Behaviour of Aluminium in Alkaline and Neutral Tartrate and Citrate Solutions

Abstract

The anodic polarisation of aluminium (2S) in a solution containing 1 M-sodium hydroxide, 0·3/ sodium chloride and 1–10% sodium tartrate and saturated with calcium hydroxide has been studied. The anode utilisation efficiency has been determined at various current densities starting from 2 mA cm^?2. It has been found that the corrosion of aluminium in a solution containing 10% tartrate, alkali and chloride is reduced by addition of calcium hydroxide. It has, however, been observed that under similar conditions, tartrate causes a greater degree of polarisation than citrate, indicating that tartrate may not be as effectiveas citrate in complexingaluminium and may even favour anodic oxidation.     

Laboratory-scale performance of a binary Cu-Al alloy as an anode for aluminium electrowinning

A binary Cu-Al alloy (9.4 wt.% Al) has been investigated as a potential inert anode for aluminium electrowinning. Anodes have been tested in a laboratory electrolysis cell both with and without preformed oxides. Electrolysis was conducted in cryolitic electrolytes with anode current densities of 0.5 A cm⁻². The anodes operated satisfactorily as measured by electrical parameters. However, substantial corrosion of the Cu-metal substrate was observed. The external oxide generated on pre-treated anodes was porous and allowed the electrolyte to penetrate through to the Cu-metal whereby corrosion was initiated. An untreated anode formed an in situ surface alumina film, but this did not prevent corrosion of the substrate.     

The mechanism of caustic cracking of carbon steels—I. Influence of electrode potential and film formation

The anodic behaviour of a 0·1% carbon steel wire in 10M sodium hydroxide solution at 121°C has been studied at different electrode potentials under static conditions, and while the wire yields at strain rates between 1·5 and 436%/min.The static material forms a fairly coherent and adherent film of magnetite in the potential range ca. ?0·60 to ?0·85 V(she), while the anodic current density falls to ca. 0·2 mA/cm² (at ?0·70 V) in ca. 40 min. When such a specimen is made to yield at 436%/min, the overall current density continuously rises to over 8 mA/cm² at the bared metal area produced by the cracking of the oxide film. This current density is sufficient to account for the rate of crack propagation measured microscopically on specimens strained at 1·5%/min. Equivalent results are reported for potentials over the whole range ?0·60 to ?0·85 V(she).On either side of this potential range little or no adherent film is formed, the anodic current density does not fall below ca. 1 mA/cm² and on straining rises to no more than ca. 5 mA/cm²; and no cracks are produced.The results strongly support the theory that crack propagation occurs because bared metal at the yielding advancing edge of a stress-raising crack can dissolve several hundred times as fast as that at the static crack sides, which are continuously protected by the growth of film. The crack thus maintains its acuity, and the raised stress at its edge maintains ductile yielding of the metal so that the electrochemical crack advancement proceeds without the need for any mechanical cracking.A comparison with previously reported work on the same steel in hot concentrated nitrate solutions shows that the range of anodic current densities found on bared metal, and the corresponding range of crack propagation rates, are about an order of magnitude less in the present hot concentrated hydroxide solution.     

Electrochemical properties of aluminum anodes in gel electrolyte-based aluminum-air batteries

Various concentrations of potassium hydroxide (KOH) solution electrolytes were gelled with a hydroponics gelling agent and used in aluminum-air (Al-air) cells. An aluminum plate and a single air-cathode were used as the anode and cathode, respectively. The cells were discharged at a constant current density of 0.08, 0.80 and 1.60 mA/cm². The 0.6 M KOH concentration gave the highest capacity and power density of 105.0 mA h/g and 5.5 mW/cm², respectively. The capacity of the fabricated cell decreased when the KOH concentration went beyond 0.6 M. The corrosion of Al to Al(OH)₃ as shown by the structural and surface morphology observations was the main factor for the failure of the cells.     

Effect of current density on composition and structure of electrodeposited Au–Ni alloy coatings

Abstract

The effect of current density on composition and structure of galvanic Au–Ni alloy coatings electrodeposited from weakly acidic additive free electrolyte was investigated. At low current density (up to ～10 mA cm^?2), light yellow coloured alloys enriched with Au are deposited. At higher current density the Ni content is abruptly increased and the coatings become coarse and dark. Deposits with an average content of Ni up to ～50 at-% were obtained. Only a small amount of Ni (up to 20 at-%) takes part in the formation of non-equilibrium super saturated Au–Ni solid solution. The remainder of the Ni is deposited in the interglobular space as an amorphous Ni oxide–hydroxide or as Ni bearing hydroxide salts. Besides Ni, the alloy coatings contain C, N, O, K and H.     

