Open Access

Potential of Azadirachta indica as a green corrosion inhibitor against mild steel, aluminum, and tin: a review

Journal of Analytical Science and Technology20156:26

https://doi.org/10.1186/s40543-015-0067-0

Received: 14 May 2015

Accepted: 21 September 2015

Published: 9 October 2015

Abstract

Azadirachta indica (AZI, commonly recognized as “Neem”) is noteworthy both for its chemical and for its biological actions. It is one of the most fruitful sources of secondary metabolites in nature. To date, more than 300 natural products have been isolated from different sections of the tree, with new compounds added to the list every year. As a contribution to the current interest on green corrosion inhibitors, the present study aims at broadening the application of plant extracts for metallic corrosion inhibition by investigating the inhibiting properties of A. indica especially for mild steel, aluminum, and tin. In the present article, we discuss the potential of AZI extract as a corrosion inhibitor on metal surfaces, especially of mild steel, aluminum, and tin. The adsorption isotherm studies, chemical composition of AZI, effect of temperature on inhibition efficiency and computational analysis related with AZI adsorption on metals have also been discussed in detail. This work will further help in the understanding of the adsorption mechanism involved and hence inhibition effect of plant extract against metal corrosion.

Keywords

Green chemistry Azadirachta indica Corrosion Green corrosion inhibitors Computational calculations

Review

Introduction

“Green chemistry” provides an opportunity to design any research in non-polluting way with minimum production of waste and minimum consumption of energy. It is a philosophy which is equally applicable in all fields wherever chemistry involves (Sharma et al. 2010a; Sharma et al. 2011; Sharma et al. 2009a; Linthorst 2010). “Corrosion” is a phenomenon where chemistry helps to explain its mechanism and role of ions and energy behind it. It is simply a destruction of materials resulting from an exposure and the interaction with the environment. One of the latest and popular approaches is the use of substances called corrosion inhibitor. These inhibitor molecules consist ofheterocyclic compounds with polar functional groups (e.g. N, S, O, and P) and conjugated double bonds with different aromatic system. Basically, these substances adsorb on the metal surface to block the destruction reaction with aggressive media. They are both physically and chemically active adsorbate type substances (Thompson et al. 2007; Buchweishaija 2009). It is a major problem that must be confronted for safety, environmental, and economic reasons in various chemical, mechanical, metallurgical, biochemical, and medical engineering applications and more specifically, in the design of a much more varied number of mechanical parts which equally vary in size, functionality, and useful lifespan. Corrosion attack can be prevented by various methods such as materials improvement, combination of production fluids, process control, and chemical inhibition. Among these methods, the implementation of corrosion inhibition is the most excellent approach to avoid disastrous destruction of metals and alloys in corrosive media. The use of corrosion inhibitors is the most economical and convenient technique to control corrosive attack on metals. Corrosion inhibitors are chemicals either synthetic or natural which, when added in small amounts to an environment, decrease the rate of attack by the environment on metals. A number of synthetic compounds are known to be applicable as good corrosion inhibitors for metals (Quraishi et al. 2012; Kabanda et al. 2012a; Ebenso et al. 2012a). The importance of a corrosion study depend in the fact that corrosion causes great loses to our economy and is a major threat for human safety. Corrosion costs worldwide are therefore on the order of US$552 billion (Chauhan and Gunasekaran 2007; Schmitt et al. 2009a). Even countries like India is suffering badly due to this problem of corrosion (Sharma and Sharma 2011). Several efforts have been made using corrosion-preventive practices, and the use of green corrosion inhibitors is one of them (Anuradha et al. 2008; Mudhoo and Sharma 2010; Sharma et al. 2010b; Sharma et al. 2010c; Aboia and James 2010; Sharma et al. 2009b; Sharma et al. 2009c). On the other hand, the attractiveness and utilization of synthetic compounds as a corrosion inhibitor has come under severe criticism due to the harsh environmental regulations and toxic effects of synthetic compounds on human and animal life. Consequently, there exists the need to build up a new class of corrosion inhibitors with low toxicity, eco-friendliness, and good efficiency. Throughout the ages, plants have been used by human beings for their basic needs such as assembly of food stuffs, shelters, clothing, fertilizers, flavors and fragrances, medicines, and last but not least, as corrosion inhibitors (Ajmal et al. 1994; Bentiss et al. 2002). The use of natural products as corrosion inhibitors can be traced back to the 1930s when plant extracts of Chelidonium majus (Celandine) and other plants were used for the first time in H2SO4 pickling baths (Sanyal 1981). After then, interest in using natural products as corrosion inhibitors increased substantially and scientists around the world reported several plant extracts as promising green anticorrosive agents (Schmitt et al. 2009b). Most of the gums were also reported as good corrosion inhibitor due to their gum-metal complex forming capacity, availability of п-electrons and hetero atoms, and less toxic properties (Peter et al. 2015). The adsorption of organic molecules depends on the presence of п-electrons and hetero atoms (Jin et al. 2006; Raja and Sethuraman 2008a). Although synthetic organic inhibitors have shown effective corrosion inhibition, their cost, toxicity, and non-biodegradability lead us to look for green options. In this review, we are discussing about the various plant extract and especially Azadirachta indica as green corrosion inhibitor for mild steel, Al, and tin (Tables 1, 2, and 3).
Table 1

