Jordan Journal of Chemistry Vol. 9 No.3, 2014, pp. 149-158
JJC
Inhibition of Corrosion of Aluminium in NaOH Solution by Leave
Extract of Mesembryanthemum nodiflorum
a
b
b
Tareq M. A. Al Shboul , Taghreed M. A. Jazzazi , Tareq T. Bataineh , Mahmoud A. Alb
a
Qudah , Albara I. Alrawashdeh
a
Department of Chemistry and Chemical Technology, Faculty of Science, Tafila Technical University, Tafila,
Jordan
b
Department of Chemistry, Faculty of Science, Yarmouk University, Irbid, Jordan
Received on March 30, 2014
Accepted on Jun. 26, 2014
Abstract
Corrosion inhibition of aluminum in 1M NaOH solution by Mesembryanthemum
nodiflorum leaves extract was investigated using the weight loss technique. A plant extract
o
solution of 14 g/L at 50 C was found to inhibit the corrosion of aluminum with an inhibition
efficiency of 95.1%. The inhibition efficiency was found to increase with increasing the
concentration of the plant extract at 50 oC. Different adsorption isotherms, Langmuir and
Temkin, were tested to investigate the nature of adsorption.
Keywords: Mesembryanthemum nodiflorum; inhibitors; corrosion; Aluminum; weight
loss.
Introduction
Aluminum and its alloys are very important materials with many applications in
industry due to their low cost, light weight and high thermal and electrical
conductivities.
[1]
The corrosion of aluminum and its alloys was the subject of several
studies due to the high technological value and wide range of industrial and household
applications. In neutral aqueous solution, aluminum and its alloys are very good
corrosion resistant materials due to the formation of a passive film.
The corrosion of aluminum in different media has been studied. Numerous
inhibitors have been used to control the corrosion of aluminum. Sansevieria trifasciata
extract,
[2]
Capparis deciduas,
delonix regia extract
[5]
[3]
[4]
polyethylene glycol, imidazoline derivatives
and
have been used to prevent the corrosion of aluminum in acidic
media. In alkaline solution, gongronema latifolium extract,[6] methyl orange,[7] bismark
brown dye,
[8]
[9]
adathoda vasica leaves extract, onion and its extract
[10]
have been used
as inhibitors to prevent the corrosion of aluminum. The extracts of these materials
generally contain mixtures of compounds having atoms like S, O and N. The presence
of these atoms in molecules will enhance the corrosion inhibition process.
[11-13]
Several
investigators have reported the inhibition of corrosion using eco-friendly, readily

Corresponding author: e-mail: [email protected]
149
available and eco-acceptable environmental and economic natural products as
corrosion inhibitors.
[14-18]
They have observed that the solutions made of the extracts of
the leaves serve as excellent corrosion inhibitors. Recently Batainah et al. have
studied the corrosion behaviour of aluminum in sodium hydroxide containing Plumbago
europaea leaves extract.
[19]
Irshedat et al. have reported the inhibition of aluminum
corrosion by Lupinus varius l. extract in a basic medium using weight loss technique.
[20]
The Mesembryanthemum nodiflorum extract contains the indole alkaloids I-IV as major
chemical constituents.
[21]
In this study, the effect of Mesembryanthemum nodiflorum
extract was studied as a corrosion inhibitor for aluminum in 1M NaOH solution in the
temperature range of 25-50 °C.
OCH3
OCH3
N
CH3
O
Mesembrine
OCH3
OCH3
N
CH3
OCH3
OCH3
N
CH3
O
Mesembrenone
Mesembrenol
III
II
I
OH
OCH3
OCH3
NH
CH3
N
Tortuosamine
IV
Experimental
A stock solution of plant extract was obtained by drying the plant for 4 hours in
o
an oven at 80 C and grinding it to become a powder. A weight of 7.0 g of the dried
leaves powder was refluxed in 500 ml of 1M sodium hydroxide for 2 hours. The
refluxed solution was filtered to remove any contamination and then stored. This
solution was used to prepare the inhibitor test solutions of 2.8, 5.6, 8.4, 11.2 and 14
g/L through dilution with 1M NaOH. Commercial 99.96% pure aluminum specimens of
the dimensions 3.0 x 1.0 x 0.03 cm were cleaned and polished using a solution of 85%
H3PO4 and 15% HNO3 at 80 ˚C, washed with distilled water, then placed in a solution
of 40% (wt/v) sodium hydroxide at 50 ºC for 20 second. The aluminum specimens
were rinsed again with distilled water, immersed in 1:1 (v/v) HNO3, washed with
distilled water, and then dried and stored in moisture-free desiccators. For the weight
loss determination, the aluminum specimens were hanged and immersed in the
vessels of the test solutions each containing 10 ml of 1M NaOH. Different
concentrations of the extract (2.8-14 g/L) were added to the vessels at 25-50 ºC. After
2 hours, the aluminum specimens of each test were taken out and washed in acetone
then rinsed with distilled water, dried and reweighed. The weight loss was determined
for each specimen by calculating the difference between the initial weight and the
weight after the removal of the corrosion product using a digital analytical balance with
a precision of 0.0001 g. Three experiments were performed for each concentration of
150
the inhibitor. The average weight losses of the three experiments were taken as the
weight loss of the aluminum specimen for each concentration.
