Characteristics of ceramic electrode for AMTEC

In this paper the authors show that TiN, NbN and TiC electrodes prepared from metal or respective compound powders by a screen printing method work as well as AMTEC electrode (26th IECEC). TiC electrode (Thickness:2 - 3 μm, 800 degrees C, 0.07 Pa) shows the highest power density (0.40 W/cm2) in the authors work. This shows that AMTEC electrode can be prepared by screen printing method from metal or ceramic powders. The maximum power densities of TiN, NbN and TiC depend markedly on the degree of vacuum of low temperature room of AMTEC. In the measurements of NbN electrode (thickness: 2 - 3 μm), the power density of AMTEC increased from 0.12 W/cm2 (at 130 Pa) to 0.27 W/cm2 (at 0.037 Pa) with improvement of vacuum. TiC electrode shows same tendency. This indicates that the transfers of sodium vapor through electrode give an effect on the power density. Electrode characteristics under AMTEC operation were measured by interruption method and a.c. impedance analysis. These measurements (NbN electrode) show that the AMTEC cell has impedances due to interface of Na/BASE or BASE/electrode, in addition to an ohmic resistance. The overvoltage η resulted from polarization was linearly depending on the logarithm of current density (J) at higher overvoltage region