Chemical compatibility of rare earth apatite with yttria-stabilized zirconia

The chemical compatibility of a series of rare earth apatite (RE-apatite), with Y2O3-stabilized ZrO2 (YSZ) has been investigated. Three types of RE-apatite powders with different ionic radius (RE = Gd, Nd and La) were prepared, and bulks prepared from the powder mixtures of RE-apatite and YSZ were heat-treated at 1300 °C up to 100 h in this study. It was found that Gd-apatite reacted with YSZ and formed a reaction layer (Gd2Si2O7) at the Gd-apatite/YSZ interface. Meanwhile, the intense Gd3+ diffusion resulted in the formation of Gd solid solutions in YSZ and much YSZ phase transformation. In contrary, as for Nd- or La-apatite/YSZ composite, which has larger ionic radius, no reaction product was observed at interface and there was less RE diffusion into YSZ as well as YSZ transformation. These results clearly indicated that large ionic radius of RE3+ could enhance the chemical compatibility of RE-apatite with YSZ.