Ngk Spark Plug Company, Limited

Toshihiko Aoyama

Yoshiro Noda

Haruhisa Shiomi

Yoshitake Kawachi

Ken Minoha

Yoshiro Suematsu

Yasuhiro Ujita

A ceramic heater with a specified ratio of electric resistance for the heat generating portion and the lead portion of a heat generating resistor is provided. The ceramic heater has a ceramic substrate comprising alumina as a main ingredient and a heat generating resistor composed only of tungsten, or a heat generating resistor comprising at least one of 3 to 30% by weight of alumina and 10 to 40% by weight of rhenium, and at least one of tungsten and molybdenum. Particularly, the ratio of the electric resistance can be controlled and the adhesion of ceramic substrates for sandwiching the heat generating resistor can be improved, for example, by means of disposing slits to the lead portion and/or changing ingredients constituting the lead portion. The ceramic heater is capable of reaching a predetermined temperature in a short time, has high adhesion between the heat generating resistor and ceramic substrates and excellent durability and can be used in an oxygen sensor.

Ceramic heater and oxygen sensor using the same

An alumina-based sintered material for ceramic heater having a resistance heater embedded in its ceramic material. With the total amount of Al.sub.2 O.sub.3, SiO.sub.2, MgO and CaO being 100 wt %, the sintered material contains 91 to 97 wt % of Al.sub.2 O.sub.3, 1 to 8 wt % of SiO.sub.2, 0.2 to 1.2 wt % of MgO and 0.2 to 1.2 wt % of CaO, the total amount of MgO and CaO being 0.4 to 1.8 wt %, whereas, for the total amount of Al.sub.2 O.sub.3, MgO and CaO of 100 wt %, 0.1 to 15 wt % of (a) at least one of rare earth elements and groups IVa excluding Ti, Va and VIa of the Periodic Table are contained in the sintered material. In place of (a), 0.2 wt % or less of other elements (Na, K, Fe, Ti etc.) may also be contained in an amount not more than 0.2 wt %, calculated in terms of oxides.

Alumina-based sintered material for ceramic heater

In the joining structure of the solid electrolytic element, terminals connected to the heating element and the electrodes are attached through metallic oxide layers onto the solid electrolytic layer. The thermal conductivity coefficient of the metallic oxide layers is larger than that of the solid electrolytic layer. The thermal expansion coefficient of the metallic oxide layers is the same as or smaller than that of the solid electrolytic layer. Consequently, when the lead wires are soldered to the terminals, heat is quickly conducted to the terminals, enhancing the fluidity and the solderability of the soldering material. Since excess heating is not required for soldering, the solid electrolytic layer is prevented from deteriorating due to heat. Since a low-melting solder is not used, the joining structure has high heat resistance. Moreover, during soldering, the metallic oxide layers do not detach from the solid electrolytic layer due to heat.

Structure for joining a wire to a solid electrolytic element

An oxygen sensor comprising a hollow cylindrical member closed at one end but open at the other to admit a reference gas. There is at least one radial through-hole in the hollow cylindrical member. An oxygen-ion conductive solid electrolyte later has at least one pair of electrodes on its opposite sides. The electrolyte layer is wrapped around the hollow cylindrical member with the electrode on its inner side facing the through hole. In other embodiments, an oxygen sensor is provided which is very insensitive to the direction of flow of the gas to be analyzed. The electrodes of the sensor are spaced at substantially equal intervals on the circumference of a cylindrical solid electrolyte layer in registry with through-holes formed in a hollow tubular member surrounded by the electrolyte layer. A heating unit may be formed on either the inner or outer surface of the solid electrolyte layer.

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Aichi, Japan

Toshihiko Aoyama