32

CHAPTER-II

LITERATURE SURVEY, SCOPE AND OBJECTIVES OF THE

PRESENT STUDY

2.1. Literature survey

Al is highly reactive metal that has high resistance to corrosion in many

environments because of the presence of a thin, highly adherent film of aluminium

oxide. Pourbaix diagram shows that aluminium oxide film is stable in the pH range

of 4.0 to 9.0 [1]. Outside this pH range, the aluminium oxide film dissolves rapidly

in strong acids and bases. The rate of corrosion cannot be predicted solely by the

pH, but depends on the specific ions present, their concentration and temperature.

Inhibitors are generally used in the industrial process to control metal dissolution,

especially in acidic environment. Most of the efficient inhibitors used in industry are

organic compounds that possess at least one functional group, which is considered

as the active centre for the adsorption process. Several researchers have made an

attempt to study the inhibiting action of various organic compounds on the corrosion

of aluminium and its alloys in acid media. The toxicity of organic corrosion

inhibitors to the environment has prompted the search for green corrosion inhibitors.

Green inhibitors are biodegradable and do not contain heavy metals or other toxic

compounds. The brief review of the research work carried out is presented below.

2.1.1. Organic chemicals as corrosion inhibitors in hydrochloric acid

medium.

The molecules most often used as corrosion inhibitors are nitrogen, sulphur,

oxygen and phosphorous containing compounds. These compounds get adsorbed

onto the surface of metal from the bulk of environment forming a film at the metal

surface. Organic inhibitors generally have hetero atoms. O, N, S and P are found to

have higher basicity and electron density and thus act as corrosion inhibitor. O, N,

and S are the active centres for the process of adsorption on the metal surface. The

inhibition efficiency should follow the sequence O < N < S < P. The existing data

show that most organic inhibitors are adsorbed on the metal surface by displacing

water molecules on the surface and forms a compact barrier. Availability of non-

33

bonded electron (lone pair) and p-electrons in inhibitor molecules facilitate electron

transfer from the inhibitor to the metal. A coordinate covalent bond involving

transfer of electrons from inhibitor to the metal surface may be formed. The strength

of the chemisorptions bond depends upon the electron density on the donor atom of

the functional group and also the polarisability of the group. When H atom attached

to the C in the ring is replaced by a substituent group (–NH2, –NO2, –CHO, or –

COOH) it improves inhibition. The electron density in the metal at the point of

attachment changes resulting in the retardation of the cathodic or anodic reactions.

Electrons are consumed at the cathode and are furnished at the anode. Thus,

corrosion is retarded. Reviews includs extensive listing of various types of organic

inhibitors in different media..

Aroson and Yoffe [2] studied the retardation by surface active substances on

the corrosion of aluminium. Sundararajan and Rama Char [3] assessed the corrosion

rates and inhibition efficiencies for 99.5% aluminium in hydrochloric acid solution,

with the following inhibitors: acridine, thiourea, nicotinic acid, dextrin and tannic

acid, of which acridine was the best. Polarisation studies with thiourea indicated that

anodic polarisation was negligible, whereas cathodic polarisation was considerable,

so that the corrosion process with this inhibitor appeared as essentially under

cathodic control. Abd El Kader and Shams El Din [4] studied the dissolution of Al

in 3N HCl and 2N NaOH solution by varying concentrations using the thermometric

method. It depends on the rise in temperature (∆T) and the reaction number (R.N.)

of solution concentration. The alkylamines were more strongly adsorbed than the

alkylammonim ions and interfered with the anodic reaction.

Desai et al. [5] determined the combined effect of external cathodic

polarisation and organic inhibitors for Al-2S, Al-65S and Al-57S in HCl. It was

observed that several inhibitors become more effective under the influence of

external cathodic polarisation, as for instance 2-butanone for Al-2S and Al-65S and

cyclohexanone for Al-57S. Aliphatic as well as in aromatic amines and their

inhibitive action for the corrosion of Al-2S in HCl were analysed by Desai et al. [6].

The order of efficiency in ethylamines and ethylanilines were tertiary > secondary >

primary, whereas in methylamines and methylanilines, the secondary amine was the

most effective inhibitor.

34

Saleh and Shams EL Din [7] studied the effect of number of aliphatic,

aromatic, amino acids as well as of their anions, on the dissolution of Al in 2N HCl

and 1.5N NaOH by thermometric method. In acid solution, all additives act as

cathodic inhibitors. Issa et al. [8] found that chloral hydrate, methyl ethyl ketone,

pinacolone and mesityl oxide on the corrosion inhibitive effect of aluminium in HCl

solution. The results indicated that all the studied compounds were classified as

weekly adsorbed substances. Amarnath Maitra and Barua [9] evaluated the

inhibition efficiency of dicyandiamide on the acid corrosion of pure aluminium in

0.5, 1.0, 1.5, and 2.0N hydrochloric acid. The inhibition efficiency increased with

the increase in concentration of the inhibitor but reaches a maximum at certain

inhibitor concentration beyond which it remains practically constant.

Desai et al. [10] described the performance of aliphatic polyamines and

ethanolamine as corrosion inhibitors for Al-51S in hydrochloric acid solution. All

inhibitors were predominantly cathodic in action. Ramakrishnaiah and Subramanyan

[11] investigated the effects of some organic compounds namely formamide,

pyridine, gramine, dipyridyl, piperidine, benzoyl piperidine and dibenzyl disulphide

on the corrosion of 2S aluminium in 1M sodium hydroxide and 1M hydrochloric

acid and inhibition efficiency was high and maximum for HCl, contrary to its

behaviour in sodium hydroxide and does not possess any beneficial effect on the

influence of these compounds. Moussa et al. [12] tested the inhibitive effect of

aluminium corrosion in hydrochloric acid by Girard's T and P, oxalic, malonic,

succinic acid, hydrazides and acetophenone G-T by thermometric and weight loss

measurements. The results indicated that all the studied compounds were classified

as weakly adsorbed substances except acetophenone G-T which was strongly

adsorbed. Subramanyan and Ramakrishnaiah [13] assessed the effect of some amino

compounds on the corrosion of aluminium. Darwish [14] investigated the effect of

furfural on the corrosion of aluminium in sodium hydroxide, potassium hydroxide

and hydrochloric acid solutions.

Hassan et al. [15] analysed the inhibitive effect of some hydrazine

derivatives on the dissolution of aluminium in 2N hydrochloric acid solution. The

results were found in good agreement with the thermometric and weight loss

methods. Aljinovic and Gotonac [16] assessed the thymol as corrosion inhibitor for

35

the dissolution of Al and Zn in HCl with and without thymol addition. The analysis

of the results showed the different corrosion inhibition efficiencies for Al and Zn.

Abd-El-Nabey et al. [17] evaluated the corrosion behaviour of aluminium in water-

organic solvent mixtures containing HCl using thermometric, hydrogen evolution,

weight loss and Tafel extrapolation methods. The data were interpreted in terms of

the dependence of corrosion rate on the structural properties of water-alcohol

mixture.

Ahmed et al. [18] studied the effect of some hydrazone compounds on the

corrosion behaviours of aluminium in hydrochloric acid and sodium hydroxide

solution. Fouda et al. [19] investigated the inhibitive effect of some

thiosemicarbazide derivatives towards the corrosion of aluminium in 2M HCl using

thermometric, weight loss and hydrogen evolution methods. The three independent

methods gave similar results. Ahmed et al. [20] assessed the inhibitive effect of

some morpholine and thiosemicarbazide derivatives on the dissolution of aluminium

in 2M HCI using thermometric, weight loss and hydrogen evolution methods. It was

observed that the percentage inhibition of aluminium increased with the increase in

inhibitor concentration and decreased with rise of reaction temperature. Brett [21]

studied the aluminium corrosion in hydrochloric acid solution. Mourad et al. [22]

investigated the inhibitive action of dimethyltin dichloride towards the corrosion of

aluminium in hydrochloric acid and sodium hydroxide solutions.

Fouda et al. [23] studied the corrosion rate of aluminium in 2N hydrochloric

acid solution at 27ºC with and without addition of phenyl semicarbazide derivatives

(10-3-10

-5 mol/L). From the adsorption isotherm, some thermodynamic data for the

adsorption process (∆Gºads and f) were calculated. Hassan et al. [24] determined the

inhibition of aluminium corrosion by benzoic acid and its derivatives in solutions of

hydrochloric acid and sodium hydroxide using weight loss and hydrogen evolution

methods. Benzoic acid and its derivatives inhibited acidic and alkaline corrosion.

Moussa et al. [25] studied the inhibition of carboxylic acids of aluminium corrosion

in hydrochloric acid and sodium hydroxide solutions using weight loss and

hydrogen evolution methods. The inhibition efficiency in NaOH was higher than

that of HCl solutions.

36

Mourad et al. [26] tested the inhibitive effect of butyltin trichloride on

dissolution of aluminium in sodium hydroxide and hydrochloric acid. Elneami and

Fouda [27] studied the influence of the corrosion of aluminium in HCl and in

NaOH by the addition of pyrrole, 2-methyl pyrrole and pyrrole-2-carboxyaldehyde

by the thermometric and weight loss methods. The degree of surface coverage (θ) of

the adsorbed inhibitors was determined from the R.N. value. Thermodynamic

parameters for the adsorption process are also discussed.

Mourad et al. [28] assessed the corrosion of metallic aluminium in 2N

hydrochloric acid solution in the presence of L-analine, L-tyrosine, L-histidine and

L-tryptophan as corrosion inhibitors using hydrogen evolution and thermometric

methods. The two methods gave similar results. The inhibition depended upon the

concentration of the inhibitors and their chemical structures. The adsorption of these

additives on aluminium obeyed the Frumkin adsoption isotherm. Mourad et al. [29]

studied the dissolution of aluminium in 2M hydrochloric acid in the presence of

sodium soya sulphonate (SSS) as corrosion inhibitor using hydrogen evolution and

thermometric methods. The two methods gave consistent results. The results

indicated that the inhibitive effect of the sulphonated mixture relates to

chemisorption mechanism on the metal surface via electrons in the double bond.

Fouda et al. [30] investigated the inhibitive effect of oximes, β-diketones and

hydrazides on the corrosion of aluminium in 2M HCl galvanostatically. The order of

decreased inhibition efficiency among the three groups of compounds was: oximes >

β-diketones > hydrazides. Soliman and Mourad [31] studied the dissolution of

aluminium in 2M HCl solution in the presence of sodium caster sulphonate (SCS)

using thermometric and hydrogen evolution methods. The results showed that the

additive retards the dissolution due to its chemisorption on the metal surface via

electrons of the double bond. The inhibitor obeyed the Frumkin isotherm. Gohar et

al. [32] assessed the inhibition of aluminium corrosion in 2.3M HCl solution in the

presence of some [(substituted benzylidene)dithio] diacetic acids using weight loss

and hydrogen evolution methods. The inhibition efficiencies depend upon the nature

of substituted aromatic ring and the inhibitor concentration. The activation energy of

inhibitor decreased in the same order as the percentage reduction in the corrosion

rate.

37

Khamis and Atea [33] reported that the selected compounds based on

heterocyclic triazolines were used to determine the parallel structure-corrosion

inhibition relationships for the corrosion of Al in HCl solution. Fouda et al. [34]

evaluated the dissolution of aluminium in HCl and NaOH solutions in the presence

of semicarbazide, thiosemicarbazide and sym.diphenylcarbazide as corrosion

inhibitors using thermometric, weight loss and polarisation methods. The three

methods gave consistent results. Gomma and Wahdan [35] analysed the corrosion

inhibition of Al in hydrochloric acid solution by some Schiff bases in relation to the

concentration of the inhibitors as well as the temperatures. Polarisation studies

indicated that the compounds used were cathodic inhibitors. El-Mahdy and

Mahmoud [36] tested the inhibition of aluminium in 0.5M hydrochloric acid (HCl)

solution by 5-Benzylidine-1-Methyl-2-methylthioimidazole-4-one using weight loss,

polarisation resistance and hydrogen evolution methods. It indicated that inhibition

efficiency (%IE) increased with increase in inhibitor concentration. It decreased in

activation energy and increased in %IE in the presence of inhibitor. The increase in

temperature indicated the chemisorption of inhibitor molecules. Garrigues et al. [37]

assessed the corrosion inhibition of pure aluminium by 8-hydroxy-quinoline (8-HQ).

In acidic solutions, 8-HQ does not modify the corrosion mechanism of aluminium.

Al Gaber et al. [38] studied the use of 6- amino - 4- (4-phenyl)-l,4- dihydro -3-

methylpyrano [2,3- c] pyrazole -5- carbonitrile and some related compounds as

corrosion inhibitors for aluminium in 2M HCl solution by the thermometric method.

The inhibition efficiency of the additives was related to the absolute value of the

Hamment constant.

Moon and Pyun [39] analysed the corrosion behaviour of aluminium during

cathodic polarisation in deareated, acidic, neutral, alkaline and aqueous solutions by

measuring the weight loss, hydrogen evolution rate, open circuit potential and

potentiostatic current transients measurements. On the basis of the experimental

results, it was suggested that the cathodic corrosion of pure aluminium proceeds by

the chemical dissolution of the oxide film at the oxide/electrolyte interface and

simultaneously by oxide formation at the aluminium/oxide interface. Mahmoud and

El-Mahdy [40] tested the effect of some triazoline derivatives on aluminium in

hydrochloric acid solution by gasometry, weight loss and potentiodynamic methods.

