K. Konig et al. Joumal of the European Ceramic Sociery 30(2010)1131-1137 illustrates the fracture surface of the CNT-coated silicon carbide EPD technique and aqueous suspensions. Since the SiC fibres fibre tow after the deposition with SiC. It is clear that the uni- were shown to be negatively charged within a wide range of formly distributed nanotubes on the SiC fibres are coated by Sic pH values, we used negatively charged CNTs and Sic particles particles, while the gaps between them are not filled with parti- for the EPD experiments. Steel, copper, and graphite electrode cles. Obviously, when the SiC fibres were attached directly to the were employed. Using steel electrodes at voltages greater than anode and therefore acted as the deposition electrode, the parti- 2.8 V, meant bubbles disturbed the deposition, while using cop- cles formed a coating on the fibre fabrics, which prevented any per and graphite deposition electrodes successfully suppressed further infiltration of the gaps close to the electrode. Eventually, the bubbles'formation, which is a requisite for the formation of this effect led to the formation of inaccessible voids between the solid pore-free deposits fibres, which could no longer be filled with the depositing SiC In the electrophoretic deposition of CNTs onto SiC fibres in particles. This behaviour is schematically described in Fig 6a. contact with the positive electrode, a continuous layer of CNts able the deposition of Sic particles in these spaces was formed on the fibres. The subsequent deposition of the Sic between the fibres, the infiltration of the CNT-coated Sic-fibre particles on the CNT-coated fibres yielded a thick Sic layer on mat with SiC powder was performed by placing the mat in front SiC fibres; however, the spaces between the fibres through the of the anode but not in direct contact with it, as described in our thickness of the fibre mat were not completely filled and the previous work. As shown schematically in Fig. 6b, the fabric infiltration of the fibre mat was not achieved. A more efficient was attached to a cellulose membrane and was separated from infiltration of the CNT-coated SiC fibres was achieved by placing the anode using a Teflon spacer. According to a mechanism the fibres close to the anode, but not in direct contact with it. In proposed elsewhere, > with this configuration the SiC particles this way the particles migrated to the electrode through the fibre are forced to move through the negatively charged fibre mat to mat and gradually filled it. reach the electrode; thus, they first deposit on the membrane. We demonstrated that EPD is a highly efficient method to coat Next, they gradually fill the fabric in front of the membrane, SiC fibres with a layer of CNTs, which results in a nanostruc- nd finally, the deposit is additionally formed on the front side tured interphase layer in the Sic-fibre-reinforced SiC ceramics of the fabric. The macroscopic view of the green SiC infiltrated Future work will determine whether or not the presence of CNT presented in Fig. 7a. It is evident that the particles are deposited toughness of these composite materialsnductivity and fracture sample, which formed in 5 min on the graphite anode at 30 V, is coating will lead to enhanced thermal ce on both sides of the SiC fibre mat, indicating that the particles were able to migrate through the fabric Acknowledgements In order to verify the effectiveness of the EPd of CNTs onto SiC-fibres. and the infiltration of the CNt-coated fibre This work, supported by the Slovenian Research Agency mats with SiC powder, the samples were subsequently infiltrated within the project J2-7506 and by the European Communities with an Al-phosphate solution and sintered at 1300C for 3 h in under the Contract of Association between EURATOM and the an argon atmosphere. The Al-phosphate provided a secondary- Ministry of Higher Education, Science and Technology of the phase precursor that enables the low-temperature densification Republic of Slovenia, was carried out within the framework of of SiC. +o After sintering, the matrix phase filling the gaps the European Fusion Development Agreement. The content of between the CNT-coated fibres is composed of Sic particles the publication is the sole responsibility of its authors and it doe embedded in an aluminium-containing secondary phase. The not necessarily represent the views of the European Commission DS spectrum of the Sic-based matrix material is presented in or its services K. Konig would like to thank the European Commission for The fracture surfaces of the composite illustrated in Fig. 7c the financial support(mobility grant) of her stay at Imperial and e reveal that even the narrow spaces between the fibres College London, UK, where a part of this work was performed are filled with the Sic matrix, as desired. A few unfilled gaps Mr. Bingan Chen(Imperial College London) is acknowledged still remain, however, which could be addressed by a further for experimental support improvement of the process. Moreover, from the higher magni- ication image in Fig. 7f, it is evident that the CNT-coating is References still present on the fibres after the high-temperature treatment. 1. Muroga, T, Gasparotto, M. and Zinkle, S.J., Overview of materials research 4. Conclusion for fusion reactors. Fusion Eng. Des., 2002, 61-62, 13-25. 2. Tavassoli, A. A F, Present limits and improvements of structural materials The aim of the work was to produce a new grade of 3. Snead, LL and Weber, w.J., Promise and challenges of Sice/Sic compos- ites for fusion energy applications. J. Nucl. Mater, 2002, 1057, 307-311 electric-field-assisted processes for the coating and infiltration. 4. Vicens, J Farizy, G and Chermant, J.L., Microstructures of ceramic com- This was done in two steps: firstly, the SiC fibres were coated posites with glass-ceramic matrices reinforced by SiC-based fibres. Aerosp by CNTs and, secondly, the coated fabric was infiltrated with a Sci. Technol.,2003,7,135-146 SiC-powder suspension 5. Deng, F, Zheng, Q-S. Wang, L -F and Nan, C.