In this study, calcium carbonate (CaCO3) microparticles having pH-sensitive properties were loaded with sodium lignosulfonate (SLS), a corrosion inhibitor. Scanning electron microscope (SEM), UV–VIS spectrophotometer (UV-vis), X-ray diffraction (XRD), and attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR) were applied to evaluate the properties of the synthetic microparticles. This material could lead to the release of corrosion inhibitor under different pH conditions of the aqueous media. However, the extent of release of the corrosion inhibitor in the acidic media was higher, leading to enhanced shielding effect of the Q235 steel. These microparticles can serve as anti-corrosion additive for epoxy resin-coated Q235 steel. Electrochemical experiments were used to assess the anti-corrosive ability of the epoxy coatings in simulated concrete pore (SCP) solution, confirming the superior corrosion inhibition of the epoxy coating via incorporation of 5 wt % calcium carbonate microparticles loaded with SLS (SLS/CaCO3). The physical properties of coating specimens were characterized by water absorption, contact angle, adhesion, and pencil hardness mechanical tests.

The corrosion mechanism and behavior of Q235 steel treated with sodium lignosulfonate and a mixture of sodium lignosulfonate and sodium silicate inhibitors in simulated concrete pore (SCP) solutions containing 0.08-mol/L NaCl were evaluated using polarization methods, electrochemical impedance spectroscopy, scanning electron microscopy, weight-loss measurements, and potential-of-zero-charge analysis. Results verified that the inhibition efficiency rapidly increased as the sodium lignosulfonate content increases, and the adsorption process mainly comprised chemisorption. The optimum sodium lignosulfonate concentration was 0.0015 mol/L. Sodium lignosulfonate and sodium silicate showed a synergistic inhibition effect in SCP solutions, with the highest inhibition efficiency of 98.8% achieved when 0.0005-mol/L sodium lignosulfonate and 0.0005-mol/L sodium silicate were used.

Purpose This paper aims to report the influence of hexamethylenetetramine (HMTA) on phosphate coatings formed on AZ31 magnesium alloys. Design/methodology/approach These phosphate coatings were obtained by immersing magnesium alloys in phosphate baths with HMTA. The morphology and composition of the phosphate coatings were investigated via scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. Findings The phosphate coatings were mainly composed of CaHPO4·2H2O. The HMTA concentration in the phosphate bath influenced the crystallization and corrosion resistance of the phosphate coating. Originality/value The polarization curve shows that the anti-corrosion qualities of the phosphate coating were optimal when the HMTA concentration was 1.0 g/L in the phosphate bath. Electrochemical impedance spectroscopy (EIS) shows that the electrochemical impedances increased gradually when the HMTA concentration varied from 1.0 to 3.0 g/L.

Hot dip galvanizing technology is now widely used as a method of protection for steel rebars. The corrosion behaviors of Q235 carbon steel and hot galvanized steel in a Ca(OH)2 solution with a pH from 10 to 13 was investigated by electrode potential and polarization curves testing. The results indicated that carbon steel and hot galvanized steel were both passivated in a strong alkaline solution. The electrode potential of hot dip galvanized steel was lower than that of carbon steel; thus, hot dip galvanized steel can provide very good anodic protection for carbon steel. However, when the pH value reached 12.5, a polarity reversal occurred under the condition of a certain potential. Hot dip galvanized coating became a cathode, and the corrosion of carbon steel accelerated. The electrochemical behaviors and passivation abilities of hot dip galvanized steel and carbon steel were affected by pH. In the higher pH solutions, passivation occurred with ease.

Hexagonal boron nitride (h-BN) has the outstanding properties of high-temperature stability, electrical insulation and impermeability against water, oxygen and corrosive ions. However, BN easily agglomerated in the coating, resulting in coating microporous defects and reducing the anticorrosive properties. Thus, h-BN was modified through a two-step treatment, hydroxylation and silanisation. h-BN modified by silane coupling agent 3-glycidoxypropyltrimethoxysilane (KH560) was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Then, the corrosion resistance of the BN-KH/epoxy resin coatings was measured by electrochemical testing. The results demonstrated that the corrosion current density of the coating with modified h-BN nanosheets was decreased from 2.67×10 -7 A•cm -2 to 5.28×10 -8 A•cm -2 compared with that of the pure epoxy resin. The impedance of the composite coating with modified h-BN is 5.27×10 7 Ω•cm 2 , approximately 20 times higher than that of the coating with the original h-BN (1.95×10 6 Ω•cm 2 ) and the EP coating (4.26×10 5 Ω•cm 2 ), indicating that BN-KH can protect the coating from damaging corrosive ions and that BN-KH/EP can maintain an excellent anticorrosion property.