Directional Solidification with Constant Ice Front Velocity in the Ice‐Templating Process

Abstract

An exponential cooling function for the directional solidification of liquids with constant ice front velocities is investigated with respect to an enhanced control over the ice-templating process. It is mathematically derived and set into relation to other cooling functions found in literature. A theoretical limit of applicability is discussed and a mathematical expression for the maximum sample size realizable with this new approach is derived. Experimental results from the time-resolved direct measurement of the ice front evolution during the directional solidification of pure water and a ceramic b-tricalcium phosphate (b-TCP) suspension in a cooling room environment are presented. These results are compared to the results of numerical simulations. Ice front velocities from 10 to 50 mm s -1 are realized.

Novel freeze-casting device with high precision thermoelectric temperature control for dynamic freezing conditions

“…The cooling source most often consists of a liquid refrigerant brought into thermal contact with a cold finger or a plate of a material with large thermal conductivity. 1,3,4,13,15,16 In the most common freeze-casting setup, a copper rod is immersed directly into a container of liquid nitrogen. Temperature control of the nonimmersed end of the rod is then achieved by either varying the level of nitrogen in the container 3 or by a heating sleeve installed at the top of the rod typically equipped with a thermocouple and proportional-integral-derivative (PID) control.…”

“…Temperature control of the nonimmersed end of the rod is then achieved by either varying the level of nitrogen in the container 3 or by a heating sleeve installed at the top of the rod typically equipped with a thermocouple and proportional-integral-derivative (PID) control. 1,3,4,13,15,16 In such a setup, one side of a suspension contained in a mold can be brought into contact with the copper rod. This type of setup is thus referred to as a one-sided setup.…”

“…3,7 However, this requires a clear visual distinction between the solid phase and the liquid phase, which is not always the case. 23 Temperature measurements of the freezing suspension, either by attaching thermocouples 15 or by the use of thermal infrared imaging, 24 pose an alternative tracking method granted that the exact solidification temperature of the suspension is known. The solidification temperature of the suspension moreover defines the desired working range of the freeze-casting setup.…”

“…7,12 However, to achieve a constant freezing front velocity, dynamic freezing conditions must be implemented to counteract the increasing thermal resistance from the frozen body. Various dynamic temperature profiles of the cooling source during freeze-casting have been tested, where both linear, 3,6-8 exponential, [13][14][15] and parabolic 10 freezing functions significantly increased the homogeneity of structural features and dimensions of microchannels throughout the sample length.…”

Heat flux balance description of unidirectional freezing and melting dynamics on a translational temperature gradient stage

“…In the 1980's, a similar stage was applied to study cryopreservation of biological samples and freeze casting studies [6,7,8]. Recently this setup was used for 3D imaging of ice growth [9,10], measurement of water freezing point depression [11], ice-templating of ceramics [12] and for cryopreservation of adherent cell cultures [13].…”