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Phosphates are used by drinking water utilities to 1) reduce iron/manganese aesthetic problems by sequestration, 2) inhibit calcium carbonate scale formation via threshold inhibition, and 3) reduce corrosion of pipes by forming protective pipe scales. Orthophosphates can control lead, copper and iron corrosion through the formation of durable, low solubility scale, but are widely believed ineffective for sequestration or anti-scaling. Conversely, polyphosphates are effective sequestrants and anti-scalants, but can increase corrosion of plumbing materials. Here, we first critically reviewed the current state of the science, operational guidance, and knowledge gaps related to use of orthophosphate and polyphosphates for all three objectives. Three major gaps in understanding were identified and then addressed in subsequent chapters: 1) use of phosphates to achieve both sequestration and anti-scaling 2) mechanisms of iron sequestration, and 3) stabilization of magnesium silicate scale linings in a distribution system. In the critical review, we holistically conceptualize phosphate use as a three-dimensional (3-D) challenge of optimizing sequestration, anti-scaling and corrosion control. Despite nearly a century of widespread use, there is a poor scientific and practical understanding of how to use phosphates to achieve each of these key objectives, much less achieve synergies and avoid antagonistic effects. Many water systems are reliant on trial-and-error methods, or guidance from vendors of these proprietary chemicals, creating potential inefficiencies or even adverse unintended consequences. Effective sequestration of iron and manganese, to prevent formation of visible discoloration, can occur through four possible mechanisms which are undoubtedly dependent on the water chemistry (e.g., pH, hardness, redox). Anti-scaling of calcium carbonate occurs through threshold inhibition and crystal distortion, but sometimes phosphates can encourage scaling due to the precipitation of calcium phosphate. Corrosion control via orthophosphate is often effective, but polyphosphates can sometimes increase lead or copper levels in drinking water. Despite their widespread use in scientific studies, it was discovered that standardized measurements of color and turbidity do not fully account for the range of subjective consumer observations regarding cloudy or discolored water. At a constant apparent color of 110 Pt-Co, testing illustrated that relatively non-offensive air bubbles had a high turbidity of 74 NTU compared to just 0.1 NTU for offensively orange fulvic acid. Additionally, factors such as background color, type of light source, and direction of light significantly influenced perception of discolored water. For instance, under typical laboratory lighting conditions (light from above) with a white background, colors caused by iron, manganese, and fulvic acid were very prominent, whereas white calcium carbonate and magnesium silicate particles were more challenging to see. But white particles became much more prominent when the light source was from below or there was a darker background. A study of Fe sequestration was conducted to elucidate a mechanistic basis for the empirical trends revealed in the utility field study. As revealed in the literature review, polyphosphates could sequester Fe by inhibiting any step of the reaction sequence Fe2+ oxidation  precipitation of Fe(OH)3  particle agglomeration to visible sizes. Phosphates generally inhibited Fe2+ oxidation above about pH 7-8, dependent on chain length, and catalyzed oxidation at lower pHs. But in oxygenated waters above about pH 7, the dominant mechanism of sequestration was some combination of Fe3+ complexation and colloid stabilization at small particle sizes that were practically invisible. Increasing the phosphate chain length, phosphate concentration, and Si concentration caused more effective Fe sequestration, whereas Ca, Mg, and increased pH hindered its effectiveness. It was also discovered that orthophosphate can be an effective sequestrant under ideal conditions, polyphosphate can sequester more than 1 mg/L Fe despite some claims to the contrary, and Ca at very high doses can precipitate polyphosphates. During this dissertation work, a novel, thick (~1 mm), glassy magnesium silicate (MgSi) scale was discovered covering much of the pipe surfaces in a large water distribution system. This MgSi lining was hypothesized to be an extremely effective means of corrosion control that was important to maintain in its present state, as dissolution could cause it to detach from pipes, whereas further precipitation could clog them. To better understand how to maintain the scale, factors affecting the formation and dissolution of the MgSi solid were examined. Phosphate corrosion inhibitors had little effect on MgSi solubility at pH 8.5 and 10, while hexametaphosphate (HMP) and zinc orthophosphate slightly reduced Mg and Si dissolution rates at pH 7. Zinc orthophosphate reduced Mg dissolution by 50% and completely inhibited Si dissolution from the solid, while HMP decreased dissolution of Mg by 32% and Si by 63%. The magnesium silicate did not precipitate below pH 10 without the presence of a pre-existing seed solid. With a pre-existing seed