Color evolution and phase transformation behaviors of core-shell yellow iron(III) oxy-hydroxide pigments.

: This manuscript reports on color evolution and phase transformation of alpha-FeOOH and silica-coated alpha-FeOOH pigment. Goethite alpha-FeOOH, a yellow pigment, is the principle coloring agent in yellow, but it is not stable in the high temperature. To obtain stable and bright color of alpha-FeOOH, alpha-FeOOH nanorods were coated with silica. Core-shell pigments were calcined at high temperatures (300 and 1000 degrees C) and characterized by scanning electron microscopy (SEM), CIE L*a*b* color parameter measurements, transmission electron microscopy (TEM) and UV-vis spectroscopy. The yellow alpha-FeOOH was transformed to alpha-Fe2O3 with red, brown at 300, 1000 degrees C, respectively. In contrast, the silica-coated a-FeOOH retained a red coloration with high a* value at 300 and 1000 degrees C.