Solid insulator and method of manufacturing the same

A columnar solid insulator body comprising one of (i) cristobalite porcelain containing 10 wt % or less cristobalite crystals and (ii) non-cristobalite porcelain, said body being produced by a method comprising the steps of:

• sintering a green solid insulator body at a temperature higher than 1000.degree. C.;
• cooling the sintered solid insulator body within a first cooling temperature region from the sintering temperature to 600.degree. C., a second cooling temperature region from 600.degree. C. to 500.degree. C., and a third cooling temperature region from 500.degree. C. to room temperature, wherein an average cooling speed Za .degree. C./hr within the first cooling temperature region is determined in relation to the diameter X, in mm, of the solid insulator body, and is equal to {-1.0 X+400.ltoreq.Za.ltoreq.-2.4 X+900}, an average cooling speed Zb .degree. C./hr within the second cooling temperature region is equal to {-0.25 X+80.ltoreq.Zb.ltoreq.-0.45 X+160}, and an average cooling speed Zc .degree. C./hr within the third cooling temperature region is greater than or equal to Zb;
• wherein strain within a diametrically outer portion of the insulator body is greater than strain within a diametrically inner portion of the insulator body, such that the insulator body as a whole is in compression, and a difference, Y, between strain in the diametrically outer portion and strain in a diametrically central portion is Y.ltoreq.(1.76.times.10.sup.-6) X, wherein X is the diameter of the columnar solid insulator and ranges from 20 mm to about 250 mm.