Volume 17 Preprint 32
Corrosion inhibition and hydrogen permeation studies of (6R, 7R)-7-[[(2R)-2-amino-2-phenylacetyl]amino]-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid on SS 304 in 3.5% NaCl solution-Part I.
K.Raja, P.A.Jeeva, S.Karthikeyan
Keywords: Corrosion inhibitor, impedance, hydrogen permeation, adsorption
The influence of (6R,7R)-7-[[(2R)-2-amino-2-phenylacetyl]amino]-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid (APMC) on corrosion and hydrogen permeation through stainless steel 304 in 3.5%NaCl has been studied using weight loss measurements and various electrochemical techniques. The compound is found to be more inhibitive in sea water medium. Potentiodynamic polarization studies clearly indicate that APMC behaves as a cathodic inhibitor. Hydrogen permeation studies and AC impedance measurements also prove an improved performance of the compound in 3.5% NaCl. The adsorption of this compound on the stainless steel surface obeys Temkinâ€™s adsorption isotherm.
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Corrosion inhibition and hydrogen permeation studies of (6R, 7R)-7[[(2R)-2-amino-2-phenylacetyl]amino]-3-methyl-8-oxo-5-thia-1azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid on SS 304 in 3.5% NaCl
K.Raja1, P.A.Jeeva1, S.Karthikeyan1*
School of Mechanical and building Sciences, VIT University, Vellore -632014 , India
Surface Engineering Research lab,Centre for Nanobiotechnology, VIT University,
The influence of (6R,7R)-7-[[(2R)-2-amino-2-phenylacetyl]amino]-3-methyl-8oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid (APMC)
on corrosion and
hydrogen permeation through stainless steel 304 in 3.5%NaCl has been studied using
weight loss measurements and various electrochemical techniques. The compound
found to be more inhibitive in sea water medium. Potentiodynamic polarization studies
clearly indicate that APMC behaves as a cathodic inhibitor. Hydrogen permeation
studies and AC impedance measurements also prove
an improved performance of the
compound in 3.5% NaCl. The adsorption of this compound on the stainless steel surface
obeys Temkin’s adsorption isotherm.
Keywords : Corrosion inhibitor, impedance, hydrogen permeation, adsorption
corresponding author (firstname.lastname@example.org)
Thiourea and its derivatives have been studied for more than four decades because
they inhibit the corrosion of steels and are superior to amine-based inhibitors in acid
. Organic compounds containing sulphur, nitrogen and oxygen atoms are
capable of retarding metallic corrosion. As the thiourea molecule contains one sulphur
and two nitrogen atoms, thiourea and its derivatives are potential corrosion inhibitors.
While extensive investigations have been carried out on inhibitor properties of thiourea,
due attention has not yet been paid to a systematic study of inhibitor action of thiourea
derivatives. However, several substituted thiourea have been investigated as corrosion
inhibitors 4. Most of the effective organic inhibitors have heteroatoms such as O, N, S
containing multiple bonds in their molecules through which they can adsorb on the metal
. The corrosion inhibiting property of these compounds is attributed to their
molecular structure. The lone pair determines the adsorption of these molecules on the
metal surface. All the above studies reveal the one common observation that thiourea
derivatives can be regarded as excellent corrosion inhibitors. But studies on the influence
on hydrogen permeation through steel substrate during pickling are very
scarce. A good inhibitor should have the following two important requisites: (1) it should
have very good inhibition efficiency and (2) it should bring down the hydrogen
permeation current to a considerable extent. Some organic compounds give very high
values of inhibition efficiency, but they have a negligible effect in reducing the hydrogen
permeation current and vice versa. Compounds which come under this class produce
hydrogen embrittlement in a later stage by the combination of permeated atomic
hydrogen. This delayed failure creates cracking, pitting, breakage, etc., on the metal
SS 304 of size 4 x 1 x 0.020 cm were used for weight loss and hydrogen
permeation studies. A SS 304 cylindrical rod embedded in araldite resin with an exposed
area of 0.283 cm2 was used for galavanostatic polarisation and AC impedance
The inhibitor was preliminarily screened by a weight loss method described
potentiodynamically (1 mA s-1) using corrosion measurement system BAS Model: 1OOA
computerised electrochemical analyser (made in West Lafayette, Indiana) and PL-10
digital plotter (DMP-40 series, Houston Instruments Division). A platinum foil,
Hg/Hg2Cl2/3.5%NaCl was used as auxiliary and reference electrodes, respectively. The
hydrogen permeation study was carried out using an adaptation of the modified
Devanathan and Stachurski’s two compartment cell, as described earlier. Double layer
capacitance (Cdl) and charge transfer resistance values (R,) were obtained using AC
impedance measurements as described in an earlier publication.” The surfaces of
corroded and corrosion inhibited SS 304 specimens were examined by diffuse reflectance
studies in the region 200- 700 nm using U-3400 spectrometer (UV-VIS-NIR
Spectrometer, Hitachi, Japan).
Results and Discussion
Weight loss and Gasometrical measurements
Table 1 gives the values of inhibition efficiency for different concentrations of
APMC for the corrosion of stainless steel in 3.5 % NaCl obtained from weight loss and
gasometric measurements. It is found that the compound inhibits the corrosion of steel in
neutral media . 9.
