Abstract
Non-isothermal decomposition of chromium chromate hexahydrate, Cr2(CrO4)3−6H2O, was studied on heating up to 600°C in different dynamic atmospheres of N2, O2 and H2, using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). The results obtained at various heating rates (2–20°C min−1) were used to derive kinetic (E a and lnA) and thermodynamic (ΔH, C pand ΔS parameters.
It has been found that the activation energies of the dehydration and decomposition steps in N2 are generally larger than in H2 atmosphere, and the reverse is true for the enthalpy change of the decomposition. Thus, it has been concluded that the reductive decomposition (in H2) is easier than the thermal decomposition (in N2 or O2) of the chromate. Irrespective of the gas atmosphere applied, the eventual decomposition product was a mixture of α-Cr2O3 and non-crystalline chromate species, γ-Cr2O3+x. Above 400°C in H2 atmosphere, more deoxygenation of the non-crystalline chromate takes place at high rates of heating to give α-Cr2O3.
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Halawy, S.A., Fouad, N.E., Mohamed, M.A. et al. Kinetic and Thermodynamic Parameters of the Decomposition of Chromium Chromate in Different Gas Atmospheres. Journal of Thermal Analysis and Calorimetry 65, 167–176 (2001). https://doi.org/10.1023/A:1011536920701
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DOI: https://doi.org/10.1023/A:1011536920701