IR-SPECTROSCOPIC INVESTIGATIONS ON PHOSPHATED GALVANIZED STEEL

Hopeite-type phosphate coatings in which zinc is replaced by other met als like nickel, manganese and magnesium are of great interest as conv ersion coatings on galvanized steel in the automotive and appliance in dustries. The analytical characterization of such coatings produced in special processes is not possible by XRD because the different types of hopeite are isomorphic. In this paper it is shown that the kind of metal substitution is responsible for certain specific features in the infrared reflection spectra. Furthermore the structural changes cause d by dehydration due to heating of the coatings were studied and diffe rences in the thermal stability of the different coatings thus could b e observed.