Porous W-Ni alloys synthesized from camphene/WO₃-NiO slurry by freeze drying and heat treatment in hydrogen atmosphere

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 °C, 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 °C and sintered at 1000 °C 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.