COPPER NIOBIUM AND COPPER TUNGSTEN COMPOSITES AS PLASMA TORCH CATHODES

This work was performed to screen potential cathode materials for. use in arc heaters with cylindrical electrodes. It focused on hot isostat ic pressing consolidated copper composites; 10% composites of copper w ith tungsten and niobium as well as 1.5% niobium were used. The compos ite cathodes were tested in pure Ar, He and N2 as well as in mixtures of Ar with CO, N2 and H-2, at atmospheric pressure and currents up to 150 A. The arc was driven around the circumference of the cathode with an external magnetic field. The results are compared with those using pure copper cathodes. The Cu-W cathode showed a better arc stability and lower erosion rates than copper. The Cu-Nb cathode showed much low er erosion rates and much better arc stability than copper for almost all the different operating conditions and may be considered a promisi ng new electrode material. The experimental results corroborated previ ous interpretations of the relationships between arc velocity, erosion rate, surface drag and electrode surface composition.