Structural characteristics of pyrocarbon-fumed silica

Two series Of pyrocarbon/fumed silica (CS) samples at different carbon concentrations C-C = 0.5-64 wt.% (first series, CSI) and 2.6-53 wt.% (second series, CSII) synthesised by means of pyrolysis of CH2Cl2 at fumed silica substrate (S-BET = 297 (CSI) and 232 (CSII) m(2) g(-1)) under slightly different conditions were studied by using TEM, FTIR-PAS, DTG, and nitrogen adsorption-desorption methods. On methylene chloride carbonisation, disordered carbon deposits can form mainly in the inter-particle volume of secondary particles (aggregates of primary particles and agglomerates of aggregates) covering the surfaces of primary silica particles; therefore, marked reduction of the pore (gaps between primary particles) volume and the specific surface area is observed with increasing Cc. Estimation of distributions of the pore f(SCD)(R-p) and particle f(a) sizes using a self-consistent method with binary regularisation with respect to both f(ACD)(Rp) and f(a) shows that the average size of particles increases (silica particles are covered by pyrocarbon) and individual pyrocarbon particles (up to 50 nm according to TEM) also appear. Structural parameters of carbosils are characterised by nonlinear changes with increasing carbonisation time. Surface functionalities on CS samples correspond to aromatic and twinned CC bonds with contribution of oxygen-containing groups. (C) 2003 Elsevier Science B.V. All rights reserved.