On the deposition and polymorphism of CaCO3 crystals in the presence of the tetrapod-shaped ZnO nanomaterials and polydimethylsiloxane composite

The calcium carbonate (CaCO3) scale generated in water pipes and heat exchangers causes serious problems such as pipe blockage and corrosion. This study investigates the effect of the 4-to-10 μm-long and 350-to-700 nm centering-nucleus-wide ZnO tetrapod-like nanomaterials and polydimethylsiloxane composite (t-ZnO/PDMS) on deposition and polymorphism of CaCO3 crystals on the stainless-steel substrate. The results showed that the t-ZnO/PDMS coating inhibited CaCO3 depositions and represented an excellent antifouling coating. The weight-based inhibition efficiencies of CaCO3 deposition were up to 81.3% and 63.2% at 20 °C and 60 °C, respectively. The t-ZnO/PDMS coating also exhibited good inhibition in the presence of liquid flow. The inhibition is primarily because the very fine concave-convex microstructure of the t-ZnO/PDMS coated surface lowered the surface energy of the substrates, making it difficult for CaCO3 crystals to adhere to the surface. Also, metastable vaterite and aragonite precipitations were dominant in the t-ZnO/PDMS coated coupons at 20 °C and 60 °C, respectively, whereas the uncoated coupon exhibited calcite as the predominant polymorph in all the studied conditions. The t-ZnO/PDMS composite subject to the liquid flow made calcites distorted and framboidal vaterite aggregates, likely due to their mechanical effects. The inhibition of CaCO3 depositions is due to achieving hydrophobicity on substrate surfaces, changing preferential polymorph formation, and tailoring the morphology of the given polymorph by the t-ZnO/PDMS composite.