Oil of Ricinus Communis as a Green Corrosion Inhibitor for Copper in 2 M Nitric Acid Solution

Oil of Ricinus Communis as a Green Corrosion Inhibitor for Copper in 2 M Nitric Acid Solution

Sara Houbairi, Abdeslam Lamiri, Mohamed Essahli.

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

Abstract The corrosion behavior of copper in nitric acid with and without the addition of Rcicinus communis oil at various concentrations was investigated with techniques such as weight loss, measurements of electrochemical polarization and electrochemical impedance spectroscopy (SIE). The results obtained show that the copper corrosion rate decreases with the increase in concentration of Rcicinus communis oil to 99% to 250 ppm. Rcicinus communis oil acts as a mixed inhibitor. The effect of temperature on copper corrosion indicates that the effectiveness of inhibition of the natural material remains constant with increasing temperature. The values of inhibition efficiency obtained from weight loss, polarization curves and EIS are in good agreement.

Keywords corrosion inhibition, copper, Ricinus communis oil, adsorption, nitric acid.

1. INTRODUCTION

   The growing need for corrosion inhibitors is becoming increasingly necessary to stop or delay maximum attack of a metal in an aggressive solution. The main areas of application are acid pickling, industrial acid cleaning, acid descaling and oil well acidification. Considerable efforts are provided to find suitable compounds to be used as corrosion inhibitors in various corrosive environments. Many studies have been conducted to study the corrosion activity of the extracts of natural substances [1-10]. These organic compounds are generally aromatic plant extracts, spices and medicinal plants. Natural antioxidants are environmentally harmless substances. Their use as corrosion inhibitors was preferred, since it represents the advantage of being economical and environmentally friendly. These benefits have prompted researchers to examine extracts of natural substances as corrosion inhibitors. Menthe [11], Lippia spicata [12], thyme [13,14], jojoba oil [15], rosemary oil

   [16], eugenol [17] bgugaine [18], the mugwort [19], have been shown to be very effective corrosion inhibitors for iron and steel in acid. Research has shown that jojoba and bgugaine represents a 100 % efficiency for the protection of steel in acidic medium [15-18].

   The aim of this study is the study of the inhibition of the corrosion of copper by 2M HNO3 Rcicinus communis oil gravimetrically electrochemical polarization methods and electrochemical impedance spectroscopy. The effect of temperature was also studied.

2. MATERIALS AND METHODS

   1. Extraction of Ricinus communis oil

      Ricinus communis was collected in the region of Settat, Morocco. The ripe fruit of the plant are dried in the laboratory in the shade at room temperature for one week to reduce its moisture content. After shelling of fruits recovered seeds were crushed.

      The oil was obtained by the method of Soxhlet 3h using hexane as the extraction solvent. The yield of oil was 30%. This oil yield was calculated based on the dry matter.

      1. After extraction, a portion of the oil was used for the analysis of the chemical composition Liquid chromatography high performance coupled to mass spectrometry, and the other part was used for the tests of the anti-corrosion activity.

      2. After extraction, the oil was recovered and stored in a dark bottle and stored at 4 ° C before use.

   2. Preparation of the solution

      The solution of HNO3 2 M was prepared by dilution of analytical grade HNO3 67% with distilled water. Test solutions were freshly prepared before each experiment by adding the oil directly to the etching solution. Experiments were conducted in triplicate to allow determination of reproducibility.

   3. Gravimetric measurements

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

   4. Measures electrochemical

      The electrochemical experiments were performed in a pyrex cell, equipped with a conventional three-electrode: 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 electrode ECS as saturated calomel reference electrode. The copper disc was abraded with sandpaper to different

      particle size up to 1200, degreased with acetone, rinsed with distilled water and dried before each test water. The measurements are performed with an assembly comprising a potentiostat-galvanostat PGZ100, radiometer type associated with "voltamaster4" software.

      The current-potential curve is obtained by 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.

      Chrono amperometric curves were plotted at a potential of 155 mV for 3600 sec.

      The measures electrochemical impedance spectroscopy (EIS) were performed with the same electrochemical system. The frequencies between 100 KHz and 10 Hz were superposed on the corrosion potential. The diagrams given in the impedances are Nyquist representation.

   5. iodometric titration

   Cupric ions Cu2 + were determined by an indirect assay (iodometric), which involves two successive reactions.

