NOTE
An Approach to Hierarchically Structured Porous Zirconia Aggregates each of which we have earlier described. Polymerization-induced colloid aggregation (PICA) (10, 11) has been used to synthesize micrometer-scale Presented here is a simple, inexpensive approach to aggregating porous zirconia particles for use in high-performance liquid chromatography colloids into hierarchically structured spherical particles. Succes- (HPLC). In this method, the formation of monodisperse spherical aggregate sive aggregation steps are used to assemble a particle that is selfparticles is induced by urea-formaldehyde (UF) polymerization and adsimilar on two size scales and is permeated by an ordered pore sorption. The resulting particles have a high porosity which is exceptionally network with a bidisperse size distribution. The structure of the resistant to high-temperature sintering (12). We have also described an oil micro-and macropore networks as well as the mechanical integrity emulsion (OE) method to synthesize aggregates tens of micrometers in of the structure can be controlled by varying sintering conditions. diameter (13). Here a stable zirconia sol is mechanically dispersed into