The corrosion inhibition of ranitidine on mild steel in hydrochloric acid medium was studied employing chemical and electrochemical methods. The results showed that the studied compound possessed good interaction on the metal surface and control both anodic and cathodic reactions. Studies pertaining to the determination of corrosion rate, percentage inhibition efficiency and variation of inhibitor concentration and temperature for the corrosion control process. Both anodic and cathodic polarized potentials were measured under galvanostatic and linear polarization techniques. The corrosion current density, corrosion potentials, Tafel slops and percentage inhibition efficiency were calculated. Thermodynamic parameters for the adsorption process were calculated and interpreted. The percentage inhibition efficiency obtained from both the methods was good agreement with each other. The corrosion protection was explained on the basis of adsorption of inhibitors on the metal surface. Adsorption of a compound on the mild steel surface was confirmed by FTIR spectra.

1. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
IRJC
Chemical and electrochemical studies of ranitidine as a
corrosion inhibitor for mild steel in hydrochloric acid
medium
SK Rajappa,*1
BM Praveen2
and TV Venkatesha3
1*
Department of Chemistry, Karnatak University’s, Karnatak Science College, Dharwad-580 001, India.
2
Department of Chemistry, School of Engineering, Mukka, Mangalore, India.
3
Department of Chemistry, Kuvempu Univestry, Shankaraghatta, India.
The corrosion inhibition of ranitidine on mild steel in hydrochloric acid medium was studied
employing chemical and electrochemical methods. The results showed that the studied
compound possessed good interaction on the metal surface and control both anodic and
cathodic reactions. Studies pertaining to the determination of corrosion rate, percentage
inhibition efficiency and variation of inhibitor concentration and temperature for the corrosion
control process. Both anodic and cathodic polarized potentials were measured under
galvanostatic and linear polarization techniques. The corrosion current density, corrosion
potentials, Tafel slops and percentage inhibition efficiency were calculated. Thermodynamic
parameters for the adsorption process were calculated and interpreted. The percentage
inhibition efficiency obtained from both the methods was good agreement with each other. The
corrosion protection was explained on the basis of adsorption of inhibitors on the metal
surface. Adsorption of a compound on the mild steel surface was confirmed by FTIR spectra.
Key words: Adsorption, corrosion inhibitor, inhibitor efficiency, polarization, ranitidine.
INTRODUCTION
Steel metal has been widely used in different conditions
in several industries for handling all type of solutions
including alkalies, acids and salt solutions. Generally mild
steel is used in refining crude oil, acid pickling, industrial
cleaning, acid descaling, oil–well acid in oil recovery and
petrochemical processes (Divakara Shetty et al., 2006).
Corrosion is an electrochemical process by which
metallic surfaces react with their environment causing the
metal to lose its material properties due to surface
deterioration. Important pickling acid in industries is
hydrochloric acid, which is accepted in ferrous alloy
industries. Scales and rust present on the steel surface
was also removed by hydrochloric acid (Fontana MG
(1987)). The use of organic compounds as corrosion
inhibitors is one of the most practical methods for
protection of metals against corrosion, especially in acidic
media (Praveen et al., 2010; Leelavathi et al., (2013).
Various types of chemical inhibitors like organic and
inorganic compounds, pharmaceuticals drugs, dyes and
even plant extracts were developed to control corrosion
(Rajappa et al., 2008)
Several drugs have been investigated as corrosion
inhibitors for various metals in acidic media (Shukla et al.,
2010). The aim of this study is to investigate the
corrosion inhibitive properties of ranitidine on the
corrosion of mild steel in hydrochloric acid medium using
chemical and electrochemical techniques.
*Correspondence author: SK Rajappa, Department of
Chemistry, Karnatak University’s, Karnatak Science
College, Dharwad-580 001, India. Email:
drrajappask@gmail.com, Tel.: 91-9620626968, Fax: 91
836 2446601
International Research Journal of Chemistry
Vol. 1(2), pp. 010-017, December, 2014. © www.premierpublishers.org. ISSN: 0278-5125x
Research Article

2. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
Rajappa et al. 010
Experimental Details
Mild steel sample having the composition C= 0.05%, Mn
= 0.35%, P = 0.032%, S = 0.033% and the remainder
being Fe was selected. Coupons of rectangular
specimens of the size 5 x 1 x 0.1 cm were used for mass
loss measurements. For polarization measurements, the
working electrode was cut from mild steel and 1 cm2
was
exposed rest of the area was embedded in chemical
resistant epoxy resin. The samples were degreased with
the vapours of trichloro ethylene followed by mechanical
polishing with different grits sizes (200-1200) SiC papers.
The samples were rinsed with ethanol, followed by
distilled water. The polished samples were immersed in
50 mL of test solution maintained at 298 ± 1K. A R grade
chemicals and doubled distilled water were used for the
preparation of test solutions. Duplicate experiments were
performed in each case and the mean vales of the losses
in weight were recorded.
Mass loss measurements were carried out by weighing
the specimens before and after immersion 50 mL acid
solution at different time intervals in the absence and
presence of various concentration of ranitidine. Runs
were also done at 1M and 2M HCl concentrations and at
different temperatures.
The corrosion rate of mild steel was calculated using the
formula:
Where Vcorr = Corrosion rate (mg cm-1
h-1
), Δm = mass
loss (mg), S= surface area (cm
2
) and t= time (h). The
percentage inhibition efficiency (%IE) was calculated
using the relation:
Where Vcorr is the corrosion rate of mild steel in acid
solution and V1
corr is the corrosion rate of mild steel in
acid solution containing inhibitor.
A conventional three- electrode cell consisting of mild
steel as working electrode with exposed surface area of
1 cm
2
was employed for polarization studies. Saturated
calomel and platinum were used as reference and
counter electrodes respectively. The anodic and cathodic
polarized potentials were measured under galvanostatic
condition using Equiptronic digital potentiometer (Model
EQ 600). The Tafel lines were constructed by plotting a
graph of potentials against log(current density).The
corrosion current density (Icorr) was determined by
extrapolating the cathodic and anodic Tafel lines. Using
the corrosion current density, the %IE was calculated
using the relation:
Where Icorr is the corrosion current of mild steel in acid
solution and I1
corr is the corrosion current of mild steel in
acid solution containing inhibitors.
The adsorption of ranitidine was confirmed by FTIR
spectrum. The mild steel specimens was immersed in
test solution for a period of 3 hours, the specimens were
taken out and dried. The surface film was scratched
carefully and its FTIR spectra were recorded using
Nicolet Avtar FT-IR instrument.
The ranitidine compound was used for corrosion
inhibition studies. The structure of the compound was
given in the figure 1.
Figure 1. Structure of Ranitidine
Chemical name
2-(((5-((dimethylamino)methyl)-
2furanyl)methyl)thio)ethyl)-N'-methyl-2-nitro-1,1-ethene-
diamine.
Ranitidine inhibitor supplied from Rantac tablet Supplied
by Allied Chemicals & Pharmaceuticals (P) LTD. Rantac
150 mg Tablet contains Ranitidine hydrogen chloride IP
168 mg Equivalent to Ranitidine 150 mg and coated with
orange colour film. The film was clearly removed and
resulting white colour Ranitidine hydrogen chloride is
dissolved in dilute hydrochloric acid. If any insoluble film
is present, this is removed by filtration. Hydrochloric acid
solution containing ranitidine hydrogen chloride was used
for the corrosion inhibition studies.
RESULTS AND DISCUSSION
Mass loss measurements
Table 1 showed the corrosion rate (Vcorr) and percentage
inhibition efficiency (%IE) of varying concentration of
ranitidine in 1M HCl & 2 M HCl at 303 K. The results
showed that mass loss decreased and the percentage
inhibition efficiency was increased with increasing
ranitidine concentration in both acid concentrations.
However maximum %IE was found to be 95.36 and 94.20
in 1M HCl & 2 M HCl respectively at 2 x 10
-3
mol dm
-3
ranitidine concentration. Further increase in the inhibitor
concentration no change in the %IE and 2 x 10-3
mol dm-3
was considered as optimum inhibitor concentration.
Vcorr =
Δm
St
%IE =
V1
corr
Vcorr
1- X 100
%IE =
I1
corr
Icorr
1- X 100
H3C
N
CH3
O
S
N
H
NH
H3C
N+
O
O-

3. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
Int. Res. J. Chem. 011
Table 1. Corrosion rate & %IE of mild steel in 1M HCl and 2M HCl at 303K.
Inh. Conc.[M] 1 M HCl 2 M HCl
Corrosion rate
(mg cm
-1
h
-1
)
%IE Corrosion rate
(mg cm
-1
h
-1
)
%IE
0 0.01915 ---- 0.02205 ----
2.5x10
-4
0.00532 72.29 0.00682 69.07
5x10-4
0.00208 90.18 0.00306 86.12
10x10-4
0.00114 94.24 0.00156 92.92
20x10-4
0.00076 95.36 0.0014 93.65
Figure 2. Tafel plots for mild steel in 1 M HCl in presence of different concentration of inhibitor at 303K.
Electrochemical method.
Polarization measurements:
Anodic and cathodic polarized potentials were recorded
in the absence and presence of inhibitor for mild steel at
303 K. Figure 2 gave the anodic and cathodic polarization
curves for mild steel in presence and absence of inhibitor
in 1M HCl. It is evident from the figure; the anodic and
cathodic curves are polarized nearly to the same extent it
indicated that the inhibitor was mixed type of corrosion
inhibitor (Chaudhary RS (1999)).
The plots showed that, cathodic & anodic curves tended
towards a continuous linear shape at lower current
-0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2
-6.5
-6.0
-5.5
-5.0
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
Log(i)in
A.Cm
2
E(Potential) in volts
0.00025 M
1M HCl
0.0005M
0.0005M
M
MMMM
MMMm
mM
0.001 M
0.002 M
0.003M

4. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
Rajappa et al. 012
Table 2. Corrosion parameters obtained from polarization method for mild steel in 1M & 2M HCl containing various
concentration of inhibitor at 303K.
Concentrati
onof Acid(M)
Conc
n
.
(mol dm-3
)
-Ecorr
(V)
Icorr
(A cm-2
)
ba
(V/dec)
Bc
(V/dec)
C.R.
(mm/yr) %IE
1M HCl
0 0.465 4.87x10
-3
0.253 0.145 57.8 -
2.5x10-4
0.476 2.78x10-3
0.311 0.149 32.9 43.00
5x10-4
0.482 1.87x1 0.305 0.176 21.9 62.00
10x10-4
0.474 1.04x10-3
0.283 0.135 12.3 79.00
20x10
-4
0.480 2.72x10-4
0.233 0.157 3.2 94.00
2M HCl
0 0.462 5.20×10-3
0.222 0.191 69.0 -
2.5x10-4
0.486 3.56x10-3
0.321 0.209 42.0 31.50
5x10-4
0.495 2.66x10-3
0.308 0.195 31.0 48.80
10x10-4
0.464 1.54x10-3
0.297 0.161 16.4 72.00
20x10-4
0.482 7.90x10-4
0.267 0.169 6.0 90.00
Figure 3. Nyquist plots for mild steel in 1M HCl in the absence and presence of
different inhibitor concentrations at 303K.
densities. This effect could result from the formation of an
organometallic protective layer on the electrode surface
and decreased electron transfer rate at the interface.
Thus the cathodic reaction would act substantially under
charge transfer control. The protection action can
attributed to the nitrogen and sulphur atoms can donate
the lone pair of electrons to the metal surface to adsorb
more easily and hence reduce the rate of corrosion.
The corrosion parameters obtained by polarization
method for mild steel were presented in the table 2. The
results showed that the maximum inhibition efficiency
was found to be 94.00% and 90.00% in 1M HCl and 2M
HCl respectively at 20 x 10
-4
M concentration of inhibitor
at 303 K. The percentage inhibition efficiency obtained
from the polarization technique was in good agreement
with those obtained from the mass loss experiment.
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
5
0
-5
-10
-15
-20
-25
Z''
(Ohm.
cm2)
Z'(Ohm.cm2)
1M Hcl
0.00025M
0.0005M
0.001M
0.002M
0.003M

5. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
Int. Res. J. Chem. 013
Figure 4. Electrical Equivalent circuit
model used to fit impedance data.
Table 3. Electrochemical impedance parameters for mild steel in 1M and 2M HCl in the presence and
absence of inhibitor at 303 K.
Concentration
of Acid(M)
Concn
.
(M)
Rs (ohm) Rp (ohm) CPE (F) %IE
1M HCl
0 1.65 12.5 6.91 x 10
-5
-
2.5x10-4
1.71 22.9 4.68x 10-5
45.00
5x10-4
1.64 30.5 3.58 x 10-5
59.00
10x10-4
1.50 54.6 2.13 x 10-5
77.00
20x10-4
1.16 85 1.62 x 10-5
92.00
2M HCl
0 1.34 13 7.10×10
-5
-
2.5x10
-4
1.42 16.4 3.99 x 10
-5
20.00
5x10
-4
1.85 30 3.38 x 10
-5
56.00
10x10
-4
1.14 41.1 3.07 x 10
-5
76.00
20x10-4
1.27 88 1.45 x 10
-5
85.20
Electrochemical Impedance method
Electrochemical impedance measurements were carried
out using an electrochemical system Frequency
Response Analyzer (FRA). The results can be interpreted
in terms of the equivalent circuit of the double layer,
which has been used to model the iron-acid interface .
The corrosion behavior of mild steel in acid solution in the
presence of ranitidine was investigated by
Electrochemical impedance spectra (EIS) at 303 K.
Figure 3 and 4 show a typical set of Nyquist plots for mild
steel in 1M HCl in the absence and presence of various
concentrations of inhibitor. The impedance response of
mild steel in uninhibited HCl is significantly changed after
addition of ranitidine to the corrosive medium. The
semicircle radii depend on the additive concentration.
The diameter of the capacitive loop increased with
increasing concentration of ranitidine. Resistance
polarization (Rp) is inversely proportional to the corrosion
current and was used to calculate the %IE from the
following equation
Where, R1
p, and R1
p,o are the polarization resistances with
and without the additives, respectively. Impedance
parameters for mild steel in 1M and 2M HCl with and
without inhibitors were presented in table 3. The Rp &
%IE values increased with additive concentration and the
capacitance values (CPE) decreased, indicating the
formation of a surface film.
Effect of Temperature
The effect of temperature on corrosion rate and
percentage inhibition efficiency of the inhibitor was
carried out at three different temperatures by mass loss
method. Table 4 shows the values of corrosion rate &
%IE in 1M HCl solution containing optimum concentration
of the inhibitor. The results revealed that the corrosion of
mild steel increased in acid solutions and also the acid
containing inhibitor with increase in temperature from 303
K, 313 K and 323 K. This is due to the desorption of
inhibitor molecules from the metal surface and increase
in transport action of H
+
ions to the electrode surface and
subsequent reduction of H+
ions.
The values of activation energy (Ea) was calculated from
the slope of the straight line obtained by plotting log V
verses 1/ T according to the Arrhenius equation:
V= Aexp (-Ea / RT).
C
RsRp
W
%IE =
Rp,i – R1
p,o
Rp,i
x 100

6. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
Rajappa et al. 014
Figure 5. Arrhenius plots of corrosion rate in absence and presence of optimum concentration of
inhibitor for mild steel in1 M HCl.
Table 4. Corrosion rate and percentage inhibition efficiency of mild steel in 1M HCl at different temperatures.
Temperature (K)
Corrosion Rate (mg cm
-2
h
-1
)
%I.EBlank Inhibitor
303K 0.0190 0.00125 95.36
313K 0.0454 0.0041 90.81
323K 0.00965 0.0107 88.90
Ea (kJ mol-1
) 15.238 21.095
The Ea values were given in the table 4, it was found that
for inhibited systems were higher than for the uninhibited
system. Due to this increase in the activation energy the
dissolution decreased. However with increase in
temperature there was an appreciable decrease in the
adsorption of the inhibitors on the metal surface and a
corresponding rise in the corrosion rate occurred.
Adsorption isotherm
The values of surface coverage  were evaluated using
the values of % IE resulted from the mass loss in 1M HCl.
Figure 6 shows a plot of log(/1- ) v/s log C gave a
straight line, it indicate that corrosion control take place
via adsorption process. The adsorption of the inhibitor
molecule on mild steel surface obeys Langmuir
adsorption isotherm. The adsorption of ranitidine
molecules formed a barrier, which prevented the contact
of metal with electrolyte. Hence the corrosion rate was
reduced.
Thermodynamic parameters
Thermodynamic parameters such as enthalpy of adsorption

7. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
Int. Res. J. Chem. 015
Log C
Figure 6. Langmuir adsorption isotherm for mild steel in 1M HCl containing various concentration of inhibitor from mass
loss study.
Figure 7. FTIR spectrum of ranitidine compound scrapped from the corroded steel surface.
(∆H0
ads), free energy of adsorption (∆G0
ads) and entropy of
adsorption (∆S0
ads) for the adsorption process were
calculated using the following equations these values
were presented in table 5.
Enthalpy of adsorption: ∆H
0
ads – RT,
Free energy of adsorption: G
o
ads= -2.303 RT log (55.5K)
K = 1 / C X  / (1- )
Where ‘K’ is adsorption constant, ‘C’ is the concentration
of the inhibitor and ‘’ be the surface coverage.
Entropy of adsorption (So
ads) : Go
ads = Ho
ads - TSo
ads
Table 5. Thermodynamic parameters for corrosion of
mild steel in presence of optimum concentration of
inhibitor in 1M HCl.
Thermodynamic Values
Parameters (kJ mole
-1
)
∆Hads -20.492
∆Gads -7.758
∆Sads 0.0932

8. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
Rajappa et al. 016
Figure 8. FTIR spectrum of Ranitidine compound.
The negative values of enthalpy of adsorption and free
energy of adsorption and positive value of entropy of
adsorption indicated the spontaneous adsorption of an
inhibitor on the mild steel surface. The positive ∆Sads
value suggested that the adsorption of an inhibitor is an
exothermic process and is always accompanied by
increase of entropy. It was interpreted that the adsorption
of an organic compound which was accompanied by
desorption of water molecules from the metal surface.
Fourier Transform Infrared Spectroscopic studies
(FTIR)
FTIR studies was undertaken to confirm the adsorption of
inhibitor on mild steel surface. Figure 7 & 8 shows the
FTIR spectra of the pure sample of ranitidine compound
and the scrapped compound from the corroded metal
surface. The characteristics peaks at 3260.50, 3199.35
and 3103.46 cm
-1
attributed to the stretching vibration of
the –N-H bond of the amino group. These peaks do not
appear in the IR spectrum of the scrapped compound.
The disappearance/modification of these bands indicates
that the formation of chemical bonds between nitrogen
atom of the compound and the metal surface. The
available data indicated a wide range of values
concerning peaks at different domain in 3199.35 to
2467.64, 1700 to 1370, 1200 to 1000 and 800 to 450 cm-
1
. The IR spectrum of scrapped compound shows several
modifications in these four domains. These data indicated
the participation of functional groups in the metal /
inhibitor interactions (Morris RT, Boyd.(1973).
CONCLUSION
The chemical and electrochemical corrosion studies
show that ranitidine is found to be effective corrosion
inhibitor for mild steel in HCl acid solution. The maximum
percentage inhibition efficiency is found to be 95.53 % at
2 x 10-3
M inhibitor concentration in 1 M HCl at 303 K.
The studies revealed that the inhibitor controls the rate of
both anodic & cathodic reactions and acts as a mixed
type inhibitor. The corrosion control takes place via
adsorption process and obeys Langmuir’s adsorption
isotherm.
The thermodynamic parameters indicate the
spontaneous adsorption of inhibitor on the mild steel
surface and control the corrosion to a greater extent.
FTIR studies shows the interaction of ranitidine with
metal surface through hetro atoms present in the
compound and form a barrier between the metal –
solution interface and isolate the metal from the corrosive
medium. Ranitidine compound is soluble in water and
non toxic and can be used as effective corrosion inhibitor
for mild steel in acid medium.

9. Chemical and electrochemical studies of ranitidine as a corrosion inhibitor for mild steel in hydrochloric acid medium
Int. Res. J. Chem. 017
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Accepted 29 November, 2014.
Citation: Rajappa SK, Praeen BM, Venkatesha TV
(2014). Chemical and electrochemical studies of
ranitidine as a corrosion inhibitor for mild steel in
hydrochloric acid medium, International Research Journal
of Chemistry 1(2): 010-017.
Copyright: © 2014 Rajappa et al. This is an open-access
article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium,
provided the original author and source are cited.