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• 1.Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061Electrochemical Behaviour of AA6063 Alloy in Hydrochloric Acidusing Schiff Base Compounds as Corrosion Inhibitors.Sanaulla Pathapalya Fakrudeen*, Lokesh H. B**, Ananda Murthy H. C***,Bheema Raju V. B****.* Department of Engineering Chemistry, HKBK College of Engineering, Nagawara, Bangalore Karnataka, India** Department of Engineering Chemistry, Vivekananad Institute of Technology, , Bangalore-Karnataka, India.*** Department of Engineering Chemistry, R N Shetty Institute of Technology, Bangalore, Karnataka, India.**** Department of Engineering Chemistry, Dr. Ambedkar Institute of Technology,, Bangalore , Karnataka, India.ABSTRACT The electrochemical behavior of however, are reactive materials and are prone toaluminium alloy AA6063 were investigated corrosion. A strong adherent and continuoususing Schiff base compounds namely N, N-bis passive oxide film is developed on Al upon(Salicylidene)-1, 4-Diaminobutane (SDB) andexposure to aqueous solutions. This surface film isN, N-bis (3-Methoxy Salicylidene)-1, 4amphoteric and dissolves when the metal isDiaminobutane (MSDB) as corrosion inhibitors exposed to high concentrations of acids or basesin presence of 1M Hydrochloric Acid by weight[1]. Hydrochloric acid solutions are used for acidloss,Potentiodynamicpolarization(PDP), cleaning,acid de-scaling, chemical andelectrochemical impedance spectroscopy(EIS)electrochemical etching in many chemical processand scanning electron microcopy (SEM). industries where in aluminium alloys are used. It isPotentiodynamic polarization study revealedvery important to add corrosion inhibitors tothat the two Schiff bases acted as mixed typeprevent metal dissolution and minimize acidinhibitors. The change in EIS parameters isconsumption [2]. Most of the efficient acidindicative of adsorption of Schiff bases oninhibitors are organic compounds that containaluminum alloys surface leading to formation ofmainly nitrogen, sulfur or oxygen atoms in theirprotective layer. The weight loss study showed structure. The choice of inhibitor is based on twothat the inhibition efficiency of these compoundsconsiderations: first it could be synthesizedincreases with increase in concentration and conveniently from relatively cheap raw materials;vary with solution temperature and immersion second, it contains the electron cloud on thetime. The various thermodynamic parameters aromatic ring or electronegative atoms such aswere also calculated to investigate thenitrogen, oxygen in relatively long-chainmechanism of corrosion inhibition. The effect of compounds. Numerousorganic substancesmethoxy group on corrosion efficiency wascontaining polar functions with nitrogen, oxygen,observed from the results obtained between and sulphur atoms and aromatic rings in aSDB and MSDB. The effectiveness of these conjugated system have been reported as effectiveinhibitors were in the order of MSDB>SDB. Thecorrosion inhibitors for aluminium alloys [3-5].adsorption of Schiff bases on AA6063 alloy Some Schiff bases have been reported earlier assurface in acid obeyed Langmuir adsorption corrosion inhibitors for aluminum alloys [6-8], ironisotherm. The surface characteristics of [9-10] and copper [11-12]. Compounds with -inhibited and uninhibited alloy samples were bonds also generally exhibit good inhibitiveinvestigated by scanning electron microscopy properties due to interaction of orbital with metal(SEM). surface. Schiff bases with RC = NR as general formula have both the features combined with theirKeywords: Electrochemical techniques,structure which may then give rise to particularlyCorrosion, Schiff base, Adsorption, Aluminum potential inhibitors.alloy.The present work is aimed at investigating1. Introduction: the inhibitive ability of two Schiff base molecules Corrosion of aluminum and its alloys hason corrosion of AA6063 in 1M Hydrochloric acidbeen a subject of numerous studies due to theirmedium. The weight loss, potentiodynamichigh technological value and wide range of polarization and electrochemical impedanceindustrial applications especially in aerospace andtechniques were employed to study inhibitive effecthouse-hold industries. Aluminum and its alloys,of two Schiff base molecules at different concentrations. The effect of temperature, 2049 | P a g e

2. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061immersion time on corrosion behaviour of samples were cut into cylindrical test specimensaluminium alloy was also studied in absence andand moulded in cold setting Acrylic resin exposingpresence of inhibitor at various concentrations. For a surface area of 1.0 cm2 for electrochemicalfurther confirmation aluminum alloy samples were measurements. For weight loss experiments theanalyzed by scanning electron microscopic (SEM)cylindrical alloy rods were cut into 24 mm dia xtechnique. 2mm length -circular cylindrical disc specimensThe inhibition effect of Schiff base compounds are using an abrasive cutting wheel and a 2mmreported on steel [13-14], Copper [15], and pure mounting hole at the centre of the specimen wasaluminium and its alloys [16-19], in acidicdrilled. Before each experiment, the electrodesmedium. However, no substantial work has beenwere abraded with a sequence of emery papers ofcarried out on corrosion inhibition of aluminium different grades (600, 800, and 1200), washed withalloys in acidic medium by Schiff bases. Thus, itdouble distilled water, degreased with acetone andwas thought worthwhile to study the corrosiondried at 353 K for 30 min in a thermostated electricinhibition effect of Schiff base compounds oven and stored in a moisture-free desiccator priornamelyN,N-bis(Salicylidene)-1, 4- to use. The corrosive medium selected for thisDiaminobutane (SDB) and N, N-bis (3-Methoxy study was 1M hydrochloric acid, which wasSalicylidene)-1, 4 Diaminobutane (MSDB) on prepared from analytical grade 37 percent acidAA6063 Alloy in 1M Hydrochloric acid medium. concentrated (Merck ) in double distilled water.2. Experimental2.1 Materials The alloy samples were procured fromM/S. Fenfe Metallurgical, Bangalore, India. Thetypical chemical composition of AA6063 alloy inweight percentage is shown in Table 1. The alloy Table-1. Typical Chemical Composition of AA 6063ElementCu MgSiFe Mn Ti Cr ZnOthers AlWt.% 0.10 0.45 -0.2 - 0.35 0.10 0.10 0.10 0.100.15 Reminder0.900.6 MaxMaxMaxMaxMax Max2.2 Inhibitor. melting points, Fourier transform infrared The Schiff Bases were prepared by the spectroscopy (FT-IR) and Proton Nuclear Magneticcondensation of respective aromatic aldehydes with Resonance (1H NMR). The structure, moleculareach of diamines as per the reported procedure formula, molecular mass, melting points are shown[20]. All reagents used were of analytical grade in Table-2.procured from Sigma Aldrich.N,N-bis(Salicylidene)-1,4-Diaminobutane (SDB) wasN,N-bis(Salicylidene)-1,4-Diaminobutaneprepared by slow addition of Salicylaldehyde (2IR (KBr cm-1): 3400(OH), 3054(=C-H), 2903(-mmol) in 30 mL methanol over a solution of 1,4-CH), 1628(C=N). 1diaminobutane (1mmol) in 30 mL methanol andHNMR (CDCl3): 1.79-1.82(t, 4H, -CH2CH2-), N,N-bis(3-MethoxySalicylidene)-1,4- 3.62-3.65(t, 4H, -CH2-N) 6.847.31 (m, 8H, ArH).Diaminophenelyne (MSDB) by slow addition ofMethoxysalicylaldehyde (2 mmol) in 30 mL 8.34(s, 2H, N=CH), 13.49 (s, 1H, OH),methanol over a solution of 1,4-diaminobutane (1 N,N-bis(3-Methoxy Salicylidene)-1,4-mmol) in 30 mL methanol taken in a 250 mLcondensation flask. In each case, 2-3drops of acetic Diaminobutaneacid was added to the mixture of aldehyde and IR (KBr cm-1): 3429(OH), 2996(=C-H), 2932(-diamine with stirring at constant temperature 25Cfor 1 hour. Further the mixture was refluxed for 4-5 CH), 1628(C=N). 1253(-OCH3).hours on a water bath, heating occasionally to 1HNMR (CDCl3): 1.80-1.83(t, 4H, -CH2CH2-), improve the yield of the product. The reactionmixture was cooled to room temperature overnight 3.63-3.66(t, 4H, -CH2-N) 3.90(s, 6H, -OCH3),and the colored compound was filtered off and 6.777.2 (m, 6H, ArH). 8.32(s, 2H, N=CH), 14.00dried. The compounds were recrystallised withethanol. The product identity was confirmed via (s, 1H, OH), 2050 | P a g e 3. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061 Table-2. The structure, molecular formula, molecular mass, melting pointsStructure and Name Molecular Formula Molecular MeltingMassPointCH N(CH2)4 N CHC18H20N2O2296.3689C OH HON,N-bis(Salicylidene)-1,4-Diaminobutane (SDB) CH N (CH2)4NCH O OH HO O H3C CH3C20H24N2O4356.42 152C N,N-bis(3-Methoxy Salicylidene)-1,4-Diaminobutane(MSDB) 2.3 Weight loss measurementsexperiments were measured after immersion of alloyWeightlossmeasurementswere specimens for 30 minutes to establish a steady state performed on aluminium alloys as per ASTM open circuit potential in absence and presence of Method [21]. The test specimens were immersed inhibitors at 303 K. in 100mL 1M hydrochloric acid solution in absence and presence of different concentrations (25,50,75 Tafel plots were obtained using and 100 ppm ) of SDB and MSDB at differentconventional three electrode Pyrex glass cell with temperature ranges (303, 313, 323 and 333 K) in alloy specimen (1cm2) as working electrode (WE), thermostated water bath. The difference in weight platinum electrode (Pt) as an auxiliary electrode and for exposed period of 2, 4, 6 and 8 hours was taken standard calomel electrode (SCE) as reference as the total weight loss. The weight loss electrode. All the values of potential were referred to experiments were carried out in triplicate andSCE..Tafel plots were obtained by polarizing the average values were recorded. The corrosion rateelectrode potential automatically from 250 to + was evaluated as per ASTM Method [21]. The250 mV with respect to open circuit potential (OCP) percentage of inhibition efficiency (WL%) andat a scan rate 1mV s 1. The linear Tafel segments of the degree of surface coverage () were calculatedanodic and cathodic curves were extrapolated to using equations (1) and (2):corrosion potential (Ecorr) to obtain corrosion current densities (Icorr). The inhibition efficiency was evaluated from the Icorr values using the following Wo Wi (1) relationship (3):WL% = x 100Wo i0corr icorr(3)p% =x 100i0corrWo Wi(2) = 1Where, i0corr and icorr are values of corrosion current Wo densities in absence and presence of inhibitorrespectively.Where Wi and Wo are the weight loss values of aluminium alloy sample in the presenceEIS measurements were carried out in a and absence of the inhibitor and is the degree offrequency range from 100 kHz to 0.01 Hz with surface coverage of the inhibitor. small amplitude of 10mV peak -to-peak, using ACsignal at OCP. The impedance data was analyzed2.4 Electrochemical measurements. using Nyquist plot and Echem software ZSimpWinPotentiodynamic polarization (PDP) andversion 3.21 was used for data fitting. Theelectrochemical impedance spectroscopy (EIS)inhibition efficiency (Rct %) was calculated frommeasurements were performed using CH660cthe charge transfer resistance (Rct) values usingelectrochemical work station. All electrochemical following equation (4): 2051 | P a g e 4. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061 Rict R0ct Rct % = x 100 (4)-0.5 Rict-1.0 0 Where, R ct andRictare the charge transfer -1.5resistance in absence and presence of inhibitor, respectively. -2.0-2log i / mA / cm-2.5 2.5 Scanning electron microscopy (SEM).The surface morphology of the corroded surface in -3.0the presence and absence of inhibitors were studied-3.5Balnk63using scanning electron microscope (SEM) [ModelNo JSM-840A-JEOL]. To understand theSDB25ppm-4.0SDB50ppmmorphology of the aluminium alloy surface in theSDB75ppmabsence and presence of inhibitors, the following -4.5SDB100ppmcases were examined.-5.0 (i) Polished aluminium alloy specimen.