Amorphous lanthanum oxyhydrate was synthesized by various procedures under
various conditions. Thermolysis of air-dry specimens, both freshly prepared
and aged, was studied by thermal analysis. It was found that there exist m
any amorphous lanthanum oxyhydrates, which differ in composition and therma
l behavior from stoichiometric lanthanum trihydroxide. The factors governin
g the thermal behavior of the oxyhydrates were revealed.