The Electrochemical Deposition of Zn-Mn Coating from Choline Choloride-urea Deep Eutectic Solvent

Electrochemical and microscopic techniques were used for characterization of Zn˗Mn coatings electrodeposited from choline chloride˗urea deep eutectic solvent. Cyclic voltammograms show that there was no discernible Mn reduction peak when only Mn2+ was present in DES solution. The distinct Mn peak developed only upon addition of Zn2+ to the solution, probably due to previous Zn nucleation on the steel substrate. It was found that 22-27 wt.% Mn, was deposited at current densities of 3-8 mA cm-2, amounts significantly higher than in aqueous electrolytes. Since higher deposition current densities resulted in the formation of a porous surface consisting of clusters of nodular crystallites, the optimal deposition c.d was determined to be 3 mA cm˗2

Hardness and corrosion resistance of Zn−Mn/Al2O3 composite coatings produced by electrochemical deposition

The aim of this study is development and characterization of the novel Zn-Mn/Al2O3 composite coatings. The coatingswere electrodeposited with constant current density on steel, from chloride solution, without any commercial additives. TheZn−Mn alloy coatings that show high corrosion resistance, may be used in future as an alternative to cadmium coatings.However, the pure Zn and Zn alloy coatings are characterized with poor mechanical properties. Therefore, in this work thealumina particles were incorporated into the Zn-Mn matrix, and the hardness and corrosion resistance of the obtainedcomposite coatings were tested. The mechanical and ultrasound agitation were used to achieve good dispersion of platingsolution and homogeneous co-deposition of second phase. The goal was to examine the effect of the agitation type in bath,on the attributes of the deposited composite coatings. The incorporation of Al2O3 particles was enhanced when themechanical agitation of the solution was applied. However, in case that this agitation method was used, the agglomeration ofthe alumina particles occurred. In contrast, when an ultrasonic agitation of the plating solution was applied, the uniformdistribution of the alumina particles could be achieved. The presence of particles in the matrix, along with appliedultrasound, resulted in grain refinement and homogeneous microstructure. The Al2O3 nanoparticles incorporated in Zn-Mnalloy matrix, resulted in a significant increment in the indentation hardness and a modest increase in the coating corrosionresistance. However, the coating hardness increased with alumina addition, only in case when an ultrasonic agitation of theelectrodeposition solution was used

A review of the electrochemical corrosion of metals in choline chloride based deep eutectic solvents

Deep eutectic solvents (DESs) are a class of mixtures with melting points notably lower than those of their raw constituent components. These liquids have found a tremendously wide spectrum of applications in the last two decades of their research, so their contact and interaction with technical metals and alloys are inevitable. Therefore, the corrosivity of DESs towards metals is an extremely important topic. This review summarizes research efforts collected in the last two decades related to the corrosion rate of various metals in different DESs. Since the DESs are mainly composed of organic raw compounds, and by their physicochemical properties they may be regarded as a separate class of ionic liquids, the literature data about DESs corrosivity has been compared to the data related to the corrosivity of various organic solvents and ionic liquids as well. All the results gained until now show significantly low corrosivity of DESs. This observation is discussed in relation to the chemical composition of DESs. The absence of the oxidizing agents, the inhibitory action of organic ions and molecules, high viscosity and low electrical conductivity have been recognized as the main factors contributing to the low metal corrosion rate in DESs

The influence of substituted aromatic aldehydes on Zn-Mn alloy electrodeposition

Additives are necessary in the electrodeposition of Zn-Mn alloys at high current density, in order to reduce hydrogen evolution reaction and prevent dendrite formation. The influence of two aromatic aldehydes, 4-hydroxy-benzaldehyde and 3,4-dimethoxy-benzaldehyde, as the additives in Zn-Mn plating electrolyte, is examined in this work. The coatings characterization by scanning electron microscopy and X-ray energy dispersive spectroscopy, as well as the examination of additives effect by electrochemical methods, indicate a complex involvement of additive molecules in hydrogen evolution, as well as in Zn2+ and Mn2+ reduction. Consequently, the levelling action can be achieved and the chemical composition of the Zn-Mn alloy can be tailored, by adding the proper additive type and concentration in the plating electrolyte. [Projekat Ministarstva nauke Republike SRbije, br. III 45019

Zn-Mn alloy coatings electrodeposited from acidic sulfate-citrate bath

The Zn-Mn alloy electrodeposition on steel substrate from sulfate-citrate bath was investigated using cyclic voltammetry. In a metal ion-free solution, an electrochemical analysis showed that increasing the citrate concentration induces the increase in the overpotential for hydrogen evolution reaction, with an optimum citrate concentration of 0.6 mol dm-3. Cyclic voltammograms recorded in the electrolyte with Zn2+ and Mn2+ ions, reveal that the potential of Zn-Mn alloy electrodeposition (-1670 mVSSE) stands between those of pure Zn (-1500 mVSSE) and pure Mn (-1850 mVSSE) electroreduction. The effect of [Mn2+]/[Zn2+] ratio in the electrolyte on the Mn content in the obtained Zn-Mn coatings was studied. It was found that the Mn content increases with increasing the [Mn2+]/[Zn2+] ratio in the electrolytic bath. The surface morphology and crystalline phase structure of Zn-Mn deposits were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), respectively

