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.

Corrosion resistance coating applied on Q235 carbon steel in a chloride-rich environment was explored in our research. The coating as a barrier inhibits the penetration of the corrosion medium and provides active corrosion protection for Q235 carbon steel. Halloysite nanotubes (HNTs) were loaded with sodium lignosulfonate (SLS) under vacuum conditions. 4.53% of loading efficiency was validated by thermogravimetric analysis (TGA). The deposition of polyelectrolyte layers including poly­(dimethyl diallyl ammonium chloride) (PDDA) and poly­(styrenesulfonate) (PSS) not only resulted in controlling the release rate of SLS but also enabled the HNTs to possess pH-responsive release property. The modified HNTs were defined as “PSS/PDDA/SLS/HNTs”, which were characterized by SEM, TEM, FTIR, and zeta potential analyses. TGA elucidates that PSS/PDDA/SLS/HNTs exhibit superior thermal stability. The results of UV–vis spectroscopic analysis confirm that HNTs exhibit a higher release amount in an alkaline medium than in neutral and acidic conditions. Afterward, PSS/PDDA/SLS/HNTs were mixed with the epoxy coating, which was applied on Q235 carbon steel immersed in 3.5 wt % NaCl solution. Electrochemical measurements illustrate the excellent corrosion resistance of the epoxy coating with the addition of PSS/PDDA/SLS/HNTs. Also, water contact angle analysis demonstrates the modification of the epoxy coating with decent hydrophobicity.

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