Synthesis of aligned porous sn by freeze-drying of tin chloride/camphene slurry

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 °C 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 °C. Improved dispersion stability of camphene slurry and the homogeneous frozen body was achieved using the oxidized Sn powder at 670 °C 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 °C 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.