Preparation And Properties Of Inorganic Pigments With High Near-Infrared Reflectance By Solution Combustion Method

Solar radiation can cause heat accumulation on the surface of buildings,aggravating the heat island effect.The use of high near-infrared（NIR）reflective pigments can effectively reduce the surface temperature of objects and alleviate energy consumption caused by the heat island effect.Currently,developing a simple and efficient preparation method to develop environmentally-friendly and high near-infrared reflective pigments is the only way to promote the application of energy-saving and thermal insulation coatings.In this paper,the inorganic pigment powders with NIR reflectance were synthesized using solution combustion method,and the samples were characterized by various test methods.The experimental results of this paper are divided into the following points:（1）The YB_1-xMn_xO₃（x=0,0.01,0.02,0.03,0.04 and 0.05）NIR reflective inorganic pigments possessed a hexagonal phase structure.The crystal morphology of the pigments produced some porous structures,and the particle size could reach around40 nm.Moreover,they exhibited good acid and alkali resistance（ΔE^*<5）.The color of the powders changed from white to gray-blue due to the doping of manganese ions.As the doping amount raises,the Eg value increases from 2.03 e V to 2.14 e V,which may be due to the charge transfer between the O 2p valence band and the Mn 3d conduction band.The YB_0.97Mn_0.03O₃ pigment had the best color performance（L^*=69.75,a^*=-5.46,b^*=-6.36）with a NIR reflectance of 66.18%.Through the simulation of energy consumption in buildings using Energy Plus software,it was found that after applying the pigments,the surface temperature of the building could be reduced by 2 to 4℃,which had a certain heat insulation effect.（2）The Yb₄Al_2-xMn_xO₉（x=0,0.05,0.10,0.15 and 0.20）NIR reflective inorganic pigments did not change their crystal structure with the increase of Mn doping amount,and the crystal morphology was porous and spongy.In addition,the pigments had good acid and alkali resistance（ΔE^*<5）.Due to the Mn doping,the color of powders varied from white to blue.The Eg value increased from 2.43 e V to 2.54 e V,which was mainly due to the introduction of the 3d orbital of Mn³⁺between the 2p orbital of O^2-and the3d orbital of Yb³⁺.When x=0.20,L^*=60.5762,a^*=-4.6701 and b^*=-15.09,the pigment showed the best color performance with a NIR reflectance of up to 69.75%.In addition,under the irradiation of infrared lamp,the surface temperature of the prepared Yb₄Al_1.8Mn_0.2O₉ coating was 20.1℃lower than that of blue commercial coating,indicating a significant insulation effect of this pigments.Compared to YB_1-xMn_xO₃inorganic pigments,the pigments exhibited a deeper blue color and higher near-infrared reflectance.（3）The Ba La_2-xTb_xZn O₅（x=0,0.05,0.10,0.15 and 0.20）NIR reflective inorganic pigments had a pure quadrilateral structure,the grain morphology was granular,and the particle size could reach nanometer level.They also had good acid and alkali resistance（ΔE^*<5）.The color of the powders changed from white to yellow with the increase of Tb³⁺ions.This was possibly due to a transition of La 3d→O 2p to Tb 3d→O2p,leading to the charge transfer between the conduction bands.When x=0.20,L^*=78.2406,a^*=1.6279 and b^*=45.3,the pigment showed the best color with a NIR reflectance of 86.93%.Furthermore,under the irradiation of the infrared lamp,the surface temperature of the prepared Ba La_1.8Tb_0.2Zn O₅ coating was 15℃lower than that of the yellow commercial coating,indicating that the pigments had potential applications in thermal insulation using yellow pigments.In summary,the three different colors of high NIR reflective pigments prepared by solution combustion method not only exhibit good color properties,but also have good thermal insulation properties.Additionally,as a type of heat-reflective insulation material,they will hold potential for valuable applications.