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     

Pulse nickel electrolytic colouring process of anodised aluminium

The influence of frequencies of periodic reverse current on the morphology of nickel-pigmented aluminium finishes has been studied. The pigmentation of the anodised aluminium was realised by electrolytic colouring in electrolytes with additives and in additives-free electrolytes. Additives-free electrolytes generally provide advantageous quality of pigmentation with regular and homogenous nickel morphology on the aluminium substrate at all applied frequencies. The presence of 5-sulphophtalic acid additive strongly influences the deposit quality. The deposits obtained from nickel sulphate electrolytes at all used frequencies with the use of periodic reverse current with citrate acid and sulphosuccinic acid additives provide the similar poor quality of colouring under studied plating conditions.     

Electrodeposition of aluminium-copper alloys from alkyl benzene electrolytes

An experimental programme in which aluminium-copper alloys were electroplated from alkyl benzene/ AlBr₃ electrolytes is described. The investigation showed that Al-Cu alloys (0–3.5 wt% Cu) can be plated onto steel and that the resulting coatings are bright, adherent and less porous than equivalent coatings of pure aluminium. The composition of the cathode deposits can be readily controlled by using Al-Cu anodes of specified copper content. About half the copper dissolved from the anodes is transferred to the cathode, the remainder being precipitated from the electrolyte as CuBr. Coating composition varies with current density and this parameter can also be used to control the process. In a parallel investigation, potential differences between aluminium and a number of other metals (Zn, Pb, Cd, Sn, Cu, Ag) were measured. Potential differences in the alkyl benzene electrolytes were found to be 10–30 times less than in aqueous electrolytes which indicates that the alkyl benzenes should be useful for plating other alloys in addition to those of aluminium and copper.     

铝在路易斯酸性1-烯丙基-3甲基米唑氯铝酸离子液体中的低温电沉积(英文)

Lewis acidic 1-allyl-3-methylimidazolium chloroaluminate ionic liquids were used as promising elec-trolytes in the low-temperature electrodeposition of aluminium.Systematic studies on deposition process have been performed by cyclic voltammetry and chronoamperometry.The surface morphology and X-ray diffraction(XRD) patterns of deposits prepared at different experimental conditions were also investigated.It was shown that the nu-cleation density and growth rate of crystallites had a great effect on the structure of aluminium deposited.The crys-tallographic orientation of deposits was mainly influenced by temperature and current density.Smooth,dense and well adherent aluminium coatings were obtained on copper substrates at 10-25 mA?cm?2 and 313.2-353.2 K.More-over,the current efficiency of deposition and purity of aluminium have been significantly improved,demonstrating that the ionic liquids tested have a prospectful potential in electroplating and electrorefining of aluminium.     

Ionic conduction in anodic oxide films on aluminium in molten LiNO3 + KNO3 + NaNO3 electrolyte

Steady-state ionic conduction studies in the anodic growth of films on aluminium in molten LiNO₃ + NaNO₃ + KNO₃ have been made. The breakdown voltage of the film is 73 V, unaffected by change of cd or temperature. The film-forming characteristics of anodic oxide films on aluminium in molten salt electrolytes are different from that of anodic films formed in aqueous electrolytes. The Tafel slope decreases with increase of temperature. Dignam's equation for ionic conduction has been examined critically. His parameter μ^* depends on temperature, whereas i₀ and φ are temperature-independent, which explains the variation of Tafel slope with temperature.     

Anodic behaviour of aluminium in halogenated media. Electrogenerated alkylation catalysts

The anodic dissolution of aluminium in electrolytes in which alkyl- mono- or polyhalides are present together with aromatic compounds, gives rise to the in situ formation of the well known Friedel-Crafts catalysts, promoting the chemical alkylation of the aromatic ring with the halide. A chemical reaction dissolving aluminium is activated by the electrochemical one, and , after the passage of a limited amount of charge, becomes predominant. At this stage the process becomes strongly exothermic, cannot be controlled by electrochemical means and proceeds until one of the reagents, aluminium or the halide, is almost completely consumed. The resulting “red oils” are good catalysts even for alkylations in which halides different from the starting one are employed.     

