| 摘要 |
The objective of the present invention is to provide a spark plug which is provided with an insulating body that has excellent corrosion resistance and exhibits excellent withstand voltage characteristics and mechanical strength at high temperatures, thereby being suppressed in decrease in the withstand voltage characteristics and mechanical strength in cases where the temperature is further increased from a high temperature. A spark plug of the present invention is provided with an insulating body that is composed of an alumina-based sintered body which contains an Si component and a rare earth element component at content ratios satisfying the conditions (1) and (2) described below and which has alumina particles and an alumina grain boundary phase having a composite oxide crystal phase satisfying the condition (3) described below. (1) 0.05 ≤ content ratio (mass%) of Si component in terms of oxide ≤ 0.45 (2) 2.5 ≤ [(content ratio of rare earth element component in terms of oxide)/(content ratio of Si component in terms of oxide)] ≤ 4.5 (3) a composite oxide crystal phase containing at least two components that are selected from among an Al component, an Si component, group 2 element components and rare earth element components |