Plants as corrosion inhibitors against mild steel corrosion

Study Conducted

Plant product

Solution

Effect of temperature on percentage inhibition efficiency

Effect of concentration on percentage inhibition efficiency

Methods

Adsorption type and isotherm used

Reference

Eichhornia crassipes is noted as one of the most important and noxious freshwater weed; the extracts of its leaves and roots were reported as good corrosion inhibitor for mild steel corrosion in HCl solutions using gasometric technique, and its modeled structures provides additional insight into the mechanism of inhibitory action by DFT

E. crassipes (leaf and root)

HCl

Decrease with rise in temperature

Increase

Gasometric technique

(Physically adsorbed)

Ulaeto et al. 2012

Nauclea latifolia commonly known as pin cushion tree is a straggling shrub or small spreading tree that belongs to the family Rubiaceae. The effects of ethanol (ENL), alkaloids (ANL), and non-alkaloids (NNL) extracts from the root of N. latifolia on the dissolution of carbon steel in H2SO4 solutions were shown their effective inhibition by followed trend ANL>ENL>NNL. Gasometric method was use to perform practical data and obtained results show that percentage inhibition efficiency increase with concentration but decrease with rise in temperature

N. latifolia (root)

H2SO4

Decrease with rise in temperature

Increase

Gasometric technique

Temkin

Okafor et al. 2013

Banana peel extract (constituent of this extract is bananadine (3Z,7Z,10Z)-1-oxa-6-azacyclododeca-3,7,10-triene) was reported as a good corrosion inhibitor with Zn in distilled water for carbon steel corrosion by the weight loss, thermometric , FTIR, and AFM analysis. Obtained results show that percentage inhibition efficiency first decrease with the addition of Zn but after increasing Zn concentration it increased

Banana peel extract + Zn

Distilled water

First decrease with Zn after increase with increasing concentration of Zn inhibition efficiency increases

Weight loss, thermometric , FTIR, and AFM analysis

Sangeetha et al. 2012

By the use of quantum chemical calculations, the active compound were reported as follows: (Kalmegh) Andrographis paniculata— andrographolide, (Meethi Neem) Murraya koenigii— mahabinine and pyrayafoline, (Bael) Aegle marmelos—skimmianine, (Kuchla) Strychnos nuxvomica—brucine, (Shahjan) Moringa oleifera—arginine, (Orange) Citrus aurantium—threonine, and (Arjun) Terminalia arjuna—sitosterol, Due to these active molecules, they show their inhibition effect for corrosion

The extracts of (Kalmegh) Andrographis paniculata, (Meethi Neem) Murraya koenigii, (Bael) Aegle marmelos, (Kuchla) Strychnos nuxvomica, (Shahjan) Moringa oleifera, (Orange) Citrus aurantium, and (Arjun) Terminalia arjuna

HCl

DFT, molecule analysis, and quantum calculations

Singh et al. 2013

Aloe vera plant belongs to the family of Liliacea. The constituents of gel are polysaccharides, glycoproteins, vitamins, mineral, and enzymes. Obtained results show its synergistic type effect, and percentage inhibition efficiency was decrease with rise in temperature and increase with increasing extract concentration

Aloe vera

HNO3

Decrease with rise in temperature

Increase

Gravimetric technique

Chemisorption

Gupta and Jain 2014

C. sinensis leaf extract reported as a corrosion inhibitor in aqueous medium by the use of weight loss, UV, and FT-IT methods. Obtained results show that inhibition efficiency increase with increasing inhibitor concentration but decrease with rise in temperature

C. sinensis leaf extract

Aqueose

Decrease with rise in temperature

Decrease

Weight loss method, pH, UV–vis, and FT-IR

Physical adsorption

Yamuna and Athony 2014

Hibiscus rosa-sinensis leaves extract reported as a good corrosion inhibitor for mild steel in HCl medium by the use of weight loss and EIS techniques. Obtained results show that the percentage inhibition efficiency was increased with the increasing temperature and concentration and show mixed-type inhibitor effect, and adsorption process was spontaneous and followed the Langmuir, Flory-Huggins and Freundlich adsorption isotherms

