Transformation of Ba-Al-Si precursors to celsian by high-temperature oxidation and annealing

Journal Article · Wed Feb 01 04:00:00 EST 1995 · Metallurgical Transactions, B (Process Metallurgy); (United States)

DOI:https://doi.org/10.1007/BF02648986· OSTI ID:6545648

Schmutzler, H J; Sandhage, K H ^[1]

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1. Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering

Celsian (monoclinic BaO [center dot] Al[sub 2]O[sub 3] [center dot] 2SiO[sub 2]) is being considered as a matrix material for ceramic composites used in high-temperature structural applications. The present article describes the synthesis of celsian by the oxidation and annealing of solid, malleable, metallic Ba-Al-Si precursors. The phase and microstructural evolution after various stages of oxidation at 300 C to 1,260 C in pure oxygen at 1 atm pressure have been examined by X-ray diffraction (XRD) and electron microprobe analyses (EPMA). Barium peroxide, BaO[sub 2], formed rapidly during oxidation at 300 C, with aluminum and silicon remaining largely as unoxidized particles in a BaO[sub 2] matrix. Between 300 C and 500 C, barium orthosilicate, Ba[sub 2]SiO[sub 4], formed by a solid-state reaction between barium peroxide and unoxidized silicon. Further exposure to temperatures between 500 C and 1,200 C resulted 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 [center dot] Al[sub 2]O[sub 3] [center dot] 2SiO[sub 2]). Celsian was then obtained by further exposure to peak temperatures [le] 1,260 C.

• OSTI ID: 6545648
• Journal Information: Metallurgical Transactions, B (Process Metallurgy); (United States), Journal Name: Metallurgical Transactions, B (Process Metallurgy); (United States) Vol. 26:1; ISSN MTTBCR; ISSN 0360-2141
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201* -- Ceramics
Cermets
& Refractories-- Preparation & Fabrication
360202 -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
CHEMICAL REACTION KINETICS
HEAT TREATMENTS
KINETICS
MICROSTRUCTURE
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
REACTION KINETICS
SILICON COMPOUNDS
SILICON OXIDES
SYNTHESIS