Influence of External Treatments on Electret Behavior

Abstract

The following effects of external treatments upon electrets have been observed. (1) When the surface of an electret which exhibited a homocharge was planed in a lathe, the sign of the equivalent surface charge changed to that of the heterocharge. This heterocharge then decayed and the homocharge finally became dominant again. The magnitude of the final homocharge was smaller than that of a control electret which was not planed. (2) Repeated planing of an electret, with time allowed for recovery between successive planings, resulted in repetition of the cycle described in (1). (3) Wax dummies (not subjected to an electric field during manufacture) which were given a frictional charge and then planed, showed no reversal of sign; they did exhibit a small recovery after being planed. (4) Electrets subjected to 100% relative humidity exhibited an abrupt decrease in equivalent surface charge. Removal of the moisture resulted in a gradual, slight recovery. (5) The curve relating the equivalent surface charge and the logarithm of the pressure of the air surrounding an electret, has the same form as the curve of the sparking potential for air versus the logarithm of the pressure. Thus, all the treatments described resulted in a decay of the homocharge, followed by a partial recovery upon removal of the disturbing influence. The observed behavior can be explained in terms of the electret mechanism proposed by Gross.