Improvement of the Thermal Insulation Performance of Silica Aerogel by Proper Heat Treatment: Microporous Structures Changes and Pyrolysis Mechanism

Zhiyi Lun,Xudong Cheng,Yong Zhou,Lunlun Gong,Zhongxin Zhang,Yurui Deng,Yuelei Pan

doi:10.3390/gels8030141

Abstract

A simple heat treatment method was used to optimize the three-dimensional network structure of the hydrophobic aerogel, and during the heat treatment process at 200–1000 °C, the thermal conductivity of the aerogel reached the lowest to 0.02240 W/m·K between 250 °C and 300 °C, which was mainly due to the optimization of microstructure and pyrolysis of surface groups. Further Fluent heat-transfer simulation also confirmed the above results. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used to finely measure the pyrolysis process of aerogels, and the pyrolysis process of aerogel was divided into four stages. (I) Until 419 °C, as the temperature continued to rise, surface methyl groups were oxidized to form hydroxyl. (II) As the temperature reached to 232 °C, the oxidation proceeded. In addition, inside the aerogel, because of lacking oxygen, the reaction produced CH4 and C–Si bonds would form. (III) After 283 °C, Si–OH groups began to condense to form Si–O–Si, which optimized the three-dimensional network structures to be beneficial to improve the thermal insulation performance of silica aerogel. (IV) When it reached 547 °C, the chemical reaction was terminated, and all the primary particles gradually fused into secondary particles and sintered to form clusters.

Highlights

With the increasing demand for energy utilization [1,2,3] and the importance of thermal safety, the application range of thermal insulation materials has gradually expanded
Silica aerogel treated by high-temperatures would shrink (Figure S1), and with the increase in the heat treatment temperature, the thermal conductivity exhibited significantly decrease to the lowest of 0.02242 W/m·K at 300 ◦C and increase from 350 ◦C to 1000 ◦C
In order to study the mechanism that the thermal insulation performance of silica aerogel changes with the heat treatment temperature, the influence of temperature on the hydrophobic group and structure had been analyzed

Summary

Introduction

With the increasing demand for energy utilization [1,2,3] and the importance of thermal safety, the application range of thermal insulation materials has gradually expanded. Insulation materials with excellent performance can significantly reduce the heat loss in some scenes [4,5,6], and control the temperature in certain technological processes [7] and improve the stability of high-temperatures [8], which plays an important role in industry and commerce [9]. As a material with excellent performance, silica aerogel has extremely low density and thermal conductivity [10,11]. The heat transfer process requires numerous pores, resulting in aerogels’ thermal conductivity significantly lower than that of air. The resulting aerogel films [14], fibers [15], boards [16], blankets [17], and other products have been widely used in thermal insulation systems in construction, petroleum, chemical, and other fields

Methods

Results

Conclusion