{Comparative analysis of adsorption and corrosion inhibitive properties of ethanol extract of Dialium Guineense leaves for mild steel in 0.5 M HCl}


 

doi:10.5599/jese.486  219 

J. Electrochem. Sci. Eng. 8(3) (2018) 219-226; DOI: http://dx.doi.org/10.5599/jese.486  

 
Open Access : : ISSN 1847-9286 

www.jESE-online.org 
Original scientific paper 

Comparative analysis of adsorption and corrosion inhibitive 
properties of ethanol extract of Dialium Guineense leaves for 
mild steel in 0.5 M HCl 

Shola Elijah Adeniji, Bamigbola Abiola Akindehinde 

Department of Chemistry, Ahmadu Bello University Zaria, Nigeria 

Corresponding author - E-mail: shola4343@gmail.com;  

Received: December 4, 2017; Revised: March 16, 2018; Accepted: March 19, 2018 
 

Abstract 
Adsorption and corrosion inhibitive properties of ethanol extract of Dialium guineense 
leaves for mild steel in 0.5 M HCl was studied using the gravimetric method. The results 
showed that the ethanol extract of Dialium guineense leaves is a good corrosion inhibitor 
for mild steel in 0.5 M HCl. The inhibition efficiency was found to increase with increase in 
the concentration of ethanol extract of Dialium guineense leaves up to the maximum of 
92 %, but at the same time it decreased as the temperature was increased. Corrosion 
inhibition by the extract of Dialium guineense leaves is carried out by adsorption 
mechanism with the kinetics of corrosion following the pseudo first order reaction with 
high correlation. Thermodynamic consideration revealed that adsorption of the ethanol 
extract of Dialium guineense leaves on mild steel surface is an exothermic and 
spontaneous process that fitted the Langmuir adsorption isotherm. The values of 
activation energy and Gibb’s free energy were found within the range of limits expected 
for the mechanism of physical adsorption. 

Keywords 
Corrosion rate; Dialium guineense; inhibitor efficiency; Langmuir isotherm; mild steel 

 

Introduction 

Corrosion is a deterioration of a metal due to its interaction with the environment such as water, 

acid, alkaline, air etc. Due to corrosion, many useful properties of a metal such as malleability, 

ductility and electrical conductivity are lost. Metals are particularly prone to corrosion in 

hydrochloric and sulphuric acids that are in turn widely used for acid pickling, industrial acid 

cleaning, acid descaling and oil-well cleaning [1]. In such conditions, use of inhibitors became one 

of the most practical methods for protection against corrosion. Synthetic organic compounds are 

widely used as corrosion inhibitors for the prevention of corrosion of many metals and alloys in 

http://dx.doi.org/10.5599/jese.486
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J. Electrochem. Sci. Eng. 8(3) (2018) 219-226 CORROSION INHIBITIVE PROPERTIES OF Dialium Guineense 

220  

various aggressive environments. Some of the synthetic organic compounds that show good anti-

corrosive activity are, however, highly toxic and can cause hazards to both human and the 

environment during their application [2]. The environmental hazards caused by the use of synthetic 

inhibitors have always been a global issue. In order to avoid these hazards, the researchers have 

focused their attention on developing cheap, non-toxic, biodegradable and environment friendly 

natural products of plant origin as corrosion inhibitors [3]. Plant extracts, including that of Dialium 

guineense leaves, have already been reported to be environmental friendly, readily available, 

renewable and acceptable source of a wide range corrosion inhibitors by some researchers [4–18]. 

The antioxidant and antimicrobial activities of Dialium guineense leaves extract has also been 

reported [19]. The present study aims to investigate inhibitive properties of Dialium guineense 

leaves extract for corrosion of mild steel at 303 K and 333 K, using the gravimetric technique and 

experiments performed with and without the extract present in 0.5 M HCl. 

Experimental techniques 

Preparation of plant extract (inhibitor)  

Fresh leaves of Dialium guineense were obtained from Ahmadu Bello University botanical garden. 

The leaves were firstly rinsed with distilled water to remove foreign particles and then sun dried, 

ground and soaked in ethanol for 2 days. After 2 days, the sample was cooled and filtered. The 

filtrate was subjected to evaporation at 79 °C in order to leave the sample free from ethanol. 

Different concentrations of the extract were prepared by dissolving 0.1, 0.2, 0.3, 0.4, and 0.5 g of 

the extract in 1dm3 of 0.5 M HCl, respectively. 

