Kinetics and mechanism of high-temperature oxidation of the heterophase ZrSi2-MoSi2-ZrB2 ceramics

The kinetics and mechanism of high-temperature oxidation of dense heterophase ZrSi2-MoSi2-ZrB2 ceramics at a temperature of 1650 °C are studied. The ceramics were fabricated by hot pressing of composite powders prepared by self-propagating high-temperature synthesis with magnesiothermic reduction. The oxidation kinetic curve is described by the power-law function, which indicates that the evolutionary changes in the structure of the formed oxide films significantly affect the course of the oxidation process. The oxidation mechanism involves formation of a multi-layered structure of heterogeneous oxide film, partial dissociation of the ZrSiO4 phase, and formation of secondary MoB and Mo5Si3 compounds. The influence of the ZrSi2, MoSi2 and ZrB2 phases on the structural and morphological features of the formed oxide films and the efficiency of their protective action are shown. Silicon is reduced and zirconium is simultaneously oxidized to ZrO2 in the ZrSi2-ZrSiO4 system at temperatures above 1620 °C in the absence of oxygen or in low-oxygen environment.