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

1995 Fiscal Year Final Research Report Summary

• Project/Area Number: 05555197
• Research Category: Grant-in-Aid for Developmental Scientific Research (B)
• Allocation Type: Single-year Grants
• Research Field: Metal making engineering
• Research Institution: Tohoku University
• Principal Investigator: SUITO Hideaki Tohoku University, Institute for Advanced Materials Processing, Professor, 素材工学研究所, 教授 (70030054)
• Co-Investigator(Kenkyū-buntansha): FUJIWARA Ryuji Yamari Electronite Co., Ltd., Research and Development Division, Manager, 企画開発室, 室長 ; TAKAHASHI Jun-ichi Tohoku University, Institute for Advanced Materials Processing, Research Associa, 素材工学研究所, 助手 (20261472) ; INOUE Ryo Tohoku University, Institute for Advanced Materials Processing, Associate Profes, 素材工学研究所, 助教授 (70111309)
• Project Period (FY): 1993 – 1995
• Keywords: Mullite / Electrochemical sensor / Solid electrolyte / Liquid iron / Aluminum activity / Silicon activity / Oxygen activity

Research Abstract

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.