ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 4, pp. 605!609. + Pleiades Publishing, Inc., 2006.
Original Russian Text + N. A. Ogurtsov, G. S. Shapoval, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 4, pp. 614 !618.
AND CORROSION PROTECTION OF METALS
Protective Properties of Electrochemical Polyaniline
Coatings on Low-Carbon Steel
N. A. Ogurtsov and G. S. Shapoval
Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of the Ukraine, Kiev, Ukraine
Received May 4, 2005
Abstract-Protective properties of polyaniline coatings electrochemically deposited in the galvanostatic mode
from oxalic acid solutions onto the surface of low-carbon steel were studied by measuring polarization curves.
Electrically conducting polymers, such as, e.g.,
polyaniline, have been the object of intensive scien-
tific studies during the last two decades. According
to , they can reduce the rate of corrosion of low-
carbon steel by a factor of 10
. These materials can
replace the widely used noxious pigments of the pas-
sivating type, based on chromates and lead compounds
[2, 3]. Moreover, coatings based on these materials
have already been developed and are employed in
Germany for corrosion protection of carbon steel at
wastewater treatment plants, sea ships, and port con-
structions . This made it possible to replace, in
a number of cases, stainless steel with carbon steel
protected with a paint coating based on polyaniline .
The protective properties of polyaniline can be
used not only as a component of paint coatings, but
also in coatings that contain no additional polymeric
binder. However, films of chemically synthesized
polyaniline, and especially those in the doped form,
show poor adhesion to the metal and, as a rule, cannot
be used in practice. In contrast, electrochemically syn-
thesized polyaniline can form sufficiently stable coat-
ings on the metal surface. However, in this case, too,
researchers encounter certain difficulties. The elec-
trochemical synthesis of polyaniline is performed at
anodic potentials in an acid medium, and, therefore, it
is complicated by fast dissolution of the metal. There-
fore, this process commonly cannot be performed on
the surface of low-carbon steel. However, it has been
found that in some solutions, e.g., in oxalic ,
p-toluenesulfonic , and phosphoric [10, 12, 13]
acids, aniline can be polymerized.
Based on this circumstance, the Camalet et al. 
suggested using electrosynthesis of polyaniline, in-
stead of the environmentally hazardous phosphating
and chromating, to produce an anticorrosive prime
layer. At present, the protective properties of the
above-mentioned coatings remain poorly understood.
Separate experiments have been described in the lit-
erature, which employed methods for determining
the amount of iron that passed into a 0.4 M NaCl +
0.1 M HCl solution [6, 7, 11] and the time depen-
dence of the electrode potential in 0.1 M K
solutions (pH 2 and 4.5) [9, 10, 13].
The aim of this study was to examine the influence
exerted by the aniline polymerization conditions on
the anticorrosive properties of the resulting coatings
and the fundamental aspects of deposition of these
coatings. In addition, the properties of polyaniline
and conventional phosphate coatings were compared.
Chemically pure grade NaCl and HCl and analyt-
ically pure grade oxalic acid were used in the study
without additional purification; KCl of chemically
pure grade was preliminarily twice recrystallized.
Aniline of pure grade before use was purified by frac-
tional distillation at reduced pressure in an argon flow
and was stored under argon in a dark vessel with
ground-glass stopper, placed in a refrigerator.
Polyaniline coatings were deposited and their prop-
erties studied on edges of cylindrical steel (St.3) elec-
trodes (area 2.06 mm
), whose lateral surfaces were
insulated with epoxy resin. Preliminarily, the elec-
trodes were polished with a fine emery paper (Carbi-
met, Grid 600, USA), after which their surface was
degreased with soda, washed with distilled water, and