Two AlN materials with different impurity contents have been studied by TEM. Impurities are found to modify the microstructure of the material by forming polytypoid grains, precipitates of Al₂O₃ and FeAl₂O₄. The 27 R polytypoid is mostly present as a whole in one grain, but mixtures of polytypoids or compositional modulation are also found. Almina precipitates are either intragranular or at triple points. The spinel phase shows a perfect epitaxy with the polytypoid phase. Complicated arrangements of dome like defects are present in most AlN 2 H grains and are chemically induced.

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The influences of a variety of organic polymers on the properties of the resultant gel films have been studied in the system B₂O₃-SiO₂, with the aim of the application of these gel films to the fine-patterning process. Among the polymers examined, polyether glycols such as polyethylene glycol and polytetramethylene glycol were found to be the most suitable for the patterning process. These compounds are considered to soften effectively the resultant gel films, which enables one to leave patterns on the films. The addition of polyether glycols had no bad influences on the optical properties of the finally obtained glass films, since the additives had been eliminated completely during the heat-treatment. The newly-developed process is applicable to the formation of fine-patterns in submicrons.

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A new type of linear motor using a piezoelectric actuator has been developed in which a mechanically resonating part slides on a stationary rail. The slider consists of two bimorphs, or a multilayered piezoelectric actuator with a bonded elastic vibratory fork. The key to obtaining a smooth movement is to realize a slight deviation in the resonance frequency of each leg of the fork so that the moving direction can be controlled by changing the drive frequency.

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The hydration process of low silica containing calcium aluminate glasses in high-alumina cement was studied. The glasses with the compositions; SiO₂ 0-15%, CaO 25-50%, Al₂O₃ 45-60%, were prepared by fusion and quenching in water. The mechanism of the hydration varied discontinuously in the above composition range. The ratio of CaO to Al₂O₃ in glass seems to determine the mechanism of hydration process of low silica containing calcium aluminate glass. The hydration process of calcium aluminate glasses studied was classified into several types, in view of similarity of the hydration process of crystalline calcium aluminate (12CaO⋅7Al₂O₃, CaO⋅Al₂O₃, CaO⋅2Al₂O₃).

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The pressureless bonding of 3Y-TZP and Fe using Ti sheets (thickness: 0.5mm, 0.02mm) and a bonding agent has been studied. A specimen consisting of 3Y-TZP and Fe between which an agent and Ti sheet is inserted is heat-treated at 900°-1100°C for a considerable length of time in an Ar stream. To reduce the residual stress upon the interface which is caused from the thermal expansion coefficient difference between 3Y-TZP (α=8.8×10^-6/°C) and Fe (α=13×10^-6/°C), the optimum Ti sheet thickness has been found to be 0.5mm. When bonding is made employing a 0.5mm-thick Ti, the bonding tensile strength of 20°C/min in Ar has become more than 140MPa. The mean bonding strength of the specimens has been 50MPa with the use of a 0.5mm-thick Ti sheet under quite the same conditions. The structure of the well bonded interface has been found to be as shown below. 3Y-TZP/Titanium oxides layer (TiO, Ti₂O)/Ti-rich layer (Ti with scanty Cu)/Cu-Ti alloy layer (CuTi₂)/diffusion layer (CuTi₂ containing Fe)/Fe(α-Fe). Utilizing the same method, bonding of 3Y-TZP with Nb, Ta (purity: 99.9%) and SUS 304 has been carried out by the heat-treatment. With the 0.5mm-thick Ti sheet, the bonding strength of TZP and Nb/Ta specimen has become more than 105MPa and 120MPa, respectively. However, the bonding strength of the 3Y-TZP and the SUS 304 has been found to be just approximately 30MPa. Such bonding strength is expected to be furthermore increased in parallel with the raise of the heating rate (20°C/min).

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Lamellar Al₂O₃ ceramics were fabricated by the slip casting method, using two types of Al₂O₃ powders having different particle sizes and densification behavior between each other. The lamellar ceramics have the structure of alternating dense and porous layers with respective thickness, λ_D and λ_P, ranging from 60 to 500μm, and the volume fraction of the dense layers, V_D, from 0 to 100%. The lamellar structures were controlled by changing the casting time and using the centrifugal force for draining the Al₂O₃ slurries during green forming. Fracture strengths of the lamellar ceramics were measured by three-point bending. Some of the lamellar ceramics showed higher flexural strength than monolithic, dense Al₂O₃ (-335MPa). The maximum strength, -400MPa, was obtained for the lamellar ceramic with V_D=89±3%, λ_D=500μm, λ_P=60μm. The high strength is discussed from the view point of the crack deflection in the porous layers.

