SPARK PLUG, ALUMINA INSULATOR FOR SPARK PLUG, AND METHOD OF MANUFACTURING THE SAME

摘要

An insulating material mainly containing alumina and having a Na content of a range from 0.07 to 0.5 weight % in terms of Na2O. Such a Na content is fairly high and has conventionally been thought absurd. The insulation resistance at high temperatures and the mechanical strength are unexpectedly not low. The material has a good performance compared to those of conventional insulating materials having Na contents lower than that of the material of the invention. As a result, in place of conventional low-soda alumina, intermediate-soda alumina or plain-soda alumina which are much more inexpensive. The manufacturing cost of an insulator (2) for spark plugs and further the manufacturing cost of a spark plug (100) made thereof can be drastically lowered.