| 摘要 |
PROBLEM TO BE SOLVED: To aim at suppressing deterioration of grain boundary intensity and improving durability, in relation to a spark plug provided with a noble metal chip mainly composed of Pt and containing Rh. SOLUTION: The noble metal chip 31 is arranged at a tip of a center electrode 5 of the spark plug 1, a cylindrical noble metal chip 32 is arranged at a tip of a ground electrode 27, and the gap between both the noble metal chips 31 and 32 is used as a spark discharge gap 33. The noble metal chip 32 is mainly composed of Pt, and contains 3 mass% of Rh or more. And also, a protrusion length from a main body of the ground electrode 27 to a tip of the noble metal chip 32 is 0.3 mm or more, with a cross-section area of 0.79 mm<SP>2</SP>or less. Then, at least either W or Mo is contained, with its total content of 0.1 mass% or more and 3 mass% or less. COPYRIGHT: (C)2008,JPO&INPIT
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