Microstructure characterization and thermionic emission performance of barium-tungsten cathode

The effect of the parameters (sintering temperature, pressure, holding time) of spark plasma sintering technique on the W porosity of Ba-W cathode was studied by orthogonal method. When the W porosity varied in the range of 23%−30%, the corresponding process parameters were obtained. On this basis, the spherical and traditional irregular W matrix with different porosity were sintered. The results show that the spherical porous W particles were packed and arranged orderly, and the pore size distribution was concentrated and uniform. When the porosity of spherical W was 26.3%, the size of the median pore was 1.41 μm. The vickers hardness of spherical tungsten matrix was lower than that of conventional irregular tungsten matrix. Under the condition of pulse width 10 μs and frequency 1000 Hz, the impulse current density of Ba-W cathode increased at first and then decreased with the increase in porosity. The maximum current density belonged to the Ba-W cathode with the matrix porosity of 26.3%. At 1050 ℃, the off-point emission current density of Ba-W cathode reached 24.62 A/cm2, the corresponding zero-field current density and workfunction were 7.62 A/cm2 and 1.95 eV, respectively.