1. Co-adsorption of chitosan and iodide ions on St37 steel
surface in 15% H2SO4 solution
Moses M. Solomon, Husnu Gerengi, and Tugce
Kaya
Corrosion Research Laboratory
Department of Mechanical
Engineering, Faculty of Engineering
Duzce University, 81620, Duzce Turkey
KORSEM2016

2. SCOPE
What is it all about?
How did you do it?
What did you find out?
What can you say about the findings?
Word of thanks

3. WHAT IS IT ALL ABOUT?
Life Cycle of Steel Product
Industrial processes that aid
corrosion

4. Corrosion – control measures
 Use of protective coatings
 Application of protective electrical current
 Drying of air and gases to keep humidity below
corrosion risk level
 Use corrosion inhibitors
Common corrosion inhibitors
 Inorganic (Chromates, phosphates, nitrates,
etc.)
 Organic (Hetero and unsaturated compounds)

5. Problems of common inhibitors
 High cost
 Environmental issues
 Plant extracts
Polymers
• Why chıtosan
Second most abundant natural polymer
to CMC
Cost effective
Readily available
Ecofriendly
• Issues wıth polymers
 Insolubility
 Moderate inhibitive ability
• Improvement attempts on
polymers inhibition ability
 Copolymerising
 Cross linking
 Blending
 Compositing
 Addition of substances that
exert synergistic effect

6. HOW DID YOU DO IT?
St37 steel
15% H2SO4 solution
1 g/L chitosan
2 g/L chitosan
3 g/L chitosan
4 g/L chitosan
5 g/L chitosan 5 g/L chitosan +
5 mM KI
(a) System

7. (b) Methods used
i. Weight loss technique ii Electrochemical methods

8. WHAT DID YOU FIND OUT?
Table 1: Calculated values of weight loss (g), corrosion rate (mpy), surface coverage (ϴ) and inhibition
efficiency (%η) for St37 steel corrosion in 15%H2SO4 solution in the absence and presence of different
concentrations of Chitosan, KI, and chitosan + KI at 25 oC from weight loss measurements
System/Concentration Weight loss (g) Corrosion rate (mpy) Surface coverage (θ) %η
Blank 0.4212 2003.34 – –
1g chitosan 0.2088 993.11 0.50 50.43
2g chitosan 0.1920 913.20 0.54 54.42
3g chitosan 0.1869 888.95 0.56 55.63
4g chitosan 0.1867 888.00 0.56 55.69
5g chitosan 0.1690 803.81 0.60 59.86
5 mM KI 0.1260 599.29 0.71 70.09
5g chitosan + 5 mM KI 0.0081 38.53 0.98 98.08
AT
W
mpyCR



6
1045.3
)(
(Umoren et al. 2015)
1001%
0







W
We

(Verma et al. 2016)
where CR = corrosion rate; W = weight loss (g); ρ=density of metal specimen (g/cm3); A = surface
area (cm2); T = temperature (K); Wa and We = weight losses of St37 steel coupon in the absence
and presence of additives

9. Figure 1: Variation of (a) corrosion rate (mpy) and (b) percentage inhibition efficiency (𝜼)
with selected concentration of chitosan and chitosan-iodide ions combination at different
temperatures
0
5000
10000
15000
20000
25000
30000
0 1g chitosan 3g chitosan 5g chitosan 5g chitosan + 5mM
KI
corrosionrate(mpy)
system/concentration
(a)
25˚C 40˚C 50˚C 60˚C
0
10
20
30
40
50
60
70
80
90
100
1g chitosan 3g chitosan 5g chitosan 5g chitosan + 5mM
KI
%η
system/concentration
(b)
25˚C 40˚C 50˚C 60˚C

10. Electrochemical results
(a) PDP (a) (b)
Fig. 2: Potentiodynamic polarization curves obtained for St37 steel in 15% H2SO4solution (a) without and with
different concentrations of chitosan and (b) in the absence and presence of 5g chitosan, 5 mM KI, and
chitosan-iodide combination at 25 oC
Fe + H2O ↔ [FeOH] 𝑎𝑑𝑠+ H+
+ 𝑒−
(A)
[FeOH] 𝑎𝑑𝑠
𝑟𝑑𝑠
[FeOH]+
+ 𝑒−
(B)
[FeOH]+
+ H+
→ Fe2+
+ H2O(C)
Bockris et al. (1961) Eq (Oguzie, 2005)

11. Table 2: Potentiodynamic polarization parameters for St37 steel in 15% H2SO4 in the
absence and presence of different concentrations of chitosan, KI, and chitosan + KI at
25oC
System/Concentration −𝑬 𝒄𝒐𝒓𝒓
(mV/SCE)
𝑰 𝒄𝒐𝒓𝒓
(µA cm-2)
𝜷 𝒂
(mV dec-1)
𝜷 𝒄
(mV dec-1)
𝑪 𝑹(mpy) %η
Blank 421.0 395.0 125.5 75.0 74.13 –
1g chitosan 418.0 242.0 113.6 95.6 45.43 38.73
3g chitosan 401.0 236.0 79.8 74.7 44.28 40.25
4g chitosan 391.0 199.0 90.0 71.6 37.31 49.62
5g chitosan 409.0 185.0 93.1 97.9 34.8 53.16
5mM KI 393.0 81.5 84.2 95.2 17.78 79.37
5g chitosan + 5mM KI 399 9.15 58.2 43.6 1.72 97.68
1001% 0







corr
corr
i
i
 (Achary et al.2008)

12. (b) EIS
Fig. 3: Electrochemical impedance spectra for St37 steel in 15% H2SO4 solution
in the absence and presence of various additives in Nyquist representation

