Historically, the presence of microalgae (algae hereafter) in natural waters has been viewed as a nuisance due to its adverse impact on water quality. More recently, however, algae are being investigated as potential sources of biofuel and a range of natural products. These applications require the development of large-scale cultivation systems for mass production that include growth, harvesting, concentration, and product recovery components. While challenges still remain with respect to many of the processes involved in mass production, one of the most technically and economically challenging steps is harvesting the algae from dilute growth cultures, especially in systems where chemical additives are of concern either within the algae concentrate or the effluent water. For this reason, a pH-induced flocculation/deflocculation method using the hydroxides of alkali or alkaline earth metals (e.g., lime, caustic soda) is of particular interest for algae harvesting as Na, Ca and Mg are typically present in natural waters. The goal of this research was to determine the underlying mechanisms responsible for algae coagulation by magnesium and calcium and to evaluate the potential of these mechanisms for harvesting algae for a range of synthetic and field source water chemistries. In the first two phases of this research, the mechanisms for coagulation with magnesium and calcium were studied independently. A series of bench-scale experiments were designed to isolate the potential mechanisms of algae destabilization associated with each of these cations as a function of water chemistry, and microscopic analyses were performed to characterize the flocculated algae/precipitate mixtures. In the third phase of this research, removal of algae in field source waters was evaluated with respect to the underlying science elucidated in the previous phases. The results indicate that the dominant algae destabilization mechanism associated with magnesium shifts from Mg adsorption/charge neutralization to Mg(OH)2(S) precipitation-enhanced coagulation with increasing pH. Moreover, dissolved Mg2+ adsorption to the algae surface led to effective algae coagulation, while minimizing the mass of precipitated Mg(OH)2(S). For Ca, this research identified the importance of the nucleation process (heterogeneous vs. homogeneous nucleation) on algae removal efficiency. Heterogeneous nucleation is a key factor for optimizing algae removal; thus, the degree of oversaturation with respect to CaCO3(S) is a crucial operating parameter. This research demonstrated that the algae harvesting process using pH-induced flocculation/deflocculation method can be optimized for a wide range of source waters if the water chemistry (e.g. pH, ion concentration, alkalinity, ionic strength) is properly incorporated into the system design. / text