Results and Discussion
Weight loss technique is the simplest method for studying the corrosion process.
The basic property determined for corroded specimens is the weight loss taking place
over the period of exposure, being expressed as the corrosion rate.
[22, 23]
Figure 1
shows the plot of weight loss (in mg) for the aluminum specimens versus the extract
concentration of Mesembryanthemum nodiflorum for 120 min immersion period in 1M
NaOH at different temperatures. There is a clear decrease in the weight loss of Al
specimens as a function of the extract concentration. This indicates that the observed
corrosion inhibition can be attributed to the adsorption of inhibitor onto the metal
surface; the inhibitor acts thus as an adsorption inhibitor. Also, the effect of the
temperature on aluminum corrosion in 1M NaOH solution was studied over the
temperature range of 25-50 °C in the absence and presence of different concentrations
of the inhibitor. The weight loss of Al was found to increase with increased
temperature.
weight loss (mg)
250
200
150
wt/25˚C
100
wt/30˚C
50
wt/40˚C
0
wt/50˚C
0
5
10
15
Extract conc. g/L
Figure 1: The weight loss curves of aluminum due to corrosion in 1M NaOH in
presence of Mesembryanthemum nodiflorum extract (2.8 – 14 g/L) at various
temperatures.
The inhibition efficiency (%I) of the inhibitor and the surface coverage (θ) of the
extract of Mesembryanthemum nodiflorum on the Al specimen surface were calculated
from the following two equations:
%I 
Wi  W f
Wi

 100%
Wi  W f
Wi
Where Wi and Wf are the weight losses of Al specimen in the absence and presence of
the inhibitor, respectively.
151
The inhibition efficiency was accordingly calculated and is shown is table 1 as a
function of the extract concentration and as a function of temperature. It is clear that
the inhibition efficiency for aluminum in 1M NaOH solution increases with the increase
in extract concentration and also with increasing the temperature. The maximum
inhibition efficiency of 95.1% was observed for an extract concentration of 14 g/L at 50
°C. This high inhibition efficiency can be attributed to the fact that the inhibitor
molecules are adsorbed onto the aluminum surface, forming thus a protective layer
that inhibits corrosion. Figure 2 shows the change in inhibition efficiency as a function
of
the concentration of
Mesembryanthemum nodiflorum extract at different
temperatures. It is also here clear that for the same NaOH solution, the inhibition
efficiency increases with increased temperature.
Table1: Change of inhibition efficiency of Mesembryanthemum nodiflorum extract at
different concentrations for aluminum in 1M NaOH solution for 120 min immersion
period at different temperatures (25-50 ºC).
Extract conc. g/L
2.8
5.6
8.4
11.2
14.0
%I at 25 ºC
63.4
74.0
78.2
80.9
82.1
%I at 30 ºC
71.5
79.9
83.3
85.2
86.9
%I at 40 ºC
76.8
84.1
89.7
92.1
93.1
%I at 50 ºC
80.9
88.2
92.2
94.4
95.1
100
90
80
70
%I
60
%I at 25˚C
50
%I at 30˚C
40
%I at 40˚C
30
%I at 50˚C
20
10
0
0
5
10
15
Extract conc. g/L
Figure 2: Change in inhibition efficiency as a function of the Mesembryanthemum
nodiflorum extract concentration for 120 min immersion period at different
temperatures.
The inhibition efficiency of the Mesembryanthemum nodiflorum extract could be
attributed to the presence of organic chemical compounds. Previous study has shown
that the Mesembryanthemum nodiflorum extract contains alkaloids I-IV as major
constituents.
[20]
It is clear that these constituents contain heteroatoms such as oxygen
152
and nitrogen atoms, as well as conjugated double bonds. Therefore, the adsorption of
these component molecules on the Al metal surface could take place via electrostatic
attraction between the charged metal surface and the charged inhibitor molecules and
also due to the π-electrons interaction with the metal.
