The experimental data for ion exchange equilibria between (Fe, Mn, Mg)TiO₃ ilmenite solid solution and 2N (Fe, Mn, Mg)Cl₂ aqueous chloride solution by Kubo et al. (1992) were re-analyzed taking into consideration the formation of FeCl₃-_aq and MnCl₃-_aq. As a result, the newly obtained excess Gibbs energy of mixing for (Fe, Mn, Mg)TiO₃ ilmenite solid solution was slightly smaller than that obtained by Kubo et al. (1992), where 2N (Fe, Mn, Mg)Cl₂ aqueous chloride solution was assumed as an ideal solution.

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A conversion process from potassium tetratitanate fibers into potassium hexatitanate fibers was investigated to develop potassium hexatitanate fibers which are usable as a filler for fiberreinforced aluminum alloys. Calcined potassium tetratitanate fibers were dispersed in water. By titrating the above mentioned suspension with an aqueous HC1 solution to adjust the pH value at 9.0, the fibers with TiO₂O/K₂O molar ratio=6.02 was obtained. The product thus obtained was heated at 1000°C for 30min, then highly crystallized potassium hexatitanate fibers having a crystallite size of 76nm were obtained. An AC4C aluminum alloy matrix composite reinforced with the obtained potassium hexatitanate fibers was fabricated by squeeze casting. Mechanical properties were examined on the obtained composites. The hardness of the composite was uniform at any locations. The mechanical properties of the composites increased by theT6 heat treatment.

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The hydration, time-averaged and dynamic structures of adsorbed water on clay minerals have been reviewed to clarify the nature of clay hydration and the difference in structure between adsorbed and free water. Hydration of the clay minerals involves three kinds of water adsorption on the surface in interlamellar, intraaggregate and interaggregate pore spaces. The hydration mechanism and factors influencing hydration are quite different in these hydration modes. Water molecules in the clay interlayers have statistically and dynamically a more rigid structure than that in bulk liquid water. Especially, the thermal motion of water bound to divalent cations is restricted and similar to that of normal ice (Ih).

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Clay minerals are major constituents of the earth's surface materials and are widely distributed as weathering products of interior materials of the earth crust. It is well known that the clay minerals play an important role in environmental processes through its high reactivity with both inorganic and organic ions and/or molecules. Therefore, more studies concerning the earth's surface materials involving clay minerals are strongly required to understand the environments of life support systems. Generally, clay minerals can be divided into the following two categories; 1) crystalline materials, and 2) noncrystalline materials. Extensive studies have been conducted on mineralogy of the crystalline materials, whereas little is known for the noncrystalline materials. In this paper, the author reviews noncrystalline materials formed in weathering environments on the earth crust, and shows some examples of noncrystalline materials formed by natural weathering and artificial hydrothermal reactions. Two different natural materials are described; one is weathering products formed on the surface of volcanic glass in Ito pyroclastic flow deposit, the other is precipitates on the surface of K-feldspar in Yakushima granite. The noncrystalline materials formed by artificial hydrothermal reactions are products of the reaction between volcanic glass and aqueous solution, and precipitates in a oneelemental system of Al and a two-elemental system of Al-Si.

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