THERMOGRAVIMETRIC STUDY OF THE 800-DEGREES-C REACTION OF ZIRCONIA STABILIZING OXIDES WITH SO3-NAVO3

A thermogravimetric study was made of the reaction of the zirconia stabilizing oxides, In2O3, Sc2O3, Y2O3, and MgO, with molten NaVO3 at 800-degrees-C under SO3 partial pressures of 10(+2) to 10(-3) Pa. The melt composition is determined by: 2NaVO3 + SO3 reversible V2O5 + Na2SO4. No reaction of In2O3 was found at SO3 partial pressures up to 5 x 10(+1) Pa where the reaction, In2O3 + V2O5 = 2InVO4, commenced. Reaction of Sc2O3 occurred at about 5 x 10(-1) Pa of SO3, with SCVO4 formed. Reaction of Y2O3 and MgO with the NaVO3 melt began, on the other hand, at SO3 partial pressures too low to be measured (<10(-3) Pa). In2O3 and SC2O3 are thus potentially superior to Y2O3 and MgO as stabilizers for hot corrosion resistant zirconia thermal barrier coatings. Certain other information concerning the thermochemistry of the SO3-NaVO3 system was also revealed.