Skip to Main content Skip to Navigation
Theses

Hot pressing of thermoelectric materials for high temperature energy harvesting

Abstract : Energy recovery by thermoelectric effect is a promising technology which offers greatreliability. In the range of high temperatures, it is necessary that the thermoelectric generatorshave to be made of bulk material to increase electrical power. In the literature,nanostructuring decreases the thermal conductivity and therefore enhances the conversionefficiency. On the contrary, the effect of porosity is a matter of debate.In this work, n-type Si80Ge20 alloy prepared by mechanical alloying is investigated. It isa typical material for high temperature applications (around 800◦C). The nanocrystallinepowder is compacted uniaxially at room temperature and then hot pressed. In addition tothe microstructural characterization, thermoelectrical and mechanical properties are identifiedexperimentally. This study shows that the grain size is kept below 200nm. The bestmeasured figure of merit is slightly slightly larger than one for dense specimens. However,the porous samples have low electrical conductivity which limits their final thermoelectricrendering.The mechanical behaviour of the powder is modelled through simulations using thediscrete element method (DEM). This approach has the advantage of following the evolutionof particle rearrangement during densification and provides useful information onmicrostructural parameters. Numerical microstructures obtained from DEM simulationsare then used for calculations of thermal and electrical conductivities. The samples aremodelled by three phases according to their properties : SiGe matrix, pores and grainboundaries. The conductivities ratio is maximal for 30% of residual porosity. This resultis explained by the analytical model that takes into account the thermal resistance ofthe grain boundaries as well as microstructure evolution during the densification process.Based on these findings, an alternative processing route is proposed to build an optimizedmicrostructure.
Complete list of metadata

Cited literature [144 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-01128810
Contributor : Abes Star :  Contact
Submitted on : Tuesday, March 10, 2015 - 2:09:05 PM
Last modification on : Thursday, November 19, 2020 - 3:54:18 PM
Long-term archiving on: : Thursday, June 11, 2015 - 11:00:56 AM

File

2013GRENI096.pdf
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-01128810, version 1

Collections

Citation

Achraf Kallel. Hot pressing of thermoelectric materials for high temperature energy harvesting. Materials. Université de Grenoble, 2013. English. ⟨NNT : 2013GRENI096⟩. ⟨tel-01128810⟩

Share

Metrics

Record views

698

Files downloads

500