Chapter II Review of Literature -...

Chapter II

Review of Literature

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CHAPTER II

REVIEW OF LITERATURE

The natural sea water is a complex mixture of inorganic salts such as

chlorides, sulphates, fluorides, nitrates, nitrites, phosphates, etc of Na, Ca, Mg, K, Fe

and other heavy metals. In addition to the salts, it contains dissolved gases such as

carbon dioxide and oxygen, suspended impurities, organic matter and

microorganisms. Hence the sea water is a very intensive corrosive medium for the

corrosion of metallic structures and thereby causing huge problems to the industrial

sector. Hence protection of metal structures against in sea water environment is

become a major industrial problem. The sea water find wide applications in power

plant, cooling tower system, condenser, compressor, oil-refineries and heat

exchangers, etc., as a coolant, which causes severe corrosion problems such as loss in

efficiency, shut-down, loss in production, replacement of the corroded components,

release of toxic corrosion products to the environment and explosion in pipe lines,

etc.

The organic compounds provide extensive corrosion inhibition property has

been published [1]. The high corrosion inhibition efficiency of organic molecules due

to the presence of hetero atoms such as nitrogen, oxygen, sulphur and phosphorus, ∏

bond, multiple bonds or aromatic rings which are adsorbed on the metal surface by

blocking the active sites of the metal surface. Moreover the order of the inhibition

efficiency of the hetero atoms follows O < N < S < P [2-5]. The process of inhibition

either due to the adsorption or phase layers on the metal surface by the inhibitor

molecules [6]. At the same time the corrosion inhibitors such as chromates and

nitrites, etc are ruled out due to their toxic nature and they cause environmental

hazard [7]. Though different methods such as alloying, anodic protection, cathodic

protection and electroplating, etc available for corrosion control of metal structures in

sea water, the use of inhibitors is unique and effective especially in case of cooling

water system [8].


28

II.1. Study of corrosion inhibition of various metals and alloys in natural and

synthetic sea water environment

Sea water is the well known aggressive medium containing high chloride ions

causing severe corrosion problems to the metals and alloys. Based on the metal /

environment combinations, different types of inhibitors are used in suitable

concentrations for corrosion control. The use of inhibitors is an important method of

protecting materials against corrosion. The various inorganic and organic compounds

have been tried and reported as inhibitors for metals and its alloys in neutral chloride

medium. The inhibitors contain hetero-atoms such as N, O, S and P can coordinate

with the corroding metal ions, through their electrons and hence protective films are

formed on the metal surface so that corrosion is prevented [9-124].

Inhibitors:

Both inorganic compounds [22, 24, 25, 29, 32, 40, 46, 63, 68, 71, 82, 84, 88,

89, 103, 108, 109, 119], and organic compounds – naturally available [13, 30, 70, 96,

97, 121, 124] and synthesized compounds [9-12, 14-21, 23, 26-28, 31, 33-39, 41-45,

47-62, 64-67, 69, 72-81, 83, 85-87, 90-95, 98-102, 104-107, 110-117, 119, 120, 122,

123] have been used to control the corrosion of various metals and its alloys in

natural/artificial sea water medium.

Metals:

The inhibitors have been used to control the corrosion of various metals such

as Fe [20, 26, 32, 35, 46, 79, 81, 106, 108], carbon steel (CS) [10, 11, 13, 16, 21, 23,

31, 40, 48-51, 62, 63, 66, 70, 71, 75, 78, 82-84, 94, 104, 107, 118, 120, 121, 123],

mild steel [9, 12, 43, 52, 43, 65, 69, 80, 114], stainless steel (SS) [87, 88, 91, 93], Al

and its alloys [17, 18, 22, 24, 29, 45, 64, 68, 74, 77, 103, 109, 112, 115, 119], Zn and

its alloys [25, 85], Cu and its alloys [14, 15, 19, 27, 28, 30, 32-34, 36-38, 41, 42, 44,

47, 54-61, 67, 72, 73, 76, 81, 86, 89, 90, 92, 95-102, 105, 110, 112, 113, 116, 117,

122, 124] and Ni and its alloys [32, 39] in natural/artificial sea water medium.

Medium:

The inhibition efficiency (IE) of various inhibitors, in controlling corrosion of

metals and its alloys in natural sea water medium [9, 10, 13, 14, 29, 35, 42, 43, 70, 75,

77, 78, 85, 88, 89, 96-98, 109, 111, 112] and artificial sea water medium [11, 12, 15-


29

28, 30-41, 44-69, 71-74, 76, 79-84, 86, 87, 90-95, 99-108, 110, 113-124] have been

studied.

Additives:

Along with the inhibitors, substances like EDTA [9], Al3+ and Mg2+ [11], Ca2+

[11, 50], Zn2+ [12, 21, 23 , 31, 66, 79, 80], thiosulphate [16], docosanol [42], KI [49],

sodium benzoate [52], oxalic acid [53], sulphide [59], carbon black [62], Ni2+ [66],

cysteine [117] and SiO2 [118] have been used to enhance the corrosion inhibition

process. More over, ammoniac [34], ethanol [36, 61, 83, 96], dil. NaOH [40], toluene

[61], acetic acid [71] and ammonia [113] have been employed as solvent for the

dissolution of inhibitors.

Temperature:

The IE of various inhibitors have been evaluated at room temperature [9-46,

48, 49, 51-70, 72-79, 81-95, 97-106, 108-124], and also at higher temperatures [47,

50, 71, 80, 89, 96, 103, 107].

pH:

The IE of various inhibitors have been evaluated at neutral pH [9-47, 49, 61-

94, 96-101, 104, 106, 107, 109-115, 118-120, 122-124], and also at pH 4.0 [48, 103],

6.8 [60], 6.0 [95, 105, 117], 6.5, 7.0 and 9.0 [102], 8.0 [108] and 4.6 [121].

Methods:

The IE of various inhibitors have been studied using different techniques such

as weight loss method [9, 10, 13, 14, 16, 18, 21-23, 27-28, 36, 37, 42, 47, 54, 57, 58,

60, 62, 70-72, 76, 79, 80, 88, 91, 93, 98, 100, 102, 119, 124], pH variation [44, 54, 57,

114], potentiodynamic polarization [11-18, 20, 22, 25-34, 36-39, 41-45, 47-50, 53-58,

60-64, 66-84, 87, 89, 91, 93-95, 99-107, 109-113, 116-124], electrochemical

impedance spectroscopy (EIS) [14, 15, 18-20, 22, 28, 30, 31, 34, 36-41, 43-46, 48-50,

52-56, 58, 60, 62, 64-70, 72, 74, 75, 77, 78, 81, 82-84, 86, 90, 94, 95, 99-107, 110-

115, 117, 118, 120-124], open circuit potential (OCP) [32, 45, 46, 64, 71, 81, 87, 101,

123], chronoamperometry [45, 111], inductively coupled plasma atomic emission

spectroscopy (ICPAES) [73, 112], cyclic voltammetry (CV) [15, 17, 29, 37, 39, 45,

61, 63, 85], electrochemical frequency modulation (EFM) [72, 99, 122], quartz crystal


30

analysis (QCA) [45, 60, 76], molecular stimulation [99, 122], gravimetry [95],

thermogravimetric analysis (TGA) [52, 94], stalagmometry [75], electrochemical

noise analysis (ENA) [19, 24, 107], electron probe microanalysis (EPM) [25, 119],

coupling test [40], kinetic model technique [35], capillary gas chromatography (CGC)

[9], growth curve method [9] and scanning vibrating electrode technique [46] have

been employed.

Adsorption isotherms:

The adsorption behaviour of the atoms/ingredients present in the inhibitor over

the metal surface has been investigated and the type of adsorption isotherm such as

Langmuir adsorption isotherm [10, 13, 18, 20, 42, 43, 60, 67, 72, 74, 76, 81, 96, 97,

112], Freundlich adsorption isotherm [27], Frumkin adsorption isotherm [47] and

Temkin adsorption isotherm [94, 97], have been proposed, and it is supported by

various thermodynamic parameters such as changes in free energy, enthalpy and

entropy.

Surface analysis:

The protective films formed on metal surface, during the process of corrosion

protection of metals by inhibitors, have been analyzed by various surface

morphological studies such as UV-visible spectroscopy [18, 36, 70, 94, 96, 97, 102],

fluorescence spectroscopy [12, 21, 23], Raman spectroscopy [58, 83], FTIR [15, 21,

23, 28, 33, 36, 49, 51, 57, 61, 70, 78, 79, 94, 96, 97, 102, 112], EDX [22, 36, 47, 54,

63, 74, 78, 84, 85, 95, 110, 112, 124], XRD [10, 18, 21, 40, 59, 94, 96, 98, 103, 106,

114], Auger electron spectroscopy [14, 31, 82], XPS [20, 25, 31, 32, 56, 63, 73, 82,

91, 93, 108, 120], ESCA [100, 102], STM [20, 43], SEM [18, 22, 30, 32, 36, 40, 42,

47, 54, 59, 60, 63, 64, 68, 76-78, 80, 84, 85, 92, 98, 100, 102, 103, 106, 109, 110,

112-115, 123], and AFM [38, 49, 56, 61, 70, 101, 104, 120, 121]. It has been

observed that the protective film consists of the metal-inhibitor complex at the anodic

sites of metal surface and in some cases, Zn(OH)2 is deposited on the cathodic sites of

the metal surface, if Zn2+ is used along with the inhibitor.

Plant and animal materials:

Extracts of various parts of the plants such as leaves [97], flowers [70] and

seeds [30, 96], and animal products such as honey [13], protein [121] and fungicides


31

[124] have been used as corrosion inhibitors since they are eco-friendly, non-toxic,

bio-degradable and cost effective.

Solvents:

Solvents such as water [13, 30, 70, 97] and ethanol [96], have been used to

extract the ingredients present in plant and animal products.

The various inhibitors used to prevent corrosion of various metals and alloys in sea

water are given in Table I.

Table I. Inhibitors used to prevent corrosion of metals in sea water

S.No Metal Medium Inhibitor Additive Method Findings Ref

1 Mild steel

Sea water (Dona Paula Bay, Arabian Sea)

Exopolysaccharide (EPS)

10-mM EDTA, 2N HCl

Weight loss, capillary gas chromatography and growth curve experiments.

EPS is a strong corrosion inhibitor, protective film consists of metal-polysaccharide complex and EPS served as a structural matrix polymer.

9

2 Carbon steel Sea water

Non-ionic polyoxy ethylene monopalmitate (Pa EO), cationic hexadecyltrimethyl ammonium bromide (HTABr) and anionic sodium dodecyl sulphate (SDS).

-

Weight loss study and X-ray diffraction analysis.

IE increases with inhibitor concentration, obeys Langmuir isotherm and the order of inhibition is SDS < HTABr < Pa EO.