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Zirconium oxynitrides (ZrON) were prepared by heating ZrO₂ or ZrN powders in NH₃ at 1100°C. Single phased β-ZrON and γ-ZrON were obtained by controlling the heating time. Tetragonal ZrO₂ formed under some cases changed to monoclinic ZrO₂ by mortar milling. Phase stability of β-ZrON against heating in the stream of N₂-H₂ gas mixture (3:1) was examined. β-ZrON was oxidized to form m-ZrO₂ by heating below 1100°C for a long time. When β-ZrON was heated at 1000°C or higher temperature in a short time, β′-ZrON and a small amounts of m-ZrO₂ and ZrN were formed. β′-ZrON and ZrN decreased and m-ZrO₂ increased with heating time between 1000° and 1100°C. Three phases, i.e., β′-ZrON, m-ZrO₂ and ZrN, coexisted above 1200°C, and the ratio of each phase was almost constant.

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This investigation was carried out to understand the remarkable change in electric resistance of thermistor material before and after the glass-coating process adopted in making the commercial thermistor. The thermistor material was made from nitrates of Mn, Fe, Co and Ni with the molar ratio of 6.1:2.9:1.3:1.0 by firing at 1400°C in air atmosphere. Electric resistance of the thermistor material was measured continuously in the temperature range from room temperature to 700°C, with a rate of 1°C/min, in air and nitrogen. In air, a remarkable change in electric resistance was observed between 300° and 500°C, and this change was reversible in both heating-up and cooling-down processes. In nitrogen, a similar change in electric resistance appeared in the heating-up process. However, no detectable change was observed in the cooling-down process in nitrogen. X-ray diffraction analysis of heating-up process in air revealed that the crystal change, in which mixed crystal of cubic and tetragonal spinel transfered to cubic spinel, occurred between 420° and 480°C. This crystal change in air was reversible and was observed in both heating-up and cooling-down processes. On the other hand, in the case of nitrogen, similar crystal change was observed only in heating-up process, and no crystal change occurred in cooling-down process. In heating-up process in nitrogen, the starting mixed crystal of cubic and tetragonal spinel changed to cubic spinel above 480°C, and this cubic spinel remained unchanged even though heat-treated up to 1000°C. In cooling-down process in nitrogen, cubic spinel structure remained unchanged to room temperature. These results propose that the effect of glass-coating on electric resistance of thermistor material is attributed to crystal change before and after the glass-coating.

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The chemical reaction to form dielectric thin films of Sr(Zr_0.2Ti_0.8)O₃ by an RF magnetron sputtering method using a ceramic target has been investigated. The amount of extracted Sr by water, Zr/Sr atomic ratio and the lattice constant in addition to other electric and optical characteristics of the film were measured to examine the progress of the reaction. As the results, the chemical reaction to form the perovskite type dielectric thin films with the composition described above was found to be well promoted in the sputtering conditions; substrate temperatures above 450°C, sputtering gas pressure at ≈6×10^-3 Torr, sputtering gas mixing ratio O₂/Ar of ≈3/1, target-substrate distance of 50-60mm, and sputtering power density at ≈4W/cm², obtaining the good electric and optical characteristics.

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Thermal and mechanical properties of two-phase composite sintered-materials consisting of ZrO₂ with 3mol% Y₂O₃ and various volume fractions of CaF₂ were measured. The composites were made by hot-pressing micronized powders at 1300°C under 30MPa pressure. No phase except ZrO₂ and CaF₂ was observed by the X-ray diffraction method in the composites, and no crack in sintering bodies was observed by scanning electron microscope. Thermal expansion coefficient increased with increasing CaF₂ content, in agreement with the prediction obtained by the Turner's equation for thermal expansion coefficients of composites. Bending strength decreased with increasing CaF₂ content. The composite containing 50vol% CaF₂ showed a high thermal expansion coefficient of 15×10^-6/°C and a bending strength was approximately 350MPa. These properties are similar to that of stainless steel and Al₂O₃, respectively.

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Chemical deintercalation of lithium ions was attempted on Li₂MoO₃ with a structure related to the α-NaFeO₂ type structure. The lithium ions in Li_2-xMoO₃ were removed up to x=0.77 by oxidation, and its structure remained almost unchanged. The evolution of the lattice parameters for deintercalation compounds was divided into two parts; the regions of 0<x≤0.51 and 0.51<x≤0.77. In the first region, both a- and c-axes increased with an increase of x. In the second region the a-axis increased with increasing x, while the c-axis remained unchanged. This behavior could be explained by the existence of Mo-Mo bonding and immigration of lithium ions from the ((Li_1/3Mo_2/3)O₂)n layer to the interlayer spaces. Magnetic properties of Li_2-xMoO₃ exhibited temperature-independent paramagnetism.

