substituted imidazoles as corrosion inhibitors for n80 steel in...

Indian Journal of Chemical Technology

Vol. 20, November 2013, pp. 363-370

Substituted imidazoles as corrosion inhibitors for

N80 steel in hydrochloric acid

M Yadav1,

*, P N Yadav2 & Usha Sharma

1

1Department of Applied Chemistry, Indian School of Mines, Dhanbad 826 004, India 2 Department of Physics, Post Graduate College, Ghazipur 233 001, India

Received 23 June 2012; accepted 2 March 2013

Three synthesized imidazole derivatives, namely 1-[hydrazinyl(4-methoxyphenyl)methyl]-1H-imidazole [HMPMI],

1-[hydrazinyl(phenyl)methyl]-1H imidazol [HPMI] and 1-[hydrazinyl(chlorophenyl)methyl]-1H-imidazol [HCPMI] have

been used as corrosion inhibitors for N80 steel in 15% HCl using weight loss, electrochemical polarization, AC impedance

and SEM techniques. The results show that the inhibition efficiency of all inhibitors increases with the increase in inhibitors

concentration. All studied inhibitors act as mixed inhibitors and obey the Langmuir adsorption isotherm. Corrosion

inhibition takes place through adsorption phenomenon.

Keywords: Corrosion inhibition, Electrochemical impedance spectroscopy, Electrochemical polarization, Imidazoles,

N80 steel

N80 steel is widely used as a construction material for

pipe work in the oil and gas production, such as down

hole tubular, flow lines and transmission pipelines in

petroleum industry. Mineral acids particularly

hydrochloric acid are frequently used in industrial

processes involving acid cleaning, acid pickling, acid

descaling, and oil well acidizing1-3

. Acidization of a

petroleum oil well is one of the important stimulation

techniques for enhancing oil production. It is

commonly brought about by forcing a solution of

15 – 28% hydrochloric acid into the well to open up

near bore channels in the formation and hence to

increase the flow of oil. To reduce the aggressive

attack of the acid on tubing and casing materials

(N80 steel), inhibitors are added to the acid solution

during the acidifying process. Most of the well-known

acid inhibitors are organic compounds containing

nitrogen, oxygen and/or sulphur atoms, heterocyclic

compounds and pi-electrons4-7

. The polar function is

usually regarded as the reaction centre for the

establishment of the adsorption process8. It is

generally accepted that organic molecules inhibit

corrosion via adsorption at the metal–solution

interface9,10

, resulting in formation of adsorption layer

as a barrier thus isolating the metal from the

corrosion11

. The effective acidizing inhibitors that are

usually found in commercial formulations are

acetylenic alcohols, alkenyl phenones, aromatic

aldehydes, nitrogen-containing heterocyclics,

quaternary salts and condensation products of

carbonyls and amines12-14

. However, these inhibitors

suffer from drawbacks, such as they are effective only

at high concentrations and are harmful to the

environment due to their toxicity. Hence, it is

important to search for new nontoxic and effective

organic corrosion inhibitors for N80 steel – 15%

hydrochloric acid system. Imidazole derivatives,

because of their good solubility, high stability, and

lower toxicity, have been widely used15-19

. The

encouraging results obtained with imidazole

derivatives have incited us to synthesized some

imidazole derivatives and extend their use in the

corrosion inhibiting action on N80 steel in 15% HCl

solution.

Thus, the present study was aimed at preparing

three imidazole compounds namely 1-[hydrazinyl

(4-methoxyphenyl)methyl]-1H-imidazole [HMPMI],

1-[hydrazinyl(phenyl)methyl]-1H imidazol [HPMI]

and 1-[hydrazinyl (chlorophenyl) methyl] -1H-

imidazol [HCPMI] to assess their inhibitive properties

for oil-well tubular steel (N80) in 15% hydrochloric

acid solution.

______________

* Corresponding author.

E-mail: [email protected]

INDIAN J. CHEM. TECHNOL., NOVEMBER 2013

364

Experimental Procedure Materials

The working electrode and specimens for weight

loss experiments were prepared from oil-well N80

steel sheets having the %wt composition: C 0.31,

Mn 0.92, Si 0.19, P 0.01, S 0.008, Cr 0.20,

Fe remainder (in %wt).

