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Titleα-Sialon ceramics synthesised from a clay precursor by carbothermal reduction and nitridation
Publication TypeJournal Article
Year of Publication1998
AuthorsEkström, T., Shen Z.-J., Mackenzie K.J.D., Brown I.W.M., and White G.V.
JournalJournal of Materials Chemistry
Pagination977 - 983
Date Published1998
ISSN09599428 (ISSN)
AbstractSimultaneous carboreduction and nitridation (CRN) of Y2O3 doped SiO2/clay or elemental Si/clay mixes at atmospheric pressure were used to prepare low-cost powders of α-sialon composition. The synthesised products contained crystalline phase mixtures of α- and β-sialon and Y3Si6N11. Subsequent hot pressing of the CRN powders at 1800°C resulted in poorly densified materials from mixtures with low Y2O3, whereas high Y2O3 gave dense ceramics. The addition of SiO2 to the starting mix resulted in ceramics containing substantial amounts of very fine SiC particles distributed in a matrix of β-sialon and glass. Solid state MAS NMR indicates that the crystalline SiC observed by XRD after hot-pressing is also present in an XRD-amorphous form in the prepressed powders, and that hot-pressing causes the Al-N units to become overall more oxygenated, with the conversion of β-sialon to α-sialon and the formation of small amounts of polytypoid sialons. The hardness, HV10, and fracture toughness, K1C, of the densified materials were ca. 18 GPa and 3 MPa m1/2, respectively. The use of elemental Si produced less SiC, the major phase in these ceramics being α-sialon and a residual glassy phase observable by electron microscopy. The hardness and toughness of these densified materials was ca. 20 GPa and 3 MPa m1/2, respectively.

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