Spark plug

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PROBLEM TO BE SOLVED : To provide a spark plug with an insulator having an excellent voltage-endurance performance under a high-temperature condition. SOLUTION : A spark plug comprises an insulator composed of an alumina-based sintered compact. Supposing that the total amount of Al components, rare earth element components, and components included at 5 mass% or more to a total mass of the alumina-based sintered compact in terms of oxide is 100 mol% (in terms of oxide), the content of the Al components in the alumina-based sintered compact is 90.0-99.99 mol% in terms of oxide, and the content of the rare earth element components is 0.01-10 mol% in total. Supposing that the total mass of the alumina-based sintered compact is 100 mass%, the content of Na components is 0.001-0.020 mass% in terms of oxide, the total content of Group II element components is 0.1 mass% or less, and the total content of Si and B components is 0.1 mass% or less. SELECTED DRAWING : Figure 1 COPYRIGHT : (C)2018, JPO&INPIT