Oxidized aluminum overcoat for solid electrolyte sensor

Claim 2

In a method of making a porous refractory overcoat on a noble metal electrode of a solid electrolyte exhaust gas oxygen sensor, the improvement which comprises: coating a slurry of aluminum flakes onto the noble metal electrode, drying the coating, and then oxidizing the aluminum flakes in situ by heating the coating in an oxidizing atmosphere wherein a strongly bonded and durable flake-like porous refractory overcoat is inexpensively formed on the noble metal electrode.

Claim 3

In a method of making a porous refractory overcoat on a noble metal electrode of a solid electrolyte exhaust gas oxygen sensor, the improvement which comprises: coating a slurry of aluminum flakes having a maximum dimension of about 10 micrometers, an organic binder and a vehicle onto the noble metal electrode, drying the coating and then heating the coating in an oxidizing atmosphere to at least form a rigid exoskeleton of aluminum oxide on each flake, that is interlocked with aluminum oxide exoskeletons on adjacent flakes wherein a strongly bonded and durable porous refractory overcoat about 0.1-0.3 millimeter thick is inexpensively formed on the noble metal electrode.

Claim 4

In a method of making a porous refractory overcoat on a noble metal electrode of a solid electrolyte exhaust gas oxygen sensor, the improvement which comprises: coating a slurry of aluminum flakes having a maximum dimension of about 10 micrometers, an organic binder and a vehicle onto the noble metal electrode, drying the coating and then heating the coating in an oxidizing atmosphere to at least form a rigid exoskeleton of aluminum oxide on each flake, that is interlocked with aluminum oxide exoskeletons on adjacent flakes wherein a strongly bonded and durable porous refractory overcoat about 0.1-0.3 millimeter thick is inexpensively formed on the noble metal electrode.

Claim 5

In a method of making a porous refractory overcoat on a platinum exhaust electrode of a zirconia-type exhaust gas oxygen sensor, the improvement which comprises: applying a coating about 0.1-0.3 millimeter thick on said platinum electrode of a slurry containing about 1 part organic binder for every 2-3 parts aluminum flakes of a maximum dimension of about 1-10 micrometer, drying the slurry coating, heating the dried coating in air to burn out the binder, and then heating it further in air to a temperature of about 600°-800° C. for about 1-3 hours, effective to form a strongly bonded matrix of aluminum oxide that serves as a protective refractory overcoat on said electrode.

Claim 6

In a method of making a porous refractory overcoat on a platinum exhaust electrode of a zirconia-type exhaust gas oxygen sensor, the improvement which comprises: applying a coating about 0.1-0.3 millimeter thick on said platinum electrode of a slurry containing about 1 part organic binder for every 2-3 parts aluminum flakes of a maximum dimension of about 1-10 micrometer, drying the slurry coating, heating the dried coating in air to burn out the binder, and then heating it further in air to a temperature of about 600°-800° C. for about 1-3 hours, effective to form a strongly bonded matrix of aluminum oxide that serves as a protective refractory overcoat on said electrode.