Surface protection of mild steel in acidic chloride solution by 5 nitro 8 hydroxy quinoline

Sundaravadivelua,⇑ a Department of Chemistry, The Gandhigram Rural Institute-Deemed University, Gandhigram 624 302, Tamil Nadu, India b Centre for Research, Department of Chemistry, Mahe

Full Length Article

Surface protection of mild steel in acidic chloride solution by

5-Nitro-8-Hydroxy Quinoline

R Ganapathi Sundarama,b, M Sundaravadivelua,⇑

a Department of Chemistry, The Gandhigram Rural Institute-Deemed University, Gandhigram 624 302, Tamil Nadu, India

b

Centre for Research, Department of Chemistry, Mahendra Engineering College (Autonomous), Mallasamudram, Namakkal 637 503, Tamil Nadu, India

a r t i c l e i n f o

Article history:

Received 14 September 2016

Revised 5 December 2016

Accepted 24 January 2017

Available online xxxx

Keywords:

Acidic chloride solution

MS

NHQ

WL

SEM

FT-IR

a b s t r a c t

The effect of commercially available quinoline nucleus based pharmaceutically active compound 5-Nitro-8-Hydroxy Quinoline (NHQ) against the corrosion of mild steel (MS) in 1 M acidic chloride (HCl) solution was investigated by chemical (weight loss – WL) and electrochemical (Tafel polarization, Linear polariza-tion and Electrochemical impedance spectroscopy) techniques From all the four methods, it is inferred that the percentage of inhibition efficiency increases with increasing the inhibitor concentration from

50 to 300 ppm The adsorption behavior of inhibitor obeyed through Langmuir isotherm model Thermodynamic parameters were also calculated and predict that the process of inhibition is a sponta-neous reaction EIS technique exhibits one capacitive loop indicating that, the corrosion reaction is con-trolled by charge transfer process Tafel polarization studies revealed that the investigated inhibitor is mixed type and the mode of adsorption is physical in nature The surface morphologies were examined

by FT-IR, SEM and EDX techniques Theoretical quantum chemical calculations were performed to con-firm the ability of NHQ to adsorb onto mild steel surface

Ó 2017 Egyptian Petroleum Research Institute Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

1 Introduction

Iron is the most abundant element by mass of the earth Iron

and its alloys are widely used in many applications, which have

resulted in research into the corrosion resistance in various

aggres-sive environments [1] The corrosion protection of iron and its

alloys especially mild steel in corrosive environments have

attracted the attention of many investigators[2–6] Acid solutions

mainly hydrochloric acid is widely used in industry for the removal

of corrosion products which in turn accelerates corrosion Because

the cost of hydrochloric acid is very low than other mineral acids

To protect the surface of mild steel and also prevent the further

form of corrosion products, the use of inhibitor is one of the

impor-tant practical methods[7,8] Most of the heterocyclic organic

com-pounds have been reported in literature as efficient corrosion

inhibitors for mild steel in acid medium[9–18]

The corrosion inhibition is a surface process, which involves

adsorption of the molecule on the metal/alloy surface The

adsorp-tion is favored by heteroatoms like sulphur, nitrogen, oxygen,

phosphorous and p electrons present in the studied molecule The adsorption depends mainly on the electronic structure of the molecule[19] Nowadays several heterocyclic compounds are used

as a corrosion inhibitors but, unfortunately some heterocyclic com-pounds are environmental toxic, high cost, very poor solubility in water and easily unavailable Therefore, the selection of the inhibi-tor is mainly based on the availability, low cost, non-toxic, biodegradable, renewable material and the presence of groups or atoms which aid the adsorption of inhibitor to the metal/alloy sur-face Moreover, the investigated inhibitor is commercially avail-able, low cost, and soluble in water Furthermore, it is an environmental friendly inhibitor Because it acts as an antibiotic and have also been used in an anticancer setting In the view of these favorable characteristic properties, 5-Nitro-8-Hydroxy Quinoline was chosen for the corrosion studies

In the present study, NHQ has been investigated for its corro-sion inhibition efficiency Weight loss studies, polarization (Tafel and Linear) studies and impedance studies were employed to investigate the inhibition efficiency of NHQ on MS in acidic chlo-ride solution FT-IR, SEM and EDX studies were employed to con-firm the nature of the adsorbed (protective) film The results of quantum chemical methods were correlated with experimental results

http://dx.doi.org/10.1016/j.ejpe.2017.01.008

1110-0621/Ó 2017 Egyptian Petroleum Research Institute Production and hosting by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Peer review under responsibility of Egyptian Petroleum Research Institute.

