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.
The behaviour of visual purple at low temperature
