ISSN:
1573-4803
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Maschinenbau
Notizen:
Abstract The phenolic coatings used to protect the steel of railway tanks during the shipment of concentrated sulphuric acid have been studied by microbeam PIXE and a.c. impedance measurements. After repeated washing and filling cycles, these coatings begin to lose their resistance to corrosion but the breakdown mechanism is not presently well understood. A 20 μm focused proton beam has been used to scan the approximately 200 μm thick coatings to obtain the depth profiles of sulphur, which, as sulphate ions, are thought to migrate towards the steelcoating interface and initiate the breakdown process. Parallel electrochemical impedance spectroscopy (EIS) measurements have been performed to determine the electrical properties of the metal-coating system. Samples were exposed to concentrated sulphuric acid for periods of up to six months. The microbeam PIXE results indicate that the sulphur concentration has reached a saturation level after about ten weeks, which coincides with the onset of appreciable corrosion as determined from the impedance measurements. Two additional samples, which were treated to repeated cycles of immersion in acid followed by rinses in water, lost a large fraction of titanium at the exposed surface and after some twenty cycles were easily delaminated from the substrate, suggesting one possible breakdown mechanism. The use of an inexpensive proton microprobe provides a simple and rapid quantitative evaluation of sulphur concentrations and depth profiles.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00580147
