This study focused on the kinetic data measurements, such as diffusion coefficient D and exchange current density i_0 of the electrochemical reactions of corrosion products (Fe, Cr and Ni ions) and corrosive species (OH-), and corrosion studies of structural materials (SS 316H and Alloy 617), including static corrosion and galvanic corrosion, in molten MgCl2-NaCl-KCl and/or NaF-KF-UF4-UF3 salts in a temperature range of 600 to 800C. The study applied the semi-differential (SD) analysis method and innovative fitting method for the kinetic property data measurements in the multicomponent system of NaF-KF-UF4-UF3 salts. In molten MgCl2-NaCl-KCl salts, the measured D_(OH^- ) has the largest value followed by D_(〖Cr〗^(2+) ), D_(〖Fe〗^(2+) ), D_(〖Cr〗^(3+) ) and D_(〖Ni〗^(2+) ) at the studied temperatures, and none of the diffusion coefficients depends on the ion concentration in the studied concentration range and all of them followed the Arrhenius law. At the same temperature, the measured D_(Fe^(2+) ) and D_(〖Cr〗^(2+) ) values in molten NaF-KF-UF4-UF3 salts were slightly smaller than those obtained in molten MgCl2-NaCl-KCl salts. The non-linear curve fitting technique was applied to determine the exchange current density i_0, charge transfer coefficient α, limiting current density i_L and standard rate constant k^0 values. i_0 and k^0 followed the Arrhenius law. The obtained fundamental data can be applied to corrosion models which make the corrosion rate prediction possible in a static system from the experimental kinetic data. Corrosion studies of SS 316H and Alloy 617 in thermal purified molten NaF-KF-UF4-UF3 salts were performed for 120 hours. Based on the post-test analysis, the major metal species corrosion products were Cr, Fe and Mn in SS 316H tests, and Cr, Co, Ni in Alloy 617 tests. The measured UF4/UF3 ratio increased after corrosion tests because some of the U3+ was oxidized to U4+ by corrosive impurities and corrosion products during tests. Cr depletion and salt penetration were observed at grain boundaries (GBs) for both SS 316H and Alloy 617. For Alloy 617 specimens, the corroded area could be divided into two parts: the first part (near the surface) where Cr was completely depleted, and the second part (underneath the first part) where Cr was partially depleted. For SS 316H specimens, the average attack depth was larger than that of Alloy 617. Mo segregation was observed in the matrix of SS 316H specimens but was found to be enriched at GBs in the second part of Alloy 617 specimens. The corrosion study of Alloy 617 with time was also conducted for 72 hours and 32 hours, respectively. A thin layer composed of Fe, Co, Ni and Mo was found on the surface of the specimen, which was different from the previous 120-hour tests. In the salt, the concentration of Cr kept increasing with time, while for the other identified corroded elements, i.e., Fe, Co, Ni and Mo, their concentrations increased first, then decreased until becoming zero or stable. In the galvanic corrosion study of Alloy 617/graphite in molten NaF-KF-UF4-UF3 salts, the galvanic corrosion rate of Alloy 617 at 750C was about four times of that at 650C in the 2-hour tests, which indicated that temperature has a significant effect on the galvanic effect. In the 120-hour galvanic corrosion test, the galvanic corrosion rate became slightly larger with time in the studied system. Similar to the previous 120-hour Alloy 617 corrosion test, the corroded area of the post-test specimen was divided into two parts. The measured attack depth in both parts were much smaller compared with that in the 120-hour Alloy 617 test. This was because of the lower corrosive impurity concentrations in the salt used in the test. The salt in the galvanic corrosion test has been used in the previous corrosion test, during which the corrosive impurities were consumed, which made the salt less corrosive. Finally, it is necessary to point out that all the salts used in the present work were only thermally purified, which is effective in the removal of moisture but not in the removal of oxide impurities. Therefore, further studies are needed to understand the oxides' impacts on the corrosion behavior, especially on the salt penetration. / Doctor of Philosophy / Molten salt is a promising candidate that can be used as fuel and coolant in the molten salt reactors (MSRs). Besides, it can also be used as thermal energy storage, heat