joining temperature decreased to around 1275°C and the maximum joint strength was 73MPa. A modified layer in the insert material was observed in the zirconia adjacent to the joint interface. For the Diop-An glass, the insert layer was amorphous and no crack was not observed in the zirconia, the modified layer, the insert layer or at the joint interface.

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Y₂O₃-doped low purity β-Si₃N₄ powder was ball-milled for 6 to 100h. The effects of ball-milling time on the properties of the powder and the hot-pressed body were investigated. As increasing ball-milling time, average particle size and crystallite size decreased and the amount of SiO₂, carbon, some metallic impurities and lattice strain increased for the ball-milled powder. The increase of SiO₂ was ascribed to the mechanochemical reaction of H₂O contained in the milling fluid with newly formed powder surfaces. The source of carbon was both the milling fluid and the container. The increase of Al and Mg was explained by the wear of milling balls. Sintering behavior and microstructure of the sintered bodies were influenced by the powder properties modified by different ball-milling time. Mechanical properties were strongly dependent on their microstructures.

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