DEVELOPMENT OF POROUS ZIRCONIA SPHERES BY POLYMERIZATION-INDUCED COLLOID AGGREGATION - EFFECT OF POLYMERIZATION RATE

Polymerization-induced colloid aggregation is used to synthesize spher es of narrow size distribution which are porous aggregates of ZrO2 col loids. Variation of the reaction pH has been investigated to determine the optimum rate of polymerization of the urea-formaldehyde resin. At the optimum rate, a colloid packing structure is formed where a balan ce of high porosity and high strength of the aggregates is achieved. T his optimum coincides with the maximum yield of the similar to 5 mu m sintered (polymer-free) particles. Particles synthesized at pH values below the optimum are mechanically weak; some are hollow spheres. Vari ation of the pore structure, and thus colloid packing structure, is el ucidated by nitrogen adsorption and apparent density measurements. Dif ferences on either side of the optimum pH are related to the efficienc y of polymer-bridge formation between colloids.