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Influence of pressure and dwell time on pressure‐assisted sintering of calcium cobaltite
Author(s) -
Bresch Sophie,
Mieller Björn,
SchönauerKamin Daniela,
Moos Ralf,
Reimann Timmy,
Giovannelli Fabien,
Rabe Torsten
Publication year - 2021
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.17541
Subject(s) - materials science , microstructure , tape casting , sintering , figure of merit , dwell time , texture (cosmology) , cobaltite , thermoelectric effect , composite material , porosity , metallurgy , optoelectronics , medicine , clinical psychology , image (mathematics) , physics , artificial intelligence , computer science , thermodynamics
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.