Plant-Derived Nanoparticles for Advanced Ni–P–TiO2 Composite Coatings on AH36 Marine Steel

The synthesis of electroless Ni–P–TiO2 composite coatings on marine grade AH36 steel was done using plant-extract-derived titanium dioxide nanoparticles in the present work. TiO2 nanoparticles were synthesized using Indigofera tinctoria extract as an efficient reducing and capping agent by the green method. Anatase, rutile, and amorphous polymorphs were obtained by controlled temperature calcinations and characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). They were then dispersed in a premixed bath of electroless Ni–P (including sodium hypophosphite, ammonium chloride, and sodium tri-citrate) with the zwitterionic surfactant for enhanced particle dispersion. One hybrid composite and three single-phase TiO2 composites with different contents were coated at 85◦C for 1 h. The coated samples presented a homogeneous structure in sizes of grain with apparent improvement in microhardness and improved corrosion resistance. A higher TiO2 -added composite coating shows well-defined surface features, as well as superior electrochemical performance. Thickness of the coating was correlated with the phase and elemental composition of particles. The Tafel test showed a marked reduction in the corrosion current density and an increase of anti-corrosion for marine environments. It can be presumed that the green synthesis of Ni–P–TiO2 is a multilayer, promising economical and environment-friendly approach for enhancing the corrosion resistance and durability of AH36 marine steel.