29.1 New Products: Nano Estel: early research findings

17/01/12

During the conference of Società Chimica Italiana, held in Lecce, they presented the findings of the research conducted by professor Maurizio Lichelli and his associates at the Chemistry Dept. of the University of Pavia. The related experimental investigation had been performed on very porous bio-calcarenite (Pietra di Lecce) by using three different nanoparticles based products and the well known ethyl-silicate.

These four consolidating agents belong to two categories as follow:
-the alkaline hydroxides that form carbonates: Ca(OH)2 and Sr(OH)2-the silicon based products: Ethyl silicate and Nano EstelIt is important to keep in mind that both evaporation of water for Nano Estel and hydrolysis and polymerization in ethyl-silicate lead to an amorphous aggregate as well, that is silica gel. 
At first they moistened the samples by the mean of capillary motion and by a brush, then let them to react for a specific time. They measured the water absorption and the permeability to the aqueous vapor and performed the chemical characterization of the specimens through Energy-dispersive X-ray spectroscopy (SEM-EDX).
In addition the stone samples were subjected to accelerated aging process (15 cycles of salt crystallization) according to UNE-EN(12370) and weighed in order to evaluate the effect of the salt and the degradation of the stone surfaces.
When applying the ethyl silicate by the mean of capillarity absorption, the full permeation confers high resistance to the aging crystallization process with solution of salts. When using a brush (the most realistic procedure in any shop floor or building yard) to application of 
nanoparticles products is fairly good as reported below:

treatment                             weight loss %

not treated                                 18.94
SiO2 nanoparticles                       8.28 
Ca(OH)2 nanoparticles                  5.18
Sr(OH)2 nanoparticles                   4.18
ethyl silicate                                 3.54


Again ethyl silicate gives proof to be the most efficient consolidating agent (the percentage of weight loss after such a severe test is just one fifth compared to the reference stone sample).
On the other hand 
nanoparticles do not confer such an efficient barrier to the aqueous vapor. Variations of permeability of the samples are reported below.

T
reatment                                Permeability decrease (%)
SiO2 nanoparticles                                    14.5 
Ca(OH)2 nanoparticles                               24.8 
Sr(OH)2 nanoparticles                                18.3 
ethyl silicate                                              43.1 

SEM-EDX measurements revealed that ethyl silicate goes deeply inside the specimens whereas the nanoparticles based products penetrate just around one millimeter inside the surface. This outcome is consistent with the limits of nanoparticles, already observed on the Ca(OH)2 nanoparticles.

Conclusions


Ethyl silicate gives proof to be the best agent capable to deeply penetrate the stone cross section and to confer excellent consolidation, even on very porous carbonate stone substrate such as Lecce stone.
Nanoparticles based products can be regarded as a good choice for a skin-deep treatment.
Those findings need to be compared with tests on silicatic stones such as sandstone/arenite in the next future.
Let's stay tuned! New updating articles are on the way.

References

Licchelli M., Weththimuni M., Zanchi C.; "Nanoparticles For the consolidation of Lecce Stone”, Atti del XXIV Congresso Nazionale della Società Chimica Italiana, Lecce, 11-16
th September, 2011.


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