On the high temperature oxidation of MoSi2 particles with boron addition

Boron doped MoSi2 particles have been envisioned as sacrificial particles for self-healing thermal barrier coatings (TBCs) but their oxidation behaviour is yet not well understood. In this work, oxidation of MoSi2 based particle is studied in the temperature range of 1050 to 1200 °C. The oxidation proceeds from a transient to a steady-state oxidation stage. The kinetics during steady-state oxidation is captured with a thermal diffusion-based model. As compared to the oxidation of pure MoSi2 particles, the addition of boron strongly enhances the silica formation. Also, a finer dispersion of MoBx in the MoSi2 matrix accelerates the formation of silica. The oxide growth rate constant increases proportional with the boron content of the MoSi2 particles. This enhanced oxidation is related to the microstructure of the oxide scale. Upon oxidation, boron yields B2O3, which promptly merge with SiO2 to form amorphous borosilicate, hindering the formation of crystalline SiO2. Consequently, the migration of oxygen in the borosilicate oxide scale is faster than in the silica oxide scale on pure MoSi2 particles.