Abstract: Nanosized spinel type cobalt blue pigments of CoAl₂O₄(AB₂O₄) were hydrothermally synthesized using CoCl₂·6H₂O, ZnCl₂, AlCl₃ and CrCl₃·6H₂O as raw materials. Colorimetric analysis, X-ray diffraction (XRD), transmission electron microscope (TEM) and High resolution transmission electron microscope(HRTEM) were employed to investigate the effects of various amounts of Zn²⁺ doping at A site and Cr³⁺ doping at B site and various hydrothermal temperatures on the coloration, crystal phase compositions, crystal size and interplanar spacing of the CoAl₂O₄ spinels. The results indicated that Zn²⁺ and Cr³⁺ doping cause incomplete crystal growth and result in smaller particles than that of undoped spinels obtained at the same hydrothermal conditions. Zn²⁺ doping at A site lowered the synthesis temperature of the spinel crystalline colorants. Co_0.95Zn_0.05Al₂O₄ pigments with good coloration were obtained at 230℃. The hues of the as-prepared pigments changed from blue to green with increased amount of Zn²⁺ doping, and the coloration of samples became lighter. Similarly, the hues of the pigments also changed from blue to green with increasing the amount of Cr³⁺, but the coloration became deeper. Zn2+ doped spinels are of better coloration than that of Cr³⁺ doped.

Key words: CoAl₂O₄, pigments, Zn²⁺ and Cr³⁺ doping, solid solution