Identification of permethyloctasilsesquioxane by a novel method: Collecting smoke formed by chemical changes in a methylsilsesquioxane blanket at 2000-2500 °c using gas chromatography-mass spectrometry

Abstract

This study examined the high-temperature combustion behavior of methylsilsesquioxane (MSQ) aerogels, as well as aerogel and ceramic blankets synthesized using methyltrimethoxysilane (MTMS), a common precursor for both MSQ aerogels and polyhedral oligomeric silsesquioxanes (POSSs). Combustion tests were conducted at extreme temperatures ranging from 2000 to 2500 degrees C. During these tests, smoke was collected and analyzed using gas chromatography-mass spectrometry (GC-MS), which detected a novel compound, permethyloctasilsesquioxane (POSS-like), formed during combustion. Since MTMS is a common precursor for MSQ and POSS, it is possible that POSS-like structures could be synthesized directly via high-temperature treatments. This result could bypass conventional methods requiring complex, multi-step chemical procedures and provide new insights into the chemistry of materials exposed to high temperatures. The results demonstrated that burning an aerogel blanket at such elevated temperatures induces significant changes in chemical composition and releases volatile organic compounds (VOCs), which are critical for future studies. X-ray photoelectron spectroscopy (XPS) analysis indicated shifts in the silicon-oxygen (Si-O) peak from 102.59 to 103.67 eV in ceramic blankets and from 102.59 to 103.64 eV in aerogel blankets, suggesting the breakdown of existing bonds and the formation of new chemical structures. Additionally, various analytical techniques including Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) coupled with FTIR (TGA-FTIR) were utilized to elucidate chemical transformations occurring during combustion. X-ray diffraction (XRD) analysis confirmed the formation of alpha-cristobalite and other silica polymorphs, indicating in situ ceramization of the aerogel framework under extreme thermal stress. Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) analyses revealed substantial reductions in surface area and mesoporosity after combustion, reflecting compaction and degradation of the porous architecture.