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

The electrodeposition of aluminium on brass (63/37) from a dry AlCl₃/NaCl melt (80wt.% purified AlCl₃, 20 wt.% NaCl) using static as well as rotating cathodes and a variety of conditions has been studied. The current efficiency of the process is very high and the electrodeposits are smooth, fine grained and silver white in appearance. Although at lower temperatures, there is a tendency for flakes to be formed locally these are easily removed and do not affect the overall quality of the electroplate.     

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.     

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.     

High speed zinc electrowinning system using a hydrogen anode and a rotating aluminium disc cathode

The performance of a novel high speed zinc electrowinning system using a hydrogen anode and an aluminium rotating disc cathode (1 m diam.) was investigated under various experimental conditions. This new type of zinc electrowinning system was continuously operated at a current density of 70 A dm^–2, which is twelve times higher than that usually employed. Current efficiency is 90% at 50 A dm^–2 in an electrolyte containing 60 g dm^–3 Zn + 160 g dm^–3 H₂SO₄, the zinc purity being at least 99.999%. The energy usage of the system is 1650 kWh per tonne of zinc, 380 m³ of H₂ gas being required.     

Electrochemical properties of aluminium anodes for Al/air batteries with aqueous sodium chloride electrolyte

In order to develop the new anode materials for Al/air batteries, electrochemical properties of pure aluminium (99.999 %), technical grade aluminium (99.8 %) and the alloys with indium and tin, i.e. Al—0.1 % In, Al—0.2 % Sn and Al—0.1 % In—0.2 % Sn have been investigated in 2 mol dm⁻³ NaCl solution. The aluminium materials were polarized anodically in the range 20–100 mA cm⁻² for a 30 min period. During the anodic polarization variation in potential was recorded as a function of time and the simultaneous hydrogen evolution was measured. The rate of hydrogen evolution reaction was found to increase with increasing anodic polarization which is characteristic of the negative difference effect. The additional information concerning the corrosion behaviour of the tested materials was provided by light microscope imaging. The results show that the examined technical grade aluminium alloys could serve as suitable anodes for Al/air batteries containing sodium chloride electrolyte; with Al–In exhibiting the most remarkable characteristics. The addition of In as alloying component to aluminium reduces electrode polarization, decreases hydrogen evolution rate and increases the anode efficiency.     

Hexamethylene diisocyanate crosslinking 2‐hydroxypropyltrimethyl ammonium chloride chitosan/poly(acrylonitrile) composite nanofiltration membrane

The effects of membrane preparation conditions on membrane properties were studied in detail. The results suggested that composite nanofiltration (NF) membrane from 2.0 wt % 2‐hydroxypropyltrimethyl ammonium chloride chitosan (HACC) vaporized for 2.5 h at 50°C, and then crosslinked for 9 h at 50°C with hexamethylene diisocyanate (HDI)/ethanol (0.45/50 wt/wt) were found to have optimal performance. The resultant membrane was called HACC/PAN [poly(acrylonitrile)] NF membrane. The characteristics of this membrane such as pure water permeability, molecular weight cut‐off, rejection of salts, and swelling were investigated. And its cut‐off molecular weight (MWCO) was ～520 Da. At 25°C and 1.0 MPa, the permeability of water was 17.24 L/h m² MPa. Swelling in water decreased and rejection of salts increased with increasing HDI concentration, indicating pore contraction and increase in hydrophobicity as well as pore tortuosity due to crosslinking. The order of rejection to different salt solutes followed the decreasing of CaCl₂, MgCl₂, NaCl, KCl, and Na₂SO₄, suggesting that this membrane was positively charged. The rejections to MgCl₂ and CaCl₂ were more than 0.90; therefore, this membrane can be used for hardness removal in water treatment process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007.     

The reduction of ferric chloride by aluminium in aluminium chloride melts

The rate of reduction of FeCl₃ to FeCl₂ by metallic aluminium in AIcl₃ melts has been studied at 212, 227 and 242 °C. Within the range of conditions investigated, the rate of reduction was proportional to the ferric ion concentration in the melt and to the surface area of the aluminium. After an initial coverage of the aluminium by a protective film of iron the reduction proceeded effectively only to the ferrous state.     

Influence of different anions on the behaviour of aluminium in aqueous solutions

The influence of chloride, sulfate and perchlorate anions on the behaviour of native oxide layers on aluminium is investigated using electrochemical techniques. Due to its influence on the open circuit potential and the cathodic side of the polarization curve the oxygen concentration has been carefully controlled. Two kinds of attack on a commercially pure aluminium (99.5 wt %) have been observed. In all the investigated 0.5 M Cl^–, 0.5 M ClO^– ₄ and 0.5 M SO^2– ₄ aqueous solutions the metal is corroded around the iron and silicon containing precipitates, but only in Cl^– and ClO^– ₄ solutions is crystallographic pitting observed. Comparison with high purity aluminium (99.99 wt %) shows that pitting corrosion is not influenced by the presence of impurities in the aluminium alloys, but by the presence of anions in solution. The pH and/or oxygen concentration determine whether or not the pitting potential coincides with the corrosion potential.     

