Anticorrosion Protection of New Composite Coating for Cobalt-Based Alloy in Hydrochloric Acid Solution Obtained by Electrodeposition Methods

Abstract

In this work, electrochemical deposition techniques (galvanostatic and potentiostatic) were used to obtain coatings of a new composite polymer, 3-methylpyrrole—sodium dodecyl sulfate/poly 2-methythiophene (P3MPY-SDS/P2MT), on cobalt-based alloy samples for anti-corrosion safety. The use of sodium dodecyl sulfate as a dopant ion in electrosynthesis can have a relevant effect on the anticorrosive property of the composite polymer layer by blocking the entry of corrosive ions. The cobalt alloy specimen had an important impact on the electrochemical performance of the composite coating and this together with the presence of the polymeric layer was achieved by simultaneously constitution of a complex oxides film and polymeric layers. The polymeric coatings were analyzed using scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and cyclic voltammetry (CV) methods. The corrosion protection of the P3MPY-SDS/P2MT-covered cobalt-based alloy was explored using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization procedures in a 1 M HCl solution. The corrosion speed of the P3MPY-SDS/P2MT-covered cobalt-based alloy was observed to be ~10 times less than an uncovered specimen, and the effectiveness of the composite layers of this coating is greater than 91%. This superior efficaciousness was obtained by the electropolymerization of P3MPY-SDS/P2MT at current densities of 1 mA/cm² and 0.5 mA/cm², applied potentials of 0.9 V and 1.0 V, and a molar ratio of 5:1. Corrosion test results indicate that the P3MPY-SDS/P2MT coatings provide a good result: protection against the corrosion of a cobalt-based alloy in aggressive solutions.

1. Introduction

Currently, the defense of metallic materials utilizing polymers as advanced covering materials is one of the most interesting exploration fields [1,2,3,4,5,6,7,8]. The deterioration of metallic materials causes considerable economic and technical preoccupation. In manufacturing processes, the surfaces of metallic materials used are exposed to seriously corrosive acidic and basic solutions which induce corrosion, an appreciable form of destruction. Some research studies conducted on the protection of metals in the field of technology have established that the use of composites is the most effective and simple method of preventing damage to metallic samples in aggressive solutions [9,10,11,12,13,14,15,16,17,18]. The acquisition of novel composites from a distinct monomer was carried out to increase the physicochemical features of a coating, extend its long-term defense, to increase adhesion, and to improve its electrochemical characteristics. One of the main aspects of using conducting polymers for the corrosion protection of these materials is their permeability to water, which can cause the transfer of existent corrosive constituents to the metal zone. These composite coatings frequently increase the endurance of metals in the face of several aggressive factors. The effectiveness of these defensive layers that ensure a barrier on the surface can be determined by different constituents: the type of conducting polymer, the electrochemical deposition practice that was employed on the electrode substrate, and the corrosive media [19,20,21,22,23,24,25,26,27]. The use of electropolymerization procedures, nanostructured coverings, the implementation of inorganic–organic coatings, and cathodic and anodic defenses are practices for the anti-corrosion defense of metals and their alloys. Metals and their alloys are broadly used in various areas such as chemical production, petroleum manufacturing and refining, the building industry, engineering equipment, industrial apparatus, and marine procedures; this has perfected the exploration of anticorrosion performance in various aggressive media. While corrosion is an actual element in the deterioration of manufacturing structures, a considerable number of determinations were effectuated to establish processes to diminish corrosion and “wear costs”. The protective mechanisms of conductive polymers have been explained using numerous hypotheses, such as that conductive polymers cause an electric field on the material substrate, preventing the passage of electrons from the metal to the oxidizing medium; that conductive polymers engender a dense and short porosity layer on the specimen substrate, constituting a barrier between the metal and the aggressive medium; and that they make formatting a protective metal oxide film onto the surface of the sample possible. Many research studies have established that conductive polymers in various situations can recover their original mechanical and electrical characteristics without important degradation [28,29,30,31,32,33,34]. Conducting polymers are effective for fast doping and de-doping with high charge densities; consequently, they are materials with special properties for use in various electrochemical processes. Conducting polymers are also an interesting molecular model owed to their significant ability to change characteristics whenever actuated by an electric sign. Conducting polymers like polythiophene, polypyrrole, and polyaniline and their derivatives are currently the most widely used polymers for coating protection [35,36,37,38,39,40,41,42,43,44,45,46]. Hence, it is assumed that the integration of hydrophobic functional groups increases the protective capacity of polymers. Dopants incorporated into polymers provide control over the electrodeposition practice and the attributes of the achieved polymeric composites [47,48,49,50,51,52,53,54]. The application of dopant ions in electrochemical polymerization can have an important effect on the number-selective ion exchange of polymers. In various situations, the incorporation of great hydrophobic dopant ions (surfactants) results in an efficient cation exchange with a fully hydrophobic character.

Cobalt alloy materials possess interesting properties; specifically, they demonstrate good physical properties and chemical and mechanical resistance and function at extreme temperatures, e.g., they endure serious deterioration due to metal-to-metal contact, wear, hot corrosion, and the erosion of aircraft motor components. Co alloys are frequently utilized in the automotive industry in various components, in nuclear reactors, and in different areas of the petrochemical, energy, and food industries. Cobalt alloys with different alloying elements to improve their properties are also used in the aerospace industry, in medical equipment, as particular metallic biomaterials, and as finishings for industrial instruments for woodworking [52,53,54,55,56,57]. The corrosion and wear of Co alloy were explored in highly acidic and basic environments, in chlorinated and saline media, in a sulfuric acid medium, and in slightly alkali media (at a pH of 10); though the outcomes of these tests are difficult to explore, and general corrosion parameters were complicated to obtain. Protective action on a Co alloy is especially important and has been considered by a great number of researchers. At present, research on the operation of inhibitors on Co substrates and their protection process has been completely intensified, and exciting developments have been made in corrosion control [51,52,53,54,55,56,57]. Tengda Ma et al. investigated the protection efficiency of disulfide derivatives against Co alloy corrosion in an alkaline environment; the corrosion protection performance of DDA and DPD reached up to 90%. Additionally, R. Popuri et al. estimated the corrosion protection effectiveness of potassium oleate as an inhibitor on Co; their outcomes indicated that the corrosion rate of Co in the presence of PO is ~9–10 times lower than when uninhibited. M. Behazin et al. studied the influences of γ-radiation on the corrosion of a Co alloy at pH values of 6.0, 8.4, and 10.6, and the results of this study indicate that γ-irradiation raises the oxidation rate of Co, but this effect intensifies with changes in pH. Irina Smolina et al. explored the wear and corrosion resistance of laser surface alloyed (LSA) cobalt alloy rhenium by utilizing an LDF diode laser (4000 W) [51,52,53,54,55,56,57].