⇑ Corresponding author.

E-mail addresses: chemistryganpath17@gmail.com (R Ganapathi Sundaram),

msundargri@gmail.com (M Sundaravadivelu).

Contents lists available atScienceDirect Egyptian Journal of Petroleum

j o u r n a l h o m e p a g e : w w w s c i e n c e d i r e c t c o m

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5-Nitro-8-2 Material and experimental procedure

2.1 Preparation of specimen

The mild steel (MS) specimen of dimension 3.5
1.5
0.2 cm

in size with 1 hole in the upper edge was used for the weight loss

measurement and 1.0
1.0
0.2 cm in size was used for the

sur-face study For an electrochemical investigation, 1.0 cm2 area of

the MS specimen was exposed to the 100 ml of 1 M acidic chloride

(HCl) solution and the balance being covered by commercially

available resin The surfaces of the mild steel specimens were

pol-ished with various grades (1/0–7/0) of emery papers and then

degreased with acetone Finally, it is dried in air drier before all

the investigation The composition (wt.%) of the mild steel is:

C 0.104, Mn 0.580, P 0.035, S 0.026 and balance is Fe

2.2 Preparation of acidic chloride solution

The acidic chloride solution (1 M HCl) was prepared by dilution

of analytical grade 37% hydrochloric acid with bidistilled water

2.3 Preparation of inhibitor solution

The investigated inhibitor molecule 5-Nitro-8-Hydroxy

Quino-line was purchased from Sigma-Aldrich and used as a green

corro-sion inhibitor in an acidic chloride medium It is commercially

known as Nitroxoline The optimized structure of NHQ is given in

Fig 1 The investigated compound contains many active centre’s

like 3 oxygen and 2 nitrogen atoms The preparation of different

concentrations (50–300 ppm) of inhibitor solution was done

according to the standard method as described earlier[20]

2.4 Weight loss studies

In this study, the pre-cleaned and pre-weighed mild steel

spec-imens were suspended in 100 ml of 1 M acidic chloride (HCl)

solu-tion with and without various concentrasolu-tions of inhibitor for a

period of 3 h After that, the mild steel specimens were taken

out, washed with distilled water, dried with air drier and weighed

accurately The weight loss studies were made in triplicate and the

loss of weight was calculated by taking an average (mean) of these

values The standard deviation in the observed weight loss values

was calculated and reported The corrosion rate (CR) is calculated

by the following equation

CR¼W

where W is the average (mean value) weight loss of three mild steel

specimens, S is the total area of mild steel specimen and t is the

immersion time

From the calculated CR value, the inhibition efficiency (IE%) was calculated according to the following equation:

IEð%Þ ¼ Wo Wi

Wo

where Woand Wiare the corrosion rate in the absence and presence

of various concentrations of NHQ, respectively

2.5 Electrochemical studies Electrochemical studies (AC impedance measurements, Tafel polarization measurements and Linear polarization measure-ments) were carried out by using CH-Electrochemical analyzer model 760 D with CHI 760 D software The used electrochemical analyzer contains three electrodes that are working electrode, aux-iliary electrode and reference electrode In this setup, the mild steel act as a working electrode, a saturated calomel electrode as a ref-erence electrode and the platinum foil as an auxiliary electrode Before starting the measurements, the working electrode (MS) was allowed to reach steady-state value of OCP All the three elec-trodes were kept immersed in blank and various concentrations of inhibitor solution The measurements were carried out after

