The effects of starting precursors on the carbothermal synthesis of SiC powders

Two kinds of SiO2: colloidal silica (L) and quartz (Q), are mixed with two kinds of carbon sources: acetylene carbon black powder (C) and phenolic resin (P), to study the effects of the starting precursors on the carbothermal synthesis of SiC. β-SiC starts to form at 1300 °C for 4 h of heat treatment and becomes the only crystalline phase at 1500 °C for 4 h of heat treatment, regardless of the starting SiO2 and carbon sources. The characteristics of the synthesized SiC particles strongly depend on the characteristics of the carbon sources. The carbon sources also affect the stability of SiO2 structures. In samples containing carbon black powder, whether it is amorphous silica or quartz, the SiO2 transforms into cristobalite at synthesis temperature. In contrast, in samples containing pyrolyzed carbon from phenolic resin, the SiO2 reacted with carbon in its original crystal forms. The structural difference in SiO2 may affect the synthesis of SiC powders. Our results indicate that the amorphous silica could result in higher residual carbon than quartz. In addition, the SiC particles in the samples with amorphous silica appear to be more resistant to partial sintering than those in the sample with quartz.