CHAPTER II

REVIEW OF LITERATURE

The consequences of corrosion are many and the effect of these on the safe,

reliable and efficient operation of equipment are often more serious than simple loss mass

of a metal. Corrosion can be minimized by employing suitable strategies which retard

the corrosion reaction. It is widely accepted that inhibitors especially the organic

compounds can effectively protect the metal from corrosion. Several works have been

done with compounds containing polar functions on the corrosion inhibition of metals in

various aqueos media. Polymer functions as corrosion inhibitor because of their ability to

form complexes through their functional group, with metal ions which occupy large area

and by so doing blanket the metal surface from aggressive environment.

An overview of chemical abstracts provides valuable insight into the extent and

nature of studies undertaken in this field. The practice of corrosion inhibition in recent

years has become oriented towards health and safety considerations. Consequently

greater research efforts have been directed towards formulating environmentally

acceptable organic compounds and polymers as corrosion inhibitors for metals is

reviewed and presented under the following headings.

Acid Media Inhibitors for Iron.

Polymers – the effective inhibitors

Non-nitrogenous polymers

Polymeric inhibitors for ferrous materials in acid media.

Poly amino derivatives as Inhibitors

Poly Heterocyclic compounds as Inhibitors

Polymeric inhibitors for ferrous materials in neutral media

Polymeric inhibitors for non- ferrous materials in neutral media

Polymeric inhibitors for non- ferrous materials in acid media

Polymer composites for corrosion inhibition.

2.1 CORROSION OF METALS

The ancient Greek Historian Heyrodotus (Fifth century BC) and the ancient

Roman naturalist, Piny the Elder (First century BC) mentioned the adsorption of tin for

the protection of iron from corrosion. Alchemists through centuries made fertile attempts

to transform base metals in to noble ones. Early attempts to mitigate corrosion of metals

were empirical and centered largely on the use of organic and metallic coatings.

Inhibitors for acid corrosion of metals were known from middle ages. These were

obvious measures to protect metallic structures constructed by early artisans, often at the

expense of much time and very hard labour.

Lomonosov (1743 – 1750) was the first to make broad systematic experiments on

the study of the action of acids on metals.

Faraday (1820 – 1882), established a very important relationship between

chemical action and the generation of electric current.

Davy (1826) proposed an electrochemical method using sacrificial anode for the

protection of copper sheathed ocean going ships.

De La Rive (1830) attributed the pronounced corrosion of impure zinc metal to

the operation of short-circuited microcells on the metal surface.

Marangoni and Stephanelli (1872) used extracts of glue and gelatin and bran to

inhibit the corrosion of iron in acids. This and subsequent discoveries of effective

corrosion inhibitors were to large extent: the result of empirical studies.

Wagner (1938) proposed a mixed potential theory. The theory proclaimed that

(i) any electrochemical reaction comprised of two or more partial oxidation and reduction

reactions, (ii) there can be no net accumulation of electrical charges during an

electrochemical reaction and the potential at the entire surface of an isolated electrode

should be the same.

The first patent in corrosion inhibition was awarded to Baldwin (1960) British

patent 2327 which involved the use of molasses and vegetable oils for pickling steel sheet

in acid. Later, increased research activities in corrosion inhibition studies were started.

2.2 ACID MEDIA INHIBITORS FOR IRON

The potentiodynamic studies for the anodic dissolution of iron and the behaviour

of some corrosion inhibitors as well as the potentiodynamic measurements of polarization

curves on Armco iron in acid medium in the presence of thiourea derivatives were

studied by Cavallaro et al (1963 and 1964).

The effect of inorganic anions, organic compounds and combinations of the

two on corrosion of mild steel in various acids has been determined by

Norman Hackerman et al (1966). From corrosion rates of steel in acids, the order of the

degree of adsorption of anions was concluded to be I-> Br

-> C1

-> SO4

2-> CIO4

-.

They found that the largest effects on corrosion mitigation were observed for I- and I

- in

combination with amines.

Francies M Donahue et al (1967) have studied the effect of aniline and aniline

derivatives on the electrochemical characteristics of iron in H2SO4. It was found that iron

corrosion was inhibited primarily by an adsorption mechanism, as well as surface

chelation process. The studies of corrosion rates of Armco iron in presence of

ring-substituted anilines were also correlated by the LFER predicated on inhibition by

adsorption.

Takao Murakawa et al (1967) studied the synergistic effect of anions for the

corrosion inhibition of iron by amines in H2SO4. They found that the inhibition action

was enhanced by the addition of anions with amines due to preferential adsorption of

inhibitor on iron surface.

The adsorption of amine salts of oleic acid was investigated on iron in 0.5M

H2SO4, by Szauer and Brandt (1981). It was observed that the adsorption process

proceeded through the preferable bonding between oleic acid and the metal surface.

Aksut (1983) studied the corrosion of iron in propargylic alcohol and sulphuric

acid, and the reduction mechanism involving propargylic alcohol. He found that

propargylic alcohol did not show any inhibiting action on this system. Ateya et al (1984)

studied the effect of Thiourea on the corrosion kinetics of mild steel in H2SO4.They found

that thio urea showed maximum efficiency at higher concentrations.

Schmitt and Bedbur (1985) studied the AC impedance behaviour of high-purity

iron and mild steel in de-aerated 10% HCl under free corrosion at room temperature in

the presence of quaternary ammonium compounds such as pyridinium and quinolinium

derivatives. It revealed that the inhibition efficiency increases with increasing number of

aromatic systems in the molecule and is determined not only by geometric and electronic

molecule factors influencing the adsorption but also by dielectric effects exerted by the

inhibitor molecule after adsorption.

A general comprehensive analysis of mechanism of corrosion inhibition was

given and it was suggested that the formation of a compact three - dimensional protective

layer on the electrode surfaceis the key for effective inhibition of corrosion. The attack of

Cl-, Br

-, and F on the passive layer of iron has been studied using XPS (Khalil et al 1985).

A pronounced thinning of the oxide film was found. The effect decreases in the sequence

of ions mentioned above and increases with halide concentration.

Lajos Meszaros and Laszlo Simor (1990) have studied the inhibitory efficiency

of glycine derivatives for the oil industry. They found that the inhibitors assumed to act

by reducing the coverage of the intermediates of metal dissolution. The cathodic reaction

is hindered to a lesser extent.

Bockris and Bo Yang (1991) studied the mechanism of corrosion inhibition of

iron in acid solution by acetylenic alcohols. It is suggested that formationof a compact

three-dimensional protective layer on the electrode surfaceis key for effective inhibition

of corrosion.

The inhibitive effect of progargyl alcohol and ethyl cyclohexanol on the corrosion

behavior of carbon steel was studied by Rauscher et al (1993), in aerated and de-aerated

solutions of 5% hydrochloric acid at 30° C by polarization methods. It was observed that,

the species with carbonyl groups in conjugation with C=C bonds took part in an

oligomerization reaction and the time dependence of the corrosion results showed a

remarkable performance.

The inhibition mechanism of benzyl thiocyanate for iron corrosion in 1N HCl and

1N HClO4 was investigated using polarization measurements and surface analysis by

Noriyuki Ohno et al (1994). A protective film formed on the iron surface by the

oxidative addition reaction of the thiocyanate with iron was characterized using X-ray

photoelectron and reflection FTIR spectroscopy. A markedly high inhibition efficiency of

this inhibitor was reported for iron corrosion in 1N HClO4 at high concentrations, but not

in 1N HCl.