-0.5-0.6-0.7 -0.8-0.9 -1.0-1.1 (ii) Aluminium alloy specimen dipped in 1M HCl. E / mV vs. SCE (iii) Aluminium alloy specimen dipped in 1M HCl 1(a) containing 100 ppm of Schiff base.)3. Results and Discussion3.1 Potentiodynamic polarisation (PDP)-0.5 The polarization measurements of -1.0AA6063 alloy specimens were carried out in 1M-1.5Hydrochloric acid, in the absence and in thepresence of different concentrations (25 -100 ppm)-2.0of SDB and MSDB at 303K in order to study the-2 log i / mA cm-2.5anodic and cathodic reactions. The Fig.1(a) and (b).represents potentiodynamic polarisation curves-3.0(Tafel plots) of AA6063 alloy in 1M Hydrochloric-3.5acid in absence and presence of variousBalnk63-4.0concentrations of SDB and MSDB at 303K MSDB25ppmrespectively. The electrochemical parameters i.e. -4.5 MSDB50ppmcorrosion potential (Ecorr), corrosion current density MSDB75ppm-5.0 MSDB100ppm(icorr), cathodic and anodic Tafel slopes (ba and bc)associated with the polarization measurements of-5.5 -0.5 -0.6-0.7-0.8 -0.9 -1.0-1.1SDB and MSDB are listed in Table.3. Theinhibition efficiency (p %) of inhibitors at E / mV vs. SCEdifferent concentrations was calculated from the1(b)equation (4). It is observed from the PDP resultsFigure. 1. potentiodynamic polarisation curvesthat, in presence of inhibitors, the curves are shifted(Tafel plots) of AA6063 alloy in 1Mto lower current density (icorr) regions and TafelHydrochloric acid in absence and presence ofslopes ba and bc values increased with increase invarious concentrations of (a) SDB and (b)concentration of inhibitors showing the inhibitionMSDB at 303Ktendency of SDB and MSDB. The corrosionpotential (Ecorr) values do not show any appreciableshift, which suggest that both inhibitors acted asmixed type but predominantly cathodic inhibitors[22-23]. This can probably be due to the adsorptionof protonated Schiff base molecules on the cathodicand anodic sites2052 | P a g e 5. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061Table.3. Potentiodynamic polarisation parameters of AA6063 alloy in 1M Hydrochloric acid in absence and presence of various concentrations of SDB and MSDB at 303K3.2 Electrochemical impedance spectroscopy.The effect of the inhibitor concentration on theimpedance behavior of AA6063 alloy in 1M60Blank63SDB25ppmHydrochloric acid was studied and Nyquist plots of50SDB50ppmAA6063 in absence and presence of various SDB75ppm40SDB100ppmconcentrations of Schiff bases are given in Fig 2 (a)and (b).302-Z i / cm It is clear from the figure that the 20impedance diagrams obtained yield a semicircle10shape. This indicates that the corrosion process ismainly controlled by charge transfer. The general 0shape of the Nyquist plots is similar for all samples -10of AA 6063 alloy, with a large capacitive loop at-20higher frequencies and inductive loop at lowerfrequencies. The similar impedance plots have been 0 10 20 30 40 50 602 7080 90100 110 2(a) Zr / cmreported for the corrosion aluminum and its alloysin hydrochloric acid [24-30].Blank63The Nyquist plot with a depressed semicircle with 80MSDB25ppmthe center under the real axis is characteristic70MSDB50ppmMSDB75ppmproperty of solid electrode and this kind of60MSDB100ppmphenomenon is known as the dispersing effect [31- 5032]An 40 2equivalent circuit fitting of five elements was used -Z i / cm30to simulate the measured impedance data of20AA6063 alloy is depicted in Fig.3.10 0-10-20-30 2(b) 0 10 20 30 40 50 60 70 280 90100 110 120 Zr / cm2053 | P a g e 6. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061Figure. 2. Nyquist plot for AA6063 alloy in 1M [35]. The double layer capacitance (Cdl) can beHydrochloric acid in absence and presence of calculated from the equation.(6) [36].various concentrations of (a) SDB and (b) MSDB (6)at 303K Cdl = Y0 (max) n 1 Where Cdl is the double layer capacitance and max is the angular frequency at which Z reaches maximum and n is the CPE exponent. The electrochemical impedance parameters Rs, Rct, , CPE, n and Cdl are listed in Table-4. The inhibition efficiency was evaluated by Rct and Cdl values of the impedance data, it is shown from Table.