Weight measurements

The specimens for the weight loss experiments

were of the size 3 cm × 3 cm× 0.1 cm and for

electrochemical studies the size of the electrodes was

1 cm × 1 cm × 0.1 cm with a 4 cm long tag for

electrochemical contact. Both sides of the specimens

were exposed for both the techniques. The specimens

were mechanically polished successively with 1/0,

2/0, 3/0 and 4/0 grade emery papers. After polishing

with the paper of each grade, the surface was

thoroughly washed with soap, running tap water,

distilled water and finally degreased with acetone.

The samples were dried and stored in a vacuum

dessicator before immersing in the test solution. For

weight loss experiments 300 mL of 15% hydrochloric

acid solution was taken in 500 mL glass beakers with

lids. The inhibition efficiencies (%IE) were evaluated

after a pre-optimized time interval of 6 h using 20, 50,

100, 150, 200 and 250 ppm of inhibitors. The

specimens were removed from the electrolyte, washed

thoroughly with distilled water, dried and weighed.

The inhibition efficiencies were evaluated using the

following formula:

% IE = 100iW W

W

−× … (1)

where W is the weight loss in absence of inhibitor;

and Wi, the weight loss in presence of inhibitor.

Electrochemical procedure

The electrochemical experiments were carried out

in a three necked glass assembly containing 150 mL

of the electrolyte with different concentrations of

inhibitors (20 - 200 ppm by weight) dissolved in it.

The potentiodynamic polarization studies were carried

out with N80 steel strips having an exposed area of

1 cm2. A conventional three electrode cell consisting

of N80 steel as working electrode, platinum as

counter electrode and a saturated calomel electrode as

reference electrode were used. Polarisation studies

were carried out using VoltaLab 10 electrochemical

analyser and data was analysed using Voltamaster 4.0

software. The potential sweep rate was 0.1 mVs-1

. All

experiments were performed at 25 ± 0.2°C in an

electronically controlled air thermostat. For

calculating % IE by electrochemical polarization

method, the following formula was used:

0

0

% 100inhI IIE

I

−= × … (2)

where I0 is the corrosion current in absence of

inhibitor ; and Iinh, the corrosion current in presence of

inhibitor.

AC-impedance studies were carried out in a three

electrode cell assembly using computer controlled

VoltaLab 10 electrochemical analyzer, as well as

N80 steel as the working electrode, platinum as

counter electrode and saturated calomel as reference

electrode.The data were analysed using Voltamaster

4.0 software. The electrochemical impedance spectra

(EIS) were aquared in the frequency range from

10 kHz to 1mHz at the rest potential by applying 5mV

sine wave AC voltage. The charge transfer resistance

(Rct) and double layer capacitance (Cdl) were

determined from Nyquist plots. The inhibition

efficiencies were calculated from charge transfer

resistance values by using the following formula:

% IE = ( )

( )

100ct inh ct

ct inh

R R

R

−× … (3)

where Rct is the charge transfer resistance in absence

of inhibitor ; and Rct(inh), the charge transfer resistance

in presence of inhibitor.

Synthesis of inhibitors

The imidazole derivatives 1-[hydrazinyl(phenyl)

methyl]-1H-imidazole (HPMI), 1-[hydrazinyl(4-meth-

oxyphenyl)methyl]-1H-imidazole (HMPMI), and

1-[hydrazinyl(4-chlorophenyl)methyl]-1H-imidazole

(HCPMI) were synthesized by the reported method20

as shown in Scheme 1. A mixture of imidazole

(0.1 mol), hydrazine hydrate (0.1 mol) and

4-subsituted benzaldehyde (0.1 mol) in ethanol was

refluxed for 5 h. It was cooled and poured in to ice-

cold water. The precipitate was obtained in a few

Scheme 1 Synthetic route of inhibitors: HMPMI, HPMI and

HCPMI

YADAV et al.: SUBSTITUTED IMIDAZOLES AS CORROSION INHIBITORS FOR N80 STEEL IN HCl

365

mints, collected by filtration. The precipitate was

dried and recrystallised by absolute ethanol.

Results and Discussion

Weight loss measurement

The percentage inhibition efficiencies (% IEs) in

presence of 20, 50, 100, 150, 200 and 250 ppm

concentration of HMPMI, HPMI and HCPMI have

been evaluated by weight loss technique at 250C and

the results are summarized in Table 1. It is evident

from these values that all the three inhibitors are

significantly effective even at low concentrations like

20 ppm and there is a linear increase in %IE in the

whole range of concentrations studied. The %IE of all

the three studied inhibitors increases on increasing the

concentration of inhibitors and becomes almost

constant above 200 ppm concentration.The structure

of the inhibitors are given in Scheme 2.

