CHARACTERIZATION OF ANTI-CORROSION TRIAZOLE FILM By ...

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CHARACTERIZATION OF ANTI-CORROSION TRIAZOLE FILM
By
K. K. Taha & A. Muhideen
KEY WORDS: zinc, corrosion, inhibition, mercaptotriazole, sea water.
ABSTRACT
Mercaptotriazole (MTRA) was used to inhibit the zinc corrosion by the Red
sea water. The cyclic voltammetric study revealed that the anodic and
cathodic peaks disappeared. The surface morphology of scanning electron
microscopy (SEM) indicated a rough surface of zinc when exposed to sea
water and smooth surface when the inhibitor was added. The energy
dispersive x-ray analysis (EDAX) experiment supported the binding of the
sulfur atom of MTRA on zinc surface.
: ����ﻟا
ﺓﺭﻴﺴﻝﺍ ﻱﺭﻭﺩ ﺔﺴﺍﺭﺩ ﺕﻔﺸﻜ.
ﺭﺤﺒﻝﺍ ﺀﺎﻤﺒ ﻙﻨﺯﻝﺍ لﻜﺂﺘ ﻁﻴﺒﺜﺘﻝ ﻲﺘﻴﺭﺒﻜﻝﺍ لﻭﺯﺍﺭﺘﻝﺍ ﺏﻜﺭﻤ ﻡﺩﺨﺘﺴﺍ
ﻲﻨﻭﺭﺘﻜﻝﻻﺍ ﺢﺴﻤﻝﺍ ﺭﻬﺠﻤ ﻡﺍﺩﺨﺘﺴﺎﺒ ﺢﻁﺴﻝﺍ ﺔﺴﺍﺭﺩ ﺩﻨﻋ . ﺕﻔﺘﺨﺍ ﺩﻗ ﺩﻌﺼﻤﻝﺍﻭ ﻁﺒﻬﻤﻝﺍ ﻡﻤﻗ ﻥﺍ ﺔﻴﺘﺍﺫﻝﺍ
ﻥﻋ لﻴﻠﺤﺘﻝﺍ
. ﺱﻠﻤﺍ ﺢﻁﺴﻝﺍ ﺕﻠﻌﺠ ﺩﻗ ﻁﺒﺜﻤﻝﺍ ﺔﻓﺎﻀﺍ ﻥﺍ ﻻﺍ ﹰﺎﻨﺸﺨ
ﻥﺎﻜ لﻜﺂﺘﻤﻝﺍ ﻙﻨﺯﻝﺍ ﻥﺍ ﻅﺤﻭﻝ
. ﻙﻨﺯﻝﺍ ﺢﻁﺴﺒ ﻁﺒﺜﻤﻝﺍ ﺀﻰﻴﺯﺠ ﻲﻓ ﺕﻴﺭﺒﻜﻝﺍ ﻁﺎﺒﺘﺭﺍ ﻡﻋﺩ ﺔﻴﻨﻴﺴﻝﺍ ﺔﻌﺸﻷﺍ ﺕﺘﺸﺘ ﻕﻴﺭﻁ
INTRODUCTION
The marine environment with its high concentration chlorides, sulphate salt
and carbon dioxide and oxygen gases in addition to other impurities has
severe corrosivity [Li, 2001]. The high humidity also increases the corrosion
rate of metals in the sea coastal areas. The use of zinc sheets as roofing
material and in galvanization of steel makes the study of its corrosion an
important theme. The use of organic compounds as corrosion inhibitors is a
common way of protecting metal surfaces from being corroded [Leroy,
1978]. Triazoles were used as corrosion inhibitors for bronze [Dermaj et al ,
2007], steel [Weihua et al, 2007], aluminum [Zheludkevich et al, 2005], and
brass [Ravichandran et al, 2005] in different media.
MATERIALS AND METHODS
2-Mercaptotriazole (MTRA) Analytical Grade (AR) (Merck-Germany) was
used without purification and the red sea water was used for making
inhibitor solutions. About 6.00 cm 2 from HG zinc (high-grade zinc, 99.95 %
pure) sample was cut and covered with epoxy adhesives resin except 2 cm 2
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area at the lower part which was exposed to corrosive medium i.e. Red sea
water. The zinc electrode was polished with sand paper, washed in running
tap water, rinsed in distilled water before exposure to sea water and sea
water containing 0.01M MTRA inhibitor. The cyclic voltamograms were
obtained using an electrochemical system Autolab (Netherlands) at
corrosion potentials over a potential window between –2000 and 550 mV (vs
SCE) at sweeping rate of 10 mV/s. A three compartment cell with zinc as
working electrode, platinum foil and saturated calomel electrode as counter
and reference electrodes respectively were used for CV studies The scanning
electron micrographs of the polished zinc surface after exposure to sea
water and sea water containing 0.01M inhibitor were taken using vacuum
scanning electron microscope model JEOL JSM-5600 LV interfaced to a
computer and JSM software. The energy dispersive x-ray analysis (EDAX)
studies calibration was done with respect to Co Kα = 6.9254 keV and Co Lα
= 0.7763 keV.
RESULTS AND DISCUSSION
Organic compounds containing heteroatoms find application as
corrosion inhibitors as these atoms with lone pairs of electrons are a site of
their binding to metal surfaces [Leroy, 1978]. Triazoles derivatives are
becoming very important both as corrosion inhibitors for metals [Wang,
2001, Dermaj et al, 2007, El-sayed et al, 2007 and Taha, 2002] and as ligands
especially for complexation with transition metals [Raicheva et al, 1993].
The high inhibition efficiency for triazoles is attributed to their structures as
proved by ab initio quantum chemical calculations [Weihua et al, 2007]. The
correlation between the molecular modeling about the structure and
electronic effect and inhibition efficiency was studied by Bentiss et al
[2001].
Figures 1and 2 show the cyclic voltammetric response of zinc in the Red sea
water without and with the inhibitor. The results tabulated (Table 1) reveal
an anodic and a cathodic peak at 378 mV and – 1030 mV with currents 20.48
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mA and -76.38 mA respectively without inhibitor. The anodic peak may be
due to the zinc dissolution i.e. oxidation process (Zn Zn +2 ), while the
reduction peak may be oxygen reduction
(O 2 + 2H 2O + 4 ē 4OH - ) taking place in presence of the inhibitor the anodic
peaks vanished as well as the cathodic peaks. The disappearance of the
peaks indicates that the inhibitor has hindered both anodic and cathodic
reactions leading to the inhibition of zinc corrosion. These findings agree
with the fact that the triazole derivative inhibitors are mixed inhibitors
[Zheludkevich et al, 2005] which suppress the anodic and cathodic currents
[Ravichandran et al, 2004 and [Kareema et al, 2004].
I (mA)
-2.5 -2 -1.5 -1 -0.5 0 0.5 1
-200
Fig. (1): CV for Zn in sea water
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E (V)
1000
800
600
400
200
0
-400
-600
-800
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I (mA)
-2.5 -2 -1.5 -1
0
-0.5
-0.0001
0 0.5 1
E (V)
Fig. (2): CV for Zn in sea water + MTRA
Table (1): Anodic and cathodic peaks from cyclic-voltammograms
Compound Anodic Peak Cathodic Peak
E anodic (mV) I anodic (mA) E
(mV)
cathodic I cathodic (mA)
Zn + Sea water 378 20.48 -1030 -76.38
Zn +Sea water + MTRA …… ….. …… ……
The SEM photographs for the corroded zinc surface and the surface after
addition of inhibitors are shown in figures 3 and 4 respectively. The
inhibitors function by adsorption on metal surface forming a film. The
evidence for the presence of the film on zinc surface comes from SEM
photographs where fine surface film is seen on the surface exposed to sea
water containing the inhibitor (Fig.4) when compared to the surface exposed
to sea water without inhibitor (Fig. 3). Figure (3) shows large grained
morphology with deep terraces while the films obtained in the presence of
inhibitors show smooth small grained surface [Taha, 2002]. A previous study
[Ravichandran et al, 2005] with SEM technique supported the formation of a
compact surface film on brass surface in presence of the triazole inhibitor.
Kunitsugu [Kunitsugu, 2001] suggested that the inhibitors formed protective
films of Zn (II) salts or complexes on zinc surface together with zinc
hydroxide and oxide to prevent corrosion. Mercaptotriazole was found to be
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0.0005
0.0004
0.0003
0.0002
0.0001
-0.0002
-0.0003
-0.0004
-0.0005

