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Synthesis of BaAl 2 Si 2 O 8 from Solid Ba‐Al‐Al 2 O 3 ‐SiO 2 Precursors: II, TEM Analyses of Phase Evolution
Author(s) -
Zhang XiaoDong,
Sandhage Kenneth H.,
Fraser Hamish L.
Publication year - 1998
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.1151-2916.1998.tb02724.x
Subject(s) - materials science , amorphous solid , analytical chemistry (journal) , annealing (glass) , cristobalite , transmission electron microscopy , silicon , phase (matter) , mineralogy , crystallography , chemistry , metallurgy , nanotechnology , quartz , organic chemistry , chromatography
Conventional transmission electron microscopy (TEM), coupled with energy‐dispersive X‐ray (EDX) analysis, has been used to examine the intermediate phases produced during the transformation of Ba‐Al‐alpha‐Al 2 O 3 ‐SiO 2 (cristobalite) precursors into celsian, BaAl 2 Si 2 O 8 . Analyses were conducted on samples that had been exposed to pure, flowing oxygen at peak temperatures of 300°C for 24 h, 650°C for 72 h, or 900°C for 24 h. Particles of Al 2 O 3 retained after the 300‐900°C heat treatments were coated with a layer of BaAl 2 O 4 . An amorphous, alumina‐poor Ba‐Al‐Si‐O (G1) phase was observed in contact with residual SiO 2 particles after the 650°C heat treatment. Although not a starting component of the precursor, elemental silicon was also detected after the 300‐900°C heat treatments. Silicon particles produced during the 300°C heat treatment were surrounded by an amorphous Ba‐Al‐Si‐O (G2) phase that contained more alumina than the G1 phase. Fine‐grained barium orthosilicate (Ba 2 SiO 4 ) and sanbornite (BaSi 2 O 5 ) were observed after the 650°C treatment, along with thin, plate‐shaped grains of BaAl 2 Si 2 O 8 . The latter two phases were surrounded by an amorphous Ba‐Al‐Si‐O (G3) phase that possessed less alumina than the G2 phase. Smaller platelets of BaAl 2 Si 2 O 8 were also detected after the 300°C treatment. After annealing at a peak temperature of 1650°C, BaAl 2 Si 2 O 8 was the only silicate compound detected by TEM. Novel reaction paths to BaAl 2 Si 2 O 8 , which are consistent with the present TEM observations and prior XRD and SEM/EDX analyses (Part I), are discussed.