Hussain, N and Mullis, A orcid.org/0000-0002-5215-9959 (2018) Microstructure characterisation of drop tube processed SiGe semiconductor alloy. In: Roosz, A, Veres, Z, Sveda, M and Karacs, G, (eds.) Proceedings of the 7th International Conference on Solidification & Gravity 2018. Solidification and Gravity 2018, 02-06 Sep 2018, Miskolc-Lillafüred, Hungary. , pp. 291-296. ISBN 978-963-508-889-8
Abstract
Si-Ge based thermoelectric materials are of interest due to the challenges associated with energy recovery from waste heat in industrial processing. A directionally solidified, chill cast ingot of Si70Ge30 was broken into pieces before being subject to rapid solidification in reduced gravity. Drop-tube processing was employed to produce a powder sample with particle diameters in the range 850-150 μm. Solidification occurred under reduced gravity conditions during free-fall down the tube. Cooling rates of between 1800 and 20000 K s-1 were achieved among the various particle sizes. EDX analysis was used to confirmed that the starting material, drop-tube particles and a small amount of residual material left in the crucible were all the same composition. Scanning Electron Microscopy (SEM) was used to analyse the resulting microstructure as a function of cooling rate.
The as-solidified microstructure consists of relatively large Si-rich grains with Ge localised at the boundaries, in line with the expected solidification pathway. The Ge is found to form numerous small Ge rich grains which decorate the boundaries of the much larger Si-rich grains, resulting in highly bimodal grain size distribution. This has not previously been reported in the scientific literature. The effect of cooling rate on grain size was studied using SEM and quantitative image analysis, with grain size being found, as expected, to decrease with increasing cooling rate. Point Energy Dispersive X-Ray (EDX) was conducted on all samples at areas of interest; with the larger Si rich grains showing more Si than the original alloy composition (approx. 5-15% more). The small Ge rich grains showed relatively small amounts of Si (between 3-15%). The segregation and heterogeneity found in the microstructure of rapidly solidified particles, alongside the correlation in grain sizes determined by cooling rate, would be important in understanding and improving the conversion efficiency of SiGe whilst also maximising the cost-efficiency.
Metadata
Item Type: | Proceedings Paper |
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Authors/Creators: |
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Editors: |
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Copyright, Publisher and Additional Information: | This is an author produced version of a paper published in Proceedings of the 7th International Conference on Solidification & Gravity 2018. |
Keywords: | Thermoelectric Materials; Drop-tube processing; Silicon-Germanium |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemical & Process Engineering (Leeds) |
Funding Information: | Funder Grant number European Space Agency 400015236/02/NL/SH |
Depositing User: | Symplectic Publications |
Date Deposited: | 17 Sep 2018 12:24 |
Last Modified: | 18 Sep 2018 08:28 |
Status: | Published |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:135637 |