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Spectrographic Determination of Impurities in Molybdenum: Influence of a Diatomic Gaseous Reaction Product on the Arc Excitation in Argon

Volume 25, Number 3 (June 1971) Page 305-312

Morris, W.F.; Worden, E.F.


A spectrographic method has been developed for the determination of 24 trace elements in MoO3. The method is particularly effective for the refractory elements Nb, Ta, Zr, Ti, and V, which are difficult to determine by conventional spectrographic procedures. High sensitivity is achieved in a low amperage are in argon as a consequence of certain thermochemical reactions which occur in the anode during the arcing process. Although it would appear that the discharge takes place in argon, in fact a small quantity of CO is evolved into the are when MoO3 is reduced in the anode. The evolution of CO changes the composition of the are gas and is essential to the ultimate vaporization and excitation of metal impurities. This paper presents time-resolved spectra, anode temperature, and are gap voltage measurements which demonstrate the effect of CO.