Phase Diagram for the SiF4 Join in the System SiO2-Al2O3-SiF4 |
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| Authors: | John R Moyer&#; |
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| Affiliation: | The Dow Chemical Company, Midland, Michigan 48674 |
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| Abstract: | Alumina reacts with 1 atm of SiF4 below 660°± 7°C to form A1F3 and SiO2. At higher temperatures the product is a mixture of fluorotopaz and AIF3. Mixtures of fluorotopaz and AIF3 decompose in 1 atm of SiF4 at 973°± 8°C and form tabular α-alumina. The equilibrium vapor pressure of SiF4 above mixtures of fluorotopaz and AlF3 is log p (atm) = 9.198 – 11460/ T (K). Fluorotopaz itself decomposes at 1056°± 5°C in 1 atm of SiF4 to give acicular mullite, 2Al2O3.1.07SiO2. Alumina and mullite are stable in the presence of 1 atm of SiF4 above 973° and 1056°C, respectively. The phase diagram of the system SiO2-Al2O3-SiF4 shows only gas-solid equilibria. |
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