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Environmentally friendly leaves are used as corrosion inhibitor for low carbon steel in acidic environment

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  • Save International Journal of M aterials and Chemistry 2013, 3(3): 64-68 DOI: 10.5923/j.ijmc.20130303.04 The Use of Eco-Friendly Leaf as a Corrosion Inhibitor of Mild Steel in an Acidic Environment Francis O. Nwosu1,*, Lebe A. Nnanna1, E. Osarolube2 1Department of Physics/Electronics, Abia State Polytechnic, Aba Nigeria 2Department of Physics, University of Port Harcourt, Choba Nigeria Abstract The leaf ext ract of Achyranthes aspera L was investigated for corrosion inhibition of mild steel in 1.0M HCl med iu m at room temperature. Grav imetric technique was used to study the corrosion behavior in the absence and presence of different concentrations of the leaf extract. The result obtained showed that the Achyranthes aspera L is a good inhibitor for mild steel in 1.0M HCl solution. The corrosion rate and inhibition efficiency were calculated. The inhib ition efficiency calculated showed a great percentage result with optimu m value of 82.3%. Achyranthes aspera L extract was adsorbed on the mild steel surface in accordance with Langmu ir, Fru mkim, and Flory-Huggins adsorption isotherm models. The negative adsorption energy ΔGads obtained inferred that the adsorption rates were spontaneous and the interaction between the inhibit ive molecules was found to be repulsive. Keywords Achyranthes aspera L, Corrosion Rate, Inhibition Efficiency and Adsorption Isotherm Mechanism 1. Introduction Corrosion phenomena, control and prevention are unavoidable major scientific issues that must be addressed daily as far as there a re increasing needs of metallic materials in all facets of technological develop ment.[1] Mild steel, a structural material is applied in many areas some of which includes reaction vessels, pipes, tanks, et cetera which are known to corrode invariably in contact with various solvents. On the other hand, acid solutions are often used in industry for clean ing, descaling and pickling of metallic structures, processes which are normally accompanied by considerable dissolution of the metal. Fro m the point of view of nation’s economy, financial imp lications and hazards, it is necessary to adopt appropriate means and ways to reduce the losses due to corrosion and some of the measures employed(include anodic and cathod ic p rotection, lubricat ion, paint ing and electroplating) have been adopted. However, one of the best op t ions availab le fo r th e p rotect ion o f met als ag ainst corrosion involves the use of inhibitors[2]. Coupling to the h azardous n atu re o f co rros ion , mos t o f th e co rros ion inh ib ito rs are synth et ic ch emicals , expens iv e and very hazardous to environment. Therefore, it is desirable to source for environmentally safe, economical, green inhibitors[3][4] [5][6][7][8][9]. As a result, there has been a wide spread research on the use o f p lant ext racts and their iso lates * Corresponding author: (Francis O. Nwosu) Published online at Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved as corrosion. [10] reported that some researchers have worked on some naturally occurring materials such as Gum Arabic, Raphia, hookeri, Ipomoea Invaculcerata, Vigna unguiculata, Pachylobus edulis, Ginseng root, Dacroydes edulis, Zenthoxylum alatum, Hisiscus sabdairffa, Datura stramonium, Li monene, prosopis, to mention but a few; and they were found to be good corrosion inhibitors. Therefore, the present study aims at investigating the inhibit ive effect and adsorption properties of Achyranthes aspera L (Aa) leaves extract on mild steel corrosion in 1.0 M Hydrochloric acid using gravimetric techniques. Aa is co mmon ly called devil’s horsewhip. It is a vascular plant widely found in temperate reg ion. It belongs to the family o f A maranthacae and has med icinal properties used on tetanus, snake bits, treat ment. Traditionally, the p lant is used in asthma and cough. It is pungent, antiphlegmatic, antiperiodic, diuret ic, purgative and laxative, useful in oedema, dropsy and piles, boils and eruptions of skin et cetera[11] 2. Materials and Methods 2.1. Mil d Steel Preparation The mild steel used in the studies was analyzed using optical emission spectrometry and consists (in % weight): C(0.0285), Si(0.0096), P(0.0096), Mn(0.1965), Ni(0.0153), Cr(0.0124), Mo(0.0027), Cu(0.0137), Sn(0.043), W(0.0052), Zn(0.031), As(0.0037), Ru(0.0028), and Fe(99.657%). The metal sheet was cut into sample with the following International Journal of M aterials and Chemistry 2013, 3(3): 64-68 65 dimensions of 30 x 30 x 1 mm and used for corrosion studies. 