38

The three techniques were in good agreement with the decrease of inhibition

efficiency and with the increase in inhibitor concentration.

Metikos-Hukovic et al. [41] tested the corrosion kinetics of 99.6%

aluminium covered by a thin spontaneous oxide film in hydrochloric acid solution

with and without the presence of substituted N-aryl pyrroles using electrochemical

impedance spectroscopy and quasi steady state polarisation. Osman and Abad El

Rehim [42] found the inhibitive effect of some ethoxylated fatty acids St(EO)80,

OL(EO)20, OL(EO)40 and OL(EO)80 on the corrosion of two types of aluminium,

Al(1) and Al(2) in 1 M hydrochloric acid solution by weight loss method. It is found

that the results agreed with Langmuir, Frumkin, Flory-Huggins isotherm and the

kinetic-thermodynamic model.

Yadav [43] studied the inhibitive efficiencies of pyridine and some of its

derivatives in relation to the corrosion of Al (grade 1100) in 1% HCl at 25, 35, 45

and 55ºC. All of the inhibitors acted predominantly on cathodic sites and only

partially effective on anodic sites. Madkour et al. [44] investigated the inhibitory

effect of some bis- and mono-azo dye derivatives on corrosion of aluminium in 2M

HCl and 2M NaOH solutions by weight-loss, thermometric and polarisation

measurements. In general, the role of the inhibitor has both kinetic and

thermodynamic implications. Tianpei Zhao and Guannan Mu [45] reported the

adsorption and corrosion inhibition of the anion surfactants such as Dodecyl

Sulphonic acid sodium salt (DSASS), Dodecyl Benzene Sulphonic acid sodium salt

(DBSASS), Sodium Dodecyl Sulphate (SDS), on the aluminium surface in HCl

solution using weight loss method. According to experimental results, the relations

between the adsorption and corrosion inhibition of the surfactants on aluminium

surface were discussed. Abdallah [46] assessed the inhibiting effect of four

compounds of tetradecyl-1, 2-diol propenoxylates on the dissolution of aluminium

in 1M HCl using weight loss and polarisation measurements. The results showed

that these compounds were adsorbed on the aluminium surface according to the

Freundlich isotherm. Bansiwal et al. [47] analysed the inhibition of aluminium

corrosion in HCl solution by four Schiff bases: 2-anisalidine-pyridine, 2-anisalidine-

pyrimidine, 2-salicylidine-pyridine and 2-salicylidine-pyrimidine by the mass loss

and thermometric methods. Values of inhibition efficiency obtained from the two

39

methods were in good agreement and were dependent upon the concentrations of

inhibitor and acid.

Xiao-Ci et al. [48] assessed a quantum chemical study of the corrosion

inhibition properties of pyridine and its derivatives on aluminium in hydrochloric

acid. The models of the inhibitors adsorption on the Al-surface were optimised with

the MNDO method. The co-adsorption of the inhibitor and Cl−

and Hads were

discussed. Fouda et al. [49] investigated the effect of benzaldehyde, 2-

hydroxybenzoyl hydrazone derivatives on the corrosion of aluminium in

hydrochloric acid using thermometric and polarisation techniques. Polarisation

measurements indicated that the rate of corrosion of aluminium rapidly increased

with temperature over the range 30-55°C both in the absence and in the presence of

inhibitors. Samarkandy et al. [50] evaluated the corrosion of aluminium in 2M HCl

using ethoxylated fatty acids, derivatives of benzaldehyde and derivatives of

phenanthroline. The corrosion rates were correlated with Hammett constants.

Ekpe et al. [51] assessed the inhibition of corrosion of aluminium in HCl by

solution mixtures of derivatives of thiosemicarbazone at 303-313K and

concentration range of 1x10-5

to 5x 10-4

M using weight loss method. The inhibition

efficiency increased with increase in iso group in the mixtures, which was attributed

to the interaction of the molecules which resulted in exposing of the mixture. Kinetic

treatment of the results gave a first order type of mechanism. Mohamed et al. [52]

reported the 2, 4-dihydroxybenzaldehyde-3-thiosemicarbazone (I) and acetone 4-

phenyl-3-thiosemi-carbazone (II) as inhibitors for iron and aluminium in 0.5M and

2M HCl. The corrosion rate (icorr) was found as a result of the function of

concentration of inhibitor, temperature of the medium and the nature of the inhibitor.

Quantum chemistry was applied and the results of HOMO-LUMO calculations were

correlated with data obtained from chemical and electrochemical investigation.

El-Etre [53] investigated the inhibition efficiency (%IE) of vanillin towards

the corrosion of aluminium in 5 M HCl solution using weight loss measurement,

hydrogen evolution method, thermometric and potentiostatic polarisation

techniques. It was found that adsorption of vanillin on aluminium surface followed

Langmuir adsorption isotherm.

40

Abd El Rehim et al. [54] determined the corrosion inhibition characteristics

of 1,1(lauryl amido)propyl ammonium chloride, as a cationic surfactant (CS), on

aluminium in HCl solution in the temperature range 10-60°C by weight loss,

potentiodynamic polarisation and electrochemical impedance spectroscopic (EIS)

techniques. Results obtained from the three methods were in good agreement.

Metikos-Hukovic et al. [55] found that the inhibition activity of some substituted N-

arylpyrroles on aluminium corrosion in HCl using potentiodynamic and impedance

spectroscopy techniques. All investigated compounds were acted as cathodic-type

inhibitors. Grubac et al. [56] studied the inhibition action of N-arylpyrroles on

aluminium corrosion in 0.17 mol dm-3

HCl in the temperature range 20-60ºC using

potentiodynamic and impedance spectroscopy techniques. The kinetic corrosion

parameters analysed in terms of the impedance data, showed a satisfactory

agreement with those obtained by the potentiodynamic method.

Abd El Rehim et al. [57] assessed the corrosion inhibition of Al, (Al+6%Cu)

and (Al+6%Si) alloys in 1.0 M HCl using dodecyl benzene sulphonate as an anionic

surfactant (AS) inhibitor.in the temperature range 10-60◦C by weight loss,

potentiodynamic polarisation and electrochemical impedance spectroscopic (EIS)

measurements on using dodecyl benzene sulphonate as an anionic surfactant (AS)

inhibitor. The surfactant acts predominately as cathodic inhibitor. The inhibition

efficiency increased with an increase in the surfactant concentration, but decreased

with an increase in temperature. Shankar Lal Meena et al. [58] studied the corrosion

of aluminium metal in both acidic (0.1N HCl) and alkaline (0.1N NaOH) solutions

by Tafel polarisation method. Inhibition increased with the concentration of

inhibitors in acidic medium while inhibition decreased with the increase in its

concentration in alkaline medium.

Monajjemi et al. [59] studied the effect of new corrosion inhibitors

namely, pyridine, 2-methylpyridine (2-Picoline), 4-methylpyridine (4-Picoline), 2,

4-dimethylpyridine (2,4-Lutidine) on the corrosion of aluminium surface in

hydrochloric acid and nitric acid at the HF and B3LYP level using the ab initio 6-

31G and LANL2CZ basis sets from the program package Gaussian 98 (A.7 public

Domain version). The calculated results indicated that the compounds were

41

adsorbed on the metal surface and the organic inhibitor was adsorbed at the Al-

surface in an inclined state.

Branzoi et al. [60] evaluated the electrochemical behaviour of pure

aluminium in HCl solution of different concentrations, in the presence and absence

of organic inhibitors by potentiostatic and potentiodynamic methods. The sigmoidal

shape of the adsorption isotherm confirmed the applicability of Frumkin’s equation

to describe the adsorption process of the three surfactants tested in 0.5M HCl

solution on an aluminium electrode. Foad El-Sherbini et al. [61] reported the

inhibition of three ethoxylated fatty acids of different molecular weights on the

corrosion of aluminium in both 1.0M HCl and 1.0M H2SO4 solutions at different

temperatures (25-55◦C) by weight loss and potentiodynamic polarisation techniques.

The inhibition efficiency for the three fatty acids increased with the increase in the

inhibitors concentration but decreased with increase in temperature. Frumkin

adsorption isotherm fitted well with the experimental data. Bereket and Pinarbasi

[62] analysed the inhibitive behaviour of benzotriazole, 5-methyl benzotriazole, 5-

chloro benzotriazole and 5-nitrotriazole on the corrosion of pure aluminium in 1.0M

HCl by the potentiostatic polarisation technique. From the corrosion rates obtained

at different temperatures, activation parameters for the corrosion processes such as

activation energies Ea, activation enthalpies ∆H* and activation entropies ∆S* were

determined.

Abd El Rehim et al. [63] reported the use of the potentiodynamic

polarisation and electrochemical impedance spectroscopy technique (EIS) in the

corrosion inhibition process of pure Al, (Al + 6%Cu) and (Al + 6%Si) alloys in

1.0M HCl solution at the open circuit potential (OCP) in the temperature range 10-

60ºC using dodecyl phenol ethoxidate. The inhibition efficiency increased with an

increase in the surfactant concentration, but decreased with an increase in

temperature. Maayta et al. [64] evaluated the inhibition of corrosion of aluminium

(Al) in hydrochloric acid (HCl) by sulphonic acid (SA), sodium cumene sulphonate

(SCS), and sodium alkyl sulphate (SAS) using weight loss and potentiostatic

polarisation methods. The efficiency of inhibitors increased in the order: SAS < SCS

< SA in the studied concentration range. These results indicated the increased

aluminium dissolution with the increase in temperature. Abdallah [65] investigated

42

the corrosion behaviour of aluminium in 2M HCl solution in the absence and

presence of four compounds of antibacterial drug namely ampicillin, cloxacillin,

flucloxacillin and amoxicillin using hydrogen evolution, weight loss, and

potentiostatic polarisation techniques. The adsorption process followed Langmuir

adsorption isotherm. The effect of temperature on the rate of corrosion was also

studied. Bereket et al. [66] determined the effects of benzimidazole-2-tione and

benzoxazole-2-tione derivatives on the corrosion of aluminium in 0.1M HCl by a

potentiostatic polarisation technique. Activation energies Ea, activation enthalpies

∆H* and activation entropies ∆S* were determined by the corrosion currents

measurement at different temperatures.

Oguzie et al. [67] evaluated the effect of methylene blue (MB) dye on the

electrochemical corrosion of aluminium in HCl solution using gravimetric method at

303 and 333 K. Synergistic effects increased the inhibition efficiency on addition of

halides namely: KCl, KBr and KI. The activation energy values suggested that the

inhibitor molecules were physically adsorbed on the Al surface. Sastri et al. [68]

analysed the corrosion inhibition of Al by methyl pyridines in terms of the Hammett

equation and the terms of a new equation relating the degree of inhibition log (i/io)

with the reaction of the electronic charge due to the substituent in the molecule. The

new relationship was useful in predicting that new inhibitors offer a greater degree

of inhibition than currently known inhibitor system.

Al-Raishdeh and Maayta [69] investigated the inhibition effect of cetyl

trimethylammonium chloride (CTAC) on aluminium in HCl and NaOH solutions by

weight loss and potentiostatic polarisation measurements. The results indicated

increased Al dissolution with increase in temperature. It was found that the

adsorption of CTAC on the Al surface followed Temkin isotherm in HCl and

Langmuir isotherm in NaOH. Sastri et al. [70] analysed the quantum chemical

parameters for inhibitor compounds like substituted pyridines, anilines, guanides,

azoles, oxadiazoles, diols and diamines. The calculated quantum chemical

parameters of inhibition molecules were useful in predicting the corrosion inhibition

performance of the inhibitors that lead to a rational method of the selection of

inhibitors.

43

Aytac et al. [71] assessed the inhibition effect of some Schiff bases

namely 2-hydroxyacetophenone etansulphonylhydrazone, Salicylaldehyde

etansulphonylhydrazone, 5-bromosalicylaldehyde-etansulphonylhydrazone and 5-

chlorosalicylaldehyde-etansulphonylhydrazone on the corrosion of AA3102

aluminium in 0.1M HCl by means of the hydrogen evolution and electrochemical

impedance spectroscopy. The hydrogen evolution tests showed that the corrosion

resistance was greatly enhanced in the presence of inhibitors. These results were

confirmed by the impedance measurements in terms of an increase in the resistance

and by a decrease in the capacity of interface on inhibitor addition.

Ashassi-Sorkhabi et al. [72] investigated the inhibition effect of some amino

acids such as alanine, leucine, valine, proline, methionine, and tryptophan towards

the corrosion of aluminium in 1M HCl + 1M H2SO4 solution using weight loss

measurement, linear polarisation and SEM techniques. Inhibitor concentration

increased with increase in inhibition efficiency and inhibition efficiency decreased

with increase in temperature. It was found that adsorption of used amino acids on

aluminium surface followed Langmuir and Frumkin isotherms.

