An oxygen sensor using a process of high-temperature oxidation of metal
- Tohoku Univ., Sendai (Japan). Research Inst. for Scientific Measurements
Oxygen sensors using stabilized ZrO{sub 2} as the electrolyte are used for steel making and heat engines to obtain high performance. An oxygen sensor is proposed which is represented by an electrochemical cell metal {vert_bar} oxide scale {vert_bar} sensing electrode, where the metal, its oxide scale, and sensing electrode work as reference electrode, electrolyte, and sample electrode, respectively. Here the oxide scale is required to be an oxide-ion conductor, and the sensing electrode is not to be reactive with the oxygen. It is expected that the electrolyte is self-restorative because it can be reformed by high-temperature oxidation. The electromotive force (EMF) measurements were carried out at 873 K with cells using zirconium as the metal electrode and Pt as the sensing electrode. At p{sub o{sub 2}} = 1--10{sup {minus}4} atm, the EMF vs. log p{sub o{sub 2}} plot lies on a straight line and its gradient is 2.303 RT/4F, suggesting unity of the oxide-ion transference number at the surface of the scale. The EMF steeply decreases with decreasing p{sub o{sub 2}} at p{sub o{sub 2}} < 10{sup {minus}4} atm, which cannot be explained by the increase in the electronic conductivity. The oxidation behaviors showed linear oxidation. Assuming repetition which constituted of parabolic oxide film growth until a certain thickness and its crack formation, the linear rate constants were described as a function of the oxygen partial pressure. It was considered that the steep decrease in EMF is caused by the change of the rate-determining process to form the scale.
- OSTI ID:
- 345331
- Journal Information:
- Journal of the Electrochemical Society, Vol. 146, Issue 4; Other Information: PBD: Apr 1999
- Country of Publication:
- United States
- Language:
- English
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