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

Abstract

The synthesis of Cu2S from copper foils embedded in sulfur has been studied by DTA from 25 to 600 degreesC 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 degreesC. 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. (C) 2001 Elsevier Science B.V. All rights reserved.