A borosilicate glass powder was solidified with a NaOH solution or distilled water by the hydrothermal hot-pressing technique. The effect of hydrothermal conditions on the compressive strength was investigated, and the densification mechanism of the glass powder during the hydrothermal hot-pressing was discussed in terms of isothermal shrinkage. The glass powder was successfully solidified by hydrothermal hot-pressing at a reaction temperature lower than that of an ordinary pressure sintering. The solidified body obtained in the presence of distilled water (10wt%) at 280° had a high compressive strength of about 2300kg/cm². The analysis of initial densification process of the glass powder in hydrothermal hot-pressing with Murray's rate equation revealed that the densification proceeds both by viscous flow and by rearrangement process. Analysis of the shrinkage rates with a rate equation of hydrothermal reaction suggested that the dissolution of particles into solution controlled the initial densification of the glass powder, and that the alkaline metal acted as a catalyst.

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The optical absorption spectra of VO²⁺ ions dissolved in PbO-B₂O₃ and R₂O-PbO-B₂O₃ glasses (R=K or Na) have been measured. By using the spectral results, the bonding mode of Pb in the glasses has been discussed. Judging from the dependence of peak position for B₂*-E_π* transition on the glass composition, it is suggested that although Pb behaves as a network modifier in the glasses, a part of Pb contributes to the formation of glass network. This relation is discussed on the basis of the relation between the peak wave number and ratio of four-coordinated B atoms to the total B atoms (N_4B). On the assumption that the Pb ratio used in the formation of the glass network is α(x-0.2) in xPb(1-x)B₂O₃ glasses and (x+y-0.2) in xR₂OyPbO(1-x-y)B₂O₃ glasses, the value of α is calculated to be 2.04.

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Hydrothermal reaction sintering is one of the methods to prepare oxides ceramics. Metals, intermetallic compounds or alloys are sealed in a Pt capsule with water. On heating they react with high pressure high temperature water, and produce metal oxides and hydrogen gas. At high temperatures, hydrogen gas diffuses out of the capsule, then the capsule containing oxide powders is compressed by outside gas pressure. The oxide powders, therefore, can be sintered in the capsule as in HIP (hot isostatic pressing). By this method, we can obtain a metal-oxide composite by the control of water to metal or alloy ratio in the capsule. The known quantities of alloy powders; water-atomized permalloy powder (Fe-47wt% Ni<#100, and Fe-36wt% Ni<#100) and redistilled water were hermetically sealed with an electric arc in a platinum capsule 2.7mm inside diameter, 0.15mm thick and 35mm long. This capsule was treated at 100MPa, 800°-1000°C, for 10-240min in a high pressure high temperature apparatus using Ar gas as pressurizing medium. The produced sintered ceramics were examined by X-ray diffraction, optical and scanning electron microscopy, and energy dispersive spectroscopy (EDS). The products are composed of oxide matrix and disperse alloy phase. According to the X-ray diffraction and EDS, the oxide phase contained only iron as cation. Selective oxidation of iron, therefore, was occurred under the hydrothermal conditions as well as in air. Magnetite and wüstite were observed as iron oxide phase. The ratio of magnetite and wüstite is dependent on temperature, quantity of H₂O, and time. When a specimen is treated at high temperatures, for a long time, or with a little quantity of H₂O, wüstite phase is a main phase. When the opposite conditions, magnetite is a main phase. This tendency results from both the kinetics and the thermodynamics. The composites showed superposed magnetic properties of Fe-Ni alloy and iron oxides, magnetite and/or wüstite.

