Calcium alkoxides for stone consolidation: Investigating the carbonation process

Despite the importance of carbonation in many processes, still the reaction needs investigation. The reaction is essential for the effectiveness of consolidants, based on CaCO3 forming products, used in stone conservation. Research on carbonation of two calcium alkoxides products, developed during the Nanomatch project, is presented in this paper and the results discussed and compared with those reported with the most used nanolimes. Calcium tetrahydrofurfuryloxide (Ca(OTHF)2), dissolved in four different solvents, and calcium ethoxide (Ca (OEt)2), diluted in ethanol, were applied on glass slides and their carbonation kinetics investigated together with their coatings after being kept in uncontrolled and controlled RH conditions (50% and 90%). This allowed to understand the evolution and the phases formed along the process. Carbonation follows the two pathways already reported for alkoxides; it is a quick process and eventually leads to the formation of the most stable crystalline phase (calcite), with high humidity favouring this final step. Alkoxides resulted thus to be suitable compounds for stone conservation, where full carbonation and formation of calcite needs to be obtained for the effectiveness of consolidation.