Author : Lora Birkefeld Younkman
Publisher :
ISBN 13 :
Total Pages : 436 pages
Book Rating : 4.:/5 (339 download)
Book Synopsis Development and Characterization of Ceramic-Based Carbon Monoxide Sensors by : Lora Birkefeld Younkman
Download or read book Development and Characterization of Ceramic-Based Carbon Monoxide Sensors written by Lora Birkefeld Younkman and published by . This book was released on 1995 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: In recent years, the importance of monitoring combustion processes for fuel efficiency and pollution control has necessitated the development of reliable gas sensors for high temperature in situ detection. Semiconductor gas sensors have been developed for a wide range of reactive gases, but are typically nonselective to any particular gas in gaseous mixtures. The objective of this research was to develop fast-responding solid-state sensors for the selective detection of CO gas at elevated temperatures, as well as to understand and characterize the associated sensing mechanisms. From preliminary dc electrical resistance measurements, the sensing properties of various semiconducting oxides were investigated, and Mo03- and Ti02-based systems were selected as candidate sensor materials. Mo03 was found to display an ON/OFF-type sensing behavior. X-ray photoelectron spectroscopy (XPS) results indicated that the sensitivity could be attributed to the surface reduction of Mo03 to the Mo02 phase. The Ti02 sensor displayed a gradual drop in electrical resistance with increasing CO concentration but suffered from H2 interference. Two different mechanisms were proposed (based on recovery characteristics) to describe the sensitivity of Ti02: a surface-controlled mechanism for CO, supported by XPS data, and a bulk-diffusion controlled mechanism for H2. Through second phase additions of 10 wt% Y203 and 10 wt% Al203, the sensor was made selective to CO and H2, respectively with no interference from NOx. Fe and Pd catalyst additions improved both the response time and the lower limit of CO detection. A sensor device of (Ti02-10 wt% Y203)-5 wt% Pd was developed with optimized geometry, electrode configuration, and processing conditions. A prototype device was sucessfully tested in an automobile engine for over 50 cycles, responding quickly and reversibly under revving and idling conditions. Immittance spectroscopy (IS) was employed to characterize the electrical behavior of Ti02. By extracting the electrical parameters through lumped parameter/complex plane analysis, the sensing behavior was found to be grain boundary-controlled, with sensitivity determined by electrical barriers at the intergranular contacts. Upon exposure to CO gas, these barriers are effectively lowered, and the depletion region width decreases. The observed decrease in electrical resistance and increase in grain boundary capacitance provided evidence in support of this proposed mechanism.
