Crystal Nucleation and Growth: Supersaturation and Crystal Resilience Determine Stickability

Crystallization fouling in heat exchangers, subsurface energy production, and membrane technology remains a challenge. The reactive crystallization process is governed by whether growth or nucleation dominates the precipitation process. However, there is little direct experimental evidence on the fundamentals of nucleation and growth on surfaces over a wide range of supersaturations. We investigated the crystallization fouling of BaSO4 at 10 different supersaturations (saturation ratios from 6.6 to 457.1). We show that deposition behavior changes from a growth-dominated regime to a nucleation -dominated regime as the supersaturation increases; these changes in the dominant regime affect the resilience of the surface deposits. At low supersaturations, crystals have a secondary order, which increases their surface resilience. At high supersaturations, where nucleation processes dominate, crystals aggregate on the surface with no discernible secondary structure. At a saturation ratio of 457, nucleation processes are accelerated, causing previously aggregated crystals to become isolated. Due to increased isolation, the crystal resilience decreases, and the crystals become more vulnerable to detaching from the surface. To characterize surface deposition, we introduced the sticking factor as a measure of the stickability. We present an analysis of the stickability of BaSO4, CaCO3, and CaSO4, based on published data, and observe mean sticking factors of 1.15%, 0.80%, and 0.11%, respectively.