Pyrolysis Mechanism of SiBCN Polymer Precursor

doi:10.3724/SP.J.1077.2014.13278

Abstract

Abstract:

High temperature amorphous materials, mainly in the system of SiBCN, have aroused ever increasing attention. Effective methods should be used to study the structural changes in the process of fabrication. In this paper, the thermal stability of PBSZ and the pyrolysis mechanism of SiBCN polymer precursor were studied by SS-NMR and FT-IR. Polymer-to-ceramic transformation can be divided into three stages as follows. The first stage is the production of initiator in which, the tertiary carbon dehydrogenates to quaternary carbon free radical. The second stage is propagation and termination in which, quaternary carbon free radical attacks methyl group to turn the methyl group into new free radical. With increasing temperature, the free radical attacks Si-CH₃ and results in a new free radical. The propagation of the chain occurs when new free radicals are generated, while the termination occurs after the free radicals combination with each other. The third stage is polymer-to-ceramic transformation. Through dehydrogenation, ceramics are produced from the intermediate inorganic products, and amorphous continuous 3D mesh structures are formed. The first and second stages are organic transformations and the third stage is an inorganic transformation. There are four elements in the ceramic, including Si, B, C and N.

Key words: MNR, FT-IR, SiBCN, Polyborosilazane

CLC Number:

TB35

LI Ya-Jing, ZHANG Yue. Pyrolysis Mechanism of SiBCN Polymer Precursor[J]. Journal of Inorganic Materials, 2014, 29(3): 321-326.

Figures/Tables 8

Fig. 1 Reaction paths presenting the synthesis of polymer precursor

Fig. 2 TGA/DSC curves for weight loss and heat flow of the preceramic polymer under inert atmosphere

Fig. 3 Gas release situation of pyrolysis of the preceramic polymer under inert atmosphere

Fig. 4 13C-NMR spectra of SiBCN ceramics at different pyrolysis temperatures

Fig. 5 11B-NMR spectra of SiBCN ceramics at different pyrolysis temperatures

Fig. 6 29Si-NMR spectra of SiBCN ceramics at different pyrolysis temperatures

Fig. 7 FT-IR spectra of PBSZ-derived ceramic at different pyrolysis temperatures (a) Precursor; (b) 200℃; (c) 450℃; (d) 600℃; (e) 800℃; (f) Ceramic

Table 1 Analysis of FT-IR spectra of PBSZ-derived ceramics at different pyrolysis temperatures

	Precursor	200℃	450℃	600℃	800℃	Creamic
γN-H	3383	3444	3405	3444	3429	3447
γ_asCH₃	—	—	—	2973	—	—
γ_asCH₂	2925	—	—	2924	—	—
γ_sCH₂	2855	—	—	2854	—	—
δ_s(C-) CH₃, δ_sCH₂	1460	—	—	—	—	—
δ_as(C-) CH₃, δCH₂	1407	—	—	—	—	—
δ_s(C-) CH₃	1363	1389	1389	1388	—	—
γC-C	—	—	—	—	1369	1372
δ_s(Si-) CHX	1265	1269	1268	1276	—	—
γ B-C	1045	1038	1033	1041	1068	1082
γSi-N	926	883	879	—	—	897
γSi-C	783	779	779	775	794	801

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