Alumina-Doped Silica Aerogels for High-Temperature Thermal Insulation.

Yu Wu,Jun Shen,Ze Zhang,Lin Liu,Xiaodong Wang

doi:10.3390/gels7030122

Abstract

In this study, we used two methods to prepare alumina-doped silica aerogels with the aim of increasing the thermal stability of silica aerogels. The first method was physical doping of α-Al2O3 nano powders, and the second method was to create a chemical compound via the co-precursor of TEOS and AlCl3·6H2O in different proportions. The shrinkage, chemical composition, and specific surface area (SSA) of samples after heating at different temperatures were analyzed. Our results show that the silicon hydroxyl groups of samples derived from AlCl3·6H2O gradually decreased and nearly disappeared after heating at 800 °C, which indicates the complete dehydration of the silicon hydroxyl. Thus, the samples exhibited a large linear shrinkage and decreased SSA after high-temperature heat treatment. By contrast, samples doped with α-Al2O3 powders retained abundant silicon hydroxyl groups, and the 6.1 wt.% α-Al2O3-doped sample exhibited the lowest linear shrinkage of 11% and the highest SSA of 1056 m2/g after heat treatment at 800 °C. The alumina-doped silica aerogels prepared using a simple and low-price synthesized method pave the way for the low-cost and large-scale production of high-temperature thermal insulation.

Highlights

Silica aerogels are considered important and useful materials due to their nanoporous structure, ultra-low density, low thermal conductivity, high porosity and high specific surface area
The color of AL samples changed from brown to white as the temperature increased from 500 ◦ C to 700 ◦ C, which indicates the decomposition of organic groups
In order to analyze the thermal stability of samples, we focused on the linear shrinkage of all the samples after heat treatment from 300 to 1000 °C with an incremental step of 100 °C (Figure 5)

Summary

Introduction

Silica aerogels are considered important and useful materials due to their nanoporous structure, ultra-low density, low thermal conductivity, high porosity and high specific surface area. Following about 90 years of development, the production of silica aerogels has been industrialized, and they have been widely applied, especially in the thermal insulation field [1,2,3,4]. Fabricating silica-based aerogels with enhanced heat resistance using an inexpensive process is critical to the development of industrial high-temperature applications. Aluminum alkoxides are the main precursors used to fabricate alumina or alumina composite aerogels, they have some defects that render them unsuitable for industrial production. Wu et al [32] fabricated Al2 O3 -SiO2 composite aerogels via TEOS and AlCl3 ·6H2 O as precursors, which showed a γ-Al2 O3 phase and high SSA of 630.6 m2 /g after heat treatment at 600 ◦ C. The SSA of Al2 O3 -SiO2 composite aerogels decreased to 277.7 m2 /g due to volume shrinkage after heat treatment at 1000 ◦ C

Methods

Results

Conclusion