Methods for Enhancing the Thermal Durability of High-Temperature Thermoelectric Materials

Abstract

Thermoelectric materials such as Skutterudites and Magnesium Silicides are being investigated as promising alternatives for medium to high temperature waste heat recovery in the transport sector and industry. A critical success factor for the thermoelectric material is its stability over time when exposed to rapid heating and cooling during its lifetime. In this work the different degradation issues at high temperature are examined for these thermoelectric materials, and several means of enhancing durability have been evaluated. Initial thermal durability studies have been performed with Skutterudites and Magnesium Silicides with candidate coatings for protecting the materials from oxidation and sublimation during thermal cycles in air for up to 500 hours and up to 873K. The samples were then characterized by SEM and EDS. The results showed that it is possible to decrease degradation of the thermoelectric material without compromising the overall thermoelectric efficiency.

Thermoelectric Properties of Bi‐Doped Mg2Si0.6Sn0.4 Solid Solutions Synthesized by Two‐Step Low Temperature Reaction Combined with Hot Pressing

“…The sample exhibited only clear Bragg peaks from the face‐centered cubic (fcc) antiflourite structure with the space group Fm3m. Throughout all three aforementioned synthesis stages, a weak diffraction peak at 2θ ≈ 43° represents a small amount of MgO impurity. This is a common impurity for all Mg 2 Si‐based materials, as Mg is volatile and highly reactive to residual oxygen at high temperatures via the oxidation process of every type of Mg 2 Si‐based compounds . The amount of MgO is more or less the same after the two heating stages, but a small increase is monitored on the powdered samples of the sintered pellets.…”

Thermal stability of Mg2Si0.4Sn0.6 in inert gases and atomic-layer-deposited Al2O3 thin film as a protective coating

“…[2][3][4][5] However, the thermal stability issue of Mg 2 Si x Sn x solid solution is a major obstacle that must be tackled before the material can be applied in practical thermoelectric devices. [6][7][8][9][10] Tani et al found that Mg 2 Si starts to react with air signicantly above 723 K and the oxidation layer develops into the sample by oxygen diffusion. 6 Bourgeois et al studied the thermal stability of Mg 2 Si 1Àx Sn x solid solutions by in situ temperature X-ray powder diffraction in Ar gas.…”

“…8 Skomedal et al pointed out that in Mg 2 Si 1Àx Sn x compounds, Sn-rich solid solutions decompose faster at lower temperatures compared to the Si-rich solid solutions. 9 Yin et al examined the thermal stability of Mg 2 Si 0.3 Sn 0.7 in vacuum as well as in air. When heated at 773 K in vacuum, the Mg 2 Si 0.3 Sn 0.7 solid solution suffers a severe Mg loss due to the high vapor pressure of Mg; when heated in air without protection, the sample was oxidized.…”

“…Tani et al fabricated a 0.7 mm b-FeSi 2 lm on Mg 2 Si pellet by RF magnetron-sputtering deposition in order to protect Mg 2 Si from oxidation at 873 K. 6 Skomedal et al briey reported a micronsized Al 2 O 3 coating that effectively protects the Mg 2 Si 0.4 Sn 0.6 bulk from degradation at 673 K. However, the detail of the Al 2 O 3 coating was not revealed. 9 Yin et al applied a BN coating on Mg 2 Si 0.3 Sn 0.7 by spraying a layer of 0.5 mm BN, which provides a good protection of the sample up to 773 K; however, the carrier density in the sample deteriorates at 823 K. 10 Most thermal stability studies of Mg 2 Si 1Àx Sn x reviewed above were performed in air. In this work, we investigated the thermal stability of Mg 2 Si 1Àx Sn x in inert gas atmospheres, where physical properties were monitored during thermal cycles.…”

Long‐Term Stability of (Ti/Zr/Hf)CoSb1−xSnx Thermoelectric p‐Type Half‐Heusler Compounds Upon Thermal Cycling

“…[7] Inexplicably,t he effect of thermal cycling on the thermoelectric material itself is mostly neglected. Af ew investigations of bismuth tellurides [14,15] and skutterudites [16,17] can be found. Them ost detailed study on thermocyclic stability has the purpose of finding as tandardr eference material for Seebeckc oefficient measurements by comparing constantan to SiGe.…”