Proceedings of the 7th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21)
Prague, Czech Republic Virtual Conference – August, 2021
Paper No. iccpe 109
DOI: 10.11159/iccpe21.109

Comparison of Corrosion Protection Efficiency of Two Kinds of Amino
Acids
Albana Jano1, Alketa Lame2, Efrosini Kokalari2 and Valbona Hoxha11

Polytechnic University of Tirana,
Tirana/Albania
albana.jano@fin.edu.al, bonahoxha@gmail.com
2
University of Tirana
Tirana/Albania
Alketa.lame@fnsh.edu.al, efrosinikokalari@fshn.edu.al
Abstract. Corrosion is an inevitable natural phenomenon. The amino acids are green corrosion inhibitors due to their nontoxicity andbiodegradability. For this reason they are a good choice for corrosion protection. As inhibitors, we have used two amino acids, lysine andmethionine. They have shown good inhibitor properties in protection of low allow carbon steel against the corrosion in acidic media. Theaim of this study is to compare corrosion protection efficiency of these amino acids. Material under investigation is low alloy carbon
steel marked as: Steel 39, Steel 44 and the corrosion media is: 1M H2SO4 + 10-3mol/L Cl- (in form of NaCl). A Tafel polarization technique
was used for investigation of corrosion inhibitor efficiency. The results present that methionine is more protective again acidic corrosion
and the steel 44 is more sustainable again sulfuric acidic corrosion. The best case in the respect of corrosion sustainability for steel 44 isin presence of 1g/L methionine with protection efficiency respectively 81.27%.
Keywords: amino acid, protection efficiency, carbon steel, Tafel polarization

1. Introduction
The high costs of corrosion have a significant effect on the national economy. Mild steel are the most commonly used
construction materials due to its low cost, strength and ease of fabrication but they are affected greatly by its high corrosion
rate caused by aggressive acids.(1) Reducing corrosion can be performed by the addition of corrosion inhibitors in smallconcentrations. Research on organic compounds reveals that compounds containing hetero atoms such as sulphur,
phosphorous, nitrogen or oxygen and compounds containing double bonds and triple bonds inhibit corrosion of metal by
surface adsorption.(2) The use of corrosion inhibitors with a minimal or zero negative effects is one of the most importantpractical methods for protection against corrosion.(3) Amino acids are environmentally friendly, non-toxic, biodegradable
and relatively cheap. The main aim of our study is to compare the corrosion inhibition effect of methinine and lysine insulfuric acid solution containing chloride ions in form of NaCl for equal concentration of two extracts. For this aim,
potentiodynamic polarization technique was performed.

2. Experimental
Material under investigation are two marks of low alloy carbon steel, manufactured in KURUM factory, Elbasan,
respectively St39, St44, intended for concrete armor. The mild steel electrode composition is:MMME 118-1

Table 1: Composition of low alloy carbon steel tested.
SiMn

CrNi

CuP

S

Steel 39

0.37

0.17

0.51

0.60

0.60

0.30

0.040

0.040

Steel 44

0.445

0.348

0.780

0.118

0.263

0.324

0.07200.0440Element(Mass%)C

The samples used for the potentiodynamic measurements are prepared from steel bars in cylindrical shape with sizes(D=6mm, d=4mm) and fixed inside a Teflon tube with epoxy resin as shown in figure.
Before the potentiodynamic
measurements the surface of steel samples, before fixed inside the Teflon, were polished with emery paper (250 – 1000),
cleaned with be distilled water, dried, degreased with acetone, cleaned with be distilled water again, and finally dried.(4,5)
Each experiment was performed with freshly prepared solution and a clean set of electrodes.

Fig.1: Preparing of the samples for potentiodynamic measurements

The test solutions were in 1.0 M sulfuric acid + 10-3 Cl- solutions. Methionine and lysine were used as green inhibitors,
whose chemical structures are given in figure.

Fig.2: The structure of lysine-a- and methionine –b-All tests were obtained in deaerated solutions. The concentration range of inhibitor employed was 0.75 and 1g/L as presented
in Table 2.

MMME 118-2

Table 2: The matrix for potenciodynamic measurements.
[1]
[8]
[15]
[22]
[29]
[36]
[43]
[50]

Nr

1
2
3
4
5
6

[2]

Blank
1

[9]
[16] +[23][30] +[37] +
[44]
[51]

[3]

Blank
2

[10]
[17]
[24] +[31][38][45] +[52] +[4][5]

Concentrations ofmethionine (g/L)[11] 0.75[18][25][32] +
[39]
[46]
[53]

[12] 1
[19]
[26]
[33]
[40] +
[47]
[54]

[6]

