Seed Extract of P sidium guajava as Ecofriendly Corrosion Inhibitor for Carbon Steel in Hydrochloric Acid Medium

J. Mater. Sci. Technol., 2011, 27(12), 1143-1149. Seed Extract of P sidium guajava as Ecofriendly Corrosion Inhibitor for Carbon Steel in Hydrochloric Acid Medium K.P.Vinod Kumar 1), M. Sankara Narayana Pillai 2) and G. Rexin Thusnavis 3) 1) Department of Chemistry, University College of Engineering, Nagercoil, Anna University of Technology, Tirunelveli, Nagercoil-629004, Tamil Nadu, India 2) Department of Chemistry, Noorul Islam University, Kumaracoil, Nagercoil, Tamilnadu, India 3) Department of Chemistry, St. Xavier s Catholic College of Engineering, Chunkankadai, Nagercoil-629003, Tamil Nadu, India [Manuscript received June 13, 2011, in revised form August 19, 2011] The anticorrosion characteristics of the seeds of Psidium guajava (P. guajava) fruits on carbon steel in acid medium were examined with weight loss data and subsequently thermodynamic factors such as heat of adsorption of the inhibitor on the metal surface (Q), change in entropy ( S), change in free energy of the reaction ( G), corrosion rate (CR) and energy of activation for corrosion reaction of carbon steel (E) were also evaluated. Adsorption isotherm was plotted to study the adsorption of the inhibitor on the metal surface with increasing concentration of the inhibitor. The functional groups responsible for inhibition were investigated using Fourier transform infrared (FT-IR) spectra. Electrochemical parameters were evaluated through the potentiodynamic Tafel polarization and impedance spectral studies. Scanning electron microscopy (SEM) micrographs were recorded to investigate the change in surface morphology. The complete study reveals the efficiency of seed extract of P. guajava as a safe, ecofriendly and alternate corrosion inhibitor for carbon steel in acid medium. KEY WORDS: P sidium guajava Ecofriendly (P. guajava); Steel; Corrosion; Polarization; Impedance; 1. Introduction Psidium guajava (P. guajava), commonly known as guava, belongs to the family of Myrtaceae. The plant is widely spread in tropical and semitropical regions. The fruits and leaves of the plant are popular for food and medicinal values. Metals and their alloys have a lot of applications in our day-to-day lives. But most of them have a tendency to form their stable compounds through oxidation process when exposed to various environments. Carbon steel is an industrially important alloy of iron, which is widely used in petrochemical, automobile, metallurgical and many more industries. Regardless of its application in various industries, it Corresponding author. Ph.D.; Tel.: +91 4652 260510; Fax: +91 4652 260511; E-mail address: nanjilvino@rediffmail.com (K.P.V. Kumar). is highly inclined to rusting in adverse environment, particularly in HCl medium. In industries, particularly in petrochemical and refineries where carbon steel is employed as an engineering material, and HCl is also exercised for acidification, cleaning and surface treatment besides other applications. Hence it has become obligatory to protect the alloy from dissolution. Out of several methods, addition of corrosion inhibitors in small quantities is proved to be a simple and effective method for the prevention of corrosion, especially in acidic medium. Organic compounds with electronegative hetero atoms are proved to be successful corrosion inhibitors [1 7] ; most of them are not so cost effective and toxic. Naturally occurring, cheap and ecofriendly corrosion inhibitors from plant materials can be identified, which could address both economic and environmental concerns. The present study focuses on the corrosion

