The electrodeposition of chromium is a technologically vital process, which is principally carried out using aqueous chromic acid. In the current study, it is shown that eutectic mixtures of urea and ...hydrated chromium(
iii
) chloride provide a liquid which reduces the toxicological issues associated with the current aqueous Cr(
vi
) electroplating solution. Using EXAFS, mass spectrometry and UV-Vis spectroscopy, it is shown that chromium is present predominantly as a cationic species. Conductivities are higher than for most comparable ionic liquids. It is shown that the electrodeposition of chromium is electrochemically reversible, with a current efficiency much higher than in aqueous electrolytes. Surface tension and density measurements indicate that hole theory is a valid model to describe transport properties in these liquids. Bulk Cr deposits are not macrocrystalline but they are generally crack-free. The deposits have a hardness of 600 ± 10 Vickers and, as such, are comparable to deposits from aqueous systems.
The electrodeposition of hard chromium is demonstrated from a novel deep eutectic solvent with high current efficiency resulting from a cationic metallic species in the liquid.
The effects of nicotinic acid (NA), boric acid (BA) and benzoquinone (BQ) on the electrodeposition of Zn have been studied in a choline chloride (ChCl) ethylene glycol (EG) based deep eutectic ...solvent (DES), (1ChCl:2 EG), and for the first time a bright zinc coating has been achieved when NA was used.
In metal electroplating processes, small-molecule additives are often included in the plating bath to improve properties of coating such as brightness, roughness, thickness, hardness and resistance to corrosion. The effects of additives on the electrodeposition of Zn from aqueous solution have been extensively investigated. However, very few studies have considered the effects of additives on the electrodeposition of Zn from ionic liquids or deep eutectic solvents. The electrochemical properties of the plating liquid have been studied here using cyclic voltammetry, chronocoulometry, chronoamperometry and microgravimetry (EQCM). Redox peak currents decrease when additives were included in the Zn solution and total charge was also reduced in experiments where additives were present. The Zn deposition in the absence of additive is in good agreement with an instantaneous growth mechanism at short experimental time scales (being indeterminate over longer periods), however, this changes to one of a progressive growth mechanism when additives were included in the coating bath. The current efficiency of zinc deposition in the DES without additives was 95%, which was reduced when additives were included. The resultant surface morphologies, thickness, topography, roughness and crystal structure of the Zn coating were revealed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD), demonstrating that those additives serve as effective brighteners that can produce highly uniform and smooth zinc deposits.
Glycerol eutectics as sustainable solvent systems ABBOTT, Andrew P; HARRIS, Robert C; RYDER, Karl S ...
Green chemistry : an international journal and green chemistry resource : GC,
01/2011, Letnik:
13, Številka:
1
Journal Article
Recenzirano
In this work the use of glycerol as a hydrogen bond donor in Deep Eutectic Solvents is studied. The physical properties of choline chloride mixtures with glycerol are quantified and it is shown that ...eutectic mixtures can circumvent some of the difficulties of using glycerol as a solvent viz. high viscosity and high melting point. The solvent properties are characterised using polarity parameters and the values are similar to other ionic liquids although it is shown that this procedure is a poor method of characterising Lewis basicity. The application of these liquids to the esterification of glycerol is used as a demonstration of the ability to tune a reaction with the quaternary ammonium halide acting as a quasi-protecting group. The liquids represent a sustainable way of preparing non-toxic, tuneable solvent systems.
The amphiphilic nature of many pharmaceutical active ingredients often makes them difficult to solubilise and leads to significant wastage through non-optimal dosage. In this study it is shown that ...highly concentrated liquid formulations can be produced from pharmaceutical active ingredients which either contain a strong hydrogen bonding functionality e.g. -OH or -COOH or a quaternary ammonium moiety. These mixtures can overcome solubility issues in water as the eutectics prevent recrystallization of the active ingredient when dispersed in water. The depression of freezing point for these eutectic mixtures is modelled using the enthalpy of hydrogen bond formation which was calculated using calorimetric data. The study also demonstrates that complex drug molecules which exhibit polymorphism such as Adiphenine and Ranitidine can be formulated into a homogeneous liquid and the hydrogen bond donor can also be a pharmaceutical active ingredient e.g. aspirin.
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Deep eutectic solvents (DESs) are mixtures of quaternary ammonium halides with hydrogen bond donors and are increasingly being used in applications where they are in contact with metals. This study ...investigates the corrosion of iron, nickel and aluminium in DESs. It shows that none of the metals show significant corrosion when glycerol is used as a hydrogen bond donor but when an acidic hydrogen bond donor such as oxalic acid is used, both iron and aluminium show catastrophic corrosion as may be expected. Surprisingly, however, nickel does not corrode in the acidic DES, Oxaline. The differences in corrosion observed for aluminium and iron are explained in terms of passivating films and the slowness of the oxygen reduction reaction despite the relatively high gas solubility. The high chloride ion content (roughly 4 mol dm−3) has a relatively small effect on the corrosion of the three metals. The formation of a passive layer as a result of hydrogen bond donor-metal ion complexes is shown to be more important. It is proposed that the low corrosion rates of some metals resulted from the slow rate of the cathodic reaction resulting from the high viscosity, low activity of water and low proton mobility.
