Analysis of porous structures of graphitic cathode materials and the correlation to penetrated sodium

Abstract

Cathode materials used in aluminum reduction cell today are of porous structure. This work is aimed to have better control of the cathode quality through quantitatively analyzing the pore structure and its correlation to the penetrated sodium (metallic Na and NaF). The cathode samples were made of graphite aggregate and pitch, and formed with various pressures (12 - 36 MPa). Image analysis was applied to characterize their porous structures. XRD and SEM-EDS were used to analyze the penetrated sodium in the cathode samples. When the forming pressure was 20 MPa, the cathode density got to its maximum value (1.58 g/cm3) with the minimum total porosity (21.96 %) and the least pore number (549). When the forming pressure rose from 12 MPa to 36 MPa, the pore connectivity was from 9.81 % up to 37.95 % while the shape factor increased from 1.98 to 2.21 and the depth of sodium penetration became longer from 6 mm to 30 mm. In addition, ultrasound applied can reduce the penetrated sodium in the cathode.