Hydrated Sodium Aluminosilicates Relating to Nepheline=Carnegieite Minerals

Relations among the Crystal Lattices and Thermal Transformations

Abstract

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.
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.
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.