<p>Water hardness indicates the concentration of calcium and magnesium ions in water. Water with high concentrations of these ions is described as hard water and water with low concentrations is described as soft water. Water that is too hard or too soft can lead to technical and economical problems. In collaboration with Midvatten AB, groundwater hardness in the Badelunda esker between Leksand and Avesta has been mapped, and an attempt has been made to explain the variations. For this purpose, different GIS programs, such as ArcView, ArcInfo, IDIRISI, and one geochemical modelling program, PHREEQC, has been used. GIS programs were used for digitising geological and hydrological maps and then for combining them with other kinds of data. Simulations of chemical equilibria have been accomplished using PHREEQC.</p><p>The absolutely most important factor that affects groundwater hardness is dissolution of carbonate minerals. The dissolution is controlled by access to these minerals and pH value of groundwater. Soil samples taken along Badelunda esker indicated the presence of carbonate minerals, and showed significant variation in carbonate content. PHREEQC simulations have indicated that samples from most of wells were saturated with calcite, it means there is no lack of carbonates. The simulations indicated even the importance of carbon dioxide pressure for pH and hardness in groundwater. Because this pressure is much higher under the ground than in the atmosphere the pH value will change as soon the water comes in contact with atmospheric air. Measurements of pH in field are quite complicated and are not usually performed in the field. In this work, pH values were obtained from laboratory analyses, and no measurements were made in the field.</p><p>Also road salt effects hardness. From several wells located closely to way 70 were received data showing rising chloride contents and hardness during last 30-40 years. The direct effect of road salt on hardness (exchange of Ca2+ by Na+) was investigated using simulation in PHREEQC. Results of simulations showed that effect of road salt on groundwater hardness are of secondary significance.</p><p>In some cases, extreme values in groundwater hardness could be explained by infiltration of surface water or by the occurrence of relict seawater.</p> / <p>Hårdhetsgrad anger koncentration av kalcium- och magnesiumjoner i vatten. Vatten med höga koncentrationer av dessa joner betecknas som hårt och vice versa. Både för hårt och för mjukt vatten innebär tekniska och ekonomiska problem. På uppdrag av Midvatten AB har ett försök att kartlägga och förklara variationen i grundvattnets hårdhet i Badelundaåsen mellan Leksand och Avesta genomförts. I arbetet användes olika GIS-program, såsom ArcView, ArcInfo, IDRISI, och ett geokemiskt modelleringsprogram, PHREEQC. GIS-programmen användes för digitalisering av geologiska och hydrologiska kartor och sammanställning av dessa kartor med andra typer av data. I PHREEQC genomfördes simuleringar av kemiska jämvikter.</p><p>Den absolut viktigaste faktorn som påverkar grundvattnets hårdhet är upplösning av kalkrika mineral. Upplösningen styrs av tillgången på kalkrika mineral och vattnets pH-värde. Jordprover som upptogs längs Badelundaåsen visar på att det finns kalkrika mineral i marken och att karbonathalten i materialet varierar betydligt. Jämviktssimuleringar med PHREEQC visade dock att prover från de flesta brunnar var mättade med avseende på kalcit. Det innebär att tillgången på karbonat inte är den begränsande faktorn. Dessa simuleringar visade dessutom att koldioxidtrycket är en viktig faktor som påverkar pH-värde och hårdhet. Koldioxidtrycket i atmosfären är mycket lägre än det som råder under markytan och därför förändras den kemiska jämvikten i grundvattnet så fort det kommer i kontakt med atmosfärsluften. pH-mätningar i fält är tidskrävande och brukar inte utföras vid vanlig provtagning. I examensarbetet ingick inte några egna vattenprovtagningar. Analysresultat som användes i examensarbetet var framtagna på laboratorium, d.v.s. pH-mätningar utfördes inte i fält.</p><p>Salt som sprids ut på vägar under vintertid har också en hårdhetsökande effekt. Från flera vattentäkter som ligger i närheten av riksväg 70 (Rv70) erhölls tidsserier som visade på stigande trender i både kloridhalter och hårdhet. Den ökade trafikbelastningen på riksväg 70 har sannolikt en betydande påverkan på grundvattenkvalitet. Beräkningar och simuleringar utförda inom ramen för detta examensarbete visade att vägsaltets effekt på grundvattenhårdhet är av sekundär betydelse.</p><p>Inblandning av ytvatten respektive relikt vatten förklarade exceptionellt låga respektive höga hårdhetsvärden i vissa brunnar.</p>

Magnesium (Mg) and its alloys provide numerous unique benefits as potential resorptive biomaterials and present the very real possibility of replacing current metallic implant materials in a variety of roles. However, considerable research remains before Mg alloys may be accurately screened and used in vivo. Most critically, a more comprehensive understanding of the corrosion of Mg alloys in vitro is needed. This research program critically examined the types of in vitro experiments that may be performed on Mg alloys, investigated the numerous variables that affect Mg biodegradation when undertaking these experiments, explored the electrochemical performance of several biocompatible Mg alloys, and developed a novel process for producing ordered Mg structures. The benefits and drawbacks of a range of in vitro tests were first investigated. The key strengths and weaknesses of each test were identified and recommendations provided for their respective use in the quest to determine Mg alloy biodegradation. The most common variables applicable to all in vitro experiments were then explored in detail, and their effect on the biocorrosion of a number of Mg alloys was determined. Recommendations were then made for the appropriate control of the different experimental variables based on these findings. For the first time, the mechanistic control of Mg biodegradation by the microstructure of biocompatible alloys has been examined. This allows for greater understanding of the reasons for varied corrosion of alloys in bio-electrolytes, and is a step towards the effective design of Mg alloys for different bio-applications. A novel method to produce ordered Mg structures was developed, with relevant processing parameters investigated in light of their effect on biocorrosion and mechanical performance. Overall, the results and findings from this research further our understanding of the potential of Mg alloys as suitable biomaterials, and advance our knowledge of how to proceed towards the goal of using such alloys for biological applications.