10

3 Steel 3.5% NaCl and sea water

Thiourea (TU) Al3+, Ca2+ and Mg2+.

Potetentiodynamic polarization study.

Cathodic inhibitor, IE in presence of Al3+ ion is about 90% and interpretation of corrosion inhibition mechanism and cathodic control.

11

4 Mild steel

Chloride medium

2-carboxyethyl phosphonic acid (CEPA) and ethyl phosphonic acid (EPA)

Zn2+

Polarization study and fluorescence spectra.

Mixed-type inhibitor, IE decreases as the immersion period increases and IE of CEPA is better than CPA.

12


32

5 Carbon steel

High saline water

Natural honey (NH)

-

Weight loss and potentiostatic polarization technique.

IE increases with inhibitor concentration, but decreases due to the growth of fungi and obeys Langmuir adsorption isotherm.

13

6 CuNi 10Fe

Sea water Sodium-diethyl-dithiocarbamate (NaDDTC)

-

Weight loss, polarization measurements, EIS and Auger electron spectroscopy (AES) studies.

Mixed-type inhibitor and the inhibition film do not lose efficiency even at anodic polarization.

14

7 Cu Aerated 3% NaCl solution

2-mercapto-1-methylimidazole (McMIm)

-

Electrochemical polarization, impedance spectra, cyclic voltammetry and IR spectra techniques.

Mixed-type inhibitor, excellent inhibitor for Cu corrosion and IE from cathodic Tafel plots and polarization were in good agreement.

15

8 Carbon steel

5% NaCl + 0.5% acetic acid

n-dodecylquinolinium bromide (DDQB), n-dodecylpyridinium chloride (DDPC), benzyl,sterayl,dimethyl ammonium chloride (BSDMAC), 1-(2-amminoethyl)-2 n-tridecyl-3 imidazoline (IMI-13), 2-n-hyxyl-3 imidazoline (IMI-6), 2-n-tridecyl-3-imidazoline (IMI) and N-phenyl-cinnamyliden-imine (PH-ATC).

S2O32-

Weight loss and polarization studies.

IE of the inhibitor ranging between 74 and 96% and IE of DDQB, DDPC and IMI were almost same.

16

9 Al – Brass

3.5% NaCl solution and sea water

Anionic sodium dodecyl benzene sulphonate (SDBS), DPh(EO)9 and cationic 1,1-lauryl amido propyl ammonium chloride (LAPACI)

-

Potentiodynamic polarization and cyclic voltammetric studies.

IE increases with inhibitors concentration and the order of inhibition is SDBS > LAPACI > DPh(EO)9

17


33

10 Arsenical Al brass

3.5% NaCl solution

1,2,4,5 tetrazo spiro (5,4) decane-3 thione

-

Weight loss, potentiodynamic polarization and impedance measurements, UV, XRD and SEM studies.

Mixed-type inhibitor and obeys Langmuir adsorption isotherm.

18

11 Brass

3% NaCl and artificial sea water

Benzotriazole (BTA), gluconic acid sodium salt (GASS) and polyphosphoric acid sodium salt (PP)

-

Electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ENA).

BTA shows excellent corrosion inhibition in both media than the others, PP is not shows effective inhibition and GASS shows maximum inhibition at the concentration of 0.01 M.

19

12 Fe

3.0 mol / L NaCl solution saturated with 0.1 MPa CO2

Imidazoline amide (IM)

-

Electrochemical impedance spectrum, polarization curves, scanning tunneling microscopy (STM) and XPS studies.

Obeys Langmuir adsorption isotherm and thermodynamic theory, ∆Go = 30.4 kJ / mol, pendant functional group of IM plays key role in the inhibition and the increase of temperature and chloride ion decreases the adsorption potential.

20

13 Carbon steel

Neural aqueous environment containing 60 ppm Cl-

Carboxymethyl phosphonic acid (CMPA) and 2-carboxyethyl phosphonic acid (2-CEPA)

Zn2+

Weight loss, XRD, FTIR and luminescence spectral studies.

Mixed-type inhibitors, synergistic effect, IE of CEPA better than CMPA and the protective film consists of Fe2+-phosphonate complex and Zn(OH)2.

21

14

AA5083 Al-Mg

alloy

3.5% NaCl solutions

CeCl3 and LaCl3 -

Weight loss, electrochemical techniques, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies.

Cathodic inhibitor, 250 ppm CeCl3 and 250 ppm LaCl3 shows highest IE and interpretation of inhibition mechanism.

22


34

15 Carbon steel

60 ppm Chloride media

Sodium dodecylsulphate (SDS)

Zn2+

Weight loss study, FTIR and fluorescence spectra.

Mixed-type inhibitor, IE 93%, Synergistic effect exists between SDS and Zn2+, and protective film consists of Fe2+-SDS complex.

23

16

Al-Mg alloy

AA5083

3.5% NaCl solution

CeCl3 - Electrochemical noise measurements.

The usefulness of robust statistical parameters, wavelet transform and transient shapes were illustrated.

24

17 Zn

Aerated 0.5 M NaCl solution

CeCl3 and sodium octylthiopropionate (NaOTP)

-

Potentiostatic measurements, XPS and electron-probe microanalysis techniques.

Synergistic effect exists between the inhibitors and combined IE is 95%.

25

18 Fe NaCl solution

Piperidin-1-yl-phosphonic acid (PPA) and (4-phosphono-piperazin-1-yl) phosphonic acid (PPPA)

- Potentiodynamic polarization study.

Shifting of pitting potential in the positive direction and the decrease of corrosion current illustrates the inhibitive effect of the inhibitors and PPPA has better IE than PPA due to the adsorption of NCH2PO3H group on the metal surface.

26

19 Cu NaCl solution

Imidazole derivative

-

Weight loss and electrochemical polarization studies.

Inhibitors with a phenyl ring have better IE and obeys Freundlich adsorption isotherm.

27

20 Brass

Neutral aqueous NaCl solution

N-[1-(benzotriazol-1-yl) methyl] aniline (BIMA) and 1-hydroxy methyl benzotriazole (HBTA)

-

Weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) and FTIR studies.

Mixed-type inhibitor, dezincification factor calculated and characterization of protective film.

28


35

21 Al

Marine water (Cochin estuary)

Cerium -

Weight loss, linear sweep voltammetry, and potentiostatic polarization techniques.

Cathodic inhibitor, protective layer consists of CeO2, Ce treatment on pure Al has significant corrosion inhibition.

29

22 Cu 0.1 M NaCl solution

Tannin (extracted from Tamarix articulate)

-

Polarization curves, impedance measurements and SEM studies.

Anodic inhibitor, IE is 93.2% at concentration of 2g/l, protective film formation and explanation for the inhibition process.

30

23 Carbon steel

Neutral chloride solution

N-phosphono-methyl-glycine (NPMG)

Zn2+

Electrochemical impedance measurements, polarization curves, XPS and AES techniques.

Mixed-type inhibitor, IE increases from 85 to 95% when inhibitor concentration increased from 10 to 100 mg/L and formation of protective film.

31

24 Fe, Ni and Cu

3% NaCl solution

Calcium monofluoro phosphate (CM)

-

Potentiodynamic polarization, open circuit potential, XPS and SEM techniques.

Anodic inhibitor, Increasing concentration of inhibitor shifts corrosion potential in positive direction and formation of protective layer.

32

25 Cu 3% NaCl and 0.5 M HCl

Bis-(1-benzotriazolymethylene) -(2,5-thiadiazoly)-disulfide (BBTD)

-

Potentiodynamic polarization and FTIR techniques.

Mixed-type inhibitor, BBTD behaves better in 3% NaCl than in 0.5 M HCl and protective layer consists of Cu(I).

33

26 Cu-30Ni alloy

3% NaCl solution

3-amino-1,2,4-triazole (ATA)

Ammoniac

Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) and non-linear regression methods.

Mixed-type inhibitor, IE is 98% which is enhanced in presence of ammoniac and kinetic parameters were evaluated from Levich-Koutecky relation.

34


36

27 Fe

NaCl-bicarbonate solution and sea water

Phthalic acid and salicylic acid

Kinetic model experiment.

Phthalate ion decreases the Fe(II) oxidation rate where as salicylate ion increases oxidation due to the formation of Fe(II)-salicylate complex.

35

28 Cu 3.0% Nacl solution

N-Phenyl-1, 4-phenylenediamine

1% EtOH

Weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy, FTIR and UV-visible, SEM and EDAX studies.

Mixed-type inhibitor, protective film formation and the order of corrosion of Cu is oxygenated > aerated > deaerated solutions.

36

29 Brass Artificial sea water

N,N-dibenzotriazol-1-ylmethylaminomethane (DBMM) and 3-hydroxypropyl benzotriazole (HPBT)

Weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), cyclic voltammetry and current transient techniques.

Mixed-type inhibitor, formation of protective film and inhibition of anodic dissolution of brass in artificial sea water effectively.

37

30 Cu-Ni alloy

0.2 M NaCl solution

Dodecylamine

Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and AFM studies.

Cathodic inhibitor, IE increases with inhibitors concentration increased from 0.0005 M to 0.005 M and adsorption of dodecylamine on Cu-Ni alloy surface.

38

31 Nickel plated copper

3.5% NaCl solution

Polyaniline (PANI)

Cyclic voltammetry, AC impedance spectroscopy (EIS) and polarization curves.

PANI modified nickel plating provided much better barrier property to copper for longer periods.

39

32 Carbon steel

3% NaCl solution

TiO2 dil NaOH

Electrochemical impedance spectroscopy (EIS), coupling test, XRD and SEM techniques.

Decrease of film resistance, film formed at 120 V can serve as photoanode and film accelerates the corrosion in the dark.

40


37

33 Brass 0.10 M NaCl solution

2-[(E)-pyridin-2-ylimino)]phenol (L1) and 2-[(pyridin-2ylamino)methyl]phenol (L2)

-

Potentiostatic polarization and AC impedance methods.

IE increases with inhibitors concentration and protective film formation.

41

34 Cu Sea water Poly(N-hexadecylaniline)

Docosanol

Weight loss, potentiodynamic polarization and SEM studies.

IE is 95%, stable and strong film formation over metal surface and obeys Langmuir-Blodgett adsorption isotherm.

42

35 Mild steel

Sea water Polyhydric alcohol phosphate ester (PAPE)

-

Polarization curves, electrochemical impedance spectroscopy (EIS) and scanning tunneling microscopy (STM) studies.

Mixed-type inhibitor, obeys Langmuir adsorption isotherm and complex film formation due to the interaction of R1 function of PAPE and Fe2+, Mg2+, Ca2+, etc

43

36 Cu 3.0% NaCl 2-amino-5-ethyl-1,3,4-thiadiazole (AETDA)

-

Weight loss, pH, potentiodynamic polarization, potentiostatic current-time and electrochemical impedance spectroscopy (EIS), SEM and EDX studies.

