3.1. Influence of the Al surface pretreatment
Many
researchers
have
been
reported
the
difficulties
of
deposit-
ing CPs on aluminum due to the presence of an Al2O3 barrier
film [4,24]. In order to remove the oxide layer or to diminish its
thickness,
several
pretreatments
have
been
used,
such
as,
abra-
sion
with
emery
paper,
immersion
for
10
min
in
1.0
mol
L−1 HCl
at
55 ◦C, immersion for 5 min in 1.0 mol L−1 NaOH at 22 ◦C followed by
immersion for 5 min in 1.0 mol L−1 HNO3 at 22 ◦C and galvanostatic
activation
for
120
s
at
27
mA
cm−2 in a mixture of 0.1 mol L−1 HNO3
and
0.1
mol
L−1 Py
[8].
Fig.
1
shows
the
voltammograms
obtained
for
Al-1100
electrodes
in
a
0.1
mol
L−1 SDBS
and
0.1
mol
L−1 Py
solu-
tion at 0.020 V s−1, after the above cited pretreatments. The SEM
images in Fig. 2 showing the AA 1100 surface after different pre-
treatment conditions and potentiodynamic polarization allow to
conclude that high current values are due to the marked corrosion
caused
by
SDBS.
This
feature
evidences
that
the
deposition
of
the
polymer film is incipient and occurs at some sites on the surface. On
the other hand, for galvanostatic activation, the current values were
very low and the image shows few points of PPy deposits. Accord-
ing to Hülser [8], during galvanostatic activation, pits are formed
and become filled with polypyrrole. The coating obtained by this
way
was
slightly
conductive
and,
under
the
experimental
condi-
tions
studied,
showed
the
lowest
dissolution
rate
in
SDBS
medium.
Thus, the working electrode was pretreated by galvanostatic acti-
vation
for
120
s
at
27
mA
cm−2 in
a
mixture
of
0.1
mol
L−1 HNO3
−1