34

CHAPTER - II

REVIEW OF LITERATURE

Most of the industries require water for cooling purpose. The major

problems in the industrial use of cooling water systems are corrosion of the metal

equipment, contamination of the circulating water with microorganisms and scale

formation. Inhibition of corrosion and scaling can be done by the application of

inhibitors. It is noted that the effect of corrosion inhibitors is always caused by

change in the state of surface being protected due to adsorption or formation of

hardly soluble compounds with metal cations. Review including extensive listing of

various types of organic inhibitors has been published. The molecules most often

used as corrosion inhibitors are nitrogen, sulphur, oxygen and phosphorous

containing compounds [1-6]. These compounds get adsorbed onto the surface of

metal from the bulk of environment forming a film at the metal surface. The

inhibition efficiency increases in the order O < N < S < P [7].

The corrosion inhibition of metals in acidic media by different types of

organic compounds has been widely studied [8-13]. The inhibition action of organic

molecules is primarly due to their adsorption on the surface of the metal through the

presence of active centres.

II.1. Study of corrosion inhibition by phenols

Rodge et al [14] have evaluated the effects of phenol on the corrosion of

mild steel in various concentrations of nitricacid. The percent loss in weight was

found to increase linearly with increase in acid concentration. The trend observed in

IE values is in the order as p-cresol > m- cresol > 2- naphthol > phenol >

1-naphthol > 2-nitrophenol.

Viswanathan and Haldar [15] have reported the inhibitory action of methoxy

phenol (MPH) and nonyl phenol (NPH) on corrosion of N80 steel in 15 % HCl at

different period of exposure (6 to 24 h) and temperature (30 to 110º C). Both these

compounds inhibit corrosion by adsorption mechanism and follow Temkin isotherm.

35

Polarization studies indicate that the compounds are mixed type inhibitors. The

FTIR spectral analysis of the surface product suggests the involvement of hydroxyl

group of these inhibitor molecules in the adsorption process.

Kulkarni et al [16] have studied the inhibition by phenols on the corrosion of

mild steel in nitric acid, sulfuric acid and hydrochloric acid media. The observed

trend among the phenols in corrosion inhibition efficiency is p-cresol > m- cresol >

phenol > 2- naphthol > 1-naphthol > 2-nitrophenol. 2-Nitrophenol shows oxidizing

nature in all the acids over the range of concentrations used.

Prevention of the corrosion of brass and mild steel in cooling water systems

by inhibitors has been studied by Ravichandran et al [17,18]. Mannich base

derivatives namely 4-methyl-2-formyl-6-(piperidine-1-ylmethyl) phenol (MFPP)

and 4-methyl-2-formyl-6-(morpholine-1-ylmethyl) phenol (MFMP) exhibited good

inhibition efficiency towards corrosion of brass under varying experimental

conditions.

Viswanatham et al [19] have analysed the corrosion inhibition efficiencies of

ortho and para substituted phenol (phenol, o-cresol and p-cresol) as corrosion

inhibitors of N80 steel in 15 % HCl at different temperatures and exposure time

(6-24 h) at a fixed inhibitor concentration by weight loss method and potentiostatic

polarization method. The adsorption of all the three compounds on steel followed

Temkin adsorption isotherm. Potentiostatic polarization study revealed that all the

inhibitors mentioned above are mostly anodic type.

Benchekroun et al [20] have studied the inhibition of iron corrosion in 1M

HCl by 2-aminothiophenol (ATP) and 2-aminophenyldisulfide (APDS) by using

Electrochemical impedance spectroscopy (EIS). Results showed that these

compounds act by adsorption on the metal surface and cause an increase of the

polarization resistance and a decrease in double layer capacity. Change of

impedance diagrams with immersion time and inhibitor concentration revealed the

formation of a protective layer, which is more adherent and more resistive with

APDS than with ATP.

36

The corrosion inhibition characteristics of 2-aminothiophenol (ATP) and

2-cyanomethyl benzothiazole (CNMBT), on two types of steel in IM HCl at

different temperatures were studied by Abd El-Rehim et al [21]. The effects of the

inhibitors on the general corrosion were investigated by gravimetric and

galvanostatic polarization techniques. The inhibition efficiency of CNMBT is higher

than that of ATP.

The effect of some phenols (phenol, resorcinol and pyrogallol) on the

corrosion of Al, Cu and Al-Cu alloys in NaOH solutions was examined by

Shayeb et al [22] with potential time, polarization and weight loss measurements.

The addition of phenols decreased the extent of the corrosion of Al, Cu and Al-Cu

alloys, apart from Cu in pyrogallol, the inhibition efficiency in general increases

with increase in concentrations of the additives. The inhibition was explained on the

basis of adsorption of phenols on the electrode surface.

Bouayed et al [23] have made an experimental and theoretical study of

corrosion inhibition on metallic iron surfaces by organic molecules. The inhibition

efficiency of phenol, thiophenol and aniline have been compared through

gravimetric and electrochemical experiments.

Aluminium pigments are found to corrode with the evolution of hydrogen

when in contact with water- butyl glycol mixtures at pH 10. Muller [24] investigated

that the corrosion reaction can be inhibited by ortho-substituted phenol and

ortho-substituted aniline derivatives and showed that ortho-substituted aniline

derivatives are ineffective corrosion inhibitors. The measurements of the evolution

of hydrogen was used to study relative differences in behaviour between ortho

substituted phenol derivatives.

Rengamani et al [25] have studied the influence of amino phenols on the

corrosion and also hydrogen permeation of mild steel in 1M HCl and 0.5M H2SO4

using weight loss, gasometeric measurements and various electrochemical

techniques. All the isomers of aminophenol inhibit the corrosion of mild steel in

37

IM HCl and accerlate in 0.5 M H2SO4. Except PAP, all other aminophenols in

1M HCl, enhance the permeation current in both the acids.

Talati and Modi [26] have evaluated the inhibition of the corrosion of B26S

aluminium (Al-4 % Cu alloy) in a solution of NaOH by polyhydric phenols. The

inhibitive efficiency of phenol, resorcinol and phloroglucinol increases with

inhibitor concentration but decreases with increase in alkali concentration. At 1%

concentration in 0.1 M NaOH at 30ºC, the efficiency of the inhibitors increases in

the order: phloroglucinol (98.9 %) > pyrogallol > resorcinol > catechol >

hydroquinone > phenol (83.2 %)

The effect of aminophenols on the corrosion of M57S alumininum

(Al-2 % Mg alloy) in phosphoric acid was studied by Talati et al [27].

