Volume 17 Preprint 42
Corrosion inhibitive properties and adsorption behaviour of Bismuth oxy chloride on Mild steel & Aluminium in NaCl medium
S.Chitra, B.Anand, R.Vaidiyanathan,V.Balasubramanian
Keywords: Mild Steel; Corrosion; Adsorption; Bismuth oxy chloride; Antimicrobial agent
The corrosion inhibition of Aluminium & Mild steel in sodium chloride solution by Bismuth oxy chloride has been studied using weight loss & adsorption parameters techniques. The obtained result revealed that Bismuth oxy chloride performed well as corrosion inhibitor in both the materials. The inhibition efficiency increased with increasing inhibitor concentration .The maximum inhibition occurs through adsorption of the Inhibitor molecule on metal surface without modifying the mechanism of corrosion process. The adsorptions parameters were used to evaluate the inhibitive property of bismuth oxy chloride.
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Corrosion inhibitive properties and adsorption behaviour of
Bismuth oxy chloride on Mild steel & Aluminium in
S.Chitra1, B.Anand2, R.Vaidiyanathan1*,V.Balasubramanian2*
Center for Research, Department of Chemistry, Mahendra Engineering College,
Namakkal, Tamilnadu, India
Department of Chemistry, Mahendra College of Engineering, Salem, Tamilnadu, India
electrolyte. Oxidation reactions and metal
dissolution occur at the anodic site while cathodic
reactions are reductive . Equation 1 displays the
anodic dissolution of a metal.
The corrosion inhibition of Aluminium & Mild
steel in sodium chloride solution by Bismuth oxy
chloride has been studied using weight loss &
adsorption parameters techniques. The obtained
result revealed that Bismuth oxy chloride
performed well as corrosion inhibitor in both the
materials. The inhibition efficiency increased with
increasing inhibitor concentration .The maximum
inhibition occurs through adsorption of the Inhibitor
molecule on metal surface without modifying the
mechanism of corrosion process. The adsorptions
parameters were used to evaluate the inhibitive
property of bismuth oxy chloride.
Me → Men+ + ne-
Due to the interplay between anode, cathode and
electrolyte, it can result in a variety of corrosion
forms including uniform or general corrosion,
pitting corrosion, galvanic corrosion, and crevice
corrosion, cracking and dealloying (jones 1996).
Corrosion is of enormous economic concern, and it
has been estimated that corrosion-related issues cost
approximately 3-4 percent of GNP of industrialized
nations [4-5]. These costs include replacement of
materials, monitoring costs, maintenance and
repairs, insurance to guard against failures,
redundant equipment and costs associated with
remediation of spills caused by corrosion failures
(javaherdashti 2008). Most of the commercial
inhibitors are toxic in nature; therefore, replacement
by environmentally benign inhibitors is necessary.
Many studies have been carried out to find suitable
non-toxic compounds to be used as corrosion
inhibitors for these metals in different aqueous
solutions [6,7].Among them very few are eco
friendly natural products , pharmaceutically active
compounds i.e. antibiotics, antibacterial etc . The
use of pharmaceutical compounds offers interesting
possibilities for corrosion inhibition due to the
presence of hetero atoms like nitrogen, sulphur and
oxygen in their structure, and they are of particular
interest because of their safe use, high solubility in
water and high molecular size. Some of the
azosulpha, piperazine derivative and antimalarial
Keywords— Mild Steel; Corrosion; Adsorption;
Bismuth oxy chloride; Antimicrobial agent
Aluminium (Al), Mild steel (MS) and its alloys are
widely used in technology because of their low
density, agreeable appearance, and corrosion
resistance. This relevance usually induces serious
corrosion effects on equipments made up of iron,
aluminium and its alloys. The use of the inhibitor is
most possible approaches for protecting engineered
materials against corrosion, especially in basic
media. For these reasons, the corrosion inhibition
of Al, MS in aqueous solution has attracted the
attention of many investigators .Corrosion can be
defined as the degradation or destruction of a metal
or metal alloy due to electrochemical reactions with
the environment . Basically, corrosion involves
three components: an anode, a cathode and an
drugs have been reported as good corrosion
inhibitors [9, 10 &11].In the present work mainly
focussed to find the environmentally safe, non-toxic
inhibitor that would be used for inhibiting the
corrosion of Mild Steel and Aluminium. The use of
such substances will establish, simultaneously, the
economic and environmental goals. Bismuth has an
atomic number 83 and a molecular weight 208.9
It has a white crystalline nature and
occurred in two valencies (+3 and +5) [12-16].
