| abstract |
A spark plug includes an insulator formed of a ceramic material. The ceramic material comprises A1 2 O 3 in an amount of 98.00 wt% to 99.50 wt%; Group 2 oxides in an amount of 0. 1 6 wt% to 0.70 wt%; SiO 2 in an amount of 0.25 wt% to 0.75 wt%. Group 4 oxides i n an amount of 0.01 wt% to 0. 16 wt%. Group 1 oxides in an amount less than 0.0060 wt%, and P 2 O 5 in an amount of less than 0.0040 wt%. The AL 2 O 3 is formed of particles having a D50 median particle size by volume of 1.2 μιη to 1.8 μη. The ceramic material is pressed, sintered, and formed to a predetermined shape. The sintered ceramic material includes a glass phase comprising the AI 2 O 3 , Group 2 oxides, and SiO2. The sintered ceramic material also includes secondary crystals of calcium hexa-aluminate (CaAl 12 O 19 ) spinel (MgAl 2 O 4 ), anorthite (CaAl 2 Si 2 O 8 ), and mullite (Al 6 Si 2 O 13 ). |