Aluminium alloys for aluminium primary cell

Aluminium has not widely been used for anode material for primary cells, despite its attractive properties. Aluminium loses a great part of the potential when anodically polarized, and is easily coroded in aqueous solution with hydrogen evolved. Aluminium alloys derived from high purity aluminium (99.999%) were prepared for application to primary dry cell. Small amounts of the following elements were added to aluminium: Zn, Sn, Bi, In, Mg. The electrode potential, the anode Faradaic efficiency and the rate of corrosion of the alloy specimen sheet (10 × 10 × 0.5) were measured in 1 M AlCl₃ aqueous solution. The rate of corrosion significantly increased after anodic polarization (anodic dissolution). The electrode potentials at open circuit and anodic polarization (10 mA cm⁻² shifted remarkably in the negative direction by alloying. The anode Faradaic efficiency and the rate of corrosion depended upon the alloy composition. The alloy, Al-3.0 Zn-0.13 Sn-0.01 Ga-0.07 Bi (% w/w), gave the best results. The anode efficiency amounted to 99.7% as compared with 87.4% for 99.999% Al. The average rate of corrosion was reduced to 0.03 mg cm⁻² h⁻¹ (short term) and 0.01 mg cm⁻² h⁻¹ (long term). These electrochemical properties will improve the characteristics of aluminium dry cells.     

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.     

Improvements of anode properties of aluminium alloys for aluminium primary cell: heat treatment and corrosion inhibitors

Improvements of anode properties of aluminium alloys were attempted for application to a primary dry cell. Heat treatments were investigated chiefly for the alloy A1—3.0Zn—0.13Sn—0.01Ga—0.07Bi(% w/w) derived from high purity aluminium (99.999%). The solution heat treatment (homogenization) of the alloy at 400°C for 4 h presented the best anode properties, ie the faradaic efficiency and the rate of corrosion in 1 M AlCl₃ aqueous solution as the electrolyte. The average grain size diameters of the alloy specimens were also measured after heat treatment at various temperatures. The electrochemical properties were discussed in connection with the structures of alloy. Corrosion inhibitors were investigated for suppression of corrosion rates. Addition of agar and α-amilase to 1 M AlCl₃ significantly reduced the current loss (100 — faradaic efficiency, %) and the rate of corrosion. The alloy mentioned above treated at 400°C (homogenization) combined with agar (2 g l⁻¹) as a corrosion inhibitor gave the best electrochemical properties; the faradaic efficiency 99.8% and the average rate of corrosion 0.008 mg cm⁻² h⁻¹ (short term) and 0.005 mg cm⁻² h⁻¹ (long term).     

Electrochemical formation and characteristics of aluminium hydroxide on a platinum substrate from dimethylsulphoxide and water mixtures

Results obtained with Al(ClO₄)₃ in DMSO solutions with different water content at a Pt substrate are presented. Different negative potential perturbations produce the reduction of water molecules from the aluminium ion coordination sphere yielding hydrogen gas and a film of aluminium hydroxide solvated by water and DMSO molecules. The inhibiting effect of the electroformed film and its water content depend on the negative potential value reached. Potentiodynamic i/E profiles present two main cathodic current peaks which are related to [Al(DMSO)_6-iH₂O_i]³⁺ complexes with i = 1 and 2, through the current dependences with water and aluminium ion concentrations. Bulk diffusion of the complexes, charge-transfer reactions and the inhibiting nature of the film formed were thoroughly investigated. Molecular hydrogen is oxidized at positive potentials yielding hydrogen ions which in turn produce a partial recovery of the electrode activity.     

无机缓蚀剂对铝合金缓蚀作用的研究

通过电化学极化曲线方法和电化学阻抗（ＥＩＳ） 研究了碳族元素含氧酸盐对铝合金在３ ．５ ％ （ 文中所叙述的３－５ ％ 的ＮａＣｌ 均指质量分数,以下不再另注）ＮａＣｌ 溶液中的缓蚀作用．实验结果表明,在氯化钠溶液中添加低浓度的碳酸钠和硅酸钠及高浓度的硅酸钠对铝合金具有较好的缓蚀作用,而添加低浓度的碳酸氢钠后缓蚀效率却很低,甚至没有缓蚀作用．碳酸钠和硅酸钠对铝合金的缓蚀作用是通过抑制铝合金的阴极反应和阳极反应,在铝合金的表面形成不溶的沉淀膜和ｐＨ 效应实现的．碳酸钠在一定程度上能够提高铝合金的抗点蚀的能力．     

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.     

