Physical and chemical properties of sol-gel processing

Abstract

Sol-gel processing is known as a novel technique to synthesize glasses using liquid chemicals. Hydrolysis reaction can basically determine a polymeric structure resulting in glasses of different properties. The hydrolysis reaction of tetramethyl orthosilicate, TMOS, is investigated at pHs of 4.9, 6.0, 7.5 of water, and with the chemical additives: formamide, acetone, methanol acetonitrile, and dioxane. The chemical additives are used for a solvation effect, and the water of different pHs is used as a catalyst. The experiment has been completed as a function of time, and at pressures from 1 to 2 kilobars. The rate constant is determined using Raman spectroscopy. The roles of viscosity, pressure induced mobility, concentration of hydronium and hydroxyl ions, volumes of activations, dipole moment, dielectric constant, and hydrogen bonds are discussed. After hydrolysis and polymerization, gelation occurs. The Positronium Decay Technique is also used to measure pore sizes of the silica gels. The results are compared with the BET method. The gels of pores larger than 50 A are used to synthesize titanium and boron doped gels and to characterize their physical properties. Infrared spectroscopy is used to identify Si-O-Ti and Si-O-B bonds.