Studies on fluorination of Y₂O₃ by NH₄HF

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.