Resistance of zinc thermal sprayed coatings on different corrosive environments

Zinc coatings on ferrous substrates are possible to be applied with thermal spraying. In the present work the corrosion behavior of zinc thermal sprayed coatings deposited on low carbon steel St-37 was examined in a simulated marine atmosphere (salt spray chamber-SSC) and in a dry atmosphere at elevated temperature (400 degrees C). The corrosion progress was examined by means of optical microscopy, scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. From this investigation it was deduced that in the SSC the coating is uniformly corroded, while the main corrosion products are hydrated zinc oxides and chlorides. By contrast at 400 degrees C only a thin, compact and continuous film of ZnO is formed on top of the coating, which remains adherent to the ferrous substrate.