Abstract
Abstract The metastable nepheline-type solid solution in the CaO–Al2O3–SiO2 system shows the best crystal development upon devitrification on the CaAl2O4–CaAl2Si2O8 join. The crystallization occurs through the devitrification of glass at relatively low subsolidus temperatures, around 1000°C in the air. The X-ray powder diffraction patterns of the solid solution can be indexed on the basis of a hexagonal unit cell of the nepheline structure without exception. The cell parameter a of the solid solution is similar to that of nepheline, while its parameter c is smaller than that of nepheline and corresponds to that of high-temperature tridymite. When the cell parameters of the solid solution on the join are plotted against the composition, there is a break in the slope at Ca6Al12Si4O32, though the cell volume varies continuously. The nepheline-type solid solution on the join may be expressed as Ca8−(1⁄2)x\Box(1⁄2)xAl16−xSixO32, where \Box means the interstitial vacant site. The relationship between the cell parameter and the composition suggests that there should be two kinds of Ca-sites in the structure of the present solid solution, and that these kinds correspond to the alkali sites of two different sizes in the nepheline structure.
Published Version
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