On Nitriding Reactions in the Silicon-Silica System

In order to make sintered body consisting of pure Si2ON2, nitriding reactions of silicon-silica system were studied experimentally.The results obtained were summarized as follows:1) When compacted mixtures of silicon and quartzite powders having mole ratios from 1.0 to 3.5 for Si/SiO2 were heated at 1450°C for 3 hours in nitrogen atmosphere, sintered bodies containing Si2ON2 were obtained.However, almost pure sintered body of Si2ON2 was produced from the mixture having the mole ratio of 3.0.2) When compacted mixture of silicon and α-cristobalite, or fused silica powders in place of quartzite powder having the mole ratio of 3.0 for Si/SiO2 was heated slowly and treated with nitrogen over 1400°C, similar sintered body of Si2ON2 were obtained.3) The formation of Si2ON2 from the compact started at about 1100°C and was almost completed at the temperature range from 1400° to 1450°C.4) Reaction of silicon, silica and nitrogen to form Si2ON2 was expected to proceed in two steps as follows:1/2SiO2+1/2Si=SiOSiO+Si+N2=Si2ON2and reaction of silicon and nitrogen to form Si3N4 was not favorable to obtain pure Si2ON2 body, because it was rather difficult to change Si2ON2 from Si3N4.