| abstract |
The problem to be solved by the present invention is to provide a spark plug which achieves a high withstand voltage characteristic under a high temperature and is less likely to degrade the withstand voltage characteristic under a high temperature. The spark plug which concerns on this invention is a spark plug provided with a center electrode, an insulator, and a metal shell, The said insulator is equipped with the alumina group sintered compact containing a silicon component, a group 2 element component, and a rare earth element component, The said alumina group The sintered compact is composed of a glass phase and an alumina crystal phase as a result of analysis by X-ray diffraction. The grain boundary phase of the alumina-based sintered compact is observed with a transmission electron microscope, and the alkali metal component and the rare earth element in a circular spot having a diameter of 0.3 nm. The average value which computed the weight ratio [alkali metal / rare earth element] of the oxide conversion of a component in 30 spots is 0.01-1.0, It is characterized by the above-mentioned. |