Volume 16 Preprint 10


Improvement of corrosion resistance of anodized aluminium surfaces

S.Karthikeyan, P.A.Jeeva, V.Raj , Devanthranath Ramkumar, N.Arivazhagan,S.Narayanan

Keywords: Anodizing, sealing, corrosion

Abstract:
An attempt has been made to develop a corrosion resistant anodized aluminium film using a special sealing free from rare earths based on Cellulose acetate phthalate (CAP) and Sulfamethoxazole (SM) drugs in a quantitative way.The corrosion resistance of the anodized aluminium surfaces was enhanced by the above compounds in the presence of anionic surfactant. The performance of the sealant film was screened through potentiodynamic polarization and A.C impedance analysis. The calculations of quantum mechanical descriptors such as the localization of frontier molecular orbital’s, EHOMO, ELUMO, energy gap (ΔE) and dipole moment (µ), were used to substantiate the effective adsorption of the blended drugs on anodized surfaces. AFM studies justified the formation of protective layer on anodized metal.

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Improvement of corrosion resistance of anodized aluminium surfaces ISSN 1466-8858 Volume 16, Preprint 10 S.Karthikeyan1*, P.A.Jeeva2, S.Narayanan2 submitted 1 February 2013 V.Raj3 , Devanthranath Ramkumar2, N.Arivazhagan2, Surface Engineering Research lab, Centre for Nanobiotechnology, VIT University, VelloreVellore-632014,India 632014,India 1* 2School of Mechanical &Building Sciences, VIT University,VelloreUniversity,Vellore-632014,India 3Advanced Materials Research Laboratory, Laboratory, Periyar University, SalemSalem-11,India *Corresponding author (skarthikeyanphd@yahoo.co.in) ( Abstract An attempt has been made to develop a corrosion resistant film using a special sealing free from rare earths anodized aluminium based on Cellulose acetate phthalate (CAP) and Sulfamethoxazole (SM) drugs in a quantitative way.The corrosion resistance of the anodized aluminium surfaces was enhanced by the above compounds in the presence of anionic surfactant. The performance of the sealant film was screened through potentiodynamic polarization and A.C impedance analysis. The calculations of quantum mechanical descriptors such as the localization of frontier molecular orbital’s, EHOMO, ELUMO, energy gap (∆E) and dipole adsorption of the moment (•), were used to substantiate the effective blended drugs on anodized surfaces. AFM studies justified the formation of protective layer on anodized metal. Key words Anodizing, sealing, corrosion 1 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 10 submitted 1 February 2013 Introduction The anodized aluminium is widely used in the fields of aerospace, automobile, electronic products, etc. The life of the anodized film is short due to presence micro pores in the aluminium oxide which pervades the entry of foreign materials, when it is exposed to acidic and hard water media. Organic compounds containing sulphur, nitrogen and oxygen atoms are capable of reducing metallic corrosion in aggressive media. Several substituted thiourea and drugs compounds have been investigated as corrosion retarders 1-5 for the aluminium and its alloys. All the above studies reveal the one common observation that thiourea derivatives can be regarded as excellent corrosion reducers for aluminium. The so far reported sealing solution involved the utility of Nickel acetate and rare earth metals which are toxic . The present formulation is absolutely free from versatile and eco friendly in nature. approach blending is available for the earth metals , inexpensive, As far as we know, no systematic corrosion protection of anodized film by drugs in sealing agent. The present paper describes a preparation of special sealing agent based on Sulfamethoxazole aluminium rare in (SM) 1N drugs HCl using cellulose acetate phthalate (CAP) on corrosion potentiodynamic resistance polarization of and and anodized impedance methods. The quantum mechanical descriptors substantiate the performance of the blended drugs in sealing solution by virtue of forming a strong adherent layer on the metal surface. Materials and Methods Aluminium specimens of compositions, Cu = 0.15%, Mg = 0.5%, Mn = 0.1%, Si = 0.5%, Zn = 0.5%, and Aluminium remainder, and of size 5 cm2x 0.02cm anodizing and 1cm2 x 0.02 cm for potentiodynamic were used for polarisation , AC impedance measurements and AFM analysis. 