Local scaling of CaCO3 on carbon steel surface with different corrosion types

Effect of the passive films on CaCO3 scale depositing on Q235 steel: Electrochemical and surface investigation

The deposition of the CaCO₃ scale in circulating cooling water is a common and serious concern in the industry, which hinders the heat transfer, reduces water flow and blocks membrane filters. This paper aims at studying the effect of the γ-Fe₂O₃, Fe₂(MoO₄)₃·γ-Fe₂O₃ and FePO₄·γ-Fe₂O₃ passive films on CaCO₃ scale deposition on Q235 steel by electrochemical methods, including linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS) tests. The scale and corrosion inhibition performance of the passive films was evaluated by the residual current density (i_r) and charge transfer resistance (R_ct) values. Electrochemical results suggested that the passive films could inhibit corrosion and reduce the CaCO₃ scale deposition on Q235 steel and the FePO₄·γ-Fe₂O₃ complex passive film showed the best anti-scaling effect. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) tests showed that the passive films could lead to a decrease in the proportion of aragonite to calcite under cathodic water reduction conditions and the composition of the FePO₄·γ-Fe₂O₃ complex passive film could deform the CaCO₃ crystal.

Green and High Effective Scale Inhibitor Based on Ring-Opening Graft Modification of Polyaspartic Acid

Polyaspartic acid (PASP)-based green scale inhibitor has great potential application in water treatment. Here, we first synthesized PASP in ionic liquid. Then, an effective PASP-based green scale inhibitor was synthesized by ring-opening graft modification of PASP with both aspartic acid (ASP) and monoethanolamine (MEA). Its chemical composition was characterized by gel chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and 1H nuclear magnetic resonance (1H NMR). Scale inhibition efficiency was measured by static scale inhibition tests. The results showed that the new PASP-based scale inhibitor has high scale inhibition to both CaCO3 and Ca3(PO4)2. When the concentration was increased to 2 mg/L, the inhibition efficiency of the new PASP-based scale inhibitor was 99% for CaCO3, while when the concentration was raised to only 4 mg/L, its inhibition efficiency increased to 100% for Ca3(PO4)2. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the changes of crystal structure for CaCO3 and Ca3(PO4)2 after adding the new PASP-based scale inhibitor. The crystal size of CaCO3 and Ca3(PO4)2 became smaller and the crystal form became amorphous after adding the modified PASPs compared with adding pure PASP. Moreover, the modified PASP showed good biodegradation performance.