  Corrosion is an inevitable phenomenon that is inherent in metals and even
though there has been significant research on this subject, no ideal protection
has been discovered to fully prevent corrosion. However, methods such as using
protective coatings, and modifying the structure or composition of the material
have been used to slow down gradual corrosion and fortunately they proved to be
quite beneficial. The research focus has shifted to integrating novel materials
and structures to improve the corrosion resistance of composites. Carbon
nanotubes (CNTs) are an attractive and promising filler due to their chemical
inertness and high mechanical, electrical, and thermal properties. CNTs can
fill the gaps of metals and polymer-based composites by forming a passive layer
on metals and promoting sacrificial protection in zinc rich polymer (ZRP)
coatings, and can therefore function as an anti-corrosion filler. This paper
reviews the research that has been performed to better understand the influence
of CNTs on corrosion resistance in composites. Accordingly, in metal matrix
composites (MMCs), most of the work has been carried out on electrodeposited
coatings, namely Ni-based-CNT composites, which show improved corrosion
resistance by CNT addition. On the other hand, there are a few papers that have
studied the corrosion resistance of Mg-based-CNT composites and their corrosion
results contradict those obtained from other metal-CNT composites. For ZRPs or
polymer-based coatings there are a few papers that studied the effect of CNTs
on the corrosion of said composites. It is believed that CNTs can strengthen
the adhesion between the coating and the substrate and facilitate sacrificial
protection by Zn particles by forming a conductive network, hence the improved
corrosion resistance.
