| 摘要 |
<p>An object of the present invention is to provide a spark plug capable of preventing a separation of a noble metal tip and extending a service-life of the spark plug. A spark plug 1 is provided with an insulator 2, a metal shell 3, a center electrode 5 and a ground electrode 27. The ground electrode 27 includes a ground electrode main body 38 and a convex portion 34 which projects from a front end side face of the ground electrode main body 38. A noble metal tip 32 is joined to a front end face (contact face 36) of the convex portion 34. A projection length L from the ground electrode main body 38 to a front end face 37 of the noble metal tip 32 falls within the range from 0.4 mm or more to 1.6 mm or less. The noble metal tip 32 is made of a Pt alloy containing Pt as a principal component. The Pt alloy is formed so that a mean particle size thereof is 70 micrometers after being heated at 1100 degrees C under an air atmosphere for 50 hours. The Pt alloy contains at least one kind of component selected from Rh, Ir, Ni and Ru.</p> |