It is observed that HMPMI is most efficient among

all the three tested inhibitors. The protective ability of

the inhibitors for all the tested concentrations is found

to decrease in the order HMPMI >HPMI> HCPMI.

The extent of %IE of different inhibitor at fixed

concentration depends upon the surface area of the

inhibitor molecules, the number of active centers such

as N, S and O atoms and the intensities of lone pair of

electrons on these sites along with the intensities of

π-electron on aromatic rings. The percentage inhibition

efficiency exhibited by these inhibitors is high which is

supposed to be due to strong adsorption of the inhibitor

molecules on the metal surface, thereby preventing

corrosion of N80 steel in hydrochloric acid solution.

The inhibitors are expected to get adsorbed through the

lone pairs of electrons on N atoms of amino group and

imidazole ring as well as π-electron density on the

phenyl and imidazole ring by their coordination with

metal surface. The participation of phenyl ring in

addition to that of N atom during the adsorption

process may be confirmed by changing the π-electron

density on phenyl ring by substituting electron

donating (-OCH3) and electron withdrawing (-Cl)

groups. Generally, electron donating groups increase

the inhibition efficiency and presence of electron

withdrawing groups decrease the inhibition efficiency

of the inhibitors. The inhibitors HMPMI, HPMI and

HCPMI have nearly same size and number of active

centers but HMPMI shows higher inhibition efficiency

(IE%) than HPMI and HCPMI due to higher

delocalized π-electron density at benzene ring. The

delocalized π-electron density at benzene ring in case

of HMPMI is more than in HPMI due to electron

donating nature of methoxy (−OCH3) group. The

delocalized π-electron density at benzene ring in case

of HCPMI is less than in HPMI due to electron

withdrawing nature of chloro (−Cl) group. It may be

noted that there does not exist any direct correlation

between magnitude in increase in IE values and the

number of expected sites of adsorption and size. This

may be due to the fact that the number of active centers

actually involved in adsorption may be different than

the number of active centers present in the molecules

owing to their geometry.

Electrochemical polarization

Electrochemical polarization curves of HMPMI,

HPMI and HCPMI for N80 steel in 15% hydrochloric

acid at 25oC are shown in Fig.1 and various

parameters obtained are given in Table 2. The shift in

Scheme 2 Structures of three inhibitors used.

Table 1 Corrosion paramters in absence and presence of

HMPMI, HPMI and HCPMI at different concentrations

HMPMI HPMI HCPMI Conc.

ppm IE% IE% IE%

CR

mmpy

CR

mmpy

CR

mmpy

0

20

50

100

150

200

250

9.55

3.32

2.57

1.8

1.35

1.03

0.94

-

65.2

73.1

81.2

85.9

89.2

90.1

9.55

3.78

3.02

2.34

1.79

1.42

1.32

-

60.4

68.4

75.5

81.3

85.1

86.2

9.55

4.33

3.42

2.69

2.19

1.96

1.90

-

54.7

64.2

71.9

77.1

79.5

80.1


366

the cathodic and anodic partial curves in presence of

the inhibitors may be due to adsorbed inhibitor

species on the surface of the steel that affects both the

anodic and cathodic areas. The minor shift of Ecorr in

negative direction indicates the interference of these

inhibitors with the cathodic partial processes. The

variation in the values of βa and βc in presence of the

inhibitors may indicate that both the anodic and

cathodic processes are controlled. All these inhibitors

are mixed type and predominantly control the

cathodic reaction. The significant reduction in Icorr at

higher concentration level (200 ppm) indicates better

inhibition performance at higher concentration level.

It is realized from these observations that the

inhibitors molecules retard the corrosion process

without changing its mechanism in the medium of

investigation. The magnitude of the shift in current

density is directly proportional to the concentration

of the inhibitors, indicating that the inhibitive

property of the inhibitor is concentration dependent.

