Raman spectra of paratellurite, tellurite and pure TeO₂ glass were measured. The normal vibration of paratellurite and tellurite was analyzed. The spectrum of pure TeO₂ glass were deconvoluted into symmetric Gaussian functions. The normal vibrations of paratellurite are exactly described as combined representations of movement of oxygen atom in Te-_eqO_ax-Te linkage and vibrations of TeO₄ trigonal bipyramid (tbp). Compared the resolved Raman peaks of pure TeO₂ glass with normal vibration of paratellurite, all Raman peaks from 420 to 880cm^-1 are assigned to the vibrations of TeO₄ tbp and Te-_eqO_ax-Te linkage. The antisymmetric stretching vibrations of Te-_eqO_ax-Te linkage have relatively large intensities to symmetric stretching vibrations of Te-_eqO_ax-Te linkage. In pure TeO₂ glass, TeO₄ tbps are formed by most of tellurium atoms and connected at vertices by the Te-_eqO_ax-Te linkages.

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Hydrated vanadium oxides were prepared by hydrothermal treatment of aqueous VOSO₄ solutions. The products were found to take layered structures based on the V₂O₅ structure. Phases with the layer spacings of 7.1, 8.3, 13.2, 14.2 and 19.0Å were obtained and a primary product was the phase with the spacing of 14.2Å (phase I). The composition of the phase I was estimated as V₂O_5-δ⋅nH₂O(0<δ<0.2, 1.5<n<2.5). An additional phase with the spacing of 17.3Å(phase I′) was found in as-filtrated samples, which changed to the phase I by drying. The phase I transformed succesively into the phases with smaller layer spacings by dehydration on heating or evacuating. The overall transitions were as follows; I′(17.3Å)→I(14.2Å)→Iα′(12.6Å)→Iα(11.5Å)→Iβ(10.0Å)→Iγ(8.3Å). The transition from phase I to Iβ was reversible. These layer-type phases were distinguished from V₂O₅ gels.

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The densification treatment was conducted on the lead silicate glasses in order to elucidate the effect of densification on the mechanical properties and glass structure. The degree of densification for the lead silicate glasses was found to decrease with increasing PbO content, suggesting that the atomic scale voids disappear with an increase of PbO content. Young's modulus and Vickers hardness were increased by the densification treatment for all the lead silicate glasses. The temperature derivatives of Young's modulus for all the densified silicate glasses were higher than those before densification, especially remarkable in the SiO₂-rich region.
The fracture toughness was decreased by densification for the glasses with PbO>about 40mol%. The fracture surface energy showed a similar compositional change to the fracture toughness. The densification treatment was expected to make it difficult for the irreversible energy-absorption process to take place near the crack tip in the densified glass.

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ZrO₂ thin films doped with Cr were prepared on ITO coated glass substrates by magnetron rf-sputtering in a mixture of Argon and Oxygen. Al/Cr-ZrO₂/ITO structure devices were used for electrical and optical measurements. The one-light-source photocurrent and UV-stimulated photocurrent spectroscopy measurements were carried in the range of 1000nm and 340nm. These photocurrent spectroscopies suggested that an impulity level of Cr-ion and a discrete trap level exist at approximatly 2.6eV and 2.2eV below the ZrO₂ conduction band edge, respectively. C-V measurement revealed that Cr-doped ZrO₂ films have a charge storage effect.

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Three complex bismuth compounds with layer lattices were found in the system Bi₅Nb₃O₁₅-NaNbO₃; Bi_2.5Na_0.5Nb₂O₉, Bi_2.5Na_2.5Nb₄O₁₅ and Bi_2.5Na_3.5Nb₅O₁₈. From X-ray diffraction data and polarizing microscope observation, the crystal system of Bi_2.5Na_0.5Nb₂O₉ is determined to be orthorhombic with the lattice parameters a, b, c and b/a equal to 0.5462nm, 0.5470nm, 2.4912nm and 1.002 respectively at room temperature. From the heating and cooling curves of DTA, Bi_2.5Na_0.5Nb₂O₉ was found to melt congruently at 1226±5°C. The lattice parameters of the tetragonal primitive cell of each compound Bi_2.5Na_2.5Nb₄O₁₅ and Bi_2.5Na_3.5Nb₅O₁₈ at room temperature are as follows; a=0.389nm and c=4.082nm for Bi_2.5Na_2.5Nb₄O₁₅, and a=0.390nm and c=4.855nm for Bi_2.5Na_3.5Nb₅O₁₈. Bi_2.5Na_2.5Nb₄O₁₅ and Bi_2.5Na_3.5Nb₅O₁₈ were found to melt incongruently at 1208±5°C and 1219±5°C respectively. In the phase diagram, an eutectic temperature is 1208±5°C at 70mol% NaNbO₃. The phase diagram of this pseudobinary system was prepared based on the melting, liquidus and eutectic temperatures, which were measured using thermal analysis, X-ray diffraction and peterographic microscopy.

