Pyrolysis study of methyl-substituted Si-H containing gels as precursors for oxycarbide glasses, by combined thermogravimetry, gas chromatographic and mass spectrometric analysis
Pyrolysis study of methyl-substituted Si-H containing gels as precursors for oxycarbide glasses, by combined thermogravimetry, gas chromatographic and mass spectrometric analysis
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DOI：
10.1039/jm9960600585
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发表时间：
1996-04-01
影响因子：
--
通讯作者：
Soraru, GD
中科院分区：
文献类型：
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作者：
Campostrini, R;DAndrea, G;Soraru, GD
通过混合不同的含有Si-CH3和Si-H基团的乙氧基硅前驱体制备了整体透明的凝胶，其组成确保了相同数量的C-H和Si-H键。在氦气氛下对样品进行热解，结合热重分析、气相色谱和质谱分析，研究凝胶转化为碳氧化合物材料的过程。除了通常的直接热质谱分析(TG-MS)外，还成功地实现了TG-GC-MS的安排，允许对在热分解过程中同时析出的物种进行气相色谱分离，然后进行质谱分析。实验结果表明，失重分三步进行，每一步都有不同的反应。在低温下，硅氧烷网络的致密化源于进一步的缩合反应。在中等温度下，硅氧烷链发生了显著的重排，由于Si-H和Si-O键交换，挥发性硅烷和几个硅氧烷碎片释放出来。在较高温度下，检测到甲烷的生成，并将其归因于Si-C键的断裂。作为对比，还研究了只含有Si-CH3基团或Si-H基团的凝胶的热解。
Monolithic and transparent gels were prepared by mixing various ethoxide silicon precursors containing Si-CH3 and Si-H groups, the composition ensuring the same number of C-H and Si-H bonds. Pyrolysis of these samples was followed under helium how by connecting thermogravimetry, gas chromatographic and mass spectrometric analysis, to study the conversion of the gels into oxycarbide materials. In addition to the usual direct thermal and mass spectra analysis (TG-MS), a TG-GC-MS arrangement, allowing gas chromatographic separation of the species simultaneously evolving during thermodecomposition followed by mass spectral analysis, was successfully achieved. Experimental results indicate that mass loss occurs in three steps, each characterized by specific reactions. At low temperatures, densification of the siloxane network derives from further condensation reactions. At intermediate temperatures, a remarkable rearrangement of the siloxane chains occurs, with the release of volatile silanes and several siloxane fragments due to Si-H and Si-O bond exchanges. At higher temperatures, the development of methane was detected and attributed to Si-C bond cleavage. Pyrolysis of gels containing only Si-CH3 or Si-H groups was also studied for comparison.