Fluorination of α-Fe2O3 by NH4HF2 to Produce FeF3

Fluorination of α-Fe2O3 by NH4HF2 has been analyzed in this study using simultaneous thermogravimetry and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD). The results indicated that the mass ratio NH4HF2 to Fe2O3 has no influence on the fluorination process. The fluorination starts at room temperature, dominates at 175.6°C, and completes at 200°C with the formation of (NH4)3FeF6. With further heat-treatment, (NH4)3FeF6 progressively releases NH4F by the formation of NH4FeF4 at 258.1°C, then (NH4)0.18FeF3 at 320°C and finally FeF3 with minor FeF2 at 400°C. NH4F released during the decomposition of (NH4)3FeF6 will fluorinate the un-reacted Fe2O3.