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Fabrication and Secondary‐Phase Crystallization of Rare‐Earth Disilicate–Silicon Nitride Ceramics
Author(s) -
Cinibulk Michael K.,
Thomas Gareth,
Johnson Sylvia M.
Publication year - 1992
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/j.1151-2916.1992.tb04462.x
Subject(s) - devitrification , materials science , crystallization , microstructure , nucleation , phase (matter) , chemical engineering , amorphous solid , ceramic , intergranular corrosion , mineralogy , metallurgy , crystallography , chemistry , organic chemistry , engineering
The fabrication and intergranular‐phase devitrification of silicon nitride densified with rare‐earth (RE) oxide additives has been investigated. The additions of the oxides of Sm, Gd, Dy, Er, and Yb, having high melting points and behaving similarly to Y 2 O 3 , were compositionally controlled to tailor a microstructure with a crystalline secondary phase of RE 2 Si 2 O 7 . The lanthanide oxides were found to be as effective as Y 2 O 3 in densifying Si 3 N 4 , resulting in identical microstructures and densities of 98–99% of theoretical density. The crystallization behavior of all six disilicates was similar, characterized by a limited nucleation and rapid growth mechanism resulting in large single crystals. Complete crystallization of the intergranular phase was obtained with the exception of a thin residual amorphous film which was observed at interfaces and believed to be rich in impurities, the cause of incomplete devitrification.