-w, Effects High-quality, uniform, and reproducible CNT and CNT-SiC aspect ratio, and nonstraightness of carbon nanotubes on the ductivity of carbon nanotube composites. Appl. Phys. Lett. coatings on SiC fibres were produced for the first time using the 0129141-01291431136 K. König et al. / Journal of the European Ceramic Society 30 (2010) 1131–1137 illustrates the fracture surface of the CNT-coated silicon carbide fibre tow after the deposition with SiC. It is clear that the uni￾formly distributed nanotubes on the SiC fibres are coated by SiC particles, while the gaps between them are not filled with parti￾cles. Obviously, when the SiC fibres were attached directly to the anode and therefore acted as the deposition electrode, the parti￾cles formed a coating on the fibre fabrics, which prevented any further infiltration of the gaps close to the electrode. Eventually, this effect led to the formation of inaccessible voids between the fibres, which could no longer be filled with the depositing SiC particles. This behaviour is schematically described in Fig. 6a. To enable the deposition of SiC particles in these spaces between the fibres, the infiltration of the CNT-coated SiC-fibre mat with SiC powder was performed by placing the mat in front of the anode but not in direct contact with it, as described in our previous work.40 As shown schematically in Fig. 6b, the fabric was attached to a cellulose membrane and was separated from the anode using a Teflon® spacer. According to a mechanism proposed elsewhere,45 with this configuration the SiC particles are forced to move through the negatively charged fibre mat to reach the electrode; thus, they first deposit on the membrane. Next, they gradually fill the fabric in front of the membrane, and finally, the deposit is additionally formed on the front side of the fabric. The macroscopic view of the green SiC infiltrated sample, which formed in 5 min on the graphite anode at 30 V, is presented in Fig. 7a. It is evident that the particles are deposited on both sides of the SiC fibre mat, indicating that the particles were able to migrate through the fabric. In order to verify the effectiveness of the EPD of CNTs onto SiC-fibres, and the infiltration of the CNT-coated fibre mats with SiC powder, the samples were subsequently infiltrated with an Al-phosphate solution and sintered at 1300 ◦C for 3 h in an argon atmosphere. The Al-phosphate provided a secondary￾phase precursor that enables the low-temperature densification of SiC.44,46 After sintering, the matrix phase filling the gaps between the CNT-coated fibres is composed of SiC particles embedded in an aluminium-containing secondary phase. The EDS spectrum of the SiC-based matrix material is presented in Fig. 7d. The fracture surfaces of the composite illustrated in Fig. 7c and e reveal that even the narrow spaces between the fibres are filled with the SiC matrix, as desired. A few unfilled gaps still remain, however, which could be addressed by a further improvement of the process. Moreover, from the higher magni- fication image in Fig. 7f, it is evident that the CNT-coating is still present on the fibres after the high-temperature treatment. 4. Conclusions The aim of the work was to produce a new grade of CNT-coated SiC-fibres-reinforced SiC-composite by using electric-field-assisted processes for the coating and infiltration. This was done in two steps: firstly, the SiC fibres were coated by CNTs and, secondly, the coated fabric was infiltrated with a SiC-powder suspension. High-quality, uniform, and reproducible CNT and CNT-SiC coatings on SiC fibres were produced for the first time using the EPD technique and aqueous suspensions. Since the SiC fibres were shown to be negatively charged within a wide range of pH values, we used negatively charged CNTs and SiC particles for the EPD experiments. Steel, copper, and graphite electrodes were employed. Using steel electrodes at voltages greater than 2.8 V, meant bubbles disturbed the deposition, while using cop￾per and graphite deposition electrodes successfully suppressed the bubbles’ formation, which is a requisite for the formation of solid pore-free deposits. In the electrophoretic deposition of CNTs onto SiC fibres in contact with the positive electrode, a continuous layer of CNTs was formed on the fibres. The subsequent deposition of the SiC particles on the CNT-coated fibres yielded a thick SiC layer on SiC fibres; however, the spaces between the fibres through the thickness of the fibre mat were not completely filled and the infiltration of the fibre mat was not achieved. A more efficient infiltration of the CNT-coated SiC fibres was achieved by placing the fibres close to the anode, but not in direct contact with it. In this way the particles migrated to the electrode through the fibre mat and gradually filled it. We demonstrated that EPD is a highly efficient method to coat SiC fibres with a layer of CNTs, which results in a nanostruc￾tured interphase layer in the SiC-fibre-reinforced SiC ceramics. Future work will determine whether or not the presence of CNT coating will lead to enhanced thermal conductivity and fracture toughness of these composite materials. Acknowledgements This work, supported by the Slovenian Research Agency within the project J2-7506 and by the European Communities under the Contract of Association between EURATOM and the Ministry of Higher Education, Science and Technology of the Republic of Slovenia, was carried out within the framework of the European Fusion Development Agreement. The content of the publication is the sole responsibility of its authors and it does not necessarily represent the views of the European Commission or its services. K. König would like to thank the European Commission for the financial support (mobility grant) of her stay at Imperial College London, UK, where a part of this work was performed. Mr. Bingan Chen (Imperial College London) is acknowledged for experimental support. References 1. Muroga, T., Gasparotto, M. and Zinkle, S. J., Overview of materials research for fusion reactors. Fusion Eng. Des., 2002, 61–62, 13–25. 2. Tavassoli, A. A. F., Present limits and improvements of structural materials for fusion reactors—a review. J. Nucl. Mater., 2002, 302, 73–88. 3. Snead, L. L. and Weber, W. J., Promise and challenges of SiCf/SiC compos￾ites for fusion energy applications. J. Nucl. Mater., 2002, 1057, 307–311. 4. Vicens, J., Farizy, G. and Chermant, J. L., Microstructures of ceramic com￾posites with glass–ceramic matrices reinforced by SiC-based fibres. Aerosp. Sci. Technol., 2003, 7, 135–146. 5. Deng, F., Zheng, Q.-S., Wang, L.-F. and Nan, C.-W., Effects of anisotropy, aspect ratio, and nonstraightness of carbon nanotubes on thermal con￾ductivity of carbon nanotube composites. Appl. Phys. Lett., 2007, 90, 012914-1–012914-3