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An aqueous gelcasting route to dense β-Si4Al 2O2N6-0.5SiO2 ceramics
I. Ganesh, N. Thiyagarajan, D.C. Jana, P. Barik,
Published in
Volume: 91
Issue: 5
Pages: 1566 - 1571
Aqueous particulate slurries containing 45-50 vol% α-Si 3N4, α-Al2O3, and Y 2O3 powder mixtures were gelcast and sintered for 2-4 h at 1675°-1800°C to obtain dense β-Si4Al2O 2N6-0.5SiO2 ceramics. For comparison, dense ceramics of the same composition, together with a stoichiometric β-Si 4Al2O2N6, were also prepared following a conventional dry-powder pressing route. The sintered materials were thoroughly characterized for bulk density, apparent porosity, water-absorption capacity, X-ray diffraction phase, microstructure, hardness, fracture toughness, coefficient of thermal expansion (CTE), and dielectric constant at 16-18 GHz frequency. The characterization results suggest that the sintered properties of β-Si4Al2O2N6-0.5SiO 2 are little influenced by the processing route, and the in situ generated SiO2 was found to reduce the CTE and dielectric constant of β-Si4Al2O2N6 considerably. An aqueous particulate slurry containing a 48 vol% β-Si4Al 2O2N6-0.5SiO2 precursor mixture was successfully gelcast in an indigenously designed and fabricated aluminum mold to fabricate defect-free crucibles of 500 mL volume. The gelcast β-Si 4Al2O2N6-0.5SiO2 obtained from a slurry containing 48 vol% solids exhibited a bulk density of 3.13 g/cm3, a β-SiAlON phase of ∼90%, a CTE of 3.197 × 10-6 °C-1 (between 30° and 1000°C), a fracture toughness of ∼3.42 MPa·m1/2, a three-point bend strength of ∼199 MPa, and a dielectric constant of ∼6.32 at 17 GHz frequency after sintering for 4 h at 1750°C with 7 wt% Y2O3. © 2008 The American Ceramic Society.
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JournalJournal of the American Ceramic Society