Hj. Schmutzler et Kh. Sandhage, TRANSFORMATION OF BA-AL-SI PRECURSORS TO CELSIAN BY HIGH-TEMPERATURE OXIDATION AND ANNEALING, Metallurgical and materials transactions. B, Process metallurgy and materials processing science, 26(1), 1995, pp. 135-148
Citations number
56
Categorie Soggetti
Material Science","Metallurgy & Metallurigical Engineering
Celsian (monoclinic BaO.Al2O3.2SiO(2)) is being considered as a matrix
material for ceramic composites used in high-temperature structural a
pplications. The present article describes the synthesis of celsian by
the oxidation and annealing of solid, malleable, metallic Ba-Al-Si pr
ecursors. The phase and microstructural evolution after various stages
of oxidation at 300 degrees C to 1260 degrees C in pure oxygen at 1 a
tm pressure have been examined by X-ray diffraction (XRD) and electron
microprobe analyses (EPMA). Barium peroxide, BaO2, formed rapidly dur
ing oxidation at 300 degrees C, with aluminum and silicon remaining la
rgely as unoxidized particles in a BaO2 matrix. Between 300 degrees C
and 500 degrees C, barium orthosilicate, Ba2SiO4, formed by a solid-st
ate reaction between barium peroxide and unoxidized silicon. Further e
xposure to temperatures between 500 degrees C and 1300 degrees C resul
ted in the oxidation of aluminum and of residual silicon. The oxidized
silicon reacted with the barium orthosilicate matrix to yield higher
silica-containing barium silicates that, in turn, reacted with alumina
or mullite to form metastable hexacelsian (hexagonal BaO.Al2O3.2SiO(2
)). Celsian was then obtained by further exposure to peak temperatures
less than or equal to 1260 degrees C.