A simple method for the determination of the hydroxyl groups of silica was studied. A thermogravimetric analysis combiend with D₂O vapor pretreatment was applied to determine both the surface and the inner hydroxyl contents of the silica particle. The number of hydroxyl groups was calculated by the difference in the TG weight loss between the untreated and treated samples.
The reactivity of the pre-heated silica surface is represented by the degree of rehydration reaction with H₂O vapor, and it decreases with increase in the pre-heating temperature. The temperature dependency of the number of hydroxyl groups can be measured more accurately by considering the degree of rehydration.

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An apparatus for separating a specified plastic from other kinds was devised. It consisted of a triboelectric section and a separating section with both polarities. Various plastic sheets were frictionally electrified in the fluidized bed and then were blown off into the electrode unit, in which they were separated according to their own polarity.
The recovery of plastics was more than 70% beyond the electric field strength of 100kV/m, and the weight ratio of recovered plastics was more than 80% in the separation of the four kinds of plastics.

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Recently, there are various studies on the fabrication of composite particles to produce functional materials. Here, the coating mechanism of fine particles by dry impact blending is investigated theoretically and experimentally.
Coating is considered to proceed with small particles transported among the surfaces of large particles and the inner wall. Then the coating rate is reduced by a geometrical obstacle of the small particles on a large-particle surface. Their fixation effect yields the limiting coating ratio.
As a result, the coating ratio and the mobility of small particles on the large particle can be determined by the diameters of the large and small particles and the rotor speed. Therefore, the coating rate depends upon the kinetic energy of the large particle, the impact pressure on the small particle attached to the large particle surface and the kinetic energy of the rotor.

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The effect of vibration ball-milling of a SiO₂-MgO powder mixture on Mg₂SiO₄ formation by a solid-state reaction between SiO₂ and MgO was examined. The results obtained are summarized as follows:
(1) It was confirmed that Mg₂SiO₄ formation during firing was accelerated by the vibro-milling of the SiO₂-MgO powder mixture. The Mg₂SiO₄ formation reaction seemed to be a diffusion controlled process regardless of the vibro-milling and firing conditions, and the rate of this reaction obeyed the Ginstling-Brounshtein equation. The apparent activation energy of this reaction decreased from 311 to 94kJ/mol with the increase in the milling time up to 120hrs.
(2) In addition to the compositional homogenization during vibro-milling, the enhancement of the SiO₂-MgO solid state reaction due to both the activation of MgO induced by amorphization during milling and the increase in the contacts between MgO and SiO₂ under the mechanical stress was thought to largely contribute to the acceleration of the Mg₂SiO₄ formation during firing.

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