Kh. Benbouya, I. Forsal, B. Mernari, R. Touir, M. Bennajah, M. Ebn Touhami
Keywords: Corrosion inhibition, Mild steel, Acidic media, Polarization, Impedance
Abstract:
The inhibition behavior of 6-methyl-4,5-dihydropyridazin-3(2H)-one (TR) on mild steel in 1 M HCl and 0.5 M H2SO4 containing different concentration of TR was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy studies. It has been observed that corrosion rate decreases and inhibition efficiencies increases with increasing in TR concentration and immersion time in case of HCl. The recorded electrochemical data indicated the basic modification of mild steel surface as a result in a decrease in the corrosion rate. Corrosion inhibition could be explained by considering an interaction between metal surface and the inhibitor.
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ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 6-methyl-4,5-dihydropyridazin-3(2H)-one as a novel corrosion inhibitor for mild steel in acidic media Kh. Benbouyaa, I. Forsala;b*, B. Mernarib, R. Touira, M. Bennajahc, M. Ebn Touhamia a: Electrochemical corrosion and environment laboratory, IBN Tofail University, Faculty of Science, BP 133 Kenitra, Morocco b: Coordination and analytical Chemistry laboratory, Chouaib Doukkali University, Faculty of Science El Jadida, Morocco (prmernari@yahoo.fr). c : Laboratoire de Génie des Procédés industriels, Ecole Nationale de l’industrie minérale, AvHaj Ahmed CherkaouiBP 753Agdal, Rabat. Abstract The inhibition behavior of 6-methyl-4,5-dihydropyridazin-3(2H)-one (TR) on mild steel in 1 M HCl and 0.5 M H2SO4 containing different concentration of TR was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy studies. It has been observed that corrosion rate decreases and inhibition efficiencies increases with increasing in TR concentration and immersion time in case of HCl. The recorded electrochemical data indicated the basic modification of mild steel surface as a result in a decrease in the corrosion rate. Corrosion inhibition could be explained by considering an interaction between metal surface and the inhibitor. Keywords: Corrosion inhibition, Mild steel, Acidic media, Polarization, Impedance * Corresponding author. : Tel.: +212661832840 E-mail address: forsalissam@yahoo.fr © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 1. Introduction : Metals generally tend to move to its original state by corrosion process. Mild steel is an alloy form of iron, which undergoes corrosion easily in acidic medium. Acidic solutions are extensively used in chemical laboratories and in several industrial processes such as acid pickling, acid cleaning, acid descaling and oil wet cleaning etc. Also mild steel is used under different conditions in chemical and allied industries for handling alkaline, acid and salt solutions. Chloride, sulphate and nitrate ions in aqueous media are particularly aggressive and accelerate corrosion [1]. Most of the efficient inhibitors used in industry are organic compounds which mainly contain oxygen, sulphur, nitrogen atoms and multiple bonds in the molecule through which they are adsorbed on metal surface [2–6]. Moreover, many N-heterocyclic compounds have been proved to be effective inhibitors for the corrosion of metals and alloys in aqueous media [7–13]. This work deals with the study of the corrosion inhibition properties of 6-methyl-4,5dihydropyridazin-3(2H)-one (TR). The choice of this compound was based on the consideration that this compound contains π-electrons and heteroatoms such as N and O, which induce greater adsorption of the inhibitor molecule onto the surface of mild steel. The aim of this study was to determine the inhibition efficiency of (TR) as a novel inhibitor for the corrosion of mild steel in 1M HCl and 0.5 M H2SO4. 2. Experimental method: 2.1. Materials: Mild steel specimens of the following chemical composition (wt.