A study of morphological properties of SiO2 aerogels obtained at different temperatures

Jin-Jun Liao,Jian Feng,Peng-Zhao Gao,Lin Xu

doi:10.1007/s40145-018-0280-6

Jin-Jun Liao, Jian Feng + Show 2 more

Open Access

https://doi.org/10.1007/s40145-018-0280-6

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Abstract

In this paper, temperature dependence of nanoporous framework evolution process and variety of pore properties (pore volume, specific surface area (BET), and pore size) of SiO2 aerogels were characterized by FTIR, XPS, XRD, SEM, TEM, BET, BJH, etc. Results show that SiO2 aerogels treated at different temperatures all possess amorphous structure. With the increase of treated temperatures, BET values of SiO2 aerogels increase initially and then decrease, and it reaches the maximum value of 882.81 m2/g when treated at 600 °C for 2 h due to the addition of the nanopores and shrinkage skeleton of SiO2 aerogels. Higher temperatures may result in a framework transformation and particle growth; both factors could reduce the BET values of the aerogels. Nanoporous skeleton of SiO2 aerogels at room temperatures is composed of tetrahedron with a pore size of about 22.28 nm. Higher treated temperatures result in an increase of octahedron amount in nanoporous framework and a decrease of pore size. When treated at 1000 °C, an approximate dense SiO2 bulk via the framework collapse and particle growth is obtained. These varieties are derived from the formed extra bonds of Si–O–Si, higher local stress, and liquid phase between particles during heat treatment process.

Highlights

Silica (SiO2) aerogels show potential applications in the fields of catalysis, environmental protection, thermal insulation materials, electrical, optics, acoustic impedance materials, low bulk density materials (~0.03 g/cm3), nanoporous materials, high porosity (> 90 %), high surface area (500–1000 m2/g) and low thermal conductivity (0.005 W/(m·K)) materials [1,2,3,4,5], due toJ Adv Ceram 2018, 7(4): 307–316 fiber as reinforcer, which owned a low thermal conductivity of 0.022–0.028 W/(m K) and compressive strength of 1.71–3.70 MPa
It is known that the performance of a porous material depends on the pore size and framework structure [12], and these will vary at high temperatures
There are a limited number of studies that report the relationship between the nanoporous framework formation and particle growth process with the pore properties of SiO2 aerogels obtained at different temperatures [16]

Summary

Introduction

Silica (SiO2) aerogels show potential applications in the fields of catalysis, environmental protection, thermal insulation materials, electrical, optics, acoustic impedance materials, low bulk density materials (~0.03 g/cm3), nanoporous materials, high porosity (> 90 %), high surface area (500–1000 m2/g) and low thermal conductivity (0.005 W/(m·K)) materials [1,2,3,4,5], due to. There are a limited number of studies that report the relationship between the nanoporous framework formation and particle growth process with the pore properties of SiO2 aerogels obtained at different temperatures [16]. Zhou et al [13] studied the framework structure of aerogels with two different granular sizes of 5 and 20 nm They found that the small pores collapsed while the large pores expended after calcination at high temperatures. Huang et al investigated the structural changes of silica aerogels in the 950 1200 °C temperature range. Their results showed that the process consists of three steps [14,15]. The aim of this work is to study the process of SiO2 aerogel nanoporous framework formation and particle growth at different temperatures with a series of physicochemical methods, among others with FTIR, XPS, and TEM, to propose a qualitative regular polyhedron model of the process

Experimental

Results and discussion

Conclusions