Cored Cathode for Stabilization of the dc Arc

The stability of the dc arc can be increased by the use of a cathode that is cored with a material containing an element of an ionization potential lower than carbon. An effective core material developed for spectrochemical analysis is a 1:2 mixture of BaCO₃ or Li₂CO₃ and graphite powder. In the arc, the added element forms a stationary positive-ion cloud at the tip of the cathode and acts as a ballast to electron flow. Arc temperature is not lowered, as is frequently the case when a buffer is added to the anode. Current and voltage fluctuations and arc wandering are reduced, as indicated by recordings during sample consumption. Several hundred sample materials have been tested to determine the usefulness of the cored cathode.