Rare earth elements (REEs) are critically important for high-tech, renewable energy and defense industries. However, rare earth minerals (REMs) are stable compounds, requiring aggressive conditions to decompose them for their extraction and use. One exception is the ion-adsorption clays (IACs) that are mined in South China. They were formed in nature via the adsorption of the REE ions on clay minerals; therefore, they can be readily extracted into solution under mild conditions using the ion-exchange leaching process using (NH4)2SO4 as lixiviant. It also happens that IACs are the largest source of the heavy rare earth elements (HREEs) that are critical, especially for the defense industry. At present, more than 80% of the HREEs are produced commercially from the IACs mined in Southeast Asia. The objective of the present research was to study the fundamental mechanisms involved in the formation and processing of IACs using the ion-change leaching process. The first part of the project was the synthesis of IACs by contacting kaolinite samples with known concentrations of rare earth chloride (REECl3) solutions at different pHs and analyzing the synthetic IACs for XPS studies. It was found that the REE adsorption on kaolinite stays constant in acidic pHs. At pH 7 and above, adsorption density increases sharply, possibly due to the formation of REE(OH)3 and/or REE(OOH). The IACs formed under these conditions responded well to the ion-exchange leaching process by reducing the pH to below 7. In the second part of the study, the effect of iron (Fe3+) species co-adsorbing with REEs on the kaolinite surface was studied. Unlike the colloidal phases of IACs formed at pH > 7, the synthetic IACs formed in the presence of iron did not respond to the ion-exchange leaching process using (NH4)2SO4 as lixiviant. This problem has been solved by subjecting the synthetic IACs to a reducing condition to convert the Fe3+ to soluble Fe2+ species at pH < 7. The driving force for the standard exchange leaching process is the large differences between the hydration enthalpies of the Ln3+ ions that are in the range of -3,400 kJ/mole and that of the NH4+ ions (-320 kJ/mole). In the present work, alkylammonium ions (CnH2nNH4+) of varying chain lengths were used as novel lixiviants and obtained excellent results. Since these are surface active species, their concentrations in the vicinity of the clay minerals that are negatively charged would be substantially higher than in the bulk. As a result, it was possible to achieve the same level of leaching efficiencies as obtained using ammonium sulfate at approximately ten times lower reagent dosages. One of the problems associated with extracting REEs from coal-based clays is that the REE concentrations are typically in the range of 300 to 600 ppm, which makes it difficult to extract the critical materials economically using ion-exchange leaching and other processes. As a means to overcome this issue, the REE-bearing particles, including IACs and REMs, were liberated by blunging and subsequently upgraded using the hydrophobic-hydrophilic separation (HHS) process. The results showed that blunging outperformed grinding in liberating the REE-bearing particles from the clayey materials in coal. It was shown that one can improve blunging by increasing the disjoining in the thin liquid films present between clay and other minerals by controlling the double-layer (EDL) forces. These findings should enhance our understanding of the fundamental mechanisms involved in upgrading critical materials and thereby increase the economic viability of REE recovery from coal-based materials. / Doctor of Philosophy / Rare earth elements (REEs) play a vital role in numerous modern industries, advanced technological applications, and defense industries. The United States accounts for about 15 % of the global demand for REEs. However, the country heavily relies on imported Chinese raw materials, creating vulnerability in the U.S. supply chain. REEs are rarely found in concentrations suitable for mining, and in certain cases, extracting and processing conventional REE deposits come with significant environmental hazards. The limited availability of rare earth elements (REEs) raises concerns regarding their production despite their critical role in high-tech industries. Consequently, various federal agencies and private enterprises have recently attempted to identify promising alternative resources due to these complex challenges. REEs have been found in several major coal basins and are evidenced to be associated with coal byproducts such as kaolinite clays–one of the major host materials of IACs. This research investigates the recovery of rare earth elements (REEs) from clayey materials through various processes. Emphasis is placed on the synthesis of ion-adsorption clays from kaolinite, and the factors influencing the ion-exchange leaching process are being studied. Furthermore, the impact of iron co-adsorption on REE binding to kaolinite is being examined, and reductive leaching is being evaluated as a means to overcome the hindrance caused by iron passivating layers. Novel lixiviants are being tested as alternatives to conventional lixiviant ((NH4)2SO4) for REE extraction. The application of hydrophobic-hydrophilic separation techniques for extracting REE-bearing particles from coal clay samples is also being explored, with a comparison made between grinding and blunging processes. Overall, valuable insights into the efficient recovery of REEs from clay minerals are being obtained, contributing to the development of cost-effective and novel approaches for their extraction.

