Corrosion of pressureless sintered ZrB2-MoSi2 composites in H2SO4 aqueous solution

The corrosion behaviour in closed system of a pressureless sintered ZrB2-20vol%MoSi2 composite was studied in 1.8M H2So4 solution at RT, 40 and 70°C up to 90 h. The corrosion resistance is quite poor because of easy leaching of ZrB2 phase. MoSi2 and secondary phases such as ZrO2 and MoSi2 are less affected by the corrosion.After corrosion at RT and 40°C, both the weight loss and the microstructure indicate that the corrosion is not huniform through the specimens’ volume. The weight gain data are greatly influenced by the amount of preferential corrosion sites on the samples surface. 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.