Reaction-bonded mullite/zirconia composites
- CSIRO, Clayton, Victoria (Australia). Div. of Materials Science and Technology
- Technische Univ. Hamburg-Harburg, Hamburg (Germany). Advanced Ceramics Group
The feasibility of fabricating dense, low-shrinkage, mullite/ZrO{sub 2} composites based on the reaction bonding of alumina (RBAO) process and the reaction sintering of zircon is examined. Compacts pressed from an attrition-milled powder mixture of Al, Al{sub 2}O{sub 3} and zircon were heated in air according to a two-step heating cycle. The phase evolution and microstructural development during reaction bonding were traced by X-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy on samples extracted from various points along the heating cycle. It is seen that, as in conventional RBAO, Al oxidizes to {gamma}-Al{sub 2}O{sub 3} which then transforms to {alpha}-Al{sub 2}O{sub 3} between 1,100 and 1,200 C. The zircon dissociation commences at {approximately} 1,400 C and is practically complete by 1,500 C. Mullite enriched in Al{sub 2}O{sub 3} forms initially, but 3:2 stoichiometry is attained in the final product which consists of mullite, t- and m-ZrO{sub 2}, and residual {alpha}-Al{sub 2}O{sub 3}. The flexure strength of the composite is superior to that of pure mullite, and {approximately} 80% of the strength is retained up to 1,200 C. Although there was no toughness enhancement relative to mullite, this should be achievable by optimizing the fabrication procedure.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 203555
- Journal Information:
- Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 1 Vol. 79; ISSN 0002-7820; ISSN JACTAW
- Country of Publication:
- United States
- Language:
- English
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