Thermochemische und kinetische Untersuchungen der endothermen Umbildungsreaktionen des Epsomits (MgSO4 · 7H2O) |
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Authors: | K Heide |
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Institution: | 1. Fachbereich Glaschemie der Sektion Chemie, Friedrich-Schiller-Universit?t, Jena, D.D.R.
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Abstract: | Heterogeneous decompositions of MgSO4 · 7H2O (Epsomite) monocrystals were studied with thermal (DTA, DSC, TG) and thermo-optical methods. The polythermal reaction is controlled by nucleation of the reactant. This process has been considered by the Avrami-Erofe'ev equation: $$kt = - \ln (1 - \alpha )]^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 3}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$3$}}} $$ The plots and the slope which give the activation energyE+=23.5 kcal/mole (760 Torr N2, 50–100°), are obtained from the Freeman-Carroll equation. The DSC technique was used to determine the heat of decomposition (ΔH=42.3 kcal/mole, 760 Torr N2, 50–100°). The heat of transformation for the reaction 39–47° $$MgSO_4 \cdot 7H_2 O\xrightarrow{{39 - 47^ \circ }}MgSO_4 \cdot 6H_2 O + H_2 O$$ wasΔH=2.8 kcal/mole. The isothermal reaction (20°, 10?6 Torr) is controlled by first-order kinetic. |
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