The document investigates the inhibition effect of hydralazine hydrochloride on corrosion of mild steel in hydrochloric acid solution. Electrochemical measurements including polarization and electrochemical impedance spectroscopy indicate that hydralazine hydrochloride acts as a mixed-type inhibitor, reducing both the anodic dissolution and cathodic hydrogen evolution reactions. Maximum inhibition efficiency of around 72% was achieved. Thermodynamic analysis revealed that the inhibitor is adsorbed onto the mild steel surface via chemisorption. Scanning electron microscopy showed the formation of a protective film on the steel surface when the inhibitor was present.

1. The inhibition effect of hydralazine hydrochloride on corrosion of mild steel in hydrochloric acid solution
IRJCCS
The inhibition effect of hydralazine hydrochloride on
corrosion of mild steel in hydrochloric acid solution
BM Prasanna1*
, BM Praveen2
, Narayana Hebbar3
, TV Venkatesha4
, HP Sachin5
, KG
Chandrappa6
and SB Abd Hamid7
1*
Department of Chemistry, STJIT, Ranebennur-58115,Karnataka, India.
2
Department of Chemistry, Srinivas School of Engineering, Mukka-575021, Mangalore, India.
3
Department of Chemistry, Bearys Institute of Technology, Konaje-574199, Mangalore, India.
4
Department of Studies in Chemistry, Kuvempu University, Shankaraghatta,-577451, India.
5
Departement of chemistry, JNNCE, Shimoga, India
6
Department of Chemistry, Govt Engineering College, Ramanagara
7
Nanotechnology and Catalysis Research center, IPS Building, University of Malaya-50603, Kuala Lumpur,
Malayasia.
*Corresponding Author: E-mail: prasannastjit2gmail.com
The inhibition effect of the Hydralazine hydrochloride for mild steel corrosion in 1M HCl has
been investigated. Polarization measurement indicates that the Hydralazine hydrochloride
act as mixed-type inhibitor, which gives a maximum inhibition efficiency around 72 %.
Electrochemical impedance spectroscopy was used to investigate the mechanism of
corrosion inhibition gives around 76 % due to the formation of electrical double layer.
Thermodynamic parameter such as ΔG
0
ads value was obtained as -30.22 KJ/mol indications
that inhibitor shows its inhibition effect due to the chemisorptions process. Scanning
electron microscopic images gives a visual idea about the formation of the protective film
on the mild steel surface to reduce the corrosion rate. So that the Hydralazine hydrochloride
acts as an efficient mixed type corrosion inhibitor for mild steel corrosion in acid media.
Keywords: Hydralazine hydrochloride, mild steel, inhibitor, EIS, SEM, adsorption isotherm
PACS: 68.43.Mn
INTRODUCTION
Mild steel is an important category of material due to
their wide range of industrial and structural
applications. It is used in many industries under acids
for pickling, descaling, acid cleaning and other
applications. Due to their high corrosive nature acids
may cause damage to the system components. The
use of corrosion inhibitors were used to protecting
metals against corrosion (Eddy et al., 2008). The use of
organic molecules as inhibitors to control the acid
corrosion of steel is an effective and flexible method
(Abd El-Maksoud et al., 2005). In recent times much
attention is being given in developing nature friendly
inhibitors. Drugs and plant extracts are having been
reported to be good corrosion inhibitors (Pongsak et.,al
2010, Chauhan et al.,2007).Inhibitors are organic
molecules having hetero atoms like P, S, N, S, and 
electrons through which the inhibitor molecule interact
with the metal surface and get adsorbed (Ahamad et
al.,2010, Quraishi et al.,2010).The extent of adsorption
depends on physico-chemical properties of the inhibitor
molecule like functional group, geometry, electronic
density at hetero atom,  electrons, and planarity.
Hydralazine hydrochloride is an anti hypertensive drug
molecule with planar structure, which contains electron
rich Nitrogen atom and  bonds might be in favors of
its adsorption on the metal surface which gives a scope
for its study as a potential corrosion inhibitor. Present
work reveals that the inhibitive actions of Hydralazine
hydrochloride for mild steel in 1M HCl have been
studied by electrochemical methods, adsorption
consideration and scanning electron microscopy
methods.
