L’objectif de ce travail est de réaliser des suspensions aqueuses d’alumine, écoresponsables, dont le comportement rhéologique est adapté à la mise en forme par coulage en bande. En effet, les suspensions utilisées dans le procédé de coulage en bande sont classiquement composées d’une poudre céramique, d’un solvant, d’un dispersant, d’un liant et d’un plastifiant. Ces additifs sont généralement des polymères issus de la pétrochimie susceptibles de présenter des risques pour la santé de l’opérateur et/ou pour l’environnement (en particulier avec les solvants organiques). Ces travaux visent donc de substituer tous les additifs venant de la pétrochimie par des additifs écoresponsables, ne présentant aucun risque pour la santé de l’opérateur et pour l’environnement. Les travaux menés dans le cadre de cette thèse ont alors permis d’identifier des polymères naturels extraits de plantes comme des candidats prometteurs pour le remplacement des additifs organiques classiques. Puis, l’étude des interactions entre ces bio-polymères et l’alumine a mené au développement d’un protocole spécifique adapté à la formulation de suspensions d’alumine à base de ces bio-molécules. Ainsi, à l’aide de ce protocole, des suspensions aqueuses ont été réalisées avec ces additifs écoresponsables qui ont abouti à la réalisation de bandes crues facilement manipulables et ne présentant ni craquelures, ni bulles. Enfin, les densités après frittage obtenues sont proches des valeurs rencontrées dans la littérature / The aim of this work is focused on the elaboration of new alumina suspensions with biopolymer additives and rheological properties adapted to the tape casting process. The suspensions used in the tape casting process are basically composed of a ceramic powder, a solvent, a dispersant, a binder and a plasticizer. These additives are usually polymers coming from the petrochemical sector which show risks for the operator health or the environment (in particular with organic solvents). Thus, natural polymers extracted from plants were identified as promising candidates in order to substitute the classical organic additives. Then, the study of the interactions between different organic additives with alumina led to a specific protocol for the formulation of aqueous alumina suspensions with these bio-polymers. Then, mechanical properties of the green and sintered tapes were evaluated in relation with the nature of bio-polymer additives. The obtained densities are close to the values reported in the litterature

Foi estudada a cristalização de suspensões aquosas de esferas de poliestireno (850&#197, 910&#197 e 1090&#197 de diâmetro) no limite de baixas concentrações -1011 a 1013 esferas / cm3. A dependência do parâmetro de rede com a concentração original (n) da suspensão aquosa apresenta uma transição de fase da fase bcc para fcc, conforme já foi observada por outros autores. Observamos também que durante a cristalização a concentração de esferas no cristal Ra sistematicamente maior do que na solução original, portanto a água estaria sendo expelida para a solução durante a cristalização. Baseado nestas observações nós propomos um modelo de cristalização onde os cristalites (concentração n1) estão em equilíbrio termodinâmico com uma solução com concentração n2 (n1&#62 n &#62 n2), dando para cada concentração inicial um diferente parâmetro de rede determinado por este equilíbrio. Nossos resultados mostraram que o coeficiente de expulsão da água durante a cristalização é dependente do raio da esfera. Para realizar as medidas de parâmetro de rede nós adaptamos para as nossas condições particulares o método de Debye-Scherrer usado em difração de raios-X por cristais. O equivalente à fonte de raios-X era um laser de Argônio com comprimentos de onda variáveis. Diversas experiências novas são sugeridas. / The crystallization of aqueous suspensions of polystyrene spheres 850&#197, 910&#197 and 1090&#197 of diameter) was studied in the limit of low concentration -1011 to 1013 spheres / cm3. The dependence of the lattice parameter with the original concentration (n) of the aqueous suspension shows a phase transition from bcc to fcc phase as it was already been observed by others authors. We also observed that during crystallization the concentration of spheres in the crystal was systematically higher than in the original solution, showing that water should be expelled toward the solution during crystallization where the crystallites (concentration n1) are in thermodynamic equilibrium with a solution with concentration n2 (n1&#62 n &#62 n2) giving for each initial concentration a different lattice parameter determined by this equilibrium. Our results showed that coefficient of water rejection during crystallization is dependent on the sphere radius. In order to make the measurements of the lattice parameter we adapted to our particular conditions the Debye-Scherrer method used in X-ray diffraction of crystals. The equivalent to the X-ray source was a tunable Argon laser. Several new experiments are suggested.