1144 K.P.V. Kumar et al.: J. Mater. Sci. Technol., 2011, 27(12), 1143 1149 inhibition effect of acid extract of the seed of P. guajava on carbon steel in hydrochloric acid medium. The successful application of plant extracts as green corrosion inhibitor is already reported. Essential oils [8], Vegetal tannins [9], Phyllanthus amarus [10], Ficus Exasperata [11], Citrus aurantiifolia [12], Bauhinia purpurea [13], Uncaria gambir [14], Solanum Tuberosum [15], Azadirachta indica [16], Musa acuminate [17], Nyctanthes arbortristis [18], Eclipta Alba [19], and Andrographis paniculata [20] are also evaluated for anticorrosion properties. Very recently Jatropha curcus [21], Garcinia mangostana [22] and Areca catechu [23] are also proved to be effective corrosion inhibitors. 2. Materials and Methods 2.1 Carbon steel specimen The whole study was executed with carbon steel (CS) (mild steel) specimens of composition (wt%) Fe: 99.51, P: 0.08, Mn: 0.034 and C: 0.16. For weight loss and scanning electron microscopy (SEM) studies, CS specimens of size 4.0 cm 2.0 cm 0.19 cm were used. CS powder was used for Fourier transform infrared (FT-IR) spectroscopy observation, and specimens with an exposed area of 1 cm 2 were used for electrochemical studies. These specimens were initially polished with different grades of emery papers and degreased with trichloroethylene. 2.2 Preparation of the extract and corrosive environment 50 g of dried powder of P. guajava seed was mixed with 100 ml of 5% HCl and refluxed for 1 h. The extract was cooled, filtered off and made up to 100 ml using double distilled water. A stock solution of the corrosive environment was prepared using 5% (v/v) HCl solution and double distilled water. From this 100 ml each of standard solutions were prepared with and without different concentrations of P. guajava seed extract. Analytical grade pure HCl (Merck- 61752605031730) and double distilled water were used for the entire study. 2.3. Weight loss study and thermodynamic studies 100 ml test solutions in the absence and presence of different concentrations of inhibitor were prepared. Previously degreased, polished carbon steel specimens of known weight were immersed in them separately for a period of 1 h at four different temperatures viz, 303, 308, 313, and 318 K. After 1 h, these specimens were washed with double distilled water, dried well and weighed using Schimadzu AUX220 balance. 2.4 FT-IR spectroscopy studies Fourier transform infrared (FT-IR) spectra for P. guajava liquid extract and the dried adsorption product formed between finely powdered CS specimen and concentrated solution of the extract were recorded using Bruker FT-IR model-tensor 27 at a frequency range of 4000 to 400 cm 1. 2.5 Surface characterization studies Potentio-dynamic Tafel polarization plots were recorded with platinum electrode, calomel electrode and CS specimen as auxiliary, standard and working electrodes, respectively. Impedance measurements were carried out in the frequency range of 10 khz to 10 MHz. Potentio-dynamic polarization studies were carried out at a sweep rate of 1 mv/s. Potential (E) vs log(current) (logi) plots were drawn. The electrochemical parameters were studied in HCl medium and also with different concentrations of natural inhibitors using Solartron model SI1280B electrochemical measurement unit. SEM images for specimen of polished carbon steel, specimen exposed to 5% HCl corrosive environment and specimen immersed in 10% inhibitor concentration in 5% HCl were recorded using Hitachi S-3000H model scanning electron microscope. 3. Results and Discussion The fruits are very rich in seeds, which contain 14 wt% oil on dry weight, with 15 wt% proteins and 13 wt% starch [24]. Many phenolic and flavonoid were reported [25]. 3.1 Weight loss studies Weight loss studies were carried out at four different temperatures and the inhibition efficiency (IE) values calculated are presented in Table 1. From the Table, it is noted that the IE increases steadily with increasing concentration of the inhibitor. Figure 1 represents the dependence of inhibitor concentration for improved protection. The inhibition efficiency decreases with increasing temperature, though it is not so significant. A reasonable decrease in IE is observed when the exposure time is prolonged above 1 h as shown in Fig. 2. 3.2 Thermodynamic parameters of P. guajava extract The heat of adsorption (Q) was calculated by plotting a graph between log θ 1 θ against 1/T, where θ is the fraction of the metal surface covered by the inhibitor at temperature T. θ is calculated using the formula θ=(w W 1 )/W, where W and W 1 are the weight loss values in the absence and presence of the inhibitor, respectively. A negative slope, equivalent to Q/2.303R is obtained, from which Q is calculated and listed in Table 2. The Q values remain almost steady in all the different inhibitor systems which indicate the maximum adsorption of the inhibitor on the CS surface. This is reflected by the high inhibition efficiency values for all the

