Adsorption and Inhibiting Copper Corrosion in A Nitric Acid Solution by Artemisia Essential Oil

Adsorption and Inhibiting Copper Corrosion in A Nitric Acid Solution by Artemisia Essential Oil

Sara Houbairi, Mohammed Essahli, Abdeslam Lamiri

Laboratory of Applied Chemistry and Environment, Faculty of Science and Technologies, University Hassan 1, Km 3, B.P. 577, Settat, Morocco

Abstract

The inhibitory action of the Artemisia essential oil (AEO) on the corrosion of copper in a 2 M HNO3 solution in the temperature range from 283 to 313 K was measured by gravimetric, potentiodynamic polarization and electrochemical impedance spectroscopy methods. The results obtained show that the AEO inhibits the corrosion of copper in a solution of 2M HNO3 and that the effectiveness of inhibition increases with increasing concentration of the inhibitor,

and decreases proportionally with temperature.

It appears from the study of potentiodynamic polarization that the essential oil tested is a mixed type inhibitor with a cathodic predominance with its adsorption on the copper surface following the Langmuir adsorption isotherm. The kinetic data for dissolution were also studied.

Keywords: copper, corrosion, inhibition, essential oil of Artemisia, adsorption.

1. Introduction

   The use of inhibitors is one of the usual methods of protection of metallic materials against corrosion in acidic environments. Among these applications, we can cite the acid pickling, industrial acid cleaning and acid descaling. Due to the aggressiveness of most acid solutions, inhibitors are generally employed to block or reduce the corrosive attack of metallic materials. The available evidence indicates that most organic compounds act by the phenomenon of adsorption to the metal surface.

   The adsorption mechanism of the inhibitor is influenced by the nature of the surface charge and the metal, by the type of electrolyte and its aggressiveness and by

   the chemical structure of the inhibitors. The main types of interactions between the inhibitor and the metal surface are physical adsorption and chemisorption. The adsorption of the inhibitor is linked to the presence of heteroatoms such as nitrogen, oxygen, phosphorus, sulfur and/or triple bonds or aromatic rings in their molecular structure. The good results obtained with the use of natural organic compounds in inhibiting the corrosion of metals in acidic media, prompted us to test the inhibitory action of other organic compounds.

   However, most inhibitors used are toxic and cause a lot of environmental damage. In this context, we are interested in the application of non-toxic natural products as corrosion inhibitors. These products are

   used as extracts or as essential oils. We include the oils of rosemary [1, 2], clove [3], mint pulegone [4], henna, pyrrolidine,

   irniine, thyme [5, 6, 7 and 8], ginger [9],

   bgugaine [10].

   In the literature authors use natural products such as aqueous extracts of rosemary as a corrosion inhibitor of the alloy of aluminum and magnesium [11], extracts of prickly pear (Opuntia) as a corrosion inhibitor of aluminum [12] and honey as a corrosion inhibitor for steel [13]. Essential oils are known and have been used for over 7000 years. They consist exclusively of odorous volatile terpene molecules found in plants and aromatic trees.

   The aim of this study is the study of the inhibition of the corrosion of copper in a 2M HNO3 by the nontoxic essential oil of Artemisia by gravimetric, electrochemical measurements, and finally electrochemical impedance spectroscopy.

2. Materials and Methods

   1. Extraction of essential oil of Artemisia (AEO)

      Artemisia herba alba was collected in the region of Agadir, Morocco. The aerial parts of the plant are air dried in the laboratory at room temperature.

      The essential oil was obtained by steam distillation of water using a Clevenger-type distiller for 2p0min. The yield of essential oil of Artemisia is 1.1%. The essential oil yield was calculated based on the dry matter.

      After extraction, a portion of the oil was used for the analysis of the chemical composition by the technique of gas chromatography coupled to mass spectrometry. The other part was used for

      testing anti-corrosion activity. The oil obtained after extraction was recovered and stored in a dark bottle and stored at 4°C before use.

   2. Preparation of the solution

      The 2 M HNO3 solution was prepared by dilution of the nitric acid of analytical grade 67% with distilled water. Test solutions were freshly prepared before each experiment. Experiments were conducted in triplicate to determine reproducibility.

