Relationship Between Tensile Strength and Durability of Oxide Thermoelectric Modules

The durability of thermoelectric modules is investigated by conducting material property tests over a range of module preparation pressures. Tensile strength and bending strength tests are carried out at room temperature for devices comprising one-piece oxide thermoelectric elements (p-type Ca2.7Bi0.3Co4O9 and n-type CaMn0.98Mo0.02O3), silver paste, and silver sheet between two sheets of alumina substrate. Tensile strength was found to increase with device preparation pressure, reaching approximately 20 MPa for p-type devices at a preparation pressure of 6.36 MPa. The tensile strength of the n-type devices was less than 10 MPa. Module performance was tested under heat cycling and vibration by measuring thermoelectric generation properties including internal resistance, open-circuit voltage, and output power of the modules. Modules prepared at pressures above 3.19 MPa were found to have no degradation of thermoelectric properties during the vibration tests. Furthermore, no degradation during heat cycling was observed for modules prepared at 6.36 MPa. Continuous power generation tests at 973 K in air were performed for the modules prepared at 0.116 MPa and 6.36 MPa and no degradation was observed over 2400 h. For the module prepared at 6.36 MPa, no degradation was observed over 10000 h.