Testing of Minute Oxidation of the Base Metal for Oxide Cathode during the Tube Manufacturing Process

Electron emission of the oxide-coated cathode is sharply affected by slight oxidation of impurities contained in the nickel core metal. This minute oxidation occurs during ingot melting, rolling, annealing, forming and tube exhausting. A new method was developed for testing of the cathode base metal without using the thermionic emission test through electronic tubes. This new method makes use of the fact that the corrosion rate of metals in acid or alkaline solution is markedly affected by minute oxidation. The extent of oxidation, the depth of oxidation and the oxidation resisting power of the metal for cathode core can be estimated from the curve of time and the weight of metal specimen in an acid solution. Tube exhausting process can also be checked.