Sludged silicon powders that are generated during silicon ingot slicing process have potential usage as silicon source in fabricating silicon carbide powders by adding carbon. A thermodynamic calculation is performed to consider a plausible formation condition for the silicon carbide powders. A thin silicon oxide layer around silicon powder is sufficient to supply equilibrium oxygen partial pressure at the formation temperature($1400^{circ}C$) of the silicon carbide in the Si-C-O ternary system. Formation of silicon carbide by using the sludged silicon powders is more efficient than by using silicon oxide powders.