Effects of Ca/P ratio on the crystallization of apatite and anorthite were investigated by differential thermal analysis (DTA) and scanning electron microscopy (SEM) on a series of glasses with the nominal composition of 3.0 mass% MgO, 41.4 mass% SiO₂, 8.6 mass% Al₂O₃, and 47 mass% (CaO+P₂O₅). It is shown that the activation energy for apatite crystallization decreases with increasing CaO content, whereas for anorthite crystallization it is not affected by changing Ca/P ratio significantly. Liquid phase separation was found in these glasses and the P₂O₅ promoted the nucleation appreciably.

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The effects of mono- and divalent cations on the properties of multicomponent phosphate glasses were investigated. The T_g, Y_p and α were increased with increasing ionic radius of the alkali ion. As a result, the water durability of the phosphate glasses was improved. An introduction of divalent cations also resulted in the same tendency. It is evident from the IR measurement that the coordination number of cross-linking cations is increased with increasing ionic radius of the cation, and as a result, the bonding strength between cations and oxygen was weakened. It is considered that the improvement of the water durability is due to the increasing linking density, which is accompanied by increasing steric hindrance of the additional cations against attack by water molecules.

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In relation to the joining of silicon nitride ceramics to metal, the kinetics of reaction between Si₃N₄ and W has been investigated in Ar and N₂ at temperatures from 1473 to 1673 K. Using an Si₃N₄-W powder mixture, the reaction rate was determined with a thermobalance, and the reaction products were examined by X-ray diffraction. The reaction between Si₃N₄ and W started at 1473 K in Ar, but not in N₂. Tungsten nitride was not detected regardless of the atmosphere. Tungsten suicide W₅Si₃ was produced only in Ar, and it changed to WSi₂ at higher temperature and on prolonged heating. The initial rate obeyed the linear rate law and the activation energy was 278kJ·mol^-1. The rate-determining step is considered to be the chemical reaction at the interface between Si₃N₄ and W. At a late stage of reaction, the kinetics followed the parabolic rate law and the activation energy was 281kJ·mol^-1. The reaction rate is probably controlled by the solid-state diffusion through the product layer.

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Sensitivity of SnO₂ thin-film gas sensors which were fabricated by the dip-coating method was found to exponentially increase with the decrease in film thickness. This could be ascribed to the substantial increase in the resistivity of the films in air with the decrease in the film thickness, accompanied by the decrease in the size of SnO₂ crystallites.

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Gold-dispersed SrTiO₃ thin films were prepared by the r. f. magnetron sputtering method. The as-deposited films were heat-treated in air at temperatures ranging from 700 to 900°C for 1h. The optical properties of the films were compared with those of gold-dispersed BaTiO₃ and gold-dispersed SiO₂ thin films, which were prepared by the same procedure as gold-dispersed SrTiO₃ thin films. The SrTiO₃ matrix crystallized at temperatures above 700°C and fine gold particles became coarse between 800 and 900°C. For the SrTiO₃ matrix, the peak position of the surface plasmon resonance of gold particles shifted toward the longer wavelength as the volume fraction of gold and heat treatment temperature increased. The changes of the absorption peak position of the gold-dispersed SrTiO₃ thin films were similar to those of gold-dispersed BaTiO₃ thin films. Nonlinear optical property of these films was measured by the degenerate four-wave mixing (DFWM) method at 532 nm using a Q-switched Nd: YAG laser with 7-ns pulse duration. The values of x⁽³⁾/α₅₃₂ of the gold-dispersed SrTiO₃ thin films were ten times larger than those of the gold-dispersed SiO₂ thin films. In the case of SiO₂ matrix, enlargement of x⁽³⁾/α₅₃₂ in accordance with enlargement of particle size of gold originate from an increase of f₁ due to decreasing ε_m″ of gold particles. On the other hand, for the SrTiO₃ and BaTiO₃ matrices, refractive indices of the matrices increase with increasing heat treatment temperature. The enlargement of refractive index (n_s) or dielectric constant (ε_f) of the films attribute to the enlargement of x⁽³⁾/α₅₃₂ of gold-dispersed SrTiO₃ and BaTiO₃ thin films besides the enlargement of particle size of gold. In contrast, the nonlinear susceptibility of the gold particles, x_m⁽³⁾, in the gold-dispersed SrTiO₃ and BaTiO₃ thin films decreased with increasing mean particle size.

