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Major Melt—Crucible Systems
Published in Nagaiyar Krishnamurthy, Metal–Crucible Interactions, 2023
The invention of an electrolytic process for aluminium extraction was outlined in Chapter 1. Almost all the world's aluminium is produced by electrolysis in Hall–Héroult cells. During the electrolysis of alumina dissolved in molten cryolite, aluminium ions discharge at the carbon cathode and collect as molten metal at the prevailing temperature (950–965°C) in the cell. The anions discharge at the carbon anode and evolve as a mixture of carbon oxides: 20–40% CO and 60–80% CO2. The melts of aluminium and of the electrolyte are non-miscible. In the cell, electrolyte (density = 2.1 g/cm3) remains above the molten aluminium (density = 2.3 g/cm3). Typically, the depth of the molten aluminium layer is about 15–40 cm, and the depth of the electrolyte layer is 15–25 cm (Yurkov 2017).
Homopolar Motors
Published in David A. Cardwell, David C. Larbalestier, Aleksander I. Braginski, Handbook of Superconductivity, 2022
A good example of such a device for continuous duty is a 60 MW facility consisting of one driving turbine and six homopolar generators designed for electrolytic process applications such as aluminium potlines and chlorine-cell lines. Each generator unit with a nominal power of 10 MW weighs 25 tons and is 3.6 m long, 1.8 m high and 2.6 m wide. The assembly was built by General Electric's Large Motor and Generator Dept. (150,000 Continuous D-C amperes easy for acyclic generator, 1962). Six identical generators were coupled to one driving prime mover (turbine), three generators on each side. The machine offered high-speed operation (3600 RPM), permitting use of economical prime movers. Each homopolar generator unit generated 67 V and was rated for a 150 kA working current. Connected in series they provided 400 V at 150 kA. These homopolar generators had 98% or higher efficiency and were designed for several years of continuous operation without interruptions for service and maintenance. All auxiliary components were located outside the machine to allow engagement of backup equipment without stoppage of the generators.
Aluminium and its alloys
Published in William Bolton, R.A. Higgins, Materials for Engineers and Technicians, 2020
The only important ore of aluminium is bauxite, which contains aluminium oxide (Al2O3). Unfortunately, this cannot be reduced to the metal by heating it with coke (as in the case of iron ore), because aluminium atoms are, so to speak, too firmly combined with oxygen atoms to be detached by carbon. For this reason, an expensive electrolytic process must be used to decompose the bauxite and release aluminium. Since each kilogram of aluminium requires about 91 MJ of electrical energy, smelting plant must be located near to sources of cheap hydroelectric power, often at great distances from the ore supply, and from the subsequent markets. Consequently, most aluminium is produced in the United States, and in Canada and Norway. Hydroelectric power in the western Highlands enables some aluminium to be smelted in Scotland, but the bulk of aluminium used in the United Kingdom is imported.
Mineral Processing and Metal Extraction on the Lunar Surface - Challenges and Opportunities
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Matthew Shaw, Matthew Humbert, Geoffrey Brooks, Akbar Rhamdhani, Alan Duffy, Mark Pownceby
Electrochemical reduction processes reduce oxides by passing electrical energy through electrodes and an electrolyte containing or composed of the feedstock material. In an electrolytic process, two separate chemical reactions happen simultaneously, one at each electrode. These reactions are referred to as the anodic reaction (where oxidation occurs) and cathodic reaction (where reduction occurs). Equation 3 is a generalized equation for the electrolysis of a metal oxide that combines the anodic and cathodic reactions into a single equation.