ISSN:
1551-2916
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
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-Al2O3-SiO2 (cristobalite) precursors into celsian, BaAl2Si2O8. 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 Al2O3 retained after the 300-900°C heat treatments were coated with a layer of BaAl2O4. An amorphous, alumina-poor Ba-Al-Si-O (G1) phase was observed in contact with residual SiO2 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 (Ba2SiO4) and sanbornite (BaSi2O5) were observed after the 650°C treatment, along with thin, plate-shaped grains of BaAl2Si2O8. 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 BaAl2Si2O8 were also detected after the 300°C treatment. After annealing at a peak temperature of 1650°C, BaAl2Si2O8 was the only silicate compound detected by TEM. Novel reaction paths to BaAl2Si2O8, which are consistent with the present TEM observations and prior XRD and SEM/EDX analyses (Part I), are discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1151-2916.1998.tb02724.x
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