| 摘要 |
PURPOSE: Provided is a spark plug in which a noble metal spark portion is protrusively formed on a ground electrode and which is configured such that, even when used in an environment where a spark is apt to drift under a gas flow, the ground electrode is unlikely to suffer uneven ablation. CONSTITUTION: A spark plug is provided with a ground-electrode spark portion(32). The ground-electrode spark portion is formed from a noble metal which contains Pt as a main component, and is joined to a main metal portion of the ground electrode(4) via an alloy layer which has a thickness ranging from 0.5 to 100 micro meter. The ground-electrode spark portion(32) is configured such that a distal end surface(32t) facing a spark discharge gap(g) is smaller in diameter than a bottom surface(32u) joined to the ground electrode(4), and the distal end surface(32t) is protrusively located beyond the side surface(4s) of the ground electrode(4). When the ground-electrode spark portion is viewed in plane from the distal end surface(32t), a portion of the surface of the ground-electrode spark portion is viewed as a peripheral exposed-region surface(32p) which is exposed on the side surface(4s) of the ground electrode so as to surround the distal end surface(32t).
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