transfer fluid in the concentrated solar power plants, because it has high heat capacity, low vapor pressure, and high thermal conductivity. However, materials corrosion is a key concern of molten salt applications, and it is known that the corrosion by molten salts is mainly impurity driven. The impurities, such as moisture in the salts, can make the salt more oxidized, thus becoming more corrosive to corrode the structural materials. The present work focus on the kinetic property of metal specie corrosion products and non-metal impurity in the molten fluoride and chloride salts, which were directly related to the mass transfer and charge transfer process during the corrosion. Especially in the measurements of fluoride salts, innovative methods were applied which were confirmed to perform well in the multicomponent system (Fe and Cr ions coexisted). The static corrosion tests of SS 316H and Alloy 617 were conducted in molten fluoride salt at high temperatures. The main purpose was to study their corrosion behavior and understand the corrosion mechanisms. The corrosion rate of SS 316H was also estimated, which could be a crucial criterion in the material selection. In addition, the corrosion of Alloy 617 with time was also investigated. The metal specie corrosion product concentration change trends were obtained, and the corrosion behavior over the different corrosion stages was analyzed. Different corrosion phenomenon was observed in different corrosion test. Thus, they shed lights on the study of how the corrosion was developed during the corrosion process. Moreover, galvanic corrosion was another major corrosion type when two or more dissimilar materials were electrically contacted. The galvanic corrosion of Alloy 617/graphite was studied in the molten fluoride salts. The galvanic corrosion rate increased with the rise of temperature, which verified that temperature was a key factor that affected the galvanic corrosion. And the galvanic effect was also turned out to increase with time in the present study.

It is generally acknowledged that a variety of problems affecting aesthetics, health, and corrosivity of potable water can arise during installation of building plumbing systems. These include 'blue water', microbial infestation, and rapid loss of disinfectant residual, among other things. Frequently cited causes of the problems include metallic fines left in the plumbing lines from deburring, cutting and product fabrication; solder flux residuals (water soluble and petroleum based flux); and solvents for CPVC. Mechanistically, some materials such as flux contain high chloride, high ammonia and cause low pH, which can increase the corrosivity of water held in the lines. Indirect effects are also suspected to be important. For example, ammonia from flux and organic carbon from flux or PVC solvents can spur microbial growth, which in turn can reduce pH or otherwise increase corrosivity. Recent work has also demonstrated that problems with lead leaching to water from brass in modern plumbing can actually be worse in PVC/plastic than in copper systems, if certain types of microbes such as nitrifiers proliferate and drop pH. Some of the problems initiated by construction practices can persist indefinitely, causing higher levels of lead and copper in water, or longer term, contributing to failures of the plumbing system. Blue water from high copper concentrations is a confounding problem that continues to arise in some locales of the United States. One public elementary school in Miami Dade County is experiencing blue water issues as manifested by blue ice cubes and sink staining. In addition to the aesthetic problems, copper levels are above the EPA's Copper Action Level of 1.3 ppm. Bottled water has been substituted for tap water consumption, which has created a financial burden. The pH of the school's water ranges from 7.15 - 7.5 and the school itself is located 1 ½ miles off the main distribution line resulting in a very low chlorine residual of between 0.06 mg/L Cl2 and 0.18 mg/L Cl2. On site water was shipped to Virginia Tech from Miami to be used in this study. Preliminary testing showed that an increase in the pH of the water would decrease copper leaching. Several pH's were tested which revealed that increasing the pH of the water to 8.5 would drop copper below 1.3 mg/L. When these recommendations were implemented at the school, the high alkalinity and