Abstract: A spark plug is provided for an internal combustion engine and includes a center electrode having a combustion chamber end and a ceramic insulator having an end portion over which an ablative coating is formed for removing contaminants deposited thereon. The ablative coating is capable of ablating completely during sustained operation of the spark plug.

Abstract: A method is disclosed for making an aging-resistant, partially stabilized zirconia ceramic, which method is not totally dependent upon grain size control, can function to eliminate substantially any monoclinic phase that results from machining such zirconia article, and employs a novel heat treatment to do so.The method particularly comprises: (a) sintering such article at a temperature and for a period of time to produce a densified product having little or no monoclinic crystal phase when cooled to room temperature (i.e. 2550.degree.-2650.degree. F. for 0.5-4 hours); (b) subjecting the cooled sintered article a machining operation that results in the formation of monoclinic crystal phase on the surface of the part; and (c) heating said treated article to the temperature range of 1800.degree.-1950.degree. F. (982.degree.-1066.degree. C.) to re-transform monoclinic crystal structure to tetragonal crystal.