Silicon Carbide Nanostructured Matrix Composite with Carbon Nanotubes Reinforcement and Controlled Interphase – SILICARBITUBE

This project is presented in the context of the research on materials for the 4th generation of nuclear reactors. In these reactors, materials and in particular those used for fuel cladding will undergo severe temperature and irradiation conditions. The development of new refractory materials with high thermal conductivity, neutron irradiation resistance and showing reliable mechanical properties is thus required.
In this context, carbide ceramics such as SiC appear as very interesting, but their brittle behavior is a very limiting criterion for their application as structure materials. The decrease of the grain size down to the nanometric scale could improve this behavior but would also lead to a strong decrease of the thermal conductivity. In order to compensate this decrease, the addition of carbon nanotubes could enhance the thermal properties of the composite and also increase the toughness by playing the role of short fiber reinforcement. For this latter consideration, the relationship between the matrix and its reinforcement appears critical: the addition of ceramic or metal at the tube/matrix interface could allow controlling the coupling between these two elements.
In this project, the 3 partners (LFP, ICB, MATEIS) propose to elaborate composites with nanostructured SiC matrix reinforced by carbon nanotubes covered by an interphase in order to study the thermomechanical properties of the obtained composites. Several types (size, chemical composition, length, surface treatment) of nanopowders and nanotubes will be synthesized and a special attention will be paid to their association. A chemical bonding could indeed be achieved between the nanograins and the tube surface before they get mixed. This latter mixing step will either give a random orientation of the nanotubes in the matrix, or aim at the conservation of the original alignment of the tube in order to obtain anisotropic properties. A complete study will be devoted to the preparation of the green body in order to optimize the density and the pores distribution. Dispersion, mixing and granulation steps will thus be addressed. The sintering step will also constitute a key issue in this project, as it should lead to a maximum densification while keeping the grain size nanometric and preserving the nanotube and interphase structures. SPS technique, which heats the samples by means of a pulsed current will be used, because of its capacity to shorten the high temperature steps aiming at limiting grain growth. Finally, mechanical tests and thermal conductivity measurements will be performed in parallel with structural characterization in order to optimize the composite properties on the one hand, and on the second hand in order to understand at the nanometric scale the mechanisms ruling the observed properties.