Synergistic effect of Cetyltrimethylammoniumbromide with
1,3- Diaminopropane, 1-Benzylimidazole and 5-Aminotetrazole
as vapour phase corrosion inhibitor for mild steel under atmospheric aggressive
environments
V. Saini1*, H. Kumar2, S.K. Saini3
1Material Sci. &
Electrochem. Lab., Dept. of Chem., Janta Girls P.G. College, Ellenabad, Haryana
– 125102, India
2Material Sci. &
Electrochem. Lab., Dept. of Chem., Ch. Devi Lal University, Sirsa, Haryana –
125055, India
3Physics Lab., Dept.
of Physics, Janta Girls P.G. College, Ellenabad, Haryana – 125102, India
*Corresponding Author
E-mail: dony84@rediffmail.com
ABSTRACT:
Industrialization and modernization, in now
days, has made a strong demand of steel and their maintenance for a strong
infrastructure for every country in the race of survival, stabilization, growth
and competition. Atmospheric corrosion is naturally occurring deterioration
phenomenon in environment which may cause some dangerous and expensive damage
to everything from automobiles, home appliances, water systems to pipelines,
bridges and public buildings like other natural hazards such as earthquakes or
several weather disturbances. Relative humidity, temperature, sulphur dioxide
content, hydrogen sulphide content, amount of rain fall, dust and even the
position of the exposed metal exhibit marked influence on corrosion behaviour.
Atmospheric corrosion can aggressively accelerate the rate of degradation of
steel during their manufacturing, processing, storage and transportation. In
these cases, traditional methods to prevent corrosion are not suitable which
provide scope of vapour phase corrosion inhibitors (VPCI) in industries,
defense and daily life. Synergistic effect of Cetyltrimethylammoniumbromide
(CTAB) was tested for mild steel in different aggressive atmospheric conditions
with 1,3-Diaminopropane, 1-Benzylimidazole and 5-Aminotetrazole by Weight loss
test, Eschke test, Salt spray test and Sulphur dioxide (SO2) test at
50oC.
KEYWORDS: Synergistic effect, Eschke test, Salt spray test, Vapour phase
corrosion inhibitor, Weight loss test, Sulphurdioxide test, CTAB, DAP, BIZ and
ATZ.
Atmospheric Corrosion, though not a separate form of corrosion, has
received considerable attention because of the staggering associated costs that
result1-7. With large number of outdoor structures such as
buildings, fences, bridges, towers, automobiles, ships and innumerable other
applications exposed to the atmospheric environment, there is no wonder that so
much attention has been given to the subject. Atmospheric corrosion is a
complicated electrochemical process like corrosion cells consisting of base
metal, metallic corrosion products, surface electrolyte and atmosphere. Many
variables influenced the corrosion
characteristics of an atmosphere.
Relative humidity, temperature, sulphur
dioxide content, hydrogen sulphide content, chloride content, amount of rain
fall, dust and even the position of the exposed metal exhibit marked influence
on corrosion behavior, geographic location is also a factor. Atmospheric
corrosion depends not only on the moisture content present but also on the dust
content and the presence of other impurities in the air, all of which have an
effect on the consideration of moisture on the metal surface and the resulting
corrosiveness. Air temperature can also be a factor. All types of corrosion may
takes place, depending on the specific contaminants present and materials of
construction. Corvo8 and Moricelli et al.9 studied the
relationship between chloride ion concentrations with corrosion rate in
atmospheric conditions. Ericsson10
showed that NaCl can cause corrosion at very low concentration because it can
induce corrosion by SO2 on a carbon steel surface. NaCl can enhance
14 times rate of corrosion by SO2 at 9% relative humidity. In
another report of Blucher et al.11,
they have investigated adverse effect of CO2 on corrosion of
aluminium. Vuorinen et al.12 and a list of authors have worked on
organic compounds as VPCIs. Organic substances have been studied as VPCI for
mild steel were morpholine derivatives and diaminohexane derivatives13,
fatty acid thiosemicarbazides14, cyclohexylamine and
dicyclohexylamine15-16, amine carboxylates17, ammonium
caprylate18, benzoic hydrazide derivatives19, polyamines20,
bis-piperidiniummethyl-urea and β–amino alcoholic compounds21.
Apart from organic substances, natural compounds like wood bark oil22
and thyme23-24 have also been used as VPCIs. Cano et al.25 recently have proposed mechanism of
inhibition of dicyclohexaminenitrite and dicyclohexamineisonitrite against
corrosion due to vapours of acetic acid and formic acid on carbon steel.
