HOT CORROSION OF POTENTIAL THERMAL BARRIER COATING MATERIAL (SM1-XYBX)2ZR2O7 BY V2O5 AND NA2SO4

(Sm1-xYbx)(2)Zr2O7 (x = 0, 0.5, 1.0) powders are prepared by chemical-coprecipitation and calcination method, and then pressureless-sintered at 1700 degrees C for 10 h. Sm2Zr2O7 has a pyrochlore-type structure, while SmYbZr2O7 and Yb2Zr2O7 have a defect fluorite-type structure. Thermal expansion coefficient and thermal diffusivity of (Sm1-xYbx)2Zr(2)O(7) are studied by a high-temperature dilatometer and a laser flash diffusivity technique from room temperature to 1400 degrees C. Hot corrosion tests between (Sm1-xYbx)(2)Zr2O7 and three corrosive agents including V2O5, Na2SO4, and a V2O5+Na2SO4 mixture, are carried out from 600 to 1100 degrees C for 2 h and 8 h in air, respectively. Different reaction products of ZrV2O7, LnVO(4) and m-ZrO2 are identified depending upon the hot corrosion conditions, for example, ZrV2O7 and corresponding LnVO(4) at 600 degrees C for 2 h and 8 h, namely SmVO4, (Sm, Yb)VO4, YbVO4, respectively; ZrV2O7, m-ZrO2 and LnVO(4) at 700 degrees C for 2 h; m-ZrO2 and LnVO(4) either at 800 similar to 1100 degrees C for 2 h or at 700 similar to 1100 degrees C for 8 h. No reaction products are identified on Na2SO4-coated (Sm1-xYbx)(2)Zr2O7 at 900 similar to 1100 degrees C. However, m-ZrO2 and corresponding LnVO(4) are found after (Sm1-xYbx)(2)Zr2O7 exposed to Na2SO4+V2O5 (mole ratio = 1:1) at temperatures of 600 similar to 1100 degrees C. Those results are explained based on phase diagram theory, and the principles for crystal growth are used to illustrate the morphologies of reaction products LnVO(4).