Preparation of novel blue phosphate pigments in imitation of copper lazulite

Abstract

Novel blue pigments were prepared from copper, magnesium, aluminum nitrate solutions and phosphoric acid with pH adjustments (pH 5, 7, 9). The obtained precipitates were heated at 300, 500, and 700 °C for 1 h. The precipitates and their thermal products were estimated with X-ray diffraction (XRD), infrared (IR) spectra, ultraviolet–visible (UV–Vis) reflectance spectra, and L*a*b* color space. Sample without heating is light blue powder. By heating at 300 °C, the blueness of samples decreased. The hue of samples became darker by heating. The best condition for the unheated sample was pH 7, and for the heated sample was pH 5 at 300 °C. Samples prepared at Cu/Mg = 1/1 showed a* and b* values closer to zero than samples prepared with Cu/Mg = 1/0. These materials have potential as new inorganic blue pigments for inks and paints.