Abstract

Sodium aluminosilicate gels containing an extremely small quantity of alumina changed initially to clear solutions on heating. Analcime solid-solution crystals formed directly from them at 100°C, under atmospheric pressure.

The chemical compositions of the analcimes were governed by the initial ratios of soda, alumina, and silica in the gels, and were independent of the depletion of nutrient with the elapse of reaction time. According to the isomorphous substitution Si4+ ⇆ Na+Al3+, an increase of soda and alumina concentrations caused a decrease of the Si02/Al203 ratio in the analcime crystals, whereas an increase in silica resulted in an increase of the ratio.

Analcime crystals grew uniformly in size in runs of 120 hrs or shorter duration and had trapezohedral crystal habit. When analcime seeds were added to the freshly-prepared gels, they grew longer on heating in all cases. The composition of the growth zones on the crystals also was governed by the initial compositions of the fresh gels and was independent of the composition of the added seed and the length of growth time.

These results can be readily explained by assuming the existence of active chemical species of sodium aluminosilicates, a hypothesis which was proposed first by Kerr (1966). We propose that they possess fixed compositions and incipient ordered structures identical to analcimes and that they polymerize to form analcime crystals.

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