Surface force measurements previously conducted with thiolated gold surfaces showed a decrease in excess film entropy (£GSf), suggesting that hydrophobic force originates from changes in the structure of the medium (water) confined between hydrophobic surfaces. As a follow-up to the previous study, surface force measurements have been conducted using an atomic force microscope (AFM) with hydrophobic silica surfaces at temperatures in the range of 10 to 40¢XC. The silica sphere and silica plate were treated by both chemisorption of octadecyltrichlorosilane (OTS) and physical adsorption of octadecyltrimethylammonium chloride (C18TACl). A thermodynamic analysis of the results show similar results for both of the samples, that both ""Sf and excess film enthalpy ("Hf) become more negative with decreasing thickness of the water layer between the hydrophobic surfaces and decreasing temperature. |"Hf | > |T"Sf| represents a necessary condition for the excess free energy change ("Gf ) to be negative and the hydrophobic interaction to be attractive. Thus, the results obtained with both the silylated and C18TACl-adosrbed silica surfaces in the present work and the thiolated gold suefaces reported before show hydrophobic forces originate from structural changes in the medium. Thermodynamic analysis of SFA force measurements obtained at various temperatures revealed that "Sf were much more negative in the shorter hydrophobic force ranges than in the longer ranges, indicating a more significant degree of structuring in the water film when the two hydrophobic surfaces are closer together. It is believed that the water molecules in the thin liquid films (TLFs) of water form clusters as a means to reduce their free energy when they cannot form H-bonds to neighboring hydrophobic surfaces. Dissolved gas molecules should enhance the stability of structured cluster due to the van der Waals force between the entrapped gas molecules and the surrounding water molecules1, which may enhance the strength of the hydrophobic force. Weaker long-range attractive forces detected in degassed water than in air-equilibrated water was found in the present work by means of AFM force measurements, supporting the effect of dissolved gas on the structuring of water. At last, temperature effects on hydrophobic interactions measured in ethanol and the thermodynamic analysis revealed similar results as those found in water, indicating that the hydrophobic force originates from H-bond propagated structuring in the mediums. / Ph. D.

In 1982, Israelachvili and Pashley reported the first measurements of a hitherto unknown attractive force between two mica surfaces hydrophobized in cetyltrimethylammonium bromide (CTAB) solutions. Follow-up experiments conducted by many investigators confirmed their results, while others suggested that the "hydrophobic force" is an artifact due to nanobubbles (or cavitation). Evidences for the latter included the discontinuities (or steps) in the force versus distance curves and the pancake-shaped nano-bubbles seen in atomic force microscopic (AFM) images. Recent measurements conducted in degassed water showed, however, smooth force versus distance curves, indicating that the hydrophobic force is not an artifact due to nanobubbles.1, 2 Still other investigators3, 4 suggested that the long-range attraction observed between hydrophobic surfaces is due to the correlation between the patches of adsorbed ionic surfactant and the patches of unoccupied surface. For this theory to work, it is necessary that the charged patches be laterally mobile to account for the strong attractive forces observed in experiment. In an effort to test this theory, AFM force measurements were conducted with gold substrates hydrophobized by self-assembly of alkanethiols and xanthates of different chain lengths. The results showed long-range attractions despite the fact that the hydrophobizing agents chemisorb on gold and, hence, the adsorption layer is immobile. When the gold surfaces were hydrophobized in a 1 Ã 10-3 M thiol-in-ethanol solution for an extended period of time, the force curves exhibited steps. These results indicate that the long-range attractions are caused by the coalescence of bubbles, as was also reported by Ederth.5 The steps disappeared, however, when the species adsorbed on top of the chemisorbed monolayer were removed by solvent washing, or when the gold substrates were hydrophobized in a 1 Ã 10-5 M solution for a relatively short period of time. AFM force measurements were also conducted between gold substrates coated with short-chain thiols and xanthates to obtain hydrophobic surfaces with water contact angles (ï ±) of less than 90o. Long-range attractions were still observed despite the fact that cavitation is thermodynamically not possible. Having shown that hydrophobic force is not due to coalescence of pre-existing bubbles, cavitation, or correlation of charged patches, the next set of force measurements was conducted in ethanol-water mixtures. The attractive forces became weaker and shorter-ranged than in pure water and pure ethanol. According to the Derjaguin's approximation6, an attractive force arises from the decrease in the excess free energy (ï §f) of the thin film between two hydrophobic surfaces.7 Thus, the stronger hydrophobic forces observed in pure water and pure ethanol can be attributed to the stronger cohesive energy of the liquid due to stronger H-bonding. Further, the increase in hydrophobic force with decreasing separation between two hydrophobic surfaces indicates that the H-bonded structure becomes stronger in the vicinity of hydrophobic surfaces. The force measurements conducted at different temperatures in the range of 10-40C showed that the hydrophobic attraction between macroscopic surfaces causes a decrease in film entropy (Sf), which confirms that the hydrophobic force is due to the structuring of water in the thin film between two hydrophobic surfaces. The results showed also that the hydrophobic interaction entails a reduction in the excess film enthalpy (Hf), which may be associated with the formation of partial (or full) clathrates formed in the vicinity of hydrophobic surfaces. The presence of the clathrates is supported by the recent finding that the density of water in the vicinity of hydrophobic surfaces is lower than in the bulk.8 / Ph. D.

