(57) The present invention provides a tungsten-based duplex composite member, e.g., wire or rod, which combines the emissive, nonsag, or other desirable qualities of an inner tungsten-based core material with a different combination of properties, for example, resistance to attack, by the presence of a different tungsten-based material as an outer sheath or shell surrounding the core material.
In one embodiment of the present invention, an electrode is formed from a duplex composite member, composed of a thoriated tungsten core (W - ThO₂) and a thin rhenium (Re) shell.
Other embodiments of duplex composite members are provided by thoriated tungsten discharge electrodes in which it is desirable to have two different concentrations of thoria (ThO₂) in the element, a first concentration in the core of the duplex composite member and a second concentration in the shell or surface of the member.