Abstract
The electromotive force (EMF) of an oxygen concentration cell using SiO 2 -Al 2 O 3 ceramics (x = 1, 2, 3 and 4 in xAl 2 O 3 . Al 2 SiO 2 ) as a solid electrolyte was measured at 1073-1573 K in the oxygen pressure range of 1.0 × 10 −1.0 to 1.0 × 10 3.5 Pa at the anode side. The SiO 2 -Al 2 O 3 ceramics (96.2-98.5% of theoretical density) sintered at 1873-1903 K in air were annealed at 1673 K for 8 h to produce equilibrium phases before EMF measurement. Air as a reference gas and Ar-O 2 mixed gas were introduced to cathode and anode sides, respectively. The measured EMF indicates that ionic transport number (t i ) of oxygen is higher in the following order: mulliteSiO 2 composite (x = 1, 2) > mullite (x = 3) > mulliteAl 2 O 2 composite (x = 4). At lower oxygen pressures, t i decreased with decreasing oxygen pressure due to formation of electrons available for conduction
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