Sintering of aerogels for glass synthesis

Abstract

Silica glasses can be synthesized by sintering silica aerogels at temperatures ranging from 900 to 1200°C, i.e., close to half the temperatures used for glass melting. The heat treatment can be tailored to obtain either fully densified or porous glass. This paper describes the different steps of the transformation of aerogels into glass along with the textural and microstructural transformations. Different types of information are analyzed: variations in dimensional shrinkage and the apparent density as a function of the densification conditions (temperature, duration of the thermal treatment), the associated structural changes, and the changes in the porous characteristics (macro and meso porosity, average pore radius). The kinetics of dimensional shrinkage help characterize the sintering mechanism. Structural data and porous characteristics allowed us to quantify the transformation of internal aggregates and porosity. Graphical AbstractThe viscous flow-sintering model also applies to fractal aerogels. Highlights •The viscous flow sintering model proposed by Scherer is in good agreement with the sintering kinetics of fractal aerogels. •The viscosities of aerogels and the activation energies of the sintering process depends on the OH content. •The size of the aggregates decreases and the particles increase in size, fractal dimension tends to 3. •The smaller pores sinter first, this local densification causes narrowing of the macropores.

Porous glasses from aerogels: from organic liquid to mineral materials

“…Sintering identification was obtained by studying the kinetics of shrinkage. In a previous work [9,11], we have shown that both mechanisms are responsible for sintering of classical silica aerogels. At low temperatures, the low sintering is due to a slow diffusion process (500 to 700° C) [27] whereas at temperatures above 1000 ° C, the sintering is related to a viscous flow.…”

“…The "aerogel" is a solid material, amorphous and highly porous (80-99% porosity) [5] that can be transformed into silica glasses by a sequence of sintering treatments [9,10,11]. Depending on the duration of the heat treatment, porosity is progressively eliminated [11].…”

“…The "aerogel" is a solid material, amorphous and highly porous (80-99% porosity) [5] that can be transformed into silica glasses by a sequence of sintering treatments [9,10,11]. Depending on the duration of the heat treatment, porosity is progressively eliminated [11]. Silica glass and binary silicates glasses have been successfully synthesized by gelation, supercritical drying and sintering [9,12,13,14].…”

“…Silica glass and binary silicates glasses have been successfully synthesized by gelation, supercritical drying and sintering [9,12,13,14]. Previous studies shows that the sintering mechanisms is described by the viscous flow Scherer's model [9,11]. Classical silica aerogel are brittle materials [15,16] with a large pore size distribution and a fractal structure [17].…”

Fractal Structure in Silica and Composites Aerogels

“…There are currently many applications of aerogels, such as catalysts [ 2 ], insulators [ 3 ], sensors [ 9 ] environmental [ 10 ] and biomedical applications [ 11 , 12 ], etc., and the potential uses of these materials are even larger if one considers the aerogel as a precursor. Through heat treatments, the silica aerogels can indeed be sintered into silicate glasses and glass ceramics [ 13 , 14 ]. However, these porous materials can also be used as a matrix for the synthesis of multi-phase materials, doped materials, or composites.…”