Porous Cu-14 wt% Co with aligned pores is produced by a freeze drying and sintering process. Unidirectional freezing of camphene slurry with CuO-Co3O4 powders is conducted, and pores in the frozen specimens are generated by sublimation of the camphene crystals. The dried bodies are hydrogen-reduced at 500oC and sintered at 800oC for 1 h. The reduction behavior of the CuO-Co3O4 powder mixture is analyzed using a temperature-programmed reduction method in an Ar-10% H2 atmosphere. The sintered bodies show large and aligned parallel pores in the camphene growth direction. In addition, small pores are distributed around the internal walls of the large pores. The size and fraction of the pores decrease as the amount of solid powder added to the slurry increases. The change in pore characteristics according to the amount of the mixed powder is interpreted to be due to the rearrangement and accumulation behavior of the solid particles in the freezing process of the slurry.

In this study, freeze drying of a porous Ni with unidirectionally aligned pore channels is accomplished by using a NiO powder and camphene. Camphene slurries with NiO content of 5 and 10 vol% are prepared by mixing them with a small amount of dispersant at 50℃. Freezing of a slurry is performed at -25℃ while the growth direction of the camphene is unidirectionally controlled. Pores are generated subsequently by sublimation of the camphene during drying in air for 48 h. The green bodies are hydrogen-reduced at 400℃ and then sintered at 800℃ and 900℃ for 1 h. X-ray diffraction analysis reveals that the NiO powder is completely converted to the Ni phase without any reaction phases. The sintered samples show large pores that align parallel pores in the camphene growth direction as well as small pores in the internal walls of large pores. The size of large and small pores decreases with increasing powder content from 5 to 10 vol%. The influence of powder content on the pore structure is explained by the degree of powder rearrangement in slurry and the accumulation behavior of powders in the interdendritic spaces of solidified camphene.

The present study demonstrates the effect of raw powder on the pore structure of porous W-Ni prepared by freeze drying of camphene-based slurries and sintering process. The reduction behavior of WO3 and WO3-NiO powders is analyzed by a temperature programmed reduction method in Ar-10% H2 atmosphere. After heat treatment in hydrogen atmosphere, WO3- NiO powder mixture is completely converted to metallic W without any reaction phases. Camphene slurries with oxide powders are frozen at −30 oC, and pores in the frozen specimens are generated by sublimation of the camphene during drying in air. The green bodies are hydrogen-reduced at 800 oC and sintered at 1000 oC for 1 h. The sintered samples show large and aligned parallel pores to the camphene growth direction, and small pores in the internal wall of large pores. The strut between large pores, prepared from pure WO3 powder, consists of very fine particles with partially necking between the particles. In contrast, the strut densification is clearly observed in the Ni-added W sample due to the enhanced mass transport in activation sintering.

Porous Cu with a dispersion of nanoscale Al2O3 particles is fabricated by freeze-drying CuO-Al2O3/camphene slurry and sintering. Camphene slurries with CuO-Al2O3 contents of 5 and 10 vol% are unidirectionally frozen at -30oC, and pores are generated in the frozen specimens by camphene sublimation during air drying. The green bodies are sintered for 1 h at 700oC and 800oC in H2 atmosphere. The sintered samples show large pores of 100 μm in average size aligned parallel to the camphene growth direction. The internal walls of the large pores feature relatively small pores of ~10 μm in size. The size of the large pores decreases with increasing CuO-Al2O3 content by the changing degree of powder rearrangement in the slurry. The size of the small pores decreases with increasing sintering temperature. Microstructural analysis reveals that 100-nm Al2O3 particles are homogeneously dispersed in the Cu matrix. These results suggest that a porous composite body with aligned large pores could be fabricated by a freeze-drying and H2 reducing process.

The present study demonstrates the effect of freezing conditions on the pore structure of porous Cu-10 wt.% Sn prepared by freeze drying of CuO-SnO2/camphene slurry. Mixtures of CuO and SnO2 powders are prepared by ball milling for 10 h. Camphene slurries with 10 vol.% of CuO-SnO2 are unidirectionally frozen in a mold maintained at a temperature of -30oC for 1 and 24 h, respectively. Pores are generated by the sublimation of camphene at room temperature. After hydrogen reduction and sintering at 650oC for 2 h, the green body of the CuO-SnO2 is completely converted into porous Cu-Sn alloy. Microstructural observation reveals that the sintered samples have large pores which are aligned parallel to the camphene growth direction. The size of the large pores increases from 150 to 300 μm with an increase in the holding time. Also, the internal walls of the large pores contain relatively small pores whose size increases with the holding time. The change in pore structure is explained by the growth behavior of the camphene crystals and rearrangement of the solid particles during the freezing process.

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 oC and dried for the sublimation of the camphene. The green bodies were heat-treated at 400 oC for 2 h to decompose the PMMA; then, sintering was carried out at 1200 oC in a hydrogen atmosphere for 2 h. TGA and XRD analysis showed that the PMMA decomposed at about 400 oC, and WO3 was reduced to metallic W at 800 oC 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.