K.P.V. Kumar et al.: J. Mater. Sci. Technol., 2011, 27(12), 1143 1149 1145 Table 1 Weight loss data Concentration of inhibitor/% Weight loss/g Inhibition efficiency/% 303 K 308 K 313 K 318 K 303 K 308 K 313 K 318 K 0 0.0673 0.0772 0.0841 0.0922 2 0.0038 0.0047 0.0056 0.0075 94.35 93.91 93.34 91.87 4 0.0031 0.0039 0.0048 0.0061 95.39 94.95 94.29 93.38 6 0.0026 0.0033 0.0041 0.0053 96.14 95.73 95.12 94.25 8 0.0021 0.0027 0.0034 0.0042 96.88 96.50 95.96 95.44 10 0.0018 0.0023 0.0028 0.0036 97.32 97.02 96.67 96.09 Table 2 Heat of corrosion reaction (Q), entropy change ( S) and change in free energy ( G) data Concentration of inhibitor/% Q/(kJ/mol) S/(J/mol) G/(kJ/mol) 303 K 308 K 313 K 318 K 2 20.22 263.88 15.47 15.52 15.52 15.19 4 20.64 268.49 14.26 14.25 14.14 13.95 6 22.49 270.66 13.71 13.66 13.52 13.28 8 20.33 280.35 13.54 13.27 13.29 13.16 10 20.72 273.89 13.37 13.31 13.23 12.99 where, N is the Avogadro number and h is the Planck s constant. From this, S is calculated [23]. The S values are negative (Table 2) and almost similar at different concentrations of the inhibitor. These clearly indicate the decrease in randomness and therefore increase in the orderliness, viz the adsorption of the liquid phase inhibitor on the metal surface. The free energy change ( G) for the adsorption was calculated using the following formula [26] : Fig. 1 Plot between IE and concentration of inhibitor Fig. 2 Effect of time on inhibition efficiency inhibitor systems. The entropy change ( S) for the adsorption process was obtained by plotting a graph between log (CR/T ) against 1/T. The intercept obtained is equivalent to ( R ( S ) Intercept = log + Nh) 2.303R (1) G= 2.303RT log(55.5 K), where K=(θ/(1 θ))/c (2) The negative free energy change values (Table 2) predict the spontaneity of the adsorption process. The free energy change values for chemisorptions are reported between 49 and 58 kj/mol [27]. In the present case, the mean value of change in free energy for the adsorption process is 13 kj/mol. These low free energy change values in the present case confirm that the adsorption is physical in nature. The corrosion rate (mm/y) was calculated using the formula CR = 87.6W (3) DAt where W is the weight loss (mg), D is the density of carbon steel, A is the area of exposure (cm 2 ) and t is the time (h) [28]. A significant drop in the corrosion rate from the blank is observed with the addition of a very small quantity of the extract, i.e. 2% concentration of the inhibitor (Table 3). The maximum concentration of 10% inhibitor decreases the corrosion rate enormously from the blank value, i.e. by 40 times. Figure 3 further clarifies that a maximum decrease in corrosion rate is noticed at higher concentrations of the inhibitor irrespective of the temperature. Energy of activation (E) was obtained using the formula: log CR 2 = E ( 1 CR 1 2.303R 1 ) (4) T 1 T 2

1146 K.P.V. Kumar et al.: J. Mater. Sci. Technol., 2011, 27(12), 1143 1149 Table 3 Corrosion rate and energy of activation data Concentration of inhibitor/% Corrosion rate/(mm/y) E/(kJ/mol) 303 K 308 K 313 K 318 K 303 308 K 308 313 K 313 318 K 0 41.08 47.13 51.34 56.28 21.31 13.71 15.21 2 2.32 2.87 3.42 4.58 33.01 28.09 48.38 4 1.89 2.38 2.93 3.72 35.76 33.31 39.54 6 1.59 2.01 2.50 3.24 36.36 34.95 42.95 8 1.28 1.62 2.08 2.56 36.55 25.86 34.39 10 1.10 1.40 1.71 2.19 37.41 32.05 40.98 Fig. 3 Correlation between corrosion rate and concentration of inhibitor where, CR 1 and CR 2 are the corrosion rates at temperatures T 1 and T 2, respectively [29,30]. And the values are given in Table 3. The energy of activation (E) (Table 3) is always higher than the blank value for different concentrations of the inhibitor. This specifies the requirement of more energy for corrosion reaction to occur at different concentrations of the inhibitor [31]. All the above thermodynamic parameters are found to have values more or less akin at different