The influence of copper and aluminium substrates on CaCO3 polymorphism and the anti-adhesion of HEDP at 100 °C

The development of calcium carbonate (CaCO3) scale on copper (Cu) and aluminium (Al) substrates/button at 100 °C was examined in this work, examining the role of the metal and 1-hydroxyethylidene-1,1 diphosphonic acid (HEDP). The substrate was succumbed to two types of heating; direct heating (from the bottom) and indirect heating (by suspension in the solution). X-ray Diffraction (XRD) analysis demonstrated that the sludge samples from both substrates contained a binary mixture of calcite and vaterite. The scale deposited on both the bottom substrate contained only calcite, whereas the suspended Cu substrate showed presence of a binary mixture of calcite and aragonite, while Al contained only calcite. Scanning electron microscopy (SEM/FE-SEM) revealed a novel nano-spherical vaterite morphology, with particle sizes ranging from ∼10 to 300 nm. The study posits that this unique spherical shape is the primary reason for inhibition, as the particles get remained suspended in the solution, thereby preventing their adhesion or formation of one layer over another on the metal surface. This effect is achieved through the maintenance of a CaCO3-Ca-HEDP equilibrium.