Oguzie and Ebenso [73] reported the efficacy of Congo red dye (CR) as an

inhibitor of the 2M HCl solution in corrosion of mild steel and aluminium alloy

(AA 1060) and assessed the influence of halide ions on the inhibition efficiency. CR

dye reduced the corrosion rates of mild steel and aluminium in the acidic

environment. The halide additives improved the inhibition efficiency in the order

KCl < KBr < KI. Ashassi-Sorkhabi et al. [74] examined the inhibition effect of

Schiff bases such as benzylidene-(2-methoxy-phenyl)-amine (A), (2-methoxy-

phenyl)-(4-methyl-benzylidene)-amine (B), (4-chloro-benzylidene)-(2-methoxy-

phenyl)-amine (C) and (4-nitro-bezylidene)-(2-methoxy-phenyl)-amine (D) on the

corrosion of aluminium in 1M HCl by polarisation, electrochemical impedance

spectroscopy (EIS) and weight loss measurements. The adsorption of used

compounds on the aluminium surface obeyed a Langmuir isotherm and followed

physical mechanism. Thermodynamic parameters for both dissolution and

adsorption processes were determined. The quantum chemical study of the corrosion

inhibition efficiency of the Schiff bases on Al in molar HCl was carried out.

44

Yurt et al. [75] investigated the effect of newly synthesised three Schiff

bases namely, 2-[2-aza-2-(5-methyl(2-pyridly))vinyl]phenol, 2-[2-aza-2-(5-

methyl(2-pyridly))vinyl]-4-bromophenol, 2-[2-aza-2-(5-methyl(2-pyridly))vinyl]-4-

chlorophenol on the corrosion behaviour of aluminium in 0.1M HCl using

potentiodynamic polarisation, electrochemical impedance spectroscopy and linear

polarisation methods. Polarisation curves indicated that all studied Schiff bases were

acting as mixed type inhibitors. All measurements showed that inhibition

efficiencies increased with increase in inhibitor concentration. The correlation

between the inhibition efficiencies of studied Schiff bases and their molecular

structure were also investigated using quantum chemical parameters obtained by

MNDO semi-empirical SCF-MO methods.

Quraishi et al. [76] studied the corrosion inhibition of the compounds such

as 2-pentadecyl-1,3-imidazoline (PDI), 2-undecyl-1,3-imidazoline (UDI), 2-

Heptadecyl-1,3-imidzoline (HDI), 2-Nonyl -1,3-imidazoline (NI) on aluminium in

1M HCl and 0.5M H2SO4 by weight loss, potentiodynamic polarisation,

electrochemical impedance and scanning electron microscopic techniques. The

potentiodynamic polarisation data showed that the studied compounds were mixed

type inhibitors. Electrochemical impedance was used to investigate the mechanism

of corrosion inhibition. The surface characteristics of inhibited and uninhibited

metal samples were investigated by scanning electron microscope.

Elewady et al. [77] studied the role of some surfactants in the corrosion of

Al in 1 M HCl using weight loss and galvanostatic polarisation techniques.

Thermodynamic parameters for adsorption and activation processes were

determined. Galvanostatic polarisation data indicated that these compounds acted as

mixed-type inhibitors. Elewady et al. [78] investigated the corrosion inhibition of

aluminum in hydrochloric acid solution in the presence of ethyl trimethyl

ammonium bromide (ETMAB) at temperature range of 30-50ºC using the weight

loss and polarisation techniques. The addition of the anions increased the inhibition

efficiency to a considerable extent. The inhibitive action of ETMAB followed

Freundlich adsorption isotherm. Galvanostatic polarisation curves indicated that the

inhibitor behaved as mixed-type inhibitor.

45

Umoren and Ebenso [79] analysed the corrosion and inhibition behaviour of

aluminium in hydrochloric acid in the absence and presence of polyvinyl

pyrrolidone (PVP), polyacrylamide (PA) and their blends in the temperature range

of 30-60ºC using weight loss, hydrogen evolution and thermometric methods. The

inhibitors (PVP and PA) obeyed Freundlich, Temkin and Flory-Huggins adsorption

isotherms at all the temperatures. Results obtained from the kinetic and

thermodynamic parameters indicated that spontaneous adsorption of the inhibitors

on aluminium surface followed physical adsorption mechanism.

Obot and Obi-Egbedi [80] reported the inhibitive effect of 2, 3-

diaminonaphthalene (2, 3-DAN) for corrosion of aluminium in 1M HCl using

hydrogen evolution method at 30 and 60ºC. Quantum chemical calculation results

showed that 2, 3-DAN molecule possessed planar structure with a number of active

centres, which aided the adsorption process. The Mulliken charge density, the

highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular

orbital (LUMO) were found to be mainly focused around nitrogen atoms and the

cyclic of the benzene as well. The proposed physisorption mechanism supported the

calculated values of Ea, Qads and ∆Gads.

Buyuksagis and Aksut [81] studied the use of alcohols as cathodic inhibitors

in HCl solution. Experiments indicated that the alcohols adsorption on the alloys in

HCl solution obeyed Temkin adsorption isotherm. Rosliza et al. [82] tested the

corrosion inhibition of Al and its alloys using weight loss, polarisation and

electrochemical impedance spectroscopic (EIS) measurements on the corrosion

inhibition of AA6061 and AA6063 aluminium alloys in acidic solution using

sodium benzoate as an inhibitor. Electrochemical studies showed that there was a

significant increase in overall resistance after addition of sodium benzoate, when

compared to the case without inhibitor. Langmuir adsorption isotherm fitted well

with the experimental data. Negm and Zaki [83] analysed the novel series of self-

assembled non-ionic Schiff base amphiphiles as corrosion inhibitors for aluminium

(3SR) at different doses (400-10ppm) in acid medium (4N HCl) using weight loss

and hydrogen evolution methods. The corrosion measurements showed that the

synthesised non-ionic Schiff’s bases could serve as effective inhibitors. Obot and

Obi-Egbedi [84] analysed the interfacial behaviour of fluconazole (FLC) between

46

aluminium and hydrochloric acid by weight loss method at 30-50ºC. Inhibition

efficiency increased with increase in the concentration of fluconazole but decreased

with rise in temperature. The correlation of inhibition effect and molecular structure

of fluconazole was then discussed by quantum chemistry study to provide insight

into the mechanism of the inhibitory action.

Abiola et al. [85] investigated the inhibitory effect of diphenylthiocarbazone

(DPTC) and Dipheyl carbazone (DPC) on aluminium 2S alloy in 0.5M HCl using

chemical method. The adsorption of the compounds via their adsorption centres on

the aluminium surface obeyed the Langmuir adsorption isotherm. The ∆Gads values

were calculated using thermodynamic equations. Obot et al. [86] examined the

corrosion inhibition behaviour of aluminium in hydrochloric acid in the presence of

clotrimazole (CTM) and potassium iodide (KI) using weight loss method at 30 and

50ºC. The experimental results suggested that the presence of iodide ions in the

solution stabilised the adsorption of CTM molecules on the metal surfaces and

therefore improved the inhibition efficiency of CTM. The HOMO and the LUMO

electronic density of the molecule were used to explain the inhibiting mechanism.

The most probable adsorption centres were found in the vicinity of the imidazole

group.

Umoren et al. [87] studied the effect of iodide ions on the corrosion inhibition

of aluminium in 2M HCl in the presence of polyvinylpyrollidone (PVP) using

gasometric (hydrogen evolution) method at 30-60ºC. Inhibition efficiency (%IE)

increased with an increase in concentration of PVP. Increase in temperature increase

in corrosion rate but decreased in inhibition efficiency. The synergistic parameter (S1)

obtained was greater than unity, which indicated that the enhanced inhibition

efficiency caused by the addition of iodide ion was only due to synergistic effect.

Obot et al. [88] investigated Clotrimazole (CTM) [1-[(2-chlorophenyl)-

diphenyl-methyl]imidazole], an antifungal drug, as a corrosion inhibitor for

aluminium in HCl using weight loss method. The inhibition efficiency increased

with increase in the concentrations of CTM and reached 90.90% at 1 x 10-4

M, but

decreased with increase in temperature. Phenomenon of physical adsorption was

proposed for the inhibition and the process followed the Langmuir adsorption

47

isotherm and kinetic / thermodynamic model of El-Awady et al. The mechanism and

the type of adsorption isotherm were proposed from the trend of inhibition

efficiency with temperature such as Ea, ∆Gads, and Qads. Quantum chemical

calculations results showed that CTM possess a number of active centres

concentrated mainly on the imidazole moiety of the molecule. The highest occupied

molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO)

were also found around the nitrogen atoms and benzene rings.

El Maghraby [89] studied the inhibition effect of potassium iodate on the

corrosion of aluminium in 2M HCl by weight loss, polarisation and electrochemical

impedance spectroscopy (EIS) measurements. It was found that KIO3 acts as an

excellent inhibitor. Polarisation curves revealed that the used inhibitor was a mixed

type inhibitor.

Ishwara Bhat and Vijaya Alva [90] studied the inhibitive effect of 2-

chloronicotinic acid on the dissolution of aluminium in various concentration of HCl

using weight loss and polarisation measurements. The inhibition efficiency was

increased with increase in concentration of the inhibitor. The effect of temperature

also indicated the decrease in inhibition efficiency on account of the increase in

temperature. The inhibitor followed Langmuir adsorption isotherm at higher

concentrations of HCl.

Desai and Kapopara [91] studied the anisidines (o-, m-, p-) as corrosion

inhibitors for aluminium in hydrochloric acid solution. The results showed that the

inhibitors were adsorbed on the aluminium surface according to Langmuir

adsorption isotherm. Polarisation study also revealed that all the anisidines

functioned slightly as anodic but significantly cathodic inhibitors.

Umoren [92] studied the inhibitive performance of two water soluble

polymers–polyacrylamide (PA) and polyvinylpyrrolidone (PVP) on the corrosion

behaviour of aluminum alloy 3SR in HCl solution using weight loss, hydrogen

evolution, and thermometric methods at 30-60°C. Results indicated that both

polymers inhibit acid-induced corrosion of aluminum at the studied temperatures.

PVP was found as better corrosion inhibitor than PA. All measurements from the

three methods show that inhibition efficiencies increased with increase in inhibitor

48

concentration and decreased with increase in temperature. Adsorption of these

inhibitors followed Temkin and El-Awady adsorption isotherm models. Differences

in inhibition efficiency of the two polymers could be linked to their differences in

molecular structure.

Khaled and Amin [93] assessed the corrosion inhibition and adsorption

characteristics of three selected imidazole derivatives namely, 2-amino-4,5-

imidazoledicarbonitril (AID), 5-amino-4-imidazolecarboxamide (AIC) and

imidazole (IM) on aluminium in 1.0M HCl at 25ºC. Measurements were carried out

under various experimental conditions using chemical (weight loss) and

electrochemical (Tafel extrapolasion and impedance) methods. Molecular dynamics

(MD) method and density functional theory were also applied for theoretical study.

Results showed that inhibition efficiency of these compounds increased with

increase in concentrations due to the formation of a surface film on the aluminium

surface. Results obtained from theoretical study confirmed the experimental

findings.

Obot et al. [94] evaluated the effect of iodide ions on the inhibitive

performance of 2, 3-diaminonaphthalene (2, 3-DAN) in 1M HCl for aluminium

corrosion using hydrogen evolution (gasometry) measurements at 30 and 40 °C.

Some quantum chemical parameters and the Mulliken charge densities for 2, 3-

diaminonaphthalene were calculated by the AM1. Semi-empirical method provided

further insight into the mechanism of inhibition of the corrosion process. Obot et al.

[95] found the inhibitive capabilities of Clotrimazole (CTM) and Fluconazole

(FLC), two antifungal drugs, on the electrochemical corrosion of aluminium in 0.1M

HCl solution using weight loss measurements at 30 and 50ºC. At constant acid

concentration, the inhibition efficiency (%IE) increased with increase in the

concentration of the inhibitors. The reactivity of these compounds was analysed

through theoretical calculations based on AM1 semi-empirical method to explain the

different efficiencies of these compounds as corrosion inhibitors. CTM was found as

better inhibitor than FLC.

Khaled and Al-Qahtani [96] investigated the corrosion inhibition of

aluminium in 1.0M HCl in the absence and presence of different concentrations of

49

tetrazole derivatives namely, 1-phenyl-1H-tetrazole-5-thiol (A), 1-phenyl-1H-

tetrazole (B), 1H-tetrazol-5-amine (C), 1H-tetrazole (D) using weight loss,

potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS)

measurements. Potentiodynamic polarisation study showed that the inhibitors acted

as cathodic-type inhibitors. Calculated results indicated that the difference in

inhibition efficiencies between these compounds was clearly explained in terms of

Frontier molecular orbital theory. The adsorption of these compounds on the

aluminium surface obeyed Langmuir adsorption isotherm and mixed type

(physisorption and chemisorptions) mechanism.

