Porous SiOC/SiC ceramics an active-filler-catalyzed polymer-derived method

• Published in: Materials chemistry frontiers Vol. 5; no. 17; pp. 653 - 6545
• Main Authors: Rau, Advaith V, Knott, Ken, Lu, Kathy
• Format: Journal Article
• Published: 23.08.2021
• ISSN: 2052-1537
• DOI: 10.1039/d1qm00705j

In this study, bulk and porous SiOC materials were synthesized via a polymer-derived ceramic (PDC) method from a base polysiloxane (PSO) precursor and an iron (Fe) catalyst under an inert pyrolytic atmosphere. Fe catalyzes not only the formation and nucleation of β-SiC at lower temperatures but also promotes phase separation of the amorphous SiO x C y phase, compared to PDCs without the Fe catalyst. Samples with Fe pyrolyzed at 1100 °C have an appreciable β-SiC content compared to a negligible/unobservable β-SiC content in the corresponding Fe-less samples. Selective etching of the SiO 2 phase shows that Fe also induces segregation of the amorphous SiO x C y phase, yielding larger specific surface areas and gas sorption capability below 1300 °C. At 1500 °C, the pore structure changes to form interconnected networks due to the highly phase separated SiO 2 and β-SiC microstructure. A Gibbs free energy minimization method was used to determine the relative phase content of the pyrolyzed samples, with the effect of Fe quantified with simplified vapor-liquid-solid (VLS), solid-liquid-solid (SLS), and classical nucleation theories. Effects of Fe and POSS on the phase formation of SiOC between 1100 °C and 1500 °C were studied. Fe induces higher SiO 2 and SiC contents. Phase contents are calculated based on a modified Gibbs free energy minimization method.