Particle redistribution and structural defect development during ice templating

The freezing of colloidal suspensions is encountered in many natural and engineering processes. It can be harnessed, through a process known as ice templating, to produce porous materials and composites exhibiting unique functional properties. The phenomenon by itself appears simple: a solidification interface propagates through a colloidal suspension. We are nevertheless still far from a complete understanding and control of the phenomenon. Such lack of control is reflected in the very large scattering of mechanical properties reported for ice-templated ceramics, largely due to the formation of structural defects. Through systematic in situ investigations, we demonstrate here the role of suspension composition and the role of particle–particle electrostatic interactions on defect formation during ice templating. Flocculation can occur in the intercrystal space, leading to a destabilization of the solid–liquid interface and triggering the growth of crystals perpendicular to the main ice growth direction. This mechanism contributes significantly to the formation of structural defects and largely explains the scattering of compressive strength values reported in the literature.