DISCUSSION OF THE WHISKERIZING CONDITION OF SIC FROM SI3N4 AND CARBON

In order to obtain SiC whisker dispersed Si3Ni4 the reaction mechanism and the condition of SIC whiskerizing through the reaction between Si 3N4 + C was Studied thermodynamically. In this work, Si3N4 C C mixture mas heat treated in 0.1 MPa of Ar at temperatures from 1350 to 1750 d egrees C. SiC whiskers were obtained in the powder mixture heated abov e 1600 degrees C, By using the Si3N4 powder heat treated at 1100 degre es C for 24h in air, however, no SiC whiskers were obtained in the car bon mixed powder, indicating that the surface oxide of Si3N4 powder do es not take part in the SiC whisker formation reaction. The experiment ally measured nitrogen partial pressure during Sic whiskerizing was in good agreement with the equilibrium nitrogen partial pressure between Si and Si3N4, and it suggests that Si vapour is in equilibrium with S i3Ni4. Supersaturation for the carbothermal reduction of Si3N4 was cal culated as a function of temperature, Supersaturation took value 10 to 20 during SiC whiskerizing.