Volume 19 Preprint 11
GREEN INHIBITION OF CORROSION OF MILD STEEL IN ACID MEDIUM
P.A.Jeeva and S.Karthikeyan
Keywords: Mild Steel; Corrosion Inhibition; Clonazepam; Adsorption Isotherm; Green inhibitor
Corrosion behavior of mild steel in 1M Sulphuric acid with an anti-bacterial agent, viz., Clonazepam [CPZ] as corrosion inhibitor has been studied by using mass loss, potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen permeation studies. All these techniques reveal that inhibition efficiency increases with the increase in the concentration of antibacterial agent. Polarization studies indicated that inhibitor acted as cathodic inhibitor. It was found that the adsorption of green inhibitor on the mild steel surface obeying Langmuir adsorption isotherm.
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GREEN INHIBITION OF CORROSION OF MILD STEEL IN ACID
P.A.Jeeva* and S.Karthikeyan
School of Mechanical Engineering, VIT University, Vellore,
(*Corresponding author: firstname.lastname@example.org)
Corrosion behavior of mild steel in 1M Sulphuric acid with an anti-bacterial
agent, viz., Clonazepam [CPZ]
as corrosion inhibitor has been studied by
mass loss, potentiodynamic
polarization, electrochemical impedance
studies. All these techniques reveal
that inhibition efficiency increases with the increase in the concentration
of antibacterial agent. Polarization studies indicated that inhibitor acted
as cathodic inhibitor. It was found that the adsorption of green inhibitor
on the mild steel surface obeying Langmuir adsorption isotherm.
Keywords: Mild Steel; Corrosion Inhibition; Clonazepam; Adsorption Isotherm;
Mild steel is an important class of metals due to its outstanding mechanical
properties. It is widely used under different conditions in chemical and
in handling acidic, alkaline and salt solutions.
steel is used in industries as pipelines for petroleum industries, storage
tanks, reaction vessel and chemical batteries . Acid solutions are widely
descaling due to their chemical properties [2-5].
Acids cause damage to the
steel substrate, because of their corrosive nature. Several methods were
used to reduce
the corrosion of metals in acidic medium, but the use of
inhibitors is most widely employed[ 6-10].
Organic compounds are widely used as corrosion inhibitors for mild steel in
acidic media [11-16].
The rate of corrosion retards
organic inhibitors on the mild steel
by adsorption of
surface. The inhibitors block the
by replacing water molecules and form a dense
on the metal surface. The majority
of the organic inhibitors are toxic,
highly expensive and non environment friendly. Research activities in recent
times are booming on
developing the cheap, non-toxic drugs as environment
friendly corrosion inhibitors [17-21].
The aim of this study
is to examine the corrosion protection efficacy of
for mild steel corrosion in 1M H2SO4. We came to know no
inhibitor in 1M H2SO4. From the literature the higher concentration of H2SO4
brain that may become unbalanced and cause anxiety. It is used to treat
seizure disorders or panic disorder.
The inhibition efficiency of this green inhibitor was monitored using mass
techniques, hydrogen permeation studies and diffuse reflectance methods.
2. Experimental Section
electrochemical studies. The aggressive solution of 1M H2SO4 (AR Grade) was
used for all the studies.
The antibiotic namely Clonazepam
from the medicine shop and used as such. The structures of the antibiotics
are given in the figure 1.
Figure 1. Structure of Clonazepam [CZP]
molecular weight of 315.72
Electrochemical experiments were cariedout
using a three electrode cell
assembly with mild steel samples as working electrode, 4cm2 area of platinum
as counter electrode and Hg/Hg2SO4/1M H2SO4 as the reference electrode. The
examined by diffuse reflectance studies in the region 200-700 nm using U3400 spectrometer (UV-VIS-NIR Spectrometer, Hitachi, Japan).
