GB1394068A - Emissive fused electrode - Google Patents

Abstract

1394068 Cathode materials ITT INDUSTRIES Inc 11 May 1972 [17 May 1971 4 June 1971 7 June 1971 3 Dec 1971 (2)] 22133/72 Heading H1D A cold cathode comprises a fused mixture of a metal and an electron emissive material having a bulk density gradient. The mixture may be in a metal cup or form an ellipsoidal or conical pellet with a nail headed conductor extending from it; there is a void in the pellet above the electrode end. The mixture comprises 50-80% by weight of Ta powder and BaO 2 powder; C, Sr and Zr compounds may be added to retard emission. Other mixtures include W, Mo, Th, Ti, Zr, Ni and Fe powders with BaO, Ba nitrate, CaO, SrO, ZrO and Li, Ce, Na, K compounds. The cup is of Fe, Ni plated Fe, Ta, W or Mo. The powder is compressed at 1000- 4000 PSI in a cup which is then covered with an apertured lid and heated to 700-1000‹ C. This starts an exothermic reaction which continues until it self extinguishes. The resulting mixture has a concave, jagged top surface within the cup comprising 25-50 Á particles and 80% voids and a denser interior of particles less than 1 Á with only 10% voids. Pellet electrodes are formed by compressing the powder in a mould with a Ni, W, Ta, Fe or Ni lead extending into the mixture and heating. When the heating vessel is larger than the pellet and sealed, an ellipsoidal pellet is formed. When the pellet is heated in the mould covered by a vented lid with a concave inner face a cylindrical pellet with a conical end is produced in which only the end has a density gradient, the sides are smooth thereby reducing sputtering. The electrodes are used in fluorescent lamps.