   Reaction 1: 2Cu2+ + 2 I- I2 + 2 Cu+ (With potassium iodide solution)

   3 6

   Reaction 2: I2 + 2S2O 2-S4O 2-+ 2 I- (Assay solution of sodium thiosulfate)

3. RESULTS AND DISCUSSION

   1. Analysis of the chemical composition of the oil

      The oil of Ricinus communis belongs to the botanical family Euphorbiaceae and its main component: ricinoleic acid.

      The analysis of the chemical composition of the oil was achieved through Liquid chromatography high performance coupled to mass spectrometry. The retention time and the relative percentage of the various constituents of the oil are shown in Table 1.

      Table 1: Chemistry of Ricinus communis oil

      Compound Name	Retention time (min)	Percentage (%)	Chemical structure
      Palmitic acid	10.06	2.55
      Stearic acid	12.53	2.68
      Oleic acid	12.85	7.72
      Linoleic acid	13.57	9.73
      Ricinoleic acid	30.37	75.03

   2. Effect of the concentration

      • The potentiodynamic polarization measurements

        The figure 1 shows polarization plots of copper cathode and anode immersed in 2 M HNO3 at 293 K in the absence and presence of various concentrations of inhibitor. The electrochemical data, the corrosion potential (Ecorr), the cathodic Tafel slopes (c) and anode (a), the corrosion current density (Icorr) are listed in Tabe 2. The effectiveness of inhibition (%) is calculated by:

        Where I'corr Icorr and respectively represent corrosion current densities determined by extrapolation of the straight Tafel corrosion potential with and without addition of inhibitor.

        Under the experimental conditions used, the cathodic branch represents the reaction of hydrogen evolution and the anodic branch represents the dissolution of copper. Inspection of these results shows that the corrosion current density (Icorr) decreased in the presence of the inhibitor. This behavior reflects its ability to inhibit corrosion of the cook in a solution of 2M HNO3. As long as the densities of anodic and

        Icorr I

        IE % = corr

        Icorr

        × 100 (1)

        cathodic current was reduced (figure 1). It is suggested then that the Ricinus communis oil acts as a corrosion inhibitor for copper mixed type in a 2 M solution of HNO3 [19].

        250 ppm

        200 ppm

        150 ppm 100ppm 50 ppm HNO3 2M

        0,1

        2

        I / (mA/cm )

        0,01

        1E-3

        1E-4

        1E-5

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

        E / (V/ECS)

        Figure 1.Potentiodynamic polarization curves on copper in 2 M HNO3 absence and presence of Ricinus communis oil at various concentrations at 25 ° C.

        Table 2.Electrochemical parameters and inhibitory efficacy of copper and with 2M HNO3 without the adition of Ricinus communis oil at various 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	70.8	1.2074	78.8	1765.1	44.46
        Ricinus	100	64.9	0.7875	71.4	132.7	63.78
        communis oil	150	71.0	0.3776	49.9	132.3	83.28
        	200	64.9	0.1745	28.4	44.9	91.97
        	250	72.7	0.0184	34.4	77.3	99.15
        	300	71.9	0.0114	56.6	68.1	99.47

        From the potentiodynamic polarization curves, one can see that the oil causes a decrease in current density, probably due to the adsorption of organic matter present in the Ricinus communis oil in the active sites of the surface electrode. Table 2 shows that the presence of Ricinus communis oil, the corrosion potential is slightly shifted. An inhibitor can be classified as anode or cathode, if the difference in corrosion potential is above 85 mV relative to the potential of white corrosion [20]. These results suggest that the Ricinus communis oil acts as an inhibitor of the mixed type. These results show that the Ricinus communis oil can delay the anodic and cathodic reactions.The current density at the corrosion (Icorr) decreases as the concentration of inhibitor increases. The cathodic Tafel slopes (c) have significantly changed with the addition of oil (Table 2), indicating that the adsorbed molecules affect inhibiting hydrogen evolution: that is to say, the clearance hydrogen is not only reduced by the effect of locking surface.The results also shown that the anodic Tafel slopes (a) vary with the addition of the inhibitor, indicating

        modification of the process of dissolution of the metal. Indeed, the shape of the polarization curves recorded in a medium containing less than 150 ppm concentration of Ricinus communis oil is similar to that drawn in 2M HNO3. In the presence of an inhibitor concentration equal to or above 150 ppm, the anodic dissolution of copper is made by oxidation of Cu (0) Cu+ and Cu2+ ions which react with Ricinus communis oil to form a complex that provides a partial protection for copper and leads to a decrease of the anode current to its destruction. Indeed according to Figure 1, it is found that the addition of 150 ppm of Ricinus communis oil resulted in the appearance of a slight bearing passivation.

