Electrolysis expansion performance of semigraphitic cathode in [K₃AlF₆/Na₃AlF₆]-AlF₃-Al₂O₃ bath system

Abstract

The electrolysis expansion of semigraphitic cathode in [K₃AlF₆/Na₃AlF₆]-AlF₃-Al₂O₃ bath system was tested by self-made modified Rapoport apparatus. A mathematical model was introduced to discuss the effects of α_CR (cryolite ratio) and β_KR (elpasolite content divided by the total amount of elpasolite and sodium cryolite) on performance of cathode electrolysis expansion. The results show that K and Na (potassium and sodium) penetrate into the cathode together and have an obvious influence on the performance of cathode electrolysis expansion. The electrolysis expansion and K/Na penetration rate increase with the increase of α_CR. When α_CR=1.9 and β_KR=0.5, the electrolysis expansion is the highest, which is 3.95%; and when α_CR=1.4 and β_KR=0.1, the electrolysis expansion is the lowest, which is 1.28%. But the effect of β_KR is correlative with α_CR. When α_CR=1.6 and 1.9, with the increase of β_KR, the electrolysis expansion and K/Na penetration rate increase. However, when α_CR=1.4, the electrolysis expansion and K/Na penetration rate firstly increase and then decrease with the increase of β_KR.

Keywords

aluminum electrolysis / semigraphitic cathode / low temperature electrolysis / electrolysis expansion / K penetration / Na penetration

References

[1] JamesW. E., HalvorK.. Sustainability, climate change, and greenhouse gas emissions reduction: Responsibility, key challenges, and opportunities for the aluminum industry [J]. JOM, 2008, 60(8): 25-31

[2] JamesW. E.. The evolution of technology for light metals over the last 50 years: Al, Mg, and Li [J]. JOM, 2007, 59(2): 30-38

[3] LAI Yan-qing, WANG Jia-wei. Commentary on the status quo of low temperature aluminum electrolysis in the Na₃A1F₆-A1₂O₃ bath system [J]. Light Metal, 2006(9): 37–42. (in Chinese)

[4] WANG Jia-wei, LAI Yan-qing. Commentary on the status quo of low temperature aluminum electrolysis in M(K or Li)₃AlF₆-Al₂O₃ bath system [J]. Light Metal, 2007(1): 31–36. (in Chinese)

[5] YANG J H, DONALD G G, CATHERINE W, JOHN N H. Alumina solubility in KF-AlF₃-based low-temperature electrolyte system [C]// Light Metals 2007. Orlando, 2007: 537–541.

[6] RolsethS., GudbrandsenH., ThonstadJ.. Low temperature aluminium electrolysis in a high density electrolytes. Part I [J]. Aluminum, 2005, 81(5): 448-450

[7] RolsethS., GudbrandsenH., ThonstadJ.. Low temperature aluminium electrolysis in a high density electrolytes. Part II [J]. Aluminum, 2005, 81(6): 565-568

[8] SKYBAKMOEN E, SOLHEIM A, STEREN A. Phase diagram data in the system Na₃AlF₆-Li₃AlF₆-AlF₃-Al₂O₃ [C]// Light Metals 1990. Anaheim, 1990: 317–323.

[9] XUE Ji-lai, LIU Qing-sheng, OU Wen-li. Sodium expansion in carbon/TiB₂ cathodes during aluminum electrolysis [C]// Light Metals 2007. Orlando, 2007: 651–654.

[10] ZolocheyskyA., HopJ. G., ServantT., FoosnasT., OyeH. A.. Rapoport-Samoilenko test for cathode carbon materials II. Swelling with external pressure and effect of creep [J]. Carbon, 2005, 43(6): 1222-1230

[11] LüX.-j., LiQ.-y., LaiY.-q., LiJ.. Digital characterization and mathematic model of sodium penetration into cathode material for aluminum electrolysis [J]. Journal of Central South University of Technology, 2009, 16(1): 96-100

[12] LiQ.-yu.Development and industrial application of wettable inert TiB₂ cathodic composite coating for aluminum electrolysis [D], 2003, Changsha, Central South University of Technology: 39-46

[13] ChuanX.-yun.. Formation mechanism of graphite intercalation compounds [J]. New Carbon Materials, 2000, 15(1): 52-56

[14] QiuZ.-xian.Smelting aluminum in pre-baked cell [M], 2005, Beijing, Metallurgical Industry Press: 311-314

[15] ARNE P R, ANNE S, ASBJORN S, FOOSNAES T. The effect of current density on cathode expansion during strat-up [C]// Light Metals 2008. New Orleans, 2008: 973–978.

[16] XUE J L, OYE H A. Sodium and bath penetration into TiB₂-carbon cathodes during laboratory aluminum electrolysis [C]// Light Metals 1992. San Diego, 1992: 773–778.

[17] DellM. B.In Extractive metallurgy of aluminium [M], 1963, New York, Interscience Publishers: 403-405

[18] HopJ., StoreA., FoosnaesT., OyeH. A.. Chemical and physical changes of cathode carbon by aluminium electrolysis [J]. Transactions of the Institutions of Mining and Metallurgy, 2005, 114(3): 181-187

[19] MortenS., OyeH. A.Cathodes in aluminium electrolysis [M], 1994, Düsseldorf, Aluminium-Verlag: 184-190

[20] ChanB. K. C., ThomasK. M., MarshH.. The interactions of carbons with potassium [J]. Carbon, 1993, 31(7): 1071-1082

[21] YuriM., OyeH. A.. Absorption of metallic sodium in carbon cathode materials [J]. Carbon, 1996, 34(1): 37-41