  Wicks are the main component of Loop Heat Pipe systems, whereby coolant
liquid flow through their porous structure. They are usually formed by a
primary wick to produce liquid transportation by capillary force, and a
secondary wick that is continuously wetted by the liquid coolant.
Traditionally, the two wicks are manufactured separately and subsequently
joined, thereby creating an interface that reduces the liquid transfer
efficiency. In order to overcome this situation, a gradient porous wick is
proposed and successfully manufactured through the freeze-casting method in a
single operation. The influence of two different dispersant agents, KD4 and
stearic acid was studied on the processing parameters, final pore size and
morphology, and capillarity performances. A variate of gradient porosity was
obtained by applying a diverse thermal gradient and solidification front
velocity during directional solidification. The rheological characterisation of
the camphene-based NiO suspensions was performed using a rotational viscometer.
The final pore size and morphology were characterised by Optical Microscopy,
Field Emission Scanning Electron Microscopy, and X-ray computed tomography. The
use of stearic acid improves the particle stabilisation and generates pore
enlargement with an equiaxed pore structure, while commercial dispersant KD4
shows a dendritic pore morphology at lower thermal gradient.
