Due to the strongly exothermic nature of silicon nitridation, a clear understanding of the nitridation process and an effective control regime, especially when the nitridation involves a rather large mass of silicon are of commercial interest. The nitridation process was investigated by reacting "large masses" of silicon powder compacts (about 1.5 kg) in a nitriding atmosphere in which some auxiliary gases such as Ar or He were added. Because of the exothermic heat, the reaction kinetics were found to be influenced by the amount of silicon in the nitridation cycle. The effect of the additional gases (Ar and He) is enhanced as the mass of silicon loaded in the furnace increases. The kinetics and the corresponding mechanisms of the whole nitridation cycle are discussed and a mechanism for the second reaction maximum is proposed. 22 refs.