Formation of clay minerals during experimental alteration of obsidian in acetic acid and oxalic acid solutions was investigated. The experiments were carried out using 0.01N or 0.02N acetic acid and oxalic acid solutions at 150°and 200°C for 1 to 60 days. The clay minerals formed in these organic acid solutions were examined by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Variations of pHs and concentrations of dissolved elements in solutions during the reactions were measured. By reactions using acetic acid solution, pH-values of solutions retained weak acidic region of pH3.4-4.9, and formation of kaolinite proceeded during the reactions and crystallization of smectite occurred at the final stages. On the other hand, pH-values of oxalic acid solution increased rapidly to alkaline region, and then crystallization of smectite began to take place at the initial stages and proceeded throughout the reactions. The rapid increase in pH of oxalic acid was due to thermal decomposition of the organic acid, and therefore solution compositions changed drastically to the stability filed of smectite.

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In this paper we examined in detail how the mobility of kaolintite changes with salt concen tration, and how Na-kaolinite water system flocculates as salt is added at pH10. We also studied how dispersion-flocculation depends on zeta potential by comparing the results of mobility with limited viscosity, a useful way to estimate particle s
Our conclusions are as follows: 1) Because the mobility of kaolinite increases with salt concentration within the range of flocculation, experimental results don't conform to the theory of diffuse double layer.These phenomena occur because of the formation of flock, when accompanied by an increase in salt concentration. 2) In dispersion state, the relation between zeta potential and salt concentration conforms to Gouy & Chapman's theory of diffuse double layer under constant surface potential. Furthermore, the surface potential, 56mV, and the position of the slipping plane, 2.3nm, were obtained about Iriki kaoline from analysis of the experimental data. 3) It is necessary to clarify the particle state of a clay-water system when measuring the zeta potential, because mobility is heavily dependent on the dispersion-flocculation of the clay-water system.

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Dry grinding of talc was carried out using a planetary mill in the presence of metal alkoxides such as aluminum tri-sec-butoxide, silicon tetra-n-butoxide and titanium tetra-n-butoxide. These additives were found to be effective in producing fine and flaky particles with a thin width. The alkoxides having a low surface tension were spread smoothly on the whole surface forming a new surface of particles during the grinding. This resulted to the improvement of the dispersibility of groundpowders due to the reduction in adhesion forces among particles. With regard to the formation of adsorbed layer of additives, a change in the sign of residual electrostatic charge of the ground powders from negative to positive was also observed. In particular, the resuling fine powders with a desirable flaky shape is probably attributed to the chemisorption of the additive molecules on the broken bond surface, facilitating the creation of fine cracks and their propagation along the cleavage planes of talc.

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