| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug having an insulator which has alumina as a main component and more excellent dielectric breakdown characteristic at high-temperature. SOLUTION: The insulator 2 of the spark plug 100 is made of an insulating material, the main component of which is alumina, and which contains an Al component in the range of 95-99.7 wt.% in terms of Al2 O3 . Further, in the sectional structured of the insulating material, a ratio of the area occupied by alumina main-phase particles having particle diameters more than 20 μm is more than 50%. Consequently, the dielectric breakdown characteristic of the insulator can be remarkably improved, by moderately enlarging the alumina main-phase particles in this way. |