30 min of immersion time at room temperature

Impedance measurements were carried out in the frequency range from 10 kHz to 0.1 Hz with ac impedance signal of 0.01 V amplitude From this measurement, the impedance diagrams like Nyquist and Bode were plotted Rctand Cdl values were obtained from the Nyquist plots and the inhibition efficiency (IE) was calcu-lated from the following equation:

IEð%Þ ¼ R

i

ct Ro ct

Rict

" #

where Rictand Roctis the charge transfer resistance values of with and without NHQ, respectively

The Tafel polarization measurements were carried out by changing the electrode potential automatically from300 mV to +300 mV with respect to OCP at a scan rate of 0.1 mV/s From this study, the inhibition efficiency was calculated from corrosion cur-rent density (Icorr) values by using the formula:

IEð%Þ ¼ I

o corr Ii corr

Io corr

" #

where Iocorrand Iicorr are the corrosion current density values in the

respectively

For the linear polarization measurements, the potential of the electrode was scanned from0.02 to +0.02 V versus Ecorrat a scan rate of 0.125 mV/s The surface coverage (h) and inhibition effi-ciency (IE%) were calculated using the following relationship[21]

h ¼ R

i

p Ro p

Rip

" #

ð5Þ

IEð%Þ ¼ R

i

p Ro

Ri p

" #

where Ripand Roare the linear polarization resistance values in the presence and absence of NHQ, respectively

Fig 1 The optimized structure of NHQ.

2.6 Surface morphology studies

2.6.1 SEM studies

The surface of fresh mild steel, uninhibited and inhibited mild

steel specimens was analyzed by using JEOL/EO JSM-6390 model

SEM

2.6.2 EDX studies

The EDX system is also attached with a JEOL/EO JSM-6390

scan-ning electron microscopy The main purpose of this analysis is to

confirm the percentage of elements in the studied MS specimens

2.6.3 FT-IR studies

The protective film formed on the mild steel specimen is

scratched carefully and the powder obtained is mixed thoroughly

to make it uniform The FT-IR spectra are recorded by using JASCO

460 PLUS spectrophotometer over the range of 400–4000 cm1

with the resolution of 4 cm1, using the KBr disk technique

2.6.4 Theoretical studies – quantum chemical calculations

The quantum chemical calculations are performed by using

density functional theory (DFT) and utilizing the 6-31G (d,p) set

6-31+G (d,p) basis sets DFT/B3LYP is recommended for the study

of chemical reactivity and selectivity in terms of frontier molecular

orbital theory[22]

3 Results and discussion

3.1 Weight loss studies

Table 1gives the inhibition efficiency and surface coverage

val-ues of various concentrations of NHQ for the corrosion of mild steel

in acidic chloride solution From this study, the inhibition

effi-ciency was increased and the rate of corrosion was decreased with

the increase of the inhibitor concentration This trend may result

from the fact that an adsorption and the surface coverage increases

with the increase in concentration, thus the surface of the mild

steel is effectively separated from the acidic chloride medium

[23] The ‘N’ and ‘O’ atoms can donate thepelectrons to the active

sites of mild steel surface therefore the adsorption process is

increases and attain the maximum inhibition efficiency (89%) at

the optimum concentration of inhibitor[24].Fig 2represent the

inhibition efficiency and the corrosion rate of the studied inhibitor

NHQ FromFig 2the IE (%) is increases and the corrosion rate of the

mild steel decrease with the addition of NHQ, which explains the

formation of protective layer on the corroded mild steel surface

This study clearly indicates that the mild steel surface is protected

from the acidic chloride solution

3.2 Electrochemical studies

3.2.1 Impedance (EIS) studies

The impedance (EIS) studies were investigated by varying the

concentrations of NHQ in 1 M acidic chloride solution (HCl) at

room temperature From this study, the impedance diagrams were obtained and are shown inFig 3a and b The impedance data such

as Rct, Cdlandh were obtained from Nyquist plot The percentage of inhibition efficiency is determined from Rctvalues according to the above-mentioned equation and all the impedance parameters are given inTable 2 The impedance studies clearly indicate that the

