The influence of external electric field on the crystallization and adhesion characteristics of calcium sulfate-type scale: A mechanism study by DFT calculation and experiment.

Here, we investigated the effect of an external electric field (EF) on the crystallization process of calcium sulfate (CaSO4) using density functional theory (DFT) calculations and experiments, with the aim of revealing the scale inhibition mechanism of electric descaling technology for CaSO4-type scale in industrial water processes. In DFT calculation part, we predicted the evolution law of the CaSO4•2H2O crystal's dominant surfaces and distribution characteristics of surface energy by comparing the changes in lattice parameters before and after application of EF. We also calculated the adsorption energies of SO42- and Ca2+ on the surfaces of CaSO4•2H2O and chromium(Cr) crystals (simulating the chromium-plated inner wall of industrial water pipes) under EF intervention. The results show that external EF promotes the in-situ growth of CaSO4 crystals by influencing the surface energy and adsorption energy of the crystal planes. Meanwhile, the external EF can reduce the adsorption energy of scale-forming ions on the Cr crystal plane, thereby inhibiting the adhesion of CaSO4 on the pipe wall. The experimental results indicate that by regulating the parameters of the electrical excitation signal, the number of scale-forming ions in the solution and the mass of precipitates adhering to the inner wall of the water pipe can be significantly reduced, and the crystal morphology tends to be flat, which is in good agreement with the DFT calculation results. In addition, the presence of the EF enhances the hydrophobicity of the inner wall of the water pipe, thereby hindering the adhesion of scale-forming particles in water.