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 °C. Kinetics parameters corresponding to this step, such as activation energy, Eα, and apparent pre-exponential factor, ln Aaap, 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.