Mixed-type inhibitor, maximum IE is 97% at 5 x 10-3 M AETDA, protective film is formed due to strong adsorption of AETDA molecules and the order of IE is oxygenated > aerated > de-aerated solutions.

44

37 Al 0.50 M NaCl solution

1,4-naphthoquinone (NQ)

-

Potentiodynamic polarization, chronoamprometry (CA), open-circuit potential (OCP), EIS, SEM, cyclic voltammetric, and quartz crystal analyzer (QCA) techniques.

NQ shows maximum inhibition at 1.0 x 10 -3 M and protecting the pits on Al surface.

45


38

38 Fe 0.1M NaCl solution

Zinc chromate and zinc phosphate

-

EIS, scanning vibrating electrode technique (SVET) and open circuit potential (OCP) measurements.

Both inhibitors show lower inhibition efficiency.

46

39 Cu Aerated NaCl solution

Sodium oleate (OA)

-

Weight loss, potentiodyamic polarization and impedance measurements, SEM and EDX studies. Temperature: 15 – 65oC

“Green” - Mixed-type inhibitor, formation of an adsorbed film on the metal surface, IE increases with inhibitor concentration and time of immersion and adsorption obeys Frumkin’s equation.

47

40

Galvanic

electrode

(N80 (CS) + S31803 (SS))

1% NaCl solution

Dodecanoic acid and its sodium salt (DDAS)

-

Electrochemical methods, FTIR and AFM studies. pH = 4.0

Anodic inhibitor, protective layer formed on the metal surface due to the strong adsorption of the inhibitor and protective layer formed on the single CS electrode is less compact than that of on coupled CS.

48

41

Galvanic

electrode

(GE) (N80 CS +

S31803 (SS))

NaCl solution

Imidazoline derivative (MAD)

KI

Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, AFM and FTIR studies.

Cathodic inhibitors, synergistic effect exists between MAD and KI, and IE of MAD is higher in presence of KI due to the distribution of excess charge on the GE surface.

49

42 N80 steel

NaCl solution

Quaternary alkynoxymethyl amine (IMC-80-Q)

Ca2+

Electrochemical impedance spectroscopy (EIS) and polarization resistance techniques. Temperature: 57oC

IMC-80-Q shows optimum inhibitor concentration significantly increased with the increase of Cl- concentration from 3% NaCl to 4.6% NaCl solution.

50


39

43 Steel NaCl solution

Cerium and lanthanum cinnamate

-

Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy.

The corrosion protection mechanism involves adsorption of the rare earth metal-cinnamate complex and oxide film on the steel surface.

51

44 Mild steel

3% NaCl solution

Polyaniline (PANI)Sodium

benzoate

Electrochemical impedance spectroscopy (EIS) and TGA.

PANI/epoxy coating shows better IE than epoxy coating.

52

45 Mild steel

3% NaCl solution

Poly(N-methylaniline) (PNMA) and poly(N-ethylaniline) (PNEA)

Oxalic acid

Electrochemical impedance spectroscopy (EIS) and DC polarization techniques.

PNMA and PNEA exihibits effective anti-corrosive properties.

53

46 Cu 3% NaCl solution

2-amino-5-(ethylthio)-1,3,4-thiadiazole (ATD)

-

Weight loss and pH measurements, potentiodynamic polarization, potentiostatic current-time, EIS, SEM and EDX studies.

Mixed-type inhibitor, IE is 94% at 5.0 mM of ATD, strong adsorption of ATD molecules on copper surface and the order of IE is oxygenated > aerated > de-aerated media.

54

47 Cu-Ni alloys

Neutral chloride solution

Cysteine - Polarization and impedance techniques.

2.0 mM cysteine shows IE of 96%, strong physical adsorption of cysteine molecules on the alloy surface involves ∆G ~ - 37.81 kJ/mol.

55

48

Cu, Zn and

Brass (Cu-10Zn and Cu-

40Zn)

0.5 M NaCl solution

Benzotriazole (BTAH)

-

Electrochemical techniques, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) studies.

BTAH shows efficient inhibition, surface film (Cu2O, ZnO, Cu(I)-BTA and Zn(II)-BTA) provides effective barrier against corrosion.

56


40

49 Cu 3.5% NaCl solution

5-(Phenyl)-4H-1,2,4-triazole-3-thiol (PTAT)

-

Weight loss, potentiodynamic polarization, potentiostatic current time and pH measurements, and FTIR specta.

Mixed-type inhibitor, IE of 500 ppm PTAT is 13% only and that of 1500 ppm PTAT is 90%, pH values decreases with concentration of PTAT and protective film formed on copper surface due to the strong adsorption of PTAT molecules.

57

50 Cu

Aerated synthetic sea water (3.5% NaCl solution)

3-amino-1,2,4-triazole (ATA)

-

Weight loss, electrochemical, gravimetric, pH measurements and Raman spectroscopy.

IE increases with inhibitors concentration and a protective film is achieved by strong adsorption of ATA molecules on the metal surface.

58

51 Cu-10Ni alloy

3.4% NaCl salt water


S2- ion

Optical and scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies.

BTAH has very high IE at the concentration above 5 x 10 -4 M and at lower concentration pitting corrosion occur.

59


Purine (PU) -

Weight loss, electrochemical polarization, electrochemical quartz crystal microbalance (EQCM) and SEM techniques. pH = 6.8

IE increases with inhibitors concentration, adherent layer of inhibitor on metal surface account for the protective effect and chemical adsorption follows Langmuir isotherm.

60


1-decanthiol (DT), 1,9-nonanedithiol (NDT) and 1,4-benzendimethanethiol (BDMT)

Absolute EtOH,

toluene, N,N-

dimethyl formamid

e and acetonitril

e.

Polarization, electrochemical impedance spectroscopy (EIS), cyclic voltammetry, FTIR and AFM studies.

The order of IE is NDT > DT > BMDT and the solvent used for dissolving thiols have only a marginal effect on the IE.

61


41

54 Steel NaCl solution

Polyvinyl alcohol Carbon black (CB)

Electrochemical impedance spectroscopy (EIS), polarization curves, immersion measurements and salt fog tests.

Composites coatings with CB nanoparticles reduced drastically the corrosion rate of steel.

62

55 Carbon steel

Alkaline formation water containing Cl-ion

Tungstate (WO4)2-

, molybdate (MoO4)

2- and nitrite (No2)

- ions

-

Cyclic voltammetry, potentiostatic current-time measurements, scanning electron microscopy (SEM), EDAX and XPS analysis.

The rate of pit initiation decreases and the pitting potential moves to more positive direction upon the addition of inorganic anions and the order of pitting inhibition is (WO4)

2- > (MoO4)

2- > (No2)-

.

63

56 Al alloy 2024-

T3

3.5% NaCl solution

8-hydroxy-quinoline (8HQ) and 8-hydroxy-quinoline-5-sulfonic acid (HQS)

-

Open circuit potential, polarization measurements, electrochemical impedance spectroscopy (EIS) SEM and EDS studies.

Mixed-type inhibitors, adsorption of 8HQ and HQS on metal surface forms a protective layer, 8HQ has better IE than HQS.

64

57

Galvanized steel and mild steel

0.5 M NaCl aqueous solution

Polyurethane (PU)

-

Electrochemical impedance spectroscopy (EIS)

The relationship between the changes in mechanical properties and the degradation process were studied and PU coating shows higher adhesion and anticorrosion behavior.

65

58 Carbon steel

Neutral solution

Pimeloyl-1,5-di-hydroxamic acid (C7)

Zn2+ and Ni2+

Surface analytical and electrochemical techniques.

C7 offers effective corrosion inhibition in the presence of Zn2+ and Ni2+ due to the formation of stable slightly soluble complexes with these cations.

66


42

59 Cu 0.6 M NaCl and 1.0 M HCl

Cysteine -

Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies.

Maximum IE is 90%, decrease in corrosion current, shifting of corrosion potential in the negative direction and obeys Langmuir adsorption isotherm with ∆G ~ - 25 kJ/mol.

67

60 Al alloy AA201

4

3.5% NaCl solution

LaCl3 and CeCl3 -

Polarization and electrochemical impedance spectroscopy (EIS) and SEM studies.

1000 ppm of LaCl3 and CeCl3 shows significant corrosion inhibition, increase of double layer capacitance and film resistance, and film consists of precipitates of oxide/hydroxide of La and Ce.

68

61 Mild steel

0.01 M NaCl solution

Lanthanum-4 hydroxy cinnamate

-

Linear polarization resistance (LPR), cyclic potentiodynamic polarization (CPP) and EIS studies.

Anodic reaction strongly controlled and protective film formation.

69


Hibiscus rosa-sinensis linn flower extract (FE)

-

Weight loss, polarization and AC impedance, UV-visible and FTIR spectra and AFM studies.

Mixed-type inhibitor and protective film consists of Fe2+ -quercetin-3-O-glucoside complex.

70

63 St37

Carbon steel

Aerated NaCl solution

Mixture of Cerium and Lanthanum oxides (2:1)

AcOH

Weight loss, potentiodynamic polarization, open circuit potential and constant potential measurements. Temperature: 25 – 70oC

The inhibitor is suitable for carbon steel in low to chloride media and 500 ppm of inhibitor concentration has maximum IE of 76%.

71


N-(5,6-diphenyl-4,5-dihydro-[1,2,4]triazin-3-yl)-guanidine (NTG)

-

Weight loss, potentiodynamic polarization measurements, EIS and electrochemical frequency modulation (EFM) studies.

IE is 99% and obeys Langmuir adsorption isotherm.

72


43

65 Brass 0.2 M NaCl

2-mercaptobenzothiazole (MBT) and polyoxyethylene sorbitan mono oleater (Tween-80).

-

Potentiodynamic polarization, X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma analysis (ICP).

Mixed-type inhibitor, MBT and Tween-80 shows IE’s 79% and 62.5% and their combination shows IE 94% and synergistic effect controls dezincification of brass.

73

66 3003

Al alloy 0.5% NaCl solution

Propargyl alcohol (PA) and Sodium potassium tartrate (SPT)

-

Electrochemical impedance spectroscopy (EIS) and Tafel polarization techniques.

IE increases with inhibitors concentrations, PA and SPT shows significant synergistic effect and obeys Langmuir adsorption isotherm.

74

67 Steel Sea water Ca2+, Ni2+ and Co2+ Naphthalates

-

Electrochemical and stalagmometric methods.

The natural naphthalates are very good inhibitors.

75


Adenine (AD) -

Weight loss, electrochemical polarization, electrochemical quartz crystal microbalance (EQCM) and SEM studies.

IE increases with inhibitor concentration, adherent layer formed on the metal surface account for the protective effect, and chemical adsorption obeys Langmuir isotherm.

76

69 Al alloy Sea water Sodium benzoate -

Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and SEM studies.

