| 摘要 |
<p>The present invention provides a unit sheath adaptable to a glow plug or a thermocouple, which is improved in durability by the protection from burn-out of the conductive filament. The unit sheath is preferably adapted to a glow plug 10. A protective envelope 1 of ceramics high in density includes a metallic filament 4 of any one of pure tungsten, molybdenum or alloy thereof. A high-density sealant 3 hermetically closes the envelope 1 at its opened end 5. Filler 2 of non-conductive, unburned material packed in the space around the metallic filament 4 in the envelope 1. The filler contains therein an additive 7 that may be subjected to the oxidation at the temperature lower than that of the metallic filament 4. The additive 7 is composed of at least any one of a free oxygen absorber selected from the group of carbon, titanium, boron, aluminum and nitride thereof, or the mixture thereof. <IMAGE></p> |