Noor [97] evaluated the inhibitive action of some quaternary N-heterocyclic

compounds namely, 1-methyl-4[4(-X)-styryl] pyridinium iodides (X: -H, -Cl and -

OH) on the corrosion of Al–Cu alloy in 0.5M HCl solutions by potentiodynamic

polarisation, electrochemical impedance spectroscopy and weight loss

measurements. All the studied compounds showed good inhibitive characteristics

against the corrosion of Al–Cu alloy in the tested solutions and their performance

increased with increae in inhibitors concentration. Polarisation data indicated that

the studied compounds were cathodic inhibitors without changing the mechanism of

hydrogen evolution reaction. The adsorption of all inhibitors on Al–Cu alloy obeyed

Langmuir adsorption isotherm. The corrosion activation parameters (Ea, ∆H*, ∆S*

and ∆G*) were estimated and discussed.

Oguzie [98] reported the crystal violet dye (CV) as a corrosion inhibitor for

aluminium in hydrochloric acid (1mol dm-1

) and potassium hydroxide (0.5mol dm-1

)

solution in the temperature range 30-60ºC using gravimetric method. Inhibition

efficiency was more in 1M HCl (83.6%) than in 0.5M KOH (23.0%). The

calculated values of activation energy (Ea), free energy of adsorption (Gads) and heat

of adsorption (Qads) confirmed the physisorption mechanism. The inhibition

characteristics were approximated by the Freundlich adsorption isotherm.

Fouda et al. [99] analysed the aluminium corrosion rate in the absence and

presence of some tertiary ketonic Mannich bases in 2M HCl solution using weight

loss and galvanostatic polarisation techniques. The adsorption of these Mannich

bases on Al surface obeyed Temkin’s adsorption isotherm. Galvanostatic

50

polarisation studies showed that these compounds were mixed–type inhibitors.

Elewady and Mostafa [100] investigated the inhibition action of some ketonic

secondary Mannich base derivatives on the corrosion of aluminium in 2M HCl

solution using weight loss and galvanostatic polarisation techniques. The effect of

temperature on the corrosion rate was studied in order to obtain the kinetic and

thermodynamic parameters of aluminium corrosion. The adsorption process

followed Temkin adsorption isotherm. El Maghraby [101] assessed using optical,

scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy

(EDS) to study morphology, the composition of adsorbed film formed on the surface

of aluminium samples in 2M HCl solution containing 100ppm optimum KIO3 dose.

The nature and strength of the passive film and the mechanism of the formation was

explained based on detailed studies conducted under experimental conditions.

Obot and Obi-Egbedi [102] evaluated the effect of nizoral on the corrosion

inhibition of aluminium alloy AA1060 in 2M HCl solution using the mylius

thermometric method. Results revealed that nizoral acted as corrosion inhibitor for

aluminium in the acidic medium. The addition of KI to the inhibitor enhanced the

inhibition efficiency to a considerable extent. The adsorption of nizoral on to the

aluminium surface obeyed the Fruendlich adsorption isotherm.

Umoren and Solomon [103] examined the influence of bromide and iodide

ions on the inhibitive effect of polyacrylamide (PA) on aluminium corrosion in HCl

solution using weight loss, hydrogen evolution, and thermometric methods at 30 and

60ºC. The values of synergism parameter (S1) obtained for the halides were greater

than unity, suggested that the improved inhibition efficiency of polyacrylamide

caused by the addition of the halide ions was due to synergistic effect. Corrosion

inhibition could be attributed to adsorption of inhibitor molecules on the Al surface

via physical mechanism. The adsorption process followed the kinetic-

thermodynamic model of El-Awady adsorption isotherm.

Zer et al. [104] evaluated the effect of polypyrrole film on the corrosion of

Al in 0.1M HCl solution by sing potentiostatic method. The complexes of pyrrole

2-

pentamers and different anions (CO32-, NO

2-, CrO4 and DBS) were studied using ab

initio quantum chemical at the Hartree-Fock (HF) levels with STO-3G, 3-21G, 6-

51

31G(d,p) basis sets and HOMO – LUMO energy gap was calculated by B3LYP

method with 3-21G* and 6-31G(d,p) basis sets. The polypyrrole film obtained in

CrO42-

anion was determined as the most effective in prevention to pitting corrosion

of Al.

Fouda et al. [105] assessed the corrosion behaviour of aluminium in 0.5 M HCl

solution in the absence and presence of (E)-3,6-dibromo-2-((4-methoxyphenylimino)

methyl)phenol (I), (E)-3,6-dibromo-2-((4-chlorophenylimino)methyl)phenol (II)

and (E)-4-(3,6-dibromo-2-hydroxybenzylideneamino)benzoic acid (III) using

potentiodynamic polarisation, electrochemical impedance spectroscopy and

electrochemical frequency modulation techniques. Quantum chemical studies

indicated that the inhibition potentials of these compounds correlated well with

EHOMO, ∆E, η, χ, P and ∆N. A good correlation was found between the theoretical

data and the experimental results.

Mohsen Lashgari and Malek [106] investigated using phenolic inhibitors by

quantum electrochemical approaches based on density functional theory and

cluster/polarised continuum model on the corrosion behaviour of aluminium in HCl

and NaOH media. Moreover, phenol was a potential-molecule having mixed-type

inhibition mechanism. The relationship between inhibitory action and molecular

parameters was discussed and the activity in alkaline medium was also theoretically

anticipated. This prediction was in accord with experiment.

Zohreh Shahnavaz et al. [107] determined the inhibitory action of benzene-

1,2,4,5-tetracarboxylic dianhydride (PMDH) on aluminium corrosion in 1M HCl

solution by means of electrochemical impedance spectroscopy, polarisation curves

(LSV) and scanning electron microscopic techniques. Increase in temperature and

decrease in inhibitor concentrations, the rate of aluminium corrosion increased. The

surfactant acted as mixed type inhibitor and obeyed Langmuir isotherm.

Zor et al. [108] found the inhibition effect of 4-phenyl-3-thiosemicarbazide

(PT) on the corrosion of aluminium in 0.1M hydrochloric acid (HCl) solution at 298

to 343K using potentiodynamic polarisation method. The effect of temperature on

aluminium in 0.1M HCl with and without inhibitor was also analysed and the

activation energy was determined. A theoretical study of the corrosion inhibition

52

efficiencies of both PT and protonated PT was carried out using density functional

theory (DFT).

QiBo Zhang and YiXin Hua [109] investigated the effects of newly

synthesised three alkylimidazolium ionic liquids—1-butyl-3-methylimidazolium

chlorides (BMIC), 1-hexyl-3-methylimidazolium chlorides (HMIC) and 1-octyl-3-

methylimidazolium chlorides (OMIC)—on the corrosion of aluminium in 1.0M HCl

using potentiodynamic polarisation, electrochemical impedance spectroscopy and

weight loss methods. The activation energy and other thermodynamic parameters

such as enthalpy of activation (∆H), entropy of activation (∆S), adsorption

equilibrium constant (Kads) and free energy of adsorption (∆Gads) were calculated to

elaborate the mechanism of corrosion inhibition.

Oguzie et al. [110] studied the malachite green dye (MG) as a corrosion

inhibitor for aluminium in 1.0 mol dm−3

HCl and 0.5 mol dm−3

KOH using the

gravimetric method. MG inhibited the corrosion reaction in the acidic medium by

adsorption on the metal/solution interface following the Flory-Huggins isotherm.

The reactivity of the MG molecule was analysed theoretically using the density

functional theory to explain the adsorption characteristics, while molecular

dynamics simulations were performed to illustrate the adsorption structure of MG at

a molecular level. The theoretical predictions showed good agreement with

experimental results.

Sharma Pooja et al. [111] studied the corrosion inhibition of aluminium in

HCl solution by four newly synthesised Mannich bases viz. 3-oxo, 3-phenyl, N,N-

dimethyl propanamine hydrochloride (MB1), 3,5-dioxo,5-phenyl N,N-dimethyl

pentanamine hydrochloride (MB2), 2,2-dimethyl,3-oxo N,N-dimethyl butanamine

hydrochloride (MB3) and 3-oxo N,N-dimethyl butanamine hydrochloride((MB4)

using weight loss, thermometric and potentiometric methods. Results of inhibition

efficacies obtained from the said methods were in good agreement with each other.

Efficacy of inhibitor increased with increase in concentration of inhibitor as well as

that of HCl solution.

Arukalam et al. [112] evaluated the inhibitive effect of hydroxyethylcellulose

on mild steel and aluminium corrosion in 0.5M HCl solution under atmospheric

53

exposure using weight loss method. Inhibition efficiency and surface coverage were

higher in mild steel than in aluminium.

Nasim ziaifar et al. [113] studied the effect of new corrosion inhibitors, on

the corrosion of Al surface in acid media by weight loss measurements. The

inhibition efficiency of thiourea, pyridine and bis-azo dyes were found that the

corrosion of aluminium in 2.0M HCl was considerably reduced in the presence of

such inhibitors. Abood [114] determined the effects of Meloxiam drug (MEL) on the

corrosion of pure aluminium in 2M HCl using weight loss method. The

measurement showed that the inhibition efficiency increased with increase in the

concentration of inhibitor. The associated activation energy of corrosion Ea and other

thermodynamic parameters such as ∆H0

, ∆S0

, (K

) and ∆G0

were calculated

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to elaborate the mechanism of corrosion inhibition. Quantum chemical parameter

such as HOMO, LUMO and Mulliken charge etc. were also calculated using DFT

(B3LYP/ 6-311++G(d,p)). The results indicated that N and S atoms in the MEL

structure was not effected in the adsorption of drug on the Al surface. Mabrouk et al.

[115] studied the effect of a series of mono- and bis-azo dyes derived from

dihydroxynaphthalene on the dissolution of aluminium in 2M HCl solutions using

weight loss, thermometric and galvanostatic polarisation techniques. The inhibitors

were adsorbed on the surface according to the Temkin adsorption isotherm. The

results obtained from the chemical and electrochemical measurements were in good

agreement.

Muniandy et al. [116] analysed the inhibitory effect of some Schiff bases viz.

N,N′-bis(2-hydroxybenzylidene)-1,3-diaminobenzene (SB1), N,N′-bis (4-

bromobenzylidene)-1,3-diaminobenzene (SB2) and N,N′-bis (2-hydroxy-5-

bromobenzylidene)-1,3-diaminobenzene (SB3) on the corrosion of aluminium alloy

in 0.5M HCl acid using weight loss measurements, potentiodynamic polarisation

and scanning electron microscopy (SEM). The potentiodynamic polarisation curves

revealed that, all the studied Schiff bases were mixed type inhibitors with

predominantly cathodic action and their inhibition efficiencies increased with

increase in inhibitor concentration. The adsorption of Schiff bases followed

Langmuir adsorption isotherm. SEM study revealed that these compounds protected

the metal corrosion by adsorption on its surface to form a protective layer. Ozdemir

54

et al. [117] analysed the corrosion inhibition characteristics of quantised 1,(4)-

tetrakis [(2-mercapto) pyridine] phthalocyanine (I) and 2,3-octakis [(2-mercapto)

pyridine] phthalocyanine (II) on aluminium in 0.1M HCl solution by means of

potentiodynamic polarisation and electrochemical impedance spectroscopy

techniques. The inhibition efficiency increased with increase in the phthalocyanine

concentration but decreased with increase in temperature. The phthalocyanine acted

as predominately cathodic inhibitor.

Fouda et al. [118] investigated the corrosion behaviour of aluminium in 1M

HCl solution in the absence and presence of phenazone and aminophenazone using

weight loss, potentiodynamic polarisation and electrochemical impedance

spectroscopy(EIS) techniques. Potentiodynamic polarisation data indicated that

these compounds acted as cathodic type inhibitors. Quantum chemical parameters

were constructed in order to characterise the inhibition performance of the tested

molecules.

El Ashry and Senior [119] reported the quantum chemical and topological

descriptors of lauric hydrazide and its salts were correlated with their corrosion

inhibition efficiencies in steel, aluminium, copper and zinc in an aqueous acidic

environment. The quantum chemical parameters were obtained using B3LYP/6-

31G⁄⁄ optimisation. The inclusion of quantum parameters, having both charge indices

and topological indices, affects the inhibition efficiency of studied compounds

resulting in high correlation coefficient factors for the obtained equations.

Xianghong Li et al. [120] investigated the inhibition effect of

tetradecylpyridinium bromide (TDPB) on the corrosion of aluminium in 1.0M HCl

solution by weight loss, potentiodynamic polarisation, and electrochemical

impedance spectroscopy (EIS) methods. Polarisation curves revealed that TDPB

behave as a cathodic inhibitor. EIS spectra consist of large capacitive loop at high

frequencies followed by a large inductive one at low frequency. Values also confirm

the inhibitive ability.

Aysel Yurt and Ozlem Aykin [121] synthesised and evaluated the effect of

two Schiff’s bases on the corrosion of aluminium in 1.0M HCl using

potentiodynamic polarisation and electrochemical quartz crystal microbalance

55

measurements. The correlation between the inhibitor performances and their

molecular structures were investigated using quantum chemical parameters obtained

by (modified neglete of diatomic overlap) semi-empirical method. Calculated

quantum chemical parameters indicated that Schiff’s bases adsorbed on aluminium

surface by chemical mechanism.

Ishwara Bhat and Alva [122] studied the inhibition effect of

meclizine hydrochloride on the corrosion behaviour of aluminium in 1 M

hydrochloric acid medium by weight loss, potentiodynamic polarisation and

electrochemical impedance spectroscopy techniques. The adsorption of the inhibitor

on the aluminium surface followed Langmuir adsorption isotherm model. The

activation energy and thermodynamic parameters were calculated and discussed.

