Spark plug and process for fabricating the spark plug

摘要

The invention provides a spark plug having an insulator which is composed mainly of alumina, and which is more superior in voltage endurance characteristics at high temperatures as compared with the prior-art materials. An insulator 2 of a spark plug 100 is made of an insulating material which is composed mainly of alumina, and which contains Al component within a range of 95 to 99.7 wt% in weight converted to Al2O3, and in which an area ratio occupied by alumina base principal-phase particles with particle size not less than 20 mu m is not less than 50% as a cross-sectional structure of the insulator is observed. By making the alumina base principal-phase particles appropriately coarse like this, the voltage endurance characteristics of the insulator can be remarkably improved. <IMAGE>