   3. Gravimetric measurements

      Gravimetric tests were conducted by maintaining the desired temperature of the electrolyte with a FRIGITHERM thermostat. The electrolyte volume was 30mL. The samples are in rectangular form with the surface area of 9.6 cm2. Prior to measurements, they undergo a mechanical polishing with abrasive paper of different particle size up to 1200, followed by degreasing with acetone, and rinsing with distilled water and drying in air. Each value is the average of at least three tests.

   4. Measures electrochemical

      The electrochemical experiments were performed in a Pyrex cell, equipped three electrodes: copper as the working electrode in the form of discs cut with a geometric area of 1 cm2, platinum as a counter electrode and the saturated calomel/ECS electrode as the reference electrode. The copper disc was abraded with abrasive paper of different particle size up to 1200, degreased with acetone, rinsed with distilled water and dried before each test. The measurements are performed using a potentiostat-galvanostat PGZ100,

      associated with the "voltamaster4" software.

      The current-potential curve is obtained in potentiodynamic mode, the potential applied to the sample varies continuously with a scanning rate of 30 mV / min. We chose a relatively low rate of scanning to be quasi-steady. Before curve plot, the working electrode is maintained at a potential of -800 mV for 15 minutes.

      The measures of the electrochemical impedance spectroscopy (EIS) were performed with the same electrochemical system. The frequencies between 100 KHz

      and 10 mHz were superposed on the corrosion potential. The diagrams given in the impedances are Nyquist representation.

3. Results and Discussion

   1. AEO Analysis

      The analysis of the chemical composition (figure 1) of the essential oil of Artemisia herba alba, shows the presence of alpha thujone chemotype and camphor. Table 1 summarizes the main constituents of the essential oil.

      Table 1: Constituents of the essential oil of Artemisia

      Compound Name	No.	Retention time	Percentage (%)
      camphene	1	9.36	3.57
      1,8-cineole	2	12.64	9.28
      alpha thujone	3	15.56	25.99
      beta thujone	4	15.98	16.01
      camphor	5	16.97	28.96
      myrtenal	6	21.31	6.44

      Figure 1: Chromatogram of Artemisia herba alba

      1. Effect of concentration

         1. The potentiodynamic polarization measurements

            The figure 2 shows the anodic and cathodic polarization plots of copper immersed in 2

            M HNO3 at 293 K in the absence and presence of various concentrations of the inhibitor used. Electrochemical data, the corrosion potential (Ecorr), the cathodic (c) and anodic (a) Tafel slopes, and the corrosion current density (Icorr) are listed

            in Table 1. The effectiveness of inhibition (%) is calculated by:

            Icorr Icorr

            Inspection of these results shows that the density of corrosion (Icorr) decreased in the presence of the inhibitor. This behavior

            IE %=

            Icorr × 100

            reflects its ability to inhibit corrosion of the copper in a solution of 2M HNO3

            Where I'corr and Icorr represent

            respectively corrosion current densities determined by extrapolation of the straight Tafel slopes at the corrosion potential with and without the addition of inhibitor.

            Under the experimental conditions used, the cathodic branch represents the release of hydrogen and the anodic branch represents the dissolution of copper.

            The anodic and cathodic current densities were reduced (Figure 2), indicating that the Artemisia essential oil (AEO) reduces both the anodic and cathodic reactions due to its adsorption on the metal surface. It is suggested that AEO acts as a mixed type corrosion inhibitor for copper in a 2M solution of HNO3 [14].

            250 PPM

            200 PPM

            150 PPM

            100 PPM

            50 PPM HNO3

            0,1

            logI/(mA/cm2

            )

            0,01

            1E-3

            1E-4

            1E-5

            -1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6

            E / (V/ECS)

            Figure 2: Potentiodynamic polarization curves of copper in 2 M HNO3 in the absence and presence of Artemisia essential oil at different concentrations at 25 °C.