Rengamani et al (1994) studied the influence of anisidines on the corrosion of

mild steel in 1N HCl and 1N H2 SO4 by weight loss and gasometric techniques. It was

observed that the order of inhibition was para > meta>ortho.Singh et al (1995 ), studied

the inhibitive effect of hexamethylene tetramine (Hexamine) on the corrosion of mild

steel in conc. HCl solution (3N) as well as in very dilute solutions (N/200). They found

that the inhibitive effect of hexamine was moderate at higher concentration of the acids

but negligible in dilute acid solutions. Incorporation of Cu2+

, As3+

, Sb3+

and Sn2+

with

hexamine improved its performance due to its synergistic character.

Aksut and Onal (1997) have studied the effect of some organic compounds on

the corrosion of pure iron, pure chromium, and Iron-chromium alloys in acidic solutions.

They found that the organic inhibitors performed very well.

Corrosion inhibition of mild steel in acid solutions by alkyl amines and aniline in

presence of Na2SO4 and NaCl was studied by Luo et al (1998), using potentiostat,

Scanning electron microscopy, FTIR and atomic force microscope. The results showed

that chloride ions had a pronounced effect on the inhibition of amines and aniline for

corrosion of mild steel.

The inhibitive action of aliphatic and aromatic compounds such as ethanolamines,

acetylenic alcohols and benzoic acid in acid solutions has been studied by Jayalakshmi

and Muralidharan (1998). They observed that the inhibition efficiency tends to decrease

with concentration for benzoic and salicylic acids with temperature, while for ortho-nitro

benzoic acid and anthranilic acids, it increased with temperature. Anthranilic acid showed

the highest efficiency in the range of 70-80% at the temperature of 363 K. There was a

marginal decrease in efficiency with increase in immersion time.

Bentiss et al (1999) have studied the corrosion inhibition of mild steel in 1M HCl

and 0.5M H2SO4 by 3,5-bis(2-thienyl)- 4-amino -1, 2, 4 -triazoles, using weight loss

and electrochemical impedance spectroscopy methods. The study revealed that the

compound functioned as an anodic inhibitor. The adsorption of this inhibitor was found

to obey Langmuir adsorption isotherm in both the acids.

Jayaperumal et al (2000) has studied the inhibition effect of ethanolamines on

oil well tubular material in hydrochloric acid. The amines such as mono, di and

triethanolamine were employed for their inhibiting capacity by mass loss method, DC

polarization method and AC impedance method.' The inhibitor efficiency was found to

increase with increasing concentration of amines. Among these, mono ethanolamine was

found to be more effective than the other two amines.

Quraishi et al (2000) have studied the influence of 4-amino -5 mercapto -3n- propyl-

1-2-4-triazole (AMPT) on the corrosion and permeation of hydrogen through mild steel

in 0.5M H2SO4 and 1M HCl using weight loss measurements and electrochemical

techniques. AMPT was found to be more inhibitive in H2SO4 than in HCl. The adsorption

of this compound on, the mild steel surface obeyed Temkin's adsorption isotherm.

Gopi et al (2000) evaluated efficiency and the synergism of corrosion inhibitors,

thiourea derivatives, for mild steel in 1N H2SO4 solution at different temperatures

(303, 313 and 323K). A marked inhibition synergism occurred within an optimum

concentration range even at higher temperatures. The thiourea derivatives obeyed the

Langmuir adsorption isotherm.

Bentiss et al (200l), have discussed the mode of adsorption and inhibition by 2,5

bis (4 - dimethyl aminophenyl) -1, 3, 4 - Thiodiazole on steel corrosion in 1M HCl and

0.5M H2SO4. They found that the above inhibitor was more effective in HCl than in

H2SO4. It behaved as a mixed type inhibitor and adsorption was consistent with

Langmuir's isotherm.

In 0.5M HCl solutions, the effect of pyranocoumarin derivatives on the corrosion

of iron was studied by Abd El-Maksoud (2002). He proved that the compound acted as

mixed inhibitor but cathode is more preferentially polarized. The inhibitor efficiency

depends on the nature and concentrations of investigated compound.

The inhibitory activity of some o-substituted aniline on iron corrosion in

hydrochloric acid (HCl) was studied by Khaledet al (2003) in relation to inhibitor

concentration using potentiodynamic and electrochemical impedance spectroscopy (EIS)

measurements. O-Substituted anilines were found to act as mixed type inhibitors.

The inhibition of the corrosion of mild steel by penicillin V potassium has been

studied by Eddy et al (2008). Penicillin V potassium was proved to be a good inhibitor

for the corrosion of mild steel in H2SO4. The inhibition efficiency of the inhibitor

decreased with increase in temperature. Physical adsorption mechanism was found to be

consistent with the assumptions of Langmuir and Frumkin adsorption isotherms.

The adsorption of the inhibitor was also found to be spontaneous.

Inhibitive and adsorption properties of penicillin G for the corrosion of mild steel

were investigated by Eddy et al (2009) using gasometric and thermometric methods.

Penicillin G was found to inhibit the corrosion of mild steel in H2SO4. The adsorption of

the inhibitor on the surface of mild steel was found to be exothermic, spontaneous and

followed the mechanism of physical adsorption.

Ambrish Singha et al (2010) studied the corrosion inhibition on mild steel in 1M

HCl and 0.5 M H2SO4 by dapsone (4,4'-diaminodiphenylsulfone)using polarization

resistance, Tafel polarization, electrochemical impedance spectroscopy (EIS) and weight

loss measurements. Potentiodynamic polarization suggested that it acted as a mixed type

predominantly cathodic in HCl and predominantly anodic in H2SO4. Electrochemical

impedance spectroscopy was used to investigate the mechanism of corrosion inhibition.

The corrosion inhibition of mild steel in 1M HCl solution by Cefixime was

studied by Imran Naqvi (2011) at temperature range 303–333K by weight loss measurement

and electrochemical techniques i.e. Polarization Resistance, Potentiodynamic Polarization

and Electrochemical Impedance Spectroscopy (EIS). The inhibition mechanism of

Cefixime has also been discussed.

2.3 POLYMERS - THE EFFECTIVE INHIBITORS

Polymers are giant molecules made up of a large number (generally >100)

of one or more type of repeating molecular units called monomers. They are made from

organic and inorganic molecules. On the basis of the occurrence, polymers are classified

in to natural polymers, semi-synthetic polymers and synthetic polymers. The synthetic

polymers are long chain organic molecules whose dimensions could approach 105°A as

compared to simple organic molecules having dimensions of 10°A. In the last two

decades, there has been an increase in the use of polymeric compounds as corrosion

inhibitors.

High molecular weight organic compounds reduced the corrosion rate of metals

(Blair 1951, Hubert et al 1953, Pollard et al 1955, Benta1955, Purdy et al 1956 and

Sudbury et al 1958). Most of the nitrogenous materials containing the fatty chain as part

of their structure, imidozolines, quarternaries and esters are reported to have good

protective properties.

2.3.1 Non-Nitrogenous Polymers

Propargyl alcohols and other alkynols were investigated in details by

IR - reflectance spectroscopy which confirmed the formation of polymers on the mild

steel surface in HCI media (Poling 1967).

Polyglycol and poly ethyleneglycol were tested as inhibitors in 0.05N HCl solution

through electrochemical measurements at 343K by Abdel Fattah et al (1986). These

compounds get adsorbed on the surface obeying Langmuir isotherm. They offer large

surface coverage due to the long hydrocarbon chain and by the presence of OH groups.

Being hydrophilic in nature, the -OH groups counter acted the effect of chain length and

ensured higher solubilities.

Pectine (P), Carboxy methyl cellulose (CMC), polyvinyl alcohol (PVA), poly

ethylene glycol (PEG), poly acrylic acid (PAA) and sodium poly acrylate (NaPA) within

the concentration range 0.02 to 0.2 gm.dm-3

were used by El Sayed (1996) to control the

corrosion of iron in HCl, HClO4 and H2SO4 solutions.