In previous works, we studied the protection performance of different composite polymer films obtained from different conducting polymers (polyaniline, polypyrrole, and polythiophene and their derivatives: PPY-AOT/PNEA, PNNDMA/PPY-SDS, PNMPY-TW20/P3MT, PNMPY-1SSD/P2MT, and PNMPY-TRX-100/PNNDEA) under the influence of different dopants (surfactants with large hydrocarbonate chains such as AOT, SDS TRX100, TW20, 1-SSD, and SDBS) made using different electrochemical methods (potentiostatic, galvanostatic, and cyclic voltammetry procedures) on different substrates (OL 37, OLC45, OL50, copper, and brass alloy) in different corrosive environments where the results were remarkable: every time, the composite polymer films had an efficiency of over 90%, and the corrosion rate was 9–10 times lower than that of an uncoated substrate [10,14,20,38,40,50]. By exploring the efficaciousness of composite coatings, this research aims to ensure a possible method to diminish corrosion and enhance the lifetimes of metals and their alloy constituents. The motivation of this work is to obtain a novel polymer composite suitable for the corrosion protection of various metallic materials, as well as the expansion of suitable electrochemical deposition practices that will provide the ability to achieve homogeneous, compact, and highly adhesive composite coverings on metal surfaces. Another area of interest is the realization and optimization of new composite coatings with the best protective properties for certain materials in aggressive solutions. These new coatings are different from those presented in the specialized literature and have obtained better results. This work describes the electrochemical deposition and electrochemical and spectroscopic investigation of a new coating, poly (3-methyl pyrrole-sodium dodecylsulfate/2methyl thiophene) and the corrosion behavior of this composite coating. This research is a continuation of prior work on obtaining and evaluating a suitable coating for the corrosion protection of metals in aggressive environments. The new polymeric composite (P3MPY-SDS/P2MT) was electrochemically deposited on a cobalt-based alloy electrode using galvanostatic and potentiostatic practices from synthesis solutions of 0.1 M 3-methylpyrrole, 0.1 M 2-methyl thiophene, and 0.03 M sodium sulfate and a 0.2 M sodium salicylate solution. The evaluation of this composite was performed using FT-IR spectroscopy, cyclic voltammetry, and SEM methods. Corrosion tests of the P3MPY-SDS/P2MT-coated cobalt alloy were performed using potentiodynamic polarization and EIS techniques in 1 M HCl media.

2. Experimental Section

2.1. Materials and Methods

In this study, a cobalt-based alloy electrode was utilized as the working electrode for the evaluation of corrosion. The structure of the cobalt-based alloy is as follows: Co% 67, Cr% 29, and W% 4 (the alloy was from supplier TECHNOPLUS SRL-rod form, Bucharest, Romania), and the aggressive medium was 1 M HCl achieved by diluting AG 36% HCl (from Merck, Rahway, NJ, USA) with bi-distilled water. All chemicals were of reagent grade. Sodium dodecylsulfate (SDS), 3-methylpyrrole (3MPY), and 2-methyl thiophene (2MT) were from Aldrich (>98%), and sodium salicylate (C₇H₅NaO₃) was obtained from Sigma-Aldrich, St. Louis, MO, USA. In all experimental tests, synthesis media were made using bi-distilled water: 3MPY, 0.1 M; SDS 0.03 M; 2MT, 0.1 M; and C₇H₅NaO₃, 0.2 M. The electrochemical deposition and examination of the new composite material were performed using a single electrochemical cells of each of the three conventional (typical) samples installed. The working cell was connected to a VoltaLab potentiostat/galvanostat, and data were logged in computer-controlled VoltaMaster 7.09 software. The reference electrode was a saturated calomel electrode, and the auxiliary electrode was a platinum sheet. Our sample was a cylindrical cobalt-based alloy with a surface of 0.2 cm². This form is preferred as it assures a considerable region without corners. The cobalt alloy electrode was mechanically smoothed using a sequence of sheets of sandpaper of diversified sizes (200–4000 grid) until a mirror shine was achieved. The cobalt alloy sample was then washed in acetone to detach all residues, after which it was rinsed in bi-distilled water, dried at room temperature, and placed into the working cell. All tests were performed at 25 °C in atmospheric oxygen without stirring. Prior the electropolymerization of the composite, the cobalt alloy specimen was passivated in a 0.2 M sodium salicylate medium via cyclic voltammetry in a domain of −500 mV to 1500 mV for the SCE at a potential scan rate of 20 mV/s with the implementation of 3 cycles. The poly (3-methylpyrrole–SDS/2 methyl thiophene) coatings were electrochemically deposited from 0.1 M 3-methylpyrrole, 0.03 M SDS, 0.1 M 2-methyl thiophene, and 0.2 M sodium salicylate on the cobalt alloy’s passivated surface via galvanostatic and potentiostatic procedures (Scheme 1).

Electrochemical deposition was performed using the galvanostatic method at constant current densities of 0.5 mA/cm² and 1 mA/cm² and using the potentiostatic technique at potentials of 0.9 V and 1.0 V and at different molar ratios (5:1 and 1:5), and the electrodeposition was left for 10 min and 20 min. The adhesion of this coating was realized through the “standard sellotape test”, which “involves cutting the film into small squares, sticking the tape”, and then detaching it. Appropriate adhesion was determined by the ratio of the number of remaining adherent cover squares to the total number of the squares (Scheme 2). The electrochemical behavior of the composite coatings was explored in a 0.2 M sodium salicylate electrolyte using cyclic voltammetry practices. The corrosion protection of the coating and bare specimens was examined using potentiodynamic polarization procedures and electrochemical impedance spectroscopy in a hydrochloric acid solution. An investigation of Tafel polarization curves was accomplished by switching from cathodic to anodic potentials for the OCP to a scan estimate of 1 mV/s. EIS experiments were realized in the frequency range from 100 KHz to 0.04 Hz and a signal amplitude of 10 mV for the OCPs of uncoated and coated samples. All potentials were recorded vs. the SCE. Each experimental test was carried out three times to examine reproducibility.

