Scandia, yttria-stabilized zirconia for thermal barrier coatings

Seven Sc2O3, Y2O3-stabilized ZrO2 (SYSZ) powders having 7 wt.% stabilizer, which was varied from 0%-100% Sc2O3, were prepared by a sol-gel process and tested for resistance to destabilization by molten NaVO3 at 700 degrees C and 900 degrees C. The Y2O3-rich SYSZ powders were destabilized by chemical reaction with the NaVO3, with YVO4 being produced, while the Sc2O3-rich powders were destabilized by a mineralization effect (no chemical reaction) by the molten NaVO3. Aging at 1400 degrees C for 140 hrs substantially improved the vanadate resistance of the Sc2O3-rich, but not the Y2O3-rich, SYSZ powders. The SYSZ powders stabilized by Sc2O3 plus 10%-20% Y2O3, after 1400 degrees C aging, showed 5-10 times better resistance to vanadate-induced destabilization than the 100% Y2O3-stabilized SYSZ powder. In addition, the Sc2O3-(10-20%)Y2O3 powders gave less monoclinic formation, and therefore evidenced better high temperature phase stability, than the 100% Y2O3-stabilized powder during the 140 h of 1400 degrees C aging.