Mechanism and kinetics of thermal decomposition of ammoniacal copper oxalate chromate

Abstract

A complex precursor of composition Cu/Cr=1 has been synthesized, dissolving copper oxalate and ammonium dichromate in aqueous ammonia followed by evaporation and drying. The thermal decomposition of the precursor has been studied in different environments, air/argon. In air, overlapping decomposition of the complex and simultaneous oxidation of the products of decomposition (oxidative decomposition) occur in four steps and the overall process is highly exothermic, whereas the process completes in two stages only in argon preventing oxidation of the products and so resulting negligible heat of decomposition. The elemental analysis and thermogravimetric measurements suggest the stoichiometric formula of the precursor to be CuNH3C 2O4NH4CrO4. The precursor is termed as ammoniacal copper oxalate chromate (ACOC). The products of decomposition resulted in different environments have been characterized by X-ray diffraction and particle size analysis. Bi-dispersed particles of CuO•CuCr 2O4 (Adkins' catalyst) are obtained in air while mono-dispersed particles of Cu CuCr2O4 (novel Adkins' catalyst) result in argon environment. The decomposition kinetics of ACOC in argon environment has been found to be zero order and first order for the first and second steps respectively. The values of activation energy corresponding to the first and second step have been found to be 87.63 and 250.36 kJ mol -1, respectively. © 2006 Akadémiai Kiadó, Budapest.