Inhibition Effect of Azadirachta indica, a Natural Product, on the Corrosion of Zinc in Hydrochloric Acid Solution

Transcription

1 DOI /s y TECHNICAL PAPER TP 2794 Inhibition Effect of Azadirachta indica, a Natural Product, on the Corrosion of Zinc in Hydrochloric Acid Solution R. A. Prabhu T. V. Venkatesha B. M. Praveen K. G. Chandrappa S. B. Abd Hamid Received: 1 October 2013 / Accepted: 2 January 2014 Ó Indian Institute of Metals 2014 Abstract The corrosion behavior of zinc in 0.2 M hydrochloric acid solution by Azadirachta indica (AI-Neem) was investigated using mass loss, electrochemical polarization and impedance methods. Inhibition efficiency depends on the concentration of AI-Neem and it reaches maximum value at 1,000 ppm. The shape of polarization profile indicated that AI-Neem is a mixed type inhibitor with predominant cathodic effect. Adsorption of AI-Neem on the zinc surface follows Temkin adsorption isotherm. The surface morphology of zinc was studied by using scanning electron microscope images. Keywords Zinc corrosion Inhibitor Azadirachta indica leaves extract SEM 1 Introduction Zinc is an important metal with numerous industrial applications and is mainly used for the corrosion protection of steel [1 4]. The zinc coated steel materials provide a greater resistance to corrosion, but when exposed to humid atmosphere, it undergo rapid corrosion with the formation R. A. Prabhu T. V. Venkatesha (&) Department of Chemistry, Srinivas School of Engineering, Mukka , Karnataka, India drtvvenkatesha@yahoo.co.uk B. M. Praveen (&) Department of P.G. Studies and Research in Chemistry, Kuvempu University, Shankarghatta , India bm.praveen@yahoo.co.in K. G. Chandrappa S. B. Abd Hamid Nanotechnology & Catalysis Research Centre (NANOCAT), Universiti Malaya, IPS Building, Kuala Lumpur, Malaysia of corrosion products known as white rust. This is generally observed on galvanized articles and renders the plated zinc materials unsuitable for industrial applications [5]. The formation of the white rust on zinc surface is prevented by the application of chromate treatment [6]. The effluent obtained during chromate treatment induces environmental pollution. But recent environmental regulations restrict the use of chromate solution and recommended its replacement it with other non-toxic and non-polluting agents [7]. Therefore there is a need for changes in the formulation of corrosion inhibition by an increasing demand for reduced environmental impact. Among the several methods of corrosion control and prevention, the use of corrosion inhibitors is very popular. Corrosion inhibitors are substances which when added in small concentrations to corrosive media decrease or prevent the reaction of the metal with the media. Due to the known hazard effects of most of the synthetic corrosion inhibitors and the currently imposed environmental requirements for eco-friendly corrosion inhibitors, there is a growing interest in the use of natural products such as leaves or seeds extracts. Recently, plant extracts have become important as an environmentally acceptable, readily available and renewable source for a wide range of needed inhibitors. Plant extracts are viewed as an incredibly rich source of naturally synthesized chemical compounds that can be extracted by simple procedures with low cost. Several investigations have been reported using such economic plant extracts. El Hosary et al. [8] studied the corrosion inhibition of aluminium and zinc in 2 N HCl using naturally occurring Hibiscus subdariffa (Karkode) extract. It has been found that AI-Neem is a very good inhibitor for mild steel corrosion [9, 10]. Sharma et al. [11] studied preliminary studies on zinc corrosion by AI-Neem and detailed studies have been not found in the literature.

