Corrosion Inhibition and Adsorption Characteristics of Rice Husk Extracts on Mild Steel Immersed in 1M H 2 SO 4 and HCl Solutions

Transcription

1 Int. J. Electrochem. Sci., 10 (2015) Interntionl Journl of ELECTROCHEMICAL SCIENCE Corrosion Inhiition nd Adsorption Chrcteristics of Rice Husk Extrcts on Mild Steel Immersed in 1M H 2 SO 4 nd HCl Solutions K. K. Alneme 1,2,*, Y. S. Drmol 1, S. J. Olusegun 1, A. S. Afoli 3 1 Deprtment of Metllurgicl nd Mterils Engineering, Federl University of Technology, Akure, PMB 704, Nigeri 2 Deprtment of Mining nd Metllurgicl Engineering, University of Nmii, Fculty of Engineering Cmpus, Ongwediv, P. O. Box. 3624, Nmii 3 Deprtment of Civil nd Chemicl Engineering, University of South Afric, Johnnesurg, South Afric * E-mil: kklneme@gmil.com Received: 23 Octoer 2014 / Accepted: 28 Decemer 2014 / Pulished: 24 Ferury 2015 Corrosion inhiition chrcteristics of extrct of rice husk sh on mild steel in 1 M HCl nd H 2 SO 4 ws investigted in this work. The study ws crried out using mss loss, inhiition efficiency, tomic dsorption spectroscopy (AAS), FT-IR spectroscopy nd surfce nlysis s ses for ssessing the inhiition nd dsorption properties of the extrct in the cid solutions. The nlyses of the results showed tht the inhiition efficiency incresed with increse in concentrtion of the inhiitor nd decresed with temperture in oth cid solutions. The efficiency of the extrct in HCl (96%) ws noted to e more thn in H 2 SO4 (86%) solution. Thermodynmic prmeters reveled tht the dsorption of extrct onto the metl surfce ws spontneous. FTIR results showed tht the inhiition mechnism ws y sorption process, through the functionl groups present in the extrct. The SEM imges of the corrosion product confirmed the protection offered y the extrct on the surfce of the metl immersed in oth medi. The dt otined were fitted into Lngmuir nd Freundlich dsorption isotherms though the Lngmuir model ws found to e etter fitted thn the Freundlich. Keywords: dsorption; corrosion, inhiition; FTIR; mss loss; rice husk 1. INTRODUCTION Corrosion of engineering structures nd components in service hs continued to e huge source of concern to corrosion experts in the cdemi nd industries. This is primrily due to its deleterious effect on mteril integrity nd mechnicl properties resulting in filure in severe cses

2 Int. J. Electrochem. Sci., Vol. 10, [1]. A study conducted in 2002 estimted n expenditure of 3.1% of GDP s the cost of ddressing corrosion relted prolems y the US economy [2]. Considering the huge cost of corrosion monitoring nd control, gret del of efforts hve een chnneled towrds developing techniclly efficient nd cost-effective strtegies for corrosion mngement [3]. The use of corrosion inhiitors hs een very promising in this regrds prticulrly with the use of plnt sed mterils. Plnt sed inhiitors offer numer of dvntges such s iodegrdility, sence of hevy metls or other toxic compounds, vilility nd ese of processing [4]. The inhiition chrcteristics of good numer of green inhiitors hve een studied: reserchers hve reported the utiliztion of extrct from plnts such s Euphori hirt nd Dilum guineense [5] Hyptis Suveolens [6] Wter hycinth [7] Sid cut [8] Jtroph Curcs [9] Dniell Oliverri [10] Tithoni Diversifoli [11] Aloes [12] Cordi dichotom [13]. Their inhiition efficiencies nd dptility for commercil use hve een very promising nd hve rised hope for complete replcement of the more expensive nd toxic synthetic inhiitors. Nonetheless, reserch work is still needed on other potentil plnt sed inhiitors especilly those with less medicinl nd other competing pplictions. In this study, the extrct of rice husk ws utilized s inhiitor of corrosion on mild steel in HCl nd H 2 SO 4 solutions. The choice of rice husk ws sed on the results otined from its phytochemicl screening which confirms the presence of tnnins. It hs een estlished from the literture tht plnts tht contins tnnins nd flvonoids mong others could ct s effective corrosion inhiitor [14]. 2. MATERIALS AND METHODS 2.1 Mterils A cylindricl mild steel smple of composition Fe=98.3%, C=0.133%, P=0.0061%, Mn=0.82%, Cr=0.08% ws used for this study. The steel ws mechniclly cut to coupons of dimension 20 x 10 cm, nd then polished using different grdes of silicon cride pper, nd stored in moisture-free desicctors prior to use. Anlr grde HCl nd H 2 SO 4 nd distilled wter were used for the preprtion of the cid solution while rice husks (RH) were used s source of corrosion inhiitor. 2.2 Preprtion of rice husk extrct Rice husks were otined from rice processing plnt t Igemu-Ekiti, Ekiti Stte, Nigeri. The husks were gthered, sun dried nd pulverized. Aout 10 g of the pulverized husk ws weighed nd dded to 100 ml of prepred 1 M HCl nd H 2 SO 4 solutions in seprte regent ottles. The mixtures were immersed in wter th mintined t 90 o C for 3 hours, fter which they were removed from the wter th nd llowed to cool overnight. The mixtures were then filtered to otin the extrct. Stock solutions of 0.1, 0.2, 0.3, 0.4, nd 0.5 % (v/v) rice husk extrct in 1 M HCl nd H 2 SO 4 solutions were prepred from the filtrte.

