Synergistic Effect of Halide Ions on the Corrosion
Inhibition of Zinc in Hydrochloric Acid using Schiff base compound,
1-phenyl-2,3-dimethyl-4-(benzylamino)pyrazole-5-one
K.O Eberendu,
Onwu F.K
Department of Chemistry, Michael Okpara University of
Agriculture, Umudike, Abia State Nigeria
*Corresponding Author E-mail: tilasticmon@gmail.com
Abstract:
The
inhibitive effect of1-phenyl-2,3-dimethyl-4-(benzylamino) pyrazole-5-one
(PD(B)PO) on zinc corrosion in 0.1 M hydrochloric acid solution was studied
using gravimetric method. The influence of halides viz., KCl, KBr and KI on the
corrosion inhibition of PD(B)PO were also investigated. Results show that
PD(B)PO alone provided satisfactory inhibition on the corrosion of zinc and it
was also found that the inhibition efficiency increased synergistically in the
presence of halide ions. The synergistic effect of halide ions was found to
follow the order: KI > KBr > KCl. The inhibitor reduced the corrosion
rate through adsorption process and obeyed the Freundlich adsorption isotherm.
KEY WORDS: Freundlich,
adsorption isotherm, Halide ions, Inhibition efficiency, Synergistic
effect,Schiff base, pyrazole.
INTRODUCTION:
Since
the whole idea of metal protection is anchored on economic gain and
environmental sustainability, the substance to be used as metal corrosion
inhibitor must be cheap, readily available, and environmentally friendly. Zinc
is currently the fourth most widely used metal in the world after iron,
aluminum and copper[1]. Zinc alloys form important materials that are used in
automobiles, electrical components, building and house hold fixtures. The metal
itself has been seen as a material for preventing corrosion through the process
of galvanization. Since most of the above stated applications of zinc operate
in corrosive environments, the study of corrosive inhibition of zinc should be
of utmost concern.
To enhance the
efficiency of metal corrosion inhibitors, extensive studies have been
undertaken to identify the synergistic effect of other additives. It has been noted
that synergism provides a way of improving the inhibitive force of inhibitor,
decreasing the quantity of inhibitor usage, and diversifying the application of
the inhibitor in an aggressive environment [2]. The major advantages of using
Schiff bases as corrosion inhibitors lie on their ease of synthesis,
eco-friendliness and the presence of heteroatom in their molecules, which
provide many sites of adsorption to metal surface [3] The addition of halide
ions into the acidic medium in the presence of organic inhibitors has been
found to enhance the efficiency of inhibitive effects [4-7]. It is generally
seen that the addition of halide ions to the corrosive media has increased the
ability of adsorption of the organic cations by forming the interconnecting
bridge between negatively charge metal surface and inhibitor cations. The
introduction of the halide ions synergistically enhanced the inhibition
efficiency of the organic inhibitors [8-14]. The present research, therefore,
investigates the inhibition of zinc corrosion in HCl using a Schiff base
compound: 1-phenyl-2,3-dimethylbenzylaminopyrazole-5-one PD(B)PO and enhancing
its behaviour by the addition of halide ions.
EXPERIMENTAL:
Material preparation:
Tests were performed on
zinc sheets. Cutting machine was used to cut them into dimensions 3cm x 5cm x
1cm with a total surface area 15 cm2 and density of 7.1 g/ cm 3. A
small hole was bored near the upper edge of the coupons using a punch electric
drilling machine for suspension of the coupons. The coupons were then sand
papered using different grades of sand papers (rough and then smooth) until a
mirror polished surfaces were obtained. The coupons were degreased with
ethanol, washed with de-ionized water, dried in acetone and their initial
weights recorded in grams. The coupons were finally suspended using the fishing
lines for the weight loss study.
Preparation
of inhibitor solutions:
0.007 Mof the inhibitor
were employed for the inhibition studies and were prepared by dissolving the
required amount of the Schiff base compounds in 50 ml of 0.1 M HCl and stirring
at room temperature, (27±2ºC). One of the beakers containing only 50 ml of
0.1M. HCl without inhibitor was used as blank test solution. Potassium iodide
(KI), potassium bromide (KBr) and potassium chloride (KCl) solutions (1 × 10-5
– 1 × 10-1 M) were prepared in the blank solution and in 0.007 M PD(B)PO,
respectively.
Weight loss measurements:
In the weight loss
measurements, the pre-cleaned mild steel coupons were suspended in 100 mL of
test solutions maintained at room temperature (27±2ºC). All tests were made in
aerated solutions. The weight loss was determined after immersing the coupons
for 7 days, rinsed in distilled water, degreased in acetone, dried and
reweighed. The weight loss was taken to be the difference between the weight of
coupons at a given time and its initial weight. The percentage inhibition
efficiency (IE) was calculated by Eq. (1).