calcium rich water caused calcite scales to form which clogged the chemical feed nozzles. Further bench scale testing indicated that adding 2 mg/L orthophosphate corrosion inhibitor would effectively decrease copper to a level that would comply with the EPA's Copper Action Limit. Orthophosphate corrosion inhibitors are used by utilities to limit lead and copper corrosion from consumer's plumbing. An evaluation comparing the effects of both 100% orthophosphate inhibitor and orthophosphate/polyphosphate inhibitor blends was performed to study the effects they have on galvanic corrosion, metallic corrosion, microbial growth and the decay of chloramine disinfectant. On site water was sent to Virginia Tech from UNC for use in this bench scale study. The results from this study indicated that 100% orthophosphate inhibitor was the most effective corrosion inhibitor at decreasing metallic corrosion. It has long been known that microbial activity can have significant effects on water quality. This study evaluated nitrifying and heterotrophic bacterial growth in water systems containing copper pipes, a common plumbing product, and flux which is used in soldering copper pipes together in new construction. There are several types of commercially available fluxes which are often used when soldering new pipes together. Flux ingredients vary and can include extremely high concentrations of ammonia, zinc, chloride, tin, copper and TOC. Flux containing high amounts of ammonia can be detrimental to water quality because it can accelerate the occurrence of nitrification, thus creating a cascading set of problems including, but not limited to, pH decrease and copper corrosion. The results from this case study indicated that flushing a pipe system can effectively decrease the high concentrations of flux present in a new construction system; however, high levels of ammonia from flux can create an environment in which nitrifiers may proliferate within the system. Many water utilities in the United States are switching disinfection type from chlorine to chloramine due to the increased stability, longer residual time, and overall safety benefits of chloramine. Although chloramines have been found to be a desirable means for disinfection, chloramine decay is an issue of great concern because if the chloramine residual decays, it can leave a water system unprotected against microbial infestation. A preliminary examination of this issue was performed in a laboratory setting to evaluate the many components that effect the stability of chloramine decay, including alkalinity, phosphate, temperature, and various pipe materials. The results from this experiment revealed that temperature increase, pH increase, and aged tygon tubing all accelerated the rate of chloramine decay. / Master of Science

The purpose of this investigation was to determine the corrosion characteristics of Incoloy alloy 825 in 1.0 to 15.0 normal sulfuric and 0.5 to 3.0 normal hydrochloric acids at 25 to 60°C in both nitrogen-saturated and air-saturated acids, using potentiostatic polarization techniques. Anodic polarization curves were obtained by changing the potential of an Incoloy 825 test electrode and measuring the resulting current. In both acids, there is no difference in the polarization characteristics in air-or nitrogen-saturated solutions. In 1.0 to 15.0 normal sulfuric acid at 25 to 60°C, the alloy spontaneously passivates and does not exhibit a significant active region. In 0.5 normal hydrochloric acid at 25°C, Incoloy 825 is spontaneously passive, but is active at higher concentrations. At 25°C, as the hydrochloric acid concentration increases from 1.0 to 3.0 normal,the critical current density increases from 260 to 5900 microamperes per square centimeter. At 40°C, as the acid concentration increases from 0.5 to 2.0 normal, the critical current density increases from 25 to 28,000 microamperes per square centimeter. In 1.0 normal hydrochloric acid at 25°C, the corrosion rate calculated by weight loss measurements for potentiostatically controlled Incoloy 825 agrees closely with the corrosion rate calculated from polarization current densities, and indicates that the elements dissolve in the proportions present in the alloy. Potentiostatically passivated Incoloy 825 in 1.0 normal hydrochloric acid at 25°C does not exhibit a stable passive condition, reverting to the active state in less than 12 hours. / M.S.