3 Int. J. Electrochem. Sci., Vol. 10, Weight loss mesurement Weight loss studies were crried out on pre-weighed mild steel smples which were immersed in 250 ml cpcity ekers contining 100 ml of the test solutions mintined t 303, 313, 323 nd 333 K in thermostt controlled wter th. The sustrtes were held in the solutions for 4 hours fter which they re reweighed nd the difference in weight tken s weight loss. From the weight loss dt otined, the corrosion rtes (CR), inhiition efficiency (IE) nd surfce coverge (Ɵ) were clculted using equtions (i) (iii) respectively: CR (mgh -1 cm -2 ) = (i) where, W is weight loss, A is the re of the coupon in cm 2 nd T is time in hour. IE % = (1- ) x 100 (ii) where CR inh nd CR lnk correspond to the corrosion rtes in the lnk nd inhiitor solutions respectively, nd the surfce coverge clculted using: Ɵ = (1- ) (iii) 2.4 Mss loss mesurement Pre-weighed mild steel smples were immersed in 100 ml of the lnk/inhiitor solutions for 7 dys (168 hours). The weight loss of ech coupon ws determined t every 24 hour intervls y retrieving the smples from the solution, clened with cetone nd then reweighed. The mss loss for ech smple ws evluted y dividing its weight loss y the surfce re of the coupon [11]. 2.5 Atomic dsorption spectrometric nlysis Atomic dsorption nlysis ws performed using tomic dsorption spectrometer model ulk 200. This ws required to determine the concentrtion of iron (II) ions in the cidic solutions fter grvimetric mesurements. The clirtion curve of iron (II) ions ws drwn efore nlyzing the electrolyte solution. All smples contining iron ions were diluted with distilled wter to ensure tht the concentrtions of metl ions re within the rnge of the clirtion curve. 2.6 FTIR nlysis FTIR nlysis ws crried out to determine the functionl groups present in the RH extrct nd tht of the corrosion products from the mild steel corrosion set ups contining the RH extrct were crried out using Perkin-Elmer-1600 Fourier trnsform infr-red spectrophotometer. The smples were prepred for the nlysis using KBr. 2.7 Scnning electron microscopy nd energy dispersive spectroscopy (SEM-EDS) nlyses The surfce morphology of the mild steel efore nd fter immersion in the corrosion medi, nd the elementl composition of the metl surfces were exmined using JSM 7600F Jeol ultr-high