2.2. Instruments

A VoltaLab PGZ 402 potentiostat/galvanostat (Radiometer analytical, Lyon, France) configuration was used in all electrochemical determinations. Composite coverage was effectuated using a Bruker Optics Tensor 37 FT-IR spectrometer (via ATR), Ettlingen, Germany, in the spectral domain, 4000–650 cm⁻¹, at a resolution of 4 cm⁻¹. The morphologies of the covered specimens were examined by scanning electron microscopy (SEM). Substrate morphology explorations were performed by SEM in a dual-beam FEI Quanta 3D FEG model (Brno, Czech Republic) with an energy-dispersive X-ray (EDX) spectrometer operating in high-vacuum mode with an accelerating voltage of 2 kV to 30 kV. Minimal sample’s training implicates immobilizing the specimens on a double-sided carbon tape, without coating.

3. Results and Discussion

3.1. Electrochemical Deposition of P3MPY-SDS/P2MT Coating on Cobalt Alloy

Electrochemical polymerization of the 3MPY-SDS and 2MTP monomers was performed by applying the galvanostatic and potentiostatic practices on the passivated surface of the cobalt-based alloy support. The passivation technique was realized via the voltammetry process in a range from −0.5 V to 1.5 V vs. the SCE at a 20 mV/s scan rate in a 0.2 M sodium salicylate medium, implementing three cycles. These proceedings were related in prior works [10,40,51]. The insoluble constituents achieved via the passivation process are complexes of cobalt oxides and cobalt salicylates that impede the metal from dissolving without complicating the electrochemical polymerization technique [51,53,54,55,56]. By developing polymerization parameters, we were able to achieve composite films of P3MPY-SDS/P2MT that have a significant protective impact. The electrochemical polymerization of 3MP and 2MT monomers was accomplished on passivated cobalt alloy surfaces. After passivation, the electrosynthesis of the monomers was achieved without modifying the polymerization properties. A successful deposit requires a passivated layer, which could be efficacious in stopping the dissolution of the oxidizable metal without hindering the permittivity of the monomer after oxidation. The end impact is a homogeneous, dense, and adhesive polymer layer on the surface electrode. The P3MPY-SDS/P2MT coating was made from 0.2 M sodium salicylate, 0.1 M 3-methylpyrrole, 0.03 M Na dodecylsulfate, and 0.1 M 2-methyl thiophene via a galvanostatic process at current densities of 0.5 mA/cm² and 1 mA/cm² and using a potentiostatic technique at potentials of 0.9 V and 1.0 V differing molar ratios.

Electrochemical deposition was enabled for 10 min and 20 min. Figure 1 shows the “current density–time” curves through the formation of P3MPY-SDS/P2MT coatings on cobalt alloy samples at applied potentials of 0.9 V and 1.0 V and different molar ratios. After oxidation times of 600 s and 1200 s, the initial shape of the “current density–time” plot throughout the estimation of the electrochemical deposition of the polymer indicates that this submission was established by “nucleation and growth” on the cobalt alloy support [8,24,33]. Initially, the current was immediately reduced due to the “electro-adsorption” of the sodium salicylate and 3MPY:2MT monomers. After about 30 s, the current increased due to the dissolution of the passive layer and the establishment of the polymer on the cobalt alloy support. In the end stage, the current was held steady as the polymer composite was obtained on the cobalt alloy substrate. The transient change in the higher side is linear with the gradient of the nucleation period, the electrochemical examination, and the distinction in the molar ratio of 3MPY:2MT. When the potential was 0.9 V at molar ratios of 5:1 and 1:5, the current was approximately constant at 1.5 mA/cm² and 2 mA/cm²; the current was greater than in other potentiostatic electrodeposition circumstances, and the layers obtained were homogeneous and adhesive. From Figure 1, the potentiostatic electrodeposition at an applied potential of 0.9 V and a 3MPY:2MT molar ratio of 1:5 has a longer induction period for obtaining a P3MPY-SDS/P2MT layer and is less favorable for the construction of a polymer better features. Electrochemical characteristics such as the applied potential were determined to have great influence on the “induction time”.

It can be observed that the 0.9 V and 1.0 V applied potentials at molar ratios of 5:1 and 1:5 for 3MPY-SDS: 2MT each have a short induction period for the evolution of the electrodeposited film, which is appreciated for achieving high-quality coatings. SDS, as a dopant ion utilized in electrochemical deposition (present in 3MPY), can have a relevant impact on the selectivity of ion broadening by ensuring the conductivity of a polymer. A visional inspection of the cobalt alloy surface after electropolymerization revealed the formation of a black layer of P3MPY-SDS/P2MT. The coating was dense, compact, and adhered to the cobalt alloy substrate. Coating adhesion, as appraised by “the standard sellotape” method, was estimated to be ~75% [8,14,40].

Figure 2 displays the “potential–time” curves of the acquisition of the polymer film as poly (3-methylpyrrole-Na-dodecylsulfate/2-methyl thiophene) on the cobalt alloy surface (P3MPY-SDS/P2MT) at distinct applied current densities and varying molar ratios. After deposition intervals of 600 s and 1200 s, the primary configuration of the “potential–time” curves of the polymer’s electrochemical procedure indicates that the coating was achieved by “nucleation and growth” on the cobalt alloy area [8,24,33,34,35,36,40]. In Figure 2, at applied current densities of 0.5 mA/cm² and 1 mA/cm² at certain molar ratios, a shorter induction interval appears, and an induction of less than 5 s was observed in the electropolymerization of the film composite of 3MPY-SDS: 2MT; its value decreases with an increase in the molar ratio and an increasing “nucleation potential”.

The potential of electropolymerization is distinct between 0.92 V and 1.04 V for the SCE at an applied current densities of 0.5 mA/cm² and 1 mA/cm² at molar ratios of 5:1 and 1:5 for the 3MPY-SDS and 2MT. The composite coatings appear the most dense and adherent at an applied current density of approximately 0.5 mA/cm². A visional exploration of the cobalt alloy specimen through the deposit revealed the presence of a black layer of P3MPY-SDS/P2MT/cobalt alloy support. The coating adhesion, evaluated by the “standard sellotape” method, was approximately ~70%–75% [13,14,40].

3.2. Electrochemical Exploration P3MPY-SDS/P2MT Composite Coating

The electrochemical behavior of the modified P3MPY-SDS/P2MT/cobalt alloy specimen in 0.2 M C₇H₅NaO₃ (free monomer) is displayed in Figure 3 for the potential domain of −0.4 V and +1.5 V vs. the SCE and a scan speed of 20 mV/s. A cyclic voltammetry procedure was used in the prolonged potential range to take into account all the “physical and electrochemical” attributes of this coating. By exploring Figure 3, it can be stated (affirmed) that the electrochemical behavior of the covering is influenced by the number of cycles and the electrodeposition attributes. The resistance of any polymer in “reduced and oxidized” states is an important characteristic in numerous practices.