Talati and Modi have studied the substituted phenols as corrosion inhibitors

for B26S alumininum (Al-4 % Cu alloy) in solutions of sodium hydroxide by weight

loss and galvanostatic methods. At constant alkali concentration, the inhibitor

efficiency increases with the increase in the concentration of inhibitor except

hydroquinone but, for o-substituted phenols at constant concentration, the inhibition

efficiency decreases with increase in alkali concentration. The IE remains almost

constant in the range 20-50 ºC, and with time of immersion up to one hour [28-30].

Among the cresols, the better inhibitivity of p-cresols may be due to the absence of

steric hindrance. A rise in temperature increases the extent of corrosion. The

activation energies are slightly higher in inhibited rather than in uninhibited alkali.

Patel and Oza [31] have analysed the effect of some polyhydroxy derivatives

of benzene on corrosion of 70/30 brass in ammoniacal solutions. Corrosion of brass

in ammoniacal solution decreases with increase in the concentrations of the additives

such as resorcinol, hydroquinone, phloroglucinol, pyrogallol and pyrocatechol. This

reduction in corrosion rate may be attributed to the formation of continuous

protective chemisorbed layer of the additive on the corroding metallic surface.

Presence of more hydroxy groups in benzene ring may be responsible for providing

inhibition.

38

Desai and Thanki [32] reported that for inhibitor concentrations of ≤ 0.05M,

the best corrosion inhibition (95 %) of 60/40 brass in 0.2 N, 0.5 N and 1N NaOH at

35ºC for five days was provided by the m-substituted compounds such as resorcinol,

phloroglucinol and m-aminophenol. In 0.2 N NaOH, the corrosion inhibition

efficiency decreased in the order of β-naphthol > α-naphthol > 8-hydroxyquinoline >

phenol, while 8-hydroxyquinoline gave the best protection in 0.5N NaOH.

Angelis and Giorgio [33] have investigated the action of phenol,

pyrocatechol, resorcinol and hydroquinone on the corrosion of 99 % aluminium in

1N HCl. At 0.05-0.033M, phenol is the best inhibitor followed by pyrocatechol,

hydroquinone and resorcinol and concluded that the inhibiting action of phenol is

probably due to the adsorption. According to Myagkova and Putilova [34], phenol,

resorcinol and hydroquinone retard the corrosion of lead, both at room and at

elevated temperatures.

Kuestue et al [ 35] have investigated the effect of three Schiff base compounds

namely 2-{(E)-[(2-hydroxyethyl)imino]methyl}phenol(I), 2-{(E)-[(2-hydroxyethyl)

amino]ethyl}imino)methyl phenol (II) and 2, 21 – {iminobis [ethane-1,2-diylnitrilo

(E) methylylidene]}diphenol(III) at 298K by weight loss measurements,

potentiodynamic polarization and electrochemical impedance spectroscopy methods.

Results showed that compound III to be the best inhibitor with mean efficiency of

93 % at 10-2 M additive concentration.

The efficiency of steel corrosion inhibitiors in 0.1M and 1M H2SO4 of two

Schiff bases namely, 2-{[4-methoxy phenyl)imino] methyl}phenol and

1-{[(4-methoxy phenyl)imino methyl}-2naphthol, (SB-1 and SB-2) was studied by

Hasanov et al [36] using Tafel extrapolation and linear polarization methods. The

percent inhibition effiencies and surface coverage (ө) increases with an increase in

the concentration of inhibitors and these compounds act as good corrosion inhibitors

at higher concentrations.

The effect of 3 Schiff bases compounds namely (E)-2-(1-(2-(2-hydroxy ethyl

amino) ethylimino)ethyl)phenol(1), 2,21 - (1E,11E)-1,11 – (2,21-azanediyl bis

39

(ethane-2,1-diyl, bis (azan-1-yl-ylidene) bis(ethan-1-yl-1-ylidene)diphenol (II) and

2, 21- (2E,12E)-3,6,9,12-tetraazatetradeca -2,12-diene-2,13-diyl) diphenol (III) as

the corrosion inhibitors of steel in 2M HCl solution was studied by

Emreguaore et al [37] at 298K using weight loss measurements, potentiodynamic

polarization and electrochemical impedance spectroscopy methods. Results showed

compound III to be the best inhibitor with mean efficiency of 93 % at 10-2 M

additive concentration.

Aliev and Azerbaijan [38] analysed the inhibitory effect of calcium,

strontium and barium salts of carboxymethylaminomethylalkyl phenol in 2-phase

acid systems - 0.1N HCl / kerosene and 0.1N H2SO4/ kerosene. It has been

established that these compounds preserve their inhibiting properties in terms of

steel corrosion in 2-phase acid medium.

Hnini et al [39] have analysed the behaviour of methoxy-2-allyl-4-phenol

(MAP) at three forms (natural, polymerised and Chemically treated) on the

corrosion of stainless steel in phosphoric acid. The specimen was evaluated to

determine the change in the corrosion potential and resistance potential. These MAP

products have exhibited corrosion inhibition by maintaining a high resistance

potential (low corrosion rate) in each potential and results revealed that this

compound is an efficient inhibitor in all the forms, and the high inhibition efficiency

is obtained for polymerized form.

Ouchi et al [40] have analysed a corrosion inhibitor efficiently preventing

discolouration of Ag, Au, Ni, Fe, Al, Zn and alloys comprising ≥1 novel

polyoxyethylenealkylphenylether derivative and an acid. The corrosion inhibitor has

high endurance to the effect of alkali.

Protective properties of coatings were determined by Musaeva et al [41] in

crude oil, lubrication oil, sea water and acids of different concentrations by using the

bases of mixure of phenol-formaldehyde and epoxy dianoligomers modified with

terephthaldimide, bauxite sludge and acetone (solvent). It was found that developed

40

compositions protect metal against corrosion in sea water for 30 months and in

various corrosion media for two months.

The efficiency of 4-(2-pyridylazo-)-resorcinol (PAR) as corrosion inhibitor

for mild steel in H2SO4 was investigated by Dheer et al [42] using electrochemical

methods such as steady state galvanostatic and potentiostatic polarization

measurements. Potentiodynamic polarization was used to assess the ability of

hetrocyclic organic inhibitor/PAR to provide an effective barrier to corrosion in

acidic environments.

