EDTA derivatives as anticorrosion inhibitors of

Fourth Iraq Oil & Gas Conference, Basra, Dec. 13-14/2017

EDTA derivatives as anticorrosion inhibitors of Carbon Steel in acidic media Ahlam Marouf Al-Azzawi* and Kafa Khalaf Hammud** * Department of Chemistry, College of Science, University of Baghdad, Baghdad, Iraq. ** Directorate of Materials Research, Ministry of Science and Technology, Baghdad, Iraq. Corresponding author email: [email protected]

Abstract Carbon steel corrosion is an important issue in industry, oil, and other technological fields because of its bad effects on these technologies and earth plant. In this paper, several ethylene diamine tetraacetic acid derivatives were prepared and two of them were tested as inhibitor against carbon steel corrosion in acidic solutions (HCl and H2SO4) with polarization testing. The obtained data showed the corrosion of carbon steel increased with increasing temperatures (308338) oC in acid media (0.3N HCl and 0.01N H2SO4). All thermodynamic and kinetic calculations were done beside adsorption study according to Temkin model. Keywords: carbon steel, EDTA, acidic media, adsorption

‫مشتقات اثلين ثنائي االمين رباعي حامض الخليك كمثبطات تأكل للفوالذ الكربوني في‬ ‫االوساط الحامضية‬ **‫احالو يعشوف انعضاوي * و كفبء خهف حًىد‬ ‫ ثغذاد – انعشاق‬-‫* لسى انكًٍٍبء كهٍخ انعهىو – جبيعخ ثغذاد‬ ‫** دائشح ثحىس انًىاد – وصاسح انعهىو وانزكُىنىجٍب – ثغذاد – انعشاق‬ [email protected] :ًَ‫انجشٌذ االنكزشو‬ ‫الخالصة‬ ‫ٌعزجش ربكم انفىالر انكشثىًَ يسأنخ يهًخ فً انصُبعخ وانُفػ وثمٍخ انًجبالد انزكُىنىجٍخ نزبثٍشارهب انسٍئخ‬ ٍٍ‫ فً هزِ انىسلخ انجحثٍخ رى رحعٍش انعذٌذ يٍ يشزمبد اثه‬. ‫عهى هزح انًجبالد انزكُىنىجٍخ وكىكت االسض‬ ‫ثُبئً االيٍٍ سثبعً حبيط انخهٍك واخزجبس اثٍٍُ يُهى كًثجػ نذأكم انفىالر انكشثىًَ فً انًحبنٍم انحبيعٍخ‬ 1