Preparation of metal specimen 

Material used for the study was a mild steel sheet of the following composition (wt): Mn (0.6), P 

(0.36), C (0.15) and Si (0.03) and Fe (98.86). The sheet was cut into coupons, each of dimensions 

2×4×0.1 cm. Each coupon was polished with emery papers of different grit sizes in order to obtain 

a smooth surface, degreased with ethanol, cleaned with acetone and allowed to dry in air before its 

preserving in a desiccator. 

Gravimetric measurements 

The mild steel coupon was accurately weighed and fully immersed in 100 ml of corrosive solution 

(without or with the inhibitor present in 0.5 M HCl) in an open beaker. The beaker was covered with 

the aluminum foil and maintained at 303 K for different time intervals. After every 24 hours, the 

corrosive product was removed from the coupon which was further rinsed in distilled water, 

degreased with ethanol, cleaned with acetone and allowed to dry in air before the re-weight. The 

experiment was repeated at 323 K and the weight loss was determined in triplicate.  

Determination of weight loss 

The weight loss (W) was calculated using the following formula:  

W = Wi - Wf (1) 

where Wi is the initial weight in g of the coupon before immersion, while Wf is the final weight in g 

of coupon after immersion. 

Determination of corrosion rate 

The corrosion rate (CR) was calculated using the following formula: 



S. E. Adeniji and B. A. Akindehinde J. Electrochem. Sci. Eng. 8(3) (2018) 219-226 

doi:10.5599/jese.486 221 

1 87.6
CR,  mm year

W

DAt
−
=  (2) 

where W is the weight loss in g, D is density in g cm-3, A is the area of specimen in cm2 and t is time 

of immersion in hours. 

Determination of inhibition efficiency 

The inhibition efficiency (IE) was calculated using the following formula:  

1 2

1

CR CR
IE, % 100

CR

−
=  (3) 

where IE is inhibition efficiency, CR1 is corrosion rate in the absence of inhibitor, while CR2 is 

corrosion rate in the presence of inhibitor. 

Determination of surface coverage  

The surface coverage ( ) was calculated using the following formula:  

0 1

0

W W

W


−
=  (4) 

where W0 is the weight loss in absence of inhibitor, while W1 is the weight loss in presence of 

inhibitor. 

Results and discussion  

Mild steel corrosion behavior was investigated in the absence and presence of Dialium guineense 

extract in 0.5 M HCl, using the gravimetric method. The variation of weight loss with immersion time 

for the corrosion of mild steel in 0.5 M HCl containing different concentrations of ethanol extract of 

Dialium guineense leaves at 303 K is shown in Figure 1.  

 
Figure 1: Variation of weight loss with immersion time for corrosion of mild steel in 0.5 M HCl 
containing different concentrations of ethanol extract of Dialium guineense leaves at 303 K. 

It is seen in Figure 1 that the weight loss of mild steel increases with increase in immersion time 

but decreases as the concentration of the ethanol extract of Dialium guineense leaves increases. 

This implies that presence of the extract retards corrosion of the mild steel in 0.5 M HCl. As shown 

in Figure 2, the corrosion rate of mild steel in 0.5 M HCl calculated by eq. (2), decreases with increase 

in the concentration of the ethanol extract of Dialium guineense leaves, suggesting again that the 



J. Electrochem. Sci. Eng. 8(3) (2018) 219-226 CORROSION INHIBITIVE PROPERTIES OF Dialium Guineense 

222  

extract inhibits corrosion of the mild steel in 0.5 M HCl. Also, corrosion rates at all concentrations of 

inhibitor increase with the temperature increase, what is due to the increase in the average kinetic 

energy of the reacting molecule and similar to the already reported results [20,21]. 

Variations of the inhibition efficiency calculated by eq. (3) for different concentrations of the 

ethanol extract of Dialium guineense leaves at 303 K and 323 K are presented in Figure 3. Significant 

differences between inhibition efficiency of the ethanol extract of Dialium guineense leaves 

determined at 303 K and 323 K for each concentration of the inhibitor, suggest that the mechanism 

of adsorption of the inhibitor on the mild steel is physical adsorption [22]. For a physical adsorption 

mechanism, inhibition efficiency of an inhibitor decreases with temperature while for a chemical 

adsorption mechanism, inhibition efficiency increases with rise of the temperature. 
 

