Patent ID: 6566792
Filing Date: 2003-05-20
Classification: H01T

Abstract:
A spark plug comprising: a center electrode; a metal shell; an insulator comprising alumina ceramic and disposed between the center electrode and the metal shell, wherein at least part of the surface of the insulator is covered with a glaze layer comprising oxides,wherein the glaze layer comprises: 1 mol % or less of a Pb component in terms of PbO; 15 to 60 mol % of a Si component in terms of SiO2; 22 to 50 mol % of a B component in terms of B2O3; 10 to 30 mol % of a Zn component in terms of ZnO; 0.5 to 35 mol % in total of at least one of Ba and Sr components in terms of BaO and SrO, respectively; 1 mol % or less of an F component; 0.1 to 5 mol % of an Al component in terms of Al2O3; and 5 to 10 mol % in total of at least one of alkaline metal component of Na, K and Li, in terms of Na2O, K2O, and Li2O, respectively, wherein Li is essential, and the amount of the Li component is 1.1 to 6 mol % in terms of Li2O, provided that Li/(Na+K+Li) is 0.2 to 0.5 in terms of oxides thereof.