influence of copper nanoparticles capped by cationic surfactant … · 2017. 1. 17. · oxidation...

Egyptian Journal of Petroleum (2013) 22, 549–556

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FULL LENGTH ARTICLE

Influence of copper nanoparticles cappedby cationic surfactant as modifier for steelanti-corrosion paints

M.A. Hegazy a,*, A.M. Badawi a, S.S. Abd El Rehim b, W.M. Kamel a

a Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo, Egyptb Ain Shams University, Faculty of Science, Cairo, Egypt

Received 15 January 2013; accepted 14 May 2013

Available online 5 December 2013

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KEYWORDS

Cationic surfactants;

Copper nanoparticles;

NaCl solution;

Potentiodynamic

polarization;

EIS;

Corrosion protection

Corresponding author. Tel.:mail address: mohamed_hga

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Production an

10-0621 ª 2013 Productionpen access under CC BY-NC-ND l

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Abstract The synthesized cationic surfactant N-(2-(2-mercaptoacetoxy) ethyl)-N,N-dimethyldod-

ecan-1-aminium bromide (QSH) was used to prepare colloidal copper nanoparticles (CuNPs) in

water through the chemical reduction method. The obtained copper nanoparticles were character-

ized by FTIR spectrum and transmission electron microscopy (TEM). The corrosion performance

was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy

(EIS) measurements in addition to the salt spray test. The results obtained from these methods were

in good agreement. Results showed that the modified coating provide a good coverage and an addi-

tional corrosion protection of the carbon steel.ª 2013 Production and hosting by Elsevier B.V. on behalf of Egyptian Petroleum Research Institute.

Open access under CC BY-NC-ND license.

1. Introduction

Metallic nanoparticles have attracted widespread attention dueto their fascinating optical, electronic and catalytic properties

[1–4]. For many applications, small nanoparticles are prefera-ble to larger ones, because of their higher surface area to vol-ume ratio. However, as the size of the nanoparticles decreases,

the surface energy increases, favoring the aggregation of smallparticles or their growth into larger particles. It is difficult to

653529; fax: +20 222747433.o.com (M.A. Hegazy).

gyptian Petroleum Research

g by Elsevier

ng by Elsevier B.V. on behalf of E

p://dx.doi.org/10.1016/j.ejpe.2013.1

keep small nanoparticles separated. In addition to their surfaceenergy, the chemical reactivity of nanoparticles also dependsupon their sizes and smaller particles are generally much more

chemically reactive than larger particles. Copper is a naturalelement that is an essential micronutrient to ensure the well-being of all aerobic life forms. It plays a vital part in the devel-

opment and performance of the human nervous and cardio-vascular systems, as well as the skin, bone, immune andreproductive systems including gene transcription. Coppercan also inhibit the growth of microbes, thus providing a mea-

sure of protection against harmful germs and bacteria in manyenvironments. Due to environmental and biological impor-tance of Cu (II) many sensors for the determination of this

ion have been developed [5,6]. Several methods have beendeveloped for the preparation of copper nanostructures, suchas chemical reduction [7], sonochemical reduction [8], metal

vapor synthesis [9] and microemulsion techniques [10]. The

gyptian Petroleum Research Institute.

1.009

https://core.ac.uk/display/82226782?utm_source=pdf&utm_medium=banner&utm_campaign=pdf-decoration-v1mailto:[email protected]://dx.doi.org/10.1016/j.ejpe.2013.11.009http://www.sciencedirect.com/science/journal/11100621http://dx.doi.org/10.1016/j.ejpe.2013.11.009http://creativecommons.org/licenses/by-nc-nd/4.0/http://creativecommons.org/licenses/by-nc-nd/4.0/

Table 1 The chemical composition of paint

Material Formula or composition Mass percent (%)

Resin Short oil alkyd resin 19

Inorganic pigment TiO2 2

Talc Mg3Si4O10(OH)2 15

Dibutyl phthalate C16H22O4 15

Butanol C4H9OH 2

Nitrocellulose (N. C.) C6H7(NO2)3O5 4

Solvent Thinner 15

550 M.A. Hegazy et al.

chemical reduction method is the most extensively used be-cause of its simplicity, low cost and the ease of size and shapecontrol over copper nanoparticles [11]. Sodium borohydride

