Polymer Derived Silicon Carbide Ceramics for Nuclear Applications
Arreguin, Shelly Anne
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The next generation of nuclear fission and fusion reactors depends upon the development of high performance structural materials. Silicon carbide (SiC) is being considered for a variety of nuclear reactor components because it possesses outstanding physical and chemical properties, including: high thermal conductivity, high temperature stability, chemical inertness, extreme hardness and small neutron capture cross-section. However, when exposed to energetic particles, SiC is observed to experience various radiation induced defects such as: vacancy clusters, dislocation loops and network dislocations at lower temperatures and swelling of the material causing voids/cavities at higher temperatures. Recent studies have shown nanostructured interfaces and nanoscale grains are more radiation damage tolerant. Polymer derived ceramics (PDCs) provide a unique route to develop SiC ceramics with nanostructural features that can help mitigate radiation defects. A novel class of SiC ceramics with controlled microstructures has been developed through tailoring of the molecular architecture of the starting precursor (allylhydridopolycarbosilane, Starfire® SMP-10). Nanostructural features in the form of graphene layers were incorporated via excess carbon from the addition of divinylbenzene (0-5 wt%) to the liquid SMP-10. It was observed that with increasing concentration of carbon, the 6H SiC (hexagonal) phase formed at the expense of 3C SiC (cubic). The utilization of PDCs also made possible the addition of sintering additives at the molecular level through a hydroboration reaction of SMP-10 with decaborane. This allowed the boron additives to be contained within the SiC grains, as opposed to on the grain boundaries, as is observed in traditional ceramic processing. Finally, these materials were irradiated using ion accelerator facilities located at the Environmental Molecular Sciences Laboratory at the Pacific Northwest National Laboratory. AFM results indicate that utilizing PDC processing routes vs. traditional ceramic routes yielded a significant decrease in the amount of swelling from point defect accumulation due to radiation bombardment. This research contributes to current priorities in designing materials for the next generation of nuclear power plants that are anticipated to have minimal waste, decreased risk of proliferation and increased accident damage tolerance.