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.
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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