Degradation factors of a new long-life cathode

Since 2002, an accelerated life test has launched for a new long-life cathode at four different temperatures (1050°C, 1090°C, 1130°C and 1170°C) and fixed current density (2A/cm²) in IECAS. According to the relationship between the cathode life and operating temperatures, an accelerated equation has been set up. The cathode life at normal operating temperature is deducted based on results of the accelerated life test by using the accelerated equation. The results show that life of the novel cathodes exceeds 150,000 hour at 960°C with a current density of 2A/cm². The structure of this kind of long-life cathode consists of dual-layer porous tungsten matrix and dual layer coating. Top-layer porous tungsten matrix has low porosity (about 22%) that can reduce the evaporation of the active materials. Bottom layer tungsten matrix has high porosity (about 35%) that can increase the storing amount of the active materials. The cathode is first coated with noble metals Re and then coated with 50% Os-50% W alloy. The accelerated life test result shows that this kind of cathode has more life time. In order to realize the degradation mechanism of the cathode and prolong its life, the cathode surface is checked with scanning electron microscope (SEM) at the end of life. The content and variation of the various elements on the surface and longitudinal section of the cathode are analyzed with Auger electron spectroscopy (AES).