Preparation of Ultra-Fine Titanium Powder by Arc-Plasma Process

摘要

Preparation of ultra-fine titanium powder was tried by subjecting molten titanium to an arc-plasma generated in the argon-hydrogen atmosphere. The arc voltage, current and hydrogen/argon ratio were varied to optimize the powder generation. The optimum conditions were obtained at 40 V and 150 A for stabilizing arc and the hydrogen/argon ratios of 0.5 to 0.7 for achieving the generation rates of 0.18 to 0.30 g/min over reasonable periods of time. The powder generated under optimum conditions have a surface area of approximately 22 m~2/g, and the average particle size of 65 nm calculated from the surface area measurement coincides with TEM observations. XRD confirmed that particles are mostly titanium hydride (TiH_(L924)) containing small amounts of titanium (Ti) and its oxides (TiO and Ti_2O_3). All of the particu-late sizes for these phases are less than 20 nm. Powder can be dehydrogenated by heating in vacuum above 673 K, the activation energy for dehydrogenation being determined to be 95 +-5 kJ/mol by DSC experiments. This activation energy value matches well with the sum of diffusion energy of hydrogen in a-Ti and the hydrogenation energy of alpha-Ti. Also the dehydrogenation treatment does not provoke grain growth. It is therefore concluded that ultra-fine titanium powder of nano-sized crystallite sizes can be produced at a reasonable yield rate by a plasma arc process in hydrogen/Argon atmosphere and dehydrogenating the product between 673 and 873 K.