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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.