Cerium molybdenum oxides for environmentally benign pigments

Abstract

A new class of environmentally benign yellow rare earth pigments as alternatives to lead, cadmium and chromium pigments is presented. These pigments are based on cerium molybdenum oxides corresponding to the structural formulae NaCe_0.5(MoO₄) and Ce(MoO₄)₂. The coloring properties of the compositions prepared by varying the Ce:Mo ratio in the presence and absence of phosphates have been evaluated. The reflectance spectra and photoacoustic spectra indicate the absorption in visible and ultraviolet regions under 500 nm, which could originate from the O_2p-Ce_4f and the O_2p-Mo_3d double charge transfer transitions, and as a result the pigments show yellow color. In the presence of a phosphate, the products are homogeneous and crystalline at temperatures of 700 °C itself and exist as multiphasic with white colored CePO₄ being present in association with cerium molybdenum oxide. Further, the particle size of the cerium molybdenum oxide sample was lower in the presence of phosphate (116 nm).