Experimental Section
Mild steel strips were used to carry out for all the
corrosion study experiments. Mild steel Strips of
Review
International Research Journal of Chemistry and Chemical Sciences
Vol. 2(2), pp. 021-025, July, 2015. © www.premierpublishers.org. ISSN: 0278-5125.

2. The inhibition effect of hydralazine hydrochloride on corrosion of mild steel in hydrochloric acid solution
100
i
ii
η o
corr
corr
o
corr
P 


Prasanna et al. 021
Figure 1. Molecular structure
of the Hydralazine
hydrochloride.
-0.7 -0.6 -0.5 -0.4 -0.3
-5.5
-5.0
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
f
e
d
c
b
a
logi(Acm
2
)
E Vs SCE (V)
a- Blank
b- 100 ppm
c- 200 ppm
d- 300 ppm
e- 400 ppm
f- 500 ppm
Figure 2. Tafel Plots for mild steel in 1 M HCl in
presence of different Concentration of Inhibitor.
dimensions of 4 cm x 1 cm x 0.1 cm were abraded with
emery papers from grade no.80 up to 2000, washed
thoroughly with double distilled water, degreased with
acetone and dried at room temperature. This mild steel
strip with an exposed area of 1 cm
2
(rest is covered
with Araldite resin) were used for electrochemical
measurements. The corrosive media of 1M HCl
solutions were prepared by using AR grade HCl and
double distilled water. The IUPAC name of the
Hydralazine hydrochloride is 1-Hydrazinophthalazine
monohydrochloride. The molecular structure of the
inhibitor as in the Figure 1.
Molecular weight of the 1-Hydrazinophthalazine
monohydrochloride is 196.64 and which is first
dissolved into DMF solution then miscible into HCl. This
inhibitor is less toxic because it is free from cyanide,
chromate group in the molecule. So that this inhibitor
having less toxic in nature. Inhibitor solution was
prepared by weighting 100, 200, 300, 400, and 500 mg
of inhibitor per 1 ltr of 1M HCl solution.
The electrochemical measurements were carried out by
using CHI608D electrochemical work station
(manufactured by CH Instruments, Austin, USA). The
cell consists of three electrodes namely, the working
electrode (steel), counter electrode (platinum) and
reference electrode (Ag/AgCl electrode). Before each
electrochemical measurement, the working electrode
was allowed to stand for 30 min in the test solution to
establish steady state open circuit potential (OCP).
In Tafel measurements, potential-current curves were
recorded at a scan rate of 0.001 V s
-1
in the potential
range obtained by adding -0.2 and +0.2 V to the open
circuit potential (OCP) value. The corrosion parameters
such as corrosion potential (Ecorr), corrosion current
density (icorr) cathodic Tafel slope (βc) and anodic Tafel
slope (βa) were calculated from the software installed in
the instrument.
Impedance measurements were carried out by using
an AC signal with amplitude of 5 mV at OCP in the
frequency range from 100 kHz to 10 mHz. The
impedance data were fitted to the most appropriate
equivalent circuit by using Z-Simp Win 3.21 software.
Mode of adsorption can be studied by the adsorption
parameters, while fitting electrochemical impedance
data fit into an appropriate adsorption isotherm model.
Present work obeys Langmauir adsorption isotherm.
Surface morphology of the mild steel strip was studied
by scanning electron microscopy in absence and
presence of inhibitor in acid media.
RESULT AND DISCUSSIONS
Tafel Polarization measurement
The anodic and cathodic polarization curves of mild
steel in 1M HCl in the presence of different
concentrations of Hydralozine hydrochloride is given in
Figure 2. The corrosion current densities were
calculated by extrapolation of the linear parts of these
curves to the corresponding corrosion potential. Table
1 gives the electrochemical corrosion kinetic
parameters such as corrosion potential (Ecorr), corrosion
current density (icorr), cathodic Tafel slope (βc), anodic
Tafel slope (βa) and inhibition efficiency (ηp) obtained
by extrapolation of the Tafel lines.

