Development of thermally sprayed Ca_2Fe_2O_5 coatings for thermoelectrical applications

摘要

Thermoelectric generators are devices that allow the direct transformation of heat into electrical energy. The established thermoelectric materials are composed of rare, toxic and expensive elements, like Pb, Sb, and Te. Extension of use requires not only the development of thermoelectric materials consisting of non-hazardous and inexpensive elements, but also new manufacturing technologies for large devices. In this paper, thermal spraying is discussed as a potential technology for the manufacture of large area thermoelectric generators (TEG). The thermoelectric active coatings are the key for the production of a TEG by thermal spraying. Ca_2Fe_2O_5 is a promising novel thermoelectric material, which contains only abundant and non-hazardous elements and melts without decomposition. Since Ca_2Fe_2O_5 powder is not commercially available it had to be synthesized from the individual oxides. Afterwards, thermal spray feedstock powders were prepared using "agglomeration & sintering" and "sintering & crushing". Atmospheric plasma spray (F6 and Delta) was used to deposit dense coatings with thickness up to 2 mm. Characterization by means of microstructural analysis and phase compositions was conducted. The thermoelectric properties (Seebeck coefficient, electrical and thermal conductivity) of both bulk and coatings have been measured. Ca_2Fe_2O_5 can be easily processed by thermal spray but further optimization is required in order to achieve a satisfying thermoelectric performance.