著者

久保 靖 山口 悟郎 笠原 晃明

出版者

公益社団法人日本セラミックス協会

雑誌

窯業協會誌 (ISSN:18842127)

巻号頁・発行日

vol.75, no.861, pp.140-146, 1967-05-01

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Differing from the previous studies by various investigators, the present research concerns with the formation of hydrated sodium aluminosilicates by the water vapor-solid reactions. Sodium aluminosilicate phases, amorphous or crystalline with nepheline-carnegieite compositions, which were obtained by heating the mixtures, Al₂O₃⋅2SiO₂⋅2H₂O(kaolinite)+<i>a</i>Na₂⋅CO₃(<i>a</i>=1.00-2.00), up to various temperatures below 1300°C, were used as the starting solids. A silver capsule was filled with the starting solid and suspended above the liquid water in a Moley-type autoclave (Fig. 1). The bottom of the capsule was not sealed to allow the water vapor to penetrate into the capsule. The saturated water vapor pressure within the autoclave at 310°C is 100kg/cm². This condition was used throughout the present experiments. Under this condition, the reaction may well be called a hydrothermal metamorphosis.<br>As compared with the previous studies in which the thermodynamic equilibria are attained in the given homogeneous systems, the reactions in the present experiments start at the interfaces between the water vapor and the solid with a consequence that the reaction products are not necessarily equilibrated under the given experimental conditions. As the result, three sorts of hydrated phases, hydroxy-sodalite, nepheline hydrate I, and species Y (a new phase of the composition, Na₂O⋅Al₂O₃⋅2SiO₂ 1.33-1.5 H₂O, which has not been found in the previous hydrothermal studies), were formed during 1-7 days' run according to the nature of the starting solid phases. Correlations among the starting solids and the resulting hydrates are summarized in Table 2 and Fig. 2. In the table the first three columns stand for the preparation of starting solids and the forth the duration of metamorphosis, the fifth the products under the respective experimental conditions.<br>During the hydrothermal treatment, grains of the original solids as shown in the electron microphotographs of Figs. 3 (a)-(c), changed to well-shaped crystallites of the hydrates, nepheline hydrate I and species Y, as shown in Figs. 4(a)-(c), except hydroxysodalite which was formed only in massive grains. Considerable amount of water molecules may have been adsorbed on the surface of solid to gelatinize the surface and eventually to recrystallize the solid into the hydrate crystallites. The original structural framework may still be retained to some extent under these conditions. The metastable phase formation in this experiment will be treated from this point of view in a following paper.