Preparation And Solar Thermal Reflection Properties Of Doped Tungstate Material

Solar energy has made tremendous contributions to the development of mankind,and it has also brought a lot of negative effects to people’s lives,such as the high temperature in the summer and the aging of outdoor plastic products caused by solar radiation.In order to solve these problems,the work of developing new environmentally friendly materials that can lower the surface temperature of buildings and plastics has gradually attracted people’s attention.In this paper,a series of pigment samples of Mo-doped Bi₂WO₆,V-doped Bi₂WO₆,Zn/Mo doped MnWO₄ were prepared by one-step hydrothermal method.Performance testing mainly adopts X-ray diffraction analyzer（XRD）,high-resolution transmission electron microscopy（TEM）,high-resolution scanning electron microscopy（FE-SEM）,thermal analyzer（TG-DTA）,color difference meter（Lab）,UV-Vis-NIR spectrophotometer（UV-vis-NIR）and chamber simulation experiment,which are used to implement the detailed test and analyze the crystal structure,elemental composition,surface morphology,thermal stability,color characteristics,reflection properties and thermal insulation of pigment samples.The results show that:（1）Bi₂Mo_xW_1-xO₆（x=0,0.1,0.2,0.3,0.4）series of pigments are orthorhombic crystal structure,and the sample particles are composed of a large number of flower-like microspheres with a diameter of 2-3μm.And they have high temperature resistance（1000^°C）and chemical stability（ΔE^*<2）.With the increase of Mo⁶⁺doping amount,the bandgap value of the samples decreases from 2.97 eV to 2.68 eV,and the color of the samples changes from light yellow to yellowish green.The near-infrared solar reflectance of the powder samples and the corresponding coatings are 72.8%-81.0%and 56.2%-64.5%,respectively.The box simulation shows that the coating of the pigment sample(Bi₂W_0.7Mo_0.3O₆)and the coating with the traditional pigment,the internal temperature difference of the corresponding two cabinets can reach 4.2^°C,which proves that the prepared pigment has good thermal insulation properties and can be used as a new cold roofing material.（2）Bi₂V_xW_1-xO₆+δ（x=0.00,0.02,0.06,0.08）series of powder pigments are flake-shaped,and they possess high near-infrared solar reflectance（77.9%-94.9%）and good chemical stability（ΔE^*<1.5）.With the doping of V⁵⁺,the absorption edge of the samples increases from 423 nm to 524 nm,and the samples gradually changes from light yellow to bright yellow.In the infrared band（700-2500 nm）,these pigments exhibit high solar reflectance when are applied to the coating and when combined with PMMA.At the same time,the aging experiment showed that the combination of Bi₂V_xW_1-xO₆+δand PMMA effectively slowed down the aging process of plastics.Therefore,the prepared pigments can be widely used in the field of heat-insulating coating and plastic heat-resistant aging.（3）The powder samples of Mn_x Zn_1-xWO₄ and Mn_0.7Zn_0.3Mo_xW_1-xO₄（x=0,0.1,0.3,0.5）prepared at PH=5,reaction time of 6 h and reaction temperature of 150°C were all in the form of flakes,and they possess high near-infrared solar reflectance（58.99%-77.53%）.The doping of Zn²⁺/Mo⁶⁺changed the MnWO₄ sample from grayish black to reddish brown.When Mn_0.7Zn_0.3Mo_xW_1-xO₄ pigments were combined with ASA,it not only gives ASA resin reddish brown,but also the near-infrared solar reflectance（46.84%-63.29%）of the composite is significantly higher than pure ASA（34.98%）.It shows that the combination of infrared reflective pigment and plastic is an effective method to improve the heat reflection performance of plastics and delay the thermal aging of plastics.The powder samples prepared in this paper have the potential to be used as building cold pigments and plastic heat-resistant aging additives,and have certain research value in the field of heat reflection.