scale, however, the MgSi further precipitated at a pH 8.5-9 in one source water and 7.5-8 in another. Below these pH levels, scale dissolution was shown to occur. Strategies were evaluated to help identify the equilibration pH for operation of a system with varying concentrations of silica, magnesium and pH. The two-dimensional (2-D) interplay of polyphosphate use for sequestration and anti-scaling was investigated for nine small utilities who rely on groundwater in North Carolina. Bench-top testing methods were developed to determine the 'optimal phosphate doses,' defined here as the lowest level of polyphosphate that maintains visually clear water and acceptable levels of scale formation. One proprietary polyphosphate chemical had an optimal sequestrant dose that depends on the concentration of Fe, Mn, Ca, and Mg. The dose (in mg/L as P) is equal to 58.5[Fe] + 59.7[Mn] + 0.041[Ca + Mg] + 0.4669 (units mM). Interestingly, color was well correlated with particulate (> 0.45 μm) Mn (R2 = 0.79) while turbidity was mostly correlated with particulate iron (R2 = 0.60). Furthermore, neither color nor turbidity measurements were reliable predictors of discoloration detected by eye. In the three utilities with higher hardness (> 100 mg/L as CaCO3), at least 3.6X more phosphate was needed for Fe and Mn sequestration than scale inhibition. But lab testing in very hard water with 300 mg/L as CaCO3 demonstrated that achieving anti-scaling, will sometimes require more polyphosphate than that needed for control of sequestration. Overall, this dissertation advances understanding of phosphate use in relation to important problems arising in water distribution or buildings. The innovative practical testing methods, improved practical understanding, and mechanistic insights can be applied to maximized the benefits of phosphates use while avoiding detriments. This is an important first step towards developing a rational holistic framework to guide utility decision-making regarding phosphate use. / Doctor of Philosophy / Phosphates are safe chemicals dosed to drinking water for a variety of objectives. Phosphates can prevent black water caused by manganese, red water caused by iron, clogging of pipes by precipitation of CaCO3, and to control corrosion of lead, copper and iron pipes. The simplest and least expensive phosphate is orthophosphate. Several orthophosphate molecules can be joined together to form a chain of 2 phosphates (pyrophosphate), a chain of 3 phosphates (tripolyphosphates), and chains up to 100s of phosphates in length. Some utilities only use orthophosphate to control pipe corrosion, and orthophosphate is not believed to be very effective for sequestration or anti-scaling. Conversely, polyphosphates can reduce red and black water from iron/manganese discoloration, and also inhibit the formation of calcium carbonate scale, but they sometimes increase corrosion of plumbing materials. Here, we review the current state of the science, operational guidance, and knowledge gaps related to use of ortho- and poly-phosphates. Three major gaps in understanding were identified and then addressed in subsequent chapters: 1) use of phosphates to achieve sequestration and anti-scaling simultaneously, 2) improve our understanding of how phosphates stop iron and red water (i.e., sequestration), and 3) stabilization of magnesium silicate scale linings in a distribution system. In a critical review, the use of phosphate for sequestration, anti-scaling and corrosion control was comprehensively examined. Despite nearly a century of widespread use, there is little understanding of how to properly use phosphates to achieve each objective. For dosing, many water systems rely on trial-and-error methods or guidance from chemical vendors, which could lead to mistakes that cause harmful unintended consequences. This could include elevated lead and copper release at the consumer's tap, increased consumer complaints caused by aesthetically displeasing water, increased head loss in pipes, and staining of dishes and appliances. Despite their widespread use in scientific literature, traditional measurements of color and turbidity are not always perfect measures of what is seen by eye. Additionally, factors such as background color, type of light source, and direction of light significantly influence the visual properties of water. For instance, under typical laboratory lighting conditions (light from above) with a white background, colors caused by iron, manganese, and fulvic acid were most noticeable, whereas white calcium carbonate and magnesium silicate particles were more challenging to see. In contrast, all particles became more observable when the light source was positioned below. A study of iron sequestration was conducted to investigate the ability of different phosphates to reduce the formation of red-colored water. As revealed in the literature review, polyphosphates could sequester iron in 3 different ways, but experiments revealed only two would be important in waters with higher pH and oxygen. Increasing the phosphate chain length, phosphate concentration, and silica concentration caused less visual discoloration, whereas calcium, magnesium, and increased pH had the opposite effect. It was also discovered that, at very high doses of calcium, a calcium-polyphosphate solid can