Ngk Spark Plug Company, Limited

Toshiya Koide

Yoshihide Kami

Tatsuya Yamada

The invention relates to a gas sensor using a known gas sensitive element which provides an electrical output signal. For example, the sensitive element has a zirconia solid electrolyte sensitive to oxygen. The gas sensitive element is mounted on a ceramic substrate, and the substrate is partly inserted in a tubular housing, and a hermetic and electrically insulating seal column is formed in the housing to tightly hold the substrate. Lead wires protruding from the substrate are connected to external leads within the housing, and the joints are buried in the seal column. According to the invention, the seal column is formed of a glass-ceramic origitated from a glass which is composed of ZnO, B.sub.2 O.sub.3, SiO.sub.2 and MgO and has a crystallizing temperature of 740.degree.-900.degree. C. The glass-ceramic has a linear expansion coefficient smaller than that of the housing by 3.times.10.sup.-6 /.degree.C. at the most. Preferably alumina ceramic is used as the housing material. The glass-ceramic seal column is high in heat resistance and remains sufficiently airtight and electrically insulating even when its temperature exceeds 500.degree. C.

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Aichi, Japan

Toshiya Koide