A procedure for the modification of undercooling of metal droplets

Droplet emulsification — a procedure for dispersion of fine liquid metal droplets in a second phase — is a powerful technique for the study of nucleation and growth during solidification. The dispersion of bulk liquid metals as fine droplets relegates the influence of impurity particles to a limited fraction of total sample mass. The chemistry and structure of the surface coating stabilizing the metal droplets controls heterogeneous crystal nucleation and the onset temperature for solidification. To be truly useful, the droplet emulsification technique must be applicable to the high melting metals and alloys of commercial utility and the surface oxide structures native to these metals must be modifiable. A procedure for surface coating and suspension of solid metal powders in solid ceramic powder matrices has been developed which permits the study of pure metals and commercially important alloy systems, with melting temperatures between room tempe ature and 1500°C. The ceramic powder matrices have been shown to be non-catalytic to nucleation for the pure metals: Ag, Au, Cu and Ni and Co. In fact, undercoolings for these metals equal or exceed values reported by any other technique.