| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug capable of keeping a high level of airtight performance even when attached on an internal combustion engine with a high compression ratio of fuel-air mixture set.SOLUTION: A spark plug 1 comprises: an insulator 2; a center electrode 3; and a seal material 12 for fixing the center electrode 3 in a shaft hole 5 of the insulator 2. The insulator 2 and the seal material 12 satisfy the conditions (1)-(3): (1) the percentage content of Si component [SiO(seal material)] in a glass phase is 50-70 mass%; (2) the ratio [[SiO(seal material)]/[SiO(insulator)]] between Si component percentage contents is 15-66.7; and (3) the ratio [[SiO(seal material)]/[BO]] of Si component percentage content to B component's one in the glass phase is 1.45-2.50. The insulator 2 has, in a surface thereof, at least eight sets of asperities per 100 μm which are adjacent to one another with a difference of 0.5-2.0 μm in elevation. The spark plug 1 further comprises an intermediate phase having a thickness of 20-50 μm at an interface between the insulator 2 and the seal material 12. |