            Table 2: inhibitory efficiency and electrochemical parameters of copper in 2M HNO3 without and with addition of Artemisia essential oil at different concentrations at 25 °C

            Inhibitor	Cinh / (ppm)	ECorr / (mV / SCE)	ICorr / (mA / cm2)	a / (mV)	-c / (mV)	IE%
            Blank	—	65.2	2.1741	77.0	349.5	—
            	50	58.5	1.1267	49.8	320.6	48.18
            Artemisia	100	64.9	0.9842	71.4	332.7	54.73
            essential	150	60.2	0.4467	76.5	329.8	79.45
            oil	200	41.8	0.1867	83.0	335.6	91.41
            	250	42.2	0.1745	96.0	334.2	91.97

            It also appears from Tafel slopes (Figure 2, Table 2) that the adsorption of the inhibitor moving slightly the corrosion potential (Ecorr) in the most negative direction contrary to the blank, which means that the reduction of the cathodic reaction is the main effect of the corrosion inhibitor [15]. Therefore, these results indicate that AEO acts as an inhibitor of the mixed type with a predominant control of the cathodic reaction [16].

            The modes of inhibition of organic inhibitors are classified into three categories [17, 18 and 19]: geometric locking effect of the adsorbed inhibitory species, blocking of the active sites by the adsorbed species, and the electro-catalytic effect of the inhibitor or the by-products of its reactions. It was suggested that the first mode of inhibition is the result of reducing the reactive area on the surface of the corrosion resistant metal, while the other two modes of inhibition are due to changes of the average activation energy barriers of the anodic and cathodic reactions of the corrosion process. Cao explained that if the shift of the corrosion potential due to the addition of an inhibitor on the interface is negligible, the inhibition is probably caused by the geometrical locking inhibitory species adsorbed on the surface of the metal [20]. From the results of polarization, it can be concluded that the inhibition by AEO is caused by geometrical locking effect. The Tafel slopes (Figure 2) show that the addition of

            the inhibitor to the solution of 2M HNO3 does not change the mechanism of evolution of hydrogen and the reduction of H+ ions at the surface of the copper, which occurs primarily by a charge transfer mechanism [21].

            The effectiveness of inhibition increases with the concentration of inhibitor to achieve 91% to 250 ppm Artemisia essential oil by lowering the current density of a value of 2.1741 mA/cm2 to a value of 0.1745 mA/cm2.

         2. Measurements of electrochemical impedance spectroscopy

            The Nyquist representations for copper in

            2 M HNO3 solution in the absence and presence of different concentrations of AEO are given in figure 3. The impedance spectra are in the simple form of semicircles, and the semicircles diameter increases with increasing concentration of inhibitor. The presence of a single half- circle indicates that the charge transfer occurs at the electrode-solution interface, and the transfer process of the reaction of copper corrosion in the presence of the inhibitor does not alter the dissolution mechanism [22, 23]. The dielectric parameters are given in Table 3. The

            values increase with increase in the

            concentration of AEO while the Cdl values decrease. Higher values may suggest the formation of a protective layer on the surface of the electrode [24].

            250ppm 200ppm 150ppm 100ppm 50ppm HNO32M

            18

            16

            14

            -Zi (ohm.cm2)

            12

            10

            8

            6

            4

            2

            0

            -2

            10 20 30

            Zr (ohm.cm2)

            Figure 3: Nyquist Representation of copper in 2M HNO3 to different concentrations of

            AEO to Ecorr

            Table 3: Electrochemical characteristics of the impedance diagram of copper with and without addition of inhibitors in 2M HNO3, at the corrosion potential

            inhibitors	Concentration in ppm	RT / ohm.cm2	fm / Hz	Cdl / F/cm2	E%
            Blank	0	18.71	22.89	371.5	—–
            	50	35.67	12.47	357.65	47.55
            Artemisia	100	40.75	12.78	305.54	54.08
            essential oil	150	66.89	9.28	256.21	72.03
            	200	180.52	5.50	160.04	89.63
            	250	211.35	5.06	148.74	91.15

            The inhibitory effectiveness was determined by:

            component of the impedance is maximum are represented by:

            R

            R RT C = 1

            E % =

            T × 100

            T

            dl 2

            Where RT and RT 'are respectively the resistance of the charge transfer copper in 2M HNO3 in the absence and presence of inhibitor to E = 65 mV / SCE.

            The values of charge transfer resistance (RT) were calculated based on the difference in impedance between the upper and lower frequency values.

