Oxidation behaviour of a pressureless sintered ZrB2-MoSi2 ceramic composite

Ultra-refractory ceramic composites of composition ZrB2 + (5-20) vol% MoSi2 are produced by pressureless sintering at 1830°C under argon atmosphere. Sintering cycles and microstructural analysis point out that at least 20 vol% of molybdenum disilicide is necessary to obtain a dense material. Thereafter, the composite 80 vol% ZrB2+ 20 vol% MoSi2 is used to test the thermal stability under oxidizing environment. Oxidation tests are carried out in flowing synthetic air in a TG equipment from 700 to 1400°C with exposure time of 30 hours. In the low-temperature range (700-1000°C), the oxidation of the composite resembles that of monolithic ZrB2 ceramics, for temperatures >1200°C the silica resulting from oxidation of molybdenum disilicide seals the sample surface, preventing zirconium diboride from fast degradation.