Optimization of nanolime solvent for the consolidation of coarse porous limestone

Abstract

The potentialities of nanomaterials for application in the field of conservation have been widely investigated in the last two decades. Among nanomaterials, nanolimes, i.e., dispersions of lime nanoparticles in alcohols are promising consolidating products for calcareous materials. Nanolimes are effective in recovering the very superficial loss of cohesion of decayed materials, but they do not always provide sufficient mass consolidation. This limitation is mainly related to the deposition of the nanoparticles nearby the surface of the material. Experimental research has been set up with the aim of improving the in-depth deposition of lime nanoparticles. Previous research by the authors has shown that nanolime deposition within a substrate can be controlled by adapting the nanolimes properties (kinetic stability and evaporation rate) to the moisture transport behavior of the substrate. Nanolime properties can be modified by the use of different solvents. In this research, nanolime dispersions have been further optimized for application on Maastricht limestone, a coarse porous limestone. Firstly, nanolimes were synthesized and dispersed in ethanol and/or water, both pure and mixed in different percentages. Subsequently, based on the kinetic stability of the nanolime dispersions, the most promising solvent mixtures were selected and applied on the limestone. The deposition of lime nanoparticles within the limestone was studied by phenolphthalein test, optical microscopy and scanning electron microscopy. The results confirm that nanolime dispersed in a mixture of ethanol (95 %) and water (5 %) can guarantee a better nanoparticles in-depth deposition within coarse porous substrates, when compared to dispersions in pure ethanol.

Sticky rice–nanolime as a consolidation treatment for lime mortars

“…Furthermore, other studies focused on creating a CO 2 -rich atmosphere in a yeast-sugar environment to accelerate the carbonation process and to increase the in-depth carbonation [26]. Recently, other studies suggested that the type of solvent could be critical for the nanolime effectiveness in highly porous substrates [27][28][29]. These studies suggest that solvents with low evaporation rate could be more suitable for coarse porous substrates as they would reduce the back-migration of the nanoparticles thus contributing to their in-depth deposition.…”

Inorganic Nanomaterials for Restoration of Cultural Heritage: Synthesis Approaches towards Nanoconsolidants for Stone and Wall Paintings

“…It can also be added to the nanolime before application . If water is added to nanolime to increase its reactivity, the resultant formation of a Ca(OH) 2 gel may affect the particle penetration by reducing it or optimizing it …”

“…NPs can accumulate at or just under the surface of the treated material. Studies on the consolidation/transport mechanism of commercial hexagonal platelike nanolimes with sizes in the range of 50 and 250 nm were performed on Maastricht limestone, a high‐porosity yellowish limestone known as a traditional building material in the Netherlands and Belgium . The dispersion may be partially back‐transported to the surface during drying owing to the high volatility of the solvent and the high stability of the dispersion.…”

“…The dispersion may be partially back‐transported to the surface during drying owing to the high volatility of the solvent and the high stability of the dispersion. More recently, Borsoi et al . suggested that it was possible to avoid the migration of NPs back to the surface during drying by choosing the dispersive media as a function of the porosity of the substrate to be consolidated.…”

“…Solvents providing higher kinetic stability (e.g., ethanol and 2‐propanol) are more suitable for fine porous substrates . A mixture of ethanol and a low amount of water (5 %) can be a solution for good in‐depth consolidation treatment, as it partially prevents back‐transport . Back‐migration can also be avoided if water is applied immediately after treatment with nanolime …”