PREPARATION OF ULTRA-FINE TITANIUM POWDER BY ARC-PLASMA PROCESS

Preparation of ultra-fine titanium powder was tried by subjecting molt en titanium to an are-plasma generated in the argon-hydrogen atmospher e. The are voltage, current and hydrogen/argon ratio were varied to op timize the powder generation. The optimum conditions were obtained at 40 V and 150 A for stabilizing are 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 condit ions have a surface area of approximately 22 m(2)/g, and the average p article size of 65 nm calculated from the surface area measurement coi ncides with TEM observations. XRD confirmed that particles are mostly titanium hydride (TiH1.924) containing small amounts of titanium (Ti) and its oxides (TiO and Ti2O3). All of the particulate sizes for these phases are less than 20 nm. Powder can be dehydrogenated by heating i n vacuum above 673 K, the activation energy for dehydrogenation being determined to be 95 +/- 5 kJ/mol by DSC experiments. This activation e nergy value matches well with the sum of diffusion energy of hydrogen in alpha-Ti and the hydrogenation energy of alpha-Ti. Also the dehydro genation treatment does not provoke grain growth. It is therefore conc luded that ultra-fine titanium powder of nano-sized crystallite sizes can be produced at a reasonable yield rate by a plasma are process in hydrogen/Argon atmosphere and dehydrogenating the product between 673 and 873 K.