Non-isothermal kinetics studies on the thermal decomposition of zinc hydroxide carbonate

Zinc hydroxide carbonate precursor, Zn4CO3(OH)6·H2O, was synthesized from zinc sulfate using ammonium carbonate as a precipitating agent. Thermogravimetry (TG), differential scanning calorimetry (DSC), transmission electronic microscopy (TEM), infrared spectrum (IR) and X-ray diffraction (XRD) were used to characterize the precursor and the decomposed product. Non-isothermal kinetics of the thermal decomposition of zinc hydroxide carbonate were studied in nitrogen. Based on which, the kinetic parameters were obtained through mode-free method and the thermal decomposition mechanism was derived by mains of non-linear regression. The results show that the decomposition of zinc hydroxide carbonate acts as a double-step reaction, A⟷D2B⟶FnC: a reversible reaction of two-dimensional diffusion (D2), with E1 = 202 kJ mol−1, lg(A1/s−1) = 22.1, is followed by an irreversible one of nth-order reaction (Fn) with n = 0.51, E2 = 129 kJ mol−1, lg(A2/s−1) = 10.5, and the decomposition of Zn4CO3(OH)6·H2O to ZnO is accompanied by the change in particle morphology and particle size.