Improvement of Thermoelectric Properties Through Manipulation of their Microstructure: the Effect of Graphene Reinforcement

Environmental changes and extreme climate-related events are mainly attributed to greenhouse gas (GHG) emissions and are becoming a growing concern. The reported scientific evidence, highlighting such interrelationships, has convinced researchers to look for clean energy sources and improve operational efficiencies, and capture and convert the waste heat into electricity. Since almost two-thirds of energy is converted to heat and wasted, the recovery of waste heat will boost savings in fossil fuel consumption as an abundant source of energy. In this regard, thermoelectric (TE) compounds can be employed to convert the waste heat into electricity, thereby increasing the efficiencies of energy generating operations. Such an approach is even applicable to renewable energy (RE) sources. However, the applications of the thermoelectric converters necessitate the development of advanced, efficient thermoelectric materials with a high level of thermomechanical stability. This doctoral research project aims to develop and modify thermoelectric compounds by manipulating their microstructure and improving their mechanical properties by reinforcement with graphene nanoplates (GNPs). To the best of our knowledge, there is no specific report in the open literature to determine the reinforcing effects of graphene nanofillers (e.g., GNPs) on thermoelectric products. There is a lack of a comprehensive assessment in the scientific and industrial communities in evaluating the advantages and drawbacks of GNPs, as the reinforcing agent on TE compounds. In this dissertation, to assess the performance of the GNPs, three potential thermoelectric compounds, namely MnTe, CoVSn, and CuSbTe2, have been investigated. These designated compounds address the requirements for covering an extended working temperature range from low to high, examining various crystal structures (e.g., Chalcogenides and half-Heusler), and developing environmentally-friendly (i.e., lead-free) TE products. The bulk samples with the addition of small quantities of GNPs (0.25, 0.5, 0.75, and 1 wt. %) were synthesized using powder metallurgy and fabricated by spark plasma sintering (SPS). The thermoelectric factors, magnetic behavior, microstructure, and mechanical properties of the samples were evaluated and analyzed. Grain growth inhibition is the main consequence of the reinforcing GNPs, which results in an enhancement in the thermoelectric and mechanical characteristics of the nominated TE products. Scattering of electrical carriers and phonons due to the precipitation of the reinforcing GNPs in the matrix, thus providing a higher density of microstructural boundaries, improves the thermoelectric properties. Furthermore, microstructural manipulation, such as crystal/particle size reduction caused by the segregation of the reinforcing GNPs as a second phase in the matrix, enhances the mechanical characteristics of TE compounds, for example, the fracture toughness (𝐾𝐼𝐶) and hardness.

Author dc:creator

• Hooshmand Zaferani, Sadeq

Advisors dc:contributor.advisor

• Ghomashchi, Reza
• Vashaee, Daryoosh

• Graphene nanoplates
• Thermal Management
• Thermoelectric
• Waste Heat Recovery

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2440/133089

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/133089