Mixed-type inhibitor, the decrease of current density and double layer capacitance and increase of polarization resistance confirms the corrosion inhibition and protective film formation on the metal surface.

77


44


Thiomorpholin-4-ylmethyl-phosphonic acid (TMPA) and morpholin-4-methyl-phosphonic acid (MPA)

-

Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, FTIR, SEM and EDAX studies.

Effective inhibitors, corrosion potential shifted in noble direction, IE is very high even at low concentration, and bonding mechanism between the metallic surface and the inhibitors.

78

71 Armco

Fe 3% NaCl solution

Piperidin-1-yl-phosphonic acid (PPA)

Zn2+

Weight loss, potentiodynamic polarization and FTIR studies.

IE of 0.005 M PPA is 76.7% where as that of 0.005 M PPA – 20% Zn2+ is 90.2%, synergistic effect exists between PPA and Zn2+, and the protective film consists of Fe2+-PPA and Fe2+-PPA + Zn(OH)2 in the absence and presence of Zn2+.

79

72 Mild steel

3% NaCl solution

Sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP) and adenosine triphosphate (ATP)

Zn2+

Weight loss, electrochemical polarization and SEM techniques. Temperature: 30, 40 and 50oC

Mixed-type inhibitors, synergistic effect exists between phosphates and Zn2+, order of IE is STPP > SHMP > ATP, IE decreases with temperature, IE of STPP and SHMP increases with concentration and IE of ATP decreases with concentration.

80

73

Cu, Fe and Cu-

20%Fe alloy

1.0 M NaCl solution

Thiourea (TU) -

Open-circuit potential measurements (OCP), polarization and electrochemical impedance spectroscopy (EIS) studies.

TU adsorbs at the alloy surface by Langmuir adsorption isotherm, IE is 91% and corrosion rate is in the order Cu<Cu-20%Fe<Fe.

81


45

74 Carbon steel

NaCl solution

Yttrium (Y) and chromium (Cr)

-

Electrochemical measurements, Auger electron spectroscopy (AES) and XPS studies.

Crevice corrosion resistance significantly improved, surface layer consists of Y2O3 and Cr2O3 and it acts as a barrier to reduce the corrosion.

82

75 Carbon steel

5% NaCl aqueous solution

Polyaniline (PANI) EtOH

Electrochemical corrosion measurements and Raman spectroscopy analysis.

PANI –coated metal have excellent protection from corrosion and the passive layer over the surface consists of α-Fe2O3 and Fe3O4.

83

76 Steel 3.5% NaCl solution

Zinc aluminium polyphosphate (ZAPP) and zinc phosphate (ZP) .

-

EIS, linear polarization (LP), SEM and EDX studies.

The order of IE is ZAPP > ZP and formation of precipitated layer on the metal surface.

84

77 Zn Red sea water

2-mercaptotriazole

-

Cyclic voltammetry, SEM and EDAX studies.

Mixed-type inhibitor and protective film formation.

85

78 Brass-MM55 alloy

Artificial sea water

Benzotriazole -

Dynamic electrochemical impedance spectroscopy (DEIS).

Excellent inhibitor and DEIS is a relatively rapid measurement technique.

86

79 304 SSl

1.5% NaCl solution

Ciprofloxacin and norfloxacin

-

Open circuit potential (OCP) and potentiodynamic polarization techniques.

Both compounds act as anodic-type inhibitors and IE of norfloxacin is higher than ciprofloxacin.

87

80 AISI/S

AE Steel

Sea water Sodium nitrite - Weight loss method

Corrosion rate increases with time of exposure to the corrosive medium and 4% inhibitor in sea water shows optimum corrosion inhibition.

88


46

81 90-10 Cu-Ni Alloy

Sea water Thiosulphate -

Potentiodynamic polarization study. Temperature range: 25 and 50 – 80 oC

At 25 oC, the corrosion rate increases with inhibitor concentration and at 50 or 80oC inhibitor forms a protective film that effectively decreases the corrosion rate.

89

82 Brass-

118 Artificial sea water

Benzotriazole (BTA)

-

Dynamic electrochemical impedance spectroscopy (DEIS).

Excellent inhibitor and DEIS is a very useful technique in the field of inhibitor research.

90

83 AISI 430 SS

3% NaCl solution

Polyethyleneimines (PEI)

-

Weight loss, polarization and cyclic polarization measurements and XPS technique.

PEI provides the best protection against localized corrosion and acts as a diffusion barrier which follows physical adsorption.

91

84 Cu NaCl solution

Benzotriazole, phenyl derivatives of tetrazole, bypyrazoles and 2-methyl-5-mercapto-1,3,4-thiadiazole.

-

Scanning electron microscopy (SEM).

The corrosion inhibition is due to the adsorption of inhibitor molecule on copper surface.

92

85 ASTM 420 SS

3% aqueous NaCl solution

Polyethyleneimine (PEI)

-

Linear polarization, cyclic polarization, immersion tests and XPS studies.

Very good inhibitor against pitting corrosion and a dense layer of PEI prevents the diffusion of ionic species from the film by chlorine from the salt water.

93

86 Carbon steel

3% NaCl solution

Poly (aniline-co-o-toluidine)

-

Potentiodynamic polarization and EIS techniques and FTIR, UV-visible, TGA and XRD studies.

Mixed-type inhibitor, IE is 70% at 100 ppm of inhibitor and obeys Temkin adsorption isotherm.

94


47


2(β-benzenesulphonamido) ethylbenzoxazole (I), 2(β-benzenesulphonamido) ethylbenzimidazole (II), 2(β-benzenesulphonamido) ethylimidazoline(III), 2(β-benzenesulphonamido) ethyl-1,4,5,6-tetrahydropyridimine (IV)

-

Gravimetric, Potentiodynamic polarization, AC impedance and EDS methods. pH:6.0

Very good mixed-type inhibitors, the order of IE is I<II<III<IV, the best IE is 77.6% and the inhibition is due to the formation of mixed ligand complex on the brass surface and blocking the active site.

95

88 Cu and brass

Sea water

Vitis vinifera (Extract prepared from seed and skin part of grapes)

EtOH

UV, FTIR and XRD studies. Temperature: 303 K, 313 K and 333 K respectively

IE increases with inhibitor concentration but decreases with temperature and time, complex film formation, obeys Langmuir and Temkin adsorption isotherms.

96

89

Cu and its

alloy (Cu-

27Zn)

Sea water Emblica officinalis leaves extract

-

UV and IR studies. Temperature: 303 K and 333 K respectively

Physical adsorption obeys Langmuir and Temkin isotherms, which are exothermic and spontaneous.

97

90 Brass alloy

Mediterranean Sea water (MSW) and formation water (oil field water)


-

Weight loss, potentiodynamic polarization, X-ray diffraction (XRD) and SEM studies.

Mixed-type inhibitor, formation water is more corrosive for brass alloy than sea water, excellent control of dezincification of brass and IE ~ 98.15% for formation water at optimum concentration.

98


2-mercapto-4-(p-methoxyphenyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile (MPD)

-

Electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization

Mixed-type inhibitor, IE increases with inhibitor concentration and the number of electrons transferred from MPD to metal surface

99


48

and molecular stimulation (MS) techniques.

calculated by semi-empirical quantum chemical calculations.


1-phenyl-2,4-dithiobiuret (Inh I), 1-p-methoxyphenyl-2,4-dithiobiuret (Inh II) and 1-p-chlorophenyl-2,4-dithiobiuret (Inh III).

-

Weight loss, electrochemical impedance spectroscopy, polarization curves, SEM and ESCA studies.

The order of IE is Inh II > Inh I > Inh III and the inhibition is due to the formation of protective film consist of Cu(I)-inhibitor complex, CuCl or CuCl2

- complex ions.

100

93 Cu

Aerated 0.1 M NaCl solution

8-aminoquinoline (8-AQ)

-

Open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements, and atomic force microscopy (AFM) study.

Mixed-type inhibitor at concentration higher than 10-3 M, a film formed of thickness 10 μm and the interaction between 8-AQ and copper surface is most probable.

101


2,5-dimercapto-1,3,4-thiadiazole

-

Weight loss, potentiostatic polarization, AC-impedance, UV-visible, FTIR, ESCA and SEM studies. pH = 6.5, 7.0 and 9.0

Mixed-type inhibitor, IE at pH 7.0 is 94.5% and formation of protective film consist of Cu(I)-inhibitor complex, CuCl or CuCl2

- complex ions or both and no oxide on metal surface.

102

95 Al-Si alloy

3.5% NaCl solution

Alumina -

Potentiostatic polarization, EIS, SEM and XRD studies. Temperature: 25oC and 300oC pH = 4.0

Non-porous protective coating of thickness around 7μm, higher corrosion resistance and a significant decrease in diffusion of chloride ion through metal.

103


49

96 Carbon steel

200 mg / L NaCl solution

Activated starch (AS) and carboxymethylated starch (CMS)

-

13C NMR, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and AFM studies.

Modified starches have corrosion inhibitive properties, AS shows better IE than CMS, IE depends on degree of substitution, strong ionic interation between AS and Fe2+ ions, and higher protection is due to the densification of the inhibitive layer.

104


Glycine (I), L (-) aspartic acid (II), glutamic acid (III), N-benzenesulphonyl glycine (IV), N-benzenesulphonyl L (-) aspartic acid (V) and N-benzenesulphonyl L (-) glutamic acid (VI)

-

Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. pH = 6.0

Mixed-type inhibitors, order of IE is I<II<III<IV<V<VI, IE is maximum at 4 x 10-5 M concentration, IE increases due to the π electron contribution of the benzene ring and presence of more adsorption sites,

105

98 Fe

30 mg/L NaCl + 70 mg/L Na2SO4

Sodium benzoate (SB)

-

Tafel polarization curves, electrochemical impedance spectroscopy (EIS), XRD and SEM studies.

IE of SB increases as the grain size decreased from microcrystalline to nanocrystalline and it is associated with the increase of the surface energy.

106

99 Steel Salt water saturated with CO2

Hydroxyethyl imidazoline

-

Polarization curves, linear polarization curves, EIS and electrochemical noise studies. Temperature: 50oC

Anodic inhibitor, Best IE at 25 ppm and protective film formation.

107

100 Mild steel

8.6 mM NaCl solution

Molybdate (MoO4)

2- and nitrite (No2)

- ions -

X-ray photoelectron spectroscopy (XPS) technique. pH = 8.0

Anion films are ~ 5 nm deep, film consists of ferric molybdate and nitrite respectively.

108


50

101 3003

Al alloys

Sea water Calcium nitrite -

Cyclic polarization testing and SEM studies.

Formation of protective oxide layer and increase in the amount of inhibitor leads to pitting corrosion.

