TEOS-PDMS-Calcium Oxalate Hydrophobic Nanocomposite for Protection and Stone Consolidation

Abstract

A treatment for both protection and consolidation, was synthesized in a simplified procedure through the sol gel process. Synthesized nano-calcium oxalate (CaOx) was incorporated into tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS), providing a hybrid hydrophobic consolidant nanocomposite. Oxalic acid was selected due to its ability to catalyse the hydrolysis of TEOS, as a drying control agent, but also because of its contribution at the formation of the calcium oxalate in reaction with calcium hydroxide. CaOx, incorporated into the silica matrix of the final copolymer, exhibits interfacial compatibility with the stone substrate and simultaneously strengthens the treated surface, since CaOx appears to be more stable than calcium carbonate. The hydrolysis of TEOS, as well as the formation of CaOx was evaluated through thermogravimetric analysis (TG/DTA). The nanocomposite consists of particles with approximately 7–700 nm in size range, as shown in TEM images. The consolidation, in combination with the hydrophobicity of surface resulted in an increase of the resistance to decay. Mechanical properties were enhanced as evaluated by ultrasonic pulse velocity on treated and untreated surfaces. Furthermore, water contact angle, as well as water absorption by capillarity test, showed improved water repellency of treated stones. Finally, this treatment doesn’t alter the aesthetic surface parameters, a fact that is essential in cultural heritage conservation, while the consolidant remains intact under UV and moisture exposure.

Advances in the application of nanomaterials for natural stone conservation

“…The nanocomposite reached a good penetration depth inside the stone, without affecting the porosity and pore size distribution, with an improvement of the tensile strength. A further advancement of this formulation was the addition of polydimethylsiloxane (PDMS) to obtain hybrid hydrophobic consolidants, resulting in an increase in the resistance to decay and enhanced mechanical properties of the limestone [67].…”

Preliminary Investigation of Sequential Application of Different Calcium Oxalate Solutions for Carbonate Rock Conservation

“…Through the above dissolution resistant experiment, it is possible to find the effects of the calcium oxalate layer, which provides direction for the sequential application method. This research concentrates on the study of coating densification and crystal regulation, while other research gives more attention to the preparation method, application environment, and performance evaluation [6,27].…”

Self-Cleaning Coatings for the Protection of Cementitious Materials: The Effect of Carbon Dot Content on the Enhancement of Catalytic Activity of TiO2

“…Furthermore, based on the tetraethoxysilane (TEOS) effectiveness as a strengthening agent for Portland cement mortars [28], we synthesized an advanced hydrophobic consolidant, designated as FX-C, using a sol-gel process that combines TEOS, PDMS and nano-calcium oxalate (nano-CaOx) for the preservation of cultural heritage [29,30]. It was found that silicon in TEOS/PDMS copolymer can form strong Si-O bonds with hydroxyl groups of the material for preservation [31].…”