| Summary: | 碩士 === 國立臺灣科技大學 === 材料科學與工程系 === 101 === Ceria-based materials have been extensively investigated as oxygen gas sensor in automotive exhaust systems due to their excellent properties of fast response time and superior sensitivity. Since the response time and sensitivity are influenced by the ceria parameters of surface area, crystalline size and cerium valence ratio (Ce(III)/(Ce(IV)), these parameters correlate with their particle morphologies.Therefore, manipulation of particle morphology is urgent and important for application in oxygen gas sensors. However, so far, the studies of varying morphologies to investigate response time and sensitivity for the oxygen gas sensors are scarce. So, the morphologies of mesoporous, porous, core-shell and solid spherical ceria powders were prepared by spray pyrolysis, and screen printed on the alumina substrates with platinum wires. The formation of thick films with 5-11μm thickness undergoes the gel decomposition at 500oC for 5h and sintering at 1200oC for 2h, and measured the properties of response time and sensitivity. The morphology, surface area, crystalline size, and cerium valence ratio were characterized by transmission electron microscopy, BET (Brunauer–Emmer–Teller) method, X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The experimental results suggest that higher surface area and smaller crystalline size shorten response time, and higher Ce(III) concentration enhances the sensitivity of oxygen gas sensor.
Mesoporous Zr-doped ceria powders were prepared by spray pyrolysis(10ZDC、20ZDC、30ZDC、50ZDC, 10、20、30、50 mole% Zr doped ceria). And, the resistive oxygen gas sensors based on thick film made from this powder were fabricated. The response time of the thick film were investigated. The experimental results suggest that the lattice constant decrease with increasing ZrO2 concentration. Therefore, the electron hopping distance decrease, and the resistance of thick film decrease. The 30ZDC thick film had a lower latiice constant and crystallite size. Hence, it had lower resistance and a shorter response time. The results showed that 30ZDC thick film exhibited superior oxygen sensing properties.
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