CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 6
193]. As a single phase coating, titanium promotes passivity by spontaneous reaction in
electrochemical environment owing to its reactive nature, reduces the anodic activity, and thus
often used in severe conditions. Ceramic coatings such as TiO 2 is more resistant to corrosion than
their metallic counterpart due to high level of chemical inertness, easily tailorable electronic
properties, and good passivation ability in corrosive solutions. However, both metallic and
ceramic coatings contain large number of surface defects such as flaws, pores, pinholes, and intercolumnar
boundaries which have deleterious effect on the corrosion properties. Thus, in order to
reduce these surface defects and improve the corrosion performance, it is quite essential to control
the microstructure of the coated surface [194]. Duplex interlayer coatings are extremely effective
in protecting the materials by modifying the microstructure, morphology, and passivation
tendency of the base material in electrochemical solutions [195]. The interlayer reduces the
number of pinholes, and restricts the capillary action of the electrolyte at coating-electrolyte
interface thereby decreases the extent of sub-coating corrosion. Moreover, the interlayer can
increase the passivation property in the eventuality of passive film breakdown thereby galvanic
effect can be minimized which in general accelerates the corrosion rate.
In this chapter the passivation properties, and corrosion resistance of uncoated and
sputter deposited Ti, TiO 2 and duplex Ti-TiO 2 coated 304L SS have been investigated by means of
electrochemical studies in 1 M and 8 M nitric acid medium, and surface morphological
investigations. Surface morphology analysis was carried out by atomic force microscope.
Passivation property, corrosion resistance were determined by electrochemical impedance
spectroscopy, and polarization study. To evaluate the performance of each coating, protection
efficiency was evaluated from the polarization study. The results of the investigation are
highlighted in this chapter.