Nippondenso Co., Ltd.

Katsuhiko Tanaka

Masami Ouki

Masatoshi Suzuki

Toshitaka Saito

Naoto Miwa

Masatosi Suzuki

A solid electrolyte for an oxygen concentration sensor is provided by mixing ZrO.sub.2 and about 6.5 to about 8% by mol of a stabilizer such as Y.sub.2 O.sub.3, grinding the mixture to give a BET specific surface area of about 9 to 20 m.sup.2 /g, adding to the ground mixture a forming aid, forming the mixture into a predetermined configuration and firing the formed mixture at about 1420.degree. to 1570.degree. C. The electrolyte has a surface-average grain size of about 5 microns or less and a structure of a cubic phase alone at the surface thereof and, furthermore, may contain about 5% or less of a monoclinic phase per the total of the cubic and monoclinic phases, in a finely ground state.

Solid electrolyte for use in oxygen concentration sensor

A solid electrolyte for an oxygen concentration sensor is provided by mixing ZrO.sub.2 and about 7.5 to 8.5% by mol of a stabilizer such as Y.sub.2 O.sub.3, grinding the mixture to have a BET specific surface are of about 9 to 20 m.sup.2 /g, adding to the ground mixture a forming aid, forming the mixture into a predetermined configuration and firing the formed mixture at about 1420.degree. to 1520.degree. C. The electrolyte has a surface-average grain size of about 5 microns or less and a structure of a cubic phase alone at the surface thereof and even in a finely ground state.

A solid electrolyte for an oxygen concentration sensor is provided by mixing ZrO.sub.2 and about 6.5 to 7% by mol of a stabilizer such as Y.sub.2 O.sub.3, grinding the mixture to give a BET specific surface area of about 9 to 20 m.sup.2 /g, adding to the ground mixture a forming aid, forming the mixture into a predetermined configuration and firing the formed mixture at about 1420.degree. to 1480.degree. C. The electrolyte has a surface-average grain size of about 5 microns or less and a structure of a cubic phase and a monoclinic and/or tetragonal phase at the surface thereof and, furthermore, may contain about 5% or less of a monoclinic phase per the total of the cubic and monoclinic phases, in a finely ground state.

A sintered body of zirconia material for an oxygen concentration sensor exhibiting an electromotive force in accordance with the difference in the concentration of oxygen between a gas tested and a reference gas, consisting essentially of partially stabilized sintered zirconia and at least one additive selected from the group of yttrium oxide, calcium oxide and ytterbium oxide which zirconia has a cubic phase and a monoclinic phase existing in mingling relation. The ratio of the X-ray diffraction intensity of the surface (111) of the monoclinic phase to the X-ray diffraction intensity of the surface (111) of the cubic phase or the ratio I(111)/I(111) is in the range between 0.05 and 0.40, and the value of the X-ray diffraction intensity ratio caused by heating the sintered zirconia material to, and holding the same at, the temperature range between 200.degree. and 300.degree. C. minus the former ratio of the X-ray diffraction intensity is in the range between -0.05 and +0.10.

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Toyokawa, Japan

Katsuhiko Tanaka