resumo
In this work, eco-friendly magnesium-silicide (Mg2Si) semiconducting (n-type) thermoelectric pastes for building components concerning energy-harvesting devices through 3D printing, spray and electrospinning were synthetized and tested for the first time. The Mg2Si fine powders were obtained through the combination of ball milling and thermal annealing under Ar atmosphere. While the latter process was crucial for obtaining the desired Mg2Si phase, the ball milling was indispensable for homogenizing and reducing the grain size of the powders. The synthetized Mg2Si powders exhibited a large Seebeck coefficient of similar to 487 mu V/K and were blended with a polymeric solution in different mass ratios to adjust the paste viscosity to the different requirements of 3D printing, electrospinning and low-pressure spray. The materials produced in every single stage of the paste synthesis were characterized by a variety of techniques that unequivocally prove their viability for producing thermoelectric parts and components. These can certainly trigger further research and development in green thermoelectric generators (TEGs) capable of adopting any form or shape with enhanced thermoelectric properties. These green TEGs are meant to compete with common toxic materials such as Bi2Te3, PbTe and CoSb that have Seebeck coefficients in the range of similar to 290-700 mu V/K, similar to that of the produced Mg2Si powders and lower than that of 3D printed bulk Mg2Si pieces, measured to be similar to 4866 mu V/K. Also, their measured thermal conductivities proved to be significantly lower (similar to 0.2 W/mK) than that reported for Mg2Si (>= 4 W/mK). However, it is herein demonstrated that such thermoelectric properties are not stable over time. Pressureless sintering proved to be indispensable, but difficultly achievable by long thermal annealing (even above 32 h) in inert atmosphere at 400 degrees C, at least for bulk Mg2Si pieces constituted by a mean grain size of 2-3 mu m. Hence, for overcoming this sintering challenge and become the silicide's extrusion viable in the production of bulk thermoelectric parts, alternative pressureless sintering methods will have to be further explored.
palavras-chave
MG2SI; FABRICATION; FIGURE
categoria
Materials Science
autores
Marques, AC; Miglietta, D; Gaspar, G; Baptista, AC; Gaspar, A; Perdigao, P; Soares, I; Bianchi, C; Sousa, D; Faustino, BMM; Amaral, VS; Santos, T; Goncalves, AP; da Silva, RC; Giorgis, F; Ferreira, I
nossos autores
Guilherme Manuel Morais Gaspar
Bolseiro de pós-Doutoramento
Vitor Brás Sequeira Amaral
Professor Catedráticoagradecimentos
This work was mainly funded by H2020-ICT-2014-1, RIA, TransFlexTeg-645241, and ERC-CoG-2014, CapTherPV, 647596, and partially funded by FEDER funds through the COMPETE 2020 Program and National Funds through FCT Portuguese Foundation for Science and Technology under the project UID/CTM/50025/2013. And co-supported by: (1) FCT-Portugal, through the contracts UID/Multi/04349/2013 and POCI-01-0145-FEDER-016674 and (2) CICECO-Aveiro Institute of Materials through the project POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. The authors would like to thank the use of electrospinning apparatus at the Biomaterials Laboratory from Soft and Bio-functional Materials Group (CENIMAT/I3 N). And A. C. Baptista also acknowledges FCT-MEC for her postdoctoral grant with reference SFRH/BPD/104407/2014.