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The thickness accuracy in alumina ceramic green tapes made by the doctor-blade method has been improved the experiment and calculated simulation. A minimized thickness dispersion in the green tape using the one-blade construction method was derived. In this study, the thickness accuracy of the green tape made by a two-doctor-blade construction method was examined. Calculated simulation was undertaken to correlate with the experimental results. The two-blade construction method improved the unifomity in thickness. In the 1st report, the parameter of the slurry reservoir level (H_R) has been the parameter responsible for the unifomity in thickness. Simulation of the two-blade construction method was derived as follows that H_R shared smaller.
H=l₂/l₁⋅h₁³/h₂³⋅H_R+6μl₂/ρgh₂³⋅V₀(h₁-h₂)
Where, H_R is 1st reservoir level, H is 2nd one, l₁ and l₂ are 1st and 2nd blade thickness, h₁ and h₂ are 1st and 2nd blade clearance respectively, and V₀ is carrier transfer speed. When the 2nd term in the right hand of the eqution was made large, the effect of H_R could be made small. Consequently, the thickness accuracy was improved. In the experimental observation, 2nd reservoir slurry was drifted to the 2nd blade side by the transfered carrier tape. The apparent reservoir level (H) near the 2nd blade side became higher than that of mean value. The level was made the shape as sloped down to the 1st level. This sloped level had a dumping effect by shifted to foward and back. Subsequently, the apparent reservoir level (H) was kept constant. It improved to the thickness accuracy.

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The theremal fatigue behavior of 3mol% Y₂O₃-containing tetragonal zirconia polycrystals (Y-TZP) with average grain sizes of 0.4μm (Z3Y-I) and 1.0μm (Z3Y-II) was studied by quenching into water bath at 20°C. The retained strength distribution of Z3Y-I subjected to multiple cycle quench at ΔT=350° and 300°C showed a shoulder at a certain F level, which corresponds to the initiation point of thermal shock damage. The F level increased with increasing thermal shock cycle number. For Z3Y-I at ΔT=350°, the proportion of damaged specimens was half for 1 cycle quenching and most for 10 cycles. At ΔT=300°C, the proportion of damaged specimens was none for 1 cycle, a few for 8 cycles and half for 60 cycles, but at 250°C, no crack was generated at 90 thermal shock cycles. On the other hdnd, the strength distribution of Z3Y-II subjected to multiple cycle quench at 350°C was similar to that of Z3Y-I at ΔT=350°C, but those of Z3Y-II at ΔT=300° and 250° Cwere followed by decreasing standard deviation, and the difference between maximum and minimum strengths was within about 3.1% for the thermal shock cycles above fifteen. The average strength of Z3Y-II subjected to 75 thermal shock cycles at ΔT=300°Cand 90 cycles at ΔT=250°C were about 60 and 76% of the original strength before water quench, respectively. The thickness of zone transformed from tetragonal to monoclinic phase by chemical reaction with hot water was 103μm for 30 thermal shock cycles, 155μm for 50 cycles and 356μm for 75 cycles at ΔT=300°C, and 36μm for 60 cycles and 211μm for 90 cycles at ΔT=250°C.

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Thirty one kinds of clay roofing tiles were prepared under different fabrication conditions, such as deairing pressure in extrusion, grain size of clay particle aggregates, raw clay and firing temperature. Fundamental data set of frost damage for indirect evaluation of frost susceptibility were obtained by direct freezing-thawing method which has been developed by Hudec for natural aggregates in concrete. Water absorption, saturation coefficient, apparent porosity, water adsorption, bending strength, capillary water saturation and several characteristic values from pore size distribution were employed as indirect evaluation factors for frost susceptibility. Indirect evaluation procedures were undertaken as follows. First, the multi-regression equation to achieve the maximum value of a poly-nominal multi-correlation coefficient among weight loss after 130 cycles of freezing-thawing (FT130) and several characteristic variables is derived. Second, the indirect evaluation values, “Frost Index” (“FINDX”) calculated from the multi-regression equation were compared. Considering the analysed results from the time and cost saving point of view, the following reliable equation for indirect evaluation of frost susceptibility for clay roofing tiles was suggested.
“FINDX”=0.762×Ln(ADS45)+21.387×Ln(WABSB)-24.154×Ln(APPRS)+27.575 Moreover, the critical range of pore radius for frost damage of a clay roofing tile was suggested as 100-400nm from the correlation analysis between FT130 value and specific pore volume within a respective range of pore size.