It is clear from the polarization curves of the

inhibitors that the shift in current density towards

lower current density for anodic as well as cathodic

curve increases on increasing the concentration of

the inhibitor. The negative shift in the Ecorr in

presence of inhibitors on increasing the

concentration of the inhibitors is due to the decrease

in the rate of cathodic reaction. Moreover, the

increase in the cathodic and anodic Tafel slopes

(βc and βa) is related to the decrease in both the

cathodic and anodic currents. Both the inhibitors

affect both the anodic as well as cathodic sites, so

these are mixed inhibitors.

AC impedance study

The impedance data of N80 steel, recorded in

presence of 20, 100 and 200 ppm of the inhibitors

HMPMI, HPMI and HCPMI in 15% HCl solution at

25oC as Nyquist plots, are shown in Fig. 2. The

impedance data of the N80 steel electrode in presence

of 20, 100 and 200 ppm of these inhibitors were

analyzed using the equivalent circuit as shown in

Fig. 3. The impedance parameters derived from this

investigation are given in Table 3. The values of

charge transfer resistance (Rct) are obtained by

Table 2 Electrochemical corrosion parameters in absence and

presence of HMPMI, HPMI and HCPMI

Inhibitors Conc. Tafel slope Icorr Ecorr IE%

ppm Anodic βa

mV dec-1

Cathodic βc

mV dec-1

µA/cm2 mV

Blank

-

109

153

471

-468

-

HMPMI

20

100

200

112

117

121

165

169

188

155

82

46

-471

-477

-490

67.1

82.6

90.2

HPMI

20

100

200

111

114

119

162

166

183

180

108

60

-477

-462

-486

61.8

77.1

87.3

HCPMI

20

100

200

110

113

118

160

163

181

205

130

93

-467

-472

-477

56.5

72.4

80.3

Fig. 1 Potentiodynamic polarization curves in absence and in

presence of inhibitors at different concentrations


367

subtracting the high frequency impedance from the

low frequency, as shown below21

:

Rct = Zr (at low frequency) − Zr (at high frequency)

… (4)

The values of electrochemical double layer

capacitance (Cdl) were calculated at the frequency (fmax)

at which the imaginary component of the impedance is

maximal (−Zi) using the following equation22

:

Cdl=1/2πfmaxRct … (5)

The double layer capacitance Cdl is expressed in the

Helmotz model by:

0dlC S

εε

δ= … (6)

where d is the thickness of the deposite; S, the surface

of the working electrode, ε0, the permittivity of the

air; and ε, the medium dielectric constant. The

decrease in Cdl values may be interpreted either by a

decrease of local dielectric constant (ε) or by increase

in the thickness of the adsorbate layer of inhibitor at

the metal surface23,24

.

Table 3 shows that by increasing the concentration

of inhibitors, Rct values increase and Cdl values

decrease, indicating a decrease in the local dielectric

constant and/or an increase in the thickness of the

electrical double layer, suggesting that the inhibitor

molecule functions by formation of the protective

layer at the metal surface. The Cdl values tend to

decrease due to displacement of the water molecules

by the inhibitor molecules at the electrical double

layer, which suggests that the inhibitors molecules

function by adsorption at the metal solution interface 23

.

It can be seen from Table 3 that the inhibition

efficiency has increased with increase in inhibitors

concentration implying that the large charge transfer

resistance is associated with a slower corroding

system. In contrast, better protection provided by

inhibitors can be associated with a decrease in

capacitance of the metal. The depression in Nyquist

semicircle is a feature for solid electrodes, often

referred as frequency dispersion and attributed to the

roughness and other inhomogenities of the solid

Fig. 2 Nyquist plots of the corrosion of N80 steel in 15% HCl

solution without and with different concentrations of inhibitors

Fig. 3 Equivalent circuit model used in the fitting of the

impedance data of N80 steel in 15% HCl solution at 25oC

Table 3 Electrochemical impedance corrosion parameters in

absence and presence of HMPMI, HPMI and HCPMI

Inhibitors Conc.

ppm

Rct

Ωcm2

Cdl

µF cm-2

IE%

Blank - 176 662.5 -

HEPMI

20

100

200

520

1047

2022

298

140

62.8

66.5

83.2

91.3

HPMI

20

100

200

455

807

1248

352

197.2

102.9

61.3

78.2

85.9

HCPMI

20

100

200

405

630

972

341.9

291.8

173.5

56.5

72.1

81.9


368

electrode24

. The inhibition efficiencies calculated

from impedance data are in good agreement with

those obtained from electrochemical polarization and

weight loss measurement.