Manganese electrodeposition from urea-rich electrolyte

Pure manganese coatings were prepared on the steel (AISI 4340) electrode by a non-conventional electrodeposition method, in the presence of 8 mol dm(-3) of urea as a plating additive. The influence of urea on the electrodeposition of Mn was investigated by cyclic voltammetry. The morphology of the coatings was studied by scanning electron microscopy (SEM), and their elemental composition by energy dispersive X-ray spectrometry (EDS). The results showed that the presence of urea in the solution increased the current efficiency for metal reduction for around 20%, and depending on the applied deposition potential, urea may act either as a complexing agent or through the adsorption mechanism. Moreover, urea improves the characteristics of Mn deposits, i.e. their adhesiveness, porosity, compactness, and appearance. Except for oxygen, as part of the Mn corrosion product at the coating surface, no carbon or nitrogen incorporation was detected in the deposits by EDS

A Comparative Study of Zn-Mn Electrodeposition From Deep Eutectic Solvents and Aqueous Electrolytes

The production of Zn-Mn coatings with high Mn and low oxygen content from additive free choline chloride/urea deep eutectic solvent (DES) is reported in this work. Alloy coatings containing high Mn contents (~30 at.% Mn) show the highest corrosion resistance amongst zinc alloys [1]. However, in order to obtain Mn-rich deposits on steel from a simple aqueous bath, a significant cathodic polarization or high deposition current density is necessary. Under such conditions, the Zn 2+ reduction reaction is under diffusion control, leading to the formation and growth of dendrites. In addition intensive hydrogen evolution significantly reduces the current efficiency, often leading to the formation of porous coatings containing large amounts of oxygen [2]. It has been shown that a dendritic deposit formation and hydrogen reduction during Zn-Mn electrodeposition at high current densities could be prevented through use of plating additives [3]. By utilising DES instead of an aqueous electrolyte Zn-Mn codeposition was successfully achieved, with deposits containing high amounts of Mn at high current efficiencies. The amount of oxygen present in the alloy deposits obtained from DES was significantly reduced in comparison to those prepared from a normal water based electrolyte. Microstructural features and corrosion stability of the DES Zn-Mn deposits are compared with the coatings deposited from a conventional water-based electrolyte. The quantity of water absorbed from the atmosphere in the DES during both the electroplating procedure and throughout the DES storage period is also reported

The importance of using hydrogen evolution inhibitor during the Zn and Zn-Mn electrodeposition from ethaline

Cyclic voltammetry was used for the characterization of zinc electro-deposition on steel from ethaline deep eutectic solution (1:2 choline chloride:ethylene glycol). The influence of 4-hydroxy-benzaldehyde (HBA) as an additive was analyzed. It was shown that hydrogen evolution is inhibited in the presence of HBA and further significantly retarded upon addition of Zn2+ to the solution containing HBA. The cathodic peak for Zn2+ reduction in this type of ionic liquid (ethaline+HBA+Zn2+) resembles the zinc reduction in aqueous solution. The corrosion resistance of Zn coatings deposited at different current densities was evaluated by electrochemical methods, i.e., polarization measurements and electrochemical impedance spectroscopy in 3 % NaCl solution. The possibility of Zn-Mn alloy deposition from ethaline deep eutectic solvent was investigated for the first time. In addition, the corrosion stability of these alloy coatings was analyzed and compared to the stability of bare Zn coatings. It was shown that the optimum deposition current density for both Zn and Zn-Mn coatings with increased corrosion stability from ethaline + HBA electrolyte is 5 mA cm(-2)

The influence of water on the cathodic voltammetric responses of choline chloride-urea and choline chloride-ethylene glycol deep eutectic solvents

During the last decade, choline chloride-based deep eutectic solvents (DESs) have been successfully used for electrodeposition of different metals (Cr, Mn, Cu, Ag, Fe, Zn) and alloys (ZnCr, Zn-Sn, Zn-Ni, Zn-Mn, Ni-Co etc.) on different substrates, producing films with characteristics that are completely different from those obtained from aqueous electrolytes. Yet, the processes which occur in the blank electrolytes during the cathodic polarization of the DESs, are still not completely understood. Besides, the role of water molecules in these cathodic processes, has not been investigated in detail. It is almost impossible to avoid the water presence during the electrodeposition of metal coatings from DESs. The water is absorbed due to the high hygroscopicity of DESs, but is also added with hydrated metal salts. This work aims to compare the cyclic voltammograms (CVs) of DESs of different compositions. The blank DESs were the mixtures of choline chloride with urea or with ethylene glycol. The CVs were recorded in electrolytes with various ratios of choline chloride, urea, ethylene glycol, and water. The increase in the concentration of a certain substance in DES results in the increase in the cathodic voltammetric peak or the cathodic current. So, it is possible to determine the species that are reduced preferentially from the mixture of the two or three substances. The measurements taken until now, have led us to assume interesting conclusions. Namely, the species which originate from urea, ethylene glycol or water, are reduced at more positive potential than choline chloride. Besides, it seems that the electrode potential where the reduction starts is the same for these three substances (urea, ethylene glycol and water), in case that they are analysed separately. However, when both urea and water (or both urea and ethylene glycol) are present in DES, their reduction does not occur at the same potential. Instead, the water (or ethylene glycol) reduction occurs at more positive potential, which is seen as the cathodic peak, while the urea reduction in this case is hindered (shifted to more negative potential)