ًَ‫ اظهشد انُزبئج انًسزحصهخ اٌ رأكم انفىالر انكشثى‬.‫( ويٍ خالل فحص االسزمبغبة‬HCl and H2SO4) (0.3N HCl and 0.01N ‫(ِو فً االوسبغ انحبيعٍخ‬308-338) ‫ٌضداد يع صٌبدح دسجخ انحشاسح‬ ‫ رى اجشاء جًٍع انحسبثبد انحشاسٌخ – انذاٌُبيٍكٍخ وانحشكٍخ ثبالظبفخ انى دساسخ االيزضاص وفك‬. H2SO4) .Temkin ‫يىدٌم‬ .‫ ايزضاص‬، ‫ االوسبغ انحبيعٍخ‬، EDTA ، ًَ‫ انفىالر انكشثى‬:‫الكلمات المفتاحية‬ Introduction Corrosion can be defined as material degradation in both chemical and physical properties as well as its mass as a result of environmental influences reaching the most stable thermodynamic state [1, 2]. Carbon steel [3-5] as a metallic material mainly consisting of iron can be converted to its oxide, sulfide, chloride or other inorganic salts under corrosive conditions such as HCl, H2SO4, NaCl, NaOH, H2S, ….etc. To prevent this electrochemical reaction (corrosion) of metallic materials or reduced it, organic, inorganic, and organo-metallic compounds were used [6-11]. Many published papers demonstrated the effect of organic inhibitors in reducing the corrosion rate depending on their adsorption on the metallic surface especially that contained heteroatoms (N, S, O,..) such as pyridine, indole, pyrole, ….and other N-heterocyclic compounds [12-30]. Recently, we published the effect of ethylene diamine tetraacetic acid (EDTA) derivative on carbon steel in acidic medium (HCl and H2SO4) as good inhibitor [31, 32]. In this research paper, we aim to investigate the influence of EDTA prepared derivatives on carbon steel - acidic media and studying their thermodynamic and kinetic properties beside the adsorption model (Temkin). Experimental section All the required preparation and characterization beside applications details were published in Kafa Khalaf Hammud - PhD thesis, 2013 entitled: Synthesis, Characterization of New Heterocyclic Derivatives and Studying the possibility for their Applications as surfactants, antimicrobial agents, or Corrosion inhibitors [33]. Also, the required information about corrosion testing and their results were evaluated in above mentioned reference. The preparation steps can be summarized as below (Scheme -1-). Ethylene diamine tetraacetic anhydride (EDTA- anhydride) preparation step [33]: 10 gm of ethylene diamine tetraacetic acid (EDTA) , 14 mL of acetic anhydride, and 16 mL pyridine were refluxed for 12 hrs t (65-70) oC then the required

2


anhydride was filtered then washing with diethyl ether after acetic anhydride to obtain the 92% yield of solid EDTA- anhydride (m.p 190 oC). N, N substituted ethylene diamine bisamic acids and their salts synthesis steps [33]: 0.01 mole of carbazole or 2-amino pyridine in acetone (25 mL) was reacted with EDTA-anhydride (0.005 mole) by dropwise technique in cooling - stirring condition. The formed bisamic acids that filtered, washed with ether then recrystallized was converted to their corresponding sodium salts by reaction with aqueous sodium hydroxide in alcohol followed by acetone addition. The physical properties of the produced compounds are shown in Table -1-. O C CH2

HOOCH2C CH2COOH

N

Ac2O / Pyr

N

HOOCH2C

70oC / 12 hrs

CH2COOH

O CH2 C

N

O

O

N

C CH2 O

CH2 C O EDTA dianhydride

EDTA

O R'RN C CH2

O CH2 C O Na

N

CH2 C NRR' O Bisamic acids

Sodium salt NH

RR'N- =

N

HO C CH2 O

CH2 C NRR' O

O

O CH2 C OH

N

N

Na O C CH2

primary or secondary heterocyclic amines

O R'RN C CH2

NaOH

[1]

N

, N

Scheme (1)

Table -1-: Physical properties of the formed compounds [33] Comp. No.

Compound Structure N

1

HO C CH2 O

O C

CH2 C OH N CH2

3

O C

N CH2

NaO C CH2 O

O C

C O

H N

N

CH2 C ONa N CH2

80

Ethyl acetate

White

235236

50

Benzene

C O

White

-

85

Acetone

White

-

90

Ethanol

N

O

CH2

CH2 C ONa

N NaO C CH2 O

240242

N

Yield, Recrystallization % Solvent

O

CH2 N

N

C O

CH2 C OH

HO C CH2 O

N

White

O

CH2 N

2

m.p, o C

O

CH2 N

N

4

O C

Colour

N CH2

C O

H N

N

3


Results and Discussion Synthesis and characterization of the prepared compounds [33]: EDTA with the dehydration agent (acetic anhydride) with pyridine presence, EDTA-dianhydride was formed in an excellent yield that reacted with primary (2aminopyridine) or secondary (carbazole) amine to produce the corresponding bisamic acid (Scheme -1-) through amino nucleophilic attack on carbonyl in dianhydride (Scheme -2-). The final step in this work was the formation of sodium salt of the previously prepared bisamic acid (Scheme -1-) through the reaction with sodium hydroxide solution.

