Effect of high temperature oxide scale on steel surface for electroless nickel plating process and characterization of coatings

An attempt has been made for an electroless nickel plating process on two steel substrates (with and without a high temperature oxide scale at the top surface) to identify the role of a high temperature iron oxide scale on coating kinetics. This study investigated if an iron oxide scale on the steel surface acts as a catalyst and promotes faster metal deposition. Coatings were characterized by scanning electron microscopy (SEM), glow discharge oxy emission spectroscopy (GDOES), and X-ray diffraction (XRD) and an iron oxide scale was characterized by Raman spectroscopy. Chemical composition and structure of both the coatings are the same but the coating obtained on a steel substrate having a high temperature oxide scale at the top is two times thicker. The electrochemical performances of both the coated steel substrates were evaluated by Tafel and electrochemical impedance (EIS) tests in an aggressive chloride environment. The coating obtained on a steel substrate containing a high temperature oxide scale at the top exhibits better resistance against chloride attack and charge transfer than the coating obtained on the steel substrate without a high temperature oxide scale at the top. This can be attributed to the highest thickness of this coating, which has the same chemical composition of the other coating, expected to give better resistance against chloride attack and charge transfer. (C) 2009 Elsevier B.V. All rights reserved.