Effect of coating mixing conditions on the color tone of cobalt blue pigment having a core-shell structure obtained by solid phase synthesis of coated particles

A cobalt blue pigment having a core/shell structure was synthesized by solid phase synthesis of coated particles having Co(OH)₂ particles adhered onto Al₂O₃ particles. In this research, the effect of mixing conditions on the color tone of synthesized pigment was investigated. As a result, it was found that the mixing time greatly affected the amount of adhered Co source particles, and the pressing force during mixing affected inhomogeneity of adhered amount of Co source particle on Al source particle surface. However, it was found that the inhomogeneity of the amount of Co source particles is small as the influence on the color tone of the calcinated product by diffusing onto the alumina surface of Co ions during calcination at high temperature. In addition, when the mixing conditions were not appropriate and the coating amount of the Co source particles on the Al source particles was small, the lightness of the product was high and the chroma was low. One reason for this is considered to be a decrease in the shell thickness generated by the decrease in the amount of Co source particles deposited. It was also suggested that the formation of black tri-cobalt tetroxide, which is an unreacted Co source not adhering to the Al source particles, is also the reason of the decrease of chroma of the product.