[7], ethylene glycol [12] and Hydrazine hydrate [13] are fre-quently used as reductants for the synthesis of nanosized cop-per particles. However, some of the current reductants cause

significant environmental pollution. The synthesis of stablemonodisperse and uniformly-shaped copper nanoparticleshas proven difficult because of the tendency for copper to rap-

idly oxidize [14]. In addition, copper nanoparticles tend toaggregate during synthesis. Surfactants, polymers, and ligandscan be used as stabilizers in aqueous media, preventingagglomeration to yield highly stable, well-dispersed metal

nanoparticles [15]. Current investigations in surfactant scienceare driven by the requirements to design surfactants that pos-sess enhanced physicochemical properties, new surfactant uti-

lization in complex systems, and specific applications inmodern technologies [16–19].

Corrosion inhibition is generally achieved by the deposition

either of passive films or active conversion coatings on the sur-face, which is to be protected. They may offer a low density ofpores or cause surface chemical reactions in order to prevent

oxidation [20–24]. Organic coatings are widely used to preventcorrosion of metal structures due to their ease of application atreasonable cost. The coating efficiency is dependent on someintrinsic properties of the organic film (barrier effect and the

presence of inhibitors or sacrificial pigments) and the metal/substrate interface interaction in terms of adherence [25,26].The resistance of the metal/coating system is proportional to

the contact time of the system with the corrosive medium, aswell as variations in the adhesion, barrier and inhibitor prop-erties. The purpose of the present study is to prepare colloidal

copper nanoparticles and use it as modifier for steel anti-corro-sion paints. The corrosion protection property of the modifiedcoating on carbon steel was investigated using potentiodynam-

ic polarization, electrochemical impedance spectroscopy mea-surements and the salt spray test.

2. Materials and experimental methods

2.1. Synthesis and structure confirmation of the synthesizedcationic surfactant

Preparation of the cationic surfactant and confirmation of thechemical structure by FTIR, 1HMNR and Mass spectroscopy

analysis were studied [27]. The surface tension parameters ofthe synthesized cationic surfactant were also measured [27].

2.2. Preparation of copper nanoparticles (CuNPs)

Copper nanoparticles were prepared by chemical reduction ofCuCl2 using NaBH4 in solution of synthesized cationic surfac-

tant. At first, solution of CuCl2 (0.01 M) was prepared andadded to ascorbic acid (0.1 M) (as antioxidant of colloidal cop-per) with stirring for half an hour. Then a dried amount of sur-factant as a capping agent was added to the previous mixture.

A dropwise addition of NaOH solution (0.1 M) was used toadjust the pH of this mixture up to 12. After stirring for about1 h at room temperature, a solution of NaBH4 (0.1 M) (the

main reducing agent) was added to the mixture under contin-uous strong stirring for about 10 min. The initial blue color of

the reaction mixture turned yellow and eventually light-redindicating the formation of capped copper nanoparticles [28].The copper nanoparticles capped by the synthesized cationic

surfactant were separated and washed with deionized waterby centrifugation, while using acetone as a non-solvent inorder to remove excess cationic surfactant. The resulting

precipitates were dried under vacuum for 3–4 h [29].Characterization of CuNPs capped by the synthesized cat-

ionic surfactant was confirmed by FTIR spectroscopy and

TEM.

2.3. Preparation of the modified paint

The chemical composition of paint is listed in Table 1. Thepaint was formulated by the addition of nitrocellulose to the

thinner and stirred for 30 min. Then short oil alkyd resinwas added as plasticizer with stirring for 20 min. This is fol-lowed by adding CuNPs capped by the synthesized cationic

surfactant with different amounts (0.5, 1, 2, 4 wt%) to butanolwhere dibutyl phthalate and TiO2 were added to talc. Thetested paint was based on coconut oil (short oil) alkyd resin.

