| dc.contributor.author | Sharma, Anita. | en_US |
| dc.date.accessioned | 2014-10-21T12:36:20Z | |
| dc.date.available | 1994 | |
| dc.date.issued | 1994 | en_US |
| dc.identifier.other | AAINN93797 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55418 | |
| dc.description | Two oxygen sensors, A and B, employing yttria-stabilized zirconia as an electrolyte and platinum paste as electrodes, were studied using three techniques, namely exposing the sensor to rapid changes in oxygen pressure, complex impedance measurements and scanning electron microscopy. | en_US |
| dc.description | By exposing the sensor to rapid changes in pressure, response times were measured from 760 to 8 torr and at temperatures between 773 and 948 K for sensor A and between 623 and 823 K for sensor B. Experiments in which the oxygen pressure suddenly increased had faster response and the opposite dependence of response on initial pressure when compared to experiments in which the pressure suddenly decreased. For sensor A, the order of the response times with respect to final oxygen pressure was found to be about $-{1\over4}$ at 773 K, decreasing at higher temperatures. For sensor B, the order of response with respect to the pressure was close to zero at all temperatures. The activation energy was found to be $210\pm 14$ kJ mol$\sp{-1}$ for sensor A and $145\pm 14$ kJ mol$\sp{-1}$ for sensor B. The logarithm of the pre-exponential factor in units of s$\sp{-1}$ was $12.4\pm 0.5$ for sensor A and $9.7\pm 1.2$ for sensor B. The differential rate equations for various possible elementary steps were integrated and the resulting expressions were fitted to experimental curves of voltage as a function of time. Scanning electron micrographs were used to measure the electrode/electrolyte contact area for sensor A. For sensor A, the results at lower temperatures were in agreement with a model in which response is limited by the rate of conversion of electron holes and singly-charged oxide anions to neutral oxygen atoms at the surface of the zirconia. At higher temperatures, the reaction of oxide anions with electron holes could be rate limiting. | en_US |
| dc.description | Using the complex impedance technique for sensor B, the bulk and interfacial resistance and capacitance were determined at 623 to 823 K. The activation energy for the bulk conductance was 80 $\pm$ 17 kJ mol$\sp{-1}$ and for the interfacial conductance was 119 $\pm$ 17 kJ mol$\sp{-1}$. The results from the impedance experiments and response time measurements were consistent with a mechanism in which the rate is limited by diffusion of electron holes from the bulk to the electrode/electrolyte interface. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1994. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Chemistry, Physical. | en_US |
| dc.title | Kinetic studies of the response times of zirconia oxygen sensors. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