The prepared compounds were characterized through using FTIR and 1H- & 13CNMR (Table -2-) beside physical properties (Table -1-).

Table -2-: Characterization of the prepared compounds [33]. Compound

FTIR results , cm-1

1

H- & 13C- NMR results, δ= ppm 2.66-2.78: (-CH2-N-) protons 3.7: (-N-CH2-CO-)

EDTA -dianhydride

1809 and 1762: ν(C=O) anhydride 2993: ν(C-H) aliphatic

protons. 51.8-52.8: (CH2) carbons 55.2 : (-N-CH2CO-) carbons 166-173: (C=O) carbons

4

Fourth Iraq Oil & Gas Conference, Basra, Dec. 13-14/2017 ν (O-H) ν(N-H)

ν (C-H)

ν (C=O) carboxylic and amide

ν(C=C) arom.

2.77: (N-CH2CH2-N) protons 3.41-3.46: (NCH2-CO-) protons 7.15-8.11: aromatic

N

O C

protons O

CH2

HO C CH2 O

O C

N

CH2

CH2

C O

1697

ν (C-H)

1570

ν (C=O) carboxylic and amide

N

H N

3436

2997 ν(C=O) carboxylate

ν(C=C) arom.

1604

1604 1442

1570

ν(N-H) amide

ν(C=O) amide

ν(C=O) carboxylate

3437

1608

1608 1431

CH2 C ONa CH2

C O

N

O CH2 C ONa

N N

CH2

C O

H N

51.8 and 55: carbons linked to nitrogen atoms and four carbons which linked to both nitrogen and carbonyl groups respectively. aromatic carbons: 111125.9 (C=O) carboxyl and amide: 172.8

-

1701

ν(C=O) amide

N

CH2

NaO C CH2 O

3017 2951

ν (O-H) ν(N-H)

O

CH2

NaO C CH2 O

O C

3417

N

CH2 C OH N

N

N

C O

O

CH2

HO C CH2 O

N

(OH) proton

N

N

O C

11.1-11.2:

CH2 C OH

N

N

2.75: (-N-CH2-CH2-N-) protons 3.41-3.52: N-CH2-CO) protons 7.1-8: aromatic protons

-

5


Figure (1): FTIR spectrum of EDTA- dianhydride [33].

Figure (2): FTIR spectrum of compound (3) [33].

Figure (3): FTIR spectrum of compound (4) [33].

6


Figure (4): 1HNMR & 13CNMR spectra of EDTA- dianhydride [33].

7


Figure (5): 1HNMR & 13CNMR spectra of compound (1) [33]. Through the use of TGA/DTA instrument, compound [1] proved its good thermal stability as in residual at high temperatures and with no presence of water molecule in its structure. Thermal curve of compound [1] should have 266.7 oC for losing ~ 5.7% (theoretical calculations) [33]. Staphylococcus aureus, Bacillus subtilus, Escherichia coli, Pseudomonas aeruginosa aeruginosa, and Candida albicans were used to evaluate the antimicrobial activity of these species against compound [1] [Table -3-] through inhibition zone of cup-plate agar diffusion method. Compound [1] showed very highly active inhibition zone against all except Escherichia coli [33]. Table -3-: Biological activities of compound [1] against different microorganisms [33]. Comp. No.

1

Bacillus subtilus

Escherichia coli

Pseudomonas Candida albicans aeruginosa Conc., Inhibition Conc., Inhibition Conc., Inhibition Conc., Inhibition mg/ mL zone, mm mg/ mL zone, mm mg/ mL zone, mm mg/ mL zone, mm (DMSO) 24 48 (DMSO) 24 48 (DMSO) 24 48 (DMSO) 24 48 hrs hrs hrs hrs hrs hrs hrs hrs 5.0 15.0 5.0 -ve 5.0 -ve 5.0 -ve 10.0 19.0 10.0 -ve 10.0 18.0 10.0 9 20.0 20.0 20.0 -ve 20.0 20.0 20.0 10 10.0 -ve 10.0 5 10.0 10.0 -ve 20.0 -ve 20.0 -ve 20.0 20.0 -ve