A bipolar electrode cell for aluminium electrorefining

Electrorefining of aluminium was carried out at 750 °C using bipolar electrode cells with centre holes 2, 10 or 20 mm in diameter. Through the centre holes liquid electrorefined aluminium rises to the electrolyte surface. The bipolar electrode cell consists of graphite cathodes, Al–Cu–Fe–Mn or Al–Cu–Fe–Zn alloy anodes and a BaCl₂–NaCl–AlF₃–NaF electrolytic melt. The centre hole size of more 20 mm in diameter is required to continuously float up the aluminium electrodeposited onto the electrolyte surface, while the current efficiency of the cell decreases with increase of the centre hole size, from 97% at 2 mm diameter to 92% at 20 mm diameter. Aluminium of 99.97% purity precipitates at the cathode. Iron, manganese and zinc included in the alloy as impurities are hardly deposited and the concentrations of these elements in the deposit are 100, 80 and 170 ppm, respectively. In this process aluminium can be produced with an energy consumption of about 4.9 × 10³ kWh(t-Al)^–1, which is one-third smaller than that of the Gadeau process.     

AC-Impedance measurements on aluminium in chloride containing solutions and below the pitting potential

Impedance measurements were performed on aluminium in 0.5M NaCl in the frequency range 5×10^–4-10⁴ Hz and before the onset of pitting corrosion. The behaviour of the system was characterized by a high frequency capacitive loop related to the thickness of the oxide film, an inductive loop at medium frequency, which was interpreted on the basis of the dielectric relaxation model proposed by Dignam, and a second capacitive loop obtained at low frequencies which was ascribed to the film dissolution through the formation of a soluble chloride containing aluminium salt.     

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.     

Synergistic effect of halide ions and polyethylene glycol on the corrosion inhibition of aluminium in alkaline medium

The corrosion inhibition of aluminium in alkaline medium was studied at 30 and 40°C in the presence of polyethylene glycol (PEG) using gravimetric (weight loss) and thermometric techniques. The effect of halides (KCl, KBr, and KI) on the inhibitory action of PEG was also studied. It was found that PEG acted as inhibitor for aluminium corrosion in the alkaline medium. Inhibition efficiency increased with increasing inhibitor concentration. An increase in temperature led to increase in both the corrosion rate and inhibition efficiency in the absence and presence of inhibitor and halides. Phenomenon of chemical adsorption mechanism is proposed from the values of E_a, Q_ads, and ΔG obtained. The adsorption of PEG on the surface of aluminium was found to obey Flory–Huggins and Temkin adsorption isotherms. The synergism parameter, S₁ evaluated was found to be greater than unity indicating that the enhanced inhibition efficiency caused by the addition of halides is synergistic in nature. The inhibition efficiency, surface coverage and synergism parameter increased in the order; I^?> Br^?> Cl^? showing that a joint adsorption of PEG and halide ions on aluminium plays a significant role in the adsorption process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The electrolysis of Al2S3 in AlCl3-MgCl2-NaCl-KCl melts

The electrolysis of Al₂S₃ has been investigated in AlCl₃-MgCl₂-NaCl-KCl melts. Experimental results obtained at 1023 K show that dissolved Al₂S₃ can be electrolysed to give aluminium and elemental sulphur. It has been found that the limiting current density for the electrolysis of Al₂S₃ in these melts is that at the anode and it increases with increasing Al₂S₃ concentration. It appears that within the current density range 0.2 to 1.2 A cm^–2, the cathodic current efficiency of the electrolysis of 5 wt % Al₂S₃ does not vary significantly with the current density. Within that current density range, current efficiencies of about 75 to 85% are obtained.     

Development of anodes for aluminium/air batteries — solution phase inhibition of corrosion

The discharge characteristics of aluminium in inhibited and uninhibited 4 M KOH at 50°C have been explored. The performance of pure aluminium as a fuel is compared with that for two leading alloy fuels that had been evaluated in our previous work, Alloy BDW (Al–1Mg–0.1In–0.2Mn) and Alloy 21 (Al–0.2Ga–0.1In–0.1Tl). The inhibitors employed in this study, SnO ₃ ^2– , In(OH)₃, BiO ₃ ^3– , Ga(OH) ₄ ^– , MnO ₄ ^2– , and binary combinations thereof, are either present in Alloys BDW and 21 or have been investigated previously (SnO ₃ ^2– ). We found that potassium manganate (K₂MnO₄) and Na₂SnO₃+In(OH)₃ are effective inhibitor systems, particularly at high discharge rates (400 mA cm^–2), but at low discharge rates only manganate offers a significant advantage in coulombic efficiency over the uninhibited solution. Alloy BDW exhibits a very low open circuit (standby) corrosion rate, but its coulombic efficiency under discharge, as determined by delineating the partial anodic and cathodic reactions, was found to be no better than that of aluminium in the same uninhibited solution. Alloy 21 was found to exhibit a comparable performance to Alloy BDW under open circuit conditions and a much higher coulombic efficiency at low discharge rates (100 mA cm^–2), but the performance of this alloy under high discharge rate conditions was not determined. Alloy 21 has the significant disadvantage that it contains thallium.