| 摘要 |
PURPOSE:To obtain a discharge tube in which the luminance point only little shifts by making the cathode by fixing a pointed cathode section, which is prepared by impregnating a porous high-melting-point metallic base having a pointed head with a substance easily discharging electrons, to one end of a metallic bar forming a conductive path. CONSTITUTION:A pointed section 21 consisting of a porous tungsten cathode impregnated with an aluminate of an alkaline earth element which easily discharges electrons, is attached to the end of a tungsten bar 20 forming a conductive path. The porous high-melting-point metallic base is formed, for example, by subjecting a tungsten powder with a mean diameter of 2-8mu to pressure molding and then sintering the thus molded body in vacuum or in an atmosphere of hydrogen. The porosity of the metallic base is adjusted to be within the range of 10-35%. The pointed cathode section 21 and the metallic bar 20 are fixed together by high-melting-point brazing, pressure fit or similar method. |
