Electro-chemical sensor

Electro-chemical sensor to determine oxygen concentration in hot internal combustion exhaust gases comprising a closed, tubular element which includes a first tubular portion adapted to be exposed to the exhaust gases and a second portion for making an electrical connection with said first tubular portion comprising

• a solid oxygen ion conductive electrolyte;
• an electron-conductive layer on the inner surface of said solid electrolyte;
• an outer electron conductive layer on at least a portion of the outer surface of said solid electrolyte, said outer conductive layer being of a material which catalyzes the formation from said hot exhaust gases of those compounds that are thermodynamically stable at the exhaust gas temperature, said outer conductive layer having pores or fissures which are of a diameter, or width, not greater than about the thickness of said outer conductive layer;
• a protective electrically insulating coating covering said outer electron-conductive layer;
• and
• an electrically insulating coating covering at least all of the outer surface portions of said solid ion conductive electrolyte of said first tubular portion not covered by said outer conductive layer, at least the portion of said protective electrically insulating coating covering said outer electron-conductive layer being porous, whereby the entire outer surface of said solid ion conductive electrolyte which may be exposed to said exhaust gases is covered to prevent direct contact of solid ion conductive electrolyte material with exhaust gases, said porous protective electrically insulating coating comprising at least one composition selected from the group consisting of magnesium spinel, kaolin, and talc.

Electro-chemical sensor to determine oxygen concentration in hot internal combustion exhaust gases comprising a closed, tubular element which includes a first tubular portion adapted to be exposed to the exhaust gases and a second portion for making an electrical connection with said first tubular portion comprising

• a solid oxygen ion conductive electrolyte;
• an electron-conductive layer on the inner surface of said solid electrolyte;
• an outer electron conductive layer on at least a portion of the outer surface of said solid electrolyte, said outer conductive layer being of a material which catalyzes the formation from said hot exhaust gases of those compounds that are thermodynamically stable at the exhaust gas temperature, said outer conductive layer having pores or fissures which are of a diameter, or width, not greater than about the thickness of said outer conductive layer;
• a protective electrically insulating coating covering said outer electron-conductive layer;
• an electrically insulating coating covering at least all of the outer surface portions of said solid ion conductive electrolyte of said first tubular portion not covered by said outer conductive layer, at least the portion of said protective electrically insulating coating covering said outer electron-conductive layer being porous, whereby the entire outer surface of said solid ion conductive electrolyte which may be exposed to said exhaust gases is covered to prevent direct contact of solid ion conductive electrolyte material with exhaust gases;
• and
• at least said coated first tubular element has an outer protective coating of at least one porous metal selected from the group consisting of nickel, chromium, nickel-chromium alloys, silver, and gold.

Electro-chemical sensor to determine oxygen concentration in hot internal combustion exhaust gases comprising

• a closed tubular element comprising a solid oxygen ion conductive electrolyte having a closed end and adapted to be exposed to the exhaust gases, and a second connecting tubular portion integral with said first tubular portion for providing an electrical connection with said first tubular portion, said connecting portion having an outwardly extending flange therearound;
• an electron-conducting metal coating on the inner surface of said electrolyte of at least a portion of said first tubular portion;
• an electron-conducting outer layer of a material which catalyzes the formation from said hot exhaust gases of compounds that are thermodynamically stable at the exhaust gas temperature, between 0.1 and 50 .mu. m thick and having pores or fissures which are of a diameter, or width, up to about the thickness of said layer covering at least a part of the outer surface of said solid electrolyte;
• and
• a porous protective coating between 0.1 and 500 .mu. m thick and having a ratio of thickness to average diameter of pores of between 2:1 and 100:1 on said electron-conductive outer layer and also covering at least all of the outer surface portions of said solid ion conductive electrolyte of said first tubular portion not covered by said outer conductive layer and including the outer surface of said tubular element extending up to said flange and covering a portion thereof and covering all of the outer surface of said solid ion conductive electrolyte of said connecting portion up to and at least adjacent said connecting flange whereby the entire outer surface of said solid ion conductive electrolyte which may be exposed to said exhaust gases is covered to prevent direct contact of solid ion conductive electrolyte material with exhaust gases.