| 摘要 |
Disclosed is a spark plug comprising an insulator that is less likely to cause dielectric breakdown and exhibits higher withstanding voltage properties. A spark plug (1) comprises a center electrode (2), an insulator (3), and a ground electrode (6). The spark plug (1) is characterized in that the insulator (3) is formed of an alumina-base sintered compact having a theoretical density ratio of not less than 95.0% that comprises a rare earth element component, a Si component, and at least two group 2 element components, the rare earth element component being dispersed so as to satisfy the following requirement. The total number of measurement lines in which not less than 8 peaks derived from the rare earth element (RE) are observed is not less than 4 lines out of 7 lines when, in the alumina-base sintered compact, 7 measurement lines (measurement length: 180 μm) are selected followed by analysis of rare earth element (RE) present within each selected measurement line by an energy dispersion method.
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