Mechanochemical synthesis of porous silicon oxycarbide composites

The work is devoted to investigation of the process of mechanochemical synthesis of porous silicon oxycarbide composites. The synthesis was carried out by mechanical treatment of several mixtures of activated carbon and white soot with different mass ratios. Samples were investigated using such methods as X-ray diffraction, infrared spectroscopy, low-temperature nitrogen adsorption/desorption and potentiometric titration. Synchronous thermal analysis including thermogravimetric analysis and differential scanning calorimetry was performed. The results of X-ray diffraction analysis showed that no new phases were formed in the process of mechanochemical synthesis, and the structure of composites obtained can be characterized as highly amorphous. The possibility of activated carbon and white soot to be chemically bonded with the formation of silicon oxycarbides, which act as a binder in the composite structure, during intensive supply of mechanical energy to raw materials was proved. Thermal stability of silicon oxycarbides formed and the amount of free carbon that was not bonded with silicon dioxide were estimated by synchronous thermal analysis. It was established that the initial mixture composition significantly affects the surface chemistry of composites synthesized, which is expressed by a change in concentration of different surface functional groups. A possible mechanism of solid phase interaction between activated carbon and white soot resulting in the formation of Si–O–C bonds was proposed. Investigation of porous structure of composite materials obtained showed that the specific surface area and pore volume become lower with an increase in white soot concentration in the initial mixture. It is possible to adjust the porous structure of composites by changing the activated carbon to white soot mass ratio.