Egyptian Journal of Petroleum xxx (2017) xxx–xxx Contents lists available at ScienceDirect Egyptian Journal of Petroleum journal homepage: www.sciencedirect.com Full Length Article Surface protection of mild steel in acidic chloride solution by 5-Nitro-8-Hydroxy Quinoline R Ganapathi Sundaram a,b, M Sundaravadivelu a,⇑ a b Department of Chemistry, The Gandhigram Rural Institute-Deemed University, Gandhigram 624 302, Tamil Nadu, India Centre for Research, Department of Chemistry, Mahendra Engineering College (Autonomous), Mallasamudram, Namakkal 637 503, Tamil Nadu, India a r t i c l e i n f o Article history: Received 14 September 2016 Revised December 2016 Accepted 24 January 2017 Available online xxxx Keywords: Acidic chloride solution MS NHQ WL SEM FT-IR a b s t r a c t The effect of commercially available quinoline nucleus based pharmaceutically active compound 5-Nitro8-Hydroxy Quinoline (NHQ) against the corrosion of mild steel (MS) in M acidic chloride (HCl) solution was investigated by chemical (weight loss – WL) and electrochemical (Tafel polarization, Linear polarization and Electrochemical impedance spectroscopy) techniques From all the four methods, it is inferred that the percentage of inhibition efficiency increases with increasing the inhibitor concentration from 50 to 300 ppm The adsorption behavior of inhibitor obeyed through Langmuir isotherm model Thermodynamic parameters were also calculated and predict that the process of inhibition is a spontaneous reaction EIS technique exhibits one capacitive loop indicating that, the corrosion reaction is controlled by charge transfer process Tafel polarization studies revealed that the investigated inhibitor is mixed type and the mode of adsorption is physical in nature The surface morphologies were examined by FT-IR, SEM and EDX techniques Theoretical quantum chemical calculations were performed to confirm the ability of NHQ to adsorb onto mild steel surface Ó 2017 Egyptian Petroleum Research Institute Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Introduction Iron is the most abundant element by mass of the earth Iron and its alloys are widely used in many applications, which have resulted in research into the corrosion resistance in various aggressive environments [1] The corrosion protection of iron and its alloys especially mild steel in corrosive environments have attracted the attention of many investigators [2–6] Acid solutions mainly hydrochloric acid is widely used in industry for the removal of corrosion products which in turn accelerates corrosion Because the cost of hydrochloric acid is very low than other mineral acids To protect the surface of mild steel and also prevent the further form of corrosion products, the use of inhibitor is one of the important practical methods [7,8] Most of the heterocyclic organic compounds have been reported in literature as efficient corrosion inhibitors for mild steel in acid medium [9–18] The corrosion inhibition is a surface process, which involves adsorption of the molecule on the metal/alloy surface The adsorption is favored by heteroatoms like sulphur, nitrogen, oxygen, Peer review under responsibility of Egyptian Petroleum Research Institute ⇑ Corresponding author E-mail addresses: chemistryganpath17@gmail.com (R Ganapathi Sundaram), msundargri@gmail.com (M Sundaravadivelu) phosphorous and p electrons present in the studied molecule The adsorption depends mainly on the electronic structure of the molecule [19] Nowadays several heterocyclic compounds are used as a corrosion inhibitors but, unfortunately some heterocyclic compounds are environmental toxic, high cost, very poor solubility in water and easily unavailable Therefore, the selection of the inhibitor is mainly based on the availability, low cost, non-toxic, biodegradable, renewable material and the presence of groups or atoms which