Sol-gel process

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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

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
(10.) Chen, XB, Zhou, SX, You, B, Wu, LM, "Mechanical Properties and Thermal Stability of Ambient-Cured Thick Polysiloxane Coatings Prepared by a Sol-Gel Process of Organoalkoxysilanes." Prog.
The size of the silica particles and morphology of hybrids were controlled in co- polyimide based hybrids through amino-silane functionalization of silica particles prepared in situ through a self-catalyzed sol-gel process using atmospheric moisture.
"Lotus effect" superhydrophobic coatings, with a water contact angle (WCA) above 150[degrees](1,2) and contact angle hysteresis below 10[degrees], have attracted special interests due to their wide applications in anti-adhesion,(3) antifouling,(4) self-cleaning,(5-8) and microfluidic systems.(9) Until now, versatile approaches have been developed for the preparation of superhydrophobic coatings, including template-based techniques,(l0-12) plasma-enhanced chemical vapor deposition (PECVD),(13-16) electrochemical deposition (ECD),(17-18) layer-by-layer (LBL) deposition,(19) sol-gel process,(20), (21) colloidal assembly,(22-26) and so on.
In this research, modified nanopore adsorbents were synthesized by a sol-gel process first and then they were characterized by XRD, BET, IR, and SEM and other characterization instruments.
(7.) Latthe, SS, Iniai, H, Ganesan, V, Rao, AV, "Porous Superhydrophobic Silica Films by Sol-Gel Process." Microporous Mesoporous Mater., 130 (1-3) 115-121 (2010)
The sol-gel process is a chemical method to prepare inorganic materials, initially employed to synthesize high purity inorganic networks such as glasses and ceramic materials.
A few number of papers discuss the effect of sol-gel process parameter on physical properties of [alpha]-alumina nanoparticle.
Furthermore, a simple modification of the film composition can be performed directly in the sol-gel process.
It is evident that we succeeded in producing crystalline [SrTi0.sub.3] at the low temperature by a straightforward particulate sol-gel process. Therefore, this process has good potential for industrial applications because less energy is consumed during the production process.
Other subjects addressed include PL materials prepared by the sol-gel process, studies of PL spectra in INGAN/GAN heterostructures, and the role of Mn concentration in luminescence of nanocrystalline ZnS.
Groot., " Better bioactive ceramics through sol-gel process" J.
The sol-gel process is a chemical synthesis method described as the creation of an oxide network by progressive condensation reactions of molecular precursors in a liquid medium.