Zubielewicz et al26 studied
the electrochemical behavior of mixed anodic inhibitors. Batis et al.27 evaluated the performance of two
primers, first natural rust converter and other on organic primer coating
containing VPCI against atmospheric corrosion for reinforcing steel. Lyublinski28 studied
synergistic corrosion management systems by use of corrosion inhibitors. In
continuation to our earlier study29-36, in the present study, the
inhibiting properties of Cetyltrimethylamoniumbromide (CTAB) was investigated
on mild steel at 85% relative humidity and 50°C by Weight loss test, Salt spray
test in a solution of 3.0% NaCl, Eschke test and SO2 test.
Synergistic effect of CTAB were tested with 1,3-Diaminopropane (DAP),
1-Benzylimidazole (BIZ) and 5-Aminotetrazole (ATZ) to enhance the corrosion
inhibition action of CTAB.
2. MATERIALS AND METHODS:
2.1 Material
Mild steel (ASTM-283)
coupons of dimensions 3.5cm × 1.5cm × 0.025cm and of chemical composition:
C–0.17, Si–0.35, Mn–0.42, S–0.05, P–0.20, Ni–0.01, Cu–0.01, Cr–0.01 and
Fe-balance (w/w) were used.
2.2
Equipments
2.2.1
Weighing balance
Single pan analytical
balance, Precision 0.01mg, Model AB 135-S/FACT, Source Mettler Toledo, Japan.
2.2.2
Humidity chamber
Thermotech. TIC-4000N
Temperature Controller, Humidity controller with course and fine adjustments,
AC Frequency 50-60Hz, Max. voltage 300V, Source Make-Associated Scientific
Tech., New Delhi.
2.2.3
Salt spray chamber
Thermotech. TIC-4000N Temperature Controller,
Pumping system Pt-100, AC Frequency 50-60Hz, Max. voltage 300V, Source
Make-Associated Scientific Tech., New Delhi.
2.2.4
Air thermostat
Nine adjustable chambered, Electrically
controlled, Accuracy ± 0.1oC.
2.3
Methods
2.3.1
Vapour pressure
determination test
A definite amount of exactly weighted VPCI was placed in a single neck
round bottom flask fitted with a rubber cork in the neck having a glass
capillary of 1.0 mm diameter in the center of rubber cork. Then the flask was
kept in electrically controlled air thermostat maintained at the constant
temperature of 500C for 10 days. Change in weight of VPCIs was
observed by analytical balance and vapour pressure of investigated VPCI was
determined by weight loss of VPCI for time of exposure by equation 1.
Where, P = vapour pressure of VPCI (mmHg), A = area of
orifice (m2), t = time of exposure (sec.), W = weight
loss of VPCI (kg), T = temperature (K), M = molecular mass of the
inhibitor (kg) and R = gas constant (8.314 JK-1mol-1).
2.3.2
Weight loss test
Mild steel coupons were mechanically polished successively with the help
of emery papers grading 100, 200, 300, 400 and 600μ and then thoroughly
cleaned with plenty of triple distilled water, ethanol and acetone. Then coupons were dried with hot air blower
and stored in desiccators over silica gel. Weight loss tests were carried out
in an electronically controlled air thermostat maintained at a constant temperature
of 50oC. After recording the initial weights of mild steel coupons,
they were kept in different isolated chambers of air thermostat having fixed
amount of VPCI at a constant temperature of 50oC for 24 hours of
exposure time. A uniform thin film of VPCI was adsorbed onto the metal coupon
surface after 24 hours of exposure. Then these coupons were transferred to a
digitally controlled humidity chamber maintained at 85% humidity at a constant
temperature of 50oC for 10 days. Blank coupons untreated with VPCI
were also kept in humidity chamber for the same duration in the same corrosive
environment. After exposing the coupons for 10 days, coupons were taken out
from the humidity chamber and washed initially under running tap water. Loosely
adhering corrosion products were removed with the help of rubber cork and
coupon was again washed dried and then weighed again. Corrosion rate in miles
per year (mpy) and percentage corrosion inhibition efficiency (PCIE) were
calculated by using equations 2 and 3 respectively.
Where, CR = corrosion rate (in miles per
year), W = weight loss (in mg), D = density of mild steel (in g/cm3),
A = area of coupon (in sq. inch), T = exposure time (in hour).
Where, PCIE =
percentage corrosion inhibition efficiency, CRo = corrosion rate in
absence of inhibitor and CR = corrosion rate in presence of inhibitor.
2.3.3
Salt spray test
After exposing the
pre-weighted mild steel coupons to VPCI in air thermostat for 24 hours, they
were transferred to salt spray chamber having 3.0% NaCl solution maintained at
50oC for duration of 10 days along with blank coupons. After
exposing coupons for 10 days, coupons were treated in same manner as treated in
weight loss test to remove corrosion products and then CR and PCIE were
calculated.
