Fabricating metal wicks by LMC-like continuous directional freeze casting

Abstract

A novel continuous directional freeze casting technique derived from LMC (liquid metal cooling) is developed in the present study, which is named as “LMC-like freeze casting”. In this novel freeze casting method, a quartz mold containing slurry is dipped into a low-temperature bath with a constant rate to achieve directional freezing of the slurry. Under quasi-steady state conditions, the solidification front is kept above the liquid level of the low-temperature bath at a constant distance. The heat released during freezing is conducted downward axially within the solidified slurry, and then is conducted axially and radially to the low-temperature bath through the mold wall. As a result, the thermal resistance between the solidification front and the low-temperature bath is kept constant, and the solidification velocity is exactly the same as the dipping rate of the casting mold. With casting molds made from quartz, a good compromise between high casting rate and unidirectional freezing is achieved without introducing complex temperature control systems. To demonstrate the feasibility of the LMC-like freeze casting, long wicks (about 10 cm) with uniform pore size along the freezing direction are freeze-casted from aqueous nickel slurry. Permeabilities and capillary performance parameter of the fabricated wicks are measured, proving that LMC-like freeze casting technique is feasible to fabricate biporous metal wicks with aligned porosity.