Cerium Tetrafluoride. I. Preparation and reactions

Abstract

Pure anhydrous cerium tetrafluoride is best prepared by fluorinating cerium dioxide at 350-500°. A monohydrate can be obtained from aqueous solution in a variety of ways, but it cannot be dehydrated without decomposition. It loses water "zeolitically" in vacuum, showing relatively small changes in lattice parameters for loss of 70% of its water content. Thereafter the lattice collapses, forming well-crystallized cerium trifluoride and poorly crystallized "anhydrous" cerium tetrafluoride. The refractive indices of anhydrous monoclinic cerium tetrafluoride have been measured and its fluorine dissociation pressure at 500° shown to be less than 0.5 mm. At higher temperatures the tetrafluoride sublimes incongruently, and at 835-841° it melts with extensive decomposition into a fluorine-poor liquid and a fluorine-rich vapour. Cerium tetrafluoride is easily reduced to the trifluoride by ammonia and by water vapour at low temperatures. At higher temperatures it is quantitatively converted by water vapour to cerium dioxide and hydrogen fluoride. When heated with cerium dioxide it is reduced to the trifluoride with liberation of oxygen.