Synergistic regulation of the formation of yttrium oxyfluoride layer on yttrium oxide substrate by fluoride-chloride molten salts

Fluoride molten salt (KAlF4) can modify Y2O3 to form YOF, but the reaction degree of this process is difficult to control and tends to form a large amount of yttrium fluoride (YF3) with low-strength. The reaction degree of the modification process of fluoride molten salt with Y2O3 can be suppressed by the synergistic effect of chlorides (KCl-CaCl2), which is mainly determined by the diffusion of fluorine-containing complex ions (AlF4-) in the fluoride-chloride mixed molten salts (FCMMS). The low diffusion rate of AlF4- in FCMMS directly leads to the decrease of the fluorination reaction rate and delays or even prevents the deeper fluorination process. After the synergistic modulation of Y2O3 by FCMMS, only YOF is formed, and the formation of YF3 is completely avoided. The strategy and mechanism may be applied to the economical preparation of YOF protective layer or YOF powder on low-cost Y2O3 template.