Advances in molecular-simulation methods allow for ever larger systems of particles to be studied and on longer timescales. Calculations are reaching such a scale that they can be used to address a vast range of key questions across chemistry, physics, and engineering. In this work, molecular dynamics and Monte Carlo simulations are employed to address two key areas: the structure and dynamics of simple aqueous ionic salt solutions at high concentrations; and the structure, dynamics, and phase behaviour of dipolar fluids (such as colloidal ferrofluids). The first part of the work begins with a study of the structure and dynamics in metastable, supersaturated, aqueous solutions of potassium chloride, and the possible relevance of these to the phenomenon of non-photochemical laser-induced nucleation (NPLIN). It is thought that the potassium and chloride ions form long-lived, amorphous clusters that may, under the influence of nanosecond laser pulses, undergo structural reorganisation to form post-critical crystal nuclei. It is found that spontaneous nucleation does not occur on the simulation timescale, but that amorphous clusters do form with cluster lifetimes comparable to those of the shortest laser pulses that can be used in NPLIN ( 100 picoseconds). Next, an alternative scenario for NPLIN involving rapid laser heating of impurity particles is examined by simulating heated carbon nanoparticles in saturated aqueous solutions of sodium chloride. The concentration at which an aqueous sodium chloride solution first crystallises on the simulation timescale is determined. A spherical carbon impurity is then added to a system with concentration close to, but lower than, the concentration at which crystallisation occurs on the simulation timescale. The effects that adding, and heating, this impurity has on the structure of this near-crystallising system are then observed. The second part of the work discusses model dipolar fluids, of direct relevance to colloidal ferrofluids (suspensions of magnetised nanoparticles in simple carrier liquids). The two-body, dipole-dipole interaction is long-ranged and anisotropic, and it is computationally expensive to handle in molecular simulations. Here a new method is proposed that relies on a formal mapping between the partition function of a dipolar fluid and that of a hypothetical fluid with many-body, short-ranged, isotropic interactions. Only the leading-order two-body interactions (akin to the van der Waals attraction) and three-body interactions (corresponding to the Axilrod-Teller potential) are retained. It is shown that this simple model is sufficient to reproduce the characteristic particle chaining and the associated disappearance of the vapour-liquid phase transition of dipolar fluids. Finally, the dynamical response of ferrofluids to oscillating magnetic fields (the dynamic magnetic susceptibility [DMS]) is studied. The DMS of ferrofluids, predicted by a new theory that takes into account the leading-order effects of dipole-dipole interactions, are critically compared to those found using Brownian-dynamics simulations of monodisperse systems of dipolar particles. This new theory is found to provide more accurate predictions of the DMS than previous theories, with the DMS predicted to a high degree of accuracy for systems with dipolar coupling strength in the experimentally achievable region.

Metal-oxide thin films are used in a wide variety of electronic devices. Although many techniques have been developed to deposit thin films of metal oxides, there is still a need for alternative cost- and energy-effective deposition methods. Deposition of metal oxide thin films from aqueous solutions of all-inorganic metal salts is a viable method that meets these needs. Although many aqueous-deposited metal-oxide thin films have been successfully incorporated into functioning devices, many of the mechanisms that occur as precursors transition to metal oxides are not well understood. The work presented in this dissertation is primarily concerned with examining the processes that occur as metal oxide thin films form from spin-deposited aqueous precursor solutions with a particular focus on the role of H2O in these processes. Chapter I summarizes methods for thin film deposition, and describes the use of aqueous metal salt solutions as viable precursors for the deposition of metal oxide thin films. Chapter II investigates the precursor chemistry, film-formation processes and properties of LaAlO3 thin films deposited from aqueous precursors. This chapter also serves as general guide to the processes that occur as metal-oxide thin films form from spin-deposited aqueous precursors. Chapters III and IV focus on the effects of H2O(g) during spin-deposition of precursor thin films and during the annealing process in which precursors are converted to metal oxides, respectively. The presence of H2O(g) during spin-deposition has a striking effect on the thickness of the resulting thin films and also affects the elemental gradient and density profiles. During annealing, H2O(g) reduces the temperatures at which counterions are expelled and influences the metal-hydroxide framework formation and its condensation to a metal oxide. The data also indicate that H2O(g) enhances diffusion of gaseous byproducts from within the films. Chapter V focuses on precursor concentration and its impact on the thermal evolution of thin films. The processes involved in the conversion of precursors to metal oxide thin films occur at lower temperatures as precursor concentration decreases. Although this is likely in part due to thickness effects, concentration-dependent precursor speciation may also be involved in lowering the temperatures at which films densify. / 2019-02-17

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 68-69. / by Mark Johnson. / M.S.