H. rosa-sinensis (Jasud)

HCl

Increase

Increase

Gravimetric (weight loss) and electrochemical techniques

Langmuir, Flory-Huggins and Freundlich adsorption

Desai 2015a

Ilex paraguariensis extracts reported as a good corrosion inhibitor for carbon steel in HCl medium by the use of weight loss and EIS techniques. Its inhibition efficiency increased with the increase of concentration and time. Obtained results show that I. paraguariensis act as both type inhibitor and obeyed the Langmuir adsorption isotherm

I. paraguariensis

HCl

Increase

Increase

Weight loss and electrochemical measurements

Langmuir adsorption isotherm

Souza et al. 2015

Ruta graveolens extract reported as a good corrosion inhibitor for mild steel corrosion in HCl medium by PDP and weight loss method. Obtained results show that percentage inhibition efficiency increase with increasing concentration of inhibitor but decrease with rise in temperature and obeyed the Langmuir adsorption isotherm

R. graveolens extract

HCl

Decrease with rise in temperature

Increase

Potentiodynamic polarization and weight loss techniques

Langmuir adsorption isotherm

Majeed et al. 2014

Musa sapientum which is commonly called banana is a herbaceous plant, belonging to the family of Musaceae. It is reported as a good corrosion inhibitor for mild steel in H2SO4 medium with tetraoxosulphate (vi) acid by the use of E. chemical measurements. Obtained results show that corrosion rate decrease with increasing concentration rate of inhibitor but increase with rising temperature. Simply followed the physical adsorbtion

M. sapientum peels extract + concentrated tetraoxosulphate (vi) acid

H2SO4

Decrease

Increase

Weight loss, E. chemical measurements

Physical adsorption

Salami et al. 2012

Extract of fenugreek leaves reported as a good inhibitor for mild steel in HCl and H2SO4 solution but more efficient in HCl solution. Inhibition efficiency was decrease with rise in temperature but increase with increasing inhibitor concentration in HCl while both temperature and concentration increased the inhibition efficiency for mild steel in H2SO4 solution. Langmuir adsorption isotherm followed in HCl medium and Temkin followed in H2SO4 medium

Extract of fenugreek leaves

HCl and H2SO4

Decrease in HCl solution but increase In H2SO4 solution

Increase in both solutions

Gravimetric technique

Langmuir in HCl solution, Temkin in H2SO4 solution

Noor 2007

Cotula cinerea, Retama retam, Artemisia herba reported as good corrosion inhibitors for mild steel in H2SO4 medium by weight loss and EIS methods

Cotula cinerea, Retama retam, Artemisia herba

H2SO4

Weight Loss and E. chemical measurements

Raja and Sethuraman 2008b

Eclipta alba reported as an effective corrosion inhibitor for mild steel in H2SO4 medium by the use of weight loss and potentiodynamic polarization methods. Obtained results show that inhibitor behave as mixed-type inhibitor; inhibition efficiency increase with concentration value but decrease with rise in temperature. Obeyed the Langmuir adsorption isotherm

E. alba

H2SO4

Decrease with rise in temperature

Increase

Weight loss, potentiodynamic polarization, and impedance methods

Langmuir adsorption

Shyamala and Arulanantham 2009

Terminalia catappa reported as a corrosion inhibitor in HCl medium by the use of weight loss and PDP methods. Obtained results show that inhibition efficiency increased with increasing concentration of inhibitor but decrease with rise in temperature and described as mixed-type inhibitor

T. catappa

HCl

Decrease

Increase

Weight loss, polarization, FTIR, and scanning electron microscope studies

Mixed-type inhibition

Vasudha and Saratha 2011

Theobroma cacao peel polar extract reported as a corrosion inhibitor for mild steel in HCl medium by the use of weight loss method, potentiodynamic polarization, and EIS techniques. Obtained results show that inhibition efficiency increased with the inhibitor concentration level but decreased with the rise in temperature and obeyed the Langmuir adsorption isotherm

T. cacao peel polar extract (TCPE)

HCl

Decrease

Increase

Weight loss method, potentiodynamic polarization, and EIS techniques

Langmuir adsorption isotherm

Yetri et al. 2014

It’s reported that the mature leaves of Combretum bracteosum extracts inhibited the corrosion of mild steel in H2SO4 medium by the use of gravimetric and hydrogen evolution methods. Obtained results show that the inhibition efficiency increases with the inhibitor concentration and decreases with temperature. Obtained result obeyed the Frumkin adsorption isotherm