Jeyaraj and Sundaram [43] have investigated the corrosion of aluminium-

magnesium alloy by sodium hydroxide in aqueous and aqueous ethanol

(40 % vol / vol) medium by weight loss, steady state open circuit potential and

galvanostatic polarization measurements. The inhibitive effect of resorcinol is more

pronounced in the latter medium. The polarization measurements revealed that the

corrosion inhibition caused by resorcinol is of mixed nature.

The inhibitive action of corrosion of mild steel in 1N H2SO4 solutions by

resorcinol and pyrogallol was studied by Jha et al [44] and verified using

galvanostatic polarization and XPS measurements at 35 ºC. The electrochemical

results showed that these compounds predominate as anodic inhibitors and inhibition

efficiencies up to 81.66 % can be obtained. The inhibition was assumed to occur via

chemisorption of the additive molecules. XPS measurements revealed that resorcinol

was adsorbed on the specimen surface more strongly than pyrogallol.

Oxygen scavenging compositions for aqueous medium such as a boiler water

system was identified by Muccitelli and John [45] which consists of aqueous

solutions of hydroquinone-catalysed salicylaldehyde with neutralizing amine. A

typical composition can be salicylaldehyde 50-100 ppm, hydroquinone 10-20 ppm

and methoxypropylamine 5-10 ppm in water.

An O-scavenging and corrosion inhibiting agent for protecting metal surfaces

in fluids, a boiler water system studied by Schiessl and Henry [46] was obtained by

41

the reaction of hydroquinone and hydrazine in mole ratio > 0.75:1 to give the 1:1

product. Corrosion rates for mild steel, Cu, brass, admiralty metal and brass

coupons of 0.90, 0.009, 0.041, 0.021 and 0.051 mils/yr were found in boiler tests

with the compound fed to maintain a hydrazine concentration of 0.1ppm in the feed

water.

Ciuba and Stanley [47] have analysed that O is removed from boiler feed

water, boiler condensate steam systems by adding 0.2-3.5 ppm hydroquinone in a

hydrazine free aqueous solution. It has the advantage of being significantly less toxic

than hydrazine. For e.g. the oral LD50 for rat is 320 mg/kg for hydroquinone,

compared with 60 mg/kg for hydrazine.

Zhu et al [48] have investigated the corrosion resistance of stainless steels

(A1S1 316L, A1S1 304) and carbon steel in acidic waste water (pH=2.10, 30 ºC)

containing phenol using potentiostatic polarization curves and weight losses of

rotary specimens. The stainless steels have good corrosion resistance but carbon

steel (model 20) has not and it may be due to the formaldehyde in the acidic waste

water which may inhibit the corrosion of stainless steels.

Metsik and Turkson [49] have reported that the addition of 6 g/l of water

soluble shale phenols(I) consisting mostly of methyl-, dimethyl- and ethyl-

resorcinols gave 95.8 % corrosion protection to carbon steel specimens immersed in

0.01-1N HCl at 20 ºC.

Fouda et al [50] have studied the substituted phenols as corrosion inhibitors

for copper in nitric acid solution in the presence of resorcinol, o-, p- aminophenols,

catechol, o-cresol and salicylaldehyde using galvanostatic polarization and weight

loss methods. The inhibitors appear to function through general adsorption and are

due to the decomposition of HNO3 and its interference with the cathodic reaction.

According to Kim and Cho [51] the additions of dihydroxybenzenes as

corrosion inhibitors decrease the corrosion of Aluminium sheet in 0.1M-1M NaOH

solutions. The inhibitor efficiency of resorcinol [108-46-3]mchlt, catechol

42

[120-80-9] < hydroquinone [123-31-9] < (resorcinol + hydroquinone) at a

concentration of 0.005 wt % and catechol was in all cases approximately 100 % at

2 % inhibitor in 0.1M NaOH.

The influence of phenol [108-95-2], resorcinol [108-46-3], thiophenol

[108-98-5], thiobenzoicacid [98-91-9] and pyrogallol [87-66-1] on the corrosion of

copper in 0.02M NH4Cl solution was studied by Patel et al [52] and showed that

thiophenol and thiobenzoic acid were the most effective corrosion inhibitors, as

substitution by SH groups in the benzene ring was beneficial.

II.2. Zinc ions as corrosion inhibitor

Zinc ions have long been considered as valuable corrosion inhibitors for

carbon steel in aerated water because of the protection afforded by a cathodic

polarization mechanism [53,54]. However due to the problem of toxicity of Zn2+

ions, it is necessary to reduce the concentration of Zn2+ by introducing a synergist

which is environmentally friendly. Several organic inhibitors were evaluated as

excellent co-inhibitors with Zn2+ for carbon steel substrate.

Yang Zhang et al [55] have reported that iminodimethylene phosphonic acid

when used in combination with zinc and polyacrylate shows synergistic effect and

act as multifunctional inhibitor for cooling water.

Susai Rajendran et al [56] have reported the synergistic and antagonistic

effects existing among polyacrylamide, phenyl phosphonates and Zn2+ on the

inhibition of corrosion of mild steel in an aqueous neutral environment.

Meena et al [57, 58] have investigated the influence of Zn2+ on the corrosion

rate of carbon steel immersed in an aqueous environment containing 60 ppm of Cl-

and carboxymethyl cellulose (CMC). A synergistic effect is noticed between CMC

and Zn2+.

Rajendran et al have studied the role of Zn2+ in the inhibition of corrosion of

mild steel in neutral, aqueous environment, containing 60 ppm of Cl- by the

43

inhibitors-molybdates [59], HEDP[60], HEDP-molybdate [61]. Rajendran et al [62]

have reported that phenylphosphonate acts synergistically with low concentration of

Zn2+ in inhibiting the corrosion of mild steel in a neutral aqueous chloride

environment. However, at higher concentrations of Zn2+, a decrease in inhibition

efficiency is observed due to the formation of an insoluble Zn2+- PPA complex. The

presence of Zn2+ ions facilitates the transport of these inhibitors from the bulk to the

metal surface. Both cathodic and anodic reactions are controlled. Corrosion of iron-

based alloys in a circulating water is decreased by a synergistic inhibitor mixture

containing HEDP, hydroxyphosphonoacetic acid and sodium tolyltriazole[63].

