CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 6
range of corrosive environments to increase the performance of engineering materials. Moreover,
the basis for wide spread use of coatings as well as development and advancement in coating
technology is because of increasing corrosion problems, tighter economic situations, and optimal
performance of technologically important materials in various industries.
The expanding use of coatings has generated the need to understand the coating-solution
interaction in order to access their performance in corrosive environments. The basic approach of
corrosion protection using protective coating is to cut-off the interaction between substrate and
electrochemical environment by forming barrier over the surface [176-178]. The coating-solution
interaction is a complex phenomenon, and involves various factors such as barrier property,
topographical features, surface chemistry, and solution chemistry etc. The primary factor
responsible for corrosion resistance is the barrier property of the coating which is determined by
the lattice energy, bond energy, heat of formation, and band gap etc of the coated material
[176,179]. Topographical features have greater influence on the corrosion resistance. The coating
topography is largely anisotropic, and the presences of pores, pinholes, flaws on the coated surface
are detrimental from corrosion point of view [180,181]. The surface chemistry of coating such as
chemical composition of coating has its effect on the electrochemical properties at the coatingsolution
interface as well as coating-substrate interface [182,183]. Similarly, the solution
composition also has effect on electrochemical corrosion properties such as corrosion potential,
passivation tendency and corrosion current from the coated surface etc [184,185]. All the above
properties decide the life time of the coating in corrosive medium.
Metallic and ceramic coatings with good passivity, low electronic conductance or
insulating properties, and good tribological properties are known to protect the metals, and alloys
from corrosive environments [186-189]. Titanium (Ti), and titanium dioxide (TiO 2 ) are widely
used as coating materials for corrosion protection in a wide range of corrosive environments [190-