Corrosion Inhibition of Copper by Argan Oil in Acidic Solutions

33

Corrosion Inhibition of Copper by Argan Oil in Acidic Solutions

F. Mounir

, S. El Issami

, Lh. Bazzi

, O. Jbara

, A. Chihab Eddine

, M.

Belkhaouda

, L. Bammou

, R. Salghi

, L. Bazzi

.

1 Laboratoire Matériaux et Environnement, Faculté des Sciences, Agadir. Morocco.

2 Etablissement Autonome de Contrôle et de Coordination des Exportations, Agadir. Morocco.

3 Laboratoire d’Ingénierie et Science des Matériaux (LISM), Université de Reims, France.

4 Laboratoire Chimie Organique, Faculté des Sciences, Agadir. Morocco.

5 Equipe de Génie de l’Environnement et de Biotechnologie, ENSA, Agadir, Morocco.

*Corresponding author. E-mail : l.bazzi@uiz.ac.ma

Received 7 Apr 2014, Revised 10 May 2014, Accepted 10 May 2014

Abstract : Argan Oil (AO) was tested as inhibitor for copper corrosion in 2 M H3PO4 and NaCl 0.3 M. The techniques used in this work were weight loss measurements, potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS). The inhibition efficiency was found to increase with inhibitor content to attain 94% for AO at 7g/L. Inhibition efficiency E (%) obtained from the various methods is in good agreement. The temperature effect on the corrosion behaviour of copper in (2 M H3PO4+ 0.3 M NaCl) was studied by potentiodynamic technique in the range from 298 to 323 K.

Keywords: Corrosion, Copper, Inhibition, Argan Oil.

Introduction

Copper is a material with excellent electrical and thermal conductivity and is often used in heating and cooling systems. Corrosion is one of the major problems encountered in the industrial application of materials. Millions of dollars are spent by the oil industry, for instance, on the prevention of corrosion process in metals. Among the procedures used to prevent corrosion, the use of inhibitors is the most common, given that it presents some advantages of economical and environmental nature, as well as great efficiency and high applicability. It is well known that organic molecules containing heteroatoms act efficiently as corrosion inhibitors [1-18]. But, unfortunately most of these compounds are not only expensive but also toxic to living beings. It is needless to point out the importance of cheap, safe inhibitors of corrosion. Plant extracts are environment friendly, bio-degradable, non-toxic, easily available and of potentially low cost. Most of the naturally occurring substances are safe and can be extracted by simple procedures. Recent literature is full of researches which test different extracts for corrosion inhibition applications. The examples are numerous such as Argan Hulls [19], Eugenol oil [20] Cosmetic Argan Oil [21], Harmal Extract [22], Chenopodium Ambrorsioides Extract [23], Hibiscus sabdariffa [24], Oxandra asbeckii [25], Citrus paradise [26] and Anacyclus pyrethrum L.

[27].

In this work, the inhibitive action of argan oil (AO), as an inexpensive, eco-friendly, naturally occurring substance, on the corrosion of copper in 2 M H3PO4 solution containing 3.10^-1 M NaCl has been studied by

34

gravimetric method and electrochemical techniques such as potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS).

Materials and methods 1. Argan oil (AO):

The solution tests are freshly prepared before each experiment by adding the oil directly to the corrosive solution.

2. Fatty acid methyl esters composition

The analyses performed for the purpose of this study were carried out in the laboratory of the Autonomous Establishment of Control and Coordination of Export which applies the official methods of analysis for the determination of fatty acid methyl esters (FAME) in oil [28, 29]. The fatty acid methyl esters were analyzed with an Agilent Technologies 6890N gas chromatograph equipped with a capillary column (30 m x 0.32 mm; Supelco, Bellefonte, PA, USA) and flame ionization detection. The column was programmed to increase from 135 to 160°C at 2°C/min and from 160 to 205°C at 1.5°C/min; the detection temperature was maintained at 220°C, injector temperature 220 °C. The vector gas was helium at a pressure of 5520 Pa. Peak was identified by comparing retention times with those of standard fatty acid methyl esters.

3. Tocopherols composition

For the determination of tocopherols compounds a solution of 250 mg oil in 25 mL n-heptane was used for HPLC analysis. The analysis was conducted using an Agilent low pressure gradient system, fitted with a 1100 pump, a Agilent 1100 Fluorescence Spectrophotometer (detector wavelengths for excitation 290 nm, for emission 330 nm). The sample (20 µL) was injected by a Agilent LC -1100 autosampler onto a phase HPLC column 25 cm x 4 mm ID (Merck, Darmstadt, Germany) used with a flow rate of 1 mL/min and hexane/tetrahydrofuran (98:2, v/v) as mobile phase [30].

