Hanumappa H , Govindaraju T V
Keywords: : Benzofuran, polarization, inhibitor, Langmuir,1MH2S04
Abstract:
The corrosion rates of mild steel crystal plane have been determined in stirred 1M H2SO4 solution containing various concentrations (0.5M to 5.0M) of Benzofuran by weight loss and polarization techniques. The corrosion rate which was controlled by surface reaction, was found to be a function of crystallographic orientation, temperature and benzofuran concentrations. The stability of the mild steel crystal orientation in pure acid was found. The observed corrosion date indicated inhibition by surface adsorption of inhibitor molecules, following the Langmuir adsorption isotherm. The weight loss and polarization technique gave similar inhibitor efficiency values. The stability of the mild steel crystal plane was further confirmed by a thermodynamic study of inhibitor molecule adsorption.
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ISSN 1466-8858 A study Volume 8, Preprintby 16 ‘O’ and ‘N’ donors submitted of Inhibition of mild steel corrosion system13inMay 2010 Mineral acid medium Hanumappa H , Govindaraju T V Shirdi Sai Engineering College Sai Leo Nagar, Samandur PO., Anekal, Bangalore-562106 India e-mail: hanumappa_h@rediffmail.com, Ph:91-80-27840631. Fax:91-80-27830355 mob:91-9845472211 e-mail: govindaraju_tv@yahoo.com, Ph:91-80-7840630. Fax:91-80-27830355. Mob:91-9900545101/91-9880570705 ABSTRACT The corrosion rates of mild steel crystal plane have been determined in stirred 1M H2SO4 solution containing various concentrations (0.5M to 5.0M) of Benzofuran by weight loss and polarization techniques. The corrosion rate which was controlled by surface reaction, was found to be a function of crystallographic orientation, temperature and benzofuran concentrations. The stability of the mild steel crystal orientation in pure acid was found. The observed corrosion date indicated inhibition by surface adsorption of inhibitor molecules, following the Langmuir adsorption isotherm. The weight loss and polarization technique gave similar inhibitor efficiency values. The stability of the mild steel crystal plane was further confirmed by a thermodynamic study of inhibitor molecule adsorption. Key words : Benzofuran, polarization, inhibitor, Langmuir,1MH2S04 © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 1 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 8, Preprint 16 submitted 13 May 2010 INTRODUCTION The study of corrosion of mild steel in 1MH2S04 is a subject of practical significance since the acid is highly corrosive and extensively used in various industrial operations[1, 2]. Hence the use of corrosion inhibitors is essential in order to restrain the corrosion attack of acids on metallic materials[3,4]. Organic compounds containing nitrogen, sulphure and oxygen have been found to function as very effective corrosion inhibitors. Inhibitors are often used in this process mainly to control the metal loss by dissolution and also acid consumption[5,6].. the corrosion inhibition of mild steel by different organic compounds has been studied in considerable detail[7,8,9,10,11,12]. The effectiveness of these compounds as corrosion inhibitors can be attributed to the number of mobile election pairs present, the π- electron character of free electron and the electron density around the nitrogen atoms[13,14].In the present work, a benzofurans (IH1 – IH3) used as a inhibitor on the corrosion of mild steel in 1MH2S04. The effect of these organic compounds on the corrosion rate of mild steel has been studied by weight loss method, electrochemical impedance and polarization measurements. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 2 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 Experimental Volume 8, Preprint 16 submitted 13 May 2010 The metal analysis in mild steel was carried out by preparing 1ppm solution in 1:1 hydrochloric acid Thermo Jarrrl AAS corporation make SmithHeieftjee- 1000 was used for analysis (composition: Mn= 0.0326%, Fe=5.248%, Ni = 1.158%, Cu=0.917%, Zn= 0.243%, Pb = 0.1697%). Mild steel metal having a surface area of 0.985 cm2 were fixed in a Tygon tubing exposing only the desired plane. The metal plane was mechanically polished on 4/0 emery paper using ethanol as lubricant and subsequently electropolished in orthophosphoric acid (1:1) for 30 minutes at a cell potential of 12V. The metal was