A kinetic study of non-isothermal decomposition process of anhydrous nickel nitrate under air atmosphere

The non-isothermal decomposition process of anhydrous nickel nitrate under air atmosphere was investigated. The kinetic analysis of decomposition process was performed using Friedman (FR), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) isoconversional methods. The kinetic model was determined by the Málek's method. The composite differential method I was used for checking the established reaction model. It was found that the value of Ea calculated by composite differential method (Ea=147.1 kJ mol−1) represents the medium value between the values of the apparent activation energy calculated by FR (Ea,FR=152.8 kJ mol−1) and FWO (Ea,FWO=143.1 kJ mol−1) methods. Using two special functions (y(α) and z(α)), it was found that the two-parameter autocatalytic model (Šesták–Berggren (SB) kinetic model) with kinetic exponents M=0.23 and N=1.14 is the most adequate one to describe the decomposition kinetics of the studied system at various heating rates. The obtained non-isothermal differential conversion curves from the experimental data show the results being accordant with those theoretically calculated. It was concluded that the SB kinetic model can be used for a quantitative description of non-isothermal decomposition process of anhydrous nickel nitrate which involves the partially overlapping nucleation and growth phases.