Improvements in or relating to non-linear resistors
659,915. Lightning arresters. SOC. LE CARBONE-LORRAINE, and TESZNER S. March 11, 1949, No. 6701. Convention date, March 18, 1948. Drawings to Specification. [Class 38 (iv)] [Also in Group XXXVI] A resistor sensitive to voltage according to the equation R=A/V<SP>k</SP> especially suitable for use in lightning arresters, voltage surge limiters, and spark gaps, comprises an intimate coherent mixture of granules of a semi-conducting substance with an insulating binder in which are distributed granules of at least one other substance, having a secondary electron-emissive power higher than 2 and forming centres of secondary electron emission excited by primary electrons which are emitted by the semiconducting granules under the effect of an applied voltage. In the examples of manufacture fully described in the Specification silicon carbide granules form the semi-conducting constituent and beryllium oxide or copper or nickel and beryllium alloy particles form the secondary electron emission centres in a disc or rod-shaped ceramic body whose opposite faces are metallized to form electrodes. The theory of operation is discussed at considerable length with the aid of volt-ampere curves, Figs. 1 and 2 (not shown), and exaggerated representation, Figs. 3 and 4 (not shown), of the constitution of the resistor and the behaviour of the primary and secondary electrons under surge conditions. The invention is directed towards increase of the exponent k in the expression above with or without transitory hysteresis effects. As described a resistor which employs beryllium oxide crystals as the secondary electron emitters does not give a hysteresis effect, i.e. the primary and secondary electrons disappear simultaneously. Conversely a resistor which employs activated copper or nickel and beryllium alloy particles as the secondary electron emitters does give a hysteresis effect, i.e. the duration of the secondary electron emission is greater than that of the primary electron emission. It is stated that the semi-conductive granules may be sulphides, carbides, silicides, phosphides or arsenides with secondary electron emitters selected from oxides of alkaline earth or rare metals, e.g. (in addition to Be) Ba, Sr, Mg, La, Ce and Pr.