Stable and metastable equilibria in the system SiO2-Al2O3

Journal Article · Wed Jan 01 04:00:00 EST 1975 · J. Am. Ceram. Soc.; (United States)

DOI:https://doi.org/10.1111/j.1151-2916.1975.tb18770.x· OSTI ID:7296233

Aksay, I A; Pask, J A

Concentration profiles of Al/sub 2/O/sub 3/ in diffusion couples made from sapphire and fused silica were used to determine the stable equilibrium phase diagram of the system SiO/sub 2/--Al/sub 2/O/sub 3/. The intermediate compound mullite, 3Al/sub 2/O/sub 3/.2SiO/sub 2/, melts incongruently at 1828 +- 10/sup 0/C; its stable solid-solution region ranges from 70.5 to 74.0 wt percent Al/sub 2/O/sub 3/ below 1753/sup 0/C and from 71.6 to 74.0 wt percent at 1813/sup 0/C. The microstructures of diffusion zones and heat-treated specimens also indicate the incongruency of mullite. Additional information is given for 3 metastable systems: SiO/sub 2/-Al/sub 2/O/sub 3/ in the absence of mullite, SiO/sub 2/-ordered-mullite in the absence of alumina, and SiO/sub 2/-disordered mullite in the absence of alumina. Under metastable conditions, ordered mullite melts congruently at approximately 1880/sup 0/C and its solid-solution range extends up to approximately 77 wt percent Al/sub 2/O/sub 3/. The solid-solution range of disordered mullite extends to approximately equal to 83 wt percent Al/sub 2/O/sub 3/ with an estimated congruent melting temperature of approximately 1900/sup 0/C. The existence of metastable systems is associated with superheating of mullite above the incongruent melting temperature and with nucleation of alumina and mullite in supercooled aluminum-silicate liquids. (auth)

• Research Organization: Lawrence Berkeley Lab., CA
• OSTI ID: 7296233
• Report Number(s): LBL-2747
• Journal Information: J. Am. Ceram. Soc.; (United States), Journal Name: J. Am. Ceram. Soc.; (United States) Vol. 58:11-12; ISSN JACTA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
BINARY MIXTURES
CHALCOGENIDES
CORUNDUM
DIAGRAMS
DIFFUSION
DISPERSIONS
EQUILIBRIUM
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MINERALS
MIXTURES
MULLITE
ORDER PARAMETERS
OXIDES
OXYGEN COMPOUNDS
PHASE DIAGRAMS
SAPPHIRE
SILICON COMPOUNDS
SILICON OXIDES
SOLID SOLUTIONS
SOLUTIONS
VERY HIGH TEMPERATURE