2-Phosphonobutane-1, 2, 4-tricarboxylic acid (PBTCA) shows synergistic

effect with Zn2+ ions [64], Zn2+- HEDP combination [65] and MnCl2.4H2O [66].

When PBTCA is used along with Zn2+ in the corrosion inhibition of mild steel in tap

water, Zn(Ca)-PBTCA-Fe(III) - a sequestering film deposited on the surface of mild

steel inhibited corrosion effectively [64].

Venugopalan et al [67] have developed the inhibitor formulation consisting

of zinc ions, HEDP and an organic additive zinc gluconate for corrosion inhibition

of mild steel in neutral aqueous medium containing 60 ppm of Cl- ions. It is reported

that it acts as a mixed inhibitor. Complexes of HEDP with gluconate ions and

Zn(OH)2 were found on the metal surface.

Studies on ascorbate as second synergist along with Zn2+ and phosphonates

in the corrosion inhibition of carbon steel in low chloride environment were reported

by Apparao and Srinivas Rao [68].

Wrubl et al [69] have appraised the efficiency of Zn2+ - basic gluconate as a

corrosion inhibitor for mild steel in sodium chloride solution. According to them, the

inhibition is due to Zn2+ ions, Zn (C6H11O7)+ and (C6H11O7)- ion.

Manjula et al [70] have studied the corrosion behavior of carbon steel in

aqueous medium in the presence of N-cetyl-N, N, N-trimethylammonium bromide

(CTAB), Zn2+ and calcium gluconate.

44

According to Pech and Bartolo [71] the inhibitive effect of

N-phosphonomethylglycine-Zn2+ mixture on the corrosion of steel in neutral

medium is due to the retardation of anodic and cathodic process that resulted in the

formation of the film Fe- inhibitor complex and ZnO. Amino carboxylic acids and

their N-phosphonomethyl derivatives with or without the additives (Zn or

metavanadate ion) have been studied in neutral solution by Kalman et al [72].

Gunasekaran et al [73] have established the synergistic effect of tartrate with

organophosphonic acid and zinc metal ions in neutral environment on the corrosion

of steel.

Muthumani et al [74] have examined the inhibition efficiency of sodium

potassium tartrate in controlling the corrosion of carbon steel immersed in ground

water in the absence and presence of Zn2+. John Amal Raj et al [75,76] have

reported the synergistic effect of dihydroxydicarboxylic acid on the inhibition

efficiency of a phophonate-Zn2+ system in controlling the corrosion of carbon steel

in an aqueous environment containing Cl- ion.

Thangavelu et al [77] have evaluated the synergistic effect of citrate and Zn2+

on the corrosion of carbon in dilute salt solutions. Ruba Helen Florence et al [78]

have studied the corrosion inhibition of carbon steel in groundwater by adipic acid

and Zn2+ system.

Felicia Rajammal Selvarani et al [79] have reported the existence of

synergism between succinic acid and Zn2+ in controlling the corrosion of carbon

steel in well water.

Arichandran et al [80] have reported that the protective film formed on the

carbon steel immersed in well water containing citrate-Zn2+ system consists of iron –

citrate complex and Zn(OH)2.

The influence of the inhibitive system consisting of ATMP, oxalic acid or

phthalic anhydride and zinc sulphate on the rate of corrosion of steel in simulated

industrial water of variable chemical composition and in chlorinated water has been

45

studied by gravimetric method. This formulation is considered as a perspective

inhibitor for the corrosion protection of industrial cooling and heating water

installation [81].

Kubicki et al [82] have investigated the inhibitive property of amino

trimethylene phosphoric acid (ATMP) in preventing the corrosion of iron in neutral,

aqueous solution in combination with carboxylic acid and Zn2+ salts. Greatest

protective effectiveness was obtained for tricomponent composition containing

ATMP, phthalic acid or oxalic acid and Zn2+.

The existence of synergism between molybdate and Zn2+ ions has been

reported [83-86]. Corrosion inhibition efficiency of HEDP was synergistically

improved in the presence of Zn2+ ions [85, 87, 88]. The synergistic effect of Zn2+ and

HEDP in decreasing the corrosion rates of steel in seawater is observed. The

protective cathodic film on the steel consists of Mg2+ (predominant), P and Zn2+ [89]

ions.

Gonzales et al [90] have carried out electrochemical measurements and used

analytical techniques (XPS and reflection absorption spectroscopy) to investigate the

inhibition of corrosion of carbon steel by a mixture of zinc salt and phosphonic acid.

The formation of the homogeneous thin film on the surface of the metal was also

reported.

The synergistic effect of Zn2+ ion with DTPMP inhibitor has revealed by

Rai et al [91] and the corrosion inhibition efficiency was found to be 80 % after

24 hours.

Arockia Selvi et al [92] have found that a synergistic effect exists between

sodium potassium tartrate (SPT) and Zn2+ in controlling corrosion of carbon steel

immersed in rain water collected from roof top stored in a concrete tank. The

formulation consisting of 50 ppm of SPT and 25 ppm of Zn2+ offers 91 % corrosion

inhibition efficiency. Polarization study revealed that SPT-Zn2+ system behaves as a

mixed inhibitor.

46

Huo et al [93] have investigated the corrosion inhibition of carbon steel by

polyaspartic acid and also with zinc ions. The inhibition efficiency of polyaspartic

acid was excellent and the presence of zinc ions decreased the required dosage of

polyaspartic acid and the mixture was found to act as mixed corrosion inhibitor.

Rajendran et al [94,95] have identified an alternative to the chromate

containing corrosion inhibitors for mild steel in cooling water systems and evaluated

the synergistic effect of calcium gluconate (CG) and Zn2+ on the inhibition of

corrosion of mild steel in neutral aqueous environment containing 60 ppm of Cl- ion

by weight loss method and formulation consisting 50 ppm of Zn2+ and 200 ppm of

CG has 92 % inhibition efficiency and addition of 50 ppm of CTAB leads to 98 %

IE and a mechanism was proposed based on UV-Visible Absorption spectra and

FTIR spectra.

