Mechanism of Cu-S oxidation

As referred in references the surface and the internal oxidation are often present in the CuS system if the oxygen partial pressure is sufficiently hi gh. Sulfur in solid copper is found in form of a secondary phase, i.e, of t he copper sulfide inclusions, and only an insignificant amount of sulfur is dissolved. The internal oxidation of Cu-S alloys is discussed in various r eferences, but its mechanism and products were not explained till now. The purpose of our investigation was to perform the thermodynamic calculation o f all the possible reactions in the Cu-S-O system and to explain the mechan ism of oxidation in various conditions. For such a study, a model of copper with one single inclusion was made. Depending on time, it was oxidized at two different temperatures and two ox ygen partial pressures. The oxidized samples have been investigated by DTA, TG, optical and electron microscopy (SEM). It was established by the model studies that during the oxidation of the applied copper model with one cop per sulfide inclusion sulfur was diffusing through the copper-tube wall. On ly sulfur which came in contact with the oxygen atmosphere was oxidized. Du ring the oxidation a reaction between oxide and sulfide was taking place, a nd metallic copper and SO2 were formed if the layer of the copper oxide was brought enough close to the copper sulfide inclusion.