Resistance of chromated zinc coatings to the impact of microscopic fungi

Zinc coatings are used to protect metallic parts of automobiles from corrosion. Zinc protective coatings are often chromated additionally treating them in acidic solution of chromium compounds. In recent years new technologies were designed to deposit chromate films of various thickness and resistance on zinc surface from acidic solution of Cr(III) compounds. It has been noticed, that under atmospheric corrosion conditions microscopic fungi are present in the environment affect zinc coating. The aim of the presented study was to determine if zinc coatings treated with Cr(III) solution become more resistant to fungi influence or their resistance diminishes. The analysis of steel plates coated with a zinc film and treated in four different chromium solutions has shown that in all the specimens fungi of Cladosporium herbarium species were detected and their frequency of detection was quite high, sometimes up to 50 %. However, we failed to determine the regularities of distribution of some fungi on the surface of plates chromated in different solution. The comparison of changes in the surfaces of plates treated with the four solutions has shown that the plates treated in the Likonda 3Cr5 passivation solution changed least after being exposed to atmospheric conditions. Chromated plates contaminated with mixtures of different fungi and kept for 60 days at a temperature of (26 ±2) °C under humid conditions were examined by using a scanning electron microscope (EVO 5O XP Carl Zeiss STM AG, Germany) and the peculiarities of their surface damage were determined. The peculiarities of growth of some fungi species were determined on the plates chromated in the Likonda 3Cr5 and Cr(NO3)3·9H2O + malonic acid solutions. Under these conditions the fungi of Chrysosporium merdarium, Fusarium proliferatum, Paecilomyces lilacinus, Penicillium stoloniferum can either generate and promote the damage of metal surface or stabilize its corrosion processes