The cathode carbon blocks are divided into ordinary graphite cathode carbon blocks (made of calcined coal, asphalt and a small amount of graphite powder) and then processed by roasting machine), high graphite cathode carbon blocks (made of calcined coal, asphalt and more than 50% graphite powder) and fully graphitized cathode carbon blocks (made of petroleum coke), Asphalt and other raw materials are mixed, extruded, roasted at high temperature, graphitized at high temperature and machined.)
Graphitized cathode blocks are now widely used, especially in
modem high-amperage aluminum electrolysis cells. Compared to
semi-graphitic or graphitic materials, fully graphitized cathode
blocks have desired properties such as low sodium expansion, low
electrical resistivity and high thermal conductivity [1,2]. In recent
years, more and more aluminum producers have decreased
cathode voltage drop, reduced energy consumption and optimized
the operation of large-scale aluminum reduction cells to make
production costs lower. F or example, the graphitized cathode
block of Zhengzhou aluminum institute and carbon factory
association made two years industrial test in three 350 kA
aluminum reduction cells. The result showed that the cathode
voltage drop of the test cell reduced 80~100 mV compared to an
ordinary cell, current efficiency increased about 1% and per ton of
aluminum, resulting in energy savings of 300 kWh.
High quality graphite cathode carbon blocks require low resistivity, strong resistant erosion to molten salts and liquid aluminum in the aluminum electrolytic cells. High quality cathode materials can decrease cathode voltage and then reduce the power consumption, and improve service life of the cell. Applying hot mould technology under 40 M Pa pressure, different amounts of petroleum coke in anthracite mixtures is graphitized in graphitizing furnace. By the X-ray diffraction parameters, density, compressive strength and resistivity drop are measured. The experimental results show that compressive strength and volume density of graphite blocks containing 30% of petroleum coke are 1.366 g/cm3 and 4.8 M Pa, respectively, resistivity drop from 114µΩm to 13µΩm, mostly in accordance with block production requirements.
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