2.3.4
Eschke test
Kraft papers of suitable size were dipped in the VPCI for 30 seconds and
then dried to adsorb uniform layer of inhibitor on Kraft papers. Mild steel
coupons were wrapped in VPCI impregnated Kraft papers and then kept in humidity
chamber maintained at 85% relative humidity maintained at 50oC for
first 12 hours and 25oC for next 12 hours alternately for 10 days.
This temperature cycle was maintained in two sets because of formation
and condensation of vapours of VPCI on mild steel surface regularly. After
exposure time of test, corrosion parameters were determined.
2.3.5
Sulphurdioxide test
SO2 test was carried out on the mild steel coupons as in
weight loss test. SO2 gas was prepared by dissolving 0.04g of sodium
thiosulphate in 30mL aqueous solution of 1.0% NH4Cl and 1.0% Na2SO4
solution and 0.5mL of 1.0N H2SO4 was added to the flask.
Initially pre-weighed and mechanically polished mild steel coupons were placed
in air thermostat maintained at 50oC for duration of 10 days.
Definite weight of VPCIs in a petridis and flask, which is the source of SO2,
was placed in the isolated chambers of air thermostat containing mild steel
coupons. After exposing coupons for 10 days, CR and PCIE were calculated.
3. RESULTS AND DISCUSSION:
Synergistic Effect of CTAB: CTAB is a
suitable vapour phase corrosion inhibitor due to presence of a long hydrophobic
chain in the molecule of CTAB which provide it ability to form a barrier film
on the surface of mild steel to protect the mild steel from water vapours and
corrosive contents of atmosphere around the mild steel as shown in Figure-1.
But absence of any lone pair donor atom, low vapour pressure and vapour density
is the cause of low PCIE of CTAB. To increase the PCIE of CTAB, synergistic
effect of CTAB with DAP, BIZ and ATZ was tested by Weight loss test, Eschke
test, Salt spray test and SO2 test.
Figure-1 Mechanism of action of CTAB on Mild Steel Coupon surface.
3.1
Vapour pressure
determination test
Results of this test
for different combinations of CTAB are given in Table-1.
Table-1 Vapour pressures of
combinations of CTAB.
|
Combinations of CTAB |
Vapour pressure (10-2mmHg) |
|
CTAB |
0.41 |
|
CTAB + DAP |
173.74 |
|
CTAB + BIZ |
108.39 |
|
CTAB + ATZ |
10.96 |
3.2
Weight loss test
To determine the
synergistic effect of CTAB, different combination of CTAB with different VPCIs
were tested through weight loss test. By the results of this test, weight loss,
CR and PCIE of the combinations were determined which are given in Figure-2.
Results of this test are clearly showing the synergistic effect of CTAB in
which PCIE of CTAB in the combination are very good as compared with the
individual performance.
Figure-2 Weight loss(x10-1mg), CR(x10-4mpy) and
PCIE of CTAB with different VPCIs obtained from Weight loss test.
From Figure-2, it is
clear that the weight loss and CR of combinations of CTAB are very low as
compared to that of CTAB. It is due to increase in vapour pressure and vapour
density of the combinations. It is observed that specific sites of active
functional groups for the adsorption of VPCIs are increased and enhanced PCIE
of combinations.
3.3
Salt Spray Test
Results of weight
loss, corrosion rate of mild steel coupon and PCIE of different treated VPCIs
under the aggressive Cl- ions environment after 10 days exposure
time duration are given in Figure 3.
Figure-3 Weight loss (×10-1mg), CR (×10-4mpy)
and PCIE of CTAB with different VPCIs obtained from Salt spray test.
Results of this test
clearly show the synergistic effect of CTAB in which PCIE of CTAB in the
combination are high as compared with the individual performance. It is shown
that the PCIE of mixtures are higher than that of individual CTAB in salt spray
test. Corrosive effect of direct spray of chloride ions on the mild steel
coupon can be easily explained by the PCIE in this test.
3.4
Eschke Test
To determine the
synergistic effect of CTAB, different combinations of CTAB with different
vapour phase corrosion inhibitors were tested by direct contact of VPCIs on the
mild steel coupon through Eschke test. By the results of this test, weight
loss, corrosion rate and percentage corrosion inhibition efficiencies of
different combinations were determined which are shown in Figure-4.
Figure-4 Weight loss (×10-1mg), CR (×10-4mpy) and
PCIE of CTAB with different VPCIs obtained from Eschke test.
Effect of direct
contact of VPCI on the mild steel coupon can be easily explained by the PCIE in
this test. Due to direct contact of VPCI on the surface of mild steel, VPCI
produces a barrier film on the mild steel surface by the adsorption of its
vapour to protect the mild steel from the water vapours and aggressive
corrodents of atmosphere and the PCIE for combinations are enhanced from 50.69%
to 89.16% and CTAB perform an efficient VPCI due to its synergistic effect.