2.2. Mass loss studies
The concentrations of inhibitor used for weight loss and electrochemical
study were from 25x10-4M to 75x10-4M. Mild steel specimens of size 1x4 cm2
distilled water and finally dried and kept in the desicator. The mass
study was carried out at room temperature for 3 hours in 1M H2SO4. The
experiments were performed in triplicate. The inhibition efficiency (IE %)
was determined by the following equation
Inhibition Efficiency (IE %)
where W0 & Wi are the mass
(W0 –Wi /W0) X 100
loss values in the absence and presence of
2.3. Electrochemical studies
Potentiodynamic polarization measurements were done
out in a conventional
three electrode cylindrical glass cell, using CH electrochemical analyzer.
The solution was deaerated for 20 minute before carryout the polarization
10 min. until a
steady state was achieved. The mild steel surface was
exposed to various concentrations of inhibitor in 100mL of 1M H2SO4 at room
Inhibition Efficiency (IE %)
(I0 –I /I0) X 100
where I0 and I are the corrosion current density
without and with the
The potentiodynamic current-potential curves were noted
electrode potential automatically
by changing the
from -750mV to +150mV versus the
circuit potential. The corresponding corrosion current (Icorr) was recorded.
Tafel plots were built by plotting E versus log I. Corrosion Potential
(Ecorr), corrosion current density (Icorr) and cathodic and anodic slopes (βc
and βa) were calculated according to known procedures.
Impedance measurements were performed
in the frequency range from 0.1 to
10000 Hz using amplitude of 20 mV and 10 mV peak to peak with an AC signal
at the open-circuit potential. The impedance diagrams were plotted in the
nyquist representation. Charge transfer resistance (Rct) and double layer
percentage inhibition efficiency was calculated from the equation
Inhibition Efficiency (IE%) =
Cdl) x 100
where Cdl and Cdl’ are the corrosion current of mild steel with and
2.4. Hydrogen permeation studies
The hydrogen permeation study was monitored
using an adaptation of modified
Devanathan and Stachurski’s , two compartment cell as described elsewhere
. Hydrogen permeation currents were noted in the absence and presence of
2.5. Diffuse reflectance spectroscopy
The surfaces of corroded and corrosion inhibited mild steel specimens were
scrutinized by diffuse reflectance studies in the region 200- 700 nm using
U-3400 spectrometer [UV-VIS-NIR Spectrometer, Hitachi, Japan].
3. Results and Discussion
3.1. Mass loss studies
The values of inhibition efficiency (IE%),corrosion rate (CR) and surface
concentrations from the mass
loss data are
summarized in the table-1. It
inhibitor concentration. In addition the rate of corrosion has reduced with
obtained at 75x10-4 M concentrations of the inhibitor.
Values of Inhibition Efficiency, Corrosion rate and Surface
coverage for the corrosion of mild steel in 1M H2SO4 in presence of different
from mass loss measurements.
3.2. Potentiodynamic polarization studies
concentrations of green inhibitor for two antibiotics are summarized
densities (Icorr), anodic Tafel slope (βa) ,cathodic Tafel slope (βc) surface
value diminishes with increase in the concentration of the Clonazepam drug.
The inhibition efficiency (IE %) and surface coverage (θ) increases with
maximum inhibition efficiency was achieved at 75x10-4 M concentration of the
inhibitor. It has been observed that both βa
βc are reduced, but the
values of βc are decreased to a greater extent. This indicates that the
compound behaved as cathodic inhibitor.
2 Electrochemical parameters and Inhibition Efficiency for corrosion
of mild steel in 1M H2SO4 obtained by Polarization method in presence of
different concentrations of Clonazepam drug.
3.3. Electrochemical impedance studies
Values of charge transfer resistance (Rct) and double layer capacitance (Cdl)
derived from Nyquist plots are shown in table 3. The values of Rct are
appeared to increase with increase in concentration of inhibitors in 1M
H2SO4. It is cleared
that values of Cdl are fetched down by increasing
concentrations of inhibitors in the acid. This can be attributed to the
dominant adsorption of the
inhibitor on the mild steel
parameters and Inhibition efficiency for corrosion
of mild steel in 1M H2SO4 obtained by Impedance method in presence of
different concentrations of Clonazepam drug.
