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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.

Bentonite is a smectite type clay mineral and swells in water. In this thesis, the effect of acetone, methyl-ethyl ketone, n-hexane on the properties of bentonite was determined by thermal analysis and water absorption tests. The tests indicated no significant change with treating bentonite with organic liquids. Because of the swelling property, only small amount of bentonite can be suspended in water. This may limit certain applications of bentonite. In this thesis, feasibility of suspending large quantities of bentonite in a non-aqueous media was studied. The concentrations for a pumpable high solid bentonite slurry were determined. As aqueous slurry showed pumpable properties up to 30-35 pounds/barrel, this concentration was as high as 125-150 pounds/barrel for acetone, 175-200 pounds/barrel for methyl-ethyl ketone and 325-350 pounds/barrel for n-hexane. Bentonite deposite has a complicated composition, containing free silica minerals, such as quartz, cristobalite, and opal / silicate minerals, such as feldspar, mica, and zeolite / carbonates or sulfates of alkaline earth metals, such as calcite, dolomite, and gypsum / and, in addition, iron compounds and humus. As mined it is primarily broken and dried and then pulverized by means of an attrition grinding machine. In this study dispersion of raw bentonite by high shear blending and shaking forces in the presence of acetone, methyl-ethyl ketone and n-hexane and eliminating the non-clay impurities by screening were studied. Many attempts have been made to provide a bentonite composition retaining the full swelling properties of the bentonite by the addition of non-aqueous liquids for obtaining a flexible waterproofing sheet. In this research the possible method for deposition of bentonite in a sponge by saturating the sponge with bentonite using organic liquids was investigated.

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.

A variety of experiments were carried out to study the dispersion and microstructure of carbon nanotubes in aqueous suspensions and polymer composites with the goal to improve the electrical conductivity of the composites containing nanotubes. Epoxy composites containing covalently and noncovalently functionalized nanotubes were compared in terms of electrical and mechanical behavior. Covalent functionalization of nanotubes is based on chemical attachments of polyethylenimine (PEI) whereas noncovalent functionalization takes place through physical mixing of nanotubes and PEI. The electrical conductivity is reduced in composites containing covalently functionalized nanotubes due to damage of the tube?s conjugated surface that reduces intrinsic conductivity. Conversely, the mechanical properties are always better for epoxy composites containing covalently functionalized nanotubes. Clay particles were used as a rigid dispersing aid for nanotubes in aqueous suspensions and epoxy composites. When both nanotubes and clay were introduced into water by sonication, the suspension is stable for weeks, whereas the nanotubes precipitate almost instantly for the suspension without clay. In epoxy composites, nanotubes form separated clusters of aggregation, whereas a continuous threedimensional nanotube network is achieved when clay is introduced. Electrical conductivity of the epoxy composite is shown to significantly improve with a small addition of clay and the percolation threshold is simultaneously decreased (from 0.05 wt% nanotubes, when there is no clay, to 0.01 wt% when 2 wt% clay is introduced). The addition of clay can also improve the mechanical properties of the composites, especially at higher clay concentration. Weak polyelectrolytes (i.e., pH-responsive polymers) were also studied for their interaction with nanotubes and the electrical properties of the dried composite films. When dispersed by sonication, Nanotubes show pH-dependent dispersion and stability in poly(acrylic acid) water solution, as evidenced by changes in suspension viscosity and cryo-TEM images. The nanotube suspensions were then dried under ambient conditions and the composite films exhibit tailorable nanotube dispersion as a function of pH. The percolation threshold and maximum electrical conductivity are reduced when the pH is changed from low to high. Some other pH-responsive polymers were also studied, but their pH-dependent viscosity and conductivity were not as large or reversible as poly(acrylic acid).