The fundamental factor responsible for the “lifetime of a conducting polymer” is the constant chemical participation of the matrix itself [20,33,38]. The resistance of the P3MPY-SDS/P2MT polymer coverage was controlled by cyclic voltammetry (without a monomer) in a sodium salicylate medium (see Figure 3). Consequently, this coating could be frequently cycled between “oxidized and reduced” conditions without an appreciable detrioration of the composite; the current density decreased with every cycle and finally attained a steady valuable. A polymer that exhibits a minimal decrease in current density following repeated cycling is more electrochemically stable.

3.3. FT-IR Evaluations

The novel composite polymeric covering was investigated using FT-IR spectroscopy (Figure 4) in the domain of 4000–650 cm⁻¹ and at a resolution of 4 cm⁻¹ (about four scans). FT-IR techniques can be utilized to emphasize the kind of bonding utilized to obtain a polymer composite. Distinctive peaks in the FT-IR spectra of the P3MPY-SDS/P2MT/cobalt alloy covered are displayed in Figure 4. The FT-IR determinations depict the occurrence of significant “absorption bands” in the P3MPY and P2MT electrodeposited on the cobalt-based alloy’s surface. The results of the FTIR examination correspond well with the views reported in [35,36,37,38,39,49,51], in which similar peaks were noted. The prominent bands in the transmittance spectra of 3MPY and 2MT that are presented in Figure 4a,b are the consequence of the spectrum of 3MPY indicated in Figure 4a, wherein considerable proportions of the band of the aromatic ring in 3MPY are positioned at 1542 cm⁻¹ and 1451 cm⁻¹ for C=C “stretching”, which is obviously highlighted. The indicative bands at 1378 cm⁻¹ and 2941 cm⁻¹ are ascribed to the N-H “stretching vibration” of the pyrrole ring and the CH3 stretching of the 3-methylpyrrole parts. The peaks of the CH chains at 1107 cm⁻¹, 1071 cm⁻¹ and 673 cm⁻¹ that can be categorized as “in-plane and out-of-plane” are shown in the polymer. Figure 4b presents the spectrum of 2MT; the peak at 2978 cm⁻¹ is attributed to the CH₃ stretching of the 2-methylthiophene units, and the peaks attributed to the “asymmetric and symmetric” C=C “stretching vibrations” of the 2MT ring are noted at 1553 cm⁻¹ and 1421 cm⁻¹. The bands found at 1037 cm⁻¹ and 767 cm⁻¹ establish the “C-S-C stretching” vibration of the “thiophene ring”.

The P3MPY-SDS/P2MT/cobalt alloy electrodeposition spectra, grouped by electrochemical practices, are shown in Figure 4c. The distinct peaks at 3463 cm⁻¹ and 3208 cm⁻¹ are attributed to the N-H stretching vibration in the polymer. The peaks displayed at 3518 and 3432 cm⁻¹ correlate with the OH stretching of the counterions. The peaks at 3110 cm⁻¹–2905 cm⁻¹ are allocated to the CH₃ stretching of the 3-methylpyrrole constituents. The band at 1221 cm⁻¹ represents the C-N of the pyrrole ring. Important attributions of the “aromatic ring” peaks in P3MPY are evident at 1567 cm⁻¹ and 1453 cm⁻¹ for C=C stretching, an existence clearly determined. The “absorption bands” placed at 1571 cm⁻¹ and 1463 cm⁻¹ are depicted in the “stretching vibration of the quinoid rings” (Figure 4c). The bands located at 1381 cm⁻¹ and 1318 cm⁻¹ are assigned to N-H “stretching vibration” in the methylpyrrole ring; the band sat 1660 cm⁻¹ and 1645 cm⁻¹ are attributed to C=C stretching. In the P3MPY-SDS/P2MT composite spectrum, bands appropriate for the “asymmetric and symmetric C=C stretching vibrations” of the 2-methylthiophene ring are observed at 1563 cm⁻¹ and 1462 cm⁻¹ (Figure 4c) [14,35,36,37,51]. The peaks revealed at approximately 1043 cm⁻¹ and 764 cm⁻¹ are attributed to the C-S-C stretching vibration of the 2-methylthiophene ring, and the peak at 1531 cm⁻¹ is associated with the C=C “stretching vibration”. The peaks at 1451 cm⁻¹ and 1308 cm⁻¹ are attributed to the “stretching vibration” of the CH₂ and CH₃ elements in the SDS, and the short peaks at 1071 cm⁻¹ and 670 cm⁻¹ are attributed to the S=O “stretching vibration” of the SDS ions. Occurrences of the links C=O and CH are indicated by “stretching vibrations” at 1678 cm⁻¹ and 1251 cm⁻¹, and most were assumed to be related to the enhancement of SDS in the polymer matrix. (Figure 4c). The bands at approximately 1070–770 cm⁻¹ are ascribed to the “in-plane” and “out-plane” C-H of the aromatic rings and to the “out of plane” vibration of the C-H-doped P3MPY in the sodium salicylate electrolyte (Figure 4c) [35,36,37,51]. By comparing Figure 4a,b with Figure 4c, one might assume that the P3MPY-SDS/P2MT coverage is electrosynthesized over the cobalt alloy support. The indicated bands of the monomer (MPY and 2MT) are presented in the spectrum of the coverage (P3MPY-SDS/P2MT) on the cobalt alloy electrode.

3.4. Electrochemical Investigation

3.4.1. Potentiodynamic Polarization Technique

The anticorrosive properties of the P3MPY-SDS/P2MT/cobalt alloy polymeric composite were evaluated in 1 M HCl using a potentiodynamic polarization procedure and electrochemical impedance spectroscopy. The polarization curves of uncoated and coated P3MPY-SDS/P2MT/cobalt alloy samples in a 1 M HCl solution are presented in Figure 5 and Figure 6. In addition, the polarization comportment of the cobalt-based alloy specimen was realized by a cobalt alloy coated with P3MPY-SDS/P2MT made using potentiostatic and galvanostatic techniques at varied current densities and potentials at different amounts and submission times. In this work, one of the biggest practices for protecting of the cobalt alloy in an aggressive environment is the use of composite layers which mitigate the anodic or cathodic corrosion process or both. The substrates covered by the P3MPY-SDS/P2MT demonstrated an appreciable mitigation of the cathodic and anodic currents which revealed reductions in the cathodic and anodic processes. The electrochemical experiments were performed in a 1 M HCl medium to estimate the defensive action of the polymeric films against corrosion. It can be noted from Figure 5 and Figure 6 that both the anodic metal dissolution and cathodic hydrogen reduction processes were impeded by the electrodeposition of these P3MPY-SDS/P2MT composites in the corrosive environment. This occurrence reveals that this covering has considerable action against the anodic and cathodic processes of the electrochemical practice.

