An electrolytic cell is made of a steel shell with a series of insulating linings of refractory materials.
The prebaked anode is also made of carbon in the form of large sintered blocks suspended in the electrolyte.
A single Soderberg electrode or a number of prebaked carbon blocks are used as anode, while the principal formulation and the fundamental reactions occurring on their surface are the same.
An aluminium smelter consists of a large number of cells (pots) in which the electrolysis takes place.
[3][4] As three electrons are needed to produce each atom of aluminium, the process consumes a large amount of electricity.
Carbon cathode must have adequate strength, good electrical conductivity and high resistance to wear and sodium penetration.
Inhomogeneous anode quality due to the variation in raw materials and production parameters also affects its performance and the cell stability.
The anodes are manufactured by mixing aggregates with coal tar pitch to form a paste with a doughy consistency.
The green anode is then sintered at 1100–1200 °C for 300–400 hours, without graphitization, to increase its strength through decomposition and carbonization of the binder.
Higher baking temperatures increase the mechanical properties and thermal conductivity, and decrease the air and CO2 reactivity.
Temperature increases bottom to the top of the column and in-situ baking takes place as the anode is lowered into the bath.
[11] Through a review of literature, Haradlsson et al. found that inert anodes reduced the green house gas emissions of the aluminum smelting process by approximately 2 tonnes CO2eq/ tonne Al.[12] Ceramic anode materials include Ni-Fe, Sn, and Ni-Li based oxides.
[13] These anodes show promise as they are extremely stable during the reduction process at normal operating temperatures (~1000 °C), ensuring that the Al is not contaminated.
[13] Alternatively metal anodes boast high mechanical strength and conductivity but tend to corrode easily during the reduction process.
[14] The inert anode is a cermet material, a metallic dispersion of copper alloy in a ceramic matrix of nickel ferrite.
[16] Aluminium smelting is highly energy intensive, and in some countries is economical only if there are inexpensive sources of electricity.
[19][20] To reduce the energy cost of the smelting process, alternative electrolytes such as Na3AlF6 are being investigated that can operate at a lower temperature.