Impact of Porogens on the Pore Characteristics of Zirconia Particles Made by Polymer-Induced Colloid Aggregation

Zirconia particles were prepared from a 20% colloidal sol (ZrO2) by the polymer­induced colloid ag­ gregation (PICA) process, both in the presence and absence of porogens. Specifically, porous zirco­ nia particles having varying porosity were prepared by a two­step protocol wherein a porogen was first embedded during the particle synthesis, followed by its removal in a subsequent step. In this re­ search study, the ability of four different types of porogens, viz. fumed silica, micronized high molecu­ lar weight polyethylene emulsion ME09730, and microcrystalline waxes ME48040M2 and ME98040M1, to impact the pore size, porosity, and pore area were investigated. Particle morphology and porosity of the resultant particles were characterized by scanning electron microscopy, mercury intrusion–extru­ sion porosimetry, and the nitrogen adsorption–desorption sorptometry. Optimal ratios of zirconia sol and porogen to yield the largest unimodal distribution of pores were determined. Porous zirconia par­ ticles were obtained after the removal of porogen, followed by a calcination and sintering protocol. Par­ ticle aggregates were typically 7–45 μm in diameter, with BET surface areas between 21 and 54 m2/g and pores ranging from 18 to 120 nm in diameter. The nitrogen sorptometry and mercury porosimetry data of these support particles were modeled to calculate surface fractal dimension, pore accessibility parameters, pore network, and pore geometry.