GB983159A - Cathode for gas discharge tubes - Google Patents

Abstract

983,159. Cathode materials and processing. CERBERUS A.G. Jan. 8, 1962 [Jan. 17, 1961], No. 689/62. Heading H1D. A sintered cathode comprises one or more metals melting above 1100‹ C. uniformly distributed in a metal oxide component which includes at least two metals in the oxidized state, of which one A has a work function of less than 3.5 eV and the other B a work function of more than 3.5 eV, the ratio of oxide B to the metal component being between 0.5 and 1.5 mols of oxide to each gramme-atom of metal. Examples of A are Cs, Rb, K, Na, Li, Ba, Sr, Ca, Ce, La, U and Th; and of B are Al, Mg, Si, Ti, Zr, Mo, Ta and W. The metal component may comprise Zr, Mo, Ta, Ti, W, Ni, Fe and Pt. The metal oxide component may be an oxide mixture, or a mixed oxide e.g. metal molybdates, -titanates, -aluminates, -nickelates, -beryllates, -tungstates, -tantalates, -zirconates, and -niobates. The molecular ratio of A oxides to B oxides may be between 0À5 and 2 and preferably between 1.0 and 1À3, while the molecular ratio of B oxides to the metal component is preferably 1.0 to 1.2 mol. of oxide component per gramme-atom of metal component. The metal oxide and metal components are mixed in powder form, applied to a metallic terminal support, e.g. a cup or filament, and sintered, the mean grain size of both powders being between 1 and 50Á, and preferably below 20Á. Specific examples are given. The cathode 10 may be used in a switching tube 5 filled with xenon at a pressure greater than 10 mm. of Hg. A glow discharge set up between the cathode and auxiliary electrode 8 heats the cathode and changes into an arc discharge, the voltage between cathode and electrode 8 falling to 20 v. A positive impulse of 30 v. at the control electrode 7 initiates the main discharge with currents of 150 amps. per cm.<SP>2</SP> of cathode surface. The cathode may also be employed in lamps and other gas discharge tubes for continuous operation.