α′-Sialon ceramics

• DOI: 10.1038/274880a0
• Publication Date: 2005-08-02T14:09:18Z
• Authors: S. HAMPSHIRE; H. K. PARK; D. P. THOMPSON; K. H. JACK
• Keywords: Sialon

OUR previous report1 on Si–Al–O–N ceramics stated that expanded α-silicon ‘nitride’ structures had been obtained by reaction of lithium–silicon nitride, LiSi2N3, with alumina. The unit-cell dimensions of one example (a, 7.822; c, 5.677A) gave a cell volume about 3% greater than that of α-silicon nitride. Subsequent work2 showed a variation in dimensions for the α′-lithium sialon when lithium aluminate, LiAlO2, was reacted in different proportions with Si3N4. However, other phases, such as β′-sialon and nitrogen–eucryptite, were always present and the product never contained more than ∼30% of the α′ material. αν-Sialons were also found in the Mg–Si–Al–O–N system3 but again never pure, and were observed by Masaki et al.4 during the nitriding of silicon with A1N and A12O3 additions. A recent claim by Mitomo5 of α′ solid solutions of Si3N4–Al2O3 and/or Si3N4–Y2O3 occurring during the sintering of Si3N4 at 1,700–1,800 °C with Al2O3–Y2O3 mixtures prompted this report of the preparation and characterisation of pure α′-phases in M–Si–Al–O–N systems where M is Li, Ca or Y. Such phases also occur, but have not so far been prepared in a pure form, in magnesium and other sialon systems.