Adsorption isotherms

The adsorption of inhibitor molecules on the

surface of the corroding metal has been considered as

the root cause of corrosion inhibition. Assuming that

the percentage area covered by the inhibitors is

directly proportional to retardation in the corrosion

rate, the compounds should obey Langmuir

adsorption isotherm25,26

, as shown below:

log 1

θ

θ− = log A + log C −

2.3

Q

RT … (7)

where θ is the surface coverage; C, the concentration

of inhibitors; A, the temperature independent

constant; and Q, the heat of adsorption. The validity

of Langmuir isotherm is confirmed from the linearity

of the log 1

θ

θ− vs log C plot having the slope value

to be unity. The plots of log 1

θ

θ− vs log C for the

investigated inhibitors at 25°C are shown in Fig. 4.

It is observed that although these plots are linear, the

gradient are not unity, contrary to what is expected for

the ideal Langmuir adsorption isotherm equation. The

deviation in the values of the slopes of Langmuir plots

from unity may be advocated to be due to the mutual

interaction between adsorbed molecules in a close

vicinity27

. Organic molecules and metal complexes

having polar atoms or groups which are adsorbed on

the metal surface may interact by mutual repulsion or

attraction and hence may affect the heat of adsorption.

The plots of log 1

θ

θ− vs log C yield a straight line

with a correlation coefficient (R2) values 0.9891,

0.9808, 0.9935 for HMPMI, HPMI and HCPMI

respectively at 303 K. All the inhibitors follow the

Langmuir adsorption isotherm, indicating that the

adsorption of inhibitors at the surface of N80 is the

root cause of corrosion inhibition.

The adsorption of tested compounds at N80

steel/hydrochloric acid interface can be attributed to

the presence of hetero atom, imidazole ring and

aromatic ring, thus the possible reaction centers are

unshaired electron pair on nitrogen atoms and

π- electrons on imidazole ring and aromatic ring.

It is also known that the adsorption of the inhibitors

can be influenced by the nature of anions in acidic

solution. The presence of Cl- in the solution should

characterized with strong adsorbability on the

metal surface which brings about a negative

charge favoring the adsorption of cation type

inhibitors28,29

.

In aqueous acidic solution, HMPMI, HPMI

and HCPMI exists either as neutral molecule or in

the form of cations thus the adsorption of the

inhibitors as neutral molecule on the metal surface

can occur directly involving the displacement of

water molecule from the metal surface and sharing

of electrons between the nitrogen atom and the metal

surface.30

The protonated and unprotonated inhibitor

molecules may be adsorbed on the metal surface

through charge transfer or charge sharing

mechanism. These heterocyclic nitrogen compounds

may also be adsorbed through electrostatic

interaction between the positively charged nitrogen

atom and the negatively charged metal surface. 31

In addition π electron interaction between the

aromatic nucleus and the positively charged metal

surface may also play role. Among these three

inhibitors, HMPMI shows maximum inhibition

(89.21%) at 200 ppm towards corrosion of N80 steel

in 15% HCl due to presence of methoxy group which

increases electron density due to +I effect on

aromatic ring.

Fig. 4 Langmuir adsorption isotherm in presence of HMPMI,

HPMI and HCPMI


369

Microscopic Study

SEM microphotographs (Fig. 5) in absence and

presence of 200 ppm of the inhibitors at X 1000

magnification were studied to analyse the change in

the morphology of metal surface after corrosion tests

in presence and absence of the inhibitors. Steel

surface appears to be very rough in absence of

inhibitors (Fig. 5B). This is due to formation of

uniform flake type corrosion products on the metal

surface. Fig. 5 (C), (D) and (E) show that surface of

the samples become smooth due to adsorption of the

inhibitors at the surface of the sample.

Conclusion

All the studied inhibitors (HMPMI, HPMI and

HCPMI) act as efficient corrosion inhibitor for N80

steel in 15% HCl solution. HMPMI shows

appreciably higher efficiency than the HPMI and

HCPMI due to presence of electron donating methoxy

(–OCH3 ) group. HCPMI shows least inhibition

efficiency due to presence of electron withdrawing

chloro (–Cl) group. All the three imidazole

derivatives inhibit corrosion by adsorption on the

metal surface and follow Langmuir adsorption

isotherm. The results of potentiodynamic polarization

Fig. 5 SEM images of (A) polished sample (B) sample in presence of 15% hydrochloric acid solution (C) sample in presence of

200 ppm of HMPMI (D) sample in presence of 200 ppm of HPMI, and (E) sample in presence of 200 ppm of HCPMI


370

studies reveal that all the three inhibitors are

mixed type inhibitors and predominantly act on

cathodic area. In AC Impedance studies, Rct values

increase while Cdl values decrease as the

concentration of inhibitors increases, indicating the

adsorption of inhibitors at the surface of N80 steel.