(4) that charge transfer resistance ( Rct ) of inhibited system increased and double layer capacitance (Cdl) decreased with increase in inhibitor concentration. This was due to adsorption of Schiff base molecule on the metal surface, the adsorbed inhibitor blocks either cathodic or anodic reaction or both formation of physical barrier, which reduces metal reactivity. The effect of inhibitor may be due to changes in electric double layer at the interface of solution and metal electrode. The decrease in double layerFigure..3. The equivalent circuit model used to fitcapacitance (Cdl) can be caused by decrease in localthe experimental impedance data. dielectric constant and /or increase in the thickness of electric double layer, this suggest that the SchiffThe equivalent circuit includes solution base molecules inhibit the aluminium alloy byresistance Rs, charge transfer resistance Rct, adsorption at the metal acid interface. It isinductive elements RL and L. The circuit alsoevident that the inhibition efficiency increases withconsists of constant phase element, CPE (Q) in increase in inhibitor concentration which is in goodparallel to the parallel resistors Rct and RL, and RLagreement with the Potentiodynamic polarizationis in series with the inductor L. The impedanceresults.spectra for the aluminium alloy in absence andpresence of the inhibitors are depressed. TheTable-4. Electrochemical impedance parameters ofdeviation of this kind is referred as frequencyAA6063 alloy in 1M Hydrochloric acid in absencedispersion, and has been attributed to and presence of various concentrations of (a) SDBinhomogeneous of solid surface of aluminum alloy.and (b) MSDB at 303KAssumption of a simple Rct Cdl is usually a poorapproximation especially for systems showingdepressed semicircle behavior due to non idealcapacitive behaviour of solid electrodes [33]. Thecapacitor in the equivalent circuit can be replacedby a constant phase element (CPE), which is afrequency dependent element and related to surfaceroughness. CPE is substituted for the respectivecapacitor of Cdl in order to give a more accurate fit.The impedance function of a CPE is defined inimpedance [34] representation as (5). 1ZCPE =( Y0j)n(5) Where, Y0 magnitude of CPE, n isexponent of CPE, and are frequency independent,and is the angular frequency for which Zreaches its maximum value, n is dependent on thesurface morphology : 1 n 1. Y0 and n can becalculated by the equation proved by Mansfeld et al2054 | P a g e 7. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-20613.3 Weight loss measurements 90The experimental data of weight loss (w),SDBpercentage of inhibition efficiency (WL%), MSDBCorrosion Rate (C.R.) in mmpy and degree of80Surface Coverage () for AA6063 in 1MHydrochloric acid in absence and presence ofvarious concentration of SDB and MSDB Schiff 70% IEbases at 2 hours of exposure time and differenttemperature are shown in Table. 5. 603.3.1 Effect of inhibitor concentrationThe variation of inhibition efficiency (WL%) withinhibitor concentration is shown in Fig..4(a). 50Increase in inhibition efficiency at higher 0 2 4 6 810concentration of inhibitor may be attributed toTime / hlarger coverage of metal surface with inhibitor 4(b)molecules. The maximum inhibition efficiency wasachieved at 100 ppm and a further increase in90inhibitor concentration caused no appreciableSDB MSDBchange in performance3.3.2 Effect of immersion time 80The effect of immersion time on inhibitionefficiency is shown in Fig..4(b). All the testedSchiff bases show a decrease in inhibition 70% IEefficiency with increase in immersion time from 2to 8 hours. This indicates desorption of the SchiffBase over a longer test period and may be60attributed to various other factors such as formationof less persistent film layer on the metal surface,and increase in cathodic reaction or increase in 50303313323 333ferrous ion concentration [37]. 4(c) Temp / K3.3.3 Effect of temperatureThe influence of temperature on inhibitionefficiency of two Schiff bases compounds is shown Figure. 4. Variation of inhibition efficiency with (a)in Fig.4(c). The inhibition efficiency for the twoInhibitor concentration (b) Exposure time(c)Schiff base compounds decreases with increase inTemperature in 1M Hydrochloric acid for SDB andtemperature from 303 to 333K. The decrease in MSDB.inhibition efficiency with rise in temperature maybe attributed to desorption of the inhibitormolecules from metal surface at highertemperatures and higher dissolution rates ofaluminium at elevated temperatures. 90SDB 85MSDB 80% IE 75 70 65 600 25 50 75 100 125C / ppm4(a)2055 | P a g e 8. