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Science 11 January 1974:
Vol. 183. no. 4120, pp. 69 - 71
DOI: 10.1126/science.183.4120.69
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Articles

The Silica-Alumina System: Stable and Metastable Equilibria at 1.0 Atmosphere

Idotlhan A. Aksay 1 and Joseph A. Pask 1

1 Department of Materials Science and Engineering and Inorganic Materials Research Division, Lawrence Berkeley Laboratory, University of California, Berkeley 94720

Diffusion couples, consisting of sapphire and fused silica, which were annealed in the temperature range from 1678° to 2003°C and analyzed by electron beam microprobe, have provided data on the stable phase equilibrium of the silica-alumina system. Under stable equilibrium conditions, the intermediate compound of this system, mullite (3Al2O3 · 2SiO2), melts incongruently at 1828° ± 10°C and its solid solution field extends from 70.5 to 74.0 percent (by weight) alumina. The stable phase diagram is a composite of the two binary eutectic diagrams: silica-mullite in the absence of alumina and silica-alumina in the absence of mullite. Under metastable conditions, mullite melts congruently at ap 1890° ± 10°C and its solid solution field extends to ap 83.2 percent (by weight) alumina.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)