Abstract
The structure of a suspension of iron particles (about 120 AA diameter) dispersed in mercury has been studied using small-angle neutron scattering. Measurements were undertaken in zero magnetic field and in a field of 8 kOe on thin samples (0.2 mm) with a neutron wavelength of 4.7 AA to avoid absorption effects. In the momentum transfer Q ranges examined an isotropic scattering pattern was observed in zero field. In this initial zero field the radius of gyration Rg calculated from the Guinier plots for different Q regions ranged from about 12 AA to several hundred angstroms. An analysis of the scattering pattern assuming a Maxwellian distribution of the radii of gyration gave an arithmetic mean of 51 AA for Rg and a fractional standard deviation of 0.61. On applying a field of 8 kOe the scattering became highly anisotropic. A smaller anisotropy of different shape remained when the field was removed and this anisotropy was maintained for at least some hours afterwards. It is suggested that this arises because the aggregates form large structures which relax only slowly on the removal of the field. The results in conjunction with sedimentation studies indicate the presence of large aggregates of particles in the mercury carrier.