The thermal fouling data of Watkinson were recomputed on the assumption that increases in pressure drop were caused entirely by roughness of the fouling deposit and not at all by blockage. The results indicate that roughness played some role in the sand-water runs, but no role in the gas oil runs. The anomalous increases in overall heat transfer coefficient with degree of fouling in the first two sand-water runs were thus explained by the effect of roughness on liquid film heat transfer coefficient. The original loop was modified, the principal change being the replacement of the manual temperature recording system by a digital Data Logging System. Fluid and wall temperatures, as well as differential pressure, could thus be automatically recorded as a function of time. Better control of independent operating variables such as fluid velocity, inlet temperature and heat flux could therefore be achieved, and the effects of temporary fluctuations in these operating conditions could be observed and separated from fouling effects. Thermal fouling runs were made in the modified heat transfer loop on samples of Bayer Process spent liquor from the ALCAN aluminum refinery in Arvida, P.Q. The only discernible trends in the results were increases in rate and degree of fouling with increasing heat flux to a maximum value, followed by a sharp decrease, at liquor velocities less than 5 ft/sec, and the absence of thermally detectable fouling at higher velocities. The unreproducibi1ity of the results is believed to be attributable, at least in part, to changes in chemical composition of the liquor throughout the experiments. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

This thesis presents a finite element (FE) modelling approach investigating the effects of corroded shear reinforcement on the capacity and behaviour of shear critical reinforced concrete (RC) beams. Shear reinforcement was modelled using a “locally smeared” approach, wherein the shear reinforcement is smeared within a series of plane-stress concrete elements at the specific stirrup location. This was done with the objective of incorporating both the reduction in cross-sectional area due to corrosion and the corresponding expansion of corrosion products build up. Corrosion damage was incorporated through equivalent straining induced by the corrosion build up on the affected surrounding concrete where the concrete cover was treated as a thick-wall cylinder subjected to internal pressure. Strains were introduced in the FE model using fictitious smeared horizontal pre-stressing steel, with a compressive pre-straining level related to the degree of corrosion penetration of the reinforcement. The FE modelling approach was first validated against published test data of shear critical RC beams with and without stirrup corrosion. The proposed modelling approach successfully reproduces the load deformation response as well as the failure mode and cracking patterns of the published experimental tests. Upon validation of the FE model, the work was extended to a parametric analysis of important shear design variables, such as the shear span-to-depth ratio, beam width and stirrup spacing The FE analyses were carried out for three increasing levels of corrosion (low, moderate and high) applied to affected stirrups within the critical section of the beams and based on steel mass loss (10%, 30% and 50%, respectively). In general, the results show a reduction in load carrying capacity accompanied by a softening of the load-deformation curves with each increasing level of corrosion. In most of the cases, a reduction in deflection associated to peak loads was also observed for moderate and high levels of corrosion. The impact of the various parameters was studied with respect to strength and deformation, as well as crack angle and mid-height horizontal strain. This was done in an effort to compare FE values to those provided by the CSA A23.3 design equations. The CSA A23.3 shear design equations were compared against FE analysis data in terms of residual shear strength estimation and individual component contributions to shear resistance (i.e., concrete and steel). The comparisons revealed an over conservative estimation for both strength and concrete contributions and an overestimation of the steel contribution. This divergence was attributed to a transition in shear behaviour within the critical section. Based on the progression of the concrete compressive struts with increasing corrosion and predicted crack angle, it was found that stresses in affected sections are redistributed towards adjacent undamaged material. The shear resistance mechanism generally transitioned from typical beam behaviour towards an arching-dominated one. Finally, based on important findings from the literature and the work conducted within this research, important considerations for assessment practice are suggested.

Recent interest in environmentally friendly alternatives to chromate-based corrosion inhibitors has led to the development of a range of novel coating formulations. The work described in this thesis has been aimed at investigating the mechanism of self-healing and active corrosion protection of the new coatings by searching for active components that have migrated from the coating to a controlled defect. The use of glow discharge optical emission spectroscopy (GDOES) has been investigated as a tool for both the generation of a reproducible controlled defect and for elemental depth profiling of the coatings and corroded substrates. Conclusions drawn from the elemental depth profiles have been validated by a range of characterisation techniques including optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX) and electrochemical techniques. The work has focused particularly on a comparison of hybrid coatings doped with inhibitors encapsulated in nano-containers, as compared with the direct addition of inhibitor species to the coating matrix. The work also investigates the effects of inhibitor addition to sol-gel coatings or primer systems or both, highlighting possible synergistic effects of mixed inhibitor systems (for example, sol-gel coating doped with strontium aluminium polyphosphate (SAPP)) supporting primers doped with benzotriazol (BZT) or mercaptobenzothiazol (MBT). The various coatings have also been studied in the absence of inhibitor species to assess the effectiveness of the coatings as barriers between the substrate and the corrosive environment. This aspect of the study has highlighted minor inhibitive effects of some of the reagents used in the coating formulations and a major inhibitive effect of the nano-containers. The work therefore concludes with recommendations for a possible coating formulation combining the most beneficial elements of the various coatings investigated.