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Fatigue behavior of 3mol% Y₂O₃ containing tetragonal zirconia polycrystals was studied in water at 20° and 95°C, and in air at 95°C by measuring the fracture stress (σ_f) as a function of stressing rate (σ) (dynamic fatigue technique). The grain size of the specimens was 0.5μm (Z3Y-Ib) and 1.12μm (Z3Y-IIb). There were linear relationships between logσ_f and logσ in the whole range of crosshead speed (0.005mm/min to 50mm/min) in water at 20°C. Crack growth parameters N obtained from their slopes were 47.8 for Z3Y-Ib and 47.5 for Z3Y-IIb, and fatigue of their specimens was slight. For Z3Y-Ib, there was a linear relationship between logσ_f and logσ at crosshead speed of 0.005mm/min to 50mm/min in air at 95°C, too. The N value obrained from the slope was 46.4 indicating slight fatigue. On the other hand, fracture stress in water at 95°C showed a constant value above the crosshead speed of 0.5mm/min even if stressing rate increased. However, the relationship between logσ_f and logσ below 0.5mm/min was similar to that at 20°C. For Z3Y-IIb, fracture stress in air at 95°C showed a constant value above crosshead speed of 0.5mm/min. However, there was a linear relationship between logσ_f and logσ below 0.5mm/min and the slope was similar to that at 20°C. The fracture stress of Z3Y-IIb in water at 95°C showed a constant value at the crosshead speed of 0.005 to 50mm/min. The constant value in water was less than that in air.

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Iron Oxide (III) and aluminum oxide (α) were mixed at the molar ratio of 1 to 2, fired for 3 hours under various oxygen partial pressure (P₀₂); 3.9×10^-7Pa≤P₀₂≤2.1×10₄Pa at 1300°C, , or 4.0×10^-6Pa≤P₀₂≤2.1×10⁴Pa at 1400°C. The lattice constant of the iron spinel and the valence of iron ions were measured. From the X-ray powder diffraction pattern, the distribution of iron ions was obtained by the PFSR method. The lattice constant was almost constant at low P₀₂, increased gradually with the increase of P₀₂, then increased steeply at P₀₂≈10^-1.5Pa (1300°C), or P₀₂≈10⁰Pa (1400°C), and finally remained unchanged at high P₀₂. The valence of iron ions showed the similar change. At low P₀₂, the iron ions were all bivalent, and FeAl₂O₄ was produced. About 80% of the tetrahedral sites and 10% of the octahedral sites were occupied by iron ions, because of the tetrahedral site preference of Fe²⁺ ions to Al³⁺ ions. With the increase of P₀₂, a part of Fe²⁺ ions was oxidized to Fe³⁺ ions, and substituted for Al³⁺ ions with a smaller radius, resulting in an increase in the lattice constant. In iron spinel containing Fe³⁺ ions, the ratio of the tetrahedral sites occupied by iron ions increased because of their tetrahedral site preference over Fe²⁺ ions. In the low P₀₂ region, the oxidation of the iron ions and the substitution of Al³⁺ ions in the tetrahedral sites proceed stepwise with increasing P₀₂. The steep increase of the lattice constant and the amount of Fe³⁺ ions observed at a certain P₀₂ has been explained as due to the remarkable change in the cation distribution accompanying the promotion of the oxidation of Fe²⁺ ions.

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CaF₂ up to 2.5wt% was added to a mixture of 50vol% hydroxyapatite (HAp) and 50vol% zirconia containing 2mol% Y₂O₃. The mixture was hot-pressed at 1300°-1400°C and 20MPa for 10min. The sintered bodies obtained consisited of apatite (HAp and/or FAp) and zirconia (tetragonal and cubic phase). The addition of CaF₂ enhanced the densification, incresing the bending strength and hardness. The bending strength of sintered body containing 0.5wt% CaF₂ obtained at 1400°C was about 450MPa, whose value was about 12% larger than that without CaF₂. On the other hand, the fracture toughness was not improved by the addition of CaF₂. After soaking in distilled water, saline and Ringer's solution, bending strength of the composite ceramics was 12-14% lower than that in air.

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Preparation of SiC powder from SiO_2-CH₄ mixtures by RF-plasma method was investigated. The reaction product consisted of β-SiC, free carbon, Si and SiO₂. The maximum yield of SiC formation was obtained for the moler ratio [CH₄]/[SiO₂]≈3. Addition of H₂ to the reaction system suppressed the formation of free carbon, but increased the amounts of SiO₂ and Si. The crystallite size of β-SiC was in the range of 10-30nm irrespective of the reaction conditions.

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The interface-reaction controlled diffusion creep in fine-grained Al₂O₃ polycrystals was affected by the dispersion state of ZrO₂ particles. The ZrO₂ particles at grain boundaries reduced the creep rate and increased the activation energy for creep. The stress exponents were two for both pure Al₂O₃ and ZrO₂-containing Al₂O₃ polycrystals. The pure Al₂O₃ polycrystals deformed more rapidly than the superplastic ZrO₂-toughened Al₂O₃ at 1250° and 1300°C.

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For increasing the thermal conductivity of AlN ceramics, a reactive gas atmosphere was applied to the post-sintering process. The Ca content in the samples decreased as the temperature and time of the reactive gas treatment increased. The sample exposed to CF₄ gas for 5h at 1100°C showed the thermal conductivity of 230W/mK. It was suggested that under optimized conditions, selective reaction of the reactive gas with the secondary phase and/or oxygen impurities segregated at the grain boundaries increased the thermal conductivity.

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