Equilibrium shape of nickel crystal

Abstract\n The equilibrium shape of pure nickel and the effect of carbon on the changes in the equilibrium shape at 1200oC were investigated. A statistical observation over the size-dependent, time-dependent and carbon-induced morphological evolution of crystallites suggested that the equilibrium crystal shape (ECS) of pure nickel is a polyhedron consisting of {111}, {100}, {110}, and {210} surfaces. However, crystals with an extensive portion of {320} surfaces were also frequently observed. The appearance of {320} surfaces were interpreted as kinetically stabilized metastable surfaces which survived during the thermal equilibrating process possibly due to a high nucleation energy barrier for the removal of the surfaces. On the other hand, the ECS of pure nickel was observed to change drastically into a spherical shape with the facets of {111}, {100}, {110}, and {210} without exception under a carburized atmosphere, which indicates that carbon not only facilitates the surface diffusion by which energetically more stable surfaces can be easily developed but also decreases the surface energy anisotropy. Together with X-ray photoelectron spectroscopy studies, it was proposed that the carbon induced changes in the ECS may be due to a solid solution effect which could lead to a reduction in the binding energy among atoms in the bulk as well as on the surfaces.