| 简介 |
PROBLEM TO BE SOLVED : To provide a spark plug including an insulator having excellent corrosion resistance and a small degradation rate of withstand voltage characteristics and mechanical strength when temperature becomes higher than normally high temperatures, and displaying excellent withstand voltage characteristics and mechanical strength at high temperatures.
SOLUTION : This spark plug includes an insulator made of an alumina base sintered body containing an Si component and a rare earth element component at a percentage content satisfying the following conditions (1) and (2), and having alumina particles and an alumina grain boundary phase having a composite oxide crystal phase satisfying the following condition (3). (1) 0.05≤a percentage content (mass %) obtained by converting an Si component to an oxide≤0.45, (2) 2.5≤[(a percentage content obtained by converting a rare earth element component to an oxide)/(a percentage content obtained by converting an Si component to an oxide)]≤4.5, and (3) a composite oxide crystal phase containing at least two kinds of components selected from an Al component, an Si component, each component in group II elements, and each component in rare earth elements.
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