The Synthesis And Characterization Of Inorganic Pigments With High Near-infrared Reflectance

The using of thermal insulation coatings can ease the global energy crisis, mitigate the urban island effect and reduce the amount of energy consumption. With the developing of the Times and the progress of science and technology, there arises more request for the pigments of thermal insulation coatings, and now the development trend of the pigments is environment friendly, higher near-infrared reflectance, more colors and so on.Due to their higher conductivity and special optical properties of rare earth elements, the materials of La2Mo2O9and Y2Ce2O7have been used in the Solid Oxide Fuel Cell, catalyst, fluorescent material and so on. But there has not much documents about their higher near-infrared (NIR) reflectance, and color changing of doping, so in this experiment, Fe3+and Mn2+ions doped La2Mo2O9and Y2Ce2O7have been synthesized by acrylamide modified Sol-Gel method, using as two kinds of novel pigment, and the properties of samples have also been examined with X-ray diffraction analyzer (XRD), transmission electron microscope (SEM), colorimeter, UV-vis-NIR spectrophotometer. And the heat insulation performance of the pigment coatings have been studied too.For the process of precursor preparing, the mole rate of citric acid and metal ions is2:1, while the mole rate of the acrylamide and metal ions is4:1, the temperature of water bath for the solution is80℃for about3h, and the drying condition of the Gel is120℃for12h. The XRD of La2Mo2O9and YaCe22O7materials sintering at different temperature, shows that700℃is the best temperature to obtain La2Mo2O9nanoparticles with good crystal structure, while for Y2Ce2O7, the best temperature is900℃. Both of the best temperature is much lower than the temperature of traditional solid phase sintering, and accordingly more energy consumption is needed. On the other hand, doping of Fe3+and Mn2+ions makes samples lattice distorting tiny, which is mainly answering for the difference of ionic radius of Fe3+, Mn2+and Mo6+, The results also indicated that there must be small Mn ions for La2Mo2O9doped by Mn. The more important is that the doping of Fe3+and Mn2+ions changes the color of matrixes to light yellow and ash black, while deep color is one trend of inorganic pigments today, and the color changing is mainly for the reason of charge transition of3d(Fe3+)→2p(O2-) and3d(Mn2+)→2p(O2-).What’s more, the doping of Fe3+results in the NIR reflectance of La2Mo2O9and Y2Ce2O7powder samples decreasing from o.96to0.81and0.8, which is higher than the other yellow inorganic pigments during the same period. Because of deep color will absorb more solar radiation, so the NIR reflectance of La2Mo2-xMnxO9+δ powder sample shows just0.21, and the NIR reflectance of La2Mo1.95Mn0.05O9+δ pigment coating is0.18; while the value of Fe3+doped La2Mo2O9and La2Mo2O9is0.61and0.65, this is the reason of alkyd resin absorption of1100nm-2500nm.For better evaluating the insulation of the high NIR reflectance pigments, the pigments were mixed with alkyd resin equality under galvanized plate, depositing on the top of a case made with PP foam, and the case was sunshine by one infrared light; the thermometers were used to measure the indoor air temperature of cases deposited by higher NIR reflectance inorganic pigment and traditional inorganic pigments with the same color. The difference of temperature shows pigment properties of heat insulation, and for Y2Ce1.95Fe0.05O7+δ pigment coating, the result shows that the difference of temperature of two cases reaches3℃, so if this pigment coating has a wide range in big city, there will be save much and much energy in summer day.