C. bracteosum

H2SO4

Decrease with rise in temperature

Increase

Gravimetric and hydrogen evolution

Frumkin adsorption isotherm

Okafor et al. 2009

Cyamopsis tetragonoloba reported as an effective corrosion inhibitor for mild steel in HCl medium by use of weight loss, PDP, and EIS techniques. Obtained results show that inhibition efficiency increase with increasing inhibitor concentration but decrease with rise in temperature. Obeyed the Temkin and Langmuir adsorption isotherms

C. tetragonoloba

HCl

Decrease with rise in temperature

Increase

Potentiodynamic polarization

Temkin and Langmuir

Subhashini et al. 2010

Table 2

Plants as corrosion inhibitors against aluminum corrosion

Study Conducted

Plant product

Solution

Effect of temperature on percentage inhibition efficiency

Effect of concentration on percentage inhibition efficiency

Methods

Adsorption

Reference

Phoenix dactylifera reported as a good corrosion inhibitor for Al in NaOH solution by weight loss and PDP method. Obtained results show that inhibition efficiency increase with increasing temperature and concentration, followed the Temkin adsorption isotherm also

P. dactylifera,

NaOH

Increase

Increase

Weight loss, potentiodynamic polarization

Temkin adsorption isotherm

Rehan 2003

The extracts of Damsissa, Corchours oitorius reported as a good inhibitor for the corrosion of aluminum in aqueous sodium carbonate by the use of gasometry, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS)

Extracts of Damsissa, Corchours oitorius

Sodium carbonate

Decrease

Increase

Gasometry, potentiodynamic polarization

Langmuir and Flory-Huggins

Abd-El-Nabey et al. 2012

Rosmarinus officinalis reported as a good corrosion inhibitor for aluminum in NaCl solution by the use of PDP method. Obtained result obeyed the Freundlich isotherm

R. officinalis

Chloride solution

Decrease with rise in temperature

Increase

Potentiodynamic polarization

Freundlich isotherm

Kliˇski´c et al. 2000

The dissolution of Al and Zn in HCl and NaOH medium were inhibited by H. subdariffa (Karkade) extract. Obtained results show that corrosion rate increase with increasing temperature but decrease with increasing concentration. Physical adsorption phenomena were observed

H. subhdariffa extract

HCl and NaOH

Decrease with rise in temperature

Increase

Weight loss and the galvanostatic polarization

Physical adsorption

El-hosary et al. 1972

Vernonia amygdalina reported as a fine corrosion inhibitor for aluminum in HCl and HNO3 medium by the use of weight loss method. But its inhibition performance was much better in HNO3 solution as compare to HCl medium

V. amygdalina

HNO3 and HCl

Increase

Weight loss method

Avwiri and Igho 2003

Saccharides (fructose and mannose) with the addition of ascorbic acid addition, reported as a good corrosion inhibitor for Al by the method of hydrogen evolution in alkaline medium

Saccharides (fructose and mannose)

Alkaline medium

Evolution of hydrogen

Muller 2002

The inhibitive effect of leaf extracts of Euphorbia hirta and Dialum guineense on aluminum alloy (AA8011) was reported in HCl solution by the use of gravimetric technique. The results indicate that both extracts worked as good inhibitors and inhibition efficiency improved with concentration

Leaf extracts of E. hirta and D. guineense

HCl

Decrease

Increase

Gravimetric technique

Langmuir adsorption isotherm

Anozie et al. 2011

The inhibition effect of Newbouldia laevis leaves extract reported as a good inhibitor on the corrosion of aluminum HCl and H2SO4 solutions by the use of gravimetric technique. Obtained results show that N. laevis inhibitor effect was more efficient in HCl than H2SO4.

N. laevis leaves extract

HCl and H2SO4

Decrease

Increase

Gravimetric technique

Langmuir

Nnanna et al. 2012

Coconut coir dust extract reported as a good inhibitor for aluminum corrosion in 1 M HCl medium by the use of weight loss and hydrogen evolution method. It was exhibited that percentage IE efficiency increased with increasing temperature and concentration. Obtained results show the Langmuir adsorption performance

Coconut coir dust extract

1 M HCl

Increase

Increase

Weight loss and hydrogen evolution

Langmuir

Umoren et al. 2012

Table 3

Plants as corrosion inhibitors against tin corrosion

Study Conducted

Material

Solution

Effect of temperature on percentage inhibition efficiency

Effect of concentration on percentage inhibition efficiency

Methods

Adsorption

Reference

It is reported that lysine, arginine, methionine, cysteine were good corrosion inhibitors in citric acid solution by the potentiodynamic methods. Nitron-containing acids show 70 % inhibition as compared with sulfur-containing acids. All four acids act as a mixed-type inhibitor and show their inhibition effect on tin corrosion and obeyed Temkin adsorption isotherm.

