Oxidation Behavior Of C/C Thermal Protection Material In Atomic Oxygen Enviroment

C/C composites are widely used in aerospace and other fields,such as the throat insert structure of the solid rocket motor nozzle and the leading edge of the shuttle,because of a series of advantages,such as low density,high specific strength,good thermal stability,low thermal expansion coefficient.For C/C composite,a typical thermal protection material with ablation dissipation as the heat dissipation mechanism,the high-temperature oxidation of the material surface will take away a lot of heat,but at the same time oxidation will directly lead to the attenuation of the mechanical properties,thus affecting the structure stability.Therefore,it is particularly important to study the oxidation behavior of C/C heat protection materials in the real service environment(high temperature/lo w pressure/atomic oxygen).In addition,the atomic oxygen oxidation experiment of large structures in the ground cannot be carried out with the current experimental conditions.Therefore,it is necessary to study the difference between the oxidation behavi or of C/C thermal protection material under the atomic oxygen and the molecular oxygen medium and carry out the equivalence analysis between them,which provides a theoretical basis for the large / low pressure / molecular oxygen ground simulation experiment.First,the effects of temperature,pressure and dissociation degree of oxygen on the oxidation behavior of C/C materials in the atomic oxygen environment were studied from three aspects of oxidation weightlessness,the reflux of the surface and the change of the micromorphology after oxidation.The oxidation kinetics experiment of C/C composite in the temperature range of 800~2000℃ was carried out.The oxidation rate constants at various temperatures were ob tained by oxidation weight loss.The changes of the microstructure with the oxidation time at various oxidation temperatures were observed.The oxidation mechanism of C/C thermal protection materials at various oxidation temperatures was explored.Then,based on the experimental results,an oxidation model of C/C thermal protection material in low pressure / atomic oxygen environment was established.The model gives the expressions of oxidation rate when the oxidation process is controlled by carbon oxygen reaction or oxygen diffusion,and the model is in good agreement with the experimental results.In addition,according to the established oxidation model,the oxidation rates of C/C thermal protection materials under other environmental parameters is predicted.Finally,the oxidation kinetics experiment of C/C thermal protection material in low pressure / molecular oxygen environment(800~2000℃)was carried out.The oxidation rate constants and oxidation mechanism of C/C thermal protective material at various temperatures were obtained.A model of oxidation of C/C thermal protective material in the environment was established.The oxidation differences of C/C thermal protection materials in atomic oxygen and molecular oxygen environment were compared from two aspects: the oxidation rate and the microstructure of the material after oxidation.By adjusting the two parameters of oxidation time and oxidation temperature,the equivalence analysis of C/C thermal protection material under different oxidizing medium is realized.In this paper,the oxidation behavior of C/C thermal protection material in high temperature/low pressure/atomic oxygen environment was studied,which expanded the knowledge of the oxidation of C/C thermal protection materials in real service environment.The equivalence analysis of C/C thermal insulation materials under atomic oxygen / molecular oxygen environment was carried out,which provided a theoretical basis for low pressure/molecular oxygen ground simulation experiments of large structure.