GB1462639A - Oxygen measuring sensors - Google Patents

Abstract

1462639 Oxygen sensor ROBERT BOSCH GmbH 6 March 1974 [7 March 1973] 9988/74 Addition to 1385464 Heading G1N A sensor for determining the oxygen content of exhaust gases comprises a solid electrolyte tube 10 closed at one end, an outer electrode layer 13 having pores or fissures of diameter or width up to the thickness of the layer, and of a material which catalyses the attainment of equilibrium in the exhaust gases, and a porous, non-conducting layer 14 covering and rigidly connected to the outer electrode. A further layer 15 of porous refractory metal may cover the non-conducting layer. An inner electrode 12 is also provided. The outer electrode 13 may cover part or all of the solid electrolyte tube. The outer electrode layer may comprise one or more coatings of platinum, palladium or iridium or alloys of these metals with one another or with aluminium, cobalt, chromium or other platinum group metals. It may also be formed from copperchromium oxide, optionally doped with borium oxide or nickel oxide or from lanthanum-cobalt oxide, optionally doped with strontium oxide. The electrode has an average thickness between 0À02 and 20 microns. The porous, non-conducting covering layer may be an oxide, a mixed oxide, a mixture of oxides, a siliceous material or a refractory ceramic. Examples are magnesium spinel, high melting sintered glass, kaolin and talc. A fluxing agent, e.g. feldspar, nepholine syenite or wollastonite may be added. The layer has a thickness between 0À1 and 500 microns and the ratio of the layer thickness to the pore diameter lies between 10:1 and 100:1. It may be formed by sintering-on, plasma spraying, thermo vapour deposition, gas phase separation or reactive vapour deposition. The porous refractory metal layer may be of nickel, chromium, nickel/chromium alloy, gold or silver of thickness between 0À1 and 500 microns. It may be applied by sintering-on, plasma spraying, thermal vapour deposition, cathode sputtering, gas phase separation, chemical reduction or galvanic precipitation. It may be impregnated with substances which exhibit the Gelter effect relative to catalyst poisons and with gold, silver, nickel/ nickel oxide or silicon dioxide. The inner electrode 12 may be of a noble metal or a substance such as an oxide which conducts at the operating temperature. The solid electrolyte may be zirconium dioxide.