A new bath for the electrodeposition of aluminium. III. The electrochemical behaviour of the rotating aluminium disc electrode in pure AlCl3/THF-toluene solutions

The electrochemical behaviour of the rotating aluminium disc electrode in AlCl₃/tetrahydrofurantoluene solution was studied. The kinetic parameters controlling the electrode processes were investigated. The effect of the concentration of AlCl₃, the speed of rotation of the rotating disc electrode and the temperature on the cathodic and anodic current density was analysed. The results were compared with those for AlCl₃–LiAlH₄/THF-toluene solutions.     

Passivation of the aluminium cathode during deposition of aluminium from aluminium chloride-sodium chloride melts

The kinetics of aluminium deposition from NaCl-AlCl₃ melts (c_AlCl3 < 10 mol%) contained in alumina crucibles was studied by linear sweep voltammetry and potential step amperometry at temperatures around 820°C. At low concentrations (c_AlCl3 < 0.4 mol%) the reduction of AlCl₃ on liquid aluminium has been found to be diffusion controlled. At higher concentrations a passivation of the aluminium electrode was observed during the deposition reaction. The passivation appears to be caused by precipitation of alumina from supersaturated melt in the diffusion layer at the aluminium cathode.     

A new bath for the electrodeposition of aluminium. I. conductivity measurements

The conductivity of mixed hydrides of aluminium chloride and lithium-aluminium hydride in a mixed solvent of tetrahydrofuran (THF) and toluene was measured with respect to the total concentration of aluminium and also to the molar ratio of LiAlH₄ to AlCl₃. The values obtained were compared with those of the THF-benzene mixed solvent and those of the NBS (National Bureau of Standards) bath –AlCl₃ and LiAlH₄ in dithyl ether. The results showed that a solution of AlCl₃ and LiAlH₄ with a molar ratio of 3:1, respectively, in THF-toluene (80 vol% toluene) with a total concentration of aluminium of about 1.0 moll^–1, has a suitable conductivity for the electrodeposition and dissolution of aluminium. In addition to its low price, the electrolytic bath obtained has low volatility and relatively good stability with respect to the other baths studied.     

Electrode kinetics of the aluminium deposition from tetrahydrofuran electrolytes

The electrolyte applied for the study of aluminium deposition consisted of AlCl₃ and LiAlH₄ in tetrahydrofuran or tetrahydrofuran—benzene mixture. It has been shown that the kinetic parameters such as the exchange current density and transfer coefficients depend to a great extent upon the molar ratio of both components. An electrode mechanism has been suggested in good agreement with the experimental results obtained.     

Aluminium electrodeposition from AlCl3-NaCl melts on glassy carbon,platinum and gold electrodes

The electrochemical deposition and dissolution of aluminium on glassy carbon, platinum and gold electrodes in chloraluminate melts have been investigated using linear sweep voltammetry and potentiostatic pulse techniques. It was shown that deposition of aluminium on the glassy carbon electrode at low overpotentials takes place by 3-D progressive nucleation and growth, with the incorporation of atoms in the crystal lattice as the rate-determining step. At overpotentials higher than –100 mV vs Al, in the melts containing more than 52 mol % of AlCl₃, diffusion of Al₂Cl ₇ ^– , takes over the control of deposition of aluminium. Alloying of platinum and gold electrodes with aluminium from the melt occurs in the underpotential region.     

Chronopotentiometric study of aluminium deposition from MClAlCl3 melts (MNa,K and Cs)

The kinetics of aluminium deposition from NaClAlCl₃, KClAlCl₃ and CsClAlCl₃ melts (C_AlCl3 = 3 × 10^?5 ?1 × 10^?3 mol cm^?3) was studied using the chronopotentiometric technique. It was found that in the system NaClAlCl₃ the reduction of Al(III) species is controlled by diffusion only, while in the system KClAlCl₃ and CsClAlCl₃, a chemical reaction precedes the reduction step. In the two latter systems the Al(III) in the complex anion AlCl^?₄ can be reduced also directly, if current density is sufficiently high.     

