A range of organic/ inorganic additives have traditionally been added to electroplating solutions to improve brightness and encourage levelling. A limited number of studies have shown that some ...brighteners function in ionic liquids. In this study the effect of four additives; nicotinic acid (NA), methyl nicotinate (MN), 5,5-dimethyl hydantoin (DMH) and boric acid (BH), have been measured on the electrodeposition of cobalt in the 1choline chloride (ChCl): 2 ethylene glycol (EG) based deep eutectic solvent (DES). In general the addition of these additives causes the deposition potential of Co to be shifted to more negative over-potentials. No apparent change in speciation and coordination environment around the CoII centre was observed. The surface morphology was significantly changed by the addition of each of the additives, suggesting that they function by modifying the double layer. The nucleation and growth mechanism of Co deposition was found to change in the presence of these additives. Flat, shiny and high uniform cobalt layers were obtained with the additives whereas in their absence the deposit was black and dull. The additives significantly increased the hardness of the cobalt deposit and this was shown to be related to the crystal structure of the deposit which was determined using XRD.
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•Facile electro-deposition of bright Ni is possible from DES electrolytes at elevated temp. and high concentration.•Harder Ni deposits are obtained from DES than from aqueous ...electrolytes.•Similar deposition rates are measured despite the higher viscosity of the DES.•High temp. speciation of Ni2+ in DES determines morphology of deposit.•Ni deposition in DES shows a levelling effect when compared to Ni plating in aqueous electrolytes.
Metal electrodeposition using ionic liquid electrolytes and deep eutectic solvents is now well known but to our knowledge for electrolytic deposition of metals such as nickel no direct comparison has thus far been drawn between deposition using aqueous solutions and DES under otherwise identical conditions. In the current study it is shown that nickel deposition can be carried out with similar deposition rates in aqueous and ionic media despite the significant differences in viscosity and conductivity. It is, however, shown that in ionic media the morphology of the deposits is markedly different from that achieved using a Watts nickel bath and that one aspect of these differences manifests itself in significant increase in the coating hardness. It is proposed that the observed morphology differences occur due to the variations of nickel speciation in each electrolyte environment.
Organic and inorganic additives are often added to nickel electroplating solutions to improve surface finish, reduce roughness and promote uniform surface morphology of the coatings. Such additives ...are usually small molecules and often referred to as brighteners or levellers. However, there have been limited investigations into the effect of such additives on electrodeposition from ionic liquids (ILs) and deep eutectic solvents (DESs). Here we study the effect of four additives on electrolytic nickel plating from an ethyleneglycol based DES; these are nicotinic acid (NA), methylnicotinate (MN), 5,5-dimethylhydantoin (DMH) and boric acid (BA). The additives show limited influence on the bulk Ni(
ii
) speciation but have significant influence on the electrochemical behaviour of Ni deposition. Small concentrations (
ca.
15 mM) of NA and MN show inhibition of Ni(
ii
) reduction whereas high concentrations of DMH and BA are required for a modest difference in behaviour from the additive free system. NA and MN also show that they significantly alter the nucleation and growth mechanism when compared to the additive free system and those with DMH and BA. Each of the additive systems had the effect of producing brighter and flatter bulk electrodeposits with increased coating hardness but XRD shows that NA and MN direct crystal growth to the 111 orientation whereas DMH and BA direct crystal growth to the 220 orientation.
Small molecule organic additives produce smooth, bright, adherent and hard nickel coatings during electrodeposition in a deep eutectic solvent. We present a detailed study.
This report presents simple, rapid and an efficient electropolishing of Ti metal in choline chloride-based ionic liquid (so called Ethaline) at 20 °C. This electrolyte is relatively benign and ...environmentally friendly which is desirable for electropolishing. Potentiostatic method was applied to Ti electropolishing in this electrolyte. Under an electrochemical condition of 6–10 V for 30 min. and at 20 °C, a promising electropolishing process was performed without obvious gas evolution. To characterize the electropolished surface, atomic force microscope (AFM) and scanning electron microscope (SEM) were used. The achieved an apparent mirror-like finished surface with an average surface roughness (Ra) was 5.7 nm which is considerably different from that of unpolished one (Ra = 118.8 nm). The microscopic results showed leveling and brightening of the surface of Ti by carrying out the current procedure. This electrolyte provides sufficient environment to dominate the mass transport mechanism which is responsible for reduction in the surface roughness.
In this report we present a straightforward and efficient electropolishing methodology of pure metallic titanium in two different electrolytic baths; choline chloride-ethanol (ChCl-eth.) and choline ...chloride-methanol-butanol (ChCl-meth.-but.) in molar ratios of 1 : 4 and 1 : 6 : 2, respectively at 20 °C. The electrolytic baths under study possess relatively low-cost and environmentally benign. In the electropolishing processes, potentiostatic technique was applied. For the surface characterizations both atomic force microscope (AFM) and scanning electron microscopy (SEM) were used. The results showed that titanium surface was polished electrochemically at nanoscale and relatively free from defects. The working voltages of 2 and 1.2 V were applied in ChCl-eth. and ChCl-meth.-but., respectively within a time scale of 40 minutes in the present electrolytic baths. The roughness of pure metallic titanium (ca. 120.5 nm) was reduced to 0.10 nm in ChCl-eth. and 0.66 nm in ChCl-meth.-but.
