FABRICATION OF SILICON CARBIDE AND REFRACTORY METAL BASED COMPOSITES FOR NUCLEAR APPLICATIONS USING POLYMER INFILTRATION AND PYROLYSIS

摘要

This study presents a novel technique of fabricating refractory metal based ceramic composites using polymer infiltration and pyrolysis (PIP). The starting materials were either refractorymetal or metal carbide and allylhydridopolycarbosilane (AHPCS), which is an organometal polymer precursor for silicon carbide. Niobium, Zirconium (and their carbides) were used in the current study as filler in a silicon carbide matrix to obtain cylindrical pellets. These materials are being researched for possible in-core applications in gas cooled fast reactors (GFR). Polymer infiltration and pyrolysis based technique was used due to its unique control over microstructure by varying chemical composition and moreover, the possibility of net shape manufacturing at low temperatures (500-1500deg C). This leads to a flexible and relatively cost efficient approach to ceramic component fabrication. Furthermore, the processing technique involves lower energy requirements than conventional sintering processes currently in practice. Inert gas pyrolysis of AHPCS produces near-stoichiometric amorphous silicon carbide (alpha-SiC) at 900-1150deg C. Multiple polymer infiltration and pyrolysis (PIP) cycles were carried out under inert environment to minimize open porosity, densify the silicon carbide matrix and thus enhance mechanical strength of the pellet. A range of materials were fabricated by varying the constituent materials and volume fractions. Bulk characterization was performed using biaxial flexure, ring-on-ring, method that showed promising mechanical properties of these pellets.