Xerogels coatings

Figure 9.3 Optical micrographs of subcutaneous tissue showing the foreign body capsule (denoted by arrows) formed after 6 weeks at (A) bare silicone rubber elastomer, (B) xerogel-coated control, and (C) NO-releasing xerogel-coated implants. Reprinted with permission from Ref. 32. Copyright 2007 Elsevier. (See the color version of this figure in Color Plates section.)...

The exposure of as-deposited sol-gel films to a UV source is one of the most popular techniques to cure xerogel coatings. On one hand, this method has been widely applied in industrial production because of the low cost and versatility on the other hand, it is also one of the cheaper and simpler ways to obtain a lithographic technique that is widely used for producing patterned films and photonic devices such as strip waveguides. 

For this reason, corrosion inhibitors such as cerium salts or organic biocides are successfully added to the silane sol-gel layer. Akid and coworkers, for example, have developed a broad range of chromate-free xerogel coatings based on doped Ormosil formulations with very high corrosion resistance and with little evidence of change after extensive salt spray tests for a variety of different metal substrates (aluminum alloys, steel, magnesium, etc.). 

Both xerogels and aerogels are characteristically high surface area materials (surface areas normally exceed 500 m2/g). Unlike wet gels, many uses exist for dried gels due to their high surface areas and small pore sizes (typically, < 20 nm diameters). Examples include catalyst supports (12.). ultrafiltration media (18), antireflective coatings (19-20), and ultra-low dielectric constant films. (Lenahan, P. M. and Brinker, C. J., unpublished results.)... 

The 02-sensing materials based on spin-coated n-octyl-triethoxysilane (Octyl-triEOS) / tetraethylorthosilane (TEOS) composite xerogel films was synthesized and investigated99. These sensors were based on the O2 quenching of tris(4,7-diphenyl-l,10-phenanthroline)ruthenium (II)... 

Since both aerogels and xerogels have high surface areas and small pore diameters they are used as ultrafiltration media, antireflective coatings, and catalysts supports. Final densi-fication is carried out by viscous sintering. 

When multicomponent alkoxide solutions, or a single alkoxide and a soluble inorganic salt, are mixed, a multicomponent alkoxide may result. In this way, such complex oxides such as the YBCO superconductor (cf. Section 6.1.2.4) can be formed. Sol-gel processing can also be used to coat fibers for composites and to form ceramics with very fine pore sizes called xerogels. A xerogel commonly contains 50-70% porosity, a pore size of 1-50 nm, and a specific surface area exceeding 100 m /g. 

There is a variety of miscellaneous fillers that are of interest for reinforcing elastomers such as PDMS. Examples are ground-up silica xerogels,119 carbon-coated silica,120 and functionalized silica particles.121-123... 

Coustier, R, S. Passerini, and W.H. Smyrl. 1997. Dip-coated silver-doped V2Os xerogels as host materials for lithium intercalation. Solid State Ionics. 100 247-258. 

The sol-gel method for coating substrates has been used so far in several industries aerospace, optics, automotive, household machines and semiconductors. Sol-gel refers to a process in which a dispersion containing small molecules (the sol) forms a cross-linked polymer (the gel) upon drying. After the heating step, this xerogel is transferred into a dense film. This process is depicted in Fig. 

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