Zirconium oxide oxygen concentration

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. 

The probe used is an in-situ type stabilized zirconia oxygen analyzer. The zirconium oxide cell is able to measure oxygen concentrations in hot, dirty gases without sample conditioning. In addition, the moisture content of the gas has no effect on the analyzer. 

The decomposition of NO is a very slow catalytic reaction. Amirazmi, Benson, and Boudart recently studied the kinetics over platinum and over oxides of copper, cobalt, nickel, iron and zirconium from 450 to 900°C. They found that the kinetics is first order in NO with concentrations from 1.5 to 15%, and that oxygen has a strong inhibiting effect. Even at these temperatures, the kinetics is about a factor of 1000 too low for automotive usage (97). 

In the 1940 s a CVD process using a flame to produce homogeneously nucleated (powder) oxides of titanium, zirconium, iron, aluminum, and silicon was reported. A mixture of metal halide vapor and oxygen is injected through the central nozzle of a burner, with fuel gas and supplemental oxygen provided through two concentric outer rings. At 950°C to 1100 C flame temperature, the metal halide vapor decomposes to form very fine oxide powders. 

Aluminum is the third most abundant element in the earth s crust (after oxygen and silicon), accounting for 8.2% of the total mass. It occurs most commonly in association with silicon in the aluminosilicates of feldspars and micas and in clays, the products of weathering of these rocks. The most important ore for aluminum production is bauxite, a hydrated aluminum oxide that contains 50% to 60% AI2O3 1% to 20% FeiOs 1% to 10% silica minor concentrations of titanium, zirconium, vanadium, and other transition-metal oxides and the balance (20% to 30%) water. Bauxite is purified via the Bayer process, which takes advantage of the fact that the amphoteric oxide alumina is soluble in strong bases but iron(III) oxide is not. Crude bauxite is dissolved in sodium hydroxide... 

CHEMICAL PROPERTIES most zirconium compounds are considered inert zirconium metal can react with hydrofluoric acid, aqua regia, and hot phosphoric acid attacked hy fused potassium hydroxide or potassium nitrate not attacked by cold, concentrated sulfuric or hydrochloric acid resistant to attack by nitric acid very resistant to corrosion oxidizes rapidly at 6°C nitrided slowly at 700°C compact form combines with oxygen, nitrogen, carbon, and the halogens on prolonged heating FP (NA) LFLAJFL (NA) AT (NA) HF (0.0 kJ/mol crystal at 25 C) Hf (21.0 kJ/mol at 2127.85K). 

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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