Properties of silicon suspensions and slip-cast bodies

The effect of varying pH, sonication times, and solid loading of silicon powder suspensions on the properties of powder/water suspensions and on the resulting pore characteristics of slip-cast bodies was studied. Aqueous suspensions of ground an aged silicon powder (of 0.3 micron median Stokes diameter and containing 1.3 vol pct Fe2O3 powder) were prepared, with solids loading in the range of 30-56 vol pct, and were adjusted to varying pH values by addition of either HCl or NH4OH or NaOH. Suspension aliquots were sonicated for 0, 15, 30, or 60 min. Suspensions were characterized by zeta potentials, ionic strength, and viscosity. Pore characteristics of cast bodies were determined by mercury porosimetry. It was found that intermediate pH values (pH 7-9), long sonication (60 min), and high solid loadings (56 vol pct) produced samples with highest green densities and smallest median pore radius.