        To prove the formation of the complex (oil / copper), it has been a iodometric titration cupric ions to a decreased concentration of 0.0204 mol / l in a solution 2M HNO3 without inhibitor at a concentration of 0.0162 mol / l a solution containing 150 ppm of Ricinus communis oil.

        Here, three distinct regions may be identified for Cu in a medium containing Ricinus communis oil in a concentration

        varying from 50 to 250 ppm: the Tafel region extending down to the potential-current density peak due the dissolution of cuprous copper ions, the second region is characterized by the decrease of the current until the minimum is reached due to complex formation (cupric ions

        + Ricinus communis oil), the third area represents an increase the sudden current density following destruction of the complex formed which causes the dissolution of Cu. F.mounir [21] The same shape of the polarization curves of copper in 2M H3PO4 in the presence of NaCl.

        The efficiency values calculated on Icorr values obtained in the absence and in the presence of Ricinus communis oil is

        0,0008

        I / (µA / Cm2)

        0,0006

        0,0004

        0,0002

        0,0000

        150 ppm

        250 ppm

        99 % at a concentration of 250 ppm (Figure 2) inhibition.

        120

        100

        IE (%)

        80

        60

        40

        50 100 150 200 250 300

        Concentration of oil (ppm)

        Figure 2.Variation of the efficacy of inhibition of corrosion of copper in 2 M HNO3 in the presence of Ricinus oil at various concentrations at 25 ° C.

        • Chronoamperometric current-time (CT)

        Experiences chronoamperometric current time were conducted to prove the level of passivation is formed from

        150 ppm Ricinus communis oil copper in 2M HNO3 solution. The CT curves measured at 155 mV copper 2M

        nitric acid containing 150 and 250 ppm of Ricinus communis oil are shown in figure 3.

        -500 0 500 1000 1500 2000 2500 3000 3500 4000

        time (sec)

        Figure 3. Chronoamperometric curves at 155 mV for copper in 2M HNO3 containing 150 and 250 ppm of Ricinus communis oil.

        • Measurements of electrochemical impedance spectroscopy

        Representations of Nyquist for copper in 2M HNO3 solution in the absence and presence of different concentrations of Ricinus communis oil are given in Figure 4.

        The impedance spectra are simple form 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 process of charge transfer reaction of the copper corrosion inhibitor in the presence of the mechanism does not change its dissolution [22,23]. The dielectric parameters are given in Table 3. Values increase with increase of the concentration of Ricinus communis oil while Cdl values decrease. Higher valuesmay suggest the formation of a protective layer on the surface of the electrode [24]. The inhibitory effectiveness was determined

        The initial higher current is due to the dissolution of copper in the first cupric cations which in turn reacts with the Ricinus communis oil to form a complex. The current then

        by:

        R RT

        E % = T

        RT

        × 100 (2)

        decreases due to the formation of such a layer provides partial protection and does not allow the increase in current. The good efficiency of Ricinus communis oil is proven by the very low current vaue.

        Where RT and RT' are respectively the resistance of the

        charge transfer copper 2M HNO3 in the absence and presence of inhibitor to Ecorr = 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 component of the impedance is maximum (-Zmax) are represented by:

        Cdl= 1

        2

        (3)

        18

        250ppm

        16 200ppm

        150ppm

        14 100ppm

        The Cdl values are considered below those of the blank, thereby confirming the adsorption of inhibitor onto the metal surface forming an electronic double layer [25].

        These results are in good agreement with those obtained by polarization where Ricinus communis oil turns out to

        -Zi (ohm.cm2)

        12

        10

        8

        6

        4

        2

        0

        -2

        10 20 30

        Zr (ohm.cm2)

        50ppm

        HNO32M

        be a good inhibitor for copper in 2M HNO3

        efficiency of 98%.

        acid with

        Figure 4.Representation Nyquist copper in 2M HNO3 at different concentrations of Ricinus communis oil to Ecorr

        Figure 5. Equivalent circuit used for modeling the impedance diagrams made to potential corrosion.

