Comparison of oxidation resistance behavior between Y3+ and Zr4+ modified aluminum phosphate impregnated graphite

To provide an oxidation protection system for graphite at low and medium temperatures (<1000 °C), aluminum metaphosphate (Al(PO3)3) coating was prepared on graphite surface by solution impregnation technology. Y3+ and Zr4+ were added respectively to improve the oxidation resistance of the coating, and the optimum additive amount of them was explored. The results indicate that the addition of Y3+ and Zr4+ can further inhibit the volatilization of P2O5. Furthermore, the Y3+ can improve the wettability of the aluminum phosphate impregnation solution on graphite surface, and the oxidation resistance of the modified coating is better below 800 °C; the Zr4+ can reduce the coefficient of thermal expansion of the aluminum phosphate coating, which shows better oxidation resistance above 800 °C. The impregnation solution modified by Y3+ diffuses into the graphite, and the surface coating plays the role of antioxidants together with the graphite matrix. While the Zr4+ modified impregnation solution mainly forms a coating on the graphite surface, and the coating plays the major antioxidation effect.