Cadmium sulphide oxidation

Systematic investigations have been carried out on the oxidation of CdS of semiconductor purity using both DTA, and TGA, as well as chemical, mineralogical, phase X-ray analysis and scanning electron microscopy (SEM). The paper presents a three-dimensional phase diagram for the Cd–S–O system of partial pressure of SO2 and O2 against T in the temperature interval 600–1000 °C, from thermodynamic of the system. DTA, TGA and X-ray analysis of the product obtained from roasting are compared with the thermodynamic predictions from the three-dimensional diagram. Plates of hexagonal monocrystal CdS ware very porous and on oxidizing a mechanically weak layer of CdO was obtained. The CdO crystals grow both towards the core of the particle and outwards in the direction of the gas phase in the air environment through condensation of the vapour. The oxidation processes take place in a kinetically controlled regime and oxidation does not follow the classical model of the continuously shrinking unreacted core.