Sulfuric acid – corrosion results in industry has been raised because of hydrogen sulfide and sulfur oxides production in extraction and refining steps in oil. These results are effective on carbon steel especially at diluted acid concentration and producing of H2 and Fe3+ ions [4,5]. 8


To reduce the corrosion, several methods can be applied including addition of N, S, O, and / or multiple bond chemical to corrodent as economic method with great influence [34–36]. In this work, characterized carbon steel in circular form was subjected to 0.01 N sulfuric acid or 0.3N hydrochloric acid and with or without addition of our prepared EDTA – heterocyclic derivative (Tables -4- to -8-). The required equations were as below: Corrosion rate (mg.cm-2.min.-1): Rcorr. = W / S . t where W: weight loss of the tested sheets (mg), S: total area of specimen (cm2), and t: immersion time(min.). Surface coverage (θ): θ = [ wt loss (uninh.)– wt loss (inh.)] / wt loss (uninh.) Percentage protection efficiency (inhibition efficiency) P%: P % = [[ wt loss (uninh.) – wt loss (inh.)] / wt loss (uninh.)] x 100 where wt loss (uninh) and wt loss (inh.): weight loss without and with inhibitor, respectively. Our experiments were done in 2011. Different reasons were behind differences in obtained data such as: temperature time, composition of inhibitor, corrosion rate, ….etc [33, 37-40]. Polarization data can be used in calculation of transfer coefficients, polarization resistance [41] as below: αc = 2.303RT/ βc F

and αa= 2.303RT/ βa F

R: gas constant, F: the Faraday constant, βa: anodic Tafel slope, βc: cathodic Tafel slope, αa: anodic transfer coefficient, αc: cathodic transfer coefficient, T:    temperature (K). R p    at  0  i T ,C

Rp: polarization resistance, i: current density η= E-Ecorr. Η: overpotential, Ecorr.: corrosion potential, E: potential icorr = β / Rp ; β = βa βc / 2.303 (βa+ βc) Rp = βa βc / (2.303 (βa+ βc) icorr) ; icorr = β / Rp icorr. : corrosion current density Current density and potential curve is a way to study corrosion of a metal or alloy in a known medium and temperature in a cell containing both auxiliary and 9


working electrodes. Current density in corrosion (i corr.) is considered as a kinetic value in equilibrium state [42-45]. Current density values in our experiments were higher in carbon steel - acidic media without addition inhibitor than with inhibitor addition, increased with temperature changing [42-45]. Also, icorr. Values in HCl were higher than in H2SO4 solution referring to acid dissociation type. Protection efficiency (P%) might be considered under influence of temperature, acid type, composition of the tested inhibitor, hydrogen evaluation rate, and adsorption [44,45]. Values of cathodic transfer coefficient ( ≈ 0.5) or Tafel slope (-0.12 V/decade) might be attributed to discharge of the produced proton and electrochemical desorption mechanism that depended on overpotential as a result of absence of charge transfer [42, 46]. So in general, Tafel slopes and transfer coefficients were varied depending rate determining step and addition of the prepared heterocyclic EDTA derivatives. Resistance is a useful method to identify the setting of corrosion and the remedial action as well as considering it [Ecorr. / icorr.] term depending upon current density at equilibrium state [46]. The polarization resistance (Rp) values were calculated from Ecorr. / icorr. while io from RT/Rp . The tabulated values showed that the effect of temperature increasing on Rp decreasing and corrosion rate increasing. Thermodynamic and kinetic calculations represent the energy variations with state changing and in this statement corrosion represents an electrochemical reaction with maximum energy through transform by direct measurement (ΔG) or indirect by its derivation entropy ΔS and evaluation the endothermic or exothermic reaction nature by enthalpy ΔH [47].