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061 Table- 5. Weight loss parameters for AA6063 in 1M hydrochloric acid in the absence and presence of various concentrations of SDB and MSDB at 2 hours of exposure time and different temperature.3.3.4 Thermodynamic activation parameters 3.0 Thermodynamic activation parameters are Blank-63important to study the inhibition mechanism. The SDB25ppm2.5SDB50ppmactivation energy (Ea) is calculated from theSDB75ppmlogarithm of the corrosion rate in acidic solution is 2.0 SDB100ppm-1a linear function of (1/T) -Arrhenius equation (7): Log (CR) / mmy log (CR) = Ea / 2.303RT + A1.5 (7)1.0Where, Ea is the apparent effective activationenergy, R is the universal gas constant and A is the0.5Arrhenius pre exponential factor. Plots of logarithmof corrosion rate obtained by weight loss 0.0measurement versus 1/T gave straight lines and2.9 3.0 3.13.23.33 -1slope equal to ( Ea/2.303R) as shown in Figs. 5(a) (1 / T)10 / K5(a)and 5(b) for SDB and MSDB respectively. The Eavalues calculated are listed in Table.6. 2056 | P a g e 9. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061 0.53.0 Blank-63 Blank-63MSDB25ppm MSDB25ppm 0.0 MSDB50ppm2.5MSDB50ppm MSDB75ppm MSDB75ppm MSDB100ppm -1Log CR / T / mmy K MSDB100ppm-0.5 -12.0-1Log (CR) / mmy -1.01.51.0-1.50.5-2.02.9 3.0 3.13.23.30.0 3 -1(1 / T)10 / K2.93.03.13.23.36(b) (1 / T)10 / K3-1 5(b)Figure..6. Arrhenius plot of log (CR/T) versus 1/T Figure.5. Arrhenius plot of log CR versus 1/T in in absence and presence of (a) SDB and (b) MSDB absence and presence of (a) SDB and (b)MSDBTable-6. Thermodynamic parameters of activation A plot of log (CR/T) versus 1/T gave a of AA6063 in 1M HCl in presence and absence of straight line, Figs. 6(a) and (b) with a slope of ( different concentrations of SDB and MSDB H/2.303 R) and an intercept of [(log (R/Nh) + (S/2.303 R)], from which the values of S* andTable-6. Thermodynamic parameters of activation H* were calculated. The straight lines were of AA6063 in 1M HCl in presence and absence of obtained according to transition state equation (8): different concentrations of SDB and MSDBC R= RT/ N h exp(H*/ RT) exp (S*/ R)(8) Where, h is the Plank constant, N is the Avogadro number, S* is entropy of activation and H* is the enthalpy of activation. The S* and H* values calculated are listed in Table. 6 0.5Blank-63SDB25ppm 0.0SDB50ppmSDB75ppmSDB100ppm -1 Log CR / T / mmy K-0.5 -1-1.0-1.5-2.0 2.9 3.0 3.13.2 3.33 -1 (1 / T)10 / K6(a)2057 | P a g e 10. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061The Ea values of aluminium alloy in 1MWhere C(inh) is inhibitor concentration and K(ads) isHydrochloric acid in the presence of Schiff basean equilibrium constant for adsorption andcompounds are higher than those in the absence of desorption.Schiff bases. The increase in the Ea values, with The K(ads) was calculated from the intercepts of theincreasing inhibitor concentration is attributed to straight lines on the C(inh) / axis Fig.7(a) andphysical adsorption of inhibitor molecules on the standard free energy of adsorption of inhibitormetal surface [38]. In other words, the adsorptionG0ads was calculated using the relation (10);.of inhibitor on the electrode surface leads toformation of a physical barrier that reduces the(10)G0ads = RT ln (55.5 Kads)metal dissolution in electrochemical reactions [39].The inhibition efficiency decreases with increase intemperature which indicates desorption of inhibitor To calculate heat of adsorption (H0ads) andmolecules as the temperature increases [40].entropy of adsorption (S0ads) ln K(ads) vs. 1/T wasThe values of enthalpy of activation (H*) areplotted as shown in Fig.7(b). The straight linespositive; this indicates that the corrosion process iswere obtained with a sloe equal to ( H0ads / R)endothermic. The values of entropy of activationand intercept equal to (S0ads / R + ln 1/55.5). The(S*) are higher in the presence of inhibitor thanvalues of equilibrium constant (K(ads)), Standardthose in the absence of inhibitor, The increase infree energy of adsorption(G0ads ), enthalpy ofvalues of S* reveals that an increase in adsorption (H0ads) and entropy of adsorptionrandomness occurred on going from reactants to(S0ads) are listed in Table.7.the activated complex [41-43].The negative values of