Abstract: A zirconia based ceramic material having improved and well-balanced mechanical strength and toughness consists essentially of 0.5 to 50 vol % of Al.sub.2 O.sub.3 having an average grain size of 2 .mu.m or less and the balance of a partially stabilized zirconia having an average grain size of 5 .mu.m or less. The partially stabilized zirconia consists essentially of 8 to 12 mol % of CeO.sub.2, 0.05 to 4 mol % of TiO.sub.2 and the balance of ZrO.sub.2. Fine Al.sub.2 O.sub.3 grains having an average grain size of 1 .mu.m or less are dispersed within the grains of the partially stabilized zirconia at a dispersion ratio. The dispersion ratio is defined as a ratio of the number of Al.sub.2 O.sub.3 grains dispersed within the grains of the partially stabilized zirconia relative to the number of the entire Al.sub.2 O.sub.3 grains dispersed in the ceramic material, and at least 2% in the present invention. The ceramic material can be made by the following process.

Abstract: An electrostatic relay essentially comprises a fixed electrode with a fixed contact insulated therefrom, a movable electrode plate with a movable contact insulated therefrom, and a fixed pair of oppositely charged electrets. The movable electrode plate is pivotally supported at a pivot in a cantilever fashion or a seesaw fashion, and also to move about the pivot axis relative to the fixed electrode between two rest positions of closing and opening the contacts. A control voltage source is connected across the fixed electrode and the movable electrode plate to generate a potential difference therebetween. The electrets are disposed adjacent the movable electrode plate to generate electrostatic forces attracting and repelling the movable electrode plate, respectively, when the movable electrode plate is charged to a given polarity. That is, the attracting and repelling forces are cooperative to produce a torque for moving the movable electrode plate in one direction from one of the rest positions to the other.