Durability of Silicide-Based Thermoelectric Modules at High Temperatures in Air

Thermoelectric modules consisting of n-type Mn2.7Cr0.3Si4Al2 and p-type MnSi1.75 legs have been fabricated by use of composite pastes of Ag with Pt or Pd. For the module prepared by Ni-B plating and with Ag paste, the specific power density reached 370 mW/cm2 at a heat-source temperature of 873 K. Ni-B plating 5 μm thick on the surfaces of the silicide legs reduced both the internal resistance and degradation of the power generated by silicide modules at temperatures up to 873 K in air. This is because of oxidation of Al diffusing into the n-type legs and reaching the Ag electrodes on both the hot and cold sides. Ni-B plating can suppress Al diffusion into n-type legs. However, cracking was observed parallel to the contact surface in the middle of the Ni-B plating layer on the p-type legs. It was also found that incorporating Pt or Pd into the Ag paste effectively suppressed degradation of the contact resistance between the silicide legs and the Ag electrodes.