Effects upon interfacial reactions by electric currents of reversing directions

Sandwich-type reaction couples, Sn/Ni/Sn and Sn/Ag/Sn, were prepared. Two kinds of experiments were conducted: with and without the passage of a direct electric current through the couple. The specimens were placed in a furnace for pre-determined lengths of time at 180 and 200 °C for the Sn/Ni/Sn system and 160 °C for Sn/Ag/Sn. The current density was 500 A cm−2. The direction of the electric current through the couple was reversed during the reaction. Ni3Sn4 and Ag3Sn phases were formed in the Sn/Ni/Sn and Sn/Ag/Sn couples, respectively. The passage of electric current changes the elemental mass fluxes, but not the phases formed in the couples. A mathematical model was proposed to calculate the thickness of the reaction layers. It has been found that the relative magnitudes of the reaction layer thickness at the two interfaces of the couples obtained from the two kinds of experiments are different. A net enhancement in the layer growth was experimentally observed even though the direction of electric current was reversed to neutralize the effect of electromigration. It is concluded that besides producing electromigration effects, the passage of electric currents through the couples affects the diffusion properties.