Equilibrium properties of the MgO-Al₂O₃-SiO₂ (MAS) system are modeled using techniques from statistical and quantum mechanics. The fundamental structural units in this model are the closed shell ions: Mg²⁺, Al³⁺, Si⁴⁺, and O²⁻. The equilibrium properties of the MAS system are determined by the interactions among these ions and by the environment (i.e. temperature and pressure). The interactions are modeled using coulombic, dispersion, and repulsive forces. Two parameters appearing in the repulsive terms for each cation-oxygen interaction are fitted from properties of quartz, corundum, and periclase crystals. The effects of the environment on the liquid and solid compositions found in this system are calculated using a Monte Carlo technique involving the generation of a Markov chain of configurations; each configuration being a "snapshot" of the particles in the liquid or solid material being studied. The properties of the material are derived from averaging appropriate quantities over all the configurations. Enthalpies of formation, heat capacities, and volumes of seven compositions in the MAS system have been calculated using this method. All are within three percent of the corresponding experimental values. Radial distribution functions for these runs show the competition among the cations for the common anion, oxygen, under charge and mass balance constraints. The electronic structure of several molecular clusters in the MAS system are examined using ab initio linear combinations of atomic orbitals (LCAO) techniques. The assumptions used in LCAO calculations are examined and a small, balanced basis set for the MAS system is presented. The Mg-, Al-, and Si-O interactions are all found to be highly ionic using this basic set. Using a first principles technique, the two body effective pair potentials assumed for the Monte Carlo calculations were shown to be physically reasonable.

This research focuses on the spall properties of aluminum-magnesium (Al-Mg)alloys.Aluminum alloy 5083 (Al 5083) was used as a model alloy for the work performed in this study. Al-Mg alloys represent a light-weight and corrosion resistant alloy system often used in armor plating. It is desirable to process armor plate material to yield a microstructure that provides maximum resistance to spall failure due to blast and projectile impacts. The blast and impact resistance has often been quantified based on the measurement of the spall strength and the Hugoniot elastic limit (HEL). The spall properties of Al-Mg alloys were measured for four different microstructural states resultant from varying processing conditions. The four microstructures include: (a) textured grain structure from a rolled Al 5083-H116 plate, (b) sub-micron grain structure produced using equi-channel angular pressing (ECAP),(c) equiaxed grain structure, and (d) precipitation hardened microstucture from an Al-9wt.% Mg alloy. The overall results show that grain size is not the most dominant microstructural feature affecting spall strength in aluminum alloys, when the impact conditions are the same. Texture, especially if brittle inclusions align along the grains, appears to have the most dominant effect resulting in decreased spall strength. Furthermore, one-dimensional modeling shows that the inclusion size and distribution is the controlling factor for void formation during spalling. Grain size does affect the decompression rate dependence of each microstructure, whereby smaller grain sizes result in a larger power law exponent for fits of spall strength versus decompression rate. Unlike the spall strength, the HEL shows an increasing trend with decreased grain size, as would be expected from a Hall-Petch type effect, indicating that a smaller grain size is best for penetration resistance. Samples processed using ECAP alone provide the best combination of spall strength and HEL and therefore the most promise for improved blast and penetration resistance of aluminum-magnesium alloy armor plates.

Twin Screw Rheo Extrusion (TSRE) is a novel semisolid extrusion process developed at BCAST for producing simple profiles such as rods and wires of light alloys directly from melts with refined microstructures and improved mechanical properties. The process represents a shortened manufacturing route with great savings in investment, energy consumption and operation space. Research was carried out to investigate the feasibility of processing magnesium and aluminium alloys, to obtain the operations for the optimized microstructures and mechanical properties of the final product and to understand the mechanisms governing the evolution of microstructures. Experiments were conducted using an AZ91D magnesium alloy and several aluminium alloys on two specially made twin screw rheo extrusion machines and a range of conditions were tested. Results showed that the TSRE process was feasible for the AZ91D magnesium alloy and aluminium alloys, although modifications were required for processing aluminium alloys as the twin screw material used was found to react with aluminium. Analysis revealed that the extruded samples of both alloys had a uniform fine microstructure in both transversel and longitudinal directions and liquid segregation was limited, due to the application of intensive shearing during slurry making and extrusion. Low extrusion temperature was found to refine the structure and suppress the formation of the eutectic. The eutectic was easily dissolved upon heat treatment resulting in reasonable mechanical properties. Numerical analysis on thermal management was carried out and the results showed that a steady state thermal profile with a temperature gradient between the slurry feeding point and extrusion die could be established, promoting nucleation and preventing the formed solid particles from extensive growth during extrusion, which was confirmed by microstructural observations.

