Probing the early-stage/rapid processes in hydrolysis and condensation of metal alkoxides

Understanding and control of the early-stage sol-gel reaction processes involving metal alkoxides are important to many advanced materials development and applications. In this work, Fourier transform infrared spectroscopy (FTIR) and small angle X-ray scattering (SAXS) were coupled with a specially designed, rapid flow-through mixing cell for monitoring such processes. The rapid, early-stage hydrolysis and condensation of zirconium n-butoxide in ethanol were chosen as the basis for a model system. FTIR was used to study soluble-species reaction kinetics, while the SAXS technique monitored in situ the solid-phase particle formation/growth (i.e., the nucleation and aggregation kinetics of polymeric clusters/particles). Monitoring the reactions and cluster/particle growth within a millisecond time regime was achieved. In addition, key parameters such as reaction time, concentration of base (i.e., quarternary tetramethyl ammonium hydroxide), temperature, water concentration, and alkoxide concentration were fully investigated in a continuous flow-through reactor. (C) 2000 Kluwer Academic Publishers.