Kinetic and thermodynamic considerations
The corrosion rate, R’, of Al is calculated using equation 1
W mg 
Acm 2   t hr 
R' 
(1)
where ΔW is the mass loss, A is the area and t is the immersion period in the basic
solution. A plot of the logarithm of the corrosion rate of aluminum obtained from weight
loss measurements versus reciprocal temperature (1000/T) gave straight lines, as
shown in Figure 3. The activation energy (Ea) was determined by using the following
equations:
[24]
R’ = A exp (Ea/RT)
logR’ = logA- Ea / 2.303RT
where Ea is the apparent activation energy for the corrosion of Al in 1M NaOH solution,
A is the frequency factor, R is the general gas constant and T is the absolute
temperature. The values of Ea for the corrosion of Al in 1M NaOH solution were
calculated from the slopes of these lines and are given in Table 2.
The value of the activation energy for the corrosion of aluminum is high in the
-1
absence of the inhibitor (50.8 kJ mol ) which is close to that reported by Batayneh et
al.[19] for the corrosion of aluminum in 1M NaOH (49.8 kJ mol-1). Ea decreases however
in the presence of the Mesembryanthemum nodiflorum extract. This may arise from
the shift of the net corrosion reaction from that on the uncovered surface to one
log Rate
involving the adsorbed sites.[25-30]
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2 3
-0.4
0 g/L
2.8 g/L
5.6 g/L
8.4 g/L
11.2 g/L
3.1
3.2
3.3
3.4
14 g/L
1000/T, K-1
Figure 3: Arrhenius plot for aluminum dissolution in 1M NaOH in the absence and
presence of Mesembryanthemum nodiflorum extract (2.8-14 g/L).
153
Equation 2 is used to calculate the enthalpy and entropy of activation (ΔH*, ΔS*)
by applying the transition state theory (Eyring equation):
[31]
R’ = RT/N h exp (ΔS*/R) exp (-ΔH* / RT)
(2)
where h is Planck’s constant, N is Avogadro’s number, ΔH* and ΔS* are the enthalpy
and entropy of activation, respectively.
Figure 4 represents the plot of log R’/T vs. 1/T for Al in 1M NaOH, in the
absence and in presence of different concentrations of the inhibitor. The slope of the
obtained straight lines is ΔH*/2.303R and the intercept is log R/N.h + (ΔS*/2.303R).
The value of ΔH* and ΔS* were calculated and are listed in Table 2. The values of ΔH*
reflect the strong physical adsorption of the inhibitor on Al surface. The values of ΔS*
are large and negative in the absence and presence of the inhibitor. This indicates that
the activated complex represents an association rather than a dissociation step.
[31]
0
log (R/T)
-0.5
3
3.1
3.2
3.3
3.4
0 g/L
-1
2.8 g/L
-1.5
5.6 g/L
-2
8.4 g/L
11.2 g/L
-2.5
14 g/L
-3
1000/T, k-1
Figure 4: Log (R’/T) vs. 1000/T for Al coupon in 1 M NaOH in the absence and
presence of Mesembryanthemum nodiflorum extract.
Table 2: Activation parameters of the dissolution of Al in 1 M NaOH in the absence
and presence of Mesembryanthemum nodiflorum extract.
Extract conc. g/L
R2
Ea (kJ/mol)
R2
ΔH* (kJ/mol)
ΔS* (J/mol.K)
0
2.8
5.6
8.4
11.2
14.0
0.974
0.970
0.923
0.932
0.625
0.610
50.8
30.4
25.9
16.2
8.7
6.8
0.988
0.976
0.979
0.998
0.948
0.951
48.1
27.7
23.3
13.5
6.0
4.1
-71.5
-148.6
-166.7
-195.2
-226.4
-233.6
Adsorption considerations
The values of the heat of adsorption (Qads) of inhibitor on the surface of Al
specimen were calculated according to equation (3)
Qads =2.303R [log (θ2/1-θ2)-log (θ1/1- θ1)]x(T2T1/T2-T1)
(3)
where R is the gas constant, θ1and θ2 are the degree of surface coverage at
temperatures T1 and T2, respectively.
154
The values of Qads were accordingly calculated for the different inhibitor
concentrations applied in this work. It was found that all of the values of Qads were
positive for 1M NaOH extract solution and ranged from 21.9 to 55.9 kJ/mol. The
positive values of Qads indicate that the inhibition efficiency of the Mesembryanthemum
nodiflorum extract on aluminum surface increases at high temperatures.