Evaluation of low-temperature cryolite-based electrolytes for aluminium smelting

Aluminium was smelted in a laboratory-scale cell at temperatures down to 850 °C from cryolite-based electrolytes with bath ratios in the range 0.75–1.50. Electrolyses were conducted for 1–2h using a current density of 1 A cm^–2 on 5 cm² electrodes with an anode-cathode distance of 2 cm. Current efficiencies of up to 95% were recorded. In low bath ratio electrolytes, operation at alumina concentrations of 3 wt% sometimes resulted in the aluminium deposit breaking into globules which clustered around the cathode. Under constant current conditions, the critical alumina concentration for the onset of anode effect was found to be 2 wt%. The bubble evolution characteristics (i.e., size and frequency) which affect mass transfer and cell voltage were also evaluated. Overall, low-temperature cryolite-based electrolytes may offer a viable alternative to conventional compositions for aluminium smelting.Author to whom correspondence should be addressed     

Electrorefining of aluminium scrap from chloride melts

The production of aluminium of primary quality from scrap by electrorefining may become an option of strategic importance. Two important requirements are: (i) substantial energy savings compared to electrowinning, and (ii) easy recycling of alloying elements and molten electrolyte without ecological hazards. The use of molten chloride instead of fluoride electrolytes is preferred as emissions are low, purification of contaminated salts in aqueous solution is easy and oxide ceramic materials for cells and diaphragms can be used. The measurement of formal potentials of most important alloying elements shows that only manganese should be expected to cause trouble in electrorefining of aluminium scrap from alkali chloride melts. Preparative batch refining experiments show that all these alloying metals can be easily separated; manganese is very likely because its activity in aluminium is decreased by alloying or compound formation in aluminium. Results with cells divided by alumina diaphragms show that energy consumptions can be kept below 5 kWh (kg Al)^–1.     

铝合金在不同电解液体系中微弧氧化过程的研究

为比较不同电解液体系下各种工艺参数对铝合金微弧氧化膜性能及耐腐蚀能力的影响,通过微弧氧化法在NaOH、Na2S iO3、NaH2PO4、Na2CO3四种电解液体系分别制备了铝合金氧化膜。通过点滴腐蚀实验比较了四种电解液体系所得氧化膜的耐腐蚀能力,利用扫描电子显微镜(SEM)观察分析了氧化膜的表面形貌。实验表明,在这四种电解液体系中起弧电压均随浓度的降低及电极间距离的增加而逐步升高,而膜厚与氧化电压、时间的增加成正比,但成膜速率随时间的延长而逐渐减缓,在各体系中这些变化的具体情况仍有所区别。其中以NaOH体系所得氧化膜的膜层较致密,微孔分布均匀,相同条件下耐蚀性能要优于其他三种电解液体系所制氧化膜。     

Investigation of the aluminium electrodeposition process in cryolite-based melts using a rotating ring-disc electrode: evidence for the existence of a subvalent intermediate species

The rotating ring-disc electrode technique has been used to investigate the reaction mechanism of the aluminium electrodeposition process in cryolite-based electrolytes. Laboratory studies using high temperature gold-molybdenum and platinum-molybdenum rotating ring-disc electrodes have provided evidence for the existence of a subvalent intermediate species (Al (I)). In a cryolite-alumina electrolyte (bath ratio: 1.5), two well separated convective-diffusion controlled oxidation processes were observed at both a gold and a platinum ring during aluminium electrodeposition at the disc. On the basis of the data presented, a reaction scheme involving reduction of A1(III) to A1(0) via A1(I), followed by chemical dissolution of A1(0) into the bulk electrolyte was proposed. The loss of current efficiency in aluminium smelting was primarily attributed to the chemical dissolution of A1(0), rather than to the formation of a subvalent intermediate species.     

