GB1178051A - Noiseless Discharge Tube - Google Patents

Abstract

1,178,051. Cathode materials and processing. MATSUSHITA ELECTRONICS CORP. 12 April, 1967 [20 April, 1966], No. 16717/57. Heading H1D. A discharge tube, more especially a lowpressure Hg fluorescent lamp, has cathodes coated with emissive material comprising the oxides of Ba, Sr and Ca together with, in a proportion of from 0À5-10% by weight of the oxides, a substance having the composition: { ( 1-x-y)Fe : xCo : 0À5yMe} 2 B Z where 0À15 # x #0À6; 0À01 # y # 0À3; 1#z# 1À15 and wherein Me is one or more of the metals selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al and Si, and the mixture of oxides and the borides further containing, in a proportion of from 1-8% by weight of the oxides, one or more high melting point reducing metals selected from group comprising Zr, Hf, Nb and Ta. Initially, with the oxides present as carbonates, the emissive mixture may be suspended in a butyl acetate solution of nitrocellulose and applied to double or triple W coil supports, and the resulting coated coils may subsequently be heated during the degassing of the tube to convert the carbonates to oxides. The substitution of the metals Me in the iron boride helps prevent the oxidation of the borides during the heating and degassing process. Fluorescent lamps incorporating such cathodes reduce interfering noise to 15dB or less and the blackening of the lamp envelope is held at an acceptable level. A number of specific examples of the composition of the emissive material are given.