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Abstract In this study, montmorillonite (MMT) nanosheets are purified and exfoliated from a crude clay source and further twice‐functionalized with cetritrimethylammonium bromide and [3‐(2‐aminoethylamino)propyl]trimethoxysliane (AEAPTMS) to promote dispersion in the preceramic polymer. Phase profiles and compositions of MMT nanoflakes and MMT‐silicon oxycarbide (SiOC) are characterized with X‐ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The microstructures are examined by scanning and transmission electron microscopy. MMT nanoflakes are randomly dispersed in the SiOC matrix with α‐quartz forming at the MMT‐SiOC interface. Pyrolysis to 1400 °C induced the formation of SiC nanowhiskers that are observed up to 20 µm in length and 200 nm in diameter. After selective etching of SiO₂domains with HF, pore sizes and specific surface areas of MMT‐SiOC are analyzed with nitrogen adsorption. The study provided a new fundamental understanding of MMT‐SiOC interactions at different pyrolysis temperatures and also led to composites with specific surface areas reaching 120 m² g⁻¹ up to 1200 °C pyrolysis, and between 340 and 772 m² g⁻¹at 1400 °C pyrolysis and pore size distributions between 2 and 5 nm. The methodology and results presented improve the understanding and viability of 2D nanomaterial‐reinforced ceramic composites and MMT as a precursor for nanostructured SiC. 

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.