Method of making a porous ceramic protective layer on an electrode of an electrochemical sensor for exposure to hot gas

Abstract

An electrochemical measurement sensor for determining the oxygen content in gases, in particular in exhaust gases from internal combustion engines, having a solid electrolyte of stabilized zirconium dioxide and/or other oxygen ion-conductive oxides and at least one electrode on the side of the solid electrolyte exposed to the gas which is to be measured, is proposed, the electrode or electrodes containing, if desired, a ceramic support structure, and the electrode or electrodes exposed to the gas, which is to be measured, being covered by a porous ceramic protective layer of an Al.sub.2 O.sub.3 and/or Mg spinel (MgO.Al.sub.2 O.sub.3) matrix with preferably metastable ZrO.sub.2 particles incorporated therein. The use of an Al.sub.2 O.sub.3 ZrO.sub.2 mixed oxide, which is preferably obtained by coprecipitation or by combination of suspensions of separately precipitated components or by spray-calcination of a combined solution of salts of the components and which may, if desired, contain a stabilizer for the ZrO.sub.2, such as, for example, Y.sub.2 O.sub.3, for forming the protective layer makes it possible, surprisingly, to form a firmly adhering, sintering-on protective layer which has a relatively narrow pore size distribution and which allows the best possible gas access to the outer electrode of the measurement sensor. The use of the Al.sub.2 O.sub.3 /ZrO.sub.2 mixed-oxide powder also achieves very extensive balancing of the hitherto observed mismatch of mechanical stresses and layer strengths on the one hand and the desired porosity and sensor control position on the other hand.

Dependencies are inferred from the claim text.