Development of electrochemical sensor for rapid measurement of solute activities using mullite solid electrolyte

1.It was confirmed from the measurement of formation free energy of oxides(FeO，CoO，NiO)by using tablet of mullite(3Al_2O_3·2SiO_2)that mullite could be used as a solid electrolyte.2.The values for electronic conductivity limits，P_&lt；THETA&gt；，of mullite and ZrO_2-9mol%MgO solid electrolytes were estimated as log(P_lt；THETA&gt；/atm)=54.1332-7000&lt；P&gt；/atm)=27.16-75500/T，respectively/3.The values for oxygen activity obtained using a mullite or ZrO_2-plug type probe agreed satisfactorily with both those calculated from the Al/Al_2O_3 equilibrium and those estimated from the analyzed oxygen contents。The values for oxygen activity obtained using a ZrO_2-tube type probe were higher than those estimated from the analyzed oxygen contents。A polarization effect in a ZrO_2-tube type probe could not be eliminated in the measurement of low oxygen activity.4.From superaturation experiments，it could be concluded that the measured EMF by a mullite probe corresponded to the oxygen activity determined bt the Al/Al_2O_3(In Mullite)equilibrium at liquid iron/electrolyte at interface，while that of a ZrO_2-pltype be procorresponded to the supersaturated procorresponded to the supersuratedBoth results agreed well with each other.The activity of silicon in carbon-saturated Fe-Si alloys obtained by a mullite probe agreed with those calculated from the analyzed silicon contents。The measured EMF by a mullite probe corresponded to the oxygen activity determined bt the Si/SioO_2(In Mullite)equilibrium at liquid iron/electrolyte interface.6.Since the measured EMF by a mullite probe corresponded to the aluminum or silicon activity not to the oxygen activity in bulk，it could be concluded that a mullite solid electrolytecould be

1.It was confirmed from the measurement of formation free energy of oxides (FeO,CoO,NiO) by using tablet of mullite (3Al_2O_3・2SiO_2) that mullite could be used as a solid electrolyte.2.The values for electronic conductivity limits, P_<THETA>, of mullite and ZrO_2-9 mol% MgO solid electrolytes were estimated as log (P_<THETA>/atm)=54.32-137000/T and log (P_<THETA>/atm)=27.16-75500/T,respectively/3.The values for oxygen activity obtained using a mullite or ZrO_2-plug type probe agreed satisfactorily with both those calculated from the Al/Al_2O_3 equilibrium and those estimated from the analyzed oxygen contents. The values for oxygen activity obtained using a ZrO_2-tube type probe were higher than those estimated from the analyzed oxygen contents. A polarization effect in a ZrO_2-tube type probe could not be eliminated in the measurement of low oxygen activity.4.From superaturation experiments, it could be concluded that the measured EMF by a mullite probe corresponded to the oxygen activity determined bt the Al/Al_2O_3 (in mullite) equilibrium at liquid iron/electrolyte interface, while that of a ZrO_2-plug type probe corresponded to the supersaturated oxygen activity.5.The activity of silicon in Fe-Si alloys equilibrated with SiO_2 itwere determined by a mullite or ZrO_2-plug type probe. Both results agreed well with each other. The activity of silicon in carbon-saturated Fe-Si alloys obtained by a mullite probe agreed with those calculated from the analyzed silicon contents. The measured EMF by a mullite probe corresponded to the oxygen activity determined bt the Si/SioO_2 (in mullite) equilibrium at liquid iron/electrolyte interface.6.Since the measured EMF by a mullite probe corresponded to the aluminum or silicon activity not to the oxygen activity in bulk, it could be concluded that a mullite solid electrolytecould be used for Al-or Si-sensor in liquid metal.