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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• Effect of titanium addition on mechanical properties of Mo-Si-B alloys
  Won June Choi, Seung Yeong Lee, Chun Woong Park, Jung Hyo Park, Jong Min Byun, Young Do Kim
  International Journal of Refractory Metals and Hard Materials.2019; 80: 238.     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

Porous W with controlled pore structure was fabricated by thermal decomposition and hydrogen reduction process of PMMA beads and WO₃ powder compacts. The PMMA sizes of 8 and 50 μm were used as pore forming agent for fabricating the porous W. The WO₃ powder compacts with 20 and 70 vol% PMMA were prepared by uniaxial pressing and sintered for 2 h at 1200°C in hydrogen atmosphere. TGA analysis revealed that the PMMA was decomposed at about 400°C and WO₃ was reduced to metallic W at 800°C. Large pores in the sintered specimens were formed by thermal decomposition of spherical PMMA, and their size was increased with increase in PMMA size and the amount of PMMA addition. Also the pore shape was changed from spherical to irregular form with increasing PMMA contents due to the agglomeration of PMMA in the powder mixing process.

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• Synthesis of Porous Silica Particles Using Sodium Silicate Precursor for Water-Repellent Surfaces
  Young-Sang Cho, Nahee Ku, Young-Seok Kim
  JOURNAL OF CHEMICAL ENGINEERING OF JAPAN.2019; 52(2): 194.     CrossRef