Research Journal of 
Recent 
Sciences 
______
______________________________
______
___
__
_
 
ISSN
 
2277 
-
 
2502
 
Vol. 
1(
ISC
-
2011
), 
57
-
61
 
(201
2
)
 
Res.J.
Recent
.Sci.
 
 
 
International Science Congress Association
 
 
 
 
    
57
 
Azwain (Trachyspermum copticum) seed extract as an efficient corrosion 
I
nhibitor for 
A
luminium in NaOH solution
 
 
Singh A
mbrish and
 
Quraishi M.A.
 
 
Department of Applied Chemistry, Institute of Technology, 
Banaras Hindu University Varanasi,
 
UP
, 
I
NDIA
 
 
Available online at: 
www.isca.in
 
(Received 19
th
 
September
 
2011, revised
 
12
th
 
January 2012
 
, accepted
 
26
th
 
January 2012
)
 
 
Abstract
 
The present work investigates corrosion behaviour of the aluminium in 0.5 M NaOH solution in the presence of
 
Azwain 
(Trachyspermum copticum) seed extract by weight loss and electrochemical techniques. Experimental results revealed that 
inhibition efficiency increases with increasing inhibitor concentration and reached at maximum 94% at 500 ppm inhibitor 
concentration. Adsorption of inhibitor molecules on the surface of aluminium followed Langmuir adsorption isotherm model. Taf
el 
polariza
tion analyses indicated that studied compound is mixed type inhibitor. The data obtained from polarization method and 
weight loss methods were in good agreement. 
The 
Azwain (Trachyspermum copticum) seed extract 
is environmental friendly, 
biodegradable, non
toxic, cheap and easily available source of material which is used as corrosion inhibitor for aluminium metal in 
0.5 M NaOH.
 
 
 
Keywords:
 
Corrosion
,
 
p
lant extract
,
 
a
luminium
,
 
p
olarization
,
 
NaOH solution
.
 
 
 
Introduction
 
Aluminium
 
is the second most used metal after iron; it is 
used in a large number of applications by itself and is used in 
a wide range of alloys. 
Because of the low atomic mass and 
the negative value of the standard electrode potential, 
aluminium potentially attrac
ts as an anode material for power 
sources with high energy densities
1
.
 
The corrosion behavior 
of pure aluminium and its alloys in aqueous alkaline 
solutions have been extensively studied in the development 
of the aluminium anode for the aluminium/air batte
ry
2
-
5
. 
Corrosion of aluminium cause many problems viz., (
i
) 
it 
passivate the cathode active material, (
ii
) 
its solid products 
increase the electrical resistance, (
iii
) its soluble products 
contaminate the electrolyte and increase the self
-
discharge 
rate, a
nd (
iv
) the dissolved Al
3+
 
ions migrate to the counter 
anode and reductively deposit
. Despite the fact that 
aluminium/air battery is an eco
-
friendly system and the 
energy density of this system is excellent. It is not greatly 
used in practice due to severe
 
hydrogen evolution problems 
resulting from corrosion of the aluminium electrode. Thus, 
commercial application of Al and its alloys requires control 
of the hydrogen gas evolution must necessarily be achieved 
without compromising the eco
-
friendly nature of 
the system.
 
 
In efforts to mitigate aluminium corrosion, the main tactic is 
to separate the metal from corrosive environments. This can 
be achieved using corrosion inhibitors. Recently, the use of 
chemical inhibitors has been limited due to environmental 
r
egulations; Plant extracts have again become important 
because they are the environmentally and renewable source 
for a wide range of needed inhibitors. Plant extracts are 
viewed as an incredibly rich source of naturally synthesized 
chemical compounds that 
can be extracted by simple 
procedures with low cost. 
A lot of natural products were 
previously used as corrosion inhibitors for different metals in 
various environments
6
-
16
 
and their optimum concentrations 
were reported. The obtained data showed that plant
 
extracts 
could serve as effective corrosion inhibitors. It is well 
established that c
orrosion inhibition occurs via adsorption of 
their molecules on the corroding metal surface and efficiency 
of inhibition depends on the mechanical, structural and 
chemica
l characteristics of the adsorption layers formed 
under particular conditions.
 
 
As a contribution to the current interest on environmentally 
friendly, green, corrosion inhibitors, and the present study 
investigates the inhibiting effect of seed extracts of 
Azwain 
(Trachyspermum copticum)
 
on the aluminium corrosion in 
0.5 M NaOH
 
solution using the weight loss and 
electrochemical techniques
. 
 
