Polysiloxane Pyrolysis

Abstract

Different polysiloxanes were pyrolyzed to make silicon oxycarbide glasses which have been shown to be possible candidates for anode materials of Li-ion batteries. The decomposition process during pyrolysis was studied using a thermal gravimetric analyzer connected to a residual gas analyzer for three representative polymers. No silicon-or oxygen-containing gases were observed during pyrolysis. The stoichiometry of all of the final chars was measured and found to agree well with predictions calculated using the initial polymer stoichiometry, the ceramic yield, and the fact that only carbon and hydrogen atoms were eliminated during pyrolysis. For three chars with identical stoichiometry at 1000 °C, prepared from three different polymers, the local chemical environment of the silicon was studied as a function of pyrolysis temperature by X-ray absorption (XAS) near the silicon K-edge. As the samples are heated, the XAS spectra eventually become identical, once the different labile species have been eliminated, suggesting that the properties of the char are dependent mainly on its stoichiometry and not on the initial composition of the polymer precursor. The bulk properties of these three chars prepared at 1000 °C were also studied by X-ray diffraction and by electrochemical methods which showed them to be identical.

High temperature structure evolution of macroporous SiOC ceramics prepared by a sol–gel method

“…It often appears to be amorphous by X-ray diffraction but has a heterogeneous structure at nanometer-sized scale [2][3][4][5][6][7][8].…”

Amorphous Si(Al)OC ceramic from polysiloxanes: bulk ceramic processing, crystallization behavior and applications

“…Preparation of siliconoxycarbide glass from poly(methylsilsesquioxane) was reported in detail. 6 Much concentration was given in the last decade on the modification of the SiOC by aluminum and boron. 11À13 Modification was achieved by the reaction of triethoxysilane and methlydiethoxysilane with aluminum or boron containing alkoxides forming a sol-gel process in the presence of a solvent.…”

IR laser-induced carbothermal reduction of silicon monoxide

“…This nanosized material can be also useful as, e.g. catalyst support, lubricant and high-temperature coatings and can show enhanced properties in anode materials of Li-ion batteries [53].…”