Electrochimica Acta 51 (2006) 3066–3075 Formation of ultra-thin amorphous conversion films on zinc alloy coatings Part 2: Nucleation, growth and properties of inorganic–organic ultra-thin hybrid films B. Wilson, N. Fink, G. Grundmeier ∗ Christian-Doppler Laboratory for Polymer-Metal Interfaces, Max-Planck-Institut f¨ ur Eisenforschung, Max-Planck-Str. 1, 40237 D¨ usseldorf, Germany Received 25 July 2005; accepted 27 August 2005 Available online 17 October 2005 Abstract Within the two parts of this contribution a detailed investigation of the formation of ultra-thin amorphous conversion coatings on hot dip galvanised steel is reported. The second part deals with the nucleation, growth and the barrier properties of these ultra-thin films on model substrates. The chemical composition as well as the film growth kinetics of the phosphoric acid and complexing organic macromolecules within the conversion layer system on a hot dip galvanised steel substrate have been determined by infra-red reflection absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS). Film nucleation was studied by atomic force microscopy (AFM) that revealed the initial formation of individual nanoscopic islands, which depends strongly on the initial surface chemistry. Cyclovoltammetry (CV) and potentiostat measurements were performed to characterise the blocking of ion transfer and electron transfer reactions on the modified surface. An excellent correlation with the barrier properties of the film with the state of film growth and the composition of the inorganic/organic nanocomposite layer was observed. The investigations are a basis for the understanding and future development of thin conversion films on zinc alloy surfaces. Finally, Scanning Kelvin Probe measurements showed the inhibiting effect of the conversion treatment under the conditions of atmospheric corrosion. © 2005 Elsevier Ltd. All rights reserved. Keywords: FT-IRRAS; AFM; Surface electrochemistry; Conversion layer; Galvanised steel 1. Introduction Conversion layers play a dominant role in providing excellent adhesion and corrosion resistance of polymer/metal interfaces. Conversion coatings are applied in continuous steel [1,2] or alu- minium sheet production lines and within the paint shop of the automotive industry, the latter case being further complicated by requiring a multi-metal approach—galvanised steel/aluminium [3]/magnesium [4]. Processes that are in use today have a long history of scientific and empirical development. However, there is a strong need to replace the classical conversion coatings based on chromate [5] in a short period of time by new environmen- DOI of related article:10.1016/j.electacta.2005.08.030. ∗ Corresponding author. Tel.: +49 211 6792 290; fax: +49 211 6792 218. E-mail address: grundmeier@mpie.de (G. Grundmeier). tally friendly systems due to environmental and health concerns [6–8]. Moreover, the newly developed systems should match or out- perform standard technical systems with regard to efficiency, corrosion protection, adhesion and formability. Amorphous thin films deposited from aqueous solutions have high technolog- ical potential since they make use of so-called “smart green chemistries” which include phosphates [9–12], silanes [13–16], rare earth metal salts (REMs) [17–21] and transitional metals like molybdenum [22–24], zirconium [25,26] and manganese [27,28] while enabling the further use of established produc- tion routes. However, a detailed understanding of film forming reactions at the interface between the water based conversion solution and the metal surface has not been elucidated because of the complex structure of the deposited films. The objective of this work is to carry out a systematic inves- tigation into the chemical reactions that lead to the formation 0013-4686/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2005.08.041