| 摘要 |
The present invention relates to a spark plug having good combustible-gas ignitability even when the spark plug is downsized and to a method for high-yield manufacturing of a spark plug with good combustible-gas ignitability. There is provided according to one aspect of the present invention a spark plug 1 having a center electrode 2, an insulator 3 and a metal shell 4 and satisfying the following conditions (1) to (5). There is provided according to another aspect of the present invention a manufacturing method of a spark plug including the step of producing an insulator by preparing a raw material powder in such a manner that the particle size distribution ratio (90% volume diameter/10% volume diameter) between particles of 10% volume diameter and particles of 90% volume diameter in the raw material powder is 3.6 to 5.2, and then, press-forming and sintering the prepared raw material powder.
Condition (1): The insulator has a wall thickness T of 0.3 to 1.1 mm at an imaginary plane including a front end face of the metal shell.
Condition (2): A region of the insulator extending from a front end of the insulator to at least 2 mm rear from the imaginary plane is formed of an alumina-based sintered body containing a Si component, a rare earth element component and at least two kinds of Group 2 element components and being substantially free from a B component.
Condition (3): The mass ratio R RE of a mass of the rare earth element component to a total mass of the Si component, the Group 2 element components and the rare earth element component in the alumina-based sintered body is 0.15 to 0.45.
Condition (4): The mass ratio R 2 of a total mass of the components of the Group 2 elements to a mass of the Si component in the alumina-based sintered body is 0.25 or greater.
Condition (5): The alumina-based sintered body includes, in a grain boundary phase thereof, an aluminate crystal containing the rare earth element component. |
