THERMALLY-INDUCED CHANGES IN THE OXIDATION-STATE OF CERIUM(IV) - A STUDY OF CARBONATE AND CHLORO COMPLEXES

Cesium hexachlorocerate(IV), Cs2CeCl6 (I) and sodium pentakis(carbonat o)cerate(IV), Na6Ce(CO3)(5).12H(2)O (II) have been investigated in air by simultaneous TG/DTA, FTIR and XRD in order to follow the oxidation state of cerium during their thermal treatment. The thermal decomposi tion of the hexachloro compound (I) is accompanied by a double change in the oxidation state of cerium. First, in an inner reduction-oxidati on reaction, chlorine is evolved and a Cs2CeCl5 phase is obtained. The immediately starting oxidation of this Ce(III) species caused various phase transitions in the CeCl3-CsCl system formed. The presence of Cs 3CeCl6 above 400 degrees C can also be assumed and finally this phase also oxidizes into CeO2 with the formation of CsCl as by-product. In t he case of the pentacarbonato complex (II), no Ce(III) species were de tected. The final products of its decomposition were CeO2 and Na2CO3.