Preparation and Evaluation of the Ammonium Perrhenate Impregnated Ni Sponge Oxide Cathode

To improve emission performance of the Ni sponge oxide cathodes, a Ni-Re sponge was prepared by impregnating an Ni sponge in an ammonium perrhenate (NH₄ReO₄) solution and then a cathode was fabricated using this Ni-Re sponge. At 850°Cbr, the dc emission current density of a typical impregnated Ni-Re sponge cathode is 5.21 A/cm² and the pulsed emission current density reaches 35.6 A/cm² with a 10- μs pulsewidth. Lifetime tests were carried out under different temperatures. After working under 800°C for 3000 h, the decreases of the dc emission current density is less than 5% from the initial value of 1.63 A/cm². Under 780°C, the dc emission current density even rises instead of attenuating and is still 14% higher than the initial value of 1.0 A/cm² after 5000 h of operation. Furthermore, the thermal electron spectrometry analysis and the work function distribution test show that the emission uniformity of the Ni-Re sponge oxide cathode fabricated by this liquid-solid mixing method is better than that of the conventional Ni-Re sponge oxide cathode fabricated by the solid-solid mixing method.