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The research was aimed at offering chromate-free substitution surface conversion treatments applicable to bare or coated steel products, which would be at least as performing as classical cleaning, phosphating and chromic rinsing procedures in themes of corrosion resistance and compatibility with finishing lacquers or paint layers.
In all three systems that were investigated adhesion promoters were used. Adhesion promoters are organic molecules that have two reactive end groups with which they bind to the substrate and the lacquer. This way a very stable chemical bond is established between paint and metal.
On bare and Zn coated Steel two distinct methods were used to deposit chemically stable and adherent silica films. The first one is directly inspired by the sol-gel procedures developed for special optical property products by the glass industry. The second one consists in an electrochemical operation to be carried out n silicate based media, similarly to alkaline cleaning treatments classically applied to blackplate material aimed for batch-annealing. In both cases a three dimensional network of amorphous silicate is build on top of the iron or zinc-oxide. The deposited silica films are perfectly covering and homogeneous. These films are totally inactive relative to the oxygen reduction and perform equivalent to those of 20 to 40 times thicker classical phosphate layers.
Organosilanes which build a two dimensional network are applied only on zinc coated steel strips. Using arbitrary deposition conditions showed that the organosilanes improve the adhesion of an electron beam curable coating only for a short time, It was found that an additional pretreatment is necessary to provide a stable anchor point for the organosilanes. Using a silicate based cleaner to deposit silicate material on the substrate surface showed some promize, with test systems giving superior, or equivalent performance, with chromium based pretreatments in accelerated corrosion testin

Additional information

Authors: C REINART, Max-Planck-Institut fur Eizenforschung;M STRATMANN, Max-Planck-Institut fur Eizenforschung;M LAMBERIGTS, CRM;J //PJ_PJ_RPG SERVAIS, CRM;B WILLIAMS, British Steel Technical plc - Welsh Laboratories
Bibliographic Reference: EUR 18776 EN (1999) 131pp
Availability: Available from OOPEC Sales agents
ISBN: ISBN 92-828-5287-3
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