Methyltrichlorosilane modified hydrophobic silica aerogels and their kinetic and thermodynamic behaviors
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To reduce the flammability, hydrophobic silica aerogels (SAs) were modified by replacing commonly used trimethylchlorosilane (TMCS) with methyltrichlorosilane (MTCS). It was observed that the MTCS modified SAs (MSA) showed similar physicochemical properties to those TMCS modified SAs (TSA), including the density, thermal conductivity, hydrophobicity, and even thermal stability. However, the flammability of MSA was observed much lower than that of TSA, which was reflected by the significantly decreased gross calorific value (GCV). Furthermore, it was known from the kinetic and thermodynamic analyses that the pyrolysis of MSA became more difficult with the increasing conversion rate (α), which was evidenced by the fact that the apparent activation energy (E) kept rising to about 194 kJ/mol during the whole pyrolysis. Based on the changed E along the time, the pyrolysis process could be divided into two stages, in which α = 0.4 was considered as the turning point. Those main thermodynamic parameters, including pre-exponential factor (A) and the changes of enthalpy (ΔH) and entropy (ΔS), showed a quite consistent tendency with the E, whereas the change of Gibbs free energy (ΔG) almost kept unchanged. The research outcome of this study can provide a deep understanding of the pyrolysis process of SAs and render the public realize the thermal hazard risk of SAs.
MTCS replaced TMCS to modify silica aerogels to reduce the flammability.
Gross calorific value of MTCS modified silica aerogels (MSA) decreased over 50%.
Kinetic and thermodynamic behaviors of MSA were studied in detail.
The pyrolysis of MSA was difficult to proceed along the time.
This study provided a technical basis for the thermal hazards of silica aerogels.
KeywordsSilica aerogels Methyltrichlorosilanes Thermal conductivity Thermostability Kinetics Thermodynamics
This work was supported by the Fundamental Research Funds for the Central Universities (grant number 202501003, 202045001 and 502211841).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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