Rctvalue increased and Cdlvalues decreased with the addition of NHQ concentration The increasing Rctvalues imply reduced corro-sion rate in the presence of the studied inhibitor and this is because

of the increasing surface coverage of NHQ molecule on the addition and resulting in the formation of protective film on the corroded

MS surface[25,26] The decrease in Cdlvalues was due to the gradual replacement

of water molecules by the adsorption of NHQ compound at mild steel/solution interface, which led to the formation of protective film on the corroded MS surface and also prevent the further form

of corrosion products[27] FromFig 3b, the phase angle increases with increase in the investigated inhibitor concentration this is due to the adsorption

of inhibitor molecule on the surface of MS[28] According to the appearance of the phase angles versus frequency diagrams, the increasing concentration of the studied inhibitor NHQ in the pres-ence of acidic chloride solution results in more negative values of the phase angle at high frequencies, indicating superior inhibitive behavior at higher concentrations This result could be attributed

to higher corrosion activity even at low concentrations of NHQ

[5] The obtained inhibition efficiency by this study showed good agreement with the result obtained from weight loss study 3.2.2 Tafel polarization (TP) studies

Fig 4depicts the representative Tafel plots of the corrosion inhibition effect of various concentrations of NHQ on MS in 1 M acidic chloride solution at room temperature The obtained results from Tafel polarization studies are given inTable 3 Results show that the addition of inhibitor alters both thebaandbcvalues sug-gesting that the NHQ molecule reduces anodic dissolution and retard hydrogen evolution as well indicating the studied inhibitor

is a mixed nature On increasing the concentration of inhibitor, the Icorr value decreases from 2.397 mV/cm2 to 0.390 mV/cm2, which are due to the higher surface coverage of the corroded MS

[29,30] The inhibition efficiency of the studied inhibitor on the surface of corroded mild steel is 59.3%–83.7% respectively From this studies the surface of working electrode is protected from the acidic chloride solution, when the addition of inhibitor concentration

3.2.3 Linear polarization resistance (LPR) studies The linear polarization resistance (RP) parameters were obtained from the slop of polarization plots The surface coverage (h) and inhibition efficiency (IE%) were calculated by using the above mentioned equation and the values are given in Table 4 The results showed that the RPvalues increased with increase in the concentration of investigated inhibitor From this study, the highest inhibition efficiency was 83.72% obtained at the optimum Table 1

Corrosion parameters obtained from WL studies of MS in 1 M Acidic Chloride Solution containing different concentrations of NHQ.

Conc of NHQ (ppm) Weight loss value

(mg cm2)

Mean value (m) Standard deviation (Ϭ) Corrosion Rate (mm y 1 ) Surface coverage (h) IE (%)

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5-Nitro-8-concentration of NHQ The increase in the inhibition efficiencies for

corrosion of mild steel in acidic chloride solution with increasing

concentration can be explained on the basis of an inhibitor

adsorp-tion The results obtained from Tafel polarization studies showed

good agreement with the results of LPR studies

The nature of interaction between the inhibitor and the cor-roded mild steel surface can be clearly described by the adsorption isotherm This process is determined by using the surface coverage data and it plays an important role in the prediction of an adsorp-tion isotherm The degree of surface coverage (h) is calculated by using the equationh = %IE/100[31] The h values obtained from

WL studies, EIS studies, TP studies and LPR studies were tested with different types of adsorption isotherm at room temperature Among the different types of adsorption isotherm studies, Lang-muir isotherm gives the best fit at room temperature According

to Langmuir adsorption isotherm,h is related to Cinhby the follow-ing equation:

Cinh

h ¼

1

Kads

where Cinhis the inhibitor concentration (ppm),h is the degree of surface coverage and Kadsis the adsorption equilibrium constant The Kadsvalues can be calculated from the intercept lines on the

Cinh/h axis This is related toDG0adswith the following equation:

where R is the universal gas constant, T is the absolute temperature and 55.5 is the concentration of water in solution in mol L1[32] The Langmuir adsorption isotherm was drawn by plotting Cinh/h versus Cinhfor various concentrations of inhibitor and considering theh values from WL studies, EIS studies, TP studies and LPR stud-ies The obtained graph was shown in Fig 5 The straight line obtained in the graph clearly shows that the investigated inhibitor obeys Langmuir adsorption isotherm The obtained thermodynamic parameters are given inTable 5 Generally, the value ofDG0

adsless

Fig 2 Plot of Inhibition efficiency and corrosion rate of MS with various

concentrations of NHQ in 1 M acidic chloride solution.