2 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. Anodizing of Aluminium ISSN 1466-8858 Volume 16, Preprint 10 submitted 1 February 2013 The aluminium specimens of the above composition was mechanically polished and then degreased with acetone. Then the panels were subjected to anodizing as per the following experimental condition. Anode: Al panels; Cathode: Lead; electrolyte: 0.47M phosphoric acid + 0.04M Acetic acid; current: 5.7 mA cm-2; Time : 15 minutes. Thickness: 40- 50 microns. Preparation of sealing agent Exactly (1:1) ratio of A.R grade cellulose acetate phthalate (CAP) and Sulfamethoxazole (SM) drugs were dissolved in 5% sodium diacetate + 5ml of proprietary surfactant and blended well. The mixture was diluted to 500ml and then heated to 80⁰C. The sealing of anodized film was carried out by immersing the anodized plates into drugs impregnated solution. The duration of sealing process was varied as 10 minutes, 30 min, 45 minutes. After sealing, the plates were removed , washed , dried and characterized using electrochemical techniques. The thickness of the anodized film varies from 30-43•m. Evaluation anodized film after sealing process Both cathodic and anodic potentiodynamically BAS Model Lafayette, : 100A polarisation curves recorded in 1NHCl (sweep rate = 1 mVs-1) using corrosion measurement system , Indiana) computerised and PL-10 electrochemical digital plotter Instruments Division). A platinum foil of were were analyzer (DMP-40 (made series, in West Houston 4 cm2 area and Hg/Hg2Cl2 /1NHCl used as auxiliary and reference electrodes, respectively. Double layer capacitance (Cdl) and charge transfer resistance values (Rt) were measured using AC impedance measurements (EG&G Princeton Applied research model:7310) as described in an earlier publication6. Quantum calculations were performed by adapting Gaussian 03 software package. The energy of highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and dipole moment (•) of the sealing compounds were calculated with the above 3 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. given computer code package. The surface roughnesses of the anodized films ISSN 1466-8858 Volume 16, Preprint 10 submitted 1 February 2013 before and after sealing were measured by AFM (Nanosurf easy surf 2). Results and Discussion Potentiodynamic polarization studies Table 1 gives values of corrosion kinetic parameters such as Tafel slopes ( ba bc),corrosion current (Icorr ) and corrosion potential (Ecorr ) and and resistance aluminum obtained from potentiodynamic polarization curves for anodized in 1N HCl after subjected to sealing the coatings at various time intervals. It is established that enhancing the sealing timings values of both anodic and cathodic Tafel slopes sealing at various time intervals, the resistance aluminium in 1N HCl data have been was found to follow to equal improve the extent. After of corrosion of anodized mixed mode of reaction 7-8. Ecorr moved to positive direction when sealing compounds were used for corrosion studies. This can be ascribed to the formation of strongly adherent sealing film on the aluminium anodized films surface. It was noticed that which were subjected to 45 minutes sealing, for Icorr values were decreased to considerable extent in 1N HCl due to the blocking of micro pores of coatings by sealants. Impedance measurements Figure 2 indicates the corrosion protection solution before and after sealing of anodized aluminium in 1N HCl observed at various electrochemical impedance spectroscopy . The values of resistance (Rt ) begin to increase with the increasing film