Development of thermoelectric devices: design, fabrication and characterisation

Robbins, Mark 2015. Development of thermoelectric devices: design, fabrication and characterisation. MPhil Thesis, Cardiff University. Item availability restricted.

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Abstract

Improved efficiencies during waste heat recovery using currently available thermoelectric devices by increased hot-side temperatures push device materials to their operating limits. Magnesium silicide is one such material that is of interest for improved devices which can provide increased efficiencies by withstanding far higher temperatures. Within this report, progress has been made in achieving ohmic contacts for high-performance tin-antimony doped magnesium silicide and higher manganese silicide. To achieve this, a lab scale prototyping and characterisation facility was designed and tested. Furthermore, a COMSOL model was developed for module prototyping verification and has been validated using empirical data. In addition, to achieve the fabrication of a prototype module a joining process is developed for pre-contacted co-sintered antimony doped magnesium silicide and undoped higher manganese silicide. Moreover, assembly and characterisation of a prototype 7-couple module is performed followed by its characterisation data being used to validate a COMSOL model. Results showed contact sheet resistances of 8.58 ± 0.61 μΩ.cm2 and 32.7 ± 0.95 μΩ.cm2 being achieved for silver brazed antimony doped magnesium silicide and undoped higher manganese silicide, respectively. Furthermore, the prototype module created within this study has a power density of 130.29 mW/cm2 under a 300oC temperature differential. Moreover, barrier coating studies were additionally carried out for high figure of merit tin-antimony doped magnesium silicide and undoped higher manganese silicide investigating electrolytic plating, electroless plating, and sputter coating deposition techniques. Results demonstrated a sputter-coated nickel layer at a thickness of 1.2 μm with a 300 nm titanium adhesion layer results in a contact sheet resistance of 467.00 ± 8.35E μΩ.cm2 and 17.00 ± 0.13 μΩ.cm2 for silver brazed tin-antimony doped magnesium silicide and undoped higher manganese silicide, respectively. Furthermore, from the empirically verified COMSOL model a final COMSOL simulation is carried out with ideal values for the high-performance silicide material and a power density of 143mW/cm2 is calculated. These results show that improvement of the barrier layer can lead to a significantly more efficient device by incorporating higher performance, higher operating temperature materials, however with increasing dopant levels effective joining processes becomes increasingly difficult.

Item Type:	Thesis (MPhil)
Date Type:	Completion
Status:	Unpublished
Schools:	Engineering
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Uncontrolled Keywords:	Thermoelectric; Module; mid-Temperature; Joining; Silicide; Brazing.
Date of First Compliant Deposit:	1 November 2016
Last Modified:	07 Mar 2022 16:41
URI:	https://orca.cardiff.ac.uk/id/eprint/95709

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