Amino acids (lysine, arginine, methionine, and cysteine)

Citric acid

Decrease with rise in temperature

Increase but decrease after optimum concentration

Potentiodynamic polarization (PDP)

Temkin adsorption

Quraishi et al. 2004

Alanine, glycine, glutamic acid, and histidine were used as environmentally safe inhibitors for the tin dissolution process

Amino acids (glycine)

Tartaric acid

Decrease

Increase

Weight loss, SEM, and EIS

Freundlich isotherm

El-Sherif Rabab and Badawy Waheed 2011

Different varieties of holy basil, viz., Ocimum basilicum (EB), Ocimum cannum (EC), and Ocimum sanctum (ES) reported as corrosion inhibitors for tin in HNO3 solution by the use of weight loss techniques. Obtained results show that inhibition efficiency increase with inhibitor concentration. Followed Langmuir adsorption isotherm

The leaves and stem extract of different varieties of holy basil, viz., O. basilicum (EB), O. cannum (EC), and O. sanctum (ES)

HNO3

Increase

Weight loss technique

Langmuir

Kumpawat et al. 2012

Use of A. indica as a corrosion inhibitor against mild steel, aluminum, and tin corrosion

A. indica (AZI, common name “Neem”) is noteworthy for its biological and chemical uses (Fig. 1). It is known as “magical plant” for many diseases treatment (Kliˇski´c et al. 2000). It is very effective in the production of secondary metabolites (Kumar et al. 1996; Schaaf et al. 2000; Barton 1999). Neem is a member of the mahogany family, Meliaceae. Neem trees are attractive broad-leaved evergreens that can grow up to 30 m tall and 2.5 m in girth. Their scattering branches form rounded crowns as much as 20 m across. The fruit is a smooth, ellipsoidal drupe, up to almost 2 cm long (Jacobson 1986b).
Fig. 1

Main chemical compounds present in Azadirachta indica

The chemical compounds of neem belonged to a general class of natural products called “triterpenes” or “limonoids.” These limonoids have an ability to block insects’ growth who are responsible for harmful outcomes in agriculture and human health sector. New limonoids are still being discovered in neem, but azadirachtin, salannin, meliantriol, and nimbin are the best known and most significant ones (Qurasishi 2004). Nowadays, the use of neem as a corrosion inhibitorhas been widely investigated., so in Table 4, we summarize the corrosive properties of neem with respect to mild steel, aluminum, and tin metals.
Table 4

Azadirachta indica as corrosion inhibitor

Concise manner

Metal

Plant product

Solution

Effect of temperature on percentage inhibition efficiency

Effect of concentration on percentage inhibition efficiency

Methods

Adsorption type and isotherm used

Reference

Mature leaves extract of neem reported as a green corrosion inhibitor for Zn in HCl medium by the use of gravimetric and thermometric methods

Zn

Mature leaves of neem

HCl

Decrease

Increase

Gravimetric and thermometric

Physical adsorption

Sharma et al. 2010c

Dry seed extract of AZI reported as a good inhibitor for mild copper corrosion in HNO3 medium by weight loss and phytochemical analysis. Obtained results show that percentage inhibition efficiency increase with increasing concentration and show mixed type inhibition

Mild copper

Dry seeds extracts of AZI

HNO3

Decrease

Increase

Weight loss and phytochemical analysis

Mixed-type adsorption.

Sangeetha and Fredimoses 2011

There were selected plants [Occimum viridis (OV), Telferia occidentalis (TO), Azadirachta indica (AZI), Hibiscus sabdariffa (HS), Garcinia kola (GK)] which extracts reported as good corrosion inhibitors for mild steel corrosion in HCl and H2SO4 by gasometric method. Obtained results indicate that all the extracts inhibited the corrosion process in both acid media and the presence of halide additive increase inhibition efficiency due to synergistic effect

Mild steel

AZI + halide additive

HCl and H2SO4

No dependence

Increase

Kinetics activation parameters and gasometric technique

Oguzie 2008

It is reported that AZI with iodide additive shows good inhibition for Al corrosion in HCl medium by PDP method. Due to synergistic effect, the adsorption was spontaneous and followed the Freundlich adsorption isotherm

Al

AZI and iodide ions as

HCl

Decrease

Increase

PDP techniques

Freundlich adsorption isotherm

Arab et al. 2008

Azadirachta indica extract reported as an effective inhibitor for steel corrosion in the acid media by the gas volumetric techniques and obtained results show that consistence of Langmuir adsorption isotherm

Mild steel

AZI extracts

Different concentrations of HCl

Decrease

Increase

Gas volumetric technique

Langmuir isotherm adsorption (mixed inhibitor)

