Studies on lanthanoid sulphites: V. thermal decomposition of cerium and neodymium sulphites

The preparation and thermal behaviour of Ce 2(SO 3) 3· 3H 2O, Nd 2(SO 3) 3·6H 2O and Nd 2(SO 3) 3 have been studied. Cerium sulphite undergoes first dehydration which is followed by decomposition to CeO 2 in the temperature range 500 – 850 °C. The decomposition involves two intermediate phases both in air and nitrogen. According to the TG curves the phases in air are Ce 2(SO 3) 2SO 4 and Ce 2SO 3(SO 4) 2. In nitrogen, Ce 2O 2SO 4 was identified and this provides a synthetic route to cerium oxysulphate. Neodymium sulphite decomposes to Nd 2O 2SO 4 when heated in air or in nitrogen up to 950°C. The intermediate levels observed do not correspond to single phases, and the reaction mechanism depends strongly on the experimental conditions.