            The double layer capacity (Cdl) and frequency (fmax) at which the imaginary

            Figure 4: Equivalent circuit used for modeling the impedance diagrams made at the corrosion potential.

            The Cdl values are noted to be below those of the blank,thereby confirming

            the adsorption of inhibitor onto the metal surface. This forms a double electronic shell [25].

            These results are in good agreement with those obtained by polarization where AEO turns out to be a good inhibitor for copper in acidic medium 2M HNO3 with an efficiency of 91%.

            The said equivalent circuit of Randles used to study the impedance is given in Figure

4. The resistance Re of the circuit corresponds to the resistance Randles of finite conductivity of the electrolyte. The charge phenomenon of the electrode / solution interface causes the appearance of a capacitive current (represented by Cdl). The charge transfer resistance RT is identified at the charge transfer resistance [26].

1. Gravimetric measurements

   The weight loss measurements were carried out at 293 K in the absence and in the presence of different concentrations AEO samples after immersion in the etching solution of 1h. The efficiency of inhibition, IE (%), and the corrosion rate were calculated using the equations:

   =

   W 12

   weight loss for the different concentrations of AEO are summarized in Table 4. It is very clear that the AEO inhibits corrosion of copper in a solution of 2M HNO3, since the corrosion rate (W) continuously decreases with increasing inhibitor concentration at 293 K, and the maximum efficiency (88.89%) was obtained at 250 ppm. The comparison shows that the three techniques EI (%) obtained by using the impedance technique are comparable, and are parallel to those obtained by the methods of losing weight and polarization (Figure 5).

   Table 4: Corrosion rate and inhibitory efficiencies of copper in 2 M HNO3 with and without addition of the Artemisia essential oil at different concentrations at 25 °C.

   Inhibitor Concentration	W	EI
   (ppm)	(mg/cm2.h)	(%)
   Blank 0	0.09375	—-
   50	0.05208	44.45
   Artemisia 100	0.0416	55.63
   essential 150	0.03125	66.66
   oil 200	0.0109	88.37

   250 0.010416 88.89

   (

   IE (%) =

   ) × 100

   100

   IE %

   50

   weight

   loss polarisati on

   EIS

   Where 1 and 2 are the weight losses (mg) before and after immersion in the test solutions, A is the sample surface (cm2), t is the exposure time (h), and w and w' are, respectively, the corrosion rates of copper in 2 M HNO3 without and with addition of inhibitor (mg.cm-2.h-1).

   The values of the efficiency of inhibition, IE (%) obtained by using the method of

   0

   C (ppm)

   Figure 5: Comparison of the efficacy of inhibition (IE%) obtained by the use of weight loss, polarization and impedance measurements.

1. Effect of temperature

   The temperature is an important condition in the studies on the dissolution of the metal. The rate of corrosion in acidic solutions, for example, increases exponentially with increasing temperature due to the evolution of the hydrogen overvoltage decreasing [27].

   The Icorr value was obtained by extrapolating the Tafel slopes in experiments conducted at 283, 293, 303,

   and 313 K. The polarization curves for copper in a 2M HNO3 solution in the temperature range (273-313 K) are shown in Figures 6 and 7, with and without 250 ppm of AEO. The various numerical values of the variation of the corrosion current density (Icorr), the corrosion potential (Ecorr), cathodic Tafel slope (c), and anodic Tafel slope (a) to 250 ppm of inhibitor (AEO) all the studied temperatures are shown in Table 5.

   Figure 6: Effect of temperature on the anodic and cathodic reactions of copper in 2M HNO3.

   Figure 7: Effect of temperature on the cathodic and anodic reactions of copper in 2M HNO3 with 250 ppm of Artemisia essential oil.

   Table 5: Electrochemical parameters of copper in 2 M HNO3 without and with 250 ppm of AEO, at different temperatures.

