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.862, pp.183-192, 1967-06-01

被引用文献数

1

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In relation to three hydrated phases which were obtained by the reactions between the water vapor and the solid phases of nepheline=carnegieite compositions in the foregoing paper, attempts were made to establish a correlation between the structure of the starting solid and the product with a hope that the structure of the starting solid might be inherited to the product. Dehydration experiments of the products were carried out also in relation to clarifying their structural relationships.<br>X-ray powder diffractions of the nepheline hydrate I and the species Y obtained in the previousp aper and of the nepheline hydrate II which is of a low-water type closely relating to these hydrates and obtained by hydrothermal reaction after Barrer's method, were examined and are listed in Table 3-6. All these patterns can be tentatively indexed based on orthorhombic cells which are shown in the tables and also summarized in Table 7. Indexing was made by trial and error based on the available electron diffraction patterns. Some discrepancies, however, are still observed, which may suggest that dehydration occurs to some extent under high vacuum and also by electron bombardment during the electron optical observation.<br>The high temperature X-ray diffraction patterns and thermal analysis curves are illustrated in Fig. 1-8 for the nepheline hydrate I, the species Y, and the hydroxy-sodalite of the present experiments and for a nepheline hydrate II. It seems that in the former three species, some lattice distortion takes place upon partial dehydration as shown by the splitting of the diffraction peaks. The original structure, however, is nearly resumed by further dehydration and eventually goes to a nepheline structure. At the final stage of dehydration double exothermic effects in D. T. A. curves are characteristic for all of these three hydrated phases, which seems to be due to complicated transformation processes including the formation of intermediate sodium aluminosilicate phases. As compared with these, the thermal change of nepheline hydrate II is so simple that dehydration brings about the direct formation of nepheline structure as low as at 600°C. Though little can be said of the actual structures of these phases at present, close relationships between the original solid phase and hydrated product can be demonstrated by a comparison between the lattice parameters as illustrated in Fig. 13 and 15. The lattice dimensions suggest that the structural units of aluminosilicate as illustrated in Fig. 14 are inherited throughout the hydrothermal processes.

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.