Where
W and W′ are the corrosion rates of the metal coupons in the absence and
presence of inhibitors respectively.
3.
RESULTS AND DISCUSSION:
Table
1: Inhibition efficiency and degree of surface coverage values for zinc in 0.1
M HCl solution in the absence and presence of Schiff base and KI from weight
loss measurement at 27±2 ºC for 7 days of immersion time
|
System/concentration
|
Weight loss(g)
|
%IE
|
Degree of surface
coverage (θ)
|
|
Blank
|
6.00
|
-
|
-
|
|
0.007 M PD(B)PO
|
0.50
|
91.65
|
0.91
|
|
1 x 10-5 M
KI
|
3.56
|
40.67
|
0.40
|
|
0.007 M PD(B)PO +1 x
10-5 M KI
|
0.48
|
92.00
|
0.92
|
|
1 x 10-4 M
KI
|
3.49
|
41.83
|
0.42
|
|
0.007 M PD(B)PO + 1 x
10-4M KI
|
0.31
|
94.83
|
0.95
|
|
1 x 10-3M
KI
|
3.36
|
44
|
0.44
|
|
0.007 M PD(B)PO + 1 x
10-3 M KI
|
0.27
|
95.50
|
0.96
|
|
1 x 10-2 M
KI
|
3.28
|
45.33
|
0.45
|
|
0.007 M PD(B)PO + 1 x
10-2M KI
|
0.19
|
96.83
|
0.97
|
|
1 x 10-1 M
KI
|
1.76
|
70
|
0.70
|
|
0.007 M PD(B)PO + 1 x
10-1 M KI
|
0.12
|
98
|
0.98
|
Table
2: Inhibition efficiency and degree of surface coverage values for zinc in 0.1
M HCl solution in the absence and presence of Schiff base and KBr from weight
loss measurement at 27±2 ºC for 7 days of immersion time
|
System/concentration
|
Weight loss(g)
|
%IE
|
Degree of surface
coverage (θ)
|
|
Blank
|
6.0
|
-
|
-
|
|
0.007 M PD(B)PO
|
0.5
|
91.65
|
0.91
|
|
1 x 10-5 M
KBr
|
4.11
|
31.50
|
0.32
|
|
0.007 M PD(B)PO +1 x
10-5 M KBr
|
0.49
|
91.83
|
0.92
|
|
1 x 10-4 M
KI
|
4.00
|
33.33
|
0.34
|
|
0.007 M PD(B)PO + 1 x
10-4M KBr
|
0.412
|
93.13
|
0.93
|
|
1 x 10-3M
KBr
|
3.98
|
33.50
|
0.35
|
|
0.007 M PD(B)PO + 1 x
10-3 M KBr
|
0.38
|
93.67
|
0.94
|
|
1 x 10-2 M
KBr
|
3.52
|
41.33
|
0.41
|
|
0.007 M PD(B)PO + 1 x
10-2 M KBr
|
0.31
|
94.83
|
0.95
|
|
1 x 10-1 M
KBr
|
3.46
|
42.33
|
0.42
|
|
0.007 M PD(B)PO + 1 x
10-1 M KBr
|
0.35
|
95.87
|
0.96
|
Table
3: Inhibition efficiency and degree of surface coverage values for zinc in 0.1
M HCl solution in the absence and presence of Schiff base and KCl from weight
loss measurement at 27±2 ºC for 7 days of immersion time
|
System/concentration
|
Weight loss(g)
|
%IE
|
Degree of surface
coverage (θ)
|
|
Blank
|
6.0
|
-
|
-
|
|
0.007 M PD(B)PO
|
0.5
|
91.65
|
0.91
|
|
1 x 10-5 M
KCl
|
4.22
|
29.67
|
0.30
|
|
0.007 M PD(B)PO +1 x
10-5 M KCl
|
0.51
|
91.50
|
0.92
|
|
1 x 10-4 M
KCl
|
3.99
|
33.50
|
0.34
|
|
0.007 M PD(B)PO + 1 x
10-4M KCl
|
0.41
|
93.16
|
0.93
|
|
1 x 10-3M
KCl
|
3.88
|
35.33
|
0.35
|
|
0.007 M PD(B)PO + 1 x
10-3 M KCl
|
0.39
|
93.50
|
0.94
|
|
1 x 10-2 M
KCl
|
3.76
|
37.33
|
0.37
|
|
0.007 M PD(B)PO + 1 x
10-2 M KCl
|
0.29
|
95.17
|
0.95
|
|
1 x 10-1 M
KCl
|
3.16
|
47.33
|
0.47
|
|
0.007 M PD(B)PO + 1 x
10-1 M KCl
|
0.27
|
95.0
|
0.95
|
The corrosion of zinc
in 0.1 M HCl in the absence and presence of Schiff base as inhibitor, halides
and combination of halides with Schiff base was studied using the weight loss
technique at room temperature (27±2 ºC). The inhibition efficiency as a
function of concentration of inhibitors is shown in Tables 1, 2 and 3. It is
observed that as the Schiff base compound was introduced to the corrodent
solution, the weight loss of the mild steel was reduced while the inhibition
efficiency increased (up to 91.65%). It can also be seen that after the
addition of the halides into the HCl solution with Schiff base compound,
corrosion rates decreased significantly in comparison with Schiff base alone.