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Erosive wear by solid particle impingement was tested for 16 kinds of Si₃N₄ which were gas-pressure sintered at different temperatures using different raw material powders containing various amounts of additives. Testing conditions were as follows: # 30 SiC abrasive grains, abrasive grain speed of 250-300m/s and an impingement angle of 80°. The volume eroded was great when the target Si₃N₄ had a low density and large grain size. This corresponds to the tendency that the eroded volume increases with decreasing hardness and fracture toughness. The erosion results were tested four equations that relate the erosive wear to the hardness (Young's modulus) and fracture toughness of the target. The equation V∝H^-1/4K_c^-4/3, which was proposed theoretically by Evans, was found to best describe the experimental results.

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The sillimanite grains, consisting of the aggregation of fibrous crystals are generally included as a minor constituent of heavy minerals in quartz sand which are produced from Seto region, Aichi prefecture. The content of the grains is very low. The glass stones caused by the presence of sillimanite grains, however, are commonly found in the bottle glasses manufactured from the quartz sand. The reaction between sillimanite crystals and molten glasses was studied by the use of cullets of bottle glass and rectangular rods of sillimanite aggregations. The rods were prepared by grinding fibrous and tablet crystal aggregation of sillimanite. Thin sections were made from the reacted samples. The optical analysis, EPMA and X-ray diffraction analysis were used to observe the reaction zones. The structure of reaction zones was a function of reaction temperatures. The diffusion of sodium ions and change of colour were found in the reaction zones at low temperature. The needle crystals of corundum were observed at high temperature. The rate constant for sillimanite decomposition was calculated from the data of reaction test. The apparent activation energy for the decomposition of sillimanite was calculated to be 135kcal/mol. The sillimanite glass stones were confirmed by the comparison of structure found in glass stones with that in reacted sillimanite crystals. The behavior of sillimanite crystals in a tank furnace has been discussed from the structure of glass stones. Most of the sillimanite crystals, found in glass stones seem to decompose in the low temperature zone estimated to be about 1300°C.

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Silicic acid was extracted with tetrahydrofuran from an aqueous sodium metasilicate solution neutralized with hydrochloric acid. Polysilicic acid esters (PSAE) with various degrees of esterification (DE) were prepared by esterification of silicic acid with methyl, ethyl, n-propyl and n-butyl alcohols. An attempt was made to prepare fine silica powders by adding an alcohol solution of PSAE to the solvent with a low solubility of PSAE. Fine silica particles were obtained when PSAE's with DE 40-59% (Me), 30-50% (Et), 15-30% (n-Pr) and 20-30% (n-Bu) were added to water, chloroform, benzene and hexane, respectively. Silica may be formed by the condensation of PSAE when and after it was precipitated. Scanning electron microscopy showed that silica is obtained in the form of secondary particles with a size of several ten μm formed by condensation or aggregation of primary particles less than 0.1μm in diameter.

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Two kinds of Si₃N₄ powders, of which characteristics were similar to each other in morphology, crystallographic phases and chemical contents except for oxygen content, were sintered by HIP using a glass capsule without additives. The amount of oxygen content in Si₃N₄ powder had influence upon its sinterability without additives. After HIPing, the increase in oxygen content in samples was detected though no penetration of glass through a BN inner capsule into Si₃N₄ was observed. But the oxygen content in well densified bodies was relatively small.

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Si₃N₄-SiC whisker composites with whisker content up to 30wt% were prepared by heating 1700° to 2000°C for 60min in 1MPa N₂. Fully dense composites were obtained at 2000°C. The optimum content of sintering aids, Y₂O₃ plus La₂O₃, was 20 and 30mol% for the whisker content of 10 and 20wt% respectively. The room temperature bending strength were 596 and 560MPa for 10 and 20wt% additions of whisker, respectively. Moreover, these composites had strengths more than 80% of the room temperature value at 1300°C. Improvement in the strength was achieved by using sieved whisker.