The corrosion current density (i_corr), corrosion potential (E_corr), and anodic and cathodic Tafel slopes were taken into account by extrapolating the linear sides of the anodic and cathodic Tafel branches of the cobalt alloy surface coated with the P3MPY-SDS/P2MT coating; the details are shown in

Table 1. Kinetic parameters of covered and uncovered cobalt alloy specimens in 1 M HCl solutions at 25 °C.

The System P3MPY-SDS/P2MT/CoCrW	Ecorr (mV)	icorr (µA/cm2)	Rp kΩcm2	Rmpy	Pmm/year	Kg (g/m2h)	ba (mV/ Decade)	−bc (mV/ Decade)	E (%)	%P
CoCrW + 1 M HCl	−230	21	0.390	9.91	0.255	0.234	86	−90	-
P3MPY-SDS/P2MT, 1 mA/cm2, 1:5 molar ratio, t = 10 min	−146	0.67	41	0.316	0.008	0.0074	108	−102	95	0.0009
P3MPY-SDS/P2MT, 1 mA/cm2, 5:1 molar ratio, t = 10 min	160	0.39	49	0.180	0.0045	0.0042	80	−117	98	0.00003
P3MPY-SDS/P2MT, 1 mA/cm2, 1:5 molar ratio, t = 20 min	57	0.46	44	0.217	0.0055	0.0051	91	−93	97	0.00004
P3MPY-SDS/P2MT, 1 mA/cm2, 5:1 molar ratio, t = 20 min	180	0.33	59	0.155	0.0039	0.0036	119	−102	98	0.00003
P3MPY-SDS/P2MT, 0.5 mA/cm2, 1:5 molar ratio, t = 10 min	−232	0.63	37	0.297	0.0075	0.0070	94	−111	96	0.0001
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 10 min	−60	0.36	41	0.169	0.0042	0.0040	121	−87	98	0.00009
P3MPY-SDS/P2MT, 0.5 mA/cm2, 1:5 molar ratio, t = 20 min	−236	0.43	46	0.202	0.0051	0.0047	85	−88	97	0.0059
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 20 min	80	0.29	60	0.136	0.0034	0.0032	118	−94	98.5	0.00001

,

Table 2. Kinetic parameters of covered and uncovered cobalt alloy specimens in 1 M HCl solutions at 25 °C.

The System P3MPY-SDS/P2MT/CoCrW	Ecorr (mV)	icorr (µA/cm2)	Rp kΩcm2	Rmpy	Pmm/year	Kg (g/m2h)	ba (mV/ Decade)	−bc (mV/ Decade)	E (%)	%P
CoCrW + 1 M HCl	−230	21	0.390	9.91	0.255	0.234	86	−90	-
P3MPY-SDS/P2MT, 0.9 V, 1:5 molar ratio, t = 10 min	−242	0.97	36	0.451	0.011	0.010	109	−78	94	0.0007
P3MPY-SDS/P2MT, 0.9 V, 5:1 molar ratio, t = 10 min	−65	0.49	41	0.231	0.005	0.0045	107	−88	97	0.000095
P3MPY-SDS/P2MT, 0.9 V, 1:5 molar ratio, t = 20 min	−225	0.56	39	0.264	0.007	0.0066	83	−81	97	0.000016
P3MPY-SDS/P2MT, 0.9 V, 5:1 molar ratio, t = 20 min	80	0.37	44	0.174	0.0044	0.0041	77	−88	98	0.00063
P3MPY-SDS/P2MT, 1.0 V, 1:5 molar ratio, t = 10 min	−220	0.73	27	0.344	0.0088	0.0081	111	−91	95	0.0058
P3MPY-SDS/P2MT, 1.0 V, 5:1 molar ratio, t = 10 min	−130	0.47	39	0.22	0.0056	0.0052	76	−78	97	0.000054
P3MPY-SDS/P2MT, 1.0 V, 1:5 molar ratio, t = 20 min	−143	0.63	37	0.30	0.007	0.0069	69	79	97	0.0015
P3MPY-SDS/P2MT, 1.0 V, 5:1 molar ratio, t = 20 min	62	0.35	47	0.165	0.0041	0.0039	78	82	98	0.000033

and

Table 3. Kinetic parameters of covered and uncovered cobalt alloy specimens in 1 M HCl solutions at 25 °C at certain immersion periods.

The System P3MPY-SDS/P2MT/CoCrW	Ecorr (mV)	icorr (µA/cm2)	Rmpy	Pmm/year	Kg (g/m2h)	ba (mV/ Decade)	−bc (mV/ Decade)	E (%)
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 10 min 0 h	70	0.46	0.169	0.0042	0.0040	121	−87	98
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 10 min 24 h	38	1.16	0.547	0.0138	0.0129	74	−68	95
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 10 min 48 h	15	2.43	1.146	0.029	0.027	99	−86	88
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 10 min 72 h	24	3.29	1.469	0.037	0.034	93	−88	84
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 10 min 96 h	−2	4.96	2.341	0.059	0.055	95	−91	77

. Considering these polarization curves, it is evident that the corrosion potential of the covered cobalt alloy specimen is displaced at a more positive potential compared to the uncoated electrode. This situation may be due to the offensive corrosive constituents that touch the pores of the film as an effect of the formatting of the passive layers that prevent attacks on the cobalt alloy electrode.

