Zirconium oxide oxygen sensors

Principles and Development of a Thick-Film Zirconium Oxide Oxygen Sensor... 

KIMIJra et al. Zirconium Oxide Oxygen Sensor Legend of Symbols... 

While several types of oxygen sensors have been investigated for automotive use, the most common type in commercial use consists of a galvanic cell with a fully or partially stabilized zirconium oxide electrolyte. 

Zirconium oxide Piezoelectric devices, oxygen sensors. 

The lambda sensor, which is found in all motor cars with catalytic converters, is an oxygen probe based on the principle of selective electrodes. This sensor, which looks like a spark plug, has a zirconium oxide (zr02) membrane that behaves as a solid electrolyte. The external wall is in contact with the exhaust fumes while the Internal wall (the reference) is in contact with air. Between these two walls a PD appears, collected by two electrodes, which is indicative of the difference in oxygen concentrations. 

Porous ceramics are made by the sol-gel process. These ceramics have spongelike structures, with many porelike lacunae, or openings, that can make up from 25 to 70 percent of the volume. The pore size can be large, or as small as 50 nanometers (2 X 10 inches) in diameter. Because of the large number of pores, porous ceramics have enormous surface areas (up to 500 square meters, or 5,382 square feet, per gram of ceramic), and so can make excellent catalysts. For example, zirconium oxide is a ceramic oxygen sensor that monitors the air-to-fuel ratio in the exhaust systems of automobiles. 

Merilainen, P. T., Sensors for Oxygen analysis Paramagnetic, electrochemical, polarographic, and zirconium oxide technologies in Biomedical Instrumentation A Tbchnology, Nov./Dec 1989, 462-466. 

Complex FCC oxides of the fluorite type represent oxygen-conduction solid electrolytes (SOE s). They comprise a typical class of materials for the manufacture of sensors of oxygen activity in complex gas mixtures, oxygen pumps, electrolyzers and high-temperature fuel elements. These materials are based on doped oxides of cerium and thorium, zirconium and hafnium, and bismuth oxide. Materials based on zirconium oxide, for example, yttrium stabilized zirconia (YSZ) are the most known and studied among them. This fact is explained both by their processibility and a wide spectrum of practical applications and by the possibility to conduct studies on single crystals, which have the commercial name "fianites" and are used in jewelry. 

The sol-gel chemistry of Zr02 is similar to other tetravalent metal compounds such as Si02 and Ti02 Precursors such as zirconium halides and alkoxides are largely available, and they all hydrolyze rapidly in the presence of water. Zirconium oxide (and especially yttrium-stabilized Zr02 (YSZ)) is widely used as a thermal barrier but also as an ionic conductor (electroceramic). Even if it is not widely used for gas detection, its ionic conductivity makes it attractive as a sensor to control the oxygen level and thus the air/luel ratio in internal combustion engines. 

The outlook is different for the direct electrochemical determination of oxygen in the copper melt using a zirconium oxide sensor stabilized with calcium oxide (57)(80)(81)(85). This method is used to an ever-increasing extent. 

The partial pressures of oxygen, po, on both sides of the membrane are used instead of activities as in electrolyte solutions. When air is used as the reference gas on one side of the membrane, the potential of the sensor will be determined by the partial pressure of oxygen in the sample gas. In some of the latest modifications air as the reference gas has been replaced by solid nickelous oxide in contact with the zirconium dioxide providing a constant concentration of ions at the platinum contact electrode. 

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