Sodium Vanadate-SO3 Equilibria in the Hot Corrosion of Zirconia Thermal Barrier Coatings
This paper describes a thermogravimetric study of the interaction of SO3 (as from engine gas) with vanadate-sulfate deposits at 700 and 800°C, and its effect on the reaction of the melt with ceramic oxides. Experiments using NaVO3 to simulate deposits having Na/V = 1, and where the controlling reaction is: 2 NaVO3 + SO3 = Na2SO4 + V2O5, gave reproducible equilibria over the range of 100 Pa to 0.01 Pa of SO3. India (In2O3, a possible corrosion-resistant stabilizer for ZrO2) was shown to be inert to the NaVO3-Na2SO4-V2O5 melt for SO3 levels up to about 5 Pa at 800°C (0.5 Pa at 700°C), where the melt V2O5 activity becomes increased enough that InVO4 begins to form. Although slow at lower SO3 pressures, the TGA-SO3 equilibria technique promises valuable information for understanding of the thermochemistry of vanadate-sulfate melts, and the development of corrosion-resistant engine ceramics.
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