concentrations of the inhibitor. This confirms that the adsorption is high even at 2% of inhibitor concentration, which is in line with the high IE. The trend also continues at higher concentrations of the inhibitor without much variation in IE. 3.3 Adsorption studies An adsorption isotherm was plotted between logc and θ, where C is the concentration of the inhibitor. The straight-line plot obtained is verified with Temkin adsorption isotherm,which is given by θ = a + b log C (5) where a and b are intercept and slope, respectively. Mathematically, the data is found to fit exactly with the Temkin adsorption isotherm. The graph (Fig. 4) reveals that the adsorption of the inhibitor on the metal surface increases as the inhibitor concentration is raised [22]. The increased adsorption results in better corrosion prevention. 3.4 FT-IR spectra studies The comparison of FT-IR spectra of P. guajava Fig. 4 Temkin adsorption isotherm Fig. 5 FT-IR spectra of the P. guajava extract extract (Fig. 5) and the adsorption product between the extract and CS powder (Fig. 6) have undergone significant shifts in the FT-IR absorption bands for various groups. The following frequency shifts are observed for the liquid seed extract and the solid adsorption product, viz 3420.12 to 3426.82 cm 1 (alcohol), 2929.92 to 2925.24 cm 1 (methylene C-H stretching), 1637.55 to 1634.37 cm 1 (Ketonic stretching), 1409.52 to 1418.75 cm 1 (ester), 1050.36 to 1058.26 cm 1 (alcohol/ester). The above shifts in absorption bands reveal the adsorption of different components of the P. guajava extract on the carbon steel surface. Hence, the FT-IR spectra studies reveal the interaction of the inhibitor on the CS surface for adsorption in corrosion protection. 3.5 Electrochemical studies Table 4 indicates the values of electrochemical pa-

K.P.V. Kumar et al.: J. Mater. Sci. Technol., 2011, 27(12), 1143 1149 1147 Table 4 Electrochemical parameters of corrosion inhibition by P. guajava extract Concentration of inhibitor OCP E corr I corr b a b c R ct C dl IE /% /V /V /A /(V/dec) /(V/dec) /(Ω/cm 2 ) /(A/cm 2 ) /% 0 0.5151 0.4939 0.002678 150.91 226.11 5.80 6.08 10 5 2 0.4942 0.5157 1.62 10 4 110.65 217.43 166.31 2.63 10 5 93.97 4 0.4975 0.5130 9.49 10 5 106.12 186.10 271.98 3.60 10 5 96.45 6 0.4955 0.5093 8.67 10 5 88.91 173.84 162.04 2.88 10 5 96.76 8 0.5001 0.5025 7.59 10 5 92.49 181.82 316.61 3.03 10 5 97.17 10 0.4897 0.5016 6.59 10 5 90.48 185.41 297.81 2.65 10 5 97.54 Fig. 6 FT-IR spectra of the product between P. guajava extract and MS powder Fig. 7 Tafel polarization plots for different concentration of inhibitor rameters such as open circuit potential (OCP), corrosion potential (E corr ), corrosion current (I corr ), anodic and cathodic Tafel slopes (b a and b c ), charge transfer resistance (R ct ), double layer capacitance (C dl ) and IE. The addition of the inhibitor to corrosion media in different concentrations shifts both the anodic and cathodic curves of the Tafel plot to lower values of current density (Fig. 7). This reveals that the extract inhibits both cathodic hydrogen evolution and anodic carbon steel dissolution and hence functions as a mixed type inhibitor. It is obvious from the Table 4 that the I corr values decrease noticeably with increasing inhibitor concentration which is an indication of decrease in corrosion reaction. The E corr values are more negative in the presence of inhibitor than those in the blank, reflecting that the extract functions more Fig. 8 Impedance spectra for different concentration of inhibitor as cathodic inhibitor. The values of b a and b c also do not increase or decrease in a regular manner, reflecting the mixed mode of inhibition, however it is more cathodic in nature [32]. The presence of a single semi circle (Fig. 8) in the blank and different inhibitor systems corresponds to the single charge transfer mechanism during dissolution of CS, which is unaltered by the presence of inhibitor components. The R ct values are always higher for higher inhibitor concentrations than the blank value, revealing the resistance towards the charge transfer reaction, viz corrosion reaction. The lower C dl values (Table 4) from the blank as the concentration of the inhibitor increases confirm the enhancement of adsorption of the inhibitor on the metal surface. The decrease in C dl is attributed to an increase in thickness of the electronic double layer due to adsorption [32]. The adsorption is due to the electronegative hetero atoms present in the organic constituents of the extract on the electropositive metal surface. All the electrochemical parameters clearly propose that the corrosion control depends on the concentration of the inhibitor as illustrated in Figs. 7 and 8. 