Bismuth oxy chloride had O-atoms in its structure,
regarded as important factors for good
inhibitor.Therefore; Bismuth Oxy Chloride is tested
as an inhibitor for the corrosion of Mild Steel &
Aluminium in basic media. Adsorption mechanisms
were deduced through adsorption isotherms using
data obtained there from.
A. Material preparation
According to ASTM method as reported
already [12-15], mild steel strips were cut into
pieces of 5 cm x 1 cm having the following
composition (in percentage) % C=0.017; Si=0.007;
Mo=0.015; Cr=0.043 and Fe=99.686 was used.
The samples were polished, drilled a hole at
one end and numbered by punching. During the
study the samples were polished with various
grades of SiC abrasive papers (from grits 120 to
1200) and degreased using Acetone.
Wo–Wi x 100 ----------------- (1)
Where, WO and Wi (in g) are the values of
the weight loss observed of mild steel in the
absence and presence of inhibitor respectively.
IE % =
RESULTS AND DISCUSSION
Weight loss method
The comparison graph of corrosion
behaviour and inhibitor efficiency of Aluminium &
Mild Steel in 1M NaCl & 2M NaCl with bismuth
oxy chloride which was studied by weight loss
method at 2 h at room temperatures was given in
Figure 1 (a) & 2 (a). From the graph, it was
observed that the weight loss of Aluminium & Mild
steel in the aqueous solution decreases with
increasing concentration of inhibitor and the values
were tabulated in Table 1 & 2 from which it was
clear that the corrosion rate has decreased with
increasing concentration of inhibitor and inhibition
concentration of the inhibitor. In addition, the
maximum corrosion inhibition efficiency (BiOCl)
for Aluminium and Mild Steel in 2M NaCl was
84% and 89.8% respectively at 47.86 % of the
inhibitor solution for 2 hours at room temperature.
Preparation of Solutions
Corrosion parameters in absence and presence of BiOCl of
with 1M and 2M NaCl in Aluminium.
All the solutions were prepared using NICE
brand analar grade chemicals in double distilled
water and bubbling purified by nitrogen gas for 30
minutes to carry out de-aeration of the electrolytes.
C. Preparation of Inhibitor
Various concentration of inhibitor was
prepared on the basis Le Chatlier’s principle.
D. Weight loss measurement
Mild steel specimens were immersed 1M
NaCl and 2 M NaCl for 2 h at room temperature
(28 ± 2 ºC) for each inhibitor concentration. Then
the specimens were removed, rinsed in double
distilled water, acetone and the loss in weight of the
specimen was determined. From this, the inhibiton
efficiency (IE %) was calculated using the formula
It was also fulfilled that the inhibitor was
very effective for Aluminium corrosion when
Figure 2(a) - Comparison of inhibition efficiency of BiOCl
in 2 M NaCl solution on Mild steel and Aluminium at
comparing with various molality like 1M NaCl and
2M NaCl; the inhibitor efficiency was maximum in
2M NaCl than 1M NaCl. Figure 1(a) revealed the
comparison of Inhibitions efficiency of Bismuth
oxy chloride (BiOCl) (in %) in 1M NaCl and 2M
NaCl solution at two hour at room temperature.
Corrosion parameters in absence and presence of
BiOCl of with 1M NaCl & 2 M NaCl in Mild steel
The obtained results indicated that BiOCl
performs a good inhibition for the corrosion of
Aluminium and Mild Steel in basic media .From the
figure 1(a) and 2(a) the Inhibition efficiency of
inhibitor in both the Mild steel and Aluminium
metal increases as the concentration of inhibitor
increases. For Mild Steel, the highest inhibition
efficiency is obtained.
It can be seen from Table 2 that, the
addition of inhibitors to the aggressive solution
reduces the corrosion rate of mild steel. The
corrosion rate decreased and inhibition efficiency
increased with increasing inhibitor concentration
suggests that the inhibitor molecules act by
adsorption on the metal surface. From the values of
Table 2, it is clear that the BiOCl effectively
inhibits the corrosion rate of MS in both 1M NaCl
and 2M NaCl with higher inhibition efficiency in
2M NaCl medium.