 
Figure 2. Variation of corrosion rate with concen-

tration of ethanol extract of Dialium guineense  
leaves at 303 K and 323 K. 

 
Figure 3: Variation of inhibition efficiency of ethanol 

extract of Dialium guineense leaves with 
concentration at 303 K and 323 K. 

Kinetic consideration 

The kinetic study on the corrosion inhibition of the corrosion of mild steel in solution of 0.5 HCl 

by ethanol extract of Dialium guineense leaves suggests a run of the pseudo first order reaction 

according to the following rate constant equation:  

f
1

i

1
ln

W
K

t W

 
=  

 
 (5) 

In eq. (5), K1 is the rate constant for the first order reaction, Wf is the final weight of coupon after 

immersion, Wi is the initial weight of coupon before immersion, while t is immersion time.  

The consistency of K1 values listed in Table 1 suggests that corrosion of mild steel in either blank 

solution of 0.5 HCl or with different concentrations of the ethanol extract of Dialium guineense 

leaves is the first order reaction. 

Table1. Rate constant of corrosion for different concentrations of Dialium guineense leaves  
extract at different time intervals 

Time, h 

K1 / h-1 

Concentrations of Dialium guineense leaves extract, mg L-1 
0 100 200 300  400  500 

24 0.00574 0.00215 0.00179 0.00150 0.000906 0.000418 

48 0.00577 0.00225 0.00181 0.00151 0.000908 0.000425 

72 0.00581 0.00241 0.00181 0.00151 0.000915 0.000435 

96 0.00583 0.00245 0.00185 0.00153 0.000921 0.000441 

120 0.00585 0.00256 0.00185 0.00154 0.000927 0.000452 



S. E. Adeniji and B. A. Akindehinde J. Electrochem. Sci. Eng. 8(3) (2018) 219-226 

doi:10.5599/jese.486 223 

Alternatively, K1 can be determined graphically using eq. (5) written in the following form:  

1
f i

log log
2.303

K t
W W= −  (6) 

Plot of log Wf versus t yields a straight-line graph which is for different concentrations of the 

extract of Dialium guineense leaves presented in Figure 4. 

The half-life (t1/2) was determined using the following equation: 

1/2

1

0.693
t

K
=  (7) 

Calculated values of K1 and t1/2 are presented in Table 2. From the result obtained, it can be seen 

that ethanol extract of Dialium guineense leaves is a good corrosion inhibitor. 
 

 
Figure 4. Variation of log Wf vs. immersion time for the corrosion of mild steel in 0.1 M HCl 

containing different concentrations of ethanol extract of Dialium guineense leaves. 

Table 2. Kinetic parameters of mild steel corrosion inhibited by ethanol extract of Dialium guineense leaves. 

Concentration, mg L-1 Slope K1 / h-1 t1/2 / h Ea / kJ mol-1 
Blank -0.0026 0.00599 115.69 10.66 

100 -0.0011 0.00253 273.4 14.56 

200 -0.0008 0.00184 376.63 15.56 

300 -0.0005 0.00152 455.92 21.19 

400 -0.0004 0.000921 752.44 38.91 

500 -0.0002 0.000461 1503.3 63.43 

Effect of temperature 

The effect of temperature on the corrosion of mild steel in 0.5 M HCl in absence and presence of 

inhibitor was investigated using the logarithmic form of the Arrhenius equation:  

a2

1 1 2

1 1
log

2.303

ECR

CR R T T

   
= −   

   
 (8) 

In eq. (8), CR1 and CR2 are corrosion rates of mild steel at absolute temperatures T1 (303 K) and 

T2 (323 K), respectively. Ea is the activation energy for the reaction and R is the molar gas constant 

8.314 J K-1 mol-1). As can be seen in Table 2, the values of activation energy calculated by eq. (8) 

range from 14.66 to 63.43 kJ mol-1. These values are found higher than the value of 10.66 kJ mol-1 

obtained for the blank solution, which indicates an inhibition of corrosion of the mild steel in 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0.0 

 

 

 



J. Electrochem. Sci. Eng. 8(3) (2018) 219-226 CORROSION INHIBITIVE PROPERTIES OF Dialium Guineense 

224  

0.5 M HCl, caused by presence of the extract. The activation energies are also found lower than the 

threshold values of 80 kJ mol-1 required for the mechanism of chemical adsorption. This implies that 

adsorption of ethanol extract of Dialium guineense leaves on the mild steel surface obeys the 

mechanism of physical adsorption [22]. 

