Atmosphere Plasma Spray To Produce Ceramic Coating With High Infrared Emissivity At High Temperature

The high temperature infrared radiation materials are refers to ceramic materialswhich launch a certain band infrared spectrum when used at high temperature, withmany excellent properties and wide applications. At present, the stable spinelstructure infrared ceramic material has become the hot spot research. Studies haveshown that in order to improve the whole emissivity, we must improve the shortinfrared absorption coefficient and reduced the scattering coefficient. Dopingtechnology is a feasible way to manufacture high emissivity materials. By selectingreasonable materials and the heat treatment process to control the grain sizes, shapeand density, to as possible as reduce the scattering coefficient and enhance theemissivity of the surface.This article improved the preparation technology based on the previousexperiments. We mixed all the original powders with water and used the sand mill tosanding them to size0.1microns or less, increased the rate of agglomeration, liquid,and apparent density of powder. In this paper we selected the Cr₂O₃and NiO asmain ingredient, mix some special distribution rare earth oxides and other auxiliarysanding2hours with water, then made spherical powders by spray granulation andsintered the powders in high temperature furnace to obtain the composite ceramicpowders main of NiCr₂O₄, then prepared dark and uniform with high emissivitycoating on the copper sheet substrate by plasma spraying, at last using the LaSrCrO₄sol-gel to seal holes.We use particle size analyzer to detect the size of slurry after sanding todetermine the suitable grinding time, and use the SEM to observe the preparation ofpowder found that the powders became smaller, more circular and better in liquidityand apparent density after sanding. In order to get the optimum temperature forsintering, samples were sintered in1000℃,1200℃and1400℃. The XRD resultshows that the adequately reaction temperature is1400℃and the NiCr₂O₄structure at most. The highest emissivity result at600-1000℃of the coating sprayedby the powders which mixed with theTb₄O₇is0.91.The SEM of the coatings prepared by APS show that the surface of the coating is well melted but uneven, and there also exists a lot of porosity. To raise radiantemissivity, small uneven surface and small porosity is wanted. A strontium lanthanumchromate film was prepared by sol-gel with dip-coating and then the surface wasburnished precisely to prepare for another strontium lanthanum chromate film. Theprocess will be repeated until the coating has small uneven structure without porosity,which can not only protect the substrate effectively, but can also raise the coating’sradiant emissivity and service time.