2.4. Preparation of carbon steel for coating test

Carbon steel specimens of the following chemical composition(wt.%) were used in the experiments: C-0.21; Si-0.38; P-0.09;Mn-0.05; S-0.05; Al-0.01; and Fe-balance. The test specimens

were carbon steel sheets (20 · 50 mm) with a total exposed sur-face area of 2 cm2. The metallic substrate was pretreated bymechanical polishing, cleaned by immersion in a strong solu-

tion of HCl with an organic corrosion inhibitor for 10 s,washed with water, degreased for 3 min in an ultrasonic bathwith 1:1 mixture of ethanol, acetone and then the modifiedcoating was painted [30]. Curing was carried out at 40 �C for72 h to make the coating completely dry. The paint composi-tions with and without addition of the copper nanoparticlescapped by the synthesized cationic surfactant are depicted in

Table 2.

2.5. Solution

An aqueous solution of 3.5% sodium chloride was prepared bymass containing 3.5 g of NaCl in 100 g of double distilled

water as corrosive solution. The corrosion inhibition efficiencyof carbon steel electrode painted with unmodified paint (didnot contain capped copper nanoparticles) and modified paint

(containing different amounts of capped copper nanoparticles)was measured by three different techniques (potentiodynamicpolarization, electrochemical impedance spectroscopy mea-

surements and the salt spray test).

Table 2 Modified and unmodified (blank) paint compositions in grams

Paint code N.C. Butanol Thinner Dibutyl phthalate Resin CuNPs Talc TiO2

A (Blank) 2.5 0.3 6.14 1.5 3.8 – 3 1.5

B (0.5 wt%) 2.5 0.3 6.14 1.5 3.8 0.1 3 1.5

C (1 wt%) 2.5 0.3 6.14 1.5 3.8 0.2 3 1.5

D (2 wt%) 2.5 0.3 6.14 1.5 3.8 0.4 3 1.5

E (4 wt%) 2.5 0.3 6.14 1.5 3.8 0.8 3 1.5

Influence of copper nanoparticles capped by cationic surfactant as modifier for steel anti-corrosion paints 551

2.6. Electrochemical measurements

2.6.1. Potentiodynamic polarization method

Electrochemical experiments were carried out using a conven-tional three-electrode cell with a platinum counter electrodeand a saturated calomel electrode as a reference electrode

and carbon steel as a working electrode. Before each measure-ment, the working electrode was immersed in a test solution atopen circuit potential for 30 min until a steady state was

reached. All electrochemical measurements curves were re-corded by a Voltalab 40 Potentiostat PGZ 301 and a personalcomputer was used with Voltamaster 4 software. Each experi-ment was repeated at least three times to check the reproduc-

ibility. Potentiodynamic polarization measurements wereobtained by changing the electrode potential automaticallyfrom �1400 to �200 mV vs. SCE with a scan rate 2 mV s�1at 30 �C.

2.6.2. Electrochemical impedance spectroscopy (EIS)

A small alternating voltage perturbation (5 mV peak by peak)

was imposed on the cell over the frequency range of 100 kHzto 50 mHz. The EIS spectra from attached films were analyzedusing nonlinear least squares fitting (with ZSimWin) to a

R[Q[R[QR]]] model circuit as illustrated in Figure 7 [Q = con-stant phase element]. This is a typical circuit used for coatedmetals with a conducting pathway (or pore) modeled as a

resistance in series with a parallel RC combination at the metalsurface to represent the electrochemical reaction there (ormore recently RQ to represent non-ideal behavior). Thecapacitance (or Q) of the organic coating is arranged in paral-

lel with this combination and short-circuits the whole combi-nation at high frequency. EIS spectra from coating filmswhich should in principle be fitted R[C[R[CR]]], but were

actually analyzed with the circuit R[Q[R[QR]]] (Figure 7)which gave a better fit.

2.7. Salt spray test

The salt spray test is a standardized test used to check corro-sion resistance of coated samples. Coatings provide corrosionresistance to metallic parts made of steel, since coatings canprovide a high corrosion resistance through the intended life

of the part in use, it is necessary to check corrosion resistanceby other means. Salt spray test is an accelerated corrosion testthat produces a corrosive attack to the coated samples in order

to predict its suitability in use as a protective finish. Theappearance of corrosion products is evaluated after a periodof time. Test duration depends on the corrosion resistance of

the coating; the more corrosion resistant the coating is thelonger period in testing without showing signs of corrosion.Measurements were obtained using salt spray chamber modelSF/450 (England) at 35 �C.