2 The aim of this work was to investigate the potentiality of the AI-Neem extract to act as an inhibitor of zinc corrosion in hydrochloric acid. The Neem tree, a member of the Meliaceae family, appears to have originated in India and Southeast Asia. Its leaves, seeds and barks find many medicinal uses. AI-Neem is a cheap and environmental friendly substance. It acts as a non toxic natural pest control agent and its major active constituents are terpenoids such as azadirachta which are considred to be antimicrobial and insect repellent among many other actions. 2 Experimental Chemically azadirachta is a tetranortriterpenoid with a decalin segment and a modified furan segment. The chemical structure of active Azadirachta A is shown in Fig. 1. The AI-Neem powder (extract) of research quality was obtained from BIO-CON, LTD, Bangalore. It was dissolved in ethanol: triple distilled water (in 30:70 ratios) mixture and its solutions were prepared within a concentration range of 200 1,000 ppm in 0.2 M HCl solution. Zinc specimens having composition Cu 0.17 %, Ti 0.075, Al %, Pb Cd 0.003, Fe %, Sn , Mg and rest being zinc were used. They were mechanically polished using emery papers of grade no. 600, 800 and 1000 followed by washing in acetone, triple distilled water and then dried. The well polished specimens of dimension of 1 cm 9 1 cm (exposed) with a 5 cm long stem (isolated with araldite resin) were used for electrochemical measurements and cm 3 specimen was used for mass loss measurments. The corrosion of zinc specimen in HCl solution containing the AI-Neem extract of different concentrations was studied by mass loss measurements at 30 C. Mass loss measurements were carried out by weighing the zinc specimens before and after immersion in 100 cm 3 acid solutions for 2 h in the absence and presence of various concentrations of the inhibitor. Duplicate experiments were performed in each case and the mean value of the mass loss was determined. The 0.2 M HCl, was prepared by using A.R. grade HCl and triple distilled water. All experimental observations were performed in aerated and stirred solutions. The inhibition efficiency, g ml (%) was calculated by applying the following relationship g ml ð% Þ ¼ W o W 100; W o where W o and W is the average weight loss of zinc sample in 0.2 M HCl without and with inhibitor respectively. Polarization and impedance measurements were performed using an instrument Autolab PGSTAT 30 (Meltrohm SWISS MADE). A cell containing three compartments for electrodes was used. A saturated calomel electrode (SCE) and a platinum electrode were used as the reference and the counter electrodes respectively. All potentials were measured verses SCE. In the polarization method, the inhibition efficiency; g pol %, was calculated using the equation: i i0 g pol % ¼ 100; i where i and i 0 are the corrosion current densities without and with an inhibitor respectively. In the impedance measurements, the inhibition efficiency; g EIS (%) was calculated using the equation: g EIS ð% Þ ¼ R0 P R P 100; R 0 P where R P and R 0 P are the polarization resistances in the absence and presence of inhibitors, respectively. The surfaces of zinc specimen immersed for 2 h in 0.2 M HCl solution with and without the AI-Neem were scanned using HITACHI S-3000 scanning electron microscope (SEM). 3 Results and Discussion 3.1 Mass Loss Measurements The corrosion behaviour of zinc in 0.2 M HCl solution containing the AI-Neem extract of different concentrations was investigated by mass loss measurements at 30 C. The values of corrosion rates and inhibition efficiencies obtained from mass loss method at different concentrations of AI-Neem in 0.2 M HCl were shown in Table 1. It is clear that the amount of mass loss decreased with increasing additive concentration. It indicates that, the inhibition efficiency increased with the inhibitor concentration. The maximum inhibition efficiency (70 %) is obtained at 1,000 ppm. 3.2 Polarisation Studies Fig. 1 Structure of Azadirachta A (Neem component) Polarization curves for zinc in 0.2 M HCl in the absence and presence of AI-Neem extract of various concentrations at 30 C are shown in Fig. 2. Inhibition efficiency was increased with increase in inhibitor concentration and

