Determination of the Partial Contributions to the Electrical Conductivity of TiO2-SiO2-Al2O3-MgO-CaO Slags: Role of the Experimental Processing Conditions

Abstract

The electrical transport properties of molten TiO2–SiO2–Al2O3–MgO–CaO slags were determined as a function of temperature and oxygen partial pressure. To avoid the corrosion of crucible materials by this slag at ultra high temperatures, the pendant droplet technique was used inside a modified floating zone furnace. Electronic and ionic transference numbers were estimated using stepped-potential chronoamperometry experiments to quantify the contribution of the electronic/ionic conductivity to the total electric conductivity. The results show that these slags are mixed conductors, where current is carried by ionic and electronic carriers. The oxygen partial pressure dependence of the electronic transference numbers, $$t_e$$ t e , indicated a semiconducting mechanism in the molten slag. The ratio of the different valences of the transition metal ions had a predominant effect on the $$t_e$$ t e . The $${{\text{TiO}}_{2}}$$ TiO 2 content also favoured electronic conduction, while the effect of temperature and structure was less noticeable within the temperature and composition range studied.

Parameter investigation of the experimental methodology of electrical conductivity measurements for PbO containing slags

“…In a first step, the impedance is recorded as a function of the frequency via a frequency sweep for which the results can be visualised in a Nyquist plot as shown on the left side of Figure 1. This Nyquist plot can be divided into two regions: a high frequency region corresponding to an inductive tail and a low frequency region corresponding to a semiarc [20][21][22][23][24][25] . The high frequency tail is the result of the solution resistance and the induction due to the long wires needed to connect the electrodes/melt with the measurement device 20,21,23 , while the low frequency semi-arc is the result of the solution-electrode interface 6,24 .…”

“…In a second step, the solution resistance Rsolution should be determined which can be done via several methods. A first method is to fit an equivalent circuit to the recorded impedance spectrum 20,21,23,24,[26][27][28] similar to the circuit as visualised in Figure 1. This technique is more commonly known as Electrochemical Impedance Spectroscopy (EIS).…”

“…representing the ion polarization at the interface 24,28 . Other authors have included an additional Warburg diffusion element W in series with the charge transfer resistance as they found that the ion movement was limited by diffusion at low frequencies 20,21,26,29 . A second method 6,22,28 is to determine the solution resistance at the high frequency intersection of the impedance spectrum with the Zimag = 0 axis provided that the system is not influenced by large inductive effects.Therefore, this technique avoids the need for interpreting the impedance spectrum and selection of a correct equivalent circuit.…”