Performance and stability of silicide based thermoelectric modules

Long-term studies on thermoelectric generator uni-couple based on N-type magnesium silicide (Mg2.01Si0.49Sn0.5Sb0.01) and P-type higher manganese silicide (Mn0.98Mo0.02Si1.73Ge0.02) materials are presented, in the operating temperature range of 2000C-4000C. Emphasis is put on the performance and reliability of the current collector configuration, especially, on the hot side of the module and on the thermomechanical stresses that are created during operation and lifetime testing, as a result of large temperature gradients experienced across the thermoelectric legs. With silver (Ag) paste as contact material, the long term-stability of the uni-couples were carried out on non-metalized legs and gold metalized legs under ambient conditions. Under isothermal and thermocycling tests, the non-metalized legs showed a gradual decrease in open circuit voltage (after a period of 200hours) and increase in internal resistance. In contrary, the metalized leg-based module was robust and stable for the same isothermal period, however, after 300cycles the n-type material showed mechanical failure (cracks) but the p-type resisted. Post-operation analysis by SEM/EDS and mechanical testing revealed that oxidation, adherence of the contact material and diffusion of the bonding material were the cause of performance degradation of the unicouples.