Carbon nanotube/metal corrosion issues for nanotube coatings and inclusions in a matrix

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. It should be noted that this research topic is in its infancy stage and the prevalence of papers that have studied the mechanism is lacking.