3 Table 1 Corrosion parameters for Zinc in 0.2 M HCl in the presence and absence of Neem (AI) extract at different concentrations, obtained from mass loss measurements at 300 K Inhibitor Concentration (ppm) Loss in mass (mg) Corrosion rate (mg cm -2 h -1 ) Inhibition efficiency IE (%) Surface coverage (h) Blank Neem (AI) extract , Fig. 2 Polarization curves for zinc in 0.2 mol dm -3 HCl in the presence of Neem (AI) extract at different concentrations at 300 K reached to 70 % at 1,000 ppm. Electrochemical corrosion parameters, such as corrosion potential (E corr ), cathodic and anodic Tafel slopes (b a and b c ), corrosion current (I corr ) and inhibition efficiency (g p %) obtained by extrapolation of the Tafel lines are shown in Table 2. It has been reported that, a compound can be classified as an anodic or a cathodic type inhibitor on the basis of shift in E corr value. If displacement in E corr is greater than 85 mv, towards anode or cathode with reference to blank, then an inhibitor is categorized as either anodic or cathodic type inhibitor. Otherwise inhibitor is treated as mixed type. In our study, maximum displacement in E corr value was less than 85 mv indicating neem extract is a mixed type inhibitor. But from the graph it is evident that inhibitor acts as a mixed type inhibitor but more cathodic in effect. In addition to this, b c and b a values have changed with respect to inhibitor free solution so it concludes it is a mixed type inhibitor. The larger Tafel slope b c values indicate more cathodic nature of the inhibitor. Hydrogen evolution was suppressed due to the blocking of additive molecules on the metal surface Electrochemical Impedance Spectroscopy (EIS) Nyquist plots for zinc in 0.2 M HCl in the absence and presence of AI-Neem extract at various concentrations were shown in Fig. 3. It was revealed from the Nyquist plots that as the concentration of the inhibitor was increased, the diameter of the capacitive loop increased. Consequently the value of the charge transfer resistance, R P increased. This behaviour is an indication of the inhibitive action. The diameter of the capacitive loop increased with increase of inhibitor concentration. This shows the increase of R P values with increase of inhibitor concentration. As R P is inversely proportioned to the corrosion current, it was used to determine the inhibitor efficiency, g EIS %. The electrochemical impedance parameters derived from the Nyquist plots and the inhibition efficiencies (g EIS %) are shown in Table 3. It was clear that polarization resistance values were increased with increasing inhibitor concentration. Increase in the resistance, which can result from an increase in the thickness of the electrical double layer, suggests that the inhibitor molecules act by adsorption at the metal/solution interface [12]. This indicated the formation of a surface film on the zinc. Maximum inhibition efficiency was observed at 1,000 ppm of AI-Neem and above this concentration marginal changes or decrease in inhibition efficiency was observed in both chemical and electrochemical methods. So it concludes that, 1,000 ppm is considered as optimum concentration for achieving maximum inhibition efficiency Effect of Temperature Electrochemical polarisation and impedance experiments were carried out at 40 and 50 C. Inhibition efficiency was decreased at both the temperature and concentration. 1,000 ppm of AI-Neem shows inhibition efficiency of 55 and 45 % at 40 and 50 C respectively. It indicates that, adsorption of the inhibitor may be followed by the physical adsorption and it is desorbed with increase in temperature Adsorption Isotherm Organic inhibitors are found to protect zinc metal corrosion in acid medium by adsorbing themselves on metal surface. In order to gain more information about mode of adsorption of AI-Neem extract on zinc surface in HCl, attempts

