MEASUREMENT OF LADLE SLAG OXYGEN ACTIVITY USING AN ELECTROCHEMICAL SENSOR

摘要

An electrochemical sensor was used to measure the oxygen activity of ladle slags in industrial conditions and in a laboratory setting. The oxygen activity of these slags was also calculated based on their experimentally determined composition, using the thermodynamic software tool FactSage. Although there is a systematic difference between the measured and the calculated oxygen activities, it was demonstrated that the sensor is capable of measuring the influence of the slag composition on the oxygen activity. In the composition ranges of the slags studied, the influence of FeO, SiO_2 and MnO was demonstrated. The difference between the calculated and the measured values is explained by the assumption of a 'pseudo-equilibrium' state between limited amounts of slag and steel at the sensor tip. The values of some measurements are uncharacteristic. We attribute this to a broken slag layer at the sensor tip, allowing a direct contact between steel and sensor. A more stringent measurement acceptance condition could solve this problem but would also increase the number of rejected measurements. The empirical formulae that translate the measured potential into an iron oxide content must be reassessed for each steel plant. The oxygen activity of the steel should be known because it influences the measured potential. In practice the oxygen activity of the steel is known. It does not change significantly for the different steel grades produced.