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Using lime and amorphous silica as the starting materials, gyrolite (Ca₈(Si₁₂O₃₀) (OH)₄⋅7H₂O) was prepared hydrothermally with the Ca/Si molar ratio of 0.66 and 0.50 at 200°C for 0.5-128 h. The formation process was studied mainly by ²⁹Si NMR. The initially formed C-S-H consisted mainly of long chains of silicate anions. For Ca/Si=0.66, the chain which had been formed was broken, and C-S-H changed into gyrolite and xonotlite. For Ca/Si=0.50, only gyrolite was formed from a long chain of the silicate anions. It is thought that the differences of the C-S-H structures, which were formed in the initial stage, greatly influenced the final products. In addition, for Ca/Si=0.50, the Z-phase was also formed as a precursor of gyrolite and its silicate anion structure was similar to that of the gyrolite.

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The effect of excimer laser radiation to silicon nitride ceramic surface morphology was investigated. The response of the surface at irradiation to different laser fluences and in-vacuo measurements of the particle emission due to laser irradiation were examined. The irradiated surface showed pillar-like features at low fluence (20kJ/m²), however, flat surfaces were produced at high fluence (100kJ/m²). Quadrupole mass spectrometry during laser irradiation showed that the emitted particles were Si⁺, Y⁺, O and N. It is thought that the surface silicon nitride and/or grain boundary crystal phase (Si₃N₄⋅Y₂O₃) was decomposed during laser irradiation, and the resulting Si⁺ to form SiO₂ layers and/or pillars on the surface. These surface features degrated the strength of the specimens due to pore formation just under the surface.

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Grain-oriented KSr₂Nb₅O₁₅ solid solutions were prepared by hot-pressing. The compositions examined were 0.333 KNbO₃-0.667 SrNb₂O₆ (stoichiometric KSr₂Nb₅O₁₅, abbreviated as KSN 33/67) and 0.420 KNbO₃-0.580 SrNb₂O₆ (abbreviated as KSN 42/58). The maximum degree of orientation for KSN 33/67 was 0.21 as measured by the Lotgering method, whereas that for KSN 42/58 was 0.86. KSN 42/58 forms a liquid phase at the hot-pressing temperatures. The liquid phase promoted grain boundary sliding and the formation of rod-like grains with large aspect ratios during hotpressing, resulting in the large degree of orientation. The Curie temperature was dependent on the degree of orientation. Samples with larger degree of orientations had the lower Curie temperatures for KSN 33/67, for which the larger grain size was responsible. For KSN 42/58, on the other hand, samples with larger degree of orientation had higher Curie temperatures. The shift of the Curie temperature is caused by internal stress generated at the ferroelectric to paraelectric phase transition. The neighboring grains with similar orientation reduce the magnitude of the internal stress.

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Rate equations for sintering and grain growth have been proposed on the two-sphere model that simulates shrinkage processes during heating of a ceramic powder compact. In the model it was assumed that total excess energy associated with surfaces and grain boundary drives mass transport in sintering and grain growth. The rate equations formulated here show that sintering and grain growth are activated by the same kinds of driving force and processes. They show quantitatively that the sintering rate increases with a decrease in grain boundary energy and with a decrease in the grain size difference. It is found also that the grain growth of a larger grain is much slower than a smaller grain and that the growth rate of a smaller grain is accelerated remarkably when its grain size becomes smaller compared with a lager grain.

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A large number of specimens were synthesized in a wide range of cations for the Sr and Bi-sites in the Sr₅Bi₆Cu₃O₁₇ (563; R-phase) and Sr₇Bi₆Cu₄O₂₀ (764; C-phase) compositions. Superconductivity (T_c-10K) in R-phase solid solution was found only including PbO, which formulated as Sr₇(Bi₆Pb_x) Cu₄O_20+x (1<x<2). It showed that Pb addition is essential for the formation of a single R-phase superconductor. In addition, a new C-phase compound composition with (Sr₅Ba)Bi₆Cu₃O₁₈ was also found. The crystal chemical criteria favorable for the formation of R- and C-phase compounds were clarified by using the composition ratio of (A) Sr/Bi. It is represented as follows; R-phase<1.0<C-phase.

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A novel continuous reactor was developed for industrial production of monodispersed powders via alkoxide route. Couette-Taylor vortex flow was used for solution mixing. Each of Taylor vortices can be worked as a batch reaction vessel. Monodispersed silica powders were prepared by the hydrolysis of ethyl silicate with water and ammonia in ethanol using this reactor. The results were comparable to those obtained using batch process. The effect of Taylor number and residence time on the particle size, particle size distribution, yield, and particle number density of monodispersed silica powders was investigated. Monodispersed silica powders could be continuously produced for 5h using this reactor.

