Unusual wetting of liquid bismuth on a surface-porous copper substrate fabricated by oxidation-reduction process

Abstract

The unusual wetting phenomenon of liquid Bi on surface-porous copper has been studied. A porous layer was prepared at the surface of a copper substrate and the wetting behavior of liquid Bi on this layer was investigated and compared with that on a flat solid copper substrate. A surface-oxidized copper substrate was reduced at 473 K in H2 to prepare a porous layer at the surface. Since the contact angle of liquid Bi on the flat solid copper substrate was gradually declining with increasing temperature, the behavior of liquid Bi on solid copper was shown to have good-wettability. In addition, the unusual wetting behavior of liquid Bi was observed on surface-porous copper substrate. This result is evidence that the pores in the porous layer are 3-dimensionally inter-connected. This usual wetting phenomenon of liquid Bi was then applied in the joining of copper wire with the surface-porous copper substrate. Bonding was successfully achieved with a minimized weld overlay at thejoining point. © 2007 The Japan Institute of Metals.