The main problem with the production of pre-ceramic polymers, is the formation of cracks and pores upon heat treatment. It is associated with the gas release and shrinkage that occurs during the polymer-to-ceramic conversion. For the most part, this problem can be solved using so-called active fillers. These are metallic or metal silicide particles capable of reacting chemically with the decomposition products or the pyrolysis gas in the furnace during the conversion. Nevertheless, it is still difficult to sinter silicate ceramics from mixtures of oxides. Lately, experiments have shown that wollastonite (CaSO3) ceramics, a well-known bio-material, can be obtained from silicones containing calcium oxide precursors, such as micro-powders or nano-particles. In this field, a group of scientists from the University of Padova in Italy conducted a study in cooperation with ACerS Fellow Paolo Colombo and in recent work they presented an innovative processing method employing pre-ceramic polymers containing micrometer- and nanometer-sized particles of calcium carbonate, which act as reactive fillers. With the aim of obtaining wollastonite ceramics, they employed a solid and a liquid silicone in their study. Extrusion experiments were conducted on thick pastes and melts. The researchers also added hydoxyapatite powders to modify the biological response of the material. In the study, silica from the decomposition of the silicone resins reliably reacts at low temperature with the calcium oxide derived from the fillers and yielding wollastonite ceramics. This approach enables the fabrication of 3D scaffolds for bone tissue engineering via fused deposition or via conventional hot extrusion. The results provide evidence of the flexibility of the approach employing silicones containing fillers.
