GB397107A - Improvements in and relating to electric discharge devices - Google Patents

Abstract

397,107. Discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Foulke, T. E. ; 30, Evelyn Place, Nutley, New Jersey, U.S.A.) Jan. 6, 1932, No. 423. Convention date, Jan. 6, 1931. [Class 39 (i).] A cathode-glow device has at least one electrode consisting of a foundation (e.g. of nickel) having a portion of its surface to which the glow is to be confined coated with an activating substance having a work function lower than that of aluminium, whilst the remainder is coated with a material having a higher work function than that of the activating substance ; the material is such that activating substance deposited thereon is "poisoned," i.e. does not endow the material with its own lower work function. The activating substance may be barium mixed with barium oxide, whilst the other coating may be of aluminium, aluminium oxide, antimony, selenium or copper oxide. The electrode may be kept cool by mixing a material of high thermal emissivity, e.g. carbon, with the aluminium or equivalent coating. In one construction, as shown in the Figure, two plane semicircular electrodes 4 are mounted 1 mm. apart in the same plane. One face of the electrodes is coated with alkali or alkaline earth metals or compounds, preferably by the method set forth in Specification 362,347, whilst the other face is covered with finely powdered aluminium, aluminium oxide, copper oxide, antimony, selenium, or osmium. The substance is affixed bv a binder such as nitrocellulose dissolved in amyl acetate, which is reduced to carbon on heating. The edges of the electrodes 4 are turned downwards in a 90‹ arc having a radius of a few millimetres. It is stated that this reduces blackening of the bulb by sputtering. The filling may be neon or helium with a small percentage of argon at a pressure of 15-60 mm. In a modification, part of the surface of the electrodes, representing a letter or sign, may be covered with the activating substance and the remainder with the material of high work function, or vice versa. The electrodes may be semi-cylindrical or quadrants of a sphere. Reference has been directed by the Comptroller to Specifications 173,737 and 220,040, [both in Class 39 (i), Electric lamps, Arc &c.].