Effect of additive structure and size on SiO₂ formation in polymer‐derived SiOC ceramics

Abstract

Silicon oxycarbide (SiOC) ceramics with highly adjustable properties and microstructures have many promising applications in batteries, catalysis, gas separation, and supercapacitors. In this study, additive structures on the nucleation and growth of SiO2 within SiOC ceramics are investigated by adding cyclic tetramethyl‐tetravinylcyclotetrasiloxane (TMTVS) or caged octavinyl‐polyhedral oligomeric silsesquioxane (POSS) to a base polysiloxane (PSO) precursor. The effects of the 2 additives on the polymer‐to‐ceramic transformation and the phase formation within the SiOC are discussed. POSS encourages SiO2 nucleation and leads to more SiO2 formation with significantly increased ceramic yield, which subsequently leads to higher specific surface of 1557 m2/g with a larger pore size of ∼1.8 nm for the porous SiOC. High TMTVS content decreases both the specific surface area and pore volume of the resulting porous SiOCs. This study demonstrates a new approach of using Si‐rich additive POSS to increase the SiOC yield while maintaining or even increasing the specific surface area.

Kr ion irradiation study of polymer‐derived SiFeOC–C–SiC nanocomposite

“…In pure PSO systems, two mass losses were observed at 400 • C and 550 • C, respectively, due to the cleavage of C-H, Si-C, and Si-O bonds. 16,38 Thus, the observed mass loss between 394.7 • C and 584.1 • C in this study should be due to the decomposition of PSO + POSS. The mass loss for each precursor could not be delineated due to simultaneous decomposition reactions.…”

“…The main events are microstructural rearrangement and formation of amorphous SiOC in addition to redistribution of the Fe-Si, Si-O, Si-C, and Si-H bonds. 16,38 The pyrolyzed SiFeOC-C-SiC has a stoichiometry of SiFe 0.06 O 2.07 C 4.0 . The PSO precursor leads to carbon enrichment due to the inherent aromatic ring along with methyl and ethyl groups.…”

“…POSS is known to enhance SiO 2 nanodomain formation at 1300 • C in an Ar atmosphere. 38 The caged structure leads to nucleation of SiO 2 at temperatures as low as 1000 • C. 16,38 During the polymer-to-ceramic conversion in an inert atmosphere, PSO leads to simultaneous formation of Si-C bonds and Si-O bonds, resulting in SiO 4-n C n 40 along with nanodomains of amorphous SiO 2 , free carbon, and β-SiC (at ≥1300 • C, Equation 3). 14…”

“…This means that the carbon species in the SiFeOC-C-SiC ceramic is in the graphite carbon form (sp 2 bond), which is well recognized for polymerderived SiOC systems. 38,[46][47][48] In Figure 6B, the C 1s peak is deconvoluted and fitted for five peaks at 283.1, 284.8, 286.0, 287.4, and 288.9 eV for Fe-C/Si-C, C-C, C-O, C=O, and O-C=O bonds, respectively. This means that C atoms can be bonded with all the species in the SiFeOC-C-SiC ceramic.…”

Phase content prediction in polymer‐derived ceramics with metal additives

“…For all the samples, an amorphous SiO 2 halo is centered at ∼22°. The presence of this halo has been well documented [30][31][32] and will not be discussed further in this work.…”