Development of SO_x gas sensor utilizing the improved beta-alumina solid electrolyte

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The reaction between beta-alumina and rare-earth oxides (Nd_2O_3,CeO_2,Pr_6O_<11>) have been investigated. By using the thin film of rare-earth oxide and Na^+- beta-alumina pellet as samples, the following experimental results could be found. At 1073ﾟK,Pr_6O_<11> reacted with beta-alumina and the existence of some new compounds were confirmed. In the case of CeO_2 the extra pattern except the characteristic ones of CeO_2 and beta-alumina were not found and it was concluded that CeO_2 was not reacted with beta-alumina Nd_2O_3 reacted with beta-alumina and C-type compound was found and follows transformed to A-type one.The reaction between beta-alumina pellet and air-SO_x gas mixture have been investigated based on the variation of electritic conductivity of cell with time at 1023 K. The electritic conductivity changed suddenly with the gas flowing into the cell and follows kept nearly constant value it was confirmed that the surface of Na^+-beta-alumina pellet was covered by stable Na_2SO_4 phase within one hour.From above experimental results, it could be concluded that the best solid electrolyte is the Na^+-beta-alumina covered with CeO_2. The SO_x gas sensor employing Na^+-beta-alumina covered with CeO_2 solid electrolyte was constructed and the responsivility of this sensor at 873 and 1023ﾟK have been investigated. The equilibrium e.m.f. wasfound to change reliably with the change in P_<so2>. In particularly. the characterization of response to a change in P_<so2> at lower temperature was promoted by means of utilizing the Na^+-bate-alumina diskcovered by CeO_2. Many useful experimental results have been obtainedfor development the practical SO_x sensor.