The increasing use of deicing salts has caused the accelerated deterioration of bridge decks due to cracking and spalling from chloride induced corrosion of steel reinforcement. One method being considered as a possible corrosion abatement measure is the removal of chloride contaminated concrete and the chemical treatment of the partially exposed rebar through ponding and/or placement of chemically treated mortar. Reinforced concrete specimens were cast and subjected to repeated exposure to NaCl solution. Half-cell potential, corrosion rate, and chloride ion concentration measurements were conducted until the indication of active reinforcement corrosion. Chloride contaminated concrete was removed to the rebar level through a grooving process. The grooves were chemically treated through solution pondings and backfilling with treated mortar. Seventeen treatments and combination of treatments were evaluated including corrosion inhibitors, polymer sealers, and a possible chloride ion scavenging mineral. The treatment effects were monitored using half-cell potential and corrosion rate measurements. In addition, mortar cubes were cast containing various treatment concentrations and were subsequently tested for compressive strength and change in resistivity over time. Based on the electrochemical and mortar cube measurements, DCI (calcium nitrite) when applied as a ponding and mortar treatment, was determined most effective in abating corrosion after concrete removal. In addition, Alox 901, Cortec 1337, Cortec 1609, sodium tetraborate, and Zinc borate were also found effective in mitigating rebar corrosion after concrete removal; however, both the borate compounds cause set retardation of portland cement. These chemicals were recommended as candidate treatments for further evaluation in both large-scale and field experimentation. / Master of Science

A statistical analysis was conducted to investigate the effect of applied load and relative humidity of the atmosphere on the durability and coefficient of friction of five polymer coatings used to protect against fretting corrosion. Chlorine and non-chlorine containing polymers were used in this research to see if the large humidity effect seen in a previous study with polyvinyl chloride is strictly a chlorine related phenomenon. The five polymers used were polyvinyl chloride, polyvinylidene chloride, polystyrene, and two siloxane modified polyimides. Disks made of 1045 steel were coated with thin polymeric films and fretted against a 52100 steel ball. Three levels of load were used: 11.12, 22.25, and 44.5 N, and the two levels of relative humidity were less than 10% and between 45 and 55%. Amplitude of oscillation was 330 μm peak to peak, frequency of oscillation was 40 Hz, and the coating thickness was 25 μm. Statistically significant variables and interactions are identified, and reasons for their significance are discussed. Increasing the humidity had no consistent effect on the ending coefficient of friction between the polymer film and the oscillating ball, increasing the load decreased the coefficient of friction, and either increasing the humidity or load decreased the life of the coating during fretting. The extent of this reduction in life depends on the polymer. The relative humidity of the environment affected the coating life of only one of the chlorine-containing polymers. Humidity was also shown to affect the coating life of two polymers that do not contain chlorine. / Master of Science

Chloride induced corrosion of steel in concrete is one of the major forms of deterioration mechanisms found in reinforced concrete bridges. Early age corrosion damage reduces the lifespan of the bridges, which results in heavy economic losses. Research has been conducted to identify economic solutions for significantly delaying and/or preventing corrosion damage. Considering the amount of steel reinforcement used in bridge decks, the influence of as constructed parameters including clear spacing between top and bottom reinforcement bars, ratio of cathode to anode areas, and presence of stay-in-place forms on corrosion activity needs to be evaluated. The influence of the as constructed parameters have been studied using different corrosion assessment methods including resistivity, half-cell potential, linear polarization, chloride content, moisture content, and visual inspection. This study included the clear spacing distances between the anode and cathode of 51, 76, and 102 mm (2, 3, and 4-inch), number of cathodes as 1 and 2, and the presence and absence of stay-in-place forms. Data up to 15 months were taken from a previous study by Smolinski and integrated into the current study period of 35 to 45 months. A trend line may be established to illustrate the changes which took place over the missing time period, from approximately 15 to 35 months, since the specimens were maintained in controlled environment. Analysis of the data showed that there is a significant difference