Kinetics of aluminium deposition from aluminium chloride—alkali chloride melts

The kinetics of aluminium deposition from NaClAlCl₃ and NaClKClAlCl₃ melts (c_AlCl3 < 0.4 mol%) was studied by linear sweep voltammetry and potential step amperometry. The reduction of AlCl₃ on tungsten and aluminium electrodes was found to be diffusion controlled. The diffusion coefficients of AlCl₃ were: 3.5 × 10^?5 cm² s^?1 at 820°C in NaClAlCl₃, 2.7 × 10^?5cm²s^?1 at 825°C, and 2.1 × 10^?5cm²s^?1 at 705°C in KClNaClAlCl₃. The rate constant for AlCl₃ reduction at these conditions was found to be in the order of 0.2 cm s^?1, in good agreement with extrapolated literature data.     

Solute rejection by porous glass membranes. III. Reduced silica dissolution and prolonged hyperfiltration service with feed additives

It was found that inclusion of 0.3 g/l AlCl₃,6H₂O as a feed additive in hyperfiltration tests was sufficient to stabilise a porous glass membrane (batch A-1) with relatively high volume flux and modest solute rejection characteristics. One-tenth of this concentration was not sufficient. Further testing was directed toward treatment of porous glass membranes with concentrated aluminium chloride solution for a limited time, followed by hyperfiltration with a dilute feed additive. As little as 0.003 g/l AlCl₃,6H₂O stabilised batch A-1 for 80 h; while batch A-5, with lower volume flux and higher solute rejection characteristics, could be stabilised with no feed additive but only treatment with a concentrated aluminium solution every 100 h. Other experiments showed a similar equilibrium silica solubility, about 110 parts/million, in all solutions regardless of AlCl₃, HC₁, NaCl, or urea addition. The test which showed rates of silica dissolution revealed, however, that both low pH and aluminium lowered the rate of solution. The effectiveness of porous glass membrane stabilisation by aluminium treatment or reduced pH was also reflected in greatly reduced silica concentration of the effluent from hyperfiltration tests. Treatment of porous glass membranes with ferric and zirconyl chlorides was also tested, but aluminium chloride was the most effective in reducing silica loss. Chemical analysis of treated and tested membranes showed that aluminium remained in the pore structure in concentrations comparable to that of reactive silica hydroxyls. This is greater than the apparent concentration of ion exchange sites, and considerably less than total free hydroxyl concentration. Since suitable aluminium treatment or feed additive maintains membrane flux, rejection, and pore size characteristics, despite loss of soluble silica in the effluent, it appeared that added aluminium was retained in the membrane structure in amounts equivalent to the dissolved silica.     

The electrodeposition of aluminium from xylene and ether-hydride electrolytes

A comparative study of aluminium electrodeposition from xylene and ether electrolytes is presented. The kinetic parameters of aluminium deposition from the tetrahydrofuran (THF) and xylene electrolytes are presented. In the case of the THF and diethylether solutions investigations of aluminium nucleation were also made. It was found that the rate of aluminium deposition was highest in the THF electrolyte composed of AlCl₃ and LiAlH₄ in a ratio 1:1. This electrolyte is recommended for deposition of aluminium protective coatings of thickness over 20 µm     

Aluminium halides as electrolyte forming compounds in organic solvents

Dissolution of aluminium halides in polar organic solvents is demonstrated on the AlCl₃ and AlBr₃ solutions in acetonitrile. The equilibrium constant of the disproportionation reaction 2 AlX₃ ? AlX^?₄ + AlX⁺₂ was determined and showed both salts to behave as strong electrolytes in acetonitrile. Tetrahydrofuran and aromatic hydrocarbons toluene and xylene have been chosen as solvents of low polarity. Electrolyte solution in such solvents can be prepared only by addition of suitable ionization agents to the aluminium halide solution. The reactions occuring in AlCl₃ solution in tetrahydrofuran after addition of liCl and LiAlH₄ as well as in AlBr₃ solution in toluene after addition of KBr were studied conductometrically. Special attention was paid to the role of water depending upon the type of solvent in all studied types of solutions. The study was completed with calometric measurements of the dissolution heats of AlCl₃, AlBr₃ and AlI₃ in tetrahydrofuran and acetonitrile reflecting the interaction between the solvent and solute.     

