Development Of Nanocrystalline Composite Coatings For Marine Application

ABSTRACT

Failure of engineering components in service, especially in marine applications, has recently been a major global concern, and corrosion resulting from biofouling has been the primary source of these failures. Ultimately, biofouling and corrosion are detrimental to the lifespan of parts in service. Thus, there is a need to develop protective coatings which are highly resistant to the biofouling-corrosion system. This study developed affordable, eco-friendly and durable bi-phase of Zn-ZnO and nanocrystalline particulates of Arachis hypogaea (Groundnut) husks (H) and Micropogonias undulatus (Croaker Fish) scales (S) through electrolytic deposition technique; and determined the influence of process variables on the properties of the deposited coatings. Box-Behnken Design from the Minitab 17 Design of Experiment was used to analyse and model the effects of the deposition parameters and process runs on the performance properties. The coatings were characterised through Dura scan diamond-based Vickers hardness tester for microhardness properties, Potentiostat Galvanostat (PGStat 101) for corrosion properties, Optical Microscope and Scanning Electron Microscope equipped with Energy Dispersive Spectrometer (SEM/EDS) for structural characterisation. For a deeper perception of the structural morphology, Atomic Force Micrograph (AFM) was used to obtain the surface topography and undulation. X-ray diffraction was used to examine the intermetallic bi-phase existing within the interface. From the results, the crystalline structures of the deposited coated samples were made up of duplex grains of crystals and lamellar noodles at Zn-15ZnO-20H coating series. The microstructures developed at Zn-15ZnO-20S showed the formation of colonies of the homogenous equiaxed pattern at the interface situating the stability and an indication of a preferred coating. The microhardness Vickers analysis revealed the same trends based on the process variable. The x-ray diffraction study exposed the presence of a single intermetallic ZnSi, ZnAlSi, ZnSiO phases in the Zn-15ZnO-20H coatings. On the other hand, the x-ray diffraction of Zn-15ZnO-20S gave a bi and tri-phase intermetallic pattern of Zn3Ca2O, Zn4Ca2Mg2, and Zn2MgO2 at distinctive intensity micro-stable coatings. The electrochemical corrosion test of the samples exposed to a biofouling simulated solution revealed excellent durability and biofouling-corrosion polarisation resistance. The improvement in the surface properties generally had positive impacts on the developed coatings' performance. The outcome indicated that coating with Zn-15ZnO-20S compared with Zn-15ZnO-20H and Zn-15ZnO formations performed best under the biofouling-corrosion system. This study showed improved efficiency and lifespan of components and parts made of mild steel in a simulated marine environment. Thin-film application of Zn-15ZnO-20S composite is thus recommended for enhancing the performance of mild steel for marine applications.

Keywords: Corrosion, Biofouling, Electrodeposition, Mild Steel, Composite coatings.