Determining the baking isotherm temperature of Söderberg electrodes and associated structural changes

One of the most commonly employed electrode systems in industrial metal smelting applications is continuous self-baking electrodes, i.e. the Söderberg electrode system. In this system, the temperature at which transition from a liquid/soft paste to a solid carbonaceous electrode takes place is termed the baking isotherm temperature. This temperature is extremely important within the context of electrode management. In this paper, thermo mechanical analysis (TMA) was used to measure the dimensional changes that take place in coal tar pitch in the temperature range relevant to the determination of the baking isotherm temperature. It was found that the baking isotherm temperature of coal tar pitches was between 450 and 475 °C, irrespective of the initial chemical composition and physical characteristics of the coal tar pitch. Subsequent Fourier Transform Infra-Red (FTIR) analyses indicated that all coal tar pitches underwent similar compositional changes during the transition from a molten/liquid coal tar pitch to a solid carbonaceous material.