   Inhibitor	Temperature	ECorr / (mV /	ICorr / (mA	a /	-c /	IE%
   	/ (K)	SCE)	/ cm2)	(mV)	(mV)
   	283	75.8	1.5387	66.1	77.3	—
   Blank	293	64.1	1.9411	126.4	84.5	—
   	303	50.3	2.9902	123.1	91.6	—
   	313	66.4	3.6507	98.6	65.8	—
   	283	73.6	0.0787	101.4	102.5	94.88
   250 ppm	293	63.6	0.1268	77.3	124.1	93.47
   AEO	303	65.7	0.3053	68.5	114.6	89.79
   	313	82.5	0.6826	59.6	211.2	81.30

   In the absence and in presence of AEO, the Icorr value increases with increasing

   temperature. It is also evident that the AEO inhibitory properties at all temperatures studied, and the values of the effectiveness

   of inhibition decreases with increasing temperature.

   This means that the inhibitor is adsorbed on the substrate by electrostatic bonds (weak bonds). This type of temperature- sensitive links cannot fight effectively against corrosion when the temperature increases [28].

   In the case of the acid corrosion, many authors [29] use of the Arrhenius equation to account for the effect of temperature (T) on the rate of corrosion and therefore believe that the logarithm of the speed corrosion is a linear function of T-1.

   We can calculate the activation energy from the following relationships:

   Icorr = K exp (-Ea / RT)

   I = K 'exp (-E'a / RT)

   Where k and k' are constants (Arrhenius pre-exponential parameters), and Ea and E'a activation energies, respectively, in the absence and presence of the inhibitor.

   0

   Ln (Icorr ) (mA / cm2)

   Some conclusions on the mechanism of action of the inhibitors may be obtained by comparing measured Ea to both the presence and absence of the inhibitor. The figure 8 shows the Arrhenius coordinates plot in the corrosion rate of copper in 2M HNO3 in the absence and presence of Artemisia essential oil to 250 ppm.

   5

   HNO3 2M

   250 ppm AEO

   1000 / T (k-1)

   -5

   3.6

   3.5

   3.4

   3.3

   3.2

   3.1

   Figure 8: Arrhenius diagram of the dissolution of copper in 2M HNO3 at different temperatures with and without inhibitor.

   The variation of the logarithm of the corrosion current as a function of T-1 gives a straight indication of the Arrhenius law being enforced. The values of the activations obtained from these straight energies are given in Table 6.

   Table 6: Activation energy of dissolution of copper in 2M HNO3 with and without inhibitor.

   Sample Ea / (kJ / mol)

   Blank 19.38

   Artemisia

   essential oil 31.29

   From the results of Table 6 it is clear that in the presence of inhibitor the activation eergy increases, so that IE% decreases as the temperature increases. This behavior demonstrates the physisorption phenomenon of the inhibitor to the metal surface. The rate of recovery, lower at higher temperatures suggests that at these temperatures, the rate of destruction of the film physically adsorbed increases faster than its rate of formation.

   This phenomenon can also be explained by the fact that the process of corrosion of copper in the presence of the inhibitor does not only depend on the reaction which takes place at the surface of bare metal, but also the release of Cu2+ ions through the layer of adsorbed inhibitor [28, 29].

   The values of the activation energy obtained from the Arrhenius slope is 19.38 kJ mol-1 in the absence of inhibitor, this value is in agreement with the literature [30], and at a concentration of 250 ppm AEO, when the rate of recovery is maximum, and the value of the activation energy in the presence of this oil is 31.29 kJ mol-1. This confirms the physical adsorption AEO by the formation of an effective surface film.

   The kinetic parameters, the enthalpy and entropy of the corrosion process are also estimated from the study of the effect of temperature. An alternative formulation of the Arrhenius equation [31]:

   I = × exp () x exp (- )

   The positive sign of H* reflects the endothermic nature of the process of dissolution of the copper, which suggests that the slow dissolution of the copper is in the presence of inhibitor [32]. By

   comparing the values of the activation data

   corr

   S* entropy in Table 7, it is clear that the

   Where h is Planck's constant, N is the Avagadro number, S* is the entropy of activation and the H* is the activation enthalpy. Figure 9 shows plots of Ln (Icorr

   / T) versus 1 / T. Straight lines are obtained with a slope of- H* / R and an intercept of (Ln R / Nh + S* / R), from which the values of S* and H* can be calculated, these values are in Table 7.

