ELECTROCHEMICALAND SURFACE CHARACTERIZATION STUDIES ON C38 STEEL IN 1 M HYDROCHLORIC ACID MEDIUM USING PROP-2-EN-1-ONE DERIVATIVES AS CORROSION INHIBITORS

Eldesoky *5 . 1. Physics Department, Umm Al-Qura University College in Qunfudah-Female-KSA. 2. Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, Egypt and Faculty of Science, Chemistry Department, University of Tabuk, KSA. 3. Textile Technology Department, Industrial Education College, Beni-Suef University, Egypt and Chemistry Department, Faculty of Science, Jazan University, KSA. 4. Ophthalmology Dept., Faculty of Medicine, Mansoura University, Egypt and Al-Qunfudah Center for Scientific Research (QCSR), Chemistry Department, Al-Qunfudah University College, Umm Al-Qura University, KSA. 5. Engineering Chemistry Department, High Institute of Engineering &Technology (New Damietta), Egypt and Al-Qunfudah Center for Scientific Research (QCSR), Chemistry Department, Al-Qunfudah University College, Umm Al-Qura University, KSA. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

1193 rise inhibition protection, best thermal stability and prevent the odor irritating for alloys and metals in different aggressive solution [17][18][19][20][21][22] . Therefore, the improve of novel adjuster inhibitors include 4-aminoantipyrineheterocyclic ring and the research of the relations among the chemicalstructure of inhibitors and their protection led to the higher significance in theoretical points and industrial.
In this study,the protection effect and electrochemical habit of prop-2-en-1-one derivatives for C38 steel contain 1 M HClacid are given by the tafel polarization, (EIS) and (EFM) tests. SEM and EDX examination of the C38 steel in 1 M HCl surface revealed that these compounds prevented C38 steel in 1 M HCl from corrosion by adsorption on its surface to form a protective film and acts as a barrier to corrosive media.
Experimental Methods:-Materials and Medium:-C38 steel was utilized for the calculation of corrosion. It's percent composition is 0.38 wt.% C, 0.66 wt.% Mn, 0.27 wt.% Si, 0.02 wt.% S, 0.015 wt.% P, 0.21 wt.% Cr, 0.02 wt.% Mo, 0.22 wt.% Cu, 0.06 wt.% Al and the remainder iron. The corrosion dose (1 M HCl) (37%analytical grade) was ready by hydrochloric acid dilution with water double distilled. The organic inhibitors used in this study were some organic compounds [23] , listed in Table (1). Methods:-Electrochemical Tests:-Electrochemical tests were lead to three electrodes cell thermostatic utilized a Gamrypotentiostat/galvanostat/ZRA (model PCI300/4). A saturated calomel and platinum electrode were utilized as reference and auxiliary electrodes. The C38 steelelectrodes were 10x10 ml and were welded with a copper wire on one side. All methods were done at temperature (25 ± 1 O C). The potentiodynamic diagrams were measured from -50 to 50 V at a rate scan 1 mV S -1 after the steady state is approached (30 min) and the open potential circuit was observed after putted the electrode for 15 min in the solution test. The (θ) and % IE were measured from Eq. (1): 0 corr i and corr i are the current corrosion densities lack and attendance of solution inhibitor, consecutively.
(EFM) and (EIS) tests were obtain by utilized the same methods as before with a Gamry framework system depend on ESA400. EchemAnalyst 5.5 Software was utilized for drawing, graphing and fitting data. EIS tests were done in a range of frequency of 100 kHz to 10 mHz with amplitude of 5 mV peak-to-peak ac signals utilized at respective for potential corrosion. EFM had done utilized 2 frequencies 2 and 5 Hz. The frequency base was 1 Hz. In this research, we utilized a signal perturbation with amplitude of 10 mV for both frequencies perturbation of 2 and 5 Hz.

