A new bath for the electrodeposition of aluminium. II. Kinetics and mechanism of the deposition and dissolution processes

The electrodeposition of aluminium was carried out successfully in AlCl₃-LiAlH₄/tetrahydrofuran-toluene solutions. The kinetic parameters controlling the cathodic deposition and anodic dissolution of aluminium were derived. The effect of the total concentration of aluminium and the molar ratio of AlCl₃ to LiAlH₄ on the current density-potential behaviour of the rotating disc aluminium electrode was also studied. A detailed mechanism for the electrode reactions was suggested.     

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.     

High-rate plating of aluminium from the bath containing aluminium chloride and lithium aluminium hydride in tetrahydrofuran

An electrolyte for the high-rate plating of aluminium from the tetrahydrofuran solutions of aluminium chloride and lithium aluminium hydride has been developed. A smooth and coherent deposit of aluminium has been obtained at the current density of 18 A dm^–2 without stirring, whereas the conventional diethyl ether solvent bath allows good plating up to 5 A dm^–2 under the same condition. The current densities applicable are increased with an increase in the molar fraction of aluminium chloride in tetrahydrofuran. The conductivity of the plating solution was measured at various molar ratios of aluminium chloride to lithium aluminium hydride. A plateau region of the conductivity curve plotted against the molar ratio is consistent with the composition of the plating bath giving a good plating. The plateau region is enlarged with an increase in total aluminium concentration.     

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.     

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.     

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 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     

Eine neue,breit anwendbare Synthese für aromatische Aldehyde

Diformamide ( 1 ) reacts with activated aromatic compounds like toluene, anisole, m‐xylene, 1,2‐dimethoxybenzene in the presence of AlCl₃ to give N‐(diarylmethyl)‐formamides 2a—d , the corresponding aromatic aldehydes 3—6 are formed as by‐products in low yields. From N,N‐dimethylaniline and 1 /AlCl₃ the triphenylmethane derivative 7 can be obtained. The reaction of anisole with N‐methyl‐diformamide ( 9 ) affords the formamide 10 . The mixture of formamide, P₄O₁₀ and AlCl₃ reveals to be a reagent which is capable to formylate toluene and anisole, resp. Triformamide ( 14 )/AlCl₃ is an effective formylating system which allows the preparation of aromatic aldehydes (e.g. 3,4,17—32 ) from the corresponding aromatic hydrocarbons. Aluminiumchloride can be replaced by borontrichloride. The yields of the formylation reactions depend strongly from the reaction conditions (molar ratio: aromatic hydrocarbon/AlCl₃/ 14 ; solvent, reaction temperature). The scope of the reaction covers nearly complete those of the Gattermann‐Koch‐, Gattermann‐ and Vilsmeier—Haack‐reaction.     

A promising method for electrodeposition of aluminium on stainless steel in ionic liquid

A promising method for aluminium deposition was proposed by using AlCl₃/[bmim]Cl (1‐butyl‐3‐methylimidazolium chloride) ionic liquid as electrolyte. By using this novel method, the volatile and flammable organic solvent systems and the high corrosive inorganic molten salts with high temperature can be substituted, and the deposit microstructure can be easily adjusted by changing the current density, temperature and electrolyte composition. The study was performed by means of galvano‐static electrolysis and the optimum operating conditions were determined based on the systematic studies of the effects of current density, temperature, molar ratio of AlCl₃ to [bmim]Cl, stirring speed and deposition time on the quality of deposited coatings. The electrical conductivities of electrolytes were also investigated as a function of temperature (298–358 K) and molar ratio of AlCl₃ to [bmim]Cl (from 0.1:1 to 2.0:1). Dense, bright and adherent aluminium coatings were obtained over a wide range of temperature (298–348 K), current densities (8–44 mA/cm²) and molar ratio (1.6:1–2.0:1). Results from the analysis of crystal structure show that all of the electrodeposits exhibit a preferred (200) crystallographic orientation. Temperature has significant influence on the crystallographic orientation and there does not appear to be an apparent impact of current density on it. Analyses of the chronoamperograms indicate that the deposition process of aluminium on stainless steel was controlled by three‐dimension nucleation with diffusion‐controlled growth and there is a conversion from progressive nucleation to instantaneous nucleation. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

