Porous SiOC-based materials obtained from a hybrid precursor and paraffin microspheres

BOLAÑOS RIVERA, JAVIER O.; TALOU, M. H.; CAMERUCCI, M. A.

Darmstadt

Congreso; MSE 2018; 2018

Polymer-derived ceramics (PDC´s), among them SiOC-based materials, have been strongly studied in recent years due to their ultrahigh-temperature relevant properties which make them potential candidates to be applied in technological fields such as energy and environment, aerospace industry and electronics engineering. These materials are defined as intrinsically complex nanostructured materials whose chemical compositions are unique. The processing of this type of materials includes cross-linking and pyrolysis processes. The advantage of this processing resides in the possibility of fabricating ceramic parts by techniques conventionally used in the polymer manufacturing. However, the polymer-ceramic transformation is accompanied by removing of a large gas volume, which leads to a high volumetric contraction and formation of cracks. Thus, the fabrication of PDCs in bulk constitutes a huge technological challenge. The addition of a porogen agent along with a particulate filler is considered as a possible way of solution and development of hierarchical porosity.In this work, a partially condensed polysilsesquioxane (MP-POSS) with high concentration of SiOH groups was used as preceramic polymer. This hybrid precursor was synthetized by hydrolytic condensation of 3-methacryloxypropyl-trimethoxysilane (molar ratio HCOOH/Si=0.055; 50°C, 3 days) and characterized by density measurement, ATR-FTIR, 1H, 13C and 29Si liquid NMR DSC and rheological properties. In addition, paraffin wax microspheres (range of sizes between 74 and 211 µm) and SiOC powder (<74 µm) were used as porogen and filler, respectively. Porous hybrid bodies were prepared by cross-linking (25°C, 72 h, 10 vol% of triethylenetetramine) of MP-POSS/paraffin mixtures (70/20, 60/30 and 50/40 vol%) and MP-POSS/paraffin/filler (60/20/10 and 40/30/20 vol%) and by heating in air or N2 (300°C, 1h) to remove the porogen. The bodies were characterized by TGA, porosity measurements and SEM. The pyrolysis was carried out at 1000-1500°C using controlled thermal cycles in N2 atmosphere. Porous SiOC-based materials were characterized by XRD, ATR-FTIR, Raman and SEM/EDS.