GB818052A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

818,052. Cathode ray tubes; cathode materials and processing. GENERAL ELECTRIC CO. Ltd. May 29, 1957 [March 23, 1956], No. 9173/56. Class 39(1). In a cathode ray tube the thermionic cathode comprises a metal shell 7 containing electron emissive material arranged to be heated by an element 10 and the shell is provided in a part adjacent to the modulator 5 with an aperture 8 for the emission of electrodes, the aperture being arranged in alignment with and being of smaller diameter than, the aperture 13 in the modulator. The modulator may be in the form of a plate or dish, the apertures 8, 13 may be both circular and the diameter of the aperture 13 is two to four times that of the aperture 8. Preferably the modulator aperture is about 1 mm. and the cathode aperture about 0À3 mm. As shown the first anode 6 is in the form of a hollow cylinder with the end nearer the cathode 4 tapering so that the aperture 14 at its end is approximately the same diameter as the aperture 13. As shown the cathode shell consists of a metal cylinder 7 preferably of nickel with an apertured closed end directed towards the modulator but in two other embodiments the cathode shell consists of a narrow metal tube the opening at one end of which provides the cathode aperture. In a multi-gun form, the cathode shell is provided with two or more apertures each aligned with, but smaller in diameter than, a corresponding aperture in the modulator. The electrons are emitted from a porous mass 9 consisting preferably of a sintered mixture of refractory metal powder such as nickel or tungsten and of powdered emissive material such as a mixture of 70 per cent. of weight of nickel powder and 30 per cent. by weight of a triple oxide of barium, strontium and calcium together with e.g. 0À01 per cent. by weight of silicon, titanium or zirconium. Alternatively no reducing agent is present in the mixture but at least the closed end of the cathode shell is formed of titanium. Alternatively an activiting layer consisting of a sintered mixture of powdered nickel and a powdered alloy of nickel and titanium may be provided on a porous mass comprising the alkaline earth oxides and nickel. In forms having the aperture at the end of the tube comprising the cathode shell, the porous mass extends substantially the whole length of the tube. The porous mass may be formed by pressing 70 per cent. of carbonyl nickel powder with 30 per cent. powdered barium strontium and calcium carbonates and 35 per cent. of a 70-30 nickelsilicon alloy at 80 tons/sq. in. and sintering in situ in the tube at about 1050‹C. using the cathode heating element. Suitable working electrode potentials are given in the Specification. Specification 818,051 is referred to.