Oxidation Studies of SiAlON/MgAlON Ceramics with Fe₂O₃ and CaO Impurities, Part I: Kinetics

The oxidation behaviors of composites SiAlON/MgAlON phases (β-SiAlON, 15R-SiAlON and MgAlON) synthesized from the residue during the leaching treatment of salt cake and corresponding synthetic samples were investigated in air by thermogravimetric measurements. Combined kinetics, viz. linear law + arctan law + parabolic law, are used to describe the kinetics of oxidation in isothermal mode. The oxidation studies reveal the effects of impurities, namely, Fe₂O₃ and CaO, present in the salt cake residue. The addition of Fe₂O₃ results in a lower activation energy and more aggressive oxidation. The addition of CaO caused the shrinkage during the synthesis and liquid formation during the oxidation above 1673 K (1400 °C). The impurities of CaO and Fe₂O₃ in the leaching residue can result in an aggressive oxidation at low temperature and a protective oxidation at temperatures above the eutectic point.