        Table 3.Parameters electrochemical characteristics of impedance diagram of copper with and without addition of inhibitor 2M HNO3, the corrosion potential.

        inhibitor	Concentration in ppm	RT / ohm.cm2	fm / Hz	Cdl / F/cm2	E%
        Blank	0	18.71	22.89	371.5	—–
        	50	32.06	13.73	361.6	41.64
        	100	51.98	10.32	296.7	64.00
        Ricinus	150	101.59	8.46	185.1	81.58
        communis oil	200	309.75	3.53	145.6	93.96
        	250	1600.14	0.77	128.54	98.83
        	300	1653.42	0.75	127.89	98.87

        The equivalent circuit of said Randles used to study the impedance is given in Figure 5. 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 (shown denoted by the capacitor Cdl). The charge transfer resistance RT is identified in charge transfer resistance [26].

        3.2.4 Gravimetric measurements

        The weight loss measurements were carried out at 293 K in the absence and in the presence of ricinus oil at various concentrations of the samples after immersion in the etching solution of 1h. The efficiency of inhibition,

        IE (%), and the corrosion rate were calculated using the equations:

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

        Inhibitor Concentrati on (ppm)		W (mg/cm2.h)	EI (%)
        blank	0	0.093	——–
        	50	0.062	33.33
        Essential	100	0.031	66.66
        oil of	150	0.020	77.78
        Ricinus	200	0.010	88.89
        communis	250	0.0053	94.26
        	300	0.0053	94.26

        The values of the efficiency of inhibition, IE (%) obtained by using the method of weight loss for the different concentrations of Ricinus communis oil are summarized in

        W = 1 2

        (4)

        Table 4. It is very clear that the Ricinus communis oil

        inhibits the corrosion of copper in a solution of 2M HNO3,

        IE (%) = (

        ) × 100 (5)

        since the corrosion rate (W) continuously decreases with increasing inhibitor concentration at 293K, the maximum

        Where m1 and m2 are the weight loss (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, Corrosion rates of copper in 2 M HNO3 medium with and without addition of inhibitor (mg.Cm-2.h- 1). The results of the study are summarized in Table 4.

        efficacy (94.26%) 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 6).

        100

        80

        IE %

        60

        40

        20

        0

        50 100 150 200 250 300

        Weight loss polarisation EIS

   3. 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 extrapolation of Tafel straight experiments 283, 293, 303, and 313 K. The polarization curves for copper in a solution 2M HNO3 in the temperature range (273-313 K) are represented Figures 7 and 8, respectively with and without 250 ppm of Ricinus communis oil. 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 at all temperatures studied are given in Table 5.

   Figure 6.Comparison of the efficiency of the inhibition obtained with the use of weight loss, polarization and impedance measurements

   0,1

   I/(mA/cm2

   )

   0,01

   40°C

   30°C

   20°C

   10°C

   1E-3

   1E-4

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

   E / (V/ECS)

   Figure 7.Effect of temperature on the cathode and anode reactions copper in 2M HNO3

   Figure 8.Effect of temperature on the cathode and anode reactions copper with 2M HNO3 in 250 ppm of Ricinus communis oil.

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

   	(K)	SCE)	cm2)
   	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	—
   Oil of	283	71.9	0.0114	56.6	68.1	99.26
   Ricinus	293	72.7	0.0296	34.4	77.3	98.48
   comminus	303 /td>	78.8	0.0557	45.1	78.2	98.14
   	313	71.0	0.0978	49.9	132.3	97.31

   Inhibitor Temperature/

   ECorr / (mV /

   ICorr / (mA /

   a / (mV) -c / (mV) IE%

   In the absence of Ricinus communis oil, the Icorr value increases with increasing temperature, higher than that obtained in its presence. It is obvious that the Ricinus communis oil has inhibitory properties at all temperatures studied, and the values of the effectiveness of inhibition remain constant since no decrease more than 2 % with increasing temperature.

   This means that the inhibitor is adsorbed on the substrate by chemical bonds (tight binding). This type of non-temperature- sensitive connections effectively fights 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 W is a linear function of T-1. We can calculate the activation energy from the following relationships:

   Icorr = K exp (-Ea/ RT) (6) I = K exp (-Ea/ RT) (7)

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

   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 corrosion inhibitor. Figure 9 shows the Arrhenius plot of coordinates in the corrosion rate of copper in 2M HNO3 in the absence and in the presence of Ricinus communis oil to 250 ppm.