 
Material and Methods
 
Aluminium (Al
-
1060) strips were used for weight loss as 
well as electrochemical studies. The aluminium specimens 
were machined into test electrodes of dimension 8 cm � 1
 
cm 
and embedded in PVC holder by epoxy resin (araldite) 
leaving one surface of an area of 1 cm
2
 
for electrochemical 
measurements. The exposed surface was abraded with silicon 
carbide abrasive paper from 400 to 1200, degreased with 
acetone, rinsed in disti
lled water
 
and dried in the air. The 
corrosive medium was 0.5 M NaOH solution prepared from 
analytical
-
reagent
-
grade NaOH (
Merck
) and bidistilled 
Research Journal of 
Recent 
Sciences 
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_
_
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______
 
ISSN
 
2277 
-
 
2502
 
Vol. 
1(
ISC
-
2011
), 
57
-
6
1
 
(201
2
)
 
Res.J.Recent.Sci
 
 
International Science Congress Association
 
 
58
 
water. Stock solution of 
Azwain (Trachyspermum copticum) 
seed extract was extracted by reflux of 100 g of the 
dry 
materials in 500 mL bidistilled water for 5 h. The refluxed 
solution was filtered to remove any contamination. The 
concentration of the stock solution was calculated in terms of 
ppm.
 
 
Electrochemical experiments were carried out in a 
conventional three
-
electrode glass cell of capacity 100 mL, 
using a 
gamry potentiostat/ galvanostat pci 4 electrochemical 
workstation. a saturated calomel electrode (sce) equipped 
with a luggin capillary and a platinum foil of 1 cm � 1 cm 
were used as reference and counter 
electrode, respectively. 
all 
the potentials reported are with reference to SCE. Before 
measurement, the working electrode was immersed in test 
solution for approximately 30 min until a steady open
-
circuit 
potential (OCP) was reached. EIS measurement was ca
rried 
out in the 100 kHz 
-
 
10 mHz frequency range at OCP. 
 
 
The sinusoidal potential perturbation was 10 mV in 
amplitude and the cell temperature was maintained at 308 � 1 
K using a thermostatic water
-
bath. The electrochemical 
experiments data were collect
ed and analyzed by 
electrochemical software Echem Analyst ver. 5.5. The 
polarization curves were carried out from cathodic potential 
of 
-
0.25 V to anodic potential of +0.25 V with respect to the 
open circuit potential at a sweep rate of 1 MV s
-
1
. The linea
r 
Tafel segments of the anodic and cathodic curves were 
extrapolated to corrosion potential (E
corr
) to obtain the 
corrosion current densities (I
corr
). In each measurement, a 
fresh working electrode was used. Several runs were 
performed for each measurement
 
to obtain reproducible data.
 
 
The aluminium specimens of 2.5 cm � 2 cm � 0.05 cm sizes 
were used for weight loss measurements and were abraded 
with a series of silicon carbide abrasive paper (grade 600
-
800
-
1000
-
1200) and degreased with acetone, rinsed in 
distilled water, and dried in the air, and weighed accurately. 
Aluminium specimens were immersed in 100 mL of 0.5 M 
NaOH with and without addition of different concentrations 
of 
Azwain (Trachyspermum copticum) 
seed extract. The 
temperature of the corrosive system was controlled by an air 
thermostat. After 1 h immersion, the aluminium specimens 
were carefully washed in double
-
distilled water,
 
dried
 
and 
then weighed. 
 
 
The weight loss data were gained from the ave
rage value of 
three parallel samples in 0.5 M NaOH with 
Azwain 
(Trachyspermum copticum) 
seed extract at different 
concentrations. 
 
 
Results and Discussion
 
Electrochemical measurements
, 
Polarization
 
measurements
: 
Polarization curves of
 
Al in 0.5 M NaOH 
solu
tion without and with different concentrations of 
Azwain 
(Trachyspermum copticum) 
seed extract are shown in Figure 
1. It could be observed that both the cathodic and anodic 
reactions were suppressed with the addition of 
Azwain 
(Trachyspermum copticum) 
seed
 
extract, which suggested 
that the inhibitor exerted an efficient inhibitory effect both on 
anodic dissolution of metal and on cathodic hydrogen 
reduction reaction. Electrochemical parameters such as E
corr
, 
I
corr
, and anodic and catodic Tafel slopes (β
a
, 
β
c
) obtained 
from the polarization measurements are listed in Table 1. The 
inhibition efficiency (

%) was calculated by following 
equation 
17
:
 
………………………
(1)
 
I
corr
 
and I
corr(i)
 
signify the corrosion current density in the 
absence and presence of inhibitors, respectively.
 
