Reducing organic groups on hydrophobic silica aerogels (SA) is worth exploring for lowering their thermal hazard risk. In this work, we used dimethyldichlorosilane (DMDCS) to modify silica alcogels, investigated the effects of DMDCS concentration and focused on the thermal hazard assessment of the DMDCS modified SA (DSA). It was turned out that the DSA had less −CH₃ content in spite of the thermal stability close to the trimethylchlorosilane modified SA (TSA), about 240 °C. The kinetics study suggested the apparent activation energy (E_a) could be divided into two segments, corresponding to the two processes in the pyrolysis. The positive enthalpy and entropy changes indicated that the thermal oxidation of the DSA was an exothermic reaction, which could not occur without external energy supply. The average E_a of the DSA was far larger than that of the TSA and the gross calorific value of the DSA decreased by about 12% compared with that of the TSA. All these results drew a conclusion that the DMDCS modified SA reduced the thermal hazard to some degree, which provided one possible solution to further lower the thermal hazard of hydrophobic SA.

中文翻译：

---

通过使用二甲基二氯硅烷作为改性剂减少疏水性二氧化硅气凝胶的热危害

降低疏水性二氧化硅气凝胶（SA）上的有机基团对于降低其热危害风险值得探索。在这项工作中，我们使用二甲基二氯硅烷（DMDCS）改性二氧化硅醇凝胶，研究了DMCCS浓度的影响，并着重于DMDCS改性SA（DSA）的热危害评估。结果表明，尽管热稳定性接近三甲基氯硅烷改性的SA（TSA），约240℃ ，但DSA具有较少的-CH ₃含量。动力学研究表明表观活化能（E _a）可分为两个部分，分别对应于热解过程中的两个过程。焓和熵的正变化表明，DSA的热氧化是放热反应，没有外部能量供应就不可能发生。DSA的平均E _a远大于TSA的Ea，DSA的总热值比TSA降低了约12％。所有这些结果得出结论，DMDCS改性的SA在一定程度上降低了热危害，为进一步降低疏水性SA的热危害提供了一种可能的解决方案。