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A conversion process from potassium tetratitanate fibers into potassium hexatitanate was investigated to develop potassium hexatitanate fibers with negligible leachability which are usable as a filler for fiber-rein-forced polyester thermoplastic resins. Calcined potassium tetratitanate fibers were dispersed in water. By titrating the above mentioned suspension with an aqueous HCI solution to adjust the value of ([K⁺]/[H₃O⁺])^2/3=5.71×10⁵ at 60°C, the fibers with TiO₂/K₂O=5.95 was obtained. The product thus obtained was heated at 1000°C for 30min, then potassium hexatitanate fibers having a tunnel structure were obtained. Then, the water soluble potassium was further removed with an aqueous HCI solution. Potassium hexatitanate fibers having a tunnel structure whose molar ratio of TiO₂/K₂O was 6.0 was obtainable. Water soluble potassium thus prepared was only 4 mass ppm. The potassium hexatitanate fibers prepared by the novel method developed by the present authors were found useful as a reinforcing material for polycarbonate which has been known to be vulnerable to soluble potassium.

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Effect of film thickness and surface roughness of substrate on the residual stress of TiN coating prepared by arc ion plating was studied. Chipping and spalling of TiN films increased with increasing surface roughness and film thickness. The thermal stress of TiN coating was calculated by finite element method (FEM) analysis. The results indicate that the thermal stress of TiN films increased with increasing surface roughness of substrates. From stress analysis by FEM and the X-ray method, it is concluded that chipping and spalling of TiN films occurrs when the total stress consisting of thermal and intrinsic stresses generated during the deposition process exceeds the mechanical strength of the TiN films.

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Reaction behavior of Ca(OH)₂-SiO₂ system at 75°C was investigated using silica glass plate as an SiO₂ sample by SEM observation, XPS analysis and quantitative analysis of Si and Ca of the reaction products. Reaction of silica glass with Ca²⁺ at 75°C, which leads to the formation of calcium silicate hydrate C-S-H, was found to proceed in three stages; (1) At the first stage the whole glass surface was covered with the layer containing Ca²⁺ ion. (2) At the second stage crystalline C-S-H was formed by the reaction between Ca²⁺ and silica glass surface, and glass surface was exposed. (3) At the third stage the reaction with Ca²⁺ proceeded at the SiO₂ surface, and increases the amount of C-S-H. When the reaction product on silica glass surface at the beginning of the reaction was assumed to be amorphous C-S-H, the ratio of Ca/Si in the product was infinity at first, decreased as the crystal growth of C-S-H proceeded, and finally reduced to be constant. The final ratio of Ca/Si depends on the solution pH. In the solution of pH=10.7 the ratio of Ca/Si of crystalline C-S-H became 1.2.

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The correlations among Seebeck coefficient, oxygen content and superconducting property were examined for four Bi-Sr-Ca-Cu-O systems, i.e., a 2223-phase oxide, Big_1.84Pb_0.34Sr_1.91Ca_2.03Cu_3.06O_10.1-z, and three 2212-isostructural oxides, Bi₂Sr_2-xCa_1+xCu₂O_y (x=0, 0.5 and 1.0). Temperature-Programmed-Desorption (TPD) as well as Temperature-Programmed-Oxidation (TPO) measurements revealed that small amounts of oxygen (2-3×10^-5mol/g) were sorbed and desorbed reversibly for all oxides examined in the temperature ranges of ca. 100-400°C and ca. 250-600°C, respectively. In good agreement with such sorption-desorption behavior, the Seebeck coefficient (Q) of each oxide was found to change reversibly with changing temperature in the range of 100-600°C. This means that Q is a reversible function of oxygen content for each oxide. For the 2212-oxides, Q values at 100°C were in the range of ca. -10-+10μV/K and increased to the positive direction almost linearly with decreasing oxygen content, though the increments were somewhat different depending on composition. This indicates that oxygen content is directly related with the carrier concentration of each sample. Interestingly, T_c of each 2212-oxide was observed to go through a maximum with oxygen content. It was found that the highest T_c was reached at the oxygen content at which Q was brought to around zero at 100°C for each oxide. These results suggest that there exists an optimum carrier concentration giving the highest T_c in common for the three 2212-oxides tested.

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In order to study the strength evaluation method using miniature ceramic specimens, flexural fixtures for these miniature specimens were developed and mechanical strength of alumina ceramics whose size varied from 0.2(thickness)×2(width)×7(length)mm to 3×4×40mm was measured using these fixtures. The average strength of small specimens increased with decreasing specimen size. The dependence of strength on size was approximated using a Weibull size scaling with effective area.

