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Nonisothermal Kinetic Study: IV. Comparative Methods To Evaluate Ea for Thermal Decomposition of KZn2(PO4)(HPO4) Synthesized by a Simple Route

Chen, Zhipeng, Chai, Qian, Liao, Sen, Chen, Xia, He, Yu, Li, Yu, Wu, Wenwei, Li, Bin
Industrial & Engineering Chemistry Research 2012 v.51 no.26 pp. 8985-8991
activation energy, dipotassium hydrogen phosphate, engineering, raw materials, reaction mechanisms, thermal degradation, zinc sulfate
The single-phase KZn₂(PO₄)(HPO₄) was synthesized via solid-state reaction at 80 °C using K₃PO₄·3H₂O, K₂HPO₄·3H₂O, and ZnSO₄·7H₂O as raw materials. The thermal decomposition of KZn₂(PO₄)(HPO₄) experienced one step, which was the intramolecular dehydration of the protonated phosphate groups to form Zn₂P₂O₇. The apparent activation energy Eₐ was estimated with six comparative isoconversional procedures. The average value of the apparent activation energy Eₐ associated with the thermal decomposition of KZn₂(PO₄)(HPO₄) was determined to be 411.49 ± 14.37 kJ mol–¹, which demonstrates that the thermal decomposition of KZn₂(PO₄)(HPO₄) is a single-step kinetic process and can be described by a unique kinetic triplet [Eₐ, A, g(α)]. A new modified method for multiple rate isotemperature was used to define the most probable reaction mechanism g(α), and reliability of the used method for the determination of the kinetic mechanism was tested by the comparison between experimental plots and modeled results for every heating rate. The results show that the mechanism function is reliable. The value of pre-exponential factor A was obtained on the basis of Eₐ and g(α). Some thermodynamic functions (ΔS⧧, ΔH⧧, and ΔG⧧) of the transition state complex were also calculated.