Corrosion behavior of yttrium oxyfluoride ceramics in HCl, HNO3 and HF solutions at room temperature

Dense bulk of Y2O3, YOF, Y5O4F7 and Y5O4F7 + YF3 ceramics samples were immersed in HCl, HNO3, and HF solutions at room temperature. Scanning electron microscopy revealed that HCl and HNO3 severely damaged Y2O3 while these acid solutions attacked grain boundaries of YOF, Y5O4F7 and Y5O4F7 + YF3 ceramics. Energy-dispersive X-ray spectroscopy analysis resulted that Y5O4F7 + YF3 ceramics immersed in HCl and HNO3 were partially corroded in its YF3 region. Y5O4F7 showed better durability than YOF and Y5O4F7 + YF3 in viewpoint of weight losses and microstructure change. Weight change after dilute HF immersion was negligible and almost the same among the samples. Slight reaction at grain boundaries were observed in Y2O3, YOF, Y5O4F7 and Y5O4F7 + YF3 after dilute HF immersion. Y-O-F ceramics samples are as durable as conventional Y2O3 against HF.