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Corrosion inhibition by flower extracts-An over view ISSN Online: 2395-7018 Sangeetha et al.
Int. J. Nano. Corr. Sci. Engg. 2(3) (2015) 14-21 14
Corrosion inhibition by flower extracts-An over view
M.Sangeetha [a]*,S.Rajendran [b], J.Sathiyabama[c], T. Umasankareswari[d],
A Krishnaveni [e] and RM Joany[f]
Most of the flowers are coloured. Colourless flowers have attractive fragrance. Hence Extracts of flowers have active
principles containing polar atoms such as nitrogen, oxygen, sulpher and phosphorus. The active principle molecules
pump electrons towards the metal surface through these electron rich centers. Thus the release of electron from the metal
surface is prevented. Thus
Corrosion of metals is prevented by flower extracts. Weight loss and electrochemical studies have been employed to
evaluate the corrosion inhibition efficiencies of the extracts of flowers. Usually aqueous extracts are conveniently
employed. Adsorption of active principle on the metal surface obey Langmuir, temkin and frenlich absorption isotherm.
Thermodynamic parameters have been calculated. Protective film has been analysed by SEM, EDX, AFM and FTIR.
Mild steel in the metal mostly employed in these studies.
Key words: corrosion inhibitors, flower extract, green inhibitors, colored inhibitors.
Corresponding authors:
[a]. Department of Chemistry (S&H), K.S.Rangasamy College of Technology, Tiruchengode, Tamil Nadu, India, E-
mail:sangeethamanirevathi@gmail.com
[b]. Corrosion Research Centre, Department of Chemistry, RVS School of Engineering and Technology, Dindigul –624005, E-
mail: susrajendra@gmail.com ,
[c]. PG and Research Department of Chemistry, GTN Arts College, Dindigul –624005, Tamil Nadu, India,
[d] Department of Chemistry, Rajapalyam Rajus College, Rajapalayam, Inida
[e] Department of Chemistry, Yadava College, Madurai, India
[f] Sathyabama University, Chennai, India.
1. INTRODUCTION
1.1 FLOWER EXTRACT
Flower extracts have been widely used as corrosion inhibitors [1-10]. In this collection, metion may be made of
Anacyclus pyrethrum L, extract [1], Musa acuminate flower extract [2,3], Staminate flower of Cocos Nucifera
[4], Nerium oleander [5], tecoma [5], Hibiscus sabdariffa flower calyx [6], cassia auriculata [7], Hibiscus rosa-
sinensis[8,9,10]. Isolation of the active principles in the flowers is a very difficult job and time consuming also.
Moreover the active principles present in the flower may be many. Hence isolation of the pigments in pure form
is difficult. Hence many researchers simply go for aqueous extract which may contain a mixture of active
Corrosion inhibition by flower extracts-An over view ISSN Online: 2395-7018 Sangeetha et al.
Int. J. Nano. Corr. Sci. Engg. 2(3) (2015) 14-21 15
incredents this mixture will be useful for synergistic effect.hence aqueous extracts function as synergistic
inhibitiors. Apart from aqueous extracts [8,9,10] acid extracts [3,7] are also employed.
2. METALS
Majority of researchers have used flower extracts to prevent corrosion of mild steel [1, 2, 3, 4, 7, 9,10]
because mild steel is less expensive, easily available and used in various industries. Rajendran etal have used an
aqueous extract of hibiscus rosa- sinensis to inhibit corrosion of aluminium aqueous solution at pH 12.
3. CORROSIVE ENVIRONMENT
The corrosive environment may be acidic medium or basic medium or neutral medium. Sometimes sea
water, groundwater, well water and cooling water systems may be used as environment. Many researchers have used
acidic medium [1,2,3,4,5,6,7]. Rajendran etal have used basic medium [8] and neutral medium [9]. Minhaj et al have
used cooling water system and tap water [10].
4. METHODS
Corrosion inhibition efficiency of flower extracts can be evaluated by various methods. Usually weight loss
method [1, 2, 3, 4, 7, 8, 9]. Polarization and AC imprdance spectra [1, 2, 3, 4, 6, 8, 9] have been used to evaluate the
corrosion inhibition efficiency. By polarization study one can find that if the inhibitor functions as anodic inhibitor
or cathodic inhibitor or mixed type inhibitor. Anodic inhibitor controls anodic reaction (dissolution of metal eg;
M→ M2+ +2e- in acidic medium, basic medium and neutral medium) cathodic inhibitors controls the
cathodic reaction [evolution of H2 gas in the case of acidic medium and formation of OH- in the case of basic
medium and neutral medium].mixed type inhibitors control anodic reaction and cathodic reaction to an equal extent.
