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Studies on the Kinetics of Thermal Decomposition of Copper Oxalate Mixed With Silver Oxalate

K. Sarada, K. Muraleedharan


The coprecipitates, Ag2Cu(C2O4)nH2O of varying composition [Ag = (1 and 2)%], have been synthesized and were characterized by means of IR, XRD, and SEM. The decomposition of the prepared oxalates was monitored by differential scanning calorimetry (DSC) and thermogravimetry (TG). The DSC studies reveal that the decompositions of the mixed oxalates were all complex exothermic processes with resemblance to the exothermic reaction of copper oxalate and ranges from 540 to 600 K. The decomposition kinetics was studied by thermogravimetry at four different heating rates: 5, 10, 15, and 20 K/min. The TG data were subjected to linear least squares analyses (in the range α = 0.1–0.9) using the isoconversional methods of KAS, FWO, Vyazovkin, and Tang to find the values of activation energy (Eα). The activation energies of the pure copper oxalate, in N2 atmosphere, obtained by the above-mentioned methods are 192.1, 191.3, 191.9, and 192.3 kJ/mo1 and that of pure silver oxalate are 179.5, 187.4, 187.9, and 179.9 kJ/mo1, respectively. Copper oxalate coprecipitated with 1% silver oxalate gave activation energy values 206.4, 215.8, 216.6, and 206.9 kJ/mo1 and the coprecipitated with 2% silver oxalate gave activation energy values 182.8, 192.3, 193.1, and 183.3 kJ/mo1. The kinetic analysis of copper–silver oxalates prepared shows a decrease in average activation energy with increase in the concentration of silver oxalate. The variation of activation energy during thermal decomposition reflects the changing mechanism during the course of the reaction. It is observed that the activation energy of copper oxalate is decreased from its original value by the addition of 2% Ag2C2O4. Hence, it will be interesting to study further about the effect of addition of Ag2C2O4 higher than 2%.

Keywords: decomposition kinetics, differential scanning calorimetry, isoconversional methods, thermogravimetry

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