GB1097424A - Improvements in thermionic cathodes - Google Patents

Abstract

1,097,424. Cathode materials and processing. GENERAL ELECTRIC CO. March 19, 1965 [April 16, 1964], No. 11815/65. Heading H1D. A dispenser cathode is produced by first forming pellets of an activator material, consisting of a solid solution of Ba 3 WO 6 and Ba 2 SrWO 6 , by firing a mixture of barium and strontium carbonates and tungsten trioxide; finely dividing the pellets and mixing with a finely divided refractory metal e.g. tungsten, and a source of zirconium or hafnium; pressing the mixture into a cohesive form and firing in a reducing atmosphere; and finally removing a surface layer to expose a low work function surface of a porous material formed of 88% to 94% of the refractory metal, 5% to 12% of a single-phase barium strontium tungstate solid solution of composition Ba 3 WO 6 .Ba 2 SrWO 6 , and less than 1% of zirconium or hafnium. The activator material is prepared by wet milling barium and strontium carbonates with tungsten trioxide, firing the dried and compressed powder in air at a temperature exceeding 1400‹ C., and powdering the resultant material. The latter is mixed with powdered tungsten to form the porous matrix of the cathode, and powdered zirconium hydride to form the reducing agent for the activator, and is thereafter ball-milled, pressed at pressures of between 40 and 90 tons per square inch, and sintered in pure hydrogen at 1350‹ to 1900‹ C. Finally, a suitably shaped emitting surface is formed in the sintered cathode body by removing a surface layer with a high-speed cutting tool. The preferred composition is 88% tungsten, 0À75% zirconium hydride, and 11-“% activator. Preferred particle sizes and times of milling and of heat treatment are given.