Mild steel corrosion inhibition by aqueous extract of Hyptis Suaveolens leaves
Int J Ind Chem (2014) 5:5
DOI 10.1007/s40090-014-0005-9
RESEARCH
Mild steel corrosion inhibition by aqueous extract of Hyptis
Suaveolens leaves
P. Muthukrishnan • B. Jeyaprabha •
P. Prakash
Received: 23 October 2012 / Accepted: 19 December 2013 / Published online: 20 February 2014
Ó The Author(s) 2014. This article is published with open access at Springerlink.com
Abstract Hyptis suaveolens leaf extract (HSLE) as
corrosion inhibitor in 1 M H2SO4 was evaluated using
mass loss measurement as well as potentiodynamic
polarization and electrochemical impedance spectroscopy
measurements. The extract was found to efficiently
inhibit the corrosion process in 1 M H2SO4 and inhibition efficiency increased with increasing extract concentration. Maximum inhibition efficiency of HSLE in 1 M
H2SO4 was found to be 95 %. The potentiodynamic
polarization results revealed that HSLE acted as mixedtype inhibitor. The adsorption of the studied inhibitor on
mild steel obeyed Langmuir adsorption isotherm. The
nature of protective film formed on the surface of the
mild steel was confirmed by FT-IR, XRD and SEM
techniques. This study clearly shows the efficiency of
HSLE for control of mild steel corrosion in 1 M H2SO4
solutions.
Keywords Mild steel Corrosion inhibition Hyptis
suaveolens XRD Polarization SEM
P. Muthukrishnan P. Prakash (&)
Department of Chemistry, Thiagarajar College,
Madurai 625009, Tamilnadu, India
e-mail:
P. Muthukrishnan
e-mail:
B. Jeyaprabha
Department of Civil Engineering, Fatima Michael College of
Engineering and Technology, Madurai 625020, Tamilnadu,
India
e-mail:
Introduction
Mild steel is a familiar material employed widely in a
variety of industries. But the main problem of using mild
steel is its dissolution in acidic solutions. In various
industrial processes, acid solutions are commonly used for
removal of rust and scale. Use of inhibitors in these processes to prevent metal dissolution is very common [1–3].
Most of the well-known acid inhibitors are organic compounds containing nitrogen, sulfur, oxygen, heterocyclic
compounds with a polar functional group and conjugated
double bond [4–7]. These compounds are adsorbed on the
metallic surface and block the active corrosion sites [8].
Most of the synthetic chemicals are costly, toxic to both
human being and the environment. To solve the above
defects, it is necessary to develop cheap, non-toxic and
environmentally friendly natural products as corrosion
inhibitors. These natural organic compounds are either
synthesized or extracted from aromatic herbs, spices and
medicinal plants. Plant extracts are an incredibly rich
source of naturally synthesized chemical compounds that
can be extracted by simple procedures with low cost and
are biodegradable in nature. The use of these natural
compounds extracted from leaves or seeds as corrosion
inhibitors have been reported by several authors [9–16].
Subramania et al. [17] studied the corrosion inhibition of
leaf extracts of curry leaves, henna leaves as well as
extracts from seeds of Jack fruit and tamarind on mild steel
corrosion in acidic solutions. Other than the plant extracts,
pure organic compounds extracted from natural products
such as piperine [18], Ellagic acid, tannic acid [19],
tryptamine [20], caffeine [21], Pennyroyal oil [22], amino
acids [23] and caffeic acid [24] have also been used for
inhibition of corrosion. Hyptis suaveolens is easily available in India. It is a medium-sized forest tree which has
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2 m height and belongs to Lamiaceae family. It is commonly known as Wilayati tulasi. It is also used for parasitical cutaneous diseases, infection of uterus, and as
sudorific in catarrhal condition, skin disease, headache,
stomachache and snuff to stop bleeding of the nose. The
extract of this plant contains numerous naturally environmental organic compounds. The genus of H. suaveolens is
known to contain significant amount of volatile oils, starch,
protein, tannins, saponins, alkaloids, flavonoids and glycosides [25, 26]. The leaf of the plant is biodegradable and
a renewable material.
The aim of this study was to investigate the corrosion of
mild steel in 1 M H2SO4 in the presence of H. suaveolens
leaf extract by mass loss, potentiodynamic polarization,
electrochemical impedance, FT-IR, XRD and SEM. In
addition, thermodynamic and kinetic data were evaluated.
Experimental
Materials preparation
Corrosion tests were performed on mild steel specimens
with the composition of C-0.05, Mn-0.6, P-0.36, Si-0.03
and the remaining of Fe. The specimens were mechanically
cut into size of 2.5 9 2.5 9 0.4 cm dimensions and abraded with different emery papers up to 4/0 grades. Then,
they were washed with acetone, dried at room temperature
and stored in moisture-free desiccator before corrosion
tests.
Preparation of Hyptis suaveolens leaf extract
About 15 g of dried and powdered leaves of H. suaveolens
was soaked in water and ethanol for 1 day. After 1 day, the
plant extract was boiled, cooled and then triple filtered.
Excess of ethanol was removed from vacuum distillation.
The amount of plant material extracted into solution was
quantified by comparing the weight of dried residue with
initial weight of the dried plant material before extraction.
The plant extract had a dark brown color. From the
respective stock solutions, inhibitor test solutions were
prepared in the concentration range 50–250 mg l-1.
Int J Ind Chem (2014) 5:5
water, dried and then weighed. The mass loss (DM) was
used to calculate the corrosion rate (CR) and the inhibition
efficiency (IE),
CRðmpyÞ ¼ 534 DM = D S T
ð1Þ
IE % ¼ ðML0 MLi Þ = ML0 100
ð2Þ
Here DM = (ML0-MLi), where ML0 and MLi are the
mass loss of mild steel in the absence and presence of
inhibitor, respectively, D is the density of the iron
(g cm-3), S is the area of the specimen in inch2, T is the
period of immersion in hours.
Electrochemical measurements
CH electrochemical analyzer Model 604D was used to
record Tafel polarization curve and Nyquist impedance
curve. The working electrode area of 0.5 cm2 mild steel
specimen was exposed to the acid solution. Platinum and
saturated calomel electrodes were used as counter electrode
and reference electrode, respectively. All electrochemical
measurements were carried out at 308 K using 100 ml of
electrolyte (1 M H2SO4) in stationary condition. Before
each potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy (EIS) measurement, the
electrode was immersed in test solution at open circuit
potential (OCP) for 10 min to be sufficient to attain a stable
state. Potentiodynamic polarization curves were recorded
from -200 to ?200 mVSCE, (versus OCP) with a scan rate
of 5 mV s-1. AC impedance spectra were recorded in the
same instrument for polarization study using three-electrode cell assembly. The real part and imaginary part of the
cell impedance were measured in ohms for various frequencies. The charge-transfer resistance (R (...truncated)
