Abstract
Thermogravimetric studies on two varieties of calcium carbonate, namely, analytical reagent-grade and in situ product from thermal degradation of calcium oxalate monohydrate, were carried out at four rates of linear increase of the temperature. The kinetics and mechanism of their solid-state thermal decomposition reaction were evaluated from the TG data using four calculation procedures and isoconversion method, as well as 27 mechanism functions. The comparison of the results obtained with these calculation procedures showed that they strongly depend on the selection of proper mechanism function for the process. Therefore, it is very important to determine the most probable mechanism function. In this respect the isoconversion calculation procedure turned out to be more appropriate. In the present work, the values of apparent activation energy E, preexponential factor A in Arrhenius equation, as well as the changes of entropy , enthalpy , and free Gibbs energy for the formation of the activated complex from the reagent are calculated. All calculations were performed using programs compiled by ourselves.
Highlights
E thermal decomposition of calcium carbonate has been intensively studied over the years [1,2,3,4,5,6,7,8,9,10,11,12]
Apart from mechanical properties, thermal stability is one of the most important factors for the processing of polymeric materials. ermal decomposition kinetics of the polymeric materials depend from the thermal stability of the used llers, which may be characterized with its kinetic parameters such as reaction order nn, activation energy EE, and preexponential or frequency factorAA in the Arrhenius equation [19,20,21]
As has results from some critical analyses [15, 23, 24, 32,33,34,35], the correct determination of nonisothermal kinetic parameters involves the use of experimental data recorded at several heating rates. ese data have allowed applying the isoconversion methods in accessing the activation energy on the conversion degree that can be correlated with the investigated process mechanism. ese methods are recommended from ICTAC kinetics committee for performing kinetic computations on thermal analytical data [24]
Summary
E thermal decomposition of calcium carbonate has been intensively studied over the years [1,2,3,4,5,6,7,8,9,10,11,12] It is explained by great technological importance due to his various industrial applications such as manufacturing of lime and additives or llers in medicine, cosmetics, foods, plastics, printing inc and an apparent simplicity of the reaction. Aragonite has higher density and hardness than calcite and vaterite which makes it a valuable inorganic material that can be used as a ller for armature plastic, rubber, paper, glass ber, print ink, paint pigment, and composite [13, 16, 17] From another side, very interesting is the comparative kinetics studying of the thermal degradation of in situ generated calcium carbonate, obtained from the calcium oxalate monohydrate thermal degradation [14, 15]. E aim of the present paper is to compare the parameters characterizing the kinetics of nonisothermal degradation of analytical reagent-grade commercial sample of CaCO3 and insitu produced calcium carbonate from CaC2C4 ⋅ H2O, obtained on the basis of thermogravimetrical data using different kinetic equations and calculation procedures
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