Electrochemical study on equilibrium mechanisms of the Al–O with different Al contents in liquid iron

Electrochemical experiments were carried out to monitor the variations of open voltage with time during the aluminium (Al) deoxidation process for iron melt with additional Al amounts in the range of 0.01%–2.0% at the temperature of 1873 K. Thermodynamic parameters, Fick’s second law and a reaction kinetic model were used to calculate the equilibrium oxygen contents (EOCs) at the iron melt–solid electrolyte interface, reaction order and rate-limited step in the current conditions. The results show that the EOCs at the interface show a trend of decreasing first and then increasing with the increase of additional Al amounts. The turning point of the EOC change, that is, the lowest value of EOCs, corresponds to and addition Al amount of 0.5%. The reason for the appearance of the EOC turning point is that the activity coefficient of oxygen decreases with Al addition, increasing from 0.01% to 2.0%. Kinetic analysis indicates that the reaction order of an Al deoxidation reaction with 0.01% Al addition is 8. Orders 1 and 2 correspond to different stages of the Al deoxidation reaction with 0.50% Al addition. The reaction orders are all 1 for 1.0%–2.0% Al addition. The diffusion coefficient of oxygen fitted by Fick’s second law is 1.47 × 10 −6 –2.10 × 10 −5 cm 2 /s in molten steel with Al additions of 0.01%–2.0%. When the Al addition is 0.01%–0.50%, the rate-determining step of the Al deoxidation reaction is Al 2 O 3 formation and oxygen diffusion in the melt. When the Al addition is 1.0%–2.0%, the rate-determining step of the Al deoxidation reaction is the decomposition reaction of Al 2 O 3 and the diffusion of oxygen in the melt.