Synergistic effect of molybdate with zinc ions for the effective inhibition of

corrosion of mild steel was studied by Jabeera et al [96]. Zinc ions produced by the

electrolytic dissolution of zinc rods exhibited excellent inhibition efficiency together

with the synergistic combination of molybdate and nitrite. This system required

lesser quantities of molybdate and nitrite individually. Long-term OCP

measurements indicated that effective passivation occurred within four days of

immersion.

Gunasekaran et al have evaluated the synergistic inhibition offered by Zn2+

ions and 2-carboxyethyl phosphonic acid (2-CEPA) to the corrosion of mild steel in

60 ppm chloride ions [97] and calcium gluconate (CG) enhances the inhibition of the

corrosion [98-100]. Electrochemical and weight change methods were used to study

synergistic inhibition of the ternary system.

The corrosion inhibition of mild steel by 2-phosphonobutane-1,2,

3-tricarboxylic acid (PBTCA) in tap water was studied by Wang et al [101] and

results showed that PBTCA and Zn ions have obvious synergistic effect on

corrosion inhibition. Zn [Ca]-PBTCA-Fe (III) - a sequestering film deposited on the

surface of mild steel inhibited corrosion effectively. The results of static and

47

dynamic scale inhibition tests showed that the inhibition of Ca scale deposition by

PBTCA was excellent and the nucleation disturbance and crystal distortion are

caused by the presence of PBTCA.

The inhibition efficiency of potassium permanganate in controlling the

corrosion of carbon steel in an aqueous solution containing 60 ppm of Cl- in the

presence and absence of Zn2+ has been evaluated by Dhanalakshmi et al [102] .The

formulation consisting 50 ppm of KMnO4 and 50 ppm of Zn2+ offers 98 %

inhibition efficiency. A synergistic effect exists between KMnO4 and Zn2+. FTIR

spectra revealed that the protective film consists of Fe2+- permanganate complex and

Zn(OH)2 .

Li Hui et al have analysed that poly aspartic acid (PASP) was a new

environmentally friendly corrosion and scale inhibitor [103] using weight-loss

method and polyaspartic acid combined with HEDP and Zn2+ had a very good

synergistic effect on corrosion inhibition of carbon steel.

The inhibition efficiency of hibiscus rosa-sinesis Linn, in controlling the

corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl-

was studied by Anuradha et al [104]. In the presence of Zn2+, excellent IE was

shown by the flower extract. A synergistic effect exists between the flower extract

and Zn2+. Formation of protective film was confirmed by AC impedance spectra and

the film consists of Fe2+-quercetin-3-O-glucoside complex and Zn(OH)2.

A synergistic effect existing between ATMP and Zn2+ in controlling

corrosion of carbon steel immersed in rain water collected from roof top has been

investigated by Arockia selvi et al [105].The formulation consisting of 250 ppm of

ATMP and 5 ppm of Zn2+ exhibits 98 % IE. Increase in the immersion period also

showed the same IE. This suggests that a more stable and compact protective film

was formed on the metal surface.

Influence of sodium tripolyphosphate (STPP) as antiscalant on the corrosion

of carbon steel in cooling water system along with zinc ions has been studied by

48

Kumar and Chaudhary [106]. The inhibitor provided good IE and acted as an anodic

inhibitor when present alone and mixed inhibitor with zinc ions.

The effects of bivalent cations on corrosion inhibition of steel by 1-hydroxy

ethane-1,1-diphosphonic acid (HEDP) have been investigated by Felhosi et al [107].

Addition of calcium or zinc ions greatly increased the inhibition efficiency of HEDP

in a synergistic manner. The highest inhibition effect was obtained for molar ratios

of Ca/HEDP = 0.5 and Zn/HEDP = 3 for 3×10-4 mol dm-3 HEDP. The corrosion

inhibition mechanism in the presence of these additives proved to be different from

that with HEDP alone and was related to the formation of different complex species

between HEDP and cation additives.

II.3. Surfactants as corrosion inhibitors

Surfactants constitute the most important group of detergent components.

Generally, these are water-soluble surface-active agents, comprised of hydrophobic

portion usually a long alkyl chain attached to hydrophilic groups. Surfactants can be

categorized according to the charge present in the hydrophilic portion of the

molecule as

§ Anionic surfactant

§ Non-ionic surfactant

§ Cationic surfactant

§ Ampholytic surfactant

The properties of the surfactant have been extensively studied. Surfactants

have the ability to

• block the electrode surface thereby inhibiting the various redox

processes.

• solublize insoluble compounds.

• alter the properties of metal solution interface and to organize

into hydrophobic and hydrophilic regions.

• act as phase transfer or micellar catalyst.

Several surfactants have been used as corrosion inhibitors [108-113].

49

Jian and Shou [114] have reported that non-ionic surfactants have marked

inhibition efficiency on iron in acid media due to the adsorption on to the metal

surface. Osman and Shalaby [115] have investigated the inhibition effect of

non-ionic surfactants such as Tween- 20, Tween-40, Tween-60, Tween-80 and

Ol(EO) 20 on steel in acid chloride solution.

The inhibition efficiency of Tween-20 [116], Tween-40 [117], Tween-60

[118] for the cold rolled steel corrosion in sulphuric acid have been evaluated using

mass-loss, electrochemical and AFM approaches. Non-ionic surfactants prepared by

direct esterification of fatty acids (stearic, oleic, recinoleic and linoleic) with

polyethylene glycol have been used to prevent acid corrosion[119].

Shalaby et al [120] have studied the inhibition effect of non-ionic

polyoxyethylene (80) monopalmitate [Pa(EO)80], cationic hexadecyltrimethylammonium

bromide (HTABr) and anionic sodium dodecyl sulphate in sea water on carbon steel.

It was found that the inhibition efficiency increased with concentration and reached

a maximum value around their critical micellar concentration.

Migahed et al [121] have reported that the inhibition efficiency of few

non-ionic surfactants for carbon steel pipe lines, increases with increase in the

concentration until the critical micelle concentration is reached.

Shalaby and Osman [122] have established the synergism between the

anionic (sodium oleic sulfonate) and non-ionic surfactant (Tween 80).

Keera and Deyab [123] have studied the electrochemical behaviour of carbon

steel in formation water in the presence of organic surfactants cocamide

diethanolamine (non-ionic), cetrimonium chloride (cationic) and cocamidopropyl

betaine (amphoteric) and reported that inhibition efficiency of all the inhibitor

reaches a maximum around CMC.

