Preparation And Properties Of Bismuth Series Near-infrared Reflective Composite Pigments

With the development of economy,the increase of urban construction area leads to the heat island effect.The energy consumption and environmental problems are becoming more and more prominent.In order to solve these problems and implement the strategy of sustainable development,the research of new environmentally friendly and energy-saving materials that can reduce the building surface temperature has gradually been valued.In this study,a series of pigments with the formula of Bi_i-xLa_xFeO₃,BiFe_1-xA_xO₃/mica-titania,BiVO₄/mica-titania with different coverage rates and Bi1-xCexVO₄/mica-titania samples were successfully prepared by sol-gel method and precipitation method.The crystal structure,surface morphology,element content,color properties,near infrared reflectance,thermal stability and heat insulation performance have been characterized.The samples were analyzed and evaluated by X-ray diffraction analyzer（XRD）,high resolution scanning electron microscopy（FE-SEM）,inductively coupled plasma emission spectrometer（ICP）,CIE-L*a*b*color scales（Lab）,UV-vis-NIR diffuse reflectance spectroscopy（UV-vis-NIR）and box simulation,respectively.The results show that:（1）the Bi_i-xLa_xFeO₃ pigments crystallized at 600℃ with particle size about 60nm.With the increase of progressive doping of La³⁺ for Bi³⁺ in BiFeO3,the color of the pigments changes from dark brown to reddish brown and the band gap decreases from 2.24 eV to 2.03 eV.With the increase of La³⁺ in the sample,the near-infrared solar reflectance of the powder pigment（53.8%-71.8%）and the corresponding coatings（>44.1%）were increased.（2）The composite pigments of BiFe1-XAlxO3/mica-titania possess high near-infrared reflectance（57.3%-73.6%）,good thermal stability（900 ℃）and chemical resistance（△E*<1）.The doping of Al³⁺ has trifling impact on micro-morphology of BiFei-xAlxO3/mica-titania pigments,but change the absorption edge of pigments,that is,the absorption edge shift to shorter wavelength（533 run-495 nm）and change the color from brown to orange.（3）BiVO₄/mica-titania with different coverage rates and Bi1-xCexVO₄/mica-titania samples show high near-infrared solar reflectance both in powder and coating form.In the simulated experiment,the temperature of the inner surface temperature of the two pigment coatings can be reduced by 2.3 ℃ and 3.2 ℃,and the internal temperature of the box can be reduced by 4.5 ℃ and 12.2 ℃,respectively.These results indicate that the sample coatings has good thermal insulation performance as building roof material,which can reduce the accumulation of heat on the building surface and decrease the indoor temperature.Furthermore,theoretical calculation demonstrated that when these two pigments are used as roofing coatings,the annual energy savings are 3.638 MWh and 14.555 MWh,respectively.And it can also reduce emissions of greenhouse gases and many harmful gases.The series of samples prepared in this paper have great potential in serving as cool materials for building coatings,meeting the requirements of contemporary society for non-toxic,environmentally friendly and colorfully pigments.This research is also of some value in the field of heat-reflective inorganic pigments.