Modification of calcium carbonate surface properties: macroscopic and microscopic investigations

Understanding the wettability of mineral powders and its modification by th e addition of various surface active agents is crucial for many industrial applications. In many cases, wettability is investigated by macroscopic cha racterization techniques. In this framework, we decided to study non-porous calcium carbonate powders coated by known amounts of water-repellent molec ules. A detailed characterization of the interface. focusing on the analysi s nf surface heterogeneity, was carried using water vapor, nitrogen, and ar gon adsorption. It clearly reveals specific adsorption sites for water-repe llent molecules. Wettability and immersion enthalpy measurements show that saturation of the carbonate surface by water-repellent molecules is not nec essary for obtaining maximum hydrophobicity. It is reached for approximatel y one-third of surface saturation; at that point, some high-energy surface sites are still available for water and nitrogen adsorption. This suggests that wettability is not only linked to the availability of surface sites fo r water molecules.