Some plant extracts act as anodic inhibitors [1]. Some as cathodic inhibitors [10]. And many as mixed type
inhibitors [2, 3, 4, 7, 10]. It is observed that most of the flower extracts function as mixed type of inhibitors. That is
a good trend. If an extract function as anodic inhibitor, it will promote corrosion beyond the critical inhibitor
concentration, the very fact that extract of flower functions as mixed type of inhibitor is quite encouraging, since the
active principles are many containing polar atoms such as oxygen, sulphur, nitrogen and phosphorus, these active
principles coordinate with the metal ions on the metal surface through their electron rich polar atoms. These electro n
rich centers pump electrons towards the metal surface which discourage the release of electrons from the metal and
there corrosion is prevented.
4.1 ADSORPTION ISOTHERMS
The active principles in the flower extracts are adsorbed in the metal surface through the electron rich polar
atoms. Thus the electron release from the metal is prevented. This is the mechanism of corrosion inhibition.
Adsorption of thes molecules on the metal surface obey various adsorption isotherm such as Langmuir [1,3,4,7,10]
Temkin [2,3,4,7] and Freunlich [7,10].
4.2 SURFACE ANALYSIS
The protective film formed on metal surface can be analysed byn various techniques such as FTIR,
Fluorescence, XRD, SEM, EDAX and AFM. But only a few researchers concentrate on this part of study. They have
made use of SEM [2,6] EDAX [6] AND afm[9]. Only alimited number of researchers go for FTIR [8,9].
4.3 THERMODYNAMIC PARAMETERS
Corrosion inhibition by flower extracts-An over view ISSN Online: 2395-7018 Sangeetha et al.
Int. J. Nano. Corr. Sci. Engg. 2(3) (2015) 14-21 16
Some researchers have carried out their researches at various temperature and calculated thermodynamic
parameters to interpret the inhibition efficiencies [1,3,4].
5. FLOWER EXTRACT AS CORROSION INHIBITORS
Inhibition of the corrosion of mild steel in sulfuric acid by extracts of Anacyclus pyrethrum L. (leaves and
stems, AP-LS; flowers AP-F; roots, AP-R) has been studied by use of electrochemical impedance spectroscopy
(EIS) and potentiodynamic polarization. Anacyclus pyrethrum L. inhibited the corrosion of mild steel in 0.5 M
H2SO4solution. Polarization curves show that the different parts of plants act as anodic type inhibitors. Changes in
impedance data [charge transfer resistance, Rt, and double layer capacitance, Cdl] were indicative of adsorption of
the extracts on the metal surface, leading to the formation of protective films. The extent of surface coverage by the
inhibitors was determined by measurement of ac impedance; it was found that adsorption of these inhibitors on the
mild steel surface obeys the Langmuir adsorption isotherm. Activation energies in the presence and absence of AP -
LS and AP-F were obtained by measuring the temperature dependence of the corrosion current [1].
The corrosion inhibition performance of Musa acuminata flower [MAN [F] extract on mild steel in 1 N
sulphuric acid solution was monitored by weight loss measurements and electrochemical technique like
potentiodynamic measurement for various concentrations of the extract and in the temperature range 303 K to 353
K. The inhibition efficiency of MAN [F] extract increased with the increase of concentration but decreased with the
increase in temperature. Inhibitor showed a maximum efficiency of 95.01% at 2% v/v extract concentration for 5
hours immersion. The polarization curves indicated that MAN [F] acts as a mixed type inhibitor. Electrochemical
impedance spectroscopy studies showed the change in charge transfer capacitance with the change in concentration
of the flower extract. The Temkin adsorption isotherm was tested for its fit to the experimental data. Results of SEM
study on the surface morphology of mild steel in uninhibited and inhibited acid solution showed that
the corrosion rate is reduced to a low value in the presence of the inhibitor. This may be due to adsorption of
inhibitor molecules on the surface as a protective layer preventing acid attack. A mechanism of physical adsorption
of the phytochemical components on the surface of the metal is proposed for the inhibition mechanism [2].
