ROLE OF LIQUID DROPLET SURFACE-DIFFUSION IN THE VAPOR-LIQUID-SOLID WHISKER GROWTH-MECHANISM

A careful examination of the dissolution/diffusion through liquid/preciPitation steps of the well-accepted vapor-liquid-solid whisker growth mechanism has been conducted. Various diffusional processes involved in the whisker growth, such as solid surface diffusion, liquid surface diffusion, and bulk liquid diffusion, have been evaluated. It is noted that the diffusion along liquid alloy droplet surfaces, driven by both a concentration gradient and surface energy decrease, should not be ignored. Mass transport rate calculations using a simplified one-dimensional model show that the surface diffusion becomes more important with decreasing whisker diameter, decreasing solubility of growth species in the liquid phase, and increasing ratio of surface diffusion coefficient to bulk liquid diffusion coefficient. The diffusion along the liquid alloy droplet surface may play a major role in the growth of compound whiskers. Inclusion of the liquid droplet surface diffusion in the vapor-liquid-solid mechanism is proposed.