Thermal dehydration kinetic mechanism of Mn1.8Co0.1Mg0.1P2O7？2H2O using Málek’s equations and thermodynamic functions determination
(Department of Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand)
Abstract: Mn1.8Co0.1Mg0.1P2O7·2H2O was synthesized via hydrothermal method and the thermal dehydration product was confirmed to be Mn1.8Co0.1Mg0.1P2O7. The thermogravimetry/differential thermogravimetry/differential thermal analysis, Fourier transform infrared, atomic absorption spectrophotometry, X-ray diffraction and scanning electron microscopy techniques were employed for sample characterization. Non-isothermal kinetics was studied under air atmosphere at four heating rates and the single thermal dehydration process was observed. Iterative Kissinger-Akahira-Sunose equation was used to calculate the apparent activation energy Eα values. Dehydration process was confirmed to be a single-step kinetic process with the unique kinetic triplets. Málek’s equations were used to determine the kinetic model f(α) and pre-exponential factor A. ？esták-Berggren model was suggested to be the mechanism function for the dehydration process. The best fit led to the kinetic triplets of Eα=(79.97±6.51) kJ/mol, ln A=16.83 and f(α)=α0.520(1-α)1.255 (α is the extent of conversion). The thermodynamic functions of activation were calculated using activated complex theory together with A value.
Key words: non-isothermal kinetics; dehydration; kinetic mechanism; ？esták-Berggren model; thermodynamic function