4. Sterols composition

Sterol was determined by the method [29]. Sterol composition was evaluated by GLC-FID/capillary column. Briefly, sterols purified from the unsaponifiable matters by HPLC were transformed into their trimethylsilyl ethers counterparts using pyridine, hexamethyldisilazane, and trimethylchlorosilane 9:3:1 (v/v/v).

The sterol profile was analysed using a gas-phase chromatograph fitted with a chroma pack CP SIL 8 C B column (30 m x 0.32 mm i.d.) and a flame ionisation detector. The temperature of the injector and detector were both 300 °C. The column temperature was 200 °C and programmed to increase at the rate of 10 °C/min to 270

°C. The carrier gas was dry oxygen-free nitrogen, and the internal pressure was 8.6 bars. Sterol quantification was achieved by use of an internal 0.2% chloroform solution of -cholestanol.

5. Electrochemical tests

The electrochemical study was carried out using a potentiostat PGZ100 piloted by Voltamaster software. This potentiostat is connected to a cell with three electrode thermostats with double wall (Tacussel Standard CEC/TH). Saturated calomel (SCE) and platinum electrodes are used as reference and auxiliary electrodes, respectively. The working electrode is in the form of a disc from pure copper of the surface 1

35 cm².

Potentiodynamic polarization curves were plotted at a polarization scan rate of 0.5 mV/s. Before all experiments, the potential was stabilized at free potential during 30 min. The polarisation curves are obtained from −800 mV to −500 mV at 298 K. In order to investigate the effects of temperature and immersion time on the inhibitor performance, some test were carried out in a temperature range 298–323 K.

The electrochemical impedance spectroscopy (EIS) measurements are carried out with the electrochemical system (Tacussel), which included a digital potentiostat model Voltalab PGZ100 computer at Ecorr after immersion in solution without bubbling. After the determination of steady-state current at a corrosion potential, sine wave voltage (10 mV) peak to peak, at frequencies between 100 kHz and 10 mHz are superimposed on the rest potential. Computer programs automatically controlled the measurements performed at rest potentials after 30 min of exposure at 298 K. The impedance diagrams are given in the Nyquist representation. Experiments are repeated three times to ensure the reproducibility.

6. Weight loss measurements

Gravimetric measurements were carried out at definite time interval of 8 h at room temperature using an analytical balance (precision ± 0.1 mg). The copper specimens used of a total surface of 12 cm². All experiments were carried out under total immersion in 75 ml of test solutions. Prior to each gravimetric or electrochemical experiment, the surface of the specimens was polished successively with emery paper up to 1200 grade, rinsed thoroughly with acetone and bidistilled water before plunging the electrode in the solution. Pure copper samples (99%) were used. The experiments were carried out in 2 M H3PO4 medium containing 0.3 M of NaCl; it was prepared by dilution of Analytical Grade 84% H3PO4 with bidistilled water and pure NaCl.

Results and discussion

1. Argan oil analysis

The analysis of Argan oil allowed the identification of 24 components which accounted for fatty acid methyl esters (100 %) (Fig. 1), sterols (93 %) (Fig. 2) and tocopherols (96.6 %) (Fig. 3).

Figure 1. Acid methyl esters composition 0.1%

0.1%

14%

0.1%

0.1%

5.6%

45.1%

34.5%

0.3%

0.3% 0.2% myristic acide (C14 :0)

Pentadécanoic acid (C15:0) Palmitic acid (C16:0) Palmitoleic acid (C16:1) Heptadecanoique acide (C17:0) Acide Stearique (C18:0) Oleic acid (C18:1) Linoleic acid (C18:2) Linoleic acid (C18:3) Arachidique acid (C20:0) Gadoléique acid (C20:1)

36

Figure 2. Sterols composition

Figure 3. Tocopherols composition

The main constituents were - tocopherol (85.1 %), Oleic acid (46,3%), Schottenol (46%), Spinasterol (37%), Linoleic acid (34.5 %) and Palmitic acid (13.6 %).

2. Effect of concentration 2.1. Polarization curves

The cathodic and anodic polarization curves of the copper immersed in 2 M H₃PO₄ + 3.10^-1M NaCl in the presence and absence of inhibitor at different concentrations at 298 K are presented in Fig. 4. Values of the associated electrochemical parameters are given in Table 1.

