Application of solid electrochemical sulfur sensor in the liquid iron

A novel solid electrochemical sulfur sensor based on ZrO2(MgO) as solid electrolyte and CaAl2O4+CaAl4O7 as electrode coating was developed and tested in the carbon-saturated liquid iron at 1773 K. A mixture of chromium and chromium oxide was used as the reference electrode, CaS was allowed to synthesized in situ during the measurement by the CaAl2O4+CaAl4O7 coating on the surface of ZrO2(MgO) solid electrolyte to form the auxiliary electrode with residual CaAl2O4 and CaAl4O7 phase based on the reactions: CaAl2O4+S=CaS+Al2O3+[O] and CaAl4O7+S=CaS+2Al2O3+[O]. The sensor behavior in terms of response time, measurement errors, formation mechanism of auxiliary electrode and the lower limit of measurement was discussed in this study. The results indicated that the sulfur sensor showed such a superior sensing performance of theoretical response, which obeyed the Nernst relationship between the sensor EMF output and the natural logarithm of the sulfur concentration, along with the stable, continuous, and reproducible response. The variations of the EMF versus ln[wt% S] was obtained at 1773 K: E(mV)=48.371n[wt% S]+31.07. The lower detection limit of sulfur activity at 1773 K depended on oxygen activity in the liquid iron, a[S]=40.85a[O].