Effect of Impurities on the Formation of Silicon Nitride by Carbothermal reduction-Niridation of fine Hydrated Silica Powders

초록

Through the simultaneous carbothermal reduction-nitridation of fine hydrated silica powders at 1,450C for 7hrs, the single phase of alpha silicon nitride could be synthesized from pure silica and pure carbon black which was treated with HCl.When as-received carbon black was used a constant alpha/betha ratio equivalent to about 9.0 was obtained by heat treatment at 1430C for 10hrs under nitrogen/55 hydrogengas atmosphere,remaining constant, regardless of the prolonged reaction time.To investigate the effects of the impurities on the formation of silicon nitride,various oxides were added to the refined carbon black individually.Alpha silicon nitride seed accelerated the alpha phase formation, and betha phase was formed in the presence of V2O5 and CaO,while betha SiC appeared in the presence of Fe2O3, NiO and Cr2O3 respectively