The inhibition effect of acid extract of Musa acuminata flower [MAF] on the corrosion of mild steel in 1 N
hydrochloric acid solution has been investigated by potentiodynamic polarization, electrochemical impedance
spectroscopy and weight loss methods. The corrosion inhibition efficiency increases with
increasing flower extract concentration. Cathodic and anodic polarization curves showed that the Musa
acuminata flower is a mixed type inhibitor. The effect of temperature on the corrosion behaviour of mild steel in 1 N
HCl in the absence and presence of flowerextract was studied in the temperature range of 30-80 °C. Thermodynamic
consideration reveals that the adsorption of Musa acuminata flower extract on mild steel surface is spontaneous and
followed Langmuir and Temkin adsorption isotherms. The weight loss measurement results were close to
electrochemical studies. A possible mechanism for the inhibition behaviour of flowerextract by physical adsorption
of its phytochemical components on the surface of the metal has been proposed [3].
Corrosion control methods, especially the use of inhibitors, have gained monumental importance in the
present scenario of expunging corrosion and the quest for eco-friendly reasons continues. To arrive at an
inexpensive non-toxic, eco-friendly inhibitor formulations the present study on the use of
Staminate Flower extract of Cocos Nucifera has been carried out by the classical weight loss measurements and
electrochemical polarization measurements. The acid extract could bring out a maximum of 97.3% inhibition of
mild steel corrosion in 1M HCl. Thermodynamic parameters of the corrosion process were calculated from
temperature study. The adsorptive behaviour of Staminate Flower extract in acid solution may be approximated both
by Langmuir and Temkin type isotherms. The results obtained by Tafel, Linear polarization resistance, and
impedance spectroscopy have been correlated with the classical weight loss measurements. Values of Tafel constant
ba and bc confirmed that the Staminate Flower extract acts like mixed type inhibitor. Examination of the surface of
the metal in the presence of the inhibitor confirmed the deposition of inhibitor on the metal surface. The
Corrosion inhibition by flower extracts-An over view ISSN Online: 2395-7018 Sangeetha et al.
Int. J. Nano. Corr. Sci. Engg. 2(3) (2015) 14-21 17
Staminate Flower extract in HCl medium efficiently inhibits the corrosion and proved to be zero cost inhibitor, eco-
friendly, non-toxic, and highly economical [4].
Air dried flowers of Nerium oleander and Tecoma stans have been investigated for their polyphenolics. The
pigments have been found to myricetin and rutin respectively which were characterized by chromatography and
spectral studies. These pigments were screened for their antibacterial and antifungal activity against different
organisms. It was ascertained that the ethyl acetate fractions of flowers of both the plants are highly sensitive to
staphylococcus aurcus, staphylococcus albus and klebsiella sp and moderately sensitive to pseudomonas and protecs
sp. They were also found to be active antifungal agents against Candida albicans, Aspergillus niger.
The extracts were also tried as corrosion inhibitors on mild steel and aluminium in 2M HCl at 30 ± 1°C. It was
found that the percentage of inhibition increases with the increase in volume/concentration of the extracts [5].
The corrosion behaviour of recycled aluminium alloy was investigated in three solutions [S1, S2 and S3]
using potentiodynamic polarization and electrochemical impedance spectroscopy [EIS]. Solution S1 is an
aqueous extract of hibiscus sabdariffa flower calyx, S2 is an aqueous extract of lemon [Citrus lemon] and S3 is a
3.5% wt solution of cooking salt. The recycled aluminium alloy samples [bare and polished as well as corroded
samples] were characterized by optical microscopy, scanning electronic microscopy [SEM] and EDX analyses.
Surface properties were correlated with the corrosion resistance parameters of the material. The electrolytes
aggressiveness was assessed by potentiodynamic polarization and electrochemical impedance measurements. The
studies were carried out in solutions with pH = 4 and pH =8 [6].
The inhibition efficiency of acid extract of flowers of Cassia Auriculata [CAF] plant on the corrosion of
mild steel in 1 M HCl was investigated by weight loss measurements and electrochemical studies. The corrosion rate
of mild steel and the inhibition efficiencies of the extract were calculated. The results obtained showed that
the extract could serve as an effective inhibitor for thecorrosion of mild steel in HCl media. Inhibition was found to
increase with increasing concentration of the plant extract. The inhibitive action of plant extract is discussed on the
basis of adsorption of stable complex at the mild steel surface. Theoretical fitting of different isotherms, Langmuir,
Temkin, Freundlich and the thermodynamic model, were tested to clarify the nature of adsorption. Potentiodynamic
Polarisation curves revealed that this inhibitor act as a mixed type inhibitor and the inhibition efficiency of up to
74.7% can be obtained [7].
