The kinetics and mechanism of the oxidation of chromium (III) chloride

Abstract

The kinetic behaviour of anhydrous CrCl₃ in gaseous oxidising atmospheres has been examined in the temperature range 350 to 630°C in order to identify optimum reaction conditions and to establish the mechanism by which the reaction is controlled. The reaction under consideration is CrCl₃ (s) + ¾ O₂ (g) → ½ Cr₂O₃ (s) + ³/₂ Cl₂ (g). The main experimental techniques used were isothermal and programmed-temperature thermogravimetry, supplemented by scanning electron-microscopy, surface-area determinations and porosity measurements. The effects of sample pelletisation, gas flowrate, temperature, oxygen partial pressure, pellet porosity and the addition of other oxide species on the rate and extent of reaction have been studied. The reaction is shown to occur in a single step, starting at -350°C under non-isothermal conditions, and exhibiting a deceleratory rate over most of the reaction. Isothermal thermogravimetric curves were fitted to a number of kinetic rate expressions, and a series of statistical analyses used to identify the rate equation which best describes the experimental data. Supporting evidence was provided by scanning electron-microscopic examination of partially-reacted samples. It is concluded that the reaction is under chemical control, and that reaction occurs by means of a linearly-advancing reactant-product interface. The reaction kinetics can be described by a contracting-geometry rate expression.,KMBT_363,Adobe Acrobat 9.54 Paper Capture Plug-in