E c o r r ), the cathodic Tafel line slope ( β C ), anodic Tafel line slope ( β a ) and protection efficiency ( % I E ) were measured from the diagrams (see Figure 1 and Table 3). The outcome data gotten in Table 3 discovered that the i c o r r lower clearly after the appending of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile composite and % I E improve with raising the inhibitor dose. In the existence of inhibitor E c o r r , was improved with no definite trend, demonstrating that 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile composite play as mixed–kind inhibitor. The % I E was measured

Figure 1. PP plots for the corrosion of Cu in 2.0 M HNO3 in existence and lack of unlike dose of inhibitor at 30˚C ± 0.1˚C.

Table 3. Parameters gotten from PP technique for the corrosion of Cu in 2.0 M HNO3 at 30˚C ± 0.1˚C.

utilizing Equation (1):

% I E P = [ i C o r r ° i C o r r / i C o r r ° ] × 100 (1)

where i C o r r ° and i C o r r are the uninhibited and inhibited corrosion current densities, correspondingly.

Also it is clear from Table 3 that ( β a ) and ( β C ) Tafel lines keep almost unmoved upon appending of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile composite, mean rise to nearly parallel set of anodic lines slope, and nearly parallel cathodic diagrams data gotten too. Therefore, the inhibitors adsorbed play by simple blocking of the active center for two anodic and cathodic procedures. Meaning no change in mechanism of Cu in solution, and only reasons inactivation of a part of the surface with esteem to the aggressive solution [31] [32].

3.2. EIS Tests

EIS is well-established and commanding tests in the reading of corrosion. Surface characteristic and mechanistic data can be gotten from impedance diagrams [33] [34] [35] [36] [37]. Figure 2(a) & Figure 2(b) display the Nyquist (a) and Bode (b) diagrams gotten at OCP both in the attendance and lack of improving dose of examined 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c] quinoline-3-carbonitrile compound at 30˚C ± 0.1˚C. The improve in the size of the capacitive loop with the appending of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile composite at 30˚C ± 0.1˚C displays that a barrier progressively forms on the surface of Cu. Bode schemes (see Figure 2(b)), displays the incessant rise in the phase angle shift, clearly correlating with the rise of adsorbed inhibitor on surface of Cu. The Nyquist schemes do not produce perfect semicircles as predictable from the theory of EIS. The abnormality from ideal semicircle was usually credited to the frequency scattering [38] as well as to the in-homogeneities of the surface.

EIS data of the 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano [3,2-c]quinoline-3-carbonitrile campsite at 30˚C ± 0.1˚C was examine utilize the equivalent circuit (Figure 3), which signifies a single charge transfer reaction and

Figure 2. The Nyquist (a) and Bode (b) diagrams for Cu corrosion in nonexistence and existence of unlike dose of 2-amino-6-methyl-5-oxo-4-phenyl-5, 6-dihydro-4H-pyrano [3,2-c]quinoline-3-carbonitrile composite at 30˚C± 0.1˚C.

Figure 3. Equivalent circuit model utilized to fit investigational EIS.

fits well with our experimental data. The constant phase element, CPE, is presented in the circuit in its place of a pure double layer capacitor to give a more correct fit [39]. The double layer capacitance, C d l , for a circuit including

C d l = Y o ω n 1 / sin [ n ( π / 2 ) ] (2)

where Y o is the degree of the CPE, ω = 2 π f max , f max is the frequency at the impedance is maximal and the factor n is an parameter adjustable that regularly lies among 0.50 and 1.0 [40] [41] [42]. The overall figure of the plots is very like for all samples (in existence and nonexistence of inhibitor at unlike immersion times) representing that no exchange in the corrosion mechanism [43]. From the impedance data (see Table 4), we achieve that the data of R c t improves with rising the dose of the inhibitor and this designates an improvement in % I E , which in agreement with the data gotten from Potentiodynamic polarization.

In fact, the existence of inhibitor improves the data of R c t in acidic solution. Data of C d l are also brought down to the extreme extent in the existence of inhibitor and the break down in the data of CPE trails the order like to that gotten for i C o r r in this study. The lower C P E / C d l data from a break down in local dielectric constant and/or an improvement in the width of the double layer, signify that organic assembles hinder the Cu corrosion by metal/acid adsorbed [44] [45]. The % I E was measured from the charge transfer resistance data from Equation (3) [46] :

% I E E I S = [ 1 ( R c t ° / R c t ) ] × 100 (3)

where R c t ° and R c t are the resistance data nonexistence and existence of inhibitor correspondingly.

3.3. EFM Tests

EFM is a no damaging corrosion tests that can straight and quickly measure the corrosion current data without prior information of Tafel slopes, and with only a lesser polarizing signal. These benefits of EFM test make it an ideal applicant for online corrosion observing [47]. The higher strength of the EFM is the causality factors which attend as an inner check on the power of EFM calculation.

Figure 4 displays the EFM of Cu in nitric acid solution inclosing altered dose of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-

Table 4. Outcome data gotten from EIS test for Cu in 2 M HNO3 in the nonexistence and existence of unlike dose of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile compound at 30˚C ± 0.1˚C.

Figure 4. EFM data for Cu nonexistence and existence of different dose of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile composite at 30˚C ± 0.1˚C.

