Study on the Fluorination Process of Sc₂O₃ by NH₄HF₂

Research on rare-earth fluorides is of urgent and critical importance for the preparation and emerging applications of high-purity alloys. The fluorination of Sc₂O₃ by NH₄HF₂ to fabricate ScF₃ is investigated. The effects of the fluorination temperature, time and mass ratio of reactant on the fluorination rate and fluoride are discussed in this work. The fluorination reaction was first confirmed using thermodynamic calculation. The thermal and mass stability of the fluorination process were analyzed by thermogravimetric and differential scanning calorimetric (TG-DSC). The as-obtained products at different fluorination temperatures were characterized by Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results indicated that the fluorination began at room temperature (RT) with the formation of (NH₄)₃ScF₆. With the increase of temperature, the reaction proceeded sequentially through the formation of NH₄ScF₄, (NH₄)₂Sc₃F₁₁, and finally ScF₃. The fluorination rate increased with the increase of fluorination temperature and holding time. ScF₃ with a purity of 99.997 wt.% could be obtained by fluorination at 400 °C for 2 h.