Hindawi Publishing Corporation
Journal of Chemistry
Volume 2013, Article ID 835365, 9 pages
http://dx.doi.org/10.1155/2013/835365
Research Article
Corrosion Inhibition of Mild Steel in Acidic Media by
5′-Phenyl-2′,4′-dihydrospiro[indole-3,3′-pyrazol]-2(1H)-one
M. Jannathul Firdhouse and D. Nalini
Department of Chemistry, PSGR Krishnammal College for Women, Tamilnadu, Coimbatore 641004, India
Correspondence should be addressed to M. Jannathul Firdhouse; k�rdhouse�yahoo.com
Received 7 December 2011; Accepted 24 May 2012
Academic Editor: Sakir Erkoc
Copyright © 2013 M. J. Firdhouse and D. Nalini. is is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
e inhibition effect of 5
�
-phenyl-2
�
,4
�
-dihydrospiro[indole-3,3
�
-pyrazol]-2(1H)-one (SPAH) on mild steel corrosion in 1 M HCl
and 0.5 M H
2
SO
4
has been studied by weight loss, effect of temperature, electrochemical techniques, and quantum chemical studies.
e inhibition efficiency increases with increasing concentration of inhibitor but decreases with increase in temperature. e
adsorption of inhibitor on mild steel surface has been found to obey Langmuir and Temkin’s adsorption isotherm. Potentiostatic
polarization results revealed that SPAH acts as mixed type inhibitor. e values of activation energy (
), free energy of adsorption
(Δ
∘
), enthalpy of adsorption (Δ), and entropy of adsorption (Δ) were calculated. Surface analysis (SEM) was also carried out to
establish the mechanism of inhibitor on mild steel corrosion in acid medium. Quantum chemical studies using DFT were employed
to explain the experimental results obtained in this study and to further give insight into the inhibition action of SPAH on the mild
steel surface.
1. Introduction
e corrosion of metals remains a worldwide scienti�c prob-
lem as it affects the metallurgical, chemical and oil industries.
e increasing interest in the manufacture of hydrochloric
acid has created the need for obtaining information on the
corrosion resistance of mild steel to hydrochloric acid attack
[1]. Acids are widely used in industries such as pickling,
cleaning, and decaling. Because of their aggressiveness,
inhibitors are used to reduce the rate of dissolution of metals.
Compounds containing nitrogen, sulphur, and oxygen have
been reported as excellent inhibitors [2–7].
In the present work, electrochemical and nonelectro-
chemical techniques were used to investigate the inhibition of
mild steel corrosion by 5′-phenyl-2′,4′-dihydrospiro[indole-
3,3′-pyrazol]-2(1H)-one (see Figure 1) with respect to
inhibitor concentration and temperature on the inhibitor
efficiency (%) in 1 M hydrochloric acid and 0.5 M sulfuric
acid medium. Quantum chemical calculation using DFT was
employed to explain the experimental results obtained in this
study and to further give insight into the inhibition action of
SPAH on the mild steel surface.
2. Experimental
Mild steel specimen of the size (3.5 × 1.5) − 0.5 was used for
measurement of weight loss study. e strips were mechani-
cally polished using 1/0, 2/0, 3/0, and 4/0 emery papers and
�nally degreased with the organic solvent trichloroethylene
and dried before use. 1 M HC1 and 0.5 M H
2
SO
4
solutions
were prepared by the dilution of analytical grade HC1
and H
2
SO
4
with double-distilled water, respectively. e
concentration range of inhibitor used was (1 ppm, 3 ppm,
5 ppm, 7 ppm, and 9 ppm) in both the acids. e compound
has been synthesized in 3 steps. e structural formula of the
investigated compound is given below.
Weight loss measurements were carried out by weighing
the specimens in triplicate before and aer immersion in
100 mL acid solution for 3 hours in the absence and presence
of inhibitor for various concentrations.
Electrochemical measurements were carried out in a
glass cell with a capacity of 100 mL. A platinum electrode
and a saturated calomel electrode were used as a counter
electrode and reference electrode, respectively. e mild steel
electrode was then placed in the test solution (uninhibited