3-carbonitrile compound at 30˚C ± 0.1˚C. The harmonic and intermodulation peaks are obviously visible and are much greater than the background noise. The investigational EFM value was preserved utilized two unlike models: complete dispersion control of the cathodic reaction and the “activation” model. For the second, a set of three non-linear equations had been explained, pretentious that the corrosion potential does not exchange due to the polarization of the electrode working [48]. The greater signal was utilized to measure i c o r r , ( β C and β a ) and (CF-2 and CF-3). These parameters gotten from EFM were recorded in Table 5. The data demonstration that, the appending of tested composite at unlike doses to the acidic solution lower i c o r r , signifying that this composite hinder the corrosion of Cu concluded adsorption. The CF gotten under altered experimental conditions are nearly equal to the values gotten from theoretical Equations (2) and (3) representing that the calculated data are confirmed and best quality. % I E E F M was improved by improving the inhibitor dose and was measured as from Equation (4):

I E E F M = [ 1 ( i C o r r / i C o r r ° ) ] × 100 (4)

where i C o r r ° and i C o r r are current nonexistence and existence of inhibitor, correspondingly.

3.4. SEM Examination and EDX Analysis

The creation of a defending surface film of inhibitor at the electrode surface was further established by SEM clarifications of the Cu surface. Also, in order to see whether the organic additive is adsorbed on the Cu surface or not, both SEM and EDX tests were occurred. Figure 5 displays the SEM of fresh Cu surface nonexistence any appending of acid or the inhibitor. The images for Cu surface unprotected to 2.0 M HNO3 solution nonexistence and existence the appending of the optimum dose of the 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile composites are exposed in Figure 5. As

Table 5. Outcome data gotten from EFM test for Cu in 2 M HNO3 in the a in nonexistence and existence of unlike dose of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile at 30˚C ± 0.1˚C.

Figure 5. SEM images of Cu in 2.0 M HNO3 solution after inundation for 3 days nonexistence inhibitor and in existence of 11 × 10−6 M of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile.

can be gotten, there was a noticeable perfection in the surface image of Cu that was preserved with the inhibitor due to the creation of an adsorbed protecting film of the inhibitor at the Cu surface.

The EDX profile examination exists in Figure 6. The EDX review spectra were utilized to measure which elements of inhibitor existed on the electrode surface earlier and later contact to the inhibitor solution. For the coins’ nonexistence inhibitor behavior (Figure 6), only Cu was noticed. This is established by utilizing XRD, the chief corrosion yields designed on exposed Cu to nitric acid were

Figure 6. EDS images of Cu in 2.0 M HNO3 solution after inundation for 3 days nonexistence inhibitor and in existence of 11 × 10−6 M of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile.

recognized as the basic Cu nitrate, gerhardtite (Cu2(NO3)(OH)3) and to a slighter amount cuprite (Cu2O) [49] [50]. It is observed the existence of the C, O and N signal in the EDX spectra in the example of the coins showing to the inhibitor, could be qualified to the adsorption of organic moiety at the surface of Cu. The rise in quantity of C atom in the item of assembles (15.73%), specified that the liquefaction of Cu is very hinder by composite and thus shows a very high hinder capacity. Also, a strong enrichment with C is renowned in the example of campsite (see Table 6). The EDX of Figure 6 display that the O is significantly

Table 6. Element gotten from EDX of copper in 2.0 M HNO3 solution after inundation for days nonexistence of inhibitor and in existence of 11 × 10 −6 M of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile.

suppressed relative to the coins ready in 2.0 M HNO3 solution, and definitely this suppression will improve with improve examined dose and engagement time. The destruction of the O occurred due to the overlying inhibitor film. Also it is significant to notification the quantity of Cu peaks of EDX spectra is rise in the existence of inhibitor in a contrast of EDX analysis gotten in the nonexistence of inhibitor might representative that the examined molecule defensive the Cu surface in contradiction of acid corrosion. The configuration of the distinguished elements on the surface of Cu designates that the inhibitor molecule is powerfully adsorbed on the Cu creating a Cu-examined molecule bond, thus hinder the surface against corrosion.

3.5. Mechanism of Inhibition

Protection of the corrosion of Cu in 2.0 M HNO3 solution by examined composite is measured by PP measurements, EIS, EFM and SEM studies; it was obtained that the protection efficiency relies on dose, metal nature, the manner of adsorption of the inhibitors and surface environments.

The corrosion hindrance is due to the inhibitors have adsorbed at the interface of solution/electrode, the amount of adsorption of an inhibitor rely on the type of the metal, the adsorption mode of the inhibitor and the conditions of surface. Adsorption on Cu surface is expected occurred mostly among the active site involved in the inhibitor and would rely on their charge density. The lone pairs of electrons transfer on the N atoms to the Cu surface to procedure a coordinate kind of linkage is favored by the existence of a vacant orbital in Cu atom of little energy.

It was decided that the kind of adsorption rely on the attraction of the Cu to the clouds π-electron of the ring structure. Metals for example Cu, which have a better affinity near aromatic moieties, were gotten to adsorb benzene rings in orientation flat.

2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile assembled displays best hindrance power due to: i) the attendance of CH3 group which is an electron giving group, also this CH3 will improve the electron charge density on the structure, ii) its bigger size of molecular weight (329.25) that may simplify enhanced surface coating, and iii) its adsorption among five active site.

3.6. Conclusions

1) The analysis details of composite reveal that, it is an excellent corrosion hindrance for Cu in 2.0 M HNO3.

2) C d l breaks down with respect to the blank solution when adding inhibitor. This fact may be decided by inhibitor molecule adsorbed on the surface of Cu.

3) EFM can be utilized for calculation of corrosion in a lack of prior data of Tafel lines slope.

4) The morphology of Cu existence and nonexistence was observed by (SEM) and (EDX).

Cite this paper
Eldesoky, A. , Attia, A. , Ahmed, O. , Abo-Elsoud, M. , (2019) Electrochemical and Surface Characterization Studies of 2-amino-6-methyl-5-oxo-4-phenyl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile Compound on Copper in 2 M HNO3. Journal of Materials Science and Chemical Engineering, 7, 71-86. doi: 10.4236/msce.2019.712009.

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