El-Deeb and Mohamed [123] analysed the inhibitory effect of a 3-(10-

sodium sulfonate decyloxy) aniline monomeric surfactant and the analog polymeric

surfactant poly[3-(decyloxy sulfonic acid) aniline] (PC10) on the corrosion of

aluminium in 0.5M hydrochloric acid with weight loss and potentiodynamic

polarisation techniques. It was found that these inhibitors acted as mixed-type

inhibitors with anodic predominance. The adsorption of these compounds on the

metal surface obeyed Langmuir and Frumkin adsorption isotherms. The obtained

results from the weight loss and potentiodynamic polarisation techniques were in

good agreement.

Obot et al. [124] analysed the adsorption of fluconazole on aluminium

surface in 0.1M HCl solution using chemical methods at 30-50ºC. The values of free

energy of adsorption ∆Gºads were calculated from surface coverage (θ) of the studied

compound by applying the mathematical model of the Bockris- Swinklels

adsorption. Qi Zhang et al. [125] synthesised and tested the four new quaternary

ammonium gemini surfactants in the series of hexanediyl-1,6-bis-(diethyl alkyl

ammonium bromide) referred as CmC6Cm(Et)·2Br (m = 10, 12, 14, 16) as corrosion

inhibitors of aluminium in 1 mol/L HCl solution at 25°C using gravimetric,

gasometric measurements and SEM technique. On the basis of the variation of

surface coverage rates (θ) with the surfactant concentrations, the adsorption modes

56

of the gemini surfactants CmC6Cm (Et)·2Br at the aluminium /solution interface were

proposed.

Naik et al. [126] investigated the inhibition effect of p-anisidine-N-

benzylidene (p-AnNB) on the corrosion of Al-Pure in 1.0 M HCl by weight loss,

galvanostatic polarisation, and electrochemical impedance spectroscopy (EIS)

measurements. The Schiff base used for investigation was an excellent inhibitor for

Al-Pure in 1.0M HCl. The optimum concentration of this inhibitor was 0.5% with

around 99.78% inhibition efficiency. The results obtained from various techniques

were in good agreement.

Rethinnagiri et al. [127] assessed the corrosion inhibition of aluminium by 3-

amino-1,2,4-triazole in 1M HCl by weight loss and potentiodynamic polarisation

and impedance spectroscopy methods. Polarisation measurements indicated that the

inhibitor acted as mixed type inhibitor. Abdallah et al. [128] evaluated the corrosion

behaviour of aluminium and three aluminium–silicon alloys in different

concentrations of HCl solution and its inhibition by antihypertensive drugs using

potentiostatic polarisation measurements. The inhibitive action of these compounds

was due to their formation of insoluble complex adsorbed on the metal surface. The

adsorption followed Langmuir adsorption isotherm. It was found that the drugs

compounds provided protection to Al and Al–Si alloys against pitting corrosion by

shifting the pitting potential to more positive direction until critical drug

concentrations (250 ppm).

Musa et al. [129] reported the inhibitive effects of 1-(2H)-phthalazinone

(PTO) for corrosion of aluminium alloy (2024) in 1.0 M HCl solution and the

synergistic effect of KI on the corrosion inhibition efficiency using electrochemical

measurements. The synergistic effect was decreased in the concentration of PTO and

a competitive inhibition mechanism existed between KI and PTO cations.

Patel et al. [130] investigated the inhibition performance of two Schiff bases

namely, (A) Benzenamine, 2-chloro-N-[(4-methoxyphenyl)methylene] and (B)

Benzenamine, 3-chloro-N-[(4-methoxyphenyl)methy-lene] as corrosion inhibitors

for Al-Pure in 1.0 M HCl by galvanostatic polarisation measurement,

electrochemical impedance spectroscopy (EIS) and weight loss method. . Two

57

Schiff bases were shown remarkable inhibition property on the corrosion of Al-Pure

in 1.0 M HCl solution. The high inhibition efficiency was attributed to the blocking

of active sites by adsorption of inhibitor molecules on the metal surface. Patel et al.

[131] investigated the inhibition effect of newly synthesised Schiff bases

N-benzylidene benzylamine (A) and benzenemethanamine-α-methyl-N-

(phenylmethylene) (B) on the corrosion behaviour of Al-Pure in 1·0 M HCl using

galvanostatic polarisation, electrochemical impedance spectroscopy (EIS) and

adsorption studies. The results showed that (A) and (B) possess excellent inhibition

effect for the corrosion of Al-Pure and the inhibitors acted as mixed type inhibitors.

Activation energy and free energy of adsorption were also calculated.

Quraishi et al. [132] synthesised and studied the the corrosion inhibition

properties of compounds on aluminium in 1M HCl and 0.5M H2SO4 by weight loss,

potentiodynamic polarisation, electrochemical impedance and scanning electron

microscopic techniques by 2-pentadecyl-1,3-imidazoline (PDI), 2-Undecyl-1,3-

imidazoline (UDI), 2-Heptadecyl-1,3-imidazoline (HDI), 2-Nonyl-1,3-imidazoline

(NI). The values of activation energy, free energy of adsorption, heat of adsorption,

enthalpy of activation and entropy of activation were also calculated. The

potentiodynamic polarisation data showed that the compounds studied were mixed

type inhibitors. Electrochemical impedance was used to investigate the mechanism

of corrosion inhibition. The surface characteristics of inhibited and uninhibited

metal samples were investigated by scanning electron microscopy (SEM).

Ishwara Bhat and Alva [133] assessed the effect of miconazole nitrate, an

antifungal drug on the corrosion behaviour of aluminium in 1 M HCl using

potentiodynamic polarisation, electrochemical impedance spectroscopy technique

and weight loss methods. The adsorption of the inhibitor molecule was followed

Langmuir adsorption isotherm.

Weight loss, thermometric and potentiometric methods were used to study

the corrosion inhibition of aluminium in HCl solution by four newly synthesised

Mannich bases viz. 3-oxo, 3-phenyl, N,N-dimethyl propanamine hydrochloride

(MB1), 3,5-dioxo,5-phenyl N,N-dimethyl pentanamine hydrochloride (MB2), 2,2-

dimethyl,3-oxo N,N dimethyl butanamine hydrochloride (MB3) and 3-oxo N,N-

58

dimethyl butanamine hydrochloride (MB4) by Pooja Sharma et al. [134]. Results of

inhibition efficacies obtained from the said methods were in good agreement with

each other. Efficacy of inhibitors increased with increase in concentration of

inhibitors as well as that of HCl solution.

Serpil Safak et al. [135] synthesised and analysed the inhibitive capabilities

of three Schiff bases namely, 1,5-bis [2-(2-hydroxybenzylideneamino) phenoxy]-3-

oxopentane (D1), 1,5-bis[2-(5-chloro-2-hydroxybenzylideneamino) phenoxy]-3-

oxopentane (D2) and 1,5-bis [2-(5-bromo-2-hydroxybenzylideneamino) phenoxy]-3-

oxopentane (D3) on the aluminium corrosion in 0.1M HCl by means of

electrochemical impedance spectroscopy, Tafel polarisation and scanning electron

microscopy techniques. Results showed that, compounds were in accord with

Temkin adsorption isotherm. Quantum chemical calculations were performed to

provide further insight into the inhibition efficiencies determined experimentally.

Patel et al. [136] studied the corrosion inhibitor of o-chloroaniline-N-

benzylidene toward the corrosion of Al – pure in 1.0M HCl using chemical method

and electrochemical techniques such as polarisation method and electrochemical

impedance spectroscopy. The inhibition efficiency from weight loss, polarisation

study and EIS were found in good agreement one another.. The adsorption of the

inhibitor on the metal surface in the acid solution obeyed Langmuir’s adsorption

isotherm. Abd El Haleem et al. [137] tested the corrosion behaviour of Al in 2M

HCl solution in the absence and presence of phenylhydrazine, urea, thiourea, N-

allylthiourea and thiosemicarbazide using different chemical and electrochemical

techniques. The inhibitive action of these compounds was discussed in terms

blocking the electrode surface by adsorption of the inhibitor molecules according to

Langmuir isotherm and thermodynamic parameters kads was also calculated.

Makanjuola Oki et al. [138] studied the N-Butyl amine grafted into Dow

epoxy resin. The product was evaluated as an acid inhibitor by gravimetric method.

The reduction in corrosion of aluminium in 1M HCl solution was 92% at 30ºC and

83% at 60ºC with an inhibitor concentration of 100 ppm. The corrosion rate at this

concentration was 3.0 × 10-2

and 1.5 × 10−1

mm/yr at 30 and 60ºC. For the

specimens in HCl without inhibitor at 10-hour immersion period, the corrosion rate

59

was 3.8 × 10−1

and 8.6 × 10−1

mm/yr respectively, at 30 and 60ºC. Data obtained

were correlated with Langmuir isotherm.

2.1.2. Inorganic chemicals as corrosion inhibitors in hydrochloric acid medium.

Usually crystalline salts such as sodium chromate, phosphate, or molybdate

negative anions of these compounds were involved in reducing metal corrosion.

Khedr and Lashien [139] examined the influence of K+, Mg

2+, Ba

2+, Cu

2+,

Zn2+

, Hg2+

, Cd2+

, Co2+

, Ni2+

or Fe3+

on the general and pitting corrosion of

aluminium in neutral and acid media by gravimetric, potentiodynamic polarisation

and thermometric measurements together with surface analysis by XPS, Auger

profile depth analysis and examination by SEM. Cd2+

ions showed efficient

inhibition over a particularly wide concentration range which suggested their

application as an inhibitor of aluminium corrosion.

Cai et al. [140] assessed the inhibitive behaviour of cadmium sulphate

(CdSO4) on the corrosion of aluminium in 1 mol/L hydrochloric acid using

fluorospectrophotometry and mass loss technique. Result showed CdSO4 was

effective, especially at high temperatures. Corrosion rate data obtained from the two

techniques were consistent.

Bartenev and Barteneva [141] reported the effect of thallium deposition on

the corrosion rate of aluminium in hydrochloride solutions. The variations of partial

inhibition coefficients Ks and K∆E with the variations of thallium iodide

concentration and the corrosion test time were also analysed.

Bartenev [142] studied the protective action of three different compositions

of tin and cadmium chlorides on aluminium in hydrochloric solution. In inhibition

coefficients, partial effects of the surface coverage with contact deposit (I) and the

variation in the aluminium free-corrosion potential (II) were formally separated.

One of them implied independent action of inhibitors in the mixture, while the other

was based on a simplified additive model considering the specificity of the

components mixed. El-Dahana et al. [143] investigated the corrosion of aluminium

in HCl solution by hexamide-halide blends (HA-KI and HA-CaCl2) using

60

gravimetric method, open circuit potential and polarisation measurements. With the

mixed inhibitors, there was a compact adsorbed film formation on the surface of Al,

due to a synergistic action between the halides ions and HA.

El-Dahana et al. [144] investigated by scanning electron microscopy (SEM)

and Auger electron spectroscopy (AES) to study the surface morphology, the

composition and thickness of the adsorbed film formed on the surface of aluminium

samples in 2M hydrochloric acid solution containing optimum doses of the blends

hexamine–KI and hexamine–CaCl2 as inhibitors. The results explained the

effectiveness of the halide ions in facilitating the adsorption of hexamine.

Barteneva and Bartenev [145] determined the kinetics of inhibition of

aluminium corrosion with SnCl2, CdCl2, PbCl2, and the equimolar binary mixtures

under contact exchange condition. Prerequisites for synergism in these mixtures

were determined. Frignani et al. [146] tested a noticeable and persistent protective

action towards aluminium corrosion obtained by treatments with silane molecules

containing a long aliphatic chain (e.g., n-octadecyl-trimethoxy-silane, C18), C18

coatings retarded not only the cathodic oxygen reduction reaction, but also the

anodic metal oxidation process. A very prolonged action was also found towards the

pitting process in the particularly aggressive chloride solution.

Ali et al. [147] synthesised and studied the new Cu (II), Ni (II), Fe (III) and

Pd (II) Schiff base complexes derived from o-tolidine and selected aldehydes,

namely salicyaldehyde and 2-hydroxy naphthaldehyde on corrosion inhibition of Al

and Cu in 1M HCl solution and Cr-Ni steel in crude oil using N,N’ – bis

(salicyledene)-o-tolidine by weight loss method.

Bartenev and Barteneva [148] analysed the concentration effect of cadmium

chloride on the corrosion rate of aluminium under conditions of the contact

deposition of cadmium in hydrochloric acid solution. The inhibiting effect of

cadmium cations was shown to transform into the stimulating effect with an increase

in the cadmium concentration in the solution. Kyung-Hwan Na and Su-Il Pyun [149]

investigated the effects of sulphate, nitrate and phosphate ion additives on the pit

initiation of pure aluminium in a hydrochloric acid solution as a function of anion

concentration using potentiodynamic polarisation experiment and electrochemical

61

noise measurement. It was concluded that pit initiation was clearly distinguished

from uniform corrosion. Elewady et al. [150] assessed the corrosion inhibition of

aluminium in hydrochloric acid solution in the presence of ethyl trimethyl

ammonium bromide (ETMAB) at temperature range of 30-50ºC using the weight

loss and polarisation techniques. The synergistic effect of ETMAB and anions was

also discussed. Galvanostatic polarisation curves indicated that the inhibitor behaved

as mixed-type inhibitor.

