Investigation of Electrical Conduction in Iron Silicate Slags via Electrical Conductivity Experiments and Iron Redox State Determination
Pieter Jan Boeykens (Universiteit Gent)
Roman Starykh (University of Queensland)
Iulian Dugulan (TU Delft - RID/TS/Instrumenten groep, TU Delft - Applied Sciences)
Jeff Chen (University of Queensland)
Maksym Shevchenko (University of Queensland)
Lennart Scheunis (Umicore N.V., Umicore)
Amy Van den Bulck (Umicore)
Evgueni Jak (University of Queensland)
Kim Verbeken (Universiteit Gent)
Inge Bellemans (Universiteit Gent)
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Abstract
The present work aims to elucidate the influence of the iron oxidation state on the electrical conductivity of iron silicate slags through a combined approach of electrical conductivity measurements and iron redox state determination. Electrical conductivity experiments were combined with stepped potential chronoamperometry measurements to distinguish between the ionic and electronic conduction mechanism. Contrary to previous studies, the Fe3+/Fe2+ ratio was also experimentally determined via both Mössbauer spectroscopy and wet chemistry. A continuous decrease in Fe3+/Fetot ratio was found which varies accordingly to the different atmospheres applied during each experiment which confirmed that the changes in the electrical conductivity are attributed to a difference in the sample’s iron redox state. The ionic and electronic conductivity showed a linear and parabolic dependency, respectively, as a function of Fe3+/Fetot. The experimental data were compared with two models, namely, the structural ionic model of Thibodeau et al. and the electronic Diffusion-Assisted Charge Transfer (DACT) model from Barati and Coley. Regarding the former, it is found that the model overestimates the ionic conductivity due to an overestimation of the Fe2+ diffusion coefficient. The latter model was unable to reproduce the experimental data using the original model’s original r* parameter of 3.87 Å, but adaptation of this parameter to 4.67 Å provided a better fit. This suggests that the DACT model also needs to consider a slag composition dependency to accurately reproduce experimental data.