ΔG = – nFE

where ΔG: free-energy change, n:

number of electrons involved in the reaction, F : Faraday constant, and E equals the cell potential (E = Ecorr). ΔS = – d(ΔG) / dT ; ΔG = ΔH – T ΔS The rate (r) of corrosion in a given environment is directly proportional with its corrosion current density (icorr) in accordance with the relation: r= 0.13 (e / ρ) icorr where (e): the equivalent weight of the metal and (ρ):metal density. 10


log (icorr)= −Ea / 2.303 RT + log A where A: pre- exponential factor and Ea: activation energy. A = (KT/h) exp (ΔS*/ R) where K: Boltzmann constant (1.381x10-23 J.K-1), h: Planck constant (6.62608x10-34 J.S), T: temperature on Kelvin scale, R: gas constant (8.314 J/Mol. K), ΔS*: activation entropy. icorr = (RT / Nh) exp (ΔS*/ R) exp (−ΔH* / RT) ; ΔH* = Ea – RT From the comparison between the two applied EDTA- heterocyclic inhibitors in different acidic media, several important points can be noticed as below (tables -4to -8-): P% for both inhibitors were in the same range as r result of being having the same backbone (EDTA structure) substituted with aromatic – N- heterocyclic moiety (carbazole or amino pyridine) beside the effect of type of acid anion (Cl - or SO42-) and acid dissociation in aqueous solution was clear with R p, Io, ΔG, ΔS, ΔH, A, Ea, ΔS*, and ΔH* values in comparison between uninhibited and inhibited HCl and H2SO4 solutions. For example, Ea and ΔS* values for uninhibited solution were lower than inhibited solution signifying physical- sorption at the initial stage that might be changed as a result of competitive inhibitor adsorption on carbon steel surface with corrdent. The adsorption study with Temkin model presented both [4 and 3] with the effect of medium type and concentration upon corrosion process and reducing it with inhibitor addition. In our testing, sulfuric acid- EDTA inhibitor with its high dilution (0.01N) differed from hydrochloric acid (0.3N) – EDTA inhibitor as represented from Kads values (Table -8-). Acknowledgement: This research paper in mostly was done as a part of Kafa Khalaf Hammud Ph.D thesis, 2013 and contract between College of Science, University of Baghdad and Center of Petroleum Research and Development, 2011. References:

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2.

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3.

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S. Dean and G. Grab, Mater. Perform.24 (6), 21 (1985).

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G. Damon, Ind. Eng. Chem. 33(1), 67 (1941).

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S. Hossain and A. Almarshad, Corros. Eng. Sci. Technol. 41, 77 (2006).

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M. Lebrini, M. Lagrenee, H. Vezin, M. Traisnel, F. Bentiss, Corros. Sci. 49, 2254 (2007).

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M. Quraishi, M. Khan, and M. Ajmal, Anti-Corros. Method Mater. 43, 5 (1996).

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M. Abdallah, E. Helal, and A. Fouda, Corros. Sci. 48, 1639 (2006).

10. G. Trabanelli and V. Carassiti, Advances in Corrosion Science and Technology, M. Fontana and R. Staehle (Eds.), Vol. 1, Plenum Press, New York, 1970. 11. O. Riggs (Jr.), Corrosion Inhibitors, G. Nathan (Ed.), Houston, 1973; J. Rosenfield, Corrosion Inhibitors, McGraw-Hill, New York, USA, 1981. 12. S. Zhang, Z. Tao, S. Liao, and F. Wu, Corros. Sci. 52, 3126 (2010). 13. Y. Tang, X. Yang, W. Yang, R. Wan, Y. Chen, and X. Yin, Corros. Sci. 52, 1801 (2010). 14. I. Obot and N. Obi-Egbedi, Corros. Sci. 52, 198 (2010). 15. F. Bentiss, M. Traisnel, L. Gengembre, and M. Lagrenée, Appl. Surf. Sci. 161, 194(2000). 16. J. Cruz, R. Martinez, J. Genesca, and E. Garcia-Ochoa, J. Electroanal. Chem. 566, 111 (2004). 12


