K. Konig et al. /Journal of the European Ceramic Society 30 (2010)1131-1137 30 20 SDOSS-treated SiC fibres 60 Fig 3. SEM image of a CNT-coating made on a graphite electrode by EPD Fig. 2. Zeta-pote (28V.5min) Since an appropriate net surface charge of fibres is very impor- tant for efficient electrophoretic infiltration, 42 we also analysed In addition to the appropriate surface charge of the fibres, the ZP of crushed SiC fibres. The ZP vs. pH relationship is good wettability by the suspension is also an important charac presented in Fig. 2. The as-received CNT-suspension is alkaline teristic for the infiltration of the fibre mats. Consequently, we 11), and due to the presence of anionic surfactant, the CNTs decreased the natural wetting angle of the alkaline aqueous sus- are negatively charged (ZP=-45 mV). The natural pH(pH4)of pension at the SiC fibre bundle(80)by pre-treating the fibres the as-received Sic-powder suspension nearly matches the iso- with the surfactant SDoSS, to approximately 300. As show electric point, resulting in a very unstable suspension. Titration in Fig. 2, the zeta-potential of the SDOSS-treated SiC fibres with hydrochloric acid is not efficient at increasing the zeta- negative over a wide range of alkaline pH values. Hence, as pre potential(described elsewhere); conversely, titration of the sented, the pre-treated SiC fibres, the SiC powder, and the CNts Sic suspension with an appropriate amount of NaOH or TMAH are characterised with a relatively high negative zeta-potential increases the negative ZP up to-50 mV at a pH value of 10 in the alkaline pH region Fig. 4. SEM micrographs of(a) non-coated, (b-d) coated SiC fibres with carbon nanotubes at different magnificationsK. König et al. / Journal of the European Ceramic Society 30 (2010) 1131–1137 1133 Fig. 2. Zeta-potential vs. pH of the materials investigated. Since an appropriate net surface charge of fibres is very impor￾tant for efficient electrophoretic infiltration,42 we also analysed the ZP of crushed SiC fibres. The ZP vs. pH relationship is presented in Fig. 2. The as-received CNT-suspension is alkaline (pH 11), and due to the presence of anionic surfactant, the CNTs are negatively charged (ZP = −45 mV). The natural pH (pH 4) of the as-received SiC-powder suspension nearly matches the iso￾electric point, resulting in a very unstable suspension. Titration with hydrochloric acid is not efficient at increasing the zeta￾potential (described elsewhere42); conversely, titration of the SiC suspension with an appropriate amount of NaOH or TMAH increases the negative ZP up to −50 mV at a pH value of 10. Fig. 3. SEM image of a CNT-coating made on a graphite electrode by EPD (2.8 V, 5 min). In addition to the appropriate surface charge of the fibres, good wettability by the suspension is also an important charac￾teristic for the infiltration of the fibre mats. Consequently, we decreased the natural wetting angle of the alkaline aqueous sus￾pension at the SiC fibre bundle (∼80◦) by pre-treating the fibres with the surfactant SDOSS, to approximately 30◦. As shown in Fig. 2, the zeta-potential of the SDOSS-treated SiC fibres is negative over a wide range of alkaline pH values. Hence, as pre￾sented, the pre-treated SiC fibres, the SiC powder, and the CNTs are characterised with a relatively high negative zeta-potential in the alkaline pH region. Fig. 4. SEM micrographs of (a) non-coated, (b–d) coated SiC fibres with carbon nanotubes at different magnifications