Volume 5 Preprint 10
The Inhibition of Mild Steel Corrosion in an Acidic Medium by Fruit Juice of Citrus Paradisi
O.K. Abiola, N.C. Oforka, and E.E. Ebenso
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Volume 5 Preprint 10
THE INHIBITION OF MILD STEEL CORROSION IN AN
ACIDIC MEDIUM BY FRUIT JUICE OF CITRUS PARADISI
Olusegun K. Abiolaa*, N. C. Oforkaa, E.E. EBENSOb
Department of Pure and Industrial Chemistry,
University of Port Harcourt,
Port Harcourt, Rivers State – Nigeria.
Department of Pure and Applied Chemistry
University of Calabar
Name: Olusegun K. Abiola
E-mail: abiolaolusegun @yahoo.com
Tell N0. +2348033360504
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 http://www.umist.ac.uk/corrosion/jcse in due course.
Until such time as it has been fully published it should not normally be referenced in published work. © UMIST 2004.
The corrosion inhibition of mild steel in HCl solution in the presence of fruit juice of citrus paradisi at temperature range of 3050oC was studied using weight loss technique. The fruit juice of citrus paradisi acts as an inhibitor in the acid environment. The
inhibition efficiency increases with increase in inhibitor concentration but decreases with an increase in temperature. The
inhibition is attributed to the adsorption of the inhibitor on the surface of the mild steel.
Keywords: Citrus paradisi; mild steel; corrosion inhibition; adsorption.
Metals and its alloy are exposed to the action of acids in industry . Processes in which acids play a very important
part are acid pickling, industrial acid cleaning, cleaning of oil refinery equipment, oil well acidizing and acid descaling [1,2]. The
exposures can be most severe but in many cases, corrosion inhibitors are widely used in industry to prevent or to reduce the
corrosion rates of metallic materials in these acid media [2,3].
Because of the toxic nature and high cost of some chemicals currently in use it is necessary to develop environmentally
acceptable and less expensive inhibitors. Natural products can be considered as a good source for this purpose . The possible
replacement of some expensive chemicals as corrosion inhibitors for metal in acid cleaning process by naturally occurring
substances of plant origin has been studied by Hosary and Saleh .
Natural products of plant origin contain different organic compounds (e.g. alkaloids, tannins, pigments, organic and
amino acids, and most are known to have inhibitive action [4,5]. In our earlier communication  it was found that cocosnucifera
juice inhibits the corrosion of mild steel in hydrochloric acid solution (HCl). Ekpe et al.  and Saleh et al.  used the aqueous
extracts of some natural products (fruits, fruit shells, leaves, seeds) as corrosion inhibitors of some metals.
The fruit juice of citrus paradisi can be use in the production of non-toxic inhibitors to replace toxic corrosion inhibitors.
Accordingly, this work deals with the study of the corrosion inhibition properties of fruit juice of citrus paradisi. The aim of this
study was to determine the inhibition efficiency of the fruit juice of citrus paradisi as an inhibitor for the corrosion of mild steel in
0.5MHCl. Weight loss technique was employed to carry out the measurements.
Citrus species are utilized in many industries for the production of the various brands of citrus juices . The juice is
also rich in vitamin C, folic acid and significant quantities of other vitamins, pectins, flavonoids among others [8,9]. Nootkatone
contributes to the flavour of the grape fruit. At high concentration, nootkatone exerts a bitter flavour . Nitrogenous
compounds are present to the extent of 0.05 – 1.0% and most are free amino acids – asparagines, alanine, arginine, aspartic acids,
glutamine, glutathione, histidine, betaine, cysteine, proline, serine and stachydrine [6,8,9]. The principal acid in citrus fruits is
citric acid (80 – 90% of the total acids). Others are malic, tartaric, benzoic, succinic, quinic, oxalic and formic acid .
The compounds in citrus paradisi fruit juice especially the nitrogen containing organic compounds can adsorb on the
metal surface and block the active sites on the surface and thereby reduce the corrosion rate in acid environment.
The composition and preparation of mild steel coupons are described in detail as reported previously . All test
solutions were prepared from analytical grade reagents and double-distilled water. The citrus paradisi fruit juice was used as an
additive for this investigation. The additive concentration of 0.5, 1.0, 1.5, 2.0 and 2.5% volume/volume percent (v/v) were
prepared in 0.5M HCl (corrodent) solutions at 30, 40 and 50oC.
