Thermogravimetric investigations of some thioorthophosphates and thiohypodiphosphates

Abstract

By means of a thermobalance the decomposition reactions of the thioorthophosphates of gallium, indium, bismuth, copper and of the thiohypodiphosphates of cadmium, indium, manganese, lead, and tin were determined in order to find their stability regions. The experiments were performed in atmospheres of flowing nitrogen or oxygen. In nitrogen all compounds decompose into the corresponding metal sulphides and volatile phosphorus sulphides. In oxygen the thioorthophosphates are oxidized into orthophosphates, the thiohypodiphosphates into pyrophosphates. Exceptions are the copper thiophosphates Cu 3PS 4 and Cu 7PS 4 and the analogous copper selenophosphates Cu 3PSc 3 and Cu 7PSc 6, which are oxidized into copper sulphate, selenite and an unknown copper phosphate, respectively. Some decomposition diagrams indicate by various steps the occurrence of intermediate products. In the case of Cu 3PS 4 (Cu 3PSc 4) the intermediate formation of Cu 7PS 6 (Cu 7PSc 6) was proved. During the oxidation of the thioorthophosphates of gallium, indium and bismuth, the formation of monothioorthophosphates (McPO 3S) is supposed.