Microporosity evolution in polymer-derived SiOC glasses pyrolyzed in different atmospheres

Author(s)

Michele Cassetta, Herwig Peterlik, Thomas Konegger, Nicola Daldosso, Gian Domenico Sorarù, Mattia Biesuz

Abstract

Polymer-derived ceramics (PDCs) are a class of advanced materials obtained by pyrolysis in a controlled atmosphere of an organosilicon polymer. Their functional as well as mechanical properties originate from the peculiar nanostructures developed during the pyrolysis. Herein, we investigate the formation of transient microporosity in a model PDC (methyl-silsesquioxane) obtained in Ar, Ar–5%H

₂, CO

₂, and air. It is shown that a common evolution can be detected up to 700°C. At this temperature, the structure of the material in terms of chemical bonds is marginally changed (only redistribution reactions take place), but the medium-range order is clearly modified moving the system to a more disordered state (detected by small angle x-ray scattering [SAXS]) and causing the formation of a large amount of open micropores sized at about 1.2–1.7 nm. In the 700–800°C range, the proper ceramization starts causing the formation of a new class of small (around 1 nm) open micropores. These partially annihilate at 900°C in Ar and Ar–H

₂ (i.e., in the second part of the ceramization process), whereas they totally collapse in CO

₂ due to the formation of a more silica-like SiOC (less polymerized and viscous). Finally, SAXS points out the persistence of relatively large closed nanovoids of about 1 nm at 1250°C for the samples treated in Ar and Ar–H

₂. These might explain anomalies in terms of density, elastic modulus, and thermal conductivity of this class of ceramics as reported in the literature.

Organisation(s)

Dynamics of Condensed Systems

External organisation(s)

Università degli Studi di Trento, Technische Universität Wien, Università degli Studi di Verona

Journal

Journal of the American Ceramic Society

No. of pages

14

ISSN

0002-7820

DOI

https://doi.org/10.1111/jace.19816

Publication date

2024

Peer reviewed

Yes

Austrian Fields of Science 2012

103018 Materials physics, 205009 Ceramic materials

Keywords

Portal url

https://ucris.univie.ac.at/portal/en/publications/microporosity-evolution-in-polymerderived-sioc-glasses-pyrolyzed-in-different-atmospheres(fec201e4-b78e-43ba-9a90-830d04246068).html