Investigation Of High Emissivity Coatings Prepared By Plasma Spraying

High emissivity material has been widely used in the field of industrial furnaces and hypersonic vehicles,which playing an increasingly important role in these fields.When the aircraft is in high speed,the surface temperature is increased due to the strong aerodynamic heating,useing high emissivity coating as thermal protection structure can radiate heat in the form of infrared radiation to inhibit the temperature on the surface of the aircraft.Coating high emissivity material on the inner wall of industrial furnace can improve the surface radiation coefficient of the radiation heat transfer material in the furnace,so as to improve the heat transfer process and increase the utilization of energy.Mixing the ingredients of lanthanum oxide,chromium oxide,strontium carbonate,titanium oxide,samarium oxide and thulium oxide together in accordance with the molecular formula of La_0.8Sr_0.2CrO₃、La_0.8Sr_0.2Ti_0.2Cr_0.8O₃、La_0.8Sm_0.2CrO₃ and La0.8Tm0.2Cr O3 by ball milling.The powder for spraying is prepared by solid phase synthesis and sprat drying and which can be used to prepare the high emissivity coating on the super alloy substrate by air plasma spraying.The infrared radiation rate、bonding strength and thermal shock resistance of the coating is tested to analysis its performance.according to the results,the emission rate of the La_0.8Sr_0.2CrO₃ coating is 0.89 in full-wave band under 600℃-800℃and its bonding strength is 21.3MPa;The emission rate of the La_0.8Sr_0.2Ti_0.2Cr_0.8O₃ coating is 0.89 in full-wave band under 600℃-800℃and its bonding strength is 22.5MPa;The emission rate of the La0.8Sm0.2CrO3 coating is 0.88 in full-wave band under 600℃-800℃and its bonding strength is 26.2MPa;The emission rate of the La_0.8Tm_0.2CrO₃ coating is 0.88 in full-wave band under 600℃-800℃and its bonding strength is 27.5MPa.All of the coatings and spraying powder are single orthorhombic perovskite structurecoating and have not occurred spalling failure after thermal shock testing by water quenching from 1100 degrees to room temperature for 10times.It proved the coatings have good thermal shock resistance.