Zirconium oxide probes

The acidity of pillared clays has been characterized by both microcalorimetric measurements of the adsorphon of aromatic molecules and pyridine and the catalytic ethylbenzene test reaction [111]. The aromatic probe molecules used were a reactant and a product of the catalytic reaction ethylbenzene and m-diethylben-zene, respectively. In this way, only the strongest of the accessible acid sites were htrated. The heats of adsorphon of these molecules indicate that a zirconium oxide pillared clay had stronger acidity than an aluminum oxide pillared clay, whereas the pyridine results were equal for both samples. 

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. 

Zirconium oxide, stabilized with 3-8% YjO, also has been used in k-probes for determination of the partial pressure of oxygen in car exhaust fumes that makes it possible to optimize the air-fuel mixture to the engine. A similar solid electrolyte is used as a probe for determining oxygen in molten steel. 

Catalysts active in the isomerization of n-butane have been synthesized by depositing sulfate ions on well-crystallized defective cubic structures based on ZrOz. This technique for introduction of sulfates does not result in any significant changes in the bulk properties of zirconium dioxide matrix. Active sulfated catalysts were prepared on the basis of cubic solid solutions of ZrOz with calcium oxide and on the basis of cubic anion-doped ZrOz. The dependence of the catalytic activity on the amount of calcium appeared to have a maximum corresponding to 10 mol.% Ca. Radical cations formed after adsorption of chlorobenzene on activated catalysts have been used as spin probes for detection of strong acceptor sites on the surface of the catalysts and estimation of their concentration. A good correlation has been observed between the presence of such sites on a catalyst surface and its activity in isomerization of n-butane. 

The working time of HT-probes decreases quickly over glass meltings with increasing temperature [55]. Vapors of the oxides, above all of sodium, potassium, silicium, lead, an-timon and arsen condense on the probe material in the temperature gradient from the inside to the outside of the tank wall. The condensed substances penetrate into the ceramic material over grain boundaries and lead to tube bursts. Thereby the stabilized zirconium dioxid is more sensitive than alumina. Componenu which contain Si02 must not be used in HT-probes [56]. 

Corrosion-related SECM studies on both zirconium and hyperstoichiometric uranium oxide have been reported by Shoesmith and coworkers [70,71]. In both cases, their interest was in identifying areas of high cathodic activity on the substrate and then determining the electron transfer rate constant (k9) for sites of varying activity. Previously existing models for quantitative kinetic determinations have assumed a substrate of infinite dimensions. In practice, however, the active sites in localized corrosion investigations are often of dimensions similar to the microelectrode probe surface. Therefore, finite element analysis was utilized to generate theoretical PACs that allow for variation in the dimensions of both the active area and the probe, as well as in the level... 

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