Fluorination of Thorium Oxide by Ammonium Bifluoride and Its Reduction to Metal

The fluorination of thoria (ThO2) with ammonium bifluoride NH4HF2 to obtain oxygen-free thorium fluoride is reported. It is interesting to note that the fluorination starts right from room temperature to form ammonium thorium fluoride intermediate. On heating, the intermediate decomposes to form pure ThF4. It was also seen that any unreacted ThO2 reacts with the ThF4 to form ThOF2. The oxygen-free ThF4 produced was then reduced by calcium to form metallic thorium. The advantage in the process is that it can make thorium in bulk form which greatly reduces the issue of handling powders. However, as the process involves the melting of thorium, selection of suitable crucible becomes a key to its success. Yttria crucible appears to be a good choice.