as well as the sealing capacitance (Cdl) are brought ascribed to increased anodized film timings down (Table 2) with respect to thickness of anodized to significant extent sealing intervals 9-10. by the charge transfer ,while adsorption of the sealing drugs timings double layer . This can be on the micro pores of In the present study, perfect semi circles are not encountered in Nyquist plots and there is a drag is noted in the semi circles. This may be due to the fact that the corrosion resistance of sealing drugs in anodized film is partially under 4 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. charge transfer and mass transfer control. Similar observation has been made ISSN 1466-8858 Volume 16, Preprint 10 earlier by Karthikeyan et al 11 submitted 1 February 2013 for the electroless plating process. AFM studies Figure 3-6 showed the AFM results of anodized film with and without sealing at various time intervals. The average roughness values of anodized film with and without impregnation of sealants were observed at 950 nm, 350 nm(10 minutes-sealing time), 180 nm (30 minutes) and 130 nm (40 minutes) . The average roughness values of surface is smoother figure 6 (40 minutes) confirm that the than anodized metal with and without sealing at other doping intervals .This can be due to the blockening action of micro pores by sealants. Quantum Quantum mechanical studies Quantum mechanical calculations were performed to investigate the adsorption and inhibition mechanism of the sealing drugs. Figure 7 (A & B) shows the optimized structure of CAP and SM . The values of calculated quantum chemical parameters i.e. EHOMO (highest occupied molecular orbital), ELUMO (lowest unoccupied molecular orbital), ∆E (energy gap), • (dipole moment) etc. are summarized in table-3. EHOMO is related to the electron-donating ability of the molecule. In the present investigation, anodized donor-acceptor interactions between the π-electrons of heterocyclic ring and carbonyl group CMA . In the surface case of acquired on the sulfamethoxazole, basis on of of surface the adsorption of a CMA the adsorption sites were sulphoxide group, nitrogen and oxygen of hetero cyclic ring and also the vacant d-orbitals of the aluminum atom of the anodized film . The gap between HOMO–LUMO energy levels of molecules was another important factor that desires to be considered. Higher the value of ∆E of an inhibitor, higher is the inhibition efficiency of that inhibitor. A well established fact that higher the values of the dipole interactive moment, greater is the corrosion resistance of the surfaces. Based on the values of ∆E and dipole moment, the compound SM may be firmly adsorbed on aluminum metal than CMA. 5 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. Conclusions Conclusions ISSN 1466-8858 Volume 16, Preprint 10 submitted 1 February 2013 A special sealing process for industrial anodized aluminum parts has been formulated as a replacement of sealing solution containing rare earths. The present solution is metal free , inexpensive, versatile and eco friendly in nature. The corrosion resistance of the coatings have been systematically analyzed through electrochemical techniques.AFM studies demonstrated that the optimum sealing time for the coatings was found as 40 minutes. The quantum mechanical measurements confirmed the mere adsorption of the sealing compounds on the anodized coatings. The above investigation reveals that among the sealing compounds used, sulfamethoxazole (SM) adsorbs better than cellulose acetate phthalate (CAP). References: [1] ‘Rare events in pitting corrosion’, J. Bloggs, Journal of Unlikely Events, 12, 12 5, pp6-12, 2000. [1]. Theoretical study of corrosion inhibition of amides and thiosemicarbazones, Fatma Kandermirli and Seda Sagdinc, Corr. Sci., 49 ,pp2118-2130, 2007 [2]. The inhibitive action of Cyclohexyl thiourea on the corrosion and hydrogen permeation through mild steel in acidic solutions, S. Karthikeyan, S. Harikumar, G. Venkatachalam, S. Narayanan and R. Venckatesh, Int. J. Chem. Tech., 4,pp1065, 2012 ,pp [3]. Colouring of anodized aluminium by electroless method, Surface Engineering, M.Selvam, 27,PP711-718,2011. 