Fabrication of porous W by freeze-casting and hydrogen reduction of camphene-based WO 3 suspension

Abstract

In this research, freeze-casting and sintering processes were applied to fabricate porous W with macroscopically aligned pores. Initially, the raw WO₃ powder was ball-milled for 5 h to remove large agglomerates, resulting in an unimodal distribution with an average size of 250 nm. The homogeneous suspension with dispersion stability can be prepared by adding oligomeric polyester as a dispersant. After unidirectional freeze-casting of camphene suspension and sintering in a hydrogen atmosphere, the green body was completely converted to porous W. The sintered W showed that aligned large pores were generated by sublimation of directionally solidified camphene crystals. The pore size of the sintered W decreased with increasing content of solid particles, and larger pore sizes were observed in the upper region than at the bottom of all specimens. Changes in pore size have been interpreted as differences in the solidification behavior of the suspension, such as the degree of redistribution of solid particles and the solidification velocity at the freezing front.