2.8. Transmission electron microscope (TEM)

A convenient way to produce good TEM samples is to usecopper grids. A copper grid was pre-covered with a very thinamorphous carbon film. To investigate the prepared CuNPs

using TEM, small droplets of the liquid were placed on the car-bon-coated grid. A photographic plate of the transmissionelectron microscopy employed on the present work was used

to investigate the microstructure of the prepared samples.Nanoparticle size was determined by using TEM model ‘‘JeolJeM – 2100 (Japan)’’.

3. Results and discussion

3.1. Structure confirmation of the prepared surfactant self-assembling on copper nanoparticles (CuNPs)

3.1.1. Fourier transform infrared spectrometer (FTIR)

FTIR spectrum of the CuNPs capped by the synthesized cat-ionic surfactant (QSH) (Figure 1) showed the followingabsorption bands at 1053.29 cm�1 (C�N+ stretching),1412.51 cm�1 (CH2 asymmetric bending), 2865.85 cm

�1 (CH

symmetric stretching), 2926.58 cm�1 (CH asymmetric stretch-ing), 1742.03 cm�1 (C‚O stretching), 1114.70 cm�1 (C–O–Casymmetric stretching), 2594.36 cm�1 (SH stretching) and

3393.12 cm�1 (characteristic for water of crystallization) [31].

3.1.2. Transmission electron microscope (TEM)

The TEM image of the CuNPs capped by the synthesized cat-

ionic surfactant was represented in Figure 2. The TEM imageshowed the self-assembling of the prepared surfactant on thecopper nanoparticles which causes the stabilization of the nano

size of these nanoparticles due to the formation of nano shellswith the used surfactant [32].

3.2. Corrosion measurements

3.2.1. Potentiodynamic polarization measurements

The technique of cathodic and anodic polarization of metals is

frequently used to study the phenomena of metal corrosionand passivation. Tafel polarization plots were recorded for car-bon steel electrode painted with unmodified (blank) paint and

modified paint with the CuNPs capped by the synthesized cat-ionic surfactant in 3.5 wt% NaCl solution at 30 �C were repre-sented in Figure 3.

It can be clearly seen from Figure 3 that the polarization re-sponse of the electrode coated with modified paint containingdifferent concentrations (0.5, 1, 2, 4 wt%) of CuNPs capped by

the synthesized cationic surfactant is shifted toward the catho-dic side, this indicates that the CuNPs capped by the synthe-sized cationic surfactant may inhibit the cathodic reactionand enhances the corrosion resistance of the paint. The value

Figure 1 FTIR spectrum of the CuNPs capped by the synthesized cationic surfactant.

Figure 2 TEM image of the CuNPs capped by the synthesized

cationic surfactant.

-3.5

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

-1500 -1300 -1100 -900 -700 -500 -300 -100

log

(i/µ

A c

m-2

)

E vs. SCE/mV

3.5% NaCl

0.5%

1% 2%4%

Figure 3 Anodic and cathodic polarization curves obtained for

carbon steel coated with and without different concentrations of

CuNPs capped by the synthesized cationic surfactant in 3.5 wt%

NaCl at 30 �C.


of icorr for electrode painted with unmodified (blank) paint isbigger than those for the electrodes coated with modified paintcontaining various amounts (0.5, 1, 2, 4 wt%) of CuNPs

capped by the synthesized cationic surfactant as shown inTable 3. This result reveals that the capping process signifi-cantly improves the corrosion protective power of the modifiedpaint. The presence of these capped nanoparticles blocks the

pores and the holes [33]. The capped copper nanoparticlescan penetrate and diffuse easily in the coat and fill the microp-ores of the coat and hence decrease its permeability [34,35].

