Thermoelectric ceramics for generators

The manufacturing of thermoelectric modules from conventional materials is well established and widely commercially available. However, fabrication of modules based on oxide materials has been recently emerging and there exist very few reports on their performance. The oxide nature of the thermoelectric elements and the processing specifications involving very high temperatures make the fabrication a difficult task and different from that of conventional thermoelectric modules. In this work we describe (i) the fabrication of thermoelectric modules based on oxide bulk and foam materials of Ca3CO4O9 and Ca0.95Sm0.05MnO3 and (ii) the metal to ceramic contact preparation. The open porous foam structures of thermoelectric materials make it possible to design efficient thermoelectric modules for waste heat sources involving gaseous and liquid media. The possibility of direct large area physical contact of thermoelectric foam elements with hot media will make them efficient electric power generators. The open porous thermoelectric materials with introduced porosities can be good candidates to confine phonons (lattice vibrations) in order to reduce the thermal conductivity if the pores can be made sufficiently small. The performances of the modules were evaluated and possible factors limiting their theoretical performance are discussed. A parameter representing the quality of the modules termed the manufacturing factor (MF) representing the cumulative effect of various factors involved in the fabrication process is introduced and evaluated for the modules and compared to other reported modules. (c) 2007 Elsevier Ltd. All rights reserved.