SYNTHESIS OF A CERAMIC COMPOSITE MATERIAL: SiC-(W,Mo)Si 2 P.Pujalte, F.J.Narciso-Romero, R.Arpón, F.Coloma, A.Sepúlveda-Escribano, and F.Rodríguez-Reinoso. Departamento de Química Inorgánica, Universidad de Alicante. Apdo. 99. E-03080, Alicante (SPAIN) SUMMARY: The presence of residual silicon in RBSC pieces reduces their mechanical properties at temperatures higher than 1300 ºC (mp of Si = 1410 ºC). This work presents the study of the substitution of silicon by a refractory silicide (W,MoSi 2 ). The preparation variables have been the carbon source (activated carbon, graphite and coke), the particle size and the experimental conditions used. The best results were obtained when a coke of small particle size was used; in this case, even the preparation of pieces of only SiC-Coke (without using of silicide precursor) with no residual silicon was possible. The use of silicide precursor in the preforms allows the synthesis of SiC-(WMo)Si 2 pieces that have no residual silicon. In all cases the mechanical properties of pieces are enhanced when silicon is replaced by silicide. KEYWORDS: Reactive Infiltration, SiC, WSi 2 , MoSi 2 , Composites INTRODUCTION In recent years, there has been an increasing demand for high performance ceramics and composite materials for high temperature aerospace applications. A number of these applications require materials with high strength and toughness, oxidation resistance, and high thermal conductivity at temperatures approaching 1400°C. Among several options, silicon carbide, silicon nitride and SiAlON are the most attractive materials because of their low density, combined with good mechanical properties and chemical stability at high temperatures [1-12]. Reaction-bonded silicon carbides (RBSC) are fully dense engineering ceramics formed by the bonding together of silicon carbide powders with further silicon carbide produced in situ by a chemical reaction between silicon and carbon. Fabrication of RBSC involves the forming of a compact of silicon carbide, graphite and a polymeric binder by various standard polymer forming routes such as extrusion and pressing. The compact is then heated in air to remove the binder and the resulting porous compact is infiltrated with liquid silicon. The silicon raises through the porous material by capillary action, reacting with the graphite to form new silicon carbide which "bonds" the material together [13]. The final material consists of a matrix of SiC, with 10 to 55% silicon occupying the residual pore space. The presence of Si drastically reduces the mechanical properties of RBSC materials at temperatures higher than 1300°C (mp of Si = 1410°C). In addition, there are other critical issues in the fabrication of silicon carbide based ceramics which are mainly related to the fabrication of complex shapes, processing time, and temperature. A combination of these factors is the responsible for the high manufacturing cost of the final components [14].