A novel approach to consolidation of historical limestone: the calcium alkoxides

Abstract

Potential utilization of calcium alkoxides as stone consolidants was considered. Reaction of Ca(OCH 3 ) 2 , Ca(OCH 2 CH 3 ) 2 (CH 3 CH 2 OH) 4 and Ca[OCH(CH 3 ) 2 ] 2 with the atmosphere in different experimental conditions was studied. The reaction produced CaCO 3 and two different pathways seem to be involved, the first taking place through CO 2 insertion into the Ca-O bond of Ca(OR) 2 species with formation of an alkylcarbonate derivative, subsequently transformed into CaCO 3 through ROH elimination; the second takes place through hydrolysis of Ca(OR) 2 to Ca(OH) 2 , which is then carbonated to CaCO 3 . The vaterite/calcite ratios found in the final CaCO 3 vary considerably with the experimental conditions adopted. Investigations demonstrated the potentiality of Ca(OCH 3 ) 2 to act as a stone consolidant. In fact, impregnation of a porous substrate, simulating the deteriorated stone, with a methanol solution of Ca(OCH 3 ) 2 , produced a crystalline vaterite film, which gradually filled all the pores and cavities of substrate and seems to fulfil the necessary requirements for a consolidant.

Innovative consolidating products for stone materials: field exposure tests as a valid approach for assessing durability

“…Alkaline earth and semimetal alkoxides are suitable molecular precursors because the corresponding solutions or nanoparticulate inorganic sols, upon evaporation of the solvent based carrier, undergo hydrolysis and condensation or carbonation inside the porous structure of the substrate. Particularly, calcium alkoxides, acting as precursors of corresponding carbonate [14,15], can be considered for stone strengthening as an indispensable and essential preliminary action for its conservation, as demonstrated within the bilateral Italian-French GALILEO Project [16]. The same material has been used for wood as these materials, besides strengthening effects, also ensure an alkaline supply to mitigate acidic deterioration processes of cellulose structures.…”

Study of Challenging Calcium Alkoxides in Solution by Electrospray Ionization Mass Spectrometry (Part 1)

“…The ESI spectrum of the sol is characterized by a wide series of signals, some of which are difficult to attribute; only the signals at m/z 175 [Ca(OMe) 2 3 ] + , with RA ranging from 100% to 65%. It is interesting to observe that the species were also generated by Method A but they were detectable only in the precipitate ws.…”

“…[1][2][3] In the last few decades, a renewed interest has arisen toward metal alkoxides as precursors in the formation of modified surfaces [for example, coatings via chemical vapor deposition, sol-gel) 4 and in homogeneous catalysis. 5 Calcium alkoxides, like other metal alkoxides, are moisturesensitive species and easily undergo oligomerization processes that are due to the kind of metal ion allowing the coordination of a high number of donors to reach coordination saturation.…”

Consolidation of Wall Paintings and Stone

“…Finally, other researchers (Favaro et al 2008;De Zorzi et al 2009) proposed an alternative approach where calcium alkoxides (in methanol solution) impregnate porous substrates and then react with atmospheric moisture and CO 2 to form calcium carbonate in situ, which exhibits nano-structuration. The time needed for complete carbonation depends on thermohygrometric conditions and the thickness of the alkoxide particles, and ranges from 2-4 to 35-45 days.…”