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During the construction of a chemical processing plant, a polyphosphate product was selected for use as a corrosion inhibitor in the open recirculating cooling tower system. After several months of operation, problems in the system made evident the fact that polyphosphate as a corrosion inhibitor was not acceptable. An organic corrosion inhibitor was substituted for the phosphate, resulting in improved corrosion protection and the elimination of phosphate fouling.

A study of Linear Polarizations Resistance Measurements for silver metal immersed in a solution of AgNO3 and HNO3 to determine the effect of varying potential sweep rates has been made. Results indicate that for the system under investigation the Polarization Resistance is a non-linear function of potential sweep rate.

<p>A study was undertaken to achieve a better understanding of the key microstructure-performance relationships involved with the intergranular corrosion and exfoliation corrosion of Cu-lean AA7003 alloy extrusions, as a function of the heat-treated condition. The heat treatments of interest in this study include the naturally-aged T4 condition, representing the as-extruded condition, an artificially-aged T6 condition, representing a post-weld stress-relief condition, and an artificially-aged automotive paint-bake cycle condition. The influence of heat treatment on the resultant microstructure is characterized using light optical microscopy, coupled with image analysis, and electron (scanning & transmission) microscopy, coupled with energy dispersive spectroscopy. The influence of heat treatment on the corrosion behaviour is characterized using anodic polarization measurements and ASTM standardized testing to evaluate the susceptibility resistance to intergranular corrosion (ASTM G110) and exfoliation corrosion (ASTM G34).</p> <p>The cross-sectional (LT-ST & L-ST) microstructures of all three heat treatments consist of a fibrous, non-recrystallized grain structure in the interior, and a coarse recrystallized grain structure at the exterior surface. Both grain structures are slightly elongated along L-direction. The grain size distribution and grain aspect ratio distribution is weakly dependant on the heat treatment applied, and on the orientation plane. Among the two artificial aging, the T6 (post-weld stress-relief) condition has the higher micro-hardness (yield strength), as it has higher density (volume fraction) of the strengthening MgZn₂-type precipitates (η, η′ and their GP zones) within the Al matrix grains.</p> <p>Anodic polarization measurements show a more negative corrosion potential (E_corr) for the two artificially aging heat-treated conditions. The shift is believed to be due to the micro-galvanic cell activity established between the more noble Al matrix grains and the more active strengthening MgZn₂-type precipitates within the Al matrix grains, which have a significantly increased surface area (volume fraction) in the artificially-aged condition. A similar, single breakdown potential (E_b) corresponding to a pitting potential (E_pit) is observed, regardless of the heat-treated condition. The similar potential is believed to be due to localized breakdown of the passive film at the periphery of coarse second phase intermetallic particles (Al₃Fe), which remain unaffected by artificial aging.</p> <p>Of the three heat-treated conditions studied, the T6 condition exhibits the lowest susceptibility to both intergranular corrosion and exfoliation corrosion. The lower susceptibility is believed to be due to the lack of any Cu enrichment in across the grain boundary region (either in the solute depted zone or in the generic Mg(Zn,CuAl)₂ grain boundary precipitates). This lack of enrichment is believed to produce a smaller micro-galvanic cell activity across the grain boundary region, as compared to that produced when Cu is enriched across the grain boundary region, particularly in the Solute depted zone (SDZ).</p> <p><br /></p> / Master of Applied Science (MASc)

<p>A study has been conducted in mildly aggressive saline solutions to indentify subtle yet important difference in the anodic and cathodic process of three Mg-Al alloys, AZ31B, AM30 and AM60B in a partially passive state and a localized corrosion state. The influence of metallurgical factors and environment variables on the corrosion resistance and surface film breakdown process has been investigated using potentiodynamic and potentiostatic tests combined with optical microscopy.</p> <p>All three Mg-Al alloys corroded in a partially protected state under open circuit conditions in the test solution and the surface film formed on each exhibited a similar breakdown potential. This indicates that metallurgical factors such as alloying additions and the presence of the β-phase (Mg₁₇Al₁₂) did not significantly influence the surface film breakdown process. AM60B exhibited improved corrosion resistance at potentials below the breakdown potential due to the formation of a more protective surface film. The β- phase, however, did not strongly influence either the anodic process at potentials above the breakdown potential or the cathodic process. It was determined that increasing the alloy Al content increases the corrosion potential of Mg-Al alloys, but also increases the risk of localized corrosion. The similar anodic and cathodic polarization behaviour exhibited by AZ31B and AM30 indicates that a 1 wt % Zn alloying addition does not strongly influence the corrosion resistance of these alloys. The die-cast skin of AM60B exhibited better corrosion resistance than the interior at potentials below the breakdown potential due to the higher fraction of Al-rich β-phase, which improved the protective ability of the surface film. The semi-continuous β-phase network did not provide a strong micro-galvanic activity to drive anodic dissolution of the α-phase, therefore, did not significantly affect the corrosion resistance above the breakdown potential. The crystallographic texture exhibited by the extruded AM30 did not strongly affect the short-term and long-term corrosion resistance. AM30 showed a relatively steady passive state during long time exposures in a room temperature 0.01 M NaCl solution.</p> / Master of Science (MSc)

