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. 2020 Jul 16;13(14):3184.
doi: 10.3390/ma13143184.

Field-Assisted Sintering/Spark Plasma Sintering of Gadolinium-Doped Ceria with Controlled Re-oxidation for Crack Prevention

Tarini Prasad Mishra  1 , Alexander M Laptev  1 , Mirko Ziegner  2 , Sree Koundinya Sistla  3 , Anke Kaletsch  3 , Christoph Broeckmann  3   4 , Olivier Guillon  1   4 , Martin Bram  1
Affiliations

Field-Assisted Sintering/Spark Plasma Sintering of Gadolinium-Doped Ceria with Controlled Re-oxidation for Crack Prevention

Tarini Prasad Mishra et al. Materials (Basel). .

Abstract

Gadolinium-Doped Ceria (GDC) is a prospective material for application in electrochemical devices. Free sintering in air of GDC powder usually requires temperatures in the range of 1400 to 1600 °C and dwell time of several hours. Recently, it was demonstrated that sintering temperature can be significantly decreased, when sintering was performed in reducing atmosphere. Following re-oxidation at elevated temperatures was found to be a helpful measure to avoid sample failure. Sintering temperature and dwell time can be also decreased by use of Spark Plasma Sintering, also known as Field-Assisted Sintering Technique (FAST/SPS). In the present work, we combined for the first time the advantages of FAST/SPS technology and re-oxidation for sintering of GDC parts. However, GDC samples sintered by FAST/SPS were highly sensitive to fragmentation. Therefore, we investigated the factors responsible for this effect. Based on understanding of these factors, a special tool was designed enabling pressureless FAST/SPS sintering in controlled atmosphere. For proof of concept, a commercial GDC powder was sintered in this tool in reducing atmosphere (Ar-2.9%H2), followed by re-oxidation. The fragmentation of GDC samples was avoided and the number of micro-cracks was reduced to a minimum. Prospects of GDC sintering by FAST/SPS were discussed.

Keywords: chemical expansion; crack-free sintering; gadolinium-doped ceria; re-oxidation; spark plasma sintering.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Morphology of GDC10-HP powder: (a) Scanning Electron Microscopic (SEM) image; (b) Transmission Electron Microscopic (TEM) image.
Figure 2
Figure 2
(a) Setup for pressure-assisted FAST/SPS; (b) redox cycle; (c) setup for pressureless FAST/SPS; (d) fractured sample after pressure-assisted sintering (left) and sample after pressureless redox sintering (right).
Figure 3
Figure 3
(a) Shrinkage of GDC10-HP samples during free sintering in different atmospheres; (b) associated shrinkage rate; microstructure of GDC10-HP sample sintered (c) in air and (d) in Ar-2.9%H2.
Figure 4
Figure 4
(a) Mass change and (b) differential thermal analysis of GDC10-HP powder during reduction in Ar-2.9%H2 in first thermal cycle and re-oxidation in air in second thermal cycle.
Figure 5
Figure 5
Expansion of GDC10 lattice during heating in synthetic air and in Ar-2.9%H2.
Figure 6
Figure 6
Measured displacement during pressure-assisted FAST/SPS of GDC10-HP powder in different atmospheres.
Figure 7
Figure 7
Microstructure of GDC10-HP samples after pressure-assisted FAST/SPS (a) in vacuum and (b) in Ar-2.9%H2.
Figure 8
Figure 8
(a) Setup and (b) broken pellets after sintering of cold-pressed GDC10-HP sample in alumina bed with varying pressure and atmosphere.
Figure 9
Figure 9
Micrographs of pressureless sintered samples: (a) cracks formation after sintering entirely in Ar-2.9%H2, (b) nearly crack-free structure after sintering in Ar-2.9%H2 with subsequent re-oxidation.
Figure 10
Figure 10
XRD patterns for GDC10-HP samples after FAST/SPS sintering in different atmospheres.
Figure 11
Figure 11
Mass loss and CO/CO2 release when heating and cooling a GDC10-HP and carbon black powder mixture in argon.
See this image and copyright information in PMC

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