Aesthetic Effects on Granite of Adding Nanoparticle TiO₂to Si-Based Consolidants (Ethyl Silicate or Nano-Sized Silica)

• Main Authors: J. Santiago Pozo-Antonio, Daniel Noya, Cristina Montojo
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Coatings
• Subjects: titanium oxide; nanoparticle; conservation; cleaning; photocatalysis; nanoparticle concentration; physical change
• Online Access: https://www.mdpi.com/2079-6412/10/3/215

Considering that consolidant products are commonly used in the cultural heritage field and the titanium oxide nanoparticles (TiO₂) have been used to develop photocatalyst films to induce self-cleaning property, the scientific research on consolidants doped with TiO₂ is justified. However, the addition of TiO₂can affect to the physical properties of the cultural heritage object, questioning the adequacy of the procedure. In this paper, we evaluated the influence of nanoparticle TiO₂ addition to two different commercial consolidant products (ethyl silicate or nano-sized silica) on the appearance and the color of a granite and the penetration through its fissure system. The stone was previously subjected to high temperature simulating the effect of a fire and the subsequent tap water jet to cool down. Therefore, different concentrations of nanocrystalline TiO₂ (0.5, 1, and 3 wt %) were considered. The different compositions were also studied considering the compactness, the extent and the thickness of the superficial xerogel coating, and as well the penetration of the consolidant. The minimal TiO₂concentration tested (0.5 wt %) implied a low-medium risk of incompatibility as an intervention in cultural heritage field, because its low-medium potential as inducer of visible color changes of the granite surface. Regardless of the TiO₂ content, the nano-sized silica induced surface xerogel coatings more compact and continue than those formed in the ethyl silicate coated surfaces. Higher penetration rates were identified in the granite treated with nano-sized silica colloidal solution, while ethyl silicate was only found in the first few µm. It was found that penetration could depend on the application procedure, the solvent of the consolidant and the silica particle size. The TiO₂ addition reduced the penetration of the nano-sized silica consolidant.