taken out without switching off the current and washed with 10% phosphoric acid followed by distilled water. The metal was immediately transferred to the corrosion cell through the central neck, such that the desired surface was just below the surface of the solution. The metal surface was dipped in 1MH2S04 solution, stirred without and with various concentrations of benzofuran inhibitor for desired interval of time (1 to 6 hrs). Synthesis of benzofurans IH1 – IH3 The 2- carboxy benzofuran is prepared by the condensation of salisaldehyde with diethyl bromomalonate. The reaction of 2- carboxy benzofuran with hydrazine hydrate in ethanol at room temperature furnished the desired benzofuran – 2- carbohydrazide with equimolar quantity of acctyl acetone, acetophenones and subtsiutent acetophenones in ethanol with catalytic amount of acetic acid at reflux temparature yielded 2 – (3’, 5’dimethylpyrazole, - 1- carbonyl) benzofuran as a coloruless crystalline solid. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 3 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 The absence Volume 8, Preprint by 16 both IR and PMRsubmitted 13 May 2010 of NHNH2 function as indicated supported the formation of Pyarzolering system. The IR spectra of the benzofuran shows characteristic C=0 stretching frequency at 1720cm-1 The molecular formula of the benzofurans are shown below. Where R is –CH3 for IH1; A for IH2 ; A Cl for IH3. Methods Mild steel crystal plane was dissolved under stirred and unstirred conditions in areated 1MH2SO4 without and with various concentrations (0.5M to 5.0M) of benzofuran at 300C. The dissolution rates (mgcm-2h-1) were calculated by estimating the amount of mild steel surface dissolved in corrosive medium spectrophotometrically very significant inhibitory effect of inhibitors on the dissolution rate of mild steel was seen. Decrease in the corrosion rate of mild steel was found to be a function of crystallographic orientation and concentration of inhibitors. Inhibitor efficiency (I.E.), corrosion rate and surface coverage ϑ were calculated from the weight losses of the specimens in the absence and presence of the inhibitor using the equations. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 4 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 IE% = Volume 8, Preprint 16 inhibitor ] [Weight loss without inhibitor - weight loss with x100 submitted 13 May 2010 Weight loss without inhibitor The corrosion rate was calculated by measuring the amount of mild steel dissolved in the solution spectrophotometrically. Surfacecoverage (θ ) = Weightloss without inhibitor − weight loss withinhibitor weight loss without inhibitor Result and discussion Weight loss measurements The measured corrosion rates in stirred 1MH2SO4 and in presence of the three organic compounds (IH1 to IH3) at 300C are given in Table 1, from which it can be seen that the concentrations between 0.5M to 5.0M was determined after 5 hrs of immersion. The values of I.E., corrosion rate, surface coverage (θ) obtained from weight loss measurement. Inhibition efficiency is seen to increase with increasing inhibitor concentration. A maximum inhibitor (1H1 – IH3) efficiency of 96- 98% was observed at 5M. It is evident from fig 1 shows the I.E. for different concentrations of inhibitors in 1MH2SO4. All the compounds inhibit the corrosion of mild steel even at a very low concentrations (0.5M). Mild steel crystal plane was immersed for different periods in 1MH2SO4 containing 0.5M to 5.0M benzofuran at 300C. The weight loss varied linearly with immersion period with and without inhibitor on the mild steel crystal plane fig. 2. These compounds are contain very high I.E. is understandable from the electron donating properties of the different nitrogen atoms present in the molecules. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 5 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 From the Volume Preprint 16it is clear that an extensively submitted 13 May 2010 molecular structure of the 8, inhibitors delocalized orbit covers all the molecular atoms and the orbit is filled up with a number of π- electrons, they being contributed by different anchoring atoms of the molecule. It is apparent from the molecular structure that these molecules are able to absorb on the metal surface through nitrogen X-N groups and aromatic rings[15]. Inhibitor IH1 IH2 IH3 Concentration (M) 0.5 1.0 2.0 3.0 4.0 5.0 0.5 1.0 2.0 3.0 4.0 5.0 0.5 1.0 2.0 3.0 4.0 5.0 I.E. (%) 72.2 75.0 80.5 82.5 88.6 93.5 77.5 82.0 85.6 89.5 91.5 95.6 79.9 84.6 89.2 92.5 96.2 98.2 Corrosion rate 3 -2 -1 X10 (mg m h ) 25.10 13.16 20.00 16.15 13.50 10.45 23.85 22.15 18.26 15.55 13.21 9.15 19.15 17.25 13.31 08.85 04.31 02.15 Surface coverage (θ) 0.782 0.805 0.861 0.910 0.948 0.952 0.795 0.820 0.856 0.903 0.950 0.962 0.835 0.856 0.905 0.928 0.982 0.982 Table 1. Inhibition efficiencies at various concentration of inhibitors for the corrosion of mild steel in 1MH2SO4 obtained by weight loss measurements at 303K © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 6 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 8, Preprint 16 submitted 13 May 2010 IH1 IH2 IH3 100 inhibitor efficiency 95 90 85 80 75 70 0 1 2 3 4 5 concentration Fig 1. Variation of inhibitor efficiency with concentration of inhibitor at 30 oC Adsorption Isotherm Process The degree of surface coverage (θ) for different concentrations of the inhibitor was evaluated[16] from weight loss measurement (Table I). The data were tested graphically for fitting a suitable isotherm. The Langmuir isotherm was tested by plotting C/ θ versus C for all the compounds (Fig. 2). A straight line was obtained in all the compounds proving the fact that adsorption of these compounds adsorption on the mild steel surface obeys the Langmuir adsorption isotherm. 6 IH1 IH2 IH3 5 C/θ 4 3 2 1 0 0 1 2 3 4 5 Concetration Fig 2. Langmuir’s plots for corrosion of mild steel in various concentrations of inhibitors © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 7 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 Effect of Temperature Volume 8, Preprint 16 submitted 13 May 2010 To determine the effect of temperature on rate of corrosion, gravimetric measurements were carried out in the presence and absence of inhibitors at 303K and 318K in all the three organic compounds (IH1 – IH3) at 50M concentration. The corresponding results are green in Table II. The data in Table II clearly indicate an increase in corrosion rate and decrease in I.E. with an increasing the temperature. The reduced IE on increasing temperature may be due to desorption of the inhibitor from the metal surface and thus exposing the fresh metal surface for attack by acids[17]. Values of Ea were calculated by plotting log corrosion rate versus 1000/T (Fig. 3) Ea = slope x 8.314 x 2.303 kJ Values of the free energy of adsorption (∆G0ads) at various temperatures were calculated using the following equation. ∆G0ads = - RT ln (55.5K) where K=θ/C (1-θ), θ = degree of coverage on the metal surface, and C= concentration of the inhibitor in M. Values of Ea and ∆G0ads are given in table III. The less negative values of ∆G0ads with increase in temperature indicates physical adsorption of the benzofurans on the metal surface. The increase in Ea values for the inhibited solution in comparison to uninhibited solution may be due to the presence of reactive centers on the inhibitors that can block the active sites for corrosion[18]. © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 8 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 8, Preprint 16 I.E Temperature (K) (%) Inhibitor submitted 13 May 2010 Corrosion rate (mgcm-2h-1) IH1 303 308 313 318 95.2 91.2 87.5 83.1 10.45 26.16 92.21 135.05 IH2 303 308 313 318 96.2 92.5 88.2 85.6 9.15 21.01 65.00 126.50 IH3 303 308 313 318 98.2 94.8 92.5 88.9 02.15 18.25 61.20 118.15 TABLE 2. Inhibition efficiencies of the inhibitors at 5M concentration for the corrosion of mild steel in IMH2SO2 obtained by weight loss measurements. IH1 IH2 IH3 -2 -1 Log corrosion rate(mgcm h ) 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 3.12 3.14 3.16 3.18 3.20 3.22 3.24 3.26 3.28 3.30 3.32 1000/T(K) Fig 3. Arrhenius Plotes of corrosion rate verses 1000/T for mild steel in 1MH2SO4 solution in presence of inhibitors © 2010 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of 9 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 Inhibitor Volume 8,0 Preprint 16 Ea ∆G ads submitted 13 May 2010 at various Temperature (KJ) (KJ) 303K 308K 313K 318K Blank 3.982 - - - - IH1 33.25 -16.25 -14.45 -13.69 -11.12 IH2 61.05 -15.62 -12.52 -11.72 -10.01 IH3 94.60 -19.5 -15.55 -14.15 -12-72 Table 3. Values of Ea and ∆G0ads for the corrosion of mild steel in 1MH2SO4 containing 5M concentration of inhibitors. Polarization