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| Effect of Temperature on Protective Propensity of Azadirachta Indica Fruit Extract on Acid Corrosion of Mild Steel | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Paper Id :
17014 Submission Date :
2023-01-19 Acceptance Date :
2023-01-23 Publication Date :
2023-01-25
This is an open-access research paper/article distributed under the terms of the Creative Commons Attribution 4.0 International, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. For verification of this paper, please visit on
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| Abstract |
The protective propensity of ethanolic extract of Azadirachta indica fruit (EEAiF) on mild steel corrosion in 0.5N nitric acid has been investigated by weight loss technique at elevated temperatures in the range of 303 to 343 K. The inhibition efficiency (η%) has been observed significantly high (63.15%) at 303 K at concentration 0.45 %. The adsorption of inhibitor on mild steel surface have been found to obey Langmuir adsorption isotherm. It was observed to be physical , exothermic and spontaneous. The kinetic parameters such as activation energy (Ea), enthalpy of activation (ΔHact), entropy of activation (ΔSact) and thermodynamic parameters such as free energy of adsorption (ΔGads), enthalpy of adsorption (ΔHads), entropy of adsorption (ΔSads) were calculated. These Kinetic and Thermodynamic parameters indicate a strong interaction among the inhibitor and metal surface. The high protective impact is attributed owing to phytochemical constituents present in the Azadirachta indica fruit extract.
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| Keywords | Mild Steel, Acid corrosion, Azadirachta Indica, Langmuir Adsorption Isotherm, Thermodynamic Parameters. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Introduction |
Mild steel is applied broadly as a metal or alloy in numerous industrial applications. Acid solutions are applied in various industrial processes namely acid descaling and acid cleaning etc. Corrosion inhibitors are the substances added to the corrosive medium to reduce the rate of its attack on the metal or alloy [1] and these may be organic or inorganic compounds [2-4].
Numerous industries exploitation equipment made from metals under diverse circumstances ranging from mild to stiff chemical environments, making their surfaces susceptible to corrosion [5-6]. Investigation have shown that corrosion cannot be perfectly removed from metal surfaces due to the different environments in which metals are applied [7].
Azadirachta indica (Neem) is an evergreen medical plants having wide spectrum of biological and pharmacological activity. The chemical ingredients of Azadirachta indica fruit primarily are triterpenoid (metiantriol), azadirone, nimbin, nimbinin, azadirone, limocin, nimbidin, epoxyazadiradione etc. and the inhibitive effect is attributed owing to these phytochemical constituents present in the extract [8-12]. Azadirachta indica fruits extract is biodegradable and non-toxic therefore its applications would help to diminish the economic cost of corrosion monitoring as well as reduce the subsequent environmental threats.
A huge number of scientific studies have been devoted to the corrosion of mild steel and the exploitation of natural products as a corrosion inhibitors as Capparis decidua [13], Tamarindus indica [14], Prosopis cineraria [15], Azadirachta indica [16], Acacia nilotica [17] for aluminium in acidic media.
In the present work, the impact of elevation in temperature on protective propensity of Azadirachta indica fruit for acid corrosion of mild steel has been analysed at 12 hrs immersion period.
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| Objective of study | Prevention ( reduced ) of acid Corrosion of mild steel by using Azadirachta indica fruit extract. |
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| Review of Literature |
A huge number of scientific studies have been devoted to the corrosion of mild steel and the exploitation of natural products as a corrosion inhibitors as Capparis decidua [13], Tamarindus indica [14], Prosopis cineraria [15], Azadirachta indica [16], Acacia nilotica [17] for aluminium in acidic media.
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| Methodology | Preparation of Test Coupons:
Sheet of mild steel achieved locally and of 0.18 cm thickness was mechanically cut into coupons of 2.54 × 1.52 cm2 size containing a hole of about 0.12 mm diameter near the upper edge in order to the purpose of hanging in the test solution. Coupons were polished to mirror finish by applying emery paper.
Test solutions & Experimentation:
The electrolytic solutions of HNO3 were prepared by using bi-distilled water. All chemicals used were of Analar grade. Ethanolic extraction of Azadirachta indica fruits ( EEAi F ) was achieved by usingy refluxing the dried fruits in soxhlet extractor [18-19]. Each coupons was suspended by the glass hook plunge into a beaker containing 50 ml of the test solution as well as various concentration of the inhibitor (EEAi F). The investigation has been carried out at various raised temperature (303K to 343K). Subsequently 12 hrs immersion time period, test coupons were washed with distilled water and dried thereafter hanging the cleaned coupons in desiccators in order to appropriate time period [20].
