Purificationand Cleaning of Spongy Tungsten Disc Used As Impregnated Dispenser-Cathode in Vacuum

The highly purespongy tungstendisc, widely used as impregnated dispenser-cathode in microwave vacuum electronic devices, was fabricated by high (mid) frequency induction heating of W-Cu alloy in the vacuum reactor with a water-cooled condenser. The impact of heating temperature and time on porosity and purity of the spongy W-disc was investigated. The results show that the highly clean and pure spongy W-disc can be fabricated by induction heating. For example, heated at 1900 K for 60 min at 10-3 Pa, little residue Cu exist in the spongy Wdisc; and Cu formed a stalactiteon the condenser. The novel induction heating technique outperforms the conventional wet chemical method in many ways, including the environmental friendliness, much shorter time, higher purity. The surface segregation and vacuum evaporation of Cu from W-Cu alloy was theoretically analyzed. The calculated and measured results were in good agreement.