Oxidation kinetics of chromium(III) chloride

Abstract

The kinetic behaviour of anhydrous chromium(III) chloride pellets in oxygen in the temperature range 350–630 °C has been examined by isothermal and temperature-programmed thermogravimetry and scanning electron microscopy. The reaction starts at ca. 400 °C under non-isothermal conditions and exhibits a deceleratory rate. Cr₂O₃ is usually the only solid product detected, although CrO₂Cl₂ or CrOCl may form under extreme experimental conditions. Isothermal thermogravimetric curves are fitted to a number of kinetic expressions, and statistical analyses are used to identify the rate equation that best describes the experimental data. The examination, by scanning electron microscopy, of cross-sections of partially reacted samples supports the conclusion that the reaction is under chemical control, and occurs at a linearly advancing interface between the reactant and product. The reaction kinetics can best be described by a contracting-geometry rate expression.