The influence of microstructure on the corrosion behaviour of magnesium alloys has been investigated using advanced microscopy approaches including optical microscopy, SEM, TEM and SKPFM with a focus on the effect of melt-conditioned twin roll casting (MCTRC) and friction stir welding (FSW) on the resultant microstructure of magnesium alloys.The microstructure characterization revealed that intense shearing, generated through the advanced shear technology, resulted in grain refinement and a uniform distribution of the β-phase and reduced micro-porosity in the MCTRC Mg-Al alloys, of which were attributed to the enhanced heterogeneous nucleation, which resulted in a highly refined grain structure. The TRC Mg-Al alloys displayed a coarse grained microstructure, with a random distribution of grain sizes. Deformation features like twinning, localized shear, microporosity and centre-line segregation were some of the commonly observed defects in the TRC alloys. The general microstructure of the AZ series Mg-Al alloys was composed of α-Mg grains, the β-phase, rosette-shaped Al8Mn5 intermetallic particles and β-precipitates.The MCTRC Mg-Al alloys showed improved corrosion resistance owing to the reduced grain size and the β-phase network acting as a corrosion barrier, thereby retarding the corrosion process. The TRC Mg-Al alloys exhibited higher susceptibility to galvanic corrosion due to the coarse and random distribution of grain sizes, and segregation. The corrosion testing results showed different corrosion morphologies, including filiform-like and spherical channel-like along with overall general corrosion. However, galvanic corrosion, initiating at localized sites due to Al8Mn5 intermetallic particles and the Si/Fe impurities accounted for a major deterioration in the performance of the Mg-Al alloys. The polarization curves revealed no evidence of passivation, suggesting that the alloy surface was continuously attacked. SKPFM results indicated that the micro-constituents, namely Al8Mn5 intermetallic particles and the β-phase exhibited higher nobility relative to the α-Mg matrix, suggesting formation of micro-galvanic couples at localized sites leading to the initiation of galvanic corrosion.The AM60 and AZ91 Mg-Al alloys, subjected to FSW, revealed that the traverse speed had a direct influence on the weld zone microstructure, where the size of the friction stir/weld nugget zone decreased with increase in the traverse speed and the increase in the rate of deformation, led to widening of the friction stir zone, below the shoulder. The weld microstructure displayed a prominent friction stir zone, with an ultrafine grain structure of an average grain size ranging from 2-10 μm. The localized increase in temperatures, in the TMAZ, due to the lower tool rotation rates and traverse speeds, which rise above the eutectic melting point (430°C), showed evidence of partial melting followed by re-solidification of the β-phase and evidence of liquation below the shoulder regions in the TMAZ. The morphology of the β-phase clearly revealed solute segregation, inconsistent with the β-phase observed in the parent alloy microstructure.The polarization curves obtained from the weld zones in the FSW AM60 alloy showed an improved corrosion resistance compared with the parent metal zone. SKPFM results revealed that the α-Mg matrix in the friction stir zone showed higher surface potential values compared with the parent alloy microstructure, due to the dissolution of the β-phase, suggesting higher nobility. However, the polarization behaviour of the AZ91 alloys did not show a significant difference in the corrosion resistance in the weld zones due to the higher volume fraction of the β-phase in the AZ91 alloys. The immersion testing results revealed higher susceptibility to corrosion in the transition zone due to the flash formation and the banded microstructure leading to failure of the weld zone.