aid the adsorption of inhibitor to the metal/alloy surface Moreover, the investigated inhibitor is commercially available, low cost, and soluble in water Furthermore, it is an environmental friendly inhibitor Because it acts as an antibiotic and have also been used in an anticancer setting In the view of these favorable characteristic properties, 5-Nitro-8-Hydroxy Quinoline was chosen for the corrosion studies In the present study, NHQ has been investigated for its corrosion inhibition efficiency Weight loss studies, polarization (Tafel and Linear) studies and impedance studies were employed to investigate the inhibition efficiency of NHQ on MS in acidic chloride solution FT-IR, SEM and EDX studies were employed to confirm the nature of the adsorbed (protective) film The results of quantum chemical methods were correlated with experimental results http://dx.doi.org/10.1016/j.ejpe.2017.01.008 1110-0621/Ó 2017 Egyptian Petroleum Research Institute Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 R Ganapathi Sundaram, M Sundaravadivelu / Egyptian Journal of Petroleum xxx (2017) xxx–xxx From the calculated CR value, the inhibition efficiency (IE%) was calculated according to the following equation: Material and experimental procedure 2.1 Preparation of specimen The mild steel (MS) specimen of dimension 3.5 1.5 0.2 cm in size with hole in the upper edge was used for the weight loss measurement and 1.0 1.0 0.2 cm in size was used for the surface study For an electrochemical investigation, 1.0 cm2 area of the MS specimen was exposed to the 100 ml of M acidic chloride (HCl) solution and the balance being covered by commercially available resin The surfaces of the mild steel specimens were polished with various grades (1/0–7/0) of emery papers and then degreased with acetone Finally, it is dried in air drier before all the investigation The composition (wt.%) of the mild steel is: C 0.104, Mn 0.580, P 0.035, S 0.026 and balance is Fe 2.2 Preparation of acidic chloride solution The acidic chloride solution (1 M HCl) was prepared by dilution of analytical grade 37% hydrochloric acid with bidistilled water 2.3 Preparation of inhibitor solution The investigated inhibitor molecule 5-Nitro-8-Hydroxy Quinoline was purchased from Sigma-Aldrich and used as a green corrosion inhibitor in an acidic chloride medium It is commercially known as Nitroxoline The optimized structure of NHQ is given in Fig The investigated compound contains many active centre’s like oxygen and nitrogen atoms The preparation of different concentrations (50–300 ppm) of inhibitor solution was done according to the standard method as described earlier [20] 2.4 Weight loss studies W St ð1Þ where W is the average (mean value) weight loss of three mild steel specimens, S is the total area of mild steel specimen and t is the immersion time ð2Þ 2.5 Electrochemical studies Electrochemical studies (AC impedance measurements, Tafel polarization measurements and Linear polarization measurements) were carried out by using CH-Electrochemical analyzer model 760 D with CHI 760 D software The used electrochemical analyzer contains three electrodes that are working electrode, auxiliary electrode and reference electrode In this setup, the mild steel act as a working electrode, a saturated calomel electrode as a reference electrode and the platinum foil as an auxiliary electrode Before starting the measurements, the working electrode (MS) was allowed to reach steady-state value of OCP All the three electrodes were kept immersed in blank and various concentrations of inhibitor solution The measurements were carried out after 30 of immersion time at room temperature Impedance measurements were carried out in the frequency range from 10 kHz to 0.1 Hz with ac impedance signal of 0.01 V amplitude From this measurement, the impedance diagrams like Nyquist and Bode were