Sol-gel and ultrafine particle formation via dielectric tuning of inorganic salt-alcohol-water solutions

Under some conditions, inorganic salts can be as good precursors for sol-ge l-type processing as those obtained from expensive metalloorganic precursor s such as alkoxides. In this work, the formation of monodispersed hydrous z irconia microsphere particles (particularly nanosized) and gels was achieve d in solutions of zirconyl chloride dissolved in alcohol-water mixed solven ts. The dielectric property of the mixed alcohol-water solvent directly aff ects the nucleation and growth of zirconia clusters/particles in homogeneou s solutions. A lower dielectric constant of mixed solvent corresponds to a lower solubility of inorganic solute and, thus, a shorter induction period for nucleation as well as higher solid particle growth kinetics. Dynamic li ght scattering (DLS) was used to monitor the homogeneous nucleation and gro wth processes, while final particles and gels were studied by scanning elec tron microscopy (SEM) and high-temperature X-ray diffraction (HTXRD). The s ol-get processes in the mixed solvent system can be adjusted using the proc essing parameters, including the initial inorganic salt concentration (C), alcohol/aqueous medium volume ratio of the mixed solution (RH), incubation temperature (T), incubation time (t), concentration of hydroxypropyl cellul ose (HPC), and ammonia neutralization, Monodispersed submicron and nanoscal e(< 100 nm) zirconia microspheres/powders were successfully synthesized und er conditions of high RH (5) and using HPC (molecular weight of 100,000, 2. 0 x 10(-3) g/cm(3)) and ammonia neutralization. Initial salt concentration affects the particle size significantly. Gel materials were obtained under conditions of low RH (1.0). Microstructure and transparency of gels changed significantly from low (0.05 M) to high (0.2 M) concentration of the metal salt. We have also demonstrated that monodispersed particle production can be achieved not only at low temperatures (<100 degrees C) but also at room temperature using an inorganic salt precursor. (C) 2000 Academic Press.