Sol-gel process

Sol-gel process

A chemical synthesis technique for preparing gels, glasses, and ceramic powders. The sol-gel process generally involves the use of metal alkoxides, which undergo hydrolysis and condensation polymerization reactions to give gels.

The production of glasses by the sol-gel method permits preparation of glasses at far lower temperatures than is possible by using conventional melting. It also makes possible synthesis of compositions that are difficult to obtain by conventional means because of problems associated with volatilization, high melting temperatures, or crystallization. In addition, the sol-gel approach is a high-purity process that leads to excellent homogeneity. Finally, the sol-gel approach is adaptable to producing films and fibers as well as bulk pieces. See Glass

The sol-gel process comprises solution, gelation, drying, and densification. The preparation of a silica glass begins with an appropriate alkoxide which is mixed with water and a mutual solvent to form a solution. Hydrolysis leads to the formation of silanol groups (Si—OH). These species are only intermediates. Subsequent condensation reactions produce siloxane bonds (Si—O—Si). The silica gel formed by this process leads to a rigid, interconnected three-dimensional network consisting of submicrometer pores and polymeric chains. During the drying process (at ambient pressure), the solvent liquid is removed and substantial shrinkage occurs. The resulting material is known as a xerogel. When solvent removal occurs under hypercritical (supercritical) conditions, the network does not shrink and a highly porous, low-density material known as an aerogel is produced. Heat treatment of a xerogel at elevated temperature produces viscous sintering (shrinkage of the xerogel due to a small amount of viscous flow) and effectively transforms the porous gel into a dense glass.

Materials used in the sol-gel process include inorganic compositions that possess specific properties such as ferroelectricity, electrochromism, or superconductivity. The most successful applications utilize the composition control, microstructure control, purity, and uniformity of the method combined with the ability to form various shapes at low temperatures. Films and coatings were the first commercial applications of the sol-gel process. The development of sol-gel-based optical materials has also been quite successful, and applications include monoliths (lenses, prisms, lasers), fibers (wave­guides), and a wide variety of optical films. Other important applications of sol-gel technology utilize controlled porosity and high surface area for catalyst supports, porous membranes, and thermal insulation. See Materials science and engineering

References in periodicals archive ?
Self-cleaning cotton material was successfully created by coating a cotton fabric with anatase nanoparticles obtained with a low-temperature sol-gel process.
Kanaev, Oriented ZnO Thin Films Synthesis by Sol-Gel Process for Laser Application, Thin Solid Films, 428, 257 (2003).
Sol-gel process has proved to be versatile and has been widely used in the preparation of composites biomaterials [16].
Specific topics include preparing silica-encapsulated stearic acid as composite phase-change material through the sol-gel process, developing materials-by-design for carbon dioxide capture applications, the combustion characteristics and kinetics of blending coal, and the electrochemical deposition of high purity silicon from molten fluoride electrolytes.
For Sample 1, the coating on the 10 PPI metal foam was manufactured from hydrofluoric acid used as the catalyst in the Sol-Gel process, while for sample 2, the coating was prepared using ammonium hydroxide as the catalyst.
The topics include the effect of crosslinkers and fillers on microstructure and gas permeation, organic-inorganic hybrid coatings with enhanced scratch resistance properties obtained by the sol-gel process, protective coatings based on silsesquioxane nanocomposite materials, and ultrasound-assisted synthesis and its effect on the properties of calcium carbonate-polymer nanocomposites.
Effect of catalysts used in the sol-Gel process on the microstructure and absorption/desorption performance of silica aerogels, AsME 2013 International Mechanical Engineering Congress & Exposition, November 15-21, 2012--san Diego, CA.
The aim of the research was to use sol-gel process (production of silica nanoparticles) and adding copper metallic compounds to it to create superhydrophobic and antibacterial properties in cotton fabric.
2] spheres were synthesized with a sol-gel process in an aqueous solution as follows.
Zhang, "Complex permittivity, permeability, and microwave absorption of Barium ferrite by citrate sol-gel process," Rare Metals, Vol.