Getters

Getters 

(gas absorbers), substances with a high absorption capacity for oxygen, hydrogen, nitrogen, carbon dioxide, carbon monoxide, and other gases, except inert gases. The gas absorption is determined by the chemical activity of the substances when they react with the gases, as well as by their ability to dissolve them (absorption) or to hold them on the surface (adsorption). Getters are usually used in vacuum devices to absorb gases and vapors that remain after evacuation or are liberated during operation. In devices filled with inert gases they are used to remove impurities, and they are also used in vacuum pumps as the working medium. So-called vaporizing and nonvaporizing getters are used.

Vaporizing getters bind gases both when they evaporate and when they precipitate on the walls of the device, forming a metal mirror. The main vaporizing getters arefeba (barium wire in an iron envelope) and bato (a mixture of thorium and

Table 1. Main characteristics of getters
	Degassing	Temperature (° C) Gas absorption	Sputtering	Use
Feba ...............	750-800	not over 200	900-1000	Radio oscillator tubes of low and medium power; receiving amplifier tubes
Bato and batalum ...............	600-700	not over 200	900-1300	Cathode-ray tubes, miniature radio tubes, and medium-size oscillator tubes
Tseto ...............	800-900	200-600	—	Tubes in which the use of sputtering gas absorbers is impossible
Thorium ...............	800-1100 (on a metal base) 1500-1600 (on a graphite base)	400-500	—	Super-high frequency tubes, medium-power oscillator tubes
Zirconium ...............	700-1300 (to 1700 for wire)	800 (to 1600 for wire)	—	High- and medium-power oscillator tubes; ultrashortwave devices
Tantalum ...............	1600-2000	700-1200	—	Radio oscillator tubes of medium size; powerful vacuum and radio oscillator tubes
Phosphorus ...............	—	100-200	200	Incandescent lamps
Aluminum-magnesium ...............	400	adsorb gases only at moment of sputtering	450-500	Small radio receiving tubes; tubes with an oxide cathode
Titanium ...............	—	from 20 to 196	1300-2000	Sorption and getter-ion pumps

iron oxide with a barium-aluminum alloy). Nonvapòrizing getters, batalum (a mixture of barium and strontium carbonates), are usually applied as finely dispersed metallic powders to the surfaces of parts of devices or are used to make an entire part. In the nonvaporizing getters the active substances are tantalum, titanium, zirconium, barium, cerium, lanthanum and niobium, and tseto (mixed cerium, thorium, and lanthanum powders). The main properties of getters are given in Table 1.

REFERENCES

Lebedinskii, M. A. Elektrovakuumnye materialy. Moscow-Leningrad, 1956.
Kohl, W. Tekhnologiia materialov dlia elektrovakuumnykh priborov. Moscow-Leningrad, 1957. (Translated from English.)

E. N. MARTINSON