Aramaki and Fujioka (1997) haveinvestigated that the mechanism involving

Poly propargyl alcohol (PA) for iron corrosion in 0.5M HCl at room temperature using

surface enhanced Raman scattering experiments and FTIR techniques. A high inhibitor

efficiency of PA at 343K was attributed partly to the coverage of the surface with a

protective film of the polymer and partly to adsorption of allyl alcohol formed by

cathodic reduction of PA. Electro initiated polyaniline (PANI) theory was proposed.

Iron corrosion in water–PEG 400 solutions was studied by monitoring the

corrosion potential and the polarization curves (Elodie Guilminot et al 2002). PEG

adsorption at the metal surface constituted the first stage in the iron corrosion mechanism.

Iron (ions)/PEG complexes were then formed, which get diffused in solution.

The effect of octyl phenol polyethylene oxide on the corrosion inhibition of steel in

0.5M H2SO4 was studied by Algabar et al (2004). The inhibition efficiency was found to

increase with the inhibitor concentration and decreased with temperature. The activation

energy of corrosion was found to be higher in presence than in absence of the inhibitor. The

inhibitor has relatively lower inhibition efficiencies at ambient and higher temperatures.

Rajendran et al (2005) have investigated the corrosion behaviour of carbon steel

using polyvinyl alcohol (PVA) in neutral aqueous solution containing 60ppm of Cl-

in

the absence and presence of Zn2+

ions using weight loss method. It was found that a

formulation consisting of 100ppm of PVA and 75ppm Zn2+

offered 81% inhibition

efficiency to carbon steel immersed in a solution containing 60ppm of Cl-.

Ashassi-Sorkhabi et al (2006) have studiedthe inhibition effect of some PEGs of

different molecular weights (400, 1000, 4000, and 10,000 g mol−1

) on carbon steel

corrosion at 25°C in 0.5N hydrochloric acid by weight loss method and polarization and

electrochemical impedance spectroscopy (EIS) techniques. They have demonstrated that

polyethylene glycols have remarkable inhibition effect on corrosion process and their

inhibition efficiencies are between 50 and 90%. The inhibition efficiencies are increased

by increase of the inhibitors’ concentration and molecular weight.

Umoren et al (2006) have investigated the effect of halide ions on the corrosion

inhibition of mild steel using polyvinyl alcohol (PVA) in H2SO4 at 30-60°C.

The corrosion rates were determined using the gravimetric (weight loss) and gasometric

(hydrogen evolution) techniques. Phenomenon of chemical adsorption was proposed and

PVA was found to obey Langmuir, Flory-Huggins and Freundlich adsorption isotherms.

The addition of halides to PVA improves the inhibition efficiency considerably.

Umoren et al (2006) have reported that PEG is a better inhibitor than PVA. They

have studied the corrosion inhibition of mild steel in H2SO4 in the presence of

polyethylene glycol (PEG) and polyvinyl alcohol (PVA) as inhibitors at 30–60°C using

weight loss technique. The inhibition efficiency increased with increase in concentration

and temperature. Both PEG and PVA were found to obey Temkin.Frendlich and

Langmuir adsorption isotherms. The phenomenon of chemical adsorption has been

proposed from the activation parameters.

Corrosion inhibition of mild steel in sulphuric acid solution using polyethylene

glycol methyl ether (PEGME) has been reported using electrochemical polarization

techniques (Dubey et al 2007). They found that PEGME is a very effective corrosion

inhibitor for mild steel in acidic medium. Inhibition efficiency increased with increase in

the concentration of PEGME but remained the same with increasing temperature.

Adsorption of PEGME was found to follow the Langmiur’s adsorption isotherm. PEGME

was also found to function as an inhibitor of mixed type acting by blocking the active

sites on the cathodic and anodic regions.

Gum Arabic (GA) (a naturally occurring polymer) has also been reported as an

inhibitor for inhibition of mild steel corrosion in H2SO4 at 30 – 60°C using weight loss,

hydrogen evolution and thermometric measurements (Umoren 2008). Inhibition process

was afforded by virtue of the chemical adsorption of GA components onto mild steel

surface following Temkin adsorption isotherm.

The corrosion inhibition of mild steel in H2SO4 in the presence of synthetic (PEG)

and naturally occuring (GA) polymers and synergistic halide additives have been

investigated by Umoren et al (2008). Weight loss, hydrogen evolution and thermometric

methods at 30 – 60 οC are carried and the results obtained showed that inhibition

efficiency increased with increase in GA and PEG concentration.PEG was found to be a

better inhibitor for mild steel corrosion in acidic medium than GA. Phenomenon of

chemical adsorption has been observed and addition of halides enhances the inhibition

efficency of GA and PEG significantly.

2.4 POLYMERIC INHIBITORS FOR FERROUS MATERIALSIN ACID MEDIA

2.4.1 Poly Amino derivatives as Inhibitors

In recent years, polymer amines are found to be effective inhibitors for iron and

steel in acid solutions. The electrochemically modified benzidine films on iron had good

anti - corrosion properties in weak acid, neutral as well as alkaline solutions.

The polymers like carboxy methyl cellulose, poly vinyl alcohol, polyethylene glycol,

polyacrylic acid, sodium polyacrylate, acrylamide- thiomallic acid with amines have

been used studied as corrosion inhibitors for iron in acidic media.

Mann et al (1936) haveevaluated polyamide resin towards good inhibitive

properties. Inhibitive action was studied by weight loss and polarisation techniques.

The amide cation was adsorbed on the cathodic area of the mild steel surface in acid

media through nitrogen atoms there by forming a monomolecular layer over the metal

surface.

The inhibitive effect of medium — sized polymethyleneimine on the corrosion of

iron in HCl solution has been studied by Kunitsugu Aramaki and Norman

Hackerman (1969). The corrosion rate measurements on pure iron in HC1 solution have

been carried out using polarization, hydrogen evolution and weight loss methods.

They observe that the enhanced inhibition is due to the donation of the electron pair on its

nitrogen atom to the metal.

Detailed investigations carried out by Baldwin et al (1970) using polyamide

epoxy systems in acid solutions revealed that the presence of an amino group, a fatty

cyclic dimerised acid and an imidozoline ring in the polyamide resin contributed towards

its good inhibitive properties on steel.

Ghosh et al (1983) have reported amido polyamines as inhibitors for iron

surfaces in 5 N HCI at 333K offering more than 95 percent inhibition by means of weight

loss measurements. The amido polyamines (APA) form an ionisable salt in acid medium.

The positive nitrogen centers of these compounds ensured that they could not be

discharged at the cathode sites and adsorbed through the nitrogen atom. They prevent

hydrogen discharge and thereby corrosion.

Deslouis et al (1991) have determined the kinetic parameters of Fe3+

reduction

mediated by a poly aniline film using steady - state and impedance methods. They have

obtained the value of charge transfer resistance (Rct) for poly aniline as a function of

electrode potential, and employed potentiostatic measurements to determine the kinetic

parameters.

Grchev et al (1991) have studied the electrochemical behaviour of poly acrylic

acid and polyacrlyamide as inhibitors for iron and found that these inhibitors were very

effective in acid medium. Methacrylonitrile - K2S2O8 system offered inhibition by in situ

formation of polymer film. The film formed on mild steel (Mengoli et al 1991) affected

both anodic and cathodic reactions in acid medium.

The corrosion inhibition of iron in acid chloride solution offered by a new class

polymer, ortho substituted poly ethoxyaniline, a conducting polymer has been studied by

Sathiyanarayanan et al (1992). The preparation of the polymer by electrochemical method

has been reported. The polymer has been characterized by infrared and uv-vis absorption

studies. Its corrosion inhibition action has been examined by the Tafel extrapolation method,

LPR method, Impedance method and direct weight loss method. The double layer

capacitance indicated strong adsorption of polymer following the Temkin isotherm.

