An Investigation of the Microstructure in the Pest Oxide of a MoSi2- Based Composite

Journal article, 2000

The pesting of MoSi2 was investigated by performing detailed microanalysis on the pest oxide layer. The studied material was a MoSi2-Mo5i3-clay composite which had undergone pest-oxidation for 4000 hours at 450°C. Results from detailed SEM and TEM studies, including quantitative EDX analysis, on the various features in the pest oxide are presented. It was found that MoSi2, as well as the MosSi3, transforms immediately into an oxide mixture of MoO3 nanocrystals and amorphous SiO2 with significant loss in molybdenum upon oxidation. With time, part of the oxide mixture cluster into lamellar MoO3 aggregates. These aggregates disappear from the oxide after even longer times, leaving voids in the oxide structure. This allows even quicker depletion of MoO3 from the oxide, leaving dark grey regions containing mostly SO2.