Study On The Preparation And Spectral Properties Of Rare Earth Sulfides Coated Mica Pearlescent Pigments

Rare earth sulfides with their unique optical,electrical,magnetic properties have been widely applied in the fields of inorganic pigments,thermoelectric materials,optical materials etc,but the study on the infrared reflection properties was insufficient.The pearlescent pigments are based on the coating of Ce₂S₃ on the surface of mica flake powder,taking advantage of layer structure of mica and high reflectivity of Ce₂S₃,obtaining outstanding reflective thermal insulation materials and saving the dosage of cerium sulfide.On the other hand,the synthesized temperature of cerium sulfide is high under conventional conditions,which tend to self-agglomerate to influence the shading powder of pigments.By means of coating the nano cerium sulfide on the surface of mica offers an available method to prevent aggregation.In this study,the series of pigments with the formula mica/Ce₂S₃,mica/Ce_2-xY_xS₃,mica/Ce_2-xLa_xS₃ were successfully synthesized by sol-gel method followed by sulfurization.The crystal structure,the ultraviolet absorption,NIR reflectance,color properties,thermal stabilities and morphologies of composite pigments had been characterized by XRD,SEM,TG,FT-IR,UV-vis-NIR diffuse reflectance spectroscopy and CIE-L*a*b*color scales.The results show that:the optimum sulfuration temperature of mica/Ce₂S₃ was 850℃;mica/Ce₂S₃ with the molar ratio of Na⁺/Ce³⁺=0.2 had the best ultraviolet absorption capacity、color propertie and cubic structure of y-Ce₂S₃.Moreover,the doping of M³⁺(M=Y³⁺,La³⁺)ions did not change the structure of y-Ce₂S₃ phase.When the coating ratio of Ce_2-XY_XS₃ was lower than 10wt.%,the surface of mica could not be coated completely.The coating ratio of Ce_2-xY_xS₃ is excessively high,which lead to surface roughness of morphologies increases significantly and some aggregated nano particles were also formed on the coating layers.It’s essential to choose the appropriate covering amount 15wt.%.Ce_2-xY_xS₃ nanoparticles with nearly spherical morphology are homogeneously distributed on the surface of mica following with a small number of large particles under optimized coating rate.The thermal stable temperature of mica/Ce_2-xY_xS₃ can reach to 50℃,while that of pure Ce₂S₃ pigment is only 350℃.They make possible combination pigments with the widest range of applications.Simultaneously,the brightness L*values of mica/Ce₂S₃ increased significantly compared with that of the pure Ce₂S₃.They make coated pigments with good chromatic properties.The composite pigments samples changed from dull red to bright red to orange red again with the progressive doping of Y³⁺ for Ce³⁺.The NIR solar reflectance of the mica/Ce₂S₃ pigments with covering rate 15wt.%increased to 93%better than that of pure Ce₂S₃（77%）,which indicates that mica can enhance infrared reflective properties in comparison to pure Ce₂S₃.Mica/Ce_2-xM_xS₃(M=Y³⁺,La³⁺)composite pigments showed excellent ultraviolet shielding ability and higher NIR reflectance,which has the prospects of application in sun screening agent and thermal insulation coating.The small changes in △E*indicate minimal color shifts of mica/Ce_2-xM_xS₃(M=Y³⁺,La³⁺)under the accelerated UV weathering tested.Therefore,the composite pigments are light-fast,which could be applicable in outdoor architectural coatings.