EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The polymer-derived ceramics (PDCs) route is a promising way for the production of silicate-based bio-ceramic/glass-ceramic materials: through suitable heat treatment, they yield materials with a distinctive control of phase purity and microstructures. Silicone-fillers mixture can yield bio-ceramics with a well-defined crystalline phase such as Biosilicate® glass-ceramics (Na2CaSi2O6). Commercially available silicone polymers ( such as H44, Silres® MK, H62C etc.) transform to pure SiO2 upon heating in ambient atmosphere, while their pyrolysis in the non-oxidizing atmosphere gives rise to the formation of amorphous residue composed of Si-O, Si-C and free carbon. In the present work, 3D-printed Biosilicate® glass-ceramic scaffolds with hierarchically porous struts were successfully manufactured by Direct Ink Writing (DIW) and subsequent thermal treatment of H44 silicone polymer filled with anhydrous CaO, Na2O and P2O5 precursors. Natural foaming ability of H44 silicone resin was utilized to obtain open-celled hierarchical micro-porosity. Additionally, green scaffolds were fired in the air and in the N2 atmosphere to compare the effect of residual free carbon on the mechanical properties of 3D-printed scaffolds. The hierarchical structure was created through foaming, which was to the result of crosslinking of the silicone resin at low temperature (ambient temperature, 60 °C and 75 °C) before its conversion to ceramics. Pure Biosilicate single crystalline phase (Na2CaSi2O6) was obtained both in air and N2 atmosphere with the help of anhydrous sodium phosphate filler (Na2HPO4) which provides a liquid phase (remained as a glass phase after cooling at room temperature) upon firing that promoted the ionic interdiffusion. The fabricated scaffolds exhibited compressive strength values up to 8 MPa and 13 MPa after pyrolysis in air and N2 atmosphere, with the open porosity 68% vol. and 66% vol. respectively.