Spherical Alumina particles obtained by oxy-propane gas flame spraying were investigated by means of scanning electron microscope and X-ray powder diffraction. The ratio of spherical and nomspherical particle was influenced by powder concentration in the flame, carrier gas and activity of the raw alumina powders.
The surface conditions of alumina spheres were divided into two categories; dendritic and granular form.
The crystal form of sphere was composed of α-and δ-alumina. Formation of δ-alumina progressively decreased with the sphere diameter. Allotropic transformation of δ-to α-alumina was completed at 1300°C for 3h.

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Oxidation behaviors for powders of high purity Si₃N₄, synthesized Si₂ON₂ (82%+18% Si₃N₄) and sialon (z=2) were examined at 4 temperature levels (1100°-1400°C) in 5 kinds of atmosphere (po₂=10^-2.8-1atm) of O₂-N₂ gas mixture for 50 hours. After the oxidation tests, phases present on the surface and in bulk of the powder particle were determined. The oxidation proceeded to 20-60%, then its rate became slower and saturated values were obtained at higher temperature and at higher po₂. Amorphous phase first produced and was followed by crystallization to cristobalite and/or mullite. In Si₃N₄ specimen, no crystallization occurred at 1100°C, but it was easier in lower po₂ above 1200°C. Saturation at 40-60% was obtained in air (po₂=10^-0.7atm) and oxygen (po₂=10⁰atm). Parabolic rate was observed with activation energy of fairly constant values of 60-70kcal/mol independent on po₂. In Si₂ON₂, saturated values of 20-40% were observed in all of conditions and the parabolic rate decreased from higher rate at initial stage to lower one at later stage. Activation energy varied from 30 to 80kcal/mol as increasing po₂. Oxidation behavior for sialon was similar to that for Si₂ON₂.

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High pressure hot-pressing or hot isostatic pressing of Si₃N₄ were performed using various kinds of α-Si₃N₄ powders as starting materials, and relation between densification and α→β phase transformation of Si₃N₄ was studied.
There were definite correspondence between densification and phase transformation of Si₃N₄ which was strongly dependent on the starting material and hot-pressing pressure, but was not dependent on the hot-pressing temperature and duration. In the first stage densification proceeded with no phase transformation followed by the second stage with remarkable densification accompanying 20-40% phase transformation, and in the third stage a little further densification occurred during further phase transformation to 100% β phase. Therefore, densification and phase transformation of Si₃N₄ under pressure were closely associated and highly dense Si₃N₄ ceramics were obtained with complete phase transformation using the powder whose densification and phase transformation during the second stage was more dominant than other powders.

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A kinetic study was made on the hydrothermal reaction between alite and quartz. Synthesized alite powders with 3900cm²/g in surface area, or mixtures of the alite and quartz of 6-10μm in particle diameter were pelletized at various ratio. The pellets were autoclaved at 181°C under saturated vapor pressure for 0.5-72h. The hydrothermally treated samples were characterized by XRD and SEM. Unreacted alite, unreacted quartz, free lime and combined water of samples were determined, The chemical composition of the products and rate of the reaction were calculated from the experimental data.
In the alite-H₂O system, C-S-H with high CaO/SiO₂ ratio and Ca(OH)₂ were producedd at early stage of the reaction, and then C₃SH_1.5 was produced. When small amount of SiO₂ was introduced (CaO/SiO₂=1.5), C₃SH_1.5 was disapeared during the reaction proceeded and final products were C-S-H and Ca(OH)₂. In the case of CaO/SiO₂=0.8, C₃SH_1.5 was not produced from early stage and produced Ca(OH)₂ reacted again with SiO₂ to form C-S-H with the composition similar to tobermorite. Even when the large amount of SiO₂ was introduced (CaO/SiO₂=0.5), the product with lower CaO/SiO₂ ratio, such as gyrolite, was not formed, and C-S-H and unreacted SiO₂ were observed.
The reaction of alite was controlled by diffusion through the product layer arround each alite grain. The reaction of quartz was controlled by dissolution at early stage and by diffusion at later stage. The uneven surfaces of alite grain were observed at early stages, suggesting that the dissolution rate of alite varied depending on crystal surfaces.

