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Ceramic Routes for Fabrication of SiC f /SiC Composites S. Novak 1, G. Dražić 1. K. Mejak 1, T. Toplišek 1, T. Žagar 2, M. Ravnik 2 1 Department for Nanostructured.

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Presentation on theme: "Ceramic Routes for Fabrication of SiC f /SiC Composites S. Novak 1, G. Dražić 1. K. Mejak 1, T. Toplišek 1, T. Žagar 2, M. Ravnik 2 1 Department for Nanostructured."— Presentation transcript:

1 Ceramic Routes for Fabrication of SiC f /SiC Composites S. Novak 1, G. Dražić 1. K. Mejak 1, T. Toplišek 1, T. Žagar 2, M. Ravnik 2 1 Department for Nanostructured Materials, Jožef Stefan Institute, Slovenia 2 Department for Reactor Physics, Jožef Stefan Institute, Slovenia INTRODUCTION AIM Acknowledgement: The work was performed in the frame of the project “Novel processing of SiC/SiC by slip infiltration of SIC-preforms with SiC”, Euratom-FU06-CT (2004) and Fusion association contract MHST: FU06-CT UT2 (2005) CONCLUSIONS CERAMIC ROUTE TO CMC (!!) < 1500°C - Wetting - Coating Due to the extremely low neutron-activation of SiC, SiC-based composites are considered as an attractive alternative to steel based materials (e.g. Eurofer) for the first-wall blanket of the future fusion reactors. However, the current SiC f /SiC composites, produced by the CVI process does not meet all the requirements (certain amount of internal porosity and high processing cost). Consequently, alternative techniques for the material production are under development.  Using nano-sized SiC powder and Al-phosphate as transient sintering additive (TSA), SiC-based ceramics can be densified at 1450°C.  Electrophoretic deposition was confirmed to be a promising technique for fast infiltration of ceramic suspension into SiC- fibre substrate as well as to produce gas-impermeable coating at the SiC f /SiC composite.  Effective filling the SiC-fibre woven can be achieved by modification of the fibres surface using appropriate surface active agents. The critical parameters are particles surface charge and conductivity of the SiC-ethanol suspension.  Oxide layer at the SiC particles hinders the deposition and have also a detrimental effect on densification and properties of the sintered material.  Impurities in the raw materials used in this phase of the investigation, cause high activation. The main problem that needs to be solved in the case of the ceramic routes is high sintering temperature of SiC and high neutron activation of commonly used sintering additives. The main stress in the present investigation was therefore to find a sintering additive from a limited number of low-activation elements, that would enable sintering of SiC to high density at temperature below 1500°C. Candidate sintering aids, alternative to conventionally used, was selected on the base of activation cross-section data and on the survey of relevant phase diagrams. Further work: - Replacment of Al with Mg - Use of high-purity raw materials  m - 50 nm Suspension Liquid + SAA Infiltration Densification Densification of the SiC-based matrix LIMITATIONS: < 1500°C  Use of nano-powder Low-activation additives  Limited number of elements allowed Vacuum Slip Infiltration (VSI) Electrophoretic Infiltration (EPI) SiC bundle with SiC deposit Al-phosphate Mg-phosphate SiC fibres are conductive and hence applicable as an electrode in electrophoretic deposition or infiltration. SiC particles and Al-phosphate are deposited from ethanol suspension and after firing produce a dense SiC-ceramics. Deposition cell Massive SiC deposit on SiC f /SiC after 10 min of deposition at 60 V SiC powder Low-activation additives Continuous SiC fibres / woven Fracture surface of the sample with 0.5  m SiC (SEM) Polished cross-section of the sample with 50 nm SiC (SEM) Polished sample with 0.5  m SiC (SEM) Interface between SiC-fibre and matrix with 50 nm SiC (TEM) Good adhesion of the matrix material to the fibers (SEM) Crack deflection at the fibre (SEM) SiC particles at SiC fiber SiC- fibres SiC-fibre SiC f /SiC SiC deposit Counter electrode Saturated gamma activities of impurities found in used SiC powders irradiated in the central channel of TRIGA Mark II reactor as a function of cooling time. 15  m 50 nm “Jožef Stefan” Institute SiC fibre SiC-based matrix


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