Froth floatation is an important process used in the mining industry for separating minerals from each other. The separation process is based on rendering a selected mineral hydrophobic using an appropriate hydrophobizing reagent (collector), so that it can selectively attach onto the surfaces of a rising stream of air bubbles. Thus, controlling the hydrophobicity of the minerals to be separated from each other is of critical importance in flotation. If one wishes to separate plastics from each other by flotation, however, it would be necessary to render a selected plastic hydrophilic and leave the others hydrophobic. In the present work, the possibility of separating common plastics from each other by flotation has been explored. While water contact angle is the most widely used measure of the hydrophobicity of a solid, it does not give the information on the kinetics of flotation. Therefore, the forces acting between the surfaces coated with different hydrophobic polymers (or plastics) in water were measured using the Atomic Force Microscope (AFM). The results obtained with polystyrene, polymethylmethacryrate (PMMA), polypropylene (PP), and Teflon showed the existence of long-range attractive forces (or hydrophobic force) that cannot be explained by the classical DLVO theory. The surface force measurements were conducted in pure water and in solutions of surfactant (alkyltrimethylammonium chloride) and a salt (NaCl). In pure water, the attractive forces were much stronger than van der Waals force. In the presence of the surfactant and NaCl, the long-range attraction decreased with increasing concentration and the alkyl chain length. A series of contact angle measurements were conducted to determine the hydrophobicity of polystyrene (PS), polyvinyl chlorite (PVC), and polymethylmethacrylate (PMMA) in the presence of different wetting agents (surfactants). The results show the possibility of separating plastics from each other by flotation, and a series of microflotation tests conducted on PS and PVC showed promising results. / Master of Science

The objective of this thesis was to advance understanding in the field of biolubrication, finding inspiration from the human synovial joints. This was addressed by investigating the association of key biolubricants and the resulting lubrication performance. Techniques employed during the course of this work were Atomic force microscopy (AFM), Quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray reflectivity (XRR). Key synovial fluid and cartilage components like dipalmitoylphosphatidylcholine (DPPC), hyaluronan (HA), lubricin, and cartilage oligomeric matrix protein (COMP) have been used in the investigations. Focus was towards two lubrication couples; DPPC-hyaluronan and COMP-lubricin. DPPC-hyaluronan mixtures were probed on hydrophilic silica surfaces and COMP-lubricin association structures were explored on weakly hydrophobic poly (methyl methacrylate) (PMMA) surfaces. Investigations of the COMP-lubricin pair revealed that individually these components are unable to reach desired lubrication. However in combination, COMP facilitates firm attachment of lubricin to the PMMA surface in a favourable confirmation that imparts low friction coefficient. DPPC and hyaluronan combined impart lubrication advantage over lone DPPC bilayers. Hyaluronan provides a reservoir of DPPC on the surface and consequently self-healing ability. Other factors like temperature, presence of calcium ions, molecular weight of hyaluronan, and pressure were also explored. DPPC bilayers at higher temperature had higher load bearing capacity. Association between DPPC Langmuir layers and hyaluronan was enhanced in the presence of calcium ions, and lower molecular weight hyaluronan had a stronger tendency to bind to DPPC. At high pressures, DPPC-hyaluronan layers were more stable compared to lone DPPC bilayers. / <p>QC 20170210</p>