Aytac [151] a group of Cu(II), Ni(II) and Co(II) complexes of –Br and –

OCH2CH3 substituted Schiff bases as a new class of corrosion inhibitors for

aluminium in 0.1M HCl by the addition of 10ppm compound using potentiodynamic

polarisation, electrochemical impedance spectroscopy, linear polarisation method

and gas evolution tests at 25ºC. The potentiodynamic polarisation curves showed

that both the cathodic and the anodic processes of Al corrosion were suppressed and

the Nyquist plots of impedance gave mainly capacitive loop. Scanning electron

microscopy was done from the surface of the exposed sample indicating uniform

film on the surface. Abd El Aal et al. [152] tested the corrosion behaviour of Al in

2M HCl in presence of CrO42-

, WO42-

and HPO2-

ions. The inhibitive action of these

anions was discussed in terms of competitive adsorption with Cl- ions on the

electrode surface followed by a reduction mechanism to form metal oxides. The

inhibition efficiency was decreased in the order: CrO42-

> WO42-

> HPO2-

.

2.1.3. Natural products as corrosion inhibitors in acid media.

Corrosion control of metals was an important activity of technical,

economical, environmental and aesthetical importance. The toxicity of organic and

inorganic corrosion inhibitors to the environment has prompted the search for safer,

corrosion inhibitors such as green corrosion inhibitors and other more environmental

friendly corrosion inhibitors. Most of which are biodegradable and do not contain

heavy metals or other toxic compounds. Corrosion inhibition abilities of polymeric

substances, e.g. plant gums are environmentally friendly and ecologically

acceptable, have also shown that plant products are inexpensive, readily available

and renewable sources of materials. Several reviews papers have been published on

natural products as corrosion inhibitors [153-164].

62

2.1.3.1. Natural products as corrosion inhibitors in hydrochloric acid and

sodium hydroxide media

EL Horary et al. [165] studied the effect of the inhibition of the Al and Zn in

HCl and NaOH by different concentrations of aqueous extract of Hibiscus subdariffa

(Karkade) by thermometric, weight loss, and galvanostatic techniques. The two

main constituents were effective in retarding the dissolution of the two metals.

Nnanna et al. [166] analysed the inhibitive effect of leaves extract of Euphorbia hirta

on Al corrosion in HCl and NaOH solutions using gravimetric measurements at 30

and 60°C. The leaves extract was better inhibition efficiency in the acidic medium

than in the alkaline medium. The adsorption of the leaves extract was best shown by

Langmuir isotherm. Ibegbulam et al. [167] investigated the corrosion inhibition of

Al in HCl and NaOH using Chromolaena odorata leaves extract. The inhibition

efficiency increased with increase in inhibitor concentration.

2.1.3.2. Natural products as corrosion inhibitors in hydrochloric acid and

sulphuric acid media

Saleh et al. [168] investigated the inhibitive effect of aqueous extracts of

Opuntia ficus indica and Aloe eru (leaves) and Orange, Mango, Pomegranate (fruit

peels) on the mild steel, Al, Zn, and Cu in HCl and H2SO4 solutions by weight loss

and polarisation measurements. The extracts retarded the dissolution reactions to an

extent dependent on the metal used, the concentration of the additive and the type,

concentration and temperature of the attacking acid. Jain et al. [169] assessed the

inhibitive action of the acid extracts of seeds, leaves, and bark from the Ficus virens

plant towards HCl and H2SO4 on corrosion of Al using mass loss and

thermodynamic methods. It was found that the Ficus virens extract provides a good

protection against pitting corrosion in chloride ion containing solution. Vipin

Kumpawat [170] tested the inhibitive action of the ethanol extract of different parts

of the Artocarpus heterophyllus and Acacia senegal plants towards HCl and H2SO4

corrosion of aluminium using mass loss and thermometric measurements. The

values of the inhibition efficiency obtained by the two methods were in good

agreement. Rajkiran Chauhan et al. [171] analysed the inhibition of corrosion of Al

in HCl and H2SO4 solution by methanol extract of Citrullus colocynthis plant using

63

mass loss and thermometric measurements. The inhibition action depended on the

concentration of acid and inhibitor. Nnanna et al. [172] investigated the inhibitive

effect of Newbouldia leavis leaves extract on the corrosion of Al in 0.2-1.0M HCl

and 0.1-1.0M H2SO4 solutions by the gravimetric analysis. The experimental data

complied with the Langmuir adsorption isotherm. The value and sign of the Gibb’s

free energy of adsorption obtained suggested that inhibitor molecules adsorbed on

Al surface through a physical adsorption mechanism.

2.1.3.3. Natural products as corrosion inhibitors in hydrochloric acid, sulphuric

acid and phosphoric acid media

Chandrasekaran et al. [173] reported that inhibition effect of Adhatoda

vasika Alkaloids (AVA) on corrosion of aluminium in hydrochloric acid, sulphuric

acid and phosphoric acid solutions. The mass loss technique was employed at 303-

333K. The values of activation energy (Ea) and free energy of adsorption (Gads) were

also calculated.

2.1.3.4. Natural products as corrosion inhibitors in hydrochloric acid and nitric

acid media

Avwiri and Igho [174] reported the action of Vernonia amygdalida on 2S and

3RS alloys aluminium in the HNO3 and HCl corrosion using the weight loss method.

The result further showed the highest inhibition efficiency of 49.5% for the 0.1M

HCl.

Popoola et al. [175] assessed the corrosion inhibition of aluminium alloy

(99.01%) in 2M HCl and HNO3 by Arachis hypogeae natural oil using gravimetric

and potentiodynamic polarisation techniques at 25ºC. The methods for the corrosion

assessment of the aluminium were in good agreement and mixed-type corrosion

existed which obeyed Langmuir adsorption isotherms.

2.1.3.5. Natural products as corrosion inhibitors in hydrochloric acid and

phosphoric acid media

Abdulwahab et al. [176] assessed the Ricinus communis as corrosion

inhibitor for aluminium alloy in 2M HCl and H3PO4 acid solution using gravimetric

and potentiodynamic polarisation techniques at 298K. The %IE from the

64

potentiodynamic polarisation method in both conditions was significantly enhanced.

A mixed-type corrosion existed which obeyed Langmuir adsorption isotherm.

Xianghong Li and Shuduan Deng [177] reported the inhibition effect of

Dendrocalamus brandisii leaves extract (DBLE) on the corrosion of aluminium in

HCl and H3PO4 solutions by weight loss, potentiodynamic polarisation,

electrochemical impedance spectroscopy (EIS) and scanning electron microscopy

(SEM) methods. The adsorption of DBLE on aluminium surface obeyed Langmuir

isotherm in both acids. DBLE acted as a cathodic inhibitor in HCl, while a mixed –

type inhibitor in H3PO4.

2.1.3.6. Natural products as corrosion inhibitors in hydrochloric acid and

potassium hydroxide media

Rehan [178] tested the water extracts from leaves of Phoenix dactylifera,

Lawsonia inermis and Zea mays as corrosion inhibitors for steel, Al, Cu and Brass in

HCl and KOH solutions using weight loss, solution analysis and potential

measurements. The inhibition efficiency increased with increase in the concentration

of the extract. The inhibition was interpreted in terms of chemisorptions of some

active ingredients in the leaves according to Temkin isotherm. Oguzie et al. [179]

evaluated the inhibiting effect of Ocimum basilicum extract on Al corrosion in 2M

KOH and 2M HCl solutions at 30 and 60ºC. Inhibition efficiency increased with

increase in extract concentration and decreased with rise in temperature. Arora et al.

[180] evaluated the inhibition efficiency of ethanol extract of different parts of

Capparis decidua in acidic medium using mass loss and thermometric method.

Values of inhibition efficiency obtained from the two methods were in good

agreement. The effectiveness of Gongronema latifolium extract as an

environmentally friendly corrosion inhibitor for aluminium in strong acid (2M HCl)

and alkaline (2M KOH) environments was assessed by Oguzie et al. [181].

Corrosion rates were determined using the gas-volumetric technique. Inhibition

efficiency generally increased with concentration up to maximum values of 97.54

and 90.82% in 2M HCl and 2M KOH, respectively. Temperature dependence

studies revealed that the extract chemically adsorbed on the aluminium surface at all

concentrations in 2M HCl and physically adsorbed in 2M KOH and chemisorbed at

65

higher concentration. Oguzie [182] reported the inhibitive action of leaves extract of

Sansevieria trifasciata on Al corrosion in 2M KOH and 2M HCl by using the

gasometrical method. Synergistic effect increased the efficiency in the presence of

halide additives. The adsorption characteristic of the inhibitor obeyed Freundlich

isotherm.

2.1.3.7. Natural products as corrosion inhibitors in saline, acidic and alkaline

media

Al-Sehaibani [183] assessed the water extract of Lawsonia inermis leaves

powder as corrosion inhibitor for steel and commercial Al in saline, acidic and

alkaline water. It was believed that the inhibition process occured predominantly via

chemisorptions of the active species in the Henna extract.

2.1.3.8. Natural products as corrsiopn inhibitors in saline, acetic acid and

sulphuric acid media

Nuhu Ali Ademoh [184] investigated the inhibitive action of watermelon

seed oil on aluminium in saline, 1M acetic acid and sulphuric acid by weight loss

measurements. The oil was more inhibitive in acetic than sulphuric acid.

2.1.3.9. Natural products as corrosion inhibitors in ethanol and

dichloromethane media

Wan Nik et al. [185] investigated the anti-corrosive activities of Marine

extract from ethanol and dichloromethane using weight loss, potentiodynamic

polarisation and electrochemical impedance spectroscopy. This extract was believed

to form a surface layer and protects AA 5083 from reacting with the environment.

2.1.3.10. Natural products as corrostion inhibitors in ethanol, distilled water

and hydrochloric acid media

Alinnoor and Ukiwe [186] assessed the corrosion inhibition of aluminium

using different extracts of Vernonia amygdalina using gravimetric method. The

inhibition efficiency increased as concentrations of extracts increased. The inhibitior

efficiency of extract was in order: C2H5OH > distilled H2O > 1M HCl at 303K and

C2H5OH > 1M HCl > distilled water at 333K.

66

2.1.3.11. Natural products as corrosion inhibitors in sulphuric acid medium

Gas chromatography mass spectrophotometer (GCMS) analysis of Ficus

tricopoda gum in the presence of 4.75, 56.15, 32.10 and 7.00 % camphene, sucrose,

2- methylene cholestan-3-ol and 7-hexadecenal were studied by Eddy et al. [187].

Several stretching and bending vibrations were observed in the Fourier transformed

infra-red (FTIR) spectrum of the gum. The gum was found as a good adsorption

inhibitor for the corrosion of aluminium in solution of H2SO4. The adsorption of the

gum (which, followed first order kinetic) was found as endothermic at gum critical

concentration of 0.3 g/L and exothermic at concentrations above the critical limit.

The Langmuir adsorption model in describing the existent of interaction between the

molecules of the gum was complemented by the Frumkin and Dubinin-

Radushkevich adsorption models. Calculated values of activation and free energies

of activation indicated that the adsorption of Ficus tricopoda gum on Al surface was

exhibited by both physical and chemical adsorption mechanism. Sudesh Kumar and

Suraj Prakash Mathur [188] studied the corrosion inhibition of aluminium in

sulphuric acid solution in the presence of different parts of Calotropis namely,

leaves, latex and fruits using weight loss method and thermometric method. The

ethanolic extracts of Calotropis procera and Calotropis gigantea acted as inhibitors

in the acid environment. The inhibition efficiency increased with increase in

inhibitors concentration.

2.1.3.12. Natural products as corrosion inhibitors in hydrochloric acid medium

Srivastav and Srivastava [189] evaluated the various parts of plants for their

performance in the protection of steel and aluminium against corrosion under

immersed conditions. Tobacco, lignin and black pepper were effective inhibitors for

Al in acidic medium. El-Etre [190] investigated the inhibitive action of the mucilage

extracted from the modified stems of prickly pears, toward 2M HCl corrosion of

aluminium, by weight loss, thermometric, hydrogen evolution and polarisation

techniques. The inhibition action of the extract was discussed in view of Langmuir

adsorption isotherm. Tripti Jain et al. [191] tested the mass loss and thermometric

methods on Al corrosion in HCl solution by extract of different part of Ficus

67

religeosa. Values of inhibition efficiencies obtained by the two methods were in

good agreement.

Umoren et al. [192] studied the anti-corrosive effect of Pacylobus edulis

exudates gum in combination with halide ions (Cl-, Br

- and I

-) for Al corrosion in

HCl at temperature range of 30-60ºC using weight loss method. The halide ions were

in the order: I-

> Br-

> Cl-. Pachylobus edulis exudates gum obeyed Temkin

adsorption isotherm. Umoren et al. [193] found the inhibitive effect of exudates gum

from Dacroydes edulis in the corrosion of aluminium in HCl solution using weight

loss and thermometric methods at 30-60ºC. The inhibition efficiency increased with

an increase in the concentration of the exudates gum but decreased with increase in

temperature.

