| 摘要 |
PROBLEM TO BE SOLVED: To suppress troubles when a grounding electrode is formed of a noble metal alloy and to achieve a longer lifetime of a spark plug for an internal combustion engine. SOLUTION: An electrode matrix 43 of the grounding electrode 4 is formed of a Pt alloy. Further, a covering layer 44 of an Ni alloy is formed on the surface of the electrode matrix composed of the Pt alloy. At this time, the electrode matrix 43 is covered by the covering layer 44 including the jointing face 41 of the grounding electrode 4 jointed with the tip face 11 of the main fitting 1. COPYRIGHT: (C)2008,JPO&INPIT
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