Sol-gel processing of a glycolated cyclic organosilane and its pryrolysis to silicon oxycarbide monoliths with multiscale porosity and large surface areas

Author(s)

Manuel Weinberger, Stephan Puchegger, Thomas Fröschl, Florence Babonneau, Herwig Peterlik, Nicola Hüsing

Abstract

This study is related to the preparation of silicon oxycarbide monoliths comprising a hierarchical network build-up from the pyrolysis of monolithic organosilica gels. A novel glycol-modified 1,3,5-trisilacyclohexane-carbosilane "[Si(OCH2CH2OH)(2)CH2](3)" was processed via a polymerization-induced phase separation process in hydrochloric acid solution containing the Pluronic P123 block copolymer and potassium chloride. Highly porous organosilica monoliths with interconnected macropores and a large amount of uniformly sized polymer-templated mesopores within the macroscopic framework domains were obtained after supercritical fluid extraction. The monoliths were pyrolyzed in argon atmosphere at 1000 degrees C to yield silicon oxycarbide monoliths by maintaining the hierarchical porosity or the organosilica gel. Both the organosilica gels and the silicon oxycarbide monoliths were thoroughly investigated with standard characterization techniques. If no salt was used for the preparation of organosilica. gels, no distinct macroporous structures were obtained. Instead, the gets show the characteristics of typical aerogels with surface areas of 600-900 m(2) g(-1) and mesopores with pore sizes > 10 nm. A different behavior was observed if potassium chloride was added to the sols. Then, the system showed the tendency for a polymerization-induced phase separation leading to gels exhibiting multiscale porosity. The onset of the phase separation as well as the macropore/domain size thereby strongly depends on the concentration of KCl. These gels with a surface area of about 1070 m(2) g(-1) and pore diameters of about 11.6 nm were Subjected to pyrolysis at 1000 degrees C under inert gas atmosphere. Although volume shrinkages of 54% were observed, the monoliths maintained their shape and structural Features. The surface areas remained rather high with 531 m(2) g(-1), and the diameter of the mesopores dropped to 9.1 nm. From solid state NMR measurements and elemental analysis of the pyrolyzed sample, the formation of true silicon oxycarbide monoliths with multiscale porosity and a composition of SiC0.23O1.53 + 0.58C(free) were proven. From resonant ultrasound spectroscopy measurements, a Young's modulus value of 1.42 GPa was obtained.

Organisation(s)

Dynamics of Condensed Systems

External organisation(s)

Universität Ulm, Université Paris VI - Pierre-et-Marie-Curie

Journal

Chemistry of Materials

Volume

4

Pages

1509-1520

No. of pages

12

ISSN

0897-4756

DOI

https://doi.org/10.1021/cm903031d

Publication date

2010

Peer reviewed

Yes

Austrian Fields of Science 2012

103009 Solid state physics

Portal url

https://ucrisportal.univie.ac.at/en/publications/66f9d5e6-a902-4fc9-945d-5a0fe2c9ccc3