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To evaluate an effect of grain boundary crystallization on corrosion characteristics of sintered silicon nitride in alkaline, weight-loss was measured during corrosion test in boiling 30mass% NaOH aqueous solution up to 200h for as-sintered and heat-treated Si₃N₄ (1100°C, 3h+1400°C, 6h). As-sintered and heat-treated Si₃N₄ showed 0.8mass% and 0.1mass% weight decrease after 200h, respectively. The grain boundary crystallization was effective to improve the corrosion resistance of Si₃N₄. This could be attributed that quarternary oxynitrides Y₈Si₄N₄O₁₄ and Y₂₀Si₁₂N₄O₁₈, called as J-phase and H-phase, respectively, crystallized in intergranular liquid by the heat treatment, resulting in a decrease of residual secondary glass phase in grain boundaries. Mechanical characteristics including crushing load of Si₃N₄ ball, fracture toughness and hardness were evaluated, and the grain boundary crystallization improved these properties slightly.

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Mullite/zirconia composite materials were characterized in terms of electrical conductivities, structure and microstructure. It was found that the conductivity assumes a minimum at about 10mass% ZrO₂. The highest conductivity was observed in the range of 60-100mass% ZrO₂. XRD studies have revealed that the tetragonal phase of zirconia assumes the highest concentration at 60mass% ZrO₂.

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Composite silica gels containing perchloric acid HClO₄, dodecatungstophosphoric acid H₃PW₁₂O₄₀⋅29H₂O (WPA), or tetra-n-buthylammonium perchlorate (n-Bu)₄NClO₄ were prepared by the sol-gel method from tetraethoxysilane and each dopant. For all the systems no changes in conductivities were observed during gelation where the transformation from liquid to solid occurred macroscopically. The conductivities of silica gels doped with HClO₄ or WPA, the values of which were about 10^-2S·cm^-1 at room temperature and higher than those of the pure silica gels and (n-Bu)₄NClO₄-doped silica gels (10^-7S·cm^-1), did not change in the drying process from wet to dried gels.

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The SiC matrix composites reinforced with carboncoated HI-NICALON were investigated. Samples hotpressed at 1750°C had a maximum strength and K_IC of 490 MPa and 11 MPa √m at room temperature, respectively. The strength at 1300°C was higher than that at room temperature. However, the strength decreased above 1400°C. There might be an amorphous phase in the matrix which softens the samples at high temperatures, resulting in plastic behaviour at high temperatures.

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Bi₂Sr₂CaCu₂O_x single crystals were irradiated with 18MeV Fe⁸⁺ ion at room temperature. Superconductive property and microstructure of the samples after the irradiation were investigated by magnetization hysteresis (ΔM) and transmission electron microscopy (TEM). ΔM was enhanced by increasing ion dose up to 1×10¹²ions/cm², but decreased at the density of 1×10¹³ions/cm². The ion irradiation produced ellipse-like amorphous defects with the size of several nm, which may behave as flux pinning centers inside the crystals. The defects were formed in the band region of 0.5μm at the depth of about 4.5μm from the surface. The number of defects were equal to several times of applied ion dose. The optimum dose for improving superconductivity should be dominated by the defect size and spacing of defects to avoid overlapping among the defects.

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Mullite composite ceramics reinforced with 10, 20 and 30vol% a-alumina whiskers were prepared by hotpressing at 1500 to 1800°C under 30 MPa for 30min. The mechanical properties of the hot-pressed bodies were investigated. Considerably dense composites were obtained at 1700°C with a whisker content of up to 30vol%. No change in room temperature bending strength was observed by addition of whiskers. The sintered bodies obtained at 1700°C had the highest room temperature bending strength of around 380 MPa. Although the high temperature strength showed complicated dependence on whisker content, the composite with a whisker content of 30vol% had almost the same high temperature strength as monolithic mullite. Increasing whisker content increased monotonously hardness and elastic modulus. The fracture toughness of a composite with a whisker content of 30vol% was 1.5 times larger than that of monolithic mullite, due to crack deflection by whiskers and to the increase of elastic modulus.

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The formation of ferroelectric Pb(Zr, Ti)O₃ thin films was carried out by spin-coating and pyrolysis of the metal naphthenates. The solution for spin-coating was prepared by mixing Pb, Zr and Ti naphthenates at the Pb:Zr:Ti molar ratio of 1.05:0.52:0.48. Homogenous precursor films spin-coated on Pt plates were heat-treated in air at 500°C for 5 min for crystallization into the single-phase ferroelectric perovskite Pb(Zr, Ti)O₃. The resultant film shows good ferroelectric properties: the coercive field E_c and the remanent polarization P_r were estimated to be 39kV/cm and 24μC/cm², respectively.

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