Isuzu Ceramics Research Institute Co. Ltd.

Hisataka Numao

Hideo Kawamura

Hideki Kita

A ceramic sheath capable of preventing damage to conductive wire rod exhibits excellent thermal resistance and a thermal shock resistance. A conductive wire rod is provided in a protective pipe of silicon nitride, silicon carbide or SiAlON so as to extend longitudinally from one end toward the other, and buried in a filler of reaction sintered silicon nitride. The filler comprises two layers, i.e. a core portion having a low sintering time size variation ratio, and a seal portion constituting a boundary layer between the core portion and the protective pipe and having a sintering time size variation ratio higher than that of the core portion. The conductive wire rod comprises a coil of a metal wire. The coil is formed helically along its whole length, and the winding pitch of the coil is set small, large and small in this order from the front end portion of the shell of the protective pipe toward its base end portion.

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Kawasaki, Japan

Hisataka Numao