4 Int. J. Electrochem. Sci., Vol. 10, resolution field emission gun scnning electron microscope (FEG-SEM) equipped with ccessories for energy dispersive spectroscopy. 3. RESULT AND DISCUSSION 3.1 Phytochemicl screening The phytochemicl constituents of the extrcts s presented in Tle 1, shows the presence of tnnins, sponins mong others. The presence of these compounds hs een reported to promote the inhiition of mild steel in ggressive cidic medi [15]. Tle 1. Phytochemicl constituents of rice husk extrct Phytochemicl constituents Sponins Tnnins Flvonoids Legl Test Keller Killni R-HCl R-H 2 SO FTIR nlysis of the extrct nd corrosion product Figure 1. IR spectrum of HCl extrct of RH Presented in Figures 1 4 show the FTIR spectr of the RH extrct nd the corrosion product. It cn e seen tht the IR spectr of the rice husk extrcts from HCl nd H 2 SO 4 solutions (Figures 1 nd 2) show similr nds. The rod nd otined t 3333 nd 3396 cn e ssigned to OH. The frequency t 2080 nd corresponds to C-H stretching, nd the one t cm -1

5 Int. J. Electrochem. Sci., Vol. 10, corresponds to C=C. Compring the spectr of the rice husk extrcts from oth cidic medi with tht of the solid corrosion product (Figures 3 nd 4), it is oserved tht there re shifts in the frequencies. The shifts in the spectr indicte tht the interction etween the extrcts nd mild steel occurred through the functionl groups presents in them. Moreso, it cn e ffirmed tht the functionl group hs coordinted with Fe 2+ formed on the metl surfce resulting in the formtion of Fe 2+ extrct complex on the metl surfce, which promotes the inhiition of the metl smple. Figure 2. IR spectrum of H 2 SO 4 extrct of RH Figure 3. IR spectrum of solid corrosion product in the HCl extrct of RH

6 Int. J. Electrochem. Sci., Vol. 10, Figure 4. IR spectrum of solid corrosion product in the H 2 SO 4 extrct of RH 3.3 Mss loss mesurement The vrition of mss loss in the sence nd presence of the rice husk extrcts from HCl nd H 2 SO 4 Solutions re presented in Figure 5. It cn e oserved from the Figure tht the mss loss incresed with increse in exposure time. Also, the ddition of rice husk extrct from HCl solution resulted in significnt reduction in the mss loss of the mild steel sustrte in comprison with the lnk solution. The rice husk extrct from H 2 SO 4 solution on the other hnd could not reduce the mss loss significntly s tht of rice husk extrct from HCl solution. Ehterm [16] suggested the mechnism tht would hve led to the performnce of RHCl thn RH 2 SO 4, he noted tht the cid s nions of cids (Cl or SO 4 2- ) dsor physiclly on the positively chrged metl surfce, giving rise to net negtive chrge on the metl surfce. Then the orgnic ctions re physiclly ttrcted to the nions lyer which is formed on the metl surfce. According to the ionic volume of the cid s nions the smllest nion (Cl ) ttrcted fster to the metl surfce thn the iggest one (SO 4 2- ) leding to good inhiitor performnce in HCl. The reduction in mss loss in the presence of the extrct hs een ttriuted to the dsorption of phytochemicl constituents (Tle 1) which re present in the extrct. Srth nd Vsudh [17] opined tht the dsorption of such compounds on the metl surfce cretes rrier for chrge nd mss trnsfer leding to decrese in the interction etween the metl nd the corrosive environment.

7 Int. J. Electrochem. Sci., Vol. 10, Figure 5. Vrition of mss loss with rice husk () HCl nd () H 2 SO 4 cid extrcts s function of time The plots of the dissolution of Fe 2+ in the electrolyte (otined from AAS nlysis) s function of the extrct concentrtion re shown in Figure 6. These plots serve s confirmtory test to wht ws otined from the mss loss mesurement. It is seen tht there is stedy decrese in the concentrtion of Fe 2+ in the electrolyte s more extrcts re dded. This indictes tht the dsorption of the extrct on the metl surfce reduced the oxidtion of iron tom Fe to Fe 2+. Figure 6. Plots of the concentrtions of iron (II) ions in 1 M () HCl nd () H 2 SO 4 cids fter grvimetric mesurements 3.4 Effect of temperture on the inhiition efficiency nd corrosion rte The vritions of inhiition efficiencies (IE) with temperture for the mild steel sustrtes in HCl nd H 2 SO 4 solutions with nd without the rice husk extrct from oth cidic solutions re

