Lutetium Fluoride: Oxide Converted in HF and Argon at 750 °C, then Melted in HF to Remove the Last Oxygen (Henderson, Ames 1970)

Lutetium metal made from its fluoride is only as clean as the fluoride. Henderson converted rare-earth oxides in a stream of hydrogen fluoride and argon at 750 °C, then melted the product in hydrogen fluoride so the last oxide turned to fluoride as well; he found the method good for every rare-earth fluoride from lanthanum to lutetium except europium. Result: LuF3 with under 50 ppm oxygen, melting at 1184 °C. Source: D. C. Henderson, The Preparation and Some High Temperature Properties of the Rare Earth Trifluorides (Iowa State University / Ames Laboratory, 1970), pp. 17-34, 67. Anhydrous hydrogen fluoride is deadly and burns deep into skin. Picture drawn by Youblob.