Yao Xia

Thermal degradation kinetics study of curcumin with nonlinear methods

The results of TG/DTG when curcumin was used as the food colouring agent indicated that the processing temperature of the food should not exceed 190°C. The decomposition process of curcumin involved two stages. The results of Eα values, determined by an advanced isoconversional method, showed that the two stages were both single-step processes. The most probable mechanisms of the two stages were estimated by using comparative and nonlinear model-fitting methods. The mechanisms obtained from the two methods are the same, which are the assumed random nucleation and its subsequent growth for stage I and one-dimensional diffusion for stage II, respectively. The values of pre-exponential factor A for both stages were obtained on the basis of Ea and g(α). Besides, some thermodynamic functions (ΔS(≠), ΔH(≠) and ΔG(≠)) of the transition state complexes for the two stages were also calculated.

Nonisothermal kinetics study with advanced isoconversional procedure and DAEM

The precursor of LiNiPO4 was synthesized by solid-state reaction at low-heating temperature using LiOH·H2O and NH4NiPO4·H2O as raw materials. LiNiPO4 was obtained by calcining the precursor. Based on the advanced isoconversional procedure and the distributed activation energy model (DAEM), the activation energies calculated indicated that the thermal process involved two stages which stage II was a kinetically complex process, but stage I was single-step process. The most probable mechanism for the stage I is random nucleation and subsequent growth. DAEM and nonlinear model-fitting method were applied to study the stage II of decomposition process of the precursor. The distributions of activation energy, f(Ea) and values of preexponential factor A of the stage II of the thermal decomposition of precursor were obtained on the basis of DAEM. The results of nonlinear model-fitting method showed the most probable mechanisms of the parallel reactions for stage II are chemical reaction and nucleation.