Galvanic function of zinc-rich coatings facilitated by percolating structure of the carbon nanotubes. Part II: Protection properties and mechanism of the hybrid coatings

• Polypyrrole coated carbon nanotubes were incorporated into zinc-rich hybrid paints.
• Various types and amounts of functionalised nanotubes were embedded in coatings.
• The coatings with less functionalised carbon nanotubes provided better protection.
• Cathodic protection enhanced by the non- and the percolating conducting fillers.
• Galvanic efficiency improved better with the kinetically non-percolating particles.

Innovative zinc-rich hybrid paint coatings were developed using nano-size particles composed of alumina hydrate modified with polystyrene-sulfonate (PSS) doped polypyrrole (PPy) and either purified or functionalised multi-walled carbon nanotubes (MWCNTs). General properties of the particles and their dispersions were characterised in 1st part of the work. Corrosion protection characteristics of the hybrids were examined on low-carbon steel panels by immersion and salt-spray chamber tests. Immersion tests were monitored by electrochemical impedance spectroscopy (EIS). Primers were analysed by glow-discharge optical emission spectroscopy (GD OES) and surface of the steel substrates was investigated by X-ray photoelectron (XPS) and FT-Raman spectroscopy. Improved barrier and galvanic function of the hybrids over traditional zinc-rich paints (ZRPs) were evidenced by performance metrics. Optimal protection characteristics were found when content of the particles was close to the statistical and kinetic percolation thresholds. Advanced protection mechanism of the hybrids is discussed on function of the nano-size filler benefiting the utilisation of sacrificial current output of the anodic zinc along with taking into account aspects of the multiple percolation theory. The interpretation given in this work is intended to facilitate design of next generation of corrosion protecting metal-rich coatings.