Propriétés mécaniques de matériaux enchevêtrés à base de fibre de chanvre et matrice cimentaire

La compréhension des mécanismes d'interactions entre les fibres et la matrice cimentaire est indispensable afin de mieux appréhender le comportement mécanique du composite. Les fibres de chanvre, par une forte teneur en pectine, fixent sur leur surface les ions calcium Ca2+ et les ions hydroxyles OH-. On observe un déficit en ions hydroxydes et calcium dans la phase interstitielle, entraînant une inhibition des hydrates de silicate de calcium (CSH) et, par conséquent, induisant des retards de prise. Le milieu alcalin, imposé par le ciment, élimine les sucres circulants à la surface des fibres et dégrade les hémicelluloses, ce qui permet d'augmenter la rugosité des fibres. La fixation des ions calcium à la surface des fibres se traduit par une forte adhésion entre ces dernières et la matrice cimentaire. Il en résulte une amélioration des propriétés mécaniques du composite. Ces composites possèdent une grande souplesse ainsi qu'une plus grande résistance en flexion que le ciment seul, caractéristiques très intéressantes pour certaines applications du bâtimen

Powder granulation by colloidal way : elaboration of tailored millimetric ceramic sphere

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Elaboration of tailored millimetric porous ceramic spheres by colloidal way

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Ceramic shaping by destabilisation of aqueous oxide suspensions. Application with concentrated or diluted suspensions

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Fabrication of titania dense layers by electrophoretic deposition in aqueous media

International audienceFabrication of titania dense layers by electrophoresis in aqueous media has been studied according to the suspension formulation. Stable titania suspensions with negatively charged particles are obtained by adding either the strong basis (C2H5)4NOH, or the Tiron molecule or a salt of polymethacrylic acid. To prevent water electrolysis at the anode which is the collecting electrode, ethanol is added as cosolvent. A concentration of 10 vol% is sufficient to avoid gaseous emission at the anode and to keep a stable suspension suitable for electrophoretic deposition (EPD). The parameters influencing the deposit kinetic of particles are studied, such as the concentration of ethanol, of solid and of dispersant, and the current intensity applied. Finally, it is possible to fabricate layers with a relative density of 60% with a very narrow size distribution of pores

Use of Polyelectrolyte Complexes as a Binding Agent in the Granulation Process of Titania Particles

International audienceThe process of powder granulation by the colloidal way allows to shape millimetric ceramic spheres with a homogeneous distribution in terms of size and shape. This process is based on the coalescence of agglomerates in diluted media. This occurs because grains are partially covered by a ''binding'' agent. The system studied is based on a titania (anatase) powder granulated by a mixed system of a polyanion, the poly(sodium 4-styrenesulfonate), and a polycation, the chitosan. The reaction of condensation between the two polyelectrolytes leads to in situ formation of filaments acting as efficient binding agents. By selecting the suitable ratio between the two polymers, this formulation makes it possible to granulate the titania powder while retaining its purity. Organic filaments favor the coalescence step and also prevent the formation of cracks within the granules. The microstructural arrangement results from a ''snowball'' growth mechanism and from the migration of the grains due to the capillary forces occurring during the drying stage