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Porous CeOX/SiC nanocomposites prepared from reverse polycarbosilane-based microemulsions

: Kockrick, E.; Krawiec, P.; Petasch, U.; Martin, H.-P.; Herrmann, M.; Kaskel, S.


Chemistry of Materials 20 (2008), No.1, pp.77-83
ISSN: 0897-4756
ISSN: 1520-5002
Journal Article
Fraunhofer IKTS ()

Reverse microemulsions consisting of aqueous cerium nitrate solution as the internal phase and polycarbosilane dissolved in heptane as the continuous phase were used as a precursor for the controlled synthesis of dispersed cerium oxide particles inside a porous SiC matrix. According to dynamic light scattering experiments, the effective diameter of the cerium hydroxide particles obtained after ammonia addition is effectively controlled in a range of 2 10 nm with the molar water/surfactant ratio (Rw )
6 16). Pyrolysis at 1200 to 1500 °C produces materials with specific surface areas up to 240 m2 g-1.
Whereas crystallization of the matrix is achieved only at higher temperature, cerium oxide particles form agglomerates composed of smaller nanoparticles that tend to dissolve into the ceramic matrix at 1500 °C leaving macropores behind. The high specific surface area is attributed to the presence of mesopores with a broad size distribution.
Excess carbon present after pyrolysis is removed by oxidation at 900 °C causing a significant decrease of the surface area for high surface area materials, whereas intermediate surface area materials (50 -100 m2 g-1) show a high textural stability.