Multifunctional Ceramic Matrix Composites for Nuclear Applications by James Wade-Zhu
YCN Research in Spot - September 2020
Nuclear fission/fusion reactors present some of the harshest environments for materials, operating at high temperatures in radiologically and/or chemically aggressive atmospheres. Continuous silicon carbide fibre-reinforced silicon carbide composites (SiC/SiCf) are particularly attractive for these applications because of their high temperature capability (>1600°C), good corrosion/oxidation resistance and small irradiation-induced swelling up to extreme irradiation doses (~100 dpa). However, SiC/SiCf is limited by its intrinsically low thermal conductivity (~10 W/mK) and the properties continued decline under neutron irradiation. This has raised concerns regarding the thermal performance of SiC/SiCf, specifically the material’s ability to efficiently transfer thermal energy from fuel-to-coolant for processing and to dissipate high heat loads away from core components.
My work seeks to address this through the development of multifunctional diamond-SiC/SiCf composites. Here, the extreme thermal conductivity of diamond (2300 W/mK) is used to introduce an additional thermal functionality to SiC/SiCf in the form of heat-exchange capabilities. Engineering such complex, multi-scale architectures has many challenges, requiring innovations in manufacturing. At the University of Birmingham, we have developed a novel process of “microwave chemical vapour infiltration (M-CVI)”. This process involves the decomposition of gaseous phases to produce deposits of nuclear-grade (high-purity, stoichiometric, nanocrystalline) SiC around SiCf preforms (see Figure). With microwave heating, these gaseous phases are able to flow deeper into the SiCf preforms before depositing, producing SiC matrices that are denser (>95% dense) and require less time to produce (<100 hrs). This is particularly advantageous for the manufacture of multifunctional diamond-SiC/SiCf composites, where the partial densification of SiCf preforms with diamond particles can inhibit gas flow during M-CVI processing, resulting in excessive residual porosity. Future work will involve working closely with the University of Pisa (Italy) to produce larger samples for mechanical testing and ion irradiation studies at the Ruđer Bošković Institute (Croatia). This work is funded by the EUROfusion Fellowship scheme and supported by the Culham Centre for Fusion Energy (UK).