The glass transition temperature of anhydrous amorphous calcium carbonate

Author:

Bissbort Thilo1ORCID,Hess Kai-Uwe1ORCID,Wilding Martin2,Schawe Jürgen E.K.34,Purgstaller Bettina5,Goetschl Katja E.5,Sturm Sebastian6,Müller-Caspary Knut6,Sturm Elena V.1,Schmahl Wolfgang1,Griesshaber Erika1,Weidendorfer Daniel1,Dietzel Martin5,Dingwell Donald B.1

Affiliation:

1. Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstraße 41/III, 80333 München, Germany

2. U.K. Catalysis Hub, Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Campus, Oxfordshire OX11 0FA, U.K.

3. Mettler-Toledo GmbH, Heuwinkelstrasse 3, CH-8603, Nänikon, Switzerland

4. Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland

5. Institute of Applied Geosciences, Graz University of Technology, Rechbauerstrasse 12, 8010 Graz, Austria

6. Fakultät für Chemie und Pharmazie, Physikalische Chemie, Ludwig-Maximilians-Universität München, Butenandstr. 5-13, 81377 München, Germany

Abstract

Abstract Amorphous calcium carbonate (ACC) is the least stable polymorph of calcium carbonates. It has been identified to play an important role in nature (e.g., biomineralization and speleothem formation), where it acts as a precursor for the transformation to more stable polymorphs such as calcite. Furthermore, the use of ACC in technical applications requires a robust understanding of the material’s properties. We present the first study that reveals the existence of a glass transition for synthetic and anhydrous ACC. The glass transition occurs at 339 °C. Such measurements are impossible with conventional differential scanning calorimetry (DSC) due to the high tendency of ACC to crystallize. Fast scanning DSC with heating rates of 500 °C/s and higher, however, can be used to separate the endothermic glass transition signature from the exothermic crystallization event since crystallization is shifted to higher temperatures. This allows the detection and quantification of the glass transition for ACC. These observations indicate that ACC is a structural glass and are especially significant because the synthesis of ACC, precipitation from a solution followed by lyophilization, contrasts with the more conventional and well-known route of glass formation–the rapid cooling of a melt. Moreover, we prove that a structural glass can be produced from a simple single-component carbonate system.

Publisher

Mineralogical Society of America

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