956 Wang et al.
Asian J. Chem.
TABLE-2
ELECTROCHEMICAL PARAMETERS FOR CORROSION OF MILD STEEL IN 5 wt. %
HCl IN THE PRESENCE OF DIFFERENT CONCENTRATIONS [C2Et]Br
Inhibitor
conc. (mM)
Potentiodynamic polarizations parameters
ba (mVdec-1) bc (mVdec-1) Icorr (mAcm-2)
Impedance parameters
C (µF/cm2)
Rct (Ω cm2)
12.2
Ecorr (mV/SCE)
IE (%)
IE (%)
-
Blank
2
-518
-526
-525
-490
-508
-520
72
80
86
77
82
85
-106
-103
-108
-104
-130
-123
0.416
0.227
0.149
0.619
0.874
0.661
-
176
48
35
33
25
23
45.4
64.1
85.2
79.0
84.1
33.8
64.1
66.3
73.9
80.0
82.0
4
36.5
10
20
40
46.8
61.2
67.9
Electrochemical corrosion parameters such as corrosion
potential (Ecorr), cathodic and anodic Tafel slops (ba, bc) and
corrosion current density (Icorr), obtained by extrapolation of
Tafel lines, are collected in Table-2. The values of cathodic
tafel slope (bc) and anodic tafel slope (ba) of [C2Et]Br are found
to charge with the concentration of the inhibitor, indicates that
the inhibitor controlled both anodic and cathodic reactions.
on the metal surface. The greatest inhibition is observed at a
concentration of 40 mmol/L. The inhibition efficiencies, calcu-
lated from impedance results, show the same trend as those
obtained from polarization and weight loss measurements. In
fact, the presence of [C2Et]Br is accompanied by the increase
of the value of Rct in an acidic solution indicating a charge
transfer process mainly controlling the corrosion of mild steel.
I0 − Icorr
Conclusion
IE =
× 100%
(2)
I0
From the overall experimental results and discussion the
following conclusions can be deduced: (1) The [C2Et]Br is a
new water soluble inhibitor for mild steel in 5 wt. % HCl. The
inhibition efficiency increases with an increase of inhibitive
concentration to attain a maximum value of 80.4 % at 40 mmol/
L. There are good agreements between the inhibition efficiencies,
obtained from gravimetric method and electrochemical measu-
rements; (2) The potentiodynamic polarization curves indicated
that the inhibitors inhibited both anodic metal dissolution and
also cathodic hydrogen evolution reactions and acted as mixed
type inhibitors in 5 wt.% HCl solution; (3) The electrochemical
impedance study shows that the application of [C2Et][Br]
inhibitor significantly increases Rct values and decreases Cdl
values in 5 wt.% HCl, suggesting that corrosion inhibition takes
place by adsorption.
Equation (2) was used to calculate the IE, where I0 and
Icorr are the corrosion current density values without and with
inhibitor, respectively. The obtained results show that the inhi-
bition efficiency increases, while the corrosion current density
decreases when the concentration of the inhibitor increases.
This could be explained on the basis of inhibitor adsorption
on the metal surface and the adsorption process enhances with
increasing inhibitor concentration. The results obtained from
the polarization measurements are in good agreement with
those obtained from weight-loss method.
Electrochemical impedance measurements: The corro-
sion behaviour of mild steel in acidic solution in the presence
of [C2Et]Br was investigated by the EIS. The impedance spectra
were analyzed by fitting to the equivalent circuit model shown
in Fig. 2b. It is apparent that the impedance spectra obtained
yields a semi circular shape. This indicates the corrosion of
the mild steel in 5 wt. % HCl is mainly controlled by a charge
transfer process.
ACKNOWLEDGEMENTS
This work was financially supported by Hunan Science and
Technology (Project No. 2010GK3167) and Hunan Provincial
Key Laboratory of Materials Protection for Electric Power and
Transportation (Changsha University of Science and Technol-
ogy) (No.2011CL04).
Table-2 collects various parameters such as charge-transfer
resistance (Rct), double layer capacitance (Cdl) and percentage
inhibition efficiency (IE) calculated from eqn. (3), where Rct(inh)
and Rct are the charge-transfer resistance values with and with-
out inhibitor, respectively.
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1
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(4)
2πfmaxRct
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