Comparative study of the kinetics of the thermal decomposition of synthetic and natural siderite samples

The mechanism of the thermal decomposition of two siderites (a pure synthetic and a natural Mg-containing sample) has been determined from comparison of the results obtained from linear heating rate (TG) and constant rate thermal analysis (CRTA) experiments in high vacuum. The thermal decomposition of the synthetic siderite takes place approximately 200 K below the decomposition temperature of the natural sample. The mechanism and the product of the thermal decomposition are different for the siderite samples. In fact, an A2 kinetic model describes the thermal decomposition of the synthetic siderite, whereas the thermal decomposition of the natural sample obeys an F1 kinetic law. Decomposition products of the synthetic siderite are iron and magnetite, those of the natural siderite are wüstite and minor magnetite.