%) were used for the experiment: C=0.11, Si=0.24, Mn=0.47, Cr=0.12, Mo=0.02, Ni=0.1, Al=0.03, Cu=0.14, W=0.06, Co<0.0012, V<0.003 and the remainder Fe. The structural formula of inhibitor is shown in Fig. 1. Its concentration was varied from 10-4 M to 10-2 M. The electrolyte solution 1M HCl and 0.5M H2SO4 were prepared from commercial 37% HCl and 98% H2SO4, respectively, and distilled water. H3 C O N N H Fig.1 : molecular structure of inhibitor © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 2.2. Gravimetric measurements: The mild steel sheets of 2cm×5cm×0.05cm were abraded with emery paper (grade from 400 to 1200) and then washed with distilled water and acetone, dried at room temperature. After weighing accurately, the specimens were immersed in corrosive medium with and without the addition of different concentrations of inhibitor for 6 h. The mild steel sheets were then taken out, washed with distilled water and acetone, dried and weighed accurately. The average weight loss of three substrate sheets could be obtained. The inhibition efficiency (IE %) of inhibitors on the corrosion of mild steel was calculated as follows: IE % 0 100 0 (1) Where ω0 and ω are the values of the average weight loss without and with addition of the inhibitors, respectively. 2.3. Electrochemical measurements Electrochemical measurements were conducted in a conventional three-electrode cylindrical glass cell at 20°C with a platinum counter electrode (CE) and a saturated calomel electrode (SCE) as the reference electrode. The working electrode (WE) was in the form of a square cut from mild steel embedded in epoxy resin of polytetrafluoroethylene (PTFE) so that the flat surface was the only surface in the electrolyte. The working surface area was 1cm2. The polarization curves were recorded by using a potentiostat/galvanostat (PGZ100). The potential increased with a speed of 1 mV/s and started from potential of -750 mV to -100 mV vs. SCE for 1M HCl and 0.5M H2SO4 at 20°C. The IE% was defined as: 0 icorr icorr IE % 100 0 icorr (2) 0 Where icorr and icorr are the corrosion current densities values without and with inhibitor, respectively. 2.4. EIS measurements: The electrochemical impedance spectroscopy measurements were carried out using a transfer function analyser (VoltaLab PGZ 100), with a small amplitude ac. Signal (10 mV rms), over a frequency domain from 100 KHz to 10 mHz at 20°C. The results were then analysed in terms of equivalent electrical circuit using bouckamp program [14]. The charge transfer resistance Rct, is obtained from the diameter of the semicircle in Nyquist representation. The inhibition efficiency of the inhibitor has been found from the relationship: © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 IE % Rct Rct0 100 Rct submitted 25 January 2010 (3) Where Rct0 and Rct are the charge transfer resistance values in the absence and the presence of inhibitor, respectively. 3. Results and discussion: 3.1. Gravimetric measurements: Tables 1 and 2 show the result for mild steel in corrosive medium in the absence and presence of TR at 20°C. The inhibition efficiency was greater than 92% and 21% in case of 1M HCl and 0.5M H2SO4, respectively. TR inhabited the corrosion of mild steel in both acids. As corrosion rate decreased, inhibition efficiency increased with increasing TR concentration in the test solution. This inhibition can be due the formation of an organic film on the metal surface through sharing electrons between nitrogen or oxygen and iron atoms. However, inhibition efficiency values are maximum in case of 1M HCl than 0.5M H2SO4. This is probably due to the lesser surface coverage in H2SO4 solution. Again chloride ions have a greater adsorption tendency than sulphate ions on steel [15]. Table 1: inhibition efficiency for various concentration of TR for the corrosion of mild steel in 1 M HCl obtained from weight loss measurements at 20°C (6h of immersion) Inhibitor conc. (M) Blank 10-4 10-3 5 ×10-3 10-2 Corrosion rate (mg.cm-2.h-1) 3.026 0.241 0.110 0.057 0.045 inhibition efficiency, IE (%) --92 96 98 98 Table 2: inhibition efficiency for various concentration of TR for the corrosion of mild steel in 0.5M H2SO4 obtained from weight loss measurements at 20°C (6h of immersion) Inhibitor conc. Corrosion rate inhibition efficiency, (M) (mg.cm-2.h-1) IE (%) Blank 7.243 --10-3 5.728 21 5×10-3 4.657 35 10-2 4.100 43 5×10-2 3.237 55 © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 3.2. Potentiostatic polarization