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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-
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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.
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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
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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.
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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.
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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.
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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
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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.
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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
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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
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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.
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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.
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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.
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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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