Field and laboratory studies to evaluate the influence of Wet&Dry atmospheric depositions on weathering steel

In this work, an innovative perspective was applied to study the effect that atmospheric depositions have on material corrosion. The influence of different atmospheric conditions on corrosion process was investigated using weathering steel (WS) both in natural exposures and laboratory tests. Specifically, the influence that different start time of material exposure and consequently different atmospheric conditions could have on the early stage of corrosion was evaluated by means of WS field exposures in terms of colour measurements, surfaces characterization, ions amount contained in the patina and corrosion rates. To achieve the maximum information and highlight possible correlations, all the significant variables were processed by Principal Component Analysis (PCA). Additionally, by means of the application of Design of Experiment as chemometric tool, laboratory tests (alternate immersion accelerated ageing tests) were performed on WS to evaluate the interaction among particulate matter inorganic anions and to investigate in more realistic conditions the influence of different amounts and proportions of chlorides, sulphates and nitrates on corrosion rate and metal release, underlining also competitive and synergic interactions between them. As well, through this approach it was possible to directly relate and predict the trend of the measured response factors within an experimental domain that represents different atmospheric compositions and build models that take into account also possible changes in the concentration of pollutants of growing interest. Lastly, in order to further investigate the action of particulate matter on different kind of materials and on differently oriented surfaces, a new developed device (called “Deposition Box”) to sample dry deposition was tested and validated through SEM/EDS analysis combined with the freeware software ImageJ. “Deposition Box” allows achieving reproducible samples of particulate matter (PM) dry deposits and to sample also fine particles (0.4 – 5 μm2) making the study of dry deposits less tricky.