K.Raja, P.A.Jeeva, S.Karthikeyan
Keywords: Corrosion inhibitor, impedance, hydrogen permeation, adsorption
Abstract:
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 Temkin’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 solution-Part I. K.Raja1, P.A.Jeeva1, S.Karthikeyan1* 1 2 School of Mechanical and building Sciences, VIT University, Vellore -632014 , India Surface Engineering Research lab,Centre for Nanobiotechnology, VIT University, Vellore -632014,India Abstract 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 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 Temkin’s adsorption isotherm. Keywords : Corrosion inhibitor, impedance, hydrogen permeation, adsorption 2* corresponding author (skarthikeyanphd@yahoo.co.in) 1 Introduction 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 media 1-3 . 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 surface 5-8 . 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 of APMC 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 2 hydrogen. This delayed failure creates cracking, pitting, breakage, etc., on the metal surface. Experimental 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 measurements. The inhibitor was preliminarily screened by a weight loss method described earlier. [9] Both cathodic and anodic polarisation curves were recorded 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.[4] 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). 3 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 interactions: 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. 4 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 corr are very much similar to those reported earlier 12,13 . 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 I corr 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. 5 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 14 .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 16 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 6 18 who also found that hydrogen permeation current increases with increase in the concentration of di-ortho tolyl thiourea. Impedance studies 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. Conclusions 1. (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 retards the dissolution of SS 304 in 3.5%NaCl. 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. 7 5. The adsorption of the APMC on SS 304 surface obeys Temkin’s adsorption isotherm. References: 1. Singh I., Inhibition of Steel Corrosion by Thiourea Derivatives,Corrosion ,1993, 49, 473. 2. AgrawalR., Namboodhri T.K.G., Inhibition of sulfuric of 410 stainless steel by thioureas, Corr. Sci, 1990,30, 37. 3. Sekine.I.A.,Masuko.A.,Senoo.K., Corrosion of AISI steel in formic acid and acetic acids, Corr. Sci., 1987, 43 , 553. acid 316 corrosion stainless 4. Quraishi M.A., Ansari F.A., Jamal D., Thiourea derivatives as corrosion inhibitors for mild steel in formic acid, Materials Chemistry and Physics, 2003,30, 687. 5. Quraishi M.A., Khan M.A.W, Ajmal M., Influence of some thiazole derivatives on the corrosion of mild steel in hydrochloric acid Anti-Corros.Methods Mater, 1996,43, 5. 6. Murlidharan, S; Iyer, S.V.K., Influence of N-heterocyclics on corrosion inhibition and hydrogen permeation through mild steel in acidic solutions, Anti-Corros. Methods Mater,, 1997, 44, 100. 7. Al-Andis N., Khamis E., Al-Mayouf H., Aboul b Enicm., Electrochemical studies of two corrosion inhibitors for iron in HCl, Corros. Prev. Cont rol, 1995, 42,13. 8. Hammouti B., Aouniti M., Taleb, Bri ghli M., Kertit S. L-Methionine methyl ester hydrochloride as corrosion inhibitor of iron in 1M HCl,Corrosion, 1995, 51,441. 9. N.V.Lakshmi, S.Karthikeyan, N.Arivazhagan, Azithromycin : A Potential Corrosion inhibitor for Aluminum 2024 in acidic medium, Journal of corrosion Science and Engineering, Vol No.17,2014 10. Devanathan,M.A; Til ak,B., The Structure of the Electrical Double Layer at the Metal-Solution Interface, Chem.Revs, 1965,65,635. 11. A. S. Ismail , P. B. Andeng and A. A. El-meligi, Investigating Corrosion Behaviour of Aluminium and Aluminium-Copper Alloy in H2SO4 as Anodizing Solution, Journal of corrosion Science and Engineering, Vol No.17,2014 8 12. B. Anand, Corrosion Efficiency in Controlling Mild Steel in Sulphuric Acid Medium Using Formazan Derivative as Inhibitor, Journal of corrosion Science and Engineering, Vol No.16,2014 13.Reeta Agarwal,Namboodri, T.K.G., The inhibition of sulphuric acid corrosion of 410 stainless steel by thioureas, Corros.Sci, 1990,30,37 14. Madhavan,K. PhD Thesis,Mechanism of Corrosion and its inhibition, Alagappa Uni versity,Indi a,June 1996. 15. Waiter,W; Voss. The Chemistry of Amides, Interscience publishers, Newyork, 1970,383. 16. Gu Hough; Zhou Zhongbai ;Tao Yingachu and Yao Luaw. Study on the effect of thiourea and its derivatives on hydrogen permeation rate in steel in hydrochloric acid solution,Chemical abstracts, 98,38540n. 17. Trabanelli,G and Zucchui F.Revon, Sulphur containing organic compounds as corrosioninhibitors Corrosion and coatings, 1973,1,47. 18. Lahiri,A.K, Banerj ee, N.G, Dissolution of steel and absorption of hydrogen by steel during acid picking in presence of inhibitor, NML Tech.Journal, 1963, 5,33 9 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 gasometrical measurements. Concentration Inhibition efficiency of Inhibitor Weight loss Gasometrical (mM) Studies measurements 1 80.2 80.5 5 84.3 84.6 10 90.3 90.5 50 94.3 94.6 100 97.2 97.6 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 studies. Concentration Ecorr (mV) of Inhibitor (mM) Tafel slopes in mV in dec-1 Icorr -1 mA cm ba Inhibition efficiency (%) bc Blank -511 65 117 2.77 --- 1 -495 73 126 0.44 84.2 10 -483 74 136 0.29 88.6 50 -477 76 149 0.15 94.0 100 -471 85 164 0.08 95.3 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. 10 Concentration of Inhibitor Steady state permeation current (µA) (mM) 1M HCl Blank 21.9 1 26.6 10 28.5 50 29.0 100 31.8 Table 4.Impedance parameters for the corrosion of SS 304 in salt water 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 HCl of Inhibitor Charge Double layer (mM) Transfer capacitance resistance (Rt) (Cdl) µF.cm-2 Ohm.cm2 Blank 4.4 242 1 36 174 10 43.5 134.2 50 79.4 118.3 100 89.3 97 11