Abstract Simultaneous interpenetrating networks (IPNs) comprising of polymethylsilsesquioxane (PMSQ) and phenolic resole (PF) systems at various PMSQ to PF ratios (0–75% w/w PF) which formed the matrix resin for 60% w/w short silica fibre reinforced composites (SR-PMSQ-PF) are subjected to a controlled heating regime in argon atmosphere at 1500 °C to investigate the microstructure and phase evolution based on IPN composition. This study aims at giving an insight into thermal, mechanical and chemical stability of silicone-phenolic IPN composites, particularly for high temperature thermal protection applications as in aerospace. The morphology and microstructure of the pyrolysed composites are well characterized using Raman and FTIR spectroscopy, XRD and SEM-EDS and based on this a mechanism for microstructure evolution is proposed. It is inferred that the pyrolysis of SR-PMSQ-PF composites results exclusively in the formation of cristobalite silica. In addition to that, the formation of SiC is also facilitated particularly in nano dimension with increase in phenolic content, by carbothermal reduction of silica derived from PMSQ and silica fibre predominantly through solid-vapour phase reaction along the (111) crystalline plane. The systematic evaluation of microstructure and morphology of pyrolysed SR-PMSQ-PF IPN composites is useful to define specific thermal protection applications for these composites.

中文翻译：

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热解短纤维增强聚甲基倍半硅氧烷-酚醛互穿网络的微观结构和相演变

摘要 由聚甲基倍半硅氧烷 (PMSQ) 和酚醛树脂 (PF) 系统组成的同时互穿网络 (IPN) 以不同的 PMSQ 与 PF 比率（0–75% w/w PF）组成，形成了 60% w/w 短二氧化硅纤维的基质树脂增强复合材料 (SR-PMSQ-PF) 在 1500 °C 的氩气气氛中进行受控加热，以研究基于 IPN 成分的微观结构和相演变。本研究旨在深入了解有机硅-酚醛 IPN 复合材料的热、机械和化学稳定性，特别是在航空航天等高温热保护应用中。使用拉曼光谱和 FTIR 光谱、XRD 和 SEM-EDS 对热解复合材料的形貌和微观结构进行了很好的表征，并在此基础上提出了微观结构演变的机制。据推断，SR-PMSQ-PF 复合材料的热解仅导致方石英二氧化硅的形成。除此之外，随着酚类含量的增加，特别是在纳米尺寸上，通过碳热还原 PMSQ 和二氧化硅纤维，主要通过沿 (111) 晶面的固-气相反应，碳化硅的形成也有促进作用。对热解 SR-PMSQ-PF IPN 复合材料的微观结构和形态进行系统评估有助于定义这些复合材料的特定热保护应用。通过碳热还原源自 PMSQ 的二氧化硅和二氧化硅纤维，主要通过沿 (111) 晶面的固-汽相反应。对热解 SR-PMSQ-PF IPN 复合材料的微观结构和形态进行系统评估有助于定义这些复合材料的特定热保护应用。通过碳热还原源自 PMSQ 的二氧化硅和二氧化硅纤维，主要是通过沿 (111) 晶面的固-汽相反应。对热解 SR-PMSQ-PF IPN 复合材料的微观结构和形态进行系统评估有助于定义这些复合材料的特定热保护应用。