The corrosion chemistry of two active-metal systems has been studied primarily with X-ray Photoelectron Spectroscopy. First, the interaction of metallic lithium thin films with simple glass surfaces was investigated. Li was deposited on SiO₂, sodium silicate, potassium silicate, and B₂O₃ glasses in an ultra-high vacuum deposition and analysis chamber. The reaction of Li with SiO₂ results in substantial reduction of the glass matrix to form a thin product layer. A negatively-charged Si species was identified based on an unusually low XPS Si(2p) binding energy. The interaction of Li with alkali silicate glasses resulted in substantially less matrix breakdown than for SiO₂, but exchange of lithium for either sodium or potassium cations occurred at the Li/glass interface. The reaction between Li and B₂O₃ was limited to the top layers of the glass, as a passivating layer formed at the Li/B₂O₃ interface. Investigations into the oxidation of polycrystalline iron surfaces were initiated. Clean surfaces were exposed to controlled amounts of pure oxygen gas. The resulting oxide composition and thickness was determined using ultraviolet photoelectron spectroscopy (UPS), electron energy loss spectroscopy (EELS), and XPS. The results indicated the formation of a bilayer structure, with FeO near the oxide-metal interface, and Fe₃O₄ at the outer surface. Film growth was approximately logarithmic with time, and was strongly pressure dependent. Studies of the electronic properties of the characterized iron oxide surfaces were conducted by measuring the rate of electron transfer between the surface and redox-active species in an electrochemical cell. A strong dependence on film thickness was indicated. Photoemission of electrons from a solid is an inherently complex process; this is especially the case for XPS of clean and oxide-covered active metals. Improved theoretical models of XPS lineshapes were developed which provided new insight into the physical processes involved in photoemission. Additionally, these models provided improved qualitative and quantitative data interpretation through the use of least-squares fitting techniques.

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.

Steven Michael Ford, do hereby declare that this thesis is my own unaided work. This thesis has not been submitted in part or in full at this or any other university. This report is submitted in fulfilment of the degree of Master of Science in Engineering at the University of the Witwatersrand. / Aluminium, although often possessing adequate strength and toughness for a specific application, may be deemed unsuitable due to a less than satisfactory corrosion resistance. This unacceptable behaviour is especially prominent in the local mining industry where aluminium alloys corrode severely in the high chloride and sulphate containing waters. Of notable importance and the major motivating force for this research was the historically poor perfomance of aluminium alloy mine cages, which are suited to the task excepting for their unsatisfactory corrosion resistance. Of general importance however, is that the mining sector in South Africa represents a sizeable portion of the economy and could thus become a much greater consumer of aluminium if the metal's corrosion resistance could be improving Apart from varying the composition of the alloy, the other basic technique of increasing a metal's resistance to an environment is by applying a coating of some sort. This research looks into the use of aluminium-based metal sprayed coatings as a form of protection for various aluminium and steel substrate alloys. The purpose of a metal sprayed layer is not merely to isolate the substrate from the environment, hut also to act as a sacrificial anode at regions where the substrate is exposed. Previous work suggested that alloys of aluminium/zinc/indium produced excellent sacrificial anodes and were thus selected for this research. The zinc and indium were always alloyed with pure aluminium, with the percentage zinc varying between 0 and 12%. All the coating alloys were sprayed on a AA6261 and AA5083 aluminium alloys, a metal matrix composite and a mild steel alloy, Various electrochemical and immersion trials were then carried out in several synthetic mine waters and other corrosive media. The basic conclusion to be drawn from the results achieved is that the optimum coating for a particular substrate alloy is the one that provides the greatest potential difference between it and the substrate, while still lasting the required lifetime of the component. The reason for this is that the greater the potential difference, the better the sacrificial protection and hence the better the protection offered to any exposed areas on the surface. The fact that the coating corrodes away with time means that a balance must be found between sacrificial behaviour and required lifetime. / Andrew Chakane 2018

The use of stainless steel alloys in reinforced concrete structures has shown great success in mitigating corrosion in even the most severe of exposures. However, the use of high-strength stainless steels (HSSSs) for corrosion mitigation in prestressed concrete (PSC) structures has received limited attention. To address these deficiencies in knowledge, an experimental study was conducted to investigate the feasibility of using HSSSs for corrosion mitigation in PSC. The study examined mechanical behavior, corrosion resistance, and techniques for the production of HSSS prestressing strands. Stainless steel grades 304, 316, 2101, 2205, 2304, and 17-7 along with a 1080 prestressing steel control were included in the study. Tensile strengths of 1250 to 1550 MPa (181 to 225 ksi) were achieved in the cold-drawn HSSSs. 1000 hr stress relaxation of all candidate HSSSs was predicted to be between 6 and 8 % based on the results of 200 hr tests conducted at 70 % of the ultimate tensile strength. Residual stresses due to the cold drawing had a significant influence on stress vs. strain behavior and stress relaxation. Electrochemical corrosion testing found that in solutions simulating alkaline concrete, all HSSSs showed exceptional corrosion resistance at chloride (Cl-) concentrations from zero to 0.25 M. However, when exposed to solutions simulating carbonated concrete, corrosion resistance was reduced and the only HSSSs with acceptable corrosion resistance were duplex grades 2205 and 2304, with 2205 resistant to corrosion initiation at Cl- concentrations up to 1.0 M (twice that in seawater). Based on these results, duplex grades 2205 and 2304 were identified as optimal HSSSs and were included in additional studies which found that: (1) 2304 is susceptible to corrosion when tested in a stranded geometry, (2) 2205 and 2304 are not susceptible to stress corrosion cracking, and (3) 2205 and 2304 are susceptible to hydrogen embrittlement. Efforts focused on the production of 2205 and 2304 prestressing strands showed that they could be produced as strands using existing ASTM A416 prestressing strand production facilities. Due to the ferromagnetic properties of 2205 and 2304, a low-relaxation heat treatment was found to be a viable option to reduce stress relaxation and improve mechanical properties. The overall conclusion of the study was that HSSSs, especially duplex grades 2205 and 2304, show excellent promise to mitigate corrosion if utilized as prestressing reinforcement in PSC structures exposed to severe marine environments.

Indiana University-Purdue University Indianapolis (IUPUI) / This work is focused on developing viable self-healing coatings, especially considering the viability of the coating in a commercial context. With this in mind, finding low cost healing agents, with satisfactory healing and mechanical properties as well as adapting the healing system for use in coatings was required. Seven potential healing agents were evaluated and an air-drying triglyceride (linseed oil) was identified as the candidate healing agent. Different encapsulation techniques were evaluated and ureaformaldehyde microcapsules were chosen as the candidate encapsulation technique. Self-healing coatings were fabricated using urea-formaldehyde encapsulated linseed oil. EIS, SEM and TGA technologies were used to evaluate mechanical performance, corrosion resistance, and self-healing performance.