   HNO3 2M

   Ln (Icorr / T ) (mA /

   cm2)

   250 ppm AEO

   3.1 3.2 3.3 3.4 3.5 3.6

   -0.01

   1000 / T (k-1)

   Figure 9: Relationship between Ln (Icorr

   / T) and 1000 / T at different temperatures

   Table. 7: The values of the activation parameters H* and S* of copper in 2M HNO3 in the absence and presence of 250 ppm of Artemisia essential oil at

   T = 293K

   activation entropy decreases negatively to a great extent in the presence of AEO more than absence of the inhibitor, thus reflecting the formation of a stable layer of controlled inhibitor on the surface of copper [33].

   Moreover

   G* = – R× T× Ln (55.5 × K) K = / C × (1-) (10)

   Where R is the universal gas constant, 55.5 is the concentration of water in mol / L, is the degree of coverage of the metal surface, and C is the concentration in ppm of the inhibitor.

   The negative value of G* = -58.26 kJ / mol, indicating spontaneous adsorption of inhibitory molecules on the surface of copper. G* value obtained indicates that the adsorption occurs by the mechanism physisorption.

   1. Adsorption isotherm

The adsorption on the surfaces of corrosion has never reached a real equilibrium and

Inhibitor

H*

(KJ /

mol)

S* (J /

mol-1.K-

1)

tends to reach a state of adsorption equilibrium. However, when the corrosion

ppm)

Inspection of these data revealed that the thermodynamic data (S* and H*) for the reaction of copper dissolution in 2 M HNO3 in the presence of inhibitor is greater than in the absence of inhibitor.

quasi-equilibrium state. In this case, it is reasonable to consider that the adsorption thermodynamic quasi-equilibrium isotherms using appropriate balances [34]. The adsorption behavior provides information on the interaction between the

adsorbed molecules and their interactions with the surface of the electrode [35].

Ln / 1-

It has been reported that the adsorption of the inhibitor molecules depends on a variety of factors, for example the presence of functional groups (or electron donor or withdrawal), steric factors, the distribution of load on the donor atom, the orbital nature of electron donors, the nature of the metal substrate, and the type of interaction between the organic molecules and the metal surface [36]. The adsorption isotherms of temkin, frumkin and langmuir were used to represent the adsorption AEO on the copper surface. The correlation coefficient, R2, was used to choose the isotherm that best matches the experimental data. The recovery rate () at different concentrations for the inhibitor tested in 2M HNO3 was assessed from measurements of weight loss.

1.4

1.2

1

0.8

0.6

0.4

0.2

0

-0.2 3.7

-0.4

R² = 0,9959

Ln C

5.7

5.2

4.7

4.2

Figure 10: Model Langmuir isotherm for the adsorption of the inhibitor on the surface of the AEO copper in 2 M HNO3 at 25 °C.

The curve representing ln ( / -1) as a function of ln [C], where C is the concentration of inhibitor, is a straight line (Figure 10) indicating that the adsorption of the inhibitor on the surface of the copper plate is according to the Langmuir model:

Ln ( / 1-) = K ln [C]

The strong correlation (R2 = 0.965) for a portion of the field of isothermal Langmuir adsorption inhibitor confirms the validity of this approach.

Based on the Langmuir isotherm, we can put an approach to the representation of adsorption phenomena, which is based on three assumptions, explaining that the adsorption is localized and does not give rise to the formation of a monolayer, and all sites are equivalent and the surface is uniform, and that there is no interaction between the adsorbed molecules which allows to consider the adsorption energy as constant [37].

Conclusion

The following conclusions can be drawn from this study:

• AEO is an effective inhibitor of the corrosion of copper in a solution of 2M HNO3 AEO efficiency increases with the concentration to achieve 91% to 250 ppm.

  -The study results suggest that AEO behaves as mixed type inhibitor with dominant cathodic reaction control.

  -Results from electrochemical impedance spectroscopy indicate that the adsorption of AEO on the surface of the copper increases the strength and reduces the transfer capacity of the double layer.

• The adsorption of the copper AEO in a 2M solution of HNO3 is done according to the Langmuir adsorption isotherm, with a high correlation coefficient. The adsorption process is a stable endothermic process.

-The efficiency determined by electrochemical polarization inhibitors, Electrochemical impedance spectroscopy,

and gravimetric values are in good agreement.

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