between the spacing values (2, 3, and 4-inch) through all forms of evaluations. Regarding the other parameters, no significant difference was identified. Variations in resistivity with increasing spacing, even when the water-cement ratio was kept at 0.50, maybe the result of the difference in unit consolidation between the clear spacing specimens. Thus, the corrosion mechanism observed in this study may be resistivity-controlled. Also, autopsy showed that corrosion on the top bars was in general agreement with the measured corrosion activity. The bottom bars had no visible corrosion and the chloride had not penetrated to the bottom bars, regardless of the separation distance between the top and bottom bars. For this laboratory study, the measurements showed that macrocell corrosion influence on the total corrosion was insignificant. / Master of Science

Aluminum salts are used as the primary coagulants in the majority of United States drinking water treatment plants. Despite decades of practical experience, there are important knowledge gaps regarding the effects of residual Al on distribution system materials as well as specific types of solids formed. The first phase of this work examined the formation of aluminosilicate deposits in copper and lead pipes using water from Denver, Colorado. It was anticipated was that these deposits could form barrier films on the pipe, protecting it from corrosion. However, the deposits had slightly detrimental effects on leaching of metal to water, and higher levels of aluminosilicates could further worsen corrosion by-product release. The second phase of work attempted to extend understanding of aluminum solubility controls by accounting for effects of sulfate and formation of solids other than Al(OH)₃ during water treatment. Sulfate was found to destabilize small Al(OH)₃ colloids resulting in agglomeration into larger flocs from pH 5.0-6.2 . At pH 9.0 and above, Al-Mg, Al-Mg-Si and Al-Si solids were discovered to control Al solubility, while also having significant impacts on the precipitation of calcite in the presence of silica and overall softening effectiveness. This could be of considerable importance to water treatment practice. These solids also had some potential for removal of arsenic, TOC and boron. / Master of Science

The economic impact of metallic corrosion on global infrastructure, spanning pipeline networks, bridges, refineries, and automobiles, is considerable. In 2013, it accounted for 3.4% of the global GDP, totaling US$ 2.5 trillion. Organic coatings have gained significance as a prominent strategy to address this widespread issue. Polyaniline (PANI), a conducting polymer, has long been recognized as an effective anti-corrosion coating. This study explores the potential of polyaniline analogs and their nanocomposites as candidates for protective organic coatings in corrosion control applications. Initially, the investigation focuses on conducting polymers with side chains comprising long, branched alkyl groups as potential corrosion suppression coatings. These polymers, containing carbazole, phenothiazine, and phenoxazine cores, serve as analogs to polyaniline. Prepared through the Buchwald/Hartwig coupling reaction, these polymers demonstrated promising corrosion suppression capabilities, as tested by potentiodynamic polarization studies and electrochemical impedance spectroscopy (EIS). Morphological characterization using scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that phenothiazine- and carbazole-containing polymers exhibit excellent corrosion resistance, with phenothiazine displaying a protection efficiency (PE) of 95.9% and 89.0% respectively, outperforming polyaniline coating. Further exploration involved the derivatives of phenothiazine-based PANI analogs, specifically poly(heterocyclic diphenylamine) (poly-HDA), prepared through the Buchwald/Hartwig coupling reaction. Evaluation through weight loss, potentiodynamic polarization, and EIS in a 3.5 wt.% NaCl solution showcased the reduced corrosion current density on surfaces coated with long-branched alkyl-substituted phenothiazine-based PANI analogs. Moreover, the reinforcement of the phenothiazine-based PANI analog polymer was achieved by creating an epoxy-based nanocomposite with 2,5-dimethyl-1,4-phenylenediamine functionalized graphene oxide (PT/DPPD-fGO) at varying concentrations into an epoxy anticorrosive coating for AISI 4130 steel from corrosion. Results from immersion in 5 % sodium chloride solution, coupled with standard electrochemical measurements, demonstrate that PT/DPPD-fGO effectively protects AISI 4130 steel from corrosion, with coatings containing 5 % PT/DPPD-fGO exhibiting the best corrosion performance among the tested specimens. The results indicate the potential of phenothiazine- and carbazole-based PANI analogs, along with their nanocomposites, as candidates for protective organic coatings in transportation, aviation, marine, and oil and gas industrial applications.

