Effect of Co and Pr doping on the properties of solar-reflective ZnFe2O4 dark pigment

Abstract

High NIR-reflective Co-doped ZnFe2O4 black pigments were synthesized by a simple solid-state reaction of ZnO and Fe2O3 in the presence of 3 to 30 wt.% Co3O4 at 1000 and 1100 °C. A series of black pigments with low L∗ values in a range of 25.5-26.5 and NIR reflectance of 39.5-48.7% were obtained at 1000 °C while the pigments with comparable L∗ values and slightly lower NIR reflectance were obtained at 1100 °C. A change of the pigment property could be attributed to substitution of Co2+ for Zn2+ as revealed by XRD analysis as well as reflectance spectra. Calcination of ZnO and Fe2O3 in the presence of 3 to 30 wt.% Pr6O11 at 1100 °C resulted in dark brown composite pigments consisting of ZnFe2O4, PrFe2O3 and unreacted Fe2O3 with L∗ value around 40 ±1 and NIR reflectance in a range of 48-50%.