Observations and Mechanism of CaSO4 Fouling on Hydrophobic Surfaces

Pool boiling of CaSO4 solution on prepared microscale and nanoscale hydrophobic titania-fluoroalkylsilane (TiO2-FPS) composite coatings on polished AISI304 stainless steel (SS) substrates was carried out to evaluate the antifouling behavior of these surfaces. Lower fouling resistance and looser, slender, and larger CaSO4 crystals on hydrophobic TiO2-FPS coatings were observed compared to those on the TiO2 coatings and SS surfaces. The colloidal interaction energies between crystalline particles and coated surfaces were analyzed by using the extended Dejaguin-Landau-Verwey-Overbeek (XDLVO) theories to explore the possible mechanism of inhibition of fouling. The results of the XDLVO analyses generally agree to the experimental observations. The Lewis acid-base component contributes most of the total XDLVO interaction energy. Low surface free energy and electron donor component of heat transfer surface lead to a low fouling resistance and a small initial deposition rate of CaSO4 fouling. On the basis of the XDLVO evaluations, a key strategy to reduce the CaSO4 deposition rate on heat transfer surface is suggested.