Materials Science and Engineering A284 (2000) 301 – 306 Enhancement of self-sustaining reaction Cu 3 Si phase formation starting from mechanically activated powders F. Bernard a, *, H. Souha a,b,c , E. Gaffet b a LRRS, UMR5613 CNRS /Uniersite ´ de Bourgogne, BP47870 F -21078, Dijon cedex, France b UPR 806 CNRS, Groupe ‘Nanomate ´riaux’, Uniersite ´ de Technologie de Belfort -Montbe ´liard, F -90010, Belfort, France c Laboratory of Physical Chemistry, Faculty of Science, Dhar El Mehraz, BP 1716, Fes, Morocco Received 20 July 1999 Abstract Mechanical high-energy ball milling of an 3Cu +Si elemental powders mixture was used to activate a self-sustaining combustion reaction or so-called self-sustaining high-temperature synthesis (SHS) to form the copper silicide phase, a reaction for which the thermodynamic criterion proposed by Munir for self-propagation reaction is not favorable. A complete characterization of the end-products was performed with X-ray diffraction analysis and scanning electron microscopy. Thermal and structural information describing the combustion front initiated by heating up a sample to 180°C in a Cu/Si system is communicated. This paper clearly shows that the mechanically activated self-sustaining high-temperature synthesis process produces a pure Cu 3 Si compound in spite of the limitation imposed by the thermodynamic criterion. In addition, it seems that the reactivity of Cu 3 Si elaborated from the mechanically activated SHS process towards CuCl is greater than the reactivity of Cu 3 Si reference powder. This difference is mainly due to the crystallite size. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Cu 3 Si; Nanostructured materials; Mechanically activated powders; Self-propagating high-temperature synthesis; X-ray diffraction analysis; CuCl www.elsevier.com/locate/msea 1. Introduction Chlorosilanes, which are the starting materials in the production of a variety of silicones, are prepared by a gas-solid reaction between CH 3 Cl and excess silicon in the presence of the alloy Cu 3 Si as catalyst [1–4]. In actual practice a large quantity of silicon is reacted in the solid phase with a small quantity of CuCl (8–10 wt.%) to prepare the contact mass for the main reac- tion. The contact mass consists of silicon and catalytic quantities of Cu 3 Si phase and its selectivity is defined by the ratio CH 3 SiCl 3 /(CH 3 ) 2 SiCl 2 . Most of the re- searchers consider that the formation of Cu 3 Si is achieved by the reaction between Si and CuCl, to give divided Cu and gaseous SiCl 4 , Cu then diffusing into the remaining Si matrix to form Cu 3 Si [5]. In this reaction, the quality of the silicon metal is considered to be one of the most important factors for both the reactivity and the selectivity of in contact mass. The formation of the Cu 3 Si compound has been studied by different methods such as those using solid – solid reac- tions, solid – gas reactions [6,7] or melting environment [8,9]. Nevertheless, due to the complexity of the reac- tional mechanisms and the difficulty to obtain a pure Cu 3 Si compound, another elaboration process using a mechanical treatment has been investigated. Recently a new variation of the self-propagating high-temperature synthesis (called hereafter SHS) pro- cess was proposed by Gaffet and Bernard [10,11] cou- pling a short duration high-energy ball-milling step to a self-sustaining combustion reaction. The so-called MASHS (mechanically activated self-propagating high- temperature synthesis) was applied successfully to pro- duce nanosized intermetallics compounds [12,13]. In addition, the high energy ball milling of Fe +2 Si (at.%) elemental powders mixture was used to activate self-sustaining combustion in the case of iron disilicides synthesis for which, according to Munir [14], the ther- * Corresponding author. Tel.: +33-3-80396125; fax: +33-2- 80396167. E-mail address: fbernard@u-bourgogne.fr (F. Bernard) 0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0921-5093(00)00749-8