Binder Induced Porosity in Tape Casting

Abstract

Anionic stabilized binders can be used to create directional porosity in tape-and slipcast alumina. Anionic latexes can stabilize drying channels perpendicular to the direction of casting and are therefore perfectly suited to create such controlled porosity in tape cast material. The surfactant separates from the polymer and creates voids and channels in the matrix, and this phenomenon is referred to as phase separation. Samples of alumina were prepared with two different latex binders, one stabilized with anionic surfactant, the other non-ionic. The samples were slip and tape cast. The anionic latex caused a distinct drop in sintered density with increasing binder content for the two coarser powders tested in the experiments. The non-ionic latex does not influence the density in this fashion. The green densities were not much influenced by latex addition. Both latexes decrease the green density with increasing additions. The influence of particle size distribution is apparent both in sintered and green materials; coarser particles give less dense sintered material but more dense in prior to heat treatment. If the particle size is sufficiently small, the effect of phase separation is not apparent in neither the green nor sintered material.