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An internal heating hydrothermal apparatus which can be used up to 1000°C and 300MPa, was designed to realize high temperature hydrothermal conditions. Transparent beryl crystals were grown in 0.025-0.05N NaOH solutions on the seed above 600°C and 160MPa. Step and pyramidal growth patterns were observed on the surfaces of the crystals grown on the seed crystals with a (1120) and s (1121) faces. Relatively high growth rate (30-40μm/day) was attained for the both seed crystals. Water molecules and alkali cations were incorporated into the channels of the beryl structure as in natural emeralds.

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The method for determining free silicon in sintered Si₃N₄ by laser Raman spectrometry has been studied. In this study, it was found that the amount of free silicon can be determined from the Raman peak intensity ratio I. 521cm^-1/I. 206cm^-1, in which the peak of 521cm^-1 is assigned to free silicon and that of 206cm^-1, to skeleton vibration of β-Si₃N₄. The results obtained by using this method are as follows:
(1) The increase in sintering temperature and time tends to increase the amount of free silicon.
(2) The variation of free silicon content at the surface part from place to place is greater than that at the inside part.
This method makes it possible to measure the amount of free silicon in β-Si₃N₄ easily, and possibly gives instructive information such as the condition for avoiding precipitation of free silicon.

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The frost durability of autoclaved light weight concrete (ALC) was improved by heat treatment of surface coating with inorganic (lithium silicate) nonflammable solution. Such great enhancement in frost durability is achieved probably by the formation of an almost crack-free film which is coated by several times of soak-drying processes on the internal surface of large cavities in ALC without losing permeability.

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The high thermal conducting mechanism of AlN ceramics has been investigated by the relationship between microstructure and thermal conductivity of the samples which were obtained by pressureless-sintering at 1900°C for 1-24h with Y₂O₃ 2 at% addition as a sintering aid. The thermal conductivity increased gradually with increasing sintering time from 199W/m·K at 1h to 266W/m·K at 24h. Microstructure was investigated by SEM, TEM and powder X-ray diffraction together with quantitative analysis of Y and O contents. AlN grain size increased from 4μm at 1h to 12μm at 24h and the grain boundary phase gradually concentrated to triple points and the amount of this phase decreased with sintering time. Furthermore, grain boundary phase composition changed from Al₂Y₄O₉(Al₂O₃⋅2Y₂O₃) at 1h to Y₂O₃ at 24h. This change seems to occur through selective reduction and nitrization of Al₂O₃ in Al₂Y₄O₉ with an increase in sintering time. These results show that the decrease in phonon scattering at grain boundaries improves the thermal conductivity.

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The effects of HIPing parameters such as temperature, pressure and time and powder characteristics on the densification of presintered alumina were studied to establish a theoretical densification model of HIPing. The characteristics of sintered bodies examined are the density and grain size. The obtained results were analyzed by the Ashby's densification model. The HIP sintering of alumina was governed by the grain boundary diffusion of aluminum ion. The densification rate increased markedly with increasing temperature and pressure of HIPing, and with decreasing grain size. The densification was accompanied by the grain growth. The densification rate predicted by the model agreed well with that by the experiments, if proper diffusion coefficients and grain growth rate were accomodated in the analysis.

