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The polymer coatings considered in this thesis work principally by creating a barrier, in order to prevent a corroding medium such as water and / or oxygen from contacting the surface of the underlying metal. Such coatings are subject to attack from the environment in which they are placed. This attack can lead to failure of the coating and corrosion of the underlying metal. In this thesis, three principle means of coating degradation, leading to subsequent corrosion of the substrate have been considered: Mechanical damage of the coating, the effect of ultra-violet light weathering and filiform corrosion. Electrochemical measurements have been made in order to attempt to quantify both the degree of coating breakdown and the extent of corrosion of the substrate. The principle method for measuring coating breakdown and substrate corrosion utilised in the work for this thesis was Electrochemical Impedance Spectroscopy (EIS). EIS, in principle, allows both changes in coating porosity resulting from coating breakdown, and the extent of corrosion of the substrate to be measured. The extent of delamination under polymer coatings on defects of different sizes and on different substrates has been measured. The effect of ultra-violet light weathering of polymer coatings was measured using EIS and correlated with measurements of light reflection of the coating. Filiform corrosion was induced on two different substrates, coated with various coatings. The effect of substrate and coating on filiform corrosion growth rate and mechanism has been considered.

The corrosion behaviour of pure copper, zinc and aluminum in selected commercial beverages was studied. Experiments were also conducted in the presence of citric and phosphoric acid to investigate their role in the corrosion process in these beverages. Two experimental approaches were used to investigate the corrosion behavior: a chemical method in which the dissolved metal concentration was measured after immersion of a sample in a beverage and an electrochemical method using the Tafel extrapolation technique. The metal surfaces were also examined by SEM/EDX after the immersion tests and electrochemical polarization. Among the important conclusions from this research are that the order in which the various beverages affect the corrosion rate as evaluated by Tafel extrapolation of the polarization curves did not agree with the order based on measurement of the dissolved metal concentration as determined by the immersion tests except when a 1- day immersion test was used for Al. The dissolved Al, Zn and Cu concentrations obtained from short-term immersion tests differed from those measured in long-term tests, although the same ranking of the corrosiveness of the seven soft drinks was obtained after 1- and 3- day immersion tests. These discrepancies likely stem from the complicated dynamics of the corrosion of these metals and the various physical, chemical and electrochemical processes that take place in these beverages. No simple correlation was found between the beverage properties and composition and the dissolved copper, zinc and aluminum concentrations after immersion, whether based on short-term or long-term tests. However, the corrosion rate of copper in the 7 soft drinks as determined by the Tafel extrapolation method was found to depend on the pH. Uniform corrosion was observed in all iv cases except for Al immersed in Gatorade. Pitting cavities were observed on the surface of Al after both the 5-day immersion test and Tafel polarization measurements. Of the beverages considered in this study, Gatorade was consistently found to be the most corrosive for the three test metals.

In the present study, the corrosion behaviour of several magnesia-chrome (MC) and magnesia-alumina spinel (MA) bricks against fayalite type slags was investigated and the role of the spinel phases was highlighted . The experimental results revealed that the corrosion resistance of the MC bricks was superior to the MA bricks against KIVCET slags in static and dynamic conditions . As a result of the interaction between MgO from MC bricks and the slag, a modified forsterite phase (Mg, Fe, Zn, Ca)₂SiO₄ was formed, which destroyed the precipitated complex spinel bonds at the grain boundaries of periclase and magnesia-chromia spinel . Furthermore, both MgO and MgO-MgAl₂O₄ spinel in the MA brick dissolved into the slag, which resulted in modified forsterite phases of (Mg, Fe, Zn, Ca)₂SiO₄ and (Mg, Fe, Zn)(Fe, Al)₂O₄ complex spinels, respectively. In addition, the accretion formation in the KIVCET furnace was investigated through solubility experiments of Cr₂0₃ in the KIVCET slag with various amounts of lead, which revealed that the net contribution of Cr₂0₃ to the spinel formation is the highest in the barren (no Pb) slag, followed by high-lead (11% Pb) and it is the lowest for the low-lead (6% Pb) slag. The amount of spinel solid solution increased consistently with increasing Cr₂0₃ dissolved and the PbO existent in the slag. From examinations of several used bricks from the tuyere area of a Peirce Smith nickel converter, it was found that the corrosion is due to the interaction of the partially oxidized matte penetrating deep into the brick and the magnesia grains forming (Mg, Fe, Ni, Co) xOy spinels . Analyses of brick samples used in the KIVCET Electric Furnace roof identified deep reaching sulphation, which weakened the bonding phase between coarse magnesia grains. In the Bottom Blown Oxygen Converter, a highly aggressive lead and bismuth oxide rich slag penetrated deep into the brick, which destroyed the grain boundaries, causing the refractory to be easily eroded at the refractory-slag interface. Our studies concluded that the spinel phases, either as magnesium chromate, magnesium aluminate or complex spinel [(Mg, Fe)(Cr, Al, Fe)₂O₄], enhanced the corrosion resistance of a basic refractory to fayalite type slags from the non-ferrous smelting and converting furnaces.

Thesis (Ph.D.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ.128-134 )

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 69-74). Also available via the Internet.