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Here we describe the electrolytic deposition of Zn, Sn and Zn/Sn alloys from a solution of the metal chloride salts separately in urea and ethylene glycol/choline chloride based ionic liquids. We ...show that the deposition kinetics and thermodynamics differ from the aqueous processes and that qualitatively different phases, compositions and morphologies are obtained for the metal coatings in the different ionic liquid systems. We have quantified the electrochemical stripping responses using cyclic voltammetry together with compositional analysis using SEM/EDAX and X-ray diffraction. The differences in electrochemical responses are rationalised in terms of the speciation of both Zn and Sn chlorides in the ionic liquids that have been identified using FAB mass spectrometry. Also we demonstrate that composite metal coatings,
e.g. containing Al
2O
3 particles, can be obtained from these liquid systems by virtue of the stable liquid suspensions. This novel feature of these liquids is a function of their relatively high viscosity.
Eutectic mixtures of quaternary ammonium salts with Lewis or Brønsted acids have been described as ionic liquid, but doubt exists over the compositional range for which this description is valid. In ...the current work, the conductivity, viscosity, density, and surface tension of a number of glycolic mixtures with choline chloride are measured over the mole fraction range 0 to 0.33. The data are fitted to hole theory, and it is proposed that the composition at which the measured conductivity matches the theoretical value is the point at which hole mobility becomes the dominant mechanism for charge mobility. For the mixtures of ethylene glycol and butanediol, this occurs at a ChCl mole fraction of approximately 0.2.
Aluminum-based batteries are a promising alternative to lithium-ion as they are considered to be low-cost and more friendly to the environment. In addition, aluminum is abundant and evenly ...distributed across the globe. Many studies and Al battery prototypes use imidazolium chloroaluminate electrolytes because of their good rheological and electrochemical performance. However, these electrolytes are very expensive, and so cost is a barrier to industrial scale-up. A urea-based electrolyte, AlCl3:Urea, has been proposed as an alternative, but its performance is relatively poor because of its high viscosity and low conductivity. This type of electrolyte has become known as an ionic liquid analogue (ILA). In this contribution, we proposed two Lewis base salt precursors, namely, guanidine hydrochloride and acetamidine hydrochloride, as alternatives to the urea-based ILA. We present the study of three ILAs, AlCl3:Guanidine, AlCl3:Acetamidine, and AlCl3:Urea, examining their rheology, electrochemistry, NMR spectra, and coin-cell performance. The room temperature viscosities of both AlCl3:Guanidine (52.9 cP) and AlCl3:Acetamidine (76.0 cP) were significantly lower than those of the urea-based liquid (240.9 cP), and their conductivities were correspondingly higher. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) showed that all three electrolytes exhibit reversible deposition/dissolution of Al, but LSV indicated that AlCl3:Guanidine and AlCl3:Acetamidine ILAs have superior anodic stability compared to the AlCl3:Urea electrolyte, as evidenced by anodic potential limits of +2.23 V for both AlCl3:Guanidine and AlCl3:Acetamidine and +2.12 V for AlCl3:Urea. Coin-cell tests showed that both AlCl3:Guanidine and AlCl3:Acetamidine ILA exhibit a higher Coulombic efficiency (98 and 97%, respectively) than the AlCl3:Urea electrolyte system, which has an efficiency of 88% after 100 cycles at 60 mA g–1. Overall, we show that AlCl3:Guanidine and AlCl3:Acetamidine have superior performance when compared to AlCl3:Urea, while maintaining low economic cost. We consider these to be valuable alternative materials for Al-based battery systems, especially for commercial production.
Due to their high metal content, printed circuit boards (PCBs) are an attractive resource for metal recovery. Until now, the dissolution and subsequent recovery of metals from PCBs involve either ...pyro- and/or hydrometallurgy. Such processing routes are typically very energy intensive and generate large volumes of solid residues and wastewater, which require energy to be further treated and disposed. Thus, there is a need to develop more energy-efficient and environmentally-compatible processes. This study investigates the use of catalytic dissolution of metals from PCBs in a eutectic solvent formed from calcium chloride hexahydrate and ethylene glycol (EG) as a potential autocatalytic methodology for selective metal recovery from PCBs. Two oxidising agents, FeCl
3
and CuCl
2
, were used as redox catalysts as both of them demonstrate high solubility and fast electron transfer. The catalysts selectively etched copper, allowing gold and nickel to be recovered by simple filtration. Leaching rates determined with an optical profiler showed that CuCl
2
enabled faster leaching kinetics compared to FeCl
3
and this is discussed in terms of the dissolution mechanism.
Catalytic dissolution of metals from printed circuit boards using a calcium chloride-based deep eutectic solvent.
Silver is an important metal for electronic connectors, however, it is extremely soft and wear can be a significant issue. This paper describes how improved wear resistant silver coatings can be ...obtained from the electrolytic deposition of silver from a solution of AgCl in an ethylene glycol/choline chloride based Deep Eutectic Solvent. An up to 10-fold decrease in the wear volume is observed by the incorporation of SiC or Al
2
O
3
particles. The work also addresses the fundamental aspect of speciation of silver chloride in solution using EXAFS to probe solution structure. The size but not the nature of the composite particles is seen to change the morphology and grain size of the silver deposit. Grain sizes are shown to be consistent with previous nucleation studies. The addition of LiF is found to significantly affect the deposit morphology and improve wear resistance.
Composites of silver with SiC and Al
2
O
3
particles are prepared using ionic solvents and shown to have improved wear resistance.
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