4 Table 2 Corrosion parameters for Zinc in 0.2 M HCl the presence and absence of Neem (AI) extract at different concentrations, obtained from polarization measurements at 300 K Inhibitor Concentration (ppm) -E corr (mv) i corr (ma cm -2 ) b a (mv dec -1 ) -b c (mv dec -1 ) g pol (%) Blank Neem (AI) extract ,000 1, Table 3 Electrochemical impedance parameters for Zinc in 0.2 mol dm -3 HCl in the presence and absence of Neem (AI) extract at different concentrations, at 300 K Inhibitor Concentration (ppm) R P (X cm 2 ) g EIS (%) Blank 10.7 Neem (AI) extract , Fig. 3 Nyquist plots for zinc in 0.2 mol dm -3 HCl in the presence of Neem (AI) extract at different concentrations at 300 K were made to fit experimental data with several adsorption isotherms like Temkin, Langmuir, Freundlich, Frumkin, Bockris Swinkels and Flory Huggins isotherms. The best fit was obtained with Temkin s isotherm which is in good agreement with equation h ¼ klnc: where C is the inhibitor concentration, h is the degree of surface coverage defined as g ml (%)/100 at different concentration of inhibitor and k is an adsorption coefficient. A plot of h against log C gave almost a straight line (Fig. 4). From the graph it was found that the extent of the adsorption of molecules was increased with the increase of concentration of the inhibitor. Table 1 reveals that Inhibition efficency increased with increase in the inhibitor concentration. This behavior could be attributed to the increase of the surface coverage (h) due to the adsorption of the inhibitor molecules as the inhibitor concentration was increased Scanning Electron Microscopic Studies (SEM) Figure 5a, b show the SEM images of zinc surface after immersed in 0.2 M HCl and HCl containing 1,000 ppm of AI-Neem extract. The SEM technique was carried out for the zinc surface exposed to 2 h in presence and absence of Fig. 4 Temkin isotherm for the adsorption of Neem (AI) extract on the zinc surface the inhibitor. A comparision of the SEM micrographs revealed that the specimen immersed in the inhibitor solution (Fig. 5b) is in better condition than that in its absence which was heavily damaged by aggressive ions (Fig. 5a) in 0.2 M HCl. In the presence of inhibitor, the micrographs showed the formation of smooth films on the zinc surface. This observation indicated that corrosion rate was reduced due to the adsorption of inhibitor molecules on the metal surface which forms the protective layer.

5 Fig. 5 Scanning electron micrographs of the zinc surface after 2 h immersion at 300 K in (a) 0.2 mol dm -3 HCl (b) 0.2 mol dm -3 HCl? 1,000 ppm Neem (AI) extract Mechanism of Inhibition The mechanism of inhibition of corrosion is generally believed to be due to the formation and maintenance of a protective film on the metal surface. The corrosion inhibition of zinc in acidic solution by the inhibitor molecules can be explained on the basis of adsorption on the metal surface. The protection action of the inhibitor can be attributed to the presence of several aromatic rings, heterocyclic rings, COOCH 3, OC 2 H 5 and OH groups in the molecule. Adsorption of these molecules may occur through their oxygen active centres. Further the molecules are big enough to block more surface area of the zinc. The inhibitor molecules can also adsorb on the metal surface in the form of negatively charged species which can interact electrostatically with positively charged metal surface. 4 Conclusions On the basis of the experimental evidences, the following conclusions are arrived. AI-Neem extract is found to be fairly good inhibitor for zinc in HCl. Inhibition efficiency increases with concentration of the inhibitor. The inhibitor acts as mixed type but predominantly cathodic in nature. The results obtained from the mass loss, polarization and EIS methods match each other. The inhibitor obeys Temkin Adsorption isotherm in HCl medium. References 1. Rajappa S K, Venkatesha T V, and Praveen B M, Bull Mater Sci 31 (2008) Shylesha B S, Venkatesha T V, and Praveen B M, Der Pharma Chemica 2(2010) Shylesha B S, Venkatesha T V, and Praveen B M, Adv App Sci Res 2 (2011) Shanbhag A V, Venkatesha T V, Prabhu R A, Praveen and B M, Bull Mater Sci 34 (2011) Aramaki K, Corros Sci, 44 (2002) Arenas M A, and Damborenea J J, Surf Coat Technol 187 (2004) Bellezze T, Roventi G, and Fratesi R, Surf Coat Technol 155 (2002) El Hosary A A, Saleh R M, and Ahams El Din A M, Corr Sci, 12 (1972) Quraishi M A, Farooqi I H, and Saini P A, Corrosion 55 (1999) Ekpe U J, Ebenso E E, and Ibok U J J W, Afr Sci Assoc 37 (1994) Sanjay K S, Gargi J, Jyoti S, and Ackmez M, Int J Appl Chem 6 (2010) McCafferty E, and Hackerman N, J Electrochem Soc 119 (1972) 146.