Role of Redistribution Reactions in the Polymer Route to Silicon–Carbon–Oxygen Ceramics

Abstract

Redistribution reactions are used in the synthesis of several preceramic polymers. Moreover, redistributions play a major role in the pyrolysis of these precursors. Examples of thermal redistributions involving the exchange of SiOO/ SiOX bonds (X ‫؍‬ O, H, C, . . . ) in polysiloxanes, precursors to silicon-oxygen-carbon ceramics, are given. Redistributions account for the escape of volatile organosilicon compounds, decreasing the yield and modifying the composition of the final ceramic. Moreover, they deeply modify the environment of Si atoms in the residue. At ϳ900°C, SiOO/ SiOC redistributions have reached equilibrium, leading to a random, entropically controlled distribution of SiO x C 4؊x sites. At higher temperatures, redistribution equilibria are displaced by the crystallization of SiC. Thus, the structure of the silicon oxycarbide phase (environment of Si atoms) is dependent on the O/Si ratio of the glass and the pyrolysis temperature, but is not directly dependent on the structure of the precursor.

Influence of Boron on the Microstructure of Polymer Derived SiCO Ceramics

“…[16,20,21] Both filled systems exhibit the same volatile species as analyzed by mass spectroscopy. No gaseous boron containing species could be detected indicating that the amount of boron remains constant during pyrolysis.…”

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

“…Although the SiOC ceramic has attracted increasing interest for its high-temperature stability, low-cost and processing versatility, the micro-structural stability was affected by many factors, such as the molecular structure of precursor, the pyrolysis conditions and the composition of ceramics [9][10][11][12][13][14][15].…”

Sol–gel derived Si/C/O/N‐materials: molecular model compounds, xerogels and porous ceramics

“…A detailed investigation of the crystallization behavior of the amorphous Si/C/O/N ceramics and the dependence of the Si/C/O/N network structure after annealing at various temperatures on the structure and chemical composition of the starting polymer is the major point of interest for our future work. While for Si/C/O materials a purely statistical distribution among possible SiC 4−x O x sites has been reported, [55] a strong influence of the precursor structure on the ceramic structure has been found for Si/C/N materials, especially when silazanes are compared with silylcarbodiimides. [56] …”