The effect of the mixing method on the characteristics of hybrid-structure W powder with nano and micro sizes is investigated. Fine WO₃ powders with sizes of ~0.6 μm, prepared by ball milling for 10 h, are mixed with pure W powder with sizes of 12 μm by various mixing process. In the case of simple mixing with ball-milled WO₃ and micro sized W powders, WO₃ particles are locally present in the form of agglomerates in the surface of large W powders, but in the case of ball milling, a relatively uniform distribution of WO₃ particles is exhibited. The microstructural observation reveals that the ball milled WO₃ powder, heat-treated at 750°C for 1 h in a hydrogen atmosphere, is fine W particles of ~200 nm or less. The powder mixture prepared by simple mixing and hydrogen reduction exhibits the formation of coarse W particles with agglomeration of the micro sized W powder on the surface. Conversely, in the powder mixture fabricated by ball milling and hydrogen reduction, a uniform distribution of fine W particles forming nano-micro sized hybrid structure is observed.

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An optimum route to synthesize Ti-Mo system powders is investigated by analyzing the effect of the heat treatment atmosphere on the formation of the reaction phase by dehydrogenation and hydrogen reduction of ball-milled TiH₂-MoO₃ powder mixtures. Homogeneous powder mixtures with refined particles are prepared by ball milling for 24 h. XRD analysis of the heat-treated powder in a hydrogen atmosphere shows TiH₂ and MoO₃ peaks in the initial powders as well as the peaks corresponding to the reaction phase species, such as TiH_0.7, TiO, MoO₂, Mo. In contrast, powder mixtures heated in an argon atmosphere are composed of Ti, TiO, Mo and MoO₃ phases. The formation of reaction phases dependent on the atmosphere is explained by the partial pressure of H2 and the reaction temperature, based on thermodynamic considerations for the dehydrogenation reaction of TiH₂ and the reduction behavior of MoO₃.

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The effect of sublimable vehicle composition in the camphor-naphthalene system on the pore structure of porous Cu-Ni alloy is investigated. The CuO-NiO mixed slurries with hypoeutectic, eutectic and hypereutectic compositions are frozen into a mold at -25°C. Pores are generated by sublimation of the vehicles at room temperature. After hydrogen reduction at 300°C and sintering at 850°C for 1 h, the green body of CuO-NiO is completely converted to porous Cu-Ni alloy with various pore structures. The sintered samples show large pores which are aligned parallel to the sublimable vehicle growth direction. The pore size and porosity decrease with increase in powder content due to the degree of powder rearrangement in slurry. In the hypoeutectic composition slurry, small pores with dendritic morphology are observed in the sintered Cu-Ni, whereas the specimen of hypereutectic composition shows pore structure of plate shape. The change of pore structure is explained by growth behavior of primary camphor and naphthalene crystals during solidification of camphor-naphthalene alloys.

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