A study on the corrosion resistance of magnesium potassium phosphate cement coatings with surface hydrophobic treatment by HDTMS

Magnesium potassium phosphate cement (MKPC) coatings exhibit excellent bonding properties and environmental friendliness. However, as an inorganic coating, MKPC coatings exhibit poor impermeability. This study utilized hexadecyltrimethoxysilane (HDTMS), CaCl₂ and NaHCO₃ to achieve hydrophobic treatment of the MKPC coating surface. Effects of hydrophobic treatment on the properties of the coating and substrate were characterized by various tests, and mechanisms of corrosion resistance were explored. The results indicate that reducing the surface energy of the coating by HDTMS can improve hydrophobicity of the coating, and increasing the surface roughness by generating CaCO₃ can further enhance the hydrophobicity. Surface treatment enables the coating to maintain prolonged hydrophobicity in a 3.5% NaCl solution. Meanwhile, hydrophobic treatment inhibits the formation of hazenite, enhances the permeability resistance of MKPC, and can provide a long-term improvement in the corrosion resistance for low carbon steel, the best sample exhibited a corrosion current density that was one-third that of the untreated sample after 28 d of immersion.