Effects of Atmospheric Composition on the Molecular Structure of Synthesized Silicon Oxycarbides

Abstract

The dependence of silicon oxycarbides' chemical composition and molecular structure on their reaction conditions was tested by varying the atmosphere under which pyrolysis was performed. To obtain the silicon oxycarbides, densely cross‐linked silicone resin particles with an averaged diameter of 2 μm were pyrolyzed in various atmospheres of H2, Ar, and CO2, in the temperature range 700°C–1100°C. The residual mass of resin after pyrolysis was almost constant at 700°C, although their apparent colors varied distinctly. The sample obtained from the H2 atmosphere was white, whereas that obtained from the CO2 atmosphere was dark brown. Fourier‐transform infrared (FT‐IR) spectra of the residues suggested that the Si–O–Si network evolution was accelerated in the CO2 atmosphere. Beyond 800°C, the chemical compositions of the compounds obtained from a H2 atmosphere increasingly approached near‐stoichiometric SiO2–xSiC composition with increasing the pyrolysis temperature. Compounds from a CO2 atmosphere approached a composition of SiO2–xC with no free SiC as the pyrolysis temperature increased. In the products from an Ar atmosphere, SiO2–xSiC–yC compositions were typically obtained. The observed effects of the pyrolysis atmosphere on the resulting chemical compositions were analyzed in terms of thermodynamic calculations. Electron spin resonance (ESR) spectra revealed broad and intense signals from products obtained from either Ar or CO2. Estimating from the signal intensity, the residual spin concentrations were in the range 1018–1019 g−1. Meanwhile, the spectra from the samples obtained in H2 showed weak and sharp signals with estimated spin concentrations ranging from 1016–1017 g−1. This signal attenuation may have been due to the hydrogen capping of dangling bond formed during pyrolysis.

Sintering of porous alumina using an alumina slurry containing aluminum and polysiloxane

“…27 In this case, polysilsesquioxane is one example of an organosilicon polymer that can be transformed into aluminum silicate or silicon oxycarbide after heating at temperatures ≥700°C. 28,29 These results therefore account for the observed wetting of the alumina surface with aluminum.…”

Influence of SiC/Silica and Carbon/Silica Interfaces on the High‐Temperature Creep of Silicon Oxycarbide‐Based Glass Ceramics: A Case Study

“…Recently, it was found that upon the proper choice of the pyrolysis atmosphere, two special SiOC compositions can be accessed: The pyrolysis of a polysilsesquioxane under hydrogen atmosphere leads to the selective elimination of the segregated carbon phase, whereas the pyrolysis of the same precursor under CO 2 atmosphere leads to the selective elimination of the network carbon . Thus, the thermal conversion of the precursor in H 2 atmosphere delivers an SiOC glass with negligible amount of segregated carbon; whereas its conversion in CO 2 delivers a nanocomposite consisting of vitreous silica and segregated carbon, that is, C/SiO 2 …”

Structure and properties of white Si–O–C(–H) ceramics derived from polycarbosilane by thermal oxidation curing and H₂ decarbonization process

“…In a previous study, we assigned this band to "inorganic SiC", which appeared during pyrolysis as compensation of the sharp absorption band at 790 cm ¹1 assigned to organic SiCH 3 groups in precursors. 1), 3) In the 200 and 240°C samples, however, we observe a broadband absorption covering the range of 900850 cm ¹1 . They are possibly assigned to various kinds of SiC bonds which have different peak positions in terms of surrounding environments.…”