Copper-gold alloys involving 10 and 33 mole % Au and Ag-Au alloys involving 12 mole % Au are attacked by liquid or gaseous sulfur above 400~ very rapidly with formation of a composite scale consisting of an outer homogeneous sulfide layer and an inner two-phase layer involving Au-rich alloy and sulfide in accord with theoretical considerations regarding the instability of a plane alloy-sulfide interface. The tendency to form a rugged alloysulfide interface decreases with higher Au contents especially at lower temperatures and the rate of attack by sulfur decreases accordingly. Silvercopper alloys involving 40 mote % Cu are also rapidly sulfidized at 400~ and yield a single sulfide layer of uniform thickness. Nickel-copper alloys sulfidized at 400~ yield a scale consisting of an outer layer which is supposedly digenite Cul.sS, and an inner layer which is supposedly a solid solution of Cu~S in nickel sulfide.
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