Ph Colomban, M. We association with a primary matrix made of infil- with the same kind of fibre(Novoltex" from SEP, trated alumina powder. Le hailan, 33165 Saint Medard en Jalles, france). The idea of using liquid ceramic precursors for This linkage is obtained by passing fibre thread the consolidation of a fibre preform originates fro through the sheets to form stitches. The fibre vol the processing route used for C/C composites ume fraction is -28%. The fibre diameter ranges (infiltration of pitch or of phenolic resin). Similar between 7 and 10 um. The 8-mm thick preform is routes have been tested for the preparation of Sic cut to form a 40 mm X 120 mm plate matrix composite using polysilane precursors. .8 Preparation of composite materials by infiltration 2.2 Powder and slurry of oxide porous bodies with organic metallic A submicron powder (AKP50 from Sumitomo) reagents has been recently discussed by Honeyman- consisting of spherical, well-crystallized a-alumina Calvin and Lange, but the case of oxide matrix particles, of mean diameter 0- 1-0-3 um and 3D fibre reinforced bodies has not been consid- specific area 10 m"g, is used as the matrix starting ered except for the experimental details given material. A 300 g/litre alumina slurry is prepared our patent. by dispersion in water with addition of nitric acid (pH=4), with the help of mechanical and ultra sonic stirring for 1 h. Aggregates larger than 2 Experimental Procedure 0.6 um are eliminated by overnight sedimentation Figure 1 shows a schematic of the two-step infil- Ultrasonic mixing is carried out for 15 min just tration process. The first step(stages 1 and 2)con- before use. The aggregate size distribution is sists in the preparation of a powder compact checked using a HORIBA CAPA 700 size analyser within the fibre preform by slip-cast infiltration (stage 1), the specimen being dried and the 2.3 Monoliths and composites strengthened by heating(stage 2). The second step The slurry is slip-cast under 2 MPa air pressure consists in the infiltration of the strengthened through the fibre preform plate using the tech- body with a liquid precursor(stage 3) that is nique previously described by Jamet et al converted into a gel by reaction with water (or A filter paper under the preform plate is used to diols)(stage 4) and then into a refractory phase retain the thinner particles inside the preform during pyrolysis(stage 2). The second step can be (Fig. 1). a drilled aluminium plate acts as a repeated many times mechanical support. Nevertheless, some of the first particles with mean diameter below 0-05 2.1 3D preform are not retained in the preform. a vacuum The carbon fibre preform consists of sheets of felted applied under the filter paper support to promote fibres which are sewn along the third dimension rapid slip-casting (<2 h). Then, the infiltrated 3 R江BE分587 TED IMMERSION Alkoxide(s) 2 PYROLYSS 2MPa Aluminum support 1000°C 3-10 Cycles 10m日 3D FIBER PREFORM Fig. 1. Flow diagram of two-step infiltration process, first using a pressure-assisted slip-casting infiltration device and second by in situ hydrolysis-polycondensation of a specihc interphase precursor.1476 Ph. Colomban, M. Wey association with a primary matrix made of infil￾trated alumina powder. The idea of using liquid ceramic precursors for the consolidation of a fibre preform originates from the processing route used for C/C composites (infiltration of pitch or of phenolic resin). Similar routes have been tested for the preparation of Sic matrix composite using polysilane precursors.7,8 Preparation of composite materials by infiltration of oxide porous bodies with organic metallic reagents has been recently discussed by Honeyman￾Calvin and Lange, 9 but the case of oxide matrix 3D fibre reinforced bodies has not been consid￾ered except for the experimental details given in our patent.‘O 2 Experimental Procedure Figure 1 shows a schematic of the two-step infil￾tration process. The first step (stages 1 and 2) con￾sists in the preparation of a powder compact within the fibre preform by slip-cast infiltration (stage l), the specimen being dried and then strengthened by heating (stage 2). The second step consists in the infiltration of the strengthened body with a liquid precursor (stage 3) that is converted into a gel by reaction with water (or diols) (stage 4) and then into a refractory phase during pyrolysis (stage 2). The second step can be repeated many times. 2.1 3D preform The carbon fibre preform consists of sheets of felted fibres which are sewn along the third dimension, 1 PRESSUREASSISTED m.TRA TION with the same kind of fibre (Novoltex@ from SEP, Le Haillan, 33165 Saint Medard en Jalles, France). This linkage is obtained by passing fibre thread through the sheets to form stitches. The fibre vol￾ume fraction is -28%. The fibre diameter ranges between 7 and 10 pm. The &mm thick preform is cut to form a 40 mm X 120 mm plate. 2.2 Powder and slurry A submicron powder (AKPSO from Sumitomo) consisting of spherical, well-crystallized a-alumina particles, of mean diameter 0.1-0.3 pm and specific area 10 m2/g, is used as the matrix starting material. A 300 g/litre alumina slurry is prepared by dispersion in water with addition of nitric acid (pH = 4), with the help of mechanical and ultra￾sonic stirring for 1 h. Aggregates larger than 0.6 pm are eliminated by overnight sedimentation. Ultrasonic mixing is carried out for 15 min just before use. The aggregate size distribution is checked using a HORIBA CAPA 700 size analyser. 2.3 Monoliths and composites The slurry is slip-cast under 2 MPa air pressure through the fibre preform plate using the tech￾nique previously described by Jamet et al.” A filter paper under the preform plate is used to retain the thinner particles inside the preform (Fig. 1). A drilled aluminium plate acts as a mechanical support. Nevertheless, some of the first particles with mean diameter below 0.05 pm are not retained in the preform. A vacuum is applied under the filter paper support to promote rapid slip-casting (~2 h). Then, the infiltrated 3 MMZRSION Akoxide (s) Gaz 2MPa +G __. ,., 1 [Filter _,.__” 3-N Cycles l~m$lAzkktY 3D FIBERPREFORM HYDROLYSIS￾POLYCONDElVSATION Fig. 1. Flow diagram of two-step infiltration process, first using a pressure-assisted slip-casting infiltration device and second by in situ hydrolysis-polycondensation of a specific interphase precursor