Troch-Nagels et al (1992) studied electron conducting coating of mild steel by

electro polymerization. They obtained poly aniline in nitric acid solution. On iron

surface, the films had a good structure but were brittle and powdery on surface. Further,

they continued the study on poly pyrrole, which was prepared using Na2SO4 solution,

formed a conductive polymer and ensured good corrosion resistance of the substrate, but

they were brittle and adhesion to the substrate was not high.

Isaosekin et al (1992) have synthesised polymer films based on aniline, phenol

type monomers and studied behaviour of corrosion protection behaviour of the films on

mild steel. The polymerization of ortho-phenetidine (Sundeep Kumar et al 1993) leads

to the formation of two types of polymers. The polymer is soluble in dimethylsulfoxide

(DMSO) and N-methylpyrollidine (NMP), whereas the red form of the polymer is also

soluble in methanol and ethanol. Thesealcoholic solutions of the polymers were used as

corrosioninhibitors for iron in 1.0 N HCl medium.

The inhibitive action of ortho - methoxy substituted polyaniline, on the corrosion

of iron in acidic chloride solution has been evaluated by Electro chemical impedance

spectroscopy, polarization and weight loss techniques by Sathiyanarayanan et al (1994).

The inhibition efficiency was found to be 80 - 88% even at 25ppm concentration. Double

layer capacitance data indicated a strong adsorption of polymer following the Temkin

adsorption isotherm, which was largely responsible for its inhibition action.

Muralidharan et al (1995) have studied the inhibitive action ofPoly amino

benzoquinones (PAQ) on the corrosion of mild steel in 1N H2SO4 and 1N HCl solutions.

They get strongly adsorbed on the active sites and form a protective film affecting both

anodic and cathodic reactions.

Ahmed and MacDiarmid (1996) have studied the inhibition of corrosion of

steels in 0.1M HCl using conducting polymers. Stainless steel was made passive by applying

a potential of about 0.1V vs SCE and a current of about 100 A/cm2. The conducting

polymer emeraldine was applied chemically on the surface of the stainless steel.

Pre-treatments with some chelating agents inhibited the corrosion of stainless steel in

0.1M HCl for about 1 month.

The corrosion inhibition on mild steel in H2SO4 and IN HCI solution by polyamide

macrocylic compounds. 3, 4: 11, 12 dibenzo - 2,5 : 10, 13 tetra oxo 1,6,9,14 - tetra

azocyetohexa decane has been investigated using electrochemical impedance spectroscopy,

linear polarization resistance and weight loss measurements. The compounds have been

proved as mixed inhibitors (Ajmel et al 1998).

A mechanistic investigation of poly aniline corrosion protection using the

scanning reference electrode technique has been carried out by Patrick et al (1999).

It was observed that phosphoric acid salts of poly aniline (PANI) are more effective for

corrosion protection than sulphonic acid salts. They proposed a model, which entails

deactivation of the metal surface through anodization of the metal by PANI and

formation of an insoluble iron - dopant salt at the metal surface.

Pud et al (1999) have investigated the nature of the oxide layer formed between

poly aniline (PANI) and steel, when the PANI was applied in different ways. They made

the coatings of pure undoped PANI cast from solution and this coating after doping as a

film on the substrate. They also compared the coatings of pure PANI/sulfonic acids

adducts formed from the outset in the doped state through casting from xylene or

chloroform solutions. These workers have found that the formation of pure doped PANI

coatings by casting doped PANI from solutions cannot give as good results as does the

two stage process.

Muralidharan et al (2000) havesynthesised and examined the use of polyamino

quinines (PAQ) as corrosion inhibitors for steel and iron surfaces in acid medium by

electrochemical impedance spectroscopy. They found that PAQs could fulfill the specific

requirements such as the ability to form defect free and compact - barrier type film through

chemisorptive interactions with the metal surface, thus promoting monolayer/ multilayer

formation.

Poly(styrene sulphonic acid)-doped polyaniline has been synthesised and the

influence of this polymer compound on the inhibition of corrosion of mild steel in 1M

HCl has been investigated by Manickavasagam et al (2002) using weight loss

measurement, galvanostatic polarisation studies, electropermeation studies and A.C.

impedance measurements. The polymer acts predominantly as an anodic inhibitor and

performed as effective corrosion inhibitor. The adsorption of this compound on the mild

steel surface obeys Temkin's adsorption isotherm.

Kraljic et al (2004) have studied o-phenylenediamine containing polyaniline

coatings for corrosion protection of stainless steel. It was observed that the addition of

o- phenylenediamine with poly aniline increases corrosion inhibition for stainless steel.

Jeyaprabha et al (2005, 2006) have studied the polymer amines such as poly

(aniline), poly (diphenylamine) and poly amino quinone) in 0.5M H2SO4 solution.

They have found that poly (diphenylamine) was highly effective in comparison with poly

(aniline). The higher efficiency of polymer amines is due to the presence of extensive

delocalization of π electrons, which can interact with the iron electrode surface.

The abovethree polymers were found to act as mixed type of inhibitors and obeyed

Temkin adsorption isotherm.

The copolymers from different feed ratios of N-(acryloxymethyl) benzotriazole

(AMBT) and methyl methacrylate (MMA) have been synthesised using free radical

solution polymerization technique and characterised using FT-IRand 13

CNMR

spectroscopy. The thermal stability of the polymer has been studied using thermo

gravimetric analysis (TGA), the polarisation and impedance measurements showed

different corrosion protection efficiency with change in composition of copolymers.

It has been observed that the copolymer obtained from 1:1 mole ratio of AMBTand

MMA exhibited better protection efficiency than other combinations (Srikant et al 2006).

The copolymers from different feed ratios of N-(methacryloyloxymethyl)

benzotriazole (MMBT) and methyl methacrylate (MMA) have been synthesised using

free radical solution polymerization technique and characterized using FT-IR and 13

C

NMR spectroscopy by Srikanth et al (2006). The corrosion behaviors of mild steel

specimens dip coated with different composition of copolymers have been evaluated by

potentiodynamic polarization and electrochemical impedance spectroscopic (EIS)

method. These electrochemical properties were observed in 0.1M HCl medium. It has

been found that the corrosion protection properties are owing to the barrier effect of the

polymer layer covered on the mild steel surfaces.

Aziz Yagan et al (2006) have investigated the corrosion inhibition of poly

(N-ethylaniline) (PNEA) coatings on mild steel in aqueous acidic solutions using

potentiondynamic technique.Corrosion test results showed that corrosion resistance of

PNEA coatings decreases with increasing concentrations of oxalic acid in polymerization

solution.Decreasing acidity of the polymerization solution causes more effective

protection against corrosion in aqueous acidic corrosive medium.

Electrochemical polymerization of o-nitroaniline has been carried out by

Sachin et al (2007) using graphite electrode in hydrochloric acid medium. The corrosion

behavior of the modified steel surface has been tested by weight-loss, potentiodynamic

polarization and electrochemical impedance spectroscopic technique in 1N solutions of

H2SO4, HCl and NaCl at 303 K. The surface of the steel specimen before and after

treatment with poly nitroaniline has been investigated by scanning electron microscopy

images. The FTIR spectra of the polymer were recorded. The results indicated that the

surface modification of steel specimens enhanced the resistance to corrosion in the

corrosive media.

The inhibitive effect of p-toluidine and poly(p-toluidine) on corrosion of iron in

1M HCl has been studied by the electrochemical methods such as impedance, linear

polarization and Tafel polarization techniques (Manivel and Venkatachari 2007).

