Thermal-Treated Pitches as Binders for TiB 2 /C Composite Cathodes
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HE growth of primary aluminum production was increased rapidly in recent years.[1] Especially in China, the primary aluminum output was 12.85 million tons, which occupies 35 pct of the global total output in 2009. Meanwhile, some progress has also been made in aluminum electrolysis technology. New technology has reduced specific energy consumption to some extent. However, the industry still requires 13,000 to 15,000 kW h/t-Al (more than two times the amount) compared with the theoretical consumption of 6160 kW h/t-Al required for the electrochemical decomposition of alumina (with carbon anode).[2] The low-energy efficiency is attributed to poor wettability of carbon cathode in molten aluminum, which makes the gap requirement between the anode and the cathode (ACD) 4 to 6 cm in order to mitigate the negative influence of molten aluminum movement and the electrolyte interface deformation brought on by electromagnetic forces on the current efficiency. The TiB2 inert wettable cathode material is promising because of its advantageous wettability in molten aluminum. A stable aluminum layer of only 3 to 5 mm can be formed, which greatly XIAO-JUN LU¨, Lecturer, JIAN XU, Master, and JIE LI, YANQING LAI, and YE-XIANG LIU, Professors, are with the School of Metallurgical Science and Engineering, Central South University, Changsha 410083, P.R. China. Contact e-mail: csulightmetals02@ 163.com Manuscript submitted January 20, 2011. Article published online July 27, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
reduces the disturbance in the magnetic field. Subsequently, the voltage drop between the anode and the cathode, and the energy consumption may be markedly decreased after TiB2 inert cathodes are applied to aluminum reduction cells.[3] Presently, a TiB2/C composite cathode is regarded as the most practical and potential wettable cathode, which can be applied to not only the present aluminum reduction cells to save energy but also to the newly drained aluminum reduction cells to innovate technology for aluminum electrolysis.[4] Apart from high strength and good conductivity, both wettability by molten aluminum and good resistance to high-temperature corrosion of molten cryolite are essential for cathode materials used in aluminum electrolysis. The structure of the carbonaceous aggregate particles of the current carbon cathode material is stable because they are calcined at a higher temperature before use. But the structure of binders is less stable than carbonaceous aggregate particles because they are not calcined before use. Therefore, the binders are easier to make into prior corrosion regions of carbon cathodes.[5] Currently, TiB2/ C composite cathodes are fabricated by powder metallurgy with TiB2 powders and carbonaceous particles as aggregates and coal tar pitch as binders.[6] However, TiB2 powder itself is a material of high strength, high conductivity, and high resistance to corrosion. Compared with carbon cathodes, introducing TiB2 powders into a TiB2/C composite cathode increases the difference between aggregate particle
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