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Glasses in the system Y₂O₃-Al₂O₃-SiO₂ were employed as a model of grain boundary phase of Si₃N₄-Y₂O₃/Al₂O₃ ceramics and examined their physical properties and structure by means of IR spectroscopy. The glass compositions studied were xY₂O₃⋅(60-x) Al₂O₃⋅40 SiO₂ in wt%, where x=30, 40 and 45. It was found that the substitution of Y₂O₃ for Al₂O₃ increases the density, glass transition temperature, elastic constants and Vickers hardness, but decreases fracture toughness. These results were explained from a proposed structure that Y³⁺ ions act as network modifiers in contrast to Al³⁺ ions which are supposed to be a network former. On the basis of measurements of the properties of the glasses, some properties of Si₃N₄-Y₂O₃/Al₂O₃ ceramics were discussed. The Vickers hardness of Si₃N₄-Y₂O₃/Al₂O₃ ceramics had similar dependence on Y₂O₃/Al₂O₃ molar ratio with that of the model glasses. The flexural strength of the ceramics was related to the microstruc ture, more specifically to the aspect ratio of the Si₃N₄ grains and phase composition, rather than that of grain boundary phase.

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A commercial reaction-sintered silicon carbide (RS-SiC) was heat-treated at 1600°C in vacuum to remove the free Si, and the resulting SiC bulk with about 19% porosity was further heat-treated at 1600°-2000°C for 0.2-20h in vacuum of 0.65Pa. Although the second heat-treatment did not significantly change the porosity, grain growth and oxygen content in the porous RS-SiC, the heat-treatment at 1780°C for 2h increased the bending strength of the porous RS-SiC from 205MPa to 322MPa and caused the transition from intergranular to transgraular fracture. The strengthening effect may be attributed to the increased bonding area between grains due to evaporation-condensation and surface diffusion, and to relaxation of stress concentration due to the change in pore shape. However, the strength decreased by heat-treatment at 1780°C for 10h or 2000°C because of the decrease in the bonding area and the volume of SiC matrix due to the decomposition of the SiC in vacuum.

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Synthesis reactions of SiC whiskers from silica and carbon were studied. Blended raw materials containing silica, carbon, and catalysis were heated to a temperature from 1300° to 1500°C in a stream of hydrogen. The obtained SiC whiskers had diameters from 0.3 to 0.5 micron and lengths from 10 to 100 micron. The SiC whiskers were beta-type silicon carbide. Total yield of the whiskers based on quantities of Si in the raw materials ranged from 92 to 95%. Scanning electron microscopic analysis revealed that SiC whiskers grew by the VLS process in which materials were transported through the vapor phase. It is considered that Si atoms transferred as SiO (g) and C atoms as hydrocarbon such as CH₄ and C₂H₂. Ratedetermining steps of the whisker synthesis reaction were analyzed by measuring the volume of CO(g) generated as a function of reaction time. Depending on the reaction time, the rate-determining step varied from one to the other. The first step is the removal of CO (g) from the reaction system, because the reaction rate under a given experimental condition remained constant during the first stage and the reaction rate in this stage increased with an increase in hydrogen flow rate. The reaction rate in the second stage decreased with time and gave good agreement with Mampel's reaction rate equation (phase boundary controlled reaction). The activation energy derived from the rate constant of the Mampel's equation was approximately 20kcal/mol. Therefore, the second rate-determining step was considered to be the formation of hydrocarbons on surface of carbon raw materials.

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In order to clarify how the fracture strength depends on the grain boundary structure in covalent-bonded SiC, 6H-type α-SiC Bicrystals with twist misorientations around ‹0001› axis were prepared by a hot press technique at 2270K under 40MPa in a vacuum of 2.7MPa. The grain boundary structure was observed by high resolution electron microscopy and the fracture strength was measured by the three-point bending test. The results obtained are summarized as follows.
(1) An amorphous-like layer was observed along the boundaries prepared. The structure was like the extended grain boundary reported for sintered SiC. The thickness of the boundary was about 1nm irrespective of the twist misorientation. The thickness is thinner than those observed in sintered SiC probably because of the low index boundary plane.
(2) Twist misorientation dependence of grain boundary strength was weak, which is presumably caused by the isotropic nature of the extended grain boundary.
(3) The extention of the boundary is considered to come of the polarity in SiC because the boundary with a misorientation of 0°±2° extended also.
(4) The boundary structure is thought to depend on the preparing process. Coincidence site lattice boundaries are likely to be formed by sublimation-recrystallization or chemical vapor deposition, while extended grain boundaries are formed by sintering because each grain is constrained by surrounding grains during sintering.