109


N-decyl-3-amino-1,2,4-triazole

-

Potentiodynamic measurements, electrochemical impedance spectroscopy (EIS), SEM and EDAX studies.

Mixed-type inhibitor and IE increases with inhibitor concentration.

110

103 Al

Arabian Gulf Sea water (AGS) and 3.5% NaCl solution.

3-amino-5-mercapto-1,2,4-triazole (AMTA)

-

Cyclic potentiodynamic polarization (CPP), Chronoamperometric current-time and electrochemical impedance spectroscopy (EIS) measurements.

AGS is more corrosive than 3.5% NaCl solution and IE of AMTA is higher for AGS than 3.5% NaCl solution.

111

104 Brass

Sea water (Eliot beach-southern coast of Chennai, India)

2-amino-5-ethyl-1,3,4-thiadiazole (AETD), 2-amino-5-ethylthio-1,3,4-thiadiazole (AETTD) and 2-amino-5-tert-butyl-1,3,4-thiadiazole (ATBTD)

-

Potentiodynamic polarization, EIS, inductively coupled plasma atomic emission spectroscopy (ICP-AES) and SEM, EDAX and FTIR studies.

Mixed-type inhibitors, IE% increases with inhibitor concentration, obeys Langmuir adsorption isotherm, control of cathodic reaction and dezincification of brass.

112

105 Cu70-30Ni Alloy

Aerated 3% NaCl solution

3-amino-1,2,4-triazole (ATA), 3-4’-bitriazole-1,2,4 (BiTA) and 2-mercaptobenzimidazole (MBI)

NH3

Potentiodynamic measurements, electrochemical impedance spectroscopy (EIS) and SEM studies.

Mixed-type inhibitor controls both anodic and cathodic reactions and IE increases with inhibitors concentrations and corrosion rate decreases.

113

106 Mild steel

3.5% NaCl solution

Zinc acetate (ZA), zinc acetylacetonate (ZAA) and zinc gluconate (ZG)

-

Electrochemcial impedance spectroscopy (EIS), pH, XRD and SEM techniques.

ZG shows better IE than the others and it forms insoluble protective film over metal surface

114


51

107 Al-Cu alloy

Chloride solution

Cerium diphenyl phosphate (Ce(dpp)3)

-

SEM and ToF-SIMS coupled with electrochemical impedance spectroscopy (EIS) measurements.

Strong corrosion inhibitor and formation of a protective complex oxide film of Al and Ce.

115


N,N-bis (3-carbomethoxy-5-methylpyrazol- 1-ylmethyl) cyclohexylamine (BiPyA)

-

Potentiodynamic polarization and linear polarization (LRP) techniques.

Efficient mixed-type inhibitor, IE’s from Tafel plots and LRP method are in good agreement and BiPyA adsorbed on the copper surface according to Langmuir isotherm.

116


α-benzenesulphonamido-β-(2-imidazolynyl) ethanoic acid (RmH) and 1-benzenesulphonamido-1,2-bis(2-imidazolynyl)ethane (RbH)

Cysteine

Potentiodynamic polarization and electrochemical AC impedance studies. pH = 6.0

Very good mixed-type inhibitors and antifouling agents, IE of the two inhibitors is higher than 80%, order of IE is RbH > RmH and IE of RmH is increased due to synergistic effect of cysteine and this effect was not observed in case of RbH.

117

110 Galvan

ized steel

0.1 M NaCl solution

Cerium (IV) oxide SiO2

Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).

Cathodic inhibitor and mechanical treatment performed on the CeO2 and SiO2

particles promote the formation of an effective corrosion pigment.

118

111 Al alloy 2024-

T3

0.05 M NaCl solution

Cerium cinnamate (CC)

-

Polarization measurements, immersion tests, XPS and electron-probe microanalysis (EPM).

Anodic inhibition is due to the deposition film and protection mechanism involves deposition of CC and then hydrolysis of cerium ions to form Cerium oxide/hydroxide.

119


52

112 Carbon steel

Alkaline chloride solution

1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4)

-

Electrochemical measurements, AFM and XPS studies.

Mixed-type inhibitor, obeys Langmuir adsorption isotherm, inhibitor controls anodic and cathodic processes effectively and blocks the access of chloride ions to the metal surface.

120

113 Carbon steel

NaCl solution

Mussel adhesive protein (Mefp-1) (derived from marine mussel Mytilus edulis)

-

Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and AFM studies. pH = 4.6

Mefp-1 confers significant corrosion inhibition, within a short exposure time, the IE is increases with chloride concentration, but for longer exposure the IE is increases with lower chloride concentration and the protective film consists of bovine serum albumin (BSA).

121


2-carboxymethylthio-4-(p-methoxyphenyl)-6-oxo-1,6-dihy-dro-pyrimidine-5-carbonitrile (CPD)

-

Electrochemical frequency modulation (EFM), EIS, potentiodynamic polarization and molecular stimulation (MS) techniques.

Mixed-type inhibitor, IE increases with inhibitor concentration and adsorption obeys Langmuir isotherm.

122

115 Carbon steel

0.5 M NaCl solution

Thiadiazole derivatives

-

Open circuit potential (OCP), Tafel polarization, electrochemical impedance spectroscopy (EIS) and SEM techniques.

Anodic inhibitor, IE increases with inhibitor concentration and decreases with temperature, obeys follows Langmuir isotherm and inhibitor acts as retarding catalyst for pitting corrosion.

123


53


Fungicides (Myclobutanil and hexaconazole)

-

Weight loss, electrochemical measurements, SEM and EDX studies.

Mixed-type inhibitors, obeys Langmuir adsorption isotherm and good performance at different temperatures.

124

II.2. Study of corrosion inhibition by carboxylic acids

The carboxylates contain the carboxylic acid group (– COOH) which can bind

to a metal cation and has higher stability with greater chelating capability. They have

good chemical stability and show excellent corrosion inhibition by forming a stable

thin film over metal surface contact with corrosive environment. They are capable of

forming coordination complexes with Fe2+, Fe3+,Cu2+, Pb2+, Mn2+ , Ni2+and Co3+, etc .

Thus the complex formed on the metal surface in the form of thin protective film is

passive and thereby the metal has been prevented from corrosion and scale formation.

Several carboxylates such as ethylenediaminetetraacetate [125-130], sodium salicylate

[131], sodium cinnamate [132], anthranilate [133], adipate [134], citrate [135],

succinate [136], tartrate [137] and oxalate [138, 139], have been used as inhibitors.

Moreover carboxylic acids with certain synergists such as Zn2+ [136, 137, 140, 141]

and surfactants [142], etc show better inhibition against corrosion of metals in an

aqueous environment.

II.2.1. Corrosion inhibition by ethylenediaminetetraacetic acid (EDTA)

EDTA is a member of the polyamino polycarboxylic acid family of ligands.

It usually binds to a metal cation through its two amine and four carboxylates. EDTA

has higher stability with greater chelating capability which supports the formation of

strong coordination complexes with Fe2+, Fe3+,Cu2+, Pb2+, Mn2+ and Co3+, etc. in the

form protective film on the metal surface. Hence it shows excellent corrosion

inhibition of metal structures in corrosive environment.

Umamathi et al. [125] investigated the synergistic effect of sodium salt of

etheylenediminetetraacetic acid (EDTA-Na) and Zn2+ in controlling corrosion of

carbon steel in an aqueous environment containing 60 ppm chloride using weight loss,

potentiostatic polarization and AC impedance spectra. The IE due to the influence of


54

Na3PO4 on the formulation consists of EDTA (50 ppm) – Zn2+ (50 ppm) were found

to increase from 73 % to 98%. A suitable mechanism for corrosion inhibition has

been proposed on the basis of electrochemical studies and FTIR spectra. Also it is

found that the protective film consists of Fe2+ - EDTA, Fe2+ - Na3PO4 complexes and

Zn(OH)2.

Ahmed Y. Musa et al. [126, 129] compared the corrosion inhibition of EDTA-

Na and EDTA with thiourea (TU) on the corrosion of mild steel in 1M HCl using the

techniques such as weight loss study, potentiodynamic polarization and

electrochemical impedance spectroscopy (EIS). The polarization curve indicates that

the EDTA-Na, EDTA and TU behave mainly as mixed-type inhibitors. The charge

transfer mechanism of EIS explains the corrosion inhibition process.

Qing Qu et al. [127] have studied the effect of EDTA-Na on the corrosion

inhibition of cold rolled steel in the presence of benzotriazole (BTA) in 0.1M HCl

medium using Tafel polarization curve and EIS. The polarization curve results show

that the EDTA alone acts an anodic type inhibitor while the combination of EDTA

and BTA acts as mixed type inhibitor and mainly inhibits anodic reaction. EIS study

reveals that the corrosion reaction is controlled by charge transfer process. FTIR and

AFM studies were used to characterize the corrosion surface of cold rolled steel. The

probable mechanisms have been proposed to explain the experimental results.

SHAO Hai-Bo et al. [130] investigated the cooperative inhibition effects of

alkaline earth metal ions and EDTA on the corrosion inhibition of pure aluminium

(Al) in 4 mol/L KOH solution using the studies such as hydrogen collection,

polarization curve and EIS. It was found that Al exhibits minimum corrosion rate in 4

mol/L KOH solution containing 0.02 mol/L EDTA, saturated Ca(OH)2 and saturated

Sr(OH)2. EDAX analysis showed that alkaline earth metal ions and EDTA have no

contribution to the formation of the surface film on Al. Therefore the inhibition effect

may be caused by the adsorption of the inhibitor molecule on Al surface. This fact

indicates that these two ions act as interface inhibitors rather than inter-phase ones.

Niu Lin and Chen Xiao [143] have studied the differences of corrosion caused

by halide ions on iron in alkaline media using electrochemical methods. The order of


55

pitting corrosion caused by Cl-, Br- and I- on iron has been interpreted. It was found

that the influence of F- on the anodic process of iron was remarkably different from

that of other halide ions. The pitting corrosion inhibiting action of F- and EDTA was

interpreted by complexing and precipitating effects.

BAI Wei et al. [144] reported that the synergistic inhibition effect of Na2MoO4

and EDTA on the corrosion of cold rolled steel in HCl solution using weight loss and

polarization studies. Both Na2MoO4 and EDTA show moderate inhibitive effect on

the corrosion and acts as anodic type inhibitor. The adsorption of Na2MoO4 and

EDTA on the steel surface obeys Temkin adsorption isotherm. Polarization study

reveals that the complex of Na2MoO4 and EDTA functions as a mixed type inhibitor,

mainly inhibiting the anodic reaction. The synergistic inhibition mechanism has been

proposed.