The inhibition efficiency, (gp) of the CuNPs capped by the syn-thesized cationic surfactant was calculated from the polariza-tion data as follows [36,37]:

gp ¼icorr � iocorr

icorr

� �� 100 ð1Þ

where icorr and iocorr are the corrosion current densities in the

presence of unmodified and modified paints, respectively.Figure 4 shows the change in gp with the amount of the

CuNPs capped by the synthesized cationic surfactant in the

paint. Data in Table 3 showed that, the protection efficiencyof the investigated CuNPs capped by the synthesized cationicsurfactant decreases with increasing the amount of CuNPs

capped in the paint. As inferred from icorr values, the stabilityand corrosion protection of the investigated paints were de-creased in the following order:

0:5%CuNPs>1%CuNPs>2%CuNPs>4%CuNPs>0%CuNPs

Data in Table 3 showed that, the slopes (ba) and (bc) of theanodic and cathodic Tafel lines are almost independent of

paint composition, which means that changing the amountof CuNPs capped by the synthesized cationic surfactant in

Table 3 The electrochemical kinetics parameters of the potentiodynamic polarization curves for carbon steel coated without and with

different concentrations of the CuNPs capped by synthesized cationic surfactant in 3.5 wt% NaCl at 30 �C

Conc. of colloidal CuNPs (wt%) Ecorr (mV) icorr lA cm�2 ba (mV dec

�1) bc (mV dec�1) gp(%)

0.00 �633.4 11.09 201.9 �362.7 �0.5 �676.6 0.364 317.7 �374.0 96.71 �734.2 0.631 313.6 �278.5 94.32 �737.6 1.116 323.2 �399.5 89.94 �767.8 1.698 286.3 �388.9 84.7

Figure 4 Relation between inhibition efficiency for carbon steel

painted with and without different amounts of the CuNPs capped

by the synthesized cationic surfactant.

Figure 5 Nyquist plot of the coating system for carbon steel

painted with paints containing different amounts of the CuNPs

capped by the synthesized cationic surfactant in 3.5 wt% NaCl at

30 �C.


the paint does not significantly change the mechanism of the

corrosion process. So the role of modification is concernedwith mainly blocking the active reaction sites inside the poresand holes. When the coated specimens were exposed to

3.5 wt% NaCl solutions, the corrosive agents (H2O, Cl� ions)

of the medium reached the metal/coating interface through thepores and corroded the base metal surface (active sites). Rust

under coating probably possesses a high adherence to the me-tal surface [38].

When the content of the CuNPs capped by the synthesizedcationic surfactant in coating is low (0.5 wt% in the

paint and decreased the inhibition efficiency. The CuNPscapped by the synthesized cationic surfactant at concentrations>0.5 wt% can easily agglomerate and are converted to micron

size as a result of a large specific surface area and high surfaceactivity [39]. In spite of this, addition of high concentrations(>0.5 wt%) of the CuNPs capped by the synthesized cationicsurfactant into the paint may enhance the stress and decrease

the porosity of the paint but the agglomerated CuNPs cannoteasily diffuse through all or most pores and blocks the insideactive sites. Consequently, the corrosive agents of the medium

penetrate across the coating and corrode the metal. These pro-cesses can explain why the inhibition efficiency of CuNPs de-creased with increasing its amount than >0.5 wt% in themodified paint.

3.2.2. Electrochemical impedance spectroscopy (EIS)

Electrochemical impedance spectroscopic measurements for

the painted carbon steel electrode have been made in3.5 wt% NaCl solution. The Nyquist plots for the measure-ments were recorded and shown in Figure 5.

The curves in Figure 5 exhibit a non perfect semicircle. The

recorded semicircles revealed that the rate determining step isthe charge transfer one. The diameter of the semicircle in thepresence of the unmodified paint is usually smaller than those

obtained in the presence of modified paints indicating inhibi-tion influence of the CuNPs capped by the synthesized cationicsurfactant in the paint. On the other hand the diameter of the

semicircle decreases with increasing the amount of CuNPscapped by the synthesized cationic surfactant from 0.5 up to4 wt%. This behavior can be attributed to the increase in grain

Figure 7 Equivalent circuit of steel sheet coated with CuNPs

capped by the synthesized cationic surfactant in 3.5 wt% NaCl

solution.


size of CuNPs capped by the synthesized cationic surfactant asa result of agglomeration. This effect can be visualized quanti-tatively from the decrease of the charge transfer resistance Rctvalues with increasing the amount of CuNPs in the paint asshown in Figure 6. The high Rct values at low concentrations(0.5 wt%) of the CuNPs capped by the synthesized cationic

surfactant in the modified paint can be attributed to the de-crease of the area of the active sites on the carbon steel surface.This behavior may be due to blocking of the holes and pores of

the paint by adsorption of CuNPs capped by the synthesizedcationic surfactant on the active sites.

