CARBONITRIDING REACTION OF CLAY - KINETICS OF BETA'-SIALON FORMATION BY MEANS OF WEIGHT-LOSS MEASUREMENT

The kinetics of the clay carbonitriding reaction was studied. Two clay s, whose mineralogic components are kaolinite and quartz, were mixed w ith carbon black at various carbon/clay ratios in pellet form. Runs we re performed in a vertical reactor in the temperature range 1335-1432 degrees C with a 2.21 min(-1) nitrogen flow. Conversions were determin ed from the weight loss that pellets experienced at different reaction times. Kinetic analysis showed that the experimental data fitted the Hulbert model, and the activation energies were 350 to 427 kj mol(-1). The diffusional control model and the nuclei growing model were rejec ted. The kinetic values found were correlated with measurements carrie d out by X-ray diffraction. When the initial slopes (X=kt) were used f or kinetic analysis, only the activation energy obtained for beta-SiC formation and SiO(g) volatilization were taken into account. The activ ation energies were compared with those obtained by other authors for this type of reaction.