Influence of graphene addition on the mechanical and surface properties of vitreous enamel coatings

Vitreous enamel is a very interesting coating for both aesthetical and technical purposes. The deposition of enamel coatings can be exploited on different materials, such as steel, cast iron and aluminium alloys, and it allows to greatly improve their mechanical, chemical, corrosion and thermal protection properties. Despite their high hardness, enamel coatings show limited abrasion resistance, mainly due to their vitreous nature and brittle behaviour. Recently, many studies tried to improve the abrasion resistance of enamel coatings through the modification of frit composition or through the addition of mill additives or hard particles. Another possible option to address the limited mechanical properties of enamel coatings could be represented by the use of graphene, as it has self-lubricating properties. Different concentrations of graphene flakes (0.25 wt.%, 0.50 wt.% and 1.00 wt.%) were added to the frit to study their influence on the enamel abrasion resistance. The performances of modified enamels were assessed exploiting mass loss, gloss and roughness measurements after different abrasion cycles, and microscopy investigations were carried out in order to evaluate the damage mechanism. Electrochemical Impedance Spectroscopy measurements were carried out in order to assess the protection properties and the produced defectiveness of the coating. An improvement of the coating abrasion resistance was obtained introducing 0.25 wt.% graphene inside the enamel matrix, although a loss of aesthetical properties was observed.