Thermal decomposition kinetics of magnesite from thermogravimetric data

Thermal decomposition kinetics of magnesite were investigated using non-isothermal TG-DSC technique at heating rate (beta) of 15, 20, 25, 35, and 40 K min(-1). The method combined Friedman equation and Kissinger equation was applied to calculate the E and lgA values. A new multiple rate iso-temperature method was used to determine the magnesite thermal decomposition mechanism function, based on the assumption of a series of mechanism functions. The mechanism corresponding to this value of F(a), which with high correlation coefficient (r-squared value) of linear regression analysis and the slope was equal to -1.000, was selected. And the Malek method was also used to further study the magnesite decomposition kinetics. The research results showed that the decomposition of magnesite was controlled by three-dimension diffusion; mechanism function was the anti-Jander equation, the apparent activation energy (E), and the pre-exponential term (A) were 156.12 kJ mol(-1) and 10(5.61) s(-1), respectively. The kinetic equation was d alpha/dT=10(5.61)/beta exp(-18777.9/T)x{3/2(1+alpha)(2/3)[(1+alpha)(1/3)-1](-1)}, and the calculated results were in accordance with the experiment.