precipitate. During this work, we also discovered a magnesium silicate (MgSi) scale covering much of the pipe surfaces in a large water distribution system. This MgSi lining is believed to protect underlying pipe materials from corrosion. To maintain the benefits of this protective scale, factors influencing its formation or dissolution were tested. The MgSi precipitated above pH 8.5-9 in one source water and 7.5-8 in another if a seed of the scale was present. Below this pH, the scale dissolved. The dosing of some phosphates slightly reduced the amount of scale which dissolved at a lower pH, but had no influence over the formation of more scale at higher pHs. Strategies were then evaluated to help the utility identify a good pH to operate the system, and to maintain the MgSi scale. The use of polyphosphate for sequestration and anti-scaling was investigated for nine small groundwater utilities in North Carolina. Laboratory experiments were conducted to determine the lowest level of polyphosphate that maintains visually clear water and acceptable levels of scale formation. This 'optimal polyphosphate dose' could be predicted by the iron, manganese, magnesium, and calcium concentrations of the water, at least for the utilities tested. Even in the three utilities with highest hardness in the study, more phosphate was needed for sequestration than inhibiting the formation of calcium carbonate scale. But lab testing in another very hard water with 300 mg/L as CaCO3, did demonstrate anti-scaling will sometimes require more polyphosphate than that required for sequestration. Overall, this dissertation advances understanding of phosphate use and abuse in relation to important problems arising in water distribution or buildings. The testing methods and improved practical understanding will help maximize the benefits of phosphates while avoiding detriments. This is an important first step towards developing a framework to guide utility decision-making regarding phosphate use for the benefit of consumers.

The replacement of chromate conversion coatings for zinc coated components has been necessitated by the materials finishing industries due to the inherent toxicity issues with Cr(VI) and the legislative enforcement of WEEE and ELV Directives by the European Union. Current replacements are based on non-chromate , Cr(III) systems, these may be perceived by some to be problematic as they still contain chromium . Molybdate based conversion coatings have long been viewed by many researchers to be a viable non-chromium alternative due to their low toxicity. An extensive literature review of the research carried out in the last 20 years was carried out, highlighting areas of interest for improving the corrosion resistance of the coatings studied. These were, primarily, the synergesis that exists with molybdate and phosphate compounds for corrosion resistance and the incorporation of nanoparticle silica into treatment solution. Also discovered was the importance of the acid used to adjust treatment solution pH, immersion time, oxidising agent additions and the incorporation of rare earth metal species. Silicate sealant layers were also highlighted as a post treatment. Molybdate-based coatings were formed on commercial electrodeposited acid zinc surfaces. Many treatment conditions were investigated, and initially performance analysed using DC Linear Polarisation Resistance (LPR) trials. Subsequently, the highest performing coatings were subjected to the more aggressive, industry standard, ASTM B 117 Neutral Salt Spray (NSS) corrosion test. The highest performing molybdate coatings were found to have an average LPR of ~ 9 000 Ω. cm2, in contrast to ~ 12 000 Ω. cm2 for the Cr(VI) based reference. NSS results were amongst the highest performing for molybdate based coatings documented, at 24 h until 5% white rust, however remained inferior to Cr(VI) coatings, which lasted 120 h. The highest performing coatings were characterised using FEG-SEM, Cryofracture EDXA and site specific AES. These techniques revealed that the enhanced molybdate coatings had a columnar structure that was around 300 nm thick, with pores that appeared to expose the substrate. AES showed this type of coating to have a mixed Mo, P and Zn oxide surface. Corrosion initiation was also studied; this can be thought of as an investigation to determine the point(s) of weakness or the mechanism that causes coating failure. Coatings were immersed in 5 % wt/ vol NaCl(aq) until they showed any surface change. Initial signs of corrosion were deemed to be any appearance of pitting or discolouration of the film, not a voluminous corrosion product. Untreated Zn, Cr(VI) and simple molybdate coatings were studied as well as enhanced molybdate coatings. There were clear differences in the way the coatings behaved at the onset of corrosion. Cr(VI) coatings delaminated, leaving an area of decreased Cr concentration. The enhanced molybdate coatings failed by the appearance of localised pores of ~ 70 µm in diameter. Substrate exposure was indisputably the reason for coating failure in chloride environments. In light of the work carried out in the present thesis the outlook for the use of molybdate as a potential replacement for chromate for the conversion coating of electrodeposited zinc surfaces is a positive one.