plotted Rct and Cdl values were obtained from the Nyquist plots and the inhibition efficiency (IE) was calculated from the following equation: " # Rict Roct Rict 100 ð3Þ where Rict and Roct is the charge transfer resistance values of with and without NHQ, respectively The Tafel polarization measurements were carried out by changing the electrode potential automatically from 300 mV to +300 mV with respect to OCP at a scan rate of 0.1 mV/s From this study, the inhibition efficiency was calculated from corrosion current density (Icorr) values by using the formula: " # Iocorr Iicorr 100 IE %ị ẳ Iocorr ð4Þ where Iocorr and Iicorr are the corrosion current density values in the absence and presence of various concentrations of NHQ, respectively For the linear polarization measurements, the potential of the electrode was scanned from 0.02 to +0.02 V versus Ecorr at a scan rate of 0.125 mV/s The surface coverage (h) and inhibition efficiency (IE%) were calculated using the following relationship [21] h¼ " i # Rp Rop 5ị Rip IE %ị ẳ Fig The optimized structure of NHQ Wo Wi 100 Wo where Wo and Wi are the corrosion rate in the absence and presence of various concentrations of NHQ, respectively IE %ị ẳ In this study, the pre-cleaned and pre-weighed mild steel specimens were suspended in 100 ml of M acidic chloride (HCl) solution with and without various concentrations of inhibitor for a period of h After that, the mild steel specimens were taken out, washed with distilled water, dried with air drier and weighed accurately The weight loss studies were made in triplicate and the loss of weight was calculated by taking an average (mean) of these values The standard deviation in the observed weight loss values was calculated and reported The corrosion rate (CR) is calculated by the following equation CR ẳ IE%ị ẳ " i # Rp Rop Rip 100 ð6Þ where Rip and Rop are the linear polarization resistance values in the presence and absence of NHQ, respectively Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 R Ganapathi Sundaram, M Sundaravadivelu / Egyptian Journal of Petroleum xxx (2017) xxx–xxx 2.6 Surface morphology studies 2.6.1 SEM studies The surface of fresh mild steel, uninhibited and inhibited mild steel specimens was analyzed by using JEOL/EO JSM-6390 model SEM 2.6.2 EDX studies The EDX system is also attached with a JEOL/EO JSM-6390 scanning electron microscopy The main purpose of this analysis is to confirm the percentage of elements in the studied MS specimens 2.6.3 FT-IR studies The protective film formed on the mild steel specimen is scratched carefully and the powder obtained is mixed thoroughly to make it uniform The FT-IR spectra are recorded by using JASCO 460 PLUS spectrophotometer over the range of 400–4000 cm1 with the resolution of cm1, using the KBr disk technique 2.6.4 Theoretical studies – quantum chemical calculations The quantum chemical calculations are performed by using density functional theory (DFT) and utilizing the 6-31G (d,p) set 6-31+G (d,p) basis sets DFT/B3LYP is recommended for the study of chemical reactivity and selectivity in terms of frontier molecular orbital theory [22] Results and discussion room temperature From this study, the impedance diagrams were obtained and are shown in Fig 3a and b The impedance data such as Rct, Cdl and h were obtained from Nyquist plot The percentage of inhibition efficiency is determined from Rct values according to the above-mentioned equation and all the impedance parameters are given in Table The impedance studies clearly indicate that the Rct value increased and Cdl values decreased with the addition of NHQ concentration The increasing Rct values imply reduced corrosion rate in the presence of the studied inhibitor and this is because of the increasing surface coverage of NHQ molecule on the addition and resulting in the formation of protective film