Patent GB-440100-A (GB)
Title: Improvements relating to electrical discharge tubes
IPC: H01T1/24
Filed: 1934-04-20
Abstract: 440,100. Discharge apparatus. DUFFENDACK, O. S., 2107, Devonshire Street, and WOLFE, R. A., 66, Harpst Street, both in Ann Arbor, Michigan, U.S.A. April 20, 1934, Nos. 11980 and 11981. Convention dates, May 1, 1933 and March 23, 1934. Drawings to Specification. [Class 39 (i)] A tube containing one or more inert gases has a discharge gap between the closely spaced surfaces of large area of two electrodes, the spacing between which is not greater than 1À75 mm., and the active portion of at least one electrode is composed of a homogeneous alloy of work function not exceeding 2À4 volts. The term " inert gases includes any gas which is not dissociated into non-volatile components or which does not react, and of which none of its dissociated components react, with any material inside the tube during operation. The electrodes may be parallel discs, which may have hollowed faces, or faces with rounded edges, or discs with hollowed out backs and central recesses, or portions of spheres, or cylinders with open or closed ends fitting one inside the other, or one electrode may be a sphere and the other a disc with a concave spherical surface. The electrode spacing is preferably greater than 0À1 mm., and in tubes described in the Specification is 0À2 mm., 0À5mm., and 1 mm. The electrodes may be made of a homogeneous alloy of nickel and barium with a 0À7 per cent barium content, or of alloys of nickel, copper and barium with or without chromium, or of aluminium or copper and barium, as described in Specification 441,464 (as open to inspection under Sect. 91). The electrodes may be out-gassed by operating the tube at a high voltage and low current with a neon filling, or by high frequency heating, or by preliminary treatment in a separate chamber. The gas filling may comprise neon, argon, helium, krypton, xenon or mixtures with or without mercury, caesium, potassium and lithium, for example neon with 0À01 to 1À0 per cent of argon or mercury. Mercury acts as a getter, particularly for hydrogen and nitrogen. The filling may also be neon at 65 cm. with argon at 0À01 mm. and mercury vapour at saturation. Caesium, potassium and lithium also act as getters and may alloy with the electrodes. The neon filling is purified by passing it through cocoanut charcoal cooled by liquid air temperature, and flashing getters of magnesium, barium, lithium or combinations of these. The pressure of the filling may be from 0À5 cm. to above atmospheric, preferably 70 to 75 cm. One or both of the electrodes may be heated to increase electrode emission. The tube may be operated at the temperature of liquid air viz. - 196‹ C. After a period of use coatings on the envelope produced from the electrodes, for example coatings of copper oxide, nickel oxide and barium, nickel and copper metal from electrodes containing nickel, copper and barium, have a photo-electric emission. Chromium may also be emitted from the electrode. Light-sensitive coatings may be applied to the tube or to the electrodes or to a third member. If the tube is supplied with a voltage slightly less than the breakdown voltage, photo-electric emission from the coating serves to " trigger-off " the discharge which may be of several amperes. The tube is primarily intended for use in the sparking- plug ignition circuit described in Specification 427,679, [Group XXVII], but may also be used as a lightning arrester or protector for transmission lines.