Hybrid Sol–gel Clear Coatings for Decoration Brass Profiles

Abstract

Frequently, it is desired that the original reddish to gold tones of copper, brass, and bronze surfaces are preserved when they are used in decorative areas, which are mainly interiors, but are also in architectural elements exposed to the environment. This can be achieved by applying a clear protective coating that not only creates a weather barrier, which prevents further deterioration of the surfaces, but also protects the surfaces against mechanical aggressions such as abrasion (dust), rubbing (during cleaning), or scratching. The objective of this work was to evaluate the relative performance of clear coatings: the acrylic varnish Incralac and a hybrid sol–gel coating, and some hard coatings (TiN and TiZrN) obtained by ionic deposition. The wear resistance of the three types of protective layers was investigated with linear scratch and abrasion tests. The results indicated great improvements in the wear resistance of brass by applying the hybrid sol–gel coating. The tested varnish, known for its high corrosion resistance, had very poor wear resistance. For hard coatings negative results observed for corrosion and abrasion resistance can be explained by the layer being too thin and porous. The hybrid sol–gel coating gives the best compromise in terms of tarnishing, corrosion (salt spray and atmospheric exposure), scratching, wear, application, aestheticism (coloration, brightness), and cost.