Carbosil samples at different carbon concentrations C-C = 0.5-64 wt % were synthesized by means of pyrolysis of CH2Cl2 at a fumed silica substrate (S-BET X 300 m(2) g-l) and studied by using IR, TEM, nitrogen adsorption/desorption, electrophoresis, and photon correlation spectroscopy. During methylene chloride carbonization, the disordered carbon deposit can form mainly in the interparticle volume of fractal aggregates of primary silica particles; therefore, a marked reduction in the pore volume and the specific surface area is observed with increasing C-C. Changes of the pH(IEP) value and zeta potential zeta(pH) for the aqueous suspensions of carbosils are relatively small with increasing C-C due to the availability of oxidized carbon fragments and the silica patches without carbon coverage. The effective diameter of particles (aggregates and agglomerates) of X/SiO2 in the aqueous suspensions is larger at X = C than that of mixed oxides at X = TiO2 or GeO2 at a given concentration of the second X phase.