Thermodynamic consideration 

The heat of adsorption (Qads) for the ethanol extract of Dialium guineense leaves on mild steel 

was calculated using equation (9):  

2 1 1 2
ads

2 1 2 1

2.303 log log
1 1

T T
Q R

T T

 

 

    
= −    

− − −    
 (9) 

where 1 and 2 are the degree of surface coverage of the inhibitor at the absolute temperature 

T1 (303 K) and T2 (323 K), respectively and R is the molar gas constant. The values of Qads calculated 

using eq. (9) are reported in Table 3. These values are negative and range from −9.80 to 

−52.97 kJ mol-1, indicating that adsorption is an exothermic process.  

The values of free energy of adsorption (∆Gads) for the ethanol extract of Dialium guineense 

leaves are calculated using the following equation [23]:  

∆Gads = −2.303 R T log (55.5Kads) (10) 

where R is the molar gas constant, T is absolute temperature, 55.5 is the molar concentration of 

water in mol L-1 and Kads is the equilibrium constant of adsorption defined as [24]: 

ads
(1 )

K
C




=

−
 (11) 

Values of ∆Gads calculated using eq. (10-11) are reported in Table 3. The values of ∆Gads range 

from −6.76 to −17.05 kJ mol-1 and tend to be more negative with rise in the concentration of the 

inhibitor. This indicates that adsorption of the ethanol extract of Dialium guineense leaves on the 

mild steel surface is spontaneous and the strength of adsorption increases with increase in 

concentration of the inhibitor. It is also a significant to note that values of ∆Gads that are less negative 

than -40 kJ mol-1 suggest the mechanism of physical adsorption.  

Table 3. Thermodynamic parameters for adsorption of ethanol extract of  
Dialium guineense leaves on mild steel. 

Concentration, g L-1 Qads / kJ mol-1 
∆Gads / kJ mol-1 

303 K 323 K 

0.1 -9.80 -18.43 -6.76 

0.2 -8.25 -16.95 -8.83 

0.3 -13.85 -16.65 -10.58 

0.4 -33.85 -17.45 -12.83 

0.5 -52.97 -18.80 -17.05 

Adsorption isotherm 

Adsorption isotherms are very important in characterizing inhibition of the corrosion reaction. 

The most frequent isotherms used are Langmuir, Freundlich, Temkin, Flory-Huggin, Frumkin, 

Parsons, Bockris-Swinkel and Dublin-Radushkevich. In this study, the Langmuir isotherm was found 

suitable for the experimental findings and is used to describe the adsorption characteristics of the 

inhibitor. 



S. E. Adeniji and B. A. Akindehinde J. Electrochem. Sci. Eng. 8(3) (2018) 219-226 

doi:10.5599/jese.486 225 

Langmuir isotherm 

Langmuir adsorption isotherm is expressed by the following equation:  

log (C/ ) = log C + log (1/Kads) (12) 

where Kads is the equilibrium constant of adsorption, C is bulk concentration of adsorbing (inhibitor) 

species and   is the degree of surface coverage. As shown in Figure 5, a plot of log C/ versus log C 

yields a straight-line graph.  
 

  
        -1.2          -1.0           -0.8          -0.6           -0.4          -0.2            0.0 

log (C / g L-1) 
 

Figure 5. Langmuir isotherm for the adsorption of ethanol extract of Dialium guineense leaves 
on mild steel surface 

The linear plots presented in Figure 5 having slopes and correlation coefficients (R2) listed in Table 

4, indicate that adsorption of the inhibitor is highly consistent with the Langmuir adsorption 

isotherm. The values of Kads at two temperatures were determined from the intercept lines on the 

log (C/ ) axis and listed in Table 4, together with ∆Gads values for the inhibitor adsorption on the 

surface of mild steel, calculated using eq. (10).  

