Kinetics and Mechanism of Thermal Dehydration of KMnPO₄·H₂O in a Nitrogen Atmosphere

Abstract

The potassium manganese phosphate monohydrate (KMnPO4·H2O) was confirmed to dehydrate in a single step process. Therefore, the thermal transformation of this compound is an ideal case for testing the kinetic models and calculation procedures. The kinetics of thermal dehydration of this compound was studied using thermogravimetry (TG) at four heating rates by Ozawa and KAS methods. The calculated activation energy values from both methods are very close to each other. Four calculation procedures based on a single TG curve and the isoconversional method, as well as 26 mechanism functions were carried out. The mechanism function of dehydration with the integral form g(α) = 1 − (1 − α)1/3 and the differential form f(α) = 3(1 − α)2/3 can be suggested to be the mechanism of phase boundary reaction (spherical symmetry) for the title compound. In this work, the kinetic parameters and the transition state thermodynamic functions for the dehydration process of KMnPO4·H2O are reported for the first time.

Studies of thermal decomposition kinetics and temperature dependence of thermodynamic functions of the new precursor LiNiPO4·3H2O for the synthesis of olivine LiNiPO4

“…The most probable mechanism function, g(a), for the dehydration process of the hydrate precursor was determined using the equation [23,42] …”

“…The degrees of conversion a corresponding to four heating rates taken from two selected temperatures (175 and 180°C) were substituted into 35 types of mechanism functions [43]. The most probable mechanism function exhibits the slope and the linear correlation coefficient r 2 closest to -1.0000 and unity, respectively [41][42][43][44].…”

“…(9)-(12), the mechanism functions were estimated by plotting of the left-hand sides of Eqs. (9)-(12) by substituting g(a) from 35 mechanism functions [28] versus 1000/T for different a values (0.1-0.9 with increment 0.1) at the single b give rise to a single master straight line [42]. The activation energy and pre-exponential factor were calculated from the slopes and y-intercepts of the straight lines [42].…”

“…(9)-(12) by substituting g(a) from 35 mechanism functions [28] versus 1000/T for different a values (0.1-0.9 with increment 0.1) at the single b give rise to a single master straight line [42]. The activation energy and pre-exponential factor were calculated from the slopes and y-intercepts of the straight lines [42]. The model with the highest correlation coefficient is the best-fit kinetic model; meanwhile, the calculated activation energy values from four heating rates must close to the values calculated from the iterative methods [28,42,45].…”

“…The activation energy and pre-exponential factor were calculated from the slopes and y-intercepts of the straight lines [42]. The model with the highest correlation coefficient is the best-fit kinetic model; meanwhile, the calculated activation energy values from four heating rates must close to the values calculated from the iterative methods [28,42,45].…”