SYNTHESIS OF POROUS ZIRCONIA SPHERES FOR HPLC BY POLYMERIZATION-INDUCED COLLOID AGGREGATION (PICA)

Porous, spherical zirconia particles with a narrow particle size distr ibution, which are useful as chromatographic packing materials for hig h performance liquid chromatography (HPLC), were synthesized by polyme rization-induced colloid aggregation (PICA) first described by Iler an d McQueston (U.S. Patent 4,010,242, 1977.) and the effects of a number of crucial processing variables were examined. In this method, an aqu eous zirconia sol consisting of 700 angstrom (mean diameter) particles is mixed with urea and formaldehyde, which are polymerized by the aci dic sol. Urea-formaldehyde polymer adsorbs onto the ZrO2 colloids, ent raining the Colloids in the precipitation of the polymer gel and thus allowing the colloids to aggregate. Features of the aggregation proces s are elucidated from responses of the process to variations in temper ature, reaction mixture composition, and solvent polarity. Our results suggest that the aggregation process resembles those reported for the bridging flocculation of colloids by adsorbed polymers. Porous zircon ia particles obtained after polymer combustion and sintering of the ag gregates are 3.5 mum in diameter with a surface area of 13 m2/g, a por osity of 29% and pores ranging from <50 to 350 angstrom in diameter. T he particles are strong enough to withstand the packing of a HPLC colu mn. (C) 1994 Academic Press, Inc.