Investigation of the Reaction between Fe 2 0 3 and Si Activated by Ball Milling Giorgio Concas 3 , Francesco Congiu 3 , Anna Corrias b , Carlo Muntoni 3 , Giorgio Paschina b , and Daniela Zedda b a Dipartimento di Scienze Fisiche, University di Cagliari and Istituto Nazionale di Fisica della Materia, Via Ospedale 72, 1-09124 Cagliari, Italy. b Dipartimento di Scienze Chimiche, Universitä di Cagliari, Via Ospedale 72, 1-09124 Cagliari, Italy. Z. Naturforsch. 51a, 915-922 (1996); received April 1, 1996 The path of the reaction between Fe 2 0 3 and Si, activated by high energy ball milling, has been investigated by X-ray diffraction and Mössbauer spectroscopy. Hematite reduction involves oxygen transfer from Fe to Si with the formation of intermediate phases containing Fe(II), which are then reduced to Fe(0). A steady state is reached in the milling process where the reduction of stoichiomet- ric amounts of Fe 2 0 3 and Si is not complete and an amount of Fe(II) in an amorphous matrix still remains. The same intermediate compounds are also observed in the milling process of mixtures with higher Fe 2 0 3 /Si molar ratio. Key words: Mechanosynthesis, Nanocomposite, Reduction reaction, Mössbauer spectroscopy, X-ray diffraction. Introduction In the field of composite materials, nanocomposites consisting of metal particles embedded in either an insulating matrix or an immiscible metallic matrix have recently found much interest [1-6] because of their peculiar electric, magnetic and catalytic proper- ties [1, 2, 7-10], Several methods are suitable for the preparation of these materials [2, 4]; among them high energy ball milling seems to be a particularly versatile method [11-19], T h i s technique can be applied to the prepara- tion of nanocomposites, either through an intimate mixing of the metal and matrix component [11 -13] or through the activation of solid state reactions, in which the nanocomposite is the final product [14-19], The most extensively experimented solid state reac- tions are those involving oxygen transfer from metal oxides to aluminium [15, 16, 18], Also Mg, Zn, Fe, B, and Si have been used as oxygen acceptors [14, 15, 17-19], The complete transfer of oxygen is not always pos- sible; in this case a steady state is reached in which the desired products are accompanied by by-products. It is therefore of interest to study the reaction path in Reprint requests to Prof. Giorgio Paschina, Fax +39 70 66 92 72. such systems in order to fully exploit the capabilities of this preparation method. The aim of this work is to investigate the intermedi- ate phases and final products of the reaction between Fe 2 0 3 and Si by means of X-ray diffraction and Mössbauer spectroscopy. 1. Experimental Procedure Three mixtures of Si (Fluka 99.9%) and Fe 2 0 3 (Carlo Erba 99%) powders were milled in a Fritsch Pulverisette 5 planetary ball mill. The weight of the reagents was adjusted according to the following Fe 2 0 3 /Si molar ratios: 2 Fe 2 0 3 /3 Si, 4Fe 2 0 3 /3Si, 12Fe 2 0 3 /3Si, where the first molar ratio corresponds to the com- plete exchange reaction stoichiometry. The metal volume fractions in the samples, calcu- lated considering a complete reduction of Fe 2 0 3 to Fe, are 26%, 41% and 68%, respectively; the samples will be hereafter referred to as 26 F, 41 F, and 68 F; the suffix xh, where x indicates the milling hours, will be used when required. 20 grams of each mixture were sealed in a 250 ml stainless steel vial with balls of the same material (di- ameter 8 mm) in argon atmosphere. Full/void volume 0932-0784 / 96 / 0700-927 $ 06.00 © - Verlag der Zeitschrift für Naturforschung, D-72072 Tübingen