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TitleAdditives to promote the nitridation and sintering of a sialon composite
Publication TypeJournal Article
Year of Publication2011
AuthorsCalloch, P., White V., Ryan M., Brown I.W.M., and MacKenzie K.
JournalJournal of the Australian Ceramic Society
Pagination74 - 81
Date Published2011
ISSN0004881X (ISSN)
KeywordsBoron, Boron nitride, Calcium, Calcium aluminate cement, Calcium oxides, Cement additives, Ceramic structure, Firing temperature, Fracture, Fracture toughness, Gibbsites, Hydrated lime, MAS NMR, nitridation, Phase diagrams, Rate of reaction, Raw materials, Reaction bonding, Resistance to thermal shock, Silicate minerals, Sintered alumina, Sintering, Sintering Aid, Specific effects, Target composition, Thermal shock, Thermal shock resistance, Thermogravimetric analysis, Titanium, Titanium nitride, Titanium oxides, yttrium, Yttrium aluminium garnet, Zirconium
AbstractMixtures of silicon (which converts to Si3N4) and alumina (Al 2O 3) were heated in nitrogen to prepare a composite sialon body. The effect of a range of nitridation additives designed to improve the yield and the rate of reaction have been explored, together with a range of sintering aids. The additives included are oxides of calcium, titanium, zirconium, iron, a refractory cement, gibbsite raw material to replace alumina and boron nitride. The nitridation and sintering were performed separately to assess the specific effects of each additive. Thermogravimetric analysis informed the choice of nitridation and sintering firing temperatures. The nitridation firings at 1400°C formed mainly β-sialon with minor amounts of O-sialon, mullite, corundum and other sialon phases. After sintering (typically at 1600°C), all the samples contained β-sialon and X-phase as predicted from the position of the target composition on the sialon phase diagram. The samples with calcium hydroxide or calcium aluminate cement exhibited the best porosity and density. The fracture toughness improved uniformly with BN addition up to a maximum of 4.2 MPa.m -1/2 but did not improve the resistance to thermal shock of the sialon composite. 11B MAS NMR studies show that the BN remains unreacted in the fired ceramic structure.

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