on the corroded MS surface [25,26] The decrease in Cdl values was due to the gradual replacement of water molecules by the adsorption of NHQ compound at mild steel/solution interface, which led to the formation of protective film on the corroded MS surface and also prevent the further form of corrosion products [27] From Fig 3b, the phase angle increases with increase in the investigated inhibitor concentration this is due to the adsorption of inhibitor molecule on the surface of MS [28] According to the appearance of the phase angles versus frequency diagrams, the increasing concentration of the studied inhibitor NHQ in the presence of acidic chloride solution results in more negative values of the phase angle at high frequencies, indicating superior inhibitive behavior at higher concentrations This result could be attributed to higher corrosion activity even at low concentrations of NHQ [5] The obtained inhibition efficiency by this study showed good agreement with the result obtained from weight loss study 3.1 Weight loss studies Table gives the inhibition efficiency and surface coverage values of various concentrations of NHQ for the corrosion of mild steel in acidic chloride solution From this study, the inhibition efficiency was increased and the rate of corrosion was decreased with the increase of the inhibitor concentration This trend may result from the fact that an adsorption and the surface coverage increases with the increase in concentration, thus the surface of the mild steel is effectively separated from the acidic chloride medium [23] The ‘N’ and ‘O’ atoms can donate the p electrons to the active sites of mild steel surface therefore the adsorption process is increases and attain the maximum inhibition efficiency (89%) at the optimum concentration of inhibitor [24] Fig represent the inhibition efficiency and the corrosion rate of the studied inhibitor NHQ From Fig the IE (%) is increases and the corrosion rate of the mild steel decrease with the addition of NHQ, which explains the formation of protective layer on the corroded mild steel surface This study clearly indicates that the mild steel surface is protected from the acidic chloride solution 3.2 Electrochemical studies 3.2.1 Impedance (EIS) studies The impedance (EIS) studies were investigated by varying the concentrations of NHQ in M acidic chloride solution (HCl) at 3.2.2 Tafel polarization (TP) studies Fig depicts the representative Tafel plots of the corrosion inhibition effect of various concentrations of NHQ on MS in M acidic chloride solution at room temperature The obtained results from Tafel polarization studies are given in Table Results show that the addition of inhibitor alters both the ba and bc values suggesting that the NHQ molecule reduces anodic dissolution and retard hydrogen evolution as well indicating the studied inhibitor is a mixed nature On increasing the concentration of inhibitor, the Icorr value decreases from 2.397 mV/cm2 to 0.390 mV/cm2, which are due to the higher surface coverage of the corroded MS [29,30] The inhibition efficiency of the studied inhibitor on the surface of corroded mild steel is 59.3%–83.7% respectively From this studies the surface of working electrode is protected from the acidic chloride solution, when the addition of inhibitor concentration 3.2.3 Linear polarization resistance (LPR) studies The linear polarization resistance (RP) parameters were obtained from the slop of polarization plots The surface coverage (h) and inhibition efficiency (IE%) were calculated by using the above mentioned equation and the values are given in Table The results showed that the RP values increased with increase in the concentration of investigated inhibitor From this study, the highest inhibition efficiency was 83.72% obtained at the optimum Table Corrosion parameters obtained from WL studies of MS in