Chemical Species in Hydoroxochromium(III) Solution and Synthesis of Chromia Pillared Fluorine Micas

Abstract

In order to clarify the features of complex formation and characteristics of pillared micas, chromia pillared fluorine micas were prepared from polynuclear hydroxochromium (III) solutions (PHC) having different OH/Cr ratios and expandable Lit-exchanged fluorine mica [Li_0.8Mg_2.2Li_0.8(Si₄O₁₀)F₂]. The chemical species in PHC as well as the intercalated species into the interlayer region of mica were identified by high performance liquid chromatography (HPLC). At the early stages of adding NaOH solution to chromium (III) chloride solution, Cr-oligomers such as dimer and trimer were formed with decreasing a monomeric species. However, when the OH/Cr ratio of PHC increased, polynuclear hydoroxochromium (III) with widely distributed molecular weight were formed. Ratios of the monomer, oligomers and polymers in PHC changed with heat treatment; the dimer and trimer were transformed into the tetramer and polymers having apparent fractional molecular weight of 10000-300000. When solutions containing polymers of low average molecular weight were used, oligomers (trimer, tetramer etc. ) were selectively intercalated. On the other hand, when solutions containing polymers of higher average molecular weight were used, monomer was also intercalated, resulting in the decrease of the amount of fixed Cr. The basal spacing d₀₀₁ of pillared micas (200°C) showed almost constant value despite the difference in the amount of fixed Cr. This indicates no distinct relation between basal spacing and amount of fixed Cr.