Investigation of the microstructure and corrosion resistance of hydrothermal-synthesized MFI zeolite coating on H13 steel

Abstract

Three different processes (non-3-aminopropyltriethoxysilane (APTES) pretreatment followed by one-step hydrothermal synthesis, APTES pretreatment followed by one-step hydrothermal synthesis, APTES pretreatment followed by two-step hydrothermal synthesis) were used to synthesize an MFI zeolite coating on mechanically polished H13 steel to improve corrosion resistance. The coatings synthesized by the different processes were remarkably different in terms of zeolite particle size, thickness, density, and corrosion resistance. In the case of the MFI zeolite coating synthesized on non-APTES-pretreated H13 steel, a non-dense gel layer and poorly intergrown zeolite particle layer lowered adhesion strength and corrosion ability, whereas the presence of the APTES film increased the density of the gel layer. Consequently, it showed better adhesion strength, and corrosion resistance with a lower corrosion current density (Icorr) and higher impedance value at 0.01 Hz. The adhesion strength and corrosion resistance of the MFI zeolite coating was further enhanced by two-step hydrothermal synthesis because the gel layer became denser and thicker in the early stages of secondary synthesis. The molten immersion test also indicated that the MFI zeolite coating had a high corrosion resistance in molten aluminum.