Cathode spots on the surface of nanostructured W alloys

The tracks of cathode spots produced after arcing on the surfaces of nanostructured W alloys were investigated using a scanning electron microscope (SEM). For nanostructured W-2%ThO2 cathodes, the distribution of cathode spots was dispersed and their geometrical properties were completely controlled by the shape and size of ThO2. For nanostructured W-20%Cu cathodes, the spots were also separated on Cu-rich phase. The results showed that cathode spots on the surface of nanostructured W alloys were quite different from those on the surface of commercial W alloys with coarse grain size, and the microstructure of the cathode materials had significant influence on the cathode spots propagation. Also, space-charge regions induced by internal electric field at the interface which responded to the effect of microstructure on cathode spots were suggested.