Concentrationsof[7]
lysine (g/L)[13] 0.75 [14] 1
[20]
[21]
[27]
[28]
[34]
[35]
[41]
[42]
[48] +[49][55][56] +The measurements were carried out with a potentiostat/galvanostat. Electrochemical measurements were done using
Potenciostat galvanostat tip TACUSSEL PJT 24-2. For this purpose, a conventional three-electrode cell was used, composedof Hg/Hg2SO4 saturated K2SO4 reference electrode, a platinum electrode as auxiliary electrode, and the mild steel substrates
as the working electrodes. The Potentiodynamic polarization curves were obtained by potencial scan rate 3x10-2 V/min.
(6,4)
Deaerating of the solution was realized using a stream of pure nitrogen inside the solution for 30 min and above
solution for 5 min. Corrosion current density determined using the cutting point of Taffel extrapolation line and Faradays
law, equation 1 (4,6):
𝑉𝑐𝑜𝑟𝑟 = (𝐾 ∗ 𝑎 ∗ 𝑖) ⁄ (𝑛 ∗ 𝐷)
(1)
Where: a - is the atomic weight of the metal (a=56g/mol), i -the current density in (μA/cm2), n -the number of electrons
exchanged during metal dissolution (n=2), D -the density in (g/cm3) (d=7.86g/cm3) and K is a constant which equals to
0.00327 if corrosion rate (Vcorr) is calculated in [mm/y]. Corrosion inhibitor efficiency calculated by formula 2 (7):Inhibitor Efficiency (%) = [(CR uninhibited – CR inhibited)/ CR uninhibited] x 100(2)

Where: CR uninhibited - is corrosion rate of the uninhibited system, CR inhibited - is corrosion rate of the inhibited
system. This essentially examines the ratio of the inhibited and uninhibited corrosion rates and expresses this as a percentage.

3. Results
Potentiodynamic polarization curves and the corresponding average Tafel line for steel 39 (best case) with 78.88 %protection efficiency in de-aerated 1M H2SO4 solution, with 10-3M chloride ions in presence of 1g/L Lysine and for steel 44(best case) with 81.27 % protection efficiency in presence of 1 g/L methionine, were presented in figures: 3; 4, respectively.
Figures 5, 6 represent the potentiodynamic polarization curves and the corresponding average Tafel line in presence of
0.75g/L respectively for steel 39 and steel 44 (the worst case with lower protection efficiency 54.31 and 34.44%).

MMME 118-3

3.5

4
3.5
3

2.5
log i(µA/cm2)

log|icorr|(μA/cm²)

y = -8.9225x - 6.4654

3y = -7.3836x - 5.1899

2.5
2

2

1.5

1.5

1

1

0.5

0.5

0-1.1

0-1.1

-1 Potencial (V) -0.9-0.8

Fig.3: Potentiodynamic curves and Tafel extrapolationsfor Steel 39 in de-aerated H2SO4 solution with 10-3M
chloride ions in presence of 1 g/L lysine.

-0.9

-0.8

Potencial (V)Fig.4: Potentiodynamic curves and Tafel extrapolationsfor Steel 44 in de-aerated H2SO4 solution with 10-3M
chloride ions in presence of 1 g/L methionine.

43.5
y = -11.619x - 8.7346

y = -14.513x - 11.156

3.5

3

3
log|icorr|(μA/cm²)

log|icorr|(μA/cm²)

-1

2.5
2
1.5
10.5
-1.05

2.5
2
1.5
1

-0.95

0.5

-0.85

Potencial (V)Fig.5: Potentiodynamic curves and Tafel extrapolations for
Steel 39 in de-aerated H2SO4 solution with 10-3M chloride
ions in presence of 0.75 g/L lysine.

-1

-0.95

-0.9

-0.85

Potencial (V)Fig.6: Potentiodynamic curves and Tafel extrapolations for
Steel 44 in de-aerated H2SO4 solution with 10-3M chloride
ions in presence of 0.75 g/L lysine.

The results, in form of corrosion rates in (mm/year), calculated using corrosion current density (icorr) and protections
efficiency of different concentration of additives against corrosion, are given in Table 3.

MMME 118-4

Table 3: Corrosion rates and protection efficiency for St.44, St.39 in de-aerated H2SO4 solutions with 10-3 M chloride ions (blank ) inpresence of methionine and lysine.
Concentration methionine

Concentration of lysine

Mark ofsteel
materialBlank

Vcorr
mm/y

Vcorr
mm/y

Prot.
Eff.%

Vcorr
mm/yProt.
Eff. %

Vcorr
mm/y

Prot.
Eff.%

Vcorr
mm/y

Prot.
Eff.%

Steel 39

2.32

0.77

66.8

0.59

74.14

1.06

54.31

0.49

78.88

Steel 44

3.31

0.83

74.92

0.62

81.27

2.17

34.44

1.0368.88

0.75g/L

1 g/L

0.75g/L

1 g/L.

