Sheated heater, glow plug

摘要

[Objective] To improve durability of a sheath heater. [Means for Solution] A sheath heater includes a sheath tube, a heating unit, and a magnesium oxide. The sheath tube is a tubular member whose one end is closed. The heating unit generates heat by transmission of electricity and is arranged inside the sheath tube. The magnesium oxide is arranged between the sheath tube and the heating unit and filled directly in contact with the sheath tube. The sheath tube is not thermally contracted when a temperature is increased from 20°C to 1200°C. In the sheath tube, an average thermal expansion rate is equal to or more than 13 × 10 -6 /K and equal to or less than 18 × 10 -6 /K when the temperature is increased from 20°C to 1200°C.