Improvements in or relating to electron discharge devices employing secondary electron emission and electrodes for use therein

670,554. Electrode materials. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Oct. 26, 1946 [Nov. 7, 1945], No. 29631/45. Class 39 (i). A secondary electron emitting electrode comprises a conductive support and a relatively thick coating, i.e. greater than 10-4 inches thick, of an intimate mixture of oxides of magnesium and barium containing at least 15 per cent and preferably 34 per cent barium oxide. The permitted range of barium oxide is 20-50 per cent. The base may be of nickel, platinum or goldplated molybdenum. Nickel is cleaned at red heat to remove the harmful oxide coating and a thin coating of magnesium applied, e.g. by evaporation, to yield a coating less than 10-6 inches thick. 40 per cent of barium carbonate and 60 per cent magnesium oxide are mixed and sintered for 1 hour at 1200‹ C. in air. The mixture is ball-milled in acetone containing nitro-cellulose and deposited by cataphoresis on the nickel base. The electrode is assembled in a valve, e.g. as described in Specification 601,966, which is degassed and heated to between 700-900‹ C. Heating is by primary electron bombardment or by an auxiliary heater. Specifications 670,582, 670,583 and 670,593 also are referred to.