Measurements The cathodic and anodic polarization of mild steel surface was carried out Galvan statically in stirred 1MH2SO4, and in the presence and absence of different concentrations of IH1, between 0.5 and 15mA cm-2at 300C is shown in fig. 4. Similar polarization studies were made for other inhibitors. Electrochemical parameters such as corrosion current density (icorr) and corrosion potential (Ecorr) calculated from Tafel plots are given in Table IV. The inhibitor efficiencies were also calculated from the polarization data by using the equation * i −i %P = x100 i Where i and i* are the corrosion currents in the absence and presence of the inhibitor. At any given concentration on the mild steel surface, the % P values from weight loss data are in good agreement with the values obtained from polarization studies. © 2010 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 10 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 8, Preprint 16 Inhibitor Inhibitor Tafel scope concentration (± 5 mV decad-1) anodic cone (M) Anodic Catholic submitted 13 May 2010 Inhibition Icorr Efficiency (mA cm-2) (%) Blank - 65.15 116.20 0.25 - IH1 0.5 46.85 105.06 0.12 83.5 2.5 42.12 86.28 0.10 89.2 5.0 51.50 109.15 0.11 96.0 0.5 48.10 106.15 0.14 85.6 2.5 41.56 92.86 0.10 91.1 5.0 53.75 110.10 0.12 98.5 0.5 50.68 108.15 0.14 84.5 2.5 45.25 95.50 0.11 93.2 5.0 52.00 111.85 0.13 98.9 IH2 IH3 TABLE 4. Variation of percentage inhibitor efficiency (%P), corrosion current density [Icorr) and anodic and cathodic Tafel slope in stirred IMH2SO4 containing different concentration of benzofuran at 300C. 4.5 corrosion potential 4.0 3.5 H1 H1 H2 H2 H3 H3 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0 0 1 2 3 4 5 Icorrosion Fig 4. Corrosion current density verses corrosion potential and anodic and cathodic Tafel slope in stirred 1M H2SO4 at 30 0C © 2010 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 11 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 Conclusion Volume 8, Preprint 16 submitted 13 May 2010 The inhibitor efficiency of mild steel dissolution by the tested inhibitors follows by the order IH3 > IH2 >IH1.T the higher inhibition efficiency of the inhibitors is due to the presence of electron releasing substitution groups. The inhibition efficiency increases with increase in inhibitor concentration, immersion time. Benzofurans showed a maximum I.E. of 96-99%. The increase in cathodic Tafel scopes revealers that the inhibitors are controlling the cathodic reaction. The less negative values of ∆G0ads with increase in temparature indicate the physical adsorption of the inhibitors on the metal surface. The adsorption of the benzofarns on the metal surface obeys the Langmuir adsorption isotherm. Reference 1. Ronggang Hu, Andreas Ornberg, Jinshen Pan, J. Electrochem. Soc., 156 (2009) 2. Pruthiviraj R.D Res J. Chem-Environ-1 (2008)12 3. S.K.A. Ali, M.T. Saeed, S.V. Rahman, corros, sci. 45 (2003) 253. 4. Vishnudevan M and Natesan M. Bull elutrochem, 16 (2000) 49 5. Ateya B.G., Anaadouli, B.E & Nizamy F.M., Corrosion Sc., 24 (1984) 497. 6. Hetticarachchi S, Chan WY, Wilson R B & Agarvala VS, Corrosion, 45 (1989) 30. 7. Al- Abdullah MM & Abu – Orabi S T, Corrosion, 22 (1991) 150 8. Bilgie S & Aksut A A, Br Corros J, 28 (1993) 497. © 2010 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 12 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 9. Volume 8, Material Preprint 16 13 May 2010 Gamal K Gamma & Wahdaen MH, Chem phys. 39 (1994)submitted 142 10. Sathiyanarayanan S, Balakrishnan K, Dhawan SK & Trivedi DC, Electochem Acta, 39 (1994) 831. 11. Ajmal M, Rawart & Quaraishi MA, Anticorros Meth Mater 45 (1998) 419 12. Mhadevan K, Kartikeyan S, Rengamani S & Venkatakrishna Iyer S, J Electrochem Soc- India, 49 (2000) 136 13. A. Selvaraj, R. Anuradha, K. Sudha, S. Chitra & K. Parameshwari, Bull Electrochem 21 (2005) 247. 14. R. Hariahraputran, A. Subramania, A.A. Antony, P.M. Sankar, A. Gopalan, T. Vasudevan, S.V.K. Iyer, Br Corr J. 33 (1998) 214 15. S. Muralidharan, M.A. Quraishi, S.V.K. Iyer, Corr sci 37 (1995) 1739. 16. S. Rangamani, S. Maralidharan, M. Anbukulanthainatha , S.V.K. Iyer, J. Appl, Electrochem, 24 (1994) 355. 17. S.T. Keera, Br. Corr J. 36 (2001) 261 18. M.S. Abdel- Aal, M.S. Morad, Br. Corr, J. 36 (2001) 253. © 2010 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 13 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.