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The purpose of this paper is to report on the use of phosphorylated polyphenol (PP)-coated galvanised iron (GI) surface to study the degradation of coating with different time intervals and long-term exposure in different salty media.

The as-obtained PP complex on GI was evident by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The coated coupons were exposed to different salty media such as 3.5 per cent NaCl, 1.5 per cent Na₂SO₄ and tap water at set time intervals. Electrochemical polarisation was performed to study the anodic and cathodic polarisation behaviour at each time interval.

The adherent foliolate nanopattern of iron zinc phosphate and zinc dihydrogen phosphate on GI surface was evident by SEM, FT-IR, EDS and XRD. The coated coupons exhibited good corrosion resistance. This coating performs as an alternative to time-consuming multistep operations of phosphating treatment.

The mode of the experiment treatment using modified PP coating especially on GI in different corrosive exposures at set time intervals is a novel approach in this research.

The aim of this study was to evaluate the corrosion inhibition efficiency of steel samples in different environments before and after the treatment with rust metamorphose (RM), which is formulated in this research study and shows excellent adherence over the rusted surface of substrate because of the presence of the P-O-Fe bond.

An RM solution (phosphorylated polyphenol) was synthesised and characterised using Fourier transform infrared spectroscopy (FT-IR), and then the degree of protection offered by it to steel surfaces with and without the treatment with the RM solution in different atmospheres was evaluated;. Before and after treating with the RM solution, the corroded steel samples were characterised using X-ray diffraction (XRD), FT-IR, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The study of the passive behaviours of the corroded steel samples and RM-treated steel samples was done in different simulated atmospheres.

This RM solution is phosphorylated polyphenol solution (proved by FT-IR), which acts as a corrosion inhibitor on corroded steel surfaces because of the formation of a passive and symmetric adherent layer of phosphorylated polyphenol–iron complex (confirmed by FT-IR, XRD, EDS, SEM and adhesion X test). The significant improvement in corrosion resistance in splash conditions of 3.5 per cent NaCl, tap water and 1.5 per cent Na₂SO₄ was found with the treatment of phosphorylated polyphenol-based RM.

The development of RM and its characterisation with performance evaluation in different atmospheres is a novel approach in this research.

This paper aims to investigate the potential of sol-gel coating as replacement for hazardous hexavalent chrome passivation treatment for galvanised iron (GI) sheet. Generally, corrosion resistance properties of the GI sheet are increased by hexavalent chrome passivation treatment. But hexavalent chrome is hazardous and not environment friendly.

The aim of this study was to understand the effect of nano zinc oxide (ZnO) on corrosion behaviour of sol-gel coating prepared by hydrolysis of the 3-(Glycidoxy propyl) methyl diethoxy silane (GPTMS) and tetra-ethyl-orthosilicate (TEOS). The morphology of the film was characterised by a scanning electron microscope (SEM). The corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation curve and salt spray test.

From a different corrosion resistance study, it has been observed that sol-gel coating doped with 1 per cent nano ZnO rendered maximum corrosion protection. Beyond 1 per cent of nano ZnO, corrosion resistance property of coated galvanised steel sheet decreased drastically which may be due to agglomeration of nano ZnO and high water permeability of coated galvanised steel sheet.

The anti-corrosive property of the coating can be tested by means of atmospheric exposure which produces a real-time evaluation of the anti-corrosive nature of the coating under natural conditions rather than using an accelerated laboratory test.

It may be useful for other metal industry like aluminium. The work can be used as a guiding chemistry for development of chrome-free passivation for aluminium.

It has the potential to replace hexavalent chrome passivation.

The use of nano ZnO in sol-gel polymer matrix for the development of corrosion resistant chrome-free polymer coating for galvanised steel sheet and its corrosion resistance study (EIS curve fitting, capacitance value and water permeability) is a novel approach in this research.