Joining two dissimilar metals, specifically Mg and Al alloys, using conventional welding techniques is extraordinarily challenging. Even when these alloys are able to be joined, the weld is littered with defects such as cracks, cavities, and wormholes. The focus of this project was to use friction stir welding to create a defect-free joint between Al 2139 and Mg WE43. The stir tool used in this project, made of H13 tool steel, is of fixed design. The design included an 11 mm scrolled and concave shoulder in addition to a 6 mm length pin comprised of two tapering, threaded re-entrant flutes that promoted and amplified material flow. Upon completion of this project an improved experimental setup process was created as well as successful welds between the two alloys. These successful joints, albeit containing defects, lead to the conclusion that the tool used in project was ill fit to join the Al and Mg alloy plates. This was primarily due to its conical shaped pin instead of the more traditional cylindrical shaped pins. As a result of this aggressive pin design, there was a lack of heat generation towards the bottom of the pin even at higher (800-1000 rpm) rotation speeds. This lack of heat generation prohibited the material from reaching plastic deformation thus preventing the needed material flow to form the defect free joint.

Eclampsia is a hypertensive disorder of pregnancy and a leading cause of maternal death. The primary explanation for eclampsia is that it represents a form of hypertensive encephalopathy (HTE) with neurological symptoms including headaches, nausea, vomiting, visual disturbances, and seizures. The etiology of HTE involves an acute increase in arterial blood pressure that exceeds the autoregulatory capacity of the brain leading to forced dilatation of cerebral vessels, decreased cerebrovascular resistance, hyperperfusion, blood-brain barrier (BBB) disruption, and vasogenic cerebral edema formation. Due to the central role of the cerebral circulation in mediating these symptoms, a better understanding of how pregnancy affects the cerebral circulation is important to the treatment and prevention of eclampsia. A central goal of this dissertation was to determine pregnancy’s effect on cerebral blood flow (CBF) autoregulation, edema formation, and BBB permeability during acute hypertension. Women with eclampsia often seize at lower blood pressures than HTE patients. We hypothesized that pregnancy may predispose the brain to eclampsia by lowering the pressure of autoregulatory breakthrough and enhancing cerebral edema formation. Using an in vivo model of HTE, we found that the pressure of autoregulatory breakthrough was not different between nonpregnant (NP) and late-pregnant (LP) rats; however, cerebral edema formation was significantly increased only in LP animals. Nitric oxide synthase inhibition significantly increased the upper limit of autoregulation in both NP and LP animals and attenuated cerebral edema formation in LP animals. BBB permeability during acute hypertension was not different between these groups. Magnesium sulfate (MgSO4) is widely used to treat eclampsia despite an unclear mechanism of action. A second goal of this dissertation was to determine the cerebrovascular effects of MgSO4 during pregnancy. Specifically, we investigated the effect of MgSO4 on in vitro resistance artery vasodilation and in vivo BBB permeability during acute hypertension. We hypothesized that dilation to MgSO4 would be greater in mesenteric than cerebral vessels. MgSO4 elicited concentration-dependent vasodilation in all arteries, as determined by measuring lumen diameter of isolated and pressurized arteries, however, mesenteric arteries were considerably more sensitive than cerebral arteries. In addition, there was no effect of pregnancy on MgSO4 sensitivity in mesenteric arteries, whereas pregnancy decreased sensitivity to MgSO4 in cerebral arteries. We further hypothesized that MgSO4 would decrease BBB disruption during acute hypertension, thereby protecting the brain in eclampsia. Using an in vivo model of HTE, we showed that MgSO4 treatment decreased BBB permeability during acute hypertension in LP rats, with the greatest effect observed in the posterior cerebrum. In conclusion, this dissertation determined CBF autoregulation and cerebral edema formation during pregnancy, and also the effect of MgSO4 on cerebral resistance artery vasodilation and BBB permeability during acute hypertension in LP rats. Although pregnancy did not influence autoregulatory breakthrough, cerebral edema formation was enhanced in LP animals and this may potentiate neurological symptoms in eclampsia. In addition, MgSO4-induced cerebral vasodilation is likely not a primary mechanism of eclampsia treatment, rather MgSO4 may limit edema formation by attenuating BBB permeability during hypertension.

