|18-028||María Laura Sandoval||Talou, M.(Instituto de investigaciones en Ciencia y Tecnología de Materiales); Sandoval, M.L.(Instituto de investigaciones en Ciencia y Tecnología de Materiales); Camerucci, M.A.(Instituto de investigaciones en Ciencia y Tecnología de Materiales); Bolaños Rivera, J.(Instituto de investigaciones en Ciencia y Tecnología de Materiales);||Polymer-derived ceramics (PDCs) constitute a novel type of materials which are receiving special attention due to their ultrahigh-temperature relevant properties. These materials are defined as intrinsically complex nanostructured materials whose chemical compositions are unique, and their processing 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 porogen along with particulate filler is considered as a possible way of solution and development of hierarchical porosity.
In this work, a polysilsesquioxane (MP-POSS) with high concentration of SiOH groups synthetized by condensation of 3-methacryloxypropyl-trimethoxysilane (molar ratio HCOOH/Si=0.055; 50°C, 5 days) and characterized by density measurement, ATR, RMN and DSC, was used as preceramic polymer. In addition, sucrose particles (D50=90µm) and SiOC powder (D50=30µm) were used as porogen and filler, respectively. Porous hybrid bodies were prepared by cross-linking (60°C, 1.5h, 10 vol% of triethylenetetramine) of MP-POSS/sucrose/filler (55/20/25 and 55/25/20 vol%) mixtures and heating (220°C, 2h), and characterized by porosity measurements and SEM. The pyrolysis was carried out at different temperatures (1000-1500°C) using controlled thermal cycles in N2. Porous SiOC-based materials (porosity=43-55%) were characterized by XRD, SEM/EDS, FTIR and Raman. All the materials (SiOxC(1-x/2)+C) presented amorphous free-carbon (clusters) and carbon bonded to Si, while those obtained from 1330°C shown the development of whiskers (SiOC0.5) with core-shell structure (nucleus of SiC and shell of amorphous silica).