A direct determination of the anisotropy of the surface free energy of solid gold, silver, copper, nickel, and alpha and gamma iron

Abstract

Small metal paticles (~ 1 μ dia.) resting on an inert substrate have been equilibrated in a vacuum or in a hydrogen atmosphere in an essentially closed system so as to achieve an equilibrium shape dependent only on the anisotropy of the surface free energy of the solid metal. The γ plots of these metals result directly from a determination of these equilibrium shapes. The equilibrium shapes (and γ plots) of all the f.c.c. metals are essentially the same as those predicted by correcting the pairwise interaction model of surface energy for the free energy contribution of kinks on surface steps. In the case of b.c.c. alpha-iron impurity effects are evident and these readily explain the (small) variance between experiment and the same theory. The surface free energies of f.c.c. metals vary by about 16 per cent of the mean. The surface free energy of alpha-iron varies by at lesat 20 per cent of the mean. The effect of oxygen on the γ plots of a number of f.c.c. metals is now clearly established as deepening the {100} and {111} cusps so as to cause the equilibrium shape to become faceted.