The effectiveness of poly (p-toluidine) was found to be high in comparison with that of

the monomer. The results showed that p-toluidine and poly (p-toluidine) suppressed both

cathodic and anodic processes of iron dissolution in 1M HCl.

The synergistic effct of poly acrylamide (PA) and iodide ions on the corrosion

inhibition of mild steel in H2SO4 have been studied by Umoren et al (2007) using weight

loss and hydrogen evolution methods.It is found the inhibition efficiency of PA

synergistically increased on addition of KI. Frendlich, Temkin and Flory-Huggins

adsorption isotherms are found and phenomenon of physical adsorption is proposed from

Ea and ΔG obtained.

The chemical synthesis of water soluble self-doped polyanthranilic acid using

various oxidizing agents has been reported by Sudhishkumar Shukla et al (2008) for the

corrosion inhibition studies. They proposed the use of such functionalized self doped

conducting polymer to get higher solubility and corrosion efficiency. The corrosion

inhibition property of the polymer has been demonstrated for mild steel in acidic

environment using electrochemical impedance spectroscopy, Tafel polarization and

weight loss methods.

The corrosion inhibition of iron in 0.5M H2SO4 by polyaniline in the presence of Zn2+

and Mn2+

ions (1×10−3

M) has been studied using electrochemical impedance spectroscopy,

linear polarization and Tafel polarization methods (Sathiyanarayanan et al 2008).

It has been reported that the metal cations are found to interact directly with polyaniline

via protonation of imine nitrogen atom of quinoid groups of polyaniline inducing

chemical and conformational changes of polymer.

The corrosion inhibition of poly (aniline-formaldehyde) on mild steel in 1.0N HCl

has been evaluated using potentiodynamic polarization, linear polarization, electrochemical

impedance spectroscopy and weight loss measurements. The results showed that poly

(aniline-formaldehyde) as a mixed inhibitor controls mild steel corrosion through

adsorption mechanism. It showed more than 90% inhibition efficiency with 10 ppm.

(Quraishi et al 2009).

The inhibition properties of the electroprepared poly (o-phenylenediamine)

P(oPD)on the corrosion rate of mild steel in HCl solutions have been investigated by

Abd-El Rehim et al (2010) using weight loss and potentiodynamic polarization

techniques. Langmuir isotherm fits well with the experimental data. The thermodynamic

parameters reveal that the inhibition of corrosion by P(oPD) is due to the physical

adsorbed film on the metal surface. P(oPD) in acid solution suppresses the corrosion rate

of mild steel indicating that the polymer act as the mixed type of corrosion inhibitor.

2.4.2 Poly Heterocyclic Compounds as Inhibitors

In situ Polymerization of heterocyclic compounds, such as pyrrole and thiophene

produces homogenous, adhesive films on the metal surface. These films are electronically

conducting and can be used as inhibitors for steel corrosion (Skotheim 1986).

Joshi and Srivastava (1989) haveproved that polyvinyl pyrrolidone having

molecular weight of the order of 10,000 to 40,000 as an effective inhibitor for iron in 5N

H2SO4 solution using linear polarisation and impedance spectroscopic methods.

Hasse and Beck (1994) have studied the electrodeposition of N-subsituted

polypyrolles on iron and the corrosion inhibiting polymer layers strategy. From the

purely aqueous electrolyte solution in 0.1M oxalic acid, polymer films were obtained

with current efficiencies of 10-80%. Current efficiencies decreased with increasing size

of the N-substituent. The deactivation of iron in the presence of oxalic acid was attributed

to the formation of iron (II) oxalate interlayer.

Polarization and weight loss studies (Jianguo et al 1995) have showed both

polyvinylpyrrolidone and polyethylenimine as effective inhibitors for low carbon steel

corrosion over a wide concentration range of aqueous phosphoric acid (H3PO4) solutions.

Both the polymers retard the anodic and cathodic corrosion reactions. They get adsorbed

on the surface hindering the anodic reaction and thereby corrosion.

Beck et al (1996) haveused electrochemical impedance spectroscopy (EIS) to

investigate the effect of electrochemically formed polypyrrole and polythiophene layers

on corrosion rate of iron in acid media. Inhibition of corrosion was only observed for

coatings greater than 1 mm thick and this effect was attributed to a barrier effect.

Ferreira et al (1996) have electrosynthesised strongly adherent poly pyrrole

coatings on iron and mild steel in aqueous nitric acid. Several chemical pretreatments of

the metal surfaces have been compared and the result showed that a treatment by 10%

aqueous nitric acid inhibits iron dissolution without preventing the pyrrole oxidation.

Abed et al (1999) haveinvestigated poly (4 - vinyl pyridine poly - 3 - oxide

ethylene) as inhibitor for Armco iron in H2SO4 by means of linear polarisation and

electrochemical impedance spectroscopy techniques. Then observed that 99 percent

inhibition was due to adsorption and the adsorbed molecules obeyed Frumkin isotherm.

The effect of poly (4-vinylpyridine isopentyl bromide) (P4VPIPBr) in three

degrees of quaternisation (6, 18 and 79%) on the corrosion of pure iron in1.0M sulphuric

acid was investigated by potentiodynamic, polarisation resistance and weight loss

measurements. The polarisation measurements showed that the compound acts as a

cathodic inhibitor and gets adsorbed on the pure iron surface according to the Frumkin

adsorption isotherm model (Chetouani et al 2003).

The influence of poly (4-vinyl pyridine)-poly 3-oxide-ethylene) tosyle, on the

corrosion inhibition of iron in 1.0M sulphuric acid medium was studied using weight loss,

polarisation resistance, potentiodynamic and electrochemical impedance spectroscopy

measurements. This polymer was an excellent inhibitor and its inhibition efficiency increased

with the increase of concentration to attain 100 percentages. Potentiodynamic polarisation

studies clearly revealed that it acts as mixed type inhibitor (Chetouani et al 2004).

The effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M sulfuric

acid in the presence of poly (4-vinylpyridine) has been studied by Lahcène Larabi (2004)

using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization

and polarization resistance measurements. The results obtained showed that poly

(4-vinylpyridine) effectively reduced the corrosion rate of mild steel.

The influence of' 3,5-dimethyl-IH-pyrazole (P1), pyridine (P2) and 2-(3-methyl-

1H-pyrazol-5-yl) pyridine (P3) on the corrosion inhibition of steel in 1.0 M hydrochloric

acid solution is studied using weight-loss, potentiodynamic and EIS measurements.

The results obtained showed P3 as the best inhibitor and its inhibition efficiency

increased with the increase of concentration to attain 89% at 10-3

M. Potentiodynamic

polarisation studies clearly revealed that it acts essentially as a cathodic inhibitor.

The inhibitor studied reduced the corrosion rates. Inhibitor efficiency (%) values obtained

from various methods used are in good agreement (Bouklah et al 2005).

Electropolymerisation of pyrrole on iron electrodes in the presence of sodium bis

(2-ethyl hexyl) sulfo succinate in a wide pH interval has been carried out by Lehr and

Saidman (2007). The characterisation of the films is done using electrochemical

techniques, scanning electron microscopy and Infrared spectroscopy. The effects of

various parameters on electrodeposition have been investigated. The electrochemical

synthesis of polypyrrole results in improved anticorrosion properties.

Inhibition of corrosion of mild steel by homopolymer and bilayer coatings of

polyaniline (PAni) and poly pyrrole (Ppy) have been studied by Aziz Yagan et al (2007)

using potentiodynamic polarization, Tafel test and electrochemical impedance spectroscopy

techniques in various aqueous oxalic acid solutions. The electroactivity and corrosion

tests showed that prepassivation process improved anticorrosive properties of Ppy and

PAni/Ppy bilayer coatings.