Extruded Al-Mn alloy are used in heat exchanger applications due to their light weight and good thermal conductivity. Depending on the application, the units may be subjected to external corrosion, which can lead to perforation of the tube. The industrial test most commonly used to assess heat exchanger alloys is the seawater acetic acid test (SWAAT). This is a cyclic fog at 40°C and pH 2.9. In the present study, it was found that pits developing in extruded Al-Mn tubes during the SWAAT test are purely crystallographic. Furthermore, a mechanistic understanding for crystallographic pitting has been developed. The SWAAT test can be of relatively long duration and, typically, does not yield information on the underlying corrosion initiation and propagation mechanisms. In the present study, alternate methods to assess pitting corrosion were elaborated. A drop testing procedure has been successfully implemented to study the mechanism of pit initiation. It was revealed that pits initiated within the aluminium matrix in the vicinity of grain boundaries. A close link between large second-phase particles and pit initiation was established. No preferred grain orientation for pit initiation was evident. Scanning electron microscopy and associated tomography were undertaken for the first time to clarify the mechanism of pit propagation. The pit walls were oriented {100}, while the fast-dissolving planes were {110} and {111}. The findings were in accordance with previous literature. Corrosion penetrated deeper into the alloy when the corrosion front was close to a grain boundary. Pit walls were cathodic to the aluminium matrix, possibly due to enrichment of alloying elements at pit walls. The effect of alloy additions on the corrosion behaviour of extruded aluminium alloys was investigated. Alloys with varying copper, iron and manganese contents were compared. Shot noise analysis and post-mortem analyses were undertaken. The increased amount of manganese in solid solution delayed the transition from micropits to stable pitting. This delay is attributable to second-phase particles that are less cathodic to the aluminium matrix in alloys with increased manganese content. Increasing copper decreased the size of the dissolved polyhedra during stable pitting. Furthermore, pits propagated faster in alloys rich in copper. This could be attributed to an increased level of copper enrichment at the pit walls. Finally, more second-phase particles were present in alloys with increased iron levels. Additionally, pits located in those alloys propagated deeper than pits located in alloys with low levels of iron. A competition between two different types of cathodes, enrichment layer and second-phase particles, is suggested. In conclusion, the effect of microstructure and alloy additions on the corrosion mechanism for crystallographic pitting developed during the project was clarified.

The goal of this thesis is to probe the functionality of 2-mercaptobenzimidazole (MBI) as corrosion inhibitor of carbon-steel in both strong and weak aqueous acidic solutions (HCl and H2CO3). To achieve this target electrochemical techniques have been employed, in combination with substrate analysis. Concerning aqueous HCl media, results demonstrate that MBI is an effective corrosion inhibitor, functioning essentially equally well in 1 M, 0.1 M, and 0.01 M HCl concentrations. X-ray photoelectron spectra suggest that MBI is typically bound to the surface in two tautomeric forms (thione and thiol). Furthermore, these data indicate that substrate termination varies as a function of both HCl and MBI concentration, with the interface consisting of MBI bound to film-free carbon-steel on highly inhibited substrates. In further work, the impact of dissolved oxygen, solution temperature, and immersion time on MBI performance in HCl solutions has been assessed. The latter two parameters have considerable influence on MBI inhibition efficiency. More specifically, it was found that MBI decreases dramatically its inhibition efficiency between 60°C and 70°C in 1 M HCl, and also apparently work less well as substrate immersion time increases. As regards MBI performance in deaerated CO2-saturated NaCl (0.62 M) solution, results demonstrate that MBI effectively inhibits corrosion within the parameter space explored i.e. solution temperatures of 30°C and 55°C and total applied pressures (p(H2O) + p(CO2)) of 1 bar and 20 bar. The performance of MBI does not vary greatly for different combinations of these temperatures and pressures. Post immersion substrate characterisation with XRD and SEM indicate that no significant surface scaling occurs under these conditions.

Lifetime prediction of components in Alloy 600 is a major concern for nuclear power plants. Alloy 600 components have been shown to be susceptible to stress corrosion cracking (SCC). In the 1990’s, an engineering model was developed in order to predict the life time as a function of the main macroscopic parameters (stress, environment, material), based on laboratory results. This model has since been used to predict the ranking of various Alloy 600 components, using the knowledges of the manufacturing and service conditions for each component. It was applied successfully in the case of forged control rod drive mechanism (CRDM) nozzles. However, it was found necessary to improve this model to account for the strain history of the different components. Predictions using the model, investigated from an array of test results on Alloy 600 in laboratory primary water, have demonstrated that the time for initiation differed significantly according to the strain path applied to the specimen. The present work is dedicated to assess SCC results from samples with different strain paths and different level of cold work in order to better understand the manufacturing conditions on SCC. The samples are machined in three different directions and tested at different durations in order to model the time for transition (transition between slow and fast propagation) as a function of cold work, strain path and stress. Thermomechanical treatments are also applied on two different heats of Alloy 600: forged WF675 (very susceptible to SCC in as received conditions) and rolled 78456/337 (non susceptible to SCC in as-received conditions) in order to transform the forged microstructure into a microstructure close to the rolled microstructure and vice-versa. These microstructures are then tested in primary conditions and the results are compared to the results obtained on as-received material in order to get a better understanding of manufacturing process and microstructure parameters regarding SCC behaviour.