In this study, titanium(Ti) meshes and porous bodies are employed to synthesize carbon nanotubes(CNTs) using methane(CH4) gas and camphene solution, respectively, by chemical vapor deposition. Camphene is impregnated into Ti porous bodies prior to heating in a furnace. Various microscopic and spectroscopic techniques are utilized to analyze CNTs. It is found that CNTs are more densely and homogeneously populated on the camphene impregnated Ti-porous bodies as compared to CNTs synthesized with methane on Ti-porous bodies. It is elucidated that, when synthesized with methane, few CNTs are formed inside of Ti porous bodies due to methane supply limited by internal structures of Ti porous bodies. Ti-meshes and porous bodies are found to be multi-walled with high degree of structural disorders. These CNTs are expected to be utilized as catalyst supports in catalytic filters and purification systems.

This paper proposes a novel way of fabricating aligned porous Sn by freeze-drying of camphene slurry with stannic oxide (SnO2) coated Sn powders. The SnO2 coated Sn powders were prepared by surface oxidation of the initial and ball-milled Sn powders, as well as heat treatment of tin chloride coated Cu powders. Camphene slurries with 10 vol% solid powders were prepared by mixing at 50 oC with a small amount of oligomeric polyester dispersant. Freezing the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at −25 oC. Improved dispersion stability of camphene slurry and the homogeneous frozen body was achieved using the oxidized Sn powder at 670 oC in air after ball milling. The porous Sn specimen, prepared by freeze-drying of the camphene slurry with oxidized Sn powder from the heat-treated Sn/tin chloride mixture and sintering at 1100 oC for 1 h in a hydrogen atmosphere, showed large pores of about 200 μm, which were aligned parallel to the camphene growth direction, and small pores in their internal walls. However, 100 μm spherical particles were observed in the bottom part of the specimen due to the melting of the Sn powder during sintering of the green compact.

This study reports a simple way of fabricating the porous Cu with unidirectional pore channels by freezedrying camphene slurry with Cu oxide coated Cu powders. The coated powders were prepared by calcination of ball-milled powder mixture of Cu and Cu-nitrate. Improved dispersion stability of camphene slurry could be achieved usingthe Cu oxide coated Cu powders instead of pure Cu powders. Pores in the frozen specimen at -25oC were generated bysublimation of the camphene during drying in air, and the green bodies were sintered at 750oC for 1 h in H2 atmo-sphere. XRD analysis revealed that the coated layer of Cu oxide was completely converted to Cu phase without anyreaction phases by hydrogen heat treatment. The porous Cu specimen prepared from pure Cu powders showed partlylarge pores with unidirectional pore channels, but most of pores were randomly distributed. In contrast, large andaligned parallel pores to the camphene growth direction were clearly observed in the sample using Cu oxide coated Cupowders. Pore formation behavior depending on the initial powders was discussed based on the degree of powder rear-rangement and dispersion stability in slurry.

Porous Ti-systems with unidirectionally aligned channels were synthesized by freeze-drying and a heat treatment process. TiH2 powder and camphene were used as the source materials of Ti and sublimable vehicles, respectively. Camphene slurries with TiH2 content of 10 and 15 vol% were prepared by milling at 50˚C with a small amount of oligomeric polyester dispersant. Freezing of the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at -25˚C while unidirectionally controlling the growth direction of the camphene. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was heat-treated at 1100˚C for 1 h in a nitrogen and air atmosphere. XRD analysis revealed that the samples composed of TiN and TiO2 phase were dependent on the heat-treatment atmosphere. The sintered samples showed large pores of about 120 mm which were aligned parallel to the camphene growth direction. The internal wall of the large pores had relatively small pores with a dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry. These results suggest that a porous body with an appropriate microstructure can be successfully fabricated by freeze-drying and a controlled sintering process of a camphene/TiH2 slurry.

In order to fabricate the porous Mo with controlled pore characteristics, unique processing by using powder as the source and camphene as the sublimable material is introduced. Camphene-based 15 vol% slurries, prepared by milling at with a small amount of dispersant, were frozen at . Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at , and sintered at for 1 h. After heat treatment in hydrogen atmosphere, powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores due to the difference in the camphene growth rate during freezing process. The size of small pores was decreased with increase in sintering temperature, while that of large pores was unchanged. The results are strongly suggested that the porous metal with required pore characteristics can be successfully fabricated by freeze-drying process using metal oxide powders.

In order to fabricate the porous metal with controlled pore characteristics, unique processing by using metal oxide powder as the source and camphene as the sublimable material is introduced. CuO powder was selected as the source for the formation of Cu metal via hydrogen reduction. Camphene-based CuO slurry, prepared by milling at with a small amount of dispersant, was frozen at . Pores were generated subsequently by sublimation of the camphene. The green body was hydrogen-reduced at for 30 min, and sintered at for 1 h. Microstructural analysis revealed that the sintered Cu showed aligned large pore channels parallel to the camphene growth direction, and fine pores are formed around the large pore. Also, it showed that the pore size was controllable by the slurry concentration.