Musa et al. [145] investigated the ability of 4-amino-5-phenyl-4H-1, 2, 4-

triazole-3-thio (APTT), EDTA and thiourea (TU) for mild steel corrosion in 1 mol/L

HCl solution at 30oC. Tafel polarization and EIS were used to investigate the

influence of these organic compounds as corrosion inhibitors and the results obtained

are in a good agreement. The IE increases with the increase of the inhibitor

concentration. The adsorption of the inhibitors on the mils steel surface follows

Langmuir adsorption isotherm and the free energy of adsorption indicates that the

adsorption of APTT, EDTA and TU molecules is a spontaneous process and a typical

chemisorption.

Ellina lunarska and Olga Chernyayeva [146] have studied the corrosion rate,

hydrogen permeation rate and stress corrosion cracking of Al in NaOH solution in the

presence of corrosion inhibitors such as H3BO3, EDTA, KMnO4 and As2O3 using

polarization and XPS analysis. The observed different influence of corrosion

inhibitors on the hydrogen uptake was associated with the different chemical

composition and structure of the surface film formed on Al under the various

conditions.

Iwona Flis-Kabulska [147] investigated the effect of anodic polarization on

hydrogen entry into iron at cathodic potentials in 0.1 M NaOH without and with


56

EDTA / Na2MoO4 at 25oC using open-circuit potential. The effect of pre-polarization

at various potentials on hydrogen entry into iron during cathodic potential sweeps has

been studied by the measurement of the hydrogen permeation rate through a 35 μm

thick iron membrane in 0.1 M NaOH without and with EDTA / Na2MoO4. Two types

of the enhanced hydrogen entry at low cathodic polarizations were distinguished. It is

suggested that both types can be explained by acidification at the metal surface, the

former due to anodic oxidation of iron, and the later due to cathodic reduction of

oxide layer. XPS analysis revealed the presence of hydrated Fe-O species of

unidentified valence. EDTA and Na2MoO4 increase the efficiency of hydrogen entry,

and molybdates also strongly increases cathodic currents of hydrogen entry ratio.

Some of the effects of these additives can be explained in terms of their effect on

surface layers.

de Oliveira and Carlos [148] have studied the influence of EDTA-Na /

HEDTA-Na (N-(2-hydroxyethyl)ethylenediaminetriacetic acid – tri sodium salt) on

silver-copper electro-deposition from ammonium hydroxide solution using the

techniques such as voltammetry, chronoamperometry, scaning electron microscopy

(SEM) and energy-dispersive X-ray spectroscopy (EDS). The deposits obtained at -

0.450 V, increasing either the silver content in the silver-copper deposit or the charge

density of deposition leads to dentritic growth. Moreover, dentritic growth decreases

as the concentration of EDTA-Na or HEDTA-Na increases. EDS analysis of the

deposits obtained at -0.2000 V showed co-deposition of copper with silver, which was

attributed to Cu (I) disproportionation to Cu(0) and Cu(II). Moreover, the silver-

copper deposits obtained at -2.000 V, from a solution containing EDTA-Na or

HEDTA-Na, were non-dendritic in spite of the high silver content. The presence of

EDTA-Na and HEDTA-Na improved the silver-copper morphology. EDS indicates

that the silver-copper electro-deposition was a supersaturated solid solution.

Joshi et al. [149] have made a comparison between the passivation behaviour

of carbon steel in the presence of EDTA, Ni (II) and LiOH in dosed deoxygenated

alkaline pH water at 473 K. In the presence of EDTA at 523 K, a better protective

magnetite film is formed on a single-alloy system of carbon steel as compared to a

simple LiOH treatment under similar conditions of initial pH and dissolved oxygen.

EDTA treatment gives rise to a lower base metal loss and a lower corrosion product


57

releae, as compared to the LiOH treatment. However, the formation of protective

magnetite film in EDTA and LiOH media at 473 K on carbon steel in the presence of

galvanically decoupled Monel alloy 400 revealed that the EDTA process results in

increased base metal loss from carbon steel and Monel alloy 400, increased corrosion

product release.

Palmer and Boden [150] have used alkaline EDTA for chemical cleaning

agent in many heat exchange systems for removing magnetite. For steel systems,

especially at temperatures in the range of 70 – 150oC, high corrosion rates can occur.

The EDTA acts as a cathodic stimulant and high rates of corrosion can occur even in

the absence of dissolved oxygen. This corrosion behaviour has been demonstrated in a

two compartment cell with a steel electrode and sodium hydroxide in one vessel

connected to another vessel containing sodium hydroxide and EDTA with inert Pt

electrode. After operating the cell for several hours the decomposition products of

EDTA were collected and analyzed by IR and NMR spectroscopy. There was

evidence of the reduction of carboxylic acid groups to aldehydes and possibly

hydroxyl compounds. This indicates that the type of inhibitor that might be used to

reduce corrosion of the steel without reducing the rate of magnetite dissolution.

Gallic acid (GA) as a corrosion inhibitor of carbon steel in chemical

decontamination formulation has been reported [151]. It was found to GA provide

corrosion inhibition to carbon steel at 4.25 mM concentration. The inherent stability

to radiation degradation as compared to other reductant and coupled with anionic

nature with respect to removal using ion exchange column makes it suitable for using

both reductant as well as corrosion inhibitor in dilute decontamination formulations

operating in the regenerative mode. A formulation containing GA along with EDTA

was found to be more efficient in dissolving hematite and providing 31% corrosion

inhibition to the carbon steel.

Bonaccorso et al. [152] have studied the pitting corrosion resistance of nickel-

titanium (Ni-Ti) rotary instruments with different surface treatments in 17% EDTA

and NaCl solutions. Electrochemical measurements were carried out by using

potentiostatic polarization on electropolished RaCe, non-electdropolished RaCe and

physical vapour deposition (PVD) coated alpha systems. On the basis of

electrochemical tests, no localized corrosion problems are expected in EDTA. In


58

NaCl, pitting potential occurred at higher values for the electropolished and PVD

instruments. There appears to e a risk of corrosion for Ni-Ti instruments without

surface treatments in contact with NaCl. Ni-Ti files with PVD and electropolishing

surface treatments showed an increase corrosion resistance.

II.2.2. Corrosion inhibition by succinic acid (SA)

Ramakrishnan et al. [153] have examined the dicarboxylic acids such as

oxalic, malonic, succinic and glutaric as possible complexing agents for copper (Cu)

using dominated chemical mechanical planarization (CMP) process. At pH 3.0–4.0,

oxalic and malonic acids are most effective for abrasive-free Cu removal. The rates

of Cu dissolution and polish (with or without abrasives) are correlated with pH

dependent distributions of mono-anionic (for oxalic and malonic) and neutral (for

succinic and glutaric) acid species. The surface morphological studies of a Cu can be

obtained by abrasive-free CMP in these acids.

Amin et al. [154] investigated the chemical and electrochemical studies on the

corrosion inhibition of low carbon steel in 1M HCl by succinic acid (SA). Weight

loss, potentiodynamic polarization and EIS techniques were applied to study the metal

corrosion behaviour in the absence and presence of different concentrations of SA at

the temperature, 15 – 65oC. The thermodynamic parameters revealed that the

corrosion inhibition by SA is due to the formation of physisorbed film of the inhibitor

on the metal surface. Adsorption of SA was found to follow Temkin adsorption

isotherm. The IE of SA was temperature dependent and its addition leads to an

increase of the activation corrosion energy. The results obtained from the above

studies are in reasonably good agreement.

Selvarani et al. [136] have examined that the synergistic effect of succinic acid

(SA) and Zn2+ in controlling corrosion of carbon steel in well water using weight loss,

polarization, EIS and FTIR studies. A formulation consists of 50 ppm SA and 50 ppm

Zn2+ has an IE, 70%. The influence of the biocides such as CTAB and CPC on the IE

of the system has also been studied. At a lower pH (= 6) the IE, decreases and at

higher pH (= 8) the IE, increases. Polarization studies reveal that SA – Zn2+ system

functions as a mixed type inhibitor. AC impedance spectra confirm the formation of


59

protective on the metal surface. The FTIR spectra reveal that the protective consists of

SA – Fe2+ complex and Zn(OH)2.

Xiong et al. [155] investigated the corrosion inhibition of a green scale

inhibitor, polyepoxysuccinic acid (PESA) using dynamic tests. It is found that when

PESA is used alone, it had good corrosion inhibition. So, PESA should be included in

the category of corrosion inhibitors. But the synergistic effect between PESA and

Zn2+ or sodium gluconate (SG) is poor. However, the synergistic effect among PESA,

Zn2+ and SG is excellent and the IE for carbon steel is higher than 99%. The

mechanism explains that corrosion inhibition of PESA is not affected by carboxyl

group, but by the oxygen atom inserted. The existence of oxygen atom in PESA

molecular structure makes it easy to form stable chelate with pentacylic structure.

Amin et al. [156] studied the effect of SA on the corrosion inhibition of a low

carbon steel (LCS) electrode in aerated non-stirred 1.0 M HCl solutions in the pH

range (2–8) at 25 °C using weight loss, polarization, EIS, EDX and SEM techniques.

The OCP as a function of time till steady-state potentials were also established.

Results obtained showed that SA is a good “green” inhibitor. The polarization curves

showed that SA behaves mainly as an anodic inhibitor. EDX and SEM observations

of the LCS surface confirmed existence of a protective adsorbed film of the inhibitor

on the electrode surface. The IE increases with increase in SA concentration, pH and

time of immersion. Maximum IE, 97.5% is obtained at SA concentrations >0.01 M at

pH 8. The results obtained from weight loss, polarization and EIS are in good

agreements.

Giacomelli et al. [157] have studied the inhibition of SA on the corrosion

resistance of mild steel in H2SO4 by means of potentiodynamic polarization, EIS,

weight loss and optical microscopic analysis. The results suggest that SA, slightly

shifting the corrosion potential towards less negative values and decreasing both the

anodic dissolution of mild steel and the hydrogen evolution reaction. IE up to 80%

were recorded for pH = 2 and 3 solutions, whereas no effect was perceived for pH>4

solutions. The results have been understood taking into account the solution

composition as function of pH.


60

II.2.3. Corrosion inhibition by oxalic acid (OA)

Pastore et al. [158] have summarized the results of testing on salts of organic

acids for evaluating their use as inhibitors of rebar corrosion in chloride-contaminated

concrete. Initially a screening based on electrochemical tests in alkalinized calcium

hydroxide solutions was performed on a number of carboxylic acid salts with different

number of carbon atoms in the chain and carboxylic groups, also covering substances

with hydroxyl and amine group substituents. The screening was completed by testing

on carbon steel rebars in concretes with chlorides and substances added at 1:1 molar

ratio, focused on sodium lactate, sodium oxalate and sodium borate for comparison.

The monitoring of free corrosion potential and linear polarization resistance of steel

bars has confirmed significant inhibition only for lactate. Results of further tests in

saturated calcium hydroxide solution are reported in order to assess the IE of lactate

as a function of its content, chloride content and pH.

