GB1115236A - Improvements relating to methods of manufacturing oxide-coated cathodes - Google Patents

Abstract

1,115,236. Cathode materials and processing. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 2 June, 1966 [5 June, 1965], No. 24574/66. Heading H1D. In the manufacture of an oxide coated cathode a coating of barium and strontium carbonates applied to the cathode support is first heated to convert it into oxides, then heated again in an atmosphere of carbon monoxide and carbon dioxide to reconvert the oxides into carbonates. The cathode is then built into an electron tube and the carbonates converted again into oxides by firing the cathode during evacuation of the tube. The process allows greater control over the thickness of the oxide layer since on final conversion to oxide the layer shrinks only 1 to 2%. The barium-strontium carbonate coating may be formed on a nickel cathode support by painting, spraying or by cataphoresis. The first conversion to oxide takes place in an evacuated vessel at between 1000‹ and 1100‹ C., the vessel is then filled with a mixture of carbon monoxide and carbon dioxide, formed, for example, by equal parts by weight of these gases, and the cathode heated at between 800‹ and 850‹ C. to reconvert to carbonates. The cathode support is cooled whilst still in the gas mixture. The final oxide coating may be between 50 and 100 microns thick and the interelectrode spacing may be less than 100 microns. Before mounting in the tube the cathode may be coated with a protective layer of nitrocellulose.