Ultra-high temperature ablation behavior of MoAlB ceramics under an oxyacetylene flame

The ultra-high temperature ablation of a polycrystalline, fully dense, predominantly single phase MoAlB ceramic discs under an oxyacetylene flame is examined. The linear ablation rate decreases from 1.3 mu m/s during the first 30 s to - 0.7 mu m/s after 60 s when the surface temperature reached about 2050 degrees C (with a flame temperature around 3000 degrees C). Up to 60 s, the MoAlB is ablation resistant due to the formation of a protective and viscous surface Al2O3 layer. As the ablation time is prolonged, the protective Al2O3 scale becomes porous and is almost fully destroyed at the central ablation region after 120 s. This accelerates the formation of large amounts of volatile species (mainly B and Mo oxides), resulting in a reduction in the ablation resistance.