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

Abstract

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 arc 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 arc gap voltage measurements which demonstrate the effect of CO.