17. A. Abdennaby, A. Abdulhady, S. Abu-Oribi, and H. Saricimen, Corros. Sci. 38, 1791 (1996). 18. Z. Tao, S. Zhang, W. Li, and B. Hou, Corros. Sci. 51, 2588 (2009). 19. Q. Qu, S. Jiang, W. Bai, and L. Li, Electrochim. Acta 52, 6811 (2007). 20. R. Hudson, T. Bulter, and C. Warning, Corros. Sci. 17, 571 (1977). 21. M. Veloz and I. Martinz, Corrosion 62, 283 (2006). 22. A. Ouchrif, M. Zegmout, B. Hammouti, S. El-Kadiri, and A. Ramdani, Appl. Surf. Sci. 252, 339 (2005). 23. K. Tebbji, A. Aouniti, M. Benkaddour, H. Oudda, I. Bouabdallah, B. Hammouti, and A. Ramdani, Prog. Org. Coat. 54, 170 (2005). 24. S. Abd El-Maksoud, Appl. Surf. Sci. 206, 129 (2003) 25. M. Bouklah, N. Benchat, B. Hammouti, and A. Aouniti, Mater. Lett. 60, 1901(2006). 26. M. Düdükcü, B. Yazici, and M. Erbil, Mater. Chem. Phys. 87, 138 (2004). 27. A. Popova, M. Christov, S. Raicheva, and E. Sokolova, Corros. Sci. 46, 1333 (2004). 28. L. Tang, X. Li, Y. Si, G. Mu, and G. Liu, Mater. Chem. Phys. 95, 29 (2006). 29. X. Li, S. Deng, H. Fu, and G. Mu, Corros. Sci. 51, 620 (2009). 30. X. Li, S. Deng, and H. Fu, Corros. Sci. 52, 2786 (2010). 31. A. Al-Azzawi and K. Hammud. J. Chem. Pharm. Res. 6(7), 2808 (2014). 32. A. Al-Azzawi and K. Hammud. J. Petroleum Res. Studies. (under publication). 33. K. Hammud. Synthesis, Characterization of New Heterocyclic Derivatives and Studying the possibility for their Applications as surfactants, antimicrobial agents, or Corrosion inhibitors. Ph. D thesis, Department of Chemistry, College of Science, University of Baghdad, Baghdad, Iraq, 2013. 34. M. Lebrini, M. Lagrenee, H. Vezin, M. Traisnel, F. Bentiss, Corros. Sci. 49, 2254 (2007).

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35. M. Quraishi, M. Khan, and M. Ajmal, Anti-Corros. Method Mater. 43, 5 (1996). 36. M. Abdallah, E. Helal, and A. Fouda, Corros. Sci. 48, 1639 (2006). 37. G. Trabanelli and V. Carassiti, Advances in Corrosion Science and Technology, M. Fontana and R. Staehle (Eds.), Vol. 1, Plenum Press, New York, 1970. 38. O. Riggs (Jr.), Corrosion Inhibitors, G. Nathan (Ed.), Houston, 1973. 39. J. Rosenfield, Corrosion Inhibitors, McGraw-Hill, New York, USA, 1981. 40. Z. Panossian, N. Almeida, R. de Sousa, G. Pimenta, and L. Marques, Corros. Sci. 58, 1 (2012). 41. R. Revie and H. Uhlig, Corrosion and Corrosion Control: an Introduction to Corrosion Science and Engineering, 4th ed. John Wiley & Sons, Inc., New Jersey, USA, 2008. 42. L. Al-Shama'a, PhD thesis, Chem. Dept., College. Sci. Baghdad Univ. (1999). 43. J. Bockris and A. Reddy, Modern Electrochemistry, Ionics, Vol. 2, 2 nd (Ed.), Kluwer Academic Publishers, New York, USA, 2002. 44. A. El- Sayed, J. Appl. Electrochem. 27, 193 (1997). 45. T. Poornima, N. Jagannatha, and A. Shetty, Portugaliae Electrochimica Acta 28(3), 173 (2010). 46. R. Revie and H. Uhlig, Corrosion and Corrosion Control: an Introduction to Corrosion Science and Engineering, 4th ed. John Wiley & Sons, Inc., New Jersey, USA, 2008. 47. Z. Ahmed, Principles of Corrosion engineering and Corrosion Control, Elsevier Science & Technology Books, New York, USA, 2006.