Giacomelli et al. [138] investigated the effects of oxalic acid (OA) on the

corrosion resistance of carbon steel in 10-7 – l0-3 M H2SO4 (pH = 2.5-6.0) using

polarization and immersion tests. The results suggest that OA is a good corrosion

inhibitor for carbon steel, exhibiting IE ranging from 50% to 85% in dilute

10-7 – l0-5 M OA solutions of pH > 3.0, where as for pH < 3.0 solutions, an increase in

corrosion rate was found. Weight loss tests carried out by immersing carbon steel

specimens into OA-containing solutions during at least 6 hours revealed only positive

IE values, regardless of both solution pH and OA content.

Baah et al. [139] investigated the inhibition effect of oxalic acid (OA) on the

corrosion of Cu in concentrated propionic acid (PA) and dilute citric acid (CA)

solutions. The Cu samples in acid solutions were left in a water bath for a period of

six days and examined everyday. The solutions were continuously fed with oxygen

and the temperature of the solutions always maintained at 30oC. The OA in all the

cases behaved like an inhibitor under the experimental conditions. The increase in the

mass of Cu samples confirms the formation of oxide layer on the metal surface.

Ferky [159] studied the electrochemical behaviour of pure Ti and Ti-6Al-4V

alloy in OA solution using various electrochemical techniques such as OCP,

potentiodynamic polarization, EIS and surface examination by SEM. The influence of


61

concentration and temperature on the electrochemical behaviour of Ti and its alloy

were also studied. The results of polarization measurements showed that corrosion

current density (Icorr) increases with increasing either temperature or OA concentration

for both samples. Moreover, the value of Icorr for Ti was found to be lower than that

for Ti–6Al–4 V alloy, where the corrosion resistance for Ti was always higher. The

effect of additives as SO42− and Cl− ions was studied. The results indicate that the

oxide film resistance (Rox) value decreases with increasing the concentration of SO42−

ion. However, for Cl− ion, the value of Rox decreases with increasing Cl− ion

concentration up to 1 mM before it starts to increase at higher concentrations. EIS and

polarization results are in good agreement with each other and confirmed by SEM.

Isao Sekine et al. [160] investigated the corrosion behaviour of ferritic Type

430 and Type 444 stainless steels in OA solutions by measuring weight loss, DC

polarization, and natural electrode potential (NEP) variations with time. Elements

dissolved in OA solution after weight loss test were analyzed by atomic absorption

analysis (AAS) and by ultraviolet absorption spectroscopy (UV). The stability

constants for the formation of Fe2+ oxalate and Cr3+ oxalate complexes were obtained,

and the relation between the stability and corrosion behaviour was also investigated

from thermodynamic parameters. The AAS clarify that the amount of dissolved Cr

was the same as that of corroded Cr, and hence Cr seemed to be completely dissolved

into the solution. The UV spectra reveal that the formation of [Fe(C2O4)3]4− and

[Cr(C2O4)3]3− in the solutions after weight loss test. The formation of these complexes

was also estimated from the values of successive stability constants. Thermodynamic

parameters for the formation of Fe2− oxalate and Cr3+ oxalate were obtained from

Van't Hoff plot. The Gibbs free energy values for formation of Fe2+ oxalate and Cr3+

oxalate became larger with increasing solution temperature.

Bazeleva [161] studied the influence of oxalic acid (OA) on the corrosion of

VT1-0 Ti in a water-ethyleneglycol (EG) heat carrier system using the regression-

analytic and regression models. The corrosion loss of VT1-0 Ti has been evaluated

as a function of time and the coefficients of acceleration of corrosion depending on

the concentration of OA and temperature. It is shown that, in a 66% solution of EG,

OA intensifies the process of corrosion of VT1-0 Ti for concentrations higher than


62

0.1% due to the formation of complexes of the products of oxidation of Ti with

oxalate anions, especially at elevated temperatures.

El-Taib Heakal et al. [162] investigated the corrosion characterization of

AZ91D alloy in aqueous sodium oxalate (SO) solutions with various concentrations

using different electrochemical techniques such as open circuit potential (OCP), EIS

and CV. The corrosion rate and consequently the rate and extent of hydrogen

evolution were found to increase significantly with increasing oxalate anion

concentration and temperature or with decreasing the pH of solution. The additions of

various anions over the lower concentration range (0.001–1.0 mM) in the blank SO

solution increases to a varying extent the corrosion rate of the alloy and hence

increases the hydrogen evolution rate and decreases surface film stability in the

following order Cl− > SO42− > F−. On the other hand, addition of phosphate anion

exhibits a reverse trend, where the active corrosion rate decreases with increasing

PO43− anion concentration, implying that this anion acts as a passivator for AZ91D

alloy. The obtained electrochemical results are further confirmed by SEM analysis.

Kandhasamy kamaraj et al. [163] synthesized oxalate doped polyaniline

(PANI) and applied for corrosion protection of mild steel in acid and neutral

environment. It is observed that the oxalate ions form a stable iron oxalate layer on

mild steel thereby the metal has been protected from corrosion. The impedance values

from EIS confirm the protection of mild steel.

Fekry and Tammam [164] have studied the corrosion behaviour of Mg alloy in

sodium oxalate (SO) solution using potentiodynamic polarization and EIS techniques.

The corrosion rate increases with increasing oxalate concentration. The

electrochemical behaviour of Mg alloy in 0.1 M SO at 298 K has been studied in

presence of anions such as Br−, Cl− or SiO32−. It was found that the corrosion rate of

0.1 M SO containing silicate ion is lower than the blank (0.1 M SO) which is

confirmed by SEM. However, for the other added ions Br− or Cl−, the corrosion rate is

higher than the blank.


63

II.3. Study of corrosion inhibition by amides, urea (U) and thiourea (TU)

The organic amides such as urea (U) and thiourea (TU) have planar structure.

They show excellent corrosion inhibition and scale prevention due to the presence of

oxygen and sulphur atoms respectively with two nitrogen atoms, which can form co-

ordination complex with Fe2+, Fe3+, Cu2+, Zn2+ and Co2+, etc. They find applications

in open re-circulating cooling water system, cooling water systems, cooling towers,

condenser and compressor systems, heat exchangers, etc [126, 129].

Jiang Fang and Jie Li [165] have performed quantum chemical calculation on

the amides such as urea (U), thiourea (TU), thioacetamide (TA) and

thiosemicarbazide (TS) using the semi-empirical method. The clear correlations

obtained between corrosion inhibition and IE, and some quantum chemical

parameters such as highest occupied molecular orbital (HOMO), lowest occupied

molecular orbital (LUMO) energy levels, HOMO – LUMO energy gap and electronic

density, etc. The calculated results indicate that the great difference of IE’s between

these amides can be explained well in terms of Frontier molecular orbital theory

(FMO). The agreement with the experimental data was found to be satisfactory.

Altaf et al. [166] have studied the inhibitive action of urea on the corrosion

behaviour of Cu in borate buffer of pH (8.4) using CV and EIS techniques.

A consistent trend of increase in IE was observed as a function of concentration of U.

The adsorption of U on Cu surface obeys the Langmuir adsorption isotherm with

∆G = −35.2 kJ/mole and adsorption constant K = 2.7 × 104 dm3/mol. Impedance

measurements confirm that the increase in charge transfer resistance with increasing

concentration of urea.

Huicheng Yu et al. [167] have improved the electrochemical performance of

trivalent-chrome coating on Al 6063 alloy in 3.5 % NaCl solution at 25 °C through

the addition of U and TU. The potentiodynamic polarization and EIS techniques have

been used to study the electrochemical behaviour of coatings. The corrosion

resistance of coatings is improved greatly by adding a small amount of inhibitors,

whereas the excessive addition deteriorates the corrosion resistance. The addition of

TU presents better effect than U. To explain the EIS results of the coatings, a simple

equivalent circuit was designed.


64

The EIS parameters were obtained by fitting the EIS plots. The results of the

polarization curves and EIS show that the inhibitor-containing coatings present better

corrosion resistance than the coating without inhibitor. The morphology and

composition and valence state of the conversion coatings were examined by SEM and

EDS and XPS, respectively. The obtained results indicates that the trivalent Cr

coating was developed on Al 6063 alloy, U and TU inhibitors were also deposited on

the substrates, respectively. A noticeable chemical shift was also observed.

Singh et al. [168] have studied the inhibition and polarization properties of

urea (U), thiourea (TU), acetyl thiourea (AcTu), phenyl thiourea (PhTu), o-tolyl

thiourea (o-tol Tu), m-tolyl thiourea (m-tol Tu), p-tolyl thiourea (p-tol Tu), 1:3-

diphenyl thiourea (di-phTu), 1:3-di-o-tolyl thiourea (di-o tol Tu), 1:3-di-m-tolyl

thiourea (di-m-tol Tu) and 1 : 3-di-p-tolyl thiourea (di-p-tol Tu) for Al (1060) in 20%

HNO3. The IE’s of the inhibitors were determined at 25°, 35° and 45°C and it has

been observed that the percentage IE’s of the inhibitors increase with increase in

temperature. All the inhibitors except urea obey the Langmuir adsorption isotherm

below the inhibitor concentration of 300 ppm, but in no case are slopes equal to unity

observed. At and above the concentration of 300 ppm, the effectiveness of the

compounds decreases, this is attributed to their action as cathodic depolarizers. The

inhibitive performance of the compounds is discussed in the light of electronic effects

in the TU. The potentiostatic anodic polarization curves in the presence of the

inhibitors shift towards lower current density region as compared with the curve of

the uninhibited solution, but there is no proper correlation between the inhibition

efficiencies and the current densities required for the passivation of Al.

Hosseini and Salari [169] have investigated the corrosion inhibition of

stainless steel (SS) 302 by 1-methyl-3-pyridine-2-yl-thiourea (MPT) in acid medium

using potentiostatic polarization study. MPT acts efficiently in 1M H2SO4 than in 1M

HCl, perhaps the adsorption through the lone pair of heteroatoms and ∏ electrons of

the MPT molecule outweighs the adsorption due to the cationic form of the MPT

molecule on the metal surface. This adsorption follows Temkin’s adsorption isotherm.

The corrosion current density of SS in acidic medium decreases with an increase of

MPT concentration while corrosion potential increases. The calculated values of

thermodynamic parameters such as free energy, energy of activation, enthalpy and


65

entropy of corrosion indicate the spontaneous adsorption of the inhibitor on the

surface of stainless steel.

Divakara Shetty et al. [170] studied that the inhibition of corrosion of mild

steel in HCl by N-cyclohexyl-N’-phenyl thiourea (CPTU) using potentiodynamic

polarization technique which reveals that the CPTU is an excellent anodic inhibitor.

The maximum IE (98.72%) of the inhibitor was obtained in 50 ppm at 28oC in 0.1 N

HCl medium. The inhibition of CPTU is directly related to the spontaneous and strong

adsorption of the CPTU on the mild steel surface as elucidated from the values of free

energy and energy of activation.

