Patent ID: 6274971
Filing Date: 2001-08-14
Classification: C03C,H01T

Abstract:
A spark plug comprising:a center electrode;a metallic shell disposed so as to surround the center electrode;a ground electrode, one end of the ground electrode being connected to the metallic shell, while the other end of the ground electrode facing the center electrode;an insulator disposed between the center electrode and the metallic shell such that the insulator covers the outer surface of the center electrode; anda glaze layer mainly formed of oxides and adapted to cover at least a portion of the surface of the insulator, whereinglaze which forms the glaze layer predominantly comprises Si, B, Zn, and Ba, and two co-added alkali metal components selected from among Na, K, and Li, wherein the amount of Si is 18 to 35% by weight as reduced to SiO.sub.2, the amount of B is 25 to 40% by weight as reduced to B.sub.2 O.sub.3, the amount of Zn is 10 to 25% by weight as reduced to ZnO, the amount of Ba is 7 to 20% by weight as reduced to BaO, and the amount of each of the two co-added alkali metal components is 3 to 9% by weight as reduced to Na.sub.2 O, K.sub.2 O, or Li.sub.2 O.