Table 4: Langmuir adsorption parameters and free energy of adsorption of ethanol extract 
Dialium guineense leaves on mild steel surface 

T / K Slope R2 log Kads Kads 
∆Gads / kJ mol-

1 

303 0.8432 0.9977 -0.0071 0.9838 -10.08 
323 0.8204 0.9968 -0.0611 0.8688 -10.41 

Conclusion 

Ethanol extract of Dialium guineense leaves effectively inhibited corrosion of mild steel in 

0.5 M HCl. Inhibition efficiency of the extract increased with increase of concentration of Dialium 

guineense leaves but decrease with rise in the temperature. This suggests that corrosion inhibition 

can be attributed to the physisorption mechanism. The mechanism of physisorption was further 

confirmed by examining the values of apparent activation energies and heat of adsorption. The 

adsorption of the ethanol extract of Dialium guineense leaves inhibitor on mild steel surface is an 

exothermic and spontaneous process that fits the Langmuir adsorption isotherm. 

References 

[1] J. A. Selvi, S. Rajendran, V. G. Sri, A. J. Amalraj, B. Narayanasamy, Portugaliae Electrochimica Acta 27 
(2009) 1-11. 

303 K 

323 K 

0.0 

 

-0.2 

 

-0.4 

 

-0.6 

 

-0.8 

 



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226  

[2] A. Chinweuba, Journal of Natural Science Research 4 (2014) 3180-3186. 
[3] A. Fouda, Y. Aggour, G. Bekheit, M. Ismail, International Journal of Advance Research 2 (2014)1158-

1170. 
[4] M. Abdallah, Portugaliae Electrochimica Acta 22 (2004) 161-175. 
[5] A. Chetouani, B. Hammouti, M. Benkaddour, Pigment and Resin Technology 33 (2004) 26-31. 
[6] S. Rajendran, V. G. Sri, J. Arockiaselvi, A. J. Amalraj, Bulletin of Electrochemistery 21 (2005) 367- 377. 
[7] M. Sethuraman, P. Bothi Raja, Pigment and Resin Technology 34 (2005) 327-331. 
[8] M. Bendahou, M. Benabdellah, B. Hammouti, Pigment and Resin Technology 35 (2006) 95-100. 
[9] O. K. Abiola, N. Oforka, E. Ebenso, N. Nwinuka, Anti-Corrosion Methods and Materials 54 (2007) 219–

224. 
[10] E. Osarolube, A. O. James, Journal of Emerging Trends in Engineering and Applied  Sciences 5 (2014) 

51-55.  
[11] N. E. Ibisi, D. O. Okoroafor, C. C. Amuta, IOSR Journal of Applied Chemistry 10 (2017) 70-78. 
[12] L. Afia, R. Salghi, L. Bazzi, M. Errami, O. Jbara, Intertional Journal of Electrochemical Science 6 (2011) 

5918-5939. 
[13] D. Ben, R. Salghi, A. Zarrouk, S. S. Al-Deyab, H. Zarrok, B. Hammouti, Intertional Journal of 

Electrochemical Science, 7 (2012) 6234-6246. 
[14] M. Ouariachi, J. Paolini, A. Bouyanzer, P. Tomi, B. Hammouti, R. Salghi, Journal of  Medicinal Plants 

Research 5 (2011) 5773-5778. 
[15] M. Benabdellah, B. Hammouti, M. Benkaddour, M. Bendahhou, A. Aouniti, Applied Surface Science 

252 (2006) 8341-8347. 
[16] L. Bammou, M. Mihit, R. Salghi, L. Bazzi, A. Bouyanzer, B. Hammouti, Intertional Journal of 

Electrochemical Science, 6 (2011)1454-1467. 
[17] A. K. Olusegun, N. C. Oforka, E. E. Ebenso, Corrosion Science and Engeneering 8 (2004) 1-5. 
[18] A. Bouyanzer, B. Hammouti, Pigment and Resin Technology 33 (2004) 287- 292. 
[19] G. I. Ogu, J. Ezeadila, J. M. Ehiobu, Pharmacy and Pharmacology Research 1 (2013) 1-7. 
[20] E. Ebenso, N. Eddy, A. Odiongenyi, African Journal of Pure and Applied Chemistry 2 (2008) 107-115. 
[21] N. Ibisi, V. Uwakwue, Global Journal of Environmental Science and Technology 2 (2015) 355-359. 
[22] A. Fouda, H. Tawfik, A. Badr, Advances in Materials and Corrosion 1 (2012) 1-7. 
[23] A. Hamdy, N. S. El-Gendy, Egyptian Journal of Petroleum 22 (2013) 17-25 
[24] E. A. Noor, Journal of Applied Electrochemistry 39 (2009) 1465-1475. 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

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