Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 5(2), 11-16, February (2015) Res. J. Chem. Sci. International Science Congress Association 11 Azole Drug : A Novel Inhibitor for Corrosion Nirmala Baby1*, P.Manjula, S.Manimegalai1*Department of Science and Humanities, Christian College of Engineering and Technology, Oddanchatram, Dindigul, Tamil Nadu, INDIA Head, Department of Chemistry, APA College for Women, Palani, Dindigul, Tamil Nadu, INDIA Department of Chemistry, APA College of Arts and Culture, Palani Dindigul, Tamil Nadu, INDIAAvailable online at: www.isca.in, www.isca.me Received 20th December 2014, revised 24th January 2015, accepted 8th February 2015 Abstract Heterocyclic compounds with atoms like N, O, and S are good corrosion inhibitors for metals and alloys. Molecules containing both N and S have good inhibition property when compared with molecules containing only N or S. A good inhibitor of corrosion should be alkaline. Azole drugs such as Fluconazole, Ketoconazole and Clotrimazole are good corrosion inhibitors due to the presence of aromatic rings, hetero-atoms and alkaline character. The rate of corrosion and inhibition efficiency of mild steel in the absence and presence of Fluconazole (FA) and Zn2+ containing 60ppm chloride ion has been studied by mass loss method. The inhibition efficiency of the system with 220ppm FA and 50ppm Zn2+ was high. AC impedance spectra, polarization study, Fourier Transform Infra Red spectra were analysed for knowing the nature of protective coating formed. Keywords: Azoles, corrosion, green inhibitors, hetero-atom, mild steel. Introduction The irreversible interfacial reaction of a metal with its environment is called corrosion. The use of inhibitor is one of the best methods of protecting steel from corrosion. The capability of inhibitor depends on the environment, metal surface, interfacial electrochemical potential and structural aspect of inhibitor. The genuine material used in many industries is mild steel owing to its low cost and good mechanical properties. Corrosion of mild steel is an academic as well as industrial concern for the current years. Azoles are five-membered heterocyclic ring compounds with at least one hetero atom of nitrogen, sulphur or oxygen. The presence of free electron pairs play a significant role in inhibition due to the specific interaction between functional groups, metal surface and hetero atoms like N, O and S1-3. Increased inhibition takes place due to the combination of both factors4-8. Literature survey reveals that triazole derivatives has been used as inhibitors for corrosion in mild steel for a long time9,10 as they adsorb on the mild steel and decrease the corrosion rate by blocking the active sites11-13. Fluconazole is a widely used bis-triazole antifungal drug. It has five-membered ring structures containing three nitrogen atoms14. The current study is carried out to calculate the inhibition efficiency of FA-Zn2+ system by mass loss methods, identify the mechanism of corrosion inhibition by electrochemical studies and examine the type of protective coating formed on the surface of mild steel by FTIR spectra. Material and Methods Mass loss studies: Different concentrations of inhibitor with 60ppm Cl- ion and Zn2+ ions were taken in 100ml glass beakers. Accurately weighed mild steel specimens in triplicate were immersed in the beaker for one day. After required time of immersion, the specimens were taken out, washed with clean water, dried and finally weighed. From the difference in weights of the specimen, the rate of corrosion is calculated using the relation: Corrosion rate = Loss in mass in milligrams Surface area of the metal specimen in dm x Period of immersion in days The inhibition efficiency was calculated using the relation IE = Where: X1 =Loss in weight of the specimen in the absence of inhibitor, X = Loss in weight of