Investigation on the properties of Ta doped Ti3SiC2 as solid oxide fuel cell interconnects

Abstract

The oxidation behaviours and electrical properties of 5 at% Ta doped Ti₃SiC₂ solid solution have been investigated at 800 °C in air for up to 500 h. The oxidation kinetics of (Ti_0.95Ta_0.05)₃SiC₂ follows a parabolic law. The oxidation rate constant is 7.33 × 10⁻¹⁴ g² cm⁻⁴ s⁻¹, which is lower than those of Ti₃SiC₂, (Ti_0.95Nb_0.05)₃SiC₂ and Crofer 22 APU. Ta doped r-TiO₂ formed (Ti_0.95Ta_0.05)₃SiC₂ during the oxidation process. Ta doping can limit the outward diffusion of Ti by decreasing the native Ti interstitials concentration and simultaneously restraining the inward diffusion of oxygen by decreasing the O vacancy concentration. As a result, the oxidation resistance is significantly improved and the oxide scale structure of Ti₃SiC₂ changes from a double-layer to a monolithic layer. The ASR of (Ti_0.95Ta_0.05)₃SiC₂ after oxidation at 800 °C in air for 500 h is 29.5 mΩ cm², which is much lower than that of Ti₃SiC₂. Ta doping can increase the electron concentration in r-TiO₂ and thereby increase the electrical conductivity of r-TiO₂. Therefore, the ASR of (Ti_0.95Ta_0.05)₃SiC₂ after oxidation is lower compared to that of Ti₃SiC₂.