Mondeling Emissivity Of Infrared Low Emissivity Coating Based On Rough Surface

With the development of electronic technology,the infrared stealth technology in various weapon platform systems is widely applied,especially the low infrared emissivity coating.The infrared emissivity of the coating is closely related to matrix resin,low emissivity flake pigment composition and structure,flake pigment orientation arrangement,pigments varieties and volume concentration and coating surface state,however,there is few report about the mechanism of the influence of the coating surface roughness on the infrared emissivity.In this paper,the relationships between the infrared emissivity of the coating and the surface roughness(?),inverse root-mean-square surface slope(a/?),thickness and volume concentration of flake pigment were established by using the rough surface model and the improved Kubelka model.It provides theoretical guidance for the design and preparation of infrared low emissivity coating.The main work is divided into the following aspects:(1).According to the transmission process of infrared light within the coating,the entire coating with plenty of oriented flake pigments is simplified to discrete multilayer structure.The upper layer of the coating is the rough-surface layer and the calculation of reflection properties of rough surfaces are based on physical optics.The lower layers of the coating are equivalent to superposition structure layers where flake pigments are almost uniform and horizontal orientation and the calculation of reflection properties of superposition structure layers are based on geometrical optics.(2).The effects of coating surface roughness,inverse root-mean-square surface slope,metal pigment content and thickness on the emissivity of the coating are studied.The larger inverse root-mean-square surface slope tends to obtain a lower coating emissivity.The influence of the rough surface on the emissivity of the coating is mainly through two factors: surface roughness(?)and inverse root-mean-square surface slope(a/?).The former mainly affects the specular reflection,and the latter mainly affects the diffuse reflection.Because the roughness value of the coating is roughly 3?m from the following calculations,in these cases the surface can be considered to be optically-rough.Then the diffuse component dominates,and specular component has aweak effect on reflection,for an optically-rough surface.Therefore,the increasing inverse root-mean-square surface slope of the coating helps to reduce the negative effect of the rough surface of the coating on the emissivity.The minimum emissivity of the coating can be obtained,for a/??7.When the pigment thickness is 0.8?m and the volume concentration is 0.55,the infrared emissivity increases significantly from 0.176 to 0.242 in 8-14?m,for the inverse root-mean-square surface slope changing from 1 to7.(3).The validity of the model is verified by comparing the theoretical calculations to an experimental measurement.The influence of root-mean-square roughness,volume concentration of flake pigment and other factors on the emissivity of the coating was proved.The results show that the larger inverse root-mean-square surface slope tends to obtain a smaller emissivity for the consistent volume concentration of flake pigment.The larger volume concentration of flake pigment is inclined to obtain a smaller emissivity for the approximately invariable root-mean-square surface slope.A low infrared emissivity coating with a thickness of 50?m and an emissivity of0.2 was designed according to the simulation.The coating with the emissivity of about0.2 can be obtained by controlling the construction process so that the inverse root-mean-square surface slope of the coating is greater than or equal to 7,the volume concentration of flake pigment is 0.55 and the thickness is less than 1.2?m.