the specimen in the presence of inhibitor. Potentiodynamic polarization studies: Polarization study was carried out using three electrode cell assemblies. The reference electrode used was saturated calomel electrode (SCE) and the counter electrode is a rectangular platinum foil. The working Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(2), 11-16, February (2015) Res. J. Chem. Sci. International Science Congress Association 12 electrode is a metal piece with exposed area of 1cm. Corrosion parameters such as corrosion potential (E Corr), corrosion current (I Corr) and tafel slopes (anodic ba and cathodic ca) were calculated. The percentage of inhibition efficiency was calculated from ICorr using the relationship15. IE % = Where: ICorr = Density of corrosion current in the absence of inhibitor, ICorr = Density of corrosion current in the presence of inhibitor AC impedance measurements: The real part (Z) and imaginary part (Z11) of the cell impedance for various frequencies was measured in ohms. The charge transfer resistance (R) and double layer capacitance (Cdl) values were calculated. The inhibition efficiency of the inhibitor was calculated using the relation: Where: Rt = Charge transfer resistance in the absence of inhibitor, Rt = Charge transfer resistance in the presence of inhibitor Fourier Transform Infra Red spectral study: The mild steel specimens were immersed in a solution containing the inhibitor solution, 60ppm Cl ion and Zn2+ ions for 1 hour. After 1 hour, the specimens were taken out from the beaker and dried at room temperature. The protective film formed on the surface of the metal specimen was removed and mixed with KBr pellets in the form of a tablet. The FTIR spectra were recorded with a Perkin-Elmer 1600 Spectrophotometer. Results and Discussion Analysis of mass loss studies: Effect of concentration of inhibitor: Table-1 shows the rates of corrosion and inhibition efficiencies of mild steel in an environment containing 60ppm Cl- ion. The solution with 50ppm Zn2+ ions and 20ppm FA has an inhibition efficiency of 2%. The solution with 50ppm Zn2+ions and 140ppm has an IE of 43% but the solution containing 50ppm Zn2+ ions and 220ppm FA has 72% IE. When the inhibitor concentration increases above 220ppm the IE reduces to 53%. It is seen that as the inhibitor concentration increases, the protective film formed on the metal surface gets broken and mixes with the solution. Hence the best formulation with high inhibition efficiency is the system with 220ppm FA and 50ppm Zn2+ ion. Effect of Immersion time: Table-2 shows the variation in the inhibition efficiency with the time of immersion. It was found that as the time of immersion increases, the inhibition efficiency decreases. This is due to the fact that the protective film formed on the metal surface is not able to bear up the hit of Cl- ion. The film is broken down and hence the IE decrease slightly with increase in the period of immersion. Table-1 Effect of concentration of inhibitor on mild steel in neutral aqueous environment containing 60ppm of Cl- ionInhibitor System : FA + Zn 2+ Immersion Period : One Day Cl - (ppm) FA (ppm) Corrosion Rate (mdd) Inhibition efficiency (%) Zn 2+ Zn 2+ 0 ppm 10 ppm 25 ppm 50 ppm 0 ppm 10 ppm 25 ppm 50 ppm 60 0 24 18 17 21 - 21 33 3 60 20 25 19 18 23 -6 19 31 2 60 60 26 23 19 18 -10 2 24 31 60 100 20 25 15 15 -17 -4 36 57 60 140 24 25 19 14 -2 -4 24 43 60 180 24 2 17 9 0 13 28 62 60 220 23 22 17 7 2 9 28 72 60 260 22 24 17 11 6 0 28 53 Table-2 Effect of Immersion time on mild steel in neutral aqueous environment containing 60ppm of Cl- ionInhibitor System : FA + Zn 2+ Immersion Period(Days) 1 3 5 7 CR in the absence of inhibitor 23.5 22 20 18.5 CR in the presence of inhibitor 6.5 6 5 4 IE % 63 57 50 48 Analysis of Potentiodynamic polarization study: Polarization study was used to identify the formation of protective coating