| 摘要 |
A spark plug exhibits a satisfactory withstand voltage characteristic and sufficient mechanical strength in a high temperature environment exceeding 700° C. The spark plug has a center electrode, an insulator, and a ground electrode, characterized in that the insulator is formed of an alumina-based sintered material containing an Si component, a Group 2 element (2A) component, and a rare earth element (RE) component; that the alumina-based sintered material has an RE-&bgr;-alumina crystal phase; and that the mean crystal grain size DA(RE) of the RE-&bgr;-alumina crystal phase and that of alumina DA(Al) satisfy the following relationship (1): 0.2≦̸DA(RE)/DA(Al)≦̸3.0. |
