Fabrication of TiB 2 and TiB 2 /FeB composites by mechanically activated borothermic reduction of ilmenite
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Fabrication of TiB2 and TiB2yFeB composites by mechanically activated borothermic reduction of ilmenite P. Milleta) Department of Applied Mathematics and Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia
T. Hwang Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia (Received 8 December 1994; accepted 4 January 1996)
TiB2 and TiB2yFeB composites have been formed at temperatures below 1000 ±C, directly from ilmenite sand by reaction with amorphous boron. The structural transformations occurring during high-energy mechanical milling pretreatment and subsequent annealing of different mixtures of the constituents have been studied. On heating at temperature below 800 ±C, complete borothermic reduction of the ilmenite structure is accomplished. The mixture so obtained with an ilmenite-boron ratio equal to 1y6 undergoes a sequence of reactions on further heating to form TiB2 , FeB, and the amorphous phase B2 O2 .
I. INTRODUCTION
The synthesis and the study of the properties of existing and new composites are currently the topics of intense research worldwide. The development of new processing routes with the ultimate goal of improving material properties at lower cost is the major driving force. The ability to produce composites starting directly from mineral sands presents one alternative, for by reducing the number of steps involved in composite production, costs should be significantly decreased. Such an approach is not new, but only a few experiments have been performed. For example, an iron based Ti(O, C) metal matrix composite can be formed by carbothermic reduction of ilmenite.1 Also, a zirconium diboride can be formed by a self-propagating high-temperature reaction of B6 Si with zircon sand (ZrSiO4 ).2 The use of highly energetic ball milling during mineral processing to induce solid-state reactions or to increase the reactivity of the milled powder, so-called mechanical activation, has proved to be an efficient process for a number of applications.3,4 More recently we have shown that it was possible to extract TiO2 by leaching the milled product obtained from mechanochemical treatment of ilmenite sand assisted by surface active agents.5 The positive influence of a mechanochemical treatment on the borothermic reduction of titania, to produce a)
Author to whom correspondence should be addressed. Present address: Centre d’Elaboration de Matiriaux et d’Etudes Structurales, CNRS, B.P. 4347, 29 rue Jeanne Marvig, 31055 Toulouse Cedex, France. J. Mater. Res., Vol. 11, No. 4, Apr 1996
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TiB2 at temperatures below 1100 ±C,6 suggests the possibility of similar treatment in the case of ilmenite sands which constitute the natural major source of titanium dioxide. In this work, we report the preparation of T
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