An evaluation of NMR cryoporometry, density measurement and neutron scattering methods of pore characterisation

Sol-gel silicas with nominal pore diameters ranging from 25 Angstrom to 500 Angstrom were studied by NMR cryoporometry, and by neutron diffraction and small angle scattering from dry silicas over the Q range 8.10(-4)Angstrom (-1) less than or equal to Q less than or equal to 17 Angstrom (-1). Densit y and imbibation experiments were also performed. Geometric models of porou s systems were constructed and were studied by both analytic techniques and Monte-Carlo integration. These models, combined with the information from the above measurements, enabled the calculation of the fully density correc ted solid-solid density correlation functions G(r) for the sol-gel silicas, deduction of the (voidless) silica matrix density, measurement of the sili ca fraction in the grain and of the packing fraction of the silica grains a nd an estimation of the water equivalent residual hydrogen on the dried sil ica surface. In addition, the pore diameter D, pore diameter to lattice spa cing ratio Dia, and pore and lattice variance sigma could also be measured. White the NMR cryoporometry pore diameter measurements for the sol-gel sil icas show excellent co-linearity with the nominal pore diameters as measure d by gas adsorption, and the calculated pore diameters from the measured ne utron scattering show surprisingly good agreement with these measurements a t large pore diameters, there is a divergence between the calibrations for pore diameters below about 100 Angstrom. (C) 2001 Elsevier Science Inc. All rights reserved.