CATHODIC NANOCOATING TECHNOLOGY FOR CORROSION CONTROL OF STEEL STRUCTURES

Traditional organic coatings which provide cathodic protection such as zinc-rich coatings exhibit several major drawbacks.  To achieve electrical conductivity zinc-rich coatings rely on tangential contact between zinc dust particles.  This results in over pigmentation of the binder exceeding the critical pigment volume concentration of the resin system.  This results in an inferior coating with poor physical and mechanical properties.  In addition, zinc-rich coatings limit the amount of corrosion protection they can provide. 

The use of fullerene nanotubes, also called buckytubes, results in a network of carbon nanotube ropes which strengthens and stiffens the film while building an electron path through the binder system.  Chemical bonding in nanotubes is described by applied quantum chemistry, specifically, orbital hybridization.  The chemical bonding of nanotubes is composed entirely of sp2 bonds, similar to those of graphite.  These bonds, which are stronger than the sp3 bonds found in diamonds, provide nanotubes with their unique strength.

The mechanical and electrical properties of the nanotubes contribute to the critical corrosion control properties of these coatings.  The electrical properties of the tubes enables the coatings to overcome a basic problem associated with organic coatings, they are non-conductive.  In this coating system the nanotube provide a highly conductive electron path through the binder.  In the event of a coating break a cathodic potential is established.  Electrons are transferred from an optimized amount of sacrificial metal particles such as zinc or aluminum through the resin system to the steel substrate. 

In addition, the mechanical properties of the coatings are greatly enhanced by the reinforcement of the resin system by the nanotube ropes.  The insertion of the material dramatically increases the stiffness and modulus of the coating film.  Impact resistance, tensile strength, and adhesion properties of the film are superior to organic zinc coatings.