In this work, cobalt electroplating from homogeneous oxidation of cobalt powder via iodine as a chemical oxidizing agent and from CoCl2·6H2O in choline chloride-ethylene glycol electrolytic bath was ...carried out at 90 °C. As relatively high temperature and corrosion resistive coating material, cobalt electroplating was performed. A number of electrochemical, spectroscopic and microscopic techniques, such as, cyclic voltammetry (CV), chronocoulometry, UV-visible spectroscopy and scanning electron microscopy (SEM) were used in fabrication and characterizations of the electroplated cobalt. The progressive nucleation mechanism is followed in case of cobalt electroplating using cobalt powder in the presence of iodine. The mirror-like surface (i.e., smooth surface) surface has been obtained when cobalt powder utilized with the aid of iodine as shown in the SEM images. The effectiveness of the existence of iodine and cobalt powder was evidenced from chronocoulometry in which huge number of charge was released during the electrochemical course.
Electroactive polymers such as polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene) have many potential applications, but the nature of the electrolyte can be adversely affected on mass ...transport processes – of electronic charge, electroneutrality counter-ions (“charge-balancing”), reactant species, and mobility of polymer segments. In this study, polyaniline (PANI) films have been prepared in deep eutectic solvent (Oxaline, a eutectic mixture of oxalic acid and choline chloride) and acidic aqueous media using cyclic voltammetry associated with the electrochemical quartz crystal microbalance (EQCM). PANI was found to grow in both liquids although the rate of growth was slower in Oxaline than aqueous acid due to the higher viscosity of the former. The results showed that PANI electrodes made in aqueous solutions grow by an autocatalytic mechanism, unlike those in deep eutectic solvents (DESs). The stability and durability of some films was examined in DESs and aqueous solutions at 25 °C and 50 °C. The results showed the mobile species are different when cycled in the DES compared to aqueous media. For films grown in different media but cycled in aqueous acid, the anion (HSO4−) was found to dominate the mobile species. However, the mass behaviour of PANI electrodes (deposited from aqueous/Oxaline-DES) in DESs (Ethaline) at 50 °C was most strongly associated with cation (Ch+) egress (i.e., mass decrease) during the oxidation reaction and cation (Ch+) ingress (i.e., mass increase) during the reduction reaction. In addition, the results showed that temperature plays an important role in increasing the rate of diffusion and the stability of mass change in viscous ionic liquids.
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This report presents influence of water and copper salt on the anodic dissolution of metallic copper in a eutectic solvent of choline chloride and ethylene glycol (DES) in a 1 : 2 molar ratio. The ...mechanism of copper dissolution anodically was investigated using anodic linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Atomic force microscope (AFM) was used to examine the morphology and topography of the surface after electrochemical dissolution course. The addition of 1, 4, 8, 16 and 20 vol% of water cause pitting and has no significant impact on the electrochemical behavior, in particular the shape of anodic linear sweep voltammetry remains unchanged. The more profound effect was seen from the microscopic analysis. The addition of 0.1 and 0.81 M CuCl2 into this eutectic solvent resulted in relatively high resistance at the interfacial region where charge transfer occurs during anodic dissolution of metallic copper using impedance responses. The results confirmed that water will not affect anodic dissolution behavior and the chemistry of dissolution in the deep eutectic solvent.
In this report, we present a simple, efficient and promising methodology of electroplating cobalt in the mixture of choline chloride and ethylene glycol in 1:2 mol ratio in the presence of hydantoin ...(HD) as an additive. The bulk electroplating was carried out at a constant current density of 2.8 mA cm-2 for one hour and at 90 ºC. A range of electrochemical, spectroscopic and microscopic techniques were used in the characterizations of the mechanism and thick film formed from electroplating processes of copper coated by cobalt. The film thickness of Co was calculated and found to be 8.31 and 23.54 μm in the absence and presence of hydantoin, respectively. The hardness test indicates the dense Co film formation on copper sheet. The mirror-like Co film will be shown using SEM and photograph.
This work presents an efficient and facile electrodeposited nickel using an organic additive, namely hydantoin (HD) from choline chloride and ethylene glycol in 1:2 mol ratio. It has also been shown ...that a relatively high brightness of the nickel deposits. The electrochemical properties of the Ni electrolyte in the absence and presence of HD have been examined via cyclic voltammetry, chronocoulometry, and chronoamperometry. The inclusion of HD causes the deposition potential of nickel to shift to more negative overpotentials. From the UV-spectra, it has been confirmed that the speciation of the nickel solution remained unchanged even over a wide range of temperature and coordination environments around the nickel centre. The presence of HD participates in interfacial region, in other words, acts an effective species in the nucleation and growth mechanisms of Ni deposition. A mirror-like and shiny nickel layers free of crystal grain have been achieved in the presence of HD when hydantoin was utilized as an effective additive. From the x-ray diffraction (XRD), the impact of the HD additive on the crystal growth along the 200 and 220 orientations during bulk deposition has been proved.
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