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Nondestructive testing of defects in adhesive joints

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Abstract:<br />

Effect <strong>of</strong> nano TiO2 <strong>in</strong> conduct<strong>in</strong>g polyanil<strong>in</strong>e composites for<br />

smart corrosion prevention coat<strong>in</strong>gs<br />

C.R.Siju*and S.Radhakrishnan #<br />

Polymer Science and Eng<strong>in</strong>eer<strong>in</strong>g Division.<br />

National Chemical Laboratory,<br />

Pune 411 008, India<br />

# Email: s.radhakrishnan@ncl.res.<strong>in</strong><br />

Coat<strong>in</strong>gs prepared from polyanil<strong>in</strong>e- nanoTiO2 particles synthesized by <strong>in</strong> situ polymerization<br />

were found to exhibit excellent corrosion resistance much superior to polyanil<strong>in</strong>e <strong>in</strong> aggressive<br />

environments. The corrosion studies were carried out on steel plates coated with these<br />

formulations conta<strong>in</strong><strong>in</strong>g 10% polyanil<strong>in</strong>e prepared with different concentrations <strong>of</strong> nanoTiO2 by<br />

electrochemical impedance spectroscopy at periodic <strong>in</strong>tervals dur<strong>in</strong>g exposure to hot sal<strong>in</strong>e (65 o<br />

C) conditions for prolonged durations over a period <strong>of</strong> 90 hours. The open circuit potential<br />

(OCP) derived from Tafel plots was found to shift to more anodic side much above that <strong>of</strong> bare<br />

steel with time. The presence <strong>of</strong> nano-TiO2 was found to be vital <strong>in</strong> prevention <strong>of</strong> corrosion and<br />

the shift <strong>of</strong> OCP to anodic side depended on the concentration <strong>of</strong> nano TiO2 used. From these<br />

data, one could envisage more than 100 times improvement <strong>in</strong> the corrosion resistance especially<br />

for polyanil<strong>in</strong>e prepared with 4.18% nano TiO2. The exceptional improvement <strong>of</strong> performance <strong>of</strong><br />

these coat<strong>in</strong>gs has been associated with the <strong>in</strong>crease <strong>in</strong> barrier to diffusion as well as transport <strong>of</strong><br />

charge by the nano sizeTiO2, redox properties <strong>of</strong> polyanil<strong>in</strong>e and very large surface area available<br />

for the liberation <strong>of</strong> dopant for the prevention <strong>of</strong> corrosion with self heal<strong>in</strong>g effect.<br />

Key words: Conduct<strong>in</strong>g polymer, anti corrosion, nano-composite, titanium dioxide<br />

coat<strong>in</strong>g<br />

1. Introduction:<br />

Polyanil<strong>in</strong>e (PANI) is one <strong>of</strong> the important conduct<strong>in</strong>g polymers which has been studied<br />

extensively for various applications such as sensors, transparent conductor, ESD and EMI<br />

protection, electrochromic displays etc. This polymer has been found to be an important<br />

constituent <strong>in</strong> coat<strong>in</strong>gs and recently that it has drawn attention as an effective material for<br />

corrosion protection. It has been reported that PANI based coat<strong>in</strong>gs can prevent corrosion even <strong>in</strong><br />

scratched areas where bare steel surface is exposed to the aggressive environment. The anti<br />

corrosive coat<strong>in</strong>gs can be prepared from chemically synthesized PANI as dispersion coat<strong>in</strong>gs or<br />

PANI may be directly deposited on metal by electrochemical method as a first coat. Chemically<br />

synthesized PANI by conventional route does not dissolve <strong>in</strong> common organic solvents and hence<br />

it has to be blended with other polymers for its applicability <strong>in</strong> coat<strong>in</strong>gs.<br />

The barrier properties can be enhanced if one uses appropriate fillers <strong>in</strong> the coat<strong>in</strong>gs. Further, it<br />

has been shown that nano-particulate fillers give much better barrier properties even at low<br />

concentrations than conventional micron size additives. As titanium dioxide (rutile or anatase) is<br />

commonly used as a pigment material for pa<strong>in</strong>ts, it is thought worthwhile to use nano-particulate<br />

TiO2 as a metal oxide additive <strong>in</strong> the composite which can give better dispersion <strong>of</strong> the<br />

formulation as well barrier properties <strong>in</strong> the coat<strong>in</strong>gs. In fact, it is anticipated that hybrid

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