Gogoi and Barhai [171] have studied that the corrosion inhibition of carbon

steel in open recirculating cooling water system of petroleum refinery by thiourea

(TU) and imidazole (I) in presence of zinc sulphate using weight loss and polarization

methods. The values of IE from weight loss method are in good agreement with those

obtained from polarization studies. Polarization study indicates that imidazole

suppress the cathodic corrosion reaction where as TU inhibits anodic corrosion

reaction in these particular blends of inhibitor. The inhibition of corrosion is due to

the formation of an adsorbed passive film on the metal surface as observed from SEM

and EDS results.

El-Egamy [81] have studied the electrochemical behaviour of copper (Cu),

iron (Fe) and Cu–20%Fe alloy in 1.0 M NaCl solution of pH 2 using the thiourea

(TU) as inhibitor. The studies such as OCP, polarization and EIS have been used.

The results showed that the corrosion rates (CR) of the three electrodes follow the

sequence: Cu < Cu–20%Fe < Fe. Polarization of the Cu–20%Fe electrode in the range

-0.70 V to -0.45 V (SCE), shows that iron dissolves selectively from the Cu–20%Fe

electrode surface and the rate of the selective dissolution reaction depends on the

applied potential. At anodic potential of -0.45 V, TU molecules adsorb at the alloy

surface according to the Langmuir adsorption isotherm. Increasing TU concentration

(up to 5 mM), decreases the selective dissolution reaction and the inhibition efficiency

g reach 91%. At TU concentration > 5 mM, the dissolution rate of the Cu–20%Fe

electrode increases due to formation of soluble TU complexes. At cathodic (-0.6 V),

the IE of TU decreases markedly owing to a decrease of the rate of the selective


66

dissolution reaction and/or desorption of TU molecules. The results indicate that TU

acts mainly as inhibitor of the selective dissolution reaction of the Cu–20%Fe

electrode in chloride solution.

Lin et al. [11] have studied the corrosion inhibition of steel by thiourea and

cations (Al3+, Ca2+, Mg2+) under incomplete cathodic protection in a 3.5% NaCl

solution and sea water using potentiodynamic polarization study. The results of

polarization study reveal that TU can behave as cathodic inhibitor and the IE of Al3+

is about 90%. The suitable mechanism for corrosion inhibition process has been

obtained.

Qian-qian [172] investigated the corrosion behavior of A3 carbon steel in

0.5mol/L H2SO4 solution and in the mixture of 0.5mol/L H2SO4 and thiourea (TU)

using polarization curve and EIS studies. The obtained results explains the mixed –

type inhibitor nature of TU.

Heming [173] synthesized the derivatives of lauric acyl thiourea and studied

its inhibition performance for CO2 corrosion by traditional weight-loss and EIS

methods. The results indicate that the IE can reach to 91.49% for the CO2 corrosion

when its concentration is 0.10 g/L. The polarization curves analysis reveals that the

inhibitor is an anodic type, and EIS study shows that the inhibitor is due to the

negative catalytic mechanism.

Guang-Chao et al. [174] investigated the corrosion behavior of stainless steel

(SS) in dilute H2SO4 containing TU using weight loss method and electrochemical

dynamic potential reactivation (EPR) technology. The effects of temperature and

acidity were also studied. The results showed that the IE was greatly affected by H2S.

The IE of TU decreases with increase in temperature, which is due to the production

of H2S during hydrolysis of TU.

Xiao-ying et al. [175] have studied the inhibitive action of cetylpyridinium

bromide (CPB) and thiourea (TU) and the synergistic action of CPB and TU on the

corrosion behaviour of X70 steel in 10 mmol/L H2SO3 using polarization and EIS. It

was found that the inhibitive effect of CPB and TU increases with the increase in


67

concentration of CPB and TU respectively. A combination of CPB and TU gives a

synergistic effect.

Quraishi et al. [176] synthesized new TU derivatives and used to evaluate

corrosion inhibition of mild steel in 20% formic acid by weight loss and

potentiodynamic polarization methods. All the TU derivatives have shown very good

IE in the formic acid. IE of these compounds has been found to vary with the

concentration of the compounds, solution temperature, immersion time and

concentration of the acid solution. The adsorption of these compounds obey Temkin’s

adsorption isotherm. The values of activation energy (Ea) and free energy of

adsorption (∆Gads) indicates that physical adsorption on the steel surface.

The polarization study reveals that all the compounds are mixed type inhibitors.

Xiyun Yang et al. [177] obtained the mechanism of gold dissolution in acidic

TU solutions using CV, EIS and linear sweep voltammetry (LSV).

Bolzan et al. [178] have studied the anodic behaviour of Cu in aqueous 0.5 M

H2SO4 containing TU or formamidine disulphide (FD) at 298 K, using

electrochemical polarization, chemical analysis, UV, XPS and EDAX analysis.

The corrosion reactions depend on the applied potential and initial concentration TU.

The formation of this film depends on certain critical TU/copper ion molar

concentration ratios at the reaction interface. For E≥0.075 V, soluble Cu(II) ions in

the solution are formed and the anodic film is gradually changed to another one

consisting of copper sulphide and residual copper. The new film assists the localized

electro-dissolution of Cu. A suitable mechanism has been proposed for the corrosion

inhibition.

II.4. Corrosion inhibition by biocides

Microbial colonization of metals and alloys of industrial usage takes place

through the formation of biofilms made of bacteria, extracellular polymeric

substances (EPS) and mainly water. These biological deposits can drastically modify

the corrosion behavior of structural metals and alloys enhancing localized alterations

in the type and concentrations of ions, pH, and oxygen levels. However, biofilms also

facilitate the formation of diffusion barriers to the exchange of chemical species from


68

and towards the metal/solution interface. The problems due to biocorrosion and

biofouling of industrial systems range from heavy microbiological contamination with

consequent energy and efficiency losses to structural failures owing to corrosion.

The use of appropriate monitoring strategies complemented with field and laboratory

microbiological techniques is necessary to reach a proper understanding of the effects

derived from microbiological activity and the role of biofilms in the corrosion

reaction to later implement effective control and preventive countermeasures. It must

be emphasized that this assessment should be made for each industrial system,

considering its previous history, present operational conditions, physicochemical

composition of the intake water and the number and identity of microbial

contaminants [179].

Zhao Kaili [180] investigated that the pipelines during and after hydrotesting

are vulnerable to microbiologically influenced corrosion (MIC), which can result in

severe pinhole leaks. The MIC process during hydrotesting was found to be

dependent on water sources due to different concentrations of nutrients and native

organisms. In order to accelerate the MIC process, a simulated worst-case scenario

with a lab strain SRB (sulphate-reducing bacteria) and key nutrients added proved to

be a useful approach. Furthermore, the technique of polymerase chain reaction (PCR)

was adopted to MIC research for detecting very low concentrations of targeted

planktonic microbes. A novel MIC mitigation method, using biocides THPS

(TetrakisHydroxymethyl-Phosphonium Sulphate) and glutaraldehyde, in combination

with EDTA was found to be more effective for controlling the growth of planktonic

SRB. A mechanistic THPS degradation model, with great consistency to experimental

results, was developed to predict residual THPS concentration to assure that it does

not fall below the desired minimum required for MIC control. Based on the

mechanism of biocatalytic cathodic sulphate reduction (BCSR), a first generation

MIC mechanistic model was developed to predict the MIC pitting rate under certain

conditions; thus providing a basis for a more comprehensive mechanistic MIC

modeling.

Rongjun Zuo [181] summarized the review on recent progress in microbial

corrosion control using beneficial bacteria biofilms. The possible mechanisms may

involve, the removal of corrosive agents (such as oxygen) by bacterial physiological


69

activities (e.g., aerobic respiration), growth inhibition of corrosion-causing bacteria by

antimicrobials generated within biofilms (e.g., sulfate-reducing bacteria (SRB)

corrosion inhibition by gramicidin S-producing Bacillus brevis biofilm) and

generation of protective layer by biofilms (e.g., Bacillus licheniformis biofilm

produces on Al surface a sticky protective layer of γ-polyglutamate). The successful

utilization of this novel strategy is much helpful in the field of corrosion engineering

and biofilm biology.

Rajendran et al. [23] have evaluated the IE of sodium dodecylsulphate (SDS)

in controlling corrosion of carbon steel immersed in the chloride environment in the

presence and absence of Zn2+ using weight loss, UV and FTIR studies. The results

obtained indicate that SDS – Zn2+ system shows a synergistic effect, formulation

consists of 100 ppm of SDS and 75 ppm of Zn2+ has 93% IE and the protective film

consists of Fe2+ - SDS complex and Zn(OH)2.

Sharma et al. [182] investigated that the inhibitive effect of N-cetyl, N,N,N-

trimethylammonium bromide (CTAB) on acid corrosion of mild steel in H2SO4 at

different temperatures. Galvanostatic and potentiostatic studies were performed to

determine the corrosion current, IE, passivation current and passivation potential

range. The parameters so obtained were used to explain the effectiveness of inhibitor

when present in different concentrations. The changes take places on the metal

surface with respect to change in CTAB concentration and the extent of corrosion

inhibition have been identified using SEM studies. The results obtained are in direct

agreement with the electrochemical studies.

Shanthy et al. [183] evaluated the IE of CTAB – Zn2+ system in controlling

corrosion of carbon steel in well water using weight loss, potentiodynamic

polarization and EIS studies. Enumeration of microorganisms from well water and

biocidal efficiency of inhibitor system determined by serial dilution technique and

spread plate method. The maximum IE is found to be 98%. Polarization reveals that

the inhibitor functions as anodic type and EIS study confirms the formation of

protective film on the metal surface. FTIR spectra suggest that the protective film

consists of Fe2+ - CTAB complex and Zn(OH)2. The optimum concentration of CTAB

for destroying the bacteria such as escherichia coli, salmonella and shigella is > 25


70

ppm. At > 25 ppm of CTAB, it shows 100% biocidal efficiency in well water

containing 5 ppm of Zn2+.

Jizhou Duan [184] has characterized the bacteria in the anaerobic biofilm on

rusted carbon steel immersed in natural seawater by culturing and molecular biology

techniques. Two types of anaerobic bacterium, sulphate-reducing bacteria

Desulfovibrio caledoniensis and iron-reducing bacteria Clostridium sp. uncultured

were found. The compositions of the rust layer were also analyzed. The corrosion

mechanism has been investigated based on the isolated sulphate-reducing bacteria and

mixed bacteria cultured from rust layer in laboratory culture conditions. It is found

that single species produced iron sulfide and accelerated corrosion, but mixed species

produced sulfate green rust and inhibited corrosion. The anaerobic corrosion

mechanism of steel has been proposed along with environmental significance.


References


71

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