3.4. UV spectral reflectance studies
The reflectance plots
for polished specimen, specimen dipped in 1M H2SO4 and
progressively diminishes for the specimen dipped in 1M H2SO4 solution. This
observation unveils that the change in surface property
is due to the
corrosion of mild steel in acid. Also the reflectance percentage of steel
in the presence of green inhibitor
is higher than steel as immersed in
transformed further due to the formation of protective layer
on the mild
thickness of the inhibitor film formed on metal surface. Similar findings
has been made by Madhavan etal .
UV Reflectance curves of mild steel in 1M H2SO4 solution with
of the inhibitor.
3.5. Adsorption isotherm and thermodynamic parameters
The inhibitive action of inhibitor in extremely belligerent media is due to
its adsorption on the metal surface.
The degree of surface Coverage (θ) for
different concentrations of Clonazepam in 1M H2SO4 has been calculated from
loss, polarization and electrochemical impedance studies. The attained
data was tested graphically for fitting suitable isotherm [30-32]. Almost a
straight line was obtained by plotting log (C/θ) Vs log C shown in Figure-3,
which demonstrates that the adsorption of these compounds on steel surface
observes Langmuir adsorption isotherm.
The Langmuir isotherm for the adsorbed layers is given by the equation
process. Adsorption equilibrium constant [Kads] and free energy of adsorption
[∆G0ads] were calculated using the equation
Kads= 1/Cinh x
-2.303RT log [55.5Kads]
Where 55.5 is the molar concentration of water in solution . R is
the gas constant, T is the temperature. The values of adsorption equilibrium
constant [Kads] and free energy of adsorption [∆G0ads] are given in table-4.
The negative values of [∆G0ads] pointed out that adsorption of inhibitor is
spontaneous process. It is
that values of
[∆G0ads] is of order 20
kJmol-1 or lower indicates a physisorption, those of order of -40kJmol-1 or
higher involve charge sharing or transfer from the inhibitors to the metal
chemisorptions [36-38]. The values of free energy of
adsorption [∆G0ads] in our experiment lies in the range -28 to -32 kJmol-1,
signifying that the adsorption is not a simple physisorption, but it may
contain some other interactions .
Table 4: Gibbs free energy parameters and adsorption equilibrium constant
[K] of green inhibitor
at various temperatures evaluated by weight loss
3.6. Hydrogen permeation measurements
Hydrogen permeation currents are recorded in H2SO4 in the absence and presence
of Clonazepam drug. This study has been taken up with a plan of selecting
The values of permeation current with respect to time are
given in table-5.
The inhibitor brings down the permeation current to the extent of 50%. Thus
a definite correlation exists between the corrosion inhibition efficiency
and the extent of reduction in the permeation current of this compound. It
is a known fact that lower βc value for an inhibiting compound, the smaller
is the corrosion and hydrogen ingress on the metal. An increase in the βc
value, leads to rise in the energy barrier for proton discharge and increase
hydrogen through the steel surface .
Table 5: Values of permeation current
presence of green
for mild steel in 1M H2SO4 and in
inhibitor with respect to change in time
Permeation Current (A
3.7. Mechanism of corrosion inhibition
The adsorption of Clonazepam
onto the mild steel surface is found to be
electrostatic attraction between charged species in the solution and the
metal surface. If the metal surface is positively charged, the adsorption of
negatively charged species is facilitated. Positively charged species can
charged metal surface and allows positively charged species to adsorb on it.
Thus the adsorption of Clonazepam
may take place in two different ways as
statically to the anion covered mild steel surface through their
(ii) The inhibitors may compete with acid anions for the sites at the
water covered surface and adsorb by donating electrons to the mild
steel surface [40- 42].
1. The use of Clonazepam antibiotic as
green corrosion inhibitor in 1M
polarization, impedance measurements and
hydrogen permeation studies.
is further confirmed by diffuse reflectance spectra .
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