Abstract
It is generally accepted that the degree of carburization and the hue of the surface have an important effect upon the electron emission of carburized Th-W filament. Experimentally we analysed these facts, referring to the data formerly published. The hue results from the thin layer of the free carbon on the suface. We measure the free carbon in the filaments having different degrees of variation of resistance at room temperature before and after exhaustion. The results of the statistical study about the commerical transmitting tubs in production and of the observation of activation phenomena of experimental diodes, it may be summerised as follows :(1) The layers of free carbon make the activation rate and further the total emission decrease. (2) Both the fine grained structure and the removal of carbon layers enhance the electron emission of decarburized filaments. (3) It is supposed that ThO2 is decomposed partially already during carburization.We are justified in saying that the electron emission characteristics is not directly related to the degree of carburization, which is defined only by the ratio of cold resistance before and after carburization.
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