TMPAC-AlCl3离子液体中恒电流电沉积铝

合成了不同TMPAC和AlCl₃摩尔比的TMPAC-AlCl₃离子液体,并测定了其在不同温度下的电导率。在摩尔比为1:2的TMPAC-AlCl₃离子液体中进行了恒电流电沉积实验,研究了温度、电流密度、搅拌速度和添加剂甲苯等对沉积层的影响。结果表明:在相同条件下摩尔比为1:2的TMPAC-AlCl₃离子液体电导率最大,当温度为80℃,电流密度为20 mA·cm^-2,搅拌速度为500 r·min^-1时,沉积层质量较好且电流效率较高;甲苯的加入,增大了TMPAC-2AlCl₃离子液体的电导率,降低了槽电压,当添加甲苯的体积分数为50%,电流密度为23 mA·cm^-2时,可以得到较为致密、色泽良好、平整而均匀的沉积层。     

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.     

Characterization of polypyrrole films incorporating various anions

The conductivity of polypyrrole films has been enhanced by electrochemical post-deposition doping with various anions. The change of conductivity was found to depend on the type and concentration of the anion. Results for the polypyrrole films doped with anions of H₂SO₄, (C₂H₅)₄N(O₃SC₆H₄CH₃), KI, CH₃C₆H₄SO₃H · H₂O (p-toluene sulphonic acid monohydrate), AlCl₃, KBrO₃ and HNO₃ showed that in the case of H₂SO₄, (C₂H₅)₄ N(O₃SC₆H₄CH₃) and CH₃C₆ H₄SO₃ H · H₂O the conductivity can be enhanced by up to a factor of two, from a value of 67 S cm^–1 up to 165, 102 and 95 S cm^–1, respectively. Doping with I^– had a negligible effect on the conductivity which was about 71 S cm^–1, while in the case of AlCl₃, KBrO₃ and HNO₃ the conductivity of the polypyrrole decreased significantly for certain anion concentrations.     

Electrochemistry of room-temperature chloroaluminate molten salts at graphitic and nongraphitic electrodes

The electrochemistry of unbuffered and buffered neutral AlCl₃-EMIC-MC1 (EMIC =1-ethyl-3-methylimidazolium chloride and MC1= LiCl, NaCl or KCl) room-temperature molten salts was studied at graphitic and nongraphitic electrodes. In the case of the unbuffered 1 : 1 AlCl₃ : EMIC molten salt, the organic cation reductive intercalation at about –1.6 V and the AlCl₄ ^– anion oxidative intercalation at about +1.8 V were evaluated at porous graphite electrodes. It was determined that the instability of the organic cation in the graphite lattice limits the performance of a dual intercalating molten electrolyte (DIME) cell based on this electrolyte. In buffered neutral 1.1 :1.0:0.1 AIC1₃: EMIC : MCl (MC1= LiCl, NaCl and KCl) molten salts, the organic cation was intercalated into porous and nonporous graphite electrodes with similar cycling efficiencies as the unbuffered 1 : 1 melt; however, additional nonintercalating processes were also found to occur between 1 and –1.6 V in the LiCl and NaCl systems. A black electrodeposit, formed at –1.4 V in the LiCl buffered neutral melt, was analysed with X-ray photoelectron spectroscopy and X-ray diffraction and was found to be composed of LiCl, metallic phases containing lithium and aluminium, and an alumina phase formed from reaction with the atmosphere. A similar film appears to form in the NaCl buffered neutral melt, but at a much slower rate. These films are believed to form by reduction of the AlCl₄ ^– anion, a process promoted by decreasing the ionic radius of the alkali metal cation in the molten salt. The partially insulating films may limit the usefulness of the LiCl and NaCl buffered neutral melts as electrolytes for rechargeable graphite intercalation anodes and may interfere with other electrochemical processes occurring negative of –1 V.     

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.     

Effect of ammonia content on the stability of the cellulose cuprammonium complex in spinning solution

Conclusions Using a spectrophotometric method of investigation, it has been shown that in cuprammonium spinning solutions the complex compounds of copper, ammonia, and cellulose contain principally the tetraamine ion Cu(NH₃) ₄ ²⁺ .By using the molar value of the NH₃/Cu ratio in CCAC, one can calculate the free ammonia content of the spinning solution and of the precipitation bath.Translated from Khimicheskie Volokna, No. 2, pp. 30–32, March–April, 1987.     