2.2. Preparati on of A. aspera L. (devil’s horsewhi p) Extr act The extract was prepared accord ing to[12]. Aa leaves were collected fro m Federal Un iversity of Technology Owerri (FUTO) in Imo State, Nigeria. They were washed with plenty water, air d ried and ground to powder form. The extraction was done in a reflu x setup for 3 hrs at a constant temperature of 75°C using 10g of air dried devils horsewhip in 300 ml of 1.0 M HCl solution. The solution was cooled under atmospheric pressure. The filtrate measured. Different concentrations of the inhibitor were p repared fro m the filtrate and the corrosive environ ment in the range 100, 150, 200, 250 and 300 g/L. 2.3. Gravi metric Techni que Gravimetric technique used was according to the description by[13]. A ll reagents used were BDH grade. Prior to measurement, each sample was degreased in ethanol, the surface smoothened using sic emery paper (of grades 400, 600, 800 and 1000) and then double washed with distilled water and air dried after dipping in acetone. The samples were weighed using FA2104A analytical electronic d igital weighing balance (sensitivity of 0.0001). The specimen were imme rsed in 250 ml beaker containing 240 ml of 1.0 M HCl solution of different concentrations (0, 100, 150, 200, 250 and 300 g/L) of the prepared inhibitor at room temperature (303°K). The set up were exposed for a period of five days after which the specimen were taken out, washed, dried and weighed accurately. Triplicate experiments were perfo rmed in each case and the mean value reported. corrosion rates in the absence and presence of inhibitor, res p ectiv ely . Figure 1. Mass loss for mild steel in the difference concentration of Aa at toom temperature exposured for 5days Figure 1 shows the variation in mass loss for mild steel in the absence and presence of inhibitor. It indicated that the mass loss of mild steel for blank solution is much higher than that obtained for solution containing various concentrations of Aa extract. This imp lies that the presence of the inhib itor showed significant impact on the reduction of the corrosion rate of mild steel in 1.0 M HCl. 3. Results and Discussion The mass losses of mild steel sample in 1.0 M HCl solution, with or without different concentrations of the investigated inhibitor, were recorded after 5 days of immersion at room temperature. The corrosion rate (CR) of mild steel, inhib ition efficiency and surface coverage of Aa form the weight lost measurement were calculated using the Equations 1, 2 and 3 respectively CR = ∆W Atρ (1) %IE = 1 − CRinh CRblank  ×100 (2) θ = 1− ρ inh ρ blank  (3) Where %IE is the inhibit ion efficiency, Ɵ is the surface coverage, ΔW is the mass lost (in grams), A is the surface area of the samp le (in cm2), ρ is the density (in g/cm3), t is the period of exposure (in hours), CRinh and CRblank are the Figure 2. Inhibition Efficiency of Aa on mild steel in 1.0 MHCl solution Figure 2 shows the trend of the inhibition efficiency of the leaf extract and it could be seen that the %IE increases linearly with the inhibitor concentration. It can be observed that the inhibition efficiency increased and the corrosion rate decreased as the inhibitor concentration increased. The maximu m value of inhibit ion efficiency was 83.6%. It could be considered that Achyranthes aspera L as inhibitor of mild steel to 1.0 M HCl solution given the high level of the inhibit ion efficiency. However, the surface coverage on the mild steel by the leaf ext racts increases as the inhibitor concentration increases. This shows a potential in the adsorption mechanis m of the Aa. 3.1. Ads orpti on Mechanism 66 Francis O. Nwosu et al.: The Use of Eco-Friendly Leaf as a Corrosion Inhibitor of M ild