| 摘要 |
A spark plug includes an insulator made of an alumina sintered body containing Al 2 O 3 as a principal component and additional components including; an Si component, a Ba component, an Mg component, a Ca component, an Sr component, and a rare earth element component. When the additional components are expressed as oxides including R SiO2 , R BaO , R MgO , R CaO , R SrO , and R RE2O3 , contents (mass %) of the sub-component satisfy expressions (1) to (6) as follows: (1) 1.0 ‰¤ R SiO2 ‰¤ 5.0; (2) 0.5 ‰¤ R BaO ‰¤ 5.0; (3) 0 ‰¤ R MgO ‰¤ 0.18; (4) 0 ‰¤ R MgO /R BaO ‰¤ 0.36; (5) 0.3 ‰¤ (R MgO +R CaO +R SrO ) ‰¤ 1.8; and (6) 0 ‰¤ R RE2O3 ‰¤ 0.1. |