Thesis (M.Sc.(Chemistry)) -- University of Limpopo, 2018. / Refer to the document / NRF-Sasol Inzalo Foundation

Abstract Zinc is a common metal, and has a central role in the production of galvanised bulk products, battery applications and fertilisers. Its production relies mainly on the leaching of zinc minerals with sulfuric acid, followed by purification and electrowinning. In this thesis an internally consistent thermodynamic model for the industrially important ZnSO₄-H₂SO₄-H₂O system was developed. Model parameters were optimised using available literature data and new experimental freezing point and density data determined in this work. With Gibbs energy minimisation algorithms embedded in commercial software, such as ChemSheet and FactSage, the developed model can be used to calculate easily phase equilibria and thermodynamic properties of aqueous zinc sulfate solutions and solid zinc sulfate phases, including activity coefficients, enthalpy changes, heat capacities, densities and solubilities, in a wide range of temperature, pressure and sulfuric acid concentrations. Solution non-ideality was treated with the original Pitzer model with electrostatic mixing terms included. Applicability of thermodynamic approach and the developed model was demonstrated by two separate case studies on the hydrometallurgical zinc process. Precipitation of amorphous silica during hot acid leach was studied experimentally. Its solubility in the process solution was also successfully predicted using the thermodynamic approach. To study crystallisation of gypsum during the gypsum precipitation stage, the model was expanded by addition of the Ca²⁺ ion. The model calculations showed good agreement with the experienced Ca²⁺ levels. The results of this thesis have found immediate use in understanding the various stages of the electrolytic zinc process. The obtained results also form a basis on which new, more advanced tools for managing and studying the process can be developed. / Tiivistelmä Sinkki on yleinen metalli, ja sillä on keskeinen rooli sinkittyjen terästuotteiden, paristojen ja jopa lannoitteiden valmistuksessa. Sen tuotanto perustuu sinkkipitoisten mineraalien rikkihappoliuotukseen, muodostuneen prossessiliuoksen puhdistukseen ja lopulta metallisen sinkin elektrolyysitalteenottoon. Tässä työssä kehitettiin termodynaaminen malli teollisesti tärkeälle ZnSO₄-H₂SO₄-H₂O -systeemille. Malliparametrit määritettiin kirjallisuudessa esitetyistä tuloksista ja tässä työssä tehdyistä uusista jäätymispiste- ja tiheysmittauksista. Käyttämällä kaupallisia Gibbsin energian minimointialgoritmiin perustuvia ohjelmistoja, kuten ChemSheet tai FactSage, tässä työssä kehitetyllä mallilla voidaan helposti kuvata sinkkisulfaattipitoisten vesiliuosten faasitasapainoja ja laskea systeemin termodynaamisia ominaisuuksia. Malliin sisällytettyihin ominaisuuksiin kuuluvat systeemin komponenttien aktiivisuudet, entalpiamuutokset, lämpökapasiteetit sekä tiheydet laajalla lämpötila-, paine- ja rikkihapon pitoisuusalueella. Liuoksen epäideaalisuutta kuvattiin Pitzerin ioniaktiivisuusmallilla. Työssä sinkkisulfaattiliuoksille kehitettyä mallia testattiin kahdessa sinkintuotannon kannalta keskeisessä tapaustutkimuksessa. Amorfisen piidioksidin saostumista vahvahappoliuotuksen aikana tutkittiin kokeellisesti ja laskennallisesti. Amorfisen piidioksidin liukoisuus prosessiliuokseen ennustettiin onnistuneesti. Kipsinpoistoprosessin tutkimusta varten mallia laajennettiin lisäämällä siihen Ca²⁺-ioni. Mallilla laskettiin kipsin liukoisuus prosessiliuokseen. Saadut tulokset vastasivat hyvin käytännössä havaittuja arvoja. Tutkimuksen tuloksia on suoraan hyödynnetty sinkintuotantoprosessin ymmärtämisessä. Ne myös mahdollistavat jatkossa edistyneempien työkalujen kehittämisen niin prosessin hallintaan kuin tutkimukseenkin.

