Near-infrared reflective coatings based on Ca1-xNdxAl12-xNixO19 blue pigments, prepared by solution combustion synthesis

Abstract

Blue pigments based on Ca1-xNdxAl12-xNixO19 (x = 0–0.7 apfu) were obtained by an ecological, fast and energy efficient approach, namely solution combustion synthesis. The formation of nanocrystalline solid solutions was confirmed by X-ray diffraction investigation results. Increasing the degree of substitution resulted in intensification of color, decrease in crystallite size, and decrease in total solar reflectance. The CIE L*/a*/b* values of the composition with x = 0.5 were 80.9/-8.8/-30.0, while the total solar reflectance was 70.0 %. The obtained pigments were used to develop NIR-reflective (cool) coatings, applied onto black and white opacity charts made of glossy cardboard, metal, fibercement and ceramic substrate. The dispersion media tested were: an aqueous acrylic resin, an epoxy resin, and a clear ceramic glaze. Pigments based on Ca1-xNdxAl12-xNixO19 showed very good stability in acidic and alkaline environments but were dissolved by the glaze-generating melt. Exposure of the films to near-infrared radiation demonstrated the thermo-reflective efficiency of Ca1-xNdxAl12-xNixO19-based pigments. The acrylic resin proved to be the most suitable dispersion environment for maximizing the thermo-reflective properties, being clearly superior to epoxy.