A novel processing approach for free-standing porous non-oxide ceramic supports from polycarbosilane and polysilazane precursors
In this contribution, a low-pressure/low-temperature casting technique for the preparation of novel free-standing macrocellular polymer-derived ceramic support structures is presented. Preceramic polymers (polycarbosilane and poly(vinyl)silazane) are combined with sacrificial porogens (ultra-high molecular weight polyethylene microbeads) to yield porous ceramic materials in the Si—C or Si—C—N systems, exhibiting well-defined pore structures after thermal conversion. The planar-disc-type specimens were found to exhibit biaxial flexural strengths of up to 60 MPa. In combination with their observed permeability characteristics, the prepared structures were found to be suitable for potential applications in filtration, catalysis, or membrane science.
Elaboration de membranes non-oxydes de type SiBC pour la maîtrise de la contamination dans les réacteurs à eau pressurisée
Ce travail de these a porte sur le developpement de membranes ceramiques pour la filtration de colloides issus de la corrosion dans le circuit primaire des REP. La voie des polymeres preceramiques a ete mise en œuvre par la synthese d’un polyborocarbosilane (PBC) a partir d’allylhydridopolycarbosilane conduisant a une ceramique de type SiBC. Des billes de PMMA mono disperses d’une taille de 1,5 et 0,3 µm ont ete preparees pour servir d’agent porogene pour creer une porosite controlee. Des objets micro-cellulaires 3D de forme circulaire ont ete elabores par pressage uni-axial avec ajout de billes de PMMA commercial pour servir de support macroporeux. Une etude de cristallinite a haute temperature (> 1000 °C) a ete realisee, montrant son influence sur la stabilite du materiau. La couche selective a ete preparee par dip-coating a partir de differentes formulations de barbotine contenant du PBC et les billes de PMMA elaborees. La stabilite physico-chimique des supports micro-cellulaires a ete etudiee grâce a des essais de vieillissement en micro-autoclave en milieu primaire simule. La resistance a la filtration a ete testee grâce a un essai sur un dispositif de filtration connecte a un moyen d’essai de laboratoire permettant de simuler les conditions des REP.
Fabrication of porous preceramic polymers using carbon dioxide
Porous materials have a unique set of properties— low density, low thermal conductivity, high permeability, high surface area, high thermal shock resistance, high specific strength and high resistance to chemical corrosion—which make them good candidates for both structural and functional applications, such as thermal insulators, lightweight structural components, catalysts, absorbents, and filters [1–3]. The properties of porous materials are influenced by their relative density and the morphology, i.e., the size and distribution of the pores. The porosity characteristics can be varied in a wide range of values depending on the fabrication method [2]. Various processing routes have been proposed for the production of porous ceramics: (1) the immersion of an open-cell polymeric foam into a ceramic slurry and subsequent pressureless