Iron-silica and nickel-silica nanocomposites prepared by high energy ball milling
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Iron-silica and nickel-silica nanocomposites prepared by high energy ball milling Anna Corrias,a) Guido Ennas, Anna Musinu, Giorgio Paschina, and Daniela Zedda Dipartimento di Scienze Chimiche, Universit`a di Cagliari, Via Ospedale 72, 09124 Cagliari, Italy (Received 28 April 1996; accepted 23 June 1997)
Metal-silica nanocomposites with different metal volume fractions have been prepared via solid state exchange reactions induced by ball milling followed by a reduction treatment in H2 flux. In nickel-containing mixtures oxygen transfers directly from NiO to Si while NiO is reduced to Ni. When NiO is present in a large ratio, its excess can be reduced by a thermal treatment in H2 flux. Nickel crystallites are obtained with nanometer size in the milling process and there is no significant growth during thermal treatment. Similar process conditions applied to Fe-containing mixtures give rise to a more complex reaction path which prevents the complete conversion of Fe(III) to Fe. Nickel-silica and iron-silica nanocomposites are also produced by ball milling mixtures of either nickel or iron with amorphous silica. I. INTRODUCTION
Ball milling techniques have been shown to be suitable for preparing a large variety of powdered systems through solid state reactions.1,2 Repeated fracture and cold welding of powder particles can give rise to an intimate mixing at atomic level which promotes interdiffusion of the starting components, which is an essential condition for the reaction to take place. Ball milling has been largely applied to obtain amorphous and nanocrystalline alloys starting from elemental components.1,2 More recently it has been applied to the preparation of nanocomposite powders constituted of metal particles of nanometer dimension embedded in a nonmetallic medium, through displacement reactions such as Mx Oy 1 zR ! xM 1 Rz Oy .3–8 Some authors have also prepared the same products by milling M and Rz Oy powder mixtures.9–11 Nanocomposite materials can also be prepared by other techniques, such as deposition methods, sol-gel process, impregnation, reduction, etc.12–14 They display a rich variety of interesting chemical and physical properties which, besides reaping benefits from individual components, can be enhanced by controlling particle size and metal volume fraction x.12,15–18 So far, ball milling has been mostly applied to produce metal-alumina nanocomposites through solid state reactions between aluminum and metal oxides;4,5,7,19 silicon has been less frequently used as an oxygen acceptor.4 On the other hand, metal-silica nanocomposites have attracted much attention because of their magnetic, electric, and catalytic properties.15–18 We will report herewith the results of the ball milling preparation of a series of nickel-silica and iron-silica a)
Author to whom correspondence should be addressed. e-mail: [email protected]. J. Mater. Res., Vol. 12, No. 10, Oct 1997
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