Hybrid Materials Based on ZnO Nanoparticles and Organo-Modified Silica Coatings as Eco-Friendly Anticorrosive Protection for Metallic Historic Artifacts

Abstract

Cultural heritage metallic artifacts are often subjected to environmental factors that promote degradation through corrosion processes. Anticorrosion protection is needed both for the long-term preservation of outdoor monuments and the short-term conservation of archaeological artifacts. In this work, functional nanocoatings based on ZnO nanoparticles (NPs) in a silica matrix are prepared as a replacement for a commercial Incralac lacquer. Facile sol–gel synthesis is employed for obtaining silica filmogenic materials, using tetraethoxysilane (TEOS) and 3-glycidyloxypropyl trimethoxysilane (GPTMS). Silica-based nanocomposite coatings, with and without ZnO NPs and benzotriazole (BTA) as anticorrosion agents, applied on copper coupons by brushing are characterized by using VIS and FTIR spectroscopy, SEM and AFM and compared to Incralac lacquer as reference materials. The optical and morphological properties of the proposed silica coatings are similar to the Incralac specimens. The protective effect against corrosion is investigated on the copper coupons as model metallic objects subjected to a corrosion test by using potentiodynamic polarization in a 3.5% NaCl solution at ambient temperature. The influence of the presence of BTA and ZnO NPs in both silica and Incralac coatings is studied, and the variations in the anticorrosive, morphological and optical properties with the concentration of ZnO NPs are evidenced. The presence of moderate concentrations of ZnO in both nanomaterials leads to changes in the color parameters slightly above the limit accepted in the field of cultural heritage (ΔE* 5.09 and 6.13), while a high ZnO concentration of 3% leads to higher values (ΔE* > 10). Regarding the anticorrosive effect, the silica-based coatings with ZnO and BTA present similar efficiencies to that of the Incralac reference material (corrosion rates in the range of 0.044–0.067 mm/year for silica coatings compared to 0.055 mm/year for Incralac).