Combustion synthesis of a blue Co-doped zinc aluminate near-infrared reflective pigment

•A low cobalt content blue spinel Zn0.9Co0.1Al2O4 pigment was obtained.•The time effective and energy efficient combustion synthesis was used.•The pigment shows an intense blue color and high total solar reflectance.•Pigment features (TSR = 63%) recommend it as a NIR-reflective pigment.

A near-infrared reflective blue pigment with a low cobalt content, Zn0.9Co0.1Al2O4, was prepared by solution combustion synthesis, which proved to be time-effective and energy-efficient. No additional annealing was required as the elevated temperature developed during the exothermic self-propagating combustion reaction (1428 °C) enabled the direct formation of a Zn0.9Co0.1Al2O4 solid solution having an appealing blue color: L* = 67.9, a* = −3.7, b* = −39.0. The resulting blue pigment had an average particle size of 6.1 μm and a BET surface area of 6.5 m2/g. The total solar reflectance of the pigment (63%) recommends the use of Zn0.9Co0.1Al2O4 as a near-infrared reflective blue pigment for cool coatings. The ability of the pigment to reflect the near-infrared radiation was confirmed by measuring the surface temperature of an aluminum sheet painted with an acrylic coating containing 30 % wt. pigment, that had a total solar reflectance of 59%. The excellent properties of Zn0.9Co0.1Al2O4, color and solar reflectance, together with the low cobalt content and the advantages of self-propagating combustion reaction recommend the use of combustion synthesis for the preparation of blue Zn0.9Co0.1Al2O4 near-infrared reflective pigments.