L’utilisation des combustibles fossiles (énergies non renouvelables) est responsable de l’augmentation de la concentration en gaz à effet de serre dans l’atmosphère. Parmi les solutions de remplacement envisagées, l’hydrogène apparaît comme le vecteur énergétique le plus séduisant. Son stockage dans des intermétalliques permet d’obtenir des capacités massiques et volumiques (e.g. 140 g/L) supérieures à celles obtenues en voie liquide ou sous pression (respectivement 71 et 40 g/L). Nous avons élaboré des composés à base de Mg et de terres rares (e.g. Y, Ce et Gd) dérivant des phases de Laves cubiques AB2. Leurs propriétés physico-chimiques ont été étudiées (hydruration, électrochimie, magnétisme, …). Les conditions de sorption (P et T) se sont révélées particulièrement favorables (i.e. absorption à température ambiante et pression atmosphérique). Par ailleurs, afin d’améliorer la cinétique de sorption du magnésium métallique, les composés précédemment élaborés ont été utilisés comme catalyseurs. Ainsi, GdMgNi4 a été co-broyé avec du magnésium et les vitesses d’absorption et de désorption du composite sont supérieures à celles obtenues pour les composites Mg+Ni ou Mg+V qui sont des références. Une approche théorique (DFT) a permis de modéliser la structure électronique des composés ternaires (i.e. TRMgNi4) et ainsi de prédire ou de confirmer les résultats expérimentaux. Enfin nous avons étudié de nouveaux intermétalliques riches en terre rare (TR4MgNi) dont les capacités d’absorption en hydrogène sont élevées (2H/M). / The use of fossil fuels (non-renewable energy) is responsible for increasing the concentration of greenhouse gases in the atmosphere. Among the considered alternatives, hydrogen is seen as the most attractive energy vector. The storage in intermetallics makes it possible to obtain mass and volume capacities (e.g. 140 g/L) higher than those obtained by liquid form or under pressure (respectively 71 and 40 g/L). We have synthesised Mg and Rare Earth based compounds (RE = Y, Ce and Gd), derived from the cubic Laves phases AB2. Their physical and chemical properties have been studied (hydrogenation, electrochemistry, magnetism, ...). The conditions of sorption (P and T) are particularly favorable (i.e. absorption at room temperature and atmospheric pressure). Besides, to improve the sorption kinetics of metallic magnesium, the compounds developed previously were used as catalysts. Thus, GdMgNi4 was milled with magnesium and the speeds of absorption and desorption of the mixture are found higher than those obtained for the composites Mg+Ni or Mg+V, which are reference systems. A theoretical approach (DFT) was used to model the electronic structure of the ternary compounds (i.e. REMgNi4) and thus to predict or confirm the experimental results. Finally we have studied new intermetallics rich in rare earth (RE4MgNi) whose hydrogen absorption capacities are high (2H/M).

Philosophiae Doctor - PhD / Magnesium hydride has long been regarded as a promising candidate for lightweight hydrogen storage applications, owing to reasonably high theoretical capacity (7.6 wt. %). It is burdened by slow absorption/desorption kinetics which has been the target for improvement of many research groups over the years. Nanostructured MgH2 prepared by high energy reactive ball milling (HRBM) of Mg under hydrogen atmosphere with the addition of V or Ti results in modified MgH2 that demonstrates superior hydrogenation/dehydrogenation kinetics without a crippling compromise in storage capacity. Mg – FeV nanocomposites prepared via ball milling of Mg and FeV raw materials demonstrated up to 96.4% of the theoretical storage capacity and comparable kinetics to Mg - V prepared via the same method using pure refined V (which is far costlier than FeV). In both cases, the hydrogenation/dehydrogenation kinetics was much improved than pure Mg alone, as evidenced by faster hydrogenation times. In terms of cyclic stability, Mg – 10FeV demonstrated improvement over pure Mg with final absorption and desorption capacities of 4.93 ± 0.02 wt. % and 4.82 ± 0.02 wt. % respectively over 30 cycles. When compared against Mg – V, Mg – FeV showed slightly inferior improvements, attributed to incomplete hydrogenation of V in the presence of Fe. However, they share similar crystalline BCC, BCT – V2H and FCC - VH phases with the size of less than 10 nm and demonstrated the same behaviour at high temperatures; at temperatures approaching 400 °C, particle sintering became an issue for both nanocomposites resulting in a drop in absorption capacity even in the first cycle. The further inclusion of carbonaceous species showed several effects, one of which was an improvement in hydrogen uptake speed as well as kinetics for the addition of 5 wt. % activated carbon. For the sample with 5 wt. % graphite, the appearance of an initial incubation period of up to 60 minutes was noted, presumably corresponding to the duration of time when the carbon was sheared and crushed before hydrogenation commences.