An investigation of the bias curves from Figure 5 and Figure 6 and Table 1 and Table 2 shows that the electrochemical characteristics of the bare and deposition-coated cobalt alloy specimens at applied potentials of 0.9 V and 1.0 V and current densities of 0.5 mA/cm² and 1 mA/cm² at 10 min and 20 min for molar ratios of P3MPY-SDS/P2MT of 5:1 and 1:5 decreased like those for the cobalt alloy in the 1 M HCl medium. This coating has an excellent protective ability, whereas the P3MPY polymer was doped with sodium dodecyl sulfate. This SDS surfactant, applied in polymerization as a “dopant ion”, can have a substantial influence, changing the ion selectivity by contributing to the conductivity of polymer. The presence of the hydrocarbonate chains of SDS that “competitively adsorb” over the cobalt alloy substrate impedes the active centers and, as a result (effect), the Cl⁻ corrosive agent is obstructed from attacking the cobalt alloy surface, and protection is achieved [23,24,25,26,27,39,51]. Determinations (measurements) indicated that the corrosion speed of the P3MPY-SDS/P2MT-covered cobalt alloy was about ~10 times less than that noted for the uncoated cobalt alloy It is clear that these coatings hindered the effect of the attacking element (HCl) on the cobalt alloy. The corrosion behavior of the P3MPY-SDS/P2MT composite layer determined that the covered cobalt alloy had a significantly greater protective action and inferior corrosion speed than the bare cobalt alloy. Determinations of the defense performance of these coverings in times of immersion are shown in Figure 7 and Table 3. The impact of increasing the immersion period from 0 to 96 h on the corrosion defense of P3MPY-SDS/P2MT composite against the corrosion of the cobalt alloy in a 1 M HCl solution was investigated using potentiodynamic polarization. The effectiveness of the protection slowly decreases with increasing time. It can be seen that after an immersion time of 72 h, a slight increase in the corrosion rate is indicated. This is due to the degradation of the substrate’s morphology with the increasing immersion period as an effect of the alteration of the active area and may be caused by some existent defects on the defensive layer that allow for the admission of corrosive agents to the cobalt alloy–coating interface. The data reveal that the process of the redox reaction is complicated and may be led by electrolyte diffusion. It was determined that the cobalt alloy specimen had an important impact on the electrochemical performance of the composite layers and that with the presence of the polymeric layer, anodization of these coated samples was achieved through the simultaneous formation of a complex oxide film and polymeric layers. Analyzing Figure 5, Figure 6 and Figure 7 and Table 1, Table 2 and Table 3, it is indicated that the lowest corrosion speed and the highest protection performance were obtained by the P3MPY-SDS/P2MT composite at 0.9 V and 1.0 V, at current densities of 0.5 mA/cm² and 1 mA/cm² (at a 5:1 molar ratio, t = 20 min) at current density (at 5:1 and 1:5 molar ratios), and a very good defense was achieved at 1.0 V and 1 mA/cm² (at a 1:5 molar ratio, t = 10 min) versus the uncoated substrate in a 1 M HCl environment.

The corrosion processes of the composite-coated cobalt alloy and the bare sample in the HCl medium can be effectuated as follows [5,23,24,25,26,27,35,52,53,54,55,56,57,58]:

Anodic Process:

The dissolution of the metal (M=Co-Cr-W) as an anodic mechanism.

M→Mⁿ⁺ + ne⁻.

P3MPY_undoped − ne⁻→P3MPY_doped.

P2MT_undoped − ne⁻→P2MT_doped.

Cathodic process:

Oxygen reduction as a cathodic process.

2H⁺ + 2e⁻→H₂.

$\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.O_2+H_{2}O+2e\to 2H{O}^{-}$.

P3MPY_doped + ne⁻→P3MPY_undoped.

P2MT_doped + ne⁻→P2MT_undoped.

In the acid medium, the metal is oxidized to a superior valence state by dissolving in an anodic process. Products dissolved in the medium as oxygen and hydrogen ions are reduced by electrons accepted from the metal in a cathodic process.

The porosity (P) of the polymer composite (P3MPY-SDS/P2MT) (Table 1 and Table 2) is a particular parameter that must be evaluated whenever determining if a coating is adequate or not to protect the surface against corrosion. The porosity of the coating was estimated by the following Relation (1):

$$P=\frac{\mathrm{Rp}\left(\mathrm{uncoated}\right)}{\mathrm{Rp}(\mathrm{coate} d)}{10}^{-({\rm I}\Delta E_{corr}{\rm I}/{\beta }_a)}$$

(1)

P is the total porosity, Rp is the polarization resistance for the covered and uncovered cobalt-based alloy, ΔE_corr is the difference between the corrosion potential values of the covered and uncovered specimens, and β_a is the anodic Tafel slope of the uncovered cobalt-based alloy. In addition, the porosity values of the P3MPY-SDS/P2MT-coated cobalt alloy, determined via an electrochemical procedure, are 0.00001, 0.00003, 0.00005, 0.00009, and 0.0001 (at 0.5 mA/cm² and 1 mA/cm² current densities and at 0.9 V and 1.0 V applied potentials at a 5:1 molar ratio). The appreciable size of the porosity in the P3MPY-SDS/P2MT layer demonstrates a considerable enhancement of the protection action by obstructing the access of the aggressive agent (Cl⁻) to the cobalt alloy substrate as well as reducing the corrosion of the underlying cobalt alloy surface. The P3MPY-SDS/P2MT coatings were found to exhibit a lesser porosity value, indicating that the composite layer presented a dense and uniform construction of the coating.

3.4.2. Electrochemical Impedance Spectroscopy (EIS) Examinations

The anticorrosive activity of the P3MPY-SDS/P2MT composite coated onto a cobalt alloy in an HCl medium was analyzed using electrochemical impedance spectroscopy (EIS). Impedance tests were effectuated at the OCP in the frequency interval from 100 KHz to 0.040 Hz with an AC wave of ±10 mV (peak to peak), and the impedance determinations were accomplished at a rate of 10 points per decade of change in frequency. EIS results provide insight into the estimation of the defensive characteristics of the coating as an anticorrosion safety layer. Figure 8a–d depicts the Nyquist impedance data achieved for the P3MPY-SDS/P2MT coatings on the cobalt alloy surface and for the uncovered cobalt alloy in a hydrochloric acid medium. It can be observed from Figure 8 that the Nyquist plots for the cobalt alloy specimen showed a small capacitive loop, establishing that “charge transfer” proceeding was prevalent during the corrosion process. The Nyquist plots (Figure 8a–d) for the P3MPY-SDS/P2MT-coated cobalt alloy surface indicate one semicircle, which is characteristic for a charge transfer reaction. Hence, the dimensions of the capacitance loops of the composites are larger than that of the uncoated working electrode and the dimensions of these loops increase once the coatings are perfected, suggesting that these P3MPY-SDS/P2MT coatings provide greater defense properties to the specimen in HCl. It is noted from the Nyquist graphs that the impedance process of the cobalt alloy was considerably changed by the deposition of the covering, indicating that the defense layer produced was determined by the use of the P3MPY-SDS/P2MT composite. Likewise, these capacitive loops are not precise semicircles, and the shape (appearance) is ascribed to frequency dispersal, specifically due to the rugosity and inhomogeneity of the working electrode zone.