Impedance is totally complex resistance when a currentflows through a circuit made of capacitors, resistors, insula-

tors, or any combination of these [40]. The Nyquist plots ob-tained for investigated painted carbon steel exhibit generalbehavior where the double layer of the interface of metal/solu-

tion does not behave as an ideal capacitor.For better understanding of the mechanisms of the corro-

sive processes, which occur at the surface of the samples stud-

ied, we have applied the fitting of the experimental impedancespectra using the appropriate equivalent electric circuits(EECs). In our work, the constant phase element (CPE) was

used in the equivalent circuits instead of the ideal electricalcapacitance. The element describes better the behavior of thecoatings having heterogeneities of the mesostructure and/orof the chemical composition. The electrochemical behavior

of coating systems under study is well described by EEC withtwo series parallel R-CPE circuits (Figure 7). It is known thatRe is the electrolyte resistance, Rp is the coating pore resis-

tance, Qc and n1, respectively, represent the magnitude andexponent of the constant phase element (CPE) of the compos-ite coating. Qdl and n2, respectively, represent the magnitude

and exponent of the constant phase element (CPE) of the dou-ble layer, which reflect states of the electrochemical reactionsunder the coating. The impedance of this element (ZCPE) is gi-

ven according to the following equation [41,42]:

ZCPE ¼1

QoðjxmaxÞn ð2Þ

where Qo is a frequency-independent constant, J2 = �1,xmax = 2pfmax, fmax is the frequency at which the imaginary

Figure 6 Variation of charge transfer resistance with CuNPs

capped by the synthesized cationic surfactant percent in the paint.

component of the impedance is maximal and n is the exponen-tial coefficient. For n = 0, ZCPE represents a resistance with

R ¼ Q�1o , for n = 1 a capacitance with C = Qo, for n = 0 aWarburg impedance with w = Qo and for n = �1 an inductivewith L ¼ Q�1o .

The calculated values of the impedance parameters derived

from the Nyquist plots using the selected equivalent circuitmodel (Figure 7) are listed in Table 4. The inhibition efficiency,(gI), of the CuNPs capped by the synthesized cationic surfac-tant was calculated from the charge transfer resistance accord-ing to the following equation [43,44]:

g1 ¼Rct � Roct

Rct

� �� 100 ð3Þ

where R0ct and Rct are charge transfer resistance values ob-tained for carbon steel electrode in 3.5 wt% NaCl solution pla-ted with unmodified and modified paints, respectively.

The values of gI were calculated and listed in Table 4. It isseen that the corrosion inhibition efficiency of the paint in thepresence of CuNPs capped by the synthesized cationic surfac-

tant is maximum at 0.5 wt% and decreased with increasingtheir amounts in the paint.

The double layer capacitances, Cdl, for a circuit including a

CPE were calculated from the following equation:

Cdl ¼ QdlðxmaxÞn�1 ð4Þ

where xmax = 2pfmax and fmax is the frequency at which theimaginary component of the impedance is maximal.

The calculated Cdl values are listed in Table 4. It is clear

that from these values the presence of the CuNPs capped bythe synthesized cationic surfactant in the paint resulted in asignificant decrease in the values of Cdl. However, the valuesof Cdl started to increase with increasing the amount of the

CuNPs capped by the synthesized cationic surfactant in thepaint. The increase in Cdl values could be resulted from a de-crease in the effective thickness of the electrical double layer.

Coating capacitance reflects the content of water penetrat-ing the coating and becomes large with the increase of watercontent in the coating [45,46]. Water in a coating is a necessary

factor for the start of the corrosion process [47] and causesblistering of the coating and thus results in loss of its adhesionand deterioration of its mechanical properties [48]. Because of

strong hydrophobicity and filling action, CuNPs capped by thesynthesized cationic surfactant at low concentrations(0.5 wt%) can prevent the diffusion of H2O to the metal-coat-ing interface and cause smaller coating capacitances.

