Carbothermal reduction and nitridation synthesis of silicon nitride by using solution combustion synthesized precursors

Carbothermal reduction and nitridation synthesis of Si3N4 was investigated by using precursor powders prepared by a solution combustion synthesis method. Glycine or urea (fuel), ammonium nitrate (oxidizer), silicic acid (Si source), and sucrose (major carbon source) were dissolved completely in water. This solution was dried and then heated to undergo the solution combustion synthesis reaction, resulting in a homogeneous mixture of nano-sized carbon and SiO2 particles, which was used as the precursor powder for the carbothermal reduction and nitridation synthesis of Si3N4. When the carbothermal reduction and nitridation reaction was carried out at 1,425–1,450 °C for 4 h, formation of Si3N4 can be detected only when the C/SiO2 weight ratio is greater than ~2.0. The Si3N4 yield increases rapidly as the C/SiO2 weight ratio is increased from ~2.0 to 2.8 and decreases with further increase in the C/SiO2 ratio. The α-phase content increases with increasing C/SiO2 weight ratio and decreases with increasing temperature. Depending on the C/SiO2 ratio, a Si3N4 yield of ~80 wt% and an α-phase content of ~90 wt% could be obtained.