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Electrochemical immersion sensors

Deoxidation of steel melts by aluminium, manganese or chromium was investigated using the solid electrolyte measuring technique. New types of electrochemical immersion sensors were developed and successfully applied for direct determination of these elements in liquid steel.

The ionic and electronic conduction behaviour of zirconium dioxide and thorium dioxide based solid electrolytes was measured at extremely low oxygen partial pressures in deoxidized steel melts. The performance of conventional chromium chromium oxide and new Cr MgO MgCr2O4 Cr CaO CaCr 2O4 and niobium niobium oxide reference electrode materials was explored for long term electromotive force (EMF) measurements and appropriate conditions were examined to avoid polarization effects.

The new type of immersion sensor consists of a solid electrolyte plug and a reference material contained in an insulating, thin walled ceramic tube and a cavity at the sensor tip where molten aluminium, manganese or chromium containing iron is saturated with aluminium, manganese or chromium oxide.

Reliable correlations of measured EMF from the new sensors and aluminium content were found after extended periods of 30 to 40 mins. EMF measurements in iron oxygen aluminium melts covered with a calcium oxide saturated CaO Al2O3 CaF2 slag have shown that the oxygen activity at a given aluminium content is determined by the composition of the residual inclusions in the metal rather than by slag composition.

Further EMF measurements were made in iron oxygen manganese melts saturated with (Fex Mn1-x)O, manganese oxide or manganese oxide aluminium oxide plus aluminium oxide. Reliable correlations of measured EMF from the new sensors and manganese content were found in the range of 1 to 20 weight percentage manganese.

EMF measurements were also performed in iron oxygen chromium melts saturated with chromium oxide.

Data for the reaction equilibria of deoxidation with aluminium, manganese or chromium and for interact ion parameters of these elements in liquid iron based solutions were derived from the experimental results.

Reported by

Institut fuer Eisen- und Stahltechnologie
Leipziger Strasse 34
09596 Freiburg
Germany
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