Hydroxypropylmethylcellulose (HPMC), which is available in different degrees of substitution and viscosity designations, is one of the most commonly used cellulosic polymers in aqueous film coating. It is relatively easy to process due to its non-tacky nature and has been known to produce smooth and clear films. For aqueous film coating, it is cost effective to use a coating formulation containing a high concentration of polymer without affecting the viscosity or spray rate and compromising on the quality of the film coat. Hence, it is ideal to use a polymer of low viscosity grade. The rheological properties of HPMC with various viscosity grades were determined. It was found that HPMC Methocel E3 had the lowest viscosity and was the least affected by the increase in polymer concentration. Additives can modify the film properties, including the glass transition temperature of the coating polymer. Glass transition temperature influences the viscosity of the coating solution and the mechanical properties, adhesion and permeability of the film coat. Various concentrations of different additives were incorporated in HPMC formulations to study the effect on these properties. Some long-chain fatty acids were included in the study to investigate if their hydrophobic carbon chains could retard moisture permeation of HPMC films. It was observed that HPMC films containing water-soluble additives produce films with clarity similar to those without additives, whereas those with hydrophobic additives tend to be patchy or hazy in appearance. A vinyl pyrrolidone / vinyl acetate copolymer (S630) was investigated for its influence on HPMC films, comparing the results with a commonly used plasticizer, polyethylene glycol (PEG) and another copolymer, polyvinyl alcohol (PVA). Intrinsic properties of the solutions, such as viscosity and glass transition temperature, were evaluated. / The effect of S630 on the film properties, such as physical appearance, surface roughness, moisture permeation and mechanical properties, as well as its ability to promote better adhesion of the film coat to the core surface, were compared. S630 was found to be effective both as a film-former and plasticizer, reducing the glass transition temperature and viscosity, but enhancing the tensile strength, elongation and work of failure of the cast film. The water vapour permeability was slightly increased but not to the same extent as with polyethylene glycol PEG). A 10% concentration of this copolymer increased the adhesive strength and toughness of the HPMC film coat. Aqueous film coating was carried out in the ultra-coater, using HPMC coating formulations containing 8% w/w of solids, without or with 10% concentration (based on dry weight of total solids) of the additives, PEG, polyvinyl alcohol (PVA) and S630, for coating the tablets. Capsule-shaped lactose tablet cores of specific surface area, hardness, weight, friability and disintegration time were used to study the process variables. Process variables, including air flow rate, temperature and humidity, coating application rate or pump flow rate, atomising air pressure and speed of the rotating disk, were investigated in order to obtain the optimum operating conditions for these solutions. It was found that the process parameters were similar for all the coating formulations containing 8% solid. The additives used in the coating formulations had little influence on the coating process. The ultra-coater was an effective unit for the aqueous film coating of tablets with a batch size of not less than 5 kg.

Uniformly distributed ZnO nanorods with diameter 70-100 nm and 1-2μm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip (needle shape) to flat tip (rod shape). These kinds of structure are useful in laser and field emission application. / Singapore-MIT Alliance (SMA)

Biotinylated and non-biotinylated copolymers of ethylene oxide (EO) and 2-(diethylamino)ethyl methacrylate (DEAEMA) were synthesized by the atom transfer radical polymerization technique (ATRP). The chemical compositions of the copolymers as determined by NMR are represented by PEO₁₁₃PDEAEMA₇₀ and biotin-PEO₁₀₄PDEAEMA₉₃ respectively. The aggregation behavior of these polymers in aqueous solutions at different pHs and ionic strengths was studied using a combination of potentiometric titration, dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM). Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers form micelles at high pH with hydrodynamic radii (Rh) of about 19 and 23 nm, respectively. At low pH, the copolymers are dispersed as unimers in solution with Rh of about 6-7 nm. However, at a physiological salt concentration (cs) of about 0.16M NaCl and a pH of 7-8, the copolymers form large loosely packed Guassian chains, which were not present at the low cs of 0.001M NaCl. The critical micelle concentrations (CMC) and the cytotoxicity of the copolymers were investigated to determine a suitable polymer concentration range for future biological applications. Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers possess identical CMC values of about 0.0023 mg/g, while the cytotoxicity test indicated that the copolymers are not toxic up to 0.05mg/g (> 83% cell survival at this concentration). / Singapore-MIT Alliance (SMA)