Research On Photostability Of Mica-titania Reflective Pigment Doped With Ions

The surface temperature of buildings must be risen when they are exposed to sunlight,the exterior temperature may reach as high as70～80℃in the summer. This phenomenon isvery popular in Southern China, where the summer is so long. The high temperature transferfrom outdoor to indoor cause great building energy consumption （mainly air conditioningenergy consumption）, and the heat island effect make it more serious. Using reflectiveinsulation materials is an effective way to reduce air conditioning energy consumption andenchance comfortability when live indoor. Reflective insulation coating is applied more andmore popular because of its high reflectivity, light weight, and convenient construction. It caneffectively reduce the surface temperature of buildings and improve temperature environmentof indoor.The insulation performance of coating depends on the reflectivity of pigments, thehigher reflectivity, the better insulation performance. Mica-titania reflective pigment is aideal reflective insulation pigment because of high reflectivity, non-toxic, acid resistance,alkali resistance, heat resistance and chemical stability, et al. However, Mica-titaniareflective pigment has poor photostability due to the photocatalytic of TiO₂, which candegradate coating and shorten the life of coating.In this paper, the influence of the specificsurface and the crystal phase of TiO₂on the photostability of mica-titania refletive pigmentwere studied, doping with ions make the pigments have both high photostability and highreflectivity, and the mechanism was also analyzed.The research results are showed as follows:（1） TiO₂crystal of mica-titania reflectivepigment （blank sample） are mainly anatase at800℃, and there are60.5%rutile at1000℃.The photostability of pigments were improved as the increase of the calcination temperature,but the degradation rate of RhB for pigment was as high as78.5%at800℃,22.1%was alsoobtained at1000℃.（2） Sn⁴⁺ion effectively promote the formation of rutile, rutile wereincreased with the increasing of Sn⁴⁺dosage, There was63.5%rutile when pigment dopedwith1.0%Sn⁴⁺at800℃, and the degradation rate of RhB was18.0%, lower than blanksample at1000℃.（3） Fe3+ion effectively promote the formation of rutile, There was60.3% rutile when pigment doped with1.0%Fe³⁺at800℃, and Cr³⁺do not promote the formationof rutile. However, both Cr³⁺and Fe³⁺effectively improved the photostability of pigments,the degradation rate of RhB for pigment doped with0.5%Cr³⁺and1.0%Fe³⁺at800℃were2.2%and3.7%, lower than Merck pigment.（4） The photostability of pigments are higher,the degradation resistance of coatings are better. The surface of coatings prepared withpigments doped with0.5%Cr³⁺,1.0%Fe³⁺at800℃and Merck pigment were not changedafter14d UV aging. The reflectivity of mica-titania reflective pigment were little influencedby doped with ions, and pigments with little reflectivity difference, less than3.0%. Thethermal insulation performance of coatings prepared with those pigments were approaching.The maximum difference of heat-insulating temperature rise was only1.4℃.