HOT CORROSION OF POTENTIAL THERMAL BARRIER COATING MATERIAL (SM_(1-x)YB_x)_2ZR_2O_7 BY V_2O_5 AND NA_2SO_4

摘要

(SM_(1-x)YB_x)_2ZR_2O_7 (x = 0, 0.5, 1.0) powders are prepared by chemical-coprecipitation and calcination method, and then pressureless-sintered at 1700 °C for 10 h. Sm_2Zr_2O_7 has a pyrochlore-type structure, while (SM_(1-x)YB_x)_2ZR_2O_7 and Yb_2Zr_2O_7 have a defect fluorite-type structure. Thermal expansion coefficient and thermal diffusivity of (SM_(1-x)YB_x)_2ZR_2O_7 are studied by a high-temperature dilatometer and a laser flash diffusivity technique from room temperature to 1400 °C. Hot corrosion tests between (SM_(1-x)Yb_x)_2ZR_2O_7 and three corrosive agents including V_2O_5, Na_2SO_4, and a V_2O_5+Na_2SO_4 mixture, are carried out from 600 to 1100 °C for 2 h and 8 h in air, respectively. Different reaction products of ZrV_2O_7, LnVO_4 and m-ZrO_2 are identified depending upon the hot corrosion conditions, for example, ZrV2O7 and corresponding LnVO_4 at 600 °C for 2 h and 8 h, namely SmVO4_, (Sm,Yb)VO_4, YbVO_4, respectively; ZrV_2O_7, m-ZrO_2 and XnVO4 at 700 °C for 2 h; m-ZrO_2 and InVO_4 either at 800-1100 °C for 2 h or at 700-1100 °C for 8 h. No reaction products are identified on Na_2SO_4-coated (Sm_(1-x)Yb_x)_2Zr_2O_7 at 900-1100 °C. However, m-ZrO_2 and corresponding LnVO_4 are found after (Sm_(1-x)Yb_x)_2Zr_2O_7 exposed to Na_2SO_4+V_2Os (mole ratio = 1:1) at temperatures of 600-1100 °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.