Corrosion of pressureless sintered ZrB2–MoSi2 composite in H2SO4 aqueous solution

The corrosion behaviour in closed system of a pressureless sintered ZrB2–20 vol% MoSi2 composite was studied in 1.8 M H2SO4 solution at RT, 40 and 70 °C up to 90 h. The corrosion resistance is quite poor because of the easy leaching of ZrB2 phase. MoSi2 phase and secondary phases such as ZrO2 and Mo5Si3 are less affected by acidic corrosion. After corrosion at RT and 40 °C, both the weight losses and the microstructural features indicate that the corrosion is not uniform through the specimens’ volume. The weight gain data are greatly influenced by the amount of preferential corrosion sites on the samples surfaces (pores or scratches remaining after polishing). At 70 °C, the leaching of ZrB2 is very fast and gas evolution occurs. Pourbaix diagrams indicate that at 70 °C ZrB2 phase is less stable than MoSi2 and the formation of Zr4+ cations.