Hydroxyapatite coatings for marble protection: Optimization of calcite covering and acid resistance

Calcium phosphate coatings for marble conservation: Influence of ethanol and isopropanol addition to the precipitation medium on the coating microstructure and performance

“…However, results obtained so far on the protecting ability of so-formed HAP coatings over marble have been not as good as theoretical considerations would suggest [1,22]. This has been ascribed to the presence of microcracks and pores in the coating, which let acid reach the substrate and trigger its dissolution.…”

“…To prevent cracking of the coating, the reduction of the DAP concentration by adding ethanol to the DAP solution was investigated, as first proposed in [22]. The effect of adding increasing amounts of ethanol to an aqueous solution containing 0.1 M DAP and 0.1 mM CaCl2 was evaluated.…”

“…Because a higher amount of PO4 3-ions (needed to form HAP) is expected to form from DAP dissociation in water at higher pH [19], the effect of increasing the pH of the DAP solution to 10 was investigated. In a previous study, we tried to increase the pH using NaOH [22], but the resulting coating exhibited limited acid resistance, likely because of the formation of soluble phases [22]. Therefore, in the present study we used NH4OH to adjust the pH, to prevent the cation from the base from influencing the coating composition.…”

“…To speed up coating formation at low DAP concentration, addition of a calcium source (e.g., 0.1 mM CaCl2) has proven to have a strong impact [20]. Nonetheless, the coating obtained in these conditions is still patchy [22]. In a recent study, we have shown that it is possible to reduce the DAP concentration and still achieve complete coverage of the marble surface with a crack-free coating, by adding small amounts of ethanol to the DAP solution [22].…”

“…Nonetheless, the coating obtained in these conditions is still patchy [22]. In a recent study, we have shown that it is possible to reduce the DAP concentration and still achieve complete coverage of the marble surface with a crack-free coating, by adding small amounts of ethanol to the DAP solution [22]. Starting from this work, the present study has the following goals: 1) To elucidate the influence of ethanol on formation of the CaP coating and systematically investigate how the ethanol concentration, the reaction time, the pH and the DAP concentration, as well as the type of alcohol, influence the surface coverage, the mineralogical composition and the presence of microcracks and pores in the coating.…”