Advanced Ceramics from Preceramic Polymers and Nano-fillers

Commercial silicone resins (“silicones”) filled with ceramic nanoparticles have been employed for the preparation of mullite and β-SiAlON ceramics. Dense, pure, crack free mullite were prepared by the heating in air of a mixture of silicone resin and alumina nanoparticles in the temperature range 1200-1500°C. The high reactivity of Al2O3 towards silica, coupled with nanometric size, led to a large volume fraction of mullite crystals even at low firing temperatures (1250°C). β-SiAlON ceramics were prepared by the heating of mixture a mixture of silicone resin and nanoparticles consisting of both Al2O3 and Si3N4, in the temperature range 1450-1550°C in nitrogen atmosphere. The formation of SiAlON was found to be preceded by the formation of intermediate alumino-silicate phases like mullite and sillimanite, successively reduced (due to the carbon content of the ceramic residue of silicon resins) and nitrided. Although some oxide contamination was still present after the high temperature treatment, a high β-SiAlON yield (about 80%) was achieved. The use of nano-filled silicones provides a promising route for the fabrication of advanced ceramic components by exploiting polymer processing techniques, with the achievement of complex shapes.