Creep Behavior and Change of Porous Structure of Graphite Cathode Material in NaF-AlF3-Al2O3Melt under External Pressure

Abstract

Investigation of creep behavior of graphite cathode material during aluminum electrolysis in NaF-AlF3-Al2O3 melt were carried out under external 4 MPa pressure with modified rapoport method in a laboratory cell at 965 °C. The effects of cathode current density (i=0 A/cm2, 0.25 A/cm2, 0.50 A/cm2 and 1.0 A/cm2), cryolite ratio (CR=2.34, 3,0 and 4.0) of the cryolitic melts have been investigated. The results demonstrate that increasing current density or CR value can yield enlarged creep strain. The porous structures of the cathode samples were characterized using image analysis, in which the porosity increased with more long and narrow pores appearing after 150 min of electrolysis. The information acquired from this work can be valuable in materials selection and performance improvement of graphite cathodes.