Investigation of reactions between vanadium oxide and plasma-sprayed yttria-stabilized zirconia coatings

The phase evolution occurring during the reaction between corrosive V2O5 (Tm = 690 °C) and a plasma-sprayed 7 wt.% Y2O3–ZrO2 (YSZ) coating from 700 to 900 °C has been investigated in situ by X-ray diffraction. The temperature and time of interaction between the V2O5 and YSZ coating determines the phases observed. Between 700 and 750 °C, reaction products of ZrV2O7 and YVO4 were observed within minutes of reaching the test temperature. m-ZrO2 was observed after 220 and 60 min at 700 and 750 °C, respectively. The simultaneous formation of both ZrV2O7 and YVO4 at the beginning of the reaction along with the delay of the m-ZrO2 formation suggests similar reactivity between both Zr and Y with V2O5. The weight percent of the ZrV2O7 phase began to diminish after 150 and 60 min at 700 and 750 °C, respectively. For reaction temperatures of 800 and 900 °C, there is a rapid decrease in the amount of t′-ZrO2 and a rapid increase in the amount of m-ZrO2 with reaction time. YVO4 was also observed at these reaction temperatures. SEM and TEM microstructural observations confirmed the phases detected from the in situ XRD experiments. Reactions between YSZ and V2O5 suggest that the formation of a liquid phase due to the high solubility of both zirconia and yttria in vanadia is the dominate mechanism that damages the coating. The thermal conductivity of a plasma-sprayed YSZ coating reacted with up to 1 wt.% V2O5 did not significantly change due to the small volume affected.