Formation mechanism of microcrystalline spherical graphite particles in solidified nickel

Nickel is a well known catalyst that can readily transform carbon into graphite at high temperature. In our designed arc-discharge experiments, diamond easily dissolved in melted nickel and became small graphitic flakes. After the melted nickel had cooled and solidified, there were many microcrystalline-sized spherical graphite particles found on the nickel grain boundaries, surprisingly. It is interesting that only at the hotter area would the spherical graphite be found. This leads to our proposed forming mechanism: the spherical graphite particles were formed during the solidification of nickel. Because the temperature and solubility are high at the hotter area (zone A), the crystallization and growth of graphite became transport-controlled, instead of surface-controlled, and therefore the most common shape of the particles was spherical. This phenomenon, as far as we know, has not been previously observed.