Study On The Enhancement Of Antioxidant Activity And Its Mechanism Of ZrB₂

With the development of Aeronautics and Astronautics and the pursuit of space exploration,the demand for ultra-high temperature ceramic materials is increasing.Ultra-high temperature ceramic materials include boride,carbide metal materials.ZrB₂is a kind of boride with strong covalent bond,high melting point of 3040^oC,high chemical stability,high thermal conductivity and electrical conductivity.It is suitable for extreme environment and has wide application prospect in the field of aeronautics and Astronautics.However,as a thermal protection material,ZrB₂ is easy to be oxidized in practical application,which limits its application.Therefore,how to improve ZrB₂’s oxidation resistance is always a difficult problem in aerospace field.In this paper,the oxidation of ZrB₂ at high temperature has been studied,especially the improvement of the oxidation resistance and hydrophobicity of ZrB₂ ceramic powders and coated ZrB₂@MFx ceramic materials,therefore,it provides the technical support for the thermal protection materials used in the next generation of aircraft.The main contents of this thesis are as follows:（1）according to the equation of ZrB₂synthesis,the theoretical temperature of ZrB₂ synthesis is calculated to be 1509^oC,a molten glass phase is formed on the surface of the product ZrB₂（ZrB₂@MFx）at high temperature to form a stable protective layer.The formation of a stable"protective layer"can effectively insulate the oxygen diffusion from the air into the ZrB₂ ceramic material.Stable protective layer formed by zirconium boride can improve the oxidation resistance of ZrB₂ at 700^oC¹200^oC.（2）High temperature oxidation resistance and hydrolysis,the high temperature oxidation behavior of ZrB₂@MFx ceramic powders was investigated in the temperature range of 200^oC to 1400^oC,the essential contribution of fluoride content in starting materials of ZrB₂ synthesis to the improvement of high temperature oxidation resistance of ZrB₂@MFx ceramic powders was studied.The change of microstructure and phase of ZrB₂@MFx ceramic powders at high temperature was explained and the model of high temperature oxidation resistance mechanism of coated ZrB₂@MFx ceramic powders was established.The hydrophobicity of ZrB₂@MFx and ZrB₂ powders were investigated under 200^oC hydrothermal treatment combined with the hydrophilicity of ZrB₂ and ZrB₂@MFx.（3）preparation and characterization of ZrB₂@MFx ceramic powders by plasma spraying and according to the optimum synthesis process of ZrB₂@MFx ceramic powders.ZrB₂@MFx ceramic powders were prepared into coatings,the effects of plasma spraying technology such as spraying power,powder feeding rate,coating thickness and grain size on the properties of the coating were systematically studied,the influence of fluoride content on the antioxidation and hydrophobicity of ZrB₂@MFx coating was investigated.