Capillary Infiltration Rates into Porous Media with Applications to Silcomp Processing

The rate of capillary rise of a liquid into a porous medium made up of consolidated particulates is analyzed. The infiltration distance is parabolic in time and can be modeled using the Washburn analysis. The effective pore radius is measured to be one to two orders of magnitude smaller than the particle size, particle spacing, and the median pore size as measured by mercury porosimetry. This result is interpreted using a modification of the Washburn model which models the porous medium as a single pore with varying diameter. Using a two-sized single pore model, the predicted infiltration rate is consistent with the measured values. In applying the two-sized single pore model to the reactive capillary infiltration of silicon into a carbonaceous preform in the Silcomp process, the effect of pore closure by the conversion of carbon to SiC is predicted. Using pore closure dimensions measured in a partial infiltration experiment, a decrease in the infiltration rate constant is predicted and is consistent with the measured infiltration rate.