Y. Leconte (Sp), N. Herlin-Boime, D. Porterat, C. Reynaud, DSM/DRECAM/SPAM/LFP, Gif sur Yvette (France)
Refractory carbide nanostructured ceramics appear to be promising materials for high temperature applications requiring hard materials such as nuclear energy industry. When compared to conventional materials, nanosized ceramics show enhanced mechanical properties and are supposed to exhibit a better resistance under irradiation. In order to elaborate such nanomaterials, SiC nanopowders were synthesized by gas phase laser pyrolysis while TiC and ZrC nanopowders were produced by liquid phase laser pyrolysis. The powders were characterized by thermogravimetric analysis, X-ray diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy.
SiC nanopowders were obtained from a mixture of silane and acetylene, and were composed of crystalline grains with sizes in the 7 – 43 nm range depending on the synthesis conditions. A solution of titanium isopropoxide was laser-pyrolysed with ethylene as sensitizer in order to synthesize Ti/C/O powders. These powders were composed of crystalline TiO2 nanograins and free C. Annealing under argon enabled the formation of TiC through the carburization of TiO2 by free C with a close control of the final TiC stoichiometry. The final TiC grain size was about 80 nm. Zr/O/C powders were prepared from a solution of zirconium butoxide and were composed of ZrO2 crystalline nanograins and free C. The same thermal treatment as for TiC, but with higher temperature, showed the formation of crystalline ZrC with a final grain size of about 40 nm.
Nanocrystalline ceramics were elaborated by different sintering methods without any additives (ultra high pressure, HIP, SPS). The optimisation of the sintering conditions is still under investigation to choose the most appropriated way enabling the conservation of the nanosized structure together with a satisfying densification. The first studies lead by ultra high pressure (8 GPa) fast sintering show a densification of 95 % for SiC and 93 % for TiC with no significant grain growth.