Patent ID: 7969077

Claim:
A spark plug comprising: an insulator having a central bore; a feed-through wire disposed in said central bore; a non-conductive glass seal between the insulator and the feed-through, wherein said glass seal has a vesicular structure and is a fused or sintered glass matrix of substantially lead free first and second glass materials; said first glass material including, in % by weight relative to the total weight of the first glass material, 19% to 24.5% SiO 2 , 35% to 41% B 2 O 3 , and 19% to 24% Al 2 O 3 ; said second glass material including, in % by weight relative to the total weight of the second glass material, 40% to 55% Bi 2 O 3 , 0.5% to 10% SiO 2 , 20% to 35% B 2 O 3 , and 23% to 33% ZnO; said first glass material having a first glass transition temperature and said second glass material having a second glass transition temperature, wherein the first glass transition temperature is 10 to 50 degrees Celsius apart from the second glass transition temperature.