Plasma polymerization - a new and promising way for the corrosion protection of steel

Abstract

In this paper the glow discharge process is used for the deposition of ultrathin (d < 10 nm) plasma polymers on iron specimens. The plasma polymer serves as an interfacial polymeric layer between the passive iron surface and a conventional pigment free water based 1-component primer. Sample, were fixed in the grounded electrode of an audio frequency discharge (4 kHz). Cleaning of the iron surface was achieved by an oxygen plasma treatment and Plasma polymers were deposited from a mixture of hexamethyldisilane ((CH 3 ) 3 Si-Si(CH 3 ) 3 ) and argon. The modification of the surface structure was investigated by the use of quartz crystal microweighing (QCM) and infrared spectroscopy under grazing incidence (IRRAS) as in-situ methods. Both the iron oxide as well is the plasma polymer are characterized in detail by infrared spectroscopy and photoelectron spectroscoopy (XPS). The corrosion performance of primer coated samples was tested according to the kinetics of cathodic delamination which was measured in-situ by the Scanning Kelvinprohe (SKP). While the pure oxygen plasma treatments leading to a contamination free and thickened oxide layer, does not influence the delamination kinetics the existence of an only 5 nm thick plasma polymer at the metal-primer interface leads to a significantly decreased rate of undermining.