| 摘要 |
<p>A glaze layer (2d) formed on the surface an alumina-based insulator (2) of a resistor spark plug (100) contains SiO2 (18-35% by weight), B2O3 (25-40% by weight), ZnO (10-25% by weight), BaO (7-20% by weight), Na2O (3-9% by weight), and K2O (3-9% by weight). Since the difference between the coefficient of linear expansion of the glaze and that of the alumina-based insulating material is relatively small, the glaze layer (2d) is less susceptible to cracks and the like. Also, since the glaze has a softening point lower than that of conventional lead-silicate-glass-based glaze, the glost-firing temperature can be as low as 800-950 DEG C. Therefore, even in the case where glost firing is performed concurrently with a glass sealing step, a center electrode (3) and a terminal metal piece (13) are less susceptible to oxidation. Further, even though the content of the alkali metal component is high, a good insulating performance is obtained, so that excellent flashover resistance is attained. <IMAGE></p> |
