Previous work in our laboratory showed that the type of surface preparation of the steel prior
to coating had a dramatic effect on the subsequent corrosion protection afforded in immersion
tests and in salt spray testing. Particularly water jetting led to better performance. It is
generally accepted that factors such as removal of impurities and introducing surface
roughness to steel to obtain better adhesion through the mechanical interlocking of polymeric
structure and the metal surface play a part. However it is postulated that the ease of
breakdown of the oxide film is also critically important and varies between surface
preparations. This was investigated in the present study where 5 different surface preparation
methods (abrasive blasting, water-jetting, abrasion, acid pickling and degreasing) were
applied to the mild steel surface and each resultant surface was characterised using
electrochemical methods. The Scanning vibrating electrode technique (SVET) was performed
in dilute saline water to detect anodic and cathodic sites on the surface and also to determine
the intensity of electrochemical activity at these sites. Scanning electron microscope (SEM)
together with energy dispersive X-ray spectroscopy (EDX) was used to characterise the
surface structure and its chemical composition. Changes in open circuit potential have been
monitored during the time of exposure to electrolyte in order to investigate the general surface
activity. The electrochemical impedance spectroscopy (EIS) was employed to analyse the
charge transfer situation on the metal surface. Results using these techniques will be presented
and discussed. An anticipated outcome from this work is development of a simple
electrochemical method to assess that a metal surface is in a condition suitable for coating.
This could also be used as a way of checking that standard pretreatments had been effective
and assist in the development of new ones