Oguzie 2006

AZI reported as Al corrosion inhibitor in HCl medium by the use of weight loss and thermometric methods. Obtained results show that adsorption was exothermic, spontaneous, and obeyed the Freundlich, Temkin, and Flory-Huggins

Al

AZI

HCl

Decrease with rise in temperature

Increase

Weight loss and thermometric

Freundlich, Temkin, and Flory-Huggins

Ebenso et al. 2004

AZI leaves reported as a corrosion inhibitor for mild steel in H2SO4 medium by the use of weight loss technique

Mild steel

AZI leaves

H2SO4

Weight loss technique

Physical adsorption

Ebenso et al. 1998

Ethanolic extract of AZI fruit reported as a good inhibitor for aluminum corrosion in HCl medium by the use of weight loss thermometric method. Obtained results show the presence of physical adsorption process like percentage inhibition efficiency increase with increasing concentration but decrease with rise in temperature and followed Langmuir adsorption isotherm

Al

Ethanolic extract of AZI fruit

HCl

Decrease with rise in temperature

Increase

Weight loss thermometric

Langmuir adsorption isotherm

Sharma et al. 2013

AZI mature leaf extract reported as good inhibitor for mild steel corrosion in HNO3 medium by the use of gravimetric method. Obtained results show that percentage inhibition efficiency increased with increasing concentration but get down with the rise in temperature. Adsorption process was exothermic and consistent and best fitted into Frumkin adsorption isotherm

Mild steel

AZI mature leaf extract

HNO3

Decrease with rise in temperature

Increase

Gravimetric techniques

Frumkin adsorption isotherm

Sharma et al. 2010d

UAE neem extract reported as a good inhibitor for carbon steel corrosion in HCl medium by the use of weight loss method and obtained results show that percentage inhibition efficiency increase with increasing inhibitor concentration but decrease with rise in temperature and data was fit into Temkin adsorption isotherm

Carbon steel

UAE neem extract

HCl

Decrease with rise in temperature

Increase

Weight loss method

Temkin adsorption isotherm

Ayssar et al. 2010

The inhibition effect of AZI extract reported as good inhibitor on stainless steel corrosion in HCl and H2SO4 medium by the weight loss method. Obtained results show that extract of AZI was better inhibitor as compare with other extract

Stainless steel

Plant extract

HCl + H2SO4 + tetraoxosulphate (IV) acid + trioxnitrate (V) acid solution

Decrease at high temperature

Increase

Weight loss method

Physical adsorption

Obiukwu et al. 2013

It is reported that ethanol extract of leaves and seeds of A. indica shows its effective inhibition effect on mild steel corrosion in H2SO4 medium by the use of gasometric, gravimetric, and IR methods. Corrosion inhibition efficiency of the leaves is better than that of the seeds .According to findings, the reaction followed the physical adsorption and fit in Flory-Huggins adsorption isotherm

Mild steel

Ethanol extracts of seeds and leaves

H2SO4

Decrease

Increase

Gravimetric, gasometric, and IR methods

Flory-Huggins adsorption isotherm

Eddy and Mamza 2009

It is reported that the inhibition effect of AZI extract on mild steel corrosion in acidic medium was good but it’s more clearly visible in HCl medium as comparison with H2SO4 solution. In HCl medium the percentage inhibition efficiency was increase with increasing concentration of inhibitor but it gets down on high temperature. Obtained results show the physical adsorption performance

Mild steel

Extract of AZI leaf

HCL and H2SO4

Decrease with rise in temperature

Increase

Weight loss and PDP method

Physical adsorption

Loto et al. 2011

Neem leaf extract reported as a good corrosion inhibitor for mild steel in chloride medium by the gravimetric method. It showed a comparison with or without neem leaf extract in salty water medium with heat treatment. IE increased with the increasing concentration of inhibitor in chloride- and heat-treated chloride medium but its decreased without inhibitor in chloride- and heat-treated chloride medium

Mild steel

Extract of AZI leaf

Chloride (salty water medium)

Increase in neem + chloride medium but decrease in only-chloride medium

Increase in neem + chloride medium but decrease in only-chloride medium

Gasometric

Tuaweri et al. 2015

Neem bark reported as efficient corrosion inhibitor for mild steel in HCl medium by the use of PDP method. Percentage IE efficiency increased with increased concentration but decreased with the rise in temperature and reported data fit into Langmuir adsorption isotherm

Mild steel

Neem ark

HCl

Decrease with rise in temperature

Increase

Potentiodynamic polarization

Langmuir (mixed-type inhibition )

Desai 2015b

Arab et al. (2008) found that AZI extract inhibits the corrosion of aluminum in 0.5 M HCl. Sharma et al. (2013) investigated the inhibitory efficacy of ethanolic extract of A. indica fruit for acid corrosion of aluminum.