Aluminium deposition and dissolution in aluminium chloride—n-butylpyridinium chloride melts

Glassy carbon and tungsten electrodes were used to investigate the mechanism of aluminium deposition and dissolution reactions in the AlCl₃—n-butylpyridinium chloride melts at ambient temperature. Chronopotentiometric results indicate that the electrodeposition of aluminium from the melt is kinetically complicated. Current reversal chronopotentiometry showed that the corrosion rate of aluminium is linearly proportional to the acidity of the melt at a given temperature. Besides impurities, the major cause of the corrosion of the deposited aluminium over a wide composition range of the melt was also found to be due to the organic butylpyridinium cation (BuPy+) serving as an electron acceptor in the corrosion process when freed from ion-pair interaction with AlCl⁻₄.     

Aluminium composite coatings containing micrometre and nanometre-sized particles electroplated from a non-aqueous electrolyte

The electrolytic codeposition of micro- and nano-sized particles with aluminum from a nonaqueous electrolyte is investigated. SiC, SiO₂, Al₂O₃, TiB₂ and hexagonal BN particles were codeposited with aluminium from an AlCl₃/dimethylsulfone (DMSO₂) electrolyte. The effect of particle concentration and current density on the codeposition rate of SiO₂ with aluminium was investigated. The codeposition of the various particles with Al from AlCl₃:DMSO₂ solutions is very high. The amount of codeposited particles is Langmuir dependent on the particle concentration in the electrolyte. In contrast, the effect of the current density on the amount of codeposited SiO₂ is small.     

Electrochemical reduction of potassium from potassium chloride in propylene carbonate electrolyte with aluminium anodes

Potassium has been cathodically deposited in a propylene carbonate electrolyte with concurrent dissolution of aluminium. Starting with an AlCl₃-free electrolyte, changes in the composition and conductivity of the electrolyte, as well as those of the electrode potentials, were measured as a function of charge passed. Anodic and cathodic current efficiencies were both close to 100%. The observed behaviour is consistent with the overall reaction stoichiometry This reaction and its analogues for other alkali metals may conceivably form the basis of practical processes at ambient temperatures for the recovery of alkali metals from their chlorides with concurrent production of aluminium chloride.     

Investigation of the 1-methyl-3-ethylimidazolium chloride-AlCl3/LiAlCl4 system for lithium battery application Part I: Physical properties and preliminary chronopotentiometric study

The applicability of the 1-methyl-3-ethylimidazolium chloride — AlCl₃ system for lithium battery application was investigated. Lithium chloride was found to dissolve up to 1.59 mole ratio of LiAlCl₄/MeEtImAlCl₄ upon reaction between LiCl and AlCl₃ in the melt. Density, conductivity and viscosity of the melt upon addition of LiAlCl₄ were determined. The density was found to increase monotonically from 1280 to 1480 kg m^–3, while the conductivity decreased rapidly from the initial value of 5.6 mS to a steady plateau at 3.4 mS. The viscosity was varied from 1.46 Ns m^–2 to a small but distinct initial fall prior to rising to 2.75 Ns m^–2 when the mole ratio of LiAlCl₄ increased from zero to 1.59. The chronopotentiometric studies indicate a satisfactory electrochemical behaviour with no apparent attack of the melt by the formation of the reactive lithium alloys. 350 cycles were achieved with cycling efficiency over 90% using an optimal c.d. of 6 mA cm^–2 for lithium deposition on aluminium substrate in the melt. Prolonged cycling improved the nucleation rate but led to an increase in the internal resistance and a gradual reduction in the charge and discharge capacity.     

The electrodeposition of aluminium on mild steel from a molten aluminium chloride-sodium chloride bath

The electrodeposition of aluminium on mild steel from a dry and HCl-free AlCl₃/NaCl melt (80 wt% purified AlCl₃, 20 wt% NaCl) has been studied. Electropolishing the substrate in the same electrolytic bath produced satisfactory electroplates with almost 100% current efficiency. The quality of the plate has been examined through photomicroscopy of the cross-section, profilometry, electron microscopy, and electron microprobe analysis of the surface of the electroplate. It has been suggested that the greyish colour of the plate is most probably due to the presence of iron as an impurity in the electroplated aluminium.     

