The Corrosion Protection Behaviour of Zinc Rich Epoxy Paint in 3% NaCl Solution

Electrochemical impedance spectroscopy (EIS) in the l00 kHz-10 mHz frequency range was employed as the main electrochemical technique to study the corrosion protection behaviour of zinc rich epoxy paint in 3% NaCl solution. The EIS results obtained at the open-circuit corrosion potential have been interpreted using a model involving the impedance of particle to particle contact to account for the increasing resistance between zinc particles with immersion period, in addition to the impedance due to the zinc surface oxide layer and the electrical resistivity of the binder. Galvanic current and dc potential measurements allowed us to conclude that the cathodic protection effect of the paint takes some time to be achieved. The loss of cathodic protection is due to a double effect: the decrease of the Zn/Fe area ratio due to Zn corrosion and the loss of electric contact between Zn to Zn particles. Even when the cathodic protection effect by Zn dust become weak, the substrate steel is still protected against corrosion due to the barrier nature of the ZRP film reinforced by Zn.

Smart ZnS@C filler for super-anticorrosive self-healing zinc-rich epoxy coating

The zinc-rich epoxy cathodic protection coating is the most widely used anticorrosion material for marine steel.However,traditional conductive fillers lack the intelligent self-healing effect,which limits the long-term anticorrosion performance.Herein,with uniform carbon-coated ZnS(ZnS@C)nanoballs as the smart active release filler,we propose an anticorrosive and self-healing zinc-rich maleic anhydride epoxy coating.Due to the high pore filling efficiency of the nanoballs,the water vapor transmission rate of the coating with an initial corrosion efficiency of 99.92%and a low-frequency impedance of|Z|f=10mHz=3.88×10^(10) Ω·cm^(2),was reduced by 52%.The carbon-shell of the nanoball increases electron transmission paths in the coating and improves conductivity by nearly two orders of magnitude,which effectively activates more Zn-sites and extends the cathodic protection time.Moreover,once the steel-substrate undergoes regional corrosion,the SO_(4)^(2-)hydrolyzes from the ZnS-core of the nanoball and reacts with iron ions on the corroded area accurately and intelligently to fill the gap and self-heals into a new dense barrier layer(Fe_(2)(SO_(4))_(3),etc.),which significantly improves the shielding protection ability during the long-term usage of the coating.The effective anticorrosion time of the proposed coating could be up to 3,400 h.

A sandwich-like structure hybrid coating of cold galvanizing coating/polydopamine on hot-dip galvanized steel with enhanced adhesion and corrosion resistance

This study aims to enhance the adhesion strength and anti-corrosion performance of the cold galvanizing coating(CGC)applied on the hot-dip galvanized steel(HDG).Polydopamine(PDA)is deposited on the HDG surface with different time ranges and as an interlayer between CGC and HDG through covalent immobilization.The surface morphology and the covalent interaction between PDA/HDG are exhibited by scanning electron microscope(SEM),atomic force microscopy(AFM)and X-ray photoelectron spectroscopy(XPS).The pull-off adhesion tests before and after neutral slat spry tests show an enhanced dry adhesion strength and less adhesion loss of the hybrid CGC/PDA coated HDG compared with the direct CGC coated HDG.In addition,open circuit potential(OCP)reveals that the corrosion protection performance of the hybrid CGC/PDA coated HDG increases by 200%(up to 201 d)and the corrosion density icorrattaining about 4.45×10^(-7)A/cm^(2).Electrochemical impedance spectroscopy(EIS)measurements and X-ray diffraction(XRD)analysis confirm that the precipitate of the stable chelation formed by PDA and Zn^(2+)between CGC and HDG substrate can also improve the corrosion protection performance.Such a strategy of strengthening adhesion and forming the chelate compound at the HDG surface promises a new route to corrosion protection of CGC on HDG.