Thermal decomposition kinetics of nickel(II) and cobalt(II) azo barbituric acid complexes

Thermal decomposition kinetics of ML2 (M = Ni(II) and Co(II); L = 5-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)hydrazono)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) complexes were investigated by thermogravimetric analysis (TGA). The first decomposition process of the NiL2 and CoL2 complexes occurs in the temperature range of 320-350 degrees C. Kinetics parameters corresponding to this step, such as activation energy, E., and apparent pre-exponential factor, In A(aap), were calculated from the thermogravimetric data at the heating rates of 5, 10, 15 and 20 K min(-1) by differential (Friedman's equation) and integral (Flynn-Wall-Ozawa's equation) methods. The results show that the activation energy evidently depends on the extent of conversion. As far as their activation energy is concerned, NiL2 complex shows a higher thermal stability than the CoL2 complex. (C) 2009 Elsevier B.V. All rights reserved.