The corrosion inhibition and adsorption properties of neem (AZI) mature leaves extract as a green inhibitor of mild steel (MS) corrosion in nitric acid (HNO3) solutions have been studied and investigated by Sharma et al. (2009a; Sharma et al. 2010c; Sharma et al. 2010d) using a gravimetric technique for experiments conducted at 30 and 60 °C. According to Ayssar et al. (2010), the aqueous neem leaves extract was found to be an excellent potential corrosion inhibitor for carbon steel in 1.0 M HCl. Obiukwu et al. (2013) mentioned that the A. indica had a better effect with an inhibitive efficiency of 85 % for stainless steel. Investigation of Eddy and Mamza (2009) demonstrates that the rate of corrosion of mild steel in H2SO4 increases with the increase in the concentration of the acid and that ethanol extracts of the seeds and leaves of A. indica inhibit the corrosion of mild steel in H2SO4. According to Loto et al. (2011), the corrosion inhibition performance of neem leaf (A. indica) extract on the corrosion of mild steel was achieved in the dilute hydrochloric acid at 0.25 g/l extract concentration and also at 30 °C. In a recent study by Desai (2015a), it has been discussed that in HCl, AZI was an effective inhibitor against mild steel corrosion, the rate of corrosion increases with the increase in acid concentration and temperature. He also observed that a straight line in the plots of Langmuir adsorption isotherm suggests that the inhibitor’s adsorption on steel followed Langmuir isotherm. Polarization study involved in this case indicates that the inhibitor functions as a mixed inhibitor (Desai 2015b). In an another study carried out by Ajanaku et al. (2015), authors highlighted that in the corrosion inhibition study of AZI against aluminum metal in 1.85 M hydrochloric acid, the rate of the reaction has been studied by monitoring and measuring the volume of hydrogen gas evolved and the results were supported by various adsorption theories and the surface morphology studies using scanning electron microscopy (SEM). Authors suggested that the plant extract retards the acid-induced corrosion of aluminum and the volume of hydrogen gas evolved reduced with increasing extract concentration. Also, the Langmuir isotherm as the best model for the adsorption of A. indica indicates the suggested mechanism of adsorption—chemisorption (Ajanaku et al. 2015). A research conducted by Jain et al. (a research group at Tata Steel, Jamshedpur) published in Tata Search (2014) also highlighted the inhibition effect of AZI against mild steel in acid media (HCl and HNO3), and the results of weight loss studies correlated well with polarization studies (Jain et al. 2014).

In a very interesting study by Bhola et al. (2014) published in Engineering Failure Analysis, authors investigated the inhibition effect of AZI extract on microbiologically influenced corrosion of API 5L X80 line pipe steel by a sulfate reducing bacterial (SRB) consortium. On the basis of the field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS) studies, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), and open circuit potential (OCP) were used to investigate the in situ corrosion behavior, and they concluded that neem extract has the capability to reduce the biocorrosion rate by approximately 50 % (Bhola et al. 2014), which is fairly high and very encouraging, clearly underlining the importance of AZI extract as a corrosion inhibitor.

Corrosion inhibition by AZI and computational modeling

Computational methods are more and more appropriate in the study of corrosion inhibition capacity because they have the potential to support in the design of new compounds with good corrosion inhibition properties. These studies are assisting in reducing the experimental costs for testing many compounds with the objective of synthesizing the ones that have high promise for corrosion inhibition. Density functional theory (DFT) and molecular dynamics (MD) approaches are increasingly used for predicting the inhibition potential of compound for corrosion on geometrical, electronic, and binding property bases on metal surface (Kabanda et al. 2012b; Kabanda and Ebenso 2012; Ebenso et al. 2012b). Recently, more corrosion publications contained substantial quantum chemical calculations and molecular dynamics simulations (Obot et al. 2013; Kabanda et al. 2013; Obot and Gasem 2014). Such calculations are usually used to explore the relationship between the inhibitor molecular properties and their corrosion inhibition efficiencies. The use of quantum chemical methods in corrosion inhibitor studies of large number of small organic compounds has been highlighted by Gece (2008) and Obot (2014) in their detailed review. Attempt has also been made recently to extend the application of DFT-based quantum chemical and molecular dynamic simulations methods in order to understand the mechanism of adsorption of plant extract components on metal and alloys surfaces (Oguzie et al. 2013; Oguzie et al. 2010; Oguzie et al. 2012a; Umoren et al. 2014; Oguzie et al. 2012b; Obi-Egbedi et al. 2012). This is because the major criticism of the use of plant extract as corrosion inhibitor is often the inability to pinpoint which of the component(s) is/are actually responsible for the observed corrosion inhibition effect given that they are comprised of mixtures of organic compounds.

