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Thermal decomposition of mixed calcium oxalate hydrates - kinetic deconvolution of complex heterogeneous processes.

Authors :
Svoboda R
Olmrová Zmrhalová Z
Galusek D
Brandová D
Chovanec J
Source :
Physical chemistry chemical physics : PCCP [Phys Chem Chem Phys] 2020 Apr 28; Vol. 22 (16), pp. 8889-8901. Date of Electronic Publication: 2020 Apr 14.
Publication Year :
2020

Abstract

Differential scanning calorimetry (DSC), thermogravimetry (TG) and in situ XRD were used to study dehydration and consequent decomposition reactions of mixed calcium oxalate hydrates. As the complex dehydration kinetics exhibited certain trends with respect to the applied heating rate, the modified multivariate kinetic analysis approach (based on averaged curve-by-curve optimizations) was employed to obtain a full kinetic description of the data. The Šesták-Berggren equation was used to model the two consequent dehydration reactions. Good agreement was found between the kinetic parameters calculated from the DSC and TG data - approximate values of activation energies were 68 and 81 kJ mol <superscript>-1</superscript> for the trihydrate → monohydrate and monohydrate → anhydride transformations, respectively. A procedural methodology was developed to predict both dehydration kinetics and hydrate content ratios. For the calcium oxalate decomposition the TG technique provided very precise single-step prediction with an activation energy of 180 kJ mol <superscript>-1</superscript> . DSC on the other hand provided complex information on joint decomposition and carbon monoxide oxidation reactions - the proposed reaction mechanism includes completion of two reaction paths composed of consequent chemical reactions. A mechanistic view of the complex reaction path is discussed in terms of the diffusion barrier limiting the oxidation step.

Details

Language :
English
ISSN :
1463-9084
Volume :
22
Issue :
16
Database :
MEDLINE
Journal :
Physical chemistry chemical physics : PCCP
Publication Type :
Academic Journal
Accession number :
32289819
Full Text :
https://doi.org/10.1039/c9cp06867h