SEM-EDX Tests:-
The surface of C38 steel was obtain by keeping the coins for 3 days putted in 1 M hydrochloric acid with and lack of perfect dose of prop-2-en-1-one derivatives, after abraded mechanically utilized unlike papers emery up to grit size 1200. Then, after this time immersion, the samples were lotion gently with distilled water, carefully dried and mounted into the spectrometer attendance of further treatment. The surface of alloy was tested utilized an X-ray diffractometer Philips (pw-1390) with Cu-tube (CuK α , l = 1.54051 Ǻ), (SEM, JOEL, JSM-T20, Japan).

Results and Discussion:-
PotentiodynamicPolarization Measurements: -Polarization tests were done to gain knowledge concerning the kinetics of the cathodic and anodic reactions. Figure  1 shows the polarization behavior of C38 steel electrode in 1 M HClwithout and with unlike dose of inhibitor (1). Figure 1 gives that both the cathodic and anodic reactions are impressive by the putting of investigated prop-2-en-1one derivatives and the protection efficiency improve as the inhibitor dose rise, but the cathodic reaction is more inhibited, i.e the addition of prop-2-en-1-one derivatives lower the anodic liquefaction of alloyand prevent the cathodic reactions. Therefore, prop-2-en-1-one derivatives are play as mixed kind inhibitors.
The data in Table 2 given corrosion current density lower obviously after the appending of inhibitors in 1 molar acid and % IE rise with higher the dose of inhibitor. The E corr with inhibitor was improve with no definite trend, lead to that these inhibitorsplay as mixed-kind inhibitors. %IE p was record by utilized equation:

%IE p =[i o corr -i corr )/i o corr ]x100
(2) where i corr and i o corr are the inhibited and lack inhibited current corrosion densities, respectively.
It is evident from Table 2 that the (β a ) and (β c ) Tafel lines equal upon unchanged appending of organic derivatives, improvement to a nearly parallel set of anodic lines, and almost parallel cathodic curves record too. The inhibitors adsorbed lower the surface area for corrosion without impressive of the mechanism corrosion of alloy in acidic solution [24,25] . The orders of % IE were: (1) > (2). This order may lead to free electron pair in substituent in the molecular structure, N 2 atom andπ electrons on aromatic nuclei of the inhibitor. This method confirmed the rise in ability of (1) to inhibit in acidic corrosion of alloy as analogy to (2).  (EIS) Tests:-EIS is a powerful method in the research of corrosion. Mechanistic information, properties of surface and kinetics of electrode can be given from impedance plots [26][27][28][29][30] . The Nyquist diagrams do not give best semicircles as theory expected of EIS. The change from ideal semicircle due to the dispersion of frequency [31] as well as to the inhomogeneity's of the surface. EIS of the additives organic were calculated utilized the equivalent circuit, Figure 3, the best fit circuit in our experimental data results [32] . The C dl (double layer capacitance) is measured from Eq. After test the shape of the Nyquist curves, the corrosion process was controlled mainly charged-transfer [33][34][35][36] . From the EIS data (Table 3), we noted that the data of R ct rise with rising the dose of the inhibitors and this lead to a rise in % IE, which in obeys with the mass reduction results given. Data of capacitance double layer are also lower to the maximum inhibitor extent. The lower in CPE/C dl data from a lower in local dielectric constant and/or an improve in the double layer thickness, given that organic derivatives protect the C38 steel from corrosion [37,38] . The main advantages of EIS are to follow the corrosion behavior of the metal with constant time. The inhibition efficiency was calculated from the charge transfer resistance data from equation (4) [39] :

% IE EIS = [1 -(R°c t / R ct )] x 100
(4) where R o ct and R ct are the charge-transfer resistance values without and with inhibitor, consecutively.