It is suggested from the results obtained from SEM

and Langmuir adsorption isotherm that the

mechanism of corrosion inhibition is occurring

through adsorption process.

Acknowledgement

Financial assistance from Indian School of Mines,

Dhanbad under FRS to one of the authors (M Y) is

gratefully acknowledged.

References

1 Vishwanatham S & Haldar N, Corros Sci, 50 (2008) 2999.

2 Abd El-Maksoud S A & Fouda A S, Mater Chem Phys, 93

(2005) 84.

3 Migahed M A & Nassar I F, Electrochim Acta, 53 (2008)

2877.

4 Muralidharan S, Quraishi M A & Iyer S V K, Corros Sci, 37

(1995) 1739.

5 Bentiss F, Lebrini M, Lagrenee M, Elfarouk A & Vezin H,

Electrochim Acta, 52 (2007) 6865.

6 Cruz J, Martinez R, Genesca J & Garcia-Ochoa E, J

Electroanal Chem, 566 (2004) 111.

7 Khaled KF, Babic-Samradzija K & Hackerman N,

Electrochim Acta, 50 (2005) 2515.

8 Roberge P R, Handbook of Corrosion Engineering

(McGraw-Hill, New York), 1999.

9 Olivares-Xometl O, Likhanova N V, Domínguez-Aguilar M

A, Arce E, Dorantes H & Arellanes-Lozada P, Mate Chem

Phys, 110 (2008) 344.

10 Quartarone G, Battilana M, Bonaldo L & Tortato T, Corros

Sci, 50 (2008) 3467.

11 Ebenso E E, Bull Electrochem, 19 (2003) 209.

12 Poling G W, J Electrochem Soc, 114 (1967) 209.

13 Neemla K D, Saxena R C & Jayaraman A, Corros Prev

Cont, 6 (1992) 69.

14 Frenier W, Growcock F, Dixon B & Lopp V R, Corrosion,

44 (1988) 590.

15 Stupnicek-Lisac E, Gazivoda A & Madzarac M, Electrochim

Acta, 47 (2002) 4189.

16 Sivaraju M, Kannan K & Elavarasan, S, Orient J Chem, 25

(2008) 67.

17 Khaled, K F & Amin M A, J Appl Electrochem, 39 (2009)

429.

18 Zhang D Q, Gao L X & Zhou G D, Corros Sci, 46 (2004)

3031.

19 Christov M & Popova A, Corros Sci, 46 (2004) 1613.

20 Radha Krishnan Surendra Kumar, Akbar Idhayadhulla &

Abdul Jamal Abdul Nasser, Orbital Ele J Chem, 3(1)

(2011) 32.

21 Yadav A P, Nishikata A & Tsuru T, Corros Sci, 46 (2004)

169.

22 Galal A, Atta N F & Al-Hassan M H S, Mater Chem Phys,

89 (2005) 38.

23 McCafferty E & Hackerman N, J Electrochem Soc, 119

(1972) 146.

24 Bastidas J M, Polo J L & Cano E, J Appl Electrochem, 30

(2000) 1173.

25 Popova A & Christov M, Corros Sci, 48 (2006) 3208

26 Singh M M, Rastogi R B & Upadhyay B N, Corrosion, 50

(1994) 620.

27 Singh M M, Rastogi R B & Upadhyay B N, Bull

Electrochem, 12 (1996) 26.

28 Antropov L I, Makushin E M & Panasenko V F, Inhibitors of

Metal Corrosion (Russia), (Technika, Kiev), 1981.

29 Rozenfield I I, Corrosion Inhibitors (Russia) (Khimia,

Moscow), 1977.

30 Hackerman N & Makrides A C, J Phys Chem, 59 (1955) 707.

31 Man C A, Trans Electrohem Soc, 69 (1936) 105.

substituted imidazoles as corrosion inhibitors for n80 steel in...

Documents