Abstract

The production of oxide filaments of barium and strontium in an emitting condition is investigated from the standpoint of determining the advantages of several apparently different methods of producing this type of cathode as used by several different companies. It is found that all methods amount to the same thing and are different only in degree.

The fundamental underlying action of all methods is that the filament to become emissive must undergo a gaseous bombardment, which presumably causes a breaking down of the higher oxides or compounds, as the carbonate, to the lower oxides or pure metal, and conversely, this breaking down must be caused by or accompanied by a gaseous discharge in order to produce an active filament. The gas most suitable for this action is best obtained from the filament and is best produced from a carbonate that has not been reduced until put in vacuo, and that the gas then liberated and used is probably CO₂.

These conclusions are arrived at by experiments on several different types of filaments containing relatively different amounts of combined or baked-on coating to uncombined coating and in every case results favor those filaments containing most uncombined coating.

Some secondary conclusions are that the baked on coating serves little or no purpose except as a mechanical bond and that the core material on which the coating can be placed may be of a wide variety of material.

© 1929 Optical Society of America

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