on the surface of the metal. When such coating is formed the corrosion current (ICorr) decreases 16-23. The corrosion parameter of mild steel immersed in various test solutions obtained by polarization study is given in table-4 and the polarization curves are depicted in figure-1. When mild steel is immersed in neutral aqueous solution containing 60ppm Clion, the corrosion potential is -644 mV Vs SCE. When 50ppm Zn2+ is added to the solution the corrosion potential decreases to -550 mV Vs SCE. The corrosion potential is slightly increased to -560 mV Vs SCE when 220ppm of inhibitor is added. But the formulation containing 60ppm Cl- ion, 50ppm Zn2+ and 220ppm FA decreases the corrosion potential to -547 mV Vs SCE. The corrosion current for aqueous solution containing 60ppm Cl- ion is 6.29x10-5 A/Cm but it decreased to 1.31 x 10-5A/cm for the formulation consisting of 60ppm Cl- ion, 220ppm FA and 50ppm Zn2+. The IE% has increased. This is due to the formation of a protective coating on the surface of the metal. Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(2), 11-16, February (2015) Res. J. Chem. Sci. International Science Congress Association 13 Figure-1 Polarization curves of low carbon steel immersed in various test solutions, - + - 60 ppm Cl ion, - - 60 ppm Cl ion + 50 ppm Zn2+ ion, - - 60 ppm Cl ion + 220 ppm Inhibitor, - - 60 ppm Cl ion + 220 ppm Inhibitor + 50 ppm Zn2+ ion Table-3 Effect of pH on mild steel in neutral aqueous environment containing 60ppm of Cl- ion Inhibitor System : FA + Zn 2+ Cl(ppm) FA (ppm) Zn 2+ (ppm) pH CR (mdd) IE% 60 220 50 4 7 69 60 220 50 7 2 89 60 2 20 50 9.2 6.5 48 Table-4 Tafel polarization corrosion parameters of mild steel in neutral aqueous environment containing 60ppm of Cl- ion obtained by potentiodynamic polarization studySystem Ecorr (mv Vs SCE) bc (mv) ba (mv) Icorr (A/cm) IE % Aqueous solution containing 60ppm Cl - ion -644 127 114 6.29x10-5 - Aqueous solution containing 60ppm Cl- ion +50ppm Zn2+-550 134 105 1.84x10-5 71 Aqueous solution containing 60ppm Cl- ion +220 ppm FA -560 130 99 2.51x10-5 60 Aqueous solution containing 60ppm Cl- ion +220 ppm FA +50 ppm Zn2+ -547 114 101 1.31x10-5 79 Table-5 Linear polarization resistance corrosion parameters of mild steel in neutral aqueous environment containing 60 ppm of Cl- ion obtained by polarization study System Rp (Ohm) IE % Aqueous solution containing 60ppm Cl- ion 1482 - Aqueous solution containing 60ppm Cl- ion +50ppm Zn2+4936 70 Aqueous solution containing 60ppm Cl- ion +220 ppm FA 3486 57 Aqueous solution containing 60ppm Cl- ion +220 ppm FA +50 ppm Zn2+6360 77 The Tafel slope for ba and bc are almost equal. The inhibitor showed the mixed inhibitor mainly cathodic. The anodic and cathodic tafel slopes are comparatively equal in the presence of inhibitor which indicates that the formulation containing FA and Zn2+ function as a mixed type inhibitor restricted by both anodic and cathodic reaction to the same extent. Conversely the cathodic tafel slope is somewhat higher as there was a shift in the corrosion potential to the cathodic side. The percentage of inhibition efficiency and linear polarization resistance parameters are shown in table-5. The IE was calculated by the relation IE % = Where: R = Polarization resistance in the absence of inhibitor, 2 = Polarization resistance in the presence of inhibitor. It is inferred from table-5 that as the polarization resistance increases from the system containing 60ppm Cl- ion (1482 ohm) to the formulation containing 60ppm Cl- ion, 50ppm Zn2+ and 220ppm FA (6360 ohm), the IE also increases with addition of inhibitor. Study of AC impedance measurements: The AC impedance spectra of mild steel immersed in neutral aqueous solution consisting of 60ppm Cl- ion, 60ppm Cl- ion + 50ppm Zn2+, 60ppm Cl- ion +220ppm FA and 60ppm Cl- ion + 220ppm FA + 50ppm Zn2+ are depicted in figure-2 (Nyquist