8 Int. J. Electrochem. Sci., Vol. 10, presented in Figure 7. From the Figure ( nd ), it is oserved tht on the verge the inhiition efficiencies of the HCl solution contining HCl extrct of rice husk is generlly higher thn the H 2 SO 4 solution contining H 2 SO 4 extrct of rice husk. It cn lso e oserved tht the inhiition efficiency decreses with increse in temperture for oth cidic medi. Amrish et l [18] ttriuted this ehvior to incresed rte of dissolution process of mild steel nd prtil desorption of the inhiitor from the metl surfce with higher temperture. However, in H 2 SO 4 solution the inhiition efficiency vlues re more sensitive to the extrct concentrtion s reflected y the significnt increses in inhiition efficiencies in comprison to the HCl solution where there re mrginl chnges in the inhiition efficiencies with increse in the extrct concentrtion. Figure 7. Vrition of inhiition efficiency of () HCl nd () H 2 SO 4 extrcts of RH with concentrtion t K. Tle 2. Corrosion rtes (CR) of mild steel in HCl nd H 2 SO 4 in the sence or presence of RH extrct Acid medium Concentrtion of HCl Corrosion rte (mg cm -2 h -1 ) extrct RH of (% v/v) 303K 313K 323K 333k 1 M HCl Blnk Acid medium Concentrtion of H 2 SO 4 Corrosion rte (mg cm -2 h -1 ) extrct RH of (% v/v) 303K 313K 323K 333k 1 M H 2 SO 4 Blnk

9 Int. J. Electrochem. Sci., Vol. 10, Tle 2 shows the vlues of corrosion rte t different tempertures nd concentrtions of the extrct. From the Tle, corrosion rte in oth the sence nd presence of the extrcts increses with increse in temperture. This result is expected ecuse s the temperture increses the verge kinetic energy of the recting molecules increses therey speeding up the rection rte [19]. Nonetheless, the corrosion rte vlues decrese with increse in the concentrtion of the extrct. 3.5 Apprent ctivtion energy of metl dissolution process The corrosion rte vlues otined in Tle 1 were used to evlute the ctivtion energy using eqution (iv). A plot of log of corrosion rte (CR) otined from grvimetric mesurement ginst 1/T produced stright line in oth sence nd presence of the extrcts s shown in Figure 8 (vi) where CR is the corrosion rte, E is the pprent ctivtion energy, R is the molr gs constnt, T is the solute temperture nd A is the frequency fctor. Figure 8. Arrhenius plot for mild steel corrosion in () HCl nd () H 2 SO 4 extrcts of RH with concentrtion t K. The vlues of ctivtion energy otined from the slope (-E/ 2.303R) re presented in Tle 3 from which it is oserved tht the E vlues otined in the presence of the extrcts re higher thn in the sence except t 4% (v/v) concentrtion in 1 M HCl. Similr trends from ws een used to estlish tht when the E increses in the presence of inhiitor such rection process is interpreted