EFM Method:-
The advantages of EFM test give it an ideal for online monitoring of corrosion [40] . The causality factors is higher strength data of the EFM which act as an internal check on verified data and of the EFM test. The CF-2 and CF-3 are record from the frequency spectrum of the responses current. The data of (EFM) in acidic solution with and 1197 without various doses of prop-2-en-1-one derivatives given in Figure 4. The same plots were obtained for other compound (not shown). The two higher peaks, with amplitude of about 200 µA, are the given to the 40 and 100 mHz (2 and 5 Hz) excitation frequencies. The EFM experimental data were utilized two unlike models: diffusion complete control of the cathodic reaction and the "activation" model [41] . The higher peaks were utilized to measure the (i corr ), (CF-2 and CF-3) and (β c and β a ). The EFM parameters were given in Table 4 show that, the appended of any one of tested compounds at a given dose to the acidic solution lower the current corrosion density, lead to these compounds protect the corrosion of alloy through adsorption. The best data of CF-2 and CF-3 in Table 4 are similar to their theoretical data of 2.0 and 3.0, respectively lead to the calculated value are quality good.

(SEM) Tests:-
The micrography given from coins of C38 steel without and with of 11 x 10 -6 Mprop-2-en-1-one derivatives after putted for 3 days given in Figure 5. The surfaces suffer from severe corrosion attack in the blank sample. Due to the stress out when the compound adding in the solution, the morphology of alloy surfaces is quite unlike from the preceding one, and the tests surfaces were smoother. We observed a film formation which distributed in a random way on the whole alloy surface. This may be interpreted as due to the adsorption of the prop-2-en-1-one derivatives on C38 steel surface merger into the passive film in order to the active site block on alloy. Resulting in a lower in the contact among alloy and the aggressive medium and sequentially obtain best inhibition effect [42,43] .

(EDS) Test:-
The EDS spectra were utilized to measure the elements found on the surface of C38 steel and after 3 days of covered in the lack and attendance of 1M HCl. Figure 6 gives the EDS result measured on the composition of C38 steel only without the acid and inhibitor modified. The EDS record that only oxygen and iron were observed, which given that the passive film found with only Fe 2 O 3 .
The EDS tests of C38 steel in 1 M HCl only and with of 11x10 -6 M of prop-2-en-1-one derivatives portrays in Figure 6. The spectra give additional lines, lead to the presence of C (the carbon atoms of prop-2-en-1-one derivatives). These values give that the O and C atoms covered surface. The elemental observed is record in Table 5.   iii) The lower in %IEcorrosion with improve temperature lead to desorption of the adsorbed inhibitor molecules obtain. iv) The %IE relies on charge density and their equipment of adsorption centers in the molecule.
It was observed that the type of adsorption relies on the affinity of the C38 steel towards the clouds of π-electron of the ring. Metals such as iron, which have a higher attract towards aromatic moieties, were obtain to adsorb benzene rings in orientation flat. The order of lowering the % IE are given: 1 >2.
Compound (1) exhibits excellent inhibition power due to: (i) the presence ofp-OCH 3 group which is an electron donating group with negative Hammett constant (σ = -0.27), Also this group will increase the electron charge density on the molecule,(ii) its larger molecular size that may facilitate better surface coverage, and (iii) its adsorption through two active centers. Compound (2) has the lowest inhibition efficiency. This is due to presence of p-Cl which has positive Hammett constant (σ=+0.23), i.e. group which lower the electron density on the molecule and hence, lower inhibition efficiency.

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Conclusion:- All the investigated compounds are good corrosion inhibitors for C38 steel in 1 M HCl solution. The effectiveness of these inhibitors depends on their structures. The variation in inhibitive efficiency depends on the type and the nature of the substituent present in the inhibitor molecule.  Double layer capacitances decrease with respect to blank solution when the inhibitor added. This fact may explained by adsorption of the inhibitor molecule on the C38 steel surface.  EFM can be utilized as a fast and nondestructive tests for calculation of corrosion without prior information of Tafel lines  The data from electrochemical tests were in best agreement. The % IE of these compounds investigated is: 1 > 2.  The heteroatoms N and O are the active sites ofthe prop-2-en-1-one derivatives. It can adsorb on Fe surface firmly by donating electrons to Fe atoms and accepting electrons from 3d orbital of Fe atoms.