Oxidation behaviour of arc-melted and uniaxial hot pressed MoSi2 at 500 °C

Samples of MoSi2 were synthesised by arc melting and uniaxial hot pressing from different starting materials in order to distinguish the effects of sample preparations on the occurrence of the pest phenomenon, i.e. the rapid fragmentation of the pieces. The arc-melted samples presented cracks and porosities after preparation whereas the hot pressed samples were well densified (>95%). The pest appeared after no more than a few hours of exposure in air at 500 °C for arc-melted samples, whereas the sintered MoSi2 samples with our experimental conditions were not at all affected. The corrosion products consisted of stoichiometric MoO3 and SiO2 mixtures. Both isothermal and cyclic oxidation measurements over long durations (>2000 h) support these results. It appears that the oxidation kinetics of hot pressed samples are governed by surface or phase boundary reactions and consequently depends on the grain size and the distribution of the initial SiO2 particles, i.e. on the MoSi2 microstructure.