 
It is evident from t
able 1 tat values of β
c
 
had small changes 
with increasing extract concentration, which indicated that 
the 
Azwain (Trachyspermum copticum) 
seed extract was 
adsorbed on the metal surface and the addition of the 
inhibitor hindered the alkali attack on the aluminium 
electrode. Therefore, the inhibitor molecules did not change 
the hydrogen evolution reaction mechanism. In anodic 
domain, the value
 
of β
a
 
decreases with the presence of 
Azwain (Trachyspermum copticum) 
seed extract. 
 
 
Te sift in te anodic Tafel slope β
a
 
might be attributed to 
the modification of anodic dissolution process due to the 
inhibitor modules adsorption on the active sites. 
Compared to 
the free NaOH solution, the cathodic and anodic curves of 
the working electrode in the alkaline solution containing the 
Azwain (Trachyspermum copticum) 
seed extract shifted 
obviously to the direction of current reduction, as it could be 
seen fr
om these polarization results; the inhibition efficiency 
(

%) increased with extract concentration reaching a 
maximum value of 90% at 500 ppm. In literature 
18
, it is 
reported that only when the open circuit potential (OCP) 
displacement is at least 85 mV i
n relation to the one 
measured for the blank solution, can a compound be 
recognized as an anodic or cathodic inhibitor. Therefore, 
Azwain (Trachyspermum copticum) 
seed extract might act as 
a mixed
-
type inhibitor.
 
 
Electrochemical impedance spectroscopy 
(EIS) 
measurements
: 
Equivalent circuit used is shown in Figure 2. 
Nyquist plots of aluminium in 0.5 M NaOH solution in the 
absence and presence of different concentrations of 
Azwain 
(Trachyspermum copticum) 
seed extract are given in Figure 
3, where it can 
be observed that the diameter of the 
semicircle increases with increasing 
Azwain 
(Trachyspermum copticum) 
seed extract concentration. This 
increase in capacitive semicircles 
suggests that the inhibition 
action of these inhibitors is due to their adsorption
 
on the 
metal surface without altering the corrosion mechanism.
 
 
Research Journal of 
Recent 
Sciences 
______
_
_
_______________________________
______________
_
______
 
ISSN
 
2277 
-
 
2502
 
Vol. 
1(
ISC
-
2011
), 
57
-
6
1
 
(201
2
)
 
Res.J.Recent.Sci
 
 
International Science Congress Association
 
 
59
 
Table
-
1
 
Electrochemical polarization parameters and the 
corresponding inhibition efficiencies for Al in 0.5 M 
NaOH solution in the absence and presence of different 
concentrations of 
Azwain (
Trachyspermum copticum) 
 
seed extract
 
 
Inhibitor
 
E
corr
 
I
corr
 
β
a
 
β
c
 

 
(ppm)
 
(V/SCE)
 
(mA 
cm
–
2
)
 
(V dec
–
1
)
 
(V 
dec
–
1
)
 
(%)
 
0.5 M 
NaOH
 
–
1.54
 
59.8
 
8.746
 
0.56
 
-
 
300
 
–
1.51
 
7.7
 
1.334
 
0.23
 
87
 
400
 
–
1.51
 
6.8
 
1.001
 
0.14
 
89
 
500
 
–
1.50
 
5.8
 
1.000
 
0.21
 
90
 
 
 
Figure
-
1 
 
Polarization curves for Al in 1 M NaOH in 
Presence
 
of 
different concentrations of 
Azwain (Trachyspermum 
copticum) 
seed extract
 
 
Further, the figure manifested two depressed capacitive 
semicircles, typical of Randles element, at higher and lower 
frequencies
 
regions, separated by an inductive loop at 
intermediate frequencies. Inductive loops can be explained 
by the occurrence of adsorbed intermediate on the surface. 
Therefore, adsorbed intermediate species such as Al
+
ads
 
and 
Al
3+
(ads)
 
might be involved in Al dissolution process 
19
. The 
capacitive semicircle at higher frequencies is attributed to the 
redox Al
–
Al
+
 
reaction since it was assumed to be the rate 
determining step in the charge transfer process
 
20
. 
 
 
Therefore, the resistance 
value obtained from intercepts of 
the first capacitive semicircle with real axis corresponds to 
the Al
–
Al
+
 
charge transfer resistance. On the other hand, the 
second capacitive semicircle could be attributed to the fast 
complementary redox Al
+
–
Al
3+
 
reaction
. The curve 
manifested that addition of extract to alkaline NaOH solution 
leads to increase the size of the capacitive semicircles, 
indication for increasing the resistances and decreasing 
corrosion rate.
 
