{'fraction_non_alphanumeric': 0.02425026271117937, 'fraction_numerical': 0.013741815536334977, 'mean_word_length': 4.930968360498562, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Electrochemical Characterization of Electrodeposited Ni-titanium Dioxide Deposits on Copper and their Corrosion Study

This work aimed to produce and characterize composite coatings of nickel incorporating TiO2 nanoparticles on a copper substrate. These deposits were obtained from watts bath. In the study, the cyclic voltammetry technique was employed to provide a better understanding of the cathodic behavior of nickel deposition. The effects of the potential scanning rate and the effect of cathodic limits on cyclic voltammograms deposition of Ni in Primitive Watts Bath (BWP) were determined. The composite coatings of nickel incorporating TiO2 nanoparticles were characterized using various electrochemical techniques such as open circuit potential (OCP) and potentiodynamic polarization measurements, and electrochemical impedance spectroscopic methods. The current density values for the Ni-TiO2 in the case of 5 g/L and 10 g/L of TiO2 determined from the polarization curves recorded in 3.5% NaCl indicate that the corrosion process on nickel incorporating the TiO2 nanoparticle composite surface is slower than on pure nickel. The TiO2 particles embedded in the electroplated nickel, increase the polarization resistance and decrease the corrosion rates as compared with electrodeposited pure nickel. Electrochemical impedance spectra obtained at the open-circuit potential (OCP) in 3.5% NaCl showed an increase of polarization resistance with time in all cases.


INTRODUCTION
The study of corrosion phenomena is a field of materials science that appeals to concepts of chemistry as well as physics. Corrosion is a critical global problem that strongly affects natural and industrial environments Subedi et al. 2019). Today, it is generally accepted that corrosion and pollution are interrelated harmful processes, as many pollutants accelerate corrosion, and corrosion products such as rust also pollute water bodies (Dahal et al. 2021;Gautam & Bhattarai 2013). Both are pernicious processes that undermine the quality of the environment, the efficiency of industry, and the sustainability of infrastructure assets (Devarakonda & Koka 2018;Valdez et al. 2012). Therefore, the study of corrosion phenomena and the means of protection which at least reduce its effects if not being able to eliminate it represent a certain interest for industrialists as well from the point of view of safety industrial than economic.
Among the means which are frequently used to combat the phenomena of corrosive, we can cite the coatings of the parts to be protected. Composite coatings are the most effective. Indeed, composite coatings are experiencing a development growing industrial thanks to the particular properties conferred on them by the incorporation of solid particles (Kumar et  The incorporation of such electro active metals in particulate form within composite coatings represents a natural extension of conventional metallurgical approaches, potentially minimizing the amount of metal deployed to inhibit corrosion, permitting the development of ultra-thin coatings, and allowing for additional functionality. Co and TiO 2 are in great demand for the generation of particles and composite coatings on steel and alloys with other metals (Basavanna & Naik 2012;Dikici et al. 2010). Zn-Co coatings are reported to have attracted greater interest due to their corrosion protection than Zn coatings; they also have characteristics similar to those of Zn-Ni. Subsequently, the potential advantage of Co addition in bath has been recognized to give resistance to abrasion and improved coating properties (Dikici et al. 2010). Titanium dioxide (TiO 2 ) with a metallic coating significantly contributes to wear and corrosion resistance, The need for improved coatings with better properties has developed the requirement for the use of composite electrodeposits, by embedding solid particles in the structure of nickel, such as titanium oxide (TiO 2 ) which is a hard compound, chemically stable, and irreducible. In this context, the objective of this work is the electrochemical characterization of the composite coatings nickeltitanium oxide (TiO 2 ), to improve the corrosion resistance of the deposits. These coatings are obtained by electro deposition technique from a bath of sulfate nickel on a copper substrate. The characterization has been carried out by corrosion.

MATERIALS AND METHODS
The electrochemical experiments were performed in a three-electrode cell with a capacity of 100 mL and which are connected directly to a VOLTALAB PGZ 402 type potentiostat/galvanostat, controlled NJST | Vol 20 | No. 1 | Jan-Jun 2021 Electrochemical Characterization of Electrodeposited Ni-titanium Dioxide Deposits on Copper and their Corrosion Study by a microcomputer (voltamaster software) for recording the data. The working electrode was a copper disc, the reference electrode was a Hg/ Hg 2 Cl 2 /KCls electrode, and the counter electrode was a platinum foil. The Ni and Ni-TiO 2 films were galvanostatically deposited on the copper substrate. The basic composition of electrolyte and deposition parameters is given in (Table 1). Cyclic voltammetry (CV) was used to define potential regions and to characterize the Ni deposition process. The scanning rate effect on the deposition process was investigated, and the effects of cathodic limits on cyclic voltammograms deposition of Ni were investigated in a primitive watts bath (BWP).
Corrosion test was carried out in 3.5% aerated NaCl solution, at room temperature. Open-circuit potential (OCP) measurements were performed as a function of time. Anodic and cathodic polarization curves were recorded in a potential range of E = Ecorr ± 200 mV for kinetic studies, with a scan rate of 5 mV/ s. Electrochemical impedance spectroscopy measurement was performed at the OCP. The impedance spectra were acquired in the frequency range 100 kHz to 10 MHz at 5 points per hertz decade with AC voltage amplitude of ± 10 mV.

