Paracrystalline structure of activated carbons

Structural studies by means of neutron diffraction of activated carbons, pr epared from a polymer of phenol formaldehyde resin by carbonization and act ivation processes, with variable porosity, are presented. The neutron scatt ering data were recorded over the range of the scattering vector Q from 2.5 to 500 nm(-1) The structure of activated carbons has been described in ter ms of disordered graphite-like layers with very weak interlayer correlation s. The model has been generated by computer simulations and its validity ha s been tested by comparison of the experimental and calculated intensity fu nctions. Modelling studies have shown that the model containing 3-4 layers each about 2 nm in diameter accounts for the experimental data and that gra phite layers are randomly translated and rotated, according to the turbostr atic structure. Near-neighbour carbon-carbon distances of about 0.139 nm an d 0.154 nm have been determined. The Debye-Waller factor exp(-Q(2)sigma (2) /2) with sigma = sigma (0)rootr suggests a paracrystalline structure within a single layer. The value of the interlayer spacing of 0.36 nm has been fo und from paracrystalline simulations of the layer arrangement in the c-axis direction. The high quality of the experimental data has enabled determina tion of the coordination numbers, the interatomic distances and their stand ard deviations using a curve-fitting procedure over the Q-range from 250 nm to 500 nm, providing structural information about short- and intermediate- range ordering.