3. The inhibition effect of hydralazine hydrochloride on corrosion of mild steel in hydrochloric acid solution
Int. Res. J. Chem. Chem. Sci. 022
Table 1. Tafel and AC impedance results for the corrosion of mild steel in 1 M HCl in the presence of different
concentrations of Hydralozine hydrochloride
Inhib.
con
n
(ppm)
Ecorr
(V)
I corr
(A cm
-2
)
Corrosion
rate
(mpy)
βc
mV/de
cade
βa
mV/de
cade
% ηp Rp
Ωcm
2
Cdl
( µF
cm
-2
)
% ηz Surface
coverage
(θ)
Blank -0.51 0.51 36.43 -5.701 5.888 - 6.094 5558 - -
100 -0.48 0.48 15.83 -6.014 7.172 50.0 12.01 3772 49.2 0.492
200 -0.49 0.49 14.53 -7.020 7.569 53.8 12.55 1267 51.5 0.515
300 -0.50 0.50 11.78 -6.624 7.143 60.2 15.48 0582 60.7 0.607
400 -0.52 0.52 11.50 -6.805 7.376 66.7 20.85 0557 70.77 0.707
500 -0.50 0.50 11.23 -7.342 7.474 72.0 25.57 0470 76.1 0.761
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
-1
-2
-3
-4
-5
-6
-7
500 ppm
400 ppm
300 ppm200 ppm
100 ppm
1M H cl
ZImg
......ohmcm
2
Zreal
.......ohm cm
2
Figure 3. Nyquist plot for mild steel in absence
and presence of inhibitor.
Where, iºcorr and icorr are corrosion current in the
absence and presence of inhibitor, respectively.
In acidic solutions, the anodic reaction of corrosion is
the passage of metal ions from the metal surface into
the solution and the cathodic reaction is the discharge
of hydrogen ions to produce hydrogen gas or to reduce
oxygen. The inhibitor may affect either the anodic or
the cathodic reaction, or both (Musa et al., 2010).
From the Figure 2. It is clear shows that with the
addition of inhibitor to 1M HCl affects both the anodic
and cathodic parts of the curve. This indicates that the
addition of inhibitor to acid solution reduces the anodic
dissolution of metal and also impedes the cathodic
hydrogen evolution reaction (Prasanna et al., 2014).
Table 1. shows that there is a corrosion current density
( icorr) decreased with increase in inhibitor
concentration and displacement of corrosion potential
(Ecorr) of toward positive direction which suggests that
Hydralazine hydrochloride behaves as a very good
corrosion inhibitor for mild steel in 1M HCl solution. If
the displacement in Ecorr is more than ±85 mV/SCE with
respect to the corrosion potential of the blank, the
inhibitor can be considered as cathodic or anodic type
(Jayaperumal et al.,2010).If the change in Ecorr is less
than 85 mV, the corrosion inhibitor can be regarded as
a mixed type inhibitor. The maximum displacement in
our study was less than 20 mV, this indicates,
Hydralozine hydrochloride acts as a mixed type
inhibitor. The increasing of cathodic tafel slope (βc) and
anodic tafel slope (βa) increasing with the increasing
inhibitor concentration is the indication of Hydralazine
hydrochloride inhibits both anodic and cathodic
reactions.
Electrochemical impedance spectroscopy(SEM).
The impedance spectra (Nyquist plots) of mild steel in
1M HCl containing various concentrations of
Hydralazine hydrchloride inhibitor at 303K temperature
is as shown in Figure 3. The experimental results of
Electrochemical Impedance spectroscopic (EIS)
measurements obtained for the corrosion of mild steel
in 1M HCl in the absence and presence of various
concentration of Hydralazine hydrochloride is given in
Table 1. Measured impedance data were analyzed by
fitting in to an equivalent circuit. Table 1 Consists of
Polarization resistances (Rp), double layer capacitance
(Cdl) and inhibition efficiency (η) can be calculated by
the fallowing equation.
η =
Where Rp(inhibitor) and Rp are the charge-transfer
resistance in the presence and absence of inhibitor
respectively. From the Figure 3. Nyquist’s plot consist
of depressed semicircles with center under real axis.