The electrochemical deposition of Zn–Mn coating from choline chloride–urea deep eutectic solvent

Electrochemical and microscopic techniques were used for the characterisation of Zn–Mn coatings electrodeposited from choline chloride–urea deep eutectic solvent. Cyclic voltammograms show that there was no discernible Mn reduction peak when only Mn²⁺ was present in DES solution. The distinct Mn peak developed only upon addition of Zn²⁺ to the solution, probably due to previous Zn nucleation on the steel substrate. It was found that 22–27?wt-% Mn deposited at current densities of 3–8?mA?cm^?2, amounts significantly higher than those obtained from aqueous electrolytes. Since higher deposition current densities resulted in the formation of a porous surface consisting of clusters of nodular crystallites, the optimal deposition c.d was determined to be 3?mA?cm^?2.     

Structure and Properties of Nickel Deposited at High Current Densities

Deposition and codeposition of nickel and chromium from organic and inorganic solvents are reviewed. It is shown that ductile adherent chromium deposits can be obtained from an acetone bath using 1–10 mA/cm² at 15°C. Pure nickel deposits are obtained from an acetone bath using up to 20 mA/cm² at 15°C and an acetic acid bath using 1–30 mA/cm² at 20°C. It is further shown that additions of chromic chloride to a methanol bath lead to deposition of pure nickel deposits from 1–15 mA/cm² at 20—40°C. An optimum quantity of 20 g/1 of chromic chloride gives a cathode efficiency of 100 per cent at 10 mA/cm². All the baths are shown to function in the presence of water. Codeposition is obtained from a methanol bath at 50 mA/cm² at 20°C. It is shown that aluminium can be directly plated with nickel from a methanol bath, although consistently good adhesion is not obtained.     

Electrocrystallization of nanocrystallite calcium phosphate coatings on titanium substrate at different current densities

Calcium phosphates were electrocrystallized on titanium substrate by electrochemical deposition technique, in which the electrolyte was 0.167 M CaCl₂ and 0.1 M NH₄H₂PO₄. Different current densities (0.375, 1.5, 3, 6 mA/cm²) were applied. The pH of the solution after mixing of equal volumes was 4.6. The surface morphology, chemical composition and phase identification of the coatings were investigated by scanning electron microscopy associated with an energy dispersive spectrometer (SEM-EDXS) and X-ray diffractometry (XRD). Effects of the current density on the morphology and the structure of the coating were also discussed.The results showed that at all current densities tested, the coating is brushite (dicalcium phosphate dihydrate CaHPO₄ · 2H₂O). Furthermore, the results showed that coating thickness and weight gain are increased and the morphology changed with increasing deposition current density (from 0.375 to 6 mA/cm²). On contrary, thickness and weight gain are decreased with sodium hydroxide treatment. NaOH treatment converts brushite of Ca/P ratio 1:1 to hydroxyapatite of Ca/P ratio of 1.667. So, chemical analysis of the solution shows soluble P₂O₅ content. Coating thickness at 6 mA/cm² was about 20 and 30 µm with and without treatment, respectively. It decreased to about 9.5 and 12 µm at 0.375 mA/cm² current density, with and without treatment, respectively. However, the formed phase is not changed with increasing current density. In addition, it is found that, even at high current density (6 mA/cm²), no hydroxyapatite was directly electrocrystallized due to low corresponding potential (less than 5 V) and low corresponding voltage (468 mV).     

Über den Einbau von Phosphor in Aluminiumhydroxide und anodische Aluminium-Oxidschichten

The Incorporation of Phosphorus into Aluminium Hydroxides and Anodic Aluminium Oxide Films The in corporation of phosphorus during the anodic oxidation of high purity aluminium in phosphoric acid solutions increases with formation voltage (20 V to 100 V) and formation temperature. There is a minimum of phosphorus incorporation at a current density of 5 mA/cm². For this case, a dependence of porous oxide layer formation and an impurity ion incorporation with current density is discussed. Aluminium covered with a hydroxide film produced by a pretreatment with hot water before anodic oxidation exhibits phosphorus contents independent of formation voltage and current density but increasing with temperature. Hence, it follows, that no porous layer is formed and that phosphorus is incorporated predominantly by chemical reaction of hydroxide and phosphoric acid. The concentration of phosphorus is determined by using the radiotracer method.     

Control of morphology and orientation of electrochemically grown ZnO nanorods

We report the direct electrochemical deposition of ZnO nanorods on an indium tin oxide substrate. The morphology and orientation of the grown ZnO nanorods were investigated as functions of the current density. It is likely that the concentrations of OH^? and Zn²⁺ ions, which could be controlled by varying the current density, determine the shape and alignment of the ZnO nanorods. The nanorods were tilted, hexagonal, and prismatic at a low current density (0.1 mA/cm²) and vertically aligned and obelisk-shaped at high current densities (greater than 0.6 mA/cm²). By using the low and high current densities sequentially in a two-step growth process, vertically aligned, hexagonal, and prismatic ZnO nanorods could be grown successfully. The underlying mechanism responsible for the growth of the ZnO nanorods is also discussed.     

