Analysis of the current distribution in an aluminum electrolysis cell with copper collector-bar cathode assembly

Understanding the magneto-hydrodynamic forces generated due to the external magnetic field and current density distribution within the cell (current in cell linings) is important in the optimization of cell dynamics. It is well documented that these factors play a crucial role in establishing the metal-pad stability of the cell. Conventional cells use the cathode-collector-bar assembly to carry the current through molten aluminium, the cathode and the steel collector-bar to nearest external bus. The electrical conductivity of the steel is so poor relative to the molten aluminium that the outer third of the collector bar carries the maximum load, which in turn increases the horizontal components of the current within the cell. Previous studies have modelled improvement in the cell instability through external magnetic compensation by redistributing current in the cathode busbar. Very little to date has been published on work to improve the current distribution within the cell. In this work, the current distribution in an aluminium electrolysis cell with copper collector-bar was predicted using finite element modelling. A 2D cross-section of a commercial cell was used under steady conditions of electrical fields in anode, electrolyte, molten aluminium and copper cathode-assembly. Different shapes and sizes of the cathode assembly are also considered to optimise the distribution of current throughout the cathode lining. The findings indicated that the copper-bar of similar size to steel could save voltage up to 150 mV. There is a reduction of more than 70% in peak current density value due to the copper inserts. The predicted trends of current distribution show a good agreement with previously published data.

One-Step synthesis of the pine-shaped nanostructure of aluminum nitride and its photoluminescence properties

An array of pine-shaped nanostructures of aluminum nitride (AlN) was synthesized through direct reaction between Al vapor and nitrogen gas in direct current (DC) arc discharge plasma without any catalyst or template. The as-prepared nanostructure consists of many pine-needle-shaped leaves with conical shape tips. The structure, morphology, and optical property of the nanostructure have been characterized by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and photoluminescence. A possible growth mechanism of the pine-shaped nanostructure was discussed. Two factors were found to be essential for branched nanostructure growth, i.e., the reaction time and N2 pressure. The photoluminescence spectrum of the nanostructure of AlN revealed an intense emission band, suggesting that there may be potential applications in electronic and optoelectronic nanodevices.

Effect of aluminum on the corrosion resistance of low-alloy steel in 10wt% sulfuric acid solution

The aqueous corrosion behavior of low-alloy steel with aluminum contents was examined in a 10 wt% H₂SO₄ (pH 0.13) solution using electrochemical techniques and surface analyses. The corrosion resistance of the new alloy steel was evaluated in terms of electrochemical parameters, such as passive current density, film, and charge transfer resistances. The results showed that a high Al content in the steel imparted better passivation behavior resulting in a lower corrosion rate. It related to the enrichment of iron carbonate and hydrocarbon by the dissolution of the carbide phase.

Optimizing oxygen transport through La0.6Sr0.4Co0.2Fe0.8O3-δ hollow fiber by microstructure modification and Ag/Pt catalyst deposition

This work compares the oxygen permeation fluxes of five different La0.6Sr0.4Co0.2Fe0.8O3−δ membranes (e.g. disk, conventional hollow fiber, modified hollow fiber, Ag- or Pt-deposited hollow fiber membranes) to elucidate the dominance of a particular oxygen transport limiting step (e.g., bulk-diffusion or surface reaction) within each of these membranes. At 900 °C and 100 mL min–1 helium gas sweep rate, the oxygen fluxes for disk, conventional hollow fiber, modified hollow fiber, Ag-deposited modified hollow fiber, and Pt-deposited modified hollow fiber membranes are 0.10, 0.33, 0.84, 1.42, and 2.62 mL min–1 cm–2, respectively, denoting enhanced performance in this sequential order. More than 300% enhancement of fluxes is evidenced by modifying the geometry from disk to conventional hollow fiber. This is attributed to the thickness reduction from 1 mm to 0.3 mm, thus implying bulk-diffusion and surface reaction as the jointly limiting transport step for this disk membrane. In contrast to a conventional hollow fiber that has a sandwich cross-sectional structure (e.g. dense center layer sandwiched by two finger-like layers) as well as dense outer and inner circumference surfaces, the modified hollow fiber has only one dense layer in its outer circumference surface with finger-like porous layer extending all the way from outer cross-sectional part to the inner cross-sectional part. This microstructural difference, in turn, provides substantial reduction of membrane thickness and enlarges surface reaction area for modified hollow fiber (relative to conventional hollow fiber), both of which contributes to the reduced bulk-diffusion and surface reaction resistance; evidenced by almost 250% oxygen flux enhancement. To enhance the performance even further, catalyst (e.g., Ag or Pt) deposition on the outer circumference surface of modified hollow fiber can be utilized to reduce its dominating surface reaction resistance. While both catalysts increase the oxygen fluxes, Pt reveals itself as the better candidate relative to Ag due to melting-induced aggregation and growth of Ag at 950 °C.

Mana Taonga and the public sphere: a dialogue between indigenous practice and Western theory

Recent re-conceptualizations of the ‘public sphere’ facilitated a much needed shift in thinking about identity politics ‘from a substance … to a movement’ (Weibel and Latour, 2007). This laid the foundation for dissolving the ‘emanatist vision’ (Bourdieu, 1990) of self-explanatory and perpetual systems and structures towards the interrogation of actions and performances that simultaneously constitute and are affected by such wider socio-political realities. Most academic contributions, however, remain on a normative or theoretical level without offering empirical insights.

This article introduces Mana Taonga as an Indigenous Māori concept of cultural politics embedded in current museum practice at the Museum of New Zealand Te Papa Tongarewa (Te Papa). It creates a dialogue between Indigenous Māori practice and Western theory leading to a refined understanding of performative democracy within a museum as forum, or public sphere. The authors argue that a specific museum offers a particular place, space and empirical reality to interrogate seemingly universal concepts such as ‘culture’ and ‘politics’ by blending theoretical notions with an awareness of institutional contexts and practices.

Effects of high salt concentration and residue on copper and aluminum corrosion

Traditional researches on metal corrosion under salt solutions deposit conditions are usually carried out by visual, electron microscopic observations and simple electrochemical measurement via a traditional one-piece electrode. These techniques have difficulties in measuring localized corrosion that frequently occur in inhomogeneous media. This paper reports the results from the experiments using specially shaped coupons and a relatively new method of measuring heterogeneous electrochemical processes, namely, the wire beam electrode(WBE). Preliminary results from copper and aluminum corrosion in highly concentrated sodium chloride solutions with and without solid deposits show that the method is useful in simulating and studying corrosion especially localized corrosion in pipelines.