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The composite with Si₃N₄ matrix, doped with 2wt% Al₂O₃ and 5wt% Y₂O₃, and 50wt% SiC powder having mean particle size of 0.3, 0.7 and 1.0μm were fabricated by hot-pressing at 1850°C under a pressure of 300kg/cm² for 1 hour, and their mechanical properties were investigated. The composite with 0.3μm SiC showed a bending strength of 93kgf/mm², which is slightly lower than that of monolithic Si₃N₄, 100kgf/mm². The strength of the composite decreased with increasing mean particle size of SiC, suggesting that large size particle becomes defects in the sintered body. Fracture toughness of the composite, about 7MNm^-3/2, doesn't depend on the particle size, and is almost same as that of monolithic Si₃N₄.

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Needle-like mullite was prepared by leaching out the silica glass from New Zealand kaolin fired at 1550° to 1700°C. High-temperature properties of the needle-like mullite, such as thermal expansion and thermal shock were examined. Needle-like mullite 1-6μm long, 0.1-0.5μm thick was obtained at 1550° and 1600°C, and 10-20μm long, 1-2μm thick, at 1650° and 1700°C. The specific surface area of these crystals grown at 1550° and 1650°C were 8.2 and 4.1m²/g respectively, and did not decrease with reheating in the temperature range from 1000° to 1650°C for 20-30h. The axial thermal expansion coefficients of crystals at 25°-800°C were α_a=2.2, α_b=3.9 and α_c=4.5×10^-6/°C. No evidences of fracture and crack were detected on quenching needle-like mullite crystals from 1150°C to 0°C.

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A TiN-Al₂O₃ composite powder was synthesized by the floating-type fluidized-bed CVD. Al₂O₃ particles were floated in an N₂/NH₃ gas mixture, and TiCl₄ was fed to deposit TiN. The composite powders obtained and the ceramics were examined by an electron probe microanalyzer (EPMA). The TiN content in the composite powder was controlled by the flow rate of carrier gas of TiCl₄. It was deduced that the composite powder was formed by deposition of fine TiN particles onto Al₂O₃ particle surfaces, aggregating to about 3μm. Ceramic from the composite powder containing 12.5wt% TiN was conductive. Its microstructure suggested that TiN was uniformly dispersed as compared with mechanical mixing.

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A Chemically machinable photosensitive glass was shown to have a high potentiality as a material for new type particle track detectors. Micro crystals grow only along the alpha particle track in the glass through two steps of heat treatment, 500°C for 1h and 600°C for 5min, and the micro crystals grown in the glass are selectively etched in HF 3% solution. The etchpits are observed and counted using either scanning electron micrographs or an optical microscope with TV monitor. The proportionality of the number of etchpits to the alpha particle fluence is fairly good after the correction for the etchpits overlapping.

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TiO₂ films were obtained from Ti(OC₃H₇)₄ vapor with a high growth rate of ca. 40nms^-1 by laser assisted CVD. In particular, laser beam increased the growth rate at 400°C more than 2.5 times. These increases in the growth rate might be attributable to the promotion of a homogeneous nucleation by laser beam in the gas phase above the substrate. Anatase films emerged at 500°C or above without the assistance of laser beam instead of amorphous films at lower temperatures. On the other hand, anatase films emerged even at 400°C or above with the assistance of laser beam. The activation energy for TiO₂ film formation by this work was 17kJmol^-1 similar to that by the traditional CVD.

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β-SiC was synthesized by irradiating of continuous wave YAG laser into a SiO₂-C mixture with various C/SiO₂ mole ratios under flowing Ar. Curled and entwined SiC whiskers having an average diameter of 0.08-0.16μm and a length of more than 100μm were obtained. The SiC whisker completely covered the surface of particles. SiC was formed by the reaction of SiO₂ with C via Si. A mixture in which coarse C particles are covered with fine SiO₂ particles was preferable to that in which coarse SiO₂ particles are covered with fine C particles for synthesis of SiC by the reaction of SiO₂ with C.

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