27 [4]. Diphenolic Schiff bases as corrosion inhibitors for aluminium in 0.1 M HCl: Potentiodynamic polarisation and EQCM investigations, Aysel Yurt and Ozlem Akym, Corr. Sci., 53, 53, PP 3725-3732,2011. [5].Quantum mechanical approach for electroless plating process, S. Karthikeyan, P.A. Jeeva, SNar. ayanan, K.N. Srinivasan and X. Hu, Surface Engineering, 28 ,PP743-746, 2012. [6].Erosion–corrosion behaviour of nano-Al2O3 reinforced Ni based alloying layer in acidic slurry flow, C.Z. Zhuo, J. Xu, D.Z. Han and L.L. Liu, Surface Engineering, 26 ,PP159-167,2011. [7]. Effects of five additives on electrochemical corrosion behaviours of AZ91D magnesium alloy in sodium chloride solution, Y. Dai, Q. Li, H. Gao and L.Q. Li, F.N. Chen, F. Luo and S.Y. Zhang,Surface Engineering, 27 ,PP536543,2011. [8].A. Rahman, V. Chawla, R. Jayaganthan, R. Chandra, and R. Ambardar, Hot corrosion of nanostructured Cr/Co-Al coatings, , Surface Engineering, 28 (2012), 285-293. [9]. Effect of bond coat surface roughness on oxidation behaviour of air plasma sprayed thermal barrier coatings, Surface Engineering, C. Che, G.Q. Wu, H.Y. Qi, Z. Huang and X.G. Yang, 24 ,pp 276-279,2008. [10]. The Influence of Macro thiourea Derivative on the Corrosion of Mild Steel in Marine Environment, S. Karthikeyan, P.A. Jeeva, X. Hu, S. Harikumar and S. Narayanan, Oriental Journal of chemistry, 28 ,pp 14431448,2012. [11].Impedance measurements for electroless nickel plating process, S.Karthikeyan, K.N. Srinivasan, T. Vasudevan and S. John, Port.Electrochimica.Acta, 24 ,pp 405-413,2006. 6 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. TABLE 1: Potentiodynamic polarization of anodized aluminium. ISSN 1466-8858 Volume 16, Preprint 10 Experiment Ecorr Icorr (mV vs SCE) (•Acm-2) βa Medium: 1N HCl submitted 1 February 2013 βc IE (mV dec-1) (mV dec-1) (%) - θ Pure Al -282.14 539.47 72.0 116.4 - 10 min -232.31 110.62 62.1 94.5 79.49 0.79 30 min -210.63 81.22 51.3 86.2 84.94 0.85 45 min -189.27 27.58 34.2 78.4 94.88 0.95 TABLE 2: Impedance data for the corrosion inhibition of anodized aluminium. Medium: 1N HCl 1N HCl Operating conditions Charge resistance (Rt) Ohm.cm2 No sealing 49 Transfer solution Double capacitance (Cdl) layer •F.cm-2 232 Sealing timing 10 minutes 144 68 (Thickness-30•m) 30 minutes 167 45 (Thickness-40•m) 45 minutes 177 28 (Thickness-43•m) 7 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. TABLE 3: Quantum mechanical parameters for sealants ISSN 1466-8858 Volume 16, Preprint 10 on the corrosion of submitted 1 February 2013 anodized Al Dipole moment LUMO (eV) HOMO (eV) ∆E (Cal.Mol1) Cellulose acetate phthalate (CMA) .0.434 -7.424 6.99 4.1 Sulfamethoxazole (SM) -1.199 -9.542 8.343 4.5 Inhibitor (Debye) Legends for figure 1. Tafel polarisation plots for the corrosion inhibition of anodized aluminium with and without sealing. 2. .Nyquist diagram for the corrosion inhibition of anodized aluminium with and without sealing. 3. AFM images for Anodized Al (No sealing) 4. AFM images for Anodized Al 5. AFM images for Anodized Al 6. AFM images for Anodized Al (sealing timing: 10 min) (sealing Time :30 minutes) (sealing Time :40 minutes) 7. (a) Optimized structure of Cellulose acetate phthalate (CAP) , (b) HOMO view, (c) LUMO view 8. (a) Optimized structure of Sulfamethoxazole [SM] (b) HOMO (c) LUMO view view 8 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 10 submitted 1 February 2013 Figure 1 Figure 2 9 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 10 submitted 1 February 2013 Figure 3 Figure 4 Figure 5 Figure 6 10 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 10 submitted 1 February 2013 (a) (b) (c) Figure 7 11 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 10 submitted 1 February 2013 (a) (b) (c) Figure 8 12 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work.