Synthesis of novel white pigments by shaking cerium compounds with phosphoric acid

Rare earth ores are mined with a mixture of various rare earth elements, of which cerium is abundant and in greater supply than demand. Therefore, new applications for cerium are being explored, and its potential as a pigment for cosmetics is being considered. Cerium phosphate pigments have been investigated for their biocompatibility, and in this study, we attempted to develop pigments in which the surfaces of cerium compounds (oxide, carbonate, hydroxide, and oxalate) are reacted to phosphates by shaking with phosphoric acid. The chemical composition of the prepared samples was evaluated by X-ray diffraction patterns and infrared spectra. The particle size distribution was measured by a centrifugal precipitation particle size distribution analysis system. The color hue was evaluated by UV–visible reflection spectra and L*a*b* values. The oxidation catalytic activity of samples was also evaluated using aqueous ascorbic acid solutions. The cerium compounds reacted partially with phosphoric acid by shaking treatment, resulting in a change in hue. Furthermore, several reducing agents were added during shaking to improve whiteness, because tetravalent cerium tends to form yellow compounds and trivalent cerium tends to form white compounds.