10 Int. J. Electrochem. Sci., Vol. 10, s physicl dsorption [20]. This then denotes tht the phytochemicl constituents in the extrcts re wekly onded or dsored on the mild steel surfce. The ctivtion energy in the sence of the extrcts is nd kj/mol in 1 M HCl nd H 2 SO 4 respectively. They re lower thn the vlues otined in the presence of inhiitor. The vlues in the presence of the HCl nd H 2 SO 4 extrct of RH rnged from to (men = kj/mol) nd to kj/mol (men = J/mol) respectively. 3.6 Enthlpy ( H) nd entropy ( S) of metl dissolution process The enthlpy ( H ) nd entropy ( S ) of ctivtion of corrosion process were clculted from n lterntive formultion of Arrhenius eqution [21]. where CR is the corrosion rte t Temperture T, R is the molr gs constnt, n is Avogdro s constnt, nd h is the Plnck s constnt. A plot of log CR / T versus 1/T produces stright line (Figure 9) with slope of (- H / 2.303R ) nd n intercept of (log( R / nh ) + S / 2.303R ) from which the vlues of ΔH nd ΔS were clculted nd presented in Tle 3. (v) Tle 3. Activtion energy, enthlpy nd entropy prmeters of the mild steel dissolution in HCl nd H 2 SO 4 in the presence nd sence of RH t temperture rnge of K Acid medium Concentrtion of HCl extrct RH of (% v/v) Activtion energy, E (kj mol -1 ) Enthlpy of ctivtion, H (kj mol -1 ) Entropy of ctivtion, S (J mol -1 k -1 ) 1 M HCl Blnk Acid medium Concentrtion of H 2 SO 4 extrct RH of (% v/v) Activtion energy, E (kj mol -1 ) Enthlpy of ctivtion, H (kj mol -1 ) Entropy of ctivtion, S (J mol -1 k -1 ) 1 M H 2 SO 4 Blnk

11 Int. J. Electrochem. Sci., Vol. 10, The results show tht the enthlpy of ctivtion vlues re ll positive, which reflects the endothermic nture of the mild steel dissolution process. Moreso, the enthlpy of ctivtion in the presence of the extrcts is more thn in the lnk solution. This indictes tht mild steel dissolution requires more energy in the presence of the extrct thn in the sence. Figure 9. Trnsition stte plots for mild steel corrosion in () HCl nd () H 2 SO 4 extrcts of RH with concentrtion t K. 3.7 Adsorption isotherm The Lngmuir dsorption isotherm ws pplied to investigte the mechnism of the corrosion inhiition y using eqution (vi): = + C (vi) where C is the inhiitor concentrtion, θ (IE/100) is the surfce coverge nd k ds is the dsorption equilirium constnt which Kds denotes the strength etween dsorte nd dsorent [22]. The plot of C/θ versus C is liner s shown in Figure 10 indicting tht the dsorption of the inhiitor on the surfce of mild steel is consistent with Lngmuir isotherm nd the slopes otined re unity. The correltion coefficient (R 2 ) of the dsorption isotherm dt shows tht Lngmuir isotherm is est fitted into the experiment with R 2 rnges from nd for HCl nd H 2 SO 4 extrct of RH respectively, t tempertures studied.

12 Int. J. Electrochem. Sci., Vol. 10, Figure 10. Lngmuir dsorption isotherm plots for the dsorption of () HCl nd (B) H 2 SO 4 extrcts of RH with concentrtion t K. The vlues of correltion coefficient (R 2 ) nd dsorption coefficient (Kds) re presented in Tle 4. The vlues of Kds show tht dsorption coefficient decreses with increse in temperture. Similr result ws lso reported y [23]. This is n indiction tht the inhiition efficiency decreses with temperture. Tle 4. Lngmuir isotherms prmeter Concentrtion of HCl extrct RH of (% v/v) Concentrtion of H 2 SO 4 extrct RH of (% v/v) Temperture R 2 K ds Slope R 2 K ds Slope 303K K K K SEM nlysis The SEM microgrphs of the mild steel efore nd fter immersion in HCl nd H 2 SO 4 in the sence nd presence of the rice husk extrct re presented in Figures The surfce morphologies served s good indictor of the severity of corrosion ttck.

13 Int. J. Electrochem. Sci., Vol. 10, c Figure 12. SEM imges of the mild steel () efore immersion, fter immersion in the () lnk nd (c) extrct solutions of HCl c Figure 13. SEM imges of the mild steel () efore immersion, fter immersion in the () lnk nd (c) extrct solutions of H 2 SO 4