Les microsystèmes regroupent sur un même substrat des fonctions électroniques, mécaniques, optiques, chimiques ou biologiques et sont fabriqués par les procédés de la microélectronique. Leurs particularités géométriques les rendent extrêmement sensibles aux forces de surfaces qui peuvent conduire à leur collage définitif, notamment lors de l'étape de libération. Cette thèse porte sur la compréhension de ce phénomène. Pour cela une mesure des forces d'adh´esions entre deux surfaces de silicium en milieu liquide a été entreprise à l'aide d'un appareil de mesure des forces de surface et à l'aide de microstructures. L'impact de la tension de surface de différents liquides sur l'adhésion a été étudié. L'étude de la rugosification du silicium par gravure humide, caractérisée par microscope à force atomique ; et l'impact cette rugosité sur l'adhésion a également été menée. Enfin, un procédé industriel original de libération par voie humide sans démouillage des substrats a été développé.

This thesis examines the formation of Polyelectrolyte Multilayers (PEM) on cellulose fibres as a new way of influencing the fibre surface and the adhesion between wood fibres. The aim of the study was to enhance the fundamental understanding of the adsorption mechanisms behind the formation of Polyelectrolyte Multilayers on cellulose fibres; to study how the properties of the layers can be influenced and to show how the properties of the layers influence the adhesion between the fibres and the strength of paper sheets made from the PEM treated fibres. Different polyelectrolyte systems are known to form PEMs with different properties, and in this work two different polymer systems were extensively studied: poly(dimethyldiallylammonium chloride) (PDADMAC) / poly(styrene sulphonate) (PSS), which are both strong polylectrolytes (i.e. are highly charged over a wide range of pH) and poly allylaminehydrochloride (PAH) /poly acrylic acid (PAA), which are both weak polyelectorlytes (i.e. sensitive to pH changes). PEMs were also formed from PAH/ poly(3,4-ethylenedioxythiophene):PSS (PEDOT:PSS), in order to form electrically conducting PEMs on fibres and PEM-like structures were formed from polyethylene oxide (PEO) and polyacrylic acid (PAA). In order to study the influence of the PEM on adhesion and paper strength, fibres were treated and used to form sheets which were physically tested according to determine the tensile index and strain at break. Both these systems were studied using different molecular mass fractions. High molecular mass PDADMAC/PSS (&gt;500k/1000k) had a significantly greater influence as a function of the number of layers than low molecular mass PDADMAC/PSS (30k/80k). In contrast, sheets made from high molecular mass PAH/PAA (70k/240k) showed a significantly lower increase in strength than sheets made from low molecular PAH/PAA investigated earlier. Both these systems had a greater influence on paper strength when the cationic polyelectrolyte was adsorbed in the outermost layer. The amount of polyelectrolytes adsorbed on the fibres was determined using polylectrolyte titration (PET) and destructive analytical methods. Adsorption to model surfaces of silicon oxide was studied before the adsorption on fibres, in order to understand the influence on PEM properties of parameters such as salt concentration and adsorption time. Adhesion studies of surfaces coated with PAH/PAA using AFM, showed an increase in adhesion as a function of the number of adsorbed layers. The adhesion was higher when PAH was adsorbed in the outermost layers. Individual fibres were also partly treated using a Dynamic Contact Angle analyser (DCA) and were studied with regard to their wettability. In general, the wettability was lower when the cationic polymer was outermost. The level of adhesion and paper strength are discussed in terms of rigidity and wettability and the PEMs demonstrating a large number of free chain ends, a large chain mobility and a low wettability was found to have the greatest influence to adhesion and paper strength. / QC 20100823