M. Tech. Engineering Metallurgy. / Aims to improve the mechanical and chemical properties of mild steel, by developing highly corrosion resistant surface coatings of zinc-aluminum using the electro-deposition techniques. Properties that are targeted are specifically hardness, wear and corrosion resistances.

No description available.

The research reported herein describes the study activities performed by University of Central Florida (UCF) on behalf of the Town of Jupiter Water Utilities (Town). The Town recently changed its water treatment operations from a combination of reverse osmosis (RO), lime softening (LS) and anion-exchange (IX) to a combination of RO, IX and nanofiltration (NF). Although this treatment change provided enhanced water to the surrounding community in terms of better contaminant removal and reduced DBP formation potential, integration of the NF process altered finished water quality parameters including pH, alkalinity and hardness. There was concern that these changes could result in secondary impacts related to accelerated corrosion of distribution system components and subsequent regulatory compliance. In addition, replacement of the LS process altered the in-plant blending operations by creating an unstable intermediate blend composed of RO and IX waters. There were concerns that this intermediate blend was affecting the integrity of in-plant hydraulic conveyance components. UCF developed a corrosion monitoring study to assess the potential impacts related to internal corrosion, water quality and regulatory compliance after integrating NF into the existing water supply. The intended purpose was to further highlight the complexities of corrosion, describe a unique approach to corrosion monitoring as well as offer various recommendations for corrosion control in a system that relies on a blended water supply. Research was conducted in three phases to address the in-plant and distribution system corrosion issues separately and identify appropriate corrosion control treatment alternatives. The three test phases included: a baseline conditions assessment to iv compare corrosion of the intermediate RO-IX blend with the finished water blend (ROIX-NF); an in-plant corrosion control evaluation; and a distribution system corrosion control evaluation. A test apparatus was constructed and operated at the Town’s facilities to monitor corrosion activity of mild steel, copper and lead solder metal components. The test apparatus consisted of looped PVC pipe segments housed with electrochemical probes and metal coupons to monitor corrosion rates of the metallic components. Electrochemical probes containing metal electrodes were used to obtain instantaneous corrosion rates by means of the Linear Polarization Resistance (LPR) technique while the metal coupons were gravimetrically evaluated for weight loss. The electrochemical probes permitted daily monitoring of each metal’s corrosion rates while metal coupons were analyzed at the conclusion of testing and used for comparison. Different test waters flowed through the corrosion rack according to each test phase and relative corrosion rates were compared to evaluate corrosion control techniques. Study findings indicated that the intermediate blend was more corrosive, in general, then the final blend; however, research also indicated that the final blend of water was increasing lead and copper concentrations within the distribution system. An orthophosphate corrosion inhibitor was evaluated for in-plant corrosion control. The inhibitor’s performance was assessed by comparing mild steel corrosion rates with and without the chemical. In addition, secondary impacts related to introduction of the chemical were evaluated by pre-corroding the metallic components prior to the introduction of the inhibitor. Results indicated that the inhibitor marginally decreased corrosion rates and increased the turbidity of the water supply. Based on these v observations, it was concluded that the inhibitor was not a viable solution for in-plant corrosion control. To resolve in-plant corrosion issues, recommendations were made for modification of in-plant blending operations to eliminate the corrosive intermediate blend from the process allowing the RO, IX and NF treated waters to be blended in a common location. The effectiveness of a poly/ortho blended phosphate chemical inhibitor was evaluated for reducing lead and copper corrosion to resolve distribution corrosion issues. A 50/50 poly/ortho blend was selected because of its analogous use in similar municipal water facilities. Metallic corrosion rates, particularly lead and copper, were compared with and without the inhibitor to assess the performance of the chemical. Like the previous test phase, the metallic components were pre-corroded prior to the chemical’s introduction to determine if secondary impacts could result from its presence. Results indicated that lead and copper corrosion rates were lower in the presence of the inhibitor, and secondary impacts related to increased turbidity were not observed for this chemical. Based on these results, it was recommended that a poly/ortho blended phosphate be used to decrease lead and copper corrosion within the Town’s distribution system.