Figure 8 Salt spray test of steel painted with different paints, (A–E) with CuNPs capped by the synthesized cationic surfactant. (A)

without CuNPs, (B) is 0.5 wt% of CuNPs, (C) is 1 wt% of CuNPs, (D) is 2 wt% of CuNPs and (E) is 4 wt% of CuNPs.

Table 4 The electrochemical kinetic parameters of impedance for carbon steel coated without and with different concentrations of

CuNPs capped by synthesized cationic surfactant in 3.5 wt% NaCl at 30 �C

Conc. of colloidal

CuNPs (wt%)

Qc (lX�1 sn cm�2) n1 Rp (kX cm

2) Qdl (lX�1 sn cm�2) n2 Rct (kX cm

2) g (%)

0.00 30.37 0.80 0.50 150.60 0.57 3.97 –

0.5 3.37 0.65 23.11 12.06 0.53 187.60 97.88

1 11.74 0.31 10.01 24.38 0.78 101.80 96.10

2 11.84 0.41 9.17 25.18 0.60 52.00 92.37

4 13.37 0.50 5.49 59.67 0.57 16.63 76.13


3.2.3. Salt spray test

The coated specimens were subjected to diagonal scratches

with the help of a sharp knife in order to expose the base metalto a continuous salt fog chamber of 3.5 wt% NaCl solution.The salt spray test of the carbon steel coated by unmodified

(blank) and modified paint with CuNPs capped by synthesizedsurfactant carried out for 500 h at 35 �C is shown in Figure 8.

Corrosion products are seen mainly on scratched area of

some coated specimens. Furthermore as shown in Figure 8,the spreading of corrosion underneath the coating film de-creased in the order:

0:5% CuNPs > 1% CuNPs > 2% CuNPs > 4% CuNPs

> 0% CuNPs

This behavior further supported the results obtained fromthe electrochemical measurements

4. Conclusions

A colloidal dispersion solution of CuNPs was prepared using

the chemical reduction method of CuCl2. The FTIR andTEM results confirmed the self-assembling of the synthesizedsurfactant on the prepared CuNPs to form nanoshells. The

results also show the role of the prepared surfactant to preventthe aggregation CuNPs in solution. The following conclusionscan be drawn from this study:

1. The prepared CuNPs capped by the surfactant were used asa modifier for steel anti-corrosion coating and the maxi-mum inhibition efficiency was obtained at 0.5 wt%.

2. Potentiodynamic polarization, electrochemical impedancespectroscopy measurements and the salt spray test gavesimilar results.

3. The corrosion inhibition efficiency of the investigated

paints was increased in the following order: 0.5% CuN-Ps > 1% CuNPs > 2% CuNPs > 4% CuNPs > 0%CuNPs. This behavior further supported the results

obtained from the salt spray test.4. EIS results showed that the charge transfer resistance (Rct)

values increased while capacitance values (Cdl) decreasedwith increasing CuNPs percent.

5. The polarization results showed that the maximumdecrease in icorr was observed at 0.5 wt% CuNPs cappedby the synthesized cationic surfactant.

6. Salt spray tests indicated that the spreading of corrosionunderneath the coating film decreased with increasingCuNPs percent.

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Influence of copper nanoparticles capped by cationic surfactant as modifier for steel anti-corrosion paints1 Introduction2 Materials and experimental methods2.1 Synthesis and structure confirmation of the synthesized cationic surfactant2.2 Preparation of copper nanoparticles (CuNPs)2.3 Preparation of the modified paint2.4 Preparation of carbon steel for coating test2.5 Solution2.6 Electrochemical measurements2.6.1 Potentiodynamic polarization method2.6.2 Electrochemical impedance spectroscopy (EIS)

2.7 Salt spray test2.8 Transmission electron microscope (TEM)

3 Results and discussion3.1 Structure confirmation of the prepared surfactant self-assembling on copper nanoparticles (CuNPs)3.1.1 Fourier transform infrared spectrometer (FTIR)3.1.2 Transmission electron microscope (TEM)

3.2 Corrosion measurements3.2.1 Potentiodynamic polarization measurements3.2.2 Electrochemical impedance spectroscopy (EIS)3.2.3 Salt spray test

4 ConclusionsReferences

influence of copper nanoparticles capped by cationic surfactant … · 2017. 1. 17. · oxidation...

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