Interfacial chemistry and pressure filtration of silicon nitride suspensions

Similar to many colloidal oxides and other finely divided solids silicon nitride powders (Si 3 N 4 ) acquire an electrical surface charge when dispersed in aqueous solutions. The surface charges are on account of two ionizable surface groups, silanol (Si-OH) and secondary amine (Sia-NH) groups, and are compensated by a surrounding electrical double layer which acts as a counter charge. The net interaction between any two spherical particles was estimated by using the DLVO theory. The pressure filtration with constant filtration rate is characterized by three different stages: cake growth, cake compression and relaxation. With increasing filtration rate the flow resistance of the cake increases and the permeability decreases. Homogeneous packing structures with fractional green densities up to 0.6 could be achieved.