The corrosion behavior of mild steel in sulphuric acid solution containing various

concentrations of a co-polymer formed between maleic anhydride and N-vinyl-2-

pyrrolidone (VPMA) has been investigated by Ganesha Achary et al (2008) using

weight-loss, polarization and electrochemical impedance techniques. Scanning electron

microscopy (SEM) studies of the metal surfaces confirmed the existence of an adsorbed

film and the adsorption followed the Langmuir isotherm.

The corrosion inhibition of mild steel in IM H2SO4 in the presence of

polyvinylpyrolidone (PVP) and polyacrylamide (PA) as inhibitors at 30 – 60°C has been

studied using gravimetric and gasometric techniques (Umoren et al 2008). The results

obtained indicated that increase in temperature increased the corrosion rate and thereby

decreased the inhibition efficiency.

2.5 POLYMERIC INHIBITORS FOR FERROUS MATERIALS IN NEUTRALMEDIA

In cooling water systems, various cationic and anionic polymers have been

studied. Poly ethylene oxide (PEO) and poly di - Methyl sulphoxide (PDMS) are found to

be effective inhibitors for ferrous and non - ferrous materials in fresh water systems.

The efficiency has been examined by impedance spectroscopy, weight loss and

potentiodynamic methods (Ahmad 1988).

Sekine et al (1992) haveused polyethylene imine and its derivatives, poly

acrylamine (PAAM) and poly dicyano diamide derivative as cationic polymers.

Polymaleic acid and its derivatives and poly acrylic acid and its derivatives as anionic

polymers were found to be antiscaling and corrosion inhibitors in cooling water systems.

The inhibitory action of 3-(trimethoxysilyl) propanethiol-1 (TMSPT) on carbon

steel corrosion in 3.5% solutions NaCl of different pH has been examined by means of

polarization technique by Beccaria et al (1994). Electrochemical and weight loss tests

showed that the inhibitory action of TMSPT increases with increasing TMSPT

concentration, and decreases with increasing exposure time. TMSPT acts as cathodic

inhibitor reaching a comparable inhibiting power.

Santos et al (1998) haveproved that in 3% NaCl solutions, polyaniline coated

mild steel and stainless steel specimen’s exhibit enhanced corrosion protection.

A monolayer of 11-mercapto-1-undecanol adsorbed on the electrolytically

reduced iron surface has been modified with tetra ethoxy silane, octyl triethoxy silane

and/or octa decyl triethoxy silane (TES). The two dimensional polymer film of the

monolayer modified twice with TES and subsequently with C18 TES protects iron in

aerated 0.5 M NaCl solutions (Katsuhisa Nozawa et al 1999).

Sathiyanarayanan et al (2006) havestudied about the inherently conducting

polymers such as polyaniline and polypyrrole containing organic coatings which offer

corrosion protection of steel in acid and neutral media. The use of chemically prepared

poly diphenylamine (PDPA) in vinyl coating for corrosion protection of steel in 3 percent

NaCl solution has also been studied. The corrosion protection performance of the coating

on steel has been evaluated by EIS for a period of 80 days. It has been found that the

coating containing 3 percent PDPA is able to protect steel very effectively.

The hybrid material polypyrrole / P W12O3-

40 has been electro synthesized by

Bonastre et al (2006) on carbon steel electrode in acetonitrile medium; These hybrid

coatings have been examined against corrosion in chloride containing 0.05 M NaOH.

Polarisation resistance and Fe2+

concentration measurements showed that the obtained

coatings provide good protection against corrosion in chloride containing media.

Anticorrosion performance of polyaniline emeraldine base / epoxy resin (EB /ER)

coating on mild steel in 3.5 percent NaCl solutions at various pH values has been

investigated by Chen et al (2007) through electrochemical impedance spectroscopy

(E1S) for 150 days. In neutral solution (pH 6.1), EB / ER coating offered very efficient

corrosion protection with respect to pure ER coating. The observation of a Fe2O3 / Fe3O4

passive film formed on steel confirms that the protection by EB is mainly anodic.

The electrochemical copolymerization between pyrrole and o-toluidine has been

studied as an alternative method for obtaining good quality coating (low permeability and water

mobility, high stability), which could also be easily synthesized on steel. The protective

behaviour of these coatings has also been investigated (Yalcinkaya et al 2008) against

mild steel corrosion in 3.5% NaCl solution, by means of electrochemical impedance

spectroscopy and anodic polarization curves. It is found that the monomer feed 8:2 ratio

gives the most effective coating against the corrosion of mild steel.

The effect of polyethyleneimine (PEI) as a corrosion inhibitor for ASTM 420

stainless steel in 3% aqueous NaCl solution has been studied by Matjaž Finšgar (2009).

The results of linear polarization and cyclic polarization measurements indicate high

inhibiting effectiveness of polymer.Immersion tests in the presence of PEI showed

remarkable protection against uniform corrosion. The film persistency immersion testing

indicated that the protective layer is formed and stable in a non-inhibited NaCl solution.

2.6 POLYMERIC INHIBITORS FOR NON – FERROUS MATERIALS IN

NEUTRAL MEDIA

Hyuncheol Kim et al (1998) have synthesized the copolymer poly vinyl

imidazole (VI) and vinyl trimethoxy silane (VTS) in benzene at 68°C as a novel

corrosion inhibitor for copper. Corrosion protection capabilities of the copolymer at

360°C in air areimproved by increasing the mol ratio of VTS in the feed. This is due to

the improved thermal stability and the reactivity olthe copolymer with copper.

Beccaria et al (1999) have evaluated the inhibitory action of meta acryloxy

propyl methoxy silane (MAOS) on the corrosion of aluminium in 3.5 percent NaCI

solutions.Their results reveal that the siloxane polymeric film formed by MAOS acts as a

good corrosion inhibitor.

He et al (2000) have employed the POP poly (3-octyl pyrrole) coatings to

simulate a defect through the coating to the aluminium metal surface. The sample is

immersed in either 3% NaCl (steel) or in dilute Harrison solution (aluminum), an aqueous

solution consisting of 0.35% (NH4)2SO4, 0.05% NaCl. The authors have considered POP

as component of active corrosion resistant coating system.

The effect of various concentrations (0.5 to 30 ppm) of polyacrylamide samples

which have different molecular weights (sample A = 3.4 x 104, B = 1.52 x 10

4 and C = 1

x 104 g mol

-1) and poly (propenoyl glycine) (sample D) which has the same degree of

polymerization (Dp) as sample C on the corrosion behaviour of tin in 1M NaCl solution

have been investigated by Sayyah et al (2001) at 20°C using potentiodynamic

polarization technique. It is revealed that the inhibition efficiency of polymer increases in

the order of A<B<C<D depending on the molecular weight.

The admicellar polymerization process has been adopted to deposit polystyrene

(PS) and poly (methyl methacrylate) (PMMA) (Matarredona et al 2003) onto

aluminium 7075 surfaces. The characterization of the films has been performed using

FTIR spectroscopy, scanning electron microscopy and atomic force microscopy.

The accelerated corrosion tests reveal the protective characteristics of PMMA. Image

analysis has been used to quantify the extent of corrosion in the crevice.

Tuken et al (2005) have studied the effect of films formed from polypyrrole

polyindole (Pin/PPy) and polypyrrole polythiophene (PPy/PTh) on copper corrosion in

3.5% NaCl. They have found that PPy protects copper surface against corrosion and

concluded PPy/Pin and PPy/PTh film as efficient corrosion inhibitors for copper.

