Microstructure and physicochemical properties of a thermally sprayed coating depend on the dynamics of the particles interacting with the spray jet. This is especially the case for electrical properties. In this study, different spraying processes were used to spray p-type and n-type half-Heusler powders. Thermoelectric powders, Hf20Zr75Ti05CoSb80Sn20 (p-type) and Hf60Zr40NiSn98Sb02 (n-type), were selected due to their interesting electrical properties. The spray processes were evaluated based on coating composition and mechanical property measurements. The only coatings of practical interest were those that were plasma sprayed and they were examined in detail to assess the effect of process parameters on coating properties.

This study assesses the potential use of thermally sprayed dicalcium diiron pentaoxide (Ca 2 Fe 2 O 5 ) for thermoelectric generators. Ca 2 Fe 2 O 5 coatings up to 2 mm thick were produced by atmospheric plasma spraying and examined. Compared to the bulk material, the coatings exhibit lower thermal and electrical conductivity. The Seebeck coefficient could not be measured, and the thermoelectric performance was inadequate. The limitations derive not only from the thermal spray process, but also the material itself.

The work presented in this paper addresses some of the challenges of manufacturing thermoelectric (TE) generators by thermal spraying. One of the main obstacles is achieving good coat-on-coat bonding between different types of materials. The coatings must also be mechanically stable and optimized for their respective function. At least four types of materials are required, including electrical insulators, conductors, and thermoelectrically active p- and n-type semiconductors. Four ceramic and three metal feedstock powers were deposited by APS, HVOF, and HVAF spraying using special masking systems, substrate pretreatments, and layer thickness monitoring. After process optimization for each material, multilayer TE generator modules were successfully produced.

SrTiO x is an expected oxide thermoelectric material, which performance can be improved by doping Y 3+ in place of Sr 2+ . However, the maximum content of Y 3+ is limited to about 10% because of the phase transformation in the equilibrium sintered material. By contrast, plasma sprayed (Sr, Y)TiO x , which was essentially rapidly quenched, could solve Y up to 20% of Sr-site without the second phase, and produce the increase in the electric conductivity and the decrease in the thermal conductivity. But the absolute value of Seebeck coefficient decreased with an increase of Y content. As the result, the ZT value, which showed the performance for thermoelectric power generation, was reached only 0.1 in the Y content range 10% to 25% of Sr site.