Study On The Control Method Of Visible-Infrared Optical Properties Of Pigments And Coating Materials

In the field of functional materials,it’s necessary to adjust the visible-infrared optical properties of materials according to the needs of practical applications.In this paper,based on the potential application requirements of building energy-saving coatings and multi-spectrum compatible stealth,the controllable adjustment methods of optical properties of materials in visible-near-infrared and thermal infrared bands are studied.In order to meet the requirement of multi-spectrum compatible stealth of infrared stealth coating,a new type of Al/Ni core-shell pigment was obtained by in-situ coating magnetic metal Ni layer on the surface of flake aluminum powder.The effects of reactant concentration,reaction temperature and reactant dripping speed on the structure and morphology of Al/Ni core-shell pigment were studied,and the optical-radar compatible stealth effect of the coating was verified.In order to meet the demand of titanium dioxide in visible-near infrared band,polychromatic coating pigments were prepared by transition metal ion doping to regulate the electronic structure of TiO₂ and solid phase sintering to optimize the intrinsic spectral properties of TiO₂.The effects of metal ions on the phase structure,particle morphology and optical properties of titanium dioxide were studied.Its reflection characteristics and thermal insulation properties in visible light and near infrared are verified.The details of this paper are as follows:（1）The influence mechanism of structural parameters such as Ni shell thickness and surface roughness on the spectral reflectivity of Al/Ni core-shell pigments is discussed by using geometrical optics theory and surface roughness theory,and the structural design requirements of core-shell materials are optimized.Then,flake Al/Ni core-shell pigments were prepared by displacement reaction,and the effects of different reactant concentration,reaction temperature and NH₄F dripping rate on the coating amount,morphology and visible-infrared spectrum properties of Ni shell were studied systematically.The experimental results show that the increase of reactant concentration and reaction temperature is helpful to increase the deposition rate of Ni²⁺on the surface of flake aluminum powder,increase the coating amount and surface roughness of Ni shell,reduce the visible light reflectivity of flake aluminum powder,and only slightly reduce the reflectivity of infrared band.However,the effect of different NH₄F dripping rates on Al/Ni core-shell pigments is relatively small.（2）The magnetic properties of powder samples were tested by vibrating sample magnetometer,and the electromagnetic parameters of powder samples were measured by coaxial transmission/reflection method.The results show that with the increase of the molar ratio of Al:Ni²⁺in the solution and the reaction temperature,the relative content of Ni layer on the surface of flake aluminum powder is increased,the dielectric constant of flake aluminum powder is significantly decreased,the magnetic properties of Al/Ni core-shell pigment are effectively improved,and the magnetic loss is increased.Based on the composite coating structure of infrared low emissivity-radar absorbing coating,the radar reflectivity of the composite coating was tested,and combined with the analysis of impedance matching theory,with the increase of Ni content,the dielectric constant of the coating decreased,the impedance value of low infrared emissivity decreased effectively,and the transmittance of low infrared emissivity to radar wave was increased.（3）In order to meet the regulation requirements of visible light and near infrared light,the solid phase ball milling method was used to modify TiO₂,and V,Fe,Co and Mn transition metals were selected as impurity ions to systematically study the effects of doping on the electronic structure,morphology and optical properties of TiO₂ powder.The results show that when TiO₂ is doped with different metal ions,the band gap of TiO₂ decreases,the absorption of visible light increases,and the phase transition temperature of TiO₂ decreases.The difference is that in the anatase doped TiO₂ powder,the influence on the band gap E_g is limited,and the four pigments brown（V）,blue（Co）,red（Fe）and khaki（Mn）are lighter,the effect of near infrared reflectivity is also low,and the particle size of the sample changes little.However,in the rutile type,the particle size of the sample is much larger than that of the anatase type,the maximum reduction of the band gap 1.3ev,the enhancement of the absorption of visible light,and the four colors of dark brown（V）,green（Co）,yellow（Fe）and light gray（Mn）are obtained,so that the reflectivity in visible light-near infrared is about 10-20%lower than that of anatase.（4）After the doped TiO₂ powder was prepared into color coating,a thermal insulation test system was built by simulating sunlight with a full spectral lamp,and compared with the fully absorbed carbon black coating to explore the reflection characteristics and thermal insulation performance of the color coating in the visible-near infrared band.The results show that due to the dispersion of the powder in the resin,the gap between the particles becomes larger,which increases the scattering of visible light,so that the reflection of the coating in the visible band is lower than that of the powder material.A horizontal comparison of the coating samples made of the two crystal forms of TiO₂ shows that the visible-near infrared reflectivity of the coating is about 15%lower than that of the rutile type,mainly because the particle size of the rutile type is larger than that of the anatase type.Reduces the scattering effect of the coating on the near infrared band.This also directly affects the thermal insulation performance of the coating:after irradiating for the same time,the temperature of the coating doped with TiO₂ is 6℃-22℃lower than that of carbon black,and the average temperature of rutile coating is about 8℃lower than that of anatase coating.The temperature of the coating doped with Fe in several transition metal ions has been reduced by about 16℃and has obvious thermal insulation performance.