| Summary: | 碩士 === 逢甲大學 === 材料科學與工程學系 === 102 === In the present study, zirconia-doped ceria (ZDC) solid solution powders were prepared from cerium nitrate hydrate (Ce(NO3)3) and zirconium nitrate hydrate (ZrO(NO3)2) by spray pyrolysis (SP) and co-precipitation (P). The as-prepared powders were screen-printed onto electrode-patterned substrates for oxygen sensing applications. The effects of sintering condition and sintering temperature on the microstructure, concentrations of Ce3+, electrical properties and oxygen sensitivity of ZDC thick films within a temperature range 550800°C were investigated. The responses of the specimens to oxygen partial pressure change at 600, 700 and 800°C were also discussed.
X-ray diffractometry identified the ZDC powders as a phase of ceria-zirconia solid solution. The ceria-based powder obtained from spray pyrolysis was observed to be hollow spherical in shape with a wide range of particle size distribution, showing a well connecting behavior after sintering. The co-precipitated powder had a rod-like shape and exhibited a high surface area. However, the coating showed a island-like morphology after sintering. The sensitivity of specimens prepared from P powder was not increased as significant as expected. This may result from the limitation of effective contact area of the sensor during sensing process. The width of pores for ease of gas diffusion is also needed to be considered. The XPS identified that the formation of Ce3+ ions can be increased under the lean oxygen partial pressure.
Under different sintering conditions, the grain growth of ZDC films was enhaced with the increase of heat treatment temperature. ZrO2 phase could be observed in the specimens sintered at high temperatures in nitrogen. This probably results from the ionic radius mismatch of Zr4+ in ceria, decreasing the amount of Ce3+. The electrical conductivity was increased with increasing the grain size, but this resulted in lower response rates. An appropriate amount of the second phase could inhibit grain growth and was conducive to dynamic response performance for oxygen sensor application.
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