Umoren et al. [194] investigated the effect of exudates gums from

Pachylobus edulis (PE) and Raphia hookeri (RH) as corrosion inhibitors for

aluminium in HCl by weight loss and thermometric measurements at 30-60ºC. Both

inhibitors obeyed Temkin adsorption isotherm. Exudates gum from RH was a better

inhibitor than PE. Arab et al. [195] analysed the synergistic action caused by iodide

ion on the corrosion inhibition of Al in 0.5M HCl in the presence of Azadirachta

indica (AZI) plant extract by potentiodynamic polarisation and impedance

techniques. The inhibition efficiency increased with increase in AZI extract

concentration. Gupta and Jinendra Singh [196] studied the natural products such as

Bixin, Zenthoxlum almauta, Echitamine and Nyctanthin on Cu, Al and Mild-Steel in

0.5N HCl solution at 30 to 40ºC by weight loss measurements. Natural products

protected metals from the corrosion with great efficiency. James [197] reported the

inhibition efficiency of acetone extract of red onion skin on Al in HCl solution by

weight loss measurements. The inhibition efficiency was depended upon the

concentration of inhibitor and temperature. Obot and Obi-Egbedi [198] assessed the

inhibitive action of the ginseng root on Al corrosion in HCl solution using weight

loss method at 30-60ºC. Inhibition efficiency increased with increase in

concentration of the inhibitor but decreased with increase in temperature. The

adsorption of extract components onto the Al surface was a spontaneous process and

followed the Freundlich adsorption isotherm.

68

Umoren et al. [199] analysed the corrosion inhibition of aluminium in HCl

solution in the presence of exudates gum from Raphia hookeri at temperature range

of 30-60ºC using weight loss and thermometric analysis. The exudates gum obeyed

Temkin adsorption isotherm and kinetic-thermodynamic model at all the

concentrations and temperatures studied. Ating [200] determined the inhibition of Al

in HCl solution by the ethanol extract of the leaves of Ananas sativum using weight

loss and hydrogen evolution methods. Activation parameters such as activation

energies, activation enthalpy and activation entropy were evaluated from the effect

of temperature on the corrosion and inhibition process. Nair et al. [201] studied the

inhibitory property of the Piper nigrum Linn. seeds in HCl on Al alloy (AA1100) by

weight loss method. The inhibition efficiency increased with increase in inhibitor

concentration. Surface analysis was carried out by FT-IR to ascertain the anti-

corrosive property of the inhibitor.

Nnanna et al. [202] assessed the corrosion inhibition of Al alloy (AA3003) in

0.5M HCl by extracts of Euphorbia hirta and Dialum guineense using gravimetric

method at 30 and 60ºC. Adsorption of both plant extracts on the Al alloy was

obeyed the Langmuir adsorption isotherm. The phenomenon of physical adsorption

was proposed by the obtained thermodynamic parameters. Al-Turkustani et al. [203]

evaluated the inhibition efficiency of the corrosion by Aloe extract in absence and

the presence of iodide ions by mass loss, hydrogen evolution, polarisation and

impedance techniques. The addition of iodide ion enhanced the inhibition efficiency.

It was found that Aloe plant acted as mixed type inhibitor.

Obot et al. [204] tested the extract of Ipomoea invulcrata (IP) as corrosion

inhibitor for aluminium in 1M HCl at 30-60ºC using the conventional weight loss

method. The enhancement of inhibition efficiency of IP with the addition of KI and

KSCN was also studied. The adsorption of IP was in accord with the Langmuir

adsorption isotherm. The mechanism of physical adsorption was proposed.

Adeyemi and Olubomehin [205] evaluated the inhibitive effect of water

extract of the bark of Anthocleista djalonensis (WEAD) on acid corrosion of Al using

the gravimetric method. The inhibition efficiency increased with concentration and

decreased with immersion time. Abiola and Tobun [206] analysed the ability of Cocos

69

nucifera L. water (CW) as non-toxic corrosion inhibitor for Al in 0.5 mol. L HCl,

using chemical method. The inhibitive action was attributed to the adsorption of the

inhibitor molecules on metal surface followed by Langmuir adsorption isotherm. Obot

and Obi-Egbedi [207] studied the leaves extract of Chromolaena odorata L. as green

inhibitor for aluminium in 2M HCl using gasometrical and thermometric methods at

30 and 60ºC. The adsorption of Chromolaena odorata L on Al surface was in accord

with Langmuir adsorption isotherm.

LI Xiang-hong et al. [208] tested the Bambusa subaequalis leaves extract as

an environmentally-friendly inhibitor. The inhibition effect of the leaves extract on

the corrosion of cold rolled steel and pure Al in 1.0 mol/L HCl using weight loss and

potentiodynamic polarisation methods. For Al, the plant inhibitor had a moderate

inhibitive performance.

Obot et al. [209] studied the corrosion inhibitive effect of Aningeria robusta

extract for Al in 2M HCl solution and the influence of potassium iodide additives

using hydrogen evolution method at 30 and 60°C. The mechanism of chemical

adsorption was proposed for the plant extract and physical adsorption for the extract-

iodide mixture.

Nnanna et al. [210] studied the effect of Euphorbia hirta leaves extract on the

corrosion of Al in 0.5M HCl using gravimetric measurements. The value and sign of

the Gibb’s free energy of adsorption suggested that inhibitor molecules

spontaneously adsorbed onto the Al surface through a physical adsorption

mechanism. Rajendran [211] evaluated the isolation, characterisation,

pharmacological and corrosion inhibition studies of flavonoids obtained from

Nerium oleander and Tecoma stans. It was found that the percentage of inhibition

increased with increase in volume/concentration of the extracts.

Ajayi et al. [212] reported the deterioration behaviour of Al alloy in 2M HCl

solution in the presence of Chromolaena odorata extract using gasometrical method.

The outcome revealed that corrosion rate was obtained at optimum inhibitor

concentration of 0.16M. Reduction in the corrosion rate was observed with increase

in extract concentration.

70

Anozie et al. [213] assessed the inhibitive effect of leaves extracts of

Euphorbia hirta and Dialum guineense on aluminium alloy (AA8011) in 0.5M HCl

solution using gravimetric technique at 30 and 60ºC. Adsorption of both leaves

extracts on the aluminium alloy obeyed the Langmuir adsorption isotherm. The

phenomenon of physical adsorption was proposed from the obtained thermodynamic

parameters. Nnaji Nnaemeka [214] evaluated the corrosion inhibition of aluminium

in HCl by leaves extract of Anthocleista djalonensis at 30-60˚C using weight loss

and thermometric methods. Temperature studies revealed the decreased in inhibition

efficiency with rise in temperature. The adsorption of the leaves extract of

Anthocleista djalonensis on aluminium in HCl solution obeyed the Langmuir,

Temkin, Freundlich and El-Awady adsorption isotherms.

Aboila et al. [215] assessed the inhibitive effect of Gossipium hirsutum L.

leaves extract on Al in 1M HCl solution by weight loss method. The inhibition

efficiency increased with increase in concentration of the extract at 30°C. LIU Jian-

xiang et al. [216] investigated the inhibition effect of the solid extract from the

leaves extract of Neosinocalamus affinis on the corrosion of Al in 1.0 mol/L HCl by

weight loss method. The results showed that the extract acted as a good inhibitor in

HCl for Al.

DENG shu-duan 1 et al. [217] studied the inhibition effects of leaves extracts

of Neosinocalamus affinis, Acer buergerianum and Machilus yunnanensis on the

corrosion of Al in HCl solution by mass loss and potentiodynamic polarisation

methods. Inhibition efficiency value increased with the increase in inhibitor

concentration while decreased with the increase in immersion time, temperature and

acid concentration. Polarisation curves revealed that three leaves extracts behaved as

mixed-type inhibitors.

LIU Jian-xiang [218] studied the corrosion inhibition effect of

Dendrocalamus latiflorus munro leaves extract on Al in HCl solution by weight loss

method. Dendrocalamus latiflorus munro leaves extract was a good corrosion

inhibitor to Al in HCl solution and it was considered as an excellent environmental-

friendly plant inhibitor.

71

Dubey et al. [219] evaluated the extract of different parts of plant like seeds,

leaves, stem were used as inhibitors for Al in HCl medium by naturally occurring

Withania somnifera (Ashwagandha) extract. Leaves extract was found more

effective as corrosion inhibitor at lower temperature and showed maximum

corrosion inhibition efficiency. Wan Nik [220] tested the corrosion behaviour of Al

alloy by Lawsonia inermis using weight loss method, Fourier Transform infrared

(FT-IR), electrochemical impedance spectroscopy and potentiodynamic polarisation

studies. The value for charge transfer resistance (Rct) decreased as a result of

increased in the degree of protection of AA 5083. Rajendran and Karthikeyan

[221] tried the Cassia auriculata flowers extract as a corrosion inhibitor on

aluminium and mild steel in 2M HCl at 30±1ºC by weight loss, potentiodynamic

polarisation and impedance methods. It was ascertained that the percentage of

inhibition increased with the increase in concentration of the extracts but decreased

with an increase in temperature.

Ajayi et al. [222] examined the deterioration of aluminium alloy in 2.5M

hydrochloric acid in the presence Rauvolfia vormitoria extract using gasometric and

gravimetric methods. The results showed that extract quantity increased, weight

loss measurements also increased but inhibition efficiency decreased. Also, the

metal surface-phytoconstituent interaction mechanism was consistent with the

Temkin adsorption isotherm.

Alinnor and Ejikeme [223] tested using plant extract of Ocimum

gratissimum leaves to prevent corrosion of aluminium in acidic medium by

gravimetric method. The inhibition efficiency of different extracts of 1M HCl,

ethanol and distilled water was determined.

Oluseyi et al. [224] tested the corrosion inhibition effect of Vernonia

amygdalina extract on aluminium in 0.5M HCl solution using gravimetric method at

40ºC temperature. The corrosion inhibition efficiency of the extract increased with

incease in concentrations in the corrosion medium. The surface coverage of the

extract obeyed Langmuir adsorption isotherm. Hence, the corrosion inhibition effect

of the extract was rationalised via adsorption mechanism.

72

. Ali and Foaud [225] reported the inhibition of Al corrosion in 2M HCl

solution using Morus nigra L. extract by weight loss, electrochemical polarisation

technique and hydrogen evolution measurements. The inhibition efficiency

increased as the extract concentration increased and decreased with increase in the

temperature. Moreover, the thermodynamic parameters of the adsorption process

were also calculated. It was found that the extract provided a good protection to Al

against pitting corrosion in chloride ion containing solutions.

Ituen and Udo [226] studied the inhibitive property of aqueous stem and

leaf extracts of Costus afer in hydrochloric acid on aluminium corrosion using

weight loss and hydrogen evolution methods. Results indicated that the stem extract

contained alkaloids, flavonoids, phenols, tannins, anthraquinones, glycosides, and

terpenoids whereas saponins, flavonoids, tannins, glycosides and phlobatannins was

detected in the leaf extract. Values of corrosion inhibition efficiency obtained from

hydrogen evolution method ranged from 58.93 - 49.43 % and 65.43 - 51.28 % at 303

- 333K for LE and SE respectively. From weight loss measurements, the values

ranged from 56.21 to 46.71 % and 61.14 to 50.19 % for leaves extract and seed

extract respectively at 303–333K. The extracts of C. afer inhibited the corrosion

process via physical adsorption mechanism and the adsorption process was best

approximated by the Freundlich adsorption model. Arrhenius and transition state

plot afforded kinetic and thermodynamic parameters like activation energy, enthalpy

change, entropy change and change in free energy of adsorption. The higher

corrosion inhibition efficiency of the stem was rationalised in terms of its many

phytochemical constituents which were rich sources of some heteroatoms like

oxygen and nitrogen, usually implicated in corrosion inhibition. Babatunde et al.

[227] assessed the inhibitive effect of leaves extract of Irvingia gabonensis on the

corrosion of aluminium in 1 M HCl solution using chemical method at 30, 35 and

40ºC respectively. The inhibition efficiency for the extract increased with increase in

concentration of the extract and decreased with increase in temperature. The

phenomenon of physical adsorption was proposed on the basis of thermodynamic

parameters that govern the inhibition process.

Shashi Sharma et al. [228] assessed the effect of some ion-additives on the

inhibitive effect of extract of Trigonella foenum graceums seeds (TfgS) on acid

73

corrosion of aluminium alloy (AA6063). An optimum concentration (1.056 g/L) of

the inhibitor was used for the 0.05 g/L of various ion-additives (halide and Zn2+

ions) in 0.5 N HCl at room temperature employing weight loss method. The

inhibition efficiency increased synergistically on adding the additives.

Umoren et al. [229] studied the corrosion inhibition of aluminium in 1M HCl

by Coconut coir dust extract (CCDE) using weight loss and hydrogen evolution

methods at 30 and 60ºC. Inhibition mechanism was deduced from the temperature

dependence of the inhibition efficiency and was further corroborated by the values

of activation parameters obtained from the experimental data.