The inhibition efficiency was calculated from polarization measurements according to following equation:

100 I

I' - (%) I

E

corr corr corr

i   (1)

where Icorr and I’corr are the corrosion current densities for copper electrode in the uninhibited and inhibited solutions, respectively.

3.5% 0.2%

85.1%

7.8%

a-tocopherol b- tocopherol g- tocopherol Delta- tocopherol 37% 46%

5.2% 4.2%

0.3%

0.3%

Schottenol Spinasterol D-7-avenasterols Stigmasta-8,22-dien-3-ol Campesterol

Cholesterol

37

-0,6 0,0 0,6

1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0,01

I (A. cm-2 )

E (V/SCE)

Blank 0,5 g/L 1 g/L 2 g/L 4g/L 5g/L 6 g/L 7g/L

Figure 4. Cathodic and Anodic polarisation curves of copper in (2M H3PO4+ 3.10^-1 M NaCl ) at different concentrations of OA.

It was observed that both the cathodic and anodic curves showed lower current density in the presence of the Argan Oil than that recorded in the acid solution without the oil. This indicates that the addition of AO to acid solution reduces the anodic dissolution of metal and also impedes the cathodic hydrogen evolution reaction [31].

In Table 1 the potentiodynamic polarization parameters including corrosion current densities (Icorr), corrosion potential (Ecorr), cathodic Tafel slope (bc), anodic Tafel slope (ba), and inhibition efficiency (IE%). It can been seen from the Table 1 that Icorr decreased noticeably with increase in AO concentration which implies that AO behaves as a very good corrosion inhibition for copper in (2M H3PO4+ 0.3M NaCl) solution. An inhibitor, in general, can be classified as an anodic-type or cathodic-type when the change in Ecorr value is larger than 85 mV [32]. But in this study, the largest displacement exhibited by the oil was 30 mV, from which it can be concluded that AO acts as a mixed type inhibitor. On the other hand, the anodic and cathodic slope values of inhibited solution have changed with respect to uninhibited solution which also reiterates that the oil is mixed type effect [33].

Table 1. Electrochemical parameters of copper at various concentrations of OA in (2M H₃PO₄+ 0.3M NaCl) and the corresponding inhibition efficiency.

x (g/l)

Ecorr

(mV/SCE)

Icorr

(µA/cm²)

ba

(mV/dec)

bc

(mV/dec)

IE (%)

(2M H3PO4

+ 0.3 NaCl)

+ X g/L AO

0 -177 36 68 -297 -

0.5 184 23 60 -280 36

1 -179 17 62 -350 53

2 -176 14 63 -350 61

4 -178 13 58 -410 64

5 -210 10 69 -415 72

6 -209 6 71 -350 84

7 -207 2 58 -407 94

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2.2 Electrochemical impedance spectroscopy measurements

EIS measurements were carried out to determine the kinetic parameters for electron transfer reactions at the copper/electrolyte interface and simultaneously about the surface properties of the investigated system and the shape of the impedance diagram will provide mechanistic information. The Nyquist impedance plots obtained for copper electrode in the absence and presence of AO in (2M H3PO4+ 0.3M NaCl) are shown in Fig. 5.

Figure 5. Nyquist diagrams for copper electrode in (2M H3PO4+ 0.3M NaCl) with and without AO after 30min of immersion at Ecorr.

The inhibition efficiency can be calculated by the following formula:

( ) 100

%

0 

 

t t t

Rt R

R

E R (2)

where and are the charge transfer resistances in inhibited and uninhibited solutions respectively.

The values of the charge transfer resistance were calculated by subtracting the high frequency intersection from the low frequency intersection [34]. Double layer capacitance values Cdl were obtained at the frequency (fmax), at which the imaginary component of the Nyquist plot is maximum, and calculated using the following equation.

1 max. ) f

2

( ^

 Rt

Cdl



Figure 5 that a single semicircle has been observed at high frequency. This can be attributed to charge transfer of the corrosion process, and also, the diameter of the semicircle increases in increasing AO concentration. It is apparent from the Table 2 that the presence of AO in acid media leads to decrease in Cdl values. The decrease in Cdl values can be attributed to the decrease in local dielectric constant and/or an increase in the thickness of the electrical double layer [35]. Meanwhile the increase in Rt values indicates that the extent of adsorption with increase in oil concentration and also the adsorbed oil forms a protective film on the copper surface which becomes a barrier to hinder the mass and charge transfer processes.

0 100 200 300 400

0 100 200 300

7 g/L 6 g/L 5 g/L 4 g/L 2 g/L 1 g/L 0.5 g/L Blank

- Z im(.cm2 )

Z_r(.cm²)

39

Table 2. Impedance parameters for corrosion of copper in (2M H3PO4+ 3.10^-1 M NaCl) at various concentrations of AO.