Although experimental studies on the application of AZI extract as a green corrosion inhibitors for different metals and alloys have been extensively reviewed in the work; the mechanism of interactions between the AZI extract component and the metal surfaces at the atomic level using molecular modeling studies is lacking and is still a matter of speculation. This difficulty can be tackled by the methodology of density functional theory and molecular dynamics simulations where selected DFT reactivity parameters of the individual major extracts components such as energy of the highest occupied molecular orbital (E HOMO), energy of the lowest unoccupied molecular orbital (E LUMO), energy band gap (ΔE), and the interaction energy between the extract components and the metal surface can be correlated with the corrosion inhibitive effect of the plant extract. According to the description of frontier orbital theory (ObiEgbedi et al. 2011), HOMO is often associated with the electron-donating ability of an inhibitor molecule. High E HOMO values indicate that the molecule has a tendency to donate electrons to the metal with unoccupied d orbitals. E LUMO indicates the ability of the molecules to accept electrons (Obot and Obi-Egbedi 2010). The lower the value of E LUMO of inhibitor molecule is, the easier its acceptance of electrons from the metal surface (Obot et al. 2009). The gap between the LUMO and HOMO energy levels of the inhibitor molecules is another important index, low absolute values of the energy band gap (ΔE = E LUMO − E HOMO) can indicate a good stability of the formed complex on the metal surface, therefore increasing the adsorption of a molecule on the metal surface (Xia et al. 2008). Some important reactivity parameters from DFT and molecular dynamics simulations (MDS) are summarized in Table 5. Also, Figs. 2 and 3 show examples of molecular modeling of major extract components from some plants used as corrosion inhibitors.
Table 5

Important molecular descriptors derived from DFT and molecular dynamics simulations (Obot et al. 2013)

Descriptors

Explanation

Global quantum chemical descriptors

 

E HOMO

Energy of the highest occupied molecular orbital

E LUMO

Energy of the lowest unoccupied molecular orbital

IP(≈‐ E HOMO)

Ionization potential: removing an electron from a molecular system X (X→X+ + e)

EA(≈‐ E LUMO)

Electron affinity: attaching an additional electron to a molecular system X (X + e→X)

\( \mu ={\left(\frac{\delta E}{\delta N}\right)}_v \)

Chemical potential, defined as the change in electronic energy E upon change in total number of electrons N

χ = − μ ≈ − 1/2(E HOMO + E LUMO)

Absolute electronegativity

\( \eta =-{\left(\frac{\delta \mu }{\delta N}\right)}_v\approx -\left({E}_{\mathrm{HOMO}}-{E}_{\mathrm{LUMO}}\right) \)

Molecular hardness, defined as the change in chemical potential μ upon change in total number of electrons N

\( S=\frac{1}{2\eta } \)

Molecular softness

Α

Molecular polarizability; note that molecules arrange themselves towards a state of minimum polarizability and maximum hardness

\( \omega =\frac{\mu^2}{2\eta }=\frac{\chi^2}{2\eta }. \)

Electrophilicity index

Charge distribution

 

QA(r)

Net atomic charges (at atom r)

E interaction = E total − (E surface + E inhibitor)

Where E total is the total energy of the metal surface and inhibitor, E surface is the metal surface energy and E inhibitor is the energy of inhibitor molecule from plant extract

Fig. 2

Computational modeling of capsaicin and dihydrocapsaicin (the two main extract components of Capsicum frutescens) (Oguzie et al. 2013)

Fig. 3

The highest occupied molecular (HOMO) orbital density of a ascorbic acid, b riboflavin (RB), c thiamine (TH), and d nicotinic acid (NA) which constitute the main constituents of Spondias mombin extract (Obi-Egbedi et al. 2012)

Conclusions

From the above discussion, it is quite obvious that AZI is an effective green corrosion inhibitor against various metals, especially for mild steel, aluminum, and tin. A lot of potential is still untapped especially computational modeling of the major extract components of AZI on different metal surfaces, and many other plant materials and should be further explored by researchers working in the area of corrosion science and engineering. This will help in the understanding of the adsorption mechanism and hence inhibition effect of plant extracts against metal corrosion. Also of importance is the exploration of AZI and other plant materials in other corrosive environment such as CO2 corrosion, H2S corrosion, and in cooling water systems.

Declarations

Acknowledgements

The author (AP) thankfully acknowledges the scholarship given by the president of the JECRC University for her PhD work.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors’ Affiliations

(1)
Green Chemistry and Sustainability Research Group, Department of Chemistry, JECRC University
(2)
Centre of Research Excellence in Corrosion, King Fahd University of Petroleum and Minerals

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