Steel in an Acidic Environment Adsorption isotherm is necessary in studying the mechanis m of adsorption and also the adsorption characteristics of the inhibitor. Studies have shown that the inhibit ion of metal corrosion by organic compounds is attributed to either the adsorption of inhibitor molecu le or the formation of a layer of insoluble co mplex of the metal on the surface which acts as a barrier between the meta l surface and the corrosive mediu m[14]. The study found that there is no insoluble material on the metal surface, and th is suggests that the inhibitive action of the Aa leave extract may be due to its adsorption on the metal surface. In accounting for the observed protective effect, it should be noted that experiments was carried out in biochemistry laboratory, Abia State Polytechnic, Aba, Nigeria shows that the extract co mprise mixtu re of organic and resinous matter (sapogenins, alchorneine, alchorneinone, alkaloids, anthranilic acid, gentisinic acid yohimb ine, flavonoids, glycosides) some of which have good corrosion inhibiting abilities. The co mplex chemical co mpositions make it rather difficult to assign the inhibiting action to a part icular constituent or group of constituents. Nevertheless, the net adsorption of the e xtract organic matter on the meta l surface creates a barrier to charge and mass transfer, thus protecting the mild steel surface fro m corrodent attack[15]. The degree of protection varies for different extracts, with notable sensitivity to the inhibitor concentration.[10] reported that leaf ext ract fro m Chlomolaena odorata L. (LECO) contained similar constituents and the leaf extract showed a good inhibit ive action against the corrosion of Al in 2 M HCl. However,[16] accounted that the relationship between inhibit ion efficiency and the bulk concentration of the inhibitor at constant temperature is known as isotherm; thus the following insight into the adsorption process. Several adsorption isotherm were attempted to fit surface coverage values to classical isotherm of Lang muir, Temkin, Fru mkin, Flory-Huggins[17]. Furthermore, the value of the correlation (R2) was used to determine the best fit isotherm which was obtained for Langmu ir, Fru mkin isotherms and Flo ry - Hu g g in s . 3.2. Lang muir Adsorpti on Isotherms Lang muir adsorption isotherm is calcu lated fro m the experimental data and can be expressed according to Equation 4[18]  c  = 1 + c θ  k (4) C is the inhibitor concentration, Ө is the surface coverage. Figure 3 shows that a plot of C/Ө versus C yields a straight line with R2 = 0.994 and slope 1.105. The plot clearly reveals that the surface adsorption process of Aa extract adheres to Lang muir adsorption isotherm as the plot has linearity and good correlation coefficient. The application of Lang muir isotherms to the adsorption of Aa on the surface of mild steel indicated that there is no interaction between the adsorbate and the adsorbent. Therefore, one can infer that physisorption occurred. C/ Ɵ 400 350 300 250 200 150 100 50 0 0 y = 1.105x + 30.018 R² = 0.9946 C 200 C/Ɵ 400 Figure 3. Langamiur adsorption isotherm for Aa in 1.0 M HCl According to[19] Lang muir adsorption isotherm is an ideal isotherm for physical adsorption where there is no interaction between the adsorbate and adsorbent. The equilibriu m constant of adsorption is related to the free energy of adsorption according to equation 5[20][21]. ∆Gads = −2.303 RT log (55.5K ) (5) Where R is the gas constant (8.314 kJ/ mo l); and T is the temperature (K). The constant value of 55.5 is the concentration of water in solution in mol/ l. The value of ΔGads for the inh ibitor on the surface of mild steel is given -10.1kJ/ mol; since ΔGads is very below 40kJ/ mol, it corroborates that the adsorption process is physisorption. The negative value of ΔGads indicated spontaneous adsorption of the inhibitor on the mild steel surface. 