A PULSED-FIELD GRADIENT NMR TECHNIQUE FOR THE DETERMINATION OF THE STRUCTURE OF SUSPENSIONS OF NON-BROWNIAN PARTICLES WITH APPLICATION TO PACKINGS OF SPHERES

The internal structure of systems of particles in a liquid is studied with a novel NMR technique based on the measurement of the squared mod ulus of the magnetization in presence of a pulsed field gradient. The formalism is analogous to the one used in classical scattering techniq ues (light, X-rays, neutrons); it allows similar information to be obt ained about the structure tin particular, the structure factor S(q)). The main improvement is that the range of particles sizes is 10 mu m t o 1 mm, as compared with the range of the scattering techniques (< 5 m u m). The NMR technique was validated by studying packings of spherica l particles of mean diameter 240 mu m created by sedimentation. The pr ofile of the experimental squared modulus of the magnetization versus the wave vector provides results for the mean size of particles and th e compacity. The main feature is that it depends on the pair distribut ion function, and the present results are in good agreement with a mod el based on the Percus-Yevick approximation. This technique is then pa rticularly adapted to systems such as non-Brownian suspensions, fluidi zed beds, porous media, and sediments. (C) 1998 Academic Press.