It can be concluded from the these results confirm that AO exhibits good inhibitive performance for copper in 2M H3PO4+ 0.3M NaCl solutions, and the data obtained from EIS are in good agreement with those obtained from potentiodynamic polarization method.

2.3. Weight loss, corrosion rates and inhibition efficiency

The inhibition effect of AO at different concentrations on the corrosion of copper in 2 M H3PO4 + 3.10^-

1 M NaCl solution was studied by weight loss measurements at 298 K after 8 h of immersion period. We noted that Ew (%) was calculated as follows [36]:

100 W

W' - (%) W

Ew

corr corr

corr 

 ₍₄₎

where Wcorr and W'corr are the corrosion rate of copper in 2 M H3PO4 + 3.10^-1 M NaCl in the absence and presence of AO inhibitor, respectively.

Table 3. Copper weight loss data and inhibition efficiency of AO in 2 M H3PO4 + 0.3 M NaCl

The values of percentage inhibition efficiency (Ew%) and corrosion rate (W’corr) obtained from weight loss method are given in Table 3. It can be seen that AO efficiently inhibits the corrosion of copper in 2 M H3PO4 + 0.3 M NaCl solutions. Data in Table 3 reveal that the inhibition efficiency increases with increasing concentration of AO. The corrosion inhibition can be attributed to the adsorption of AO molecules at

Concentrations (g/L)

Rt

(Ω.cm²)

fmax

(Hz)

Cdl

(µF/cm²)

ERt

(%)

Blank 0 50 63 49 -

(2M H3PO4

+ 0.3 NaCl)

+ X g/L AO

0.5 80 47 42 37

1 100 45 35 50

2 121 44 30 59

4 132 43 28 62

5 150 40 26 67

6 180 39 23 72

7 400 23 10 88

x (g/L) W’corr (mg.j^-1. dm⁻²) Ew (%)

(2M H3PO4

+ 0.3 NaCl)

+ X g/L AO

0 162 -

0.5 105 35

1 79 51

2 70 57

4 60 63

5 52 68

6 44 73

7 13 92

40

copper/acid solution interface [37]. This confirms the results obtained by potentiodynamic and Electrochemical Impedance Spectroscopy (EIS) (Fig. 6).

Figure 6. Comparison of inhibition efficiency (E%) values obtained by weight loss, polarization and EIS methods.

3. Effect of temperature 3.1 Polarization curves

The effect of temperature on the inhibited acid–metal reaction is very complex, because many changes occur on the metal surface such as rapid etching, desorption of inhibitor and the inhibitor itself may undergo decomposition [38]. However, it was found that few inhibitors with acid-metal systems have specific reactions which are effective at high temperature as (or more) they are at low temperature [39-41]. The effect of temperature on the corrosion for copper electrode in (2M H3PO4+ 0.3 NaCl) is studied. For this purpose, the potentiodynamic polarization are being employed with the range of temperature 298, 303, 313 and 323K for 30 min of immersion, in the absence and presence of 7 g/L of inhibitor (Figs. 7 and 8). Corresponding data are given in Table 5.

-0,6 0,0

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0,01

I (A. cm-2 )

E (V/SCE)

298K 303K 313K 323K

Figure. 7 Potentiodynamic polarisation curves of copper in (2M H3PO4 + 3.10^-1M NaCl) at different temperatures

41

-0,6 0,0

1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0,01 0,1

I (A. cm-2 )

E (V/SCE)

298K 303K 313K 323K

Figure. 8 Potentiodynamic polarisation curves of copper in (2M H3PO4 + 3.10^-1M NaCl)in the presence of 7g/L of AO at different temperatures.

Table 5. Effect of temperature on the copper in (2M H3PO4 + 0.3 M NaCl) and at 7g/L of AO.