Electrocatalytic performance of Pb−Ru pyrochlore prepared by the amorphous citrate precursor method for bifunctional air electrodes

Pb−Ru pyrochlore has been of interest as bifunctional electrocatalyst for an air electrode. An amorphous citrate precursor (ACP) process has been optimized to prepare Pb−Ru pyrochlore powders with high surface areas with consequent improvement of its electrocatalytic performance in an air electrode. The surface area of the final powder is 30 m²/g, which is larger than the value obtained by the conventional hydroxide method. A PTEF-bonded gas diffusion electrode loaded with pyrochlore catalysts prepared by the ACP method showed good bifunctional performance. The electrode loaded with only 10 mg/cm² of pyrochlore powder prepared by ACP showed good bifunctional performance, i.e. 100 mA/cm² for oxygen reduction and 100 mA/cm² for oxygen evolution, at 0.6 and 1.6 V vs. RHE, respectively. This performance compares well to the results from lower-area pyrochlore at much higher loading.     

α-Ni(OH)2 electrodeposition from NiCl2 solution

α-Ni(OH)₂ was synthesized from a NiCl₂ solution by electrodeposition method. In order to conduct a systematic study on the effects of experimental parameters, a series of electrolyte initial pH values, current densities, electrodeposition temperatures, and electrodeposition time were used. Cyclic voltammetry results demonstrated a side reaction of Ni²⁺+2e→Ni. The X-ray diffraction analysis, Fourier-transform infrared spectrum, and the color of the product showed that pure α-Ni(OH)₂ could be obtained in the initial pH value range of 2–5.86, current density range of 10–25 mA/cm² electrodeposition temperature range of 25–35 °C, and electrodeposition time range of 1.0–3.0 h. When electrodeposition temperature increased to 45 °C, a mixture of α-Ni(OH)₂ and metallic Ni was obtained. A current density higher than 30 mA/cm² resulted in the sample with features of β-Ni(OH)₂. A small amount of metallic Ni existed in the as-prepared sample when current density decreased to 5 mA/cm². A slight increase of electrolyte pH was observed with increasing initial solution pH and current density. Electrodeposition mass revealed a slight decrease with initial pH decreasing and showed an almost linear increase with current density increasing. The slope of the curve for electrodeposition mass versus electrodeposition time remained stable in the first 2.0 h and then decreased.     

Structural evaluation of brushite/gelatine coatings on graphite substrate

Brushite is one of the most frequently formed products of the electrochemical deposition. It has shown excellent biological behaviour of calcium phosphate coatings on carbon composites. Calcium phosphate coatings were obtained by the electrochemical deposition from the solution of calcium and phosphate ions at pH = 2.4 and with 0.2 or 1 wt.% gelatine addition. Graphite substrate was used as cathode and Pt basket as anode. Electrochemical deposition of brushite/gelatine composite layer was carried out at current densities from 5 to 20 mA/cm². Coatings were examined before and after annealing at 850 °C in Ar. The large channels were observed in coatings at higher concentrations of gelatine and high current densities in microstructure. The adhesive strength of thin brushite/gelatine coating was around 7 MPa. Linear dependence of deposit weight increase with electrolysis time was observed. Similarly, the gelatine content in coating rose linearly with gelatine concentration in electrolyte. After annealing of coatings at 850 °C in argon, the brushite was transformed to hydroxyapatite and CaO, the size of the needle-like brushite particles decreased and small spherical or regular shaped particles of CaO were formed. The weak bonding of thermal treated brushite/gelatine deposits to graphite was found.     

Influence of Chloride Ion in Acid Tin Methanesulphonate Electrolytes

The effects of trace amounts (<500 mg l^?1) of chloride ions in acid tin methanesulphonate plating solutions are presented. Thermodynamic calculations show the main species in the stannous methanesulphonate electrolytes is stannous ion and soluble complexes of Sn(II)-Cl are present. Solubility calculations show no formation of an insoluble Sn(II)-Cl complex. Electrochemical studies reveal the role of chloride ion is significant in inhibiting stannous reduction in low current density areas and only at very high Cl^? concentrations where the current is kinetically controlled. At typical plating current densities of about 20 mA cm^?2 to 40 mA cm^?2, the current is under diffusion control and commercial plating lines should not expect any difficulties from trace amounts of chloride in the electrolyte during tin plating.     