Table 2 Corrosion parameters obtained from EIS studies of MS in 1 M Acidic Chloride Solution containing different concentrations of NHQ.

Conc of NHQ (ppm)

Y max

(Ώ cm 2 )

R ct

(Ώ cm 2 )

C dl

(lF cm 2 )

Surface coverage (h)

IE (%)

Fig 4 Tafel plots for MS corrosion in 1 M acidic chloride solution with various concentrations of NHQ.

Fig 3 (a) Nyquist plots for MS corrosion in 1 M acidic chloride solution with

various concentrations of NHQ (b) Bode plots for MS corrosion in 1 M acidic

chloride solution with various concentrations of NHQ.

negative than 20 kJ mol1 signifies physisorption and the value

more negative than about 40 kJ mol1 indicates chemisorptions

[33] From this study the calculatedDG0

adsvalues indicates, the pro-cess of adsorption is through physisorption

3.3 Surface studies

3.3.1 SEM studies

The SEM images of fresh mild steel, mild steel in acidic chloride

solution and mild steel in acidic chloride with NHQ (300 ppm) are

shown inFig 6a–c This analysis clearly shows that the inhibition

effect is increased remarkably in the presence of optimum concentration of NHQ

3.3.2 EDX studies The EDX images of fresh mild steel, uninhibited and inhibited mild steel with acidic chloride solution are shown in Fig 7a–c, respectively The analysis ofFig 7b indicates the presence of iron, oxygen, carbon and chlorine peaks; whereas the surface of inhibited mild steelFig 7c indicates the presence of iron, oxygen, carbon and nitrogen peaks In this analysis, new peak nitrogen is obtained in the plot (Fig 7c) This is due to the adsorption of inhibitor molecules

on the surface of mild steel This analysis also proves the adsorption

of inhibitor molecules on the surface of corroded mild steel 3.3.3 FT-IR studies

The FTIR spectrum is recorded to confirm the interaction of inhibitor molecule with the mild steel surface The FTIR spectrum

of pure NHQ and adsorbed protective film formed on the MS sur-face after immersion in 1 M acidic chloride solution containing

300 ppm of NHQ at room temperature are shown inFig 8 The pure NHQ spectra shows the IR frequency bands of theAOH, C@N and

C@C having stretched at 3219 cm1, 1624 cm1 and 1570 cm1 respectively The NHQ protective film formed MS surface shows the presence ofAOH, C@N and C@C groups at the frequencies of

3423 cm1, 1623 cm1and 1501 cm1 respectively So, it is con-firmed that the studied inhibitor NHQ is strongly adsorbed on the MS surface

3.3.4 Theoretical studies – quantum chemical calculations The quantum chemical calculations are powerful tools for studying corrosion inhibition mechanism Furthermore, the results

of quantum chemical calculations could be obtained without labo-ratory measurements, thus saving time and equipment[34] The chemical reactivity of studied molecule is often discussed in terms

of quantum chemical parameters such as the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbi-tal (LUMO) and electron density parameters like dipole moment (m) The energy of the HOMO (EHOMO) represents the ability of the molecule to donate a lone pair of electrons and the higher the

EHOMOvalue, the greater the tendency of the molecule to donate electrons to an electrophilic reagent [35] and the lower ELUMO, the greater the tendency of the molecule to accept electrons from the metal atoms The HOMO and LUMO electron density distribu-tion of the investigated inhibitor NHQ is shown inFig 9a and b) For the HOMO of the investigated molecule, it can be observed that the benzene ring,AC, AN and AO have a large electron density The results from theTable 6show that the NHQ has high EHOMOand low

ELUMOvalues and the energy difference between EHOMOand ELUMO

(ΔE) informs the reactivity of the investigated inhibitor molecule; results shows that the smaller theΔE value, the greater the reactiv-ity of the molecule The examined inhibitor NHQ has the smallest value ofΔE (0.1328 eV) and it is therefore most reactive molecule

[36] The higher the dipole moment, the higher is the polarity of the molecule [37] Higher value of dipole moment has found to

Table 3

Corrosion parameters obtained from TP studies of MS in 1 M Acidic Chloride Solution containing different concentrations of NHQ.