No description available.

This dissertation consists of four papers concerning impacts of zinc orthophosphate (ZOP) inhibitor on iron, copper and lead release in a changing water quality environment. The mechanism of zinc orthophosphate corrosion inhibition in drinking water municipal and home distribution systems and the role of zinc were investigated. Fourteen pilot distribution systems (PDSs) which were identical and consisted of increments of PVC, lined cast iron, unlined cast iron and galvanized steel pipes were used in this study. Changing quarterly blends of finished ground, surface and desalinated waters were fed into the pilot distribution systems over a one year period. Zinc orthophosphate inhibitor at three different doses was applied to three PDSs. Water quality and iron, copper and lead scale formation was monitored for the one year study duration. The first article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on surface characteristics of iron corrosion products in a changing water quality environment. Surface compositions of iron surface scales for iron and galvanized steel coupons incubated in different blended waters in the presence of ZOP inhibitor were investigated using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) / Energy Dispersive X-ray Spectroscopy (EDS). Based on surface characterization, predictive equilibrium models were developed to describe the controlling solid phase and mechanism of ZOP inhibition and the role of zinc for iron release. The second article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total iron release in a changing water quality environment. Development of empirical models as a function of water quality and ZOP inhibitor dose for total iron release and mass balances analysis for total zinc and total phosphorus data provided insight into the mechanism of ZOP corrosion inhibition regarding iron release in drinking water distribution systems. The third article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total copper release in a changing water quality environment. Empirical model development was undertaken for prediction of total copper release as a function of water quality and inhibitor dose. Thermodynamic models for dissolved copper based on surface characterization of scale that were generated on copper coupons exposed to ZOP inhibitor were also developed. Surface composition was determined by X-ray Photoelectron Spectroscopy (XPS). The fourth article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total lead release in a changing water quality environment. Surface characterization of lead scale on coupons exposed to ZOP inhibitor by X-ray Photoelectron Spectroscopy (XPS) was utilized to identify scale composition. Development of thermodynamic model for lead release based on surface analysis results provided insight into the mechanism of ZOP inhibition and the role of zinc.

