OXIDATION OF ALKALINE-EARTH-METAL SULFIDE POWDERS AND THIN-FILMS

The oxidation of CaS and SrS powders and thin films was studied in sit u up to 1300 degrees C by thermoanalytical techniques (TG, DTA and hig h-temperature XRD) while FTIR and powder XRD were used to analyse ex s itu the solid reaction intermediates and products. CaS powder starts t o oxidize to CaSO4 around 500 degrees C but the oxidation is not compl ete because of a competing reaction, i.e. the decomposition of CaSO4 t o CaO, which is significant above 1000 degrees C. SrSO4 is more stable and therefore SrS completely oxidizes to SrSO4 before the decompositi on starts. FTIR and XRD failed to detect CaSO3 or SrSO3 at any stage o f the heating process. Particle size appears to have a marked effect o n the decomposition of powders, while moisture plays only a minor role . Thin films appear to be more stable towards oxidation but they react around 1000 degrees C with the silicon substrate.