Studies on fluorination of Y2O3 by NH4HF2

Fluorination of Y2O3 by NH4HF2 to obtain pure YF3 is studied in this work by observing the mass changes at room temperature and by employing TGA and DTA at higher temperatures, and observing the subsequent phase changes by X-ray diffraction. Fluorination begins at room temperature with the formation of (NH4)3Y2F9 and NH4F, and continues with the later further fluorinating any leftover Y2O3 to ammonium yttrium fluorides with the evolution of NH3. Similarly, on heating a mixture of Y2O3 and NH4HF2, the reaction proceeds sequentially through the formation of (NH4)3Y2F9, NH4Y2F7 and finally YF3. Any Y2O3 still remaining reacts with YF3 to form yttrium oxyfluorides, which continue as impurity. Substantial evaporation of NH4HF2 is possible even before it could participate in the reaction. This disturbs the stoichiometry of the charge causing oxygen to remain in final YF3. The compound reported in literature as YF3·1.5NH3 appears to be NH4Y2F7.