13. Table 3: Electrochemical impedance parameters for St37 steel 15% H2SO4 in the absence and
presence of different concentrations of Chitosan, KI, and chitosan + KI at 25 oC.
System/
Concentration
𝑹 𝒔
(Ω𝐜𝐦 𝟐
)
𝒀 𝟎𝟏
(µF/𝐜𝐦 𝟐
)
× 𝟏𝟎−𝟑
𝒏1 𝑹𝒄𝒕
(Ω𝐜𝐦 𝟐
)
𝒀 𝟎𝟐
(µF/𝐜𝐦 𝟐
)
× 𝟏𝟎−𝟑
𝒏2 𝑹 𝒇
(Ω𝐜𝐦 𝟐
)
𝑪 𝒅𝒍
(µF𝐜𝐦 𝟐
)
𝝌𝟐
× 𝟏𝟎−𝟒
%η
Blank 0.6528 1.515 0.9188 41.99 6.573 0.6592 5.057 960.49 5.264 –
1g Chitosan 0.7557 4.292 0.7518 54.58 0.792 0.8853 10.07 822.99 3.076 23.07
3g Chitosan 0.6813 1.565 0.9333 59.92 8.710 0.6225 10.59 673.08 3.385 29.92
4g Chitosan 0.6941 0.404 0.6973 61.05 1.212 0.9667 12.80 582.20 1.744 31.22
5g Chitosan 0.6519 3.667 0.6858 79.20 0.999 0.9504 12.92 252.90 1.439 46.98
5mM KI 0.7499 1.305 0.9701 217.6 3.533 0.6069 17.79 145.09 0.838 80.70
5g Chitosan +5 mMKI 0.6284 0.930 0.9107 577.1 4.160 0.5543 30.12 34.71 1.267 92.72
1001%
0







ct
ct
R
R
 (Achary et al.2008)

14. (c) DEIS
System/
Concentration
𝑹 𝒔
(Ω𝐜𝐦 𝟐
)
𝒀 𝟎𝟏
(µF/𝐜𝐦 𝟐
)
× 𝟏𝟎−𝟑
𝒏1 𝑹𝒄𝒕(Ω𝐜𝐦 𝟐
) 𝒀 𝟎𝟐
(µF/𝐜𝐦 𝟐
)
× 𝟏𝟎−𝟑
𝒏2 𝑹 𝒇(Ω𝐜𝐦 𝟐
) %η
Blank 0.657 1.111 0.9639 39.59 4.082 0.6700 13.95 –
5g Chitosan 0.6718 0.752 0.8372 108.40 0.573 0.9232 17.17 63.48
5g Chitosan +5 mMKI 0.8747 0.237 0.9429 674.4 0.177 0.9998 95.82 94.19
Fig. 4: DEIS spectra
Table. 4: DEIS parameters

15. (b)
(c)
(d)
(e)
(f)
(g)
(h)
Fig. 5: SEM images and EDX spectra for St37 steel in (a, b) abraded state, (c, d) exposed to 15% H2SO4 solution, (e, f)
exposed to 15% H2SO4 solution containing 5 g chitosan, and (g, h) exposed to 15% H2SO4 solution containing 5 g
chitosan in combination with 5 mM KI after 10 h of immersion at 25 oC
Morphological studies

16. Adsorption and thermodynamic studies
Table 5
Temperature
(oC)
Langmuir El-Awady et al
Slope 𝐑 𝟐
𝟏
𝐲
𝐊 𝐚𝐝𝐬 (𝐠/𝐋) −∆𝐆 𝐚𝐝𝐬
𝐨
(𝐊𝐉 𝐦𝐨𝐥−𝟏
)
𝐑 𝟐
25 oC 3.1 0.9998 11.06 0.85 9.55 0.9433
40 oC 3.3 0.9968 10.36 0.78 9.80 0.9847
50 oC 3.2 0.9993 8.96 0.68 9.73 0.9397
60 oC 3.5 0.9931 10.36 0.66 9.98 0.9741
System/concentration 𝑬 𝒂(kJ/mol) ∆𝑯∗
(kJ/mol) −∆𝑺∗
(J/mol K)
Blank 69.58 67.49 154.58
1g chitosan 70.50 68.41 159.71
3g chitosan 67.13 65.01 161.70
5g chitosan 68.18 66.08 162.20
5g chitosan + 5 mM KI 16.83 14.00 209.82
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17. Synergistic consideration and mechanism
Table 6: Synergism parameter
Method 𝑺 𝜽
EIS 1.4
PDP 4.9
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18. CONCLUDING REMARKS
1. Chitosan moderately inhibits the dissolution of St37 steel in the acid solution
2. Addition of 5 mM KI to chitosan has significant effect on the inhibition efficiency
3. Increase in immersion time and temperature lead to increase in the inhibition efficiency of
chitosan-iodide mixture
4. Judging from the variation of inhibition efficiency with temperature and the value of
activation energy, it is concluded that physical adsorption prevails during the adsorption of
chitosan molecules on St37 steel surface while chitosan-iodide ions adsorb via chemisorption
mechanism.
5. Both chitosan and chitosan-iodide combination functioned in the studied system as mixed-
type corrosion inhibitor

19. SAY THANK YOU
 Moses M. Solomon İS grateful to The Scientific and Technological Research
Council of Turkey (TÜBITAK) for financial support under the TÜBITAK 2216 –
Postdoctoral Research Fellowship (TUBITAK 21514107-115.02-56312) and Duzce
Unıversity, Turkey for providing the facilities
The authors are grateful to Dr Kazimierz Darowicki and Pawel Slepski for
providing the DEIS software

20. THANK YOU FOR LISTENING!