Plot). The AC impedance parameters specifically double layer capacitance (Cdl) and charge transfer resistance (R) were calculated. Table–6 shows that the solution with 60ppm Clion has a charge transfer resistance value (R) of 678 ohm and double layer capacitance (Cdlvalue of 9.53 x 10-5 F. In the presence of 220ppm FA and 50ppm Zn2+, R value increased from 678 to 2330 ohm and Cdl value decreased from 9.53 x 10-5 F to 3.02 x 10-8 F. This is due to the formation of a protective coating on the metal surface. Current Potential Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(2), 11-16, February (2015) Res. J. Chem. Sci. International Science Congress Association 14 Figure-2 AC impedance spectra of low carbon steel immersed in various test solutions (Nyquist plots), - + - 60 ppm Cl ion, - - 60 ppm Cl ion + 50 ppm Zn2+ ion, - - 60 ppm Cl ion + 220 ppm Inhibitor, - - 60 ppm Cl ion + 220 ppm Inhibitor + 50 ppm Zn2+ ion Table-6 Corrosion parameters of mild steel immersed in neutral aqueous environment containing 60ppm of Cl- ion obtained by AC impedance spectra System R t (Ohm) IE % Aqueous solution containing 60ppm Cl- ion 678 9.53X10-5 Aqueous solution containing 60ppm Cl- ion +50ppm Zn2+1500 3.88X10-8 Aqueous solution containing 60ppm Cl- ion +220ppm FA 1804 3.06X10-8 Aqueous solution containing 60ppm Clion +22 ppm FA +50ppm Zn2+2330 3.02X10-8 Analysis of FTIR Spectra: Figure 3a shows the FTIR spectrum (KBr) of pure FA. The C=N stretching frequency occurs at 1620cm-1. The N-H stretching vibrations arise at 3069.84 and 3117.10 cm-124. The C-F band stretching vibrations occurs at 1386.88, 1341.55 and 1277.90 cm-1. The C-OH frequency appears at 1214.24, 1140.94, 1103.33, 1078.25 and 1011.71 cm. Figure-3b depicts the FTIR Spectrum (KBr) of the film produced on the metal surface after immersion in the solution consisting of 60ppm Cl- ion and 220ppm FA. There is a shift in the electron pair from C=N towards Fe2+ which resulted in Fe2+-FA complex on the anodic site of the surface of the metal. This is clear as the C=N stretching frequency has decreased from 1620 cm-1 to1619.31 cm-1. Figure-3c shows the FTIR spectrum (KBr) of the layer formed on the surface of mild steel after immersion in the solution consisting of 60ppm Cl- ion, 220ppm FA and 50ppm Zn2+. Due to the formation of Zn (OH) on the cathodic site of the metal surface 25, there is a band at 1310 cm-1. Thus a synergistic effect prevails in the FA-Zn2+ system and it functions as a mixed inhibitor system which is concluded from the FTIR spectral study. Conclusion The subsequent conclusions were made from the current study. The formulation consisting of 60ppm Cl- ion, 220ppm FA and 50ppm Zn2+ has an IE of 72%. Synergistic effect exists in the FA-Zn2+ system. FA-Zn2+ system show a better IE in neutral medium. As the concentration of the inhibitor and the period of immersion increases the IE of the FA-Zn2+ system decreases. Figure-3a FTIR spectra of pure FA Z || Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(2), 11-16, February (2015) Res. J. Chem. Sci. International Science Congress Association 15 Figure-3b FTIR spectra of the film formed on mild steel specimen, after immersion in the solution containing 60ppm Cl ion and, 220ppm FA Figure-3c FTIR spectra of the film formed on mild steel specimen after, immersion in the solution containing 60ppm Cl ion , 220ppm FA, and 50ppm Zn2+The protective coating consists of Fe2+- FA complex and Zn (OH) as revealed from FTIR spectral studies. A protective coating is formed on the metal surface which is studied from AC impedance measurements. The protective coating consists of Fe2+-FA complex and Zn (OH) as revealed from FTIR spectral studies. References 1.Lashgari M., Arshadi M. and Biglar M., Chem. Eng. Comm., 197, 1303-1314 (2010)2.Bentiss F., Traisnel M. and Lagrenee M., Corros. 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