It’s has been observed that the corrosion current density (Icorr) increased with the increase in AO increasing temperature. It is seen also that the Argan Oil investigated have been inhibiting properties at all temperatures studied and the values of inhibition efficiency decreases with temperature increase. We were interested in exploring the activation energy of the corrosion process and the thermodynamics of adsorption of AO. This was accomplished by investigating the temperature dependence of the corrosion current, obtained using Tafel extrapolation method. The corrosion reaction can be regarded as an Arrhenius-type process, the rate is given by:

_corr exp E^a

I A

RT

 

   (5) where Ea is the apparent activation corrosion energy, T is the absolute temperature, k is the Arrhenius pre- exponential constant and R is the universal gas constant. This equation can be used to calculate the Ea values of the corrosion reaction without and with AO. Plotting the natural logarithm of the corrosion current density

Temperature (K)

Ecorr

(mV/SCE)

Icorr

(µA/cm²)

ba

(mV/dec)

bc (mV/dec) E (%)

Blank

298 -177 36 68 -297 -

303 -157 116 63 -516 -

313 -136 174 54 -504 -

323 -128 251 50 -355 -

AO

298 -217 02 58 -407 94

303 -216 14 69 -427 87

313 -197 40 65 -341 77

323 -193 76 62 -430 71

42

versus 1/T, the activation energy can be calculated from the slope. The temperature dependence of copper dissolution in 2M H3PO4 + 0.3 M NaCl and in the presence inhibitor is presented in Arrhenius co-ordinates in Fig. 7. The calculated values of the apparent activation corrosion energy in the absence and presence of AO are listed in the Table 6. All the linear regression coefficients were close to one. The value of Ea found for AO is higher than that obtained for 2M H3PO4 + 0.3 M NaCl solution. The increase in the apparent activation energy may be interpreted as physical adsorption that occurs in the first stage [42].

Kinetic parameters, such as enthalpy and entropy of corrosion process, may be evaluated from the effect of temperature. An alternative formulation of Arrhenius equation is (6) [43]:



 



  



 



  

RT H R

S Nh

I_corr RT ^{a a}

*

*

exp

exp (6) where h is Planck’s constant, N is Avagadro’s number, S_a^*is the entropy of activation and H_a^* is the enthalpy of activation. Fig. 9 shows a plot of Ln (Icorr/T) vs. 1/T. Straight lines are obtained with a slope of

R H_a^*

 and an intercept of Ln R/Nh + R

S_a^*

 from which the values of S_a^* and H^*_a are calculated and are

given in Table 6. Inspection of these data revealed that the thermodynamic parameters (H_a^* and S_a^*) for dissolution reaction of copper in 2M H3PO4 + 0.3 M NaCl in the presence of inhibitor are higher than that obtained in the absence of inhibitor. The positive sign of H_a^* reflects the endothermic nature of the copper dissolution process suggesting that the dissolution of copper is slow [44] in the presence of inhibitor. On comparing the values of the entropy of activation S_a^* given in Table 6, it is clear that entropy of activation decreases negatively in the presence of Argan Oil than in the absence of inhibitor, this reflects the formation of an ordered stable layer of inhibitor on the copper surface [45].

3,0 3,1 3,2 3,3 3,4

-6 -4 -2

Ln (Icorr) (mA.cm-2 )

1000/T (K^-1)

Blank AO

Figure 9. Arrhenius plots of copper in (2M H3PO4 + 0.3 M NaCl) with and without 7 g/L of AO.

43

3,0 3,1 3,2 3,3 3,4

-12 -10 -8

Ln (

-2-1 I c /T)(mA.cm.K)orr

1000/T (K^-1)

Blank AO

Figure.10 Relation between Ln(Icorr/T) and 1/T at different temperatures.

We remark that Ea and H_a^*values vary in the same way (Table 6). This result permit to verify the known thermodynamic reaction between the Ea and H^*_a as shown in Table 6 [46]:

*

a a

E  H RT

(7)

Table 6. The values of activation parameters H^* and S* for copper in (2M H3PO4 + 0.3 M NaCl) in the presence and absence of 7 g/L of AO respectively.

Ea ∆Ha*(kJ/mole) ∆Sa*(J.mole^-1.k^-1) Ea - ∆Ha*

Blank 48.7 46.2 -111 2.6

Argan oil ( 7g/L ) 95 92.4 -019 2.6

Conclusion

The analysis of Argan oil shows that its composition is dominated by fatty acid methyl esters (100 %), sterols (93 %) and tocopherols (96.6 %). Argan oil (AO) shows excellent inhibition properties for the corrosion of copper in (2M H3PO4 + 0.3 M NaCl) at 298K, and the inhibition efficiency (IE), increases with increase of the AO concentration. At 7 g/L, the inhibition efficiency (IE) of AO is as high as 94 %. AO is a mixed inhibitor and its molecules block both the anodic and cathodic sites of the metal surface.The inhibition efficiency of AO is found to decrease proportionally with increasing temperature (298 to 303 K) and its addition to (2M H3PO4 + 0.3 M NaCl) leads to increase of apparent activation energy (Ea) of corrosion process.The results obtained from weight loss, polarization curves and EIS are in reasonably good agreement.

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