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 molar ratio of TiO2/SiO2 on the properties of particles synthesized by flame spray pyrolysis

Titania (TiO₂)–silica (SiO₂) nanoparticles were synthesized from sprayed droplets of a mixture of TEOS and TTIP by flame spray pyrolysis (FSP). The effect of molar ratio between TEOS and TTIP in the mixture on the particle properties such as particle morphology, average particle diameter, specific surface area, crystal structure, etc., were determined using TEM, XRD, BET, and FT-IR. A UV-spectrometer was also used to measure the absorption spectrum and the band gap energy of the product particles. As the molar ratio of TEOS/TTIP increased by increasing TEOS concentration at the fixed TTIP concentration, the average particle diameter of the mixed oxide nanoparticles increased with maintaining uniform dispersion between TiO₂ and SiO₂, and crystal structure was transformed from anatase to amorphous. The band gap energy of the TiO₂–SiO₂ nanoparticles increased with respect to the increase of the molar ratio due to the decrease of width of UV-absorption spectrum. Photocatalytic activity of TiO₂–SiO₂ composite particles decreased with the concentration of TEOS.     

Effects of anode-cathode distance on the cell potential and electrical bath resistivity in an aluminium electrolysis cell with a sloping TiB2 composite cathode

A study of the effects of anode-cathode distance (ACD) on the cell potential and electrical bath resistivity in a laboratory scale cell that utilizes a sloping TiB₂ composite cathode shows an increasing bath resistivity as the ACD decreases, due to a simultaneously increasing gaseous phase fraction in the electrolyte. The effective bath resistivity was found to increase rapidly after ACD=10 mm and was proportional to the inverse of ACD within this low ACD range studied (2–10 mm). Addition of NaCl to the electrolyte (5.5 wt%) lowered the electrical resistivity by increasing the conductivity of the electrolyte, and at low ACD it also lowered the bubble contribution to the bath resistivity, most likely due to changes in the hydrodynamic properties of the system. Lowering the cryolite ratio (i.e. molar ratio of NaF to AlF₃) resulted in a higher electrical resistivity in the electrolyte by decreasing the conductivity of the melt, as well as by changing the hydrodynamic properties of the melt, leading to an increased bubble contribution to bath resistivity at low ACD. An increase in temperature resulted in a reduced bubble contribution at low ACD in a similar manner as the NaCl addition. From these results, it is clear that for a commericial process, reduction of the ACD and optimization of process conditions to reduce the effect of bubbles should allow significant savings in the energy requirements of the Hall-Heroult process.     

Biodiesel synthesis via homogeneous Lewis acid-catalyzed transesterification

Lewis acids (AlCl₃ or ZnCl₂) were used to catalyze the transesterification of canola oil with methanol in the presence of terahydrofuran (THF) as co-solvent. The conversion of canola oil into fatty acid methyl esters was monitored by ¹H NMR. NMR analysis demonstrated that AlCl₃ catalyzes both the esterification of long chain fatty acid and the transesterification of vegetable oil with methanol suggesting that the catalyst is suitable for the preparation of biodiesel from vegetable oil containing high amounts of free fatty acids. Optimization by statistical analysis showed that the conversion of triglycerides into fatty acid methyl esters using AlCl₃ as catalyst was affected by reaction time, methanol to oil molar ratio, temperature and the presence of THF as co-solvent. The optimum conditions with AlCl₃ that achieved 98% conversion were 24:1 molar ratio at 110 °C and 18 h reaction time with THF as co-solvent. The presence of THF minimized the mass transfer problem normally encountered in heterogeneous systems. ZnCl₂ was far less effective as a catalyst compared to AlCl₃, which was attributed to its lesser acidity. Nevertheless, statistical analysis showed that the conversion with the use of ZnCl₂ differs only with reaction time but not with molar ratio.     

A xylene electrolyte modified by trimethylchlorosilane for electrodeposition of aluminium

The addition of 2–5 vol % of trimethylchlorosilane to a 2m solution of AlBr₃ in xylene gives a very convenient aluminium electroplating bath. Tendency to dendritic growth ceases and the quality of aluminium improves. Electrodeposition proceeds with high cathodic efficiency. The additive has extended the use of the electrolyte up to 1 year.