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This paper outlines how a corrosion map of zinc was developed for Abu-Dhabi. It presents inputs into the model being databases of RH, rainfall, salt deposition and time of wetness and explains how these inputs are combined to product the corrosion map of Abu Dhabi. It is found that although the corrosion rate generally falls with distance from the Arabian Gulf, corrosion rates in the hinterland of the central coast and in the Hajar Mountains are higher than would be expected from a simple dependence on distance from the coast. The higher corrosion rates around the central coast are associated with the extremely low rainfall while those in the Hajar Mountains may be associated with the transport of airborne salinity from the Gulf of Oman. In general, the corrosion rates in Abu Dhabi are much higher than observed at sites in Australia and South East Asia with similar levels of airborne salinity which is attributed to the much higher quantities of salt that are retained on metal surfaces in Abu Dhabi (relative to Australia) due to the fact that rain washing events, which are frequent and effective in Australia, are very infrequent in Abu Dhabi. [ABSTRACT FROM AUTHOR]

Anodic and cathodic polarization of zinc was carried out in 0.1 M sodium chloride (NaCl) solution with pH ranging from 1 to 13. The electrochemical data was then contrast to thermodynamic chemical equilibrium diagrams. The analysis shows that, in general, variations in corrosion of zinc with pH are associated with the cathodic currents. In acidic solutions, the active form of corrosion occurring is controlled by the kinetics of the cathodic reaction (predominantly hydrogen evolution). In the pH range (7 to 10), the lowered cathodic reaction rate reduces overall zinc corrosion rates. The surface oxides thermodynamically predicted to form in this pH (7 to 10) do not form an effective corrosion protection barrier. In alkaline conditions corrosion occurs chiefly by the formation of zinc hydroxide complexes or zinc oxides that could protect the surface depending on local pH and potential at the metal surface. This work expands the knowledge on zinc electrode kinetics over a wide range of pH and augments the existing literature on zinc corrosion. [ABSTRACT FROM AUTHOR]

Leaf litter is commonly deposited onto roofs, where it affects the local environmental conditions that control the degradation of roof sheeting and gutters. This study investigated the chemical nature and corrosivity of electrolytes resulting from the infusion of deionised water with leaf litter. Leaf litter specimens were collected from a variety of tree species commonly found in southern Australian suburbs, and from gutters in which the leaf litter had accumulated. After infusion for approximately three weeks, leaf litter suspensions were filtered and the electrolytes present in the filtrates were analysed to determine their chemical composition and pH levels. The filtrates from leaf litter obtained directly from trees tended to contain higher concentrations of salts and increased acidity compared to the suspensions from leaf litter sampled from gutters. The corrosivity of the electrolytes was explored electrochemically by potentiodynamic analysis of rolled zinc coupons immersed into the filtrates. Leaf litter was found to influence corrosion rates by increasing the acidity of solutions, and through the release of chloride ions during organic matter decomposition. Soluble products of leaf litter decomposition (i.e. fulvic acids) appeared to provide limited protection against corrosion. Over time, the aggressiveness of electrolytes in gutters should decrease as rain events leach salts from leaf litter, and pH should be buffered through the adsorption of carbon dioxide and possibly through the deposition of airborne dust such as mineralogical particles. In addition to the chemical impacts of leaf litter on corrosion, it can also result in gutters being exposed to longer periods of wetness. Data from wetness sensors installed in both clean and dirty gutters showed that, once wet, gutters containing leaf litter can take over twenty-five times longer to dry than clean gutters. Although there are many variables involved, it has been shown that leaf litter can influence long term zinc corrosion rates by a factor of over 2. [ABSTRACT FROM AUTHOR]

This paper reports on a study in which fine seawater droplets were placed on zinc surfaces for periods of 15 mm to 6 h. After each exposure, droplets were either extracted from the specimens or allowed to evaporate in laboratory conditions. Scanning electron microscopy (SEM)-energy-dispersive spectroscopy, X-ray microdiffraction, and SEM-focused ion beam studies were undertaken on the specimens after exposure, as was in Situ Raman Spectroscopy on zinc covered with a saline droplet. Approximately 30 mm after droplets were placed on the surface, a thin moisture layer (termed the secondary spreading film) spread out from the central droplet. As a function of position and time, oxide development in the central region was initially slow; however, after -30 mm, a significant local attack of the underlying microstructure occurred. Correspondingly, precipitate phases developed on top of the oxide, which produced an oxide consisting of three bands: an irregular zone with a localized metal attack and significant voids at the metal/oxide interface, overlaid by a relatively void-free layer, which in turn was overlaid by a porous zone. At the edge of the drop (before the secondary spreading), oxide growth was much faster, and the deposition of phases that precipitate in solutions appeared critical. We discuss the chemistry and identification of the various phases and the implications of oxide formation to the electrochemical processes occurring in drops. [ABSTRACT FROM AUTHOR]