This investigation includes nitridation phenomena of silicon powder compacts in air. Nitridation reaction condition has been provided with using silicon nitride bed and active carbon additive. Reaction products are Oxynitride, $alpha$-Si3N4, and $eta$-Si3N4, Oxynitride(Si2N2O) phase in formed at outer surface layer ofsilicon powder compacts. $alpha$-Si3N4, and $eta$-Si3N4 are formed at inner region of powder compacts. Microstructural observation indicates that nitridation mechanism in this work is the same as conventional nitridation mechanism nitrogen gas.