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De‐densification mechanisms of yttria‐doped cerium oxide during sintering in a reducing atmosphere
Author(s) -
Chambon Cébastien,
Vaudez Stéphane,
Heintz JeanMarc
Publication year - 2018
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.15741
Subject(s) - sintering , materials science , dilatometer , reducing atmosphere , oxygen , yttria stabilized zirconia , shrinkage , oxide , graphite , carbon fibers , pellets , metallurgy , chemical engineering , composite material , ceramic , cubic zirconia , thermal expansion , chemistry , composite number , organic chemistry , engineering
The presence of residual carbon in oxides in which the valence state can change during sintering may lead to de‐densification or swelling phenomena during the last stage of sintering. This was demonstrated by sintering a Ce 0.85 Y 0.15 O 2‐x powder compact with or without added graphite carbon in a reducing atmosphere (Ar/5 vol.% H 2 ) at 1450°C. The shrinkage behavior was studied with a dilatometer combined with an oxygen probe and a gas chromatograph to analyze the composition of the released gases. Oxide reduction during sintering leads to a significant release of oxygen. This oxygen can react with carbon to form gaseous species such as CO . These gases can be released during the second stage of sintering, that is, when the porosity is still open, but they can be trapped in the closing pores during the final stage of sintering. This causes the pressure to increase in the pores, resulting in irreversible swelling, cracking and eventually pellet fracture.