Ghebremichael et al [124] have studied the inhibition of corrosion of mild

steel in sulphuric acid by commercial surfactants such as alkylphenolethoxylate-

2000 and alkylphenylethoxylate-400. According to Bereket and Yurt [125]

50

quaternary ammonium salts behave as mixed inhibitors on the corrosion of low

carbon steel in acidic solutions and the inhibition efficiency is maximum around and

above the critical micellar concentrations.

The studies on the corrosion inhibition of iron in acidic solutions using alkyl

quaternary ammonium halides by Lin Niu et al [126] reveal that the structure of

alkyl group and the type of halide ions of these inhibitors greatly influence the

inhibition efficiency.

Saeed and Ali [127] have synthesized a variety of bisquaternary ammonium

salts which exhibit excellent inhibition for the corrosion of carbon steel.

Bernard et al [128] have reported that the inhibition efficiency increases with

increase in the polar head group size and also the length of the carbon chain of

quaternary ammonium salts due to the formation of a close packed layer. According

to Hoar and Holliday [129], the inhibiting action of CTAB is due to the adsorption

of cetylammonium cations on the most active anodic sites, which interfere with the

anodic reactions by hindering the escape of Fe2+ ions from the metal surface into the

solution.

Rajendran et al have investigated the influence of the cationic surfactant

N-cetyl-N, N, N-trimethylammonium bromide (CTAB) on the Zn2+- HEDP[130],

the Zn2+ - ATMP [131] and the Zn2+- calcium gluconate [132] systems in controlling

the corrosion of carbon steel in aqueous environment.

Manjula et al [133] have studied the corrosion behaviour of carbon steel in

the presence of N-cetyl-N,N,N-trimethylammonium bromide, Zn2+ and calcium

gluconate.

Houyi Ma et al [134] have investigated the inhibitive action of CTAB, SDS,

sodium oleate and polyoxyethylene sorbitan monooleate on the corrosion behaviour

of Cu by electrochemical impedance spectroscopy. CTAB was found to be the most

efficient inhibitor due to the synergistic effect between bromide anions and the

positive quaternary ammonium ions. Karpagavalli and Rajeswari [135] have

51

reported the application of CTAB as inhibitor for the corrosion of brass in ground

water.

Soror and El-Ziady [136] have studied the effect of CTAB on the corrosion

of carbon steel in acid. Lalitha et al [137] have shown the existence of synergistic

effect between SDS, CTAB with triazoles for the corrosion inhibitions of copper in

acid medium.

Michael L. Free [138] has related the corrosion inhibition of mild steel in

acidic medium by surfactant molecules such as cetylpyridinium chloride (CPC) and

cetyltrimethylammonium bromide (CTAB) and its ability to aggregate at interfaces

and in solution.

Lin Wang et al [139] have shown that both 2-mercaptothiazoline and

cetylpyridinium chloride function as effective inhibitors for low carbon steel over a

wide concentration range of aqueous phosphoric acid solution. According to

Abd-El-Maksoud [140] hexadecylpyridinium bromide and hexadecyltrimethylammonium

bromide, act as mixed inhibitors for iron and Cu in HCl and H2SO4 due to the potential of the

zero charge of the metal and due to the adsorption ability of chloride and sulfate ions

on the metal surfaces.

Migahed [141] has investigated the effectiveness of cationic surfactant

1-dodecyl-4-methoxypyridinium bromide as corrosion inhibitor for mild steel in

2M HCl solution by electrochemical methods.

. Osman [142] has studied the corrosion inhibition of steel in H2SO4 by

hexadecyltrimethylammonium bromide. Migahed et al [143] have synthesized the

anionic surfactant (p – myristyloxycarbonylmethoxy - p’ - sodium carboxylate -

azobenzene) and determined the inhibition efficiency of the surfactant for the

corrosion inhibition of mild steel in 1M H2SO4 by electrochemical and chemical

techniques. It was found to be a mixed inhibitor.

Suguna et al [144] have determined the corrosion rates of carbon steel in the

absence and presence of sodium dodecylsulphate and Zn2+ in aqueous solutions.

52

Rong Guo et al [145] have studied the effects of sodium dodecylsulphate (SDS) and

some alcohols (ethanol/n-butanol) on the inhibition of the corrosion of Ni.

Sayed Abdel Rehim et al [146] have reported that the inhibition of corrosion

of Al alloy in 1 M HCl in the temperature range 10-60º C occurs through the

adsorption of the anionic surfactant SDS on the metal surface without modifying the

mechanism of the corrosion process. The effect of SDS on the corrosion of Cu has

been studied in the absence and presence of benzotriazole using electrochemical

impedance and surface tension measurements [147,148].

Susai Rajendran et al [149] have evaluated the inhibition efficiency of SDS

in controlling the corrosion of carbon steel immersed in 60 ppm of NaCl in the

absence and presence of Zn2+. FTIR spectrum has revealed the presence of a film

containing iron-SDS complex and Zn(OH)2.

Monticelli et al[150] have investigated the corrosion inhibition of Al alloy

(AA 6351) in 0.01 M NaCl using inhibitors such as sodium salts of N-dodecanoyl-

N-methylglycine (NLS), dodecyl sulphate (LS), N-dodecanoyl-N-methyltaurine

(NLT) and dodecylbenzene sulfonate (DBS). The existence of synergism and

antagonism in mild steel corrosion inhibition by sodium dodecylbenzenesulfonate

and hexamethylenetetramine has been ascribed to the formation of hemi-micellar

aggregation that provoke inhibitor desorption from the metal/solution interface at

higher concentration [151].

Susai Rajendran et al [152] have reported the mutual influence of HEDP and

SDS on the corrosion inhibition of carbon steel immersed in rainwater in the

presence of Zn2+. The adsorption behaviour of dodecylamine on Cu/Ni alloy in NaCl

was studied using electrochemical and atomic force microscopy. It was found to be a

cathodic type of inhibitor [153].

Quaternary ammonium compounds [154] are a group of ammonium salts in

which organic radicals may be alkyl, aryl (or) aralkyl and the nitrogen can be a part

53

of the ring system. Many quaternary ammonium salts show excellent corrosion

inhibiting property and biocidal property.

