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.

In this work suspension-HVOF spraying (S-HVOF) was used to prepare dense and mechanical stable Al 2 O 3 sprayed coatings with high contents of α-Al 2 O 3 phase. Aqueous suspensions with various contents of powder (from 25 wt.% up to 50 wt.%) have been developed starting from two commercial α-Al 2 O 3 powders, characterized by different purity and particle sizes. The suspensions have been internally injected in a modified combustion chamber of a HVOF TopGun-torch. Coating microstructures, phase compositions and mechanical properties resulting from the interaction between suspension characteristics and spray parameters are presented. Use of suspensions with high solid contents allowed the production of thick, dense and mechanically stable coatings. The α-Al 2 O 3 was the main phase in the coatings produced through the injection of suspensions containing powders with very high purity.