Langmuir adsorption isotherm
[33-35]
[32]
was found to be suitable to fit the
experimental findings. The Langmuir adsorption isotherm is given in equation 4:
C/θ = 1/Kads + C
(4)
where C is the concentration of the inhibitor, Kads is the equilibrium constant of
adsorption, θ is the degree of surface coverage. Figure 5 shows a plot of log(C/θ)
versus log C at 25-50 ºC for the adsorption of plant extract on the surface of Al in 1M
NaOH giving a straight line (Figure 5). The suitability of the Langmuir adsorption
isotherm to fit the adsorption of the plant extract indicates the consistency of this
adsorption with the assumptions of the Langmuir adsorption model, suggesting that
there is no interaction between adsorbed species.
[36]
The adsorption parameters
deduced from figure 5 are listed in table 3. The adsorption of plant extract on Al
surface was also found to follow the Temkin adsorption isotherm (Eq (5)) which is
represented in figure 6. The adsorption parameters deduced from the Temkin
adsorption isotherm are tabulated in table 4.
exp(-2a θ) = KC
(5)
The values of standard free energy of adsorption, Gads , of plant extracts on the
Al surface from 1 M NaOH solution is calculated using Equation 6 and are listed in
tables 3 and 4.
[37]
∆Gads = - 2.303RT log (55.5 Kads)
(6)
where R is the gas constant, T is the temperature, 55.5 is the concentration of water
and Kads is the equilibrium constant of adsorption obtained from the Langmuir and
Temkin adsorption models.
The values of ΔGads were negative at 25-50 ºC. The negative values indicate
spontaneous adsorption process of the plant extract on the aluminum surface, and the
suggested mechanism is physical adsorption because Gads < 40 kJ/mol.
155
[37]
log (C/θ)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
log (C/θ) at 25˚C
log (C/θ) at 30˚C
log (C/θ) at 40˚C
log (C/θ) at 50˚C
0
0.5
1
1.5
log C
Figure5: Langmuir model for the adsorption of Mesembryanthemum nodiflorum extract
(2.8-14 g/L) on aluminum surface in 1 M NaOH solution for 2 hour at different
temperatures.
Table 3: Langmuir adsorption parameters for the adsorption of Mesembryanthemum
nodiflorum extract on aluminum in 1M NaOH for 120 min immersion period at different
temperatures.
2
∆Gads, kJmol
Isotherm
Temperature (K)
log Kads
R
Langmuir
298
303
313
323
0.135
0.168
0.189
0.263
0.999
0.999
0.893
0.999
-1
-11.5
-11.2
-11.5
-11.6
1.2
1
θ
0.8
θ at 25˚C
0.6
θ at 30˚C
0.4
θ at 40˚C
0.2
θ at 50˚C
0
0
0.5
1
1.5
log C
Figure 6: Temkin model for the adsorption of Mesembryanthemum nodiflorum extract
(2.8-14 g/L) on aluminum surface in 1 M NaOH solution for 2 hour at different
temperatures.
Table 4: Temkin adsorption parameters for the adsorption of Mesembryanthemum
nodiflorum extract on aluminum in 1M NaOH for 120 min immersion period at different
temperatures.
Isotherm
Temkin
Temperature (K)
298
303
313
323
logKads
0.721
0.662
0.625
0.524
156
2
R
0.984
0.987
0.983
0.976
∆Gads, kJmol
-14.1
-13.9
-14.2
-14.0
-1
Surface topology
Scanning electron microscope was used to investigate the topologic changes of
the aluminum surface in the absence and presence of plant extract in 1M NaOH
solution (figure 7). The corrosion of Al specimens in the presence of alkali
Mesembryanthemum nodiflorum (figure 7B) is weaker than in the case of absence of
alkali Mesembryanthemum nodiflorum (figure 7A), that proves the inhibiting effect of
alkali Mesembryanthemum nodiflorum against corrosion of Al specimens surface in 1
M NaOH solution. These observations were in agreement with inhibition efficiency
values listed in Table 1.
(A)
(B)
Figure 7: Scanning electron micrographs of (A) aluminum surface in 1.0 M NaOH
solution, (B) aluminum surface in 1.0 M NaOH solution containing 14 g/L plant extract.
Conclusions
The Mesembryanthemum nodiflorum extract was successfully used as a
corrosion inhibitor on the surface of aluminum metal in 1M NaOH solution. The
inhibition efficiency was found to increase with increasing the concentration of the
Mesembryanthemum nodiflorum extract to achieve a value of 95.1% at the maximum
inhibitor concentration of 14 g/L at 50 ºC. It was also found that the inhibition efficiency
increases on increasing the temperature. The value of the activation energy Ea was
found to be lower in the case of having the inhibitor in solution than that where it is
absent. The adsorption of the inhibitor molecules was also found to be consistent with
a physical adsorption mechanism.
Acknowledgment
The authors would like to thank the Tafilah Technical University, Yarmouk
University and the Faculty of Graduate Studies and Scientific Research for providing
financial support.
157
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