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The thermal conductivity and the thermal expansion of Si₃N₄-SiC whisker composites were investigated. Specimens were prepared by hot-pressing at 1800°C-39.2MPa-60min using Y₂O₃-La₂O₃ or MgO as a sintering aid. The thermal conductivity of composites increased with an increase in SiC whisker content. Moreover, the thermal conductivity normal to the hot-pressing direction was higher than that parallel to the hot-pressing direction due to orientation of whisker. In the system Y₂O₃-La₂O₃, an Si₃N₄ matrix showed abnormal thermal expansion above 1000°C caused by the glass phase composed of Si₃N₄, Y₂O₃ and La₂O₃, but the composites showed nearly linear thermal expansion up to 1400°C. In MgO system, linear thermal expansion curves were obtained regardless of whisker content.

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The corrosion of fused silica refractories in molten CaO-Al₂O₃-SiO₂ slag was studied. The experiment was carried out with a rotating cylindrical specimen. The retults are as follows:
(1) The diameter of specimens decreased linearly with time. The increase both in temperature and rotating speed promoted the corrosion.
(2) A thin reaction layer was observed on the surface of the specimen. The change in SiO₂ concentration in the slag was best described by a rate equation (which was derived) for the mass transport controlled mechanism. The apparent activation energy of corrosion was 64kcal/mol, implying that the corrosion is controlled by diffusion of ion in the slag.
(3) A non-dimensional equation κ=αU^0.67 was obtained, the exponent of which agreed with the literature values.

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Reactions of a Zinc metal powder with high temperature-high pressure water were studied under 100MPa. All of Zn powders changed into ZnO above 300°C within 1h in a closed system and also rapidly changed during heating upto 400°C in an open system. Zinc powder particles were disintegrated during the reaction due to volume increase in oxidation. The crystallite size of ZnO remained almost constant at 200°C, but increased with time above 300°C. The crystal growth of ZnO was observed in the open system.

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Thermal shock behavior of aluminumtitanate (AT)-mullite composite fired at 1520°C for 4h was studied by quenching into water. The critical temperature difference, ΔT_c, of the composite remained constant with increasing amount of AT up to 30wt%. But, over 50wt% AT, ΔT_c increased markedly with increasing AT content, and reached 1050°C at 85wt% AT composite. The bending strength was about 60MPa.

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A silicastone powder (low-quartz) containing Fe₂O₃ and ZrO₂ up to 30wt% was kneaded with 10N NaOH solution, and then hot-pressed at 300°C and 28MPa for 3h to produce solidified bodies. During hydrothermal hot-pressing, shrinkage of starting materials was measured. Solidified bodies containing Fe₂O₃ consisted of low-quartz, hematite and acmite (NaFeSi₂O₆). The formation of acmite suppressed linkage of silica stone grains and reduced compressive strength of the solidified bodies. It also reduced the shrinkage of starting materials. Solidified bodies containing ZrO₂ contained low-quartz and monoclinic ZrO₂. No reaction products were detected by X-ray powder diffraction. Addition of ZrO₂ up to 20wt% increased the shrinkage of starting materials and compressive strength of the solidified bodies. Mobility of silicastone grains at the early stage of hydrothermal hot-pressing was increased by addition of ZrO₂. Similar phenomenon was observed by addition of graphite, a solid lubricant.

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An electric discharge method for welding ceramics has been developed. A joining material electrically conductive at high temperature is inserted between two pieces of ceramics to be joined, and the joint region is preheated by a pair of burners of spouting combustion gas. When the joint region is heated to high temperature, a high voltage is applied between a pair of electrodes combined with the burners. The ceramics are joined by electric discharge through gas flame and the joint region. Pressureless-sintered Si₃N₄ ceramics were joined using a mixture of kaolin and CaF₂ as a joining material. Ceramics can be joined easily, in a short time, and economically by this method.

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