standard free of3.3.5 Adsorption isothermsadsorption indicated spontaneous adsorption ofIt is generally assumed that the adsorption of theSchiff bases on aluminium alloy surface. Theinhibitor at the interface of metal and solution is the calculated standard free energy of adsorptionfirst step in the mechanism of inhibition aggressivevalues for the Schiff bases are closer to 40 kJmedia. It is also widelymole1 and it can be concluded that the adsorptionof Schiff bases on the aluminium surface is moreacknowledged that adsorption isotherms providechemical than physical one [45]. The sign ofuseful insights into the mechanism of corrosion enthalpy and entropy of adsorption are positive andinhibition. The investigated compounds inhibit theis related to substitutional adsorption can becorrosion by adsorption at the metal surface. attributed to the increase in the solvent entropy andTheoretically, the adsorption process has beento a more positive water desorption enthalpy. Theregarded as a simple substitution adsorptionincrease in entropy is the driving force for theprocess, in which an organic molecule in theadsorption of the Schiff bases on the aluminiumaqueous phase substitutes the water molecules alloy surface.adsorbed on the metal surface [44]. The surface The adsorption of Schiff base on the aluminiumcoverage () value calculated from weight loss data alloy surface can be attributed to adsorption of thefor different concentrations of Schiff bases wasorganic compounds via phenolic and iminic groupsused to explain the best adsorption isotherm. The in both cases. Among these two Schiff bases, thevalue of surface coverage () was testedchelate effect of MSDB is greater than that of SDB.graphically for fitting a suitable adsorption This is due to the presence of two electron donatingisotherm. Attempts were made to fit surface groups of OCH3 in MSDB structure than SDB.coverage () values of various isotherms includingThe more efficient adsorption of MSDB is theLangmuir, Freundlich and Temkin isotherms.result of electronegative oxygen atoms present inAmong three adsorption isotherms obtained, thethe MSDB compared to SDB Structure.best fitted isotherm was the Langmuir adsorptionisotherm (C(inh) / vs. C(inh) ) Fig.7(a) with thelinear regression coefficient values (R2) in therange of 0.9994 - 0.9996. The Langmuir adsorptionisotherm can be expressed by following equation(9):C(inh)1 =+ C(inh)(9) K(ads)2058 | P a g e 11. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061 140 2 SDB-R =0.9996 1202 MSDB-R =0.9994 100C//ppm8060407(a)200 25 50 75100 125C / ppm 10.0SDBMSDB9.5 -1 ln Kads/M9.08.57(b)8.02.93.03.1 3.2 3.3 Table-7. Thermodynamic parameters for the adsorption of3 (1 / T)10 / K -1 inhibitor in 1M HCl on AA6063 alloy at different temperatures Figure.7. (a) Langmuir adsorption isotherm plot and (b) Heat of adsorption isotherm plot for SDB and MSDB 3.4 Scanning electron microscope (SEM) Scanning electron microscopy of the AA6063 sample of inhibited and uninhibited metal samples is presented in Fig. 8. The SEM study shows that the inhibited alloy surface is found smoother than the uninhibited surface.2059 | P a g e 12. Sanaulla Pathapalya Fakrudeen, Lokesh H. B, Ananda Murthy H. C, Bheema Raju V. B /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.2049-2061ab c d Figure. 8. Scanning electron micrographs of (a) Polished AA6063 alloy, (b) After immersion in 1M HCl for2h, (c) After immersion in 1M HCl for 2h in presence of 100 ppm SDB and (d) After immersion in 1M HCl for 2h in presence of 100 ppm MSDB.4. Conclusions 1. The investigated Schiff bases are good7. Scanning Electron Microscopy (SEM)inhibitors for aluminium alloy 6063 in 1Mshows a smoother surface for inhibited alloyHydrochloric acid solution.samples than uninhibited samples due to 2. In weight loss studies, the inhibition formation of protective barrier film.efficiency (WL%) of the Schiff basesincrease with increase in inhibitorReferences:concentration, whereas decreases with 1. U.Ergun, D.Yuzer and K.C.Emregul,increase in immersion time and temperature.Mater. Chem.Phys., 109(2008)492-499. 3. 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