The effects of the heat treatment temperature and of the atmosphere on the dehydrogenation and hydrogen reduction of ball-milled TiH₂-WO₃ powder mixtures are investigated for the synthesis of Ti-W powders with controlled microstructure. Homogeneously mixed powders with refined TiH₂ particles are successfully prepared by ball milling for 24 h. X-ray diffraction (XRD) analyses show that the powder mixture heat-treated in Ar atmosphere is composed of Ti, Ti₂O, and W phases, regardless of the heat treatment temperature. However, XRD results for the powder mixture, heat-treated at 600°C in a hydrogen atmosphere, show TiH₂ and TiH peaks as well as reaction phase peaks of Ti oxides and W, while the powder mixture heat-treated at 900°C exhibits only XRD peaks attributed to Ti oxides and W. The formation behavior of the reaction phases that are dependent on the heat treatment temperature and on the atmosphere is explained by thermodynamic considerations for the dehydrogenation reaction of TiH₂, the hydrogen reduction of WO₃ and the partial oxidation of dehydrogenated Ti.

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• Fabrication of Porous W-Ti by Freeze-Drying and Hydrogen Reduction of WO3-TiH2 Powder Mixtures
  Hyunji Kang, Sung Hyun Park, Sung-Tag Oh
  Journal of Korean Powder Metallurgy Institute.2017; 24(6): 472.     CrossRef

The synthesis of NiTi alloy powders by hydrogen reduction and dehydrogenation process of NiO and TiH₂ powder mixtures is investigated. Mixtures of NiO and TiH₂ powders are prepared by simple mixing for 1 h or ball milling for 24 h. Simple-mixed mixture shows that fine NiO particles are homogeneously coated on the surface of TiH₂ powders, whereas ball milled one exhibits the morphology with mixing of fine NiO and TiH₂ particles. Thermogravimetric analysis in hydrogen atmosphere reveals that the NiO and TiH₂ phase are changed to metallic Ni and Ti in the temperature range of 260 to 290°C and 553 to 639°C, respectively. In the simple-mixed powders by heat-up to 700°C, agglomerates with solid particles and solidified liquid phase are observed, and the size of agglomerates is increased at 1000°C. From the XRD analysis, the presence of liquid phase is explained by the formation and melting of NiTi₂ intermetallic compound due to an exothermic reaction between Ni and Ti. The simple-mixed powders, heated to 1000°C, lead to the formation of NiTi phase but additional Ni-, Ti-rich and Ti-oxide phases. In contrast, the microstructure of ball-milled powders is characterized by the neck-grown particles, forming Ni3Ti, Ti-oxide and unreacted Ni phase.

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• Effect of Heat Treatment Atmosphere on the Microstructure of TiH2-MoO3 Powder Mixtures
  Ki Cheol Jeon, Sung Hyun Park, Na-Yeon Kwon, Sung-Tag Oh
  Journal of Korean Powder Metallurgy Institute.2016; 23(4): 303.     CrossRef