M Acidic Chloride Solution containing different concentrations of NHQ Conc of NHQ (ppm) Weight loss value (mg cm2) Blank solution 50 100 150 200 250 300 27.3 10.8 6.9 4.9 4.5 4.0 2.9 25.8 9.7 7.3 5.3 3.9 3.5 3.5 25.6 10.3 7.1 5.6 4.2 3.9 2.7 Mean value (m) Standard deviation (Ϭ) Corrosion Rate (mm y1) Surface coverage (h) IE (%) 26.2 10.3 7.1 5.3 4.2 3.8 3.0 0.76 0.45 0.17 0.28 0.24 0.22 0.35 62.38 24.52 16.90 12.62 10.00 9.05 7.14 – 0.6070 0.7291 0.7977 0.8397 0.8549 0.8860 – 60.70 72.91 79.77 83.97 85.49 88.60 Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 R Ganapathi Sundaram, M Sundaravadivelu / Egyptian Journal of Petroleum xxx (2017) xxx–xxx Table Corrosion parameters obtained from EIS studies of MS in M Acidic Chloride Solution containing different concentrations of NHQ Conc of NHQ (ppm) Ymax (Ώ cm2) Rct (Ώ cm2) Cdl (lF cm2) Surface coverage (h) IE (%) Blank solution 50 100 150 200 250 300 5.329 12.986 15.101 18.196 19.184 22.268 35.146 10.751 25.845 30.313 36.722 38.638 44.646 70.097 2779.4 474.45 347.86 238.31 214.83 160.17 64.63 – 0.5840 0.6453 0.7072 0.7218 0.7592 0.8466 – 58.40 64.53 70.72 72.18 75.92 84.66 Fig Plot of Inhibition efficiency and corrosion rate of MS with various concentrations of NHQ in M acidic chloride solution Fig Tafel plots for MS corrosion in M acidic chloride solution with various concentrations of NHQ The nature of interaction between the inhibitor and the corroded mild steel surface can be clearly described by the adsorption isotherm This process is determined by using the surface coverage data and it plays an important role in the prediction of an adsorption isotherm The degree of surface coverage (h) is calculated by using the equation h = %IE/100 [31] The h values obtained from WL studies, EIS studies, TP studies and LPR studies were tested with different types of adsorption isotherm at room temperature Among the different types of adsorption isotherm studies, Langmuir isotherm gives the best fit at room temperature According to Langmuir adsorption isotherm, h is related to Cinh by the following equation: C inh ỵ C inh ẳ K ads h ð7Þ where Cinh is the inhibitor concentration (ppm), h is the degree of surface coverage and Kads is the adsorption equilibrium constant The Kads values can be calculated from the intercept lines on the Cinh/h axis This is related to DG0ads with the following equation: DGoads ¼ RT ln ð55:5K ads Þ Fig (a) Nyquist plots for MS corrosion in M acidic chloride solution with various concentrations of NHQ (b) Bode plots for MS corrosion in M acidic chloride solution with various concentrations of NHQ concentration of NHQ The increase in the inhibition efficiencies for corrosion of mild steel in acidic chloride solution with increasing concentration can be explained on the basis of an inhibitor adsorption The results obtained from Tafel polarization studies showed good agreement with the results of LPR studies ð8Þ where R is the universal gas constant, T is the absolute temperature and 55.5 is the concentration of water in solution in mol L1 [32] The Langmuir adsorption isotherm was drawn by plotting Cinh/h versus Cinh for various concentrations of inhibitor and considering the h values from WL studies, EIS studies, TP studies and LPR studies The obtained graph was shown in Fig The straight line obtained in the graph clearly shows that the investigated inhibitor obeys Langmuir adsorption isotherm The obtained thermodynamic parameters are given in Table Generally, the value of DG0ads less Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 R Ganapathi Sundaram, M Sundaravadivelu / Egyptian Journal of Petroleum xxx (2017) xxx–xxx Table Corrosion parameters obtained from TP studies of MS in M Acidic Chloride Solution containing different concentrations of NHQ Conc of NHQ (ppm) ba (V/dec) bc (V/dec) Ecorr (mV/SCE) Icorr (mA/cm2) Surface coverage (h) IE (%) Blank solution 50 100 150 200 250 300 6.558 7.343 6.991 6.308 6.731 7.914 8.823 6.277 6.923 7.237 7.225 7.110 7.238 8.115 243 275 299 291 329 351 288 2.397 0.9760 0.7643 0.6223 0.4991 0.4154 0.3903 – 0.5928 0.6811 0.7404 0.7918 0.8267 0.8372 – 59.28 68.11 74.04 79.18 82.67 83.72 Table Corrosion parameters obtained from LPR studies of MS in M Acidic Chloride Solution containing different concentrations of NHQ Conc of NHQ (ppm) Rp (Ώ cm2) Surface coverage (h) IE (%) Blank solution 50 100 150 200 250 300 14 31 40 52 63 74 86 – 0.5484 0.6500 0.7308 0.7778 0.8108 0.8372 – 54.84 65.00 73.08 77.78 81.08 83.72 0.40 0.35 WL EIS Tafel LPR [CInh(ppm) / Q] X 10 0.30 0.25 0.20 0.15 0.10 0.05 0.05 0.10 0.15 0.20 CInh(ppm) x 10 0.25 0.30 effect is increased remarkably in the presence of optimum concentration of NHQ 3.3.2 EDX studies The EDX images of fresh mild steel, uninhibited and inhibited mild steel with acidic chloride solution are shown in Fig 7a–c, respectively The analysis of Fig 7b indicates the presence of iron, oxygen, carbon and chlorine peaks; whereas the surface of inhibited mild steel Fig 7c indicates the presence of iron, oxygen, carbon and nitrogen peaks In this analysis, new peak nitrogen is obtained in the plot (Fig 7c) This is due to the adsorption of inhibitor molecules on the surface of mild steel This analysis also proves the adsorption of inhibitor molecules on the surface of corroded mild steel 3.3.3 FT-IR studies The FTIR spectrum is recorded to confirm the interaction of inhibitor molecule with the mild steel surface The FTIR spectrum of pure NHQ and adsorbed protective film formed on the MS surface after immersion in M acidic chloride solution containing 300 ppm of NHQ at room temperature are shown in Fig The pure NHQ spectra shows the IR frequency bands of the AOH, C@N and C@C having stretched at 3219 cm1, 1624 cm1 and 1570 cm1 respectively The NHQ protective film formed MS surface shows the presence of AOH, C@N and C@C groups at the frequencies of 3423 cm1, 1623 cm1and 1501 cm1 respectively So, it is confirmed that the studied inhibitor NHQ is strongly adsorbed on the MS surface Fig Langmuir plot (using WL, EIS, Tafel and LPR results) for MS corrosion in M acidic chloride solution with various concentrations of NHQ Table Values of DG0 and Kads obtained from Langmuir isotherm studies for the adsorption of NHQ on MS in M acidic chloride solution Method R2 Kads (104 M1) DG0ads (kJ mol1) WL EIS Tafel LPR 0.9996 0.9844 0.9985 0.9986 31.0006 26.0425 30.0997 24.0801 18.77 18.33 18.69 18.13 negative than 20 kJ mol1 signifies physisorption and the value more negative than about 40 kJ mol1 indicates chemisorptions [33] From this study the calculated DG0ads values indicates, the process of adsorption is through physisorption 3.3 Surface studies 3.3.1 SEM studies The SEM images of fresh mild steel, mild steel in acidic chloride solution and mild steel in acidic chloride with NHQ (300 ppm) are shown in Fig 6a–c This analysis clearly shows that the inhibition 3.3.4 Theoretical studies – quantum chemical calculations The quantum chemical calculations are powerful tools for studying corrosion inhibition mechanism Furthermore, the results of quantum chemical calculations could be obtained without laboratory measurements, thus saving time and equipment [34] The chemical reactivity of studied molecule is often discussed in terms of quantum chemical parameters such as the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and electron density parameters like dipole moment (m) The energy of the HOMO (EHOMO) represents the ability of the molecule to donate a lone pair of electrons and the higher the EHOMO value, the greater the tendency of the molecule to donate electrons to an electrophilic reagent [35] and the lower ELUMO, the greater the tendency of the molecule to accept electrons from the metal