Oxidation kinetics of ZrB2-and HfB2-powders and their SiC reinforced composites

Non-isothermal simultaneous thermal analysis technique elicited the peak oxidation and mass gain shifts to higher temperatures with SiC addition prompting enhanced activation energy (323 kJ/mol to 593 kJ/mol in ZrB2 and 199 kJ/mol to 207 kJ/mol in HfB2). On one hand where the peak oxidation temperature in ZrB2-SiC pellet could not be observed affirming its high oxidation resistance with negligible mass gain, whereas on the other hand the activation energy of HfB2-SiC pellet increased to 266 kJ/mol. HfB2-SiC powder is observed to follow 3D diffusion dominated (Jander equation) mechanism in which mass gain increased linearly from peak oxidation temperature similar to 710-730 degrees C at 10-20 degrees C/min heating rates till the maximum programmed temperature of 1200 degrees C. Though mass gain starts and almost ends within a range of 5 degrees C at any heating rate in the case of monolithic ZrB2 and HfB2 powders and in ZrB2-SiC composite powder at peak oxidation temperature, it (mass gain) remains almost negligible in spark plasma sintered ZrB2-SiC and HfB2-SiC composites.