Carbothermal synthesis of silicon nitride (Si3N4): Kinetics and diffusion mechanism

Sample controlled reaction temperature (SCRT) has been used for the first time to study the kinetics of the carbothermal reduction of silica in nitrogen to obtain silicon nitride (Si3N4). It is noteworthy to point out that SCRT method allows both a good control of pressure in the sample surroundings and the use of reaction rates low enough to keep temperature gradients at a negligible level to avoid any heat or mass transfer phenomena. It has been shown that the carbothermal synthesis of silicon nitride is best described by a two-dimensional diffusion kinetic model with an activation energy of about 306 kJ/mol. Effects of experimental parameters on the activation energy has been investigated. By using SCRT it has been possible to obtain ceramic powder with a determined phase composition and a controlled microstructure.