The sulfidation of two-phase Cu-Ag alloys in H-2-H2S mixtures at 550-750 degrees C

The corrosion of three two-phase Cu-Ag alloys by H-2-H2S mixtures has been studied at 550-750 degrees C under sulfur pressures below the stability of pure Ag2S. In all cases the scales are duplex and contain an outer layer of pure Cu2S and an inner complex region composed of a mixture of the Ag-rich metal phase and internal Cu2S particles. The microstructure of this region differs for the three alloys, but remains very similar for each alloy at the three temperatures. The peculiar microstructures of the scales are discussed in the light of the presence of the two phases in the alloys and of the restrictions which the limited reciprocal solubility of the two alloy components produces on the rate of their diffusion in the alloy. Copyright (C) 1996 Elsevier Science Ltd.