The effects of corrosion inhibitors on water quality and the distribution system were studied. This dissertation investigates the effect of inhibitors on iron surface roughness, copper surface roughness, and copper release. Corrosion inhibitors included blended poly/ortho phosphate, sodium orthophosphate, zinc orthophosphate, and sodium silicate. These inhibitors were added to a blend of surface water, groundwater, and desalinated brackish water. Surface roughness of galvanized iron, unlined cast iron, lined cast iron, and polyvinyl chloride was measured using pipe coupons exposed for three months. Roughness of each pipe coupon was measured with an optical surface profiler before and after exposure to inhibitors. For most materials, inhibitor did not have a significant effect on surface roughness; instead, the most significant factor determining the final surface roughness was the initial surface roughness. Coupons with low initial surface roughness tended to have an increase in surface roughness during exposure, and vice versa, implying that surface roughness tended to regress towards an average or equilibrium value. For unlined cast iron, increased alkalinity and increased temperature tended to correspond with increases in surface roughness. Unlined cast iron coupons receiving phosphate inhibitors were more likely to have a significant change in surface roughness, suggesting that phosphate inhibitors affect stability of iron pipe scales. Similar roughness data collected with new copper coupons showed that elevated orthophosphate, alkalinity, and temperature were all factors associated with increased copper surface roughness. The greatest increases in surface roughness were observed with copper coupons receiving phosphate inhibitors. Smaller increases were observed with copper coupons receiving silicate inhibitor or no inhibitor. With phosphate inhibitors, elevated temperature and alkalinity were associated with larger increases in surface roughness and blue-green copper (II) scales.. Otherwise a compact, dull red copper (I) scale was observed. These data suggest that phosphate inhibitor addition corresponds with changes in surface morphology, and surface composition, including the oxidation state of copper solids. The effects of corrosion inhibitors on copper surface chemistry and cuprosolvency were investigated. Most copper scales had X-ray photoelectron spectroscopy binding energies consistent with a mixture of Cu2O, CuO, Cu(OH)2, and other copper (II) salts. Orthophosphate and silica were detected on copper surfaces exposed to each inhibitor. All phosphate and silicate inhibitors reduced copper release relative to the no inhibitor treatments, keeping total copper below the 1.3 mg/L MCLG for all water quality blends. All three kinds of phosphate inhibitors, when added at 1 mg/L as P, corresponded with a 60% reduction in copper release relative to the no inhibitor control. On average, this percent reduction was consistent across varying water quality conditions in all four phases. Similarly when silicate inhibitor was added at 6 mg/L as SiO2, this corresponded with a 25-40% reduction in copper release relative to the no inhibitor control. Hence, on average, for the given inhibitors and doses, phosphate inhibitors provided more predictable control of copper release across changing water quality conditions. A plot of cupric ion concentration versus orthophosphate concentration showed a decrease in copper release consistent with mechanistic control by either cupric phosphate solubility or a diffusion limiting phosphate film. Thermodynamic models were developed to identify feasible controlling solids. For the no inhibitor treatment, Cu(OH)2 provided the closest prediction of copper release. With phosphate inhibitors both Cu(OH)2 and Cu(PO4)·2H2O models provided plausible predictions. Similarly, with silicate inhibitor, the Cu(OH)2 and CuSiO3·H2O models provided plausible predictions.

Magnesium alloys have been widely explored as potential biomaterials, but several limitations to using these materials have prevented their widespread use, such as uncontrollable degradation kinetics which alter their mechanical properties. In an attempt to further the applicability of magnesium and its alloys for biomedical purposes, two novel magnesium alloys Mg-Zn-Cu and Mg-Zn-Se were developed with the expectation of improving upon the unfavorable qualities shown by similar magnesium based materials that have previously been explored. The overall performance of these novel magnesium alloys has been assessesed in three distinct phases of research: 1) analysing the mechanical properties of the as-cast magnesium alloys, 2) evaluating the biocompatibility of the as-cast magnesium alloys through the use of in-vitro cellular studies, and 3) profiling the degradation kinetics of the as-cast magnesium alloys through the use of electrochemical potentiodynamic polarization techqnique as well as gravimetric weight-loss methods. As compared to currently available shape memory alloys and degradable as-cast alloys, these experimental alloys possess superior as-cast mechanical properties with elongation at failure values of 12% and 13% for the Mg-Zn-Se and Mg-Zn-Se alloys, respectively. This is substantially higher than other as-cast magnesium alloys that have elongation at failure values that range from 7-10%. Biocompatibility tests revealed that both the Mg-Zn-Se and Mg-Zn-Cu alloys exhibit low cytotoxicity levels which are suitable for biomaterial applications. Gravimetric and electrochemical testing was indicative of the weight loss and initial corrosion behavior of the alloys once immersed within a simulated body fluid. The development of these novel as-cast magnesium alloys provide an advancement to the field of degradable metallic materials, while experimental results indicate their potential as cost-effective medical devices.