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Vol. 10(2) 2009
a strong nucleophile [Saeed et al, 2005], ], which can easily bind to the zinc
ions on zinc surface.
Fig. (3) SEM of zinc surface in sea water
Fig. (4) SEM of zinc surface in sea water +MTRA
Figures (5) and (6) are the energy dispersive x-ray x analysis (EDAX) results for
zinc in sea water without and with MTRA. . When zinc was immersed in sea
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water a high percentage of chloride can be observed together with little
sulfur (Table 2). This may be attributed to the high chloride and sulphate in
sea water that lead to the corrosion of zinc. The presence of low “Zn” and
"Cl" contents and high "S" content on the surface suggests the bonding
between the inhibitor molecules and zinc substrate. Similar conclusions
were reached by Dermaj et al [ Dermaj et al, 2007] that showed the presence
of sulfur on the surface using x-ray electron dispersion analysis (EDAX)
when the sulfur containing inhibitor was used.
Fig. (5) EDAX diagram of sea water + zinc
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Fig. (6)EDAX diagram of sea water +zinc +MTRA
Table (2): Elemental content (%) on Zn surface from EDAX experiment
Medium \ Element Zn Cl
Zn + sea water 49.61 47.72
Zn + sea water + MTRA 2.56 21.33
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S
2.67
76.12
CONCLUSIONS
1. The inhibitor 2-mercaptotriazole is a promising inhibitor for zinc in
sea water.
2. The cyclic voltammetric study revealed it to function as both anodic
and cathodic inhibitor.
3. The SEM and EDAX images supported the film formation mechanism.

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