Development of zirconia electrolyte sensor with auxiliary electrode for the in situ measurement of dissolved silicon in molten iron

Abstract

In Japan, hot metal pretreatments, such as desiliconization and dephosphorization processes, are applied in most steel making companies. The key to better operation of desiliconization is to use a sensing device that allows the silicon content in molten iron to be rapidly determined. Accordingly, we have investigated a zirconia electrolyte sensor with an auxiliary electrode for the instantaneous measurement of the silicon content in molten iron. To study the effects of the auxiliary electrode, four kinds of silicon sensors coated with various forms of ZrO 2/ZrSiO 4 mixtures as an auxiliary electrode have been tested. These sensors are used for measuring the electromotive force (e.m.f.) of iron melt in a 300 kg induction furnace. The response time becomes shorter with increasing boundary density of the auxiliary electrode. Furthermore, there appears to be a better correlation between e.m.f. and silicon activity in molten iron with the use of a high boundary density. These results indicate that a kind of equilibrium, in which a SiO 2 is fixed, is formed rapidly with the increase of boundary density at the hot metal/solid electrolyte/auxiliary electrode triphasic interface. Using this sensor, the silicon content in molten iron can be estimated to within ±0.015% Si by measuring the e.m.f. and the metal temperature.