study: Figures 2 and 3 show polarization curves for mild steel in 1M HCl and 0.5M H2SO4 with and without various concentration of TR. TR suppressed the cathodic and anodic reactions. It is clear that the addition of TR hindered the acid attack on the mild steel electrode and a comparison of curves in both cases, showed that, with respect to the blank, increasing the concentration of inhibitor gave rise to a consistent decrease in anodic and cathodic current densities indicating that TR acts as a mixed type inhibitor [16,17]. The polarization parameters such as corrosion potential (Ecorr) and corrosion current densities (icorr) obtained by extrapolation of the Tafel lines are listed in table 3 and 4. The calculated percentage inhibition efficiency (IE%) of TR are also given. Analysis of these data show that icorr decreased with addition of TR in 1M HCl and 0.5M H2SO4, can be due to increase in the blocked fraction of the electrode surface by adsorption. HCl 1M -4 10 M -3 10 M -3 5.10 M -2 10 M 100 10 -2 I (mA.cm ) 1 0,1 0,01 1E-3 -0,7 -0,6 -0,5 -0,4 -0,3 -0,2 -0,1 E (V/ECS) Fig.2 : Polarization curves of mild steel recorded in 1M HCl containing different concentration of TR at 20°C © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 20 30 40 50 100 °C °C °C °C -2 I (mA.cm ) 10 1 0,1 0,01 -0,8 -0,7 -0,6 -0,5 -0,4 -0,3 -0,2 -0,1 0,0 E (V/ECS) Fig.3 : Polarization curves of mild steel recorded in 0.5M H2SO4 containing different concentration of TR at 20°C Table 3: electrochemical parameters for the corrosion of mild steel 1M HCl containing different concentration of TR at 20°C (30 min of immersion) Conc. (M) Ecorr(mV/sce) icorr (µA.cm-2) IE (%) -c(mV.dec-1) 00 10-4 10-3 5×10-3 10-2 -396 -387 -424 -443 -453 1072 108 84 50 31 125 120 131 118 109 ---89 92 95 97 Table 4: electrochemical parameters for the corrosion of mild steel in 0.5 M H2SO4 containing different concentration of TR at 20°C (30min of immersion) -2 Conc. (M) Ecorr(mV/sce) IE (%) -c(mV.dec-1) icorr (µA.cm ) 00 5×10-4 10-3 5×10-3 10-2 5×10-2 -409 -416 -406 -410 -405 -405 3749 1230 1142 1094 940 793 127 135 132 156 138 147 ----67 69 70 75 79 3.3. Electrochemical impedance spectroscopy study : The results described blow can be interpreted in terms of the equivalent circuit of the double layer shown in figure 4, which has been used previously to model the iron-acid interface [18]. The corrosion behavior of mild steel in different corrosive media in the presence of various concentration of TR was investigated by EIS at 20°C and is given in figures 5 and 6. The best © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 semicircle can be fitted through the data point in the Nyquist plot using Bockamp program [14]. The impedance diagrams obtained were not perfect semicircles. This feature had been attributed to frequency dispersion [19]. It is apparent from this plots that the impedance response of mild steel in uninhibited 1M HCl and 0.5M H2SO4 solutions has significantly changed after the addition of TR. This indicated that the impedance of inhibited substrate increases with increasing inhibitor concentration in both acids. Fig.4: Electrical equivalent circuit for the metal-acid interface 250 -4 10 M -3 10 M -3 5.10 M -2 10 M 5 HCl 1M 4 200 2 - Z i ( . c m) 3 2 1 0 0 1 2 3 4 5 6 7 2 Z r ( .c m ) 2 -Zi (.cm ) 150 100 50 0 0 50 100 150 200 250 300 350 400 2 Zr ( .cm ) Fig. 5: Nyquist plots of mild steel in 1M HCl in presence of different concentrations of TR at 20 °C © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 15 4 ,5 4 ,0 -4 5.10 -3 10 -3 5.10 -2 10 -2 5.10 H 2 S O 4 0 .5 M 3 ,5 2 -Z i (.cm ) 3 ,0 2 ,5 2 ,0 1 ,5 1 ,0 10 0 ,5 0 ,0 0 ,5 1 ,0 1 ,5 2 ,0 2 ,5 3 ,0 3 ,5 4 ,0 4 ,5 5 ,0 5 ,5 6 ,0 6 ,5 2 Z r ( .c m ) 2 -Zi (.cm ) 0 ,0 M M M M M 5 0 0 5 10 15 20 25 2 Zr ( .cm ) Fig. 6: Nyquist plots of mild steel in 0.5M H2SO4 in presence of different concentrations of TR at 20 °C The corrosion kinetic parameters such as charge transfer resistance (Rct), double layer capacitance (Cct) and inhibition efficiency (IE%) are given in tables 5 and 6. The greatest effect was observed at 10-2 M of TR in 1M HCl and at 5×10-2 M in 0.5M H2SO4. When the concentration of inhibitor