Optimization of time-temperature schedule for nitridation of silicon compact on the basis of silicon and nitrogen reaction kinetics

摘要

A time-temperature schedule for formation of silicon-nitride by direct nitridation of silicon compact was optimized by kinetic study of the reaction, 3Si + 2N_2 = Si_3N_4 at four different temperatures (1250 deg C, 1300 deg C, 1350 deg C and 1400 deg C). From kinetic study, three different temperature schedules were selected each of duration 20 h in the temperature range 1250 deg -1450 deg C, for complete nitridation. Theoretically full nitridation (100 percent i.e. 66.7 percent weight gain) was not achieved in the product having no unreacted silicon in the matrix, because impurities in Si powder and loss of material during nitridation would result in 5-10 percent reduction of weight gain.Green compact of density < 66 percent was fully nitrided by any one of the three schedules. For compact of density > 66 percent, the nitridation schedule was maneuvered for complete nitridation. Iron promotes nitridation reaction. Higher weight loss during nitridation of iron doped compact is the main cause of lower nitridation gain compared to undoped compact in the same firing schedule. Iron also enhances the amount of #beta#-Si_3N_4 phase by formation of low melting FeSi_x phase.