Effects of Rod-like Particles on the Microstructure and Strength of Porous Silica Nanoparticle Composites

This study describes the results of an investigation into the effects of the addition of rod-like silica nanoparticles on the properties of freeze-cast and sintered bodies formed from silica nanospheres. Rod-like silica particles with approximate to 220nm diameter and tunable aspect ratio from approximate to 1 to approximate to 12 (length/diameter) were prepared and added to aqueous suspensions containing 22nm spherical silica particles. After freeze casting, porous composites were created with all suspensions, which is shown to be consistent with the results of a simple analysis in which the experimental freezing rate is compared with the critical rate at which the dispersed particles can no longer be expelled from the growing ice front. The composites have elongated spherical pores, and the pore size changes slightly with increasing aspect ratio of the nanorods. Finally, it was found that the rod-like particles improve the flexural strength of the composites at both green and sintered states and this strengthening effect intensifies with increasing aspect ratio. This study provides a strategy for fabricating porous materials of improved properties and performance without compromising the porosity or changing the material composition.