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 p arabolic in time and can be modeled using the Washburn analysis, The e ffective 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 us ing a modification of the Washburn model which models the porous mediu m as a single pore with varying diameter, Using a two-sized single por e model, the predicted infiltration rate is consistent with the measur ed 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 carbo n to SIC is predicted, Using pore closure dimensions measured in a par tial infiltration experiment, a decrease in the infiltration rate cons tant is predicted and is consistent with the measured infiltration rat e.