atoms The HOMO and LUMO electron density distribution of the investigated inhibitor NHQ is shown in Fig 9a and b) For the HOMO of the investigated molecule, it can be observed that the benzene ring, AC, AN and AO have a large electron density The results from the Table show that the NHQ has high EHOMO and low ELUMO values and the energy difference between EHOMO and ELUMO (ΔE) informs the reactivity of the investigated inhibitor molecule; results shows that the smaller the ΔE value, the greater the reactivity of the molecule The examined inhibitor NHQ has the smallest value of ΔE (0.1328 eV) and it is therefore most reactive molecule [36] The higher the dipole moment, the higher is the polarity of the molecule [37] Higher value of dipole moment has found to Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 R Ganapathi Sundaram, M Sundaravadivelu / Egyptian Journal of Petroleum xxx (2017) xxx–xxx Fig SEM image: (a) Fresh MS (b) MS in acidic chloride solution (c) MS in acidic chloride with NHQ be a key factor that facilitates adsorption by influencing the transport process through the inhibitor layer adsorbed [38] 3.8163 D seems to be a higher value for dipole moment that adds to the fact that the investigated compound NHQ shows a potential ability to act against corrosion This is turn confirms the inhibition activity of NHQ V.S Sastri and J.R Perumareddi have been reported that, the smaller values ΔE and higher values of dipole moment (l) are responsible for higher inhibition efficiency [39] Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 R Ganapathi Sundaram, M Sundaravadivelu / Egyptian Journal of Petroleum xxx (2017) xxx–xxx (a) 16 cps/eV 14 12 10 O Mn C Fe P Mn Fe (b) keV 10 10 cps/eV 22 20 18 16 14 12 C Fe 10 Cl O Cl Fe 2 keV (c) Fig EDX image: (a) Fresh MS (b) MS in acidic chloride solution (c) MS in acidic chloride with NHQ Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 R Ganapathi Sundaram, M Sundaravadivelu / Egyptian Journal of Petroleum xxx (2017) xxx–xxx Fig FT-IR spectra of inhibitor (Pure NHQ) and its corresponding protective film formed MS surface after immersion in M acidic chloride solution containing 300 ppm of NHQ The studied quinoline nucleus based organic molecule NHQ act as an effective corrosion inhibitor for mild steel in acidic chloride solution The corrosion rate of mild steel is decreased with the addition of NHQ concentration and effectively secures the MS surface The investigated inhibitor can be classified as a mixed type because it retards both anodic and cathodic reactions The adsorption of studied inhibitor on the surface of MS in acidic chloride solution obeys the Langmuir adsorption isotherm Values of DG0ads in both methods (chemical and electrochemical) indicate that the inhibition process on the surface of mild steel is purely physisorption and the process is spontaneous SEM, EDX and FT-IR morphology studies were confirmed the formation of protective film on the corroded MS surface The quantum chemical approach may well be able to foretell molecule structure that is better for corrosion inhibition This theoretical study is the well supportive evidence for the formation of the protective film on the surface of MS Conflict of interests The authors declare that there is no conflict of interests regarding the publication of this paper References Fig (a) HOMO structure of NHQ (b) LUMO structure NHQ Table Quantum chemical parameters of NHQ EHOMO (eV) ELUMO (eV) ΔE = (EHOMO ELUMO) l (D) Total Energy (E) IE (%) * Η 0.2490 0.1162 0.1328 3.8163 681.428 88.60 Conclusions On the basis of all the above experimental and the theoretical results, the following points are concluded, [1] M Abd El-raouf, Olfat E El-Azabawy, R.E El- Azabawy, Egypt J Petrol 24 (2015) 233–239 [2] E.