## 3 Results
### Porosity by N\({}_{2}\) Adsorption  
The microspheres had a hierarchical micro/meso/macroporous structure which was characterized by N\({}_{2}\) gas porosimetry and mercury intrusion porosimetry. Nitrogen adsorption informs about meso and micropores, while mercury intrusion gives knowledge about macroproes. The results obtained in the nitrogen adsorption studies are summarized in Table 4.  
The proportions of the cross-linking agent used in the synthesis of the precursor particles have a great influence on the type of porosity of the SiC microspheres. Ceramic particles made of precursors obtained with a very high DVB content (A-6 and A-7), thus with a large content of C\({}_{\text{f}}\), are distinguished by a high specific surface area, SSA, which were 263 m\({}^{2}\)/g and 347 m\({}^{2}\)/g for samples A-6 and A-7, respectively. Average pore sizes were small, 2.62 nm in A-6 and 2.15 nm in A-7. The isotherms, shown in blue and green in Figure 9 for samples A-7 and A-6, respectively, have a concave shape facing the pressure coordinate, showing high nitrogen uptake at relatively low pressure. This indicates the high adsorption potential of these microspheres, which is characteristic of microspheres with narrow pores. This behavior is often observed in microporous materials [52; 53]. A significant content of micropores is manifested in a large adsorbed volume at almost zero relative pressure. From the pore distribution shown in Figure 10a,b, it can be concluded that besides micropores these are mesopores with a width of 2 to 5 nm which mainly contribute to the porosity of sample A-6. The isotherm hysteresis of this sample shown in Figure 9 reflects this mesoporosity. Only a very small fraction of the pore volume is occupied by macroproes. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{4}{c}{**Nitrogen Gas Adsorption**} \\ \cline{2-5}  & \multicolumn{1}{c}{**BET**} & \multicolumn{1}{c}{**BJH**} & \multicolumn{1}{c}{**BET**} & \multicolumn{1}{c}{**BJH**} \\  & **Surface Area** & **Pore Volume** & **Av. Pore Width** & **Av. Pore Width** \\  & **m\({}^{2}\)/g** & **cm\({}^{3}\)/g** & **nm** & **nm** \\ \hline A-1 & 10.48 & 0.072 & 21.4 & 28.2 \\ \hline A-2 & 11.24 & 0.058 & 28.2 & 32.0 \\ \hline A-3 & 12.6 & 0.052 & 14.64 & 20.8 \\ \hline A-4 & 164.9 & 0.175 & 4.70 & 5.21 \\ \hline A-5 & 204.6 & 0.195 & 4.16 & 4.59 \\ \hline A-6 & 263. 5 & 0.145 & 2.63 & 3.1 \\ \hline A-7 \({}^{\star}\)) & 347.2 & 0.091 & 2.15 & 2.9 \\ \hline A-7-1 \({}^{\star}\)) & 120.7 & 0.218 & 8.41 & 10.94 \\ \hline A-7-2 \({}^{\star\star\star}\)) & 103.0 & 0.347 & 15.81 & 15.63 \\ \hline B-1 & 53.01 & 0.281 & 20.30 & 21.47 \\ \hline \hline \end{tabular}  
* Samples A-1–A–6 were obtained from DVB/PHMS using homogenization conditions: time 90 s, velocity 7000 rpm.
*) Sample A-7 was obtained using the same DVB/PHMS ratio as in the synthesis of sample A-1–A–6, but at other homogenization conditions (time 180 s and velocity 15000 rpm). **) Sample A-7-1–A–7 was heated in air at 800 \({}^{\circ}\)C for 3 h. ***) Sample A-7–2–A-7-1 was subjected to the treatment with HF. Sample B-1 was obtained from DWTMDS/PHMS at the same conditions as samples A-1–A–6.  
\end{table} 
Table 4: Porosity results from nitrogen adsorption measurement. Figure 10: Cumulative plots of the distribution of pore width for samples A-1 and A-6: (**a**) by pore volume, (**b**) by pore surface. Figure 9: Isotherms of N\({}_{2}\) adsorption of representative ceramic microspheres, DVB/PHMS \(w/w\) ratio: A-1 = 0.17, A-4 = 0.65, A-6, A-7 = 0.97. Microspheres that were produced using a smaller amount of DVB, sample A-4, give different isotherms similar to those of type IV, according to the IUPAC classification [52] typical for mesoporous materials, Figure 9. In contrast to the microspheres with the highest C\({}_{\text{f}}\) content, isotherms are convex with respect to the pressure coordinate in the range of 0.5 to 1 relative pressure.