3.6 SEM studies Comparable to the image obtained for polished CS surface (Fig. 9), the formation of the pits, cracks and corrosion products on CS surface exposed to corrosive environment (Fig. 10) are extremely minimized in the presence of 10% inhibitor (Fig. 11). This indicates

1148 K.P.V. Kumar et al.: J. Mater. Sci. Technol., 2011, 27(12), 1143 1149 FT-IR spectra studies. The electrochemical parameters such as Ecorr, ba and bc indicate the mixed sort of inhibition. The protective nature of the extract on carbon steel through the formation of a passive layer is clearly emphasized from the SEM images. The above results indicate clearly that P. guajava extract can be an alternate, green corrosion inhibitor for carbon steel in HCl medium. Fig. 9 SEM image of polished mild steel surface Acknowledgements The authors thank the Director, CECRI, Karaikudi, India, for extending the laboratory facilities; and thank Dr. S. Muralidharan, Mr. Ravi Shankar and Mrs. Nalini, CECRI, Karaikudi, India, Dr. M. Shankara Narayana Pillai, Noorul Islam University, Nagercoil, India, and Dr. S. Athimoolam, Anna University, Tirunelveli, India for functional suggestions. REFERENCES Fig. 10 SEM image of mild steel exposed to 5% HCl alone Fig. 11 SEM image of mild steel sample exposed to 5% HCl having 10% inhibitor the formation of a passive layer on the metal surface due to the adsorption of the inhibitor components on the CS surface[33]. 4. Conclusion The weight loss data show that the corrosion inhibition efficiency of P. guajava extract increases with increasing inhibitor concentration and decreases as the temperature is raised. Thermodynamic analysis reveals the spontaneity of the adsorption reaction of the inhibitor on the metal surface. A linearity of the graph plotted between logc and θ clearly reveals the enhanced adsorption on the metal surface by inhibitor as its concentration is raised. The adsorption may be due to the lone pair of electrons present in the hetero atoms of the P. guajava extract as is revealed from [1 ] A.K. Singh and M.A. Quraishi: Corros. Sci., 2010, 52, 152. [2 ] A.A. Khadom, A.S. Yaro, A.S. AlTaie and A.A.H. Kadum: Portug. Electrochim. Acta, 2009, 27(6), 699. [3 ] P. Lowmunkhong, D. Ungthararak and P. Sutthivaiyakit: Corros. Sci., 2010, 52, 30 [4 ] K. Parameswari, S. Rekha, S. Chitra and E. Kayalvizhy: Portug. Electrochim. Acta, 2010, 28(3), 189. [5 ] A.V. Shanbhag, T.V. Venkatesha, R.A. Prabhu, R.G. Kalkhambkar and G.M. Kulkarni: J. Appl. Electrochem., 2008, 38, 279. [6 ] F.M. Bayoumi and W.A. Ghanem: Mater. Lett., 2005, 59, 3806. [7 ] M. Sharma, J. Chawla and G. Singh: Indian J. Chem. Technol., 2009, 16, 339. [8 ] N. Poongothai, T. Ramachanderen, M. Natesan and S.C. Murugavel: Mater. Perfor., NACE Int., 2009, 48(9) 52. [9 ] A.A. Rahim and J. Kassim: Recent Pat. Mater. Sci., 2008, 1, 223. [10] P.C. Okafor, M.I. Ikpi, I.E. Uwah, E.E. Ebenso, U.J. Ekpe and S.A. Umoren: Corros. Sci., 2008, 50(8), 2310. [11] N.S. Patel, S. Jauhari and G.N. Mehta: E-J. Chem., 2009, 6(S1), 89. [12] R. Saratha, S.V. Priya and P. Thilagavathy: E-J. Chem., 2009, 6(3), 785. [13] N.S. Patel, S. Jauhari and G.N. Mehta: Arab. J. Sci. Eng., 2009, 34(2C), 61. [14] M.H. Hussin and M.J. Kassim: J. Phys. Sci., 2010, 21(1), 1. [15] P.B. Raja and M.G. Sethuraman: Iran. J. Chem. Chem. Eng., 2009, 28(1), 77. [16] N.O. Eddy and P.A.P. Mamza: Portug. Electrochim. Acta, 2009, 27(4), 443. [17] N.O. Eddy, S.A. Odoemelam and A.O. Odiongenyi: Adv. Nat. Appl. Sci., 2008, 2(1), 35. [18] R. Saratha and V.G. Vasudha: E-J. Chem., 2009, 6(4), 1003. [19] M. Shyamalay and A. Arulanantham: J. Mater. Sci. Technol., 2009, 25(5), 633.

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