Glass transition temperatures and crystallization kinetics of a synthetic, anhydrous, amorphous calcium-magnesium carbonate
Abstract
We report the first calorimetric observations of glass transition temperatures and crystallization rates of anhydrous, amorphous calcium-magnesium carbonate using fast scanning differential scanning calorimetry. Hydrous amorphous Ca0.95Mg0.05CO3 · 0.5H2O (ACMC) solid was precipitated from a MgCl2-NaHCO3 buffered solution, separated from the supernatant, and freeze-dried. An aliquot of the freeze-dried samples was additionally dried at 250°C for up to 6 h in a furnace and in a high-purity N2 atmosphere to produce anhydrous ACMC. The glass transition temperature of the anhydrous Ca0.95Mg0.05CO3 was determined by applying different heating rates (1000-6000 K s-1) and correcting for thermal lag to be 376°C and the relaxational heat capacity was determined to be Cp = 0.16 J/(g K). Additionally, the heating rate dependence of the temperature that is associated with the corrected crystallization peaks is used to determine the activation energy of crystallization to be 275 kJ mol-1. A high-resolution transmission electron microscopy study on the hydrous and anhydrous samples provided further constraints on their compositional and structural states. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000629448Publication status
publishedExternal links
Journal / series
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering SciencesVolume
Pages / Article No.
Publisher
Royal SocietySubject
amorphous calcium-magnesium carbonate; glass transition temperature; lyophilization; crystallization dynamics; scanning transmission electron microscopy; fast scanning differential scanning calorimetryOrganisational unit
03661 - Löffler, Jörg F. / Löffler, Jörg F.
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