ISSN 0004-881X

Effect of Fluoride And Oxide Additives On The Phase Transformations In Alumina/Clay Ceramics

by N. Tezuka ^1*, I. M. Low ¹, I. J. Davies ², I. D. Alecu ³, R. J. Stead ³, E. G. Mehrtens ⁴ and B. A. Latella ⁴

1) Department of Applied Physics, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia
2) Department of Mechanical Engineering, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia
3) Rojan Advanced Ceramics Pty Ltd., PO Box 7126, Spearwood, WA 6163, Australia
4) Institute of Materials and Engineering Science, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234, Australia

Abstract

The effects of various types of fluorides (calcium fluoride (CaF₂), sodium fluoride (NaF) and potassium fluoride (KF)) on physical and mechanical properties, and oxides (titanium dioxide (TiO₂) and ferric oxide (Fe₂O₃)) on mullitization, in alumina/clay ceramics were investigated. Two different types of kaolin clays (Al₂Si₂O₅(OH)₄), i.e., kaolinite and halloysite, were utilised, although kaolinite mixed with the fluoride additives was dehydroxylated in advance. The fluorides generally improved sinterability of the alumina/kaolinite ceramics at temperatures approaching 1300 degC due to liquid phase sintering, but higher sintering temperatures and excess amounts of fluorides reduced the properties due to the presence of sealed porosity and glassy phases. The oxide-containing sintered samples were quantitatively analysed by X-ray diffraction (XRD) with an internal standard using the Rietveld method. The major phase was found to be mullite with the Fe³⁺ ions tending to incorporate into the mullite structure more than that of the Ti⁴⁺.

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