3.3. Frukim Ads orpti on Is otherm Fru mkin isotherm is an extension of Lang muir isotherm. It states that adsorbed molecules do interact and affect further adsorption by either repulsion or attraction of molecu les The Fru mkin isotherm widely used to quantify the interactions occurring between corrosion inhibitor and a metal surface[22][23][24], and it is expressed by the equation 6[23] exp(− fθ ) =  c 1  55.5 exp − ∆Ga0ds RT  (6) Where Ө is the degree of surface coverage, f is the interaction term parameter (if f > 0, there is a lateral attraction, if f < 0, there is a lateral repulsion between the adsorbing molecules), c (in mg/L) is the inhib itor concentration, ∆????????????0???????????????????? is the standard free energy of adsorption (kJ/ mo l). The Fru mkin adsorption isotherm is a general expression since the limiting case for which f = 0 is representative of an interaction free behavior between adsorbed species and defines the Langmuir isotherm[28][23]. Equation 6 can be rearranged to give equation 7,[23]. LogC = log θ  + Aθ + B 1−θ  (7) International Journal of M aterials and Chemistry 2013, 3(3): 64-68 67 Where A = -f/2.3 and B = (Δ????????????0???????????????????? /2.3RT) + log 55.5 and has the meaning of equilibriu m constant of the adsorption process. Equation 7 was used to plot the Frumkin isotherm (Ө against Log C) shown in Figure 4. The existence of adsorption interactions between adsorbed Aa extract and the metal surface is thus confirmed since most of the experimental data fit nicely into the Fru mkin isotherm p lot, the slight S-shape. The adsorption parameter f was -5.56 using two best values of C (100 – 300 g/L) and the corresponding Ө. The negative value of f indicates that the adsorption of the tested compound is accompanied by mutual repulsion of the inhibitor mo lecules,[17] -20kJ/ mol or less indicates electrostatic interactions between inhibitor and the charged metal surface is physisorption. Those about -40KJ/ mo l or more are indicative of charge sharing or transferring fro m organic species to the metal to form a coordinate type of metal bond is chemisorptions ,[27] In the present study, the calculated values ΔGads at 303 K (-10.1kJ/ mo l) fo r mild steel indicated that adsorption of the inhibitor on the surface of the mild steel is physisorption adsorption which implies that the films of the inhibitor was spontaneous on the surface of the metal. 4. Conclusions Figure 4. Frumking adsorption isotherm for Aa on mild steel in 1.0 MHCL 3.4. Fl ory-Huggins Isotherm The assumptions of the Flory-Huggins adsorption isotherm can be expressed according to equation 8 as reported by[25] Log θ  = Logk + xLog(1−θ ) (8) c Where x is the size parameter and is a measure of the number of adsorbed water molecu les substituted by a given inhibitor mo lecule. As shown in Figure 5, the plot of log (Ө/ C) against log (1 - Ө) gave a linear relationship (slope 1.63) with R2 = 0.739, showing that Flory-Huggins isotherm was obeyed. The value of the size parameter (x) is approximately 1. This indicates that the adsorbed specie of the inhibitor is bulky since it could d isplace more than one water molecu le fro m the metal steel surface[26]. The calculated ΔGads is -10.7kJ/ mo l. The present study found that Aa is a good corrosion inhibitor of mild steel in 1.0 M HCl mediu m at room temperature. Aa leaf extract significantly reduced the corrosion rate of mild steel in the acidic mediu m and it was found that the reduction rate of corrosion occurred with increase in the inhibitor concentration. Given this inhib ition efficiency, the value of Gibb’s free energy of adsorption indicate that Aa leaf extract is physically adsorbed on the surface and spontaneous following its correspondence to the follo wing adsorption models: the Lang muir, Fru mkin and Flory -Huggins. The interactions of the adsorbed molecules of the inhibitor are repulsive and bulky on the metal surface. REFERENCES [1] C. A. Loto, R. T. Loto and A. P. I. Popoola (2011) Corrosion and plants extracts inhibition of mild steel in HCl. International Journal of the Physical Sciences Vol. 6(15), pp. 3616-3623, [2] Abiola, O.K., Oforka, N.C., Ebenso, E.E., Nwinuka, N.M . (2007). Eco-friendly corrosion inhibitors: Inhibitive action of Delonix regia extract for the corrosion of aluminium in acidic medium. Anti-Corr. M eth. M ater. 54(4): 219-224. [3] El-Etre AY (2003). Inhibition of aluminium corrosion using Opuntia extract. Corrosion Science, 45: 2485–2495. [4] Bouklah M , Hammouti B (2006). 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