Fabrication of Porous W by freeze-drying process of camphene slurries with spherical PMMA and WO₃ powders

Porous W with spherical and directionally aligned pores was fabricated by the combination of sacrificial fugitives and a freeze-drying process. Camphene slurries with powder mixtures of WO₃ and spherical PMMA of 20 vol% were frozen at -25 °C and dried for the sublimation of the camphene. The green bodies were heat-treated at 400 °C for 2 h to decompose the PMMA; then, sintering was carried out at 1200 °C in a hydrogen atmosphere for 2 h. TGA and XRD analysis showed that the PMMA decomposed at about 400 °C, and WO₃ was reduced to metallic W at 800 °C without any reaction phases. The sintered bodies with WO₃-PMMA contents of 15 and 20 vol% showed large pores with aligned direction and small pores in the internal walls of the large pores. The pore formation was discussed in terms of the solidication behavior of liquid camphene with solid particles. Spherical pores, formed by decomposition of PMMA, were observed in the sintered specimens. Also, microstructural observation revealed that struts between the small pores consisted of very fine particles with size of about 300 nm.