Electrocatalytic properties of electrodeposited Ni–Mn–S system in alkaline electrolytes

Abstract

Ni–Mn–S was electrodeposited on mild steel from sulphate–thiocyanate baths. The resultant materials were evaluated for electrocatalytic activity towards hydrogen evolution reaction in 30 wt-% KOH. Incorporation of sulphur in Ni–Mn improves the electrocatalytic activity giving a sizeable increase in exchange current density j ₀. In Ni–Mn the hydrogen evolution reaction is through a Volmer–Tafel mechanism whereas in the Ni–Mn–S system follows a Tafel mechanism. The influence of deposition current density (CD) was investigated. Electrocatalytic activity increased with increase in the deposition CD and was maximum in samples deposited at 80 mA cm^?2.     

Mathematical modeling of electrodeposition of permalloy thin film I. direct current plating

A mathematical model is presented to describe the electrodeposition of Ni-Fe alloy film on a rotating disk electrode in chloride solution. The model incorporated with anomalous codeposition phenomena agrees well with the experimental data under a variety of conditions. The Fe content in permalloy shows a maximum at current densities between 2 mA/cm² and 5 mA/cm², then decreases monotonically as a function of the applied current density. Also experimental and simulated results are discussed in terms of solution pH, rotating disk speed, and iron concentration which affects the Fe content in the permalloy during electrodeposition.     

Polymer light-emitting diodes with polyethylene dioxythiophene–polystyrene sulfonate as the transparent anode

Polyethylene dioxythiophene–polystyrene sulfonate (PEDT–PSS) thin films spin-cast from aqueous dispersion have been used as semi-transparent anodes for polymer light-emitting diodes (LEDs). An external quantum efficiency of 2.0% was achieved with poly(2-methoxy,5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH–PPV), as the semiconducting luminescent polymer. LEDs fabricated with the PEDT–PSS anode exhibit an enhanced stress life in excess of 500 h at 70 mA/cm² under constant-current conditions (initial brightness 600 cd/m², reduced to 450 cd/m² after 500 h).     

The Cleaning of Iron and Steel

The paper reviews the present state of development of a well established process for electro-brightening aluminium. The brightening operation is carried out in a solution containing 15% wt./vol. anhydrous sodium carbonate and 5% wt./vol. anhydrous trisodium phosphate at 80–82°C. After an initial etch for 10–30 seconds, 12V d.c. is applied between stainless steel cathodes and the aluminium anode, the anode current density falling rapidly from 35A/ft² at the start to about 20 A/ft². Treatment is for 5–15 minutes, after which the article is rapidly removed and rinsed in water.

The thin oxide film produced on the metal surface by this treatment is removed by immersion in a hot solution of phosphoric and chromic acids, since it forms an easily-marked outer layer on subsequent anodising, and the article is finally subjected to the normal protective anodic treatment in sulphuric acid, after which it is sealed and waxed. For certain decorative applications the anodic film may also be dyed.

The process works best with super purity aluminium (99·99% Al) and certain alloys made from this metal, particularly those containing small amounts of magnesium, but good results can also be obtained with 99·8% Al.

The treated surface has a high reflectivity for both light and radiant heat, and the process is extensively used in the production of aluminium reflectors, as well as for a wide range of decorative purposes.     

Morphology of alpha-lead dioxide electrodeposited on aluminum substrate electrode

Alpha-lead dioxide was deposited by anodization of alkaline solution containing HPbO2- anions. Scanning electron microscopy (SEM) results show that the morphology is remarkably affected by the current density, concentration of HPbO2- anions, bath temperature and electroplating time. Compact and well adherent layers are possibly obtained under conditions of current densities ≤3 mA/cm2, electrolyte containing 4 mol/L NaOH and 0.12-0.14 mol/L lead (Ⅱ ), bath temperature of 40 ℃, and electroplating time of 2 h. EDS analyses show that the PbO2 deposited in alkaline condition is highly non-stoichiometric at high current density.     

Effect of UV–ozone treatment on ITO and post-annealing on the performance of organic solar cells

In this paper, the influence of the ultraviolet (UV)–ozone treatment of indium tin oxide (ITO) surface and the active layer post-annealing treatment on the performance of organic solar cells were investigated. Bulk heterojunction organic solar cells based on the blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) were fabricated. It is found that the devices with the UV–ozone treatment for 5 min on ITO substrates show the better performance, compared with the devices without this treatment. The results demonstrate that the short-circuit current density (J_sc) and fill factor (FF) could be improved by the post-annealing treatment. The devices with both treatments together show the best performance, with the increase of J_sc from 2.68 mA/cm² to 4.13 mA/cm² and the enhancement of FF from 32.2% to 38.8%. Therefore, the power conversion efficiency is improved from 0.62% to 1.08%. The morphology of the active layers with and without the post-annealing treatment was characterized by atomic force microscopy.