4. Discussion
The inhibitive effect for most of the organic corrosion inhibitors was attributed to the accumulation of the inhibitor
molecules by “direct” or/and “indirect” adsorption onto the metal surface, which reduces the contact of the metal with thecorrosive agents in solution. (3) The corrosion potentials (Ecorr) of mild steel in presence of methionine and lysine were
shifted toward less negative potentials, indicating enhancement in the corrosion resistance. Furthermore, it was observed thatthe corrosion current density (Icorr) in presence of the inhibitor was lower than that of corroded steel, confirming that bothamino acids promoted corrosion resistance. The values of inhibition efficiency show a higher corrosion resistance of theinhibitors. The Ecorr as function of time data for methionine revealed that Ecorr was shifted toward more positive value, while
icorr value was much lower than lysine and corroded steel. The positive shift of corrosion potential is evidently caused by therestriction of anodic reaction process. Corrosion rates were calculated to be 0.59 and 0.62 mm/year for steel in presence ofmethionine 1g/l (best case), reflecting the corrosion resistance enhancement by replacing addition of amino acids.
In case of amino acids, specifically, methionine, used in our study as acidic corrosion inhibitor for low alloy carbon
steel, the adsorption on anodic sites, dedicated the free electrons on S, N and O (of carboxylic group) atoms. S containing
amino-acid interact in molecular form via the S atoms in aliphatic chain, which may be adsorbed at anodic sites and retard
Fe electrochemical dissolution. This probably explains higher inhibition efficiency for S-containing amino acid.
The presence of R–S–R in molecular structure of methionine provokes an increase of the inhibition efficiency, which
can be attributed to the fact that the sulfur containing amino acids can be adsorbed as bidentate ligands in which surface
coordination is taking place through both the amino group (or carboxylic group) and the –S– moiety. (8,9,3)
In the other hand, lysine adsorbs on surface of middle steel this mechanism: the atoms O and N in amino acids serve asactive centers for the process of adsorption on the metal surface. Availability of no bonded (lone pair) and p-electrons ininhibitor molecules facilitate electron transfer from the inhibitor to the metal. A coordinate covalent bond involving transferof electrons from inhibitor to the metal surface may be formed. The strength of the chemisorptions bond depends upon theelectron density on the donor atom of the functional group and also the polarizability of the group. When an H atom attachedto the C in the ring is replaced by a substituent group (–NH2, or COOH) it improves inhibition. (10)

5. Conclusions
Methionine mitigates the corrosion rate of the Steel 39 from: 2.32 mm/year ÷ 0.59 mm/year with protection efficiency
74.14%.
Methionine mitigates the corrosion rate of the Steel 44 from: 3.31 mm/year ÷ 0.62 mm/year with protection efficiency
81.27%.
The steel 44 is more sustainable again sulfuric acidic corrosion and more sensitive versus presence of methionine, thansteel 39.

MMME 118-5

6. References[1] Rasha A. Ahmed, Investigation of Corrosion Inhibition of Vitamins B1 and C on Mild Steel in 0.5 M HCl Solution:
Experimental and Computational Approach, Volume 32, Number 1[2] A. Aloysius, R. Ramanathan, A. Christy, S. Baskaran, N. Antony, Experimental and theoretical studies on thecorrosion inhibition of vitamins – Thiamine hydrochloride or biotin in corrosion of mild steel in aqueous chloride
environment, June 2017Egyptian Journal of Petroleum 27(3) DOI:10.1016/j.ejpe.2017.06.003[3] B. El Ibrahimi, A. Jmiai, L.Bazzi, S.El Issami, Amino acids and their derivatives as corrosion inhibitors for metals
and alloys, Volume 13, issue 1, January 2020, Pages 740-771[4] M. G. Fontana, Corrosion Engineering, Third Edition, ISBN 0-07-021463-8, Printed in the United States of America,1986, 171-174; 153-164; 198-202; 172.
[5] 5.M. Abdallah, Guar Gum as Corrosion Inhibitor for Carbon Steel in Sulfuric Acid Solutions, Portugaliae
Electrochimica Acta 22, 2004, 161-175.
[6] E. Bardal, Engineering Materials and Processes, Corrosion and Protection, Springer-Verlag limited ISBN 1855233-758-3, London Berlin Heidelberg, 2004,5-10.
[7] E. G. Azero, L. L. Lopes, C. T. Andrade, Extraction and Solution Properties of the Galactomannan from the Seeds
of Cassia-Javanica L, Polymer Bulletin 39, 1997,621 – 625.
[8] A.Jano, A. Lame, E. Kokalari, 2014, The Inhibition Effects Of Methionine On Mild Steel In Acidic Media, Seria:Chimie, Ovidius University Annals Of Chemistry, Vol.XXV Year XXV – 2014, Number 1, ISSN:1223-7221.
[9] A.Lame, E. Kokalari, A. Jano, Migration Corrosion Inhibitor Agains Premature Failure Of Reinforced Concrete
Caused By Penetration Of Aggressive Environment, International Journal Of Ecosystems And Ecology Science(IJEES), 2014, ISSN: 2224-4980, Volume 4/3, page 491-498.
[10]
10. A. Jano, A.Lame, E. Kokalari, Lysine As A Corrosion Inhibitor For Low Alloy Carbon Steel In AcidicMedia, 2014, Seria: Chimie, Ovidius University Annals Of Chemistry, Vol.XXV Year XXV – 2014, Number 1,
ISSN:1223-7221.

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