Iceland spar calcite: Humidity and time effects on surface properties and their reversibility

• Published in: Journal of Colloid and Interface Science
• Main Authors: Wojas, Natalia A., Swerin, Agne, Wallqvist, Viveca, Järn, Mikael, Schoelkopf, Joachim, Gane, Patrick A.C., Claesson, Per M.
• Other Authors: Department of Bioproducts and Biosystems, Printing Technology, KTH Royal Institute of Technology, RISE Research Institutes of Sweden AB, Omya International AG, Aalto-yliopisto, Aalto University
• Format: Article in Journal/Newspaper
• Language: English
• Published: ACADEMIC PRESS INC ELSEVIER SCIENCE 2019
• Subjects: Calcium carbonate minerals; Capillary forces; Humidity effects; Iceland spar calcite; Nanomechanical properties; Recrystallization; Reversibility of aging effects; Surface topography; Surface wettability; Van der Waals forces; Iceland
• Online Access: https://aaltodoc.aalto.fi/handle/123456789/40356; https://doi.org/10.1016/j.jcis.2019.01.047

Understanding the complex and dynamic nature of calcite surfaces under ambient conditions is important for optimizing industrial applications. It is essential to identify processes, their reversibility, and the relevant properties of CaCO3 solid-liquid and solid-gas interfaces under different environmental conditions, such as at increased relative humidity (RH). This work elucidates changes in surface properties on freshly cleaved calcite (topography, wettability and surface forces) as a function of time (≤28 h) at controlled humidity (≤3–95 %RH) and temperature (25.5 °C), evaluated with atomic force microscopy (AFM) and contact angle techniques. In the presence of humidity, the wettability decreased, liquid water capillary forces dominated over van der Waals forces, and surface domains, such as hillocks, height about 7.0 Å, and trenches, depth about −3.5 Å, appeared and grew primarily in lateral dimensions. Hillocks demonstrated lower adhesion and higher deformation in AFM experiments. We propose that the growing surface domains were formed by ion dissolution and diffusion followed by formation of hydrated salt of CaCO3. Upon drying, the height of the hillocks decreased by about 50% suggesting their alteration into dehydrated or less hydrated CaCO3. However, the process was not entirely reversible and crystallization of new domains continued at a reduced rate. Peer reviewed