| 摘要 |
To provide a spark plug excellent in the acid resistance and high-temperature withstand voltage characteristics. A spark plug 100 including an insulator 2 being formed in an approximately cylindrical shape and having a through hole 6 penetrating in the axis direction, and a center electrode 3 inserted into the through hole 6, wherein the insulator 2 is formed by an alumina-based sintered body containing an Si component, a Ba component, a Ca component and an Mg component to satisfy the following conditions (1) and (2) and containing substantially no B component: Condition (1): the ratio RCa of the mass in terms of oxide of the Ca component to the mass in terms of oxide of the Si component is from 0.05 to 0.40; Condition (2): the ratio RMg of the mass in terms of oxide of the Mg component to the total mass of the mass in terms of oxide of the Si component, the mass in terms of oxide of the Ca component and the mass in terms of oxide of the Mg component is from 0.01 to 0.08. |
