Currently of great interest because of its application in the field of silica micro-optics, sol-gel technology has created a new class of materials that incorporate organic molecules in porous inorganic substances. Sol-gel technology can be compared to jelly: a liquid trapped by solids.

Essentially, the sol-gel process is a three-fold one: sol and gel formation, drying and densification. Sol is produced by mixing chemical ingredients which are then poured into moulds. Hydrolysis and polycondensation of the sol form the three dimensional shape required and the solution stiffens to a wet gel. The gel is left to age and a further drying step eliminates the interstitial liquid from the gel body. Heat treatment changes the porous solid into a dense homogeneous material, where no further finishing is necessary. During the process, the shrinkage is predictable: a factor of 2.5, uniform in all three linear dimensions.

Applied to silica, the technology provides an economical and practical way of moulding rather than machining complex optical micro lenses of the type used in, for example, endoscopic surgical lasers. Micro-optics with aspherical, cylindrical or other diffractive surfaces can be moulded, as can components with grooves and flanges, allowing optical systems to be simplified and miniaturised.

But the possibilities are not limited to this field. Optical and chemical sensors, scratch-resistant coatings, enzyme supports and bio-implants are some of the other uses of the technology.

Dr Carole Harrison at Nottingham Trent University is investigating electroceramics, as well as biocompatible variants that can be used as chemical sensors or implants to monitor chemical and biochemical processes in industrial, biological, and medical applications.

Design engineers who wish to get a better understanding of the sol-gel processes can contact the Sira Technology Centre.

{{Sira Technology CentreTel: 0181-467 2636Enter 401}}