Weight Loss studies
Table 1 indicates the value of inhibition efficiency (η%), Fractional surface coverage (θ ), Corrosion rate (ρcorr), Adsorption equilibrium constant (Kads) obtained at varying concentration of the inhibitors in 0.5N nitric acid solution for an immersion period of 12 hrs at various elevated temperature in the range 303 – 343 K.
From the mass loss value (ΔM), the inhibition efficiency (η%) was calculated using the following equation.
η% = [ ( ΔMu - ΔMi ) / ΔMu ] × 100
Where ΔMu is mass loss without inhibitor and ΔMi is weight loss with inhibitor.
The corrosion rate (ρcorr) in millimetre penetration per year (mmpy) can be determined by following equation
ρcorr = ( ΔM ×87.6 ) / area × time × metal density
Where ΔM weight loss expressed in mg, area expressed in cm2 of metal surface exposed, time expressed in hours of exposure and metal density expressed in g / cm3. |
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| Tools Used | Chemical, Mild Steel etc. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Statistics Used in the Study |
Formula used in this study. |
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| Analysis |
Gravimetric ( Practical) Analysis. |
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| Result and Discussion |
Weight Loss studies Table 1 indicates the value of inhibition efficiency
(η%), Fractional surface coverage (θ ), Corrosion rate (ρcorr),
Adsorption equilibrium constant (Kads) obtained at varying
concentration of the inhibitors in 0.5N nitric acid solution for an immersion
period of 12 hrs at various elevated temperature in the range 303 – 343 K. From the mass loss value (ΔM), the inhibition efficiency
(η%) was calculated using the following equation. η% = [ ( ΔMu
- ΔMi ) / ΔMu ] × 100 Where ΔMu is mass loss without
inhibitor and ΔMi is weight loss with inhibitor. The corrosion rate (ρcorr) in millimetre
penetration per year (mmpy) can be determined by following equation ρcorr =
( ΔM ×87.6 ) /
area × time × metal density Where ΔM weight loss expressed in mg, area expressed
in cm2 of metal surface exposed, time expressed in hours of
exposure and metal density expressed in g / cm3. Table 1. Corrosion Parameters for mild
steel in 0.5N HNO3 in Absence and Presence of Various
concentrations of Ethanolic Extract of Azadirachta indica fruits
(EEAiF) from Weight Loss Measurements at elevated temperatures for 12
hrs immersion period. Effective area of specimen 7.72 cm2 Immersion
time 12 hrs
Outcomes obtained from the table revealed that the
addition of inhibitor to the acid had diminished the corrosion rate (ρcorr).
The inhibition efficiency (η%) increased with increase in concentration of
inhibitors and decreased with elevation in temperature from 303 K to 343
K in 0.5N HNO3 nitric acid solution. Adsorption Isotherm : Langmuir
adsorption isotherm graph was plotted between log (θ / 1- θ) and log C. log (θ / 1- θ) = log Kads +
log C Where Kads is adsorption equilibrium
constant, the Kads value can be calculated from the intercept
line on the log (θ / 1 –θ ) axis and is related to standard free energy of
adsorption. The values of ΔG0ads at all
studied temperature can be evaluated from the equation as follows
ΔG0ads = - 2.303 RT
log (55.5 Kads ) Where R = 0.008314 KJ/ mol is the universal gas constant, 55.5 indicate the molar concentration of water in the solution whereas T is the absolute temperature in Kelvin. The values of Kads and ΔG0ads are shown in table 2 for Azadirachta indica fruit extract.
Fig.1: Langmuir adsorption isotherm curve for mild steel
in 0.5N HNO3 with fruit extract of Azadirachta
indica at different elevated temperatures at 12 hrs immersion period. Table 2. Correlation coefficient
(R2), slopes, Adsorption equilibrium constant(Kads) and
Gibbs free energy (ΔGads) from Langmuir adsorption isotherm in 0.5N
HNO3 with Fruit extract of Azadirachta indica at
different elevated temperatures.
Kinetic / thermodynamic treatment of Weight loss Results Energy of Activation Elevation in temperature has significant influence on the
corrosion phenomenon. The dependence of corrosion rate on temperature can be
expressed by the Arrhenius equation. log ρcorr. =
log A - ( Ea / 2.303
RT ) Where ρcorr is the corrosion rate, A is
the frequency factor, R is the universal molar gas constant, Ea is
the apparent activation of energy and T is the absolute temperature in kelvin. Fig.2 for Azadirachta indica indicates
the linear graph for plot of log ρcorr. versus 1 / T.
