Cohesion and Toughness Improvement of Pitch Binder by Thermosetting Resin Modification for TiB 2 /C Composite Cathode
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THE aluminum industry is an important basic industry. However, it has always been known as the ‘‘high energy-consuming’’ industry. Low energy efficiency, mainly caused by the poor wettability of the carbon cathode with molten aluminum during the electrolysis process,[1–3] is one of the reasons accounting for the high energy consumption. Early methods for improving the wettability focused on applying a TiB2 ceramic, TiB2 composite, and TiB2 coating cathode. Currently, the TiB2/C composite cathode is regarded as the most promising cathode material. The TiB2/C composite cathode is generally fabricated by the powder metallurgy method in that TiB2 powder is used as the body, carbonaceous particles as the aggregates, and pitch as the binder.[4] With good mechanical properties and electrical conductivity and resistance to the corrosion of molten electrolyte, TiB2 can be applied in a tough service environment of aluminum electrolysis. Usually, carbonaceous aggregate particles are calcined at a high temperature (about 1573 K [1300 C]) before use. XIAO-JUN LU¨, Associate Professor, JIN-LONG HOU and YUE LIN, Masters, and JIN LIU and YE-XIANG LIU, Professors, are with the School of Metallurgical Science and Engineering, Central South University, Changsha City 410083, P.R. China. YAN-QING LAI, Professor, and JIE LI, Dean and Professor, are with the School of Metallurgical Science and Engineering, Central South University, and also with the National Engineering Laboratory for Efficient Utilization of Refractory Non-Ferrous Metals Resources, Changsha City 410083, P.R. China. Contact e-mail: [email protected] Manuscript submitted February 28, 2012. Article published online April 30, 2013 4360—VOLUME 44A, SEPTEMBER 2013
Because the binder is the least stable component compared to TiB2 and carbonaceous aggregates, which easily makes it prior to corrosion,[5] it becomes the weakest part of the TiB2/C composite cathode.[6,7] Studies have found that common pitch expands severely to produce pores and cracks due to poor cohesion and toughness.[8] These pores and cracks not only degrade mechanical and electrical properties of the TiB2/C cathode materials but also become a pathway for infiltration and erosion of molten electrolyte and aluminum. Moreover, a disordered lamellar structure formed in binder carbon after the composite cathode baked[9] makes sodium penetrate into cathode easily, resulting in the formation of sodium-graphite intercalation compounds[6] and more deformation and expansion of the cathode. Therefore, modification of pitch to improve cohesion and toughness is imperative and of substantial significance. Using additives is an existing way to modify pitch.[10] In recent years, particular attention has been paid to use resin as additives because resin can create a secondary network and a new balance system by molecular interaction and chemical reaction with pitch. As we know, resin can be classified into thermoplastic resin and thermosetting resin. Most of thermoplastic resin such as polyethylene, polypropylene, polyv
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