Influence of the Nanolime Suspension Concentration on the Effectiveness of Stone Conservative Treatments

In the present work the experimental results, in relation to the synthesis and the application of particles with submicrometric dimensions (nanolimes) on stones employed in Cultural Heritage, are reported. Lime nanoparticles are typically produced by a chemical precipitation process in supersaturated aqueous solutions of the reactants (calcium chloride and sodium hydroxide); water is then substituted with 2-propanol in order to improve stability of the suspension. Morphology and dimensions of the nanoparticles are investigated by TEM technique; the produced particles are hexagonally plated and regularly shaped, with dimensions of about 200nm by side or less. In the present work the influence of the nanolime suspension concentration on the carbonatation process as well as on the effectiveness of protective treatments is analysed. In particular, two different concentrations of nanolime suspensions are applied on wrought stone samples, representative of some national and regional historical stones (Pietra Serena, Travertine, Perla d’Abruzzo and Poggio Picenze), in order to evaluate the adhesion of the superficial CaCO3 obtained (scotch tape test) and the protective effect (capillarity test) of the treatment. In particular, in order to improve the carbonatation efficiency, an ammonium bicarbonate solution is applied to stones surfaces after each nanolime treatment. The obtained results show that the nanolime superficial treatments have positive effects; the enhancement of the protective efficacy is particularly interesting, considering that the obtained values, realised with the diluted nanolime suspension, reach even an increase of about 41 %.