The structure of the compound is given in Figure 1.
Figure 1.Structure of APMC.
The inhibition of corrosion of brought about by APMC can be due to the following
1.The interaction between the lone pairs of electrons of the sulfur atom of the
organic compound and the positive charge bearing metal surface 10.
2.The interactions between lone pairs of electrons of the nitrogen atoms and the
positively charged steel surface 11.
3.The presence of phenyl amino in the inhibitor shows inductive (+I) effect may
enhance the electron density on the sulfur atom leading to effective performance .12 .
It is found that there is very good conformity between the values of inhibition efficiency
obtained by weight loss and gasometrical methods.
Potentiodynamic polarization studies
Table 2(a) and 2(b) give values of corrosion kinetic parameters such as Tafel
slopes ( ba and bc ),corrosion current (I corr ) and corrosion potential (E corr ) and inhibition
efficiency obtained from potentiodynamic polarization curves for stainless steel in 3.5%
NaCl containing various concentrations of inhibitor. It can be found from this table that
values of Tafel slopes and I
are very much similar to those reported earlier
Further it is proved that increasing concentrations of APMC boosts the values of tafel
slopes ,but the values of cathodic tafel slopes are enhanced to greater extent. So the
inhibition of corrosion of stainless steel in salt water is under cathodic control. Values of
Ecorr is shifted to less negative values when different concentrations of inhibitor were
used. This could be attributed to the formation of strong adsorbed layer of compound
on the surface of SS 304. The presence of increasing concentrations of APMC decreases
values in salt water. It can also be seen that most of the values of inhibition
efficiency determined by weight loss measurements and potentiodynamic polarization
studies are in good agreement to each other.
Hydrogen permeation measurements
Hydrogen permeation measurements results for the dissolution of stainless steel
304 without and with additions of APMC are given in Table 3. It can be visualized
from the table that the presence of inhibitor in 3.5%NaCl encourages of the ingress of
hydrogen. The enhancement in permeation current might be due to the decomposition of
APMC on the SS 304
.In all the mechanisms suggested so far, invariable the product
of decomposition of inhibitor
is H2S, which is evolved on the metal surface. Its
formation can be detected by radiometric measurements, if labeled thiourea 35 s or its
derivatives are used 15. The whole process occurs in two steps. In the first step, APMC
molecules are adsorbed on the iron metal surface through the interaction of lone pairs of
electrons of nitrogen
and sulfur. In the second stp, the adsorbed molecules of the
compound slowly undergoes chemical changes. In general, these type of inhibitor
festers with the formation of H2S by the action of hydrogen evolved on the metal.
Hough et al
reported that the enhanced permeation of hydrogen ions through
the surface of SS 304 in 3.5% NaCl may be due to the presence of increased number of
surface hydrogen atoms. This can be claimed to the inhibition of the combined hydrogen
atoms to form hydrogen molecules. Trabanelli and Zucchi 17 are of opinion that sulfur of
hydrogen sulfide acted as negative catalyst for the formation of molecular hydrogen. It
can be found from the results that the enhancement of permeation current is greater , if
the concentration of inhibitor is more as studied by Lahiri etal
who also found that
hydrogen permeation current increases with increase in the concentration of di-ortho tolyl
The results of charge transfer resistance (Rt )and double layer capacitance (Cdl)
derived from Nyquist plots are indicated in table 4.It can be noticed that the values of Rt
is found to raise with increase in concentration of inhibitor in salt water. Values of
double layer capacitance are seen to be less in the presence of APMC in 3.5% NaCl .
It is found that values of Cdl are fetched along by increasing concentrations of APMC in
salt water medium. This can be ascribed to enhancing the adsorption of compound on
SS 304 surface with increase in its concentration.
A plot of surface coverage (ø ) versus log C gives a straight line proving that the
adsorption of APMC on the SS 304 surface from both acids follows Temkin’s adsorption
isotherm. This points to corrosion inhibition by APMC, being a consequence of its
adsorption on the metal surface.
azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid retards the dissolution of
SS 304 in
2. The inhibition of corrosion of steel by the inhibitor is under cathodic control.
3. The presence of inhibitor
is found to enhance the extent of hydrogen entry
through steel surface.
4. Nyquist plots authenticate the better performance of the compound.
5. The adsorption of the APMC on SS 304 surface obeys Temkin’s adsorption
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Table 1. Values of inhibition efficiency for the corrosion of SS 304 in 3.5% NaCl in
the presence of different concentrations of APMC obtained from weight loss and
Concentration Inhibition efficiency
Table 2.a Corrosion kinetic parameters of SS 304 in 3.5%NaCl in the presence of
different concentrations of APMC obtained from potentiodynamic polarization
Concentration Ecorr (mV)
Tafel slopes in mV in dec-1
Table 3. Values of permeation current for the corrosion of SS 304 in 3.5% NaCl in
the presence of different concentrations of (6R,7R)-7-[[(2R)-2-amino-2phenylacetyl]amino]-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2carboxylic acid.
Concentration of Inhibitor Steady state permeation current (µA)
Table 4.Impedance parameters for the corrosion of SS 304 in salt water in the
resistance (Rt) (Cdl) µF.cm-2