Jin-Ying et al [155] have studied the inhibition effects of a new heterocyclic

bisquaternary ammonium salt in simulated oil field water. Weight loss

measurement, potentiodynamic polarization curves, electrochemical impedance

spectroscopy and atomic force microscopy were used to evaluate the corrosion

inhibiting performance of MBQA in simulated oil field water. Experimental data

revealed that MBQA acted as an inhibitor in the acidic environment and further

more the compound was a mixed type inhibitor. It was found that inhibition

efficiency increased with an increase in MBQA concentration at different

temperatures.

Bereket et al [156] have investigated the inhibition efficiencies of quaternary

ammonium salts, cationic surfactants and non-ionic surfactants on the corrosion of

zinc in alkaline media.The inhibiting properties of quaternary ammonium salts in

2M KOH was investigated by potentiodynamic polarization, electrochemical

impedance spectroscopy and linear polarization methods. Inhibition efficiencies

were found to be due to physical adsorption of the cathodic sides of zinc electrode

and dependence of inhibition efficiencies on substituents were found.

Bereket and Yurt [157] have studied the inhibition of low carbon steel in

0.1M HCl over the temperature range 20-60ºC at different inhibitor concentrations

by various quaternary ammonium salts and cationic surfactants. Maximum

inhibition efficiencies of cationic surfactants were observed around and above

critical micelle concentration (CMC).

The corrosion inhibition characteristics of 2-aminophenyl-5-mercapto-1-oxa-

3,4-diazole (AMOD) on mild steel in HCl solution have been studied by

Rafiquee et al [158]. AMOD is a good corrosion inhibitor in HCl solution and its

inhibition efficiency is increased markedly in presence of surfactants such as SDS,

CTAB, TX-100. TX-100 is found to be the most effective among the tested

surfactants.

54

Al-Sabagh et al [159] have prepared twelve new ethoxylated monoalkyl

bisphenol surfactants with general formula as E(X) B(Y) M(R). E(X)-degree of

ethyleneoxide units, the B(Y) is the bisphenol based on acetophenone (BAC),

cyclohexanone (BCH) or acetone (BA) and R is the alkyl chain of fatty acids and

they were tested as corrosion inhibitors for carbon steel alloy in 2M HCl solution.

The corrosion inhibition efficiency increases with increase in the degree of

unsaturation, ethoxylation and alkyl chain length. It was found that minimum

inhibition efficiency was exhibited by bisphenol BCH and maximum by bisphenol

BAC.

Atta et al [160] have investigated the inhibition of corrosion of steel in

1M HCl using the recycled polyethyleneterephthalate (PET), which was modified to

produce non-ionic surfactants. The inhibition efficiency increased with the increase

of inhibitor concentration up to their critical micelle concentrations.

Sharma and Quraishi [161] studied the influence of four gemini surfactants

namely N-trimethyl butane-diyl-1, 2-ethane-bis-ammonium bromide (BEAB),

N-hexane-diyl-1,2-ethane-bisammonium bromide (HEAB), N-dodecane-diyl-1,

2-ethane-bis-ammonium bromide (HDEAB) as corrosion inhibitors of mild steel in

1N HCl and 1N H2SO4. The inhibition efficiency of the compounds was found to

vary with their nature, concentration, solution temperature, immersion time and acid

concentrations.

The corrosion inhibition characteristics of non-ionic surfactants of the

TRITON-X series known as TRITON-X-100 and TRITON-X-405 on stainless steel

(SS) type X4cr13 in sulphuric acid were investigated by Fuchs-Godec [162]. It was

found that these surfactants act as good inhibitors in 2 mol L-1 H2SO4 solution, but

the inhibition efficiency strongly depends on the electrode potential.

Knag et al [163] have studied the portioning of

N,N,N-cetyltrimethylammonium bromide (CTAB) between the aqueous bulk and the

oil/water interface, since majority of the corrosion inhibitors used in the oil

55

production are surfactants, which are adsorbed on to the metal surfaces and also at

the oil/water interface.

Migahed et al [164] synthesised four novel non-ionic ethoxylated fatty alkyl

amine surfactants (I -IV) and investigated as corrosion inhibitors of carbon steel in

1M HCl. The inhibition efficiency for each inhibitor increased with increasing

concentration until the critical micelle concentration (CMC) was reached. Scanning

electron microscopy was used to examine the surface morphology of polished

carbon steel surface and those immersed in 1M HCl in the absence and presence of

inhibitor.

Hong et al [165] demonstrated the utility of two environmentally benign

anionic surfactants namely sodium dodecylsulphate (SDS) and ammonium

dodecylsulphate (ADS) as dissolution inhibitors for Cu CMP (Chemical mechanical

planarization) using a standard slurry (1 wt % glycine with 5wt % H2O2 at

pH = 4.0). Combined measurements of open circuit potentials and contact angles

with those of copper removal rates showed both SDS and ADS were found to be

superior to those of benzotriazole (BTA), a traditional inhibiting agent used for Cu

CMP.

Corrosion inhibitor molecules function by adsorbing to a steel surface and

thus prevent oxidation of the metal. Inhibitors investigated by in - situ

measurements based on atomic force microscopy and neutron reflectometry reported

by John Douglas et al [166] include cetylpyridinium chloride (CPC),

dodecylpyridinium chloride (DPC), 1-hydroxyethyl-2-olecimidazoline

(OHEI) and cetyl dimethylbenzylammonium chloride (CDMBAC) and has shown

that the inhibitor molecules adsorb on to a surface in micellar structure.

II.4. Trisodium citrate as corrosion inhibitor

Role of citrate ions in the phosphonate-based inhibitor system for mild steel

in aqueous chloride media was studied by Gunasekaran et al [167].

56

Choi et al [168] used a new all-organic multi-component inhibitor blend

composed of citric acid/phosphonates (hydroxyl ethylidene diphosphonic acid,

HEDP)/acrylate copolymer/isothiazolone. The effects of the inhibitor on carbon

steel dissolution in synthetic cooling water were studied through weight loss

measurements and electrochemical, scale and microorganism tests. The results

obtained from this study show that the new inhibitor can decrease corrosion, scale

build-up and microbial growth under the conditions tested. Potentiodynamic

polarization curves indicate that the blended inhibitor acted as an anodic inhibitor,

reducing metal dissolution. The nature of protective films formed on the carbon

steel was studied by using scanning electron microscopy (SEM) and Auger Electron

Spectroscopy (AES). The inhibition effects were due to the formation of protective

films which might contain calcium phosphonates and iron oxide. The inhibitor used

in this study appears to have an excellent crystal modification effect on calcium

carbonate scale. The various microorganisms used in this study were inhibited

effectively in the planktonic state.

