Recent advances in sol–gel synthesis of monolithic silica and silica-based glasses

Abstract

Studies on sol-gel synthesis of monolithic silica and silicate glasses are summarized. Major research efforts have been devoted to avoid the fracture problems, associated with the extensive shrinkage of wet gels during drying. Supercritical drying, incorporation of silica fillers, and reduction of the surface tension of pore liquid have been used to form monolithic dried gels without fracture. More recent studies have shown that wet gels derived from alkoxides can be dried in a relatively short time without fracture at ambient pressure, by employing controlled drying accompanied by the cavitation of the pore liquid, macroscopic phase separation in parallel with gelation, and fluorine modification. By optimizing the synthesis procedure, it is also possible to reduce the use of reagents such as external alcohols, organic solvents, and other additives, which are removed during synthesis and are unnecessary in the final products. Another subject of considerable interest is the development of silica-based functional glasses that are difficult to form by conventional melt-quench and vapor-phase methods, by taking advantage of melt-free processes conducted at relatively low temperatures. Most of the recent studies on the functionalization of sol-gel-derived silica glasses are concerned with the doping of nanoparticles, rare earth ions, and/or fluorine.

80SiO2‐20LaF3 oxyfluoride glass ceramic coatings doped with Nd3+ for optical applications

“…Finally, a review of sol-gel monoliths with more than 200 references focused on the preparation of silica and silica-based materials, especially SiO 2 -LnF 3 GCs, was reported by Kajihara. 32 However, in all of these works, typical LaF 3 concentration was between 5 and 10 mol%; furthermore, the same synthesis procedure was used without modifying the processing parameters. On the other hand, structural characterization of thin films together with optical properties have been poorly evaluated.…”

Fabrication and Characterization of Porous Silica Monolith by Sintering Silica Nanoparticles

“…Sol-gel processes have been widely adapted for fabricating a porous silica monolith to control a pore size [1]- [8]. On the other hand, a particulate sol-gel process, which uses silica nanoparticles as a starting material, is also attractive alternative to fabricate a How to cite this paper: Ikeda, H. and Fujino, S. (2017) Fabrication and Characterization of Porous Silica Monolith by Sin-large porous silica monolith.…”

Incorporation of epoxy resin and graphene nanolayers into silica xerogel network: an insight into thermal improvement of resin

“…The content of water, metal alkoxides, and solvent, pH value, temperature, and drying methods are important factors in microstructure of gel [16]. Xerogels are obtained by evaporation of solvent in wet gel [17]. In some cases, surface modification is employed for easy removal of solvent molecules [18][19][20].…”