Kinetics of the Thermal Dehydration of Magnesium Oxalate Dihydrate in a Flowing Atmosphere of Dry Nitrogen

Article abstract of DOI:10.1021/j100310a024

The kinetics of isothermal dehydration of MgC2O4*2H2O in a dry nitrogen flow have been studied in detail by use of many accurate thermogravimetric data acquired on a microcomputer.This dehydration proceeded as a two-dimensional phase boundary reaction, R₂.In general, the nucleation in the phase boundary reaction occurs so rapidly that the reaction rate is only determined by following the chemical process occurring at the reactant-product interface.However, the present dehydration was affected by the nucleation process, and its dehydration fraction curve showed a sigmoid character especially at lower temperatures than ca. 160 deg C.We succeeded in separately evaluating the rate constants k_N for the nucleation and k₂ for the R₂ process by detailed analysis of the dehydration fraction curve.The value of k_N became comparable to that of k₂ at lower temperatures whereas at higher temperature the former became much larger than the latter and the overall dehydration had a characteristic of natural R₂ reaction.The values of activation energies and preexponential factors for both processes were determined from the temperature dependency of k_N and k₂.Those were 430 kJ mol^-1 and 3.73*10⁴⁹ s^-1 for the nucleation process, and 111 kJ mol^-1 and 3.40*10⁹ s^-1 for two-dimensional phase boundary process, respectively.