Electrochemical corrosion could be defined as electrochemical
degradation, occurring at the metal–solution interface where the
metal is oxidized (anodic reaction) and species from the solution
such as oxygen (cathodic reaction) are reduced [1]. Electrochemical
corrosion of metals is a spontaneous process because most metals
are inherently unstable [1,2].
The three major corrosion control methods used are the corrosion
inhibitors, the cathodic protection and the barrier protection.
The purpose of barrier protection is to separate the metal substrate
from the corrosive environment. Organic coatings are the best candidate
to create such a barrier against corrosive species [1–3]. They
are widely used in corrosion protection of metallic substrates [3].
It is generally accepted that the coating efficiency in corrosive
environments depends upon the barrier properties, the adhesion
properties of the coating and the degree of environment
aggressiveness [3–5]. The barrier properties of the coatings mostly
depend upon the integrity of the binder and upon its adhesion
to the substrate. The presence of some particles like pigments
or fillers could improve these properties. Moreover, pigments
change the appearance of the coatings and help to improve many
other properties of such as UV resistance, corrosion resistance
and mechanical properties like scratch and abrasion resistance.
Unfortunately, conventional pigments at high doses have some
disadvantages such as loss of impact resistance and optical properties,
poor adhesion, reduced coating flexibility, inferior abrasion
and scratch resistance, early delamination and increase in coating
viscosity. Incorporation of nano-size pigments and fillers in the
coating is a modern approach to overcome these disadvantages
and even to improve the performance [6–9].
In this research, the improvement of the resistance to corrosion
due to the presence of nano-ZnO in an aromatic polyurethane based
waterborne coating has been investigated.