Mercury porosimetry: applicability of the buckling-intrusion mechanism to low-density xerogels

Mineral materials can be either crushed or invaded by mercury during mercur y porosimetry experiments. It has been shown here that many low-density xer ogels exhibit the two volume variation mechanisms successively, compaction followed by intrusion. when submitted to mercury porosimetry and that a uni modal pore size distribution can be obtained by applying Pirard's collapse model below the pressure of transition P-1 and Washburn's intrusion theory above P-t. To confirm the validity of the use of the buckling law, one low- density xerogel was wrapped in a tight membrane (intrusion is prevented and the sample is crushed during the whole porosimetry experiment). The analys is of the mercury porosimetry data of the wrapped sample by the buckling la w leads to a continuous unimodal distribution similar to the distribution o f the unwrapped sample obtained by applying the buckling law below P-t and the intrusion law above P-t. The position of P-t is characteristic of the t ested material: when submitted to mercury pressure. aerogels and low-densit y xerogels only collapse in case of very small aggregates whereas they are crushed and then intruded in case of larger silica aggregates. The fact tha t compacted slabs of monodisperse non-aggregated silica spheres (of the sam e size range as the xerogels and aerogels) show only intrusion during mercu ry porosimetry experiments implies that the particles need to be aggregated so that the compaction mechanism takes place. The position of the change o f mechanism from crushing to intrusion is not directly related to the size of the elementary particles but is linked to the size of the aggregates of silica particles. (C) 2001 Elsevier Science B.V. All rights reserved.