Preparation and High Temperature Inorganic Transformation of Flexible Silicone Aerogels

doi:10.15541/jim20220129

Abstract

Abstract:

Silica aerogels have wide application prospect in high temperature heat insulation due to their low density and high porosity. However, the brittleness and high cost of supercritical drying restrict their application. In this study, spongy silicone aerogels with high flexibility were prepared via Sol-Gel polymerization and atmospheric pressure drying using vinyltrimethoxysilane (VTMS) and vinylmethyldimethoxysilane (VMDMS) as precursors. The effects of precursor molar ratio on the microstructure and compressive resilience of aerogels, as well as the inorganic transformation process of aerogels in high temperature aerobic and anaerobic environments were studied. The results show that with the increase of VTMS/VMDMS ratio in the precursor, the aerogel particles become smaller and more tightly packed, and the compression resilience of aerogels also decreased. In air at 800 ℃, aerogels were transformed into inorganic SiO₂ by oxidation of organic side groups, fracture and rearrangement of main chain Si-O-Si. In N₂ at 800 ℃, aerogels were transformed into the mixture of inorganic SiO₂ and free carbon by pyrolysis reaction, and after further treatment at 1000-1400 ℃, SiO₂ and free carbon were subjected to carbothermal reduction reaction to form amorphous Si-O-C structures such as SiO₄, SiCO₃, SiC₂O₂, and SiC₃O, and a small amount of β-SiC nanowires. The Si-O-C structure formed by carbothermal reduction reaction at 1200 ℃ has optimal high temperature oxidation resistance, which can provide reference for the preparation of pyro-oxidation resistant Si-O-C aerogels.

Key words: silicone aerogel, flexibility, heat insulation, high-temperature oxidation, pyrolysis

CLC Number:

O648

LUO Yi, XIA Shuhai, NIU Bo, ZHANG Yayun, LONG Donghui. Preparation and High Temperature Inorganic Transformation of Flexible Silicone Aerogels[J]. Journal of Inorganic Materials, 2022, 37(12): 1281-1288.

Figures/Tables 8

Fig. 1 Schematic diagram of Sol-Gel process (a), IR spectra (b), NMR spectra (c) and SEM images (d-g) of aerogel samples Molar ratios of VTMS/VMDMS for aerogels (d-g) are 1, 2, 3, 4, respectively

Fig. 2 Cyclic compression stress-strain curves of aerogels (a) Stress-strain curves after 10-cycle compression; (b) Cyclic compression stress-strain curves of sample V/VM-3 Colorful figures are available on website

Fig. 3 (a, b) TG-IR spectra of sample V/VM-3 tested in air; (c) Photographs of sample V/VM-3 after heat-treated at different temperatures; (d) SEM image of sample V/VM-3 after heat-treated at 800 ℃

Fig. 4 (a, b) TG-IR spectra of sample V/VM-3 under N2 atmosphere; (c) XRD patterns, (d) NMR spectra and (e-h) SEM image of sample V/VM-3 after heat-treated at different temperatures (e) 800 ℃; (f) 1000 ℃; (g) 1200 ℃; (h) 1400 ℃

Fig. 5 Pictures of sample V/VM-3 before and after carbonization

Fig. 6 TG curves of inorganic Si-O-C aerogels

Fig. 7 XRD patterns of inorganic Si-O-C aerogels after oxidized at 800 ℃

Fig. 8 SEM image of sample T1400 after oxidized at 800 ℃

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