PHASE-DIAGRAM FOR THE SIF4 JOIN IN THE SYSTEM SIO2-AL2O3-SIF4

Alumina reacts with 1 atm of SiF4 below 660 degrees +/- 7 degrees C to form AlF3 and SiO2. At higher temperatures the product is a mixture o f fluorotopaz and AlF3. Mixtures of fluorotopaz and AlF3 decompose in 1 atm of SiF4 at 973 degrees +/- 8 degrees C and form tabular alpha-al umina. The equilibrium vapor pressure of SiF4 above mixtures of fluoro topaz and AlF3 is log p(atm) = 9.198 - 11460/T(K). Fluorotopaz itself decomposes at 1056 degrees +/- 5 degrees C in 1 atm of SiF4 to give ac icular mullite, 2Al(2)O(3) . 1.07SiO(2). Alumina and mullite are stabl e in the presence of 1 atm of SiF4 above 973 degrees and 1056 degrees C, respectively. The phase diagram of the system SiO2-Al2O3SiF4 shows only gas-solid equilibria.