Preparation And Properties Of MoSi₂ Based High Emissivity Coatings

The high infrared radiation coating of heat insulation tile can transfer the aerodynamic heat generated by ultra-high sound speed aircraft in service to the environment in the way of infrared radiation,which can effectively reduce its surface temperature.Intermetallic compounds such as MoSi₂ and refractory metal silicides are excellent coating materials in high temperature environment due to the coexistence of metallic bonds and covalent bonds in the crystal.However,it is easy to be oxidized in high temperature aerobic environment and easy to fall off after repeated use,which limits its high temperature application.In addition,the"pesting"oxidation of MoSi₂powder will occur in the medium temperature region,and the antioxidant performance of the low temperature region is insufficient.In this paper,in order to improve the low temperature oxidation resistance and high temperature emissivity of MoSi₂,the preoxidation combined with the sol-gel coating method was used to modify MoSi₂.The effects of the oxidation degrees and coated Si O₂ amount on the emissivity of the materials were investigated.In this paper,the effects of the oxidation time temperature/time,shielding the thermal radiation from resistive heating element,the removal method for Mo O₃ formed in low temperature oxidation and Si O₂ coating process parameters on the phase composition,oxidation resistance and infrared band emissivity of MoSi₂ powders were systematically investigated.It is found that the optimum preoxidation temperature of MoSi₂ is 350℃,and the optimum weight gain of MoSi₂ is 20%when the heat radiation from resistive heating element is shielded.The removal of Mo O₃ by high temperature treatment in argon is better than by ammonia leaching.The optimum mass ratio of MoSi₂（20%）is 3:1 in coating.The optimized sample has high emissivities of 0.97,0.98 and 0.96 at 200～400nm,400～700nm and 700～2600nm,respectively,whose oxidation resistance is satisfactory.The good oxidation resistance is attributed to the glassy Si O₂ shell formed on the surface of MoSi₂ particles in the sol-gel coating process.