Effect of TiB 2 Coating on Evolution of Cathode Lining during the Process of Primary Aluminum Production
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e growth of primary aluminum production was increased very rapidly in recent years in China. The primary aluminum throughput in China was over 10 million tons in 2006. Some progress has also been made in the technology of aluminum electrolysis.[1] Even 350-kA prebake aluminum reduction cells have been employed in some aluminum companies, such as Qingtongxia, Shenghuo Group, etc. The cell life, however, of prebake aluminum reduction cells in China is far shorter than that in developed countries.[2] The latter is about 3000 days, on average, but the former is less than 1300 days. The short cell life is one of the key issues to be resolved to develop further efficiency and economics in the aluminum industry of China. There are quite a few factors affecting the cell life, such as cell design, carbon block quality, selection of insulation materials, installation quality, cell startup, cell operation, etc. Resulting from expansion, the cathode lining deteriorated during the entire service of the aluminum reduction cell. The expansion has two kinds of styles: physical expansion and chemical expanQING-YU LI and JIAN-HONG YANG, Professor, and HONG-QIANG WANG, Associate Professor, are with the School of Chemistry and Chemical Engineering, Guangxi Normal University, Guilin 540041, P.R. China. Contact e-mail: [email protected] JIE LI, Professor, and YAN-QING LAI, Professor, are with the School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China. YONG-GANG LIU, Engineer, is with the Aluminum Corporation of China Limited, Guangxi Branch, Pingguo 531400, P.R. China. Manuscript submitted February 7, 2007. Article published online August 10, 2007.
2358—VOLUME 38A, SEPTEMBER 2007
sion. However, the physical expansion (thermal expansion), about 0.4 pct in the range of 25 C to 960 C,[3] is not avoidable, because the installed cell is brought from room temperature to operation temperature, around 960 C. So, the physical expansion should be considered during cell design, material selection, and operation regulations, which would not be further discussed in the present work. The chemical expansion resulting from sodium and electrolyte penetration to the carbon cathode lining, reactions between liquid aluminum and carbon, and air oxidation, etc. have a very strong impact on cell service life. Among them, the intensive expansion from rapid penetration of sodium and electrolyte is one of the main causes of the early failure or shorter life of the cell.[4–11] In the present work, the TiB2 coating was applied to the carbon cathode in order to reduce the chemical expansion or deterioration or to slow the rate of chemical deterioration. Two sizes (16 · 60-mm o.d. and 20 · 60-mm o.d.) of the cathode block cylinders were made for making the sample of the TiB2-coated cathode, and the latter one was the sample of the semigraphitic cathode block. The TiB2 powder (30 to 65 mass pct), strengthening additive (5 to 15 mass pct), resin (10 to 35 mass pct), mixture of organic solvent (10 to 30 mass pct), and composites o
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