Cracking During Lateral Drying of Alumina Suspensions

Abstract

The onset of cracking during drying of alumina suspensions cast onto a substrate has been studied experimentally. It is shown that the capillary pressure would impose a compressive stress on the particle array and cannot itself cause cracking. Based on experimental observations, it is proposed that the driving force for cracking arises from a misfit strain that occurs when repulsive layers between the particles collapse completely, after the particles have adhered to the substrate. This predicts that cracking should occur while the space between the particles is still filled with liquid, which is consistent with observations using laser speckle interferometry.

Solidification and Ordering during Directional Drying of a Colloidal Dispersion

“…In these studies, the height of a drying dispersion was monitored with a laser extensometer. The height levelled off as the dispersion solidified, but then underwent a steplike decrease of approximately 3% between the solidification and pore-emptying fronts [7,27]. The interpretation given to this was that the particles were first held in some secondary minimum, before they were forced into intimate contact.…”

“…A multi-stage solidification process has previously been suggested in the drying of colloidal alumina [7,26]. In these studies, the height of a drying dispersion was monitored with a laser extensometer.…”

“…The appearance of three distinct fronts have frequently been reported, which represent solidification, cracking, and pore opening (e.g. [3][4][5][6][7][8]). For films that are dried below their critical film thickness, the fracture front is absent, and the film dries without breaking [3].…”

“…For films that are dried below their critical film thickness, the fracture front is absent, and the film dries without breaking [3]. These processes have been shown to be driven by the compressive capillary forces that act on the menisci between drying colloidal particles [3][4][5][6][7][8].…”

Effect of drying conditions on patterned ceramic films processed by soft micromolding

“…alumina water-based slurry (median particle size 390 nm) and cast on a convex substrate were investigated by Holmes et al 24) by means of a laser scanner. These films dried in air showed a large shrinkage when passing through the so-called "packing front" from the initial supersaturated state to the saturated state, where particles assemble in a close packed array.…”