-S.M Sherif, Int J Electrochem Sci (2011) 3077–3092 [3] Tarik Attar, Lahcene Larabi, Yahia Harek, Adv Chem 2014 (2014) 1–5 [4] R Ganapathi Sundaram, G Vengatesh, M Sundaravadivelu, Adv Chem 2016 (2016) 1–9 [5] M Mahdavian, S Ashhari, Electrochim Acta 55 (2010) 1720–1724 [6] M.G Hosseini, M Ehteshamzadeh, T Shahrabi, Electrochim Acta 52 (2007) 3680–3685 [7] G Gece, Corros Sci 53 (2011) 3873–3898 [8] A.Y Musa, R.T.T Jalgham, A.B Mohamad, Corros Sci 56 (2012) 176–183 [9] Preethi Kumari, Prakash Shetty, Suma A Rao, Int J Corros 2014 (2014) 1–11 [10] Ju Hong, Li Ding, Can Sun, Jie-jing Chen, Adv Mater Sci Eng 2015 (2015) 1–5 [11] G Karthik, M Sundaravadivelu, ISRN Electrochem 2013 (2013) 1–10 [12] Sudheer, M.A Quraishi, Ind Eng Chem Res 53 (2014) 2851–2859 [13] M.A Quraishi, R Sardar, Mater Chem Phys 78 (2003) 425–431 [14] I Ahamad, M.A Quraishi, Corros Sci 51 (2009) 2006–2013 [15] R Karthik, G Vimaladevi, Shen-Ming Chen, A Elangovan, B Jeyaprabha, P Prakash, Int J Electrochem Sci 10 (2015) 4666–4681 [16] A.A Al-Sarawy, A.S Fouda, W.A Shehab El-Dein, Desalination 229 (2008) 279– 293 [17] F Bentiss, M Traisnel, M Lagrenee, Corros Sci 42 (2000) 127–146 [18] G Karthik, M Sundaravadivelu, P Rajkumar, Res Chem Interm 41 (2015) 1543–1558 [19] M.A Quraishi, R Sardar, D Jamal, Mater Chem Phys 71 (2001) 309–313 [20] R Ganapathi Sundaram, M Sundaravadivelu, G Karthik, G Vengatesh, J Chem Pharm Res (2015) 823–835 [21] M.A Sudheer, J Quraishi, Chem Pharm Res (2011) 82–92 [22] P Senet, Chem Phys Lets 275 (1997) 527–532 [23] V.M Abbasov, Hany M Abd EI-Lateef, L.I Aliyeva, E.E Qasimov, I.T Ismayilov, Mai M Khalaf, Egypt J Petrol 22 (2013) 451–470 [24] M Abdallah, Corros Sci 44 (2002) 717–728 [25] M Lebrini, M Lagrenee, H Vezin, L Gengembre, F Bentiss, Corros Sci 47 (2005) 485–505 [26] K Krishnaveni, J Ravichandran, A Selvaraj, Acta Metal Sin (English Letters) 26 (2013) 321–327 [27] P Muthukrishnan, B Jeyaprabha, P Prakash, Int J Ind Chem (2014) 1–11 [28] B.M Prasanna, B.M Praveen, Narayana Hebbar, T.V Venkatesha, H.C Tandan, Int J Ind Chem (2016) 9–19 [29] A.M Abdel-Gaber, B.A Abd EI-Nabey, I.M Sidahmed, A.M EI-Zayady, M Saadawy, Corros Sci 48 (2006) 2765–2779 [30] P.B Raja, M.G Sethuraman, Material Lets 62 (2008) 113–116 [31] R Ganapathi Sundaram, M Sundaravadivelu, Int J ChemTech Res (2016) 527–539 [32] O Olivares, N.V Likhanova, B G’omez, et al., Appl Surf Sci 252 (2006) 2894– 2909 [33] I Ahamad, R Prasad, M.A Quraishi, Corros Sci 52 (2010) 933–942 [34] R.M Issa, M.K Awad, F.M Atlam, Mater Corros 61 (2010) 709–714 [35] A Fedorov, Y.Z Zhuravlev, V.P Berveno, Phys Chem Chem Phys 13 (2011) 5679–5686 Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 R Ganapathi Sundaram, M Sundaravadivelu / Egyptian Journal of Petroleum xxx (2017) xxx–xxx [36] M.K Pavithra, T.V Venkatesha, M.K Punith Kumar, H.C Tondan, Corros Sci 60 (2012) 104–111 [37] N.O Eddy, F.E Awe, C.E Gimba, N.O Ibisi, E.E Ebenso, Int J Electrochem Sci (2011) 931–957 [38] A Popova, M Christov, T Deligeorigiev, Corros 59 (2003) 756–764 [39] V.S Sastri, J.R Perumareddi, Corros 53 (1997) 617–622 Please cite this article in press as: R Ganapathi Sundaram, M Sundaravadivelu, Surface protection of mild steel in acidic chloride solution by 5-Nitro-8Hydroxy Quinoline, Egypt J Petrol (2017), http://dx.doi.org/10.1016/j.ejpe.2017.01.008 ... 40 52 63 74 86 – 0 .54 84 0. 650 0 0.73 08 0.77 78 0 .81 08 0 .83 72 – 54 .84 65. 00 73. 08 77. 78 81. 08 83.72 0.40 0. 35 WL EIS Tafel LPR [CInh(ppm) / Q] X 10 0.30 0. 25 0.20 0. 15 0.10 0. 05 0. 05 0.10 0. 15 0.20... 7.237 7.2 25 7.110 7.2 38 8.1 15 243 2 75 299 291 329 351 288 2.397 0.9760 0.7643 0.6223 0.4991 0.4 154 0.3903 – 0 .59 28 0. 681 1 0.7404 0.79 18 0 .82 67 0 .83 72 – 59 . 28 68. 11 74.04 79. 18 82.67 83 .72... cm2) Surface coverage (h) IE (%) Blank solution 50 100 150 200 250 300 5. 329 12. 986 15. 101 18. 196 19. 184 22.2 68 35. 146 10. 751 25. 8 45 30.313 36.722 38. 6 38 44.646 70.097 2779.4 474. 45 347 .86 2 38. 31