Effect of atomic oxygen on oxidation behavior of ZrB₂-SiC ceramic composite materials

The oxidation behavior of ZrB₂-20% vol SiC ceramic composites, which is typically used as the potential composite materials of nose, in the ambience pressure of 40Pa and temperatures between 1400 and 1700°C of the atomic and molecular oxygen environment were studied. The practical situation of tip materials exposed in the plasma of high temperature, low pressure and mainly the oxygen atomics during the process of high-speed flight was simulated with the laboratory apparatus. Comparative analysis of oxidation product, chemical-bond energy, microstructure and oxide layer structure were conducted by XRD, SEM and XPS measurements. It showed that oxidation in atomic oxygen was significantly greater than molecular oxygen. With the same temperature and pressure, the material surface was fully oxidized in atomic oxygen. The formation of four-layer structures of ZrO₂, SiC depletion layer, incomplete reaction layer and unreacted layer could be found. The thickness of oxidation layer in atomic oxygen was as 1.6 times as in molecular oxygen. The research shows that low-pressure atomic oxygen environment can increase oxidation rate significantly so that decrease the low-pressure oxidation resistance.