An overview of oxidation in hybrid and glass-based protective coatings for thermoelectric materials for medium-temperature range applications

Abstract

Several oxidation protective coatings, both glass-based and ceramic/polymer hybrid coatings, for p-and n-type thermoelectrics were designed at the Politecnico di Torino in recent years, and they were characterised and tested under relevant conditions. The 'glass-ceramic route' to obtain a thermo-mechanical compatible and high-temperature resistant coated thermoelectric is discussed with some examples. Oxidation tests demonstrated the effectiveness of the coatings for the protection of both n-and p-type thermoelectrics.

Low-Cost Magnesium-Based Thermoelectric Materials: Progress, Challenges, and Enhancements

“…Nevertheless, further investigations regarding interface alterations and TE properties are necessary before application. 120 Silicon-oxycarbide (SiOC), often referred to black glass, denotes a carbon-containing silicate glass in which oxygen and carbon atoms form bonds with silicon within an amorphous network structure. This materials boasts excellent mechanical properties and chemical stability.…”

“…Additionally, they should maintain stability when in contact with chemical agents. 120 The most common coatings for high-temperature TE applications include oxides, nitrides, silicides, borides, carbides, or their mixtures. 121 Coatings like Si 3 N 4 , CrSi, Al 2 O 3 , ZrO 2 , NbN, WN, TaN, MgAlO 4 , Enamel, Nano-SiO 2 , Mo/SiO x multilayer, composite glass, aerogel, and heat resistance paint have been used to protect Skutterudites TE legs.…”

“…They should have good adhesion to TE materials and serve as an effective diffusion barrier against gases and/or liquids. Additionally, they should maintain stability when in contact with chemical agents …”

“…Following an aging test at 773 K for 120 h in air, the uncoated Mg 2 Si 0.487 Sn 0.5 Sb 0.013 sample underwent complete oxidation, transforming into a mixture of powders including MgO, SnO 2 , SnO, Sn and Si, whereas the glass coated sample appeared unaffected. Nevertheless, further investigations regarding interface alterations and TE properties are necessary before application …”

“…In short, the selections of coating should adhere to the following principles: Low thermal conductivity to minimize parasitic heat loss. Low electrical conductivity to prevent short-circuiting. Coefficient(s) of thermal expansion matching that of the TE material, ensuring good interface compatibility and stress resistance during thermal cycling. Sufficient thermal stability and mechanical strength for long-term durability. No adverse impact on TE performance. …”