Deterioration Mechanism Of Zirconium Boride In Complex Environments

Ultra-high-temperature ceramic materials which are considered as potential materials for applications in extreme environments not only have ultra-high melting points,but also high thermal conductivity,high chemical inertness,and high hardness.Among the ultra-high-temperature ceramics,ZrB2 has high strength and high electrical conductivity due to its special chemical bonding,which makes it potential for applications in the aviation,aerospace,and nuclear industries.However,ZrB2 is vulnerable to react with oxygen at high temperatures（>600℃）,leading to material failure.Scholars at home and abroad have mainly focused on the high-temperature oxidation behavior,mechanism studies,and modification strategies of ZrB2 and ZrB2-based ultra-high-temperature ceramic materials in atmospheric environments,but the deterioration mechanisms of ZrB2-based materials in complex environments such as water-oxygen coupled environments have been rarely reported.Therefore,this thesis aims to propose the deterioration mechanism of ZrB2 in complex environments and provide a theoretical basis for further improving the stability of ZrB2 in complex environments.In this thesis,I take ZrB2 powder as the research object,focus on the intrinsic deterioration mechanism of ZrB2 in the oxygen-free environment and the deterioration mechanism in the water-oxygen coupled environment.In addition,I analyze the structure and property change law of ZrB2 before and after these two environments,and elaborate the deterioration mechanism of ZrB2 in the complex environment.Therefore,the main research contents and innovations of this thesis are as follows.（1）In the oxygen-free environment,an irreversible increase in ZrB2 resistivity was found,and the microstructural evolution of ZrB2 during the warming process was analyzed by in-situ test,and the formation of nano-structured B2O3 crystal layers and pores induced by oxygen impurities was observed;the material intrinsic structural evolution mechanism was derived by combining the phase and microstructure changes,which provides a Theoretical guidance was provided.（2）To investigate the effect of water-oxygen coupled environment on the structure and properties of ZrB2,it is observed that the material undergoes a violent hydrolysis reaction at a low temperature of 190℃.Besides,this reaction produces a large amount of H3BO3 and ZrO2,which are concentrated on the surface of the material and effectively block the electron transport,leading to a sharp increase in resistivity and eventually leading to material failure.The research in this thesis is instructive for predicting the material properties and structural deterioration of hypersonic vehicles and improving material and system stability.