Weight loss measurement
Previously weighed mild steel coupons were immersed in 250ml open beakers containing 0.5M HCl solution (blank)
without additive, and additive concentration of 0.5, 1.0, 1.5 2.0 and 2.5% in 0.5M HCl solution at 30, 40 and 50oC. The variation
of weight loss was follow at 3hr. interval progressively for 15hr. at 30, 40 and 50oC. The procedure for weight loss determination
was similar to that reported previously [10,11].
The inhibition efficiency (1%) was determined from :
Wb − Wi
Where Wb and Wi are the weight loss of mild steel per unit area (mg/cm2) of coupons in the corrodent (blank) and corrodentinhibitor systems.
RESULTS AND DISCUSSION
Effect of citrus paradisi fruit juice on the corrosion of mild steel in HCl solution
Figure 1 shows the variation of the weight loss with time (hours) for mild steel corrosion in 0.5MHCl and 0.5M HCl
with various concentrations of additive (citrus paradisi juice) at 30oC. Similar trends were observed at 40 and 50°C. From the
variation of weight loss with time of immersion in HCl solution without additive compared with mild steel in HCl solution
containing the additive at 30°C (Fig. 1), there is a general decrease in weight loss, signifying the inhibition of the acid corrosion
of mild steel by citrus paradisi juice. The extent of the decrease in weight loss was found to depend on the concentration of
additive. Figure 2 also confirms that the additive is a corrosion inhibitor; since there was a general decrease in corrosion rate
(mgcm-2h-1). The corrosion rate as a function of additive concentration and at different temperatures (30 - 50°C) is shown in
figure 2. The corrosion rate decreases with increasing concentration of citrus paradisi juice at each of the temperature. This
confirms that the presence of the additive in 0.5M HCl solution inhibits the corrosion of mild steel by HCl and that the degree of
corrosion inhibition depends on the amount of the citrus paradisi juice present.
Figure 3 illustrates the variation of the inhibition efficiency, I%, versus the concentration of the additive at 30, 40 and
50°C. The inhibition efficiency increases with increasing the concentration of the inhibitor. As shown in figure 3 inhibition
efficiency increases with increase in concentration of the inhibitor up to 2.5%v/v at a maximum efficiency of 45.6%, 37.3% and
24.1% at 30%, 40 and 50°C respectively.
Figure 3 shows the effect of increasing temperature from 30°C to 50°C on the inhibition efficiency. From the plot of the
inhibition efficiency with concentration of the inhibitor and from the result given in Table 1, it was observed that with increase in
temperature there was a decrease in the inhibition efficiency of the inhibitor. This indicates that inhibition decreases as
temperature of the system increases, and on this basis we suggest the mechanism of physisorption of the inhibitor on the metal
surface. This is in agreement with the results of several investigators [2,11,12].
The surface coverage, θ at each concentration of inhibitor was evaluated using the equation .
Where Wb and Wi are the weight loss in corrodent and corrodent-inhibitor systems respectively at constant temperature.
The surface coverage data and corrosion rate are recorded in Table 2. The experimental observed linear decrease in
corrosion rate as seen in Table 2 with surface coverage, θ therefore supports the observation that the inhibitor inhibits corrosion
by being adsorbed at the reaction sites on the mild steel surface . A curtailment of these reaction sites would therefore lead to a
reduction in the corrosion rate and this may be precisely how the inhibitor achieves inhibition by being adsorbed on the mild steel
surface at the reaction sites
Figure 4 shows the plot of logarithm inhibition efficiency (I%) versus logarithm inhibitor concentration for the additive
at 30, 40, and 50°C – a linear plot is obtained which obeys the Freundlish isotherm.
From the present investigation, the following conclusions can be drawn.
The rate of corrosion of the mild steel in HCl is a function of the concentration of citrus paradisi juice.
The inhibition by this additive increased with increased additive concentration and decreased temperature.
Citrus paradisi fruit juice is a corrosion inhibitor for mild steel in HCl solution and can be used to replace toxic
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TABLE 1: The effect of fruit juice of citrus paradisi on mild steel corrosion in 0.5M HCl
Inhibitor efficiency (I%)
Surface coverage, θ and corrosion rate during corrosion of mild steel in
concentrations of the fruit juice of citrus paradisi at 30°C
0.5M HCl containing various