Stability of Mullite as Derived from Equilibria in the System CoO-Al2O3-SiO2 |
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| Authors: | R R DAYAL R E JOHNSON† ARNULF MUAN‡ |
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| Affiliation: | College of Earth and Mineral Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802 |
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| Abstract: | The free energy of reaction for the formation of mullite from its oxide components was derived from equilibrium studies in the system CoO-Al2O3-SiO2. Within this system there appears, at solidus temperature in a certain composition area, the phase assemblage mullite + silica + spinel (= cobalt aluminate) + liquid. Determination of the oxygen pressure of a gas phase at which metallic cobalt precipitates from this phase assemblage and from the phase assemblage spinel (= cobalt aluminate) + corundum in the system CoO-Al2O3 permits calculation of ΔG° for the reaction 3Al2O3+ 2SiO2= Al6Si2O13. The value obtained at 1422°C is -5.8 kcal. |
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