Electrochemical machining as a method of preparing grained aluminium surfaces

Aluminium, usually in sheet form, is often subjected to a graining process prior to further treatment. This is normally a batchwise acid pickle. A study was carried out on a laboratory scale to show that electrochemical machining can be used to produce grained aluminium surfaces by a continuous, high-rate process using non-acid electrolytes.     

Electrochemical sensor for measuring magnesium content in molten aluminium

Design, construction, and tests of magnesium electrochemical sensors using molten salt electrolytes and pure magnesium metal reference are described. Alumina as well as magnesia membrane thimbles were synthesized to use as the supporting matrixes for the liquid electrolytes. Binary as well as ternary salt mixtures containing M9Cl₂ were impregnated in thimbles of various pore sizes. The accuracy, response time, and service life of the sensors were evaluated. The magnesium contents from the electromotive force (e.m.f.) measurements were comparable with those from the atomic absorption analysis. All sensors responded instantly to the changes of magnesium concentration in aluminium melt. The service life was between 2 to 6 h and the minimum initial equilibration time was 2 min, depending mainly on the pore size of the magnesia thimble and the electrolyte salt mixture in use.     

Nature of luminescence during galvanostatic anodizing of high purity aluminium

Galvanoluminescence of high purity aluminium was found to have two fundamental origins: one was the luminescence associated with scintillation or with some concommitant side reactions, taking place at the flaws; the other was the luminescence associated with anions included in the films during anodization. The former appeared to be the origin of the luminescence in inorganic electrolytes such as ammonium borate, borax, borax plus boric acid etc; and the latter appeared to be responsible for the luminescense in organic acids and their salts, such as oxalic, citric, tartaric and succinic acids and ammonium tartrate.     

Butadiene polymerization with a rare earth compound using a magnesium alkyl cocatalyst: 2

A catalyst was developed for the preparation of high cis polybutadiene consisting of ‘didymium’ versatate — aluminium alkyl halide — magnesium dialkyl. By altering the order of component addition and using neodymium versatate, the catalyst activity and cis content of the polymer were both increased. The aluminium alkyl halide could be replaced by mixtures of aluminium trialkyl plus silicon halides or organic halides. Various additives were tried in order to reduce polymer molecular weight and to alter the molecular weight distribution.     

Molar volumes of multicharged electrolytes in water and aqueous sulphuric acid

The apparent molar volumes, φ_v, of aluminium ammonium sulphate and potassium aluminium sulphate in water and aqueous sulphuric acid (0.01, 0.05, 0.10 and 0.15 N) at different concentrations and temperatures have been estimated from the densities of the solutions measured by hydrostatic balance. The φ_v values vary linearly with square root of concentrations. The limiting apparent molar volume, φ⁰_v, and the experimental slope S_v, have been interpreted in terms of solute-solvent and solute-solute interactions, respectively. The φ⁰_v values vary with temperature and can be represented in the power series of temperature. Structure making/breaking capacity of the electrolyte is inferred from the sign of [?φ⁰_v/?T²] values. Both the electrolytes behave as structure breakers in water but structure makers in aqueous sulphuric acid. The molar expansibility, at infinite dilution have been found to be the same for both electrolytes at 290.5 K.     