increases, Cct values decrease. Decrease in the Cct, which can result from decrease in local dielectric constant and/or an increase in the thickness of electrical double layer, suggested that the TR molecules function by adsorption at metal-solution interface [18]. Similar behavior is observed in both media [17]. It is well known that the inhibitive action of organic compounds containing S, N and/or O is due to the formation of a co-ordinate type bond between the metal and the lone pair of electrons in additive. The tendency to form a co-ordinate bond and hence the extent of inhibition can be enhanced by increasing the effective electron density at the functional group of the additive [20]. In aromatic or heterocyclic ring compounds the effective electron density at the functional group can be varied by introducing different substituents in the ring leading to variations of the molecules structure. The adsorption of TR on the metal surface can occur either directly on the basis of donoracceptor interactions between the π-electrons of the inhibitor and the vacant d-orbitals of iron surface atoms or an interaction of inhibitor with already adsorbed sulphate or chlorure ions [21, 22]. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 Table 5: Data obtained from EIS measurements for mild steel in 1M HCl in the presence of different concentrations of TR. Conc. (M) Rct (Ω.cm2) Cct (μF.cm-2) IE (%) 00 6 165 ---4 10 156 12 96 10-3 270 8 97 -3 5 ×10 309 7 98 -2 10 350 7 98 Table 6: Data obtained from EIS measurements for mild steel in 0.5M H2SO4 in the presence of different concentrations of TR. Conc. (M) Rct (Ω.cm2) Cct (μF.cm-2) IE (%) 00 5 168 --5×10-4 12 59 58 -3 10 13 56 61 5×10-3 17 48 70 -2 10 19 36 73 -2 5×10 20 35 75 3.4. Effect of temperature: The effect of temperature on inhibition efficiency was determined in 1M HCl and 0.5M H2SO4 containing 10-2 M of TR at temperature range 20-50°C using potentiodynamique polarization curves. The results are given in table 7. As expected, the corrosion current density increased one order of magnitude with increasing temperature both in uninhibited and inhibited solutions, and the values of inhibition efficiency of TR were slightly decreased in the temperature range as a result of the higher dissolution of mild steel at higher temperature, which might cause the desorption of TR from the mild steel surface. Table 7: The influence of temperature on the electrochemical parameters for mild steel electrode immersed in corrosive media + 10-2 M of TR. Temperature (°C) Ecorr(mV/sce) icorr(µA.cm-2) IE% Blank solution (1M HCl) -2 10 of TR 20 30 40 50 -396 -395 -396 -404 1072 1664 2158 2743 - 20 30 40 50 -453 -417 -398 -398 31 66 166 408 99 96 92 85 © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Blank solution (0.5 M H2SO4) -2 10 M of TR Volume 13, Preprint 11 submitted 25 January 2010 20 30 40 50 -409 -434 -440 -426 3749 4358 5332 6739 - 20 30 40 50 -405 -436 -430 -428 793 1522 2255 3245 79 65 57 52 Corrosion current density for mild steel increased more rapidly with temperature in the absence of inhibitor (blank solution). These result confirmed that the TR acts as an efficient inhibitor in the range of temperature studied. The values of the apparent effective activation energy Ea were calculated from the Arrhenius equation: i corr K ' e Ea RT (4) Where icorr is the corrosion current density, K’ the Arrhenius pre-exponential factor, T the absolute temperature and R is the universal gas constant. The plots of logarithm of the corrosion current density versus reciprocal temperature T-1 are given in Figures 7 and 8. The plots obtained are straight lines and the slope of each one gives its activation energy Ea. It is evident that for the corrosion of mild steel in 1M HCl and 0.5M H2SO4, the Ea value was found equal to 23 kJ.mol-1 and 15.39 kJ.mol-1 , respectively. In the presence of TR which function as an effective inhibitor, the Ea values are higher and equal to 68 kJ.mol-1 in HCl and 36.51 kJ.mol-1 in 0.5M H2SO4. According to Gomma [23], the kinetic of such a corrosion process acquires the character of a diffusion process in which at lower temperature the quantity of inhibitor present at the metal surface is greater than that at higher temperatures. The negative slope of Ea indicates the adsorption of organic compound on the electrode surface [24]. