Influence of pressure and dwell time on pressure‐assisted sintering of calcium cobaltite
Sophie Bresch, Björn Mieller, Daniela Schönauer‐Kamin, Ralf Moos, Timmy Reimann, Fabien Giovannelli, Torsten Rabe
Abstract
Abstract Calcium cobaltite Ca 3 Co 4 O 9 , abbreviated Co349, is a promising thermoelectric material for high‐temperature applications in air. Its anisotropic properties can be assigned to polycrystalline parts by texturing. Tape casting and pressure‐assisted sintering (PAS) are a possible future way for a cost‐effective mass‐production of thermoelectric generators. This study examines the influence of pressure and dwell time during PAS at 900°C of tape‐cast Co349 on texture and thermoelectric properties. Tape casting aligns lentoid Co349. PAS results in a textured Co349 microstructure with the thermoelectrically favorable ab‐direction perpendicular to the pressing direction. By pressure variation during sintering, the microstructure of Co349 can be tailored either toward a maximum figure of merit as required for energy harvesting or toward a maximum power factor as required for energy harvesting. Moderate pressure of 2.5 MPa results in 25% porosity and a textured microstructure with a figure of merit of 0.13 at 700°C, two times higher than the dry‐pressed, pressureless‐sintered reference. A pressure of 7.5 MPa leads to 94% density and a high power factor of 326 µW/mK 2 at 800°C, which is 11 times higher than the dry‐pressed reference (30 MPa) from the same powder.