Preparation of rare earth zircon pigments by the sol-gel method

The zircon pigment powders containing Pr, Nd, Sm, Eu and Er as chromophores were successfully prepared at low heat treatment temperatures of 900-1000 degrees C by the sol-gel method using Si(OC2H5)(4), ZrOCl2 . 8H(2)O and rare earth halides as raw materials. The addition of LiCl to the starting gels was found to be very effective to prepare the pigments at such low temperatures. The obtained pigments were powdery and showed colors characteristic of the respective rare earth elements. The chemical resistivity of the pigments satis fied the criterion "5-level" of JIS-K-5101-1991. It was considered from XRD, spectral reflectance and XPS results that Nd, Sm, Eu and Pr are in trivalent state and incorporated into the zircon structure to form solid solutions. Li+ ions were considered also to be incorporated into zircon in order to maintain the electric charge balance. Pr was mainly in tetravalent state and was considered to substitute for Si4+ or Zr4+ ions in the zircon structure.