Effect of Ca and B incorporation into silicon oxycarbide on its microstructure and phase composition

Abstract

Ca‐ and/or B‐modified silicon oxycarbides were synthesized via pyrolysis of suitable polysilsesquioxane‐based single‐source precursors. Their polymer‐to‐ceramic transformation was investigated with thermogravimetric analysis, coupled with in situ evolved gas analysis. The prepared silicon oxycarbides were investigated with respect to their crystallization behavior, network architecture, and chemical compositions. The network connectivity in silicon oxycarbides can be affected/tuned upon using two different “tools”: (a) first, the use of network modifiers, such as Ca in our study, leads to a slight depolymerization of the network via generation of a small amount of Q3 sites; (b) second, the modification of silicon oxycarbide with B/Ca leads to a decrease of the carbon content in the network and thus to a significant decrease of its connectivity. Using these two different effects, the network connectivity in silicon oxycarbides can be finely tuned.

Facile Preparative Access to Bioactive Silicon Oxycarbides with Tunable Porosity

“…As shown in Figure 4, the Q 3 component is found only in the fitted spectra of Ca-containing silicon oxycarbides, i.e., SiCa5 and SiCa12, clearly demonstrating the effect of Ca as network modifier in the silicon oxycarbide network. This is in agreement with 29 Si NMR data reported on Ca-containing silicon oxycarbides prepared from a Ca-acetylacetonate-modified polysilsesquioxane [12].…”

“…Interestingly, the OV/(LO + TO) ratio shows a decreasing tendency from SiCa0 to SiCa12, implying the decrease of network carbon content with increasing Ca 2+ incorporation in amorphous network. This was reported in previous studies related to the modification of silicon oxycarbide networks with earth alkaline network modifiers [7,12].…”

“…In Figure 3a, the FTIR spectra indicate that the methyl groups were completely removed after pyrolysis. Typical O–Si–O, Si–C and Si–O–Si vibration bands were identified for SiCa0, SiCa5, and SiCa12 [12]; whereas in the case of SiCa50 the observed bands were mainly assigned to calcium silicate (pseudowollastonite) [32]. The crystallization of pseudowollastonite along with small amounts of wollastonite in SiCa50 was confirmed by XRD analysis (Figure 3b).…”

“…Moreover, the decrease of the content of network carbon with increasing Ca 2+ incorporation, which was concluded based on the evaluation of the OV/(LO + TO) ratio in the FTIR spectra, is clearly confirmed. The decrease of the carbon content in the oxycarbide network as well as its slight depolymerization due to the network modifier effect of Ca are considered to lead to decreased network connectivity in the series from SiCa0, to SiCa5, and to SiCa12 [12].…”

“…Metal-containing silicon oxycarbides have been synthesized via the so-called polymer-derived ceramic method (PDC): The incorporation of metal ions into silicon oxycarbide occurs by modifying its polymer precursors, such as polysiloxanes or polysilsesquioxanes, with suitable metal organic compounds [12,13]. Highly porous PDC derived SiOC can be achieved by choosing sol-gel synthesized precursors [3,14], using mesoporous templates [15], or applying post-synthesis treatments of HF etching or air calcination [16].…”