Composite alkaline polymer electrolytes and its application to nickel-metal hydride batteries

In order to enhance the ionic conductivity of polyethylene oxide (PEO)-KOH based alkaline polymer electrolytes, three types of nano-powders, i.e., TiO₂, β-Al₂O₃ and SiO₂ were added to PEO-KOH complex, respectively, and the corresponding composite alkaline polymer electrolytes were prepared. The experimental results showed that the prepared polymer electrolytes exhibited higher ionic conductivities at room temperature, typically 10⁻³ S cm⁻¹ as measured by ac impedance method, and good electrochemical stability. The electrochemical stability window of ca. 1.6 V was determined by cyclic voltammetry with stainless steel blocking electrodes. The influence of the film composition such as KOH, H₂O and nano-additives on ion conductivity was investigated and explained. The temperature dependence of conductivity was also determined. In addition, polyvinyl alcohol (PVA)-sodium carboxymethyl cellulose (CMC)-KOH alkaline polymer electrolytes were obtained using solvent casting method. The properties of the polymer electrolytes were characterized by ac impedance, cyclic voltammetry and differential thermal analysis methods. The ionic conductivity of the prepared PVA-CMC-KOH-H₂O electrolytes can reach the order of 10⁻² S cm⁻¹. The effect of CMC addition on the alkaline polymer electrolytes was also explained. The experimental results demonstrated that the PVA-CMC-KOH-H₂O polymer electrolyte could be used in Ni/MH battery.     

Galvanoluminescence of aluminium during anodization in non-dissolving electrolytes

Anodic galvanoluminescence (AG) of Al was established in a number of non-aqueous electrolytes. AG of high purity and silver or copper doped aluminium was investigated during anodization in an aqueous borate electrolyte (ABE) and solutions of ammonium salicylate and ammonium adipinate in dimethylformamide (DMF) and ethylene—glycol (EG). The brightness characteristics proved to be different for the aqueous and the non-aqueous electrolytes. For the latter, the AG-brightness was found to be about hundred times higher than that for pure Al in ABE, and depended neither on the ionogen concentration, nor on the metal purity. Moreover, the AG-spectrum in the non-aqueous electrolytes proved to be characteristic for the nature of the solvent (DMF and EG). On the contrary, in ABE the well-known increase of AG-brightness with doped Al was observed, the spectra having been found characteristics for the metal impurity.The findings are explained on the basis of a hypothesis about the origin of liminescent centers. According to it, both the metal impurities and the ions or molecules from the electrolyte can penetrate into the anodic film, acting there as liminescent centers. Brightness and spectral distribution of AG will then be determined by those centers, which supply the prevailing light flux.     

Localized nature of the luminescence during galvanostatic anodizing of high purity aluminium in inorganic electrolytes

Luminescence during galvanostatic anodizing of high purity aluminium containing Fe, Si and Cu as major impurities in inorganic electrolytes, typically an aqueous solution of ammonium borate, was found to be a local phenomenon which takes place at “flaws” in the growing oxide film. The intensity of the luminescence was found to be closely correlated to the concentration of “flaws” in the film: the intensity of the luminescence being roughly proportional to the concentration of “flaws” in the film. Rough estimate of the concentration of ”flaws“ in the film formed on “as received”, “chemically cleaned” and “electropolished” aluminium plate was 2 × 10⁸.3 × 10⁷ and 10⁵/cm², respectively. Any mechanism deeming the luminescence to be an electroluminescence in a homogeneous oxide with the collision excitation of the impurities or with the recombination at impurity centres has been rejected.     

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.     

Direct electrolytic reduction of solid alumina using molten calcium chloride-alkali chloride electrolytes

Solid alumina was reduced by electro-deoxidation to aluminium metal containing 1.8 and 5.4 at% Ca in molten CaCl₂–NaCl and CaCl₂–LiCl electrolytes at 900 °C, respectively. The potential-pO²⁻ diagrams for the Al–O–M–Cl (M = Na or Li, or/and Ca) system were constructed to predict equilibrium phase relationships in the electrolytes at 700 and 900 °C. It was found that calcium aluminates were formed as the main intermediate reaction products and were subsequently reduced to form the Al-rich Al–Ca alloys during electro-deoxidation. Calcium and/or lithium, at reduced activities, were created at the cathode especially at 700 °C at the same time as the ionization of the oxygen from the cathode, which resulted in Al₂Ca formation. The experimental results were consistent with the thermodynamic predictions.