B. Adsorption Isotherm
In aqueous solution, the metal surface is
always covered with absorbed molecule. Therefore,
the adsorption of inhibitor molecule from an
aqueous solution is a quasi substituted process and
the inhibitor that have the ability to adsorb strongly
on the metal surface will hinder the dissolution
reaction of such metal in the corrosive medium.
Here ,the degree of surface coverage is considered
as the determining factor that plays the main role in
adsorption depends on many factors, such as the
nature of metal, condition of metal surface ,the
chemical structure of inhibitor molecule , the nature
of its functional groups, pH and type of corrosion
medium .Basic information on the interaction
between the inhibitor and the Mild steel &
Aluminium metal surface can be proved by the
adsorption isotherm and in general, inhibitor can
function either by physical (electrostatic) adsorption
or chemisorption with the metal surface . Actually,
the adsorbed molecule may cause some difficulty
for the surface to adsorb further molecule from
neighbouring sites. To acquire more information
about the interaction between the inhibitor
Figure 1(a) - Comparison of inhibition efficiency of BiOCl
in (in %) in 1M NaCl solution on Mild steel and
Aluminium at two hour.
molecules and the metal surface, a number of
mathematical adsorption expressions have been
developed to fit the degree of surface coverage
through different adsorption isotherms in order to
provide some knowledge on the nature of
interaction of the adsorbed molecule . The
fractional surface coverage θ at different
concentrations of inhibitors 1M NaCl and 2M NaCl
solutions were determined from the weight loss
measurements data  using the formula,
(θ) = Wo – Wi ------------- (3)
Where, Wo and Wi are the values of weight loss of
uninhibited and inhibited specimens, respectively.
Where, c is the concentration of the inhibitor, θ is
the fractional surface coverage. The Langmuir
isotherm, Eq. (4), which is based on the assumption
that all adsorption sites are equivalent and that
molecular binding, occurs independently from the
fact whether the nearby sites are occupied or not,
was verified for all the studied inhibitors. The
adsorption equilibrium constant K is related to the
free energy of adsorption ∆Gads as,
−∆ G ads
process of adsorption of studied inhibitors is
spontaneous in nature [23-26]. The free energy of
adsorption of (∆Gads) for aluminium, in 1M NaCl
was found to be -4.117 kJmol−1 while for 2M NaCl
it was found to be -4.672 kJmol−1, respectively. On
the other hand the free energy of adsorption of
(∆Gads) for Mild steel, in 1M NaCl was found to be
-4.913 kJmol−1 while for 2M NaCl it was found to
be -5.602 kJmol−1, respectively.
It is well known that the values of ∆Gads in
the order of −20 kJ mol-1 or lower indicate a
physisorption while those about −40 kJ mol−1 or
higher involve charge sharing or transfer from the
inhibitor molecules to the metal surface to form a
co-ordinate type of bond.
The calculated adsorption values for the
studied inhibitor show that the adsorption is of
physical in nature, and there is no chemisorption
between the inhibitor molecule and the metal
surface. This indicates that the adsorption of
BiOCl at 2 h takes place through electrostatic
interaction between the inhibitor molecule and the
metal surface. Hence it indicates that the
interaction between the inhibitor molecule and
metal surface is physisorption.
Thermodynamic parameters for the adsorption of BiOCl in
(1M NaCl and 2 M NaCl.) on the Aluminium.
Where, Csolvent represents the molar concentration of
the solvent, which in the case of water is 55.5 mol
dm−3, R is the gas constant and T is the
thermodynamic temperature in K. The Langmuir
isotherm, Eq. (5), can be rearranged to obtain the
so that a linear-relationship can be obtained on
plotting c/θ as a function of c, with a slope of unity.
The thermodynamic parameters K and ∆Gads for the
adsorption of the studied inhibitors on Aluminium
and Mild steel is obtained by Langmuir’s
adsorption isotherm are plotted in Figure 3 & 4 and
the obtained values are given in Table 3 & 4. It was
found that the linear correlation coefficients clearly
prove that the adsorption of (BiOCl) from 1M NaCl
and 2M NaCl solutions on the Mild steel &
Aluminium corrosion obeys the Langmuir
adsorption isotherm. The negative values of ∆G0ads
for the addition of inhibitors indicate that the
Figure 3 - Langmuir isotherm for adsorption of BiOCl on
Aluminium surface studied at (1M NaCl and 2M NaCl).
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