Conc of NHQ (ppm) b a (V/dec) b c (V/dec) E corr (mV/SCE) I corr (mA/cm 2

Table 4

Corrosion parameters obtained from LPR studies of MS in 1 M Acidic Chloride Solution

containing different concentrations of NHQ.

Conc of NHQ (ppm) R p (Ώ cm 2

) Surface coverage (h) IE (%)

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

[C In

C Inh (ppm) x 10 3

WL EIS

Tafel

LPR

Fig 5 Langmuir plot (using WL, EIS, Tafel and LPR results) for MS corrosion in 1 M

acidic chloride solution with various concentrations of NHQ.

Table 5

Values of DG 0 and K ads obtained from Langmuir isotherm studies for the adsorption of

NHQ on MS in 1 M acidic chloride solution.

K ads (10 4

ads (kJ mol1)

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5-Nitro-8-be a key factor that facilitates adsorption by influencing the

trans-port process through the inhibitor layer adsorbed[38] 3.8163 D

seems to be a higher value for dipole moment that adds to the fact

that the investigated compound NHQ shows a potential ability to

act against corrosion This is turn confirms the inhibition activity

of NHQ V.S Sastri and J.R Perumareddi have been reported that, the smaller values ΔE and higher values of dipole moment (l) are responsible for higher inhibition efficiency[39]

Fig 6 SEM image: (a) Fresh MS (b) MS in acidic chloride solution (c) MS in acidic chloride with NHQ.

1 2 3 4 5 6 7 8 9 10

keV 0

2 4 6 8 10 12 14

16 cps/eV

Fe

Fe

O

keV 0

2 4 6 8 10 12 14 16 18 20 22 cps/eV

(a)

(b)

(c)

Fig 7 EDX image: (a) Fresh MS (b) MS in acidic chloride solution (c) MS in acidic chloride with NHQ.

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5-Nitro-8-4 Conclusions

On the basis of all the above experimental and the theoretical

results, the following points are concluded,

 The studied quinoline nucleus based organic molecule NHQ act

as an effective corrosion inhibitor for mild steel in acidic chlo-ride solution

 The corrosion rate of mild steel is decreased with the addition of NHQ concentration and effectively secures the MS surface

 The investigated inhibitor can be classified as a mixed type because it retards both anodic and cathodic reactions

 The adsorption of studied inhibitor on the surface of MS in acidic chloride solution obeys the Langmuir adsorption isotherm

 Values ofDG0

adsin both methods (chemical and electrochemical) indicate that the inhibition process on the surface of mild steel

is purely physisorption and the process is spontaneous

 SEM, EDX and FT-IR morphology studies were confirmed the formation of protective film on the corroded MS surface

 The quantum chemical approach may well be able to foretell molecule structure that is better for corrosion inhibition This theoretical study is the well supportive evidence for the forma-tion of the protective film on the surface of MS

Conflict of interests The authors declare that there is no conflict of interests regard-ing the publication of this paper

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Fig 8 FT-IR spectra of inhibitor (Pure NHQ) and its corresponding protective film

formed MS surface after immersion in 1 M acidic chloride solution containing

300 ppm of NHQ.

Table 6

Quantum chemical parameters of NHQ.

E HOMO

(eV)

E LUMO

(eV)

ΔE = (E HOMO  E LUMO ) l(D) Total

Energy (E)

IE (%) * Η

Fig 9 (a) HOMO structure of NHQ (b) LUMO structure NHQ.

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