In the 1940s, the whole carbon cathode tamped with carbon paste was replaced by the carbon cathode assembled with prebaked cathode carbon block, and the semi graphite cathode carbon block was used in the 1950s. Since 1980s, semi graphite cathode carbon block and graphite cathode carbon block have been used in large prebaked cells. In recent years, some large aluminum plants use graphite carbon block.
Inert cathode carbon block is a new type of cathode material developed in recent years. In addition to the good electrical conductivity, thermal shock resistance and high mechanical strength of carbon materials, the infiltration performance of liquid aluminum on carbon block is good, and it is resistant to chemical corrosion of liquid aluminum and electrolyte. The suitable materials for inert cathode are carbide (TIC), nitride (NbN) and boride (TiB2).
TiB2 coated carbon block is a mixture of TiB2, resin adhesive and carbon material, mixed with solvent, and finally mixed with curing agent. The coating is applied on the surface of common carbon block. The coating is 5-10 mm thick, cured at 150-300 ℃ for 40-50 h, and then slowly cooled. It is characterized by good conductivity, improved wettability of liquid aluminum to carbon materials, low expansion rate, and reduced penetration and erosion of sodium and electrolyte to carbon block at the bottom of the tank. Another method is to directly press a layer of carbon paste containing TiB2 on the surface of the carbon block, and then bake it together with the carbon block.