Preparation of Silicon Nitride Whiskers from Diatomaceous Earth: I, Reaction Conditions

Whiskers and powder of silicon nitride were prepared by the carbothermal reduction and nitridation of diatomaceous earth in the presence of flowing N 2 and NH 3 . The optimum temperature for the formation of Si 3 N 4 whiskers was 1350°C and the yield reached almost 20% after 24 h. The α‐Si 3 N 4 content decreased with increasing nitridation temperature. Yields of the whiskers were dependent on NH 3 concentration and the total gas feed rate. The maximum yield of inside whiskers was obtained for a 25 vol% NH 3 /N 2 mixture, while the maximum quantity of outside whiskers was produced for 75 vol% NH 3 /N 2 . The sum of the yield of the inside and outside whiskers increased with decreasing total gas feed rate. However, no nitridation of SiO 2 was observed at a feed gas rate below 0.18 mmol·min −1 . The yield of the inside whiskers increased gradually with increasing reaction time up to 36 h, whereupon a constant value was attained. Although the amount of outside whiskers produced was relatively small, the quantity seemed to increase until 60 h.