Synthesis of ultramarine analogs from erionite

Colored products have been obtained by thermal treatment of erionite mixed with elemental sulfur and alkalis (Na2CO3 or K2CO3). Synthesis at lower temperature (500 °C) resulted in forming colored materials with preserved ERI structure (particularly with potassium cations), whereas the treatment of highly alkaline mixtures at high temperature (800 °C) caused re-crystallization to SOD (when Na was used) or to unknown structures (with K). The ESR spectra of the products with preserved original ERI structure recorded at room temperature show two signals, one with g = 2.030 and another with g tensor value either 2.045 (for sodium containing samples) or 2.005 (for the potassium bearing products). The latter signal could be considered as a reflection of S2- radicals immobilized in small ε-cages, but it is more likely that it presents anisotropic component of the S3- radical spectrum. The spectra measured at 77 K show anisotropy indicating three values of orthorhombic g  -tensor, which is typical of S3- radical, although the values vary for particular samples.