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

Autoři: Svoboda Roman | Olmrová Zmrhalová Zuzana | Galusek Dusan | Brandová Daniela | Chovanec Jozef

Rok: 2020

Druh publikace: článek v odborném periodiku

Název zdroje: Physical Chemistry Chemical Physics

Název nakladatele: Royal Society of Chemistry

Místo vydání: Cambridge

Strana od-do: 8889-8901

Tituly:

Jazyk	Název	Abstrakt	Klíčová slova
cze	Tepelný rozklad směsných hydrátů šťavelanu vápenatého - kinetická dekonvoluce heterogenních procesů	Dehydratace a následný rozklad hydrátů šťavelanu vápenatého byly studovány pomocí DSC, TG a in situ XRD. Výsledky byly zpracovány za účelem dekonvoluce probíhajících procesů a stanovení kinetiky jednotlivých dějů.	štavelan vápenatý; hydrát; dehydratace; rozklad; DSC; TG; in situ XRD; kinetika; dekonvoluce
eng	Thermal decomposition of mixed calcium oxalate hydrates - kinetic deconvolution of complex heterogeneous processes	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 Sestak-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(-1) 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(-1). 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.	urinary calculi; crystal-growth; kidney-stones; activation-energy; phase-change; dehydration; whewellite; crystallization; raman; precipitation

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