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TitleThe Formation of Mullite from Kaolinite under Various Reaction Atmospheres
Publication TypeJournal Article
Year of Publication1996
AuthorsMackenzie, K.J.D., Meinhold R.H., Brown I.W.M., and White G.V.
JournalJournal of the European Ceramic Society
Issue2 SPEC. ISS.
Pagination115 - 119
Date Published1996
ISSN09552219 (ISSN)
AbstractIn addition to its importance as a high-technology ceramic, mullite is also an intermediate phase in the formation of non-oxide ceramics (sialons) by carbothermal reduction of clay minerals. This reaction involved the formation of mullite under non-oxidizing atmospheres and in the presence of carbon. The effect of eight different reaction atmospheres on mullite formation from kaolinite in the presence and absence of carbon was studied by X-ray diffraction, 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Generally, a greater amount of mullite is formed at 1200°C under vacuum and reducing atmospheres, which also produce mullites that are slightly more silica-rich (as deduced from X-ray lattice parameter measurements) but contain higher proportions of tetrahedral 27Al NMR resonance at ≈ 46 ppm, probably associated with Al* sites. Reaction systems containing either nitrogen or ammonia in the presence of carbon show NMR evidence of previously unreported early stage formation of Si-O-N bonds. Thermodynamic calculations are presented which suggest that the formation of SiO is an important factor in the complex interactions between the various solid and gaseous reactants.

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