   1000 / T (k-1)

   -6

   -8

   -10

   -12

   250 PPM Ricinus comminus oil

   -4

   3.6

   3.5

   3.2 3.3 3.4

   HNO3 2M

   3.1

   -2

   0

   1000/T (K-1)

   3.6

   3.5

   3.4

   3.3

   3.2

   250 ppm Ricinus comminus oil HNO3 2M

   3

   2

   1

   0

   -1 3.1

   -2

   -3

   -4

   -5

   Ln Icorr ( mA / cm2)

   Ln (Icorr / T) (mA/ cm2)

   Figure 9. 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 straight indicating that the Arrhenius law

   Figure 10. 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 Ricinus communis oil to T = 293K

   is enforced. The values of the activations obtained from these

   H* (KJ

   S *

   straight energies are given in Table 6.

   Table 6. Activation energy of copper dissolution in 2M

   Inhibitor / mol) (J/mole.K)

   Blank 3.518 -233.63

   Ricinus

   HNO3 alone and in the presence of inhibitor.

   communis oil

   1.401 -262.24

   Sample Ea / (kJ / mol) Blank 31.55

   Essential oil of Ricinus

   communis 23.21 From the results of Table 6 it is clear that the presence of inhibitor decreases the activation energy in the presence of inhibitor. This behavior demonstrates the phenomenon of chemisorption of the inhibitor to the metal surface of protective power which increases with temperature.

   The values of the activation energy obtained from Arrhenius straight is 31.55KJ. mol-1 in the absence of inhibitor, this value is in agreement with the literature [30], and a 250 ppm concentration of Ricinus communis oil, i.e. when the rate of recovery is maximum, the value of the activation in the presence of this oil energy is 13.35 KJ. mol-1. This confirms the chemical adsorption of Ricinus communis oil by the formation of an effective protective 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]:

   (250 ppm)

   The positive sign of H* reflects an endothermic process of adsorption, which is assigned to the chemisorptions [32]. Negative values of entropy S *, reflects an increase in the disorder that occurs during the formation of metal / adsorbed species complex [33].

   More

   G* = – R× T× Ln (55.5 × K) (9)

   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*= 38 064 kJ / mol at 25°C indicates the spontaneous adsorption process, and the stability of the adsorbed layer on the metal surface [34].

   • adsorption isotherm

     The adsorption on the surfaces of corrosion has never reached a real equilibrium and tends to reach a state of equilibrium

     I =

     × exp( ) × exp(- ) (8)

     adsorption. However, when the corrosion rate is sufficiently

     corr

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

     small, the stationary state of adsorption tends to become a quasi-equilibrium state. In this case, it is reasonable to consider that the adsorption thermodynamic quasi-equilibrium isotherms using appropriate balances. [35]

     The adsorption behavior provides information on the interaction between the adsorbed molecules and their interactions with the surface of the electrode [36].

     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 [37]. The adsorption of Temkin, Frumkin and Langmuir isotherms were used to represent the Ricinus communis oil on the surface of copper adsorption. 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.

     3

4. CONCLUSION It appears from this study that:

• Ricinus communis oil is an effective inhibitor of the corrosion of copper in a solution of 2M HNO3. Efficiency of Ricinus communis oil increases with the concentration to achieve 99 % to 250 ppm.

  -The results of polarization studies suggest that Ricinus communis oil acts as mixed type inhibitor.

• Results from electrochemical impedance spectroscopy indicate that adsorption of Ricinus communis oil on the surface of the copper increases the strength and reduces the transfer

2.5

2

Ln / 1-

1.5

1

0.5

0

R² = 0,983

capacity of the double-layer.

– The adsorption of Ricinus communis oil on the copper surface in a solution of 2 M HNO3 is done according to the Langmuir adsorption isotherm, with a high correlation coefficient. The adsorption process is an endothermic process and spontaneous.

-The efficiency determined by electrochemical polarization inhibitors, Electrochemical impedance spectroscopy, and gravimetric values are in good agreement.

-0.5 3.5 4.5 5.5

-1

Ln C

Figure 11.Moel Langmuir isotherm for adsorption of Ricinus communis oil on the surface of 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 11) indicating that the adsorption of the inhibitor on the surface of the plate Copper is according to the Langmuir model:

Ln (/ 1-) = K ln [C] (11) The strong correlation (R2 = 0.983) for the plot of land 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 (Figure 12). This allows considering constant adsorption energy [38].

Figure 12. Model adsorption isotherm according to the Langmuir adsorption of Ricinus communis oil on the surface of copper in 2 M HNO3 at 25 °C.

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