II.5. Biocides

Microbial life affects everything including many industrial processes. The

nature and activity of microorganisms determine whether their presence is beneficial

or destructive. In cooling towers, the destructive capability of these organisms is

manifested. The microorganisms that inhabit industrial cooling water systems can

adversely affect the efficiency of the operation by their sheer number and diversity,

metabolic wastes or deposits and associated corrosion. Microbiologically influenced

corrosion is emerging as a serious problem in cooling systems. Microorganisms

such as bacteria, fungi and algae can combine with organic compounds to form

biofilms. The microbes in these films produce products of metabolism that are

corrosive in nature. The result is pitting corrosion of metal components. Wooden

system support structures are also vulnerable, as wood-destroying fungi can cause

significant damage as well. To eliminate the threat of such potential problems and

achieve optimum system efficiency, microbiological activity within a system must

be properly controlled. Though a seemingly straightforward goal, cost concerns,

system operating guidelines, and additive compatibility all greatly influence

57

treatment choice. Environmental, health and safety considerations also have a great

impact to be considered as a viable option. A biocide must successfully control a

broad spectrum of microbial contamination, provide cost-effective performance and

prove compatible with other system components, while at the same time meeting

stringent environmental, health and safety standards. Literature survey has exposed a

number of biocides used along with corrosion inhibitors.

Ramesh et al [169] have investigated the inhibition efficiency of triazole

phosphonates compounds namely 3-benzyledene-amino-1,2,4-triazolephosphonates,

3-cinnamyledene-amino-1,2,4-triazolephosphonates and 3-anisalidene-amino-1, 2,4-

triazolephosphonates, along with biocide action on corrosion of mild steel . The

biocidal action of the inhibitors on the corrosion control of Cu [170] in neutral

aqueous environment was also evaluated.

Stefanova [171] has studied the biocidal efficiency of cetylpyridinium

bromide (CPB), potassium permanganate and sodium benzoate. He has reported that

the CPB has a wide range of effect for microorganisms typical for water media. Its

high biocidal efficiency is a prerequisite for its use as additive to cooling water.

Sodium benzoate and potassium permanganate act selectively to particular

representative of the microorganism in water media.

Dong-Jin Choi et al [172] have reported that the new all-organic multi

component inhibitor blend composed of citric acid/ phosphonates/ acrylate

copolymer/ isothiazolone effectively decreases the corrosion, scale built up and

microbial growth for carbon steel in open recirculating cooling water system. It is

reported that the inhibition effect is due to the formation of a protective film.

Rajendran et al [173,130,131] have studied the influence of CTAB on the

corrosion inhibition of mild steel by ATMP-Zn2+ system, and also the biocidal

efficiency of CTAB in the presence of various phosphonic - Zn2+ system and

reported that CTAB acts as an excellent biocide as monomer and also as micelle.

Bernard et al [174] have evaluated the biocidal efficiencies of the four

bactericides – organosulphur, mixed aldehyde - organosulphur, mixed aldehyde-

58

quaternary ammonium and organobromo compounds on the polluted water from

sulphuric acid manufacturing plants.

Manimegalai et al [175] have examined the inhibitive property as well as the

biocidal properties of the leaf extracts of Azadiracta Indica and reported that the

inhibitor has very effective biocidal property as well as inhibitive property for mild

steel in fresh water environment. It is reported that most of the biofilms are sensitive

to the detergent biocide SDS [176,177].

Iwalokun et al [178] have suggested the usuage of urea and SDS in the

laboratory to reduce the risk of infection with virulent proteus strains. Richard et al

[179] have investigated the effect of the surfactants such as alcohol ethoxylates,

amine ethoxylates, amine oxide and SDS on bacterial cell membranes using EPR

spectroscopy.

Lin et al [180] have reported that CPC, a quaternary ammonium salt and a

cationic surfactant has been used as a biocide in personal hygiene products. It is

reported that CPC acts as an antifungal agent [181] and as a biocide [182] for

cosmetics, toiletries and pharmaceuticals activity.

Muthukumar et al [183,184] employed biocides (cationic and non-ionic) to

study the biodegradation of diesel. Polyoxyethyleneglycol dodecylether (BRI-35)

and polyethylene glycol-p-isooctyl phenyl ether (TRITON-X-100) had higher

bacterial efficiency than dodecyl ethyldimethyl ammonium bromide (DDAB).

DDAB gave good biocidal efficiency at the interface. Among the three biocides

namely, Bronopol (2-bromo-2-nitro-propane-1,3-diol), N-Cetyl-N,N,N-

trimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB),

Bronopol was found to have higher bactericidal efficiency than CTAB and CPB,

but the cationic biocides (CTAB and CPB) showed good biocidal efficiency at the

interface.

Lakshmipriya et al [185] have studied the inhibition efficiency of an aqueous

extract of garlic in controlling corrosion of aluminium immersed in NaOH solution

59

at pH 11 and 12. The influence of CTAB (a biocide and a cationic surfactant) for the

above system was also studied.

Influence of CTAB as a biocide and sodium sulphite as an oxygen scavenger

were studied for controlling the corrosion of Aluminium using 5% aqueous extract

of onion as corrosion inhibitor at pH 11 and 12 by Susai Rajendran et al [186]. Use

of CTAB showed that the IE of the system remained unchanged and also the role of

CTAB, SDS (a surfactant and a biocide) and sodium sulphite (oxygen scavenger)

has been discussed by Sathiyabama et al [187] on the corrosion inhibition of carbon

steel immersed in well water using Eriochrome Black-T (ECB-T) as corrosion

inhibitor. Addition of CTAB, SDS, sodium sulphite does not change the excellent

inhibition efficiency of ECB-Zn2+ system.

Noreen Anthony et al [188,189] have analysed the influence of sodium

dodecyl sulphate (SDS), an anionic surfactant on Caffeine-Zn2+ and Caffeine- Mn2+

system in controlling corrosion of mild steel immersed in an aqueous solution

containing 60 ppm of Cl-. The transport of inhibitors towards the metal surface plays

a major role in controlling corrosion. Formation of micelles by the surfactant

changes the inhibition efficiency.

60

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