Activation energy values Ea were estimated from slopes of log ρcorr. versus
1 / T . The slope of Arrhenius curve is equal to – Ea /
2.303 R. The positive sign for both Ea and ΔHact indicate
the endothermic nature of corrosion process / phenomenon. Other kinetic parameters of the corrosion reaction,
namely, entropy ΔS and enthalpy ΔH of activation transition state were obtained
from the transition state equation ρcorr
= ( RT /
Nh ) e ( ΔSact / R ) e ( - ΔHact /
RT ) log ( ρcorr / T )
= [ log (R / Nh ) + ( ΔSact / 2.303
R ) ] - (ΔHact / 2.303RT ) Where ρcorr. is the corrosion
rate , h is the plank’s constant, N is the Avogadro’ s number, R is the
universal gas constant and T is the absolute temperature.
A plot of log ( ρcorr / T ) versus 1 / T
give a straight line Fig.3 were obtained with the slope of ( - ΔHact /
2.303 R ) and intercept of [ log ( R / N h ) + ( ΔSact / 2.303
R ) ] from which the values of ΔHact and ΔSact respectively,
were evaluated from the slope and intercept respectively from the linear plot .
The estimated values of Ea, ΔHact and ΔSact are
depicted in table 3 for mild steel in 0.5N HNO3. Fig. 2 : Arrhenius plots for mild steel corrosion in 0.5N
HNO3 with fruit extract of Azadirachta indica at
12 hrs immersion period.
Fig. 3 : Transition state plots for mild steel corrosion
in 0.5N HNO3 with fruit extract of Azadirachta indica at
12 hrs immersion period. Table 3 : Kinetic –
thermodynamic parameters for mild steel corrosion in 0.5N HNO3 without
and with fruit extract of Azadirachta indica at various
concentrations at immersion time 12 hrs.
Thermodynamic Parameters : Thermodynamic
adsorption parameters such as the enthalpy of adsorption ( ΔHads )
and the entropy of adsorption ( ΔSads ) were also determined
from the experimental data. ΔH0ads and
ΔS0ads are obtained using the following equation
ΔG0ads = ΔH0ads - T ΔS0ads The values of ΔS0ads was
obtained from the slope and the intercept leads to ΔH0ads (table
4). The entropy (ΔS0ads) values are positive in almost
all cases confirming that the corrosion process is entropically favourable.
Fig. 4 : Plot of ΔG0 vs T for various concentration of Azadirachta indica fruit extract in 0.5N HNO3 acid solution at 12hrs immersion period. Table 4 : Thermodynamic parameters
for mild steel corrosion in 0.5N HNO3 in the absence and
presence of various concentrations of fruit extract of Azadirachta
indica at elevated temperatures ( 303 – 343 K ) at immersion time 12
hrs.
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| Findings | Decrease in corrosion rate & increase in efficiency with increases with inhibitor concentration | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Conclusion |
Following conclusions may be drawn on the basis of the results obtained from study of the effect of elevation in temperature on the protective propensity of Azadirachta indica fruit extract on acid corrosion of mild steel in 0.5 M HNO3.
1. Azadirachta indica fruit can be good inhibitor to impede acid corrosion of mild steel in 0.5 N HNO3 at 303 K with maximum inhibition efficiency of 63.15 % at is 0.45% concentration.
2. Elevation in corrosion rate at high temperature but with the additive, a reasonable decrease in corrosion rate was observed. 3. Activation energy Eact in aggressive medium alone (blank) was observed much lower as compared to that in inhibited test solutions. Eact of EEAiF was found in the range of 13.11 to 22.39 KJ / mol.
4. The adsorption of the extract on the mild steel was spontaneous and obeyed Langmuir adsorption isotherm at elevated temperatures. 5. Entropy of adsorption decreases with increase in EEAiF indicates association of inhibitor molecules. 6. Overall, it can be concluded that Azadirachta indica fruit extract can be used as green inhibitor to replace toxic chemicals used to impede mild steel corrosion in 0.5N HNO3 at elevated temperature up to 343 K. |
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| Suggestions for the future Study | Azadirachta indica fruit extract used as potential corrosion inhibitor therefore it applied broadly inhibitor | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Acknowledgement | Author is highly thankful to Department of Chemistry, Govt. Girls College, Karauli for providing necessary research facilities. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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