The effect of layers of poly (o-anisidine) (POA) (Shinde et al 2005, Pawar et al 2007)

poly (o-toluidine) (POT) and poly(o-anisidine-co-o-toluidine (OAOT) (Pawar et al 2007,

Torresi et al 2005) formed on copper surface on copper behaviour in 3% NaCl solution

has been reported. The results obtained indicate that they are efficient corrosion inhibitors

and at concentration of 0.1M, the inhibition efficiency obtained is 85.81%, 98.00% and

99.66% for POA, POT and OAOT respectively.

Tuken et al (2006) haveinvestigated the corrosion performance of zinc modified

copper coated with polypyrrole (PPy) and polyaniline (PAni) in 3.5% NaCl solution with

the help of the electrochemical impedance spectroscopy (EIS), and anodic polarization

curves. The zinc particles improved the barrier property of polymer films and provided

cathodic protection to the substrate. The polymer film plays the role of conductor

between zinc particles and copper.

Souza de et al (2007), Vera et al (2007)have studied the influence of polyaniline

(PANI) and poly orthomethoxyaniline (POMA) on corrosion inhibition of copper in 0.1M

NaCl. The best result obtained for polyaniline has been attributed to the fact that the

polymer is involved in the formation of an oxide film on the polymer – metal surface.

This oxide film increases the barrier effect of the polyaniline film and hence the corrosion

inhibitor efficiency is high. The phenomenon of oxide formation has not been observed

with POMA (Vera et al 2007).

Lallemand et al (2007) haveelectrochemically polymerised the films of

1-Dodecylpyrrole (PyCH3) and 12-(pyrrol-l-yl) dodecane-l-thiol (PySH) on a nickel electrode

in acetonitrite medium containing the monomer and lithium perclorate as supporting

electrolyte. The presence of unbound and unoxidised thiol groups at the PySHsurface has

been evidenced together with a strong adhesion to the nickel substrate and they have

exhibited corrosion protection properties in neutral NaCl medium.

Sudheshna Choudari et al (2007 and 2010) have studied electrochemically

polymerized ortho anisidine and poly (o-anisidine)-dodecylbenzenesulfonate coatings on

copper in aqueous sodium salicylate solution to generate a uniform and strongly adherent

poly (O-Anisidine) (POA) and (POA-DBSA) coating. The corrosion protection properties

of the poly (O-anisidine) POA and (POA-DBSA) coatings in aqueous 3 percent NaCl on

copper have been examined by potentiodynamic polarisation measurements and

electrochemical impedance spectroscopy (EIS). POA and (POA-DBSA) exhibits

excellent corrosion protection properties and reduce the corrosion of copper.

2.7 POLYMERIC INHIBITORS FOR NON - FERROUS MATERIALS IN ACID

MEDIA

The effect of poly vinyl pyrrolidine (PVP) of various average molecular weight

(M - 1x104, 2.45x10

4 and 4x10

4), poly 2 - vinyl pyridine (M = 2.85x10

5) and Poly -

4 - vinyl pyridine as inhibitors for the corrosion behaviour of zinc metal in IM H2SO4 has

been studied by Mostafa AboEI-Khair et al (1986) using the weight loss

technique.They have shown that the polymers studied impart significant inhibiting effects

on the corrosion rate of zinc metal. The protection efficiency in the presence of 0.1 M

polymers reaches about 87 percent.

Adel-Sonbati et al (1993) have synthesised a new homopolymer from

cinnamaldehyde and 2-substituted aniline and its Cu(II), Ni(II), Co(II), Zn(II), Cd(II) and

Hg(II) complexes have been synthesised .The mode of bonding between Cu(II), Ni(II)

and Co(II) and the homopolymer' has been studied by IR spectrophotometry and the

corrosion inhibition of all these compounds in HCl media has also been demonstrated.

Schweinsberg et al (1996) haveinvestigated the adsorption and inhibitive effects

of polyvinylpyrrolidone (PVP) and polyethylenimine (PEI) on copper in 2 M H2SO4 at

30° C using weight loss, potentiodynamic and in situ surface-enhanced Raman scattering

(SERS) techniques. Both polymers reduce the rate of the anodic (metal dissolution) and

cathodic (O2 reduction) corrosion reactions. At all concentrations studied, PVP is found

to be a better inhibitor.

Brusia et al (1997) have studied the protection of silver and copper by the use of

polymers such as polyaniline. The addition of Kl with PA offer synergistic effects in acid

media. Electrochemical Impedance and polarisation methods have been used to study

their inhibitive action. The presence of iodide ion in the solutions stabilizes the

adsorption of PA molecules and improves the inhibition efficiency of PA.

Frignani et al (1998) have analysed the inhibition of nickel corrosion in 1N HCl

and H2SO4 solutions using 3 methyl-1-butyne-3-ol (H), its halo derivatives and 1-octyn-

3-ol (OCT) using polarisation techniques. It is revealed that these compounds form

polymeric films. OCT is more efficient than H but the efficiency of the latter can be

improved by replacing the H in C = CH by halogen, especially iodine.

Ye et al (1998) have investigated the corrosion inhibition of copper by PMTA

(1-phenyl-5 mercapto tetrazole) in acid media by weight loss, electrochemical impedance

spectroscopy, linear polarisation techniques. The polymer film has been ssfound to be

superior to those formed by tetrazole, benzotriazole, hydroxyl benzotriazole, 2 mercapto

benzothiazole, 2-mercapto benzoimidazole, imidazole and chromates.

The effects of the addition of poly (4-vinylpyridine) and its additive poly

(4-Vinylpyridine poly-3-oxide ethylene) on the corrosion of Cu60 – Zn40 in 0.51M

HNO3 have been investigated by potentiodynamic and weight loss measurements. Both

the polymers decrease the corrosion rate. The maximum of inhibition was obtained for

poly (4- vinylpyridine poly 3-oxide ethylene (100 percent) with 105M. The inhibition

efficiency obtained from cathodic Tafel plots’ and weight loss methods were in good

agreement (Abed et al 2001).

The effects of poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), sodium

polyacrylate (NaPA), polyethylene glycol (PEG), pectin (P), and carboxymethyl cellulose

(CMC) on the corrosion of cadmium in a 0.5M hydrochloricacid (HCl) solution have been

studied using both electrochemical impedance spectroscopy and Tafel plot techniques

(Khairou et al 2003). In the case of PVA and PEG which have hydroxy groups, there could

be bridging between the polymer and the surface, resulting in an inhibiting effect in the HCl

solution. PVA has much greater adsorbability on the surface than PEG at the anodic potential.

The corrosion performance of PPy coated samples have been investigated in 0.1M

H2SO4 solutions on brass and copper using the electrochemical impedance spectroscopy

(EIS), anodic polarization curves and open circuit potential (Eocp)–time curves

(Tuken et al 2004). They have shown that PPy coating has a barrier property that

protected against the corrosion of copper and brass. The polymer coatings gave better

results with copper than with brass.

The effect of two polyamide compounds on the corrosion behavior of aluminum

metal in oxalic acid solution has been investigated by Abdallah et al (2004) using

potentiostatic and potentiodynamic anodic polarization techniques.The inhibition

efficiency increases with increasing polyamide concentration until a critical value and

then decreases at high polymer concentrations, indicating low inhibition efficiency.

The adsorption process is found to obey Temkin adsorption isotherm.

The corrosion inhibition of aluminum in H2SO4 in the presence of polyethylene

glycol (PEG) and polyvinyl alcohol (PVA) as inhibitors at 30-60 °C has been studied by

Umoren et al (2007) using gravimetric, gasometric, and thermometric techniques. PEG is

found to be a better inhibitor than PVA. Increase in temperature increased the corrosion rate

and decreased the inhibition efficiency. Both PEG and PVA are found to obey Temkin

adsorption isotherm. The phenomenon of physical adsorption has been proposed from the

activation parameters obtained. The thermodynamic parameters reveal that the adsorption

process is spontaneous.

