The effects of nanoparticle addition on SiC and AlN powder–polymer mixtures: Packing and flow behavior

The development of methods to increase sintered density and improve dimensional tolerances is a crucial issue in powder metallurgy and ceramic processing. Increasing the packing density of starting powders is one effective route to achieve high sintered density and dimensional precision. The current paper presents an in-depth study on the effect of nanoparticle addition on the powder content of SiC and AlN powder–polymer mixtures. In particular, bimodal mixtures of nanoscale and sub-micrometer particles were found to have significantly increased powder volume fraction (solids loading) in the mixtures for injection molding. This observation to increasing packing density by using nanoparticles is surprising and novel since nanoparticles are known to inherently exhibit poor packing behavior. Additionally, for a given volume fraction of powder, the bimodal μ-n suspensions had a lower viscosity at any shear rate compared to the monomodal μ-suspensions. The ability to lower the suspension viscosity by adding nanoparticles to micron-sized particles has important implications for processing of particulate suspensions by powder injection molding (PIM), extrusion, slip casting and tape casting. Samples made from bimodal powders exhibited slower polymer removal during debinding and higher densification with lower shrinkage on sintering compared to the corresponding samples made from monomodal powder mixtures.