14 Int. J. Electrochem. Sci., Vol. 10, It cn e noticed from the microgrphs tht the sustrtes immersed in the cidic medi without the extrct hd more pronounced depth of pitting (Figures 12 nd 13) compred to the sustrtes which contined the rice husk cid extrcts (Figures 12 nd 13). 4. CONCLUSIONS This study investigted the properties of corrosion inhiition of extrct of rice husk sh on mild steel in 1 M HCl nd H 2 SO 4 using the conventionl grvimetric mesurements. The nlyses of the results showed tht the inhiition efficiency incresed with increse in concentrtion of the inhiitor ut decresed with temperture in oth cid solutions. The physicl dsorption mechnism of the inhiition process ws in conformtion with the dt otined, nd Lngmuir nd Freundlich models were est fitted into the otined results. The clculted ctivtion energy vlues lso conformed to physicl dsorption mechnism. The SEM imges of the mild steel smples showed tht the metl ws protected in the presence of the extrcts. References 1. Z. Ahmd, Principles of Corrosion Engineering nd Corrosion Control, Butterworth-Heinemnn, Oxford (2006) B. Rpp, Corrosion, study of degrdtion, Mterils tody, 9(3) (2006), DOI: /S (06) E. E. Eenso, Bulletin of Electrochemistry, 19(5) (2003) N. O. Eddy, E. E. Eenso, Africn Journl of Pure nd Applied Chemistry, 2(6) (2008) I. U. Anozie, C. S. Akom, L. A. Nnnn, Interntionl Journl of Pure nd Applied Sciences nd Technology, 6(2) (2011) P. Muthukrishnn, B. Jeyprh, P. Prksh, Interntionl Journl of Industril Chemistry, (2014) 5:5DOI /s D. T. Olorunto, J. A. As, S. J. Olusegun, Wter hycinth (eichhorni crssipes) leves extrct s corrosion inhiitor for AISI 1030 steel in se wter In: Lrye, S., Agyepong, S.A., Leiringer, R. nd Hughes, W. (Eds), Proceedings of 4th West Afric Built Environment Reserch (WABER) Conference, July 2012, Auj, Nigeri, U.M. Eduok, S.A. Umoren, A.P. Udoh, Arin Journl of Chemistry, 5(2012) S.J. Olusegun, B. A. Adeiz, K. I. Ikeke, M.O. Bodunrin, Journl of Emerging Trends in Engineering nd Applied Sciences, 4 (2013) N. O. Eddy, A. O. Odiongenyi, P. O. Ameh, E. E. Eenso, Interntionl Journl of Electrochemicl. Science, 7 (2012) K. K. Alneme, S. J. Olusegun, Leonrdo Journl of Sciences, 20 (2012) H. Cng, Z. Fei, J. Sho, W. Shi, Q. Xu, Interntionl Journl of Electrochemicl. Science, 8 (2013) R. Khndelwl, S.K.Aror, R. K. Updhyy, S.P. Mthur, R. Prshr, Interntionl Journl of Current Trends in Science nd Technology, 3(2) (2012) B. E. Amith Rni, Bhrthi Bi J. Bsu, Interntionl Journl of Corrosion (Hindwi), (2012) 1, Doi: /2012/ N. O. Eddy, E. E. Eenso, Africn Journl of Pure nd Applied Chemistry, 2(6) (2008) E. A. Noor, Mterils Chemistry nd Physics, 114 (2009) R. Srth, V. G. Vsudh, E-Journl of Chemistry, 7(3) (2010) 677.

15 Int. J. Electrochem. Sci., Vol. 10, A. Singh, V. K. Singh, M. A. Qurishi, Journl of Mterils nd Environmentl Science, 1 (3) (2010) E. F. Olsehinde, S. J. Olusegun, A. S. Adesin, S. A. Omogehin, H. Momoh-Yhyh, Nture nd Science, 11 (2013) J.T. Nwnne, V.N. Okfor, Journl of Emerging Trends in Engineering nd Applied Sciences (JETEAS), 2 (4) (2011) A. S. Foud, H. Twfik, A. H. Bdr, Advnces in Mterils nd Corrosion,1 (2012) E. I. Ating, S. A. Umoren, I. I. Udousoro, E. E. Eenso, A. P. Udoh, Green Chemistry Letters nd Reviews, 3(2) (2010) E. E. Eenso, N. O. Eddy, A. O. Odiongenyi, Africn Journl of Pure nd Applied Chemistry, 2 (11) (2008) The Authors. Pulished y ESG ( This rticle is n open ccess rticle distriuted under the terms nd conditions of the Cretive Commons Attriution license (