Problems with the external diffusion process for producing Nb3Sn-Cu superconducting wire

It has been observed that in the external diffusion process for producing Nb3Sn-Cu superconducting wire, dewetting of the Sn layer occurs for layer thicknesses on the order of 6 μm and larger. A mechanism for this dewetting is proposed and it is demonstrated that the problem may be eliminated by formation of an oxide skin on the outer surface of the Sn layer.