X-Ray Tomoscopy Reveals the Dynamics of Ice Templating

Abstract

Little experimentally explored and understood are the complex dynamics of microstructure formation by ice-templating when aqueous solutions or slurries are directionally solidified (freeze cast) into cellular solids. With synchrotron-based, time-resolved X-ray tomoscopy it is possible to study in situ under well-defined conditions the anisotropic, partially faceted growth of ice crystals in aqueous systems. Obtaining one full tomogram per second for ≈270 s with a spatial resolution of 6 µm, it is possible to capture with minimal X-ray absorption, the freezing front in a 3% weight/volume (w/v) sucrose-in-water solution, which typically progresses at 5–30 µm s−1 for applied cooling rates of (Formula presented.) = 1–10 °C min−1. These time and length scales render X-ray tomoscopy ideally suited to quantify in 3D ice crystal growth and templating phenomena that determine the performance-defining hierarchical architecture of freeze-cast materials: a complex pore morphology and “ridges”, “jellyfish cap”, and “tentacle”-like secondary features, which decorate the cell walls.