Abstract:Electrical resistivity of two industrial cathodes, 35% graphitic (HC35) and 100% graphitic (HC100), at high temperature was tested respectively. As the results indicate, thermal expansion of cathodes results in a change of parameters of porous structure, which in turn give rise to variation of resistivity before electrolysis. After electrolysis, the change of resistivity is ascribed to penetration between sodium and electrolyte, which is strongly affected by the porous structure of cathodes. Infiltration of sodium and electrolyte into cathode is facilitated by bigger average diameter and connectivity of pores, and smaller sinuosity of connecting pores in porous structure, In turn, a better infiltration results in bigger change of resistivity after electrolysis.