The inhibition efficiency [IE] of an aqueous extract of Hibiscus rosa-sinensis [white] in
controlling corrosion of aluminium at pH 12 has been evaluated by weight loss method in the absence and presence
of Zn2+. The formulation consisting of 8 mL flower extract [FE] and 50 ppm of Zn2+ had 98% inhibition
efficiency. Polarization study revealed that this formulation functioned as cathodic inhibitor. AC impedance spectra
revealed the presence of a protective film formed on the metal surface. FTIR spectra revealed that the protective film
consisted of a complex formed between the active principle of the flower extract and Al3+ [8].
The inhibition efficiency [IE] of an aqueous extract of white flower, namely, Hibiscus rosa-sinensis Linn., in
controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl- has been evaluated
by the mass loss method. The flower extract [FE] shows good IE. In the presence of Zn2+, excellent IE is shown by
the flower extract. A synergistic effect exists between the flower extract and Zn2+. The mechanistic aspects
of corrosion inhibition have been investigated by polarization study and AC impedance spectra. Polarization study
reveals that the formulation consisting of flower extract and Zn2+ functions as a mixed inhibitor. AC impedance
spectra reveal that a protective film is formed on the metal surface. The active principle in the flowerextract is
quercetin-3-O-glucoside. This has been confirmed by UV-visible absorption spectra. The protective film formed on
the metal surface has been analyzed by FT-IR and AFM spectra. It is found that the protective film consists of Fe2+-
quercetin-3-O-glucoside complex and Zn[OH]2[9].
The inhibitive effects of aqueous extracts of Eucalyptus [leaves], Hibiscus [flower], and Agaricus on
the corrosion of mild steel for cooling-water systems, using tap water, have been investigated by means of weight
Corrosion inhibition by flower extracts-An over view ISSN Online: 2395-7018 Sangeetha et al.
Int. J. Nano. Corr. Sci. Engg. 2(3) (2015) 14-21 18
loss [under static as well as dynamic conditions] and polarization methods. All the plant extracts were found to
inhibit corrosion of mild steel and their inhibitive efficiencies were in the order: Agaricus [85%], Hibiscus [79%],
and Eucalyptus [74%] under the static test condition. The inhibition efficiencies remain almost the same under
dynamic test condition, which are nearer to field conditions. All the inhibitors [extracts] were found to follow
Langmuir as well as Freundlich adsorption isotherms, i.e. they inhibit corrosion through adsorption. Polarization
measurements gave a similar order to inhibition efficiencies of plant extracts as that determined using the weight-
loss technique. Agaricus extract was found to be predominantly a cathodic inhibitor, while the extracts of
Eucalyptus and Hibiscus were found to be mixed inhibitors. The inhibitive effects of aqueous extracts of Eucalyptus
[leaves], Hibiscus [flower], and Agaricus on thecorrosion of mild steel for cooling-water systems, using tap water,
have been investigated by means of weight loss [under static as well as dynamic conditions] and polarization
methods. All the plant extracts were found to inhibit corrosion of mild steel and their inhibitive efficiencies were in
the order: Agaricus [85%], Hibiscus [79%], and Eucalyptus [74%] under the static test condition. The inhibition
efficiencies remain almost the same under dynamic test condition, which are nearer to field conditions. All the
inhibitors [extracts] were found to follow Langmuir as well as Freundlich adsorption isotherms, i.e. they
inhibit corrosion through adsorption. Polarization measurements gave a similar order of inhibition efficiencies of
plant extracts as that determined using the weight-loss technique. Agaricus extract was found to be predominantly a
cathodic inhibitor, while the extracts of Eucalyptus and Hibiscus were found to be mixed inhibitors [10].
Even though extracts of many natural products have been used as corrosion inhibitors [11-34], the use
of extracts of flowers is very much limited. Hence there is scope for use of extracts of flowers as corrosion inhibitors
in the near future.
6. ACKNOWLEDGEMENT
The authors are thankful to their respective managements.
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Prof. Dr. M. Sangeetha
Corrosion inhibition by flower extracts-An over view ISSN Online: 2395-7018 Sangeetha et al.
Int. J. Nano. Corr. Sci. Engg. 2(3) (2015) 14-21 21
Prof. Dr. S. Rajendran (Red Tie) and Prof. S. Syed Abuthaheer with Research Team
Received: (01-07-2015)
Accepted: (01-08-2015)
