The Reserch Of Magnesite Decomposition Thermal Calculation And Kinetics

The research background and application status of magnesite (The chemical composition is MgCO3) were introduced. The chemical process of fused magnesite produced by magnesite were given a outline. The magnesite decomposition(The chemical reaction is MgCO3→MgO+CO2) thermal calculation and kinetics were researched.The heat absorption capacity were handled by enthalpy of chemolysis when a ton of MgO were produced. The heat absorbtion Q is7.9x109J, and the energy consumption of theory is2194kWh.A series of thermogravimetry experiment were conducted in nitrogen and carbon dioxide atmosphere, the TG curves of magnesite decomposition in different condition were gained. Analyzed from the curves, the TG cure retrude with the improvement of the heating rate. The temperature-hysteresis effect were turned up. The Kinetics-Analysis software of German NETZSCH company was applied to analyse the TG curve. The kinetics triplet of magnesite decomposition:activation energy(E), preexponential(A) and machanism function(f(α))was gained. The method be used in the software is called Model Free Method that include ASTM E698, Friedman, FWO.In nitrogen atmosphere, the value of40mg and120mg activation energy and preexponential is approach. The result of ASTM E698is:40mg, activation energy E=172.3±56.9kJ/mol, logarithm of preexponential log(A/s-1)=6.97;120mg, activation energy E=176.9±24.5kJ/mol, logarithm of preexponential log(A/s-1)=7.00. When sample size continue to increase, the value of activation energy and preexponential decreased with the increase of sample size. In carbon dioxide atmosphere, the value of activation energy and preexponential decreased with the increasing of sample size. The machanism function of magnesite in two atmosphere is Three-dimensional phase boundary(R3), which equation is3(1-α)2/3.From the change of activation energy, the speed controlled procedure of different magnesite decomposition was summarized, when the sample size is smaller, the apparent activation energy value is larger, then the decomposition of magnesite is controlled by chemical reaction; when the sample size is bigger, the apparent activation energy value is smaller, then the decomposition of magnesite that affected by the heat and mass transfer will increase gradually. For the reaction in the same situation, as the temperature increasing, the apparent activation energy value reduced gradually. So it is controlled by the chemical reactions in the early decomposition, but controlled by the heat and mass transfer in the later period.