The sulfidation of a Cu-15 vol.% Nb alloy in H-2-H2S mixtures at 400-600 degrees C

The corrosion of a Cu-15 vol.% Nb alloy by H-2-H2S mixtures has been studied under 10(-12) atm S-2 at 400 and 500 degrees C and under 10(-10) atm S-2 at 500 and 600 degrees C. The alloy is a two-phase mixture of the two terminal solid solutions and is composed of a Cu-rich matrix containing particles of the Nb-rich phase elongated parallel to the sample surface and isolated mainly from each other. The alloy corroded at rates similar to those of pure copper at 400 and 500 degrees C under 10(-12) atm S-2, but more slowly than pure copper at 500 and 600 degrees C under 10(-10) atm S-2. The scales were duplex, containing an external layer of pure copper sulfide and an inner very porous region composed of a mixture of sulfides of the two metals in which, however, the core of the large Nb particles was still uncorroded.