NMR DIFFUSION MEASUREMENTS IN HETEROGENEOUS MEDIA USING PULSED RADIOFREQUENCY FIELD GRADIENTS

The measurement of self-diffusion coefficients D by the NMR spin echo pulsed-field gradient G technique can be corrupted for systems having a background magnetic field gradient G(o). The corrupting cross-term G (o)G can be eliminated by the use of alternating pulsed-field gradient sequences. Measurement of D can also be performed by a rather new tec hnique using pulsed radio-frequency field gradients and rotary echoes. This technique is basically insensitive to background gradients and d oes not generate any adverse effects such as eddy currents or sample v ibration. These methods have been applied to mesoporous solids and het eropolyacids. (C) 1998 Elsevier Science B.V. All rights reserved.