2.8 POLYMER COMPOSITES FOR CORROSION INHIBITION

PANI/inorganic composites such as PANI/TiO2, PANI/Fe2O3, PANI/MnO2,

PANI/ZrO2 and other composites like PANI/(styrene-butadiene-styrene), PANI/poly

(epichlorohydrine-co-ethyleneoxide), PANI/(PS-PMMA), PANI/(PU-PMMA) and PANI/

polyacrylonitrile (Deng et al., 2003; Biswas et al., 1999; Wang et al., 2006; Xie et al., 1998;

Gazzoti et al., 1999; Yang et al., 1993; Jeevananda et al., 2002, 2003; Pan et al., 2005)

have been reported as efficient inhibitors.

The anticorrosion protection of polypyrrole (PPy) on AISI 1010 steel (mild steel)

by the incorporation of TiO2 pigment into the PPy matrix during electrochemical

synthesis has been studied by Denise et al (2003). The morphology of the composite film

has been studied by scanning electron microscopy.The PPy/TiO2 composite shows a

considerable improvement in anticorrosion properties with respect to PPy films after

being submitted to salt spray and weight loss tests.

Mariuz and Galkowski (2004) haveproposed a novel composite organic,

inorganic coating in the form of a redox polymer film for protection of stainless steel

against general corrosion in strong acid- medium (2M H2SO4) and the polymer used is

Poly (4 - vinyl pyridine). By analogy with a conducting polymer (eg. Poly pyrrole),

introduction of the redox polymer composite film leads to stabilization of the steel

substrate's potential within the passive range.

The hybrid composite coatings containing zinc oxide (ZnO) and polyaniline

(PANI) as nano-additives dispersions have been prepared with poly(vinyl acetate)

(PVAc) by Patil et al (2006). The steel plates dip-coated with these formulations have

been tested for corrosion protection by immersion in saline water over long periods.

The coatings containing both ZnO and PANI show improved corrosion resistance as

compared to the single component coating.

The corrosion studies of polypyrrole/DGEBA (Diglycidyl ether of bisphenol A)

composite coatings on mild steel have been investigated by Uffana Riaz et al (2007).

The coating has been characterized by physicochemical as well as physicomechanical

studies while the corrosion protective performance has been evaluated by chemical

resistance in different corrosive media. The composite coatings are found to show far

superior anti corrosive performance than PANI/epoxy coatings in acid, alkaline as well as

saline environments.

It has been found by Sathiyanarayanan et al (2007) that the coating with

composite Polyaniline–Fe2O3 of 1:1 ratio of aniline:Fe2O3 offerhigher protection ability

in 3% NaCl solution. Composites have been chemically prepared by oxidative

polymerization of aniline in phosphoric acid medium with ammonium persulphate as

oxidant and characterized by fourier transform infrared spectroscopy, x-ray diffraction

andscanning electron microscopy methods.

The corrosion protective behavior of waterborne resorcinol formaldehyde (RF)-

cured composite coatings of poly(1-naphthylamine) (PNA)/poly(vinylalcohol) (PVA) has

been investigated by Sharif Ahmad et al (2008) on mild steel (MS). The corrosion

protective performance has been evaluated by physicochemical, physicomechanical,

corrosion protective efficiency and resistance in acid, alkaline and saline media by open

circuit potential (OCP) measurements. Superior corrosion protective performance has

been observed with such polymer composite coating.

Prakash Rao et al (2008) havesynthesized conducting and electroactive polymer

blends of polyaniline (PANI) with polyelectrolyte, poly(diallydimethylammoniumchloride)

(PDDMAC) by an in situ polymerization method and the resulting composites have been

characterized by fourier transform infrared spectroscopy, x-ray diffraction, uv-visible and

electrochemical techniques. The composites have been tested for their corrosion

inhibition property on pure iron in 1M HCl solutions and are found to be effective

inhibitors.

The corrosion studies have also been carried out by Radhakrishnana et al (2009)

on steel plates coated with these formulations containing 10 wt% polyaniline prepared

with different concentrations of nano-TiO2. The coatings prepared from polyaniline–

nano-TiO2 particles synthesized by in situ polymerization are found to exhibit excellent

corrosion resistance much superior to polyaniline (PANI) in aggressive environments.

Elaine Armelin et al (2009) haveemployed polymers such as polyaniline

emeraldine salt, polyaniline emeraldine base, polyaniline emeraldine salt composite with

carbon black, polypyrrole composite with carbon black and poly (3,4ethylenedioxythiophene)

doped with poly(styrene sulphonate) as anticorrosive additives. Their results indicated

that the protection against corrosion imparted by the formulations modified by the addition of

poly (3, 4-ethylenedioxythiophene) doped with poly (styrene sulphonate), polyaniline

emeraldine salt and, especially, polyaniline emeraldine base is significantly high.

The composite Poly (aniline-co-o-toluidine)/polystyrene-sulphonic acid

(COP/PSSA) samples (Neetika Gupta et al 2009) have been synthesized by free radical

chemical oxidative copolymerization of aniline with o-toluidine using ammonium

persulphate as an oxidant in protonic acid medium. They are characterized by UV-visible,

Fourier transform infrared spectroscopy, x-ray diffraction, thermogravimetry, differential

scanning calorimetry and scanning electron microscopytechniques. The properties of the

polymer composite revealed that it can be used as efficient corrosion inhibitor.

Corrosion protective performance of nano structured methyl orange (MO) doped

polyaniline (PANI) and camphorsulphonic acid (CSA) doped poly(1- naphthylamine)

(PNA) dispersed polyurethane-based composite coatings against mild steel (MS) has

been investigated out by Uffana Riaz et al (2009). The influence of the dopant on the

passivation of metal has been analyzed using two different dopants. The corrosion

protective performance of the coatings against mild steel is evaluated by the physico-

mechanical properties and corrosion rate measurements.

Polyacrylic acid/aluminium composite has been prepared using in-situ

polymerization and its maximum corrosion inhibition efficiency on flaky aluminium particles

are investigated by Hongwei Zhu et al (2010). Using scanning electron microscopy and

Fourier transform infrared spectroscopy, polyacrylic acid is found to be coated on the

surface of aluminium particles. The maximum corrosion inhibition efficiency has been

found to be 99.7%.

Polypyrrole (PPy) films containing titanate nanotubes (TiNT) (Herrastia et al 2011)

have been deposited from 0.5 moldm−3

pyrrole (Py) and 1 g dm−3

of TiNT in 0.1 moldm−3

aqueous oxalic acid on 904 L stainless steel (SS) 0.1mm thickness at 298 K. It is

observed that the corrosion rate of SS/PPy/TiTN composite in 3% w/v NaCl decreased in

the presence of the composite films.

From the literature survey, it is clearly understood that polymer amines were

evaluated for their inhibition properties on the corrosion of iron and steel in acid

solutions. Ortho substituted anilines and polyanilines were also studied. More recently

poly(di-phenyl amine) and poly(amino quinine) were reported as corrosion inhibitors of

iron in acidic media. Poly ethyleneglycol was reported as alkaline corrosion inhibitor for

aluminium.

The role of polymer composites in corrosion studies is less undertaken and the

capacity of polymer composite is found to be remarkable in various fields. Hence by

compositing Pani and its derivaties with polyethyleneglycol, the green reaction medium

better performance of corrosion inhibition can be expected with low concentrations of the

composites.

Viewing all these in mind, the present study is carried out to prepare the water

soluble polymer composite of polyethylene glycol with aniline derivatives and to study in

detail the corrosion inhibiting properties of these polymer composites on mild steel in

acid medium.