Abstract: The experimental investigation of sodium penetration and expansion of carbon-based cathodes during aluminum electrolysis was carried out in a laboratory cell. The results show that the addition of B₂O₃ can reduce the rate of sodium penetration but increase the rate of sodium expansion at the final stage. The addition of TiB₂ results in lower rates for both sodium penetration and sodium expansion. SEM-EDS analysis indicates that TiB₂ + B₂O₃ presents within the areas of binder phase of the cathode, which may play a role in reducing the rates of sodium penetration and expansion.