QUANTIFICATION OF MICROPOROSITY BY NUCLEAR-MAGNETIC-RESONANCE RELAXATION OF WATER IMBIBED IN POROUS-MEDIA

On the basis of the nuclear magnetic resonance (NMR) relaxation of imb ibed water, we evaluated the interparticle and intraparticle pore size s in packed beds of silica materials of known particle sizes and micro porous structure. The NMR relaxation distribution is scaled by the sur face relaxivity parameter rho, which incorporates a surface area to vo lume ratio (S-0/V-0) term, to yield a corresponding pore size distribu tion. The NMR-derived pore sizes of nonporous silica sand agreed with the expected interparticle pore sizes estimated from the morphology of a packed bed of spheres of comparably sized particles. The NMR-derive d intraparticle pore size for porous silica was also in good agreement with reported values for the silica materials studied. Scaling of the NMR relaxation corresponding to interparticle water by the same surfa ce interaction parameter to yield interparticle pore size in high-surf ace area porous silica material, however, grossly underestimated inter particle pore size. In these high-surface area materials the intrapart icle micropores provide a higher contribution to the N-2 measured surf ace area relative to the contribution from interparticle macropores. W hen the NMR relaxation method was used to evaluate the pore space in t he Borden Aquifer material, the NMR-derived pore sizes agreed with tho se observed in scanning electron micrographs as well as pore sizes est imated from the morphology of packed beds of comparably sized particle s. For soils and aquifer materials of low to moderate surface area the NMR-derived porosity determination may be used to adequately evaluate both solute transporting and sorbing pore sizes.