Studies of the Thermal Dissociation Kinetics of Some Arsenate Compounds

The thermal dissociation kinetics of diarsenic pentaoxide (As2O5), nickel(II) arsenate (3NiO. As2O5), cobalt(fl) arsenate (3 CoO[sm middot]As2O5), aluminium arsenate (AlAsO4) and iron(III) arse nate (FeAsO4) have been studied by T. G. technique. The activation energy δE (kcal/mol) of the dissociation reactions of each compound was dependent on the oxygen partial pressure Po2. For all the compounds mentioned above, following relations between δE and δH were found: where δH is the heat of the dissociation reaction in kcal of each compound producing 0.5mol As4O6 and 1 mol of O2 gas. The dissociation rate of As4O6 gas species from the solid surface v was obtained as follows: where K(=PAS4O61/2[sm middot]Po2) is the equilibrium constant for the dissociation reaction of each compound. Considering the above rate equations based on the rate equation of the free evaporation, mean molecular gas species AsO1.5 (Po20.5) are assumed to evaporate from all the arsenate compounds, though As4O6 molecule is the most stable in the measured temperature range.