Measurements have been performed to understand the sound source mechanism in turbulent boundary layer flow over two and three-dimensional surface discontinuities whose height is smaller than the incoming boundary layer thickness. The work was performed in two different types of boundary layers: a wall-jet flow and a conventional high Reynolds boundary layer. In the wall-jet flow, measurements of far field sound from two-dimensional forward facing steps, gaps with rounded corners and swept forward facing steps with rounded corners were made. The sound from a forward facing step is shown to exhibit effects of non-compactness. Rounding the step corner results in consistent drop in sound levels but the directivity of the sound field remains unchanged. The sound from gaps is dominated by the forward step component and remains unaffected by rounding of the backward step portion. The sound from swept forward facing steps was found to approximately obey an acoustic sweep independence principle up to a sweep angle of 30 deg when the spanwise inhomogeneity in the flow is accounted for using a simple source distribution model. Sweep independence is also observed for steps with corner rounding radii up to 25% of the step height. The work performed in the high Reynolds number boundary layer included measurements on forward facing steps with rounded corners and a three-dimensional circular embossment with the same height as the forward step. The highest Reynolds number based on discontinuity height achieved in this work was approximately 93,000. The results show that rounding the forward step corner has the same qualitative effect on far field sound as in the wall-jet boundary layer. Quantitatively, for similar boundary layer edge velocity the sound is higher than in the wall-jet flow. The near field measurements show that the separation bubble downstream of the step shrinks as the step corner is rounded while the bubble upstream remains unaffected by it. The unsteady surface force in the lower half of the vertical face of the step was found to be independent of corner rounding. The force on the downstream surface shows similar character within the separation bubble for each rounding but decays faster with increasing downstream distance due to reduced bubble size. The unsteady force measurements were applied to the theory of Glegg et al. (2014) and the resultant of the unsteady forces on the vertical face and downstream surface placed at the top corner of the step is shown to qualitatively describe the far field sound. The acoustic sweep independence principle was applied to the far field sound from the circular embossment and it has been shown that the sound from the three-dimensional geometry can be predicted with reasonable accuracy using sound from a two-dimensional forward step with the same span. / Ph. D.

In general, the stability of suspension can be studied using two methods. <i>One</i> is to directly measure the forces between two interacting surfaces in media. <i>The other</i> is to study the interfacial surface free energies of the particles in suspension. Direct surface force measurements were conducted between silica surfaces in octadecyltrimetylammonium chloride (C₁₈TACl) solutions using an Atomic Force Microscope (AFM). The results showed that the hydrophobic force existed in both air-saturated and degassed C₁₈TACl solutions. The attraction decreased with NaCl addition, and was the strongest at the point of charge neutralization (p.c.n.) of silica substrate. The force measurement results obtained in C_nTACl solutions showed that the attractions decayed exponentially and became the maximum at the p.c.n.'s. The decay lengths (<i>D</i>) increased with surfactant chain length. The measured forces were fitted to a charged-patch model of Miklavic <i>et al</i>. (1994) with rather large patch sizes. It was also found that the decay length decreased linearly with the effective concentration of the CH2/CH3 groups raised to the power of -1/2. This finding is in line with the model of Eriksson <i>et al</i>. (1989). It suggested that the long-range attractions are hydrophobic forces originating from the changes in water structure across a hydrophobic surface-solution interface. For the TiO₂/water/TiO₂ system, the Hamaker constant was found to be 4±1×10^-20 J. The force curves obtained in the TiO₂/C_nTACl system showed a repulsion-attraction-repulsion transition with increasing surfactant concentration. The long-range attraction observed between TiO₂ surfaces in C_nTACl solutions reached maximum at the p.c.n., and the decay length increased with chain length. In present work, the thin-layer wicking technique was used to determine the surface free energy (γ_s) and its components of talc samples. The results showed that the basal surfaces of talc are weakly basic while the edge surfaces are acidic. The effect of chemicals on the surface free energies of talc was systemically studied. The results showed that CMC (carboxymethyl cellulose sodium salt) and EO/PO (ethylene oxide/propylene oxide) co-polymers made talc surface hydrophilic by increasing the surface free energies, especially γ^LW and γ^-. SOPA (sodium polyacrylate) increased greatly the zeta-potentials instead of the surface free energies. / Ph. D.

O objetivo desta dissertação de mestrado é estudar técnicas numéricas para simular escoamentos incompressíveis multifásicos e implementar uma ferramenta computacional utilizando malhas hierárquicas e discretizações por diferenças finitas. São apresentados a formulação matemática e o desenvolvimento do método numérico, levando em consideração o caráter multifásico do escoamento. Foi adotado o modelo de força superficial contínua e a representação da interface foi feita pelo método de acompanhamento de fronteira. São expostos todos os testes realizados durante o desenvolvimento da ferramenta para checar cada etapa do método. Finalmente, testes visando verificar o código foram feitos e os resultados obtidos foram considerados satisfatórios para a verificação da ferramenta aqui desenvolvida. / The objective of this masters degree essay is to study numerical techniques to simulate incompressible multiphase flows and to implement a computational tool using hierachical meshes and discretizations by finite diferences. We introduce the mathematical formulation and the development of the numerical method, for the multiphase flow problem. A continuum surface force model is employed with the interface representation by the front tracking method. We show all tests performed to verify each stage of the methods development. Finally, results obtained in classical benchmark flow tests show good agreement with previous published results, corroborating the validity of this newly developed numerical tool.