The kinetics of carbon deposition on alpha-Fe and Fe-1.88 wt% Si was investigated by a thermogravimetric technique at 700-degrees-C. Iron foils (25-70-mu-m) were deposited with carbon by a CO/H-2 gas mixture. The rate of deposition increased linearly with increasing CO pressure and decreased with a silicon addition. Silicon addition affected the nucleation process and changed the morphology of the deposited carbon from a cylindrical filament for alpha-Fe to a ribbon-like filament for the Fe-1.88 wt% Si alloy.