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Optical absorption of ultra-pure glasses containing two kinds of oxides giving high index of refraction has been measured in the near ultraviolet region. The relations among the color, ultraviolet absorption edge, refractive index, Abbe's number and the wavelength of intrinsic absorption of high index glasses of ultra-high purity has been discussed.
The results obtained are as follows:
1) Logarithm of absorbance of ultra-pure glasses decreased linearly as the wavenumber decreased at the rate d(logα)/d(1/λ)≅1×10^-3cm.
2) The glasses having the absorption edge at an wavelength longer than 370nm appeared yellow or brownish yellow.
3) The wavelength of absorption edge was longer for the glass of high index of refraction, low value of Abbe's number and long wavelength of intrinsic absorption.
4) The preparation of colorless glass having the index n_D larger than 1.95, Abbe's number ν_D less than 22 or intrinsic wavelength longer than 170nm is supposed to be very difficult for the system containing PbO, TiO₂ and Nb₂O₅.

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For amorphous As₂S₃ films deposited at temperatures from -170°C to 170°C, optical absorption edges, IR spectra, and thermally induced changes of these optical properties were studied as a function of the deposition temperature. As-deposited films contained As₄S₄ and sulfur components, the amount of which was highly dependent on the deposition temperature; as the deposition temperature decreased, the amount of these components increased. From these observations, the decomposition of As₂S₃ glass to As₄S₄ and sulfur components in the evaporation process was proposed. Annealing of as-deposited films at temperatures near glass transition caused the reaction of residual As₄S₄ and sulfur components, accompanying the shift of absorption edge to lower photon energies. From the compositional analysis, it was found that the films deposited at temperatures higher than 100°C was sulfur-poor compared with the stoichiometric composition. The dependence of optical band gap on the deposition temperature for annealed films was explained in terms of the remaining As₄S₄ component and/or sulfur deficiency in the films.

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In order to establish the mechanical processing technique of ceramics, the cutting conditions and the other problems in the abrasive machining of hotpressed silicon nitride with the cutting wheel are discussed. As the cutting tool, metal and resinoid bonded diamond wheels were used, and the load current was measured and the worn grains on the surface of the wheel were observed with SEM. The main results obtained are as follows:
1) The diamond grains on the external and the side surfaces of a wheel wore out remarkably in the cutting process of hot-pressed Si₃N₄. Then the cutting load current increased on a large scale as the wear of grains. Therefore, the cutting efficiency lowered, and the dressing was indispensable in the cutting process with a diamond wheel.
2) The wear, however, was prevented by giving the taper of the order of 1/100 on the side surface, and the redress life of the cutting wheel increased with this taper of both sides.
3) The cutting energy per unit area decreased as decreasing of depth of cut.

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Studies on utilization of the inorganic residues separated from Resource Recovery System (RRS) of municipal refuses were conducted.
The separated inorganic residues can be classified into glasses, gravels and porcelains, and bones and shells. On this component system, a swelling test was performed to determine the swelling temperature. The dust discharged from the pyrolysis subsystem of the municipal refuses was used as one of the acidic additives and the relationship between the swelling and the mixing dust content was also examined. The highest allowable dust content was 30wt% in the mixture suitable for raw materials of light weight aggregates.
A 1t/d production scale pilot plant, designed from the results of the basic studies, was installed at the site of “Star Dust '80 RRS plant” and a long term running test was carried out. It proved that curing process must be introduced to avoid green pellets from breakage through transportation in the plant. From the running test optimal operational conditions of each process were determined and data for scale up were obtained.
Properties of the product obtained were as follows. Specific gravity ranges from 0.9 to 1.6, water absorption was 5 to 17%, ratio of absolute volume was 60 to 63%. Further tests were conducted according to JIS A5002 (the light weight concrete) which proved that the concrete satisfied the standard specifications. The amount of toxic materials dissolved from the products were under the regulation limits.

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