L’utilisation de ressources locales est une des facettes importantes du développement durable pour le secteur de la construction. Plusieurs types de sous-produits sont aujourd’hui à l’étude pour une utilisation dans les bétons en tant qu’addition cimentaire alternative, dans le but de développer des liants basés sur des ressources alternatives. La présente étude cherche à évaluer les performances de quatre types de sous-produits sur les propriétés des bétons armés vis-à-vis de la corrosion. La poudre de verre, les cendres volantes de papeterie, les cendres de boues d’épuration ou les sédiments calcinés présentent une nature minérale compatible avec un milieu cimentaire. Face à la problématique de corrosion des armatures, le béton constitue à la fois un milieu alcalin favorisant la passivité des aciers et une barrière de transport qui limite la pénétration de contaminants au sein de la matrice cimentaire (principalement les chlorures et le dioxyde de carbone). Les additions cimentaires doivent donc permettre aux aciers de développer un état passif et apporter à l’enrobage une densification afin de limiter la pénétration de contaminants jusqu’aux armatures. Les propriétés électrochimiques d’un acier au contact des additions ont été caractérisées et les propriétés de transfert des bétons face aux chlorures et au dioxyde de carbone ont été étudiées. L’utilisation de ces matériaux n’influe pas particulièrement sur le comportement des aciers. Toutefois, l’enrobage est d’une importance particulière, à la fois vis-à-vis de la pénétration des ions chlorure et du dioxyde de carbone, mais aussi sur la cinétique de corrosion des armatures. La réactivité des additions impacte les propriétés de transfert qui contrôlent aussi bien la cinétique de contamination des bétons que le processus de corrosion d’armatures dépassivées.

Cast iron and steel alloys are commonly used for tooling and structural components in Al production, Al die-casting and the aluminizing industry due to their favourable properties including high strength, good formability and low cost. However, the iquid Al corrosion of these materials is one of the crucial concerns in maintaining the efficient production. Al is produced by the electrolytic smelting of alumina. Cast iron and/or cast steel pipes - commonly known as „tapping pipes‟ - are used to extract the liquid Al produced by smelting. Tapping pipes mainly degrade by material loss because liquid Al reacts with nearly all metals. Failure of tapping pipes is a significant contributor to the maintenance expenses; therefore, the primary aim of this research is to develop a material to enhance the life time of tapping pipes. Various test methods were developed in order to examine the effect of molten Al environment on cast iron and steel alloys. The corrosion resistance of these alloys was determined under different conditions of Al flow and temperature. The intermetallic compounds formed by exposing the ferrous to liquid Al were characterized using the Energy Dispersive X-ray Spectroscopy (EDS) and Electron Back Scatter Diffraction (EBSD) techniques. The formation, growth and nature of reaction products were revealed to establish a link to the liquid Al corrosion resistance. A relationship between the chemical composition and liquid Al corrosion resistance of cast irons could not established in the past. In the present work, the corrosion rate was found to depend upon the graphite morphology and fraction of each Fe-C phase of cast iron matrix, which can be controlled by selecting the chemical composition. Moreover, present research suggested the guidelines for producing a cast iron with enhanced liquid Al corrosion resistance. The presence of C-rich phases, graphite flakes and cementite was found to be effective in enhancing the liquid Al corrosion resistance of gray cast irons. Conversely, a higher Si content was found to enhance the susceptibility of cast irons to liquid Al corrosion. The corrosion mechanisms for ferrous alloys in liquid Al are not fully understood. Thus the subsequent analysis of the dissolution data was supported by investigating the reaction products formed between Al and substrate materials. In addition to commonly existent ε-Fe2Al5 and ζ-FeAl3 phases, the formation of Al4C3 and κ-Fe3AlC compounds was confirmed for the first time in the intermetallic layers of ferrous alloys. The Fe3Si phase in the intermetallic layers of high Si cast irons was found, which was believed to facilitate the high corrosion rates of high Si cast irons. Moreover, the mechanism by which C in Fe-substrates affects the liquid Al corrosion resistance can be better understood given the present work. Furthermore, the analysis presented here gives an understanding of the nature, growth and dissolution of intermetallic compounds in several cast iron alloys. Higher Si additions to cast irons played an important role in molten metal corrosion by accelerating the material loss and changing the nature of intermetallic layers. The results of this study clearly indicated that the dissolution and the growth of intermetallic compounds are interrelated and the dissolution and/or spallation of the intermetallic layers may be the primary mode of liquid Al corrosion of ferrous alloys.