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 8 (a) -2 Ln icorr (µA.cm ) 7 6 5 4 (b) 3 3,0 3,1 3,2 3,3 3,4 3,5 -1 1000/T (K ) Fig.7: Arrhenius slopes calculated from corrosion current density for mild steel in: (a) 1M HCl and (b) 1M HCl + 10-2 M of TR. 9,0 8,5 8,0 -2 Ln icorr (µA.cm ) (a) 7,5 7,0 (b) 6,5 3,0 3,1 3,2 3,3 3,4 3,5 -1 1000/T (K ) Fig.8: Arrhenius slopes calculated from corrosion current density for mild steel in: (a) 0.5M H2SO4 and (b) 0.5M H2SO4 + 10-2 M of TR 3.5. Immersion time: Figures 9 and 10 show the impedance spectra after different immersion times in 1M HCl and 0.5M H2SO4 in the presence of 10-2 M TR. The evolution of the characteristics parameters associated with the capacitive loop with time is summarized in Table 8. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 In case of H2SO4, The diameter of the capacitive loop decreases in size with increasing immersion time. These results indicate that the adsorption model, arrangement and orientation of TR on the surface of the mild steel, change with time. In case of HCl, The diameter of the capacitive loop increases in size with increasing immersion time. These results indicate that the immersion time increases the chlorides quantity which will be adsorbed on the surface helping to the formation of the inhibitor layer. However as soon as all the active sites become saturated with inhibitor. Furthermore, the change in the Cct values may be caused by the gradual replacement of water molecules by the chloride anion and by the adsorption of the organic molecules on the metal surface, decreasing the extent of dissolution reaction. This difference in the inhibition in both acids can be explained by that, in case of H2SO4, FeSO4 is less soluble than FeCl2 and stay more efficiency on the steel surface. Less organic molecules are chemisorbed and therefore Cct values are more important [25,26] (see table8). 800 0.5 h 1 h 2 h 4 h 6 h 12 h 700 600 2 -Zi (.cm ) 500 400 300 200 100 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 2 Zr (.cm ) Fig.9: Nyquist diagrams for mild steel in 1M HCl containing 10-2 M of TR at different immersion time over open circuit potential. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 16 3 0 m in 1h 2h 4h 6h 2 -Zi (.cm ) 12 8 4 0 0 4 8 12 16 20 24 2 Z r ( .c m ) Fig.10: Nyquist diagrams for mild steel in 0.5M H2SO4 containing 10-2 M of TR at different immersion time over open circuit potential. Table 8: The influence of immersion time on the electrochemical parameters for mild steel electrode immersed in corrosive media + 10-2 M of TR. 1M HCl 0.5 M H2SO4 Immersion time (h) Rct (Ω.cm2) Cct(μF.cm-2) IE (%) 1/2 1 2 4 6 12 1/2 1 2 4 6 350 447 448 449 520 1160 20 11.5 9.5 6.6 6.1 7 6 6 6 6 5 35 47 55 59 59 97 98 98 98 98 99 75 56 47 24 18 4. Conclusion (1) The TR shows good inhibiting properties for mild steel in both media in practically 1.0 M HCl medium. (2) In both medium, this compound was found to affect both the anodic and cathodic processes and acts as mixed-type inhibitor. (3) This compound inhibits corrosion by adsorption mechanism and the adsorption leads to the formation of a protective adsorbed film on the metal surface film which suppresses the dissolution reaction. (4) Inhibition efficiency values are maximum in case of 1M HCl than 0.5M H2SO4. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 13, Preprint 11 submitted 25 January 2010 (5) The inhibition efficiency increases with increasing immersion time, in case of HCL, this study indicates that the TR inhibitor was strongly adsorbed on the mild steel. 5. References : 1. B.M. Praveen and T.V. Venkatesha, Int. J. Electrochem. 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Phys., 55 (1998) 131. 24. V. Branzoi, F. Branzoi, M. Baibarac, Mater. Chem. Phys., 65 (2000) 288. 25. L. Klkadi, B. Mernari, M. Trainsel, F. Bentiss, M. Lagrenée, Corros. Sci., 42 (2000)703. 26. M. Lagrenée, B. Mernari, M. Bouanis, M. Trainsel, F. Bentiss, Corros. Sci., 44(2002)573-588. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work.