Research On Preparation And Reflective Properties Of Doped-AlPO₄

Novel inorganic white pigment AlPO4 with high near-infrared reflectance(NIR)has been synthesized by a coprecipitation method.In addition,high near-infrared reflective pigments with many different colors were obtained by doping different ions(Fe,Co,Cu)into the crystal structure of AlPO4.The structures of samples were investigated by XRD and Raman spectroscopy,and the reflective properties were tested by UV-vis-NIR spectrophotometer.Furthermore,the surface appearance of powders was observed by scanning electron microscope,and the color was measured by colorimeter.Finally,we mixed the pigments with acrylic resin and obtained the corresponding coatings.The results are as followed:(1)Results showed that the calcination temperature,particle size and the pH value of the solution have great influence on the reflective properties of AlPO4.When the calcination temperature increased from 500? to 900?,the reflective properties of AlPO4 samples gradually increased until the temperature is up to 700?,then dropped down after that.When the particle size enlarged from 2.565 to 16.581?m,the reflective properties of AlPO4 samples increased and showed the highest value when the particle size is 9?m,then fell down after that.In addition,when the pH value of solution was 7,the reflective property of AlPO4 is the highest.As a result,when we calcined AlPO4 at 700?,controlled the particle size of 9?m and adjusted the pH value to 7,AlPO4 has its best reflective property(97.7%).(2)The XRD diffraction and Raman spectrogram demonstrated that the crystal structure of AlPO4 did not change with different ions(Fe,Co,Cu)added.When the concentration of Fe3+ increased,the color of powder pigments changes from white(x=0.00)to orange yellow(x=0.03–0.08),the band gap decreased from 5.98 eV to 3.60 eV and the near-infrared reflectance decreased from 97.77% to 72.56%.When the concentration of Co2+ increased,the color of powder pigments changes from white(x=0.00)to light purple(x=0.03–0.08),the band gap decreased from 5.98 eV to 3.90 eV and the near-infrared reflectance dropped from 97.77% to 76.45%.When the concentration of Cu2+ increased,the color of powder pigments changes from white(x=0.00)to green(x=0.03–0.08),the band gap decreased from 5.98 eV to 2.55 eV and the near-infrared reflectance decreased from 97.77% to 54.88%.The decrease of the band cap cause the absorption of more near-infrared radiation and that is the reason of the decrease of the near-infrared reflectance.(3)In addition,we mixed the pigments with acrylic resin and obtained the corresponding coatings.We have investigated the back temperature differences of pigment coatings used as building roof materials.Results showed that the near-infrared reflectance of Al0.97 Fe 0.03PO4 is 61.71%,and the temperature of Al0.97 Fe 0.03PO4 coating is 16.7? lower than that of the commercial pigment in similar color;The near-infrared reflectance of Al0.97Co0.03PO4 is 58.86%,and the temperature of Al0.97Co0.03PO4 coating is 10.4? lower than that of the commercial pigment in similar color;The near-infrared reflectance of Al0.97Cu0.03PO4 is 37.72%,and the temperature of Al0.97Cu0.03PO4 coating is 6.5? lower than that of the commercial pigment in similar color.In conclusion,white pigment AlPO4 and colorful pigments obtained from doping different ions into AlPO4 have good UV-vis-NIR reflectance.They could be new potential candidates for cool pigments in hot summer.