RESULTS AND DISCUSSION
A weakly ionized boric acid acts as a buffer in nickel plating electrolytes. It works by regulating the pH in the cathode film and preventing precipitation of nickel hydroxide there; its effect is maximum around pH 4 ± 1 (Vasilyeva et al. 2012;Yang et al. 2006). A preliminary study carried out by cyclic voltammetry is devoted to the electrochemical behavior of boric acid on an inert platinum electrode in a potential range of -1.5V to 1.5V / ECS at a scanning speed (vb) of 5 mV/s.
Reading the curve (Figure 1) shows that the redox of the acid is practically inactive in the potential range explored. It is clear that in this area of potential, the release of hydrogen is not a problem, which justifies the use of boric acid in industrial electrolysis.   Figure 2 shows typical voltammograms for deposition of Ni at different scan rates. All voltammograms displayed a single reduced peak of N 2+ which is transferred to higher currents and more cathodic potentials with increasing scan rate. Similarly, in the anodic zone where the anodic peak current increases with increasing scan rate and the peak position shifted towards more positive potentials. The variations in the intensity of the cathode peak and its potential represented, respectively, as a function of (v1/2) and of (log v) for the reduction of N 2+ are given in (Figure 3). We observe, also, that the relation between the current of the cathodic peak and the square root since the scanning speed is linear this linearity is expected for processes that occur under diffusion control. However, the line, not going through the origin, indicates that another additional process other than diffusion is occurring ( Figure 4 shows the effect of cathodic limits on cyclic voltammograms deposition of Ni at a potential scanning rate of 10 mV / s in the primitive watts bath. All cyclic voltammograms demonstrate almost a similar pattern as in (Figure 1), which indicates that for the different cathodic limits the deposition process follows the same trend. During the cathodic scan, a peak appeared at -1.4 V which corresponds to the reduction of N 2+ into nickel metal. This is followed by a further increase in current due to a reduction of H+. During the reversed scan, a single anodic peak at around 0.35 V was noticed which correspond to the oxidation of nickel metal into N 2+ . The oxidation peak current increased when the limit was rendered more negative, demonstrating that there is a correlation between the cathodic and anodic processes. Corrosion experiments were carried out in 3.5% aerated NaCl solution, at room temperature. The open-circuit potentials (OCP) evolution in time for nickel coating in BWP and composite coatings nickel-titanium oxide (Ni-TiO 2 ) recorded after their immersion in 3.5% NaCl solution is presented in (Figure 5). For all electrodes, a shift of the OCP towards more positive potentials is observed during the first minutes to reach a stationary state, suggesting a more noble character of the Ni-TiO 2 coating, associated with an inhibition of the anodic reaction and, consequently, with stronger corrosion resistance. The behavior and performance of metals or alloy films depended on their chemical composition and surface morphology. The interpretation of the polarization curves in the logarithmic form by nonlinear regression allowed us to obtain the kinetic parameters of the corrosion process such as the corrosion current (Icorr), Tafel slopes of the anodic (βa) and cathodic (βb) reactions, and the corrosion potential (Ecorr) (Flitt & Schweinsberg 2005) which are given by the Stern-Geary equation, as given in equation (6)  The corrosion of nickel coating in PBW in the absence and presence of TiO 2 tested in 3.5% NaCl solution was evaluated using linear polarization. The Ecorr and Icorr correlation for the Ni coatings can be seen in ( Figure 5). Figure 6 shows Ecorr shifting to more positive potentials and the Icorr shifting to lower current values for Ni-TiO 2 in the case of 5g/L and 10g/L of TiO 2 . kinetic parameters of the corrosion process obtained from the Tafel straight lines of deposits tested in 3.5% NaCl solution at 25°C are given in Table 1. As can be seen from (Table 2), the values of the Tafel coefficients in the presence of TiO 2 change in comparison with pure Ni coatings, which indicate that the TiO 2 particles influence the kinetics of both the cathodic and anodic processes. The poor results obtained in the case of 15 g/L TiO 2 in the bath can be explained by the formation of defects and dislocations or in the metal matrix, at high concentrations of the particles (Chen et al. 2006) or by non-uniform incorporation of the particles due to the formation of agglomerates.  Fig. 6. Polarization curves of nickel coating in BWP in the absence and the presence of TiO 2 tested at 3.5% NaCl solution

CONCLUSION
In the present study, Ni-TiO 2 nano-composite coatings were developed successfully by using an electro-deposition process on the copper substrate from a nickel sulfate bath. The addition of TiO 2 nanoparticles in the nickel bath with NJST | Vol 20 | No. 1 | Jan-Jun 2021 Electrochemical Characterization of Electrodeposited Ni-titanium Dioxide Deposits on Copper and their Corrosion Study different concentrations improves the electrochemical characteristics of the nickel deposit on copper such as resistance to corrosion. Corrosion tests in an aggressive 3.5% NaCl solution indicate a reduced electrochemical activity and lower corrosion rate in the case of composite deposits compared to the deposition of pure Ni, being confirmed the beneficial effect of the incorporation of TiO 2 into the Ni matrix. The best results are obtained for a concentration of 5 g/L of TiO 2 . The deposits obtained at this concentration showed improvements concerning the corrosion resistance which is greater in comparison with other concentrations. The results of the impedances are in agreement with the results of corrosion current densities and the resistance of polarization which indicates the best resistance to corrosion in the case of the deposition of Ni obtained from the bath in the presence of 5 g/L TiO 2 .

ACKNOWLEDGEMENT
Authors are grateful to the assistance of the department of chemistry, faculty of science, university of Mohamed BOUDIAF (M'sila Algeria). Thanks for technical support and laboratory facilities.