Pressure induced changes in fractal structure of detonation nanodiamond powder by small-angle neutron scattering

The results of the experiments on small-angle neutron scattering from the industrial detonation nanodiamond powder under a pressure in the range of up to 1000 MPa are reported. It is shown that at a scale of 10–100 nm the scattering is determined by the fractal pore structure within aggregates of nanodiamonds. Its fractal dimension monotonously decreases with pressure from 1.8 to 1.2, which indicates the recombination of pores as a result of mobility of nanodiamonds in the powder under pressure. The mean pore size under the highest pressure (6 nm) is close to the characteristic size of nanodiamonds in the sample (5 nm) found from the width of X-ray diffraction peaks. The difference can be explained by the existence of a non-diamond carbon shell around diamond crystallites.