<p> Poly aniline (PANI) is capable of inhibiting corrosion on iron by inducing the formation of a passive oxide film. The mechanism by which PANI does this is unknown to the scientific community. We have used photoemission spectroscopy of thin films of a model PANI oligomer to investigate the PCAT -iron interaction. </p> <p> The oligomer chosen was a phenyl-capped aniline tetramer (PC AT). Thin films of PCAT were prepared by in-vacuum physical vapor deposition to obtain extremely thin films of thickness ranging from -5A to over 1 Onm. </p> <p> Films were investigated with a photoemission electron microscope (PEEM) using synchrotron radiation to obtain spatially resolved valence band photoemission spectra. Analysis of PEEM results suggest that PCAT is capable of migrating several microns along the substrate surface, and causes a decrease in substrate work function wherever present. </p> <p> High-resolution core level and valence band photoemission spectroscopy using a laboratory-based photon source was used to characterize the substrate and PCAT properties near the PCAT-substrate interface. Characterization of an in-situ thin film deposition reveals that the iron substrate exhibits band bending in it oxide as well as a decrease in work function by 0.7eV upon adsorption of PCAT. </p> / Thesis / Master of Science (MSc)

Load controlled cyclic fatigue testing was conducted on base metal (BM) and friction stir welded (FSW) magnesium (Mg) alloy AZ31B compact tension (CT) specimens in laboratory air and a 0.05 wt. % NaCl fog environment in efforts to delineate the effects of salt fog and stir welding on fatigue performance under tension-tension loading conditions. FSW beads were produced on single piece AZ31B sheet product, simulating a pristine friction stir butt weld. Optical and electron microscopy, as well as X-ray diffraction was employed to observe the features and characteristics of fracture surfaces. The resulting stress vs. number of cycles to failure (S-N) curves demonstrated a reduction in fatigue life in a salt fog environment and an increase in fatigue life for FSW specimens compared to equivalently loaded BM specimens. Tensile frame displacement data indicated that the salt fog environment had an immediate effect on the BM samples, with an increased displacement required to meet the load control criteria. Fatigue cracks that propagated in CT samples that were notched in the direction of FSW tool travel consistently propagated towards the retreating side (RS) of the stir zone. / Thesis / Master of Applied Science (MASc)

The primary cause of corrosion in transportation structures is due to chlorides which are applied to bridge decks as deicing salts. The direct cost of corrosion damage to the country's infrastructure is approximately $8.3 billion per year. One of the most common corrosion abatement methods in the United States is the barrier protection implemented through the application of fusion bonded epoxy coatings. The purpose of this study was to investigate various coating and exposure parameters to determine their effects on the corrosion of reinforcing steel. The parameters investigated were: chloride content at the bar depth, coated bar corroded area, corrosion product color under the coating, epoxy coating adhesion, coating color, coating damage (holidays and holes), coating thickness, TGA, DSC and EDS analysis and SEM coating cracking investigation. This was accomplished by testing new coated bar specimens as well as specimens extracted from 27 bridge decks located in Virginia. This study demonstrated the following: The extracted ECR coating samples presented extensive cracking compared to the new ECR samples in which the coating cracking was limited to only one sample. The DSC results showed that both the extracted samples as well as new samples are not fully cured during the manufacturing process. The coating degree of curing data also showed that the bars are insufficiently and unevenly heated prior to the application of the powder coating. Additionally, the samples investigated presented significant permanent adhesion loss with little or no epoxy coating residue present on the bar surface, while the EDS analysis showed that once adhesion is lost, corrosion will proceed unimpeded under the coating even in the absence of chlorides. The parameters that presented a direct correlation with the observed corrosion activity were the number of holidays and the number of damaged areas per unit length of bar. This indicates that the passivation of the bare steel exposed to the concrete pore solution at the breaches in the epoxy coating is not the same as a bare bar under similar exposure conditions allowing it instead to corrode at lower concrete chloride concentration levels than bare bars. The results also show a distinct loss of quality control in the handling and possibly storage of new coated bars. The new ECR samples had significantly higher damage density than the samples extracted from concrete even though the coating is damaged during the placement of the concrete, while there was no change in the number of holidays and cure condition. Finally, the data presented further evidence that while limited, the non-destructive corrosion assessment methods available for bare steel reinforced structures may also be used on ECR reinforced structures. In particular, the corrosion rate measurements correlated reasonably well with the chloride concentrations at bar level. This indicates that while the chlorides may not influence the corrosion activity under the coating, they do influence the corrosion activity at breaches in the coating. / Ph. D.