As shown in the Tables, when 1 × 10-1 M solutions of the halides
(KI, KBr and KCl) were added into the 0.1 M HCl solution containing 0.007
MSchiff base compound, the weight loss reduced from 6.0, 0.35 and 0.27 and 0.35
g respectively. Accordingly, the percentage of inhibition efficiency increased
up to 98.0, 95.87 and 95.50% respectively. These results suggest that there is
a synergistic effect between inhibitor molecules and halide ions. Synergism of
halide ions was found to be in the order of KI > KBr > KCl with
percentage of inhibition efficiency given by the highest concentration of each
halide ions (1 × 10-1 M). Clearly, the iodide has the strongest synergistic
effect among the three halides and thus will be focused on, on the adsorption
studies.
Adsorption isotherm
studies
The
degree of the surface coverage (θ) was evaluated from the results of
weight loss measurements of zinc in 0.1M HCl in the presence and absence of the
Schiff base and halide ions inhibitors conducted at 30°C and presented in
Tables 1, 2 and 3 for KI, KBr and KCl respectively. The experimental corrosion
data were tested graphically to assess their fittings into three adsorption
isotherms viz: Langmuir, Temkin and Freundlich.Langmuir isotherm is described
by equation 2.
Where C is the inhibitor concentration, θ is the
degree of surface coverage and Kads is the adsorption equilibrium constant
[15]. (sorkhabi et al., 2005).
The plots of C/θ versus C for the two compounds
gave straight lines and are given in figure 1. The linear plots obtained with
low R2 values of (-1.04 and -0.85 for the KI and PD(B)PO
respectively.
Fig.1, Langmuir plots for PD(B)PO and KI inhibitors' synergy.
Temkin isotherm is expressed according to equation
(3): [16].
Where “a” is the Temkin interaction parameter, θ
is the degree of surface coverage of the inhibitor. K is the equilibrium
constant of adsorption and C is the concentration of the inhibitor in the acid
solution. Rearranging and taking logarithm of equation (3), equation 4 is
obtained.
Where the
Plots of θ versus log C for the two Schiff bases
gave linear graphs with R2 values of -3.008, and -4.1515 and
-3.4274, for the PD(B)PO, KI and PD(B)PO+KI systems respectively and are
presented in figure 2,this shows the fitting of experimental data into the
Temkin adsorption isotherm. Values of the Temkin interaction parameter (a)
obtained (-3.81 and -1.23 for the two Schiff base inhibitors respectively) also
support the idea that physical adsorption is applicable.
Fig. 2: Temkin plots for pd(b)po and ki
inhibitors' synergy.
Freundlich adsorption isotherm for the inhibitor
systems is obtained by the relations;
)
In the logarithmic form, it is expressed as;
The
fraction x/m in equation 5 and 6 has been found to be approximate to the
inhibition efficiencies of the inhibitors. K and n are constants. Plots of log
IE (%) versus log C produced straight lines that obeyed Freundlich adsorption
isotherm and are presented in figure 3. R2 values of 8.0373, 0.673
and 0.951 for the inhibitor systems were high, indicating that Freundlich
adsorption isotherm provides the best fitting for the experimental data. This
further supports the idea that there could have been a weak interaction between
the zinc metal surface and the molecules of the two Schiff base inhibitors
(physiosorption) [17].
Fig.2 Freundlich plots for pd(b)po and ki
inhibitors' synergy.
CONCLUSION:
Research on Synergistic
Effect of Halide Ions on the Corrosion Inhibition of Zinc in Hydrochloric Acid
using Schiff base compound, 1-phenyl-2,3-dimethyl-4-(benzylamino)
pyrazole-5-one was carried out. Results suggest that there is a synergy between
inhibitor molecules and halide ions. Synergism of halide ions was found to be
in the order of KI > KBr > KCl with percentage of inhibition efficiency
given by the highest concentration of each halide ions (1 × 10-1 M). Clearly,
the iodide has the strongest synergistic effect among the three halides and
thus will be focused on, on the adsorption studies. Accordingly, the percentage
of inhibition efficiency increased up to 98.0, 95.87 and 95.50% respectively.
Freundlich adsorption isotherm provides the best fitting for the experimental
data, which further suggest weak interaction between the zinc metal surface and
the molecules of the inhibitors (physiosorption)
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