日本金属学会誌

J. Japan Inst. Metals, Vol. 14, No. 6 (1950),
pp. 23-26

Study on Carburization of Th-W Filament (2nd Report) Cold Electric Resistance and Operating Temperature by Carburization

M. Kawakami and N. Ogasawara


Abstract:

From the result in the 1st report, we found that it was suitable to adopt the range of 2.45~3.16% as the carbon content in the carbide layer. Theoretically, we led the following formula representing the relation between the degree of carburization (S) and the ratio of increase in cold electric resistance (λ),

where ρW and ρW2C are the cold electric specific resistances in the uncarburized core and the carburized sheath.
If the carbide layer is all of W2C composition, the value of ρWW2C is 0.07, but ρWW2C is experimentally about 0.3 . The operating temperature of the carburized filament is not directly determined , because the total emissivity of W2C has not been correctly found heretofore, so that using the actual data in the transmitting tube working, the following formula was theoretically determined.

where Rθ fθ is either the ratio of the hot-to-cold electric resistance in a Th-W filament carburized, or not respectively, and ρW(T), ρW2C(T) is ρWW2C at operating temperature T respectively. At any time, the degree of carburization is obtained from the formula (1)by measuring the cold electric resistance and the operating temperature of the carburized Th-W filament is known from the formula (2). The expansion of filament by carburization is increasing as ThO2 content in W is decreasing, but the amount is negligibly small.


(Received 1949/12/10)

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