What is sol-gel processing?
It is a process for making very small particle 20 to 40 nm that are virtually impossible to make by conventional grinding. Its main use at present seems to be for optical coatings where the finer particles give better optical clarity. Manufacture of fine a ceramic fibre seems to be the other common application. How does sol-gel processing work? A liquid precursor of the particle is dissolved in a solvent, usually alcohol, water is added and then acid or base. The mixture is coated or cast. The precursor then decomposes to form the fine ceramic particles. If the particle concentration is high enough, the mixture gels. The gel is dried, and then heated at high temperature to sinter the ceramic, giving the desired ceramic film or fibre. During this drying and sintering process, shrinkage occurs through loss of solvent and air, and this shrinkage must be carefully controlled to avoid cracking. Self-cleaning textiles The German researcher Wilhelm Barthlott of the Bonn Institute of botany di
