Polyetherimide coatings for corrosion protection

The corrosion of iron or rusting causes the deterioration of the metal and its properties and renders it structurally weak and unfit for use. Rusting causes huge capital loss every year in equipment maintenance, repair, and replacement. Barrier coatings, sacrificial and noble metal coatings, inhibitor coatings and electrically resistive coatings have been developed so far to prevent corrosion. The main requirement of corrosion prevention is that metal surface is protected from the attack of oxygen, water and corrosive ions like chlorides at all times.;This study will evaluate the protection offered by coatings of commercially available polymer, Polyetherimide (PEI) against the corrosion of mild steel in seawater, along with addition of different amounts of graphene in the polymer matrix. Polymeric anti-corrosion coatings, is a much lesser explored area of research with the major challenge of low adhesion properties of most polymers to the metal substrate. This calls for preparation of substrate surface and treatment of coatings to establish good interfacial interaction of the polymer with the metallic substrate or methods for adhesion promotion to avoid delamination of coatings in water. The PEI coating preparation process was optimized before graphene addition.;The potential of the graphene to further enhance anticorrosion performance of the polymer by producing passive and active barriers was evaluated. The coatings were prepared by dip-coating methods in determined optimal conditions on clean polished mild steel coupons. The coating degradation behavior and corrosion resistance was investigated by the immersion tests (performed in 3.5 wt.% sodium chloride solution), Potentiostatic Electrochemical Impedance Spectroscopy (PEIS). Corrosion monitoring was performed using Linear Polarization (LP) technique. Other coating characteristics were studied using techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetry (TGA), Differential Scanning Calorimetry (DSC), X Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The visual appearance of coating and corrosion products was studied using Optical Microscopy (OM).;The plane PEI coatings produced, were highly stable and protective in nature. The polymer coatings possessed high impedance good barrier characteristics and chemically bonded to the steel to provide remarkable adhesion. Graphene in the polymer acted as a platelet barrier for the diffusion of oxygen, water and chloride ions by increasing the tortuosity of the diffusion pathway when added in large concentrations of at least 5 weight percent. But the main anti-corrosive effect of graphene was due to electron depletion at the metal surface and prevention of charge transfer from anode to cathode by formation of p-n junction depletion layer. This effect was achieved due to electrical properties of graphene and was not observed when graphene was replaced by graphene oxide (GO). The PEI and graphene-PEI coatings were compared with coatings of commercially available epoxy. It was observed that pure PEI and its 5 wt.% graphene coatings had better anticorrosive performance and adhesion than the epoxy coatings and provided much greater substrate protection.