The formation of Cu2S from the elements: II. Copper used in form of foils

The synthesis of Cu2S from copper foils embedded in sulfur has been studied by DTA from 25 to 600°C with a heating rate of 10 K/min. The educts and products were characterized by microscopic, microprobe and X-ray measurements. Two main reactions take place: one immediately after melting of sulfur and the other above 300°C. During the first reaction a non-uniform layer containing CuS, Cu1.1S, Cu2−xS with gaps is observed. Its copper content increases from outside to inside. After the first main effect the reaction stops due to a removal of the layer from the foil. Therefore, diffusion of copper vacancies is hindered. Starting with the second main effect, the reaction mechanism changes because Cu2−xS decomposes into copper and gaseous sulfur, which then reacts with the foil. This leads to a dense outside layer and a porous layer around the foil. Both consist of Cu2−xS. In direct contact with liquid or solid sulfur always CuS or Cu1.1S is formed whereas in contact with gaseous sulfur at first Cu2−xS appears. After the reaction either a cavity surrounded by a dense layer or a dense layer on an inner porous layer are produced which probably depends on geometry and size of the copper sample.