DEVELOPMENT OF HARSH ENVIRONMENT NITROGEN OXIDES SOLID-STATE GAS SENSORS
The goal of this dissertation was to study and develop high temperature solid-state sensors for combustion based gases. Specific attention was focused on NO x gases (NO and NO 2 ) as they are of significant importance with respect to the environment and the health of living beings. This work is divided into four sections with the first chapter being an introduction into the effects of NO x gases and current regulations, followed by an introduction to the field of high temperature NO x sensors and finally where and why they will be needed in the future. Chapter 2 focuses on the development of a gas sensor for NO x capable of operation in harsh environments. The basis of the sensor is a mixed potential response at 500/600°C generated by exposure of gases to a platinum-yttria stabilized zirconia (Pt-YSZ) interface. Asymmetry between the two Pt electrodes on YSZ is generated by covering one of the electrodes with a zeolite, which helps to bring NO/NO 2 towards equilibrium prior to the gases reaching the electrochemically active interface. Three sensor designs have been examined, including a planar design that is amenable to packaging for surviving automotive exhaust streams. Automotive tests indicated that the sensor is capable of detecting NO in engine exhausts. Chapter 2 concludes that it is difficult to measure NO or NO 2 selectively especially when both gases are present at the same time thus we have developed a strategy in chapter 3 to measure the total NO x level (NO +NO 2 ) in a background of O 2 and N 2 at high temperatures with minimal CO interference by combining a catalytic filter bed with the existing YSZ sensor device. The filter bed was composed of a Pt catalyst dispersed onto a zeolite Y support placed before a YSZ sensor having an air reference with a Cr 2 O 3 or Pt sensing electrode. Chapter 4 explores the reasons for the difference in sensitivity of metal oxide electrodes, Cr 2 O 3 and a mixed conducting perovskite La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O x , with the goal of ultimately developing a systematic method of electrode screening as compared to the random screening often found in the literature.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:no x sensors chemical mixed potential potentiometric gas analytical chemistry
Date of Publication:01/01/2003