Alka Sharma [230] assessed the inhibition of acid corrosion of aluminium

alloy (AA6063) using ethanolic extract of Ocimum tenuiflorum syn. Ocimum

sanctum Linn. leaves by chemical and electrochemical methods. Kinetic and

adsorption parameters were evaluated. The results showed that the extract could

serve as an effective corrosion inhibitor for AA6063 in 0.5 N HCl. The inhibition

mechanism was predicted on the basis of adsorption parameters and was

physisorbed on the metal surface. The experimental data were fitted in to the El-

Awady thermodynamic – kinetic model. The protective film formed on the metal

surface was analysed by FT-IR spectroscopy.

Mohd Zaidi Mat Satar et al. [231] studied the effectiveness of Nypa fruticans

extract solution to inhibit corrosion of Al in HCl medium using weight loss method.

The inhibition action of the extracts was discussed in view of Langmuir adsorption.

The results obtained proved that extract solution from each part of Nipah palm could

serve as effective inhibitor for Al in HCl media.

Jasna Halambek and Katarina Berković [232] investigated the inhibition

effect of Anethum graveolens L. essential oil on the corrosion of aluminium in 1 M

hydrochloric acid solution by weight loss, potentiodynamic polarisation, and

electrochemical impedance spectroscopy (EIS) methods. The Nyquist plots showed

that on increased inhibitor concentration, the charge transfer resistance also

increased. It also confirmed the adsorption process mechanism. Values of inhibition

efficiency obtained from weight loss and electrochemical measurements were in

good agreement. Ezeokonkwo et al. [233] investigated the exudates of Eucalyptus

74

citriodora as corrosion inhibitor of aluminium and mild steel using the weight loss

method in various concentrations of hydrochloric acid solution. The equilibrium

constants of the adsorption processes predicted better corrosion inhibition of

aluminium than mild steel. Phenomenon of physical adsorption was proposed for the

inhibitor and the process followed the Temkin adsorption isotherm. Ejikeme et al.

[234] examined the inhibitive effect of Treculia Africana leaves extract (TALE) in

the corrosion of aluminium in HCl solution using weight loss and thermometric

methods at 30-60ºC. Inhibition efficiency increased with increase in TALE

concentration, but decreased with increase in temperature. TALE interaction with

the metal surface obeyed Freundlich and El-Awady adsorption isotherms.

Omotosho and Ajayi [235] studied the acid failure of Al alloy in 2M HCl

solution in the presence of Vernonia amygdalina extract using gasometrical

technique. The analysis revealed the maximum inhibition efficiency which

corresponds to the lowest corrosion rate at optimum inhibitor concentration.

Ihebrodike Maurice Mejeha et al. [236] investigated the adsorption of Aspilia

africana extract and subsequent corrosion inhibition of Al alloy AA3003 in HCl

solution using gravimetric and electrochemical techniques. Quantum chemical

computations and molecular dynamics simulations described the individual

contributions and also observed their inhibiting effect. Nutan Kumpawat et al. [237]

studied the corrosion inhibition efficiencies of Holy basil on Al in HCl solution by

weight loss and thermometric methods in the presence and in the absence of stem

extract of three different varieties of Holy basil viz. Ocimum basilicum (EB),

Ocimum canum (EC) and Ocimum sanctum (ES). Maximum inhibition efficiency

was found to be 97.09% in 0.5N HCl solution with 0.6% stem extract. The

Langmuir adsorption isotherm indicated that surface coverage also increased with

increase in the concentration of extract of stem in HCl solution.

Fares et al. [238] tested the use of promising green eco-friendly pectin

natural polymer as successful corrosion inhibitor on the surface of Al metal in 2M

hydrochloric acid medium. The adsorption process was more favoured at lower

temperatures with larger negative standard free energy. Adsorption of pectin

macromolecules on Al surface demonstrated proper Langmuir isotherm. Fares et al.

[239] studied the iota- carrageenan, a natural polymer as a corrosion inhibitor of

75

aluminium in presence of pefloxacin mesylate acted as zwitter ionic mediator in HCl

medium. Adsorption isotherms in the absence or the presence of pefloxacin

mediator appropriately fitted in the Langmuir isotherms. Activation energy of

corrosion and other thermodynamic parameters such a standard free energy,

standard enthalpy and standard entropy of the adsorption process revealed better and

well-ordered physical adsorption layers in presence of pefloxacin.

Shudhan Deng and Xianghong Li [240] analysed the inhibition effect of

Jasminum nudiflorum Lindl. leaves extract (JNLLE) on the corrosion of aluminium

in HCl solution by weight loss, potentiodynamic polarisation, electrochemical

impedance spectroscopy (EIS) and scanning electron microscopy (SEM) methods.

Polarisation curves revealed that JNLLE acted as the cathodic inhibitor. EIS

exhibited a large capacitive loop at high frequencies followed by a large inductive

one at low frequency values.

Gayathri et al. [241] studied the anti-corrosive property of Garcinia

mangostana on Al (1100). The study was designed to screen the inhibition efficiency

of inhibitor at various concentrations at pH 1. Abdulwahab et al. [242] found the

corrosion inhibition of aqueous extract of bitter leaf on Al alloy in 0.5M HCl

solution at various temperatures and concentrations using weight loss measurement.

The inhibitive action was satisfactorily explained by both thermodynamic and

kinetic models. Manish Kumar Sharma et al. [243] assessed the plant extract of

Solanum surrattence in acetone, petroleum ether and methanol using mass loss and

thermometric measurements for corrosion of aluminium in acid solution. The

inhibitors showed efficiency at 25ºC. At higher temperature the inhibition efficiency

decreased. Soror [244] assessed the inhibitive effect of aqueous extract of Saffron

leaves toward the corrosion of aluminium in 2M HCl solution by weight loss and

electrochemical polarisation study. The extract functioned as a good inhibitor. The

plant extract behaved as cathodic–type inhibitor. Surface morphology was analysed

using SEM. The adsorption followed Temkin adsorption isotherm. Paul Ocheje

Ameh and Nnabuk Okon Eddy [245] studied the effect of Commiphora pedunculata

(CP) gum on the inhibition of the corrosion of aluminium alloy (AA 3001) in the

solution of HCl using gravimetric and thermometric methods to monitoring

corrosion. The adsorption of CP gum on the surface of aluminium was endothermic,

76

spontaneous and supported the mechanism of physical adsorption. The Langmuir

adsorption model was used to describe the adsorption characteristics of CP gum on

aluminium surface.

Nnaji et al. [246] tested that the red onion skin tannin (ROST) was an

effective corrosion inhibitor of aluminium in hydrochloric acid solutions using

gravimetric, thermometric, and UV/visible spectrophotometric techniques. ROST

adsorption on aluminium followed Langmuir isotherm in 0.1M and Fruendlich

isotherm in 0.5M HCl and 2.0M HCl at 303 Kelvin. Physical adsorption

(physisorption) of ROST on aluminium was proposed.

Ladha et al. [247] investigated the inhibitive effect of cumin (Cuminum

Cyminum) extract as corrosion inhibitor for pure aluminium in 1N HCl using

weight loss, galvanostatic polarisation and electrochemical impedance spectroscopy

(EIS) techniques. The results revealed that the inhibition efficiency increased with

increase in concentration of inhibitors but decreased with increase in temperature.

The value of apparent activation energy showed that the cumin extract acted as a

good inhibitor for pure aluminium in acid medium. Thermodynamic consideration

showed that adsorption of cumin extract followed Langmuir Adsorption isotherm.

The galvanostatic polarisation measurement indicated that the inhibitor was of

mixed type. Electrochemical impedance study results were in good agreement with

weight loss and galvanostatic polarisation studies.

Swati Yadav et al. [248] studied the corrosion behaviour of aluminium and

copper exposed to HCl solution and their corrosion inhibition in HCl containing

0.0644-1.288 g/L of Ziziphus mauritiana fruit extract as inhibitor at room

temperature using weight loss method. Corrosion rate decreased in the presence of

inhibitor compared to the free acid solution. The inhibitor obeyed Langmuir

adsorption isotherm for both the metals. Ziziphus mauritiana was a better corrosion

inhibitor for copper than aluminium. Surface analysis (FT-IR) was also carried out

to establish the mechanism of corrosion inhibition on aluminium and copper

corrosion in hydrochloric acid medium.

Jasna Halambek et al. [249] studied the ethanol solution of Ocimum

basilicum L. oil as corrosion inhibitor for aluminium in 0.5M HCl. Its inhibition

77

effect was performed using weight loss measurements, potentiodynamic

polarisation and EIS methods. Potentiodynamic polarisation measurements showed

the presence of basil oil in HCl solution influenced on current densities. EIS results

confirmed the investigated compound contained protective layer on aluminium

surface. Thermodynamic adsorption parameters showed that compounds present in

Basil oil adsorbed on aluminium surface by an exothermic process, indicate that the

adsorption mechanism was physisorption, with the adsorptive layer favouring

electrostatic character.

Petchiammal and Selvaraj [250] investigated the inhibition and adsorption

properties of alcoholic extract of Albizia lebbeck seed on aluminum in 1N

hydrochloric acid by mass loss measurement with various periods of contact and

temperature ranging from 303-333K. The observed result revealed that the

percentage inhibition efficiency enhanced with increase of inhibitor concentration

and decreased with rise in period of contact. The thermodynamic parameters viz.

heat of adsorption (Qads), energy of activation (Ea) and Gibbs free energy (∆Gads) of

adsorption values suggested that the adsorption process was exothermic and

spontaneous. The inhibitor obeyed Langmuir adsorption isotherm. The protective

film formed on the metal surface was confirmed by spectral studies namely UV, FT-

IR, EDX.

2.2. Scope of the present study

Aluminium and its alloys are used in automobiles, food-handling containers,

electronic devices, building, aviation and marine appliances [251-253]. These

frequently come in contact with hydrochloric acid solution during cleaning of scales,

acid pickling of metals, descaling, acidizing of oil wells, chemical and

electrochemical etching etc. Hydrochloric acid solutions are used for pickling of

aluminium and its alloys. It is necessary to add corrosion inhibitors to prevent metal

dissolution and to minimise acid consumption [254]. Hence studying their corrosion

behaviour in acid medium is of prime importance. Corrosion inhibitors are chemical

compounds added to the corrosive medium to reduce the rate of acidic attack on

metal and its alloys. The toxicity of organic and inorganic corrosion inhibitors to the

environment has prompted the search for safer corrosion inhibitors such as green

78

corrosion inhibitors which are more environmental friendly corrosion inhibitors. The

use of plant inhibitors is one of the most practical methods for protection against

metallic corrosion, especially in acid media.

Investigations of corrosion inhibiting abilities of tannins, alkaloids, organic,

amino acids and organic dyes of plant origin are of great interest. In addition to

being environmentally friendly and ecologically acceptable, plant products are

inexpensive, readily available and renewable sources of materials. The plant extracts

adsorb on the metal surface forming a barrier between the metal and the corrosive

environment. Some structural features of the plant extracts help them to do so. These

include the presence of oxygen, nitrogen or sulphur atoms and also the presence of

double bonds and aromatic ring. The lone pair of electrons in atoms facilitates the

adsorption process. The search for new, eco-friendly and efficient corrosion

inhibitors becomes necessary to secure the metal against corrosion. It is clear from

the literature survey that only a few numbers of investigators have worked on the

influence of leaves extracts on the corrosion behaviour of commercial Al.

In the present work, an attempt has been made to study the inhibitive action

of five different leaves extracts such as Rhinacanthus nasutus (Nagamalli),

Calotropis procera (Milk weed), Morinda citrifolia L (Noni), Cassia auriculata

(Tanners Senna) and Delonix elata (White gul mohur) in 1 M HCl solutions at four

different temperatures (303-333±0.5K). It is proposed to study the inhibition effect

at five different leaves extracts by weight loss method, hydrogen evolution method,

potentiodynamic polarisation method and electrochemical impedance spectroscopy

method. Surface analytical techniques such as FT-IR and metallurgical microscope

are be used to study the surface adsorbtion.

2.3. Objectives

Following are the objectives of the proposed research work:

• To study the corrosion behaviour of Al in the presence of the leaves extracts

as corrosion inhibitors and to select efficient inhibitors for commercial

applications.

• To evaluate the inhibiting effect of leaves extracts of each plant in 1M HCl

on aluminium using weight loss method, hydrogen evolution method,

79

potentiodynamic polarisation measurements and AC impedance

spectroscopy

techniques.

• To find the effects of concentration of the inhibitors, immersion period and

temperature on inhibition efficiency.

• To test the fitting of data in various adsorption isotherms.

• To calculate kinetic and thermodynamic adsorption parameters.

• To calculate kinetic and thermodynamic activation parameters

• To assess the inhibition efficiency using electrochemical techniques-

potentiodynamic polarisation method and impedance spectroscopy.

• To find out the pytochemical constituents present in the leaves extracts using

FT-IR.

• To analyse the surface morphology of aluminium in the absence and in the

presence of inhibitors in HCl medium.

• To propose a suitable explanation of inhibition action.

• To compare the performance of the inhibitors by chemical and

electrochemical techniques.

• To find the suitable storage condition for the extracts.

80

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