New blue pigments based on Co2+ and La3+ doped hibonite for NIR-reflective coatings

Abstract

New blue pigments based on Ca1-xLaxAl12-xCoxO19 (x = 0–0.5) were obtained by the combustion method, avoiding the expensive annealing step. The obtained pigments have a specific surface area between 3 and 5 m2/g. The crystallite size of Ca1-xLaxAl12-xCoxO19 pigments decreases from 44 to 26 nm, as the substitution degree, x, increases from 0 to 0.5 apfu. Despite the low Co2+ content (<4% mass), the pigments show intense blue shades and high total solar reflectance. CIE L∗/a∗/b∗ parameters show that, with the increase of chromophore content from 0.1 apfu (73.3/-2.6/-34.1) to 0.5 apfu (60.5/2.6/-47.0) the blue color of the pigments intensifies, whilst the total solar reflectance decreases from 70.7% (x = 0.1) to 59.6% (x = 0.5). The tests performed confirmed the possibility of using Ca1-xLaxAl12-xCoxO19 pigments in making cool, NIR-reflective coatings.