Anodic chlorination of substituted benzenes - the choice of the chlorination reagents

Some substituted benzenes ArH were anodically chlorinated in acetonitrile LiClO₄ on a platinum electrode in the presence of either Cl^? anion or a chlorinated Lewis acid (such as AlCl₃). The overvoltage on the oxidation of Cl^? caused by a strong complexation by some Lewis acid allows consideration that the anodic reaction passes through the radical cation of the aromatic substrate. In such conditions, polychlorinations are possible and in the specific case of toluene, it is shown that the reaction favors the parachlorotoluene formation. The influence of different parameters (for example, the ratio of the concentrations AlCl₃/ArH, the nature of the Lewis acid) in such a reaction are discussed.     

Role of indium in promoting anodic dissolution of Al-In alloys in non-aqueous electrolyte

Exploratory work on the anodic dissolution behaviour of aluminium and aluminium binary alloys in electrolytes in non-aqueous organic solvents is reported. Commonly used electrolytes for non-aqueous battery systems were selected on the basis of their conductivities and activities for anodic dissolution of Al and Al-alloy anodes. It is found that Al–In alloy electrodes exhibit an exceptionally active anodic dissolution behaviour in a 1 M solution of AlCl₃ in anhydrous acetonitrile. The steady-state Tafel polarization plots for dissolution of pure Al, Al–Sn, Al–Ga and Al–In alloy anodes are compared, and a.c. impedance spectra for an Al–In alloy anode in 1 M solution of AlCl₃ in CH₃CN are evaluated and discussed. The In component, like Ga or Hg, interferes with passivation of Al during its anodic dissolution and thus promotes an active condition on the metal surface leading to relatively high anodic dissolution current-densities at substantially negative electrode potentials.     

Effect of Friedel–Crafts reaction on the thermal stability and flammability of high‐density polyethylene/brominated polystyrene/graphene nanoplatelet composites

Brominated flame‐retarded high‐density polyethylene (HDPE) composites containing graphene nanoplatelets (GNPs) were prepared via melt blending. A Lewis acid catalyst, anhydrous aluminium chloride (AlCl₃), was added to initiate Friedel–Crafts reaction for promoting the dispersion of the GNPs in the polymer matrix. Transmission electron microscopy images and Raman spectroscopy revealed that the GNPs were partly unfolded and the domains became smaller in the presence of AlCl₃. Limiting oxygen index and microscale combustion calorimetry showed that the incorporation of AlCl₃ into HDPE reduced flammability and slowed down the heat release rate. Thermogravimetric analysis and char residue measurements proved that a uniform dispersion of GNPs was crucial for forming a continuous and compact carbon layer, thus isolating the underlying materials from flame and preventing heat transfer. Rheological and mechanical tests indicated that interfacial adhesion between polymer chains and GNPs was enhanced. © 2014 Society of Chemical Industry     

Pile electrique a anode d'aluminium—I electrolyte acide

An acid electrolyte (pH ) 3) for an aluminium primary battery has been studied. It contains: Al(CIO₄)₃. 1 M: AlCl₃. $\text{1}\text{30}$ M; (NH₄)₂CrO₄, $\text{1}\text{50}$ M. The performance of three binary aluminium alloys AlZn 2%; AlZn 5%; AlGa 0·3% are compared. Capacity of Al primary battery made with Al 2% is twice that of a conventional Leclanché cell on continuous discharge test. Unfortunately CrO⁼₄ disappears in presence of MnO₂ which is prejudicial to the good conservation of the aluminium cell.     

Emf measurements in the NaClAlCl3 system—I. Activity of AlCl3 in basic melts at temperatures close to the liquidus line

Emf measurements in the formation cell Al|AlCl₃(l), NaCl(l)|Cl₂ were carried out at different mol fractions of AlCl₃ in the range 0 < x_AlCl3 < 0.5. The activity of AlCl₃ increases strongly as the equimolar composition is approached, indicating the presence of a fairly stable AlCl^?₄ complex ion in such melts. Liquidus temperatures at various melt compositions were determined from emf-temperature curves as well as from cryoscopic measurements.