Optimizing Thermoelectric Properties of In Situ Plasma-Spray-Synthesized Sub-stoichiometric TiO2−x Deposits
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In this article, an attempt has been made to relate the thermoelectric properties of thermal spray deposits of sub-stoichiometric titania to process-induced phase and microstructural variances. The TiO2−x deposits were formed through the in situ reaction of the TiO1.9 or TiO1.7 feedstock within the high-temperature plasma flame and manipulated via varying the amounts of hydrogen fed into in the thermal plasma. Changes in the flow rates of H2 in the plasma plume greatly affected the in-flight particle behavior and composition of the deposits. For reference, a high-velocity oxy-fuel spray torch was also used to deposit the two varieties of feedstocks. Refinements to the representation of the in-flight particle characteristics derived via single particle and ensemble diagnostic methods are proposed using the group parameters (melting index and kinetic energy). The results show that depending on the value of the melting index, there is an inverse proportional relationship between electrical conductivity and Seebeck coefficient, whereas thermal conductivity has a directly proportional relationship with the electrical conductivity. Retention of the original phase and reduced decomposition is beneficial to retain the high Seebeck coefficient or the high electrical conductivity in the TiO2 system.
Keywordsmetastable phases plasma spray thermal spray thermoelectric properties TiO2−x titanium oxides
This work was supported by the National Science Foundation Partnership for Innovation (NSF-PFI) Program under Award Number IIP-1114205. The US-Czech collaboration included in this paper was funded in part by the NSF—International collaboration supplement. Zdenek Pala has been financially supported by the AdMat project of the Czech Science Foundation (14-36566G). Support through the Stony Brook Industrial Consortium for Thermal Spray Technology is also acknowledged. This research used resources of the Center for Functional Nanomaterials, which is a US DOE Office of Science Facility, at Brookhaven National Laboratory, under Contract No. DE-SC0012704.
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