Growth of zirconia particles by heterocoagulation, self-assembly, and convection-induced coagulation during forced hydrolysis in a refluxed reaction vessel

In literature related to forced hydrolysis of zirconia, heterocoagulation between large particulates and primary crystallites is generally accepted as the principal route of growth. Our dynamic light scattering (DLS) results revealed an S-shaped growth curve with the growth rate (slope) varying notably from one stage to the other, implying that other coagulation mechanisms may be present. Time-sequenced side-by-side electron microscopy and DLS analyses were conducted along the curves alongside with field emission scanning electron microscopy of full-grown particles. We find that particles growth follows a two-stage heterocoagulation process with primary crystallites and small particles produced from the first-stage serving as building blocks for the first and second stages, respectively. It interesting to note that growth during the second stage occurs by self-assembly and a hypothesis is proposed. Convection-induced coagulation leads to enhanced particle growth for a low precursor concentration but minimal growth for a higher one, both of which conform to the predictions of Melis et al. [AIChE J. 45, 1383 (1999)].