Plasma enhanced chemical vapor deposition (PECVD) of SiOx thin films on Portuguese limestone: An experimental study

• Deposition of SiO x thin films on oolitic limestone by PECVD from TEOS was tested. • PECVD is effective in producing crack-free SiO x films with no damage to stone substrate. • SiO x thin films by PECVD do not increase the hydrophobicity of the stone. • SiO x thin films by PECVD maintain vapor permeability of the stone. • SiO x thin films by PECVD protect stone from biological and pollutant attack. Plasma Enhanced Chemical Vapor Deposition (PECVD) of SiO x thin films has been applied to the stone surface under laboratory conditions in order to assess its feasibility as an alternative method for stone protection. SiO x thin layers were deposited on oolitic limestone lithologies known to have been used for the construction and restoration of the Batalha Monastery in Portugal surface by PECVD from tetraethoxysilane (TEOS) as the reaction precursor, in capacitively coupled parallel-plate reactor. The thickness, morphologies and chemical properties of the deposited film were characterized by attenuated total reflectance -Fourier transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopy (SEM+EDS). Laboratory simulated decay and natural aging tests were implemented to evaluate the protective effect of the deposited micron-size SiO x thin films. Results suggested that, due to the good barrier effect, SiO x films were able to isolate the stones from aggressive acidic solution, thus reducing possible dissolution-related damage. Natural aging tests proved that SiO x thin films were also able to inhibit to a high extent bio-colonization while, at the same time reducing soiling of the stone appearance. Durability and wetting property of this SiO x thin film were preliminarily assessed. This research tested, for the first time, the feasibility of applying micron-size SiO x film quickly and directly via cold plasma deposition and its versatile protection performance on carbonate stone.