Protective properties of epoxy coatings electrodeposited on steel electrochemically modified by Zn-Fe alloys

Abstract

Epoxy coatings were electrodeposited on steel and steel modified by Zn-Fe alloys using the constant voltage method. Zn-Fe alloys were electrodeposited on steel at different current densities. The effect of the Zn-Fe alloy on the corrosion behavior of the epoxy coating was interpreted in terms of the electrochemical and transport properties. It was shown that the best properties, i.e. the largest values of the pore resistance and the smallest values of the coating capacitance, a longer period of almost constant Rp and Cp values, and the smallest diffusion coefficient of water through the epoxy coating, as well as the smallest amount of water absorbed inside the epoxy coating, were found for epoxy coatings on steel modified by a Zn-Fe alloy deposited at 4 A dm-2. During prolonged exposure to 3% NaCl, this Zn-Fe alloy significantly improves the corrosion stability of the epoxy coating: almost unchanged values of Rp and Rct were observed, due to the formation of a pseudo-passive layer of corrosion products, which is a good barrier to the transport of water, oxygen and electrolyte ions.

U radu je ispitivan uticaj modifikacije čelika elektrohemijskim taloženjem Zn-Fe legura na zaštitna svojstva epoksidnih kataforetskih prevlaka na čeliku. Koroziona stabilnost zaštitnog sistema Zn-Fe legura/epoksidna prevlaka na čeliku je određivana preko vrednosti otpornosti elektrolita u porama prevlake i kapacitivnosti prevlake (metoda SEI). Sorpcione karakteristike su određivane gravimetrijskim merenjima, a količina apsorbovane vode u prevlaci termogravimetrijskom analizom (TGA). Ispitivane su brzine izdvajanja vodonika, kao prvog stupnja u kataforetskom taloženju epoksidne prevlake, na različitim supstratima, kao i kvašljivost supstrata rastvorom polimera. Pokazano je kako ova dva faktora zajedno utiču na poroznost epoksidnih prevlaka.