 
Weight loss measurements and adsorption isotherm
 
:
 
The 
values of Inhibition efficiency (

%) obtained from weight 
loss measurements for different concentrations of 
Azwain 
(Trachyspermum copticum) 
seed extract in 0.5 M NaOH are 
given in 
f
igure 4. The inhibition efficiencies, (

%) were 
calculated by the foll
owing equation:
 
        
 
     
……………….
(2)
 
 
W
0
 
and W are the corrosion rates in the absence and presence 
of the extract, respectively. The obtained results suggested 
that the inhibition efficiency increases with increasing 
concentration of extract. 
 
 
As the concentration reached 500 ppm, the inhibitio
n 
efficiency of extract obtained a high value of 94%, which 
represented excellent inhibitive property. Adsorption of 
Azwain (Trachyspermum copticum) 
seed extract can be 
explained on the basis that adsorption of the inhibitor was 
mainly via hetero atoms (vi
z., N) present in different 
constituents of extract in addition to the availability of 
π 
electrons in the aromatic system
21
. 
 
 
The phytoconstituents of 
Azwain (Trachyspermum 
copticum) 
seed extract includes Camphene, carvacrol, 
p
-
cymene, dipentene, myrcene,
 
a
-
 
and b
-
 
pinesnes, phenol, a
-
 
and b
-
plellandrenes, g
-
 
terpinene, thymine, thymol, linoleic, 
oleic, palmitic petroselinic acid, resin acids are isolated from 
fruits and seeds
22, 23
.
 
 
Conclusion
 
Azwain (Trachyspermum copticum) 
seed extract was found 
to inhibit the corrosion of aluminium in 0.5 M NaOH 
solution and inhibition efficiency increases with increasing 
extract concentration. At the highest extract concentration of 
500 ppm, the inhibition efficiency is increased markedly 
and 
reached 94%. Potentiodynamic polarization curves proved 
that the 
Azwain (Trachyspermum copticum) 
seed extract was 
a mixed
-
type inhibitor. EIS plots indicated that the charge 
transfer resistances increase with increasing concentration of 
the extract. 
The 
Azwain (Trachyspermum copticum) 
seed 
extract inhibits corrosion of aluminium in alkali media by 
adsorption mechanism.
 
 
Acknowledgement
 
We gratefully acknowledge the financial support of Council 
of Science and Industrial Research (CSIR), New Delhi, Indi
a.
 
 
 
 
 
Research Journal of 
Recent 
Sciences 
______
_
_
_______________________________
______________
_
______
 
ISSN
 
2277 
-
 
2502
 
Vol. 
1(
ISC
-
2011
), 
57
-
6
1
 
(201
2
)
 
Res.J.Recent.Sci
 
 
International Science Congress Association
 
 
60
 
Table
-
2
 
Electrochemical impedance parameters for mild steel in 1 M HCl 
 
in absence and presence of different
 
concentrations of
 
Azwain 
 
(Trachyspermum copticum) 
seed extract
 
Solution
 
Inhibitor
 
R
ct
 
Y
0
 
n
 
C
dl
 

 
 
(ppm)
 
(Ω cm
2
)
 
(10
−6
Ω
−1
s
n
cm
−2
)
 
 
(μF cm
-
2
)
 
(%)
 
0.5 M NaOH
 
0
 
9.4 � 0.04
 
65.8
 
0.827
 
44.60
 
-
 
 
300
 
29.9 � 0.3
 
40.6
 
0.923
 
24.75
 
68.54
 
 
400
 
47.2 � 0.9
 
82.5
 
0.897
 
19.43
 
79.73
 
 
500
 
63.5 � 1.2
 
32.9
 
0.854
 
15.15
 
85.10
 
 
 
 
 
Figure 
-
2
 
Equivalent circuit used
 
 
 
Figure 
–
 
3
 
Nyquist plots for aluminium in 1 M NaOH with various 
concentrations of 
Azwain (Trachyspermum copticum) 
seed extract
 
 
Figure 
-
4
 
Inhibition efficiency vs. inhibitor concentration
 
 
Figure
-
5
 
La
ngmuir 
adsorption isotherm plot
 
 
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Research Journal of 
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Sciences 
______
_
_
_______________________________
______________
_
______
 
ISSN
 
2277 
-
 
2502
 
Vol. 
1(
ISC
-
2011
), 
57
-
6
1
 
(201
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Res.J.Recent.Sci
 
 
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