The size of the semicircle increases with increase in
inhibitor concentration. The impedance diagrams
obtained are not perfect semicircles because of the
frequency dispersion of interfacial impedance, which

4. The inhibition effect of hydralazine hydrochloride on corrosion of mild steel in hydrochloric acid solution
Prasanna et al. 023
0.2 0.4 0.6 0.8 1.0 1.2 1.4
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
C/
Concentration (milli moles)
Figure 4. Langmauir adsorption isotherm.
Table 2. Adsorption parameters
Adsorption
isotherm
Model
R
2
Kads ΔGads
Kj/mol
Langmauir 0.976 2923 -30.22
(A) (B).
Figure 5. SEM Images for corrosion of mild steel (A)
in the absence and (B) presence of inhibitor
has been attributed to the roughness and non-
homogeneity of the solid surface and also to the
adsorption of inhibitor (Praveen et al.,2009).
From Table 1.The decrease in Cdl on the addition of
inhibitor to the acid solution indicates the formation of a
protective layer and which covers the surface of the
electrode. The adsorption of Hydralazine hydrochloride
on the mild steel surface decreases Cdl because they
displaced the water molecules and other ions that were
originally adsorbed on the surface. With higher
concentration of inhibitor, either the thickness of the
protective layer or the surface coverage by Hydralazine
hydrochloride increased due to more inhibitor
molecules chemically adsorbed on the mild steel
surface.
Adsorption Parameters
Inhibition effect of Hydralazine hydrochloride is
attributed due to the adsorption of inhibitor on to the
surface of mild steel. This adsorption creates a
protective film on the metal surface. The degree of
surface coverage (θ) for inhibitor was obtained from
electrochemical impedance spectroscopic data as
shown in Table 1. Different adsorption isotherms such
as Temkin, Freaundlich and Langmuir, were tested in
order to find the best fit adsorption isotherm for
adsorption of Hydralazine hydrochloride on to the
surface of mild steel. While consider the linear
regression coefficient of Langmuir adsorption isotherm
is found more close to unity as R
2
=0.976 hence, was
found best fit as shown in Figure 3.Hence adsorption of
Hydralazine hydrochloride molecule on mild steel
surface in 1M HCl solution obeys the Langmauir s
adsorption isotherm.
According to the Langmauir adsorption isotherm, free
energy of adsorption(ΔG
0
ads) can be calculated by
using the following expression,
)5.55ln(0
adsads KRTG 
Where Kads can be calculated by the intercept of the
straight line in adsorption isotherm plot as shown in the
figure 4. The computed Kads and (ΔG
0
ads) values were
reported in Table 2.
In our studies ΔG
0
ads values are found to be around
30.22 kJ mol
-1
and these data shows that Hydralazine
hydrochloride adsorbed on the metal surface
predominately by chemisorptions (Prasanna et al.,
2015).

5. The inhibition effect of hydralazine hydrochloride on corrosion of mild steel in hydrochloric acid solution
Int. Res. J. Chem. Chem. Sci. 024
Scanning electron microscopy (SEM):
SEM micrographs were recorded for mild steel in
absence and presence of optimum inhibitor
concentration of 100 mg/l in 1M HCl solution. From the
Figure 5. SEM micrograph revealed that the surface
morphology was strongly damaged in the absence of
the inhibitor, but in the presence inhibitor damage was
considerably diminished, which confirmed the high
efficiency of Hydralazine hydrochloride.
CONCLUSIONS
The Hydralazine hydrochloride was found to be a good
corrosion inhibitor for mild steel in 1M HCl. Inhibitor
acts as a mixed type and inhibitive property attributed
due to the adsorption of inhibitor on the surface of
metal, this adsorption process obeys Langmauir
adsorption isotherm model by chemically.SEM
micrographs clears that the formation of protective film
over the surface of mild steel to reduce the corrosion
process.
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Accepted 28 May, 2015.
Citation: Prasanna BM, Praveen BM, Hebbar N,
Venkatesha TV, Sachin HP, Chandrappa KG, Abd
Hamid SB (2015). The inhibition effect of hydralazine
hydrochloride on corrosion of mild steel in hydrochloric
acid solution. International Research Journal of
Chemistry and Chemical Sciences, 1(1): 021-024.
Copyright: © 2015 Prasanna et al. This is an open-
access article distributed under the terms of the
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medium, provided the original author and source are
cited.