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Table -4-: Values of the open circuit potential (OCP), the corrosion potential (Ecorr), the corrosion current densities (Icorr), weight loss (wt loss), penetration loss, protection efficiency (P%), and Surface Coverage (θ) for carbon steel in acid with inhibitor at four different temperatures. Condition

Temp., Conc. K

H2SO4 only

0.01 N

4 With 0.01 N H2SO4

50 ppm

HCl

0.3N

3 With 0.3N HCl

50 ppm

308 318 328 338 308 318 328 338 308 318 328 338 308 318 328 338

OCP, V

Ecorr, V

-0.554 -0.534 -0.546 -0.539 -0.501 -0.506 -0.507 -0.508 -0.513 -0.503 -0.492 -0.484 -0.506 -0.499 -0.501 -0.499

-0.5430 -0.5344 -0.5343 -0.5391 -0.4805 -0.4844 -0.4863 -0.4967 -0.5114 -0.4916 -0.4709 -0.4735 -0.5069 -0.4894 -0.4900 -0.4784

Icorr, Wt loss, Penetration, P% θ A/ cm-2 g.m-2.d-1 mm. y -6 (x10 ) 71.64 17.90 83.10 63.25 15.80 73.40 90.28 22.60 1.05 120.73 30.20 1.40 35.54 8.89 41.30 50.3351 0.5033 33.42 8.35 3.88 47.1518 0.4715 71.60 17.90 83.1 20.7964 0.2079 88.09 22.00 1.02 27.1523 0.2715 383.83 96.00 4.46 515.86 129.00 5.99 1310.00 329.00 15.30 3450.00 862.00 40.00 171.33 42.80 1.99 55.4166 0.5541 487.39 122.00 5.66 5.4263 0.0542 1090.00 272.00 12.70 17.3252 0.1732 2540.00 636.00 29.50 26.2180 0.2621

15


Table -5-: Values of the Tafel slopes (βa, βc) , transfer coefficients(αa, αb), polarization resistance (Rp), and equilibrium exchange current density for polarization carbon steel in acid with inhibitor at four different temperatures.

Condition

H2SO4 only 4 With 0.01 N H2SO4

HCl only

3 With 0.3N HCl

Icorr, Temp., βa , βc, Conc. A/ cm-2 V. decade-1 V. decade-1 K (x10-6) 308 71.64 -0.1287 0.1258 318 63.25 -0.1186 0.1188 0.01 N 328 90.28 -0.1478 0.1094 338 120.73 -0.1458 0.1158 308 35.54 -0.1382 0.0515 318 33.42 -0.0896 0.0408 50 ppm 328 71.60 -0.1372 0.0403 338 88.09 -0.1118 0.0562 308 383.83 -0.0945 0.0859 318 515.86 -0.0847 0.0817 0.3 N 328 1310.00 -0.0681 0.0749 338 3450.00 -0.0936 0.0973 308 171.33 -0.0871 0.0958 318 487.39 -0.0998 0.0882 50 ppm 328 1090.00 -0.0885 0.0852 338 2540.00 -0.0731 0.0713

αa

αb

Rp, Ω.cm-2 (x104)

