Preparation of Rare Earth-Zircon Pigments by the Sol-Gel Method

Abstract

The sol-gel method was applied to the preparation of the rare earth (RE)-containing zircon (RE-zircon) pigments at low heat treatment temperatures. Following results were obtained.(1) The zircon pigments containing RE's such as Pr, Nd, Sm, Eu and Er were successfully prepared from tetraethyl-orthosilicate, Si(OC2H5)4, zirconium oxychloride, ZrOCl2⋅8H2O and halides of RE's, at the heat treatment temperature as low as 900-1000°C, if LiCl was added as a mineralizer.(2) Obtained products were powdery or easily pulverized into fine powders even by fingers, meaning that the sol-gel method much reduces the vigorous crushing and grindings processes required in the commercial solid-state reaction method.(3) The color of the pigments were dull-green yellow for Pr, light purple for Nd, yellowish white for Sm and yellow to pale reddish purple for Er. The chemical resistivity of all the pigments prepared in the present work satisfied the criterion “5-level” of JIS-K-5101-1991.(4) The oxidation state of Nd and Er incorporated in the zircon pigments was considered to be trivalent on the basis of the reflectance and XPS spectra. Pr in the pigment was considered to be mainly in tetravalent.(5) XRD measurements suggested that the trivalent RE3+ ions are incorporated into the zircon structure and replaces Si4+ or Zr4+ ions to form solid solutions. Co-added Li+ ions were considered to be also incorporated into the zircon structure to maintain the electric charge balance, In the case of Pr, tetravalent Pr4+ ions probably substituted for Zr4+ or Si4+ ions in the zircon lattice.