## 3 Results  
### Precursor Polysiloxane Microspheres  
It is well known that polysiloxanes can be thermally transformed into SiC ceramics. The process is complex and requires heating above 1200 \({}^{\circ}\)C [38]. Ceramization of the siloxane polymer in an inert atmosphere above 900 \({}^{\circ}\)C first produces SiO material which contains nanodomains of free carbon, C\({}_{\mathrm{f}}\). Further heating above 1200 \({}^{\circ}\)C results in the segregations of SiO\({}_{2}\) and SiC phases, Equation (1), which is accompanied by carbothermal reduction of SiO\({}_{2}\) by the free carbon, Equation (2). If the quantity of free carbon is high enough, both processes can convert SiO to SiC and produce gaseous products that remove oxygen from the material [38; 39]. The excess of C\({}_{\mathrm{f}}\) remains in the ceramics. \[\mathrm{SiC_{n}O_{m(s)}\to SiO_{2(s)}+SiC_{(s)}+C_{f(s)}} \tag{1}\]\[\text{SiO}_{2(\text{s})}+\text{C}_{\text{f(s)}}\rightarrow\text{SiC}_{\text{(s)}}+ \text{SiO}_{\text{(g)}}+\text{CO}_{\text{(g)}}+\text{CO}_{\text{2(g)}} \tag{2}\]  
Our goal was to find a suitable precursor polysiloxane microspheres and the right conditions of the ceramization process to obtain oxygen-free SiC material with a controlled C\({}_{\text{f}}\) content, with relatively high ceramization yield and maintaining the spherical shape of the ceramic particles. The other aim was to explore the possibility of pores formation in SiC ceramics by controlling the formation of gaseous products in the carbothermal reduction process. Our previous studies showed that microspheres produced by aqueous emulsion processing of PHMS, retain their shape well in ceramization at high temperatures [35]. However, due to the relatively small amount of carbon in the polysiloxane, it is difficult to remove oxygen from the produced ceramics while providing a good SiC yield. The method to achieve this goal by other researchers was the introduction of various forms of carbon, such as charcoal [40], anthracite or graphite [27], carbon black or phenol resin [31; 33], to the precursor. In our research, additional carbon was introduced to this material through the use of a large amount of a cross-linking agent, which was divinyl benzene (DVB). As demonstrated by [PERSON] et al., PHMS cross-linked with DVB and heated to 1000-1450 \({}^{\circ}\)C gives SiC material containing a large amount of aromatic free carbon [41; 42]. We previously found that SiO microspheres obtained from modified PHMS/DVB systems were distinguished by a high content of C\({}_{\text{f}}\)[43]. Series of precursor polysiloxane microspheres were prepared using various proportions of DVB cross-linker (s.i. Figures S1 and S2). They were obtained by aqueous emulsion processing according to the method described elsewhere [35] in which the polysiloxane with partly grafted cross-linker dissolved in a water-miscible solvent is mechanically emulsified with water containing a surfactant. The synthesis of this precursor series and the detailed analysis of the chemical structure of the formed microspheres was published separately [37]. The \({}^{13}\)C and \({}^{29}\)Si MAS NMR analysis made it possible to evaluate their chemical composition. The characteristics of the fabricated microspheres are shown in supporting information (s.i. Table S1). This analysis showed that the chemical structure of these microspheres is largely influenced by the content of the cross-linking agent. A characteristic feature of these microspheres is a large number of reactive side groups on the polysiloxane chains, which are native SiH groups and SiOH groups formed during the synthesis of the microspheres. In addition, there are two types of bonds connecting the polymer chains, SiOSi bonds due to condensation of reactive groups of the polymer and Si-CH\({}_{2}\)CH\({}_{2}\)- bridges due to hydrosilylation of DVB (s.i. Table S1).