Influence of gas media on the thermal decomposition of second valence iron sulphates

FeSO4 center dot H2O and FeSO4 represent the second valence of iron sulphates. Number of studies has been done to understand formation of intermediate sulphates like FeOHSO4 and Fe2O(SO4)(2), representing the oxidation of Fe2+ to Fe3+. At selected temperatures, both the thermo-dynamical equilibrium in the Fe-S-O system and the formation of the crystal structures in the solid phase are controlled by the partial pressure of water vapour and oxygen in the gas phase. The effects of the temperature and the partial pressure of gas components on the solid-phase content are demonstrated by phase diagrams. The study puts the accent on the influence of oxygen content in gas environment on processes of thermal decomposition of FeSO4 center dot H2O and FeSO4. At three quantities of oxygen content-0% (100% Ar), 21% (dry air) and 100% (pure O-2) the processes of oxidation and formatting metastable iron sulphates were examined by several experimental techniques. The thermal decomposition of samples was investigated by TG-DTG-DTA method in the temperature range 293-1400 K. Partial pressure of water vapour was determined by the quantity of water released from dehydration process of FeSO4 center dot H2O. Infrared spectroscopy, Mossbauer spectroscopy and X-Ray powder diffraction method were used for identification of the new formed solid structures and for characterization of the content of the iron sulphates with different valencies of iron. The experimental data and their analyses give the possibility to determine the different stages of decomposition, related to the formation of intermediates. Depending on gas environment, the basic relationships for reaction kinetics is drawn. It is demonstrated on that correlation exists between the kinetic's parameters and the content of oxygen in the gas phase.