Research On Phosphates Coating For Carbon/Carbon Composite Aircraft Braker

Firstly, aluminum phosphate, manganese dehydrogenate phosphate, zinc phosphate have been studied by DTA and TG performance, several kinds of anti-oxidation coatings for C/C composites have been prepared by the means of impregnation, and then, the oxidation resistance of the coating and thermal shock resistance were tested, the performances of the coatings prepared by impregnation were compared with that by brushing. Optical, scanning electron microscopy, X-ray diffraction (XRD) were used to detect the appearance and chemical composition on the surface of the sample coating. The main findings and conclusions of this study:(1) The curing temperature of the coatings can be determined to up to400℃after the DTA and TG analysis. Zinc phosphate is easy to be volatilized, and the volatilization of aluminum phosphate is the lowest. Rapid heating and cooling are good for preparing the coating; The nucleation and grain growth of the coatings were observed in the processes of the slow heating and cooling, which led to the component segregation and holes in the coatings. It is not good for the oxidation performance of the coating.(2) When the moles of the high temperature elements (metaphosphoric acid and metaphosphoric acid manganese) to that of zinc phosphate is between2and3, the effect of anti-oxidant can be relatively good, When the proportion of ingredients is AIPO4: Mn(H2PO4)2:Zn3(PO4):CaO=2:1:2:0.1, the coating shows the best ant-oxidation performance, the weight loss is only0.95%after20h oxidation.(3) The failure of the coating prepared by impregnation is mainly caused by volatilization. To enhance the antioxidant properties of coating, the appropriate high-temperature elements can be added. The anti-volatile, thermal stability and oxidation resistance of the coating can be improved after the join of SiO2or ZrO, especially CaO. Boric acid is not good to the improvement of the oxidation resistance of the coating. In short, low volatilization coating is favorable to improve the oxidation resistance of the coatings. (4) After the thermal shock50times between900℃X3min←�'25℃×2min, the weight loss of the coating which was prepared by brushing method with the optimized phosphate solution as a binder is only1.17%. It means that the brushing method is fit for repairing the anti-oxidation coating of the carbon/carbon aircraft braker.