A heterogeneous microstructure is intentionally developed in AA2024-T3 aluminium alloy during solidification and thermomechanical processes to obtain good mechanical properties. As a consequence, the alloy is susceptible to localized corrosion, which is the major nucleus for onset of stress corrosion cracking and fatigue cracking.In this research, electron microscopy was employed to observe intermetallic particles and their periphery and monitor the initiation and development of intermetallic particle induced localized corrosion in AA2024-T3 aluminium alloy. In-situ optical microscopy, energy dispersive X-ray spectroscopy (EDX), X-ray microtomography and atomic force microscopy were also used to provide supportive evidence.Intermetallic particles with different electrochemical natures and geometries were found. The main coarse intermetallic particles are identified as S (Al2CuMg), θ (Al2Cu) and α (Al-Cu-Fe-Mn-(Si)) phases. θ (Al2Cu) and α (Al-Cu-Fe-Mn-(Si)) phases showed a relatively inert nature compared with S-phase particles. It was observed that continuous localized corrosion is associated with large clusters of S-phase and θ-phase intermetallic particles that are buried beneath surface but connected to the alloy surface. Propagating away from the intermetallic particles, corrosion developed preferentially along selected grain boundaries.Electron backscatter diffraction (EBSD) was employed to further investigate the relationship between the grain structure and the intergranular corrosion susceptibility. It was revealed that intergranular attack occurred at the grain boundaries that surround grains of relatively high stored energy. Corrosion was not confined within the region immediately adjacent to the grain boundaries, but had developed into the grains of relatively high stored energy, suggesting that grains with relatively high levels of defects are more susceptible to corrosion.

M.Tech. (Engineering: Metallurgy) / The aim of the study was to determine the slurry erosion-corrosion rates as well as electrochemical corrosion rates of WC-Fe-Ru coatings that were thermally coated using a plasma transferred arc method. The WC-Fe-Ru coatings used had different bulk Ru concentrations that varied from 0.7 to 4.1 wt% Ru. A slurry jet impingement erosion-corrosion test rig was used for the erosion-corrosion rate measurements, and an Autolab 302 potentiostat was used to measure the open circuit potential during a 12 hour exposure in the test solution, as well as a potentiodynamic scan to determine the corrosion potential...

To form Cu interconnects, dual-damascene techniques like chemical mechanical planarization (CMP) and post-CMP became inevitable for removing the "overburden" Cu and for planarizing the wafer surface. During the CMP processing, Cu interconnects and barrier metal layers experience different electrochemical interactions depending on the slurry composition, pH, and ohmic contact with adjacent metal layers that would set corrosion process. Ruthenium as a replacement of existing diffusion barrier layer will require extensive investigation to eliminate or control the corrosion process during CMP and post CMP. Bimetallic corrosion process was investigated in the ammonium citrate (a complexing agent of Cu in CMP solutions) using micro test patterns and potentiodynamic measurements. The enhanced bimetallic corrosion of copper observed is due to noble behavior of the ruthenium metal. Cu formed Cu(II)-amine and Cu(II)-citrate complexes in alkaline and acidic solutions and a corrosion mechanism has been proposed. The currently used metallization process (PVD, CVD and ALD) require ultra-high vacuum and are expensive. A novel method of Si surface metallization process is discussed that can be achieved at room temperature and does not require ultra-high vacuum. Ruthenation of Si surface through strong Si-Ru covalent bond formation is demonstrated using different ruthenium carbonyl compounds. RBS analysis accounted for monolayer to sub-monolayer coverage of Si surface. Interaction of other metal carbonyl (like Fe, Re, and Rh) is also discussed. The silicon (111) surface modifications with vinyl terminated organic compounds were investigated to form self-assembled monolayers (SAMs) and there after these surfaces were further functionalized. Acrylonitrile and vinylbenzophenone were employed for these studies. Ketone group of vinylbenzophenone anchored to Si surface demonstrated reactivity with reducing and oxidizing agents.