3.5
Sulphurdioxide test
To determine the synergistic effect of CTAB, different
combinations of CTAB with different vapour phase corrosion inhibitors were
tested by the effect of sulphate ions on the mild steel through SO2
test. By the results of this test, weight loss, corrosion rates and percentage
corrosion inhibition efficiencies of the combination were determined which are
shown in Figure-5.
Figure-5 Weight loss (×10-1mg), CR (×10-4mpy) and
PCIE of CTAB with different VPCIs obtained from SO2 test.
From the results obtained from the different
tests performed on mild steel coupons in different aggressive environments, the
PCIE of the combinations of VPCIs are analyzed to obtain the probable mechanism
and the corrosion inhibition action of VPCI as given in Figure-6.
Figure-6 Comparison of PCIE of different tested combinations in all
tests performed.
From Figure-6, it is
clear that CTAB is performing efficiently as VPCI in combinations with DAP, BIZ
and ATZ because in all combinations, PCIE are more than that of individual CTAB
(44.70%) and the combinations show inhibition action in weight loss test in the
following order:
CTAB+DAP > CTAB-BIZ
> CTAB+ATZ
Due to presence of
two amine groups having lone pair donar N atoms in the molecule of DAP and
1-BIZ, it provide active attacking site to adsorb on the surface of mild steel
coupon by acid base interaction. Vapours of DAP adsorb by chemisorptions and
form uniformly layer on mild steel coupon surface and then CTAB show further
multilayered non specific physical adsorption due to hydrophobic – hydrophobic
interaction between the propyl part of DAP and long hydrocarbon chain of the
CTAB as shown in Figure-7. Presence of methylene group near the lone pair donar
atom enhances the electron density of N atom and basic strength of 1-BIZ by
inductive effect. 5-ATZ have many active sites to attach with the surface of
metal but due to presence of many lone pair atoms, electron density become very
high so there is electron repulsion between these lone pairs in the molecule
with provide very high basic strength to the molecule. So, due to acid-base
mechanism, PCIE of 5-ATZ should be very high but actual this is not so due to
low vapour pressure.
Figure-7 Mechanism of action of CTAB+DAP on Mild Steel Coupon surface.
Due to direct contact
of NaCl salt on the surface and its hydrolysis products accelerate the corrosion
rate due to which PCIE is slightly lower than that of weight loss test from
Figure-3, it is shown that PCIE of different combinations of VPCI with CTAB is
in order:
CTAB+BIZ > CTAB+DAP > CTAB+ATZ
Presence of benzene
ring provides π-electrons systems which make 1-BIZ as a good surfactant to
show inhibition action against corrosion in Salt spray test, Eschke test. In SO2
test, although ATZ has high basic strength ATZ should show high PCIE but very
low vapour pressure lowers the PCIE of ATZ. From the results of combinations of
CTAB with different VPCIs in weight loss test, salt spray test, Eschke test and
SO2 test, it is clear that CTAB perform as efficient VPCI for mild
steel under atmospheric corrosion. In
combination of CTAB with DAP, BIZ and ATZ vapour pressure rises to a level of
best performance.
4. CONCLUSIONS:
As a result of experimental work carried out
on the performance of investigated vapour phase corrosion inhibitors, a deep
analysis of corrosion parameters obtained by corrosion testing experiments,
morphology of mild steel coupon show that CTAB perform excellent corrosion
inhibition properties against the aggressive environments of SO2 and
NaCl at high relative humidity and high temperature. From the experimental
study it is concluded that
a)
Due to rise in vapour pressure of CTAB with combinations
of DAP, BIZ and ATZ, rate of adsorption of CTAB on mild steel coupon is
increased by which CTAB form barrier layer on mild steel easily and protect
mild steel from corrodents of environments.
b)
Presence of two lone pair donar atoms in DAP and 1-BIZ
molecules increase the basic strength of combinations by which it can easily
neutralize the acidic character of environment around mils steel coupon and
retard the CR.
c)
Presence of alkyl group near the lone pair donar atom in
DAP and 1-BIZ enhance the basic strength due to +I effect and protect the mild
steel easily by neutralize of acidic environment.
d)
Presence of π-electrons provides the adsorption
system to form barrier on mild steel coupon for atmospheric corrodents.
e)
Presence of aggressive chloride ions penetrate the
barrier layer and decrease the PCIE of VPCIs and direct contact of VPCIs in
Eschke test enhance the PCIE of VPCIs.
5.
ACKNOWLEDGMENT:
We
are very thankful to Ch. Devi Lal University for provide us financial support, laboratory
and equipments facility for this research work.
6.
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Received on 20.09.2015 Modified on 11.10.2015
Accepted on 15.10.2015 © AJRC All right reserved
Asian J. Research
Chem. 8(11): November 2015; Page 675-682
DOI: 10.5958/0974-4150.2015.00108.X