0.4749 0.5320 0.4403 0.4600 0.4422 0.7043 0.4744 0.5999 0.6467 0.7450 0.9558 0.7166 0.7017 0.6323 0.7354 0.9175

0.4858 0.5311 0.5949 0.5792 1.1868 1.5467 1.6151 1.1935 0.7115 0.7724 0.8690 0.6893 0.6380 0.7154 0.7639 0.9407

0.7579 0.8449 0.5918 0.4465 1.3519 1.4494 0.6791 0.5638 0.1332 0.0952 0.0359 0.0137 0.2958 0.1004 0.0449 0.0188

Io , A . cm-2 (x10-6) 3.5015 3.2431 4.7756 6.5224 1.9630 1.8905 4.1613 5.1653 19.9195 28.7539 78.6260 212.2101 8.9704 27.2891 62.8716 154.6356

16


Table -6-: The thermodynamic quantities carbon steel in acidic medium at different concentrations of inhibitor at four different temperatures. Condition

H2SO4 Only 4 With 0.01 N H2SO4

HCl

3 With 0.3N HCl

Temp., K 308 318 0.01 N 328 338 308 318 50 ppm 328 338 308 318 0.3 N 328 338 308 318 50 ppm 328 338 Conc.

OCP, V -0.554 -0.534 -0.546 -0.539 -0.501 -0.506 -0.507 -0.508 -0.513 -0.503 -0.492 -0.484 -0.506 -0.499 -0.501 -0.499

Ecorr, V -0.5430 -0.5344 -0.5343 -0.5391 -0.4805 -0.4844 -0.4863 -0.4967 -0.5114 -0.4916 -0.4709 -0.4735 -0.5069 -0.4894 -0.4900 -0.4784

-ΔG, ΔS, kJ/mol kJ/mol. K 104.7827 103.1232 0.022 103.1039 104.0301 92.72209 93.47467 0.097 93.84131 95.8482 98.68486 94.86405 0.259 90.86957 91.3713 97.81649 94.43952 0.163 94.5553 92.31685

ΔH, kJ/mol 98.00671 96.12717 95.88787 96.59413 122.5981 124.3207 125.6573 128.6342 18.91286 12.50205 5.917573 3.829295 47.61249 42.60552 41.0913 37.22285

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Table -7-: Kinetic quantities for carbon steel in acidic media with different concentrations of tested inhibitor at four different temperatures.

Condition

H2SO4 only

4 With 0.01 N H2SO4

HCl only

3 With 0.3N HCl

Icorr, Temp., Conc. A . cm-2 K (x10-6) 308 87.24 318 250.86 0.01 N 328 234.84 338 204.78 308 46.82 318 16.88 328 24.25 50 ppm 338 29.71 318 564.95 328 844.76 338 1130.00 308 383.83 318 515.86 0.3 N 328 1310.00 338 3450.00 308 171.33 318 487.39 50 ppm 328 1090.00 338 2540.00

Ea, A, ΔS*, ΔH*, 2 kJ/mol. Molecules/ cm .s kJ/mol. K kJ/mol.

22.2106

4.4491 x 1018

0.1296

19.5300

25.3125

1.5605 x 1018

0.2322

22.5936

64.6790

7.1167 x 1015

0.3866

61.9984

77.0481

1.2890 x 1028

0.4222

74.3675

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Table -8- : Adsorption - Temkin model.

Condition

50 ppm of [4] with 0.01 N H2SO4 50 ppm of [3] with 0.3 N HCl

Temp., K 308 318 328 338 308 318 328 338

Surface coverage (θ) 0.5033 0.4715 0.2079 0.2715 0.5541 0.0542 0.1732 0.2621

Equilibrium constant of adsorption, Kads 9889.69 8707.362 2561.677 3637.392 15781.71 727.7856 2660.424 4511.002

ΔGads, kJ/mol.

-36.7817

81.83488

19