Figure 8 presents that the capacitance loop sizes for the coatings realized at potentials of 1.0 V and 0.9 V and at current densities of 0.5 mA/cm² and at 1 mA/cm² at molar ratios of 5:1 and 1:5 (at times of 10 min and 20 min) are superior in comparison to those of an uncoated cobalt alloy, implying a significant protective result for the cobalt alloy sample in aggressive environments. It can be seen in Figure 8 that the capacitance loop sizes of the P3MPY-SDS/P2MT coverings accomplished via the galvanostatic process at 0.5 mA/cm² and 1 mA/cm² current densities (at 5:1 and 1:5) are larger than those effectuated via the potentiostatic procedure at applied potentials of 1.0 V and 0.9 V; as an effect, the protection performance of this composite layer is superior. Analyzing Figure 8 and

Table 4. Electrochemical characteristics of covered and uncovered cobalt alloy electrodes in 1 M HCl solutions at 25 °C.

The System P3MPY-SDS/P2MT/Cobalt Alloy	Rs ohm·cm2	Q-Yo S·s−n·cm−2	Q-n	Rf ohm·cm2	Q-Yo S·s−n·cm−2	Q-n	Rct ohm·cm2	χ
CoCrW + 1 M HCl	1.30	4.69 × 10−5	0.89	13	1.378 × 10−5	0.86	809	8.25 × 10−3
P3MPY-SDS/P2MT, 1 mA/cm2, 1:5 molar ratio, t = 10 min	2.53	1.13 × 10−5	0.93	64	5.14 × 10−5	0.57	7.576 × 104	7.523 × 10−4
P3MPY-SDS/P2MT, 1 mA/cm2, 5:1 molar ratio, t = 10 min	2.66	1.91 × 10−5	0.98	64.73	6.73 × 10−5	0.84	8.921 × 104	3.733 × 10−3
P3MPY-SDS/P2MT, 1 mA/cm2, 1:5 molar ratio, t = 20 min	4.34	6.38 × 10−4	0.61	49	4.96 × 10−5	0.83	4.956 × 104	1.647 × 10−3
P3MPY-SDS/P2MT, 1 mA/cm2, 5:1 molar ratio, t = 20 min	2.63	7.43 × 10−4	0.63	65	1.66 × 10−4	0.93	4.976 × 104	3.935 × 10−4
P3MPY-SDS/P2MT, 0.5 mA/cm2, 1:5 molar ratio, t = 10 min	1.76	3.58 × 10−5	0.79	94.8	2.26 × 10−5	0.89	8.018 × 104	8.016 × 10−4
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 10 min	3.22	1.16 × 10−4	0.61	94.5	3.48 × 10−5	0.84	6.963 × 104	6.653 × 10−4
P3MPY-SDS/P2MT, 0.5 mA/cm2, 1:5 molar ratio, t = 20 min	5.912	3.32 × 10−4	0.64	65.2	4.94 × 10−5	0.89	7.846 × 104	1.021 × 10−3
P3MPY-SDS/P2MT, 0.5 mA/cm2, 5:1 molar ratio, t = 20 min	2.789	1.02 × 10−5	0.84	174	1.24 × 10−5	0.91	9.228 × 104	7.428 × 10−4

and

Table 5. Electrochemical characteristics of coated and uncoated cobalt alloy specimens in 1 M HCl solutions at 25 °C.

The System P3MPY-SDS/P2MT/Cobalt Alloy	Rs ohm·cm2	Q-Yo S·s−n·cm−2	Q-n	Rf ohm·cm2	Q-Yo S·s−n·cm−2	Q-n	Rct ohm·cm2	χ
CoCrW + 1 M HCl	1.30	4.69 × 10−5	0.89	13	1.378 × 10−5	0.86	809	8.25 × 10−3
P3MPY-SDS/P2MT, 0.9 V, 1:5 molar ratio, t = 10 min	0.79	3.88 × 10−5	0.88	362	7.35 × 10−4	0.74	1.71 × 104	5.10 × 10−3
P3MPY-SDS/P2MT, 0.91 V, 5:1 molar ratio, t = 10 min	0.68	3.52 × 10−5	0.61	64	2.81 × 10−5	0.89	2.15 × 104	1.87 × 10−3
P3MPY-SDS/P2MT, 0.9 V, 1:5 molar ratio, t = 20 min	1.06	4.33 × 10−5	0.84	304	2.576 × 10−5	0.89	8639	1.16 × 10−3
P3MPY-SDS/P2MT, 0.9 V, 5:1 molar ratio, t = 20 min	1.44	2.85 × 10−5	0.61	3805	5.456 × 10−5	0.88	2.77 × 105	1.86 × 10−3
P3MPY-SDS/P2MT, 1.0 V, 1:5 molar ratio, t = 10 min	0.681	7.16 × 10−5	0.61	88.5	3.305 × 10−5	0.89	8.53 × 105	3.88 × 10−3
P3MPY-SDS/P2MT, 1.0 V, 5:1 molar ratio, t = 10 min	1.03	2.79 × 10−5	0.89	2180	6.789 × 10−5	0.63	1.1 × 105	1.89 × 10−3
P3MPY-SDS/P2MT, 1.0 V, 1:5 molar ratio, t = 20 min	0.806	3.72 × 10−5	0.89	237	1.752 × 10−5	0.78	3.539 × 104	6.12 × 10−3
P3MPY-SDS/P2MT, 1.0 V, 5:1 molar ratio, t = 20 min	2.51	3.76 × 10−5	0.87	1778	9.026 × 10−5	0.66	7.24 × 105	2.59 × 10−3

, it can be assumed that the P3MPY-SDS/P2MT coatings functioned as efficacious physical barriers that prevented the offensive agents (Cl⁻) from accessing the covering, minimizing charge transfer and, accordingly, stopping the corrosion process.

The Bode plots of the P3MPY-SDS/P2MT-covered sample (Figure 9) show that the impedance modulus, at low frequencies, increases with an increase in the improvement of this composite, showing that the polymeric composite safety layer increases the anticorrosion protection of the cobalt alloy in an acid solution. In Figure 9, it is plain that the cobalt alloy exhibits one time constant at an approximate phase angle of 65° at average and low frequencies, showing inductive behavior via a weak diffusion trend. The Bode diagrams in Figure 9 show that the presence of a composite coating (P3MPY-SDS/P2MT) on the phase angle for the frequency logarithm exhibits a well-defined maximum at a phase angle of 75°–85° which corresponds to a relaxation time constant which implies capacitive behavior due to an easy diffusion tendency. Consequently, under these conditions, the covered electrodes have a good capacitive behavior according to the Nyquist data and determinations made via the potentiodynamic polarization technique. Increases in Zmod indicate an important protective action, and it is obvious that Zmod increases whenever the composite layer is improved. A greater Zmod leads a higher inhibition efficacy.

The evaluation of the impedance experiments was evidenced by matching the data with the suitable equivalent circuits indicated in Figure 10 and various impedance characteristics such as the solution resistance (R_s), the resistance of the coating film (R_f), the charge transfer resistance (R_ct), the capacitance of the coating film (C_f), the capacitance of the double layer (C_dl), which were shown in Table 4 and Table 5. In this paper, a frequency domain equivalent circuit model developed to fit and account for the acquired EIS results was proposed. In this situation, the constant phase element, CPE, is revealed in the circuit as a substitute of a pure double layer capacitor (Cdl) to provide a more accurate match. The CPE is utilized to determine the deformation of the capacitance loop, whichever attributes the heterogeneity of the zone to surface roughness and impurities. The impedance of the CPE can be analyzed as follows: Z_CPE = Y₀⁻¹ (jω)^-n, where ω is the “angular frequency”, “j” is the “imaginary number” (j² = −1), Y₀ is the corresponding amplitude at a capacitance, and “n” is the “phase shift”. The evaluation of “n” ensures attributes of the inhomogeneity status of the metal area [24,25,26,27,28,29,30,31,32,33,34,35,36,37]. A higher rating of the “n” is connected to a lower degree of roughness of the area i.n., and the inhomogeneity of the zone is diminished. The CPE can be resistance when n = 0, Y₀ = R), capacitance as n = 1 (Y₀ = C), and inductance when n = −1 (Y₀ = 1/L) or Warburg impedance as n = 0.5 (Y₀ = W), as established for the evaluation of n [8,13,23,24,25,26,27,51].

EIS determinations present that the charge transfer resistance, Rct, increased and the double layer capacitance, Cdl, decreased due to the coating. Determinations demonstrate that with the increase in the Rct by the P3MPY-SDS/P2MT-reinforced coating, the protective ability enhances substantially, which denotes that the composite achieved a remarkable anticorrosion effect for the cobalt alloy. Decreases in the Cdl may be achieved by lowering the local dielectric constant and/or raising the thickness of the electrical double layer, as an effect of the fact that the coating reacts by adsorption at the specimen–medium interface.

In this work, the P3MPY-SDS/P2MT coating deposited by electrochemical polymerization on the surface of a cobalt alloy electrode creates a protective layer on the cobalt alloy sample. Nyquist and Bode plots (Figure 8 and Figure 9, Table 4 and Table 5) suggest that the mechanism of corrosion was hindered by the deposition of the P3MPY-SDS/P2MT coating, and this occurrence was accomplished like a “diffusion barrier” in a charge transfer action.

3.5. SEM Investigations

The morphological construction of the P3MPY-SDS/P2MT composite layers made on the surface of the cobalt alloy was investigated using scanning electron microscopy (SEM). SEM images of the deposition of P3MPY-SDS/P2MT coatings under certain situations on the cobalt alloy specimen are exhibited in Figure 11. The SEM micrographs show a dark layer of the P3MPY-SDS/P2MT made by electrochemical techniques, showing that the composite covered the cobalt alloy substrate. Investigating the covered and uncovered cobalt alloys in 1 M HCl media from Figure 11, micrograph 11 a shows the polished cobalt alloy electrode (mirror shine) prepared for the electrosynthesis process, micrograph 11b represents the specimen immersed in a 1 M HCl solution, and from Figure 11c–i, it can be said that the P3MPY-SDS/P2MT covering has a uniform “cauliflower”-shaped design with a small “globular microstructure” over the surface, suggesting that the film P3MPY-SDS/P2MT deposited on the Co alloy substrate is dense and homogeneous, as previously reported in [20,33,38,39,40,51,57,58,59]. These micrographs show a uniform film was made on the cobalt alloy electrode, and the characteristics of this coverage are of such high quality that no cracks were noted on the covering. The SDS surfactant dopant integrated into polymers had a relevant effect on both the electropolymerization practice and the characteristics of the obtained coating [20,33,38,39,40,51,57,58,59]. The better coated substrate and superior adsorption result likewise demonstrate the excellent anticorrosion performance of this composite. An EDS investigation of the P3MPY-SDS/P2MT-covered cobalt alloy was effectuated, and the plots are shown in Figure 11j,k. The existence of composite layers on the cobalt alloy electrode is distinguished from the peaks of C, N, O, and S constituents in the EDS spectra. These data are in accordance with the FTIR results of the covered sample, where the ionic SDS surfactant and salicylate are presented in the polymer matrix. After an immersion time between 0 and 96 h in a 1 M HCl medium, a clear change in the substrate morphology of the covering was observed according to electrochemical determinations. This can be seen in the Figure 11g–i, which reveal the diffusion of corrosive ions Cl⁻ into the composite layer.

4. Conclusions

In this study, 3-methylpyrrole-sodium dodecyl sulfate/poly 2-methythiophene (P3MPY-SDS/P2MT) polymeric composite coatings successfully electrochemically deposited in a homogeneous, uniform, and adherent manner on cobalt alloy specimens were obtained using electrochemical techniques at certain current density and potential values in a sodium salicylate solution. The anticorrosion performance of the P3MPY-SDS/P2MT polymer composite electrodeposited under optimal circumstances was evaluated in a 1 M HCl medium using potentiodynamic polarization and EIS practices. The corrosion ratings of this P3MPY-SDS/P2MT composite-covered cobalt alloy surface are about ~10 times less than an uncoated cobalt alloy, and the protective efficaciousness of this layer is more than 91%. An examination of FT-IR plots demonstrates that the P3MPY-SDS/P2MT coating was established on the cobalt alloy substrate, and SEM images of the P3MPY-SDS/P2MT covering over a cobalt alloy show it to be compact, homogeneous, and adherent, and the attributes of this coating are the best features.

P3MPY-SDS/P2MT coatings were effectuated at potentials of 0.9 V and 1.0 V and current densities of 0.5 mA/cm² and 1 mA/cm² at a molar ratio of 5:1 for 20 min and 10 min; these revealed superior protection efficiency compared to the coating obtained at a 1.0 V potential and 1 mA/cm² current density at a molar ratio of 1:5 under the same circumstances. The anticorrosion protection characteristics of the composite P3MPY-SDS/P2MT were determined to be, in sequence, 0.5 mA/cm² >1 mA/cm² > 0.9 V > 1.0 V since the presence of this coating led to a consistent reduction